March 1, 2013 Avalanche Advisory

There remains a MODERATE avalanche danger above 5000 feet on slopes steeper than 35 degrees in the mountains of west central Montana. Natural avalanches are unlikely, but human triggered avalanches are possible. Pay attention to the snow and weather…conditions could rise to CONSIDERABLE. Some areas are receiving rain on snow this morning and we are expecting to see the warmest temperatures of the season during the next 2 days.

Good Morning! This is Tim Laroche with the West Central Montana Avalanche Center’s avalanche advisory for Friday, March 1st, 2013.

 

Weather and Snowpack Analysis

The mountains of west central Montana have continued to receive modest amounts of snowfall the past few days. Most advisory area locations picked up 4-8 inches of new snow since Tuesday’s advisory. Winds have been primarily out of the south from 8-10 mph with daytime temperatures in the upper twenties. Currently, there is scattered light snow or rain falling with temperatures in the lower thirties at most snotel locations. Winds are light at 5-7 mph out of the south and southwest.

The primary avalanche concern is the persistent slab that rests on top of a layer of facets buried 1-3 feet deep. This weakness has been gaining strength, but is still failing cleanly in stability tests on northwest through southeast aspects (aspects that have been wind loaded the past week). Steve and I rode in the Lolo Pass area yesterday and found this weakness in some of our stability tests (video) (video). This weakness was also reported by observers in the southern Bitterroots near Lost Trail Pass and observers in the northern Bitterroots from Hoodoo Pass to Lookout Pass. This is the weak layer involved in recent human triggered slides in the northern Bitterroot Mountains near Williams Lake and Surveyor Lake (profile). Many slopes in our advisory area do not harbor this weakness or it has gained enough strength to support a heavy load. Look for this weakness to see how reactive it may be before committing to steep terrain.

There are other avalanche problems to pay attention to this weekend.

  1. Shallow wind drifts have formed over the past 2 days and were easily triggered by our observers in the southern Bitterroots yesterday. These drifts should settle quickly with the warmer weather, but were sensitive yesterday.
  2. Wet loose slides were reported yesterday in all areas below 6000 feet. I expect to see this activity at higher elevations in the next 2 days. If the snow starts getting damp, get off and out from underneath any steep slopes.
  3. Cornices have grown substantially the past 2 weeks. The potential to see cornice failures will increase this weekend with the warmer temperatures.

The warm temperatures we will experience the next couple of days will be great for snow stability in the long run. They are not so good for stability in the near future. We are expecting cooler temperatures and fresh snow on Sunday. Until then, pay attention to how the snow is changing and be conservative in your decision making while you are recreating in avalanche terrain.

 

Weather Forecast and Avalanche Outlook

Today under mostly cloudy skies, we will see scattered light snow above 6000 feet and light rain below. Precipitation should end this afternoon and weak high pressure will build for Saturday. Daytime temperatures will be in the lower forties today and upper forties tomorrow as high as 7000 feet. Winds should remain light at 6-8mph out of the southwest until Sunday, when they will increase with the arrival of a cold front.

I expect the avalanche danger to remain at the current level until temperatures cool.

Steve will issue the next advisory on Tuesday, March 5th.

If you get out and have the time to send us some information about what you are seeing, please use our “public observations” link on our website or send us a quick note at [email protected] Thank you for your continued support!

Education:

We have recently added a level one avalanche class that will start March 12. You can follow this link for more information, or visit our education tab on the left side of our website.