Almost 2 feet of snow this week is healing slowly due to continued snowfall and unseasonably cold temperatures. Human triggered or natural soft slab avalanches breaking in the new snow have occurred every day this week. Evaluate terrain and bonding of storm slabs carefully. Shooting cracks indicate unstable snow.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
New snow this week has formed soft storm slabs 6" to 18" thick over a variety of slick crusts. Yesterday at higher elevations, several large natural avalanches ran in the Whitefish Range (observation) and a skier in the Flathead Range triggered a small storm slab (observation). Use extra caution in leeward terrain, on convexities, and around terrain traps. Use small test slopes and shear tests to assess the potential depth and reactivity of new snow instabilities. You can easily avoid the problem on slopes less than 35 degrees.
Apruary 2018 continues to deliver deep powder riding and sensitive storm instabilities. Most mountain stations picked up a few more inches of new snow yesterday, while Flattop SNOTEL pulled out another 8" or more (.7" SWE). Settled storm totals are now 15" to 20" in the Northern Whitefish, Glacier Park, and Flathead Ranges, and 10" or less in the Swan Range and Southern Whitefish Range. Favored areas now have 1.8" to 2.0" of snow water equivalent over the sun crusts and rain crusts that were buried at the beginning of the month. The storm snow is now warming, settling, and trending towards stability, but the process has been unusually slow thanks to un-springlike cold temperatures and widespread crusts below the storm snow. Observers yesterday reported variable instabilities. Some found the new snow was unreactive, while others noted natural storm slab avalanches running yesterday afternoon. One observer modeled our travel advice by monitoring storm depths and gradually easing into steeper terrain on smaller test slopes. He triggered a storm slab on a steep rollover - bullseye data to back off towards mellower slope angles. Without a clear pattern to these instabilities, continue to assess each slope on a case by case basis. Areas that received more snowfall or wind loading are capable of producing larger and more dangerous avalanches today.
Winds have been relatively tame since the onset of this storm, and observers have reported only light drifting near ridgetops. There is ALOT of loose snow that will readily drift if winds increase or will easily sluff if we get direct sunshine. Today's forecast is for mostly cloudy skies and light winds. An arctic cold front is forecasted to push across the Continental Divide later this evening, which could cause increased wind transport. Pay attention to the weather today; the danger will quickly rise to CONSIDERABLE if winds start cranking or if the sun makes a hard hit on the snow surface.
Apart from a gradual warming trend, today's weather will feel similar to yesterday. Mountain temperatures are in the mid 20s this morning and will rise to near freezing under mostly cloudy skies. We will see light snow showers and light winds, with a few stronger gusts closer to the Continental Divide. A weak arctic front will push temperatures back down this evening, bringing gustier winds and increased snowfall.
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Cloud Cover: | Isolated snow showers | Cooling temperatures and light snow | Light snow showers |
| Temperatures: | 35 to 40 deg. F. | 15 to 20 deg. F. | 29 to 34 deg. F. |
| Wind Direction: | SW | NW | NE |
| Wind Speed: | 0 to 10 mph | 0 to 10 mph | 2 to 12 mph, gusting to 25 |
| Snowfall: | 0 to 2 in. | 1 to 3 in. | 1 to 3 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.
