Technical NOAA Weather Discussion

FXUS66 KMTR 191608

Area Forecast Discussion
National Weather Service San Francisco Bay Area
908 AM PDT Mon Aug 19 2019

.SYNOPSIS...A deep marine layer will prevail through today,
maintaining widespread morning low clouds and cooler than normal
inland temperatures. Patchy drizzle is possible through mid
morning. Warmer temperatures will develop by midweek and continue
through the upcoming weekend as high pressure rebuilds.

&& of 9:08 AM PDT Monday...Visible satellite
imagery reveals widespread stratus coverage across the San
Francisco Bay Area and Central California Coast. The only
populated locations with clear skies at this time would be in the
interior East Bay from Pleasant Hill and points east, as well as
the parts of the Highway 17 corridor between Campbell and the
Santa Cruz-Santa Clara County line. With the marine layer in
excess of 2,000 ft -- and even 2,500-3,000 ft for some locations
-- many locations can expect the stratus to hang around later than
it usually does on a typical summer day. Along with the deep
marine layer, there are a handful of surface observation sites
that have recorded measurable drizzle in Santa Cruz County this

Made some major adjustments to the short-term sky grids, mainly
based on the satellite trends. No other changes are planned at
this time for the morning update as the short-term is on track.
For additional forecast details please refer to to the previous
discussion section.


.PREV DISCUSSION...As of 3:50 AM PDT Monday...The marine layer remains
deep early this morning with the Fort Ord Profiler indicating a
depth of more than 3000 feet. The deep stratus cloud layer has
been producing patchy drizzle overnight. The Watsonville and
Salinas Airports have reported trace amounts of precipitation and
a few locations in the Santa Cruz Mountains have picked up
measurable precipitation for the third night in a row (although
amounts are mostly only 0.01"). Conditions early this morning are
much like yesterday morning with similar marine layer depth and
light to moderate onshore flow. So, expect gradual clearing of low
clouds once again today, with some areas likely to remain under
low clouds well into the afternoon hours. Also, cooler than normal
temperatures will continue for inland areas. It appears the eddy
circulation that was over our coastal waters yesterday may be
dissipating. Thus, low level southerly flow will likely end which
should mean more afternoon clearing in the North Bay Valleys and
Santa Cruz County compared to yesterday, and also slightly warmer
temps in these areas.

An upper level ridge currently centered over West Texas is
forecast to expand westward and across southern California by
midweek. This will result in a compression of the marine layer
over the next few days. In addition, low level flow is forecast to
return to a more typical northwesterly direction which should diminish
inland marine air transport by midweek. The result will be
warming temperatures starting tomorrow, and especially Wednesday
and Thursday. An upper trough is forecast to move over the ridge
and into the Pacific Northwest on Wednesday, but is not expected
to have a material impact on our weather. By Thursday inland
valleys highs are forecast reach back into the 90s and be about
8-12 degrees warmer than today, yet not nearly as warm as last

Although the upper ridge is forecast to strengthen a bit more late
in the week and into next weekend, both the GFS and ECMWF
indicate an end to the warming trend by Friday and even some
localized cooling on Friday and Saturday. This unexpected
temperature trend can likely be attributed to the development of a
surface trough offshore by Friday (something both the GFS and
ECMWF forecast). This trough will generate light southerly low
level flow along our coast from Friday on into the weekend.
Southerly flow will allow for better inland transport of marine
air and thus put an end to the warming trend, or reverse it in
locations such as the North Bay Valleys and Santa Cruz County.

Something to watch in the longer range is the potential for a
tropical system developing off the west coast of Mexico and then
tracking northwest near the Baja Peninsula. Based on current model
output there is at least an outside chance that moisture from
this system could make it as far north as central California
during the first half of next week.


.AVIATION...As of 4:50 AM PDT Monday...Stratus in a deep marine
layer continues to advance inland. Metar observations show MVFR
cloud ceilings are fairly widespread, only far inland valleys are
holding onto VFR. Along the immediate coastline IFR is reported
along with patchy drizzle. Pressure gradients and winds should
focus more from the west today versus on Sunday, diurnal warming
and mixing winds eroding the stratus back to the coastline /VFR/
by late morning and afternoon. The WRF model then shows the stratus
layer rolling back inland this evening and tonight. Ceilings tonight
similarly returning to MVFR-IFR categories except VFR well inland.

Vicinity of KSFO...MVFR forecast until 17z then VFR, west winds
increasing to 15 knots with gusts to 20 to 25 knots 20z today.
MVFR ceiling returning by mid evening and for the overnight hours.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR ceilings until 18Z-19Z. VFR in the
afternoon then MVFR returning early to mid evening and for the
overnight hours.

&& of 8:12 AM PDT Monday...Generally light winds today
and tonight across the coastal waters as high pressure off the
California coast weakens and a surface low develops offshore of
the Pacific Northwest. Locally gusty winds are expected later
today and into tomorrow over the inner coastal waters south of
Point Sur. Mixed seas will continue with shorter period northwest
waves at around 8 to 10 seconds, a light longer period west swell,
and a light southerly swell.


     .Tday...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 5 PM




Visit us at

Follow us on Facebook, Twitter, and YouTube at:

Prepared by Weather at: Mon Aug 19 10:30:02 PDT 2019
From the National Weather Service