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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 241734

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1034 AM PDT Mon Jun 24 2019

.SYNOPSIS...A cooling trend will get underway today and continue 
through midweek, with temperatures forecast to cool by 10 to 20 
degrees by Wednesday. In addition, expect an increase in night and
morning low clouds over the next few days. Temperatures will warm
a bit late in the week and into next weekend, but remain slightly
below seasonal averages. 

&& of 9:18 AM PDT Monday...Visible satellite 
imagery reveals marine stratus impacting parts of the San 
Francisco Bay Area this morning. Observations from the terminals 
across the region indicate ceilings are around 200 to 1,000 ft AGL
with a relatively shallow marine layer. As the morning 
progresses, the low clouds will mix out of the inland valleys and 
the San Francisco Bay as mostly sunny skies return with some 
passing high clouds. Some locations along the immediate coast may 
see some low clouds linger through the day. High temperatures will
begin trending downward this afternoon as an upper level low 
gradually approaches the Pacific Northwest. The most noticeable 
cooling will be felt across the interior where temperatures will 
drop by 7-10 degrees from yesterday to today. The present short- 
term forecast remains on track; for additional details beyond Day 
1, please refer to the previous discussion section.


.PREV DISCUSSION...As of 2:55 AM PDT Monday...Low clouds and fog 
formed overnight along most of our coastline from Bodega Bay 
southward, and also locally inland through the Golden Gate and up 
the Salinas Valley. This increasing coverage of marine layer 
stratus and fog is in response to a gradual uptick in onshore flow
as the upper ridge that brought very warm temperatures to our 
inland areas over the weekend begins to break down. The marine 
layer is still relatively shallow at present, but is expected to 
deepen over the next few days as an upper trough currently 
settling over the Pacific Northwest digs south over California. 
The deepening trough will also enhance onshore flow and bring a 
cooler airmass south into California. 850 mb temperatures are 
forecast to drop from about 21 deg C presently to around 11 deg C 
by Wednesday. Thus, we can expect a robust cooling trend through 
midweek. By Wednesday, high temperatures are forecast to be as 
much as 20 degrees cooler than this past weekend's temps and be 
anywhere from 5 to 12 degrees cooler than normal.

The models are in good agreement regarding this upcoming cooling
trend and indicate that Wednesday and Thursday will be the coolest
days of the week. Slightly warmer temperatures are expected on
Friday and on into the weekend, as the core of the upper trough
lifts to the northeast. However, the longwave trough position will
remain positioned near the West Coast, and so temperatures will
likely remain at least slightly below average on through the
upcoming weekend. 

In the longer range, the ensemble mean of both the GFS and ECMWF
indicate that the longwave trough position will retrograde as we
move into early July, allowing a ridge over the Desert Southwest
to build back towards California. Thus, we may see warmer
temperatures by the July 4th holiday, especially across inland

&& of 10:25 AM PDT Monday...For 18Z TAFs. VFR. Low
clouds over the region this morning have dissipated and retreated
to the coastline as of 1730Z. Look for an increase in onshore
winds this afternoon with locally gusty conditions around the Bay
Area terminals. Low clouds will spread inland once again this
evening and persist through early Tuesday morning. 

Vicinity of KSFO...VFR. W to NW winds will increase this 
afternoon to around 15 kt with gusts to 20 kt possible. Low 
clouds will return around the terminal early Tuesday morning, yet
confidence of a ceiling developing over KSFO remains low. 

SFO Bridge Approach...Similar to SFO. However, higher confidence 
of low clouds over the approach Tuesday morning.

Monterey Bay Terminals...VFR. Slight increase in onshore flow this
afternoon. Low clouds likely to return late this evening and
persist through around 17Z-18Z Tuesday.

&& of 10:25 AM PDT Monday...Gusty northwesterly winds 
will continue over the northern outer waters and along the coast 
north of Point Reyes through Tuesday as high pressure remains over
the eastern Pacific. These winds will result in steep fresh swell
creating hazardous conditions over the waters, especially for 
smaller vessels. Winds will diminish on Tuesday as high pressure 
weakens and an upper low moves offshore of the Pacific Northwest.


     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm




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