Wind slabs on top of a surface crust are still growing from snow and moderate winds yesterday. These slabs will continue to form through the day. The avalanche danger is MODERATE above 6000' on wind loaded terrain and LOW below 6000' where we can find a loose wet avalanche problem. Be wary if the sun makes an appearance today as it can rapidly warm the surface snow increasing the instability.
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Above 6500 ft.
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5000-6500 ft.
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3500-5000 ft.
Snow and moderate winds from yesterday continue to build wind slabs on top of a surface crust. Although relatively thin in most areas, they have been reported up to a foot thick in others. Wind slabs that formed Friday night through Sunday morning have strengthened a bit but they also were deposited onto a crust and lingering instabilities remain. Due to the current southwest winds these slabs will be confined to the typical leeward aspects at upper elevations. Evaluate all wind loaded terrain before committing to a slope today. Wind slabs can be identified by cracking in the snow beneath your skis or machine along with smooth rounded pillows of snow on the leeward sides of ridgelines.
Rain at low and mid elevations yesterday saturated the surface snow. Temperatures last night dropped below freezing in almost all areas, but the refreeze at low elevations was likely fairly weak. The refreeze at mid and upper elevations should have been stronger. A telltale sign of a loose wet avalanche problem is your skis or machine sinking through the surface into the unconsolidated snow beneath. Also watch for rollerballs and pinwheels.
Mammoth cornices exist along most ridgelines across the advisory area. It's important to pay attention to what is suspended above you given the unusual size and how overhung many of these cornices are. Keep a good distance from these while traveling along ridge lines as they can pull out further back than expected, even behind the solid ground. When a large cornice falls it has the potential to trigger deep instabilities that would otherwise remain dormant resulting in a large avalanche.
Glide cracks have also been observed opening up in many locations. The first reported glide avalanche this season was March 25 and occured west of the WMR ski area in the southern Whitefish Range. There is a large amount of uncertainty associated with glide avalanches, so the best way to manage them is to avoid slopes where they are present.
Monday: Todd and Zach ventured to the Red Meadow area of the northern Whitefish Range. The depth of snow on top of the firm crust varied depending on elevation and apect, but they found up to 8 inches of snow above it at upper elevations. Rollerballs and small loose wet avalanches were easily triggered on top of the crust. We also received a report of a cornice triggered wind slab from outside the advisory area in Glacier National Park near St. Mary.
Sunday: FAC staff toured in the backcountry north of Canyon Creek in the southern Whitefish Range. Prolonged sun weakened the snow surface and allowed for small skier triggered loose wet avalanches on our descent at both upper and mid elevations. At upper elevations a 18" thick crust sat beneath the 2-3" of new snow.
Saturday: FAC staff traveled to Elk Mountain, in southern Glacier Park, where they noted active wind loading throughout the day with fresh wind slab development. Skiers in Marion Lake, in the Flathead Range, were able to intentionally trigger a wind slab avalanche that travelled 2000'. Skiers in the southern Whitefish Range observed small wind slabs that were reactive to skis and noted a glide avalanche failure.
See below for all observations this season.
Yesterday brought mixed precipitation with light snow at upper elevations and rain showers at lower elevations. Conditions should be drier today with light to moderate winds out of the west/southwest. Currently, temperatures above 6000 feet range from 23-30ºF and winds are out of the southwest at 4-18 mph with gusts to 25.
| 0600 temperature: | 23-30 deg. F. |
| Max. temperature in the last 24 hours: | 32-39 deg. F. |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 3-26 mph |
| Maximum wind gust in the last 24 hours: | 12-37 mph |
| New snowfall in the last 24 hours: | 0-2 inches |
| Total snow depth: | 86-122 inches |
| Tuesday | Tuesday Night | Wednesday | |
|---|---|---|---|
| Cloud Cover: | Partly cloudy with light to moderate winds. | Slightly increasing winds. | Better chance for precipitation and increasing winds. |
| Temperatures: | 31-46 deg. F. | 22-32 deg. F. | 34-49 deg. F. |
| Wind Direction: | West to Southwest | Southwest | Southwest |
| Wind Speed: | 9-10 | 9-11 mph with gusts to 26 | 10-14 mph with gusts to 24 |
| Snowfall: | 0 in. | 0-1 in. | 0-3 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.
