A potent storm moved into our area this morning with windy conditions and potentially moderate to heavy snow. The avalanche danger will increase throughout the day particularly on upper elevation wind loaded terrain.This snow is accumulating on a variety of surfaces including sun crusts, surface hoar, and facets. Carefully evaluate any slope you plan to recreate on. We will provide general avalanche information, and begin issuing daily advisories with hazard ratings once we have enough information.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
24 hour new snow totals as of 0600 range from 1-5 inches across our area. The new snow that we received this week has fallen on a variety of surfaces including surface hoar, facets and sun crusts. These weak layers will be put to the test today from the storm that entered our area this morning. New snowfall accompanied by moderate to strong winds will create dangerous avalanche conditions today, particularly on upper elevation wind loaded terrain. It is possible and potentially likely to trigger an avalanche today.
Near ridgelines, winds are drifting this snow onto leeward aspects and forming fresh wind slabs. As we noticed in John F. Stevens Canyon on Friday, even areas of very thin snow pack can have thick pockets of wind drifted snow. Windy conditions today will continue to redistribute this new snow and add thickness to these fresh wind slabs. Evaluate all wind loaded terrain today before committing to a slope. Look for smooth rounded pillows on leeward sides of ridges and cross loaded terrain features. Obvious signs of instability will be cracking, whumphing and hollow sounds. In areas favored by this storm dry loose avalanches on steep terrain will be possible especially on sunny aspects.
Remember, avalanches can happen any time of the year. The effect of small avalanches can be amplified by thin snow cover, exposed hazards, and narrow gullies. If there is enough snow to ski or ride, it's deep enough to slide.
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Thursday December 8, join us at the Sportsman and Ski Haus in Whitefish at 6:30 for a free 1 hour general avalanche awareness presentation.
On Wednesday December 14 join us for a free motorized avalanche awareness presentation at Penco Power Products in Kalispell at 6:30.
Yesterday (Saturday), skiers in the Marion Lake area of the Flathead Range reported moderate to strong winds along with snowfall rates of 1/2" per hour on their tour. No signs of instability were noted but they did find a buried surface hoar/facet layer 6-10" below the surface.
Also on Saturday, skiers in both the southern and northern Whitefish Range reported a thin crust 2-3" below the snow surface on all aspects above 6000'. This crust was not supportive and would break on each turn. This likely formed Friday evening as air temperatures warmed for a short duration during the storm. No other signs of instability were observed.
On Friday Mark accompanied BNSF Avalanche Safety in John F. Stevens Canyon in southern Glacier Park. They were able to intentionally trigger 2 small soft slab avalanches on a mid-elevation wind loaded southeast aspect. Moderate winds were noted at mid and upper elevations throughout their tour. Upper elevation cornice formation was impressively large for this early in the season.
Thursday, skiers in the Jewel Basin in the Swan Range reported about 10-14 inches of new snow that was poorly bonded to the old snow surface. They observed and intentionally triggered a few small avalanches on wind drifted aspects up to 12-16 inches deep, and also noticed cracking of the snowpack. On non-wind loaded terrain, they experienced dry sluffing of the new snow.
On Wednesday skiers on Mt. Aeneas in the Swan Range reported moderate winds that were forming 5-10" thick wind slabs on ridgelines. Just below the ridgelines cracking was observed but the slabs were less cohesive. On Tuesday one of these skiers noted a thin layer of facets just above a ice mass 20 cm from the ground. Partial propagation occurred in his ECT on this weak layer.
Mark visited the backcountry outside of the WMR resort on Tuesday. All aspects above 5500' had both a thin layer of surface hoar on the snow surface and a ice mass forming the basal snowpack. Sunny aspects had a thin sun crust just below the surface which failed easily in stability tests. No wind slabs were encountered on this relatively sheltered tour.
A potent winter storm moved into our area this morning with windy conditions and moderate to heavy snow lasting into tomorrow morning. As of 6:00 a.m. temperatures at upper elevation weather stations range from the low 20s F to mid 20s F with light to moderate winds accompanied by strong gusts. Wind speeds and snowfall will increase throughout the day. Upper elevation temperatures should top out in the upper 20s F today. Winds will shift to the north tonight ushering in our first arctic air of the season. Tomorrow will be cold, relatively dry with, thankfully, light winds.
| 0600 temperature: | 20-26 deg. F. |
| Max. temperature in the last 24 hours: | 21-28 deg. F. |
| Average wind direction during the last 24 hours: | SSW |
| Average wind speed during the last 24 hours: | 5-15 mph |
| Maximum wind gust in the last 24 hours: | 18-32 mph |
| New snowfall in the last 24 hours: | 1-5 inches |
| Total snow depth: | 28-49 inches |
| Sunday | Sunday Night | Monday | |
|---|---|---|---|
| Cloud Cover: | Windy with moderate to heavy snow. | Continued windy with moderate to heavy snow combined with cold temperatures. | Very light snow with cold temperatures. |
| Temperatures: | 26-33 deg. F. | 4-17 deg. F. | 11-19 deg. F. |
| Wind Direction: | West-Southwest | North | South |
| Wind Speed: | 13-17 mph with gusts to 39 mph. | 13-15 mph with gusts to 36 mph. | 5-6 mph. |
| Snowfall: | 4-11 in. | 5-10 in. | 0-2 in. |
| Snow Line: |
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.
