Technical NOAA Weather Discussion

FXUS66 KMTR 192338

Area Forecast Discussion
National Weather Service San Francisco Bay Area
438 PM PDT Thu Sep 19 2019

.SYNOPSIS...Seasonably cool conditions will persist today under
mostly sunny skies. A warming trend will begin on Friday and
continue through Saturday. A low pressure system moving southward
to our east early next week may create the potential for continued
warming temperatures, dry offshore flow and increased fire weather

&& of 02:00 PM PDT Thursday...Water vapor imagery
indicates an upper trough is centered over western Nevada and is
moving eastward. The southern portion of the trough extends over
our region, with cool temperatures aloft and northwesterly flow a
result of this feature. Dry air and subsidence on the back side of
this trough has resulted in mostly sunny skies with a little bit
of cumulus development over the terrain and no real marine layer
to speak of. Temperatures today have been mild, with upper 60s to
mid 70s observed across the area. Highs will end up being a few
degrees below seasonal averages, which combined with generally
light winds and mostly sunny skies is making for a very pleasant

An upper ridge centered over the eastern Pacific will begin to
build over the West Coast on Friday and continue to strengthen
through Saturday. Temperatures aloft will warm, with 850 mb temps
reaching approximately 15C on Friday and 17C on Saturday. The
warming aloft will translate to warming at the surface, especially
away from the coast. Inland valley locations look to warm well into
the 80s on Friday, with mid 80s to lower 90s common on Saturday.
Onshore winds will keep temperatures from rising too much at the
coast, but an increased offshore component on Saturday will help
temperatures reach the 70s to lower 80s. North to northeast winds
will be breezy at times in the North Bay Hills on Saturday
morning, but not windy or dry enough for major fire weather

On Sunday, the ridge will begin to flatten as another trough
approaches the Pacific Northwest. In response high temperatures
should cool a few degrees. The trough will then take a northwest
to southeast trajectory and is likely to follow an "inside slider"
type path, with the core of the trough moving just east of the
Sierra crest. The past several runs of the GFS deterministic have
kept the trough over Utah and Colorado, but this appears to be an
outlier compared to GFS and ECMWF ensemble means. As the trough
moves into the Desert Southwest, offshore flow will develop as
surface high pressure strengthens over the Intermountain West.
This will likely result in a significant warming and drying trend
for our area Monday through Wednesday. The exact track and
strength of the trough early next week will determine the strength
of the offshore flow and amount of drying/warming we see. This
pattern will need to continue to be closely monitored as it could
lead to increased fire weather concerns.

Warm and dry conditions look to persist through the middle of next
week. The long range ensembles are starting to hint at a trough
dropping down the West Coast next weekend, which would result in
cooler conditions for the region.


.AVIATION...As of 4:40 PM PDT Thursday...A few afternoon cumulus
clouds over the area. Drier air moves into the low levels tonight
so VFR conditions expected through Friday.

Vicinity of KSFO...A few cumulus clouds at 3000-4000 ft through
04Z then clear skies expected. West winds 15 to 20 kt with gusts to
25 kt through 04Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions are forecast to prevail
through Friday. Could see some localized stratus try to develop
overnight along the MRY Bay shoreline but confidence of occurrence
is rather low.

&& of 04:32 PM PDT Thursday...Moderate and locally gusty
northwest winds winds will continue into the evening hours over
the waters, with the strongest winds  in the outer waters north of
Point Reyes and locally south of  Point Sur along the Big Sur
coast. Winds will then gradually  subside overnight. An 11 second
northwest swell will be the  predominate wave in the waters today,
bringing the potential of  hazardous conditions from squared seas
to portion of the waters. A much lighter southerly swell will also
be mixed in.


     .Tngt...SCA...Mry Bay until 9 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm until 9 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM




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Prepared by Weather at: Thu Sep 19 18:30:02 PDT 2019
From the National Weather Service