THIS AVALANCHE FORECAST EXPIRED ON January 22, 2020 @ 7:00 am
Avalanche Forecast published on January 21, 2020 @ 7:00 am
Issued by Steve Reynaud - Tahoe National Forest

Additional snow and wind today will increase the chances of avalanches.  Large destructive avalanches continue to be a concern with weak sugary snow buried deep in the snowpack.  CONSIDERABLE avalanche danger exists at all elevations due to wind slabs and persistent slab avalanche problems.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Strong winds have been blowing snow since yesterday afternoon throughout most of the forecast area.  Winds have already increased this morning to gale force with 2 to 5'' of new snow expected today.  Wind slabs could be multiple feet deep and reactive to triggering.  Human triggered wind slab avalanches will be likely today with natural wind slab avalanches possible in the most wind prone areas.

Look for active blowing snow, cornice formation, wind pillows, and ridgeline scouring.  Avoid run out zones under large cornices and steep wind loaded terrain.  The possibility exists that wind slabs could form over areas that have the buried Jan 4 weak layer.  This setup would make for much deeper avalanches with severe consequences.  Make a travel plan that avoids these areas of concern. 

Avalanche Problem 2: Persistent Slab
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A weak layer of faceted snow exists buried 2 plus feet deep below the snow surface.  This layer continues to produce unstable snowpack test results and show signs of being reactive with whumpfing and collapsing in many areas of the forecast region.  The weak storm forecasted for today will bring 2 to 5'' of additional snow and wind to our area.  The weak layer has been slowly adjusting to the weight of the recent storm snow and reported avalanche activity has begun to taper off.  This additional load of new snow and wind blown snow could tip the balance and make avalanches easier to trigger today. 

Avalanches associated with this persistent slab problem would be large and mostly unsurvivable.  Recent avalanches on this layer have ranged from 2’ up to 8’ deep.  These avalanches could be remotely triggered, involve a large amount of snow, and have wide propagation.  This problem exists in near and below treeline areas, places that most folks equate with safer backcountry terrain.  The only effective management strategy for persistent slabs is avoidance.  Pick a different aspect where the persistent problem does not exist, or travel on slopes well below 30 degrees in steepness which are not connected above or to the side of avalanche terrain.   

recent observations
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A recent avalanche was reported from the Incline Lake Peak area that occurred yesterday (Mt. Rose area).  The avalanche was just below the ridgeline and had relatively wide propagation.  It was thought to be a wind slab, but additional information was not possible and the trigger is unknown.  This area has been heavily skied since Friday.   

Multiple observations were reported from Silver Peak (Pole Creek area).  Consistent snowpack test results pointed to propagation being likely if the Jan 4 weak layer could be triggered.  A significant whumpf was experienced while doing snowpack tests in the vicinity of a recent rider triggered avalanche that occurred over the weekend.

Observations from Stevens Peak (Carson Pass) and Horse Canyon (Bear Valley) showed the Jan 4 layer gaining some strength with not as reactive snowpack test results.

Snow transport from moderate to strong winds were reported from multiple areas starting midday.  Available snow for transport exists along many ridgeline areas.

Weather and CURRENT CONDITIONS
weather summary

A weak winter storm will bring light snow and strong to gale force SW winds to our area today.  Snowfall is forecasted to begin late morning with snow levels at 5500-6000'.  2 to 5'' of new snow is expected at pass level with a trace to an inch of snow at Lake level.  Snow should wrap up this evening with weak ridging moving into the area and warming conditions into the weekend.  Our next chance of a storm will be late in the weekend. 

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 21 to 28 deg. F.
Max. temperature: 30 to 37 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 25 to 55 mph
Maximum ridgetop wind gust: 70 mph
New snowfall: 0 to trace inches
Total snow depth: 45 to 54 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 55%. Cloudy. Chance of snow in the evening, then slight chance of snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 50%. Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%.
Temperatures: 34 to 39. deg. F. 23 to 28. deg. F. 37 to 42. deg. F.
Mid Slope Winds: Southwest 15 to 25 mph with gusts to 45 mph. Southwest 15 to 25 mph with gusts to 45 mph decreasing to 15 to 20 mph with gusts to 35 mph after midnight. Southwest around 15 mph with gusts to 25 mph in the morning becoming light.
Expected snowfall: 80% probability of 1 to 3 inches. 20% probability of 3 to 5 inches. | SWE = up to 0.15 inch. 80% probability up to 1 inch. 20% probability of 1 to 3 inches. | SWE = less than 0.15 inch. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 50%. Mostly cloudy. Chance of snow in the evening, then slight chance of snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 55%. Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 10%.
Temperatures: 28 to 34. deg. F. 20 to 25. deg. F. 33 to 39. deg. F.
Ridge Top Winds: Southwest 30 to 45 mph with gusts to 85 mph. Southwest 30 to 45 mph with gusts to 90 mph decreasing to 20 to 35 mph with gusts to 60 mph after midnight. Southwest 20 to 30 mph with gusts to 50 mph decreasing to 15 to 20 mph with gusts to 35 mph in the afternoon.
Expected snowfall: 80% probability of 1 to 3 inches. 20% probability of 3 to 5 inches. | SWE = up to 0.15 inch. 80% probability up to 2 inches. 20% probability of 1 to 3 inches. | SWE = less than 0.15 inch. No accumulation. | SWE = none.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258