Yellowstone Seven Day Forecast on 13 January 2011 by the NWS Riverton, WY

Rest Of Today...Chance of snow late in the morning...then snow in the afternoon. New snow accumulation of 1 to 2 inches. Highs 25°F to 31°F. Southwest winds around 15 mph. Chance of snow near 100 percent.

Tonight...Snow. Snow accumulation of 2 to 3 inches. Lows 18°F to 24°F. Southwest winds around 15 mph. Chance of snow near 100 percent.

Friday...Snow likely. Snow accumulation of 1 to 2 inches. Highs 27°F to 33°F. Chance of snow 70 percent.

Friday Night...Snow in the evening...then snow likely after midnight. Snow accumulation of 2 to 3 inches. Lows 15°F to 21°F. Southwest winds around 15 mph after midnight. Chance of snow 90 percent.

Saturday...Snow likely. Snow accumulation of 2 to 3 inches. Highs 25°F to 31°F. Southwest winds around 15 mph. Chance of snow 70 percent.

Saturday Night...Snow likely. Moderate snow accumulations. Lows 17°F to 23°F. Chance of snow 70 percent.

Sunday...Snow likely. Moderate snow accumulations. Highs 29°F to 35°F. Chance of snow 70 percent.

Sunday Night...Cloudy with a 50 percent chance of snow. Lows 20°F to 26°F.

Martin Luther King Jr Day...Cloudy with a 50 percent chance of snow. Highs 28°F to 34°F.

Monday Night...Mostly cloudy with a 40 percent chance of snow. Lows 14°F to 20°F.

Tuesday...Cloudy with a 50 percent chance of snow. Highs 24°F to 30°F.

Tuesday Night...Cloudy with a 50 percent chance of snow. Lows 9°F to 15°F.

Wednesday...Mostly cloudy with a 40 percent chance of snow. Highs 20°F to 26°F.

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

Mountain Weather:

Strong winds have been blowing 15-40 mph from the West and Southwest with temperatures this morning in the mid 20s Fahrenheit. Since yesterday 5 inches of snow fell near Cooke City, 2-3 inches of snow near West Yellowstone, 1-2 inches near Big Sky, and a trace near Bozeman. This pattern of snowfall should continue when more snow comes today. Temperatures will warm into the high 20s Fahrenheit and strong winds will continue blowing 15-40 mph from the West and Southwest. By tomorrow morning, 5-7 inches should fall near Cooke City and West Yellowstone, 3-4 inches near Big Sky, and 1-2 inches near Bozeman.

Snowpack and Avalanche Discussion:

The northern Madison Range:

Buried surface hoar, about 2-3 feet deep, separates the snowpack near Big Sky from the rest of the advisory area. This layer has been tricky to manage because it has unevenly gained strength and does not exist on every slope, but it will be a problem if you let your guard down. Last week one group did not find this layer in their snowpit in Beehive, but triggered an avalanche nearby in a pocket where this layer was capped by a wind drift. Another group on Fan Mountain experienced collapsing while hiking below treeline but found a deep and strong snowpack above treeline on the slope they skied. These examples demonstrate the variable and tricky nature of buried surface hoar. Despite the existence of this layer, wind slabs remain the primary concern especially in areas with a thin snowpack where recent cold weather has weakened it. Heightened avalanche conditions exist in these specific areas, and buried surface hoar requires careful snowpack evaluations. For today the avalanche danger is rated MODERATE.

The Bridger Range, 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 mostly lacks buried surface hoar or other widespread weak layers, and the snowpack is mostly strong especially where it is deep. The exception lies in areas close to ridgelines where the snowpack is thin and faceted. With a wind slab on top of this faceted snow, we have a good recipe for an avalanche. Yesterday, Doug and I skied in Hyalite Canyon touring up Flanders and descending into the main canyon where we found this combination in many areas on the west facing slopes. At the southern end of the Madison Range, skiers found some cracking in thin wind slabs; otherwise, they found a strong, right-side-up snowpack. Skiers triggered a hard wind slab resting on faceted snow last weekend south of Bridger Bowl, and skiers found a similar situation north of Bridger Bowl on Tuesday. When they stopped to assess stability, the slope collapsed and cracked, a clear sign of unstable conditions.

For today, the Avalanche Danger is rated MODERATE on all wind loaded slopes, MODERATE on all slopes steeper than 35 degrees, and LOW on less steep slopes 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