January 25, 2010 Avalanche Advisory

Hello! This is Steve Karkanen at the West Central Montana Avalanche Center with backcountry avalanche information for Monday, January 25, 2010.

Current Avalanche Danger

The avalanche danger is LOW at all elevations with the exception of recently wind-loaded terrain steeper than 35 degrees above 5000 feet where the avalanche danger is MODERATE.

Our high elevation snowpack is generally stable but isolated pockets of instability exist. These areas of concern are recently wind-loaded slopes steeper than 35 degrees mostly at the higher elevations of the advisory area.

Weather and Snowpack Analysis

Since Friday (1/22) our area has received 2 to 4 inches of snow at most SNOTEL sites but very high northeast to southeast winds. For a 24- hour period on Friday, recorded wind speeds were in the 30mph range with gusts into the 70’s. This high wind scoured the secret stashes and laid some very fine crystalline powder onto normally ignored west facing slopes. Not a lot, but if you were paying attention, you found some very good skiing over the weekend. Wind can put down more new snow on the leeward aspects than most of the storms we have seen recently.

Reports from the southern Bitterroot at Lost Trail Pass, Lolo Pass and the Rattlesnake all indicate continued strengthening of the weak layers described in earlier reports. Two buried surface hoar layers are still prominent in the upper snowpack but it takes more force to produce failures. The depth hoar at the base of the snowpack is still obvious in most pit locations and does fail but it takes a lot of force to produce failures at this level.

The problem now is how much snow or weight will it take, to initiate an avalanche. I think it will take a lot until we start seeing heavy wet Pacific storms moving through the area. For the time being, there is not much new snow in the forecast. Hence, the low avalanche danger rating.

Weather Forecast and Avalanche Outlook

Sorry, but it does not look good for new snow. A weak shortwave disturbance with limited moisture moves through the northern Rockies Monday allowing snow showers to linger through Wednesday as another trough passes through West Central Montana. Models are predicting that another high-pressure system will move in by mid-week with warm temperatures at the higher elevations.

The good news in all of this is that we currently have more stable conditions than our neighbors just 200 or so air miles east and south of us. The Gallatin NF Avalanche Center in Southwest Montana just experienced one of the largest and prolonged avalanche cycles in many years and the Sawtooth NF Avalanche Center in Sun Valley ID is currently dealing with a very dangerous snowpack condition.

Our snowpack structure was very similar to what these areas are now dealing with. So why the difference? Our entire advisory area is at lower elevations therefore influenced by warmer air temperatures and inversions. Prolonged warm or moderate temperatures strengthen weaknesses within the snowpack.

During El Nino winters, a split Jet Stream takes the heavier moisture around us to the north and south therefore fewer snowstorms. We just came out of a 2-3 year La Nina cycle that favored western Montana with above normal snowpack and happy satisfied skiers and snowmobilers.

Keep in mind that we have a snowpack structure in many areas that cannot be completely trusted. We still have potential for large destructive avalanches under the right conditions, just not now and hopefully not at all.

Thanks to those of you who continue to send us excellent snowpack profiles and very thorough reports. It makes a difference in the quality of our advisories and Dudley and I appreciate the extra time it takes for you to send this information to us. THANKS!

If you get out and see avalanche activity or want to send us quick snow observations, send us a note at [email protected] or call us at 406-530-9766. 530-9SNO.