Avalanche Advisory – 4/5/2014

THIS ADVISORY HAS EXPIRED.

Issued: April 5, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Saturday, April 5, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. This is the final scheduled advisory for the season.


MOUNTAIN WEATHER

WeatherGraphicYesterday, a storm moved through the area that brought gusty winds and left 2-7 inches of new snow that measured 0.2-0.5 inches of snow water equivalent.  Daytime high temperatures only reached the mid-30s compared to the mid-40s in the previous days. Currently, remote weather stations and SNOTEL sites are reading 28 to 32 °F with winds out of the southwest at 10-25 mph with gusts to 32 mph. Today should see partly/mostly cloudy skies with temperatures in the upper 20s to mid-30s. Light snow showers are expected through the day, increasing tonight with accumulations of 4-6 inches by tomorrow morning. Winds will be out the west and southwest 5-15 mph later this morning, increasing to 15-30 mph in the afternoon.

 


RECENT OBSERVATIONS

RecentObservationsGraphicYesterday we were in Noisy/Jewel Basin in the Swan Range. The morning was foggy and visibility was obscured, winds on the ridge were moderate to strong. There was minimal drifting of the snow (before snowfall began) since snow on the Leeward slopes was still locked up in previously formed surface crusts. The melt-freeze crust that we traveled on was supportable above 6200 feet and was present on all terrain that had slight sun exposure. Though short lived, the snow came in with moderate to heavy intensity, at times snowfall rates approached 2 inches per hour. Visibility improved in the afternoon and we could see several run outs from large south facing slide paths and no recent avalanche activity was observed. We did observe lots of roller ball activity from previous days, even on shaded aspects (photo).  Snow profiles and stability testing revealed some instability within the top foot of the snow pack, associated with melt-freeze crusts and graupel layers (profile, photo). None of these failure layers propagated fractures in extended column tests.

Glide cracks are beginning to rear their ugly heads again this spring. Erich noted a couple of glide cracks recently in the Swan Range (photo), and Glacier National Park rangers noted a few in the park.

General snow profile on north aspect at 6200 feet. Noisy Basin, Swan Range 4/4/2014

General snow profile on north aspect at 6200 feet. Noisy Basin, Swan Range 4/4/2014


Roller balls on north aspect. Noisy Basin, Swan Range. 4/4/2014

Roller balls on north aspect. Noisy Basin, Swan Range. 4/4/2014


New snow and graupel drifting along ridgeline in Noisy Basin, Swan Range. 4/4/2014

New snow and graupel drifting along ridgeline in Noisy Basin, Swan Range. 4/4/2014

 

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

Wind SlabEven with estimated wind speeds of around 25 mph along the ridgeline in Noisy Basin yesterday, we did not observe snow being transported prior to the onset of the new snow. This was due to the strong melt-freeze crust on windward slopes at our location. At high elevations where snow remained soft and available for transport, I expect wind slabs to be thicker and they should be avoided until they have had time to settle. Also remember that at lower elevations even shallow wind slabs can have big consequences if you are traveling in exposed terrain and in or above terrain traps. It remains important to assess the stability of each slope you intend to ski or ride.

 

 

 


 

Avalanche Problem #2

Deep SlabThough rather isolated in distribution and difficult to trigger the consequence of triggering a deep slab at this point would be catastrophic. In most locations we continue to find areas with shallow snow that harbor weak snow near the ground, as well as the thick rain crust from early March. Neither of these have been recent players, but they are still out there and deserve a cautious approach. Don’t let your guard down when assessing slopes for deep slab instabilities this spring and continue to avoid terrain with the highest probability of triggering these slabs such as steep rocky terrain, convex rollovers, and shallow wind scoured areas.

 


 

 

Spring can bring a mixed bag of weather and snow conditions. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions this time of year. Pay particular attention to rapidly rising temperatures or extended periods of direct sun exposure. While temperatures are not expected to get excessively warm today, it is important to remember that rapid warming and above freezing temperatures will increase the wet avalanche hazard. Even small avalanches can be dangerous when traveling in or above terrain traps. Cornices can also become more sensitive during the spring when they are exposed to direct sun exposure and warmer temperatures. Assess a ridge line suspected of having cornices from multiple angles before approaching to ensure that you will not be standing on top of one. When cornices are present below, stay well behind confirmed solid ground as they can break farther back than what might be expected and avoid traveling below them.

 


BOTTOM LINE

For today the avalanche hazard is LOW below 5500 feet. This means that human triggered and natural avalanches are unlikely, however normal caution and safe travel practices should still be exercised. Terrain above 5500 feet is rated as MODERATE, human triggered avalanches are possible, particularly on slopes steeper than 35 degrees that have a shallow snowpack. There are also pockets of CONSIDERABLE hazard in wind loaded terrain, steeper than 35 degrees, and above 6500 feet.  Human triggered avalanches are likely in this terrain. With substantial new snow expected tonight and into tomorrow, accompanied by moderate to strong winds, expect avalanche hazard to rise tomorrow. Be sure to check back this evening as we will post a spring avalanche statement.

 

Moderate_2

Low 

Considerable

 


Personal Note:

I want to personally thank those of you who took the time after a long day of skiing, riding, or working in the backcountry to send us your observations. These are invaluable in confirming suspicions, making us aware of localized events, and general  reduction of the uncertainty associated with a large advisory area. Thank you. I hope all of you have a great and safe spring and summer.

 


 

See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content

Avalanche Advisory – 4/2/2014

THIS ADVISORY HAS EXPIRED.

Issued: April 2, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Wednesday, April 2, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Saturday, April 5, 2014.


