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

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KMTR 050408
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
908 PM PDT Tue Aug 4 2020

.SYNOPSIS...Cooler conditions will continue across the region through
Wednesday, as a trough moves into the region. Light rain and
drizzle will be possible tonight and tomorrow, mainly near the
coast and even up into the coastal hills. In addition, breezy
conditions will prevail through Wednesday, with locally gusty west
to northwest winds expected during the afternoon and evening
hours. Modest warming is then forecast for late in the week and
into the weekend, but temperatures will only bounce back to near
seasonal averages.

&&

.DISCUSSION...As of 9:08 PM PDT Tuesday...From the Fort Ord
Profiler we see that the marine layer depth has increased by over
1000 ft over the last 24 hours owing to the arrival of the
offshore low. Water vapor imagery shows the center of the low
pressure due west of Fort Bragg in Northern California as it
slowly moves ashore this evening. Today`s low clouds all along the
coast will likely expand overnight, allowing for the development
of coastal drizzle, especially over the SF Peninsula and Monterey
Bay, and potentially even some light rain along the coastal hills.
Not expecting any large accumulations, but short-term model
guidance does expect a range from trace amounts to just over a
tenth or two. These conditions are currently progged to last
through most of tonight and through tomorrow morning as the marine
layer continues to deepen.

In terms of winds, the SFO-SAC gradient has been steadily
increasing this evening as the low moves ashore and sits around
4.2 hPa. Expecting similar overnight breezy conditions and
locally gusty winds to what we had last night across the gaps,
passes, and high- elevation ridges. Some of our sites have already
observed 40-45 mph gusts across the CWA, while our Altamont RAWS
has already measured a gust of 51 mph! Indeed, we will be
monitoring how winds evolve across the region through tonight and
whether or not we need to issue any wind hazards.

Expecting tomorrow to follow a similar cooling trend, with
Wednesday set to be the coldest day of the week as the low
settles over Northern California. Falling heights as a result of
the low pressure`s influence resulted in some max temps across the
interior that were over 10 degrees F cooler today than on Monday.
With the center of the low progged to settle north of our CWA,
expecting further height falls for max temps in the interior to be
up to 20 degrees cooler than what was observed on Monday. Some of
our normally warmest interior locations, such as Livermore and
Concord, may even struggle to get into the mid-to-upper-70s F!

Looking ahead into the second-half of the week, the upper-level
wave over the Gulf of Alaska that has been responsible for these
two back-to-back disturbances is progged to move ashore into
British Columbia through the end of the workweek, resulting in
greater mid-level zonal flow across the Gulf of Alaska. This setup
will allow for the mid-PAC upper-level ridge to slightly build
while the upper-level ridge over the Southwest gradually centers
itself over west Texas and also builds. This synoptic setup is
thus poised to break up the low over Northern California as its
associated trough weakens through Saturday. As such, expecting max
temps to slowly rebound after Wednesday. Nevertheless, not
expecting them to get back up to seasonal averages until this
weekend.

&&

.AVIATION....As of 04:48 PM PDT Tuesday...for 00z TAFs. The
marine layer around 2000 ft AGL patchy stratus around the Bay
Area and thick stratus and low clouds in the Monterey Bay, VFR
inland. TAFs continue to reflect the expectation of an early
return of stratus around the region tonight as the upper level
trough passes over California. Stratus clearing is expected to be
later on Wednesday with chances of coastal drizzle possible.
Clouds will remain through the day closer to the coast with mostly
clear skies inland Wednesday afternoon. Winds remain quite breezy
and onshore with locally higher gusts. Winds will taper off
slightly, but expected to be breezy through the evening. Winds
will increase Wednesday afternoon.

Vicinity of KSFO...MVFR with stratus straddling IFR/MVFR through
the evening. Winds remain onshore and gusty. Gusts will taper off
overnight, but winds will continue to be breezy. Stratus is
forecast to start to break after 17z, and lift by Wednesday
afternoon. Winds will increase and have stronger gusts once
again.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...IFR/MVFR trending to IFR later tonight.
There is a chance for drizzle early Wednesday morning, possibly
brief pockets of light rain. Winds remain onshore and breezy.
Cloud cover will lift, but linger around the Bay on Wednesday.
Winds will increase once again on Wednesday afternoon. Expect
another early return of stratus Wednesday evening.

&&

.MARINE...as of 04:36 PM PDT Tuesday...Moderate to gusty northwest
winds will continue into late this  week across the coastal waters
as high pressure remains over the  eastern Pacific. The strongest
winds are anticipated along the  inner coastal waters south of
Point Sur and north of Point Reyes.  Breezy onshore winds are also
forecast over the bays during the  afternoon and evening hours.
These winds will generate steep fresh swells resulting in locally
hazardous seas, especially for  smaller vessels.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...SF Bay until 9 PM
             SCA...Mry Bay until 9 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             SCA...Pt Arena to Pt Reyes 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...Pt Reyes to Pigeon Pt 0-10 nm

&&

$$

PUBLIC FORECAST: Diaz/MM
AVIATION: DK
MARINE: AS

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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.