THIS AVALANCHE FORECAST EXPIRED ON December 10, 2016 @ 11:58 pm
Avalanche Forecast published on December 10, 2016 @ 6:58 am
Issued by Mark Dundas - Flathead National Forest

Whitefish Range
Swan Range
Flathead Range and Glacier National Park

How to read the forecast

Rising avalanche conditions exist due to relatively warmer denser snow being deposited onto cold low density snow forming storm slabs. Increasing winds will form fresh wind slabs on leeward aspects. We will start the day with MODERATE avalanche danger above 6000 feet but this will rise to CONSIDERABLE as the day progresses. Human triggered avalanches will become likely as snow and wind continue. Evaluate all slopes before recreating on them.

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.

1. Low

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3500-5000 ft.
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    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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With the retreat of the cold arctic air the wind direction has returned to a more normal westerly flow and there remains an abundant amount of low density snow available for transport. Wind speeds are forecast to increase today and wind slabs will develop as the day progresses. These denser slabs will be deposited onto a weaker layer (the low density surface snow). Continue to look for signs of recent wind-loading such as shooting cracks, whumphing and smooth pillows of snow especially in exposed terrain above 6000 feet. 

Avalanche Problem 2: Persistent Slab
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Weak layers buried deeper in the snowpack continue to show some signs of instability. A freezing rain crust exists in the Whitefish Range. Also a layer of weak snow (facets and/or surface hoar) exists about 1.5 to 2 feet below the surface that formed last week. Recent stability tests indicate this layer has the ability to fracture, and this fracture can propagate across the slope (video). Dig into the snow and look for these potential weak layers. Where present, choose less complex terrain. Avoid areas where the snowpack is relatively shallow and steep, rocky areas.

This early in the season we have relatively limited observations due to difficult access. So there is still some uncertainty in the distribution of these layers and reactivity with the most recent snow load.

Avalanche Problem 3: Storm Slab
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Although snowfall totals are not overly impressive with the storm that moved into our area overnight, this new snow has arrived much warmer than what we have seen over the past few days. This relatively warm snow is being deposited onto a thick layer of cold low density forming a surface "upside down" snow structure. These storm slabs can be identified by cracking and whumphing. Being a surface snow problem this is relatively easy to identify by looking at the near surface snow structure.  

Forecast discussion

Loose, dry avalanches (sluffs) are also possible with the recent, unconsolidated snow. Sluffs can be dangerous in steep terrain and around terrain traps. The effects of even a small loose, dry avalanche can be amplified by traveling in or near a terrain trap like cliffs, tree islands, or narrow gullies.

Remember, the avalanche advisory is a starting point for decision making. The actual avalanche hazard could be greater or lower where you are traveling, especially due to limited early season observations.

We really appreciate the steady flow of observations. Please continue to help us out by letting us know what you are seeing out there. Remember, that even very simple observations like recent avalanche activity, no avalanche activity, or recent snow depths are a huge help. Thank you! 

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Join us on Wednesday, December 14 for a free motorized avalanche awareness presentation at Penco Power Products in Kalispell at 6:30. 

recent observations

Friday, Mark travelled to the Skookoleel area of the southern Whitefish Range. We found a snow surface on all aspects that mostly consisted of cold low density snow. On a southerly aspect we had propogation in our stability tests that mirrored what Erich found Tuesday in Big Slide.    

Also on Friday skiers in the Marion Lake area of the Flathead Range found a thick layer of low density unconsolidated snow on a southerly aspect. This layer sat on top of a crust but no results were observed in stability tests.

Wednesday BNSF Avalanche Safety travelled above Sheds 11 and 10.7. Some wind slabs had formed in cross-loaded gullies above 5000 feet but were unreactive. No avalanche activity was observed. Winds were light to calm all day with no active wind-loading.

Skiers in the southern Whitefish range on Wednesday found a freezing rain crust in their snowpit on a southerly aspect at about 6600 feet. This layer fractured and propagated across the column in a stability test. Skiers in the Middle Fork toured up Snowshed Mountain above Essex. They noted light to moderate winds that were forming thin wind slabs on easterly aspects.

On Tuesday Erich traveled in the southern Whitefish Range. We found weak layers (facets and a freezing rain crust) about 2 feet below the surface and on some aspects these layers fractured and this fracture propagated across the column - a sign of instability (video). Whitefish Mountain Resort Ski Patrol also found wind slabs to fail on the freezing rain crust in isolated locations during their avalanche mitigation work over the past two days.

Weather and CURRENT CONDITIONS
weather summary

Yesterday our area experienced another cold day under mostly cloudy conditions with precipitation moving into our area during the afternoon hours. As of 6:00 am temperatures above 6000 feet are the warmest they have been in several days and range from 13 - 21 F, and winds are 2-8 mph with gusts to 15 mph out of the south-southwest. For today expect cloudy conditions with light to moderate snow showers that will taper as the day progresses. There is a potential for snow banding to develop and deposit brief periods of heavy snow. More snow with warming temperatures are expected tomorrow.

Today’s weather observations near 6000 feet in the region
0600 temperature: 13 - 21 deg. F.
Max. temperature in the last 24 hours: 13 - 21 deg. F.
Average wind direction during the last 24 hours: South
Average wind speed during the last 24 hours: 5-10 mph
Maximum wind gust in the last 24 hours: 10-15 mph
New snowfall in the last 24 hours: 2-6 inches
Total snow depth: 36-57 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Missoula NWS
For 5000 ft. to 7000 ft.
Saturday Saturday Night Sunday
Cloud Cover: Warming with light to moderate snow showers. Light-moderate snow. Warmer temps and snow.
Temperatures: 9-20 deg. F. 8-19 deg. F. 20-28 deg. F.
Wind Direction: West - Southwest West - Southwest Southwest
Wind Speed: 8-10 mph with gusts to 21 7-10 mph 8-12 mph with gusts to 22
Snowfall: 2-6 in. 2-4 in. 4-6 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.