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

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FXUS66 KMTR 121127
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
327 AM PST Tue Dec 12 2017

.SYNOPSIS...Strong high pressure will remain in place through much
of the week and result in dry weather conditions along with above
average daytime temperatures. Clear skies and weak offshore flow
will allow for cool overnights which will warm slightly late in
the forecast period as onshore winds return.

&&

.DISCUSSION...as of 2:30 AM PST Tuesday...Dry and mild conditions
continue across the Bay Area as high pressure remains in control.
Simply put, only minor tweaks to the forecast as guidance keeps
much of CA dry through early next week.

Now for the details...latest longwave pattern shows a classic Rex
Block across the West with high pressure over the Great Basin and
low pressure over the Gulf of California. The blocking pattern has
kept stagnant weather in place the last few days. However, the
ridge of high pressure is forecast to shift westward today
weakening the blocking pattern and possibly a transition to a
pattern change this weekend and early next weak.

High pressure overhead has led to another chilly morning across
interior/protected valleys with temperatures in the upper 20s to
lower 30s. Patchy frost will be possible in these locations, but
nothing too widespread given how dry the airmass is. On the flip
side, temperatures are much warmer and in the upper 50s to lower
60s across the hills.

Given the retrograding high pressure, warming 850mb temps and
continued offshore flow above normal temperatures will continue
into the weekend. Daytime highs will be 5 to 15 degrees above
normal with readings in the mid to upper 60s across the SFO Bay Area
with 70s from the Santa Clara Valley south. A few interior spots
may even approach 80 across Monterey/San Benito. Overnight lows
will remain chilly with patchy frost and readings near freezing.
Warmer temps near urban areas, the coast and higher terrain.

Medium range models flatten the ridge as a weak boundary slides
into the PacNW Friday into Saturday. The Canadian is the most
aggressive with precip near the CA/OR border, but the EC and GFS
are much drier. For the Bay Area, no mention of precip, but cooler
temps and some clouds possible this weekend.

The ridge rebuilds Sunday/Monday with continued warm and dry
conditions. The million dollar question continues to be, when will
it rain? For several days now long range models have suggested a
pattern shift and possibly some precip around December 20. The 00Z
model run of the EC and GFS still shows that thinking, but the
Canadian not so much.

&&

.AVIATION...As of 03:27 AM PST Tuesday...for 12Z TAFs. VFR with
light winds through the period for all sites except for patchy fog
at KSTS until early this morning.

Vicinity of KSFO...VFR. Light winds through the forecast period.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Generally light winds except for E-SE
winds around 10 knots into the afternoon at KSNS.

&&

.CLIMATE...

HERE IS A LIST OF RECORD HIGH TEMPERATURES ALONG WITH THE MOST
RECENT DATE IT OCCURRED.
*SIGNIFIES THERE ARE ADDITIONAL YEARS THE RECORD WAS SET.

SF BAY AREADecember 13December 14
.LOCATION................
 HEALDSBURG..............76/191177/1942
 SANTA ROSA..............74/195872/1956
 KENTFIELD...............73/191170/1942
 SAN RAFAEL..............69/195070/1959
 NAPA....................72/193473/1959
 SAN FRANCISCO...........71/191169/1988
 SFO AIRPORT.............69/195869/1958
 OAKLAND AIRPORT.........70/195865/1958
 RICHMOND................75/195867/1983
 LIVERMORE...............73/195875/1958
 MOFFETT FIELD...........68/195372/1958
 SAN JOSE................70/195873/1958
 GILROY..................78/195872/1988

MONTEREY BAY AREA
.LOCATION................
 MONTEREY................77/195378/1953
 SANTA CRUZ..............77/194482/1953
 SALINAS.................79/195880/1988
 SALINAS AIRPORT.........80/195381/1953
 KING CITY...............79/193683/1958

&&

.MARINE...as of 02:21 AM PST Tuesday...A ridge of high pressure
remains over the coastal waters and much of the west coast. Winds
will continue to be light to  moderate with some locally breezy
conditions in the northern outer waters and along the immediate
coast south of Point Sur this  afternoon through tonight.
Northwesterly winds are then expected  to increase late this week
and into the upcoming weekend. Steadily larger, long period swell
will impact the coast mid to late this  week as well.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 PM

&&

$$

PUBLIC FORECAST: MM
AVIATION: AS
MARINE: AS

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