-- Discussion containing changed information from previous version are highlighted. --
307
FXUS66 KMTR 241757
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1057 AM PDT Mon Jun 24 2024

...New AVIATION...

.SYNOPSIS...
Issued at 1243 AM PDT Mon Jun 24 2024

Temperatures near to slightly above seasonal averages with a slight
cooldown midweek. Very low chance of elevated convection and
associated dry lightning in the southern Central Coast.

&&

.UPDATE...
Issued at 910 AM PDT Mon Jun 24 2024

The threat for high-based convection remains centered over the
Central Coast this morning, albeit low. This threat will shift
northward through the day and become more focused over the Bay Area
and North Bay late this evening, into the overnight, and early
Tuesday. We have already seen returns on KMUX Radar over southern
Monterey County and as the plume of deeper mid-to-upper level
moisture shifts northward so will the threat. That said, the ongoing
forecast remains on track with no updates anticipated this morning.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1243 AM PDT Mon Jun 24 2024

Satellite imagery shows generally clear conditions throughout the
region, with a patch of stratus along the northern coast of Monterey
Bay. The region is generally expected to remain clear through the
night, with a moderate confidence that stratus expands across the
the Monterey Bay region before clearing in the morning. Low
temperatures this morning range from the upper 40s to around 60 in
the lower elevations, and up to the low 70s in the higher
elevations. High temperatures this morning range from the mid 80s to
the upper 90s in the inland valleys, to the 70s across the Bayshore,
and the upper 50s to mid 60s along the Pacific coast.

Regarding the potential for elevated convection in the Central Coast
later this afternoon and evening: The three ingredients necessary
for any convective activity are moisture, instability, and lift. Mid-
level moisture is the most certain ingredient, with a plume of
moisture migrating northwards with PWAT values up to 1-1.25". For
context, if those values were reported at our upper air site at
Oakland airport, those precipitable water values would be at or
above the 90th percentile value for all observed soundings at this
time of year. Instability and lift are more uncertain. The NAM is
showing a plume of unstable air coming towards the north as the mid
level moisture comes through the area, but the GFS and European
models aren`t as aggressive with the MUCAPE values. As for lift, even
the NAM is not showing any significant source of vertical vorticity
in the region, so any activity would have to be topographically
forced. At this point, the most likely scenario is that mid-level
clouds and virga will come through the region, with dry air under
the elevated moist layer limiting the probability that any
precipitation reaches the ground. Perhaps a 10-15% probability for
convection in the Central Coast, and that might be a little
optimistic. The main impact if convection does develop would be the
possibility for dry lightning setting off grass and shrub fires, but
this is a "low confidence-high impact" type of event at this
stage.

&&

.LONG TERM...
(Tuesday through Sunday)
Issued at 1243 AM PDT Mon Jun 24 2024

The mid-level moisture will remain on Tuesday, with PWAT values
increasing to as high as 1.5", and so will the uncertainties
regarding instability, lift, and potential convective activity.
Wednesday sees an upper level trough move in which will push the
moisture out of our region, and herald a gradual cooling trend in
temperatures for the interior regions. By the end of the week,
temperatures across the interior will top out at around 90 in the
warmest spots, with most of the inland valleys seeing temperatures
within the 80s. Towards the beginning of July, model ensemble
clusters are indicating a couple of ridges approaching the West
Coast, with early indications of a warming trend towards the end of
the 7-day forecast.

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 1056 AM PDT Mon Jun 24 2024

VFR across the board with IