THIS AVALANCHE ADVISORY EXPIRED ON April 7, 2018 @ 4:54 am
Avalanche Advisory published on April 6, 2018 @ 4:54 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

Thursdays warm weather conditions will be pushed out of the area on Friday morning by a cold arctic front. This decline in temperatures will improve the stability of the upper snowpack as it locks the wet snow together on Friday.  Moving into the weekend the weather forecast is predicting additional snowfall that is predicted to be wet and dense. These conditions will likely increase the avalanche hazard as dense storm slabs build through the weekend.

How to read the advisory

Thursdays warm weather conditions will be pushed out of the area on Friday morning by a cold arctic front. This decline in temperatures will improve the stability of the upper snowpack as it locks the wet snow together on Friday.  Moving into the weekend the weather forecast is predicting additional snowfall that is predicted to be wet and dense. These conditions will likely increase the avalanche hazard as dense storm slabs build through the weekend.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Storm Slab
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During the past week the upper elevations have picked up an additional 18 plus inches of new snow across the Kootenai advisory area. Not a bad start to the first week of April. This new snow fell under relatively warm and wet conditions which has caused it to bond well with the dense base below it. At elevations above treeline there is some potential for this new snow to move on steep terrain and convex rolls. As the temperatures cool off Friday the snowpack will stabilize. Anticipate a potential rise in the potential to trigger storm slabs on Saturday and Sunday as another round of dense, moist snow is predicted through the weekend. 

Avalanche Problem 2: Wind Slab
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As the cold front pushes in with a northeasterly wind and light snowfall we can expect to find fresh wind slabs building on southwesterly aspects near ridgelines. These windslabs will likely be fairly thin but riders should take the time to check out the potential for wind loading in counter-intuitive locations as the wind blows in opposition to the general wind patterns on Friday.

advisory discussion

On April 5th we travelled into the Eastern Cabinets where the snowline was around 4,000' in elevation. We took temperatures multiple times during the day and picked up consistent readings between 38° and 40° at elevations up to 6,200'.  The snow was wet and dense and we observed multiple "loose-wet" slides on all aspects throughout the day. Stability tests revealed the upper 19" of new snow that fell during the week was bonded fairly well to the the dense snow below. This of new snow layer failed with hard force and showed low likelihood of propagation (ECTN21).

The big issue for avalanche stability this weekend will again revolve around our dynamic and rapidly changing weather conditions over the next 3 days. Thursdays warm temperatures and "loose-wet" avalanche problem will disappear as a cold front pushes in from the east on friday. This transition will create stable conditions on Friday as the warm, moist snow freezes together. On Saturday the National Weather Service is forecasting an "atmospheric river" to flow through the area that will add more weight to the snowpack and likely create a new layer of dense storm slab on the surface. Some educated guessing would entail that fresh snow falling under cold conditions Friday, followed by a layer of warmer and higher density snowfall on Saturday/Sunday will create a slab resting on a weak layer of colder snow.  Pay attention on Saturday and Sunday for this potential scenario. My other concern at this point is where will the snowline be this weekend? At the moment the NWS is predicting a snowline of 4,000', if the rainline rises high into the mountains the upper 2' of the snowpack will be prime for "wet-slab" avalanches as the rain increases the weight and decreases the strength of the upper snowpack.

This will be the last Advisory posted for the winter.  Thanks for reading and enjoy the spring powder!!

Weather and CURRENT CONDITIONS
weather summary 
Backcountry Forecast from NWS Missoula issued:
350 AM MDT Fri Apr 6 2018

DISCUSSION: Today the east winds and showers will be decreasing
with below normal temperatures across western Montana. Saturday
afternoon a very, very wet system will impact central Idaho and
the Clearwater mountains with close to 3 inches of rain in a
48-hour period starting Saturday morning. This is a trend upward
in the precipitation forecast. Snow levels will be very high on
Saturday, over 8,000 feet for a time, before crashing back down to
around 4,500 feet on Sunday. Central Idaho is on the far
northeastern edge of a record setting atmospheric river, which is
causing all this precipitation.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           90%          70%          90%      
Hi/Lo Temps           29 to 34     23 to 28     35 to 40 
Winds(mph)            E  8G23      E  6G16      SE  9G29 
Precip Chc            50           0            100      
Precip Type           snow         none         snow     
Liquid Amt            0.03         0.00         0.43     
Snow Ratio(SLR)       16:1         0            11:1     
Snow Amt(in)          0-1          0            3-5      
Snow Level            500          2500         4000
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.