Good morning, this is Sue Burak with the Inyo National Forests Eastern Sierra Avalanche Centers advisory posted on Sunday morning, May 18, 2008. SPECIAL ANNOUNCEMENT The last few days of unusually high daytime temperatures and warm nights have resulted in rapid snow melt. East side streams are running above normal for this time of year. The trail crossing at Genevieve Creek up Convict Canyon is impassable for most hikers and with runoff increasing with continued warm temperatures; it may become impassable in the next day or so. The first bridge crossing McGee Canyon has been lifted off the bridge supports. The best time to cross is early in the morning but remember you may have to cross again in the afternoon when flows are highest. MOUNTAIN WEATHER Hot weather continues until Tuesday when relief comes in the form of a long wave trough that will cool temperatures off by 10 to 15 F. This mornings NWS discussion mentions the possibility of cold temperatures and precipitation by the end of the week. Saturdays high temperatures were in the upper 60s and low 70s around the forecast area. The highest temperature was at Mammoth Pass, elevation 9,600 ft. with a high of 75! Main Lodge was 72F. Tioga Pass at 10,000 ft reached 68 and Gem Pass at 10,700 ft was 60 F. Charlotte Lake, one of the coldest places in the Sierra, had a high of 56F- the highest May temperature recorded since 1990. Today will be sunny with light winds. By Monday, temperatures above 9,000 ft begin to cool off, reaching the low 40s by Wednesday. Night time temperatures are ridiculously warm with lows in the 40s above 10,000 ft. Why this unseasonable warm weather? The East Asian jet is unusually strong with 115 mph winds at 35,000 ft supporting the high pressure ridge. Talk about high level support. See http://virga.sfsu.edu/gif/sathts_300_00.gif SNOWPACK AND AVALANCHE DISCUSSION For those of us trained in the energy balance approach to snow melt, we cringe when people say, its a hot day and the snow is melting. For those who read these advisories regularly, you know my pet peeve is the misconception that air temperature melts snow when temperatures are in the 40-60F range. However, when temperatures are 75F at 9,600 ft and 68 F at 10,000 ft, the air is melting as much snow as the sun. This is unusual because high elevation temperatures in the 70s are extremely rare until June and July. Its hard to get out early enough for decent skiing conditions when lows are 40 F. Night time lows have been above freezing for four days and will be warm Sunday and Monday night before the snow reverts to a frozen state. With snowpack densities over 60%, the pack is pretty stable except at the surface. Even at the surface, there is no much instability and there were only a few reports of skier triggered wet sluffs in the Tioga Pass area despite the crowds of people in steeper terrain. The usual precautions apply: avoid being on steep slopes with people skiing or riding above you. Pick a line off to the side just in case someone starts a wet sluff above you. The avalanche danger rating for the weekend is LOW in the morning, increasing to MODERATE by mid morning. BOTTOM LINE The avalanche danger rating for the weekend is LOW in the morning, increasing to MODERATE by mid morning. 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.