The Mt. Shasta Avalanche Center - US Forest Service  

Avalanche Advisory issued Saturday January 2, 2010 at 7:00 am  

By Eric White                           HAPPY NEW YEAR!

The Bottom Line:

Avalanche Danger Rating* for today:

Where:  CONSIDERABLE on wind loaded slopes near and above tree line; MODERATE elsewhere.

Primary Concern:  wind slabs on N/NE/E/SE aspects, near and above tree line

Secondary Concern:  Deep slab instability due to several weak layers lower in the snow pack

Size and Character:  medium wind slabs (hard/blocky); medium sized deep slabs

Sensitivity to Triggering:   wind slabs will be sensitive in sunshine and during the warmest parts of the day, especially for machines; deep slabs will be hard to trigger

Level of Uncertainty in today's Forecast:  Low.  Good confidence with snow conditions and weather forecast.  

The Details:

This Season:  Moderate El Nino conditions exist in the equatorial Pacific.  Climatologists predict a 33% chance of above normal precipitation for much of northern California over the next 3 months, and higher chances of above normal precipitation in central and southern California.  Since September 1, our precipitation is 74% of normal in Mt. Shasta City (NWS ASOS station).  Our biggest storm so far this season began on Columbus Day and the thin early season snowpack was subjected to very cold temperatures in early December creating a weak layer on the ground.

Weather Observations at 5 am:  We have fog in town and calm winds.  It is currently 34F in Mt. Shasta City and the barometer rising.   On Mt. Shasta:  In the Old Ski Bowl, we are measuring 51 inches of snow on the ground at 7600 ft. with 4-6 inches of new snow over the last 24 hours.  During the last storm we received 1.19 inches of water and approximately 10 inches of snow.  Temperatures were between 19F this morning to 28F yesterday and the current temperature is 19F.  Winds on the S side of Mt. Shasta at 8000 ft. (Grey Butte) have averaged 22 mph from the WSW during the last 24 hours with gusts to 42 mph from the W this morning.  Currently (6 am) winds are 30-42 mph from the W and it is 21F.   Castle/Mt. Eddy:   On Mt. Eddy we are currently measuring 41 inches of snow on the ground at 6800 ft. with 6 inches of new snow and 2 inches of settlement over the last 24 hours.  Storm total of 10 inches of new snow. Temperatures were between 20-33F and it is currently 21F.  At Castle Lake we are measuring 38 inches of snow on the ground with 4 inches of new snow and 1 inch of settlement over the last 24 hours.  Temperatures over the last 24 hours were between 25-33F and it is currently 25F.  Upper air measurements this morning show temperatures 1 degree warmer than yesterday morning. 

Weather Forecast:  High pressure has developed over California and will push a storm north of our area.  Moisture from this storm will be passing overhead bringing some high clouds to our area and drizzle in the coast range this morning.  We will see partly cloudy skies today.  Models show high pressure through the weekend with a chance of precipitation this week as storms focus north of our area.  Below tree line today temperatures will warm to the mid 30's with light and variable winds.  Above tree line, temperatures will warm to the upper 20's and winds will continue from the W to NW at 25-30 mph, gusting to 40 mph, then slowing down later today and tonight to 10-20 mph from the W. 

Snow Pack:  Powder was short lived yesterday as moist clouds brought rain and freezing rain below around 7500 ft.  With skies clearing and temperatures dropping, most areas have developed a rain crust from the rain yesterday.  In stability tests yesterday below tree line, failures occurred 1 ft. below the surface near the base of the storm snow.  In some areas the weak layer was graupel where it had collected, other areas on a density change.  Weak layers (facets) deeper in the snow pack exist, but will be hard to trigger.  The biggest concern today remains with wind slabs above tree line.  We have had steady SW to W winds for 48 hours loading N/NE/E/SE aspects and they will become even more sensitive today as temperatures warm and solar radiation effects the snow.  Avoid these wind loaded areas near and above tree line - wind slabs sound hollow and be observant for moving snow!  Shooting cracks are another sign of wind slabs and avalanche danger.

Large facets found in thick layer near ground.  Mt. Shasta, December 26, 2009, 7400 ft., NW aspect.  This weak layer has been persisting for 3 weeks and continued temperature gradients with thin snowpack will help this to remain a concern on steep slopes with sparse to no anchors.  Look for large (2-4 mm) angular grains.  The total width of this photo is 13.5 mm.

Link to short video showing shallow snowpack and facet layer on ground, 12/24/09.

Some Important Thoughts:  This advisory does not apply to Ski Areas or Highways and is for the Mt. Shasta, Castle Lake and Mt. Eddy back country.  Use this information for guidance only.  You may find different conditions in the back country and should travel accordingly.  This advisory expires at midnight tonight.  As always, use safe travel practices:  travel with a partner, travel one at a time in suspect areas, go from one island of safety to another, choose safe routes, wear a transceiver, carry a shovel and probe, and know how to use your gear!

Pilgrim Creek Snowmobile Park:  Not enough snow for grooming yet.

MSAC Upcoming Events:

Go to "Photos/Avy Shots" for photos of recent avalanches.

Go to "Forums", "Snow pack Videos" to see past snow pack videos.  

Please report weather and snow observations:  (530)926-9614  Thanks!