Backcountry Avalanche Forecast for Aspen 
Issued 02/23/2010 7:21 AM by Brian McCall

Highlights

Just a few light snow showers around the zone during the last 24 hours and accumulations of less 
that an inch showing up on weather stations. The weekend’s impressive storm dropped 3 feet of snow 
throughout many areas of the zone with higher totals around Marble and McClure Pass. Large 
avalanches have occurred in the backcountry, some running full track, reaching the valley bottoms. 
The most recent large natural avalanche reported to the office came from McClure Pass on Monday 
afternoon. This slide closed the highway around 3:30 pm.

Snowfall diminished on Monday. Clear skies and colder temperatures dominate our weather for Tuesday 
morning. Watch for an increase in Northerly winds this afternoon. The Aspen zone looks to be just on 
the edge of some stronger winds that will affect the eastern part of the state today into the 
evening hours. Drifting snow will form more dangerous slabs on Southerly aspects near and above 
treeline, stressing an already tender snowpack.

Avalanche Danger

The avalanche danger for the Aspen zone today is rated HIGH on slopes facing E-SE-S near and above 
treeline. Watch for tender slabs to form on these aspects if the forecasted Northwest winds do 
increase.  All other slopes near and above treeline and all aspects below treeline have CONSIDERABLE 
danger.

The avalanche danger has eased only slightly for today after the weekend’s large cycle of natural 
avalanches. Conditions are still very dangerous and the isolated large natural avalanches have still 
run within the last 24 hours. Conservative terrain choices still required for safe travel.

Snow & Avalanche Discussion

The weekend’s large snow storm slowly wound down on Monday. A few lingering showers brought under 1” 
of new snow in the last 24 hours. Storm totals vary from about around 25” at Sunlight Mountain, 33-36” 
at the Aspen resorts, 40” at McClure Pass, and totals likely in the 50” range around Schofield Pass. 
Periods of stronger Westerly winds did occur near and above treeline forming dangerous slabs on lee 
aspects at higher elevations. Below treeline, a very weak old snowpack was also overloaded by the 
significant weight of the new snow. Despite the end of the snowfall, we are not out of the woods yet 
with the avalanche danger. Forecasted wind at higher elevations today, especially above 12,000 feet 
may continue to load weak layers in the snowpack on higher elevation southerly aspects. Natural and 
human triggered avalanches will remain likely on wind loaded slopes above treeline today if the 
forecasted winds materialize.

A significant cycle of natural avalanches has occurred around the zone in the last few days. These 
avalanches have occurred on all aspects and at all elevations. Large natural avalanches above 
treeline were observed that often ran full track into the valley bottoms. A couple of recent 
observations note these big slides on a Northwest aspect of Ashcroft Mtn and East aspects of 
Willoughby Peak in East Snowmass creek.  Below treeline, a very weak and shallow old snowpack was 
overloaded by the stress of 2-3 feet of new snow, creating tender conditions there as well. As 
recently as 3pm on Monday, the isolated large natural avalanche was occurring. At that time, Lone 
Tree Bowl above McClure Pass ran across highway 133. The avalanche initiated on a North aspect of 
the start zone, putting 5-6 ft of debris on the highway and was over 400 feet wide. Other recent 
events include a report of one skier triggered avalanche outside the boundaries of Aspen Highlands 
on a West aspect at 10,500 ft Sunday. One person was caught and partially buried in this avalanche. 
It was 60 feet wide and ran 150 vertical ft. Also on Sunday morning, one other larger natural 
avalanche ran over County Road 3 that accesses the town of Marble. This avalanche was over 300 ft 
wide, temporarily closing that road.

For today avalanche danger will still remain HIGH on freshly loaded slopes near and above treeline. 
Another round of natural avalanches could occur as a result of the forecasted wind. With those 
significant snow totals that fell, avalanche danger will be slow to drop. Below treeline, rapid 
settlement of the new snow will help ease the danger a little quicker, but for today human triggered 
avalanche will remain probable there as well.  Lower angled slopes will still be your best choice 
for safe travel today. Give the snowpack some time to adjust to the new load before venturing into 
steeper terrain.

Weather Discussion

The low-pressure trough that brought heavy snow over the weekend is moving eastward and out of the 
state as a ridge of high pressure builds over the western United States. This morning the back edge 
of the trough is over the mountains, creating north and northeasterly flow. During the day the 
leading edge of the ridge will move westward causing the flow to back to the northwest. Skies will 
be partly cloudy to mostly clear and wind will be less than 15 mph with a few notable exceptions. 
Stronger and gusty winds are possible in the San Juan, Sawatch, Vail/Summit and Front Range zones 
along the highest terrain. The wind will continue to back to the west on Wednesday as the ridge will 
flattens. A short-wave trough moving through zonal flow is forecast to bring another shot of snow 
to the mountains Wednesday night and through Thursday.