THIS AVALANCHE FORECAST EXPIRED ON April 1, 2020 @ 6:58 am
Avalanche Forecast published on March 31, 2020 @ 6:58 am
Issued by Brandon Schwartz - Tahoe National Forest

Another persistent slab avalanche occurred yesterday afternoon. Numerous avalanche problems arising from wind drifted snow, persistent instability, and snow surface warming will coexist in the backcountry today. Avalanche danger is MODERATE at all elevations.

2. Moderate

?

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

2. Moderate

?

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

2. Moderate

?

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Strong SW ridgetop winds have been drifting snow and creating wind slabs for the past 30+ hours. Areas of unstable wind slabs formed in lee areas where drifting snow has deposited are possible above treeline and near treeline on NW-N-NE-E-SE aspects. Avalanche size is expected at D1 to D2.

Continued blowing and drifting snow, cornice formations, and new wind pillows are all clues that can be used to identify slopes where unstable wind slabs may be encountered. Identify the areas of concern and move around them with caution.

Avalanche Problem 2: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Ugh. For the past two days, snowpit data collected either adjacent to or in the crown of persistent slab avalanches from March 25 and 27 have shown significant strength gains on the buried surface hoar persistent weak layer. Just when we thought we were past this avalanche problem, another persistent slab avalanche occurred yesterday afternoon. Spatial variability is at play here with weak layer stabilization occurring at different rates in different locations. This creates increased uncertainty. Isolated persistent slab avalanches failing 1 to 3 feet deep in the snowpack may occur in areas without signs of current instability and with numerous previous tracks. Ugh. NW-N-NE aspects at all elevations remain suspect. Avalanche size is expected at D2.

Avoiding NW-N-NE aspects or using only slopes of less than 30 degrees in slope angle, not connected to steeper slopes above or to the side are the tools for avoiding this avalanche problem. The places where good powder lingers are also where is avalanche problem is more likely to be found.

  Photo: Yesterday's persistent slab avalanche.

Avalanche Problem 3: Loose Wet
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

It's almost April. The sun angle is high enough to affect N aspects and incoming solar radiation is strong. This time of year it does not take much to create snow surface warming and loose wet instability. Warm air temperatures and sunshine through the clouds today will create snow surface warming. Rollerballs and loose wet avalanches are expected today in wind protected areas on all aspects, especially around exposed rocks. Avalanche size is expected at D1 with an isolated D2 not impossible.

Overnight air temperatures were warm and this avalanche problem is expected to form quickly today. With size D1 avalanches, consequences will come from being pushed into or over downslope terrain features such as rocks, trees, cliffs, and terrain traps. These terrain features could make high consequences from an otherwise small avalanche. Rollerballs and pinwheels are indications that this avalanche problem is present.

recent observations
Submit Observations

* A persistent slab avalanche was reported yesterday afternoon from the backside of Johnson Canyon (Donner Summit area). This avalanche was snowmobile triggered on a NNW aspect in near treeline terrain at 7,500' with a crown height of 1 foot.

* On Silver Peak (Pole Creek area) snowpit tests performed yesterday in the crown of a persistent slab avalanche from March 25 showed significant improvements in stability.

* Moderate amounts of drifting snow with new wind slab formation was observed above treeline yesterday on Silver Peak (Pole Creek area).

Weather and CURRENT CONDITIONS
weather summary

A brief warmup with wind will occur today ahead of an approaching cold front. There is a slight chance of some light snow showers along the Sierra Crest west of Lake Tahoe today. Otherwise, partly cloudy skies will allow for some sunshine. Ridgetop winds are strong out of the SW and are forecast to continue into tomorrow morning. Following the cold front passage tonight, maximum daytime air temperatures will cool a bit for tomorrow and Thursday with sunny skies. The next series of storm systems is forecast for this weekend with significant snowfall possible.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 26 to 34 deg. F.
Max. temperature: 27 to 38 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 45 mph
Maximum ridgetop wind gust: 70 mph
New snowfall: 0 to trace inches
Total snow depth: 59 to 81 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Snow levels 7500 feet. Chance of precipitation is 5%. Partly cloudy then becoming clear. Snow levels 7000 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 5%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 42 to 48. deg. F. 24 to 29. deg. F. 39 to 45. deg. F.
Mid Slope Winds: Southwest 15 to 20 mph with gusts to 35 mph. Southwest around 15 mph. Gusts up to 35 mph increasing to 45 mph after midnight. Southwest around 15 mph with gusts to 40 mph.
Expected snowfall: No accumulation. | SWE = none. No accumulation. | SWE = none. No accumulation. | SWE = none.
For 8000 ft. to 9000 ft.
Tuesday Tuesday Night Wednesday
Weather: Partly cloudy. Snow levels 7500 feet. Chance of precipitation is 5%. Partly cloudy then becoming clear. Snow levels 7000 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 5%. Sunny. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures: 36 to 42. deg. F. 22 to 27. deg. F. 33 to 39. deg. F.
Ridge Top Winds: Southwest 30 to 45 mph with gusts to 75 mph. Southwest 25 to 35 mph with gusts to 70 mph. Southwest 30 to 45 mph decreasing to 25 to 35 mph in the afternoon. Gusts up to 75 mph.
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