Avalanche Advisory published on January 18, 2019 @ 7:23 am
This Avalanche Advisory expires in 1 hours, 26 minutes
This advisory is valid for 24 hours
Issued by Dave Bingaman - Payette Avalanche Center
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The Avalanche Hazard is Considerable today on steep slopes.   New snow and strong winds have made avalanches likely on upper elevation slopes where fresh wind slabs are resting on a variety of old snow surfaces.  Storm slabs will also be likely where new snow has not bonded to the older snow below.  Additional storms through Monday will bring more snow.  Expect avalanche conditions to rise through the weekend.

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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So much for a dry winter, yesterday in the mountains was far from dry.  The West Central Mountains picked up between 9 and 13 inches of new snow over the last 24 hours.  Wind was a major factor yesterday with wind speeds in the mid to high 20's through most of the day.  While winds were generally out of the SE and SW, wind slabs have formed on a variety of aspects and are resting on a variety of old snow surfaces including crusts and other firm layers.  Visibility should improve today with partial clearing before the next storm arrives this evening.  You should be able to see areas where the wind has sculpted the snow.  Areas with pillows, drifts or textured snow are indicators of wind loading.

Your best and safesty bet today is to avoid wind loaded terrain that is steep enough to slide.  You will find better skiing and riding conditions and are less likely to trigger avalanches in areas that have been protected from the winds.

Short video of conditions at 7800 ft yesterday.

 

Avalanche Problem 2: Storm Slab
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Our local Snotel sites picked up between 1.3 and 1.5 inches of Snow Water Equivelant(SWE) in the last 24 hours, some areas recieved up to 13 inches of new snow.  Upper elevations probably recieved even more.   The new snow fell on a variety of old snow surfaces left behind by the warm and sunny results of the inversion that established itself last week.  Colder temperatures in the middle and lower elevations produced surface hoar which may have been preserved, slick crusts formed on slopes that saw direct sun or went through the freeze and thaw cycle from the warm day time temperatures.  Shaded upper elevation slopes also formed near surface facets.   With the addition of yesterday's new snow you can expect to see poor bonding to the old snow below on multiple aspects. 

In addition,  the next round of storms will begin tonight with another 2 inches of SWE forecasted through Monday.  Expect HEAVY snow accumulations, INCREASING avalanche hazard and up to 20 inches of new snow in the upper elevations.  Now is the time to AVOID steep terrain, check your avy gear and skills, practice safe travel protocols and keep your eyes on your partners while you are out in the mountains.

advisory discussion

Due to the partial government shutdown, avalanche forecasting will be limited.  We expect to forecast 3 times a week until the shutdown has ended.

Your observations are very helpful to the PAC staff and help create a better picture of the complex terrain in our advisory area.  You can click on the add observations link and add as little or as much detail as you have.  It is easy to navigate and will also upload pictures easily.  Please contribute to your local forecast by sharing what you see or experience even if it is just good snow. or a trip report.

recent observations

We toured in Lick Creek yesterday to the ridges above Cly Creek.  Wet snow in the lower elevations and full blizzard conditions laid down about 9 inches of new snow through the day with local ski reports calling it 13 inches in 24 hours.  Protected, northerly slopes felt a lot deeper!  Wind was the big player with wind slabs forming near the ridgetops and strong winds moving a lot of snow around even on lower elevation slopes that were exposed to the wind.  Overall,  our snowpack reacted favorably to the warm temps last week with our older weak layers consolidating and bonding.  That being said, it is probably a good bet that our early season persistent weak layers are not going to be a factor any more.  The new snow is not sticking to the older snow below with some slick crusts and other newly formed buried weak layers resting below it.

Here is a profile from an east facing slope at 7700 ft from yesterday, it showed strong bonds in the lower snowpack with the basal facets rounding and wet enough to form snowballs.  2 weeks ago, this layer was still a sugary mess and a real concern.  Our pit tests here and on other aspects confirmed that we are going to see some poor bonding at the interface between the new and old snow surface.

