THIS AVALANCHE ADVISORY EXPIRED ON March 14, 2020 @ 5:33 am
Avalanche Advisory published on March 13, 2020 @ 5:33 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Big change is coming on Friday. A strong cold front will bring an additional foot of snow and strong northeasterly winds to the mountains area wide. Anticipate the buildup of wind slabs and drifts at all elevations this weekend. Use caution in all steep and open terrain that has been exposed to the wind. Shooting cracks, drifting snow and increases in the surface density will be your obvious clues to pay attention to this weekend.

How to read the advisory

Big change is coming on Friday. A strong cold front will bring an additional foot of snow and strong northeasterly winds to the mountains area wide. Anticipate the buildup of wind slabs and drifts at all elevations this weekend. Use caution in all steep and open terrain that has been exposed to the wind. Shooting cracks, drifting snow and increases in the surface density will be your obvious clues to pay attention to this weekend.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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With ample amounts of loose snow on the surface and more on the way we have plenty of material to create windslabs right now. On Thursday we observed southwest winds at the upper elevations, on Friday a cold front will usher in strong east, then northeast winds at all elevations. Expect reactive slabs to build in all areas that are open enough to be impacted by the winds. Steep terrain near ridgelines, gullies and chutes will all be places to find a troublesome windslab this weekend. Windslabs will likely be thicker and more dangerous at upper elevations where there is more snow for transport at this time; but, with a cold front the winds will be quite strong all the way to drainage bottoms. If the terrain is open and steep, approach with caution regardless of elevation.

Avalanche Problem 2: Persistent Slab
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I have been bantering about the buried surface hoar and the facets in the West Cabinets and Purcell Range for a while now. It has been some time since we have seen any propagation in stability tests or any avalanches on these weak layers. It's still there; but, I think at this point these weak layers are a very low likelihood for a human trigger. Triggering a windslab or cornice fall may be what it takes to cause a "step-down" avalanche on these layers. With the strong winds this weekend we may see this potential "stress-test" on the snowpack.

advisory discussion

On Thursday we toured into the East Cabinets and found a stable snowpack with some evidence of windslab development at upper elevations on leeward terrain (north and east aspects). The East Cabinets have not been harboring the buried surface hoar found in both the West Cabinets and the Purcell Range. The East Cabinets are generally taking on a bit more wind with the high and open terrain, we observed snow devils and spindrift blowing off the high ridges right away yesterday morning. Otherwise, conditions were very stable with a nice, fresh coat of snow covering the surface on all aspects, thanks to the 4-6" of fresh snow that came in Tuesday night.

All this goodness is about to change, a quick look at the weather tells it all. Winter Storm, cold front and all of it's realities will wake us up from our dreams of spring. Winter is returning today for one more reminder. With lots of soft snow already on the surface and more about to fall, wind slabs will be our primary issue this weekend. The new snow is anticipated to fall on the cold and dry side, so it shouldn't be too slabby in nature in protected areas where the timber has kept the wind off of the surface. Finding areas protected from the wind however may be challenging! By Sunday the storm looks to blow out of the area but will remain cold. If you are going out this weekend be ready for the big drop in temperatures and the wind chills that are forecast. Don't be caught off gaurd by the month of mild temperatures that have been the lately norm! Hypothermia can be just as dangerous as an avalanche, and just as likely.

Weather and CURRENT CONDITIONS
weather summary 
Backcountry Forecast from NWS Missoula issued:
350 AM MDT Fri Mar 13 2020

DISCUSSION: 

Northwest Montana: Increasing clouds today and high
easterly/northeasterly winds will precede a strong cold front
entering northwest Montana. Strong winds will set up along a very
steep surface pressure gradient as early as noon today. Snow will
start out on the light side as the deepest moisture remains on 
the windward (east) side of the Continental Divide. Temperatures 
plummet tonight with frontal passage. Overnight low temperatures 
will be in the single digits down to as low as -10F in places. 
The Cabinet, Whitefish, and Flathead will see increasing snow 
amounts through Saturday morning as additional moisture streams up
from the southwest and interacts with the arctic airmass coming 
down from the northeast. Sunday will bring lingering showers over 
the higher peaks and continuing strong winds. Winds will continue 
out of the east/northeast until around midday Sunday when the 
surface gradient relaxes. 


Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           95%          95%          95%      
Hi/Lo Temps           15 to 24     -7 to 3      3 to 12  
Winds(mph)            NE 18G32     NE 27G44     NE 25G40 
Precip Chc            60           90           100      
Precip Type           snow         snow         snow     
Liquid Amt            0.13         0.31         0.18     
Snow Ratio(SLR)       17:1         17:1         18:1     
Snow Amt(in)          2-4          5-9          3-4      
Snow Level            0            0            0
Disclaimer

Avalanche conditions change for better or worse continually. Backcountry travelers should be prepared to assess current conditions for themselves, plan their routes of travel accordingly, and never travel alone. Backcountry travelers can reduce their exposure to avalanche hazards by utilizing timbered trails and ridge routes and by avoiding open and exposed terrain with slope angles of 30 degrees or more. Backcountry travelers should carry the necessary avalanche rescue equipment such as a shovel, avalanche probe or probe ski poles, a rescue beacon and a well-equipped first aid kit.  For a recorded version of the Avalanche Advisory call (208)765-7323.