MOUNTAIN WEATHER

WeatherGraphic Yesterday saw partly cloudy skies with isolated light snow showers. Flattop Mountain SNOTEL site was the warm spot, with a high temperature of 42°F. Currently, remote weather stations and SNOTEL sites are reading 11 to 29 °F with winds out of the east at 3-5 mph. Today will see partly cloudy skies with temperatures from upper 20s to mid-30s. Light snow showers are possible this afternoon and winds will shift to 5-10 mph out of the west.

 


RECENT OBSERVATIONS

RecentObservationsGraphicYesterday Tony and I traveled into the Swede Creek drainage in the Whitefish Range. The snow surface on our ascent was a supportable melt-freeze crust on any aspect that was previously exposed to the sun. Temperatures remained relatively cool with a light breeze and intermittent clouds to keep the sun at bay. It wasn’t until late in the afternoon that the snow surface began to show signs of melting (photo). We observed some roller balls/pinwheels from steep, sun exposed slopes. In the shade, the snow remained dry and unconsolidated. A snow profile on a south aspect revealed multiple crusts in the upper snowpack that were minimally reactive to stability tests. In an area with a relatively shallow snowpack we found weak faceted snow near the ground.

Skiers in the Pike Creek drainage in the Flathead Range and in the Apgar Range last weekend encountered difficult travel conditions due to warm heavy snow and breakable crusts (observation). On Monday, skiers in the Marion/Dickey Creek drainages in the Flathead Range noted sun affected snow on solar aspects and surface snow that remained cool and dry in the shade (observation).

Glide cracks are beginning to rear their ugly heads again this spring. Erich noted a couple of glide cracks last Friday in the Swan Range (photo), and Glacier National Park rangers noted a few in the park.

Large cornices along ridgeline. Notice small woodland creature ignoring safe travel protocol around cornices. Swede Creek, Whitefish Range. 4/1/2014

Large cornices along ridgeline. Notice small woodland creature ignoring safe travel protocol around cornices. Swede Creek, Whitefish Range. 4/1/2014


Roller balls on steep slopes indicate that surface snow is starting to become wet. Swede Creek, Whitefish Range. 4/1/2014

Roller balls on steep slopes indicate that surface snow is starting to become wet. Swede Creek, Whitefish Range. 4/1/2014


An early sign that snow surface is becoming moist.  Swede Creek, Whitefish Range. 4/1/2014

An early sign that snow surface is becoming moist. Swede Creek, Whitefish Range. 4/1/2014

 

 

 

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

WetAvalGiven the time of year with longer days and increasing sun intensity, pay close attention to the effects of warming and direct sun on the snow surface. Today the wet avalanche hazard should be confined to slopes that receive prolonged direct sun exposure. Consider moving to a shaded aspect if the snow surface becomes wet and surface crusts begin to melt. Avoid steep sun exposed slopes, particularly when traveling in or above terrain traps.

 

 


 

Avalanche Problem #2

Wind SlabWind slabs can take up to a week to gain strength. Moderate to strong winds last weekend formed sensitive wind slabs and though they are moving in the direction of stability, steep wind loaded slopes should still be treated as suspect. Pockets of recently formed wind slabs were deposited on top of layers of graupel, and though this is not considered a persistent weak layer they can take a bit longer to gain strength. It remains important to assess the stability of each slope you intend to ski or ride. Additionally, large cornices exist in the area (photo), and with warming temperatures this time of year they can become particularly sensitive. Even short periods of more intense sun can make them unstable. Give cornices a wide berth when traveling above them and avoid travel below.

 


Avalanche Problem #3

Deep SlabIt’s getting late in the season, spring is in the air, and we have been talking about deep persistent slab for months. We continue to find areas with shallow snow that harbor weak snow near the ground, as well as the thick rain crust from early March. Neither of these have been recent players, but the consequence of triggering an avalanche in these deep slabs remains high. Prior to committing to a slope ask yourself, “where would I be most likely to trigger a deep slab?” More often than not, the answer will be on that steep rollover or in areas notorious for having a shallow snowpack like near those exposed rocks. Don’t let your guard down when assessing for deep slab instabilities and continue to avoid terrain with the highest probability of triggering these slabs .

 


 

Spring can bring a mixed bag of weather and snow conditions. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions this time of year. Pay particular attention to rapidly rising temperatures or extended periods of direct sun exposure.

 


BOTTOM LINE

For today the avalanche hazard is LOW below 5500 feet. This means that human triggered and natural avalanches are unlikely, however normal caution and safe travel practices should still be exercised.  Terrain above 5500 feet is rated as MODERATE, human triggered avalanches are possible, particularly on slopes steeper than 35 degrees that have a shallow snowpack. 

 

Moderate_2

Low 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content

Avalanche Advisory – 3/30/2014

THIS ADVISORY HAS EXPIRED.

Issued: March 30, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date 

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Sunday, March 30, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Wednesday, April 2, 2014.


MOUNTAIN WEATHER

WeatherGraphicIn the past 24 hours we received between .2 -.7 inches of snow water equivalent, most of which came in early yesterday. Mild temperatures and the heavy nature of the snow caused rapid settlement and snow totals measure a modest 1-2 inches according to SNOTEL sites. Ridge top winds were 15-35 mph yesterday with gusts to 54 mph out of the southwest. Currently, remote weather stations and SNOTEL sites are reading 23 to 30 °F with winds out of the southwest at 5-15 mph. Today will see partly to mostly cloudy skies this morning clearing mid-day with temperatures from upper 20s to mid-30s. Light snow showers should resume this afternoon intensifying in the evening and winds will be 5-15 mph out of the southwest.

