Good morning, this is Sue Burak with the Inyo National Forest Eastern
   Sierra Avalanche Center with an advisory for Friday, February 27, 2009.

   MOUNTAIN WEATHER

   Partly cloudy and breezy conditions will continue today. West winds
   will diminish today as a shortwave ridge builds into the area, but it
   still will be windy with gusts from 45-55 mph. Highs today above 9,500
   ft will be in the low 30s with lows in the upper teens and low 20s.
   High temperatures will be in the mid to upper 30s at the 8,000 to 9,000
   ft elevations. Temperatures will warm 5-8 F Saturday at all elevations
   as a thick band of clouds associated with the incoming storm moves into
   the area.

   This storm will be a prolonged event with pulses of precipitation
   coming Sunday night through Monday mid day. At this point in time,
   models predict snow and rain will begin Sunday afternoon in the Mammoth
   area. Snowlines will be around 8,000 ft Sunday, dropping to around
   7,500 ft. later Sunday night or early Sunday morning.

   The storm will be another northern California event with Tahoe and
   areas north getting most of the precipitation. Expect about one inch of
   water and around a foot of snow along the Sierra Crest north of
   Mammoth. Snowfall amounts drop of dramatically south of Mammoth with
   the southern Sierra expecting only snow showers with little
   accumulation from Sunday through Tuesday.

   SNOWPACK AND AVALANCHE DISCUSSION

   The nature of the avalanche hazard varies with elevation and location.
   Recent snowfall, sustained high winds from the southwest and west and
   persistent weak layers have created complex and dangerous avalanche
   conditions from the southern Sierra north to the Sonora Pass area.

   The primary avalanche concern today is unstable wind slabs. All along
   the ridgetops from Bishop Creek to Tioga Pass, strong, sustained winds
   and recent new snow from the weekend storm have created slabs. In many
   places, spectacular rivers of snow flowed down lee slopes. High
   ridgetop winds continue today and new and recent wind slabs will remain
   unstable and sensitive to human triggering.

   The other avalanche concern today is persistent weak layers. Much mid
   elevation terrain has a shallow snowpack consisting mainly of weak
   faceted snow, even after the snowpack got a little rain and some heavy
   dense snow last weekend. These areas with shallow snowpacks include
   Convict Lake and all points south to Mt. Whitney, and mid elevations
   from June Mountain to Virginia Lakes. Recent wet slab activity seemed
   to be confined to the 8,000 to 9,000 ft elevations on southeast to
   north facing slopes around the Convict Lake area. Faceted and striated
   weak snow remains above and below rain crusts and the end of January
   rain lens.

   On slopes ranging from about 8000 to 9,000 feet, wet snow avalanches
   will be the primary avalanche danger. Watch out for wet snow avalanches
   especially on steep slopes with rock outcrops- rocks get warm from end
   of February sun and can be the starting point for point release wet
   slides.

   People recreating in areas with a deeper snowpack need to remember
   buried weak snow layers were responsible for some big slides before,
   during and after the most recent storm. With deeper snowpacks, the load
   of a skier is less of a proportion of the total load on the buried weak
   layer than the snowpack, but you are still adding a load to the weak
   layer. There is no method or test available that will test deep
   instability; even if you dig to the ground, snowpit tests are reliable
   to about 1 to perhaps 1.5 meters down from the snow surface.

   Observers from the southern Sierra report the January rain layer is
   present on north and east facing snow filled gullies above 8,000 ft.
   There was one report of the layer above 10,000 ft. Persistent weak
   layers near the base of the snowpack require slope by slope evaluation
   of how reactive these weak layers might be if you plan to ski steep
   high elevation terrain that is less than about 5 feet deep.

   BOTTOM LINE

   Today the avalanche danger is estimated to be CONSIDERABLE on all wind
   loaded slopes steeper than 35 degrees. Variable conditions and
   uncertainty require conservative decision making. Pick your route
   carefully- the avalanche danger rating is only a starting point. YOU
   CONTROL YOUR OWN RISK by choosing where and when you travel. All other
   slopes will have a MODERATE danger. The MODERATE danger rating means
   there are localized or individual slopes, gullies or bowls that can be
   unstable and it is possible you could trigger an avalanche.

   Please note that the avalanche danger rating in this advisory expires
   in 24 hours. 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. Avalanche danger
   ratings are only general guidelines. Distinctions between geographic
   areas, elevations, slope aspects and slope angles should be made.