THIS AVALANCHE ADVISORY EXPIRED ON February 17, 2018 @ 7:31 am
Avalanche Advisory published on February 16, 2018 @ 7:31 am
Issued by Eric Morgan - Idaho Panhandle Avalanche Center

Selkirks/Cabinets

bottom line

Currently 10 inches of recent storm snow sitting atop an ice crust.  There is some wind affect and slight suncrust on top of the current surface.  A series of storms will be rolling in with breezy conditions forming wind slabs and loading on Noreasterly aspectsAvalanche danger will be on the rise throughout the weekend with the brunt of the storm coming in Saturday.  Red flags will be heavy precipitation and winds.  

How to read the advisory

Selkirks/Cabinets

How to read the advisory

Currently 10 inches of recent storm snow sitting atop an ice crust.  There is some wind affect and slight suncrust on top of the current surface.  A series of storms will be rolling in with breezy conditions forming wind slabs and loading on Noreasterly aspectsAvalanche danger will be on the rise throughout the weekend with the brunt of the storm coming in Saturday.  Red flags will be heavy precipitation and winds.  

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: Wind Slab
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The storms will be accomodated by breezy conditions out of the southwest today and northwest tonight in the 20mph range with gusts to 40mph.  This will make our current snow atop of the ice crust more cohesive and likely to propogate.  

Avalanche Problem 2: Storm Slab
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With 2 inches last night and 3-5 expected today followed by 8-12 Saturday, expect more of a load ontop of the icecrust.  Expect Saturday's storm to be the tipping point for our hazard rating to spike above moderate.  The icecrust will be a prime bed surface for these newly created storm slabs on all mid and upper elevation aspects.  

Avalanche Problem 3: Loose Dry
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The current concern is loose soft slabs that have been releasing on windloaded aspects just below the cornices.  

advisory discussion
.DISCUSSION...
Today and Tonight:

...Some snow and breezy wind today...

Light snow started overnight and continues primarily in the Idaho
Panhandle north of Moscow to the Canadian border. Northwest flow
continues to usher the next in a series of weather systems.
Heaviest precipitation for today will primarily be over Idaho
Panhandle and east Washington near the Idaho Border as well as the
Cascade crest. Snow levels will gradually rise from the south
with the rain/snow line north or Interstate 90/Spokane area by
noon. Valley accumulations in the Panhandle of Idaho will
generally be 1 to 3 inches except in the central Panhandle valleys
where a couple more inches may fall where the highest
precipitation totals are expected. There will be a significant
rain shadow east of the Cascades into the central Basin where very
little precipitation is expected.

As the flow orients more northwest this afternoon rain and higher
mountains snow shifts focus away from the north to the southern
Idaho Panhandle in the Moscow/Orofino/Craigmont areas. Light
precipitation in this area will continue into the overnight hours.

Stronger winds will develop this afternoon from about Wenatchee
to Pullman south toward Pomeroy. Winds 20 to 30 mph Gusting to 40
mph can be expected in this region until early evening. TC

...VERY WINDY SATURDAY...

Saturday: An upper level trough will move into the region. A
surface low will track across northern WA. This will once again
produce widespread rain and snow. There could be a quick 1-3
inches of snow across many valleys Saturday morning before the
warm front starts to move in and change the snow to rain/snow mix
or rain. The Cascade crest, and mountains of north ID will see up
to a foot of snow. The valleys of NE WA and N ID could see
moderate snow accumulations given they will remain snow for a
longer period, especially locations closer to the Canadian border
where it will likely snow all day and evening.

*WINDS: Winds will be a BIG concern as the surface low moves
 across northern WA. Models are showing the low remaining as
 strong or strengthening as it moves across the region in the
 afternoon. The latest model guidance have increased the winds
 across the region, and have followed suit. It is a fairly large
 area where the winds will blow...The Wenatchee area, Waterville
 Plateau into the Columbia Basin, Palouse/LC Valley, the
 Spokane/COE area, Lewiston area and into the Camas Prairie. The
 strong winds will start just prior to noon and will continue
 through the evening hours. The timing of strongest winds will
 depend on location, with Wenatchee seeing their strongest winds
 between 3 and 5 pm, but Pullman seeing theirs between 5 and 8 pm.
 The strongest winds will overall occur between 1 pm and 9 pm.
 Winds will also occur in the mountains south of Lake Chelan, in
 the Blue mountains as well as north ID. Have decided to issue a
 wind advisory for a large portion of the forecast area. If the
 morning model runs continue to trend as strong or stronger, it
 may need to be upgraded.
recent observations

In the Selkirks yesterday Jeff and I travelled in the Jeru and Hunt Peak areas finding a nice 10 inches of recent snow atop of a boiler plate ice crust that is 5 inches thick lower and 2 inches thick near the peaks.  Exposed areas had a slight wind crust on top with low density snow underneath to the crust.  This will be a huge weakness with the increasing load of snow expected the next few days which may be a few feet and more on windloaded aspects.  Open slopes greater than 35 degrees may become a serious problem...especially those on windloaded aspects.  There are still deeper instabilities that are of concern if triggered by an avalanche on the upper snowpack.  It is possible to trigger deeper layers by an avalanche created by this weekends storms.  

Weather and CURRENT CONDITIONS
weather summary

Weather observations from the Region
0600 temperature: 14 deg. F.
Max. temperature in the last 24 hours: deg. F.
Average wind direction during the last 24 hours: 280
Average wind speed during the last 24 hours: 10 mph
Maximum wind gust in the last 24 hours: mph
New snowfall in the last 24 hours: 2 inches
Total snow depth: 110 inches
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.

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