HMT Forecast 1/19/07
Examining last evening's GFS Pacific TPW forecast runs, several moisture plumes (including the one mentioned yesterday) tease the coastal areas north of the ARB but never make it far inland. The earliest that a plume looks like it might impinge on the ARB is maybe a week from today, Friday 1/26 at 06utc, or around midnight early Friday morning. Other than that, the progs have not changed much since yesterday. The west coast is still dominated by a high pressure ridge and a few radar echoes this morning were seen advancing westward as the surface winds were gusting out of the east in central CA.
This morning's NAM has the 500 hPa closed low pulling out of the CA region and tracking east and north making it to the TX panhandle by this Sunday at 3ut. Meanwhile, an intense short wave advances down the east side of the coastal ridge passing Salt Lake City around Sunday 12utc. This feature continues due south and finally cuts off over El Paso by Monday. The effect of this action on the ridge is to amplify it and give it a slight positive tilt. This continues to provide weak upper air velocities over the ARB and strong northern flow over UT and AZ, a bit farther east than yesterday's forecast. No major precipitation occurs over central CA for the NAM run, however there is some minor precip forecast during the last few frames of the NAM early next week, but nothing that would warrant and IOP.
Last night's GFS ensembles still paint a very dry picture for the ARB out through Sunday February 4th.
Dan Birkenheuer - ESRL/GSD