Yellowstone Seven Day Forecast on 12 January 2011 by the NWS Riverton, WY

Today: Breezy...cloudy. Chance of snow in the morning...then snow likely in the afternoon. Snow accumulation around 1 inch. Highs 19°F to 25°F. Southwest winds 15 to 25 mph. Chance of snow 70 percent. Lowest wind chill readings -17°F to -27°F in the morning.

Tonight: Breezy. Snow likely in the evening...then snow after midnight. Areas of blowing snow through the night. Snow accumulation of 1 to 2 inches. Lows 13°F to 19°F. Southwest winds 15 to 25 mph. Chance of snow 90 percent.

Thursday: Breezy...snow. Snow accumulation of 2 to 4 inches. Highs 26°F to 32°F. Southwest winds 15 to 20 mph. Chance of snow near 100 percent.

Thursday Night: Snow in the evening...then snow likely after midnight. Snow accumulation of 2 to 3 inches. Lows 18°F to 24°F. Southwest winds around 15 mph in the evening. Chance of snow 90 percent.

Friday: Snow likely in the morning...then chance of snow in the afternoon. Snow accumulation around 1 inch. Highs 27°F to 33°F. Chance of snow 70 percent.

Friday Night: Snow likely. Light snow accumulations. Lows 14°F to 20°F. Chance of snow 60 percent.

Saturday: Cloudy with a 50 percent chance of snow. Highs 25°F to 31°F.

Saturday Night: Snow likely. Moderate snow accumulations. Lows 16°F to 22°F. Chance of snow 60 percent.

Sunday: Snow likely. Moderate snow accumulations. Highs 27°F to 33°F. Chance of snow 60 percent.

Sunday Night: Cloudy with a 50 percent chance of snow. Lows 18°F to 24°F.

Monday / Martin Luther King Jr Day: Cloudy with a 50 percent chance of snow. Highs 2°F5 to 31°F.

Monday Night: Cloudy with a 50 percent chance of snow. Lows 12°F to 18°F.

Tuesday: Cloudy with a 50 percent chance of snow. Highs 22°F to 28°F.

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Avalanche Information - from the Gallatin National Forest Avalanche Center this report is by Doug Chabot

Mountain Weather:

In the last 24 hours no new snow fell. Mountain temperatures slowly climbed to 10°F, except in Cooke City and West Yellowstone where they are anchored near zero. West to southwest winds are blowing 15-25 mph under partly cloudy skies. Clouds will blanket us completely by late morning as wind speeds increase out of the southwest and gust into the 30s. Mountain temperatures will reach the high teens with scattered snow falling late this afternoon. By morning 2-4 inches are expected with more accumulating on Thursday.

Snowpack and Avalanche Discussion:

The northern Madison Range:

The mountains around Big Sky have two instabilities working against them. The first is wind slabs. These are confined to the upper elevations and ski patrols found them touchy and reactive on some slopes again yesterday. The second instability, which is trickier to assess, is the layer of surface hoar buried 2-3 feet deep on many slopes. Last Thursday a snowboarder fractured this layer in Beehive and was caught in a slide. The next day skiers got it to collapse on Yellow Mountain. This surface hoar is tricky because it's deep and strengthening. Not all slopes are prime to avalanche; thoughtful and thorough snowpack investigations are essential. Before the avalanche on Thursday the group dug a pit, found good stability, yet when the boarder descended an adjacent slope, it slid. The feathers of surface hoar managed to survive in a wind-protected pocket.

For today, the Avalanche Danger continues to be CONSIDERABLE on all wind-loaded slopes steeper than 35 degrees. All other terrain has a MODERATE Avalanche Danger.

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

Weak and unstable snow continues to be found on thin spots near the ridgelines. Yesterday in the Bridger Range, north of Wolverine Bowl, two skiers backed off a line they were inspecting when the slope collapsed and cracked above them. The snowpack was thin and the crack wide. They abandoned their plans to dig a pit and ski the gulley. There are similarities between this and Sunday's skier triggered slide in Argentina Bowl in the Bridger Range (video) (many photos). Both were very close to the ridgetop with thin snow depth. Thin snow can create weak, faceted grains. And as we're now seeing, the stress of wind-loads on these sugary facets can propagate fractures. I don't believe this recipe is confined to the Bridger Range either.

These two skiers did an excellent job traveling safe. They skied one at a time to a safe zone 100 feet off the ridgeline with the intention of testing the snow stability before committing to their line. This is a good practice no matter what the avalanche danger. They got a free pass on breaking out their shovels when the slope warned them with a whumph. This obvious sign of instability, especially on the heels of Sunday's avalanche, lends weight and seriousness to the MODERATE Avalanche Danger which is found on all wind-loaded slopes. Any slope steeper than 35 degrees will also have a MODERATE Avalanche Danger while slopes less steep will have a LOW Avalanche Danger.

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.

Beacon Park in Bozeman

Feeling rusty with your avalanche transceiver? The new beacon park at Beal Park in Bozeman is up and running. It's got four transmitters and the park is open 9 a.m. to 8 p.m. every day. The Friends of the Avalanche Center and the City of Bozeman worked together to make this possible.

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.

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

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

Gallatin National Forest Avalanche Center ~ Mammoth Weather Forecast