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

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556
FXUS66 KMTR 122343
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
343 PM 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 12:40 PM PST Tuesday...The dry and mild
weather pattern continues across the San Francisco Bay Area and
central California coast again this afternoon. A strong, upper
level ridge remains parked over the West Coast and has been
largely responsible for the extended streak of the dry conditions.
The 12Z Oakland sounding this morning recorded a precipitable
water (PWAT) value of just 0.15 inches, representing the driest
atmospheric profile at Oakland for all 12 December 12Z balloon
launches. Upper air records at Oakland date back to the 1940s,
according to the Storm Prediction Center.

This afternoon is essentially a copy/paste from yesterday: mostly
clear skies, some areas of smoke aloft, and high temperatures
generally in the 60s and 70s. Some interior areas of Monterey
County as well as San Benito County will likely crack 80 degrees
by the end of the day. These values range anywhere from about 5 to
15 degrees above middle December climatological normals. With the
exceptionally dry air mass in place and long December nights,
expect another chilly night again with many North Bay valley
locations falling back to near freezing.

Another concern associated with the extended period of dry weather
is fire weather. Sufficient rain fell in late October and
November that allowed for fuel moisture values to increase from
Monterey and points north. This increase was unfortunately short-
lived as both the recent lack of rainfall and extended streak of
above normal temperatures have consequently reversed fuel moisture
values back to well below normal levels for middle December. Our
local in-house WRF suggests another offshore wind event in the
East Bay Hills overnight tonight and into Wednesday morning with
poor relative humidity recoveries. At this point the forecasted
winds don`t appear to be as strong as this morning, but
nonetheless will be carefully watched.

The upper level ridge will remain over the West Coast through the
end of the work week. This will result in continued cool nights
and above normal afternoon temperatures region-wide with some
minor day-to-day fluctuations. The ridge will flatten on late
Friday or Saturday as a short wave approaches the Pacific
Northwest along with the return of onshore flow. Unfortunately,
models are advertising any precipitation chances to remain well to
our north in far northern California, Oregon, and Washington.
Models solutions then begin to advertise a ridge building back
over the West Coast by Sunday. There remain some hints of a
potential pattern change middle next week as the GFS and ECMWF
bring a trough into the Pacific Northwest. Meanwhile, the Canadian
model keeps the ridge in place over the West Coast. For at least
the next 7 days though, expect dry weather to continue to prevail.

&&

.AVIATION...As of 4:00 PM PST Tuesday...Offshore flow will
continue through the next 36-48 hours. Light winds will allow
patchy fog in the North Bay valleys after 09Z.

Vicinity of KSFO...VFR.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. E-SE winds to 10 knots after 08Z at
SNS.

&&

.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 10:04 AM PST Tuesday...Increasing northwest winds
over the waters beginning later today through the upcoming
weekend. The strongest winds today will be primarily be located
south of Half Moon Bay through Davenport and as well as from Point
Sur and southward. Steadily larger, long  period swell will impact
the coast mid to late this week as well.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm

&&

$$

PUBLIC FORECAST: Rowe
AVIATION: W Pi
MARINE: DRP

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