Today...Mostly cloudy with a 20 percent chance of snow. Highs 24°F to 30°F.

Tonight...Snow likely. Snow accumulation of 1 to 2 inches. Lows 12°F to 18°F. Southwest winds around 15 mph early in the evening becoming southwest around 15 mph after midnight. Chance of snow 70 percent.

Tuesday...Snow likely in the morning...then scattered snow showers in the afternoon. Snow accumulation around 1 inch. Total snow accumulation 2 to 3 inches. Highs 25°F to 31°F. Southwest winds around 15 mph early in the morning. Chance of snow 60 percent.

Tuesday Night...Mostly cloudy with slight chance of snow showers in the evening...then partly cloudy with slight chance of snow after midnight. Lows 9°F to 15°F. Chance of snow 20 percent.

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

Wednesday Night...Partly cloudy. Lows 8°F to 16°F. Lowest wind chill readings -10°F to -20°F after midnight.

Thursday...Partly cloudy. Highs 28°F to 34°F.

Thursday Night...Partly cloudy. Lows 13°F to 19°F.

Friday...Partly cloudy. Highs 28°F to 34°F.

Friday Night...Mostly cloudy in the evening then becoming partly cloudy. A 20 percent chance of snow. Lows 7°F to 15°F.

Saturday...Partly cloudy. Highs 26°F to 32°F.

Saturday Night...Mostly cloudy with a 20 percent chance of snow. Lows 8°F to 14°F.

Sunday...Mostly cloudy with a 20 percent chance of snow. Highs 23°F to 29°F.

 Hazardous Weather  Gibbon Falls Forecast  Mammoth Forecast  Midway Forecast  Norris Forecast  Old Faithful Forecast 

Mountain Weather

A fast moving weather disturbance deposited 4-5 inches of new snow in the northern Gallatin and Madison Ranges while the mountains around Cooke City picked up an additional 7-8 inches. The Bridger Range and mountains around West Yellowstone picked up 1-3 inches. Winds spiked around 8:00 PM last night with the arrival of this storm, but have gradually decreased and are currently blowing 10-25 mph out of the West North West. Mountain temperatures are averaging in the mid teens Fahrenheit with Cooke City being the coldest at 5 degrees Fahrenheit. Temperatures will gradually rise into the low 30s by this afternoon and winds will stay consistent out of the West at 10-20 mph. Southwest Montana will likely see a break in the weather this morning, but increasing clouds and a chance of mountain snow will move back into the area tonight. 1-3 inches of snow are possible by tomorrow morning.

Snowpack and Avalanche Discussion:

The Madison Range, and southern Gallatin Range, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range:

There are two main points of concern in the mountains around Cooke City, West Yellowstone, and Big Sky. The first is load adjustment. Over the past week a large amount of weight has been added to the snowpack, pushing some slopes past their breaking point. Doug and Mark visited Cooke City yesterday, where they investigated a human triggered slide and observed the large natural on Mount Republic. Doug did mention he was pleasantly surprised at how little activity there was on surrounding slopes. With new snow and wind last night, the snowpack will continue to work extra hard to find a balance. Although the snowpack lacks a persistent weak layer, the stress added by multiple inches of water and wind can take days even weeks to subside.

Our second point of concern is weak, faceted snow near the ground, which mainly exists in areas where the snowpack is shallow. South and west facing slopes appear to have the widest distribution of faceted snow near the ground, but this intermittent weak layer is not confined to specific aspects and elevations. Rock outcroppings, convex knolls, and areas heavily affected by the wind will be the most likely spots to trigger a slide on buried facets. A skier found this out near Cooke City on Saturday, when he triggered and was caught in a small slide that occurred on a rock outcropping. On Saturday, the Big Sky Ski Patrol triggered multiple deep slab avalanches on south facing slopes with explosives that ran on buried facets. These are all good indications the snowpack is struggling to find equilibrium under the weight of new and windblown snow.

The arrival of new snow and wind last night will keep the snowpack on edge. Today, human triggered avalanches are likely on all wind loaded slopes where the Avalanche Danger is rated CONSIDERABLE. Slopes without a wind load have a MODERATE Avalanche Danger.

The Bridger Range and northern Gallatin Range:

Stability assessment is a bit easier in the Bridgers and northern Gallatin Range. These two northern ranges have little in the way of buried weak layers, plus they didn't receive the same load that the southern mountains did. Yesterday, I skied near Hyalite Peak and found stable conditions in all my snowpits. My partners and I did not witness avalanche activity on surrounding peaks nor did we experience signs of instability such as cracking and collapsing; we felt comfortable skiing slopes up to 35 degrees.

A persistent weak layer and a heavy load may be lacking in the mountains around Bozeman, but triggering a slide remains possible. Yesterday, strong Southeast winds in the Bridger Range loaded northerly slopes which produce fresh soft slabs 8-10 inches deep. The Bridger Bowl Ski Patrol easily triggered these slabs with ski cut and explosives. I expect similar conditions formed in the northern Gallatin Range last night.

A second concern is weak, sugary snow near the ground that has been capped by windblown snow. The most likely areas to encounter this unfriendly combination will be upper elevation slopes that have been heavily wind affected. Avoiding steep, wind loaded terrain is the best way to avoid triggering a slide.

Today, human triggered avalanches are possible on all wind loaded slopes and slopes steeper than 35 degrees where the Avalanche Danger is rated MODERATE. Less steep slopes without a wind load have a LOW Avalanche Danger.

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

Information provided by Doug Chabot, Mark Staples, and Eric Knoff from the Gallatin National Forest Avalanche Center.

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