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HMT Forecast Tue 1/22/2008 2000UTC

Large-scale pattern continues to show E PAC ridge gradually weakening over
the next week with a series of short waves moving through the flow. Over time
they will come in less from the north and more from the west to get a
somewhat better connection with tropical moisture.

The past 24 hours has seen the heavier precip staying W of the ARB.
This ongoing system keeps giving about .1" precip every 6 hours over the ARB
until a brief finale with .2" on Thursday morning. Some heavier amounts are
forecast in a band extending to the south just N of LAX. This is rotating
around the persistant cutoff low centered just W of SFO. ESRL WRF-NMM gives
totals of 0.5-1.0" in the lower elevations of the ARB.

After an 18 hour break the next kicker system drops in from the north and
the GFS brings about .6" total between 06Z Friday and 06Z Saturday.
We again have a cutoff low positioning itself just W of SFO. The ECMWF keeps
this cutoff more offshore compared with the GFS, then kicks it out later on
a more northerly trajectory. The ESRL WRF-NMM run is more generous with the
precip giving roughly 1" during the initial 6-12 hours. This is another cold
system with 850 temps slowly rising from about -3C to -1C. Possibly a marginal
IOP event.

Following this we see the weekend storm that begins to get a better moisture
feed, starting about 06Z Sunday with just over 2" total by 00Z next Tuesday.
The GFS gives about 1" of this between 12Z Sunday and 00Z Monday. So this
might reach IOP criteria. A similar cold system with 850mb temps from
-4C to -2C. The ECMWF has a sharper trough coming in that also has good
precip amounts.

There's yet another short wave in the pipeline for the middle of next week
that has a bit better moisture feed. This one has about 2-3" total in the GFS
with most of the action next Tuesday. At this time it looks to be a better
IOP than the weekend storm though it may be a faster moving system with a
sharper open wave configuration.

Steve Albers