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: Mostly cloudy. Occasional flurries in the morning. Chance of snow 20 percent. Highs 14°F to 20°F.

Tonight: Partly cloudy. Patchy freezing fog after midnight. Lows -6°F to 0°F.

Saturday: Partly cloudy. Patchy freezing fog in the morning. Highs 16°F to 22°F.

Saturday Night: Cloudy with a 50 percent chance of snow. Lows 1°F to 7°F.

Sunday: Cloudy with a 40 percent chance of snow. Highs 15°F to 21°F.

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

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

Monday Night / New Years Eve: Partly cloudy in the evening then clearing. Lows -7°F to 1°F. * Happy New Year *

Tuesday / New Years Day: Partly cloudy. Highs 16°F to 22°F. * Happy New Year *

Tuesday Night / New Years Night: Partly cloudy in the evening then clearing. Lows 1°F to 7°F. * Happy New Year *

Wednesday: Mostly sunny in the morning then becoming partly cloudy. Highs 19°F to 25°F.

Wednesday Night: Partly cloudy in the evening then clearing. Lows 4°F to 10°F.

Thursday: Partly cloudy. Highs 19°F to 25°F.

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Mountain Weather

Since yesterday the mountains near Bozeman and Big Sky received 2 to 3 inches of snow while mountains further south received a trace to one inch. Light snow was still falling this morning but should end soon as dry air moves over southwest Montana today. Temperatures this morning were near 10 degrees Fahrenheit and should warm to the mid-teens to 20 Fahrenheit today. Westerly winds at ridgetops in the Bridger and northern Gallatin Ranges were averaging 20 mph with gusts of 30 mph. In all other areas westerly winds averaged 5 to 10 mph with gusts of 15 to 30 mph. Overall for today expect generally light winds, cold temperatures, and sunshine.

Snowpack and Avalanche Discussion:

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

Many areas have a strong snowpack but some slopes have weak, faceted snow about 1 foot above the ground with a cohesive slab on top. A few places like Mount Ellis have a completely weak and faceted snowpack with no slab. The real question is what does it take for a slope to be unstable? The first requirement is for stress from new or wind-blown snow and stress from a skier or rider to initiate a crack in the weak layer. Without much new snow and mostly calm winds, initiating a crack has become more difficult, thus avalanches have become less likely.

The second requirement is for the crack to propagate across a slope. Crack initiation plus propagation produces an avalanche. On many slopes with a strong snowpack, neither crack initiation nor propagation will occur. The problem exists mostly where the snowpack is about 3 feet deep and a slab of cohesive snow rest on weak, faceted snow about 1 foot above the ground. This combination can propagate a crack and produce an avalanche if a skier or rider finds the right spot on a slope to initiate the crack. Slopes with this layering are not obvious and can be found on S aspects in some places (photo, video) or N aspects in other places (photo, video).

Today, dig several quick snowpits in safe locations looking for shallow snow with a slab resting on weak facets that propagate a crack in extended column tests (info on snowpits and stability tests here). Then consider if the snow layering in your snowpit is similar to the layering on the slopes where you hope to ski or ride. If the snow is deep and strong, then watch for shallow wind slabs and hit it. Because human triggered avalanches remain possible today, 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 Articles, Education and (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.