THIS AVALANCHE ADVISORY EXPIRED ON January 11, 2020 @ 7:25 am
Avalanche Advisory published on January 10, 2020 @ 7:25 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

Expect significant changes and increasing avalanche hazard over the next few days.  A series of winter storms will bring 20+ inches of snow to the West Central Mountains this weekend.  New snow and gusty winds will add to the wind slab problem.  New storm slabs will also be likely and the potential for larger avalanches failing 2-4 feet down on persistent weak layers will increase as snow totals rise.

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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Old wind slabs still exist along ridgelines and throughout upper elevation terrain.  Some of these are still sensitive enough to trigger today and should be easy to spot or feel.  Dense snow or a change in the density of the snow especially if you see cracking around your skis or sled are red flags that you are on wind slabs.  

Winds will ramp up mid day today just ahead of the first wave of precipitation and will easily transport the new, light density snow we got yesterday.  As the winds increase the potential for wind slab avalanches will increase as well.  By tomorrow morning, wind slabs and new storm slabs will be likely on multiple aspects, as this storm intensifies over the next few days avalanche conditions will continue to increase.  Travel on steep slopes is not recommended.  

Avalanche Problem 2: Persistent Slab
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New snow this week and windloading are continuing to add weight and stress to our persistent weak layers.  Human triggered avalanches were reported earlier this week.  Multiple weak layers exist within our snowpack.  The storm cycle that starts today will be a major stressor to the these layers.  The depth and consequences of triggering an avalanche in these deeper layers is significant and will increase.  Conservative storm totals over the next 3 days are adding 20-30 inches of new snow plus significant windloading on some slopes to a snowpack that has poor structure.  Expect to see natural and human triggered avalanche potential increase quickly by tomorrow and through next week as multiple storms roll through the Western US.  Play it safe over the next few days and stick to lower angle slopes and slopes that are safely away from the runout zones of avalanche terrain.

advisory discussion

The Friends of the Payette Avalanche Center are hosting several avalanche classes over the next few weeks.  Take the time to take a class!  Click Here for more info.  Also, if you are interested in sponsoring a forecast or donating to the FPAC, email them to find out how you can help them bring more forecasts and more classes to the West Central Mountains.

 

recent observations

We appreciate all of the good observations that we continue to recieve.  Take a look at the Observations list to see some of the most recent ones.  These observations help the forecasters paint a better picture of conditions across the West Central.  

 

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 4 deg. F.
Max. temperature in the last 24 hours: 15 deg. F.
Average wind direction during the last 24 hours: W
Average wind speed during the last 24 hours: Calm mph
Maximum wind gust in the last 24 hours: Calm mph
New snowfall in the last 24 hours: 3 inches
Total snow depth: 42 inches
weather

Brace for impact! A series of winter storms are lined up and headed our way.

...SIGNIFICANT MOUNTAIN SNOW THIS WEEKEND INTO EARLY NEXT WEEK...

.Snow will begin across east-central Oregon and the mountains of
west-central Idaho tonight as the first in a series of low
pressure systems impacts the region. The mountains will see
periods of heavy snow through Tuesday as three separate storm
systems track through the Pacific Northwest. Valley locations will
see periods of snow through Tuesday with accumulating snow
becoming more likely heading into early next week.

IDZ011-013-033-102200-
/O.UPG.KBOI.WS.A.0001.200110T1800Z-200115T0000Z/
/O.NEW.KBOI.WS.W.0001.200110T2100Z-200115T0000Z/
West Central Mountains-Boise Mountains-Upper Weiser River-
329 AM MST Fri Jan 10 2020

...WINTER STORM WARNING IN EFFECT FROM 2 PM THIS AFTERNOON TO
5 PM MST TUESDAY...

* WHAT...Heavy snow expected. In the West Central and Boise
mountains, total snow accumulations through Tuesday afternoon of
1 to 3 feet with 4 to 5 feet possible across higher mountains.
In the Upper Weiser River basin total snow accumulations of 1
to 2 feet through Tuesday afternoon.

* WHERE...West Central Mountains, Boise Mountains and Upper
Weiser River zones.

* WHEN...From 2 PM this afternoon to 5 PM MST Tuesday.

* IMPACTS...Travel could be very difficult to impossible.

This image shows forecasted precipitation in inches of water for the next 5 days. Generally speaking, 1 inch of water equates to 10 inches of snow.

 

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Friday Friday Night Saturday
Weather: Snow likely after 11am. Mostly cloudy, with a high near 22. Calm wind becoming south southeast 5 to 7 mph in the afternoon. Chance of precipitation is 70%. Total daytime snow accumulation of around an inch possible. Snow. Low around 22. South wind 6 to 9 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible. Snow. High near 28. South southeast wind 6 to 9 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible.
Temperatures: 22 deg. F. 22 deg. F. 28 deg. F.
Wind direction: SSE S SSE
Wind speed: 5-7 6-9 6-9
Expected snowfall: 1 in. 3-5 in. 3-5 in.
Granite Mountain at 7700 feet.
  Friday Friday Night Saturday
Weather: Snow after 11am. High near 14. Wind chill values between -4 and 1. Light south southwest wind becoming south 10 to 15 mph in the morning. Winds could gust as high as 25 mph. Chance of precipitation is 90%. Total daytime snow accumulation of 2 to 4 inches possible. Snow. Low around 14. Wind chill values between -3 and 5. Breezy, with a south wind 13 to 20 mph. Chance of precipitation is 100%. New snow accumulation of 6 to 10 inches possible. Snow. High near 19. South southwest wind 10 to 15 mph, with gusts as high as 26 mph. Chance of precipitation is 100%. New snow accumulation of 5 to 9 inches possible.
Temperatures: 14 deg. F. 14 deg. F. 19 deg. F.
Wind direction: SSW S SSW
Wind speed: 10-15, gusting to 25 13-20 10-15, gusting to 26
Expected snowfall: 2-4 in. 6-10 in. 5-9 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.