This is Mark Staples with the avalanche forecast for Wednesday, March 19th, at 7:00 a.m. sponsored by the Avalanche Alliance and the Idaho State Snowmobile Association - Avalanche Fund. This forecast does not apply to operating ski areas.
It’s a cold start this morning with temperatures in the single digits F in most places but a bit warmer in the Bridgers. Winds yesterday blew from the north and started coming from the west this morning blowing 5-10 mph gusting to 15 mph.
Today will have a ridge of high pressure overhead with sunny skies. Temperatures will warm into the mid 20s F but will feel a lot warmer under the strong spring sunshine. Winds will be light but a little gusty coming from the west slowly shifting to the southwest as the next storm system approaches.
More snow will fall tomorrow but maybe only a few inches. A better chance of snow comes with another storm system this weekend.
Snowfall from last Thursday to Monday:
- West Yellowstone - 37” snow/2.9” water
- Island Park - 46” snow/4.8” water
- Cooke City - 31” snow/2.9” water
This snow was accompanied by strong winds from the west and southwest peaking Sunday night with gusts 65-100 mph. Yesterday winds blew from the north..
Wind slabs or possibly deeper persistent slab avalanches are likely on wind loaded slopes that can easily have double or triple the loading compared to non-wind loaded slopes as my partners and I found yesterday near Mt. Jefferson. Dave spotted many wind slab avalanches near Lionhead on Monday.
Avalanches are much less likely and the riding conditions will be better on slopes sheltered from the wind where the new snow is well bonded to itself. However, so much new snow has way of exposing weakness in the snowpack (this avalanche in the Taylor Fork is a good example). There are some slopes lurking out there mostly near West Yellowstone and the southern Gallatin and Madison Ranges where the snowpack is relatively shallow and weaker (slopes above Trapper Creek near Hebgen Lake come to mind).
Today human triggered avalanches are likely to happen on wind loaded slopes where the avalanche danger is CONSIDERABLE. The avalanche danger on non-wind loaded slopes is MODERATE but don’t let your guard down.
The Bridger Range received up to 15 inches of snow Sunday and Monday. Near Big Sky and Hyalite Canyon 14-24 inches of snow has fallen since late last week. Winds from both the south and the north have drifted that snow and formed many wind slabs.
As Ian and his partner found yesterday near the Throne, safe travel simply required avoiding recent drifting and riding slopes unaffected by the wind. A group further north near Frazier basin found wind slabs 1-1.5’ deep that could avalanche. These wind slabs should be gaining strength today, but I’d still avoid them.
Loose wet avalanches will happen predictably today as strong spring sunshine quickly warms sunny slopes which will become wet. Most wet avalanche activity usually happens the first time dry powder heats up from sunshine. The greatest threat from loose wet avalanches isn’t necessarily triggering one, but having one rumble down onto you from above. Go to shady slopes without recent drifting for the best snow and riding quality.
Today the avalanche danger is MODERATE with heightened avalanche conditions on wind-loaded slopes and sunny slopes where the snow becomes wet.