Good morning, this is Sue Burak with the Inyo National Forest with an
   avalanche advisory for Wednesday December 17, 2008.

   MOUNTAIN WEATHER

   Cold weather continues all this week and into Christmas week. As one
   NWS forecaster wrote last night, temperatures are cratering under clear
   skies. Mountain locations will have morning lows of below zero and only
   warm up to around 12-18 today. Expect cloudy skies and light snow
   showers today. By tonight cold north winds will usher in the next
   system for Thursday night and Friday.

   The low that produced the latest dumpage has moved west and opened the
   door for more cold systems to drop south every couple of days. At this
   point in time, models are forecasting 6-12 of snow for the Tahoe Basin
   but if the moisture band loses strength, Mammoth Mountain and the
   Mammoth Basin might be the only locations that receive a few inches of
   snow. Winds will pick up over the ridgetops by Thursday afternoon but
   will nothing in comparison to the 100+ mph winds on Friday evening and
   Saturday.

   The coldest weather of the season is due over the weekend. The pattern
   will continue to be unsettled with the position of the longwave trough
   making it possible for cold Canandian air to dominate our weather.
   There is a storm forecasted for Sunday and Monday but we need to wait a
   few days to see if our area will receive any precipitation.

   SNOWPACK AND AVALANCHE DISCUSSION

   The lack of natural avalanche activity and very limited avalanche
   activity on Mammoth Mountain yesterday suggests the period of the
   greatest instability occurred during the storm. The snow settled a few
   inches today which is a sign of increasing stability but trail breaking
   is a wallowfest.

   I did several extended column and compression tests today. The extended
   column tests showed no results while the compression test gave easy
   results on two interstorm layers. The old snow and new snow interface
   did not fail. So which is the better test?

   The consensus among avalanche forecasters is that the extended column
   test gives more reliable results than the compression test for a couple
   of reasons. The ECT tests a larger volume of snow as the width of the
   isolated column is 90 cm compared to 30 cm for the compression test.
   The number of false positives or the number of times the test result
   show the snow is unstable when it really isn't is very small compared
   to the compression test. Just think of the number of times your
   compression test gave scary results and you skied the slope anyway and
   are here today to try a new and better test. I will post more
   information on the ECT in the next couple of days.

   BOTTOM LINE

   The avalanche danger rating today is MODERATE on slopes steeper than 38
   degrees. There are isolated areas of CONSIDERABLE danger on high
   elevation, north to east facing wind loaded slopes. CONSIDERABLE means
   dangerous avalanche conditions- be conservative in your selection of
   skiing and riding terrain and put one person a slope at one time. The
   MODERATE rating means human triggered avalanches are possible and
   dangerous avalanche conditions exist on some terrain features such as
   steep rollovers and convex slopes where the snow is under tension.
   Evaluate each slope carefully and use good travel habits. Cold
   temperatures reduce the amount of snow settlement so shaded north to
   east facing slopes will have the weakest snow.

   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.