NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 010039

Area Forecast Discussion
National Weather Service San Francisco Bay Area
539 PM PDT Sat Oct 31 2020

.SYNOPSIS...Warm and dry conditions are forecast through the
weekend and into early next week, with temperatures forecast to be
as much as 15 degrees above seasonal averages. Hazardous beach
conditions are expected Sunday afternoon into Monday evening with
sneaker waves and rip currents likely along northwest-facing
beaches. Mild and dry conditions are forecast for much of next
week, with a modest cooling trend from Tuesday through Thursday.
Much cooler temperatures are expected by the end of next week,
with the potential for precipitation by late Friday.

&& of 01:45 PM PDT Saturday...A few clouds cling to
the San Francisco Peninsula Coast (Half Moon Bay) keeping temps
cool. Elsewhere around the Bay Area and Central Coast sunshine
blankets the region with above normal temperatures. Temperatures
are mostly in the upper 60s to lower 80s...and will likely rise a
tad more before the day is done.

Upper level high pressure to the north and upper level low
pressure to south will promote mild and dry conditions over the
forecast are through at least Monday. A few night and morning
clouds with patchy fog will be possible. Otherwise, mostly clear
skies can be expected. The orientation of the high and low will
help to promote dry easterly flow. The lack of onshore flow will
enhance daytime warming. Mild daytime temperatures and low
humidity will heighten fire weather concerns too, but fortunately
winds will remain relatively light. Speaking of lighter winds,
clear skies and dry conditions will help promote ideal radiational
conditions at night. Inland valleys will likely drop into the 40s
and 30s the next few nights.

The aforementioned upper low finally drifts inland on Monday, but
in its wake an upper trough approaches from the west bringing
increased onshore flow. More widespread cooling is expected
Monday to Tuesday, but still remain mild and above normal.
Temperatures then flatten Tuesday through Thursday with more zonal
flow aloft.

All focus then turns to a pattern change Friday and next weekend
with colder temperatures and possible precipitation. Medium range
operational models are surprisingly in decent agreement with the
big picture. A low pressure system is forecast to develop near the
Gulf of Alaska and then move southward toward CA. Timing would be
for development on Thursday and then progressing southward to CA
Thursday night and Friday. Precip chances initially develop over
the PacNW with a possible AR before moving south to the OR/CA. The
exact track of the low will help enhance or take away precip
chances for the Bay Area. As of now a more westward track is
developing - favoring better chances for precip. All that being
said, don`t put all your forecast eggs in the operational model
basket. Ensembles paint a slightly different story. Almost all
favor cooler temperatures, but precip varies with some members
very wet and others completely dry. Will keep forecast as is for
now - low end chance for some precip with cooler temperatures.

&& of 5:39 PM PDT Saturday...For the 00z TAFs. Early
evening satellite imagery shows fog and stratus /VLIFR-IFR/ along
coastal Sonoma and Marin counties, elsewhere it`s VFR. The marine
layer is approximately 800 feet deep. Mostly clear tonight with
exception of patchy valley fog early Sunday morning and additional
areas of coastal fog and stratus tonight and Sunday morning.

Vicinity of KSFO...VFR. Evening northwest winds to around 12 knots,
subsiding overnight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. West to northwest winds decreasing
and shifting to light land breezes tonight. West to northwest winds
redeveloping Sunday afternoon.

&& of 5:00 PM PDT Saturday...A large northwest swell
will arrive Sunday afternoon and impact coastlines through Monday
afternoon, then subsiding. Initial swell heights of 1 to 2 feet at
23 seconds is expected increasing the risk of sneaker waves. By
Sunday evening into Monday morning, wave heights of 6 to 9 feet at
periods of 18 to 20 seconds are expected, with most favored
northwest facing beaches at 10 to 12 feet. Biggest impacts will be
the increase for sneaker waves and rip currents for northwest
facing beaches from Coastal Sonoma County to Coastal Monterey

&& of 5:07 PM PDT Saturday...Northwest winds remain
light to locally moderate. Occasional stronger gusts may develop
along the the immediate coastlines. Mixed seas expected this
weekend with a light long period southwest swell mixed with a pair
of shorter period northwest swells in the near term. A larger,
longer period northwest swell train arrives on Sunday evening.






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NWS MTR Office Area Forecast Discussion