 


RECENT OBSERVATIONS

RecentObservationsGraphic

The rain was coming down yesterday morning while driving down the Middle Fork corridor, after motivating to leave the dry truck we traveled up Little Shields in the Lewis Range. The rain transitioned to snow at 5400 feet. On our ascent we found sensitive storm snow, particularly near the snow line that was slightly upside down, loose, wet avalanches were easy to trigger up to about 6000 feet. Winds were strong on the ridgelines, rapidly transporting the recent snow on to leeward slopes(photo). We did not observe any natural avalanche activity yesterday, but given the short amount of time the wind took to fill in ski tracks and our snow pit, it is possible that the evidence of any avalanche activity was quickly covered (photo). Though we did experience some cracking of the wind slabs while traveling along the ridge and on low angle slopes, they did not seem to be quite as reactive as what Erich encountered in the Swan Range on Friday. While approaching a wind loaded slope, he triggered a wind slab that was up to 20 inches deep and 200 feet wide (photo). A snow profile on a north aspect revealed a 4 inch wind slab on the surface that failed with easy force but did not propagate a fracture. We also found a 35 cm slab of recently wind drifted snow on top of an older snow surface that did propagate a fracture across an extend column with moderate force (profile, photo). On our descent we traveled very conservatively expecting to pass through the mid elevation band of unstable storm snow, but found that the upside layer that we traveled through on the way up had already settled and was not nearly as reactive as earlier in the day. Below 5000 feet shallow, loose, wet snow on top of a melt freeze crust was easy to trigger on steep slopes, but also easy to manage by staying above the moving snow and avoiding terrain traps.

Glide cracks are beginning to rear their ugly heads again this spring. Erich noted a couple of glide cracks on Friday in the Swan Range (photo), and Glacier National Park rangers noted a few in the park this past week.

We received no other observations within the past 48 hours from any other locations.

 

Ski track filling in minutes by wind drifted snow. Lewis Range 3/29/2014

Ski track filling in minutes by wind drifted snow. Lewis Range 3/29/2014

Shallow wind slab on the surface. ECTP on older wind slab. Lewis Range. 3/29/2014

Shallow wind slab on the surface. ECTP on older wind slab. Lewis Range. 3/29/2014

Cross loaded terrain features in the distance. From Little Shields, Lewis Range. 3/29/2014

Cross loaded terrain features in the distance. From Little Shields, Lewis Range. 3/29/2014

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

 

 

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

Wind SlabModerate to strong ridge top winds over the past several days created wind slabs that remain a concern today. Mild temperatures will help correct this problem faster but its best to let these slabs rest a while longer while they continue to adjust. In addition to drifting snow along the ridges yesterday, we also observed many cross loaded terrain features at mid-elevations on adjacent peaks. Continue to avoid wind loaded terrain and stick to lower angled slopes, especially when travelling in alpine areas. Large cornices exist and with warming temperatures this time of year they can become particularly sensitive. Longer days with even short periods of more intense sun can make them unstable. Give cornices a wide berth when travelling around them and avoid travel below them.


 

Avalanche Problem #2

WetAval Rain and mild temperatures yesterday made it easy to trigger shallow, loose, wet sluffs in recent snow on top of a melt-freeze crust at low to mid-elevations. Today, direct sun could increase the wet avalanche hazard on recent snow in elevations that remained cool yesterday. Wet, loose avalanches can start as small point releases, but are able to entrain recent storm snow and present a slow moving but increasing hazard particularly near terrain traps. Consider moving to a more shaded aspect if temperatures rapidly rise and sun begins to melt the snow surface.

 


Avalanche Problem #3

Deep Slab Deep slabs are still a problem given the weak snow found in shallow areas (video) as well as the rain crust from early March. Though these layers are deeply buried and difficult to trigger the possibility of an avalanche breaking on these layers still exists. The recent load placed on the snowpack combined with a human trigger in the right spot may be the tipping point for a deep slab. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. While the chances of triggering a slide on these layers may be low the consequences are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.


BOTTOM LINE

Overall, the avalanche hazard is MODERATE. This means that human triggered avalanches are possible, particularly on steep slopes with lingering storm snow instabilities and on aspects exposed to direct sun. Wind loaded slopes steeper than 35 degrees above 6000 feet are rated as CONSIDERABLE, human triggered avalanches are likely in these areas and cautious route finding is essential.  

 

Moderate_2  

Considerable

 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content

Avalanche Advisory – 3/29/2014

THIS ADVISORY HAS EXPIRED.

Issued: March 29, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Saturday, March 29, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Sunday, March 30, 2014.


MOUNTAIN WEATHER

WeatherGraphicA series of moist and progressively warmer storms impacted the advisory area over the past 48 hours. The current stream of moisture from the southwest is pointed directly at us. Currently, remote weather stations and SNOTEL sites report temperatures from 24 to 34°F with winds out of the southwest at 10-20 mph and gusts into the 30 mph range. Snowfall should continue at upper elevations with rain at lower elevations through the morning. Colder air should move into the region by this afternoon causing snow levels to drop a bit. Expect another 3-6 inches through the day with temperatures in the upper 20s to mid 30s F. Wind should be out of the southwest today at 10-25 mph and gusts into the 40 mph range particularly near the Continental Divide.

Storm totals over the past 48 hours:
Noisy Basin SNOTEL: 14 in. snow, 2.5 in. SWE
Stahl Peak SNOTEL: 10 in. snow, 1.9 in. SWE
Flattop SNOTEL: 9 in. snow, 1.1 in. SWE
Pike Creek SNOTEL: 12 in. snow, 0.7 in. SWE
Shed 7 weather station: 10 in. snow


RECENT OBSERVATIONS

RecentObservationsGraphic

It is spring and the mixed bag of weather continues as do the avalanches. Rain on new snow and heavy snow at upper elevations continue to fall throughout the advisory area. This will cause a slew of problems that include storm slabs, wind slabs, and wet avalanches. The Swan Range has received the most precipitation with impressive snow water equivalent totals (2.5 inches) over the past 48 hours.

