Avalanche Advisory for February 28, 2014

The current avalanche danger is MODERATE, or Level 2, on all terrain above 5000 feet in the west central Montana backcountry. Heightened avalanche conditions can be found on some terrain features, natural avalanches are unlikely but human triggered avalanches are possible.

This moderate rating may be short lived as a BLIZZARD WARNING has been issued by the Missoula Office of the National Weather Service. We are watching this develop and may raise the danger rating if necessary.

If you get out in the backcountry, send a quick email to [email protected] or a detailed observation. Your information is highly valued during transitional periods like we’re experiencing now. We will respect any desire to remain anonymous, we just want the information.

Hello! This is Steve Karkanen with the West Central Montana Avalanche Center’s avalanche advisory for Friday, February 28, 2014.  The avalanche danger rating expires at midnight tonight. The USDA Forest Service is solely responsible for the content of this advisory.

 

Weather and Snowpack

This is certainly shaping up to be a memorable late February.

This morning, SNOTEL stations report about a half inch of snow water accumulation in the past 24 hours with the Stuart Peak station reporting 1.6 inches.  Snowbowl reports 14 inches of new snow this morning.

Locations north of Missoula are under the influence of the arctic air spilling over the Continental Divide this morning and temperatures are in the low teens and dropping at both Stuart Peak and North Fork Jocko SNOTEL stations.  Bitterroot range SNOTEL temperatures remain near 30 degrees with much less snow accumulation.  Rain was reported up to 7500 feet yesterday in the Bitterroot.

At 5 am, the wind at Point Six is from the east at 6mph gusting to 10 and out of the west.  At the Deer Mountain RAWS station, the wind is out of the west at 13 gusting to 20 mph.

Skies cleared Tuesday and we were given a 2 day respite in the snow. Temperatures responded quickly to solar heating on most sun exposed aspects with SNOTEL stations reporting high temperatures into the forties by Tuesday and Wednesday afternoons.  We received a few reports of minor loose snow point release avalanches in the Swan and Bitterroot ranges on steep aspects affected by solar heating.

The overall snowpack has adjusted well to last weeks new load and people are skiing and riding onto steeper terrain. Warmer temperatures further settled this new snow but also left a thin sun crust on most aspects on the south half of the compass. Locations that received rain yesterday now have a rain crust.

We have not received any reports of widespread avalanche activity or reports of the usual clues of unstable conditions in the past 48 hours.

A thin layer of surface hoar formed on this sun crust in some sheltered areas Wednesday night before cloud cover moved in.

Observations from the Bitterroot, the Rattlesnake and the Seeley Lake area indicate mostly stable conditions. The area of most concern in all the profiles is how well this upper level feature adjusts to the storm slab currently forming.

The primary avalanche problem today is new storm snow slab development on the sun crust or rain crusts on slopes steeper than 35 degrees. East to southwest aspects are suspect but it should be pretty easy to stick your arm down into the snow to see if the crust is present.

Another avalanche problem to be aware of is wind slab development.  Mountain winds have been mostly calm through this morning but the weather models say this is about to change, with a vengeance. Arctic air is spilling over the divide this morning with increasing winds from the east.  This scenario loads unusual places so it will be possible to find wind slab and cornice development opposite from the expected places.

Cornices have grown with each storm and are pretty sensitive now. Many cornices have collapsed naturally in all areas after the last storm. They deserve a wide berth.

The more deeply buried facet/crust that we’ve been describing continues to gain strength but in areas with shallow snow cover, it is still producing clean failures when a lot of force is applied.  It does not propagate as it did 2 weeks ago, but it must not be ruled out as a potential problem in areas that have less than 4 feet of snow.

 

Weather and Avalanche Forecast

We are currently under a BLIZZARD WARNING for the entire area.  6-8 inches of new snow is expected with this storm with 60 mph winds.  Wind direction will be N-NE at the peak of the storm returning to a more westerly direction as the storm subsides Saturday.

Expect the avalanche danger to increase, possibly to HIGH avalanche danger levels, through the weekend. Any leeward terrain, especially the more southern aspects that have a sun crust, will have dangerous wind slab formations.

This is what we live for!  Enjoy it while it lasts, but do so in a way that you live to do it again.  Have a safe weekend!

Dudley Improta will issue the next advisory on March 4, 2014.