Avalanche Information 11/23/2013

Avalanche advisories will begin on December 7, 2013. We are collecting data currently, but your observations are very valuable to us. Please drop us a line with what you’re seeing out there. Email: fac.admin@flatheadavalanche.org or call 406.261.9873.

Mountain Weather

The northern Rockies currently sit under a high pressure system. This will continue to cause cold, clear nights and sunny days in the mountains. Mid to upper elevation temperatures rose to the upper 20s to low 30s °F and winds have been out of the south at 5-25 mph the past few days.

This high pressure will continue through at least the first part of next week. The mountains will see notably warmer temperatures than the valleys under this weather regime.

Snowpack Discussion

These sunny days make for happy people, but the current pattern of cold, clear nights in the mountains could potentially be breeding our next weak layer. We observed surface hoar on the snow surface in the Marion Lake area yesterday as a result of these cold, clear nights. We are also seeing steep temperature gradients in the top few inches of the snowpack that are causing faceted snow grains to form (video). These facets as well as graupel are sitting on top of a variety of layers including crusts depending on aspect and elevation. Isolated wind slabs also exist at upper elevations.

These facets (both surface hoar and near surface facets) are currently not a problem in terms of stability. However, if these facets persist until our next snowfall event and we get a big enough load on top of these facets, then we could begin to see our next avalanche problem. We just need to wait and see how long this weather pattern persists and how these facets develop. Even though, we are devoid of snowfall at the moment, paying attention to the weather and snowpack and how it evolves is really important. Noting the spatial extent of the surface hoar (and any weak layer) now is very useful before it becomes buried and becomes a problem. We saw these facets in the northern Flathead Range and suspect they are elsewhere. So, if you’re seeing surface hoar in other places, let us know.

The mountains of northwest Montana have enough snow for avalanches to occur as well as form cornices. Cornices can form with enough wind even without snowfall. We’ve been seeing and receiving reports of the development of sizable cornices like in the Jewel Basin in the Swan Range (photo). Cornices demand respect and should be given a wide berth when traveling near them.

 It is still early in the season and we are all a bit rusty with our avalanche gear and skills. Remember to check your beacon and replace the batteries, and make sure your shovel and probe are also in great working order. This is also a great time of year (and enough snow) to practice using your beacon.

We will update avalanche conditions as necessary until we begin our advisories on December 7. So, remember, please send us your observations. Be safe!

A cornice in the Jewel Basin, Swan Range with skier tracks and a crack.

A cornice in the Jewel Basin, Swan Range with skier tracks and a crack.