Likelihood ?CertainVery LikelyLikelyPossible
Size ?HistoricVery LargeLarge
Two layers of buried surface hoar exists on protected shady aspects at mid and upper elevations. They sheared off clean with high quality on hard compression tap test meaning that it took some hammering to get the layer to react but when the layer failed it was very clean slid with alot of energy. The first layer was 10 inches deep and the second layer was 1.5 feet deep. What is making these layers so stubborn is that there is some bonding taking place over the past few weeks with time and that there is a 1 inch plus crust 4 inches below the surface that was buried with snow earlier in the week that was beat in with the winds in the middle of the week. Just keep in mind the stubborn character of the upper pack and know that more snow will increase the load on these weak layers combined with a human trigger.
National Weather Service Spokane WA
350 AM PST Fri Mar 6 2020
The arrival of a moist frontal system Friday into Saturday will
bring a decent shot of precipitation to the Idaho Panhandle and
much of eastern Washington. Mountain showers are expected to
linger Sunday. The work week will be mainly dry with periods of
Today through Saturday night: Rain and snow returns to
portions of the Inland Northwest, especially tonight into
Saturday. One of bigger challenges in the forecast will be how
large of a snow threat there will be outside of the mountains.
First today the area will be in a southwest flow ahead of long-
wave trough, with a cold front edging east into the region.
Moisture gradually deepens as the day progresses. The threat of
precipitation will continue over the Cascades and increase over
the eastern third of WA and ID. However it is tonight into
Saturday that precipitation becomes more likely as the front
pushes further inland and interacts with some of the deepest
moisture of the system, as well as has the support of mid-level
disturbances riding along that front. This evening the highest
risk will be over southeast WA into the Panhandle. Late this
evening and overnight the precipitation expand over much of upper
Columbia Basin into northeast WA. Saturday chances remain high
across these areas until evening, when the cold front pushes east
and drier air starts to come in. This will push the primary
precipitation threat into the mountains as the night moves on.
* Temperatures and precipitation type: through this evening and
even much of the overnight models are in relatively good
agreement in indicating above freezing temperatures through the
lowest 2000-4000 feet of the atmosphere (up to about
850-800mbs). This is especially so over the upper Columbia Basin
eastward into Idaho. So largely rain is expected outside of the
mountains. Meanwhile colder air starts to come over the Cascades
into lee-side zones and deeper Columbia Basin and this starts to
push into the eastern third of WA and ID late overnight into
Saturday morning. This is when the threat of snow starts to mix
into the lower elevations and confidence is relatively high that
this will happen with the threat continuing into the afternoon,
especially away from the L-C Valley. Where confidence is less is
how effectively any of that snow may accumulate outside of the
mountains, if at all. Lows tonight drop to the lower to middle
30s of much of the region, with some 20s toward the northern
Cascade valleys to Okanogan Highlands and some areas near the
upper 30s to near 40 toward the deep basin and L-C Valley. So
for most cases outside of the mountains, the temperatures are
not conducive to efficient accumulation except perhaps on grassy
or elevated surfaces. Still the forecast contains some limited
accumulations and the precise amounts will continue to be fine-
tuned over the next 24 hours. More moderate amounts are possible
over the mountains, especially above 4000 feet. /Cote`
In the West Cabinet range of the Panhandle we encountered warm and soft surface snow conditions from low elevations up to 5000' where things cooled off and kept the snow conditions cool. From that point up to 6100' the snow was very wind affected with alot of variable conditions where the recent snow was transported in some areas creating wind slab deposits and exposing ice crust in affected areas nearby. The expected new snow will be a welcomed storm to repair the current surface conditions. Low elevation snow meltoff is starting to accelerate with more bare spots in the access areas and low spots forming in creek crossings with low elevations getting more hollow.
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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