Wildfire in California, August 7, 2019

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1046 AM PDT Wed Aug 7 2019

.SYNOPSIS...Night and morning low clouds along the coast and
locally inland will continue. Patchy drizzle will also be possible
along the coast. A cooling trend for temperatures will continue
through the end of the week, while the next warming trend for
inland areas will be early next week.

&&

.DISCUSSION...as of 09:11 AM PDT Wednesday...Stratus filled in
early this morning to many valley locations as the marine layer
deepened to between 1500 and 2000 feet. A few passing high clouds
also continue over the area with occasional high clouds moving
from south to north through the day. A few isolated returns
associated with the high clouds have been noted on KMUX radar,
mainly east of Monterey/San Benito Counties and just east of Napa
County. The high clouds and isolated showers coincide with an area
of weak elevated instability.

Models depict an upper low currently off the coast of southern
California becoming an open wave as it moves onshore tonight.
Models continue to depict some weak elevated instability, mainly
over our eastern regions through tonight as the upper wave
approaches. At this time, not expecting any showers or
thunderstorms but some isolated virga (rain not reaching the
ground) could be possible through tonight.

In terms of temperatures, the approaching trough will bring a
couple degrees of cooling mainly over inland areas this afternoon.
The cooling trend over inland areas will continue through the
weekend as an upper low, currently off the coast of Oregon, moves
onshore on Friday and Saturday. Models continue to show moisture
with the trough, but disagree on how far south it will get. A few
of the models, such as the ECMWF and the model-blend NBM, bring a
slight chance of showers to the North Bay. While the official
forecast at this time does not include a chance of precipitation,
will continue to monitor the latest trends to see if a slight
chance or chance of PoPs become warranted.

&&

.PREV DISCUSSION...as of 03:00 AM PDT Wednesday...Stratus deck has
become established once again overnight. Satellite fog product
shows a decent stratus deck from north of Point Reyes southward to
Point Conception and across the inland valleys. Fort Ord profiler
shows a slight compression of the marine layer to near 1k feet,
but that hasn't impacted the stratus push down the Salinas Valley.
Additionally, latest near term models continue to generate
accumulating precip early this morning - mostly likely a sign of
drizzle. All that being said, low clouds, patchy fog, and even
coastal drizzle will be possible through mid-late morning. Similar
to previous few days, some coastal locations will hold onto some
lingering clouds throughout the day.

The longwave pattern continues to be dominated by a persistent
upper low spinning off the Pac NW Coast. South of the parent low
is a smaller upper low spinning off the SoCal Coast. The southern
low is forecast to become more of an open wave as it drifts
eastward into SoCal later today. As the southern low opens up the
northern low will begin to slowly drift southward. This initial
eastward progression of the upper trough/lows will keep night and
morning low clouds in place the next few days. More on the
sensible weather side temperatures will cool across the board.
Today's max temps are forecast to drop several degrees over
Tuesday's max temps, especially the interior. Highs for Wednesday
will be 60s along the coast and 80s to mid 90s interior. Further
cooling is anticipated each day through the weekend with highs in
the 60s along coast and upper 70s to near 90 across the interior.
One potential hiccup in the forecast is the amount of cooling
aloft Friday night into Saturday, which could lead to mixing out
of the marine layer. For now it's hard to bet against stratus
during the summer with no offshore component so will leave it in
the forecast.

The northern upper low is ultimately forecast to sweep through
NorCal/S Oregon over the weekend. Medium range models still show
uncertainty regarding precip chances in the Bay Area. The majority
of the model guidance shows best chance for precip is north of
the Bay Area. However, the ECMWF and National Blend both indicate
a few showers over the North Bay. Will keep forecast dry at this
time, but if trend continues will need a slight mention for the
North Bay.

By Sunday into Monday the upper low will be east and high pressure
will rebuild over the region. A marked warming trend is expected
to begin late in the weekend and continue well into next week.

&&

.AVIATION...as of 10:45 AM PDT Wednesday...Lingering MVFR/IFR
ceilings around the San Francisco Bay and Monterey Bay terminals
should dissipate in the next hour or two. VFR conditions then
likely through the afternoon for most forecast sites with an
increase in onshore winds, especially at KSFO/KOAK with 20-25 kt
gusts likely. The marine layer will continue to deepen tonight
with another round of widespread MVFR/IFR conditions with brief
LIFR conditions not out of the question for KSTS/KMRY.

Vicinity of KSFO...Lingering MVFR ceilings will dissipate in the
next hour over the terminal with an increase in westerly winds by
21Z. Gusts of 20-25 kt will be possible this afternoon and early
evening. MVFR ceilings likely to return after 06Z Thursday, yet
may scatter out at times through the early morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...IFR ceilings will scatter out this
morning, first at KSNS and then between 19-20Z at KMRY. Expecting
mainly VFR conditions through the afternoon with an increase in
onshore flow. MVFR/IFR conditions likely to return by 01-03Z as
stratus pushes back inland. Cannot rule out periods of LIFR
conditions early Thursday morning as well.

&&

.MARINE...as of 10:45 AM PDT Wednesday...Modest northwest winds
across the waters will weaken through the end of the work week.
These winds will generate steep wind waves at 7 to 8 seconds today
before subsiding later this week. In addition, a longer period
southwest swell will move through the waters this week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Mry Bay
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 PM
             SCA...SF Bay

&&

PUBLIC FORECAST: ST/MM
AVIATION: RGass
MARINE: RGass

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