HMT Forecast Mon 2/18/2008 2345UTC
The big picture looks fairly similar to yesterday's forecast. The west coast
ridge will hold to keep things dry for today, though the first weak wave is
approaching as a weak low-latitude cutoff. High clouds from this are already
spreading over the ARB. Some very light precip is possible as this system
swings through between 00Z and 12Z Tue.
Close behind is our Wednesday wave breaking down the ridge further with about
.2" in the GFS from 21Z Tue to 12Z Wed (similar to the GSD WRF-NMM). A 500mb
low phasing in with this wave swings through NRN CA later Wed giving a second
shot of precip with .3" between 12Z and 21Z Wed (this isn't showing up in
the 12Z GSD WRF-NMM forecast).
Next wave in the sequence is for Thu/Fri. The GFS brings about 1.1" between
21Z Thu and 06Z Sat. This open wave (still with a double structure) ushers
in the stronger PacJET and may be a borderline IOP event. Heaviest precip is
during the day Friday as the second component phases in. 850mb temps stay at
about +1C. The ECMWF 12Z run looks fairly similar to the GFS at 12Z Fri.
The atmospheric river in the Pacific reaches its longest length at 00Z Thu
going from 130W westward to the Philippines. After that it breaks up with
pieces of it reaching CA over the next few days. The best piece to reach
CA hits the Santa Barbara area with 32mm IWV on 12Z Sat.
Correspondingly, a bit higher amplitude open wave brings more energy
into Central and SRN CA over the weekend. The ARB is in the northern portion
of the heavy precip area. The GFS gives about 2.5" between 06Z Sat and 21Z Sun
with heavier amounts to the S. Temps start out warm around +3C with fropa
about 06Z Sun dropping the 850mb temp to -3C. The ECMWF is about 6hr slower
and has more of a SW flow that could bring up moisture towards the ARB.
This looks to be the best IOP event for the week.
The long range GFS IWV field suggests the possibility of weak events on Feb 27,
Mar 1, and Mar 4.