Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 231741
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
940 AM PST Thu Feb 23 2017

.SYNOPSIS...A few lingering showers near the coast will dissipate by
this afternoon. Drier and cooler conditions are forecast through
Friday with chilly overnight temperatures. Unsettled weather
conditions return by the weekend with another storm system
approaching the coast.

&&

.DISCUSSION...as of 9:40 AM PST Thursday...KMUX radar scans show a
few isolated showers over the coastal waters with a shower or two
skirting the coast of Monterey County. A few showers may linger
across the waters through early this afternoon. Good radiational
cooling conditions with light winds and clear skies this morning
allowed temperatures to drop into the 30s with patchy frost across
the interior and high 30s to mid 40s near the coast.

Northwesterly flow aloft will trend westerly as a weak ridge of high
pressure noses into the region today into Friday. This pattern will
support continued cool and dry conditions with daytime highs into
the 50s today and Friday and persistent night time for tonight with
lows into 30s with patchy frost and freeze across the interior and
high 30s to mid 40s near the coast. A few of the coldest interior
areas will likely drop into the upper 20s. Friday night temperatures
will likely be several degrees warmer than Thursday night,
especially to the north of Monterey as mid and high level clouds
build in ahead of the next storm system.

A shortwave trough currently located over British Columbia will drop
south across the forecast area Saturday bringing increasing coverage
of showers throughout the day. There is still considerable
uncertainty with the exact timing and rainfall amounts given this
storm is only two days away. Model solutions continue to hang onto
there respective solutions with the ECMWF and now the NAM keeping a
closed low just off the coast while the GFS is more progressive with
a weaker and faster moving inside slider. Either way, rainfall
amounts with this system will likely be to be on the lighter side
with amounts less than a half of an inch, even lighter if the GFS
solution comes to pass. Limited instability may spark a thunderstorm
or two mainly offshore as it crosses the forecast area late
Saturday, provided the upper level low pressure system remains
offshore as some model guidance indicates.

Other than possibly a few lingering showers Sunday morning, weak
ridging and dry northwest flow will lead to fair skies and continued
cool conditions with only a few degrees of warming. A second trough
of low pressure, more of the inside slider variety, will bring some
cooling, increased cloud coverage and possibly some showers by
Monday. Model guidance is in better agreement with this system which
will likely support even lighter rainfall amounts than the Saturday
system.

***From previous discussion***

After the upper trough moves east, all three models build an upper
ridge over the eastern Pacific and onto the coast by the middle of
next week ushering in a warming and drying trend through 240
hours. We could certainly use a break.

&&

.AVIATION...As of 3:30 AM PST Thursday...For 12z Tafs. Current
KMUX radar shows popcorn-type showers, mainly offshore, drifting
from northwest to southeast. These light showers should remain
mainly offshore, but could affect Monterey Bay terminals, and end
later this morning. Otherwise, only a few low-to-mid level clouds
through the day, with VFR conditions prevailing. Onshore winds
will not be quite as strong today as yesterday, but could
occasionally be gusty this afternoon, 10-15 kt with gusts up to 20
kt possible. Moderate to high confidence with this forecast.

Vicinity of KSFO...VFR. Moderate west/northwest winds,
occasionally gusty this afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. A brief shower or two possible through
the morning hours, especially for KMRY. However, not mentioned in
tafs. Shower chances end by late morning. Moderate onshore winds,
with occasional gusts up to 20 kt possible in the afternoon.

&&

.MARINE...as of 2:06 AM PST Thursday...Moderate northwesterly
winds will continue through the day today and should gradually
weaken by Friday morning. Winds will then shift out of the south
on Saturday as two different storm systems approach the area.
There is still some uncertainty of how winds and seas will
respond to these systems. Latest forecast models show only
moderate winds and seas this weekend with periods of showers
likely. This will be closely monitored over the next couple of
days as new data come in.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Mry Bay
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

$$

PUBLIC FORECAST: RM/Sims
AVIATION: BAM
MARINE: BAM

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