Avalanche Information - from the Gallatin National Forest Avalanche Center

Mountain Weather:

Happy New Year’s Eve! It’s cold this morning and shouldn’t warm up much until next year. Since yesterday only a trace to two inches of new snow fell. Temperatures were in the negative teens Fahrenheit this morning though a bit warmer near West Yellowstone with winds blowing 5-15 mph from the eastern half of the compass. Mostly cloudy skies will prevent much warming and temperatures should rise to near 0 Fahrenheit. Light winds will blow 5-10 mph and shift to the north.

Snowpack and Avalanche Discussion:

The northern Madison Range:

Stability issues in the new snow will slowly diminish, but we remain concerned about a layer of surface hoar buried about 2 feet deep. While this layer does not exist on every slope, it is more widespread in the mountains near Big Sky than any other area. To further complicate matters, this layer showed some initial signs of strengthening on Tuesday along Buck Ridge, and a skier on Yellow Mountain yesterday also saw a glimmer of hope. However, this information is not bull’s eye data for today and should be stored for later use. The key data to remember are:

1. We have a widespread weak layer.
2. It was heavily stressed by recent snow and needs time to adjust.
3. This weak layer has given strong warning signs like collapsing and cracking in Beehive prior to this storm as well as an avalanche at Moonlight Basin at the end of the storm.

This avalanche does not indicate the widespread presence of facets near the ground, but it reminds us to use a little patience after a big storm, carefully evaluate the snowpack and pay attention to bull’s eye information. For today the avalanche danger is rated CONSIDERABLE.

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

The rest of the advisory area has only isolated areas with persistent weak layers. The most notable are the Bacon Rind area, Flathead Pass and South and West facing slopes on the west side of the Bridger Range. Otherwise, the primary concern is the interface between the new snow and the old snow surface. During the storm on Wednesday, ski patrollers at Bridger Bowl as well as skiers on Saddle Peak very easily triggered new snow avalanches with ski cuts. Further south near Hebgen Lake, Doug and I saw signs of this new snow instability in very minor cracking around our skis, but felt totally safe skiing non wind affected slopes less than 35 degrees. Yesterday near Mt Blackmore, a skier found a mostly stable snowpack except at the interface between the new and old snow which had not yet bonded well.

For today, human triggered avalanches confined to the new snow are likely on slopes steeper than 35 degrees, and the Avalanche Danger on these slopes is CONSIDERABLE. A few degrees less steep can make all the difference, and slopes less than 35 degrees have a MODERATE Avalanche Danger.

Gallatin National Forest Avalanche Center ~ Mammoth Weather Forecast

Yellowstone Seven Day Forecast on 31 December 2010 by the NWS Riverton, WY

Today: Mostly cloudy with a 20 percent chance of snow in the morning...then partly cloudy in the afternoon. Highs -1°F to 5°F. Lowest wind chill readings -22°F to -32°F in the morning.

Tonight / New Years Eve: Mostly cloudy in the evening then becoming partly cloudy. Patchy ice fog after midnight. Occasional flurries after midnight. Lows -9°F to -15°F.

New Years Day: Partly cloudy. Areas of freezing fog and patchy ice fog in the morning. Occasional flurries in the morning. Highs 0°F to 6°F. Lowest wind chill readings -21°F to -31°F in the morning.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. A 20 percent chance of snow. Areas of freezing fog after midnight. Lows -5°F to -11°F.

Sunday: Not as cold. Areas of freezing fog in the morning. Partly cloudy with a 20 percent chance of snow. Highs 10°F to 16°F. Lowest wind chill readings -12°F to -22°F in the morning.

Sunday Night: Mostly cloudy with a 20 percent chance of snow. Lows -4°F to 2°F.

Monday: Patchy freezing fog in the morning. Partly cloudy with a 20 percent chance of snow. Highs 16°F to 22°F.

Monday Night: Partly cloudy. Lows -6°F to 4°F.

Tuesday: Partly cloudy with a 20 percent chance of snow. Highs 16°F to 22°F.

Tuesday Night: Partly cloudy with a 20 percent chance of snow. Lows 2°F to 8°F.

Wednesday: Partly cloudy with a 20 percent chance of snow. Highs 20°F to 26°F.

Wednesday Night: Partly cloudy with a 20 percent chance of snow. Lows 5°F to 11°F.

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

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