Fourteen inches of new snow with over an inch of moisture has fallen in the mountains since about 6 PM last night. Old snow surfaces are slick and exist on west through north to east facing aspects at the upper elevations (above an elevation of 9,000 feet) and on steep north facing terrain above an elevation of 8,000 feet. Human triggered avalanches are likely in steep terrain on those old snow surfaces. These avalanches could be large enough to bury or seriously injure a person. Avalanches are unlikely at the lower elevations and in areas at the mid and upper elevations where last night's new snow has accumulated on bare ground.
West-northwest to west-southwest winds will continue to load leeward aspects. Soft slabs avalanches up two feet in depth could be human triggered on slick old snow surfaces.
( Discussion is generated from the previous day's afternoon forecast. )By Thursday night a low pressure system will move into western Washington. This system will tap into a strong push of Pacific moisture. Areas of light to moderate snowfall are forecast to develop over our mountains overnight and continue through the day. Snowfall is expected to become more widespread and increase on Friday and into Friday evening. Significant snowfall is expected in Yellowstone and the Teton, Gros Ventre and Wind River Ranges.Several inches of new snow are likely at the higher elevations overnight. Favored areas could receive 5 to 10 inches. Another 4 to 8 inches are possible on Thursday. Temperatures will remain in the 20s in the mountains. Winds overnight will be from the west-southwest at speeds of 28 to 33 with gusts to near 50 miles per hour. Thursday's winds will continue to be from the southwest at speeds of 22 to 27 with gusts to 36 miles.At the higher elevations strong winds and new snow will begin to load slick old snow surfaces. As the new snow depths increase, small natural and human triggered wind slab avalanches will likely occur on those old snow surfaces. Those avalanches will gain depth and size as this storm progresses. On Thursday new wind slabs could build to depths of 6 to 18 inches in favored areas. Monitor conditions and adjust travel plans accordingly. Avalanches are unlikely in areas where the new snow is accumulating on bare ground. The general avalanche hazard in steep terrain at the upper elevations is expected to be on the increase. The general avalanche hazard may rise from LOW to MODERATE at the upper elevations if the snowfall forecast verifies. Daily evening and morning avalanche hazard bulletins will be issued by the Bridger-Teton National Forest Avalanche Center beginning now. Updates and improvements to the internet programming necessary to post these bulletins have been conducted over the summer and therefor some new glitches are possible during the first several days of this season. Your patience is greatly appreciated.
