Western Wyoming PM Forecast

Issued on Sat December 15, 2018 7:04 PM

Situation

Mostly cloudy skies over Western Wyoming produced a few light flurries as a weak Pacific disturbance moved across the region. Temperature inversions broke down with daytime highs in the mountains near 20. The valleys climbed into the upper 30s. Southwesterly to westerly ridgetop winds ranged from 20 to 35 miles per hour.

Ridgetop winds increased overnight and remained strong throughout the day. These conditions continued to build stiffer wind slabs in leeward terrain and on cross loaded slopes. A skier triggered one of these wind slabs on Broken Branch, which is a steep, east facing slope at an elevation of 9,000 feet just south of the Jackson Hole Mountain Resort. This slide was around 10 inches deep, but ran full track.

Forecast For Sunday, December 16, 2018

A transitory ridge of high pressure will build over the region on Sunday. Expect dry conditions and decreasing cloud cover as the day progresses. Overnight lows in the mountains will be in the low teens before rebounding into the upper 20s. Southerly to southwesterly ridgetop winds will decrease to 10 to 15 miles per hour.

The general avalanche hazard is expected to be Moderate above 7,500 feet on Sunday. Up there, skiers and riders could trigger wind slabs up to two feet deep on steep, wind loaded slopes. Terrain where these slabs are stiff and drummy should simply be avoided. Warming temperatures and sunshine could increase the likelihood of triggering these slabs as the day progresses. While less likely, persistent slabs up to three feet deep remain a threat to backcountry travelers. In addition to the possibility of being human triggered, these slabs could also fail from the release of a wind slab. Below 7,500 feet, skiers and riders might be able to trigger a shallow soft slab on very steep slopes.

Trend For Monday, December 17, 2018 AND Tuesday, December 18, 2018

Dry conditions are in store into Monday before a weak disturbance moves through Monday night. A more significant system will impact the region Tuesday night through Wednesday. The general avalanche hazard will slowly decrease until the next round of snowfall commences.
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