Tonight...Windy...snow. Areas of blowing snow after midnight. Snow accumulation of 3 to 6 inches. Lows 21°F to 27°F. Southwest winds 20 to 30 mph. Chance of snow near 100 percent.

Thursday...Windy. Areas of blowing snow in the morning. Widespread snow. Snow accumulation of 3 to 6 inches. Highs 28°F to 34°F. Southwest winds 20 to 30 mph. Chance of snow near 100 percent.

Thursday Night...Breezy. Snow likely in the evening...then snow after midnight. Snow accumulation of 2 to 3 inches. Lows 16°F to 22°F. Southwest winds 15 to 20 mph. Chance of snow 90 percent.

Friday...Windy...snow. Snow accumulation of 3 to 5 inches. Highs 29°F to 35°F. Southwest winds 20 to 30 mph. Chance of snow near 100 percent.

Friday Night...Windy...snow. Snow accumulation of 3 to 6 inches. Lows 10°F to 16°F. Southwest winds 25 to 35 mph with gusts to around 50 mph. Chance of snow near 100 percent.

Saturday...Breezy...colder...cloudy. Snow likely in the morning... Then chance of snow in the afternoon. Light snow accumulations. Highs 16°F to 22°F. Chance of snow 70 percent. Wind chill readings -11°F to -21°F.

Saturday Night...Colder. Partly cloudy. A 20 percent chance of snow in the evening. Lows -3°F to 5°F.

New Years Day...Partly cloudy in the morning then clearing. Highs 18°F to 24°F.

Sunday Night...Mostly clear. Lows -5°F to 5°F.

Monday...Mostly sunny. Highs 24°F to 30°F.

Monday Night...Mostly clear in the evening then becoming partly cloudy. Lows 5°F to 13°F.

Tuesday...Partly cloudy. Highs 24° to 30°.

Tuesday Night...Partly cloudy in the evening then clearing. Lows 4°F to 12°F.

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

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Mountain Weather

This morning is warm and windy with fresh snowfall in the southern mountains. Four inches has fallen near Cooke City with 1-2 inches accumulating from the Yellowstone Club to West Yellowstone. Mountain temperatures are in the mid to high 20s Fahrenheit as westerly winds average 30-40 mph with gusts hitting 50 mph. The jet stream will keep winds strong and create favorable dynamics for snowfall. By morning there could be 1-2 inches in the northern mountains and 6-8 inches in the southern ranges.

Snowpack and Avalanche Discussion:

The Madison and southern Gallatin Ranges, the Lionhead area near West Yellowstone:

The entire Madison Range, southern Gallatins and mountains outside West Yellowstone have a weak snowpack. From the Lionhead area to slopes at Bacon Rind / Taylor Fork all have a snowpack of sugary, loose snow capped with one or two layers of surface hoar. The grain type is irrelevant. The avalanche concern is that there are multiple weak layers that will break with a new snow load. The mountains surrounding Big Sky are not much better. We found weak snow structure in Beehive Basin on Monday as we investigated Friday's skier triggered slide. Since it is still possible to trigger avalanches throughout southwest Montana, the Avalanche Danger is rated MODERATE on all slopes. In the next 24 hours more snowfall is expected in the southern mountains which could quickly elevate the Avalanche Danger to CONSIDERABLE.

The mountains around Cooke City:

The snowpack is relatively strong in the mountains around Cooke City. Faceted grains near the ground are bonding together and our primary weak layer would be close to the surface: small-grained facets that may be sitting on an ice crust, especially on southerly aspects. Additionally, new snow from last night will be blown into wind pillows. More snow is predicted which would bump up the danger, so be mindful as you ride or ski in the snowy weather. For today, the Avalanche Danger is MODERATE but could certainly rise to CONSIDERABLE.

The Bridger Range and northern Gallatin Range:

In the northern Gallatin Range, especially in Hyalite Canyon, the snowpack is strong and has good stability. While there are still islands of weak snow, like Mount Ellis where Eric found 85 cm of facets, avalanche activity and other signs of instability have been minimal since the previous storm seven days ago. Slopes that were wind-loaded and have thick drifts could still be triggered, but overall the snowpack is mostly stable.

The Bridger Range also has a snowpack that is mostly stable, but for a very different reason—it has thin coverage of loose, faceted grains, but no slab on top of it. The Bridger Bowl Ski Patrol dropped a huge cornice yesterday without triggering an avalanche, a good sign of stability on that specific slope, but overall buried facets are not to be trusted. For today, any wind-loaded slope will have a MODERATE Avalanche Danger while all other slopes have a LOW Avalanche Danger.

SPECIAL NOTE: The difference between a Moderate and Considerable danger is substantial. During Considerable danger it becomes possible to find natural avalanche activity while human triggered avalanches are likely. "Likely" is not a good thing with avalanches. If you were "likely" to win the lottery, you would play every day.

Mark 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 Events and Education, or 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.