March 16, 2012 Avalanche Advisory

Above 5000 feet, there is CONSIDERABLE avalanche danger in the west central Montana backcountry.

Heavy wet snow and a rain-on-snow scenario has elevated the avalanche danger overnight.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday, March 16th, 2012.

Weather and Snowpack Analysis

Advisory area snotel sites are showing .8 to 1.6 inches SWE in the past 24 hours. The exception is Saddle Mountain, only recording .2 inches SWE. Mountain temperatures were in the low forties yesterday and are starting to cool back down to near freezing at 4am this morning near 7000 feet. Precipitation is falling as a mix of rain and snow. Winds are currently blowing 8-12 mph out of the south and east.

Areas near the Idaho border received 12-18 inches of snow this past weak. Other advisory area locations picked up 4-6 inches of snow. We are now seeing steady rain up to 7000 feet which will cause the snow to become saturated. Watch for heavy wet slides at all elevations until the temperatures cool down later this morning.

The warm weather and sun of last week helped to settle and strengthen the snowpack, but left a stout sun or melt-freeze crust on most aspects at all elevations. Observers reported mixed results on this crust yesterday in stability tests, but with heavy wet snow or rain now affecting most of the advisory area we can expect this crust to be reactive to the new load for the next 24 hours. The main concern today will be heavy, wet snow releases on the sun and melt-freeze crust in the upper part of the snowpack and density changes within the new storm snow.

The buried surface hoar layer, down 2-3 feet, that has been the cause of recent human triggered slides has continued to gain strength. This weak layer takes a lot of force to fail, but should still not be trusted. Yesterday, we found this weak layer buried almost 3 feet deep on a northeast aspect at 7400 feet. The faceted crystals are well preserved and still quite large. So, dig down and look for this weakness before you commit to a steep slope.

Cornices are big and have started to slump with the recent warm weather pattern. Keep your distance when traveling on ridges and move quickly if you have to cross beneath these features.

Weather Forecast and Avalanche Outlook

A cold front will continue to push into west central Montana this morning. Snow levels should fall causing the rain to turn to snow down to about 4500 feet. Snow is expected to continue today with totals ranging from 7-10 inches at higher elevations. Winds will be out of the southwest at 12-20 mph. I am expecting this warm, wet pattern to stay with us through the weekend bringing additional snow accumulations and fluctuating mountain temperatures.

I expect the avalanche danger to stay the same with the chance of more snow and fluctuating temperatures through the weekend.

I will issue the next advisory on Monday, March 19th.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.