THIS AVALANCHE FORECAST EXPIRED ON March 13, 2017 @ 11:59 pm
Avalanche Forecast published on March 13, 2017 @ 6:59 am
Issued by Mark Dundas - Flathead National Forest

Whitefish Range
Swan Range
Flathead Range and Glacier National Park

How to read the forecast

Recent snowfall is being transported onto leeward slopes by moderate southwesterly winds. Wind slabs are forming on lower density snow creating dangerous avalanche conditions. The avalanche danger is CONSIDERABLE above 6000 feet where a human triggered avalanche is likely on wind loaded aspects. Carefully evaluate wind loaded terrain before committing to a slope. Below 6000 feet the danger is MODERATE where heightened avalanche conditions exist due to continued wind loading, warming temperatures and the potential of rain today.

3. Considerable

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Above 6500 ft.
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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5000-6500 ft.
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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3500-5000 ft.
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
  • 1. Low
  • 2. Moderate
  • 3. Considerable
  • 4. High
  • 5. Extreme
Avalanche Problem 1: Wind Slab
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Once again our area experienced breezy conditions through the day yesterday and overnight. Wind speeds were sufficient to continue to drift the relatively heavy surface snow at both mid and upper elevations. We were surprised to observe active wind transport in relatively sheltered mid elevation areas in the Marion Lake area yesterday. Despite the dense nature of the new snow the wind was having no problem drifting this snow onto leeward aspects. The slab that is forming is being deposited onto lower density snow and creating unstable surface snow conditions. Human triggered avalanches are likely on wind loaded terrain today and we recommend that you carefully evaluate all wind loaded terrain before committing to a slope. 

Winds and snowfall from the bountiful 2 week storm cycle have formed large cornices across our advisory area. Recent warming temperatures have weakened these features and it is best to give them a wide berth and avoid traveling underneath them. Yesterday morning BNSF avalanche safety reported that warming temperatures contributed to a cornice failure which triggered a slab avalanche in John F. Stevens Canyon.

Avalanche Problem 2: Loose Wet
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Temperatures at low elevations throughout our area have been above freezing for approximately 48 hours. Recent rain has added weight and weakened the snow surface at this elevation. Mid and upper elevations received snow over the past 36 hours but temperatures will rise above freezing today and start the weakening process in this layer. Rain entering our area this afternoon will further degrade conditions. Wet loose activity is possible at both low and mid elevations today and may affect the upper elevations if rain enters our area sooner than expected this afternoon. 

Forecast discussion
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Abundant recent snow formed a hefty slab on top of the February 10 rain crust. In isolated locations (closer to the Continental Divide) a layer of weak sugary snow (facets) sitting on top of this crust fractured and propagated across the column in stability tests. Collapsing on this layer was also reported yesterday in southern GNP. No avalanches have been reported or observed on this layer recently, BUT it is important to assess this layer by digging into the snow. That is the only way you are going to know how a layer this deep is behaving. In most locations this layer existst 2.5 to 4 feet from the snow surface. So, do your homework, and dig into the snow.

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 higher sun angle conditions can rapidly change.

recent observations

Sunday: Mark toured in the Marion Lake area of the Flathead Range where the rain/snow line was at approximately 5400'. Below 5400' the surface snow was saturated from recent heavy rain with up to 4" of new snow noted at upper elevations. Moderate winds transported snow at both mid and upper elevations throughout our tour. Cracking in the new dense snow and wind affected snow was frequent but propagation was limited. Skiers on Peak 6996 in southern Glacier Park reported snow, not rain, falling at the trailhead at 4500'. They also observed wind transporting the surface snow at upper elevations and new wind slab development. Near the summit they observed 8" of new snow and found the surface wind slab, and in sheltered areas the new snow, to be reactive but propagation was not observed.   

Saturday: Skiers in the southern Whitefish Range noted numerous small wet loose avalanches in the Skook Chutes, thin wind slabs at upper elevations and heavy wet snow below 5000 feet. Stability tests produced failures with easy force in the top 40 cm but no full propagation was observed.

Friday: Guy and Mark traveled into Noisy Basin in the Swan Range where they observed numerous thin storm slab avalanches at all elevations and on all aspects. The dense 5-6" of new snow overnight had created an upside down snow surface structure and was responsible for these slides. They had failure at several locations in their pit due to density changes in the recent snow.  In John F. Stevens Canyon, in southern Glacier Park, BNSF avalanche safety reported a number of storm slab avalanches as the arctic air retreated to the east and the day warmed.

See below for all observations this season.

Weather and CURRENT CONDITIONS
Weather Station Map
Weather Station Table
weather summary

Yesterday our area received rain, heavy at times, at low elevations with several inches of new snow at mid and upper elevations. Currently, temperatures above 6000 feet range from 26-33º F with breezy winds of 6-16 mph and gusts from 13-33. Today, we should expect temperatures warming above freezing at all elevations with precipitation moving into our area this afternoon. 

Today’s weather observations near 6000 feet in the region
0600 temperature: 26-33 deg. F.
Max. temperature in the last 24 hours: 29-37 deg. F.
Average wind direction during the last 24 hours: Southwest
Average wind speed during the last 24 hours: 6-26 mph
Maximum wind gust in the last 24 hours: 8-41 mph
New snowfall in the last 24 hours: 0-4 inches
Total snow depth: 100-131 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Missoula NWS
For 5000 ft. to 7000 ft.
Monday Monday Night Tuesday
Cloud Cover: Precipitation increasing this afternoon with warm temperatures and breezy conditions. Moderate precipitation with warm temperatures and continued breezy. Well above normal temperatures with continued precipitation.
Temperatures: 36-47 deg. F. 27-33 deg. F. 38-50 deg. F.
Wind Direction: West-southwest Southwest South-Southwest
Wind Speed: 10-12 mph with gusts to 29 7-10 mph with gusts to 25 5-8 mph with gusts to 23
Snowfall: 1-2 in. 0-3 in. 0-2 in.
Snow Line:
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.