This week produced another round of snow with accumulations in the 10-15 inch range above 6500 feet. Winds have been gusty throughout the week and mostly out of the S and SW. North and South Valley areas have both seen the same weather this week with cornices slowly growing and wind loading occurring on mostly E, NE, N and NW facing slopes. Yesterday's touring conditions and ski conditions were perfect with light density snow on all aspects. We observed active wind loading and wind slab formation throughout our tour that was mostly confined to the Northerly aspects near Secesh Summit. These slabs ranged from a few inches thick to over a foot and were just becoming sensitive to the weight of a skier by mid afternoon.
A cold front is still dominating the weather throughout the West Central area but will begin to give way to a warm front as a major storm enters the area tonight. Expect gusty winds with this next front and a warming trend for tomorrow. Also, expect the avalanche hazard to increase tonight and through the day tomorrow as 10-15 inches of warmer, higher density snow is added to the new snow total for the week.
The snow that fell throughout the week this week came in small increments of light density snow that did not have a major effect on stability. Loose, unconsolidated snow has been the trend for over a week creating a soft and unconsolidated upper snowpack. In our pit tests yesterday we saw several of these individual storm layers that were only partially bonded to the layers below creating moderate failures in compression but lacking propagation or the energy to spread out over large areas. It is possible that you could trigger a weakness in one of these layers on steep terrain resulting in a shallow slab in the 3 to 12 inch range today. Worth noting and watching over the next 24 hours is a subtle crust that was created mid morning on Monday that is between 6 and 10 inches down in the snowpack. It is starting to disintegrate but has the potential to create a weakness with the addition of our next storm's new snow and additional weight. We found this layer to be fairly widespread yesterday in the mid to upper elevations and had reports of it from the South Valley area as well.
Sluffing or loose, dry avalanche activity is also possible on steep slopes because of the light density snow right now. If you are skiing in steep, committing terrain, especially in confined terrain or above obstacles, be aware of the potential for sluffing and plan a route to avoid letting it push you where you don't want to go.
Please let us know what you are seeing in the West Central Mountains. Take the time to submit an observation or send us an email. It's easy and may save a life. If you are having trouble adding photos to your observation, send us the photo at our email address and we will add it to your observation. Click on the observation tab on the advisory page or email us at: firstname.lastname@example.org
Yesterday we were able to see a lot of terrain and multiple aspects, no recent avalanche activity was observed and none has been reported this week. The biggest factor affecting the snowpack was the wind yesterday. Gusts in the 20+ range were common throughout the day. These were actively transporting snow into the northern aspects and affecting the snowpack on exposed ridges and slopes.
The snowpack gained both strength and depth throughout the last week. We found just over 8 feet of snow around 8000 feet yesterday on a North facing slope and just under 6 feet of snow at 7500 feet in a protected basin yesterday. Basin wide snowpack surveys are showing a return to normal or above normal conditons across the mid and northern portions of Idaho. Snowpack tests are showing increasing stability and that our persistent weak layer is now getting enough weight to compress it and insulate it from the effects of skiers and riders in the McCall/ Valley County area. However, it is still present iin the snowpack and could still be a problem given the right combination of snowpack depth and additional loading. You should still be wary of slopes with a shallow snowpack where the layer is closer to the surface. and you are more likely to trigger the weak layer. This layer is also still active and producing avalanches in the mountains adjacent to the PAC advisory area.
|0600 temperature:||14 deg. F.|
|Max. temperature in the last 24 hours:||22 deg. F.|
|Average wind direction during the last 24 hours:||SW|
|Average wind speed during the last 24 hours:||10 mph|
|Maximum wind gust in the last 24 hours:||26 mph|
|New snowfall in the last 24 hours:||inches|
|Total snow depth:||inches|
.SHORT TERM...Today through Saturday...Snow showers will continue
today and this evening, mainly in the higher elevations. Later
tonight, a major snowstorm will move into the region. This one
comes in the form of a warm front, but temperatures will initially
be cold enough for snow at almost all elevations. Precip will move
into eastern Oregon around midnight and rapidly spread east into
southwest Idaho. Winter Weather Warnings and Advisories have been
determined (see below) and will be issued shortly. Snow totals
will range from 5 to 15 inches in the mountains and 2 to 6 inches
in the valleys. Only the lowest elevations of the Snake Plain may
have enough rain mixed with the snow to limit accumulations to
under an inch. Snow levels will rise Saturday afternoon as the
warm front passes, turning snow to rain at elevations below 3500
feet. However, the West-Central and Boise Mountains will continue
with a significant snowfall into the evening hours. High temps
today will be slightly above normal for most areas, with highs
tomorrow above normal south and west of a line from Burns to the
Owyhees to south of Twin Falls, where the warm front will allow
warmer air to mix down to the surface during the afternoon. North
and east of that line, temps will be held down to near or below
normal due to snowfall. In the Boise area, we expect snow to begin
around 6 am and continue into mid-afternoon before changing to
rain and ending. A snowfall accumulation forecast map will be put
out on social media soon.
.LONG TERM...Saturday night through Friday...The active weather
pattern will continue as westerly flow aloft brings a series of
Pacific weather systems across our area. The upper level flow will
shift into the northwest on Wednesday, lowering temperatures to
near normal for the remainder of the week. Valley rain and
mountain snow Saturday night will end by Sunday evening as and
upper level high pressure ridge builds over the Intermountain
Region. We can expect dry weather through Monday, but
precipitation will spread into our northern zones Monday night as
the next Pacific weather system approaches. Precipitation will be
mainly confined to the mountains of Baker County Oregon and
central Idaho Tuesday through Friday as weak disturbances embedded
in northwest flow aloft cross our area.
This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.