Wildfire in California, July 15 to 20, 2020

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1039 AM PDT Wed Jul 15 2020

.SYNOPSIS...Seasonable weather pattern with night and morning
clouds as the marine layer stays in place. Temperatures will
remain near seasonable values through the upcoming weekend. Smoke
and haze from the Mineral Fire near Coalinga will continue to
impact portions of the Bay Area and Central Coast.

&&

.DISCUSSION...as of 9:19 AM PDT Wednesday...Main update this
morning was to add smoke and haze to the forecast grids as the
Mineral Fire near Coalinga in western Fresno county continues to
belch smoke across the region. Winds aloft remain fairly light and
visible satellite confirms smoke and haze is impacting portions
of the East Bay and Santa Clara county as well as the interior
Central Coast. Otherwise the marine layer remains around 2500 feet
with morning low clouds starting to peel back to the coast.
Temperatures will remain seasonable with 60s beaches and lower 90s
well inland with pleasant 70s/80s for most of the populated areas
in-between. Places with heavy smoke and haze will be several
degrees cooler than those with full sunshine. The San Jose airport
is already reporting smoke in their official observations so
expect a brilliant sunset tonight.

Quiet and seasonable pattern is forecast to remain in place
through the end of the work week and through the weekend. Thus
expect the marine layer to remain fairly deep with slight
troughing aloft. This combined with onshore flow will keep temps
normal with no hot weather of concern. Night and morning clouds
will give way to late morning and afternoon sunshine near the
coast and bays.

&&

.PREV DISCUSSION...as of 3:53 AM PDT Wednesday...The marine layer
is approx 2,500 feet deep. The SFO to SAC pressure gradient is
2.3 mb and onshore winds prevail. Expect night and morning inland
stratus and fog intrusions typically seen in the summer through at
least late week. At 500 mb very little change is forecast in
heights through late week with 590 decameter heights varying - or
+ 1 to 2 decameters.

As mentioned in previous discussions only minor temperature
differences are forecast for today. Morning stratus clouds will
lift and retreat back to the coast, expect clear/sunny conditions
again inland. Will have to watch for possible monsoonal moisture
reaching the Sierra Nevada crest through Thursday, main result will
be slight increase in humidity recoveries and weak instability
possibly generating a few afternoon convective clouds. Over the
weekend more inland 90s can be expected with a slight increase in
500 mb height ridging and less onshore winds.

&&

.AVIATION...as of 10:31 AM PDT Wednesday...For 18Z TAF...More
typical marine layer/stratus deck this morning impacting Bay Area
terminals. As of 1730Z the marine layer is making its daily
retreat back to the coast with VFR developing at all terminals.
Other item of interest this morning is the smoke drifting to the
NW over the Bay Area from the Mineral Fire. Impacts may include
slant- range reduction, but fortunately most of the smoke should
be 4k feet and above. Expecting marine layer to move inland again
tonight.

Vicinity of KSFO...VFR conditions expected through the forecast.
Breezy west flow expected this afternoon. A little lower
confidence tomorrow AM, but for now will only carry a SCT deck.
Hi-res models keep flow favorable to allow for a cloud hole around
the terminal. Vsbys P6SM but smoke aloft may impact slant- range
vsbys in the afternoon and evening.

SFO Bridge Approach...VFR with some smoke reduction of vis
possible. Cigs will likely impact portions of the approach again
Thursday AM.

Monterey Bay Terminals...VFR developing for MRY, but VFR already
at SNS. VFR this afternoon. Cigs return early tonight. West to
northwest winds 10-15 kt after 20Z. Stratus returning early
tonight.

&&

.MARINE...as of 10:30 AM PDT Wednesday...Relatively light
southerly flow will prevail over the coastal waters as a weak
surface low drifts south. Gusty winds will be possible through the
Golden Gate and West Delta today. The sea state will be moderate
swell and moderate period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...SF Bay from 1 PM

&&

PUBLIC FORECAST: RWW
AVIATION: MM
MARINE: MM

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