Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 201800
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1100 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 11:00 AM PDT Saturday...A cold front swept
across the area earlier this morning, bringing coastal drizzle,
IFR to MVFR cigs, MVFR reductions in visibility, and gusty onshore
winds. In the wake of the front, except all but the gusty onshore
winds to dissipate this morning. Gusty onshore winds will persist
throughout the afternoon and potentially into the early evening. 
Reductions in visibility are possible overnight into sunrise 
Sunday but should mix out by 17-18Z SUN.

Vicinity of KSFO...Gusty west winds sust 25-30kt with gusts
30-40kt possible through 21-22Z SAT. Improving cigs from IFR to
MVFR then VFR through the afternoon, but lowering again overnight
into sunrise SUN.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Models show MVFR cigs persisting around
KMRY throughout the taf period though some temporary post frontal
clearing is possible. Breezy to occasionally gusty onshore winds
expected throughout the afternoon and into the evening. Lowering
ceilings overnight into early Sunday morning. Low cigs burnoff
around KSNS sooner.

&&

.MARINE...as of 10:55 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 this 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...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...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...SF Bay
             SCA...Mry Bay

&&

$$

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

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea