The Mt. Shasta Avalanche Center - US Forest Service  

Avalanche Awareness talk tonight with Dan & Brett, 6 pm, Mt. Shasta City Library - Free

Avalanche Advisory issued Friday January 15, 2010 at 7:00 am  

By Eric White                       

The Bottom Line:

Avalanche Danger Rating* for today:

Where:  Pockets of CONSIDERABLE avalanche danger on wind loaded slopes greater than 35 degrees near and above tree line SE/E/NE aspects;  MODERATE elsewhere

Primary Concern:   wind slabs near and above tree line 

Secondary Concern:  storm slabs near and above tree line on steep slopes

Size and Character:  medium sized wind slabs (blocky); small to medium sized storm slabs (soft)

Sensitivity to Triggering:   wind slabs will be easy to trigger but a little more sensitive during the warmest parts of the day; storm slabs will be less sensitive to trigger by individuals but easier for machines

Level of Uncertainty in today's Forecast:  Low.  We had a good look at the snow yesterday and feel confident in 24 hour 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 80% 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 snow pack was subjected to very cold temperatures in early December creating a weak layer on the ground. 

Weather Observations at 5 am:  We have clear skies in town and calm winds.  It is currently 34F in Mt. Shasta City and the barometer is decreasing.   On Mt. Shasta:  In the Old Ski Bowl, we are measuring 64 inches of snow on the ground at 7600 ft. with no new snow and 1 inch of settlement over the last 24 hours.  Temperatures were between 25F yesterday morning to 40F yesterday afternoon and it is currently 32F.  Winds on the S side of Mt. Shasta at 8000 ft. (Grey Butte) have averaged 12 mph over the last 24 hours and were from the WSW yesterday and the SSW over the last 12 hours.  At 6 am winds are 15-28 mph from the SW and it is 32F.   Castle/Mt. Eddy:   On Mt. Eddy we are currently measuring 43 inches of snow on the ground at 6800 ft. with no new snow and little settlement over the last 24 hours. Temperatures were between 25-36F and it is currently 33F.  At Castle Lake we are measuring 34 inches of snow on the ground with no new snow and little settlement over the last 24 hours.  Temperatures over the last 24 hours were between 28-44F and it is currently 36F. Upper air measurements this morning show temperatures a few degrees warmer than yesterday.

Weather Forecast: It looks like Winter will finally arrive this weekend and cool and wet weather will continue over the next week to week and a half.  The satellite image this morning shows a plume of moisture from the tropics heading all the way to BC, Canada.  This will bring high clouds to our area today and the first part of the storm series will arrive Saturday afternoon with most of the precipitation arriving on Sunday.  The snow level will begin dropping Saturday and Sunday to around 4500 ft. and lower on Monday.  Winds will begin increasing today in front of the changing weather.  Today, look for high clouds with no precipitation expected.  Below tree line temperatures will warm to the mid to upper 30's with winds at 10 mph from the SSE.  Near and above tree line, temperatures will reach the mid 30's with winds from the SSW at 20-30 mph, increasing to 40-45 mph.

Snow Pack:  A natural avalanche occurred yesterday morning above tree line on a SSE aspect.  While it was relatively thin (10 inches), it was wide and traveled through a boulder field, dropping 600-1000 ft.  We found similar results during stability tests (see video link below).  The top 20 inches of snow, from the surface down, looked like this:  2 inch wind slab, 8 inches of dense snow, 10 inches of lower density soft snow, sitting on a strong rain crust.  This "upside down" layering is a classic type of instability.  With this information it would be wise to continue to avoid wind loaded slopes near and above tree line and watch for failures on other aspects on steep slopes (35 degrees or greater).  One of the questions with the wet forecast is how the new storms will bond and/or affect the current snow.  Conditions were still good for riding and sliding yesterday with the dense snow keeping people near the surface.  Above tree line wind packed powder was good with OK to good conditions in the trees.  Watch for open areas to develop a thin crust this morning.

Link to video showing Rutschblock stability test 1/14/10

Link to video showing stability test 1/9/10 

Link to video showing the 1/2/10 Pelican Butte avalanche accident (recovered alive) Thanks Jim B!

Link to short video #1 from 1/2/10 showing wind loading Mt. Shasta

Link to short video #2 from 1/2/10 with Rutschblock test results, Mt. Shasta

Link to short video showing shallow snow pack 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.  

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