Another very large avalanche ran to valley bottom from the Flathead's alpine terrain during Friday's rain event. This continues the pattern of deep slab activity from high elevation, leeward aspects. Cool and calm weather is now contributing to an improving snowpack, but stay skeptical of that type of terrain. Choose routes with deep, uniform snowpacks that stay away from rocky terrain with variable snow coverage. Don't dilly dally below steep alpine faces with overhanging cornices.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Avalanches breaking on deeply buried weak layers remain a rare but deadly concern; one ran as recently as two days ago. You might still be able to trigger a deep slab from a shallow or rocky part of the slope, where weak layers are closer to the surface. You can find that kind of variable snow cover on rocky, leeward, alpine terrain, most commonly in the higher peaks of the Flathead Range and Glacier Park. At upper elevations, choose terrain carefully to stay on slopes with uniform snow coverage. Minimize your time in the runouts of suspect slopes just in case a random cornice fall acts as a trigger.
Winds have generally been light across the forecast area since yesterday, except for some locations near the Continental Divide. There are a few inches of snow to blow around at high elevations, and you may find small wind slabs below ridges or in gullies in areas where winds have affected the snow surface. Steer around drifts if you are riding above consequential terrain.
Several days of unseasonably warm temperatures have helped wind slabs from earlier in the week heal. Observations yesterday confirmed that Friday's rain event reached into upper elevations. The stout crust was observed to at least 6,800' in the Flathead Range, and likely higher in the Swan and Whitefish Ranges. Since Friday's crust formed, two to five inches of new snow has accumulated above it under light winds. The Swan Range has squeezed out the most new snow so far (.5" SWE), and we are expecting a couple of inches late this afternoon. You might be able to trigger shallow sluffs or find an isolated pocket of drifted snow, but these should all be harmless in size unless you are in extremely consequential terrain.
Deep instabilities are also continuing to adjust, although at a slower and more uncertain rate. It has been a wild month for the faceted crusts near the bottom of the snowpack. We saw continous loading with big storm totals during the first half of the month followed by a swing in temperatures from sub-zero in mid-January to spring-like weather for the past week. Loading events and temperature swings have all contributed to deep slab activity, almost entirely in the Flathead Range. Our Snowpack Tracker tool is a great resource for tracking weather and avalanche activity. Deep slab activity peaked in mid-January, during the tail of a continuous loading event (Example A, Example B). Above-freezing temperatures in the past week further shocked the snowpack, causing a few more deep slab releases. The most recent ran on Friday off of Nyack Mountain during a light rain event (See observation). Mid-pack weak layers - the small-grained facets and broken surface hoar grains surrounding crusts - were less developed than our basal weak layers and tend to gain strength quicker when they are in the middle of a thick snowpack. As surface instabilities and mid-pack weak layers are generally healing up under our current weather pattern, the danger remains higher in the Flathead Range because of our lingering concerns for deep slabs. With the much higher frequency of deep slabs in the Flathead Range, careful terrain selection is important at upper elevations today. In the northern portion of the Swan Range that we forecast for, we have yet to observe any deep slab avalanches this month. It has been a different case in the Southern Swan, near Seeley Lake. In the Whitefish Range, the problem is very hard to find: we've seen only a few avalanches break on mid-pack weak layers and one near the ground in the past month from the Northern Whitefish Range. This graphic highlights the pattern quite well. High elevation, northerly and easterly facing terrain in the Flathead Range worries us the most. Elsewhere, the snowpack is generally stable today.
Another quiet day is in store as a weak and fast-moving high-pressure ridge moves over the region. Mountain temperatures are in the upper 20's to low 30's this morning. Winds are calm to light around the forecast area. Snow showers return later this afternoon and continue into the work week, with an uptick in southwest wind speeds tomorrow. The pattern of modest snowfall and unseasonably warm temperatures continues through the rest of the month. Don't give up on winter yet, there looks to be a pattern change towards colder weather right around the time that Punxsutawney Phil emerges from his hole. That rascal.
| Sunday | Sunday Night | Monday | |
|---|---|---|---|
| Cloud Cover: | Mostly Cloudy | Mostly Cloudy | Mostly Cloudy |
| Temperatures: | 27 to 34 deg. F. | 22 to 26 deg. F. | 27 to 33 deg. F. |
| Wind Direction: | South | Southwest | Southwest |
| Wind Speed: | 2 to 12, G20 | 7 to 17, G30 | 10 to 20, G35 |
| Snowfall: | 1" to 2" in. | 0 to 2" in. | 1" to 2" in. |
| Snow Line: | 3500' | 3500' | 3000' |
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.
