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

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FXUS66 KMTR 270549
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1049 PM PDT Wed Jul 26 2017

.SYNOPSIS...A gradual warming trend will get underway through late
week and extend into next week. As the sub-tropical ridge strengthens
this weekend and next week over much of the west including California
temperatures will climb well above late July and early August averages;
it should become clearer with time as to how hot temperatures may get
and what days will be hottest over the Bay Area and north Central
Coast. The sub-tropical ridge will then become more focused over the
Desert Southwest by the middle of next week. As a result increasing
upper level southerly winds may bring remnant mid and high clouds
as far north as the Bay Area beginning Wednesday next week from then
decaying tropical cyclones moving west-northwest over the tropical
Pacific. Please stay tuned to weather updates in the days ahead.

&&

.DISCUSSION...as of 9:05 PM PDT Wednesday...Presently the marine
layer depth varies from 1,000 feet at the San Carlos sodar to
2,400 feet at the Fort Ord profiler. The Bodega Bay profiler data
is old.

A closed upper level low over far northern California will move
across the northern Great Basin tonight into Thursday. In its wake
weak upper level troughing will linger over California until this
weekend when the sub-tropical ridge strengthens over much of the
west including California. The sub-tropical ridge will persist
through next week tending to take up residence over the Desert
Southwest by the middle of next week. Large scale and increasing
subsidence underneath this ridge coinciding with long wave ridging
over the west will push temperatures upwards, but as to how hot
and when more precisely will the hot weather peak is not very
clear yet. As a result of the sub-tropical ridge eventually shifting
to the Desert Southwest increasing upper level southerly winds may
bring remnant mid and high clouds as far north as the Bay Area
beginning Wednesday next week from then decaying tropical cyclones
moving west-northwest over the tropical Pacific.

&&

.PREV DISCUSSION...as of 1:59 PM PDT Wednesday...This morning`s low
clouds have mostly mixed out for inland areas, revealing mostly
clear to clear skies across the region. Temperatures are generally
running within several degrees of what they were 24 hours ago at
this time. Afternoon high temperatures will range from the 60s to
perhaps as warm as the low 70s along the coast, and upper 70s to
low 90s for inland areas. Can`t rule out a few areas that reach
the mid/upper 90s for parts of the southern Salinas Valley,
Pinnacles National Park, and interior Monterey County.

An upper-level low just off the northern California coast will
push northeast over the next day and weaken as it continues into
the continent. By tomorrow we`ll see 500 mb heights nudge upward
by 2-4 decameters as an upper level ridge expands over the Desert
Southwest. Along with height rises, models are advertising
warming in the low and mid-levels -- 850 mb temps are expected to
warm by 2-4 deg C over the next 24 hours. As a result, we`ll see
warming conditions at the surface and a compression of the marine
layer. The challenging aspect of this is how warm will we exactly
get for Thursday and Friday. Looking at the many ECMWF ensemble
members, some of the warmest individual members are forecasting
the low 90s for tomorrow at San Jose (KSJC). With this in mind,
the official forecast for the next few days continues to follow
some of the warmest guidance. As for the potential heat levels,
there are some areas of moderate heat risk for the interior East
Bay and parts of the South Bay, but not quite enough coverage to
consider a heat advisory. We`ll continue to monitor forecast highs
and heat levels over the next few days and make changes if
necessary.

For the first half of the weekend, temperatures may cool by
a few degrees for interior locations as 500 mb heights fall with
a passing shortwave. Models begin to disagree with the placement
and strength of the ridge on Sunday, though overall begin to trend
500 mb heights back up into Monday. Into Tuesday and Wednesday
next week, models continue to advertise the upper-level ridge over
the Southwestern US. This equates to more hot weather for
interior areas as we enter the beginning of August.

&&

.AVIATION...as of 10:49 PM PDT Wednesday...For the 06z TAFs...
Stratus is making an aggressive push inland at this hour under a
2400 ft marine layer and moderate onshore gradient. IFR/MVFR cigs
anticipated to fill in over most area terminals overnight. Low
clouds will clear to the coast between 17z-18z Thursday morning.

Moderate confidence.

Vicinity of KSFO...Borderline IFR/MVFR cigs anticipated to fill
in overnight with clearing expected around 17z-18z Thursday
morning. Light to moderate west winds will prevail.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...IFR cigs will prevail through the night
with clearing expected around 18z-19z Thursday morning. Light
onshore winds will prevail.

&&

.MARINE...as of 9:00 PM PDT Wednesday...Expect increasing west to
northwesterly winds across the waters this evening especially
north of Point Reyes. A long period southerly swell will arrive
across the waters at the start of the weekend due to several
tropical disturbances in the Pacific.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay until 11 PM

&&

$$

PUBLIC FORECAST: Canepa/Rowe
AVIATION: CW
MARINE: Anna/CW


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