This Avalanche Advisory was published on February 22, 2012:
February 22, 2012 at 7:39 am | |
Avalanche danger is LOW for all elevations and aspects. Minor warming instabilities are expected on all aspects on slopes 37 degrees and steeper. Normal caution is advised. |
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Forecast Discussion:
Continued could cover last night kept air temperatures right around freezing for all elevations. Some sun is expected to show through the cloud cover today. The warm start to the morning will contribute to significant daytime warming with air temperatures in the mid 40s to low 50s expected above 7,000'. Today is expected to be the warmest day of the week. Ridgetop winds remain moderate in speed out of northeast this morning and are forecast to shift to the northwest, remaining moderate in speed. For tomorrow, the forecast calls for sunny skies, moderate speed northeast winds, and air temperatures 5 to 10 degrees cooler than today.
Observations made yesterday on Carpenter Ridge (Independence Lake area) and on Stevens Peak (Carson Pass area) both revealed evidence of a stable snowpack with wet snow forming on the snow surface on northerly aspects (pit profile, more info). Observations made yesterday on Rubicon Peak (West Shore Tahoe area) also showed a stable snowpack with evidence that initiated fractures are unlikely to propagate along the crust/facet interface at the base of the new snow from last week (videos, more info). This matches well with other observations from around the forecast area on Monday that also indicated that the once persistent weak layer of faceted snow and crust at the base of the last week's new snow is becoming less reactive by the day. This combination of weak layer and overlying slab exists in near treeline and below treeline areas on NW-N-NE aspects that were protected from scouring by strong NE winds on Feb 15. Most above treeline areas were heavily wind scoured during this event, removing the surface slab and exposing the crust at the snow surface.
Overnight cloud cover and air temperatures around 30 to 34 degrees at most elevations this morning are expected to have allowed for a weak refreeze to no refreeze of wet surface snow that formed yesterday. Areas where wet snow that formed yesterday in what had been unconsolidated surface snow on NW-N-NE-E aspects are now expected to have a breakable crust on the snow surface.
Today's Primary Avalanche Concern: Wet snow
With air temperatures climbing well above freezing and solar radiation getting closer to spring strength each day, areas of wet snow will exist on all aspects today. High density wind affected snow surfaces are expected to remain supportable. Areas of very shallow snowpack with exposed rocks and bushes will likely become unsupportable. Wet snow instability is expected to remain fairly limited and not present a significant threat to backcountry travelers. In areas where wet snow becomes boot top deep, avoiding slopes above terrain traps such as cliffs and creek beds is a good idea as these terrain features greatly magnify the consequences of an otherwise small and inconsequential wet loose snow avalanche.
Today's Secondary Avalanche Concern: Persistent Slabs
It appears that the persistent weak layer of faceted snow and crust at the base of the recent new snow is taking a break for a while and going to sleep. Finding the right isolated pocket of lingering instability and triggering a slab avalanche near or below treeline on a NW-N-NE aspect is unlikely at this time. Continue to use caution and exercise good travel habits in order to minimize risk. This weak layer will now warrant close monitoring leading up to the next snowpack loading event when it could reactivate and become unstable, possibly contributing to deep slab avalanches.
The bottom line:
Avalanche danger is LOW for all elevations and aspects. Minor warming instabilities are expected on all aspects on slopes 37 degrees and steeper. Normal caution is advised.
Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:
0600 temperature: | 30 to 34 deg. F. |
Max. temperature in the last 24 hours: | 36 to 42 deg. F. |
Average wind direction during the last 24 hours: | Northeast |
Average wind speed during the last 24 hours: | 25 mph |
Maximum wind gust in the last 24 hours: | 45 mph |
New snowfall in the last 24 hours: | O inches |
Total snow depth: | 23 to 31 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 skies becoming sunny. | Partly cloudy skies. | Partly cloudy skies becoming sunny. |
Temperatures: | 44 to 51 deg. F. | 26 to 33 deg. F. | 34 to 41 deg. F. |
Wind direction: | NW | NE | NE |
Wind speed: | 10 to 15 mph with gusts to 25 mph. | 10 to 20 mph with gusts to 30 mph. | 10 to 15 mph with gusts to 25 mph. |
Expected snowfall: | O in. | O in. | O in. |
For 8000-9000 ft: |
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Wednesday: | Wednesday Night: | Thursday: | |
Weather: | Partly cloudy skies becoming sunny. | Partly cloudy skies. | Partly cloudy skies becoming sunny. |
Temperatures: | 44 to 52 deg. F. | 27 to 34 deg. F. | 30 to 37 deg. F. |
Wind direction: | NW | N | NE |
Wind speed: | 15 to 30 mph with gusts to 45 mph. | 25 to 35 mph with gusts to 55 mph. | 20 to 30 mph with gusts to 45 mph. |
Expected snowfall: | O in. | O in. | O in. |