THIS AVALANCHE ADVISORY EXPIRED ON March 8, 2020 @ 8:29 am
Avalanche Advisory published on March 7, 2020 @ 7:29 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Hazard is Moderate today.  Last night was warm with temperatures that stayed above freezing.  The potential for wet, loose avalanches and wet sluffs will be the main concern this morning.  Cooling temperatures accompanied by moderate wind and several inches of snow this afternoon will change conditions back to winter.  Increasing hazard from storm and wind slabs will be likely later today and tomorrow where new snow is sitting on crusts and a variety of old snow surfaces.

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Loose Wet
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Wet, loose avalanches and wet sluffs have been the theme over the last 2 weeks as a spring weather pattern dominated the area.  Today is going to be an interesting day with variable conditions this morning.  Overnight temperatures at local Snotels barely dipped below 40 degrees.  There is also potential for some rain this morning in the lower elevations.

Upper elevation temps are just starting to drop as an approaching cold front brings some wintery weather back to the area.  This will cause temperatures to drop back below freezing today and add some much needed snow to the upper elevations.  There is some disagreement in the computer models as to how much snow the West Central Mountains will receive but the new snow will also be accompanied by winds in the upper 20's.  The upside is that with a couple of nights of freezing temperatures any instabilities will be confined to the new snow layers as the snow below refreezes over the next few days.

 

Avalanche Problem 2: Wind Slab
  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Today is going to be an unusual day as we transition back to winter conditions.  Forecast models show 2-4 inches of snow in some upper elevation areas and 5-9 inches in areas to the north.  Winds ramped up last night into the upper 20's.  While there isn't a lot of loose snow available for transport right now, shallow wind slabs were forming Thursday and Friday.  With the addition of a few inches of new snow, winds slabs will be building on a variety of slopes as the winds gust around the compass.  Any amount of new snow is going to have a challenge sticking to the old snow surfaces below.   Crusts on Southerly, West and East facing slopes as well as faceted snow on shady aspects will increase the potential for wind slab and storm slab activity as the snow begins to accumulate later this afternoon.  The good news is that with the exception of wind loaded areas, these instabilities will likely be shallow. Wind slabs however can grow quickly and even a few inches of snow can turn into a substantial problem with consistent wind speeds like we will see today.  Pay attention to which way the wind is blowing the new snow and watch for visual clues like drifts or dune like formations.  Old tracks that disappear close to ridgelines are also great clues about where wind slabs are forming.

recent observations

WSW winds were the theme Thursday and turned more into WNW yesterday.  Both days winds were consistent through the day with some gusts reaching into the upper 20's.  Despite the lack of fresh snow, there was snow moving and pluming off the ridges.  We saw some recent wind slab crowns near ridges on loaded northerly terrain but they were extremely isolated and the areas that were loaded were pretty easy to identify.  

Overall, we have very stable conditions as a result of the last 2 weeks of high pressure, but that is about to change.  Crusts and faceted snow have had a chance to grow and will create some shallow storm and wind slab potential later today if wind forecasts and snow totals are accurate.  Any new snow will likely have a hard time bonding to the old snow surfaces for a few days.  

Pic is of a recent wind slab on Hard Butte, the wind chart is from Granite Mt Weather Station 

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 32 deg. F.
Max. temperature in the last 24 hours: 38 deg. F.
Average wind direction during the last 24 hours: N
Average wind speed during the last 24 hours: 7 mph
Maximum wind gust in the last 24 hours: 28 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: NA inches
weather

.SHORT TERM...Today through Monday night...Cold front continues
to move through the Pacific Northwest this morning. Pre-frontal
shower activity expected during the late morning / early afternoon
hours, with coverage moving eastward through the day.
Temperatures will be 10 to 15 degrees cooler across the area
today, with wind shifting to the northwest as the front
progresses. Gusty to breezy conditions possible across portions of
eastern Oregon. Additionally, models continue to indicate
instability during the afternoon and evening, primarily over
south-central Idaho. Consequently, a few thunderstorms will be
possible beginning in the mid- afternoon hours, and ending with
the loss of daylight. Drier conditions expected across the area on
Sunday, though unsettled conditions will produce another round of
moisture for the area on Monday, with activity lingering into the
evening hours.

.LONG TERM...Tuesday through Saturday...Zonal to northwest flow will
allow for warm and dry conditions through the week. Temperatures are
expected to climb roughly 6-8 degrees above normal through Friday
ahead of the next system. An upper level trough will move through
the Pacific Northwest late on Friday, though models continue to
disagree over the system`s track. At this time, valley rain and
mountain snow is expected on Saturday as temperatures return to
within a couple degrees of normal.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Saturday Saturday Night Sunday
Weather: Rain and snow showers, mainly after 11am. Snow level 5000 feet. Steady temperature around 36. South southeast wind 6 to 9 mph. Chance of precipitation is 100%. Total daytime snow accumulation of less than a half inch possible. A 50 percent chance of snow showers before 11pm. Mostly cloudy, with a low around 20. Southwest wind around 5 mph becoming calm in the evening. New snow accumulation of less than a half inch possible. Partly sunny, with a high near 37. Light and variable wind.
Temperatures: 36 deg. F. 20 deg. F. 37 deg. F.
Wind direction: SSW SW Light
Wind speed: 6-9 5 Variable
Expected snowfall: Trace in. Trace in. 0 in.
Granite Mountain at 7700 feet.
  Saturday Saturday Night Sunday
Weather: Snow showers. Temperature falling to around 26 by 5pm. South wind 11 to 15 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 2 to 4 inches possible. Snow showers likely before 11pm. Mostly cloudy, with a low around 16. West southwest wind 5 to 7 mph becoming light and variable after midnight. Chance of precipitation is 60%. New snow accumulation of less than one inch possible. Partly sunny, with a high near 24. Calm wind becoming southwest around 6 mph in the afternoon.
Temperatures: 26 deg. F. 16 deg. F. deg. F.
Wind direction: S WSW SW
Wind speed: 11-15 5-7 6
Expected snowfall: 2-4 in. Trace in. 0 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.