THIS AVALANCHE FORECAST EXPIRED ON April 23, 2020 @ 6:42 am
Avalanche Forecast published on April 22, 2020 @ 6:42 am
Issued by Brandon Schwartz - Tahoe National Forest

Last night's snow surface refreeze is expected to be relatively weak. Rapid warming conditions early this morning will quickly create the possibility of loose wet snow avalanches at all elevations today. Cornice fall is also a possibility. MODERATE avalanche danger will form rapidly at all elevations once the surface crust melts away, exposing areas of deep wet snow.

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: Loose Wet
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A relatively weak snow surface refreeze is expected to have occurred last night. Overnight air temperatures were well above freezing in most locations at the mid and upper elevations. Snow surface refreeze last night was entirely dependent on radiational cooling of the snowpack under clear skies. The relatively strongest refreeze will have occurred on open slopes. A poor refreeze is expected to have occurred under forest canopy. Rapid warming and surface melt will occur today starting right from sunrise. The surface crust will melt away rapidly today, exposing deep wet snow, and opening the door for loose wet snow avalanches this morning. A loose wet avalanche problem is expected to form quickly today on all aspects at all elevations. Avalanche size is expected at D1 to D2, depending on what the terrain is capable of producing.

Avoid travel in avalanche terrain on slopes where marginally supportable to unsupportable deep wet snow exists. Today's winds may create some cooling and slow melt rates this morning directly along the ridgetops, but not mid slope or below.

Avalanche Problem 2: Cornice
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A weak overnight refreeze and rapid warming conditions today may fuel additional cornice fall. Large to very large cornice chunks falling onto the slopes below have destructive potential on their own. If the cornice fall triggers a loose wet or wet slab avalanche on the slope below the destructive potential will be even greater.

Stay well back from abrupt edges along ridgetops and stay out from under any cornices above you. Cornices where you can hear or see dripping water are weakening and could be nearing collapse.

 Photo: Natural cornice fall that triggered a slab avalanche yesterday on Ralston Pk (Echo Summit area).

recent observations
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* Diurnal melt-freeze conditions exist on all aspects.

* Observations made yesterday on Rubicon Peak (West Shore Tahoe area) and on Ralston and Echo Peaks (Echo Summit area) revealed a decent snow surface refreeze had occurred the night before. The surface crust had weakened substantially from melt by the late morning hours.

* A natural cornice collapse occurred just before noon yesterday at around 9,100' on the E aspect of Ralston Peak (Echo Summit area), triggering a size D2 slab avalanche on the slope below.

* Signs of layer consolidation from recent melt and rain have been observed in the top few feet of the snowpack on all aspects, minimizing the concerns for additional wet slab avalanches. Cornice fall may still be able to trigger a very isolated wet slab avalanche.

Weather and CURRENT CONDITIONS
weather summary

Air temperature inversion conditions set up last night with well above freezing air temperatures overnight at the mid and upper elevations. The coldest air last night was near the mountain valley floors. A weather system passing well to the north of the forecast area is increasing westerly ridgetop winds this morning. Moderate speed W to NW winds are forecast to continue through Thursday. Cloud cover will again increase this afternoon and tonight with no precipitation expected. A substantial warming trend is forecast for the next 7+ days.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 37 to 42 deg. F.
Max. temperature: 42 to 54 deg. F.
Average ridgetop wind direction: NE shifting to W
Average ridgetop wind speed: 13 mph
Maximum ridgetop wind gust: 35 mph
New snowfall: 0 inches
Total snow depth: 52 to 74 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 then becoming partly cloudy. Snow levels 8000 feet increasing to 10000 feet in the afternoon. Chance of precipitation is 0%. Mostly cloudy then becoming partly cloudy. Snow levels 9500 feet. Chance of precipitation is 0%. Sunny. Snow levels 8500 feet. Chance of precipitation is 0%.
Temperatures: 53 to 59. deg. F. 33 to 38. deg. F. 54 to 60. deg. F.
Mid Slope Winds: Light winds becoming west 10 to 20 mph with gusts to 30 mph in the afternoon. West 10 to 20 mph with gusts to 30 mph. West to northwest winds around 10 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Wednesday Wednesday Night Thursday
Weather: Sunny then becoming partly cloudy. Snow levels 8000 feet increasing to 10000 feet in the afternoon. Chance of precipitation is 0%. Mostly cloudy then becoming partly cloudy. Snow levels 9500 feet. Chance of precipitation is 0%. Sunny. Snow levels 8500 feet. Chance of precipitation is 0%.
Temperatures: 44 to 50. deg. F. 32 to 37. deg. F. 46 to 54. deg. F.
Ridge Top Winds: West around 10 mph increasing 15 to 25 mph with gusts up to 45 mph in the afternoon. West 15 to 30 mph with gusts to 50 mph. Northwest 15 to 25 mph. Gusts up to 45 mph decreasing to 35 mph in the afternoon.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. 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