The avalanche danger is MODERATE above 5000 feet and human triggered avalanches are possible. New snow and northeasterly winds will cause new wind slabs to form on old snow surfaces that include surface hoar and sun crusts. Older, lingering wind slabs also exist. Carefully evaluate the snowpack before committing to any slope, particularly in wind loaded terrain. The avalanche danger is LOW below 5000 feet. Advisory for other ranges here.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Before today recent south through westerly winds have formed thin wind slabs on leeward aspects and crossloaded slopes. Today, easterly winds will create fresh wind slabs on the other side of the compass (northwest through south). These slabs will form on top of a variety of old snow surfaces including surface hoar, sun crusts, and near surface facets. Wind slabs are likely to be thicker in the Flathead Range and Glacier NP where winds speeds will be higher and more snow is expected to fall. It is important to continue to treat all wind loaded areas as suspect and carefully evaluate this terrain before skiing or riding in it. Look for smooth, rounded features on the slope especially on steep convex rollovers, on leeward sides of ridges and cross-loaded gullies. Remember, that even a small avalanche can have severe consequences if you trigger it in or around terrain traps.
Today's snow surface is tomorrow's weak layer. Surface hoar and near surface facets (small, weak snow grains just under the snow surface) exist throughout the advisory area. Today's snowfall will begin to bury these weak layers, but they should not become an "out of sight, out of mind" issue. This round of snow is unlikely to produce storm slabs, but it's important to monitor the reactivity of these weak layers as new snow continues to pile up on top of them. On south aspects, a sun crust formed that could become a potential bed surface as more snow falls as well.
On another note, there are currently two deeper layers in the snowpack that were a concern earlier in the season, but we haven't observed or received reports of avalanches on these layers or reactiveness in stability tests in over 3 weeks. These layers include facets surrounding the December 9 rain crust and larger facets near the ground in areas with a shallow snowpack. It is unlikely you'll trigger an avalanche on these layers, but not impossible. It is still worth taking the time to dig into the snow and see how these layers react in the areas that you are skiing or riding, especially in areas with a shallow snowpack (less than 3-4 feet deep).
Yesterday, on Sub-Shields in southern Glacier National Park, GNP rangers observed surface hoar (though melting on southerly aspects) and a snowpack that has settled considerably since last week. Their total snow depth on a northeast aspect at about 6700 feet was 90 cm. Nearby on Snowslip and Running Rabbit Mountains, skiers observed unreactive wind slabs, plenty of surface hoar, and a decomposing December 9 rain crust near the ground (observation). Also yesterday, snowmobilers in Canyon Creek in the southern Whitefish Range noted small, loose sluffs due to abundant sunshine and warming (observation) as well as eroding surface hoar on some slopes (observation).
On Tuesday I traveled to Red Meadow Peak in the northern Whitefish Range. I observed southerly winds loading northerly aspects at upper elevations and noted that this area did not receive as much snow during the pre-Christmas storm cycle leaving only three feet of snow above the December 9 rain crust (video, observation). Also on Tuesday, experienced skiers in the Middle Fork reported sun crust conditions on a southeast aspect of Mt Penrose. They also noted substantial sluffing of the dry loose surface snow while skiing a steep northeast aspect into Rescue Creek. The quantity of this sluffing surprised them.
Monday, Mark observed a recent wind slab avalanche that appears to have been triggered by a cornice fall (photo, observation) in Rescue Creek in the Flathead Range (observation). We received multiple observations from the Middle Fork corridor in the Flathead Range as well as Glacier National Park last weekend noting wind loading, thin wind slabs, and the presence of surface hoar (observations). Also last Saturday, I witnessed a small, natural wind slab avalanche on a steep, north facing slope as well as another nearby 1-2 day old avalanche on Nyack Peak in the Flathead Range (observation).
Thanks to everyone for submitting observations. They are extremely useful for everyone.
Visit our Observations page and our You Tube channel for more observations from the entire season.
Please let us know what you are seeing out there. Your observations are important and valued.
HOW TO SUBMIT OBSERVATIONS:
Email: [email protected]
Call and leave a message: 406.387.3821
You can also submit quick observations via text: 406.241.4571 (FAC mobile)
OR
Submit Snowpack Observations: http://www.flatheadavalanche.org/node/add/snowobs
Submit Avalanche Observations: http://www.flatheadavalanche.org/node/add/avyobs
Light snowfall has just begun across the advisory area and will continue into tonight. Today, a cold air mass east of the Continental Divide has crept into our area bringing colder air temperatures so far near the Divide and moderate northeasterly wind. Currently, mountain temperatures range from 11º-30º F with winds out of the east and northeast at 3-5 mph and 13-15 mph at stations near the Divide. Today, as the cold air moves west over the Divide and moisture moves in a northeast direction 2-5 inches of snow will fall across the advisory area by tomorrow morning, winds will increase to 5-10 mph with gusts to 25 mph from the east-northeast, and temperatures will be in the teens to low 20s F.
| 0600 temperature: | 11 to 30 deg. F. |
| Max. temperature in the last 24 hours: | 34-43 deg. F. |
| Average wind direction during the last 24 hours: | Southeast shifting to Northeast |
| Average wind speed during the last 24 hours: | 5-15 mph |
| Maximum wind gust in the last 24 hours: | 8-17 mph |
| New snowfall in the last 24 hours: | 0 to a trace inches |
| Total snow depth: | 45-57 inches |
| Thursday | Thursday Night | Friday | |
|---|---|---|---|
| Cloud Cover: | Light, but widespread snowfall. Increasing easterly wind speeds and cooling temperatures. | Continued snow and increasing wind. | Continued light snowfall. |
| Temperatures: | 17 to 26 deg. F. | 3 to 15 deg. F. | 17 to 26 deg. F. |
| Wind Direction: | East-Northeast | East-Northeast | East-Northeast |
| Wind Speed: | 5-10 mph with gusts to 20 mph. | 5-10 mph. | 5-10 mph. |
| Snowfall: | 1-2 in. | 1-2 in. | 1-2 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.
