THIS AVALANCHE ADVISORY EXPIRED ON April 29, 2017 @ 9:36 pm
Avalanche Advisory published on April 28, 2017 @ 7:36 am
Issued by Zach Guy - Flathead Avalanche Center

Whitefish Range
Swan Range
Flathead Range and southern Glacier National Park

How to read the advisory

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Above 6000 ft.

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5000-6000 ft.

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3500-5000 ft.

Special Advisory Statement: Significant amounts of new snow combined with a warming trend will create dangerous avalanche conditions into the weekend, especially on Saturday.  Natural loose wet avalanches will become likely under rising freezing levels and direct sunshine (see video).  With snowfall in excess of 20" in higher terrain, these slides can entrain dangerously large volumes. Watch for rapidly changing conditions and be mindful of overhead hazards if you are traveling in the mountains this weekend.

Avalanche Problem 1: Loose Wet
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As daytime temperatures climb, fresh snow from the past few days will easily shed off of steep slopes in the form of wet point release avalanches.  Human triggered and natural avalanches will become likely during day time warming on Friday and Saturday, especially if we see periods of prolonged sunshine.  On slopes that hold more than a foot of recent snow, or in long running terrain features, these slides will be large enough to bury you.  Avoid traveling underneath gullies or steep terrain if you see rollerballs, pinwheels, or adjacent avalanche activity.

Avalanche Problem 2: Storm Slab
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1 to 2 feet of storm snow has formed fresh storm slabs at mid and high elevations.  You are most likely to encounter this problem as you move higher in elevation towards colder, more wind-affected snow.  Watch for cracking and clean sheers in the new snow to hint at instabilities, and be wary of steep rollovers or thicker wind drifts.  

advisory discussion

 Observers on the Going-to-the-Sun Road and in the Middle Fork reported 20 inches of storm snow on Thursday, with numerous large debris piles below steep terrain. Since Wednesday morning, Noisy Basin SNOTEL is showing 4" of Snow Water Equivalent, Big Mountain has picked up over 20" of new snow, and Stahl Peak SNOTEL is at 12" and counting.  I'd estimate some of the highest alpine terrain has picked up as much as 3 feet of fresh snow. Wow! Double check your calendar. It's not April Fools' Day. As a matter fact, it's almost a month later than that, which means once the temperatures rebound to seasonal norms this weekend, and if the high almost-May sun angle strikes  all this fresh snow, we are going to see a noteworthy wet loose avalanche cycle.  Keep your head on a swivel as you travel through the mountains over the next few days, being especially wary of the steep slopes above you holding on to  copious amounts of fresh snow.  Roller balls and pinwheels are Mother Nature's warning sign before she unloads a cement mixer full of wet heavy debris down on you. You want no business getting tangled in one of these types of slides. I suppose it's a  faux pas to carry a beacon, shovel, and probe on your road bike ride, but being avalanche aware on freshly plowed pavement at a higher elevations is not a bad idea this weekend.

recent observations

Numerous D1.5 to D2 natural avalanches ran on Thursday in the Middle Fork (see video) and along the Going-to-the-Sun Road; these appeared to be loose and wet loose avalanches involving the fresh storm snow, from 12" to 20" thick.  On Thursday, backcountry travelers reported easily triggered wet loose avalanches at mid elevations in the Middle Fork and a reactive snowpack on steeper terrain at Whitefish Mountain Resort. 

CURRENT CONDITIONS Today’s weather observations near 6000 feet in the region
0600 temperature: 26-31 deg. F.
Max. temperature in the last 24 hours: 31-35 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 5-12 mph
Maximum wind gust in the last 24 hours: 22 mph
New snowfall in the last 24 hours: 3-20 inches
Total snow depth: 15-133 inches
weather

In the wake of a large trough carving eastward across the West, we will see showery snowfall under cool, northwest flow on Friday.  Look for afternoon warming to cause convective pulses late Friday, before a short-lived ridge brings warmer and drier air on Saturday.  Partly cloudy skies on Saturday morning will give way to increasing clouds ahead of another round of moisture on Sunday.  

Two-Day Mountain Weather Forecast Produced in partnership with the Missoula NWS
For 3000 ft. to 5000 ft.
  Friday Friday Night Saturday
Weather: Mostly cloudy skies with intermittent snow/rain showers Lingering snow/rain showers under mostly cloudy skies Mostly dry weather under mix of clouds and sun.
Temperatures: 38-46 deg. F. 27-32 deg. F. 40-50 deg. F.
Wind direction: WNW WSW SW
Wind speed: 3-5 3-5 4-8
Expected snowfall: 0-2 in. 0-1 in. 0 in.
For 5000 ft. to 7000 ft.
  Friday Friday Night Saturday
Weather: Mostly cloudy skies with intermittent snow showers Lingering snow showers under mostly cloudy skies Mostly dry weather under mix of clouds and sun.
Temperatures: 33-38 deg. F. 24-28 deg. F. 35-43 deg. F.
Wind direction: WNW WSW SW
Wind speed: 4-6 4-6 8-15
Expected snowfall: 1-3 in. 0-2 in. 0 in.
Disclaimer

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.