Posted:
Jan 12, 2016 @ 6:21 am

On wind-loaded slopes above 7000 feet that are 35 degrees and steeper, the avalanche danger is moderate in the west central Montana backcountry.  In other terrain in the advisory area the avalanche danger is low.

Good Morning, this is Dudley Improta with the West Central Montana Avalanche Center’s advisory for January 12, 2016. This danger rating is the sole responsibility of the U.S. Forest Service, does not apply to operating ski areas and expires at midnight tonight. Logan, Brian and Travis are finishing up the field portion of the National Avalanche School in Jackson, WY; so Steve and I are issuing the advisories this week.

Weather and Snowpack

This morning, mountain winds, mainly out of the west, are blowing in the 15 mph range and gusting into the 30’s.   Mountain temperatures are ranging from 11 degrees F near Lost Trail  to 24 degrees F in the Rattlesnakes. It is snowing, with to 2 – 4 inches of accumulation overnight.

We also picked up a few inches of snow over the weekend. Specific areas, like the southern Missions and the central Bitterroots, received 6 inches of snow late Saturday and early Sunday. Higher elevation winds, mainly out of the west and southwest, blew in the 20 and 30 mph range consistently Saturday through yesterday. These winds moved all the snow available on to leeward slopes. Wind slabs are the primary problem right now and can be found on steep leeward slopes above 7000 feet. The conundrum is these leeward slopes are skiing and riding very well, and we haven’t exactly had an abundance of powder riding and skiing this season.

A secondary problem is loose snow sluffs; particularly in the areas that received the most snow. Yesterday, Steve and I triggered loose snow easily in the Rattlesnakes; but it was all on steep rollovers and aspects where the wind had deposited the new snow. This problem is going to be confined to the higher elevations as well. As one public observer noted; the sluffs “could be avoided, but were too big to ignore”.

Weather Forecast and Avalanche Outlook

Yesterday was a beautiful day to be in the west central Montana backcountry.  Yesterday’s high pressure has given way to a weak system today. Snow amounts are forecast to remain light with continuing westerly winds. There is talk of a stronger system arriving later tonight. I would expect the avalanche danger to increase with continued snow and wind.

Low and Moderate Danger

It’s easy to get complacent with periods of lower avalanche danger. We have observed quite a few less-than-safe skin tracks recently. Stick to your protocols; when negotiating avalanche hazard, only expose one member of the party at a time.

And, I would remind some that a few years ago an avalanche fatality occurred in the Bridgers when the Gallatin Avalanche Center had issued a low danger rating for the area. The accident took place in very steep, extreme terrain. In steep, exposed terrain you can never be 100 percent sure it won’t slide.

I will issue the next advisory on Thursday, January 14.

Public observations are important to the avalanche advisory and to riders and skiers.  If you would like to send us snow observations use our public observations form or e-mail us at  [email protected] .

There are openings in some Level 1 avalanche classes. For all avalanche education opportunities visit our education page.

Ski and Ride safe.

READ FULL ADVISORY  

Problem 1 - 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

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-3

    Possible

    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
    NW - Northwest

Strong winds over the weekend deposited any snow available for transport on to leeward slopes. This problem is confined to steep slopes (>35 degrees) above 7000 feet.

Problem 2 - Loose Dry

  • TYPE

    loose-dry

    Loose Dry

    Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.

  • SIZE

    3-4

    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-4

    Possible/Likely

    The likelihood of an avalanche resulting from this problem.

Some areas, like the southern Missions and the central Bitterroots received 6 inches of new snow over the weekend. There will be more snow on leeward slopes. The new snow may move on steep slopes (>35 degrees) above 7000 feet.

FORECAST & OUTLOOK

Yesterday was a beautiful day to be in the west central Montana backcountry.  Yesterday’s high pressure has given way to a weak system today. Snow amounts are forecast to remain light with continuing westerly winds. There is talk of a stronger system arriving later tonight. I would expect the avalanche danger to increase with continued snow and wind.

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.