Avalanche Advisory for Thursday, December 20, 2007 at 6:30am By Eric White The Bottom Line: Avalanche Danger Rating for today: Trend: Extreme Widespread natural or human triggered avalanches are certain High Natural and human triggered avalanches are likely. ] Considerable Natural avalanches are possible and human triggered avalanches are probable. Moderate Natural avalanches are unlikely. Human triggered avalanches are possible. Low Natural avalanches are very unlikely. Human triggered avalanches are unlikely. & Avalanche Danger is expected to Increase " Avalanche Danger is expected to continue at this rating ( Avalanche Danger is expected to Decrease Where? Above 6000 ft on Easterly and Northerly aspects greater than 35 degrees. Size and Character: Medium sized slabs below tree line and medium hard slabs ( wind slabs) above treeline. Sensitivity to Triggering: Wind slabs at and above tree line will be sensitive and could be triggered by an individual. Level of Uncertainty in forecast: Low Moderate High The next Avalanche Advisory will be posted: 12/21/07 --- 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 97% 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 over the next few months. Weather Observations: We currently have limited remote weather station data. Mt. Shasta - We currently have 43 inches of snow on the ground near tree line with around 9-12 inches of new snow over the last 24 hours. The snow settled 2+ inches overnight. In the last 24 hours temperatures have ranged between 25F to 29F at 7000 ft. and it is currently 25F. We have a storm total of 40 inches of new snow and around 4.5 inches of water content. Winds this morning above tree line were estimated at around 40 mph from the W, and around 25 mph below tree line from the W. Castle/Mt. Eddy - Mt. Eddy received around 11 inches of new snow in the last 24 hours with 3 inches of settlement. Temperatures were between 23F to 27F over the last 24 hours. We estimate around 3 feet of snow on the ground. Radar this morning shows scattered showers in the State of Jefferson. Weather Forecast: The front is moving through now and snow showers will be possible today with the snow level below town and a dusting to 2 inches possible. Temperatures will cool today as the cold air mass arrives and dry conditions are expected Friday. A few weak systems will arrive this weekend beginning Saturday morning with a stronger system Monday. We may have a break on Christmas morning with another storm arriving that afternoon. Wet weather is expected over the next week with short breaks between storms. Today, expect temperatures in the teens near tree line and below zero at upper elevations (summit wind chill of -34F!). Winds below tree line will be light from the W, while above tree line winds will be 20-30 mph from the NW. As the jet stream passes overhead tonight, expect strong winds on the upper mountain (70+mph) from the N. Winds will decrease Friday. Snow Pack: We have had 3+ feet of snow fall over the last few days, most of it landing on a thin snow pack. Natural avalanches have been reported over the last few days. My concerns today are primarily with wind loaded slopes which could have 5-8 feet of new snow, especially above tree line. I would avoid these areas which are on N and E slopes today. By Friday morning, we will see some loading to S slopes as the winds increase and change direction. Continue to use caution and be observant today, enjoying the best conditions in the trees. Many people are excited for the beginning of winter recreation, but, don't let that blind you to the sensitive conditions which exist. Continue to watch for shallowly buried rocks, sticks and logs and snow collapsing near trees and brush. 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! Please give us comments on our new format and report weather and snow observations: (530)926-9614 Thanks! Some things to consider: Backcountry travelers should make terrain, weather and snow pack evaluations as they travel over snow covered terrain. Remember that seemingly insignificant slides may be dangerous. Almost half of all avalanche fatalities occur in slides traveling less than 300 feet. Early Season Watch Outs! * Surface sluffs and wind slabs * Shallowly buried rocks and trees can cause serious damage or injury. * Sink holes around brush and small trees can be dangerous. * Snow bridges over crevasses can be touchy and unsupportable. * Shallow snowpack with cold air temperatures can produce unstable snow These are just a few things you should watch out for when traveling during the early part of the winter season. 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.