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 20 deg. F.
Max. temperature in the last 24 hours: 26 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 12 mph
Maximum wind gust in the last 24 hours: 28 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches
weather

.SHORT TERM...Today through Sunday...A few light rain and snow
showers will continue in our CWA early this morning but end
later this morning. A very moist Pacific warm front will begin
snow and rain in Harney County this afternoon. The leading
edge of pcpn will reach western Idaho around sunset, then
central Idaho this evening. Widespread pcpn, locally heavy,
will fall in our CWA tonight, then concentrate on western Idaho
Saturday morning, and central Idaho Saturday afternoon. Pcpn
will decrease in southern Harney and Malheur Counties Saturday
afternoon. The main Pacific moisture fetch will arch northward
across Baker County and western Idaho Saturday night, then sag
southward again directly over our CWA Sunday. Quite a bit of
pcpn will therefore fall on our CWA through Sunday. Snow levels
will be 3000 to 4000 feet MSL tonight as pcpn spreads in. Several
inches of snow will fall in Baker County and west Central Idaho,
and a winter weather advisory will be issued for these areas
tonight through Saturday morning. After that the Pacific warm
front will raise snow levels sharply. By Saturday evening snow
levels will range from 5500 feet MSL in Baker County and Valley
County, to 7500 feet MSL in southeast Oregon and southwest Idaho.
Snow levels will remain above 5500 feet in all areas through
Sunday as pcpn, locally heavy, continues. Free-flowing creeks
and streams will run higher. Temperatures will be about ten
degrees above normal today, then 10 to 15 degrees above normal
Saturday and Sunday.

.LONG TERM...Sunday night through Thursday...A cold front will move
through the region Sunday night into Monday morning. The core of
this system will track across SW Oregon into NW Nevada on Monday
morning. Thus, the bulk of the precipitation associated with this
system will be along the NV border. Snow levels will initially be
4500-5500ft along the front, but lower to the valley floors behind
it. Precipitation should quickly shut off behind the front. Upper
level ridging will build off the West Coast on Tuesday with
northwest flow over our area. Moisture will spill over the ridge
into the region on Tuesday afternoon as a system tracks across
British Columbia into Wyoming by Wednesday. Temperatures will be
cold enough to support snow at all locations with this system.
Tuesday will likely be the coldest day of the period, with
temperatures near normal. The upper level ridge will amplify on
Thursday and Friday with dry conditions and north-northwesterly
flow aloft. Temperatures, with the exception of Tuesday, will
remain around 5 degrees above normal for the period.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: A 20 percent chance of snow before noon. Cloudy, with a high near 34. Calm wind becoming south around 5 mph in the afternoon. Snow, mainly after midnight. Low around 26. Southeast wind 3 to 6 mph. Chance of precipitation is 90%. New snow accumulation of 1 to 3 inches possible. Snow before noon, then rain and snow. High near 35. Calm wind becoming south southeast around 5 mph in the afternoon. Chance of precipitation is 90%. New snow accumulation of 1 to 3 inches possible.
Temperatures: 34 deg. F. 26 deg. F. 35 deg. F.
Wind direction: South SE SSE
Wind speed: increasing to 5 3-6 5
Expected snowfall: 0 in. 1-3 in. 1-3 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: A 30 percent chance of snow, mainly before 11am. Cloudy, with a high near 22. West wind around 5 mph becoming south in the morning. Total daytime snow accumulation of less than one inch possible. Snow. Temperature rising to around 25 by 5am. South wind 7 to 10 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 7 inches possible. Snow. High near 29. South wind around 7 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible.
Temperatures: 22 deg. F. 25 deg. F. 7 deg. F.
Wind direction: W then S S S
Wind speed: 5 7-10 7
Expected snowfall: 2-4 in. 3-7 in. 3-5 in.
Disclaimer

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.

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