Eastern Sierra - Thu Jan 14 2010
Eastern Sierra avalanche advisory
Posted January 14, 2010 by Sue BurakUpdated January 14, 2010 - 3:51 pm
Jan 13th - The avalanche danger rating is estimated to be MODERATE today on upper elevation, northwest to northeast aspects with fresh deposits of wind transported snow. Watch out for dense deposits of wind drifted snow off ridgelines. Evaluate snow and terrain carefully and avoid convex rollovers. Avalanches will be small in isolated areas. Human triggered avalanches remain possible with these windslabs; evaluate conditions on individual slopes before riding or skiing.
Jan 13th - It felt like a spring storm yesterday-gusty winds, sun and clouds with scattered snow showers and warm temperatures. Snowfall began in earnest early this morning, with close to a foot of new snow this morning above 8500 ft. Snow will continue to fall through most of the morning. Areas south of Mammoth received only a few inches of new snow.
Snowfall started out slowly Tuesday evening-temperatures have stayed fairly warm, between 27-29F for the duration of the storm. After snowfall ends later this morning, temperatures will fall as north winds move in.
The main avalanche concern for today is windloading.
Above 8500 ft in the June and Mammoth areas, 9-12 inches of new snow came with strong southwest winds. Winds and dense new snow have created wind slabs on upper elevation northwest, north and northeast slopes below ridgelines. These areas will be sensitive to a skier or rider triggering today.
A secondary concern is weak snow near the surface of the snow now covered by close to a foot of new snow. Dry weather and cold winter nights created weak faceted snow on the surface of the snowpack. Over the last couple of days, very small amounts of new snow fell on this layer. While mild temperatures and wind destroyed much of the near surface faceted snow, it’s likely that areas of weak snow remain in sheltered areas in the trees, at treeline and possibly in the higher terrain on all aspects. This layer could be an issue today with a new snow load.
On Tuesday, we missed the brunt of a good moisture laden storm as the jet
steered the main flow north of our area. Temperatures last night resulted in
high snowlines and dense snow.
The second storm came in last night and the strong upper winds
created more upward lift resulting in high rates of snowfall early this morning.
Snow will continue through this morning with another 4-6 inches expected above 8,500 ft. Gusty strong ridgetop and mid level winds will continue through today with gusts over 70 mph.
Skies will become partly cloudy by this afternoon and Thursday will be mostly
sunny with strong northerly winds..
Elevations above 9500 ft could see 6-8” of snow today, acompanied by moderate west winds 25-30 mph. Ridgetop gusts will exceed 70 mph today. Daytime highs will be 15-20 degrees colder than Tuesday, with highs in the mid 20’s to 32 F. The dreaded north winds will blow snow around Wednesday night with windspeeds gusting to 45 mph. Thursday will be sunny and 10 degrees warmer with light north winds.
Mid elevations from 8,000 to 9500 ft could pick up 3-5 inches of new snow today, though it might be a rain/snow mix. Highs will be much cooler than Tuesday, dropping from the upper 40’s to 50F down to the mid 30’s. Thursday will warm up to the mid 40’s under sunny skies.
The big weather news brings joy to skier and rider’s hearts! One NWS forecaster told me to expect “monster’ storms next week. Things are coming together for a multiday storm event that could add 8-10” of water to the snowpack. The math is easy- 8 to 10 feet- not inches. The jet stream will be our friend next week. More on this in the next advisory.
Please note that the avalanche danger rating in this advisory expires in 24 hours. This advisory is our best interpretation of snow pack conditions and NWS forecasts issued today. Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone exists between upper and lower elevations. Avalanches do not happen by accident and most human involvement is a matter of choice not chance. Most avalanche accidents are caused by slab avalanches that are triggered by the victim of member of the victim's party. Even small slides can be dangerous. Always practice route finding skills and carry avalanche rescue gear. Remember that avalanche danger ratings are only general guidelines. Distinctions between geographic areas, elevations, slope aspects and slope angles should be made.
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