THIS AVALANCHE FORECAST EXPIRED ON April 16, 2020 @ 6:46 am
Avalanche Forecast published on April 15, 2020 @ 6:46 am
Issued by Brandon Schwartz - Tahoe National Forest

Rapid warming conditions and snow surface melt will raise concern for a variety of wet snow avalanche problems today including loose wet, wet slab, and cornice collapse. MODERATE avalanche danger is expected to form quickly today for all elevations, further increasing to CONSIDERABLE danger during the afternoon hours.

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: Loose Wet
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Inversion conditions kept air temperatures at the mid slope and upper elevations above freezing last night but skies were clear. A decent but very superficial snow surface refreeze is expected to have occurred last night from the radiational cooling of the snowpack. This refreeze is not expected to be as strong as what occurred the previous two nights. Strong mid April sunshine will rapidly melt the snow surface as the morning progresses. Once the surface crust melts away, deep wet snow prone to loose wet avalanches will exist. Avalanche size up to D2 is expected.

Anticipate rapid melt rates today, faster than what occurred on Monday and Tuesday. Avoid steep terrain in areas where the surface crust is no longer supportable. E-SE-S aspects will melt the quickest, followed by varied rates on SW-W-NW-N-NE aspects.

Avalanche Problem 2: Wet Slab
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Forecasting a wet slab avalanche is notoriously difficult. Too much uncertainty exists to assign a likelihood to this avalanche problem. The current snowpack structure may allow for the possibility of a wet slab avalanche to occur when meltwater percolates down to the March 24 buried surface hoar layer. This potential weak layer is located 1 to 2 feet below the snow surface on some open NW-N-NE-E aspects. Avalanche size is expected at D2.

As long as there was a decent to strong overnight refreeze, timing and terrain choices to avoid deep wet snow and/or steep terrain could help avoid wet slab avalanches. Any time a weak to non-existent overnight refreeze occurs or later in the day when deep wet snow exists, all bets are off.

Avalanche Problem 3: Cornice
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With above average air temperatures and a wind shift to the W, cornices will rapidly warm and melt today. Natural or human triggered cornice collapse is an elevated concern today. Large to very large cornice chunks may fall and tumble down the slopes below. These cornices chunks have destructive potential on their own. Falling cornices may also trigger loose wet or wet slab avalanches, increasing the destructive potential further.

Stay well back from abrupt edges on ridgelines and out from under cornices, especially if you can see or hear meltwater dripping from the cornice.

recent observations
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* A report was received of a large natural avalanche, possibly a wet slab that may have occurred Monday in the vicinity of Mt. Price (Desolation Wilderness area) on a NE aspect with the crown at mid slope. The avalanche was seen from afar. No other details are known.

* Diurnal melt-freeze conditions exist on all aspects.

* The March 24 buried surface hoar layer that is located 1-2 feet below the surface on some NW-N-NE-E aspects is being monitored as a potential weak layer for wet slab avalanches.

Weather and CURRENT CONDITIONS
weather summary

Air temperature inversion conditions are giving a head start to warming at the mid and upper elevations today where overnight air temperatures remained above freezing. Significant warming is expected today with above average air temperatures in the upper 40s to upper 50s at elevation. Ridgetop winds are shifting from NE to W this morning. A cold front will move through the region tonight into tomorrow bringing a decrease in daytime temperatures for tomorrow. Very light rain and snow showers are possible by this evening. Chances increase for very light showers tonight and tomorrow. Additional periods of rain and snow are in the forecast through Monday.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 33 to 40 deg. F.
Max. temperature: 42 to 52 deg. F.
Average ridgetop wind direction: NE
Average ridgetop wind speed: 17 mph
Maximum ridgetop wind gust: 59 mph
New snowfall: 0 inches
Total snow depth: 58 to 79 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny. Snow levels 7500 feet increasing to 8500 feet in the afternoon. Chance of precipitation is 5%. Partly cloudy. Slight chance of showers in the evening. Snow levels 8500 feet. Chance of precipitation is 10%. Mostly cloudy then becoming partly cloudy. Slight chance of showers. Snow levels 7000 feet. Chance of precipitation is 20%.
Temperatures: 52 to 58. deg. F. 28 to 33. deg. F. 44 to 50. deg. F.
Mid Slope Winds: Light winds becoming west 10 to 15 mph with gusts up to 25 mph in the afternoon. Light winds. Light winds.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny. Snow levels 7500 feet increasing to 8500 feet in the afternoon. Chance of precipitation is 5%. Partly cloudy. Slight chance of showers in the evening. Snow levels 8500 feet. Chance of precipitation is 10%. Mostly cloudy then becoming partly cloudy. Slight chance of snow showers. Snow levels 7000 feet. Chance of precipitation is 25%.
Temperatures: 45 to 51. deg. F. 25 to 30. deg. F. 39 to 45. deg. F.
Ridge Top Winds: West 15 to 20 mph with gusts to 35 mph. Northwest 15 to 20 mph with gusts to 35 mph. East around 15 mph with gusts to 25 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | 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