THIS AVALANCHE ADVISORY EXPIRED ON March 20, 2017 @ 11:41 pm
Avalanche Advisory published on March 20, 2017 @ 6:41 am
Issued by Mark Dundas - Flathead National Forest

Whitefish Range
Swan Range
Flathead Range and Glacier National Park

How to read the advisory

Cool temperatures overnight currently "locked up" the snowpack at all elevations and on all aspects. The avalanche danger is LOW at all elevations this morning but the danger may rise on sunny aspects as temperatures warm and the sun breaks down the surface crust. Pay attention to changing conditions at the snow surface and move to a different aspect, or end your day early, before your skis or machine start to punch through the surface crust.

1. Low

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Above 6000 ft.
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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5000-6000 ft.
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

?

3500-5000 ft.
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
  • 1. Low
  • 2. Moderate
  • 3. Considerable
  • 4. High
  • 5. Extreme
Avalanche Problem 1: Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Yesterday, despite afternoon bluebird conditions, skiers reported a strong surface crust at upper elevations which did not break down as the day progressed. The longevity of this crust was due partly to cool temperatures but mostly because of the consistent westerly winds that kept the surface cool despite the relatively intense March sun. Wind direction shifted overnight and today's winds will be from the north and east with lower wind speeds than yesterday. Sunny aspects that face opposite these winds may warm more rapidly than yesterday. Below the surface crust is a thick layer of moist unsupportable snow. My tour in the Flathead Range yesterday found my skis wallowing in this moist snow at low and mid elevations. Monitor the strength of the surface crust today and move to a different aspect before you find your skis or machine punching into the moist underlying snow. If the crust does indeed break down it will be possible for a human triggered wet loose avalanche to entrain this moist snow. Keep in mind that even short seemingly benign slopes can be dangerous when the effects of an avalanche are amplified by terrain traps like narrow gullies, cliffs, and trees.

advisory discussion

Spring can bring a mixed bag of weather conditions to northwest Montana. It can surprise us with intense snow squalls, warm temperatures, and rain-on-snow events (even in the same day). This makes it increasingly important to closely monitor changing conditions.  With longer days and a higher sun angle, conditions can rapidly change.

In isolated areas a layer of weak sugary snow (facets) sitting on top of the Feb. 10th rain crust produced unstable results in stability tests. I suspect that a few natural avalanches that occured recently were associated with that interface. This illustrates the importance of digging into the snow and continuing to assess deeper instabilities particularly after a recent, substantial load. In most locations the Feb. 10 crust is buried 2.5 to 4 feet from the snow surface.

recent observations

Sunday: Mark traveled to Cascadilla Creek in the Flathead Range where he noted numerous large avalanches that occurred during the March 15 wam rain event. In the morning the snow surface was unsupportable at low elevations and by early afternoon the sun had broken down the thin surface crust on sunny aspects at mid elevations making the surface unsupportable. Zach toured to Skook Ridge in the southern Whitefish Range where he found a strong supportable surface crust on all aspects. This crust was noticeably thicker on solar aspects and the light winds kept the surface firm through most of the day. Skiers on Elk Mountain, in southern Glacier Park, found a frozen snow surface above 5600' due to strong west winds and cool temperatures. Boot penetration was negligible.

Friday: Mark toured into Rescue Creek in the Flathead Range and observed substantial avalanche activity from the warm wet weather of 3/15. Avalanches were noted on all aspects at all elevations. Avalanche debris traveled the length of the valley floor with a destructive size of D4. A strong surface crust was present on the snow surface at all elevations. Guy rode in Hellroaring Creek in the Mission Mountains and found evidence of recent wet loose and slab avalanches. He also noted glide cracks and a stout surface crust.

Thursday: Adam and Todd were on Tunnel Ridge in the Flathead Range. Temperatures started off warm , but rapidly decreased as a cold front moved into the area. Up to about 6000 feet they found that recent melt and rain water had percolated through the entire snow pack. At 7000 feet only the upper snowpack was moist. Along the ridgeline wind direction was variable with gusts to 45 mph, but only transporting snow on the highest surrounding peaks.  WMR Ski Patrol reported natural loose, wet activity in the Skook Chutes with debris all the way to Canyon Creek.  They suspected these avalanches to have run on Wednesday (3/15).

See below for all observations this season.

Weather and CURRENT CONDITIONS
weather summary

Yesterday was a benign weather day with skies becoming mostly clear by afternoon and temperatures at upper elevation locations peaking at around the freezing mark. Currently, temperatures above 6000' range from 16-24º F with light winds of 1-5 mph and gusts to 10. Cooler temperatures are on tap for today with light winds and occasional moderate gusts out of the east-northeast. Today will be mostly dry with light precipitation moving into our area this evening.

Today’s weather observations near 6000 feet in the region
0600 temperature: 16-24 deg. F.
Max. temperature in the last 24 hours: 30-37 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 4-23 mph
Maximum wind gust in the last 24 hours: 14-40 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 86-117 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Missoula NWS
For 3000 ft. to 5000 ft.
Monday Monday Night Tuesday
Weather: Dry and cooler conditions. Light precipitation entering our area. Warming temperatures with light precipitation.
Temperatures: 27-43 deg. F. 16-26 deg. F. 33-47 deg. F.
Wind Direction: East-northeast East-northeast East
Wind Speed: 10-12 mph with gusts to 21 8-10 mph with gusts to 18 6-7 mph with gusts to 16
Expected snowfall: 0 in. 0-1 in. 0-2 in.
For 5000 ft. to 7000 ft.
Monday Monday Night Tuesday
Weather: Dry and cooler conditions. Light precipitation entering our area. Warming temperatures with light precipitation.
Temperatures: 24-34 deg. F. 13-23 deg. F. 32-41 deg. F.
Wind Direction: East East Southeast
Wind Speed: 9-10 mph with gusts to 21 10-12 mph with gusts to 23 7-8 mph with gusts to 20
Expected snowfall: 0 in. 0-1 in. 0-2 in.
Disclaimer

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 at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.