508
FXUS66 KMTR 131811
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1111 AM PDT Sat Jul 13 2024

...New UPDATE, AVIATION, FIRE WEATHER...

.SYNOPSIS...
Issued at 204 AM PDT Sat Jul 13 2024

A Heat Advisory remains in effect for elevated inland locations,
and will expire later this evening. A welcomed cooling trend will
begin tomorrow and extend through at least the middle of the
upcoming work week.

&&

.UPDATE...
Issued at 1111 AM PDT Sat Jul 13 2024

Latest statistical guidance has lowered forecast highs slightly
today, decided to nudge forecast highs downward a little today
inland valleys and along the SF Bay Shoreline.

We continue to closely monitor satellite, radar and observations
for incoming mid level moisture and instability from southern
California, however good news is model output shows plenty of
convective inhibition, greatly limiting the potential for
thunderstorms so far, which should continue into the afternoon and
evening as well. A few passing showers/sprinkles have so far
resulted in a few traces of precipitation, possibly including a
few spots of light measurable precipitation. Warm to hot inland
again today and within the lower level temperature inversion in
the hills/mountains, however cloud cover reducing incoming solar
input a little bit will help reduce highs a little compared to
Friday afternoon.

&&

.SHORT TERM...
(Today and tonight)
Issued at 204 AM PDT Sat Jul 13 2024

An upper level low currently centered 200mi offshore of
south/central California will gradually lift north over the course
of the weekend while making little gain eastward toward land with
the persistent high over the Four Corners region driving the
synoptic pattern across western CONUS. There is little to no thermal
instability associated with weak shortwave energy and PVA shifting
south to north across our area today and tomorrow. Probability of
elevated convection is too low for mentioning in the forecast but
can`t rule it out entirely. If an isolated thunderstorm develops,
dry lightning from any high based convection could spark a wild fire
as grass fuels continue to dry. Surface based convection well inland
and east of our area is expected, where continental modified
boundary layer moisture is more robust with stronger diurnal surface
heating at higher altitudes. A Heat Advisory remains in effect
through this evening for much of our elevated interior locations,
marking the end of an historic heat wave. A strengthening marine
layer through the weekend into the beginning of next week will help
the cooling trend as the offshore disturbance slowly migrates north.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 204 AM PDT Sat Jul 13 2024

By early Monday, the upper level low begins to get absorbed by
persistent NorCal offshore troughing resulting from the
amplification of the Four Corners ridge back to the northwest across
Nevada, Oregon and Washington state. The steady fetch of cooler
onshore flow will help keep temperatures around normal through at
least the middle of next week. Warmer temperatures are expected late
next week into the weekend as the ridge migrates westward next week,
steering the jet stream and cooler temperatures aloft well to our
north.

&&

.AVIATION...
(12Z TAFS)
Issued at 1057 AM PDT Sat Jul 13 2024

Low level clouds are dissipating over the region as high level
clouds move in. There is a low (<10%) chance for convective cells to
develop today. Confidence in showers or lightning at/near airports
in the Bay Area and Central Coast is too low to include in TAFs but
will continue to monitor any cells that do develop. Light rain (as
reported at SJC early this morning) may briefly impact airports but
should be short in duration and non-impactful to airport operations.
VFR conditions continue through the afternoon before MVFR to LIFR
conditions return at STS, APC, OAK, SFO, MRY, and SNS overnight.
There is a 20-40% chance of patchy fog developing in the North Bay
and Central Coast early tomorrow morning (beginning 10-12Z) which
may impact STS, MRY, and SNS. Winds generally remain out of the west
to northwest with moderate to gusty winds expected during the
afternoon before weakening overnight.

Vicinity of SFO...VFR becoming MVFR overnight. Low to moderate
confidence that MVFR CIGs will develop at SFO during the early
morning hours. Guidance indicates some potential for IFR CIGs to
develop but confidence remains higher for MVFR CIG development.
Onshore flow continues through the TAF period with moderate winds
returning during the afternoon/evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Low level CIGs have cleared out of MRY and
SNS with VFR to prevail through the late afternoon/early evening.
IFR to LIFR CIGs return this evening with overcast conditions
prevailing through mid to late tomorrow morning. There is a 20-40%
chance for patchy fog development early tomorrow morning in the
Monterey Bay region with increasing likelihood after 10/12Z. Fog may
temporarily reduce visibilities and CIG heights at MRY and SNS.
Moderate west to northwest winds return during the afternoon before
weakening overnight.

&&

.MARINE...
(Today through Thursday)
Issued at 441 AM PDT Sat Jul 13 2024

Winds across the waters reduce into the morning. Seas become
calmer as winds begin to ease. Light winds last through the
majority of next week. Significant wave heights between 10 to 12
ft continue over the outer coastal waters with peak wave heights
between 10 to 13 ft expected over the far northern outer coastal
waters.

&&

.FIRE WEATHER...
Issued at 1030 AM PDT Sat Jul 13 2024

Mid level cloud cover/moisture moving up from southern California
is resulting in widely scattered showers, a few spots have reported
a trace (and possibly light measurable precipitation) reaching the
ground. Forecast soundings show widespread convective inhibition
over our forecast area today i.e. stability greatly helping to
preclude thunderstorm development. Per satellite and high
resolution model output, mid level cloud cover over our forecast
area will help reduce incoming solar input today. 12z statistical
guidance shows slightly cooler temperature trends including inland
areas today. The marine layer temperature inversion at the mountain
tops is still quite warm, however 24 hour trends show cooler temperatures
almost everywhere this morning, also resulting in positive humidity
trends.

A well established marine layer with coastal stratus has recently
shown signs of deepening per Bodega Bay and Fort Ord profiler data.
The southerly and onshore pressure gradients and winds prevail which
will help usher higher humidity to the inland valleys, hills and
eventually mountain tops.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT this evening for CAZ504-510-513>515-
     517-518.

PZ...Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
     to Pt Reyes 10-60 NM.

&&

$$

UPDATE...Canepa
SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Kennedy

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