April 4, 2008 Avalanche Advisory

Weekend Avalanche Advisory
Posted April 4, 2008 at 0700

Hello! This is Steve Karkanen at the West Central Montana Avalanche Center with the weekend avalanche advisory for April 4-6, 2008. The avalanche danger rating expires at midnight April 4th. This report is based on field observations and data collected on Thursday and describes conditions seen at that time. This advisory is the sole responsibility of the Forest Service and does not apply to operating ski areas. John Lehrman at Backcountry Focus sponsors today’s advisory.

Weather and Snowpack Analysis

Most mountain locations received up to a foot of new snow this past week. Temperatures remained cool until Thursday when skies cleared and gave us one of the nicer days we’ve seen this winter. Temperatures shot up into the 40’s at many locations but dropped below freezing as soon as the sun went over the ridge. Shaded slopes retained the finest snow while everything on the bottom half of the compass (east to west) started the slow trip to the Pacific. Temperatures this morning are in the low 20’s at 8000′ and I would expect it to warm up again today if the sun stays out. A strong storm system is expected to make its way into the area later this afternoon bringing significant precipitation by Saturday especially in the Bitterroot Mountains. Snow levels will drop to around 4500′ as the storm passes.

Observers reported mostly stable conditions at all locations with some small point release slides observed involving the snow surface on steep sun exposed terrain. Southern aspects have the weakest snow right now as crusts that formed a few weeks ago fail cleanly under moderate force about 18” deep. These slopes are going to be heinous skiing anyway and I would avoid them during the heat of the day.

Today’s Avalanche Danger

Above 5000′ on slopes steeper than 35 degrees, the avalanche danger is MODERATE. Natural avalanches are unlikely, human triggered avalanches are possible. There may be unstable slabs on steep terrain.

Below 5000′ and on all other terrain less steep than 35 degrees, the avalanche danger is LOW. Natural avalanches are very unlikely, human triggered avalanches are unlikely. There may be isolated pockets of unstable snow at the lower elevations even during periods of LOW avalanche danger.

During periods of rapid warming or rain, the avalanche danger will quickly increase to CONSIDERABLE on all slopes steeper than 35 degrees. Natural avalanches are possible, human triggered avalanches probable.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting that a strong storm system will enter the area late Friday. Temperatures and snow levels will begin dropping as this system makes its way into Montana. The Bitterroot Mountains have the best chance for snowfall accumulation possibly heavy amounts in some locations.

This is the final avalanche advisory for this season. Mountain locations continue to accumulate snow and April can be a big snow month in the Northern Rockies. We have not seen any significant warm up or rain above 6000′ all winter. Once we have temperatures that remain above freezing for several hours or if we get any rain, I would expect to see widespread avalanche activity involving some of the now deeply buried weak layers we’ve been keeping an eye on this winter.

If you are seeking further backcountry travel information please contact the local Forest Service Ranger District Office in the area where you wish to recreate or call us at 406-329-3752.