THIS AVALANCHE ADVISORY EXPIRED ON December 19, 2019 @ 7:43 am
Avalanche Advisory published on December 18, 2019 @ 7:43 am
Issued by George Halcom - Payette Avalanche Center
advisory discussion

Our snow pack is going to be problematic for stability for some time, especially with added load from over a foot of snow with South winds upwards of 20 MPH  forecasted over the next few days. The temperatures associated with the forecasted storm are warm, and will likely form an upside down layer.  

Right now, we have a stereotypical, fairly poor, and complex snow pack with multiple weak layers.  The old October snow and early November snow that is the foundation of our snow pack has turned into Depth Hoar,  a sugary junk pile near the ground with 2 additional weak layers above including buried surface hoar and Near Surface Facets.  Avoid steep slopes especially on protected northerly slopes that have poor structure and will be getting the most load from South wind loading.  Our next update will be out on Friday, Dec 20th.  Stay safe out there.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 21 deg. F.
Max. temperature in the last 24 hours: 21 deg. F.
Average wind direction during the last 24 hours: SE
Average wind speed during the last 24 hours: 9 mph
Maximum wind gust in the last 24 hours: 21 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: NA inches
weather

 

Area Forecast Discussion
National Weather Service Boise ID
407 AM MST Wed Dec 18 2019

.SHORT TERM...Today through Saturday...Dry weather continues today
as an upper ridge over the region shifts eastward. Snow will
develop from west to east overnight as moist westerly flow pushes
into the Pacific Northwest. Southeast Oregon and the west-central
Idaho mountains will see snow begin overnight, before filling in
across the lower Snake Plain by sunrise Thursday. The heaviest
snowfall for this event will be focused across the mountains of
Baker county and west-central Idaho. The Lower Treasure Valley
will see light accumulations Thursday morning, likely initiating
around rush hour, and with temperatures at or below freezing,
expect potential for slick roads. Snow levels will rise from
lowest valley floors to around 4k feet by Thursday afternoon.
Morning snow accumulations will likely melt off during the
afternoon across lower elevation as temperatures warm above
freezing. Open terrain and higher mountains will see breezy
conditions through this event. The precipitation shifts northward
overnight as the flow aloft backs around to the southwest. This
will confine snowfall to the central Idaho mountains Thursday
night into Friday. Conditions dry out for most sites late Friday
and into Saturday as a trough deepens offshore, keeping the area
under southwest flow. Temperatures are near normal through
Thursday warming to around 10 degrees above normal for Friday and
Saturday.

.LONG TERM...Saturday night through Tuesday...A trough along the
west coast will slowly track eastward during the weekend and into
next week, supporting a chance of showers over the area each day.
The best chance for showers will be over southeast Oregon and the
mountains of southwest Idaho. Snow levels will begin around
3500-4500 feet MSL, and gradually lower to valley floors by
Monday/Tuesday. Temperatures will be on a cooling trend, but still
around 5-10 degrees above normal through the extended.

&&

.AVIATION...Mainly VFR with mid to high clouds. Patchy fog
creating IFR/LIFR at KMYL through morning. Low clouds and mountain
obscurations by this evening. Isolated snow showers will begin
over SE Oregon by 00z/Thu, and spread into SW Idaho after 03z/Thu.
Then, expect widespread snow after 12z/Thu. Surface winds: SE to
SW 5-15 kts, except NE 20-30 kts at KJER. Winds aloft at 10Kft
MSL: W to SW 20-35 kts.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Wednesday Wednesday Night Thursday
Weather: Partly sunny, with a high near 25. Calm wind becoming south around 5 mph in the afternoon. A 50 percent chance of snow after 11pm. Mostly cloudy, with a low around 16. South southeast wind 3 to 5 mph. New snow accumulation of less than one inch possible. Snow. High near 30. South southeast wind 5 to 7 mph. Chance of precipitation is 100%. New snow accumulation of 1 to 3 inches possible.
Temperatures: 25 deg. F. 16 deg. F. 30 deg. F.
Wind direction: S SSE SSE
Wind speed: calm-5mph 3-5 mph 5-7 mph
Expected snowfall: 0 in. less than one in. 1-3 in.
Granite Mountain at 7700 feet.
  Wednesday Wednesday Night Thursday
Weather: Partly sunny, with a high near 23. Wind chill values between zero and 10. South wind 10 to 14 mph. Snow likely, mainly after 11pm. Mostly cloudy, with a low around 13. Wind chill values between -1 and 4. South wind 11 to 14 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible. Snow. Steady temperature around 18. South wind 13 to 16 mph. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible.
Temperatures: 23 deg. F. 13 deg. F. 18 deg. F.
Wind direction: S S S
Wind speed: 10-14 mph 11-14 mph 13-16
Expected snowfall: 0 in. 1-3 in. 4-8 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.