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NWS Forecast Area Discussion - San Francisco Area

000
FXUS66 KMTR 201552
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
852 AM PDT Sat Apr 20 2019

.SYNOPSIS...A passing cold front will bring cooler weather and
coastal drizzle to the Bay Area Saturday. Warmer weather is
forecast on Sunday with building high pressure. A more noticeable
warming trend will develop early next week with above normal
temperatures.

&&

.DISCUSSION...as of 08:46 AM PDT Saturday...A quick moving frontal
boundary bisects the region at this hour with breezy to locally
gusty northwest winds developing in wake of its passage. The very
moist boundary layer ahead of the front resulted in widespread
drizzle with many locations reporting trace amounts to a few
hundredths of an inch near the coast and across the greater San
Francisco Bay Area. Look for cooler temperatures, breezy winds,
and partly to mostly cloudy conditions to prevail through the
remainder of the day. With this said, the ongoing forecast remains
on track with no updates anticipated at this time. For additional
information, please see the forecast discussion below.

&&

.PREV DISCUSSION...as of 03:03 AM PDT Saturday...A much deeper
marine layer is currently impacting the Bay Area ahead of an
approaching cold front. Ft Ord puts the depth near 1,800-2,000
feet this morning. Satellite imagery shows another night of
widespread coastal and inland valley stratus. Automated sensors
around the region also indicate some patchy fog with visibility
three to six miles and at times less. Additionally, Half Moon Bay
reported a few hours of -RA and drizzle has been observed here at
the forecast office. A few other sites around the region tipped
0.01" of precip this morning too. Needless to say, but a very
moist boundary layer is present this morning. Current forecast
will continue the mention of morning clouds, fog and drizzle. As
for the cold front itself, latest surface analysis puts the front
near the far Northern Sonoma county. KMUX radar imagery actually
shows a few echoes off the coast, which is likely the front. Not
expecting much precip from the front, but more drizzle from the
very moist low levels. The cold front is projected to move through
the Bay Area today, which will result in cool and cloudy
conditions. Forecast highs today will be in the upper 50s to mid
60s at the coast and 60s to lower 70s inland or several degrees
below normal.

A few low clouds will be possible tonight with some lingering
drizzle, especially Monterey/Big Sur area, as the front exits to
the east. By Sunday high pressure will begin to build over the
region which will kick off a noticeable warming and drying trend.
Temperatures on Sunday will warm three to six degrees. High
pressure will continue to build into next week and peak
Tuesday/Wednesday. Unlike the last warm up this warm up will have
some offshore flow support. Latest WRF model indicates decent NE
winds at 925mb Monday and Tuesday. Offshore flow will erode any
remaining stratus and introduce lower RH values, especially
overnight across the N and E Bay Hills. The strength of the ridge
is projected to be two to three standard deviations above normal
at 500 mb. Simply put, much above normal for this time of year
resulting in some rather warm temperatures. By Wednesday,
interior portions of Monterey/San Benito could see temperatures
in the mid 90s. Other locations around the Bay Area will not be as
warm, but 70-80s around the Bay Shoreline and widespread 80s
inland. Both Tuesday and Wednesday will see high temperatures as
much as 15 degrees above normal.

Very subtle cooling on Thursday as flow aloft become more zonal
and low level flow becomes more onshore. A bigger drop in
temperatures is forecast on Friday and next weekend as an upper
level low moves toward the PacNW. Unlike previous model runs the
GFS has now backed off on precip chances next weekend and is more
inline with the ECMWF.

&&

.AVIATION...as of 5:03 AM PDT Saturday...Ongoing onshore push of
stratus ramps up through morning per recent statistical guidance
forecasting increasing southwest to west winds by late morning and
afternoon. Metar observations range from IFR in patchy drizzle or
light rain to MVFR-VFR. LIFR probability satellite imagery shows
plenty of coastal stratus and fog converging along the coastline
and extending inland. Incoming cold front later today sweeps SE
over the area with potential for strong and gusty post frontal
winds over a large part of the area this afternoon and evening.
Winds will shift to west to northwest and leaving few-sct cloud
coverage at lower levels, in general VFR returns late today and
tonight as well as for Sunday.

Vicinity of KSFO...W-SW wind 10 to 15 knots becoming W by late
morning and increasingly strong and gusty with gusts up over 30
knots in the afternoon and evening. Ceiling lifts quickly to
MVFR-VFR by late morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Patchy drizzle or light rain in IFR
ceilings this morning, ceilings then lifting to MVFR by late
morning. Gusty winds developing in the afternoon. VFR tonight and
Sunday.

&&

.MARINE...as of 08:46 AM PDT Saturday...A cold front is sweeping
through the waters from north to south this morning. Gusty
northwest winds will prevail across the waters as a result today.
Occasional gale force gusts are possible late this morning
through the afternoon. These gusty winds will generate steep fresh
swell which is hazardous for small craft vessels. Moderate
northwest swell.

&&

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

&&

$$

PUBLIC FORECAST: RGass/MM
AVIATION: Canepa
MARINE: DRP

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