Caution advised for snow falling off of building roofs. Park accordingly.

Dangerous avalanche conditions may already exist in many back country areas, please call the Recorded Avalanche Advisory 406-587-6981 for the most current conditions.

Today: Cloudy with a 50 percent chance of snow. Highs 15°F to 21°F.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. A 20 percent chance of snow. Lows 0°F to 6°F.

Friday: Mostly cloudy in the morning then becoming partly cloudy. A 20 percent chance of snow. Highs 14°F to 20°F.

Friday Night: Partly cloudy. Lows -4°F to 2°F.

Saturday: Partly cloudy. Highs 17°F to 23°F.

Saturday Night: Partly cloudy with a 20 percent chance of snow. Lows 3°F to 9°F.

Sunday: Mostly cloudy with a 30 percent chance of snow showers. Highs 14°F to 20°F.

Sunday Night: Colder. Mostly cloudy in the evening then becoming partly cloudy. A 20 percent chance of snow showers. Lows -6°F to 2°F.

Monday: Partly cloudy. Highs 14°F to 20°F.

Monday Night / New Years Eve: Partly cloudy in the evening then clearing. Lows -6°F to 2°F. * Happy New Year *

Tuesday / New Years Day: Partly cloudy. Highs 19°F to 25°F. * Happy New Year *

Tuesday Night / New Years Night: Partly cloudy. Lows 5°F to 11°F. * Happy New Year *

Wednesday: Partly cloudy. Highs 23°F to 29°F.

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Mountain Weather

Yesterday afternoon the mountains near West Yellowstone received 2 to 3 inches of snow and other areas received about an inch. It was snowing this morning with an additional 2 inches recorded near Big Sky by 6:00 a.m. Temperatures were in the low teens Fahrenheit and high single digits Fahrenheit this morning, and winds were averaging 10 mph from the northwest with gusts of 15 to 20 mph. Snowfall will end this morning with little additional accumulation. Some snow will return tonight mainly in the mountains near Bozeman and Big Sky where 1 to 3 inches will fall. Areas further south should only receive a dusting.

Snowpack and Avalanche Discussion:

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

I wish that I could give a green light to ski, ride, and sled on all steep slopes but I can't. Even though many slopes are stable, some are not. Recent observations include:

1. Yesterday Eric skied near Hebgen Lake just north of West Yellowstone where he found strong snow on southeast aspects. He avoided northeast aspects where he found weak facets near the ground that propagated cracks in his stability tests under hard force (photo, video).

2. Doug skied a little further north near the Bacon Rind drainage and found no weak snow.

3. Two days ago near Big Sky on Wilson Peak a snowshoer was climbing a southwest facing slope with about 3 feet of snow just above treeline. The slope collapsed with a loud whumph (a clear sign of unstable snow) when his snowshoes punched through a supportable layer of snow.

Unfortunately the difference between slopes with strong snow and slopes with weak and possibly unstable snow is not obvious. We have not found a pattern with respect to aspect or elevation. To find the weakest snow, thus places to avoid, look for slopes where the snowpack is less than 3 feet deep (photo, video). On these slopes weak facets may exist in bottom foot of the snowpack. Some places like Mount Ellis have lots of weak snow but lack the overburden of a slab to provide both the stress and the structure to produce an avalanche.

Dig several quick snowpits looking signs of instability which include weak snow under a slab and extended column test results that propagate a crack. Finding this combination is enough evidence to choose a slope less than 30 degrees steepness or one with a deeper and stronger snowpack. Also identify areas on a slope with thinner snow. These areas with thin snow are possible trigger points for an avalanche. For today, variability in the snowpack makes human triggered avalanches possible and the Avalanche Danger is rated MODERATE.

Last week's period of cold, sometimes clear weather, turned the top few inches of snow into weaker, small grained facets. These did not form everywhere, and to further complicate their distribution, strong winds on Friday scoured them from some slopes too. This layer is now capped by the recent snows. It is not deep enough to be a grave avalanche concern yet, but we'll be looking for it since these layers tend to persist.

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. For links to all (photos) and (videos) listed in the above report, please visit this Link.

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

3. 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.