Today is a weather transition day as a wet and relatively warm system approaches the region. The avalanche danger is MODERATE above 6000 feet, but will rise tonight as the storm intensifies. New snow expected during day light hours should not affect stability, but pay close attention to changing weather conditions. New, thin wind slabs will form as the day progresses and a few inches of new snow will make it difficult to identify older slabs where lingering instability exists.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Yesterday the wind shifted an returned to a west and southwest direction. As the approaching storm moves into the area and brings a few inches of snow today watch for a new round of thin slabs to form on leeward slopes. In some areas the wind from earlier in the week drifted the snow onto weak, faceted surfaces and crusts that can delay the time they need to strengthen. Carefully evaluate wind loaded terrain and pay attention to signs of lingering instability in these ageing slabs. Previously wind loaded slopes may be difficult to identify with a bit of new snow on them so use caution when approaching slopes that you suspect harbor older wind slabs. There was a close call on Holland Peak (south of advisory area in the Swan Range) last weekend. A skier triggered a wind slab avalanche that failed on facets near the ground (observation).
Pay close attention to changing weather conditions today. There is a lot of moisture associated with the approaching system and if it intensifies earlier than expected avalanche danger will rise.
Relatively warm temperatures over the past few weeks helped to generally consolidate and strengthen our snow pack, but weak layers in all ranges of the snow pack still exist. Dig into the snow and look for weak, facets in the mid snow pack, isolated areas with buried surface hoar (1-1.5 feet from the surface), and/or sugary depth hoar near the ground. Where you find a weak snow pack structure terrain choice is the solution. Though the likelihood of triggering an avalanche on one of layers is low, the consequence is high. To lower the odds of triggering one of these deeper slides avoid steep slopes that have a shallow snow pack.
Thursday: A resident near the Swan Range reported glide cracks that were begining to open near Peter's Ridge on a south facing slope.
Wednesday: We were in the Six-Mile area in the Swan Range. East/northeast winds continued to drift snow onto leeward slopes. Isolated wind loaded pockets along the ridgeline produced shooting cracks and even fractures 14-16 inches deep from our weight. From a distance we could see a crown line on Hall Peak from an avalanche that likely occurred early in the week. The avalanche appeared to be on a wind loaded slope and stepped down to the ground. Distance and filled in debris made it difficult to estimate size or date of the avalanche.
Tuesday: Todd and Seth traveled up Lost Johnny to Hash Mountain in the Swan Range. Winds had shifted to the East, and although light, were increasing as the day went on. Previous wind loading was prevalent on East and North aspects, although slabs did not appear to be sensitive. Some strengthening is occurring in the snow pack, however, we still found concerning weak layers of buried surface hoar and facets around crusts. These layers were not sensitive and did not appear to be prone to propagation, but they easily could be in other locations. Adam was in the Big Slide area of the Southern Whitefish Range and also found some weak layers in the snow pack, but did not have any propagation. He did note some new surface hoar development.
Also on Tuesday, we received public observations from Running Rabbit Mountain and Cameahwait Mountain in the Flathead Range. Both reported signs of previous wind loading but no obvious signs of instability and no propagation in stability tests.
Monday: Erich and Guy traveled into the Tunnel Ridge area in the Flathead Range. They experienced strong southwest wind transporting snow to leeward aspects and even cross-loading ridges (video). They avoided wind loaded slopes, and noted the Jan. 19 crust with weak snow below it at elevations below about 6000 feet. They observed localized cracking along ridges, but observed no natural avalanche activity. BNSF Avalanche Safety toured in John F. Stevens Canyon. They noted active wind-loading onto easterly aspects above 6000 feet but did not observe any recent avalanche activity.
See below for all observations this season.
Yesterday was mostly sunny and temperatures remained cold. Currently, temperatures above 6000 feet are up from this time yesterday and range from -1-10º F. Winds shifted back to the west/southwest and are blowing 7-14 mph with gusts from 10-20 mph. Today, temperatures in the mountains should rise to the mid-upper 20s and winds will move out of the west/southwest at 5-10mph with gusts in the 20s. Clouds should move in this morning ahead of an approaching weather system and light snow is expected mid-day and increase in intensity overnight.
| 0600 temperature: | -1-10 deg. F. |
| Max. temperature in the last 24 hours: | 9-12 deg. F. |
| Average wind direction during the last 24 hours: | N/NE shift W/SW |
| Average wind speed during the last 24 hours: | 5-10 mph |
| Maximum wind gust in the last 24 hours: | 15-20 mph |
| New snowfall in the last 24 hours: | 0 inches |
| Total snow depth: | 53-67 inches |
| Friday | Friday Night | Saturday | |
|---|---|---|---|
| Cloud Cover: | Warming temps. Clouds build and light snow begins. | Increasing snow intensity. | Continued snow with rising temps and increasing wind speeds. |
| Temperatures: | 19-30 deg. F. | 9-22 deg. F. | 23-36 deg. F. |
| Wind Direction: | South-Southwest | Southwest-East | West-Southeast |
| Wind Speed: | 6-7 | 6-8 | 7-11 gusts 21-28 |
| Snowfall: | 3-7 in. | 7-18 in. | 5-11 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.
