THIS AVALANCHE ADVISORY EXPIRED ON December 16, 2016 @ 6:18 am
Avalanche Advisory published on December 15, 2016 @ 6:18 am
Issued by -
bottom line

Today the avalanche danger is CONSIDERABLE on mid and upper elevation terrain. Human triggered avalanches are LIKELY and natural avalanches are possible on all slopes over 30 degrees. If todays forecasted winds of up to 45 mph come to fruition, the avalanche danger could jump to HIGH on all wind loaded terrain in the upper elevations of the advisory area.

If triggered, an avalanche today could step down into snow from previous storms causing a much larger avalanche. 

 

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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WIth over an inch of snow water equivelant equating to 10 to 15 inches of new snow in the mountains of the advisory area, storm slabs of over a foot deep should be your main concern today, if you choose to travel in avalanche terrain.

Avalanche Problem 2: Wind Slab
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Due to the west southwest winds, wind slabs will be found in terrain that is not sheltered from the wind. Due to moderate to extreme winds throughout the day today, wind slabs will be found lower on the slope than normally expected. Even though you are mid slope you should still be on the lookout for wind slabs today and into the weekend.

advisory discussion

The PAC advisory area caught the northern edge of this most recent storm, and subsequent dangerous avalanche conditions can be found in the mountains around McCall. However, reports from just south and east of the advisory area showing more signs of instability. This weaker snowpack, coupled with higher snow totals overnight, warrant extreme caution if you are traveling in avalanche terrain south of the advisory area. Sawtooth Avalanche Center issued an Avalanche Warning last night that will last for 24 hours due to persistent weak layers in the snowpack, high winds, and high snowfall totals. Expect the avalanche danger within the Sawtooth Avalanche Centers' advisory area to be EXTREME today. This means that natural and human caused avalanches are certain.

While we DO have persistent grain types in our snowpack that could prove to cause avalanches, currently they are not our top concern. That being said, now is NOT the time to be pushing your luck in the mountains. Dangerous conditions do exist if traveling in, below, or on slopes connected to avalanche terrain.

Be sure everyone in your group has at a minimum a beacon, probe, and shovel and knows how to perform a companion rescue.

recent observations

We toured up Granite Mountain yesterday to look at how recent storms have affected the snowpack of the upper elevation on north and northeast facing terrain. We saw no evidence of natural activity, however, the results from our snowpack tests showed some possibilties of avalanches initiating at density changes throughout the snowpack. These density changes were the product of previous storms and wind activity. We did find two melt freeze crusts deep in the pack on north facing terrain. These crusts had surgary snow that also caused initiation under the stress of a compression test.

We have had reports from both the Lick Creek Summit area, and east of Landmark, of collapsing in the snowpack or 'whoomping'. This is a red flag for instabilities in the snowpack.

weather

Precipitation will continue across the advisory area today with total accumulations around 3-6 inches. Winds out of the west southwest will blow between 20-30mph with gusts up to 45mph.  Showers associated with this warm front will weaken through Friday afternoon as an assault of arctic air moves into the state. This weekend looks to be a cold one.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Thursday Thursday Night Friday
Weather: Rain and snow, becoming all snow after 11am. High near 33. South southwest wind 9 to 14 mph. Chance of precipitation is 100%. New snow accumulation of 1 to 3 inches possible. A 30 percent chance of snow. Cloudy, with a low around 14. Southwest wind around 5 mph becoming light and variable. New snow accumulation of less than a half inch possible. A 20 percent chance of snow showers. Mostly cloudy, with a high near 21. Wind chill values between -2 and 8. North northwest wind 7 to 10 mph.
Temperatures: High 33 deg. F. Low 14 deg. F. High 21 deg. F.
Wind direction: South southwest Southwest North northwest
Wind speed: 9-14 5 7-10
Expected snowfall: 1-3 in. less than 0.5 in. 0 in.
Granite Mountain at 7700 feet.
  Thursday Thursday Night Friday
Weather: Snow. High near 28. Windy, with a west southwest wind 27 to 32 mph decreasing to 18 to 23 mph in the morning. Winds could gust as high as 44 mph. Chance of precipitation is 90%. New snow accumulation of 3 to 5 inches possible. A 50 percent chance of snow. Cloudy, with a low around 10. Southwest wind 7 to 15 mph. New snow accumulation of less than one inch possible. A 30 percent chance of snow showers. Mostly cloudy, with a high near 16. Wind chill values between -11 and -21. North northwest wind 6 to 11 mph increasing to 12 to 17 mph in the afternoon. New snow accumulation of less than one inch possible.
Temperatures: High 28 deg. F. Low 10 deg. F. High 16 deg. F.
Wind direction: West southwest Southwest North northwest
Wind speed: 18-32 gusting 44 7-15 12-17
Expected snowfall: 3-5 in. Less than 1 in. Less than 1 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.