New snow overnight, combined with moderate to strong winds, has formed fresh thin wind slabs on upper elevation slopes. These slabs have been deposited onto a crust and will continue to form with today's forecasted winds. Recent warm temperatures have weakened cornices across our advisory area and should be given a wide berth. The avalanche danger is MODERATE above 5000 feet on steep wind loaded terrain.
?
Above 6500 ft.
?
5000-6500 ft.
?
3500-5000 ft.
Light snow overnight, combined with moderate winds and strong gusts, have developed thin wind slabs at upper elevations of our advisory area. With windy conditions forecast through the day these slabs will continue to form and thicken. In most locations these slabs will be deposited onto a crust which will add to their instability. Obvious signs of fresh reactive wind slabs is cracking of the snow under your skis or machine. Although they will be thin, these slabs can knock you off your feet or machine and push you into terrain traps or stands of trees. In select locations the debris from these avalanches could potentially trigger a deeper instability in the snowpack.
Older wind slabs that formed last week exist across our area. Many of these have gained strength and are not presenting obvious signs of instability. However, cornice falls over the past few days have triggered several large wind slab avalanches.
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.
With below freezing temperatures overnight, and forecast through the day, cornices have gained a bit of strength. However, recent warm temperatures and sunshine weakened the numerous large cornices in the area (photo) and they will remain relatively weak today. Friday, a cornice fall on Nyack Mountain in the Flathead Range triggered a deeper slab and resulted in a very large avalanche (observation). On Saturday, we witnessed another cornice fall that triggered a wind slab avalanche in the Swan Range (observation and video). On Monday we noted a large slab avalanche which was triggered by a cornice fall on Mt. Cameahwait in the Flathead Range. When they hit the slope these behemoths are capable of triggering even deeper weak layers that would otherwise remain dormant in the snowpack. Cornices can pull far back from behind the ridge line making it important to keep an exaggerated distance away from the edge when traveling above cornices. Avoid traveling on the slopes below cornices as well.
Also, numerous glide cracks exist throughout the advisory area (image) and several have even failed. Whitefish Mountain Resort Ski Patrol reported widening glide cracks on Thursday. Glide avalanches are very difficult to predict, so the best strategy is to avoid playing on slopes where glide cracks exist.
Fresh snow overnight fell onto a crust and will not bond to this crust well. Loose dry snow slides will be small but can knock you off your feet or machine and ruin your day.
If the sun peeks out today, even for a short period, the intense nature of the April sun will weaken the fresh snow and wet loose slides may occur.
The last advisory of the season will be issued on Sunday, April 10, 2016.
Monday: We travelled to the Tunnel Ridge area in the Flathead Range where we found a thin surface crust at all elevations which broke down by mid morning. We observed the aftermath of the recent wet loose avalanche cycle on all aspects at mid and upper elevations. We noted a large wind slab avalanche triggerred by cornice fall on Mt. Cameahwait (observation).
Sunday: Skiers in the Tunnel/Pinnacle Creek area in the Middle Fork of the Flathead Range reported hearing and seeing numerous natural wet, loose avalanches by 9:00 am. They wisely called it a day and headed home.
Saturday: We were in the Lost Johnny Drainage in the Swan Range. We observed widespread natural loose, wet activity on all aspects and large cornices. In the afternoon, we witnessed a slab avalanche triggered by cornice fall above Lamoose Lake at the head of the drainage (observation, video). On a south facing slope near 7000 feet we found a shallow snowpack that was moist throughout (photo) where there was a prominent crust about 18 inches from the surface that had pooled water above the crust. Skiers on Huckleberry Ridge in Glacier National Park found a variety of crusts in the upper snowpack and stability tests produced fractures nearly a foot from the surface. They noted thick, older windslabs that were minimally reactive in stability tests but produced clean shears (observation).
Friday: Skiers in the Cascadilla Drainage in the Flathead Range reported a large natural avalanche thought to have been triggered by cornice fall (observation). Skiers outside of the advisory in the St. Mary area of Glacier National Park reported multiple natural, loose, wet avalanches on sun exposed slopes that began at about 10:30 am.
Thursday: A skier on Glacier View Mountain in the Whitefish Range intentionally triggered a wet, loose avalanche on a north aspect at 5400 feet (observation). Whitefish Mountain Resort Ski Patrol reported skier triggered loose, wet avalanche (photo) and widening glide cracks. Erich and I observed a softening snow surface on most aspects despite cloud cover in China Basin and Werner Peak in the Whitefish Range yesterday. We did not observe any avalanche activity by mid to late afternoon (observation).
Visit our Observations page and our You Tube channel for more observations from the entire season.
Thanks to everyone for submitting observations. They are extremely useful and could help save lives.
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
After a prolonged warm spell temperatures finally dropped below freezing at upper elevation locations yesterday afternoon. Precipitation moved back into our area with most upper elevation stations reporting 3-4 inches of new snow except for Flattop which received 7 inches. Currently, temperatures above 6000 feet range from 22º-29º F, and winds are blowing out of the southwest at 8-29 mph with gusts from 13-40 mph. Today, showers will decrease and cool temperatures are on tap with highs in the mid to upper 30s F with windy conditions. Tomorrow will be warmer with dry conditions but still windy.
| 0600 temperature: | 22-29 deg. F. |
| Max. temperature in the last 24 hours: | 36-46 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 7-38 mph |
| Maximum wind gust in the last 24 hours: | 29-56 mph |
| New snowfall in the last 24 hours: | 3-7 inches |
| Total snow depth: | 79-117 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Scattered showers decreasing with cool temperatures and windy conditions. | Clearing with continued windy conditions | Warming temperatures with continued windy conditions. |
| Temperatures: | 36-47 deg. F. | 26-32 deg. F. | 46-56 deg. F. |
| Wind Direction: | West | West-Southwest | Southwest |
| Wind Speed: | 10-15 mph with gusts to 30 mph. | 10-15 mph with gusts to 30 mph. | 10-15 mph with gusts to 30 mph. |
| Snowfall: | 0-1 in. | 0 in. | 0 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.
