Today: A 40 percent chance of snow with a high near 30°F and low around 14°F. South southwest wind around 9 mph. New snow accumulation of less than one inch possible.

Friday: Mostly sunny, with a high near 28°F and low around 17°F. South southeast wind between 3 and 6 mph.

Saturday through Tuesday: Sunny, with highs in the mid 30°F and lows in the high teens and low 20°F.

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Mountain Weather

Yesterday an additional 1-2 inches of snow fell. Not much, but a little snow is better than none at all. This morning winds were blowing 15-20 mph from the Southwest with temperatures in the low teens Fahrenheit. Today will be mostly cloudy and temperatures will be in the high teens Fahrenheit. Winds will increase and blow 15-30 mph from the West. Late this afternoon some moisture should arrive from the north but only produce 1-2 inches of snow. Long range models indicate more snow for the rest of December. Keep your fingers crossed.

Snowpack and Avalanche Discussion:

The Bridger, Gallatin and Madison Ranges, the Lionhead area near West Yellowstone and mountains around Cooke City:

New snow and avalanches: Mountains near Bozeman and Big Sky received the most snow yesterday with a 48-hour snowfall of 6-8 inches while further south the 48-hour snowfall was 4-6 inches. This storm provided just enough snow for local ski patrols to ski cut soft slab avalanches, loose snow avalanches, and a few wind pillows. The Bridger Bowl Ski Patrol noted that yesterday's avalanche activity provided a small "taste of what our future looks like" because there will be significant avalanche activity once more snow falls.

A new problem: Prior to yesterday's snowfall, a combination of clear cold nights and warm sunny days significantly weakened upper layers of the snowpack. This weather metamorphosed (changed) this snow from old, broken snowflakes to weak faceted crystals, otherwise known as "near-surface facets." To compound the problem, a layer of surface hoar, formed on top of these facets in most areas (photo). Yesterday, Doug and I found this combination throughout the Taylor Fork area in the southern Madison Range (photo). Often surface hoar is destroyed by sun or wind, but yesterday's snowfall covered and preserved it. Right now these layers of near-surface facets and surface hoar make great riding conditions because the powder seems deeper than it is.

An old problem: At the bottom of the snowpack, old snow from October metamorphosed into big, depth hoar crystals. Avalanches in late November and early December occurred on this layer which hasn't gone away. It is waiting to be stressed by a load of new snow which hasn't come.

The current situation: You can find two basic snowpack structures. In some places the snowpack is greater than 2 ft deep with depth hoar at the bottom, a slab in the middle, and facets on top. On these slopes and any recently wind loaded slope, the Avalanche Danger is rated MODERATE. Other slopes have a snowpack less than 2 ft deep with depth hoar at the bottom, more facets in the middle, and near-surface facets on top (video). These slopes have a LOW Avalanche Danger if not wind loaded.

I will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations, drop us a line at mtavalanche@gmail.com or call us at: 406-587-6984.

PHOTOS, SNOWPITS, and VIDEOS

1. We've recently uploaded more photos and snowpits to our web site, more than what are linked in the advisory.

2. We're creating a series of "How To…" stability test videos. So far we've got clips on performing a CT and ECT. There are located under Stability Tests on the Resources page.

Information provided by Doug Chabot, Mark Staples, and Eric Knoff from the Gallatin National Forest Avalanche Center. For Photos and Videos, please visit the Avalanche Centers Website!

If you have any snowpack or avalanche observations, drop them a line at mtavalanche@gmail.com or call: 406-587-6984.

For detailed Avalanche Terms utilized here, please see the Avalanche Glossary.