Yellowstone Seven Day Forecast on 04 January 2011 by the NWS Riverton, WY

Today: Breezy...cloudy. Slight chance of snow in the morning... Then chance of snow in the afternoon. Highs 13°F to 19°F. Southwest winds 15 to 25 mph. Chance of snow 50 percent. Lowest wind chill readings -15°F to -25°F in the morning.

Tonight: Breezy. Cloudy with a 50 percent chance of snow. Lows -2°F to 4°F. Southwest winds 15 to 25 mph. Wind chill readings -12°F to -22°F.

Wednesday: Breezy. Snow likely. Snow accumulation of 1 to 2 inches. Highs 17°F to 23°F. Southwest winds 15 to 25 mph. Chance of snow 70 percent. Lowest wind chill readings -14°F to -24°F in the morning.

Wednesday Night: Breezy. Cloudy with a 50 percent chance of snow. Lows 8°F to 14°F. Southwest winds 15 to 20 mph.

Thursday: Cloudy with a 50 percent chance of snow. Highs 23°F to 29°F. Southwest winds around 15 mph.

Thursday Night: Mostly cloudy with a 40 percent chance of snow. Patchy fog after midnight. Lows 12°F to 18°F.

Friday: Patchy fog in the morning. Mostly cloudy with a 20 percent chance of snow showers. Highs 25°F to 31°F.

Friday Night: Cloudy with a 50 percent chance of snow. Lows 14°F to 20°F.

Saturday: Snow likely. Highs 18°F to 24°F. Chance of snow 70 percent.

Saturday Night: Colder. Mostly cloudy with a 50 percent chance of snow. Lows -2°F below to 4°F.

Sunday: Colder. Mostly cloudy with a 40 percent chance of snow. Highs 3°F to 9°F.

Sunday Night: Colder. Mostly cloudy with a 20 percent chance of snow. Lows -4°F to -12°F.

Monday: Partly cloudy with a 20 percent chance of snow. Highs 6°F to 12°F.

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

Mountain Weather:

Under clear skies, temperatures this morning are in the single digits with westerly winds blowing 15-25 mph at the ridgetops. Increasing clouds, increasing winds and an increasing chance of precipitation are on our plate for the next 24 hours. A northwest flow will push in clouds later today as mountain temperatures climb into the upper teens and winds blow West-Northwest at 20-30 mph. By morning the mountains will have 1-3 inches of new snow with showers continuing into Wednesday.

Snowpack and Avalanche Discussion:

The northern Madison Range:

Strong winds in the northern Madison Range have loaded slopes at many elevations. Avalanche activity has been minimal, but don't let that lull your sensibilities. Yesterday, the Yellowstone Club Ski Patrol sent in two pictures of an avalanche on Cedar Mountain. This slide likely broke on a buried layer of surface hoar that may have been triggered by a snowmobiler from below. A feathery layer of surface hoar is found 18 inches deep on many slopes and is our primary avalanche concern in the mountains around Big Sky. This weak layer is gaining strength, but still demands attention since it is the weakest and most unstable snow in our advisory area. For today, the avalanche danger is rated CONSIDERABLE on all wind-loaded terrain. All other slopes have a MODERATE 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:

Sunday's snowstorm dropped 10 inches of fluff in the Bridger Range and 2-3 inches everywhere else. The winds showed no such disparity and blew 20-30 mph out of the west, loading many slopes on the ridgelines as well as cross loading mid-elevation terrain. Yesterday, my partner and I did a one day blast to Cooke City and found a small wind pocket that released near Lulu Pass (photo). An even smaller slide was seen near Goose Lake and a group of riders from Saskatchewan got a wind slab to crack on Fisher Peak. In the Bridger Range skiers found that the wind slabs could be easily cut, but did not run very far or deep.

Besides the northern Madison Range around Big Sky, the rest of our advisory area lacks a widespread weak layer. On Sunday, I found stable snow in Bacon Rind (video) which I identified ten days prior as having the weakest snow in the southern mountains. It strengthened quickly. Near Cooke City, the weakest layer in my snowpits (photo) wasn't all that weak. The only instability I was concerned with was wind pillows, but these were obvious and easily avoided. For today, the Avalanche Danger is rated MODERATE on all wind-loaded terrain. A MODERATE Danger also exists on all slopes steeper than 35 degrees while lesser angled slopes have a LOW Danger.

Yesterday, I scared my partner (wife) at the top of the slope we were about to ski. After we determined it was safe, I gave her dibs on going first. She was excited—until she turned around and saw my Avalung mouthpiece deployed, ready for emergency use. That tempered her enthusiasm and she wanted to know why I pulled it out if the slope was safe. I answered, "For the same reason I keep my beacon on. You just never know." She pulled hers out too, and headed down.

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

Gallatin National Forest Avalanche Center ~ Mammoth Weather Forecast