HMT Forecast 1/16/2008 19:42 UTC
Yesterday's forecast could almost be used again today. We have clear conditions for the most part in the ARB with perhaps some gustier light winds. Temps range from 20 to 40F. The Pacific low pressure is now located near 34N 149W and the water vapor loops are slowing definite ridging occurring north of this location with the top of the ridge around 53N 153W, deflecting any moisture well away from the ARB area.
The ARB remains dry until a potential cold outbreak that is shown to start with a short wave in the EC model coming down the side of the sharp ridge off the CONUS coast. This is just north of the ARB 1/20 (Sunday) 00ut and moves through by 00utc Monday (1/21). Today's EC is not quite as vigorous as earlier runs but still maintains a 500 cutoff over central CA after Monday with a persistent duration of light precipitation marginally over and mostly south of the ARB. The GFS 00ut run has the precip starting in the ARB Monday 1/22 at 06utc through Wednesday 1/23 06utc and possibly beyond, with accumulation of roughly 0.5 inches. The ensembles still indicate that the ARB will be at the north side of this activity with most of the action to the south; this is possibly associated with moisture coming over the ridge that has by this time pulled somewhat offshore so most Pacific moisture will be on the coast or to the west of the ARB. After this episode the ensembles are still indicating the weak possibility of another precipitation event on or about 1/29-1/30. Ensemble 500 heights show the ridge continues to slowly retrograde over the next 384 hours.
Dan Birkenheuer ESRL/GSD