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022
FXUS66 KMTR 250459
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
957 PM PDT Fri May 24 2024

...New UPDATE, MARINE...

.SYNOPSIS...
Issued at 1231 AM PDT Fri May 24 2024

Cool temperatures this weekend with a slight warm up slated for
next week.

&&

.UPDATE...
-- Changed Discussion --
Issued at 957 PM PDT Fri May 24 2024

Chilly to very chilly onshore winds, having passed directly over
coastal sea surface temperatures 50F-54F, prevail this evening. A
moderate 3.1 mb SFO-SAC pressure gradient (resulting in onshore
winds) is currently stronger than the 1.8 mb ACV-SFO and 2.7 mb
SMX-SFO pressure gradients. Coastal low clouds forced upwards
over the coastal terrain is resulting in areas light measurable
drizzle and/or very light rain.

Average temperatures today were below late May normals by a few
to several degrees or more, the largest negative departures were
over the SF Peninsula, East Bay, South Bay and north Central Coast.
With more sun and less coastal influence negative temperature
departures were not as strong over the North Bay. An area of low
clouds persisted across the SF Peninsula to the East Bay today. The
high of 63F at Livermore Airport was 14F below the late May normal
high temperature 77F. San Francisco downtown (SFD) location high/low
today were 56F/49F, 56F is close but not quite a record low maximum
temperature (SFD May 24th record low max is 54F in 2009). Inland and
parts of the coastline where the sun did appear today, it was rather
nice.

The conveyor belt of chilly northwest winds and low cloud development
will continue tonight and Saturday morning. The sun will warm inland
temperatures to scale back the amount of low clouds with an inland
intrusion returning Saturday night and Sunday morning. Additional
daytime warming returns Sunday through next week.
-- End Changed Discussion --

&&

.SHORT TERM...
Issued at 205 PM PDT Fri May 24 2024 (This evening through
Saturday)

As we head into the un-official kick off to summer this weekend it
doesn`t really feel like summer. The latest 24 hour trends
indicate many locations running 5 to 10 degrees colder today than
Thursday. Why the big change? The longwave pattern changed thanks
to a passing upper level trough and a weak surface front. This
trough and colder air aloft help to increase onshore flow too.
SFO-SAC gradient is pushing 3.3mb this afternoon, which is also
stronger than yesterday. The increased onshore flow has also kept
the marine stratus lingering well into the afternoon. Pretty
impressive when one looks at the visible satellite and still sees
clouds spreading across the SF Peninsula and into the East Bay
Hills. Needless to say, temperatures were nudged downward today
around SF Bay due to lingering clouds. One final note with
today`s onshore flow, peak gusts of 45-50 mph have been observed
in the East Bay Hills.

Tonight through Saturday: Onshore flow will ease overnight, but
still remain onshore. Given persistent onshore flow will expect
another night of widespread stratus moving inland. Have added
patchy fog and drizzle to the coast/favored upslope areas. After a
cloudy start to the day on Saturday some clearing will be had, but
stratus will lingering around Monterey Bay and SF Peninsula.
Another cool day with max temps in the upper 50s/60s coast and
60s/70s inland. Forecast onshore gradients will be close 3mb again
so gusty winds in the afternoon seem plausible.

&&

.LONG TERM...
Issued at 217 PM PDT Fri May 24 2024 (Saturday night through next
Thursday)

Slight shift in the upper level pattern for the rest of the
weekend through Memorial Day will lead to a gradual warm up
through next week. 500 mb heights will increase with warming 850
mb temps all yielding warmer temperatures. Closer to seasonal
averages by the end of next week as far interior locations
approach 90 degrees. Night and morning clouds clearing back to
the coast each afternoon will also continue.

&&

.AVIATION...
(00Z TAFS)
Issued at 550 PM PDT Fri May 24 2024

Most of the region has cleared out, but MVFR stratus continues over
the SF Bay terminals and the area around MRY. Not expecting any
clearing for those terminals for the rest of the day; if they do
clear out, it will be short-lived and transitory. Breezy
northwesterly winds will continue into the evening, diminishing at
night before resuming Saturday afternoon. High confidence in further
stratus development across the region this evening, except at the
North Bay terminals where confidence is moderate. Along the coast,
and in the SF Bay and Monterey Bay regions, ceilings are expected to
decrease to IFR-LIFR. Stratus mixes out late Saturday morning with
breezy northwest flow resuming in the afternoon.

Vicinity of SFO... MVFR stratus continues through the day. Strong
west winds gusting to 30 gusts will continue through the evening. At
this time, low confidence that winds will gust above 35 knots. Will
monitor evolution of winds throughout the day and will amend TAF if
necessary. High confidence of MVFR or marginal IFR stratus at the
terminal area tonight, clearing late Saturday morning with strong
west winds Saturday afternoon.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... MRY should expect MVFR ceilings through
the day, with some greater uncertainty at SNS although continuing
ceilings are also favored there. Breezy and gusty northwest winds
continue through the evening. Overnight, ceilings drop to the IFR-
LIFR level across the region. Clearing time is expected late
Saturday morning at SNS, and a moderate confidence that MRY clears
out at a similar time as well, although some model output keeps
ceilings through Saturday.

&&

.MARINE...
(Tonight through next Thursday)
Issued at 926 PM PDT Fri May 24 2024

Mainly gusty northwest winds will continue over the coastal waters
over Memorial Day weekend and to the middle of next week. Afternoon
and evening onshore winds will also become breezy to gusty over the
bays during the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM to 9 PM PDT Saturday for Mry Bay.

     Small Craft Advisory until 3 AM PDT Sunday for Pt Arena to Pt
     Reyes 0-10 nm.

     Small Craft Advisory until 9 AM PDT Saturday for Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory from 3 PM Saturday to 3 AM PDT Sunday for
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory until 3 AM PDT Saturday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PDT Sunday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory from 3 PM Saturday to 9 AM PDT Sunday for
     Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

UPDATE...Canepa
SHORT TERM...MM
LONG TERM....MM
AVIATION...DialH
MARINE...Canepa

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