539
FXUS66 KMTR 132055
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
155 PM PDT Sat Jul 13 2024

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 145 PM PDT Sat Jul 13 2024

Heat Advisory is in effect mainly inland portions of the Bay Area
and north Central Coast until 9 pm this evening. It`s still hot
inland, however relative cooling is taking place helping to ease
things a bit due to cloud cover along with a few isolated passing
showers through the afternoon. High temperatures will continue to
ease back to normal mid July highs in the mid 80s to 90s far inland
early to mid next week. Closer to the coast and nearby coastal
valleys a maritime influence will result in cooler daytime
temperatures.

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 155 PM PDT Sat Jul 13 2024

We continue to closely monitor satellite, radar and observations
for incoming mid level moisture and instability from southern
California. So far we`re only seeing a few passing showers and
since high resolution model output shows plenty of convective
inhibition the expectation is this will continue to greatly limit
any potential for thunderstorm development through afternoon and
evening. There`s forecast steepening of the 700-500 mb temperature
lapse rates and weak mid level convective potential out ahead and
northeast of the 500 mb low, currently 275 miles west of Point
Conception, arriving late tonight and Sunday morning however just
above this the 500-300 mb layer is stable. From approx the 700 mb
level (~ 10,000 feet) downward through the 925 mb level (~ 2,500
feet) thermal ridging, stability remains in place tonight and
Sunday morning.

Warm to hot far inland again this afternoon, however cloud cover
will help reduce incoming solar input a little bit helping reduce
highs a little compared to Friday afternoon. Cooler temperatures
prevail along the coast and in the nearby coastal valleys due to
increasing maritime influence, including coastal stratus and fog.

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 155 PM PDT Sat Jul 13 2024

Summer continental surface heating continues to correspond to
strong 500 mb heights with a nearly stationary high pressure
system over the west with the center near the Four Corners. A
stable north hemispheric pattern shows signs of strengthening and
becoming unsteady again with five long wave troughs developing by
late next week. One long wave trough is forecast to slowly
progress eastward to along western North America while a long wave
ridge primarily strengthens over central Canada with an extension,
possibly the southern extension retrogressing toward the southwestern
states. The GEFS/EPS ensemble 850 mb mean temperature forecasts for
our forecast area climb back to 26 Celsius next weekend, not quite
as warm as of recent, but bears watching.

&&

.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.

&&

$$

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

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