THIS AVALANCHE FORECAST EXPIRED ON April 9, 2020 @ 6:58 am
Avalanche Forecast published on April 8, 2020 @ 6:58 am
Issued by Brandon Schwartz - Tahoe National Forest

Newly formed slabs of wind drifted snow, persistent instability, and springtime wet snow instability are all potential avalanche problems in the backcountry today. Rapidly changing weather conditions are expected again today with isolated thunderstorms possible this afternoon. Avalanche danger is MODERATE at all elevations.

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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Strong to gale force E winds last night will have drifted any snow available for transport in near treeline and above treeline areas. Potentially unstable new wind slabs are expected to exist near and above treeline where drifting snow has deposited on wind loaded and cross loaded SE-S-SW-W-NW-N aspects. Avalanche size up to D2 is possible.

Look for signs of blowing and recently drifted snow, smoother surfaces, and pillows. Areas with the most recent deposits of drifted snow are where new wind slabs will be encountered. Sunshine on newly formed wind slabs may exacerbate instability today.

Avalanche Problem 2: Persistent Slab
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There are some indications that the weak layer that has contributed to recent avalanches with persistent slab characteristics (wide propagation, failing with numerous previous tracks on the slope) is gaining strength. There is still uncertainty here with more data needed on weak layer stabilization of the barely faceted snow on the underside of the crust at the old/new snow interface. NW-N-NE-E aspects at all elevations hold lingering concern for avalanches failing along the crust located 1 to 3+ feet deep in the snowpack. Avalanche size is expected at D2 with up to D3 possible.

This is a low likelihood, high consequence event and difficult to manage as conditions will seem stable right up until an avalanche occurs. The easiest tactic is to avoid the aspects of concern or entrench on sub 30 degree slopes without steeper slopes above or to the side.

 Photo: Monday's skier triggered avalanche on Relay Pk, NV with wide propagation and numerous previous tracks.

Avalanche Problem 3: Loose Wet
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Warming today and periods of sunshine and solar radiation through and between the cloud cover will allow the strong April sunshine to create snow surface warming in wind protected areas on all aspects. This surface warming and melt will allow for the possibility of loose wet avalanches today in wind protected areas on all aspects. Avalanche size is expected at D1 to D2 depending on what the terrain is capable of producing.

Rollerballs and pinwheels are indications of the presence of this avalanche problem. Consequences from even small loose wet avalanches can come from being pushed into or over rocks, trees, cliffs, and terrain traps below. Lower angle slopes can be used to avoid this avalanche problem. While wind exposed areas will likely have sufficient convective cooling to keep this problem from forming, anticipate how conditions will change away from the ridgetops and where wind protected areas will be encountered mid slope and below.

 Photo: Loose wet avalanches yesterday on Talking Mtn (Echo Summit area), N aspect around 8,100'.

recent observations
Submit Observations

* Snowpit data collected yesterday on Donner Peak and Mt. Judah (Donner Summit area) targeting the problematic weak layer at the old/new snow interface showed significant strength gains compared to what was reported from nearby Tressle Peak on Sunday.

* Multiple loose wet avalanches were seen occurring yesterday afternoon on the N side of Talking Mountain (Echo Summit area) at around 8,100'.

* A wind slab avalanche was reported yesterday from Tamarack Peak in near treeline terrain on a N aspect at around 9,600'. The avalanche was reported at around 65 feet wide and failed 4 to 12 inches deep within the recent storm snow.

Weather and CURRENT CONDITIONS
weather summary

A weather system is passing mostly to the south of the forecast area today. Ridgetop winds increased to strong to gale force in speed out of the E overnight. Another mixed day of sun, cloud cover, and precipitation is forecast for today. Light rain and snow showers are possible at times today with isolated thunderstorms in the afternoon. Most of the precipitation will occur in areas south of Hwy 50. Periods of rain and snow showers are expected to continue tonight and tomorrow. Ridgetop winds are forecast to remain strong out of the NE through tomorrow. A day over day warming trend continues with the peak in maximum daytime air temperatures occurring Fri/Sat with continued breezy conditions.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 27 to 36 deg. F.
Max. temperature: 30 to 41 deg. F.
Average ridgetop wind direction: E
Average ridgetop wind speed: 12 mph, possibly as high as 42 mph
Maximum ridgetop wind gust: 70 mph, possibly as high as 129 mph
New snowfall: 0 to trace inches
Total snow depth: 70 to 92 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy. Slight chance of snow in the morning, then a slight chance of showers in the afternoon. Snow levels below 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 25%. Mostly cloudy then becoming partly cloudy. Chance of rain and snow. Snow levels 8000 feet. Chance of precipitation is 40%. Partly cloudy. Chance of snow and rain through the day. Snow levels 7500 feet. Chance of precipitation is 30%.
Temperatures: 44 to 50. deg. F. 28 to 33. deg. F. 46 to 54. deg. F.
Mid Slope Winds: East 15 to 20 mph with gusts to 35 mph. Northeast around 15 mph in the evening becoming light. Gusts up to 30 mph. Light winds becoming northeast around 15 mph in the afternoon. Gusts up to 25 mph.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. 80% probability up to 1 inch. 20% probability of 1 to 3 inches. | SWE = up to 0.25 inch. Up to 1 inch. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Partly cloudy. Slight chance of snow in the morning, then a chance of showers and isolated thunderstorms in the afternoon. Snow levels 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 25%. Mostly cloudy. Chance of showers and isolated thunderstorms in the evening, then chance of snow and rain after midnight. Snow levels 8000 feet. Chance of precipitation is 45%. Partly cloudy. Chance of snow through the day. Snow levels 7500 feet. Chance of precipitation is 30%.
Temperatures: 37 to 45. deg. F. 25 to 30. deg. F. 40 to 48. deg. F.
Ridge Top Winds: East 20 to 30 mph with gusts to 75 mph. Northeast 15 to 30 mph with gusts to 65 mph. Northeast 15 to 30 mph with gusts to 60 mph.
Expected snowfall: Up to 1 inch. | SWE = less than 0.10 inch. 80% probability up to 1 inch. 20% probability of 1 to 3 inches. | SWE = 0.15-0.25 inch. Up to 1 inch. | SWE = less than 0.10 inch.
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