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

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FXUS66 KMTR 202348
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
448 PM PDT Sun May 20 2018

.SYNOPSIS...Upper low over California will keep temperatures below
normal at least through Tuesday. Weak ridge builds around midweek
with temperatures near normal before another trough approaches
Friday through Sunday with onshore winds keeping temperatures on
the cool side of normal while mainly dry conditions are forecast.

&&

.DISCUSSION...as of 1:42 PM PDT Sunday...Below normal
temperatures and breezy onshore winds continue to be the main
forecast trend. So far this afternoon temps generally running from
the upper 50s beaches, 60s around the bay and 70s well inland.
Cloud decks are around 2500 feet deep along the coast due to an
upper low over the region. The Ben Lomond RAWS up in the Santa
Cruz mountains is sitting in the cloud layer and so far reporting
a high of only 49 degrees so far this afternoon. Onshore gradient
of 2.5 mb from sfo to sac is pushing some gusty winds from the
Golden Gate out into the Delta with SFO gusting to 33 mph last
hour.

Looking forward the last few nam runs have generated some coastal
drizzle tonight with cyclonic flow aloft and moist onshore flow
lifting the boundary layer. Coastal hills from San Mateo southward
to Monterey that are exposed to nw winds off the ocean is where
the modeling is showing some measurable drizzle type qpf that
should it develop will be localized.

Main forecast theme to start the work week will be continued below
normal temps and breezy onshore winds. The North Bay may see the
most sunshine on Monday with drier north/northeast flow around
the upper low. MOS data showing 79 degrees for Santa Rosa on
Monday while most cities around the Bay will see 60s once again
with some lower 70s for the Santa Clara Valley.

The upper low slowly ejects inland by Tuesday but a deep marine
layer and onshore flow will likely remain in its wake with
continued trend of below normal temps and onshore breezes.

Some weak ridging or zonal type flow develops Weds afternoon into
Thursday sending temps back to near normal.

Longwave trough approaches by Friday afternoon with onshore winds
and approaching upper low sending inland temps back below normal
once again for Saturday and Sunday of the upcoming Memorial Day
weekend. Latest ecmwf does indicate system may be progressive
with warmer high pressure by Memorial Day Monday but that scenario
may be dubious with developing tropical system in the Gulf of
Mexico potentially slowing the large scale west to east flow
across the US.

&&

.AVIATION...As of 4:48 PM PDT Sunday...It`s VFR with a few areas
MVFR ceilings mainly on the coast this afternoon. Low clouds will
generally fill in again tonight and Monday morning. Mid to high
clouds with a 500 mb closed low will slowly move eastward this
evening into Monday.

Vicinity of KSFO...MVFR ceiling tonight into Monday morning, westerly
wind gusting to 30 knots this evening. Gusty westerly wind resumes
Monday afternoon and evening.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR ceilings tonight into Monday morning.
Partial clearing possible either by late Monday morning or early
afternoon.

&&

.MARINE...as of 01:17 PM PDT Sunday...A strong north to south
pressure gradient along the California coast will maintain
moderate to strong northwesterly winds over  the coastal waters
through Monday. As a result, steep wind waves  will produce
hazardous conditions for small crafts. A long period  southerly
swell will increase and mix with northwesterly swell by  Monday
morning, gradually increasing through much of the week.

&&

.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 Reyes to Pigeon Pt 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

&&

$$

PUBLIC FORECAST: RWW
AVIATION: Canepa
MARINE: RGass

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