2006-02-16 (Thu) WX Discussion and Forecast
Continental-scale trough oriented SW-NE runs the show through the weekend. Trough axis is north of the HMT area; main baroclinic zone runs through southern Oregon, across southern Idaho, northern Utah, central Colorado. Short waves rotating around the trough focus precipitation events, but they’re pretty weak and hard to identify.
Numerical guidance suggests pcpn in the ARB begins weakly Friday afternoon, as much as ¼” by sundown in some ensemble members; probability of this much is less than 25%. Overnight the snow level descends from 3500 ft to maybe 2000 ft by sunrise Saturday. The best flow for orographic enhancement appears to be in the predawn hours, probability is about 50% for 12-hr precipitation of .5” in ARB. Low-level flow is weak and poorly organized w/r/t terrain. During the day Saturday the flow remains weak and not helpful for orographic pcpn, probably light amounts off and on all day long, maybe even into the night hours. Total precipitation for the basin is probably less than 1”.
After that, a lobe of the trough breaks off toward the southwest, leaving the target area in split flow/col configuration that appears to prevent ARB pcpn for several days.
Paul Schultz