Wind slabs were the biggest problem yesterday when we rode into Lost Johnny and Doris Creek drainages in the Swan Range. We found about 10-12 inches (25-30 cm) of new snow from Thursday into Friday (video). Moderate to strong winds created sensitive wind slabs on leeward slopes. We observed four natural slides that occurred on wind loaded slopes along the Swan crest. We also triggered two smaller wind slabs (10-20 inches deep) from the top of a ridge just by approaching the slopes (photo 1, photo 2). This evidence combined with the shooting cracks and unstable results in our stability tests (snow profiles) kept us far away from any wind loaded slope. Given the new load and the potential for storm slabs, we also stayed away from slopes steeper than 35 degrees. These problems will become even worse today with additional precipitation and continued moderate to strong winds.

We found a melt-freeze crust on all but the most shaded slopes underneath the new snow (photo) and also found this crust in the Middle Fork corridor in the Flathead Range on Thursday. This crust could provide a good bed surface for the new snow to slide on.

BNSF avalanche safety reported small wet, loose sluffs in John F. Stevens Canyon yesterday as well as other avalanche debris but did not observe any crown lines. However, they suspect these crown could have already reloaded with new and wind transported snow.

Glide cracks are beginning to rear their ugly heads again this spring. We noted a couple of glide cracks yesterday in the Swan Range (photo), and Glacier National Park rangers noted a few in the park this past week.

We received no other observations within the past 48 hours from any other locations.

 

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

 

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 10-20 inches. Width: 100 ft. 3/28/2014.

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 10-20 inches. Width: 100 ft. 3/28/2014.

 

Generalized upper snowpack structure on two different aspects in the Swan Range. 3/28/2014.

Generalized upper snowpack structure on two different aspects in the Swan Range. 3/28/2014.

 

 


 SNOWPACK DISCUSSION

Avalanche Problem #1

Storm Snow

Storm slabs and wind slabs are the main problem with heavy, new snow at upper elevations (particularly in the Swan Range) and moderate to strong winds the past 48 hours. Wind slabs were breaking yesterday about 10-20 inches deep and up to 200 feet wide. These wind slabs are sensitive particularly along ridges and cross-loaded terrain features like gullies. Avoid wind loaded terrain and stick to lower angled slopes today. Expect new storm slabs today as well with the new snow at upper elevations. Large cornices exist and with warming temperatures this time of year they can become particularly sensitive. Longer days with even short periods of more intense sun can make them unstable. Give cornices a wide berth when travelling around them and avoid travel below them.


Avalanche Problem #2

WetAval

It is hard to pin down the exact elevation of the rain/snow line this morning, but, regardless, wet avalanches will be a problem today. Rain on snow is never a good thing. We could see the whole gamut of wet avalanches today: wet loose, wet slab, and maybe even glide avalanches. Rain can accelerate the glide process so we can’t rule those out. Wet, loose avalanches can start as small point releases, but are able to entrain recent storm snow and present a slow moving but increasing hazard particularly near terrain traps. Wet slabs are difficult to predict but rain on this new storm snow could cause wet slabs at mid and lower elevations. Avoid slopes greater than 35 degrees and think about turning around when it begins to rain as conditions can change rapidly.


Avalanche Problem #3

Deep Slab

Deep slabs are still a problem given the weak snow found in shallow areas (video) as well as the rain crust from early March. Though these layers are deeply buried and difficult to trigger the possibility of an avalanche breaking on these layers still exists. The recent load placed on the snowpack combined with a human trigger in the right spot may be the tipping point for a deep slab. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. While the chances of triggering a slide on these layers may be low the consequences are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.


 BOTTOM LINE

With continued new snow, strong wind, and rain on snow  the avalanche hazard is CONSIDERABLE on most slopes and  HIGH on wind loaded slopes steeper than 35 degrees above 6,000 feet. This means that human triggered avalanches are likely, particularly on steep wind loaded slopes, and natural avalanches are possible to likely. Tricky and dangerous avalanche conditions exist so conservative decision making and terrain selection will be important today. Avoid wind loaded slopes and slopes steeper than 35 degrees. Recent and new wind and storm slab instabilities exist at higher elevations with wet avalanche problems at lower elevations. Periods of heavy snow, rain, and daytime warming effects can quickly change the likelihood of avalanches and the hazard could rise if more snow and rain fall than expected. 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

 

 

Avalanche Information Update – 3/28/2014

Good Morning! This is Erich Peitzsch with the Flathead Avalanche Center with an avalanche information update. The next regularly scheduled advisory will be issued Saturday, March 29, 2014. 

Mountain Weather

A moist system moved through the advisory area yesterday and overnight dropping 6-9 inches of new snow and 0.5 – 1.5 inches of SWE.  Storm total from the past 24 hours at SNOTEL sites and remote weather stations:
Noisy Basin (Swan Range): 10 inches snow, 1.5 inches SWE.
Stahl Peak (Whitefish Range): 7 inches snow, 1.0 inches SWE.
Flattop Mountain (Glacier Park): 6 inches snow, 0.4 inches SWE.
Pike Creek (Flathead Range): 7 inches snow, 0.3 inches SWE.
Shed 7 (Glacier Park): 6 inches snow.

Temperatures currently range from 22-29° F with winds out of the southwest at 5-20 mph and gusts into the 30 mph range. Another moist system moves into the region this afternoon/evening with snow levels potentially up to 5000 feet.

