This Avalanche Advisory was published on March 18, 2009:
March 18, 2009 at 7:00 am | |
Near and above treeline, pockets of MODERATE avalanche danger exist on N-NE aspects, 37 degrees and steeper. On E-SE-S-SW-W aspects, the avalanche danger will increase to MODERATE on slopes steeper than 35 degrees for all elevations due to daytime warming. |
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Forecast Discussion:
Mostly sunny skies, temperatures well above normal, and light west and southwesterly winds should persist across the forecast area today due to a high-pressure ridge over the region. Some clouds and slightly stronger winds may develop tomorrow afternoon as a disturbance moves towards southern California.
Yesterday, observers reported avalanches in the Mount Rose backcountry, the Mt. Judah area, and the Anderson Ridge area that occurred during the day on March 16th, overnight on the 16th, or very early morning on the 17th. These avalanches occurred on N-NE, wind-loaded, near and above treeline slopes steeper than 37 degrees. Cornices collapsing under their own weight onto hard wind slabs triggered these slides and resulted avalanches ranging from 1-2 ft deep. Below 7500' several wet point release avalanches also occurred on E-SE-S aspects during the day yesterday. Layer bonding tests and general observations yesterday in these areas showed that the wind slabs remain stiff and firm. In some areas tests showed that the wind slabs have started to bond to the snow beneath them and in other areas these bonds remained weak. Observations also showed a wide variety of snow surface conditions. Wet, rotten, unsupportable snow existed on lower elevation slopes. Some corn snow has formed on sun exposed E-SE-S-SW-W aspects between 7400' and 8500'. Firm wind slabs cover the open N-NE aspects near and above treeline. Supportable and breakable crusts also exist on almost all aspects in some areas. Above 8000' on shaded, wind-protected N-NE slopes some soft snow still exists.
Today, the first avalanche concern will be wet snow instabilities. The intense March sun, warm daytime temperatures, and weak overnight refreeze will all work together to form water in the snowpack today. This water will quickly melt the bonds holding the snowpack in place and weaken the snowpack. The snowpack could weaken to the point that a person moving across the snow could overload the snowpack and cause it to fail today. These wet snow instabilities will persist until the snowpack refreezes. They will be most prevalent on the E-SE-S-SW-W aspects that receive sun today.
The second concern will be the hard wind slabs that still exist on N-NE aspects near and above treeline. People could still trigger avalanches involving these wind slabs in some areas where they have not fully bonded to the snow below them. If they do occur, avalanches resulting from failure of these slabs should only entrain the recent storm snow.
The bottom line:
Near and above treeline, pockets of MODERATE avalanche danger exist on N-NE aspects, 37 degrees and steeper. On E-SE-S-SW-W aspects, the avalanche danger will increase to MODERATE on slopes steeper than 35 degrees for all elevations due to daytime warming.
Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:
0600 temperature: | 31 deg. F. |
Max. temperature in the last 24 hours: | 36-42 deg. F. |
Average wind direction during the last 24 hours: | Southwest |
Average wind speed during the last 24 hours: | 25 mph |
Maximum wind gust in the last 24 hours: | 49 mph |
New snowfall in the last 24 hours: | O inches |
Total snow depth: | 146 inches |
Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS
For 7000-8000 ft: |
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Wednesday: | Wednesday Night: | Thursday: | |
Weather: | Partly cloudy | Mostly cloudy | Mostly cloudy with a slight chance of showers in the afternoon |
Temperatures: | 46-53 deg. F. | 32-38 deg. F. | 48-54 deg. F. |
Wind direction: | West | Variable | Southwest |
Wind speed: | Light | Light | 10 mph |
Expected snowfall: | O in. | O in. | O in. |
For 8000-9000 ft: |
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Wednesday: | Wednesday Night: | Thursday: | |
Weather: | Partly cloudy | Mostly cloudy | Mostly cloudy with a slight chance of showers in the afternoon |
Temperatures: | 41-47 deg. F. | 32-36 deg. F. | 44-50 deg. F. |
Wind direction: | West | Southwest | Southwest |
Wind speed: | 10-15 mph with gusts to 25 mph | 10-20 mph with gusts to 30 mph | 10-20 mph with gusts to 30 mph |
Expected snowfall: | O in. | O in. | O in. |