Mountain Weather Summary


Bottom Line:
The avalanche danger will rise sharply this morning as new snow and wind create dangerous avalanche conditions. Fresh wind slabs teeter atop a weak sugary snowpack. You’re most likely to trigger a wind slab near ridgelines in exposed middle and upper elevation terrain.

We will update this post on or before December 15th, 2018. We will begin the Daily Avalanche Forecast once we get more snow.

Snowpack and Avalanche:
Last night’s snow and wind will test a thin snowpack with distinct weak layers near the surface and at the ground. A recent string of cold, clear weather has transformed the snow surface into a pile of weak sugary snow (facets) that in many places is capped with another weak layer of snow called surface hoar. In addition, many north-facing slopes at middle and upper elevation harbor an even weaker layer of facets at the base of the snowpack (depth hoar) - remnants of old snow that fell before Thanksgiving.

The overall snow structure is grim at best. Teetering atop this mess are fresh wind slabs fueled by new snow and painted into exposed terrain by moderate to strong wind. You’re most likely to encounter this problem near windblown ridge tops at middle and upper elevations. These slabs will be very sensitive to the weight of a rider and may fail naturally. Today is a great day to tune-up the sled, wax your boards and grab that giant tin of holiday popcorn and see what happens.

Mountain Weather:
Snow showers began last night ahead of an upper level trough of low pressure that’s sweeping across the forecast area early this morning. Snow accumulations as of 5AM are in the 3-6” range with a little less than that in the Wood River Valley. Expect an additional 1-3” of snow this morning before diminishing this afternoon. Daytime high temperatures will reach either side of 20 F but it’ll feel much colder than that at ridge tops were wind will blow moderate to strong from the west and northwest.

Light snow showers may linger a bit longer into the afternoon near Banner Summit and the Sawtooths while clearing to partly cloudy skies elsewhere. Wind speeds should ease again Thursday while temperatures remain cold. Another weak disturbance will bring a round of light snow showers Friday before weak high pressure builds in to dry things up over the weekend.

Check the observations page to read the latest observations from SAC forecasters and the public. Thanks to everyone that’s contributed! Yesterday in the western Smoky Mountains, SAC forecasters observed weak snow at the surface and near the ground evidenced by widespread cracking and collapsing. Similar red-flag warning signs have been noted in every forecast zone and in nearly every public observation since Thanksgiving.

If you head into the backcountry looking for early season skiing or riding, we’d love to hear what you’re seeing out there. Send us some info through our observations page or use the hashtag #sawtoothavy on Instagram or Twitter. Be sure to follow the #sawtoothavy hashtag to see what others are reporting.

Don’t miss a slideshow at Backwoods this Friday in Ketchum and a Motorized Avalanche Awareness in Pocatello - both FREE! You can find all the details and links to the Facebook event pages on our Education and Events Calendar. Check back often, we’ll be loading it with education opportunities and movie premieres from across the region!