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

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410
FXUS66 KMTR 241544
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
844 AM PDT Thu May 24 2018

.SYNOPSIS...Cloudy and cool today with increasing chance of
showers tonight into Friday as a late season low passes over the
region. Shower chances end by early Saturday morning. High
pressure builds Sunday through Tuesday with a noted warming and
drying trend.

&&

.DISCUSSION...as of 8:44 AM PDT Thursday...Visible satellite
imagery reveals another morning with low clouds blanketed over
much of the San Francisco Bay Area and central California coast.
Clouds have managed to make their way well inland up to the
Pacheco Pass along the Santa Clara-Merced County line, and south
through Monterey County all the way to the Monterey-Fresno and
Monterey-Kings County lines. Airport observations indicate cloud
bases are a bit higher than they were this time yesterday
morning...at/around 1,500 to 2,000 ft AGL. As the cloud coverage
is generally over similar locations to Wednesday morning,
temperatures are running within a degree or two from what they
were this time yesterday. Over the next 24 to 36 hours, an upper
level low will track toward the San Francisco Bay Area from the
eastern Pacific, bringing with it increased chances for shower
activity for much of the region. Rain amounts will be light with
some locations quite possibly not getting any at all. Some heavier
showers may produce upwards of a tenth of an inch of rain on
Friday morning and afternoon, with locally higher amounts for the
hills and mountains.

Made a few adjustments to sky cover to reflect the current
satellite trends; other than that no major morning updates
planned. For additional forecast details, please refer to the
previous discussion section.

&&

.PREV DISCUSSION...as of 3:42 AM PDT Thursday...Satellite shows low
clouds covering most of the region with high clouds now starting
to increase as well ahead of incoming upper low. Current obs show
cloud bases around 1500 feet most locations with another morning
of drizzle likely with abundant low level moisture and incoming
synoptic lift. Combination of cloud cover and fairly cool airmass
will mean another day of afternoon highs mainly in the 60s except
some 70s far interior valleys of the Central Coast.

Main forecast item of note will be shower chances with incoming
upper low. 06z nam and latest rap model indicate slight shower
chances by late this afternoon/early evening over the coastal
hills of Monterey county. Any late day breaks in the clouds will
help with some destabilization. Timing of upper low, which has
been pretty consistent for days now brings the core of the coldest
air through late tonight into early Friday morning. Thus we wont
have peak heating for instability. Nonetheless enough instability
to generate shower chances across much of the region Friday
morning. There remains a slight chance of thunder but for now the
forecast will just show showers as confidence for t-storms remains
low which is supported by latest spc general convective outlook
for Friday. Main impact will be for the Friday morning commute
when some rogue showers could produce wet roads with some brief
moderate showers possible. QPF numbers should be light, on the
order of a few hundredths for areas that receive showers although
localized amounts up to 0.25 will be possible.

The main shower threat should end as the sun goes down Friday
night but will hold onto slight chance showers through about
sunrise Saturday. Saturday will be a cool start to the holiday
weekend as we`ll be on the backside of the upper low with
continued strong onshore flow and cold air aloft.

Good news for the holiday weekend is building high pressure should
bring much more sunshine and warmer temperatures for Sunday and
Memorial Day with lots of highs back into the 70s and 80s away
from the coast. The surface pattern may even generate some
northerly flow which would even clear clouds at most beaches for
the second half of the holiday weekend.

Above normal temps to stay in place through Tuesday before the
next cool trough arrives midweek with another cooling trend.

&&

.AVIATION...As of 4:50 AM PDT Thursday...Widespread MVFR cigs
forecast to persist thru at least mid morning. Approaching upper
trof has allowed marine layer to deepen to approximately 3000 ft,
with a depth of around 1000 feet. This is leading to cig bases
predominately around 1500-2000 ft. Expect SCT with some patchy BKN
clouds to persist in the low to mid level into the late morning or
possibly early afternoon at some terminals. Onshore winds locally
breezy with occasional gusts to around 20kt at the windiest spots.
VCSH at the end of the taf period.

Vicinity of KSFO...MVFR thru 17-18Z this morning, then lingering
FEW-SCT low to mid level clouds as upper trof arrives. Breezy
onshore winds up to around 15k with gusts to around 20kt thru the
afternoon. Borderline VFR/MVFR cigs towards the end of the taf
period with VCSH.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR thru the mid to possibly late
morning around the Monterey Bay. Onshore winds to around 12 kt
with local gusts to around 18kt. Low to mid level few to sct
clouds will linger around the terminals thru the afternoon with
early return of borderline MVFR/VFR cigs by the evening.

&&

.MARINE...as of 08:41 AM PDT Thursday...Light to locally moderate
winds over the coastal waters today as  high pressure remains off
the immediate coast. The strongest winds today will be located in
the northern San Francisco Bay.  Northwest winds pick up by mid
day tomorrow and become locally  moderate by tomorrow night
through the upcoming weekend. Mixed  seas with a longer period
southwest swell and a smaller northwest  swell. Increasing winds
later this weekend will bring locally  steep fresh swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...SF Bay from 3 PM

&&

$$

PUBLIC FORECAST: RWW
AVIATION: DRP
MARINE: MM

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