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

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FXUS66 KMTR 212332
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
332 PM PST Wed Feb 21 2018

.SYNOPSIS...A weak weather system will impact the region tomorrow
bringing showers, a slight chance of scattered thunderstorms in
the afternoon, and lowering snow levels. This system will also bring
gusty winds tomorrow and colder temperatures Friday morning. Dry
weather and slightly warmer daytime conditions are likely for the
weekend with cooler, unsettled weather potentially returning
early next week.

&&

.DISCUSSION...as of 01:58 PM PST Wednesday...Shower activity has
moved out for the day with partly cloudy skies expected the rest
of the afternoon and evening. Unseasonably cool temperatures
continue this afternoon with forecast highs in the 50s and 40s for
higher peaks.

The main forecast concern continues to be a weak short-wave
trough that will move through the area tomorrow. This system is
expected to bring scattered rain and snow showers, scattered
afternoon thunderstorms, and widespread gusty winds to the region.
Shower activity tomorrow will be scattered with little
accumulations expected. Along with this system will come another
burst of cold air allowing for lowered snow levels to around 2000
ft and light snow accumulations possible in the higher peaks.
Sufficient instability will allow for the development of
scattered thunderstorms over parts of the North and East Bay
starting in the afternoon as forecast models show a few hundred
J/kg of CAPE over the area. Some storms may carry small hail, and
a few high elevation areas may even see a little thundersnow.
Winds will begin to pick up early tomorrow morning and increase
throughout the day. Strongest winds are expected along the coast
and in the hills with gusts over 40 MPH possible. Once the winds
subside and skies begin to clear tomorrow night, temperatures will
drop into the 30s for most areas with some valley locations in
the 20s.

Once this system moves out, dry conditions are expected Friday and
through the weekend as the persistent deep trough overhead begins
to slightly weaken and shift inland. This will allow for afternoon
highs to warm slightly over the weekend, although cool overnight
and morning lows will continue.

Looking into next week, models continue to suggest that we will
remain in a broad troughing pattern with weaker embedded systems
developing and moving through the area. Meaning cool and
unsettled weather will likely persist into early next week.

&&

.AVIATION...as of 3:30 PM PST Wednesday...Skies have cleared up
this afternoon following the passage of a dry shortwave. VFR
conditions are expected this evening before another upper level
shortwave approaches the area late tonight. Models indicate lower
level moisture after 09Z but only lasting a few hours as strong
northerly winds help to clear out the clouds after 13-14Z.

Vicinity of KSFO...VFR except for a period of lower clouds between
10Z-13Z possibly lowering into MVFR range. Offshore winds up to
10 kt switching to onshore before dark. Much stronger northwest
winds are anticipated Thursday morning after 13-14Z with
potential for an Airport Weather Warning Thursday afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR.

&&

.CLIMATE...

Here are record low temperatures and the years they occurred for
Wednesday.

Location          Wednesday

SF Bay Area

Healdsburg        28 in 1929
Santa Rosa        26 in 1913
Calistoga         25 in 2006
Kentfield         29 in 1953
San Rafael        33 in 1955
Napa              29 in 1955
San Francisco     36 in 1890
SFO Airport       34 in 1955
Half Moon Bay     31 in 2006
Oakland Airport   33 in 1955
Richmond          35 in 1981
Livermore         27 in 1955
Moffett Field     32 in 1955
San Jose          25 in 1897
Gilroy            31 in 1976

Monterey Bay Area

Santa Cruz        30 in 1955
Salinas           31 in 1970
Salinas Airport   30 in 1953
Monterey          36 in 1952
King City         23 in 1953

&&

.MARINE...as of 03:21 PM PST Wednesday...Light variable winds will
transition to increasing northerly  winds through the remainder of
the day. Northerly winds will continue to strengthen overnight and
through tomorrow, bringing very gusty winds and steep fresh swell.
Gale force gusts are possible in the outer waters tomorrow
afternoon through late tomorrow night.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Mry Bay from 3 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 9 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 9 PM
             SCA...SF Bay from 3 AM

&&

$$

PUBLIC FORECAST: AS
AVIATION: W Pi
MARINE: DRP

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