This Avalanche Advisory was published on March 3, 2009:
A strong storm system is continuing to impact the forecast area. Snow levels have lowered below 5,000' this morning and are expected to remain fairly stationary today. At 8,000', storm totals thus far are around 20 to 24 inches. Another 24 to 40 inches of new snow is expected above 7,000' during the next 24 hours. Air temperatures this morning are in the 20s in most locations. A few degrees of warming are expected to occur through the day today. Ridgetop winds remain strong out of the southwest this morning and will continue through tonight.
Yesterday, observations made on Hidden Peak (West Shore Tahoe area) indicated that snow levels had risen as high as 8,000' during this storm cycle. Between 8,000' and 9,000', a layer of higher density new snow was observed at the snow surface. This layer was sitting on top of a thinner layer of lower density new snow that fell on Sunday. Stability tests indicated good bonding of these two layers. Despite the very distinct slab characteristics, no indication of fracture propagation potential was observed. Between 7,000' and 8,000', very high density new snow was well bonded to the rain crust layer below. Below 7,000', alternating periods of rain and snow occurred during the day. This morning, some small grain faceting was noted above yesterday's rain crust at the Alpine Meadows snow study plot at 6,800'.
Avalanche activity that occurs today is expected to occur on yesterday's rain crust or fail within the storm snow. An increase in snowfall intensity today is expected to cause greater snowpack instability than what was observed yesterday. Air temperatures have cooled overnight, but are expected to warm a few degrees during the day. This will create an opportunity for weak layers to form within the new snow, especially in wind loaded areas on steep NW-N-NE-E-SE aspects. Natural and human triggered avalanches several feet deep will become possible due to the new snow amounts expected in the next 24 hours.The recent deep slab instability just above the January 22-23 rain crust has become quiet but is not forgotten. Avalanches that occur today hold a small potential to step down to this layer, creating larger and more destructive avalanches.
The bottom line:
Near and above treeline, avalanche danger is HIGH on NW-N-NE-E-SE aspects, 35 degrees and steeper. Below treeline, avalanche danger is MODERATE with pockets of CONSIDERABLE danger in open, wind affected areas, 37 degrees and steeper.
Weather Observations from along the Sierra Crest between 8200 ft and 8800 ft:
|0600 temperature:||20 deg. F.|
|Max. temperature in the last 24 hours:||31 deg. F.|
|Average wind direction during the last 24 hours:||Southwest|
|Average wind speed during the last 24 hours:||70 mph|
|Maximum wind gust in the last 24 hours:||134 mph|
|New snowfall in the last 24 hours:||8 to 12 inches|
|Total snow depth:||145 inches|
Two-Day Mountain Weather Forecast - Produced in partnership with the Reno NWS
For 7000-8000 ft:
|Weather:||Cloudy skies with snow. High intensity snowfall at times.||Cloudy skies with snow. High intensity snowfall at times.||Cloudy skies with snow, tapering to snow showers by noon.|
|Temperatures:||22 to 29 deg. F.||12 to 19 deg. F.||23 to 29 deg. F.|
|Wind speed:||15 to 30 mph with gusts to 50 mph.||15 to 30 mph with gusts to 50 mph.||10 to 15 mph with gusts to 25 mph.|
|Expected snowfall:||12 to 20 in.||12 to 20 in.||2 to 5 in.|
For 8000-9000 ft:
|Weather:||Cloudy skies with snow. High intensity snowfall at times.||Cloudy skies with snow. High intensity snowfall at times.||Cloudy skies with snow.|
|Temperatures:||21 to 27 deg. F.||10 to 17 deg. F.||17 to 23 deg. F.|
|Wind speed:||60 to 70 mph with gusts to 100 mph.||40 to 55 mph with gusts to 85 mph.||25 to 35 mph with gusts to 60 mph.|
|Expected snowfall:||12 to 20 in.||12 to 20 in.||3 to 5 in.|