The Mt. Shasta Avalanche Center - US Forest Service  

Update Wednesday, 1/13, 8 am:  The storm which started Monday night and finished this morning has brought 1-3 ft. of snow (3-4 inches of water) and moderate winds from the SE/SW and W.  Concerns are raised with this new load adding stress to the snowpack, especially near and above tree line where wind loading has increased stress on N and E aspects.  As winds move to the NW, SE aspects will become a concern.  Cornices will be touchy and wind loaded slopes and their avalanche pathways should be avoided.  Below tree line, steep slopes will also have stress from the heavy snow fall, especially where wind loaded.  The Avalanche Danger has increased from this storm - watch for the 5 Red Flags of avalanche danger:  recent or current avalanche(s), recent or current heavy snow fall, wind transporting snow, "whumpfing" sounds, shooting cracks, rain or rapid warming.  Think before you drop...  

Avalanche Advisory issued Sunday January 10, 2010 at 7:00 am  

By Eric White                       

The Bottom Line:

Avalanche Danger Rating* for today:

Where:  MODERATE avalanche danger on slopes greater than 35 degrees above 9000 ft.;  LOW elsewhere

Primary Concern:   wind slabs upper mountain 

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

Size and Character:  very small wind slabs (blocky); small to medium sized deep slabs

Sensitivity to Triggering:   wind slabs will be hard to trigger but a little more sensitive during the warmest parts of the day; deep slabs will be very hard to trigger

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.

Trend over next 4 days:  A moderate storm will arrive late on Monday and bring up to a foot of snow. Winds will increase on Monday afternoon and continue to be moderate during the storm.  Strong winds will be possible after the storm on Wednesday and Thursday.  With the forecast precipitation and winds, the avalanche danger is expected to increase Tuesday through Thursday.  Be observant, check the snow pack and evaluate the conditions and consequences before you drop in or high mark.

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 67% 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 cloudy skies in town and calm winds.  It is currently a warm 42F in Mt. Shasta City and the barometer is steady.   On Mt. Shasta:  In the Old Ski Bowl, we are measuring 43 inches of snow on the ground at 7600 ft. with a trace new snow and 1 inch of settlement over the last 24 hours.  Our instruments measured 0.03 inches of water over the last 24 hours.  Temperatures were between 29F this morning to 36F yesterday afternoon and it is currently 29F.  Winds on the S side of Mt. Shasta at 8000 ft. (Grey Butte) have averaged 9 mph over the last 24 hours and were from the WSW yesterday and the SE over the last 12 hours.  At 6 am winds are 4-14 mph from the E and it is 28F.   Castle/Mt. Eddy:   On Mt. Eddy we are currently measuring 29 inches of snow on the ground at 6800 ft. with no new snow and little settlement over the last 24 hours. Temperatures were between 32-39F.  At Castle Lake we are measuring 27 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 34-43F and it is currently 34F. Upper air measurements this morning show temperatures a few degrees warmer than yesterday.

Weather Forecast: We have had a funny arrangement this week with a weak high pressure stationary and storms pushing over it bringing us very light precipitation.  The high pressure will last into Monday and then a storm will finally push it east and bring snow.  It looks like there will be more of a focus on the central and southern part of the state as the jet stream will move south of us .  High pressure will rebuild late on Wednesday and Thursday with a cold front possible on Friday.  Today:  The low clouds should burn off and we will have some sun today with a few clouds.  Temperatures below tree line will warm to the low to mid 40's and winds will continue to be light, mostly from the SSE.  In the tree line area, temperatures will warm to the low 30's and winds will be from the SE, moving to the SW at 10-15 mph.  All elevations should see winds increasing late tonight and early Monday.  There is a possibility for some light mist/rain tonight.  Next 4 days:  Winds will begin increasing on Monday afternoon and snow will start late on Monday with the snow level starting off at 7000 ft. and then dropping on Tuesday to 4500-5000 ft.  By Wednesday, the snow level will drop to 3500 ft.  Most of the precipitation will occur during the first part of Tuesday with 10-12 inches possible.  Watch for moderate to strong SSW winds to develop late on Monday and through early Tuesday.  Winds will again increase late on Wednesday and move to the NW.

Snow Pack:  With 10 days of warm temperatures and some rain below 8000 ft., we found the snow pack becoming warm and isothermal.  What this means is that snow is becoming more stable as the layers of weak grains (facets) are changing to stronger layers (wet rounds and sintered rounds) with strength improving throughout the snow pack. The thick weak layer which formed close to the ground in November and early December, was still showing large facets, but they were changing to wet rounds.  During stability tests, it took some force to get failures and they all occurred around 6-8 inches below the snow surface in some of the wet rain layers (Rutschblock R6; Extended Column Test ECTN 11 & 27).  Video link below.  So things look pretty good, but continue to be observant for different or changing conditions.  The next storm looks like it will come in warm and bond to the snow surface, then cool down and that is usually much more stable than the opposite.  Wind loading will be the biggest concern for avalanches.  Yesterday the best skiing was above tree line where 1-3 inches of new snow sat on a firm and supportable crust.  Things will soften today with sunshine. 

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!