Our final avalanche advisory for the 2012/13 winter was issued last Friday, April 5. Since then, winter returned to the mountains with a few inches of new snow and high winds. The Missoula Office of the National Weather Service is forecasting more snow before we return to more seasonal and warmer temperatures.
Spring Avalanche Safety Considerations
In previous years we’ve seen many big snow storms pass through western Montana in April and May, this year should be no exception. These spring snows typically come in at much warmer atmospheric temperatures so it tends to bond to the old hard snow surface and settle quickly. The storm snow avalanche hazard usually abates within 24-48 hours.
Recently wind loaded terrain steeper than 35 degrees should be treated with caution during and immediately after a storm.
As soon as skies clear and temperatures warm above freezing, the wet snow avalancheAn avalanche caused by snow losing its strength after becoming damp, moist or saturated with water. danger can escalate especially on steep slopes that have recent new snow. These wet slides can entrain a lot of snow and potentially step down into the deeper, weaker snow at the ground.
Be alert to what the temperature is doing and watch slopes that have early exposure to the sun. Wet, point releaseA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or SluffA Loose Snow AvalancheA Loose Snow Avalanche or Sluff. or Sluff.. wet snow avalanches area good sign that slope stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). is rapidly decreasing. Once you see these, or start punching through the upper snowpack, move to the more shaded northerly aspects.
Much of our area has already been through several days of melt down and even rain up to 7000 feet so the bottom of the snowpack is wet and rotten and now capped with a solid melt-freeze layer several inches thick. Several melt-freeze cycles will allow for good skiing and riding conditions early in the day or during cool weather. Once it warms up again, pay attention to how the snow feels.
Cornices can be very touchy this time of year. The best advice we can offer is to stay well back on the windwardThe upwind side of an obstacle such as a ridge. Usually snow is eroded from windward slopes making them relatively safer. side of ridges and avoid travel directly underneath them. Big cornices have a nasty habit of breaking further back than you might expect and can entrain a lot of snow, kind of like a bulldozer, as they roll downhill.
We’re at the end of what will be remembered as an exceptionally safe winter. There were no avalanche fatalities in Montana this winter! It’s been a long time since we could say that. Locally, we issued only one warning for high avalanche danger in early January and investigated one avalanche incident that had a positive outcome (details here).
This can be attributed to a mostly stable early season snowpack, good assessment skills by many of you and, in some cases, shear luck. More people are recreating in avalanche terrain than ever and this year is no exception.
Our Friends group, the West Central Montana Avalanche Foundation (WCMAF), really stepped up to the plate this year. The level of service we provide would not be possible without their monetary support. This partnership between the Lolo Forest and the WCMAF has been very successful and will continue for many years, but it needs your continued support. 100% of the local fund-raising efforts by the WCMAF along with your donations pay for data collection, avalanche advisories and public avalanche education programs in west central Montana.
Thanks to all of you for your dedication to staying safe and for your support of the avalanche advisory and education program here. Have a safe, excellent summer and we’ll see you again next season!
Steve Karkanen, Dudley Improta, Tim Laroche.