HMT Forecast Sat 2/16/2008 2040UTC
West coast ridge still looks to be in place over the next few days. We also
have a PACJET in the WRN PAC with a 500mb low E of Japan and S of the Kamchatka
Peninsula. This starts to rotate through the jet as this jet moves east
during the GFS model run. Ahead of this the first short wave starting to
break down the ridge comes in on Tue Feb 19, as a fairly dry cutoff almost
sliding in under the ridge in today's 12Z GFS solution.
A second short wave mainly hits WA/OR early Wed Feb 20, with a short period of
very light precip over the Sierra Crest about 00Z Wed. The ECMWF low-res is
about 6-12 hours slower with this wave as it moves inland.
The next stronger system brings a double shot of moisture to the ARB between
about 12Z Thu Feb 21 and 00Z Sat Feb 23, totaling about 1.5" in the GFS.
At 12Z Thu Feb 21 there is a 500mb low (that was east of Japan at the model
initial time) off the BC coast and north of the PACJET. The configuration of
the low and PACJET looks pretty similar between the latest GFS and ECMWF runs.
At the same time there is a rather long atmospheric river in the GFS IWV field
showing up all the way from the Philippines to just offshore of SFO with values
of 34mm IWV. The main feed is shunted to the south by 00Z Fri Feb 22 with some
leftover values of around 28mm near SFO. By 12Z Fri Feb 23 the river has moved
south and broken up considerably. The GFS solution for this system is stronger
compared with yesterday's run.
A followon wave comes in later Sat Feb 23 into Sun Feb 24 with lighter amounts
of precip (around .4").