Posted:
Jan 6, 2015 @ 6:38 am

We are continuing the avalanche warning issued yesterday. On slopes steeper than 30 degrees the avalanche danger in the west central Montana backcountry is high. Heavy snow and strong winds from Sunday and Monday have loaded steep backcountry terrain. Travel in avalanche terrain or in avalanche run-out zones is not recommended. The area is under a winter storm warning until 11 am this morning.

This  danger rating expires at midnight tonight (January 6) and does not apply to operating ski areas.

Good morning, this Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for January 6, 2015.

Weather & Snowpack Discussion

This morning west and southwest mountain winds are blowing at 10-11 mph and gusting to 30 mph. Temperatures above 6000 feet are just below or above freezing, 27-35 degrees F.

The robust winter storm that moved through the area Sunday and Monday should begin to abate by mid-morning. Yesterday we issued an avalanche warning due to heavy snows and strong winds. Rain up to 5000 feet increased the instability of the storm snow at lower elevations; while elevations above 6000 feet accumulated warmer, heavy snows on top of the existing colder snow; and things started moving.

Slides on highways and roads were noted in the region. Snotels are showing 14 to 16 inches of snow with 2 to 3 inches of snow water  in the last 48 hours. This is a heavy load to put on the snowpack and it will take some time to adjust.

The Snowbowl Patrol triggered 1 to 1.5 foot slabs on southwest aspects with explosives yesterday. With 50-100 yards of visibility, Travis and I traveled in the Rattlesnakes near the Snowbowl Ski Area. We triggered smallish, remote storm slabs on north aspects;  but we were sticking to very safe terrain. I suspect there are larger slabs ready to go on big, steep open bowls.

I have added Steve’s pit from 1/1/15 in the photos below to remind you of the weak structure we observed on north and northeast slopes. The new, heavy snow is sitting on this weak structure in areas that north and northeast winds hammered at the end of December.

The good news is the warmer temperatures will probably help settle things out in a day or two.

Avalanche & Weather Outlook

High pressure will build into the northern Rockies this evening and into Wednesday. Temperatures may warm for elevations above 4000 feet. Moderate snowfall is predicted along the Divide on Thursday. The warm temperatures should help the snow stabilize quickly.

North Fork of Placid Creek Avalanche Incident

On December 27, 2014 four snowmobilers were caught in an avalanche near Seeley lake. There were two complete burials, but no injuries. We have posted the incident report on our documents page.

Avalanche Hazard and Weather Forecasting for Backcountry Recreationists

We are presenting a free lecture designed to improve your avalanche hazard and weather forecasting skills. Luke Zukiewicz, Snow Hydrologist with the Natural Resource Conservation Service (Montana Snow Survey Program Manager) and Lee Ann Allegretto, Meteorologist and Avalanche Program Manager with the National Weather Service in Missoula are the featured speakers.

They will be discussing how to interpret and use weather and snowpack data available  on the web.

Wednesday, January 21 –  6-8pm at the Trailhead    221 East Front Street     Missoula, MT

 

Ride and ski safe. I will issue the next regularly scheduled advisory Friday, December 9.

 

READ FULL ADVISORY  

Problem 1 - Storm Slabs

  • TYPE

    storm-slabs

    Storm Slabs

    Release of a soft cohesive layer (a slab) of new snow which breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

  • SIZE

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-7

    Very Likely

    The likelihood of an avalanche resulting from this problem.

  • ADDED DANGER

    Increased Slope Danger

    Increased/Added Danger

    There is an increased risk of avalanches on these slopes:

    N - North
    NE - Northeast
    E - East
    SE - Southeast
    S - South
    SW - Southwest
    W - West
    NW - Northwest

Sunday’s and Monday’s storms, accompanied by strong winds have loaded slopes. All slopes steeper than 30 degrees are suspect.

Problem 2 - Wind Slabs

  • TYPE

    wind-slabs

    Wind Slabs

    Release of a cohesive layer of snow (a slab) formed by the wind.  Wind typically erodes snow from the upwind sides of terrain features and deposits snow on the downwind side.  Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

  • SIZE

    4-5

    2 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-7

    Very Likely

    The likelihood of an avalanche resulting from this problem.

  • ADDED DANGER

    Increased Slope Danger

    Increased/Added Danger

    There is an increased risk of avalanches on these slopes:

    N - North
    NE - Northeast
    E - East
    SE - Southeast
    S - South
    SW - Southwest

Additional avalanche problems were created on leeward slopes by strong west and northwest winds accompanying the Sunday and Monday storms.

 

 

1/1/15 snow pit, 1/5/15 snow pit, photos from 1/5/15

FORECAST & OUTLOOK

High pressure will build into the northern Rockies this evening and into Wednesday. Temperatures may warm for elevations above 4000 feet. Moderate snowfall is predicted along the Divide on Thursday. The warm temperatures should help the snow stabilize quickly.







This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.