Avalanche Warning for February 16, 2011

The avalanche danger is HIGH on wind-loaded terrain steeper than 30 degrees. Natural avalanches are likely and human-triggered avalanches are very likely. Large avalanches are possible wherever wind slabs have formed at elevations above 5000 feet in the central and northern Bitterroot mountains and above 6000 feet in the Rattlesnake and southern Swan and Mission mountains north of Missoula.

Hello! This is Steve Karkanen with a special update to the West Central Montana Avalanche Center’s backcountry avalanche advisory for Wednesday, February 16, 2011.

All other terrain above 5000 feet and steeper than 30 degrees has CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely.  Today is a good day to play on lower angle terrain or in the trees.

In the southern Bitterroot and on all other terrain above 5000 feet, the avalanche danger is MODERATE.  Natural avalanches are unlikely, human-triggered avalanche are possible. There are heightened avalanche conditions on some terrain features.

Weather and Snowpack Analysis

This special update to the avalanche danger is based on the heavy load of new snow and high winds we are experiencing today.

SNOTEL sites in the north half of the advisory area have picked up an inch or more of Snow Water Equivalent (SWE) the past few hours and it is expected to keep snowing through the evening. Lookout Pass ski area is reporting 23 inches of new snow the past 24 hours. High W-NW winds are present at the higher elevations and easily moving snow around. The Point Six RAWS station has been recording strong SW-W-NW winds for the past few days so expect leeward terrain to be heavily loaded.  Significant cross-loading can occur during this type of weather event and lower portions of a slope can also be heavily wind-loaded.

In the Monday advisory Dudley described the concern with wind slabs that formed during high winds last weekend.  The current weather scenario has exacerbated this problem with more wind and a lot more new snow.  These wind slabs are going to be touchy for a few hours so we recommend staying away from them.  The snowpack needs a couple of days to adjust to this new load.

Weather Forecast and Avalanche Outlook

A winter storm warning is in effect until 4 pm this afternoon.  Periods of moderate to locally heavy snow with high winds are expected to continue through today.  10-15 inches is expected for the Lolo Pass area.

Expect avalanche conditions to remain HIGH for the next several hours until the snowpack has a chance to adjust to this new load.  We’ll be out poking around in several locations Thursday and I will issue an update on Friday morning.

If you do get out and see something you think is important to pass along, please send us a note at [email protected] or use our public observations web page.