Avalanche Advisory for Saturday, December 22, 2007 at 6:30am By Eric White The Details: This Season: We had a few early season hints of snow, then a dry spell with December starting to show signs of winter. Our precipitation is around 95% of normal. We currently have around 3 feet of new snow on a thin and week old snow surface. We are in a "La Nina" climate condition which often means wetter than normal winters in our area and expectations are above normal precipitation into the spring. Weather Observations: We currently have overcast skies. We have limited remote weather station data. Mt. Shasta - We have 40 inches of snow on the ground near tree line with no new snow over the last 24 hours. The snow settled 2 inches in the last 24 hours and temperatures have ranged between 5F to 26F at 7000 ft. and it is currently 18F. Winds this morning at tree line were estimated at around 39 mph from the W, and up to 23 mph from the WSW below tree line. On the upper mountain winds are estimated this morning at 40 mph from the W. Castle/Mt. Eddy - Mt. Eddy received no new snow in the last 24 hours with 3 inches of settlement. Temperatures were between 11F to 25F over the last 24 hours. We estimate around 30 inches of snow on the ground with brush showing. Lake basins reached cold temperatures of 2F yesterday morning, but are in the low 20's this morning. Weather Forecast: Over the next week, we will see a series of weak cold fronts passing through, each bringing a few inches of snow. Currently, we have a system hitting southern Alaska and the very bottom of the storm will hit our area by around 10 am today. 1-3 inches of snow are possible over the next 24 hours with the snow level near town (3-4000 ft), but reaching down to Dunsmuir (2500ft.). This storm is moving westerly which is not favorable for precipitation here. The next cold front will move in Sunday night and then again on Christmas night. For today, expect cloudy skies, light snow showers with temperatures in the mid 20's near tree line. Winds below tree line will be 5-15 mph from the SW, while at tree line, winds will be 20-30 mph from the W, moving to the NW later today. On the upper mountain, winds will be 30-40 mph from the W, then pick up this afternoon and evening as the north jet stream passes overhead. Snow Pack: We had reports from dawn patrol skiers yesterday of shooting cracks near tree line and very windy conditions. But by the time I made it up there, winds had become calm below 10,000ft. and no shooting cracks were observed near tree line. No natural avalanches were observed yesterday and during snow stability tests at 8400 ft. (SE aspect), I found moderate force failures in the top foot of snow in wind affected areas (Rutshcblock R4/Q2; Compression CTH23). I suspect at higher elevations, where wind loading occurred most of the day on S and E aspects, that things were much more sensitive. It stayed cool enough yesterday, that conditions in the trees will continue to be good. Continue to use caution near recently wind loaded areas, especially at and above tree line on south and east aspects. Watch for shallowly buried rocks, sticks and logs and snow collapsing near trees and brush. Photo of a Rutschblock test result on Mt. Shasta 12/21/07 Rutschblock test 12/21/07 on Mt. Shasta. 8400ft., SE aspect, 1pm, 26 degree slope. 25-30cm thick layer failed on first jump (160 lb skier)=R4. This would likely have failed more easily on steeper slopes, especially where greater wind loading was occurring. The slab layer was wind affected new snow where broken stellar crystals were still visible and water content of 14% was found. A thin layer of 10% water content and less wind affected snow was the weak layer and the bed surface was a dense, 20% water content layer of sintered rounds. 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 backcountry 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!