THIS AVALANCHE ADVISORY EXPIRED ON January 2, 2020 @ 7:10 am
Avalanche Advisory published on January 1, 2020 @ 7:10 am
Issued by George Halcom - Payette Avalanche Center
bottom line

Human triggered avalanches remain possible. New snow and gusty winds will create storm slabs upwards of a foot that may be sensitive. Buried Surface Hoar 1-2 feet deep and deeper Crusts/facets may be reactive. Wind slabs will be a growing problem.  Persistent weak layers have created low probability/high consequence scenario... avoid steep, and wind loaded terrain.

How to read the advisory


  • Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
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Up to a foot of new snow has fallen in the last 24 hours under windy and warmer conditions. This new snow will have slabby properties and may be sensitive to human triggers. Steep rollovers, and steep slopes during and right after the storm are going to be suspect.

 

Avalanche Problem 2: Persistent Slab
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Our persistent weak layers are doing exactly what they say. They are persisting, or still preserved in the mid and ground level of our snow pack. We have a layer of buried surface hoar about 1-2 feet down that is still propagating in our snowpit tests Tuesday.

The other persistent problem is lower in our snow pack and it could have serious consequences: facets sitting on a crust that are producing planar failures that show propagation potential. Basal facets, or sugar snow near the ground that can be anywhere from 6-12 inches sitting on rocks below a two inch crust surrounded by facets.

It is easy to get complacent about a persistent avalanche problem but it should be in the back of your mind as you travel right now,  The presence of these layers is enough to keep most seasoned backcountry travelers on lower angle slopes and away from committing terrain.  Persistent weak layers are unpredictable based on variations in the terrain and snow pack, they can also fail in unpredictable ways across a slope sometimes weeks after being buried.   

advisory discussion

FPAC is hosting a bunch of avalanche awareness classes in January including a women's only class.  Check out our Education page here.

It is easy to get complacent about a persistent avalanche problem but it should be in the back of your mind as you travel right now,  The presence of these layers is enough to keep most seasoned backcountry travelers on lower angle slopes and away from committing terrain.  Persistent weak layers are unpredictable based on variations in the terrain and snowpack, they can also fail in unpredictable ways across a slope sometimes weeks after being buried.   

recent observations

Ski touring oust side Brundage mountain yesterday, our test pits were still giving us results on buried surface hoar and facets above a crust about a foot above the ground. The results were hard to initiate, but show potential, and are not buried that deep so skiers and snowmobilers are both able to effect, or trigger the weak layers...variable depth in regards to elevation and aspect is harboring shallow, or more sensitive areas.

 

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: WSW
Average wind speed during the last 24 hours: 10 mph
Maximum wind gust in the last 24 hours: 21 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: NA inches
weather

 

Area Forecast Discussion
National Weather Service Boise ID
358 AM MST Wed Jan 1 2020

.SHORT TERM...Today through Thursday...Warm front has moved
through the region this morning, with the bulk of the
precipitation now from Boise and areas south and east. This
storm underachieved greatly with observed amounts under 50 percent
of the forecast. Expect precipitation to become showery in nature
for the remainder of the day, with the best chances focused on
the mountains. Additional snow accumulations of 2 to 4 inches are
possible over the mountains through this afternoon. There is
enough dynamics and instability for thunderstorms containing small
hail to form this afternoon as cooler air aloft moves into the
region, thus have added it to the forecast. Strong winds aloft can
easily produce wind gusts up to 50 mph this afternoon with the
showers and thunderstorms. Have issued a wind advisory for
southern Harney and Malheur Counties in Oregon and Owyhee and
Southern Twin Falls County in southwest Idaho for this afternoon.
Breezy west to northwest winds will continue into Thursday
although be below advisory level after this evening. Isolated
showers will continue in the mountains through Thursday with
partly sunny skies in the valleys. Temperatures will be around 10
degrees above normal for the short term.

.LONG TERM...Thursday night through Tuesday...An upper ridge will
provide the area with dry weather on Friday. The next upper trough
will move through on Saturday with a chance of valley rain/snow
and mountain snow, with the potential for light snow accumulations
in the Boise Mountains and West Central Mountains. The trough
will move out of the area Saturday night, followed by a series of
weaker systems Sunday through Wednesday. The chances for snow will
favor the higher elevations in the north. Snow levels will be
near valley floors. Temperatures will be 5 to 10 degrees above
normal Friday and Saturday, cooling to slightly above normal
Sunday through midweek.

&&

.AVIATION...Mountains obscured. Widespread MVFR/IFR conditions
in rain and snow transitioning to showers and isolated
thunderstorms after 18Z. Snow levels around 4000 feet north (KBKE-
KMYL) and 5000-6000 feet south. Surface winds: southwest to
southwest 10-20 kts becoming west-northwest 15-25 kts with gusts
to 40 kts. Winds aloft at 10k ft MSL: northwest 40-60 kts.

 

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Wednesday Wednesday Night Thursday
Weather: Snow showers. Some thunder is also possible. High near 31. South wind 7 to 13 mph becoming west in the afternoon. Winds could gust as high as 23 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 2 to 4 inches possible. Snow showers likely, mainly before midnight. Mostly cloudy, with a low around 22. West wind around 6 mph becoming calm. Chance of precipitation is 70%. New snow accumulation of less than one inch possible. Scattered snow showers, mainly before noon. Partly sunny, with a high near 28. West wind 3 to 6 mph. Chance of precipitation is 30%. New snow accumulation of less than a half inch possible.
Temperatures: 31 deg. F. 22 deg. F. 28 deg. F.
Wind direction: South-West West West
Wind speed: 7-13 Gusting to 23 Mph 6 Mph-calm 3-6 Mph
Expected snowfall: 2-4 in. less than one in. Less than one half in.
Granite Mountain at 7700 feet.
  Wednesday Wednesday Night Thursday
Weather: Snow showers. Some thunder is also possible. High near 24. West northwest wind 13 to 18 mph, with gusts as high as 30 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 3 to 5 inches possible. Snow showers likely. Mostly cloudy, with a low around 17. West northwest wind 7 to 11 mph, with gusts as high as 21 mph. Chance of precipitation is 70%. New snow accumulation of around an inch possible. Scattered snow showers. Partly sunny, with a high near 19. West northwest wind 6 to 9 mph. Chance of precipitation is 40%. New snow accumulation of less than a half inch possible.
Temperatures: 24 deg. F. 17 deg. F. 19 deg. F.
Wind direction: WNW WNW WNW
Wind speed: 13-18 Gusting to 30 Mph 7-11 Gusting to 21 Mph 6-9 Mph
Expected snowfall: 3-5 in. 1 in. less than one half 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.