Good morning, this is Sue Burak with the Eastern Sierra Avalanche Center with an avalanche advisory posted on January 24, 2008. Apologies for the late advisory- high speed internet access problems this morning required sending this via dialup. The beacon basin training facility at the USFS is operational. With new snowfall and windy conditions, the avalanche danger has gone up. Practice your beacon skills- your partners will appreciate your investment in their safety. MOUNTAIN WEATHER Predicting when and how much snow will fall when closed lows lurk off the west coast is a National Weather Service forecasters nightmare. The low wobbled a few miles yesterday and two feet of snow fell in Lee Vining and 28 inches ended up on June Mountain. Dont blame NWS forecasters if you are skiing over 2 feet of dry powder on June Mountain when Mammoth Mountain has only 12 inches of new. After a brief break today, another low approaches the coast, bringing another foot of snow to the higher elevations through Friday. A winter storm watch is in effect from Thursday evening through Friday evening. Winds with this system will be from the south and southwest so upslope and lake effect snow from Mono Lake will end. Todays highs will be in the mid to upper teens today with lows in the lower teens. Strong west and southwest winds are blowing in the 40-50 mph range on Mammoth Mountain and Mt. Warren. Finally, another system could bring significant precipitation late Saturday and Sunday/Monday. Forecasters are talking about a very cold system digging south along the Pacific northwest coast. A southern branch jet streak (an area of maximum wind speed) could develop and head into the central Sierra with the northern branch jet energy over the Pacific Northwest. There is a chance the two jet streams could merge or couple up. What this means is that there will be a huge amount of lift which creates a lot of instability in the atmosphere. This is very good for heavy snowfall. SNOWPACK AND AVALANCHE DISCUSSION 24 hour snowfall amounts range from 5-8 inches south of Mammoth with 12-15 above 9,000 ft in the Mammoth Lakes Basin. These are study plot measurements and do not reflect what I observed yesterday at elevations from 7,500 to 10,000 ft. In some places, the old snow surface was exposed, in contrast to wind loaded slopes with 12-18 of wind drifted snow. Mt Warren winds were pegged at 35-45 from the SSE for over 48 hours. Wind speeds greater than 10 mph will move snow. Cold temperatures and 4-6% density snow mean it takes even less wind to move snow. Yesterdays weather brought southeast winds to low and high elevations. Northwest slopes were loading quickly in the terrain I was traveling in. It was easy to trigger small slabs on west northwest to north facing slopes in lower angle terrain. It should come as no surprise to anyone that the avalanche danger has increased significantly. New snow and strong winds are the perfect setup for dry slab avalanches. Wind loading patterns are complicated because over the last two days, winds were from the southeast, especially in the Tioga Pass area. This morning, strong winds are from the southwest and west. This means slopes have been loaded on northwest to northeast aspects. I would look for wind loading on east aspects also. Look out for chalky deposits of wind drifted snow, and use caution if you are using ski cuts to test stability. Also consider consequences of triggering a slab avalanche- if you cut off a thick slab (greater than 2 feet) the uncertainty of where it will propagate increases- it could break above you. BOTTOM LINE With new snowfall with more on the way along with strong winds, expect natural avalanche activity. Human triggered avalanches are probably. The avalanche danger rating is CONSIDERABLE on all west to east slopes greater than 30 degrees AND on any slope with a wind load. Lower angle terrain not affected by the wind has a MODERATE rating. Please note that the avalanche danger rating in this advisory expires in 24 hours. This advisory is our best interpretation of snow pack conditions and NWS forecasts issued today. Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone exists between upper and lower elevations. Avalanches do not happen by accident and most human involvement is a matter of choice not chance. Most avalanche accidents are caused by slab avalanches that are triggered by the victim of member of the victim's party. Even small slides can be dangerous. Always practice route finding skills and carry avalanche rescue gear. Remember that avalanche danger ratings are only general guidelines. Distinctions between geographic areas, elevations, slope aspects and slope angles should be made.