2007-01-17-hmt_forecast
500mb low passed pretty much on track over San Francisco Bay at 09Z in LAPS
analyses with accumulating precip staying near the coast. Trace amounts of
snow were indicated by LAPS analyses in the ARB vicinity.
In today's 12Z GFS the next upstream wave passes north over WA/BC on Saturday,
then by Monday cuts off near GJT and progresses south all the way to NRN Baja
CA by Wed 24 Jan. Some GFS ensemble members have this cutoff farther east with
all members showing a ridge persisting off of or near the CA coast through
early next week. The ECMWF is slightly more progressive with the cutoff
while still maintaining a ridge over CA early next week.
The following trough shows some divergence in successive GFS runs for
the 25-27 Jan timeframe as to whether it rides north or cuts off well to the
WSW of LA. The most recent GFS run favors a more northerly position of the
still open wave near 43N 130W about to do battle with an upper level high
over ERN OR on 26 Jan at 00Z.
Overall it looks dry for the ARB through the remainder of this week and next
week. Just an outside chance of the trough late next week taking a favorable
trajectory based on model uncertainty. If we want to look at the 240hr GFS
and beyond there is a suggestion the west coast ridge may weaken by 27 Jan
and the next trough in the series could have a shot at NRN CA around
28-29 Jan. The 06Z GFS however still has a stronger ridge illustrating the
model uncertainty.
Steve Albers