THIS AVALANCHE ADVISORY EXPIRED ON December 12, 2018 @ 10:23 pm
Avalanche Advisory published on December 12, 2018 @ 5:23 am
Issued by Blase Reardon - Flathead Avalanche Center

Whitefish Range
Flathead Range and Glacier National Park

How to read the advisory

AN AVALANCHE WATCH IS IN EFFECT until Wednesday at noon.  

Dangerous avalanche conditions exist in the Whitefish Range, Flathead Range and Glacier National Park. Heavy snowfall and gusty winds have overloaded a fragile snowpack. Natural and human-triggered avalanches remain very likely. Fresh avalanches, whumpfing sounds, and shooting cracks are sure signs of danger. Avoid traveling on or below steep slopes at mid and upper elevations.

4. High


Above 6500 ft.
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

3. Considerable


5000-6500 ft.
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate


3500-5000 ft.
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
  • 1. Low
  • 2. Moderate
  • 3. Considerable
  • 4. High
  • 5. Extreme
Avalanche Problem 1: Storm Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Natural and human-triggered slabs breaking in the upper snowpack are very likely today. These can break 8-20 inches deep, at the base of the new snow or on buried weak layers that exist on both sunny and shady slopes. The size of avalanches will be greatest on slopes where wind-drifted snow is thickening slabs, and these conditions are most widespread near upper-elevation ridgelines.  Wind sheltered terrain is harboring fragile layers below the dense new snow which will be equally sensitive to human triggers.  Slides breaking in the new snow could gouge or step down into older, weaker snow, creating larger avalanches than expected.  Avoid crossing on or below slopes steeper than about 30 degrees.

advisory discussion

A powerful storm overnight has brought heavy snowfall and gusty winds to the Whitefish Range and Glacier National Park. Whitefish Mountain Resort is reporting 10 inches of new snow since Monday, and SNOTEL stations in the northern Whitefish Range and Glacier National Park are showing that much or more (Up to 1.5" of SWE).  Near Essex, storm totals look to be a few inches less. Gusty southerly and westerly winds have accompanied the snowfall, drifting snow and forming slabs and drifts that were sensitive to a person’s weight on Tuesday.

The combination of new and drifted snow has formed slabs that are overloading weak snow that was at the surface of the snowpack prior to the storm. With snowfall totals and rates peaking this morning, a natural avalanche cycle is likely underway. The likelihood of natural avalanches will diminish as snowfall tapers off. Nonetheless, it would be wise to avoid crossing under steep start zones near ridges where winds are continuing to drift snow.

Steep slopes will remain reactive to a person’s weight today.  Some avalanches may break below the new snow, in weak layers that developed during recent cold, dry weather. Multiple failure planes exist in the upper half of the snowpack. These include facets at the surface, facets near crusts, and buried surface hoar. Slides that break into older snow will be more dangerous, even on small slopes, because they’ll involve more snow. Heed clear signs of danger – fresh avalanches, whumpfing collapses, and shooting cracks.

The changing conditions make your observations even more valuable. If you get into the mountains, let us know what you see. 

Our next Avalanche Awareness talk is Thursday, December 20th at Penco Power Products at 6:30 p.m.!




weather summary

A cold front trailing behind the storm will bring burst of snow and gusty westerly winds this morning. Snowfall and winds taper off after the front passes. Thursday will see snow showers and warmer temperatures.


Two-Day Mountain Weather Forecast Produced in partnership with the Missoula NWS
For 5000 ft. to 7000 ft.
Wednesday Wednesday Night Thursday
Cloud Cover: Mostly Cloudy Mostly Cloudy Mostly cloudy
Temperatures: 24-29 deg. F. 17-22 deg. F. 26-31 deg. F.
Wind Direction: West Southwest Southwest
Wind Speed: 10-15 mph, gusting to 30 10-15 mph, gusting 25 to 30 12 mph, gusting to 25
Snowfall: 1-4" in. T-1" in. 1-2" in.
Freezing Level: 2500 feet 1500 feet 2000 feet

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

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