Eastern Sierra - Sun Apr 11 2010
Eastern Sierra avalanche advisory |
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The avalanche danger is LOW this morning. As new snow accumulates this afternoon and tonight, the avalanche danger will jump to at least MODERATE or CONSIDERABLE on Monday. There will be new snow, fresh wind slabs by Monday and a greater chance of triggering wind slabs on steep slopes This storm has the possibility of producing locally heavy snowfall. |
The calendar still reads April but the conditions will be back to January by this afternoon. It’s cold and windy, and we are about to get a winter type storm complete with a foot or more of cold dry powder and strong gusty winds. In the Mammoth area, winter like snow remains in chutes and gullies from 11,000 t around 9500 ft. Elsewhere, the snow is in transition from breakable to supportable crusts; each softening with sun and warmth by mid to late morning.
An experienced party turned around at around 11,000 ft in the Mt Morrison area on Thursday, when supportable snow from last week’s storm snow suddenly changed to a wallowfest in facets and depth hoar. Total snow depth was about 30 inches with about 10 inches of dry to moist powder sitting on top of 1.5 to 2 ft of low density facets. This is a good reminder that weak faceted snow still exists in isolated areas with shallow snowpacks. Once spring returns, areas of shallow weak snowpacks could be the next wet slab avalanche- especially in the Convict area.
Wind gusts were blowing snow off Sierra Crest ridgetops yesterday. The wind and cooler temperatures kept the snow surface from softening up above 9500 ft in the Bishop area. Southeast slopes were peppered with icy “chicken heads”. Thick melt freeze crusts above moist winter snow formed a 5-8 inches layer above the stout melt freeze formed near the end of March. Look for this layer to become a possible sliding layer once spring weather returns.
Avalanche conditions are LOW this morning but watch for wind drifts by the afternoon when snowfall begins. This advisory will be updated Monday morning.
A Winter Storm Warning has been issued for 10-18” of new snow in the upper elevations of Mono and Inyo County. The position of the jetstream and orographics favors our area and the southern Sierra. Snow will begin to fall at the higher elevations of Mono County by midday and the heavy snow is expected to fall at a rate of several inches an hour from around 5 PM this afternoon through 9AM Monday morning. Bishop Creek and areas south will see snow a couple of hours later.
Winds will mostly be from the south and southwest for this storm with average wind speeds in the 40-60 mph range with gusts to 90 mph at the mid elevations. Higher elevations will be windy with gusts up to 100 mph.
Temperatures today will really cool off with highs only to reach the mid to upper 30’s at the 8,000 to 9500 ft elevations. Higher terrain will be about 10 degrees colder than yesterday with highs reaching the upper 20’s.
For Monday, snow showers will continue all day with the possibility of a period of heavy snow showers Monday afternoon into the night. By late Monday the system moves on eastward with drying conditions on Tuesday. The Owens Valley should see some rain from this system, particularly Sunday night into Monday morning.
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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