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

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000
FXUS66 KMTR 241123
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
423 AM PDT Thu Jun 24 2021

.SYNOPSIS...Low clouds this morning turning sunny by midday with
temperatures running a few degrees below normal inland. Gradual
warming trend Friday followed by more significant inland heat this
weekend. Seasonably warm and dry pattern continues next week.

&&

.DISCUSSION...as of 3:52 AM PDT Thursday...Low clouds cover much
of the Bay Area coast and valleys early this morning with
temperatures hovering in the upper 50s to around 60 degrees as SST
have warmed to around 59 degrees given the recent ease of
upwelling northwest winds. The light nw winds over the ocean have
been induced by upper level low pressure that continues to wobble
just west of the Golden Gate and clearly shows up on water vapor
imagery. Cloud bases are fairly high this morning due to the
proximity of the upper low and disrupted inversion layer. There
could be some drizzle this morning as the sun comes up but no
other precip for the Bay Area. Latest model solutions do suggest
the synoptic lift associated with the upper low will allow for a
solid round of thunderstorms across the Central Sierra this
afternoon. As skies turn sunny this afternoon look for highs in
the 70s throughout the Bay Area with mainly lower 80s inland
keeping the below normal trend for inland highs.

The upper low will rapidly fill and dissipate overnight as the
much ballyhooed ridge over British Columbia intensifies while high
pressure west of Baja California ridges northward as well. Expect
a modest warming trend for Friday as the ridge starts to build and
temps warm closer to normal for inland areas. Saturday should see
more rapid inland warming as the ridge to our north amplifies and
sets up an odd pattern with an almost rex block type pattern along
the West Coast. The hottest weather looks to remain well to our
north this weekend. However the interior valleys will warm and
temps could reach triple digits for the far interior North/East
Bay as well as the interior Central Coast by Saturday. However
much of the Bay Area should remain seasonably warm with 90s
staying away from the Bay. No heat headlines expected at this
time.

Models indicate Saturday may be the hottest day this weekend with
a few degrees of cooling Sunday into Monday followed by another
warming trend by Tue/Weds.

&&

.AVIATION...As of 04:25 AM PDT Thursday...For the 12Z TAFs.
Coastal Profilers are picking up on a subtle compression of the
marine layer this morning, with the latest obs showing a boundary
depth of around 3000-3500 ft. As a result, observed a rapid return
of MVFR cigs across the terminals, along with some patchy IFR
along the coast and inland valleys. Will continue to observe
widespread MVFR cigs until 17Z. VFR will prevail this afternoon as
the marine layer rapidly compresses due to a building high
pressure aloft. Will still observe some onshore flow from the
weakening mid-level low just off the coast, so have adjusted TAFs
to account for breezy onshore winds along the coast and bays
(10-15kts, gusts up to 20kts). Low cigs will then quickly shroud
the coastline and bays starting around 3Z Friday as the marine
stratus flows back inland.

Vicinity of KSFO...MVFR cigs will lift by 16-17Z and make way for
breezy(15-20kts) onshore winds and VFR cigs for most of the day.
Given the compression of the marine boundary expected this
afternoon, have adjusted TAFs to account for lower cigs (10-20k
ft) and an early marine layer intrusion (4-7Z) across SFO/OAK.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs will rapidly lift over the
northern Salinas Valley while lingering stratus will be observed
along the Monterey Bay and coastal highlands. Widespread VFR for
the afternoon as the marine layer gets compressed. Will still
observe stratification this evening starting at around 3Z but
have adjusted TAFs to account for lower cig potential (1-2k ft)
given the more compressed boundary layer that the models are
suggested for tonight.

&&

.MARINE...as of 04:21 AM PDT Thursday...Light wind and seas over
the coastal waters today into Friday as a mixed swell passes
through the waters. Northwest winds gradually increase later
Friday and through the weekend with light seas increasing by
Sunday as northwest winds strengthen.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...None.

$$

PUBLIC FORECAST: RWW
AVIATION: Diaz
MARINE: RWW

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