Eastern Sierra - Fri Apr 16 2010
Eastern Sierra avalanche advisory |
Updated April 16, 2010 - 8:25 am
The avalanche danger rating is estimated to be LOW today in the Mammoth, Convict Canyon and Rock Creek. There is no information available from the Bishop Creek area and no danger rating is assigned to Bishop Creek . The LOW danger rating means the snow is GENERALLY stable and it is unlikely you will trigger a slide. LOW also means you can kick off a small slide in a few north facing areas where there are pockets of windslabs or in extreme terrain. |
The ridge that brought us pleasant weather with highs in the low 50’s yesterday has been pushed off to the east by a storm system that arrived last night and then disappeared. The clouds and scattered snow showers forecasted for today are old news. Skies are clear this morning and gusty ridgetop winds are blowing.
In the Mammoth area, damp winter snow from the weekend storm appears to have bonded to the old snow surface at least in the handful of shallow pits I dug today. Test pits in north facing terrain above 10,000 ft failed to produce any shears. Pounding on the shovel just compressed the new snow and broke it up in ragged uneven chunks. However, just because the snowpack is generally stable, does not mean you can’t trigger a small slide in really steep terrain.
At the 10, 500 ft elevation in Rock Creek Canyon on Tuesday, I found the old depth hoar layer at the bottom of a meter deep pack. The depth hoar was coarse and dense from melting and refreezing multiple times. While depth hoar is not reactive now, this layer could become a concern if spring ever comes and we get into a weather pattern where days are warm and nights stay a degree or two above freezing.
Clouds and light winds today can heat up the snowpack even more than a clear day. Watch out for small wet point releases starting above you along rock bands and cliffs. I did not see any fresh point release slides in steep north facing terrain today but with lots of damp powder in the Lakes Basin, a small point release could entrain a large amount of snow- see Josh’s observation from Tuesday. http://esavalanche.org/node/391
Clouds and light winds are expected to bring a slight chance of snow showers this afternoon. Highs at the 8,000 to 9,000 ft elevations won’t cool off much from yesterday and highs are expected to reach the upper 40’s. Higher elevations above 10,000 ft will be partly cloudy. Highs this afternoon above 10,000 ft will be in the low to mid 40’s. There will be breezy south to southwest winds between 15-25 with gusts to 35 mph.
Saturday will be sunny with clouds expected to roll in in the afternoon.
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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