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

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FXUS66 KMTR 221152
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
452 AM PDT Thu Jun 22 2017

...Hot weather continues inland through this evening...

.SYNOPSIS...Heat Advisories and Warnings are in place today
through 9 pm for dangerously hot temperatures. A shallow marine
layer along the Central Coast will keep the Monterey Bay coastal
areas much cooler. All areas start to gradually cool Friday and
through the weekend as more persistent onshore flow returns to the
region.

&&

.DISCUSSION...As of 4:06 AM PDT Thursday...Northerly gradient
down the coast is still around 6 mb and helping to support some
north/northeast winds across the North Bay hills. A few sites in
the North Bay hills are still above 90 as of 3 am with widespread
70s and 80s in the hills. There is still enough onshore flow at
the surface with 2 mb sfo to sac to allow the valleys to cool into
the 60s. Its this somewhat subtle northerly wind flow in the
hills that will set the stage for rapid warming today, especially
for the interior of the north and east bay. Essentially heat
advisories are in place near SF bay and some of the valleys with
Warnings in place for the hills and far east bay where warm
overnight lows and hot days have meant little or no relief from
the heat. The warnings/advisories remain in place through 9 pm. If
seeking relief the coast from Santa Cruz southward through
Monterey county is the place to be with an 800 foot marine layer
in place. The immediate coast will remain out of any headlines.

Even though 850 mb temps dont change too much into Friday we
expect noted cooling to occur especially for the coastal and
bayside valleys. The upper flow will become so amplified and
eventually buckle with weak surface low pressure (around 1010 mb)
developing well offshore. This in combination with the excessive
heat across the central valley will induce persistent onshore flow
Friday and through the weekend as well as a deepening marine
layer. Upshot is to expect a modest cooling trend back to more
seasonable levels.

Long range trends on the latest ecmwf show the upper pattern with
a trough off the coast suggesting near to perhaps slightly below
normal temperatures for next week. No precipitation, outside of
coastal drizzle is forecast.

&&

.AVIATION...As of 4:50 PM PDT Thursday...The marine stratus deck
is struggling under the dry, subsiding high pressure dome set up
over the area. As a result, widespread VFR conditions are being
reported at TAF sites. That said, marine stratus is still
obscuring the Monterey Bay and portion of the Northern Salinas
valley. For today, generally light occasionally breezy winds and
clear skies will prevail. For tonight, mostly clear skies with
some stratus primarily banked up along the Monterey expected.

Vicinity of KSFO...VFR. Light winds becoming breezy by the
afternoon up to 15 kt.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR at the TAF sites with LIFR to IFR
cigs due to marine stratus in the vicinity of the TAF sites. Light
winds. Low clouds will briefly return tonight but depart before
sunrise.

&&

.FIRE WEATHER...As of 4:06 AM PDT Thursday...The most critical
areas this morning will be the hills of the North Bay, especially
Napa county and around Mt St Helena where winds above 2000 feet
will be northeast and gusting 20-25 mph. Humidity values are
starting to drop down to 20-30% in the hills as of 3 am with hot
temperatures in the 80s and lower 90s at this early hour. Expect a
hot and dry day all inland areas and hills today. Main concern
this afternoon will be a transition to westerly winds should any
new starts occur.

Although onshore flow will return by tonight, the marine layer
will remain shallow and the airmass aloft will remain very warm
for a few more days. Thus, conditions in the hills will only
gradually improve from Friday through the weekend. Much improved
conditions are expected by early next week.

&&

.CLIMATE...

Here is a list of record high temperatures

SF BAY AREA              Thursday
LOCATION.................Temp/Year
 KENTFIELD................102/1989
 SAN RAFAEL................99/2006
 NAPA.....................105/1981
 SAN FRANCISCO.............97/1989
 SFO AIRPORT...............98/1989
 OAKLAND AIRPORT...........94/1957
 RICHMOND..................94/1989
 LIVERMORE................110/1961
 MOFFETT FIELD.............99/1989
 SAN JOSE.................101/1989
 GILROY...................110/1973

MONTEREY BAY AREA        Thursday
LOCATION..............   Temp/Year
 SALINAS...................89/1981
 SALINAS AIRPORT...........92/1947
 KING CITY................110/1929

&&

.MARINE...as of 04:46 AM PDT Thursday...Split flow with moderate
northwest winds primarily over the  northern outer waters with
lighter southwest winds elsewhere.  Hazardous seas from steep wind
waves and fresh swell can be  expected over the outer waters
through the day. Look for  gradually improving conditions late
today through the remainder of the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Heat Advisory...CAZ508 11 am til 9 pm
             Heat Advisory...CAZ506-513-516-518 til 9 pm
             Excessive Heat Warning...CAZ507-510>512-517 til 9 pm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm until 9 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 PM

&&

$$

PUBLIC FORECAST: RWW
AVIATION: DRP
MARINE: DRP
FIRE WEATHER: rww


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