Snowpack Discussion

Substantial weight was recently added to the snowpack, particularly in the Swan Range which saw the largest accumulation of 1.5 inches of SWE in 24 hours. Weak layers and crusts are now buried by this new snow with additional wind transported snow from strong winds.  Expect to encounter storm slabs and wind slabs on any aspect, and cross loading can create wind slabs in gullies and exposed terrain features at any elevation. Surface crusts previously existed on all but the most shaded slopes from the most recent warm and sunny periods. These crusts provide a great bed surface for this new snow to slide on. Allow the snowpack time to adjust to this new load, and avoid steep and wind loaded slopes. Avalanches can fail within the new storm snow or at the new and old snow interface. Of course, these avalanches still have the potential to step down into deeper weaker snow in the snowpack as we still contend with a deep slab avalanche potential. Also be aware of avalanche terrain above you and avoid runout zones of avalanche paths.

The next regularly scheduled advisory will be Saturday, March 29, 2014.

 

Avalanche Advisory – 3/26/2014

THIS ADVISORY HAS EXPIRED.

Issued: March 26, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Wednesday, March 26, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Saturday, March 29, 2014.


MOUNTAIN WEATHER

WeatherGraphicOver the past 48 hours a ridge of high pressure over the region has maintained dry conditions with warm daytime temperatures and light winds. Yesterday, several mountain locations had temperatures in the 50s, Flattop Mountain SNOTEL recorded a high temperature of 52°F. Overnight temperatures were slow to dip back below freezing and a few areas near the divide picked up a small amount of snow last night (up to 2 inches). Currently, remote weather stations and SNOTEL sites are reading 25 to 33 °F with winds out of the southwest at 5-10 mph and gusts to 20 mph. Today light snow showers should continue in the area with gradually lowering snow levels and winds will be 5-15 mph out of the southwest. Showery conditions look to persist through Friday with precipitation becoming more steady Friday afternoon.

 


RECENT OBSERVATIONS

RecentObservationsGraphicYesterday was a beautiful day to ride into Kimmerly Basin in the Whitefish Range. We skied out Skookoleel Ridge in the morning and found unconsolidated surface snow on shaded aspects and a supportable melt-freeze crust on sunny aspects. It did not take long for the sun to penetrate the crust formed in the previous night, by noon our skis began to sink into the snow surface on sunny slopes. We dug snow pits on south, west, and north aspects (profiles). Our most concerning find was on a south aspect in an area of relatively shallow snow (205cm). The snow on the ground was weak and faceted and our entire column failed upon isolation (ECTPV). The good news is that the weak snow near the ground in this area was bridged by a nearly 20 cm(8 inch) thick melt-freeze crust making it difficult to trigger. Though, this still serves as a reminder that these instabilities continue to exist in our snowpack and ARE buried shallower in some areas with less force required to trigger an avalanche (Photo 1,2). On shaded aspects we observed small surface hoar developing and weak snow near the surface that could become a future issue with new snow on top.  While riding out of Kimmerly Basin in the afternoon we observed relatively small loose, wet avalanche activity on sun exposed slopes (photo).

BNSF avalanche safety was in the John F Stevens Canyon yesterday and found several layers of concern that were deeper in the snowpack, stability testing produced variable results on these layers (observation).

On Sunday skiers on Peak 6996 in the John F Stevens Canyon found a small layer of weak snow 70 cm from the surface that failed in compression tests with hard force(observation).

 

Large grained depth hoar found near the ground. Skookoleel Creek, Whitefish Range. 3/25/2014

Large grained depth hoar found near the ground. Skookoleel Creek, Whitefish Range. 3/25/2014


Entire column failure upon isolating the back of the column. Skookoleel Creek, Whitefish Range. 3/25/2014

Entire column failure upon isolating the back of the column. Skookoleel Creek, Whitefish Range. 3/25/2014


Loose, wet avalanche in Kimmerly Basin. Whitefish Range 3/25/2014

Loose, wet avalanche in Kimmerly Basin. Whitefish Range 3/25/2014


Loose, wet avalanche in Kimmerly Basin. Whitefish Range 3/25/2014

Loose, wet avalanche in Kimmerly Basin. Whitefish Range 3/25/2014

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

Deep SlabThough deeply buried and difficult to trigger, the late January/early February crust/facet layer in addition to weak, faceted snow near the ground still lurks in the snowpack. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. The rain event that provided the trigger for that large avalanche cycle in early March formed a thick rain crust that now sits about 2-3 feet from the surface. This layer has shown instability in some areas with recent stability tests. The chances of triggering an avalanche on these layers may be low, but the consequences are high. It remains important to do site specific evaluation of persistent slab in the areas you are travelling and remember that tracks (even lots of tracks) do not mean stability. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether. Additionally, large cornices tower over many slopes in the area and their strength will be tested through the spring with increasing direct sun and warming temperatures. The large amount of force exerted by a falling cornice can trigger these deep instabilities. It will become increasingly important to be aware of cornices when travelling in the backcountry. As usual, give them a wide margin when above them and avoid areas below them.

 


 

Spring can bring a mixed bag of weather and snow conditions. Mountain temperatures remain near the freezing mark this morning and a small amount of precipitation is in the forecast. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions this time of year. Pay particular attention to rain falling on the snow if temperatures climb higher than expected.

 


BOTTOM LINE

For today, the overall avalanche hazard is MODERATE. This means that human triggered avalanches are possible, particularly on steep slopes and areas of shallow snow where deeper instabilities exist in the snowpack. It remains important to evaluate snowpack and terrain carefully in the specific areas that you are travelling in.

