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

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS66 KMTR 221426

Area Forecast Discussion
National Weather Service San Francisco Bay Area
726 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

&& of 07:25 AM PDT Thursday...The well-advertised
very hot Thursday is upon us. Excessive Heat Warnings cover the
interior East Bay Hills and Valleys, the North Bay Hills, the
higher elevations of Monterey County, as well as the Santa Cruz
Mountains until 9 pm PDT this evening. Heat Advisories remain in
effect for the southern Salinas Valley, interior San Benito County
including Pinnacles National Park, the Santa Clara Valley, and
the North Bay Valleys until 9 pm PDT. Furthermore, the Heat
Advisory for the San Francisco Bay Shoreline begins at 11 am PDT
this morning and goes through the evening hours. Don`t see any
reason to alter these products at this time, but will have to
consider additional headlines for Friday across the warmest

The 24 hour change in temperatures across the ASOS sites is
remarkable. At 7 am, Santa Rosa is sitting 7 degrees warmer than
24 hours ago, San Rafael 10 degrees warmer, and 8 degrees warmer
at Napa in the North Bay. Across the major airports around the
San Francisco Bay, everyone is running warmer than 24 hours ago as
well. San Francisco International Airport and is 7 degrees
warmer, San Jose 11 degrees warmer, and Oakland is 6 degrees
warmer. The marine layer is much more compressed today than
yesterday as well, limiting the inland intrusion and yielding
mostly clear skies for most. Low clouds are surging north along
the San Mateo Coast and will likely approach the Golden Gate
later this morning or afternoon. This could impact high temps
around downtown and will have to monitor carefully.

We cannot stress the hazards from this heatwave enough. Many
locations away from the coast have been above normal for over a
week. The prolonged nature of this heatwave introduces dangerous
hazards beyond the typical heatwave. Over a 30 year period, heat
is the number one weather-related killer in the United States --
131 deaths per year from 1987 to 2016 on average. Take care of
yourself, your family, and your pets. Check in on your neighbors
and the elderly. Take the necessary precautions to beat the heat:
drink plenty of fluids, limit outdoor activity during the hottest
time of the day, wear light-colored clothing, put on a hat. If you
don`t have air conditioning, consider going to a community
cooling center, a shopping center/mall, or movie theater. If
you`re parked in the shade, or even if you`re at the coast with
outdoor temperatures in the 60s: never leave children, pets, or
adults alone in a parked vehicle. Stay safe, stay hydrated, and
beat the heat.

No major changes planned to the current forecast; please refer to
the previous discussion section for additional forecast


.PREV 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


.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.



Here is a list of record high temperatures

SF BAY AREA              Thursday
 SAN RAFAEL................99/2006
 SAN FRANCISCO.............97/1989
 SFO AIRPORT...............98/1989
 OAKLAND AIRPORT...........94/1957
 MOFFETT FIELD.............99/1989
 SAN JOSE.................101/1989

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

&& of 06:53 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.


     .Tday...Heat Advisory...CAZ508
             Heat Advisory...CAZ506-513-516-518
             Excessive Heat Warning...CAZ507-510>512-517
             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




Visit us at

Follow us on Facebook, twitter, and youtube at: is the U.S. government's official web portal to all federal, state and local government web resources and services.