THIS ADVISORY HAS EXPIRED
Issued: March 8, 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 8, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Sunday, March 9, 2014.
Well, it seems like someone finally turned off the faucet…for today at least. Storm totals were impressive since Sunday (see below). A brief break in stormy weather occurs today as a short-lived ridge exists over the region. Currently, mountain temperatures range from 25-33° F and winds are out of the west-southwest at 5-17 mph. Today, temperatures will climb above freezing in many locations potentially into the mid-40s F. Intense solar warming is expected as long as the cloud cover stays away. Wind will be out of the southwest at 10-20 mph with gusts to 40 mph. Another moist system will roll through the area tonight and tomorrow with rising temperatures and the potential of snow levels rising to 7000 feet.
Snow accumulation from this past storm ranged from 15-30 inches, but the amount of weight placed on the existing snowpack is measured in snow water equivalent. True total snowfall amounts are difficult to assess from SNOTEL sites from this storm because of such warm temps, rain, and rapid settlement rates. Here are snow water equivalent (SWE) storm totals from area SNOTEL sites since the onset of the storm on Sunday, 3/2:
Flattop SNOTEL (Glacier Park): 6.5 inches of SWE.
Stahl Peak (Whitefish Range): 4.1 inches of SWE.
Noisy Basin (Swan Range): 3.6 inches of SWE.
Pike Creek (eastern edge of Flathead Range): 3.3 inches of SWE.
A widespread natural avalanche cycle began on Monday (3/3) with moderately sized natural avalanches and continued through Thursday morning with large natural avalanches occurring in all mountain ranges in our advisory area on all aspects (photos and observation). We ventured into the Lost Johnny drainage in the Swan Range on Thursday and observed debris from large, natural avalanches that occurred within the past few days.
On our way to China Basin in the Whitefish Range yesterday, we observed more large avalanches in the Apgar Range along the North Fork of the Flathead River corridor. In China Basin, we observed a heavy, wet snow surface up to about 6000 feet making riding conditions difficult. Above this, the storm snow was still heavy but not quite as wet. We found about 30 inches (80 cm) of new storm snow above an old ice crust. A layer of graupel about 14 inches from the snow surface is a concern (photo). This layer has the potential to propagate a fracture in stability tests (video and snow profile) and is susceptible to human triggering today. The old crust/facet combination from late January/early February is now deeply buried, but was potentially the failure layer of many of the natural avalanches from this past week and cannot be ruled out as a deep persistent slab problem.
We received no other field observations aside from BNSF Avalanche Safety avalanche observations and our own, so our confidence regarding snowpack stability post-storm right now is fair.
Avalanche Problem #1
Even though precipitation finally tapered and ended yesterday, storm snow is still an avalanche problem. The layer of graupel about a foot or more from the surface shows signs of instability. Typically, graupel is a short-lived instability, but it could be a problem today. Since Sunday, large loads were placed upon the snowpack, and in many locations it failed in a big way. However, there are slopes that did not avalanche and may be waiting for just the right trigger. The snowpack still needs time to adjust to this new load, and above freezing temperatures and solar warming today could exacerbate this problem and natural avalanches are a possibility today. Thus, it is important to ease into the backcountry today and carefully assess each slope. Conservative decision making and careful terrain selection will be essential in determining how reactive the new snow is to human triggering especially with warming well above freezing and intense solar input.
Avalanche Problem #2
Above freezing temperatures and intense solar input today are likely to cause wet snow problems. The snow surface is already wet from rain and is likely to become more wet today. Wet loose avalanches are likely on sunny aspects today. Avoiding sun affected slopes, particularly later in the day, will be a good idea. These types of avalanches can entrain a lot of snow especially the new surface snow. Pay attention to rapidly changing conditions and watch for signs of wet snow instability like rollerballs and point releases.
Avalanche Problem #3
This new storm buried persistent weak layers even deeper. The persistent slab on top of the mid-January crust with weak snow above the crust was a problem before this storm and can still pose a threat. Additionally, there is another layer of weak faceted snow now about 3-4 feet from the surface. Once initiated, a persistent slab has the ability to propagate long distances, change aspects, and wrap around terrain features as we witnessed with this large natural cycle. Remain vigilant in assessing slopes for persistent slab instabilities and be aware of the potential for smaller avalanches to step down into these deeper layers. Identifying deep persistent slabs is only half of the battle. Think of how and in what areas you might be able to trigger them. Continue to avoid areas where triggering these deeper slabs is more likely, such as steep convex rollovers and in areas with shallow snow often found in steep rocky terrain or scoured areas. Without the obvious signs of instability such as shooting cracks and collapsing the only way to know what you are skiing or riding over is to dig into the snow.
For today the avalanche hazard is CONSIDERABLE but could rise higher on sunny aspects with well above freezing temperatures and intense solar warming. This means that human triggered avalanches are likely and natural avalanches are possible today. The new snow still shows signs of instability and the potential of storm slab avalanches exists. Wet avalanches may also become a problem throughout the day with rising temperatures and intense solar warming. Pay attention to rapidly changing conditions and stay off of and out from under slopes affected by the sun later today. Careful snowpack evaluation and cautious route-finding are essential.
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 email@example.com. Thanks for your help.
See recent snow profiles as well as snow profiles from the entire season here.
Join us March 14, 8:00 p.m. at Penco. We are working with the Flathead Snowmobile Association for the first in a series of motorized specific backcountry safety seminars. Details 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.
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.