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

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000
FXUS66 KMTR 251148
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
448 AM PDT SUN SEP 25 2016

...Record high temperatures forecast across the San Francisco Bay
Area and North Central Coast today and Monday...

...Heat Advisory in effect for the San Francisco Bay Area and
North Central Coast from 11 AM PDT TO 8 PM PDT today and
Monday...

...Red Flag Warning in effect for the North Bay Mountains through
3 PM PDT today...

.SYNOPSIS...Strong high pressure over California combined with
offshore flow will result in record warm temperatures today and
Monday. Modest cooling is forecast for Tuesday. Much more
significant cooling is expected during the second half of the
week as an upper level trough deepens along the West Coast.

&&

.DISCUSSION...As of 3:35 AM PDT Sunday...Skies are clear across
our entire forecast area early this morning as subsidence under a
strong high pressure ridge aloft continues to warm and dry the
airmass. In addition, surface high pressure has strengthened over
eastern Oregon and Nevada, resulting in a robust offshore surface
pressure gradient of nearly 12 mb from WMC to SFO. Winds remain
light near sea level, but offshore breezes have begun to pick up
in the hills above a shallow nocturnal inversion. Northeast winds
in the North Bay Mountains are currently gusting as high as 35
mph. The combination of a very warm airmass over our region and
offshore flow will push temperatures up into record warm
territory today. In fact, high temperatures today for many
locations are forecast to be the warmest so far this year
including in Downtown San Francisco, San Jose, the Oakland
Museum, and Salinas. The heat is forecast to continue unabated
into Monday, and according to most model guidance high
temperatures on Monday will be a few degrees warmer than today.
More record highs are likely on Monday. These hot temperatures
over the next two days will create stress on anyone sensitive to
heat. One mitigating factor to the heat during the day will be
the relatively long autumn nights which will allow homes without
air conditioning to cool down. Even so, conditions during the day
will be oppressive, particularly for those living in coastal areas
who are not acclimated to such warm conditions. A heat advisory
is in effect from 11 am to 8 pm both today and Monday for our
entire forecast area.

A shortwave trough approaching the Pacific Northwest on Tuesday
will weaken the upper ridge over California and it`s expected
that light onshore flow will develop across our area. Thus we
should see at least modest cooling on Tuesday, particularly in
coastal areas where high temperatures may drop by as much as ten
degrees. Inland areas will remain very warm however. It`s not
until Tuesday night that the models indicate a good inland influx
of marine air and a return of coastal low clouds and fog.
Widespread and significant cooling is then forecast for Wednesday
and Thursday as an upper trough in the Gulf of Alaska drops southeast
towards California. On Wednesday high temperatures are forecast to
be anywhere from 15 to 25 degrees cooler compared to Monday. For
example, the forecast high in San Francisco on Monday is 90 and
on Wednesday 65.

Precipitation with the upper trough late in the week and into next
weekend is expected to remain well to our north, but it`s worth
noting that the 00Z GFS develops rain as far south as Mendocino
County by Saturday.

&&

.AVIATION...As of 4:45 AM PDT Sunday...Strong upper level high
over the area with offshore flow will keep VFR clear skies.
Non-convective low level wind shear is a possibility Sunday near
the East Bay Hills.

Vicinity of KSFO...VFR. Light winds.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR.

&&

.FIRE WEATHER...As of 3:30 AM PDT Sunday...Northeast winds have
increased in the hills since midnight, particularly at elevations
above 1500 feet in the North Bay, gusting locally as high as 35
mph at 2000 feet in Sonoma County. At the same time, relative
humidities have not recovered and in some cases RH values have
fallen below 20 percent overnight. A red flag warning is currently
in effect for the North Bay Mountains. Latest model output
continues to show gusty offshore winds across mainly the higher
elevations of northern Sonoma and Napa counties through the
morning hours, with winds then expected to gradually diminish in
the afternoon. The Red Flag warning for the North Bay Mountains is
in effect until 3 pm this afternoon. Winds are expected to remain
light from late this afternoon onward. However, hot and dry
conditions will persist through Monday with only slight cooling
expected on Tuesday. Much more significant cooling is forecast
beginning Wednesday and continuing through the second half of the
week.

In the vicinity of the Soberanes Fire: Portable RAWS stations
indicate mostly light winds below 3000 feet early this morning
with northeast winds of 10 to 15 mph with gusts to 20 mph above
3000 feet. This is consistent with latest WRF model wind guidance.
The WRF indicates easterly winds will diminish by sunrise and then
turn to the south and southwest by midday. Southwest winds are
then forecast to increase somewhat in the afternoon hours,
probably up to around 10 to 15 mph. Meanwhile, hot and dry
conditions are forecast to continue into Monday, although winds
tonight and Monday are expected to be lighter. Slight cooling is
projected for Tuesday, mainly along lower coastal slopes, with
very warm to hot conditions continuing for most other areas. Will
have to wait until Wednesday before widespread cooling occurs.

&&

.CLIMATE...Here are the record highs for September 25 and
September 26.

                   September 25                September 26
                   Record/Year                 Record/Year
Bay Area

Kentfield.............100/1964.....................99/1921
San Rafael............100/1964.....................99/1963
Napa..................101/1960....................105/1963
San Francisco..........93/1954.....................94/1992
SFO....................91/1970.....................95/1958
Oakland Museum.........95/1978.....................93/1973
Oakland Airport........94/2010.....................97/1958
Richmond...............95/1964.....................95/1963
Livermore.............101/1978....................103/1952
Mountain View..........91/1978.....................95/1999
San Jose...............97/1952.....................98/1963
Gilroy................106/1978....................104/1963

Monterey Bay Area

Monterey...............95/1954.....................98/1970
Santa Cruz............100/2010....................101/1970
Salinas................97/1960....................100/1970
Salinas Airport........99/1937.....................99/1970
King City.............105/1975....................105/1963

&&

.MARINE...As of 4:45 AM PDT Sunday...High pressure covers the
eastern Pacific and the Great Basin while thermal trough lies
along the California coast. The trough will move into the
California interior on Tuesday. Winds will become light Sunday and
Monday then increase Tuesday and Wednesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Heat Advisory...Entire San Francisco Bay Area and North
                             Central Coast from 11 am to 8 pm
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 9 AM

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: W Pi
CLIMATE: BAM
FIRE WEATHER: Dykema


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