Yellowstone Seven Day Forecast on 07 January 2011 by the NWS Riverton, WY

Rest Of Today: Mostly cloudy with a 40 percent chance of snow. Highs 26°F to 32°F.

Tonight: Chance of snow in the evening...then snow likely after midnight. Snow accumulation of 1 to 2 inches. Lows 15°F to 21°F. Chance of snow 70 percent.

Saturday: Snow likely in the morning...then snow in the afternoon. Snow accumulation of 1 to 2 inches. Highs 21°F to 27°F. Southwest winds around 15 mph in the late morning and afternoon. Chance of snow 80 percent.

Saturday Night: Colder. Snow in the evening...then chance of snow after midnight. Snow accumulation of 2 to 4 inches. Total snow accumulation 4 to 8 inches. Lows -2°F to 4°F. Northwest winds around 15 mph in the evening. Chance of snow 90 percent.

Sunday: Colder. Cloudy with a 40 percent chance of snow. Highs 7°F to 13°F.

Sunday Night: Colder. Cloudy with a 30 percent chance of snow. Lows -6°F to -14°F.

Monday: Mostly cloudy with a 20 percent chance of snow. Highs -1°F to 5°F.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows -11°F to -19°F.

Tuesday: Partly cloudy. Highs 1°F to 7°F.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. A 20 percent chance of snow. Lows -3°F to -9°F.

Wednesday: Not as cold. Mostly cloudy with a 30 percent chance of snow. Highs 12°F to 18°F.

Wednesday Night: Mostly cloudy with a 30 percent chance of snow. Lows 3°F to 9°F.

Thursday: Mostly cloudy with a 40 percent chance of snow. Highs 17°F to 23°F.

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

Avalanche Information - from the Gallatin National Forest Avalanche Center this report is by Mark Staples

Mountain Weather:

Warm weather is the word this morning with temperatures mostly in the mid to high 20s Fahrenheit. Westerly ridgetop winds calmed slightly from yesterday blowing 10-25 mph near Bozeman and 5-15 mph elsewhere. Yesterday afternoon some areas received a brief shot of freezing rain followed by a dusting of snow. More precipitation should come this afternoon possibly starting as rain before changing to snow. By tomorrow morning 2-3 inches should accumulate with more on the way. Today will have high temperatures near 30 degrees Fahrenheit with westerly winds blowing 10-15 mph.

Snowpack and Avalanche Discussion:

The northern Madison Range:

Yesterday someone was caught in an avalanche on a West facing slope in Beehive Basin near Big Sky. Although she was not injured or buried, her snowboard broke upon impact with a tree. This avalanche was about 150 feet wide, 2-5 feet deep and occurred in a gully cross loaded with wind-blown snow. It didn't run very far, but the debris was 10 feet deep on a bench where the avalanche stopped. This group dug a snowpit on a similar aspect and performed a Rutschblock test with stable results, but they reported ignoring several key factors wanting to believe the slope was stable.

1.There was significant new snow.

2.There was significant wind loading on the slope from cross winds.

3.The snowpack structure was entirely different on the slope from what they saw in their snowpit.

4.The bench created a terrain trap where the debris ran into trees and piled 10 feet deep.

Additionally they reported a false sense of security from their snowpit and stability test results as well as seeing dropped cornices on the other side of the ridge (East aspect) without triggered avalanches. These factors seem obvious in hindsight but never are in the moment, and this avalanche provides a great lesson. I've been guilty of ignoring clues and always struggle with managing the human element of decision making especially when the riding is good.

Significant new snow and wind-blown snow adds stress to the snowpack pushing any weak layer to its breaking point. The most widespread weak layer near Big Sky has been buried surface hoar, about 2-3 feet deep. While this layer has gained strength on many slopes, it remains weak on others. Wind loaded slopes remain the primary concern. In most places avalanches will break within the new snow but can break on deeper layers as yesterday's avalanche demonstrated. Today the Avalanche Danger is rated CONSIDERABLE on all wind loaded slopes. All other slopes have 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:

Yesterday Eric and I went to the Taylor Fork area hunting for instabilities but we found more face shots than weak layers. A similar report came from skiers near Cooke City where they avoided obvious pillows of wind-blown snow, found no stability issues in their snowpits, and found waist deep powder. Stability evaluations through much of the advisory area (except for the mountains near Big Sky) are relatively simple and any weaknesses are not buried deeply. On a Southwest aspect, near Skyline Ridge, Eric and I found the strongest snowpit I've seen this year. On a Northeast aspect in Sunlight Basin, we found a layer about 12 inches down that only concerned us if it had the additional load of wind-blown snow.

Today the Avalanche Danger is rated:

CONSIDERABLE on slopes steeper than 35 degrees with a wind load

MODERATE on less steep slopes with a wind load OR steep slopes without a wind load

LOW on slopes less than 35 degrees without a wind load

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