Good morning, this is Sue Burak with the Eastern Sierra Avalanche
   Center with an avalanche advisory posted for Thursday February 21,
   2008. 
   advisory.

   MOUNTAIN WEATHER

   After a clear cold night, perfect for viewing the lunar eclipse, a
   return to winter weather is here. The storm track has reopened over the
   West Coast and precipitation is expected every day for the next four
   days. There is a high likelihood of over 3 feet of new snow by Monday
   in the mountains in both Mono and Inyo counties.

   The storm for today and tonight is stronger than previously forecasted,
   with up to a foot of snow above 9,000 ft in Mono County by Friday
   morning. By Thursday afternoon the jet stream is forecasted to be
   located from Monterey Bay to Death Valley with a foot of snow expected
   above 9,000 ft in Mono County. Three to six inches of snow could fall
   along the 395 corridor, including Crowley Lake and Lee Vining.

   This storm will be accompanied with, no surprise, strong west winds.
   The wind wont be in the 60-100 mph for the Thursday event but with
   gusts over 40 mph, there will be plenty of snow moving around.

   High temperatures today will be similar to yesterday- highs around 30 F
   at 9,000 ft and in the mid 20s above 10,000 ft. Low temperatures will
   be in the low to mid teens.

   Friday will be mostly cloudy with snow showers and not much
   accumulation. Saturday morning will be the break as a potent storm
   comes in the afternoon and dumps snow in Mono and Inyo Counties
   Saturday night and into Sunday. This morning the California state
   meteorologist wrote, Saturday and Sunday bring another, juicier low
   across California. This will be very windy and wet. The long distance
   fetch that is conveying these lows into California is a jet that has
   stretched all the way back to Asia in one long, rare zonal jet stream.
   The weekend system is the crescendo of the increasing waves we've
   seen". Sounds good to me.

   SNOWPACK AND AVALANCHE DISCUSSION

   It is time to reset our terrain choices from skiing everything in sight
   to careful consideration of where wind loading is occurring. Stable
   late winter conditions will soon change with new snow and wind loading
   on lee facing slopes. As a reminder after 10 days of Low danger
   ratings, lee slopes are found behind high ridges, fall line ribs, rows
   of trees, convex parts of slopes, and gully walls.

   New snow will be falling on a variety of snow surfaces. Windward slopes
   in high alpine terrain have been stripped of snow- the Rock Creek side
   of the Wheeler Crest is a good example. On sun exposed east to west
   aspects, there is variety pack of frozen corn snow, sun crusts and wind
   board. Frozen sun crusts can be a hard bed surface for future
   avalanches to run upon. On the other hand, since sun crusts have a
   rough texture, snow deposited on the crust can bond fairly well.

   Hard dense snow compacted by the wind is the predominant snow surface
   in alpine terrain. Wind board makes a low friction sliding layer. There
   is also a lot of wind sculpted snow in west to east trending canyons
   like Piute Pass, Birch Creek, upper Horse Creek and Kidney Lake and the
   back side of Mammoth Mountain. Sastrugi can act to break up formation
   of continuous slabs unless new snow depths are greater than the height
   of the sastrugi. Some sastrugi is over two feet high.

   North and eastern aspects in sub alpine and alpine terrain are home to
   hard wind slabs as well as settled powder in glades and wind/sun
   protected gullies. With strong winds from the west and southwest and
   high precipitation rates, winds will be depositing snow onto north and
   east aspects.

   BOTTOM LINE

   With only a couple of inches of new snow falling yesterday, the
   avalanche danger rating remains LOW. In very isolated pockets of wind
   drifted snow in steep alpine terrain greater than 35 degrees, the
   danger rating is MODERATE. The danger rating in this advisory expires
   at midnight. Over the next two days, expect the avalanche danger to
   increase due to new snow and wind loading. I will be updating
   advisories on a regular basis until the storm cycle ends.

   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.