Yellowstone Seven Day Forecast on 10 January 2011 by the NWS Riverton, WY

Today: Mostly cloudy. Slight chance of snow in the morning...then scattered snow showers in the afternoon. Highs 7°F to 13°F. Chance of snow 30 percent. Lowest wind chill readings -15°F to -25°F in the morning.

Tonight: Cloudy. Scattered snow showers in the evening...then slight chance of snow after midnight. Lows -4°F to -10°F. Chance of snow 40 percent. Wind chill readings -15°F to -25°F.

Tuesday: Mostly cloudy in the morning then becoming partly cloudy. A 20 percent chance of snow. Highs 7°F to 13°F. Southwest winds around 15 mph. Lowest wind chill readings -20°F to -30°F in the morning.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. A 20 percent chance of snow. Lows -6°F to 0°F. Southwest winds around 15 mph in the evening.

Wednesday: Breezy. Not as cold. Cloudy. Chance of snow in the morning...then snow likely in the afternoon. Snow accumulation of 1 to 2 inches. Highs 16°F to 22°F. Southwest winds 15 to 20 mph. Chance of snow 60 percent. Lowest wind chill readings -14°F to -24°F in the morning.

Wednesday Night: Breezy. Not as cold. Snow likely. Light snow accumulations. Lows 10°F to 16°F. Chance of snow 60 percent.

Thursday: Not as cold. Snow likely. Light snow accumulations. Highs 25°F to 31°F. Chance of snow 70 percent.

Thursday Night: Snow likely. Light snow accumulations. Lows 17°F to 23°F. Chance of snow 70 percent.

Friday: Cloudy with a 50 percent chance of snow. Highs 26°F to 32°F.

Friday Night: Snow likely. Light snow accumulations. Lows 17°F to 23°F. Chance of snow 60 percent.

Saturday: Snow likely. Light snow accumulations. Highs 25°F to 31°F. Chance of snow 60 percent.

Saturday Night: Snow likely. Lows 12°F to 18°F. Chance of snow 60 percent.

Sunday: Cloudy with a 50 percent chance of snow. Highs 19°F to 25°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 Eric Knoff

Mountain Weather:

Frigid cold temperatures are the word this morning with most mountain locations reading 5-10 below zero F. Fortunately winds are light, blowing out of the Westsouthwest at 5-15 mph. Mountain temperatures will fight to break zero today with highs reaching 5-10 above. Winds will stay light out of the Westsouthwest under partly to mostly cloudy skies. Temperatures will plunge back to double digits below zero tonight, with a gradual warming trend starting tomorrow.

Snowpack and Avalanche Discussion:

The northern Madison Range:

The northern Madison Range, specifically the mountains around Big Sky, holds the weakest snowpack in our advisory area. The main culprit for this current designation is a layer of buried surface hoar located 2-3 feet below the surface in many areas. This layer formed over three weeks ago and has gradually gained strength. This strengthening is a trend we like to see but it does cause some stability assessment problems.

The main hurdle with this surface hoar layer is gauging its strength and distribution. A good example of this layer's unpredictable nature was the human triggered avalanche that caught a snowboarder in Beehive Basin on Thursday. This slide occurred on a Westsouthwest facing slope that does not have a wide distribution of buried surface hoar. To trigger the slide, the rider needed to find a very specific spot, which they did and produced the resulting avalanche. A good strategy for travelling in an area with buried surface hoar is to dig numerous snowpits and avoid high probability zones - specifically steep and wind loaded slopes.

Along with the lingering threat posed by the buried surface hoar, recent wind loading has created sensitive soft slabs on aspects favored by Westnorthwest winds. Triggering a pocket of wind drifted snow will likely stay confined to the new snow, but the possibility of a wind slab stepping down to deeper layers is real.

Today, human triggered avalanches are likely on all wind loaded slopes where the Avalanche Danger is rated CONSIDERABLE. Slopes that have not received wind loading 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, a skier triggered a wind slab avalanche off the south peak of Saddle while travelling to Argentina Bowl. The skier who triggered the slide was the third skier to descend the slope and luckily escaped unharmed. This is a poignant reminder that our snowpack has the potential to avalanche, primarily on slopes that have been wind loaded. Although wind loaded terrain is our main avalanche concern, triggering an avalanche on a non-wind loaded slope also remains a possibility.

Yesterday, I skied on the west side of the Bridgers and found variable conditions. My partner and I experienced collapsing and propagations during stability tests on Southwest facing slopes. However, Westnorthwest facing slopes held a deeper, more stable snowpack. The difference between a stable and unstable slope was only a matter of a few degrees in aspect. Buried facets are not widespread in the mountains of our advisory area - but they do exist. Paying close attention to shallow areas in the snowpack, such as wind scoured areas, rock outcroppings and convex knolls is an effective practice to avoid triggering a slide on deeper layers.

The slide in the Bridgers comes on the heels of a human triggered slide in the northern Madison Range. The theme to these two slides is that human triggered avalanches are likely when skiing or riding in steep, wind loaded terrain. The take home message from these two events is that our snowpack is capable of producing avalanches and backcountry travelers should practice safe backcountry protocol and be prepared if an avalanche does occur.

Today human triggered avalanches are likely on wind loaded slopes steeper than 35 degrees where the Avalanche Danger is rated CONSIDERABLE. On less steep, wind loaded slopes OR non-wind loaded slopes steeper than 35 degrees the Avalanche Danger is rated MODERATE. Generally safe avalanche conditions can be found on less steep slopes without a wind load where the Avalanche Danger is rated LOW.

Doug 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.

Feeling rusty with your avalanche transceiver? The new beacon park at Beal Park in Bozeman is up and running. It's got 4 transmitters and the park is open 9 am to 8 pm every day. The Friends of the Avalanche Center and the city of Bozeman worked together to make this service possible.

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