Advisories Archived Advisories
| MSAC Avalanche Advisory (Archived-01-03-10 13:16:21) |
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Avalanche Advisory issued Sunday January 3, 2010 at 7:00 am By Eric White HAPPY NEW YEAR! The Bottom Line:Avalanche Danger Rating* for today:
*Most avalanche accidents occur during Moderate or Considerable avalanche danger.
Where: Pockets of 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.
Trend over next 4 days: Mild weather due to stable high pressure will bring relatively warm temperatures and light winds. This will allow the snow pack to continue to strengthen. However, wind slabs near and above tree line will still be possible to trigger, although they will become more stubborn every day. I expect the avalanche danger to slowly decrease this week with only isolated areas of instability. You may find different conditions - be observant!
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 73% 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. During the last storm series (12/30-1/1) we received 1.83 inches of water and approximately 15 inches of snow and moderate (20-40 mph) WSW winds blew for 60 hours straight near and above tree line. Weather Observations at 5 am: We have clear skies in town and calm winds. It is currently 30F in Mt. Shasta City and the barometer is stable. On Mt. Shasta: In the Old Ski Bowl, we are measuring 49 inches of snow on the ground at 7600 ft. with no new snow and 2 inches of settlement over the last 24 hours. Temperatures were between 20F yesterday morning to 33F this morning and the current temperature is 33F. Winds on the S side of Mt. Shasta at 8000 ft. (Grey Butte) have averaged 17 mph from the W and E during the last 24 hours with gusts to 42 mph from the W yesterday. Yesterday winds averaged 26 mph, gusting to 42 from the W. Winds decreased last night and this morning, averaging 8 mph from the E. Currently (6 am) winds are 4-7 mph from the SE and it is 35F. Castle/Mt. Eddy: On Mt. Eddy we are currently measuring 39 inches of snow on the ground at 6800 ft. with no new snow and 2 inches of settlement over the last 24 hours. Temperatures were between 23-38F and it is currently 30F. At Castle Lake we are measuring 36 inches of snow on the ground with no new snow and 2 inches of settlement over the last 24 hours. Temperatures over the last 24 hours were between 26-39F and it is currently 38F. Upper air measurements this morning show temperatures a few degrees warmer than yesterday morning. Weather Forecast: High pressure has developed over California and will bring warm temperatures and light winds this week. There is a slight chance on Monday for a couple snowflakes, but dry and stable weather looks like it will be with us all week as storms are pushed north into BC and SE Alaska. Today: Sunshine will warm temperatures into the mid 40's below tree line and winds will be light and variable. Above tree line temperatures will reach the mid 30's and winds will be 10-15 mph from the W, moving to the SSW this evening. On the upper mountain winds will be 15-20 from the W, moving to the SW this afternoon. Next 4 days: Temperatures near tree line will slowly warm this week, reaching their warmest on Thursday. Winds below tree line will move to the SE to SW on Monday at 5 mph, then become light and variable through Thursday. Above tree line winds will be 15-25 mph from the SSW on Monday, then they will move N to E at around 10 mph Tuesday through Thursday. Snow Pack: A rain crust developed from the New Years' freezing rain. In some places it is supportable, especially for lighter people, but remains challenging and plenty of craters were formed yesterday as people tried to make some turns. Above tree line firm wind packed powder and firm wind scoured areas can be expected until the sun softens them. In stability tests yesterday just above tree line on a wind loaded SE slope (28-30 degrees), failures occurred 1-1.5 ft. below the surface near the base of the storm snow, as they did on Friday. In the Extended Column Test (ECT) failures occurred with easy to moderate force, but without propagation (ECTN10). On a Rutschblock test, it failed 1 ft. below the surface on top of an ice layer and slide smoothly on the first jump (R4 Q1). 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 Thursday, Friday and Saturday loading N/NE/E/SE aspects and they will become even more sensitive today as temperatures warm and solar radiation affects the snow. Avoid these wind loaded areas near and above tree line - wind slabs sound hollow. Shooting cracks are another sign of wind slabs and avalanche danger. For those heading into Avalanche Gulch today (Chet), I would stay on the middle moraines away from Casaval ridge, go no higher than Helen Lake and avoid the gullies. These winds slabs will become more stubborn every day this week as stability improves, but I'm going to stay away from them!
The pesky rain crust we received from a freezing rain event on New Years' Day (left photo). The right photo shows the slab released on stability tests 1/2/10 with moderate force . 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: Avalanche Awareness: Friday night, January 15, 6 pm at the Mt. Shasta Library, 515 E. Alma St. A National Weather Service Meteorologist and Climatologist will briefly discuss the climate forecast for our area at the start of the talk. Don't miss this opportunity! Avalanche Transceiver Clinic: Saturday, January 16, 9 am at The Fifth Season, 300 N. Mt. Shasta Blvd. We will do this with or without snow and dress to be outside regardless of weather. 8th Annual SNOWBALL: Saturday, January 23 beginning at 7 pm and held at the Weed Sons of Italy hall. This fundraising event by the Friends of the Mt. Shasta Avalanche Center is always a blast with tons of raffle items, music, dancing and a variety of beverages. This will be a joint event, working together with the Mt. Shasta Nordic Center. See you there! 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! The Five Red Flags of Avalanche Danger any time of year include: 1) Recent/current avalanche activity 2) "Whumpfing" sounds or shooting cracks 3) Recent/current heavy snowfall 4) Strong winds transporting snow 5) Rapid warming or rain on snow.
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