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 141159
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
459 AM PDT Sat Sep 14 2019

.SYNOPSIS...A cooling trend will begin today, mainly near the 
ocean and bays while very warm temperatures will continue inland. 
Much cooler temperatures are forecast on Sunday and Monday across
the area as a weather system moves in from the northwest. There 
is also a slight chance of rain on Monday, mainly across the 
northern half of the area. Dry weather is expected for the 
remainder of next week, along with seasonable temperatures.

&&

.DISCUSSION...As of 3:33 AM PDT Saturday...Satellite imagery 
shows clear skies over the area with no coastal stratus in sight, 
and current temperature trends are a mixed bag of a few degrees 
warmer, to a few degrees cooler, than yesterday at this time. 
Current temps are running in the upper 50s to upper 60s as of 3 
am. Surface pressure gradients are starting to show signs of 
becoming more onshore with SFO-SAC now 0.5 mb, and SFO-LAS 0.6 mb.
Models indicate a continued tightening of the onshore gradient, 
as well as increased boundary layer RH approaching the coast by 
this afternoon. Thus, cooler temperatures are expected along the 
coast, but another warm to hot day is expected inland. Look for 
another day of 80s and 90s inland, with fewer locations topping 
the century mark, but 70s at the coast. 

By Sunday an approaching upper level trough will result in cool
air spreading to inland areas with high temperatures as many as 
10 degrees cooler than expected highs today. Additional cooling is
forecast for Monday and Tuesday as the upper trough and associated
cold front moves through. In addition, rain chances are still in
the forecast for Monday as the southern portion of this system
moves across much of the area. The best chances of rain will be in
the North Bay and north of there, but there could also be light
rain chances as far south as northern Monterey and San Benito 
Counties. Forecast rainfall amounts are light, but the latest 
ECMWF still has the highest amounts, but still well under a 
quarter of an inch. 

After this system moves east, medium range models keep a long-wave
trough over the west for continued seasonably cool temperatures 
over the area through the rest of the week. 

&&

.AVIATION...As of 04:59 AM PDT Saturday...For 12z TAFs. VFR will 
continue through the morning and afternoon. A marine layer is 
starting to reform off the coast, but should not impact the 
terminals through the morning and afternoon hours. Light winds 
this morning will become onshore this afternoon. The marine layer 
offshore should continue to strengthen through the afternoon, and 
then begin to spread into coastal areas and bays this evening and 
overnight. The marine layer is expected to be shallow with IFR to 
MVFR cigs for the San Francisco and Monterey Bay terminals 
tonight. The inland terminals should remain VFR tonight given the 
shallow marine layer depth. 

Vicinity of KSFO...VFR will continue through the morning and
afternoon hours. Light onshore winds this morning will strengthen
this afternoon with sustained winds 15-20 kt and gusts 20-25 kt.
Onshore winds will weaken after sunset but remain breezy. Cigs 
could return as early as 03-06z this evening as the marine layer 
and stratus pushes into the bay. IFR cigs returning overnight 
tonight into Sunday morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR through the morning and afternoon
hours. Light winds this morning becoming onshore around 10kt this
afternoon. IFR cigs expected to return 02-04z at KMRY and around 
or shortly after 06z at KSNS. 

&&

.MARINE...as of 2:55 AM PDT Saturday...Light to moderate 
northwesterly winds will continue through the weekend with locally
higher winds developing over the northern waters and south of the
coastal capes and points through Saturday. A cold front will move
southward over the coastal waters Monday resulting in a chance of
showers. Moderate period northwesterly swell and a longer period 
southerly swell will continue through the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 2 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 PM

&&

$$

PUBLIC FORECAST: Sims
AVIATION: ST
MARINE: ST

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