Moderate_2

 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

 

 

Avalanche Information Update – 3/24/2014

Today, temperatures in some mountain locations rose to above freezing temperatures. Temperatures are expected to be warmer tomorrow increasing the wet avalanche hazard, particularly on sunny aspects.  Be aware of changing weather conditions, specifically rapidly rising temperatures. If travelling on or below sun exposed slopes consider turning around or moving to shaded areas if the snow surface becomes wet, skis or boots sink deep into the snow, or pin wheels or roller balls start to form on steep slopes. Tomorrow the potential exists for both loose, wet avalanches as well as wet slab avalanches. Keep in mind that even small avalanches can have severe consequences when traveling in or above terrain traps such as gullies, cliffs, or road cuts.  Large cornices will also become less stable with the warm temperatures in the forecast. It is important to stay well behind confirmed solid ground when travelling above cornices and avoid travel below. Aside from being a hazard themselves, cornice falls have the potential to trigger deeper instabilities within the snowpack. See Sunday’s advisory below for details on existing avalanche problems. Continue to closely monitor changes in weather conditions and maintain a conservative approach to terrain selection. FAC will be issuing a regularly scheduled advisory on Wednesday, March 26. Check the avalanche advisory for up to date information and hazard ratings.

 

Avalanche Advisory – 3/23/2014

THIS ADVISORY HAS EXPIRED

Issued: March 23, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Sunday, March 23, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Wednesday, March 26, 2014.


MOUNTAIN WEATHER

WeatherGraphicYesterday’s sunny weather transitioned to a quick moving disturbance that dropped 1-6 inches of new snow overnight throughout the advisory area. Winds shifted back to the southwest yesterday. Currently, remote weather stations and SNOTEL sites report temperatures from 18 to 23 °F with winds out of the southwest at 5-15 mph and gusts into the 20 mph range. Snowfall should taper through the day and may linger in locations closer to the Continental Divide. Expect another 1-3 inches through the day with temperatures in the mid-20s to mid-30s F. Wind should be out of the west today at 10-20 mph. High pressure builds into the region tonight into tomorrow bringing drier weather.

Storm totals over the past seven days:
Flattop SNOTEL: 33 in. snow, 4.4 in. SWE
Stahl Peak SNOTEL: 24 in. snow, 3.8 in. SWE
Noisy Basin SNOTEL: 20 in. snow, 3.0 in. SWE
Pike Creek SNOTEL: 16 in. snow, 0.6 in. SWE
Shed 7 weather station: 31 in. snow


RECENT OBSERVATIONS

RecentObservationsGraphic

Given that wind slab is our primary concern we traveled in the Lewis Range in the southern part of Glacier National Park yesterday on the hunt for this problem. We found them particularly above 6500 feet. We observed both hard and soft wind slabs on numerous aspects. These slabs were shallow (less than a foot) in the areas we investigated, but we purposefully stayed away from large, steep, wind loaded slopes. These slabs failed easily in stability tests (video) and we also observed minor cracking of wind slabs on small rollover test slopes. BNSF Avalanche Safety also observed active wind loading on Thursday in an adjacent area (observation). We also observed a skier triggered slab in Cascadilla Creek drainage (Flathead Range) yesterday morning (photo). We are not sure on the exact timing, but it occurred before Saturday morning.

We also observed weak faceted snow near the ground that failed and propagated in our stability tests (profile), and is still a concern for persistent slab potential in areas of shallow snow. These results are consistent with BNSF Avalanche Safety observations over the past 10 days in a nearby area.

The early March rain crust is noticeable in every snow pit, and appears to be behaving itself so far. However, on Thursday in the northern Whitefish Range, this layer showed the potential to propagate a fracture in our stability tests (video). On Friday, Todd was in the Six Mile Peak area in the Swan Range where he observed active wind drifting on high peaks. He found the early March rain crust buried 2-3 feet deep and the snow above and below was fairly consolidated relative to the rest of the snowpack (photo).

Skiers in the southern Whitefish Range yesterday noted a sun crust that formed Friday afternoon on most sun exposed slopes, but found soft, unconsolidated snow on shaded aspects with no obvious signs of instability and small recent activity on sun exposed slopes from Friday.

 

Cascadilla Creek basin, Flathead Range ,Middle Fork Corridor. Observed 3/22/2014.

Cascadilla Creek basin, Flathead Range ,Middle Fork Corridor. Observed 3/22/2014.

General snow profile on east aspect in the Six Mile Peak area. Swan Range 3/21/2014

General snow profile in the Six Mile Peak area. Swan Range 3/21/2014

Generalized image of upper snowpack highlighting the March 9 rain crust about 2-3 feet below the surface. Red Meadow, Whitefish Range. 3/20/2014.

Generalized image of upper snowpack. Red Meadow, Whitefish Range. 3/20/2014.


SNOWPACK DISCUSSION

Avalanche Problem #1

Wind SlabThe recipe for wind slab formation exists with over 20-30 inches of new snow in the past seven days accompanied by strong winds. The new snow overnight has even slightly buried these wind slabs so they may not be as obvious or visible. It can take up to a week for wind slabs to stabilize. These wind slabs are sensitive particularly along ridgelines and cross-loaded terrain features like gullies. Recent north winds also caused drifting snow along high elevation ridgelines potentially forming new wind slabs on slopes that are typically windward. Avoid wind loaded terrain steeper than 35 degrees and stick to non-wind affected slopes. In addition to wind slabs, cornices formed over the season can become particularly sensitive this time of year. Longer days with even short periods of more intense sun can make them unstable. Stay well clear of cornices when travelling near them and avoid travel below them.


Avalanche Problem #2

Deep Slab

Though deeply buried and difficult to trigger, the late January/early February crust/facet layer in addition to weak, faceted snow near the ground still lurks in the snowpack. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. The rain event that provided the trigger for that large avalanche cycle in early March formed a thick rain crust that now sits about 2-3 feet from the surface. This layer has shown instability in recent stability tests. The chances of triggering an avalanche on these layers may be low, but the consequences are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether. 

 


Spring can bring a mixed bag of weather and snow conditions. While overnight storm amounts aren’t particularly impressive, this new snow came in with warmer temperatures than the previous snow over the past 48 hours. Above freezing temperatures combined with any sunshine this afternoon could cause loose, wet sluffs. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions this time of year. Pay particular attention to sun exposed slopes as the day progresses.


BOTTOM LINE

For today, the overall avalanche hazard is MODERATE. This means that human triggered avalanches are possible, particularly on steep slopes and areas of shallow snow where deeper instabilities exist in the snowpack. It is also possible to trigger an avalanche within the recent storm snow from over the past week. Wind loaded slopes above 6500 feet and steeper than 35 degrees are rated as CONSIDERABLE meaning that human triggered avalanches are possible to likely in these areas. Avoid wind loaded slopes particularly at upper elevations, along ridges, and on convex rollovers.

Moderate_2

 Considerable

 


Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

 

 

Avalanche Advisory – 3/22/2014

THIS ADVISORY HAS EXPIRED.

Issued: March 22, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Saturday, March 22, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Sunday, March 23, 2014.


MOUNTAIN WEATHER

WeatherGraphicHappy spring! Since the first day of spring we picked up between 5 and 14 inches of snow and mountain temperatures have remained below freezing in most locations. In the past 24 hours, we received up to 2 inches of new snow before showers tapered. Winds shifted out of the north and have been blowing 5-15 mph in most areas with 10-25 mph winds on the high ridges. Currently, remote weather stations and SNOTEL sites are reading -7 to 13 °F with north and east winds at 5-15 mph with gusts in the high 20s. Today will see partly cloudy skies becoming mostly cloudy with temperatures from the teens up to mid-20s. Winds should be light out of the southwest with the potential for isolated light snow showers.


RECENT OBSERVATIONS

RecentObservationsGraphicYesterday we rode into the Six Mile Peak area in the Swan Range. Though the areas where we traveled were more protected, we could see wind drifting the snow on adjacent high peaks (photo). We found 20-30cm of recent, unconsolidated snow from the previous 48 hrs. Temperatures remained cold through the day and the intermittent sun had minimal effect on the surface snow. We found the early March rain crust buried 70-80 cm deep and the snow above and below was fairly consolidated relative to the rest of the snowpack (photo). We found some instability within recent snow but were unable to propagate a fracture in any of our extended column tests (profile).  On Thursday, Erich was in the Red Meadow area in the Whitefish Range and found a layer that was able to propagate a fracture on the early March rain crust during several stability tests (observation) causing this layer to remain as a concern.

 On Thursday, BNSF avalanche safety reported 20-30 cm of new snow being transported onto east aspects along the ridgeline. The layer of greatest concern that they discovered in their snow profiles was an interface between a decomposing crust and a layer of weaker snow (observation).

General snow profile on east aspect in the Six Mile Peak area. Swan Range 3/21/2014

General snow profile on east aspect in the Six Mile Peak area. Swan Range 3/21/2014


Wind transporting snow on adjacent peaks. Six Mile, Swan Range. 3/21/2014

Wind transporting snow on adjacent peaks. Six Mile, Swan Range. 3/21/2014


Generalized image of upper snowpack highlighting the March 9 rain crust about 2-3 feet below the surface. Red Meadow, Whitefish Range. 3/20/2014.

Generalized image of upper snowpack highlighting the March 9 rain crust about 2-3 feet below the surface. Red Meadow, Whitefish Range. 3/20/2014.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

Wind SlabWith recent snow accumulations and strong winds earlier in the week, the potential exists to encounter recently formed wind slabs that are still reactive. Additionally, yesterday we observed north winds drifting snow along high elevation ridgelines potentially forming new wind slabs in the alpine zones on slopes that are typically windward. When travelling in high elevations, avoid wind loaded terrain steeper than 35 degrees, stick to lower slope angles, sheltered or scoured areas. Although care should always be taken when traveling around and approaching cornices, this time of year they can become particularly sensitive. Longer days with even short periods of more intense sun than they have been previously subjected to can make them unstable. Stay well behind confirmed solid ground when travelling above cornices and avoid travel below them.


Avalanche Problem #2

Persistent SlabSeveral layers within our snowpack pose a persistent slab and deep persistent slab threat that will likely plague us for the rest of the season. Though deeply buried and difficult to trigger, the late January/early February crust/facet layer still lurks in the snowpack. The possibility for avalanches to fail in these layers still exists if they are triggered in the right spot, specifically in areas notorious for harboring shallow snow like scoured areas or steep rocky terrain. The rain event that provided the trigger for that large avalanche cycle in early March formed a thick rain crust that now sits about 2-3 feet from the surface. Weak, moist snow has been observed below this crust and is also a concern. While we have yet to hear or observe any reactivity of this layer it cannot be ruled out as a potential persistent slab problem. The consequences of an avalanche breaking on these layers are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.

 


Oh, Spring in northwest Montana! Spring can bring a mixed bag of weather and snow conditions. It is not uncommon to have sun, snow, and rain in the mountains all in one day during this time of year. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions. Pay particular attention to sun exposed slopes as the day progresses as well as rain on snow as wet avalanche conditions can change quickly.


BOTTOM LINE

For today, the overall avalanche hazard is MODERATE. This means that human triggered avalanches are possible, particularly on steep slopes and areas of shallow snow where deeper instabilities exist in the snowpack. Wind loaded slopes above 6500 feet and steeper than 35° are rated as CONSIDERABLE meaning that human triggered avalanches are likely in these areas.

Moderate_2

 Considerable

 

 


 

Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

 

 

Avalanche Advisory – 3/19/2014

THIS ADVISORY HAS EXPIRED

Issued: March 19, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Wednesday, March 19, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Saturday, March 22, 2014.


MOUNTAIN WEATHER

WeatherGraphicThe most recent storm dropped up to 10-18 inches within our advisory area and tapered late Monday night (SNOTEL and remote weather stations). Winds gusted into the 25-30 mph range. Partly to mostly cloudy skies dominated yesterday with moderate wind. Currently, mountain temperatures range from 17-25 °F with winds out of the southwest at 5-30 mph with gusts to 45 mph in southern Glacier Park. No new snow fell overnight, but another disturbance rolls through the area this afternoon through tomorrow. Today, temperatures should range from the mid-20s to low 30s F with winds 10-20 mph and gusts to 30 mph. Snow should begin this afternoon and we could see up to 6 inches by tomorrow morning at upper elevations within the advisory area.


 RECENT OBSERVATIONS

RecentObservationsGraphic

On Tuesday we traveled in the Middle Fork corridor of the northern Flathead Range. We found up to 12-18 inches (30-45 cm) of new snow. On leeward slopes we found sensitive wind slabs (photo). These were easily triggered and up to a foot thick. As they traveled downhill they would entrain both dry and wet (depending on aspect and elevation) sluffs that ran several hundred vertical feet. These sluffs were also fairly easy to trigger on steep, small test slopes (photo).

We also found the early March rain crust about 30 inches (80 cm) from the surface (profile). This crust is about 8 inches (20 cm) thick and harbors softer moist, weak snow below it (video). Most sun exposed slopes formed yet another sun crust on the surface by late in the day. The new snow on these slopes became wet and heavy throughout the day.

BNSF Avalanche Safety reported three small soft slab avalanches in John F. Stevens Canyon in southern Glacier Park yesterday involving the new storm snow. These occurred on high elevation east facing slopes and probably during the storm on Monday (photos). These slabs ran about 100-200 vertical feet. They also reported 12 inches (30 cm) in the canyon floor and 18 inches (45 cm) at upper elevations.

Skiers in the Essex area in the Flathead Range on Monday reported a few natural sluffs within the new snow and localized cracking while skiing during the storm. They found various layers to be somewhat reactive with moderate to hard force in their stability tests including the layer of moist, weak snow below the thick early March rain crust.

We received no observations from the Swan Range or the Whitefish Range so our confidence in these areas is fair.

Wind slabs were sensitive and easy to trigger. They weren't very wide, but were up to a foot deep. 3/18/2014.

Wind slabs were sensitive and easy to trigger. They weren’t very wide, but were up to a foot deep. 3/18/2014.

Both loose wet and loose dry avalanches were easy to trigger on slopes steeper than 35 degrees. 3/18/2014.

Both loose wet and loose dry avalanches were easy to trigger on slopes steeper than 35 degrees. 3/18/2014.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.

Small soft slab avalanche in John F. Stevens Canyon observed Tuesday (3/18/2014). Photo: BNSF Avalanche Safety.


 SNOWPACK DISCUSSION

Avalanche Problem #1

Wind Slab

Wind slabs were easy to trigger yesterday, and should be again today. Increasing winds and a bit of new snow this afternoon will continue to form wind slabs. These slabs weren’t particularly wide, but even a slab up to a foot deep can have high consequences. The slabs observed by BNSF Avalanche Safety occurred on easterly aspects which were loaded by wind during the recent storm. Look for and avoid convex pillows of wind-drifted snow on the lee side of ridges and other terrain features. Wind slabs are confined to leeward slopes and cross-loaded terrain features and can be avoided by sticking to sheltered or wind-scoured areas. 


Avalanche Problem #2

Persistent Slab

Several layers within our snowpack pose a persistent slab and deep persistent slab threat. The late January/early February crust/facet layer that was the weak layer responsible for the large, natural avalanche cycle almost two weeks ago still lurks. Even though it is buried deeply the possibility for avalanches to fail or step down on this layer still exists, particularly in areas of shallow snow as demonstrated by BNSF Avalanche Safety less than a week ago (video). The rain event that provided the trigger for that large cycle formed a thick rain crust that now sits about 2-3 feet from the surface. Weak, moist snow sits below this crust and is also a concern. While we have yet to hear or observe any reactivity of this layer it cannot be ruled out as a potential persistent slab problem. These layers may be harder to trigger now, but the consequences of an avalanche breaking on these layers are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.

Also, cornices are ripe and ready to fail especially during times of warm weather or rain. They can trigger deeper layers when they hit the slope so stay off of and out from underneath these giant monsters.


Oh, Spring in northwest Montana! Spring can bring a mixed bag of weather and snow conditions. It is not uncommon to have sun, snow, and rain in the mountains all in one day during this time of year. It is important to pay attention to rapidly changing conditions as weather can greatly affect snow and avalanche conditions. Pay particular attention to sun exposed slopes as the day progresses as well as rain on snow as wet avalanche conditions can change quickly.


BOTTOM LINE

For today, the avalanche hazard is CONSIDERABLE on wind loaded slopes and MODERATE on all other slopes This means that human triggered avalanches are likely on slopes where wind formed sensitive wind slabs. Deeper instabilities within the snowpack exist and it is still possible to trigger an avalanche on these deeper layers particularly in areas of shallow snow and steep slopes. It is also possible to trigger an avalanche involving the recent storm snow. Cautious routefinding and conservative decision making are essential. Identify areas of wind drifted snow and weak layers buried deeper in the snowpack and avoid these areas.

Considerable

 

Moderate_2 

 


 

Note: The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding/skiing spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.


See recent snow profiles as well as snow profiles from the entire season here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


DISCLAIMER

DisclaimerGraphic

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.