Avalanche Advisory - Thu, Jan. 26, 2017

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THIS ADVISORY EXPIRED ON January 28, 2017 @ 6:59 am
Avalanche Advisory published on January 26, 2017 @ 6:59 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

bottom line:

The primary concern for the next 48 hours is isolated and recently developed wind slabs that are sensitive to human triggering on mid to upper elevation slopes that are exposed to the wind. On Thursday these are most likely to be found on NW-N-NE-E-SE facing slopes with increasing concern with elevations over 12,000’. As winds increase with gusts up to 60mph over 10,000’ and shift out of the North and East late Thursday night thru Friday, new windslabs will form down to lower elevations below 9,000ft. These will likely be found on slopes facing SE-S-SW-W-NW. Natural avalanches are unlikely but may become possible at upper elevations on Friday, and human triggered avalanches will be possible and become likely at mid to upper elevations on Friday. Evaluate snow and terrain carefully and identify features of concern.

Avalanche Character 1: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Winds have been overall light for the past 3 days since the last major snowfall ended, with the exception for elevations over 12,000’ where moderate SW winds have transported snow over high peaks.  Wind slabs which developed during the storm at low to mid elevations have now had time to stabilize for the most part.  However, at very high elevations where snow transport has continued recent wind slabs are likely to be sensitive to human triggering.  On Thursday these are most likely to be found just below ridges and sidewalls of couloirs on slopes greater than 35 degrees facing NW-N-NE-E-SE.  As winds increase with gusts up to 60mph over 10,000’ and shift more out of the North and East late Thursday night thru Friday, new sensitive windslabs will develop.  These will most likely be found on SE-S-SW-W aspects at mid and upper elevations on Friday.

Look for clues like blowing snow, new cornice formation, denser snow patches and smooth hollow sounding snow to identify wind slabs. Do your own stability assessments in safe terrain to see how recent and sensitive wind slabs are. When in doubt avoid wind loaded features steeper than 35 degrees such as leeward convexities, slopes below ridgelines, and the side walls of gullies.

Snowpack Discussion

The last impressive storm exited the area early Monday morning leaving between 22 and 69 inches of new snow in its wake. A hefty natural avalanche cycle occurred during the storm. 2 houses in the Long Valley area below McGee Mtn were hit and damaged, luckily without personal injury. For the past 3 days we have experienced mostly clear skies, cold temperatures and mostly light winds down low. SW winds were moderate over 12,000’.  Storm slabs and wind slabs that formed during the storm from high SW winds have had time to stabilize for the most part. Concern continues to exist over wind slabs at very high elevations because of continued wind transport over high peaks, and we could see some down to mid elevations as well since winds will increase out of the NE on Friday. Earlier concerns over deep weak layers are now quite diminished due to how deeply these layers are buried, and the fact that tests have shown them to be stabilizing. As temperatures warm slightly Friday, some minor wet roller-ball activity may be seen on solar aspects around rocksat low to mid elevations, but these should stay small as temperatures will still remain relatively cold.

weather

A weak disturbance will bring increased clouds and some light snow showers to the region on Thursday, but little in the way of accumulation. Any snowfall amounts will generally be less than an inch with most areas just seeing a trace.  Temperatures will remain cold with highs in the mid teens to low 20s at 10,000'.  Winds will increase and shift direction out of the North and East late Thursday night into Friday in the 40-50mph range above 10,000', with ridges seeing gusts up to 60mph.  For Friday temperatures will warm slightly into the mid 20s to low 30s at 10,000', skies should be clear, and winds will begin to decrease in the afternoon.  Expect much warmer days and nighttime inversions for the weekend.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Thursday Thursday Night Friday
Weather: MOSTLY CLOUDY. ISOLATED SNOW SHOWERS IN THE MORNING, THEN SCATTERED SNOW SHOWERS IN THE AFTERNOON. MOSTLY CLOUDY THEN BECOMING PARTLY CLOUDY. SLIGHT CHANCE OF SNOW SHOWERS IN THE EVENING. SUNNY
Temperatures: 20 TO 26 deg. F. 3 TO 9 deg. F. 29 TO 34 deg. F.
Wind direction: LIGHT NORTH NORTH
Wind speed: LIGHT 10 TO 15 MPH. GUSTS UP TO 40 MPH GUSTS UP TO 35 MPH IN THE MORNING
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
  Thursday Thursday Night Friday
Weather: MOSTLY CLOUDY. ISOLATED SNOW SHOWERS IN THE MORNING, THEN SCATTERED SNOW SHOWERS IN THE AFTERNOON. MOSTLY CLOUDY THEN BECOMING PARTLY CLOUDY. SLIGHT CHANCE OF SNOW SHOWERS IN THE EVENING. SUNNY
Temperatures: 14 TO 22 deg. F. 1 TO 6 deg. F. 26 TO 32 deg. F.
Wind direction: NORTHWEST NORTH NORTHEAST
Wind speed: 15 TO 25 MPH WITH GUSTS TO 45 MPH 20 TO 35 MPH. GUSTS UP TO 45 MPH INCREASING TO 60 MPH AFTER MIDNIGHT 20 TO 30 MPH. GUSTS UP TO 60 MPH DECREASING TO 40 MPH IN THE AFTERNOON
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This Snowpack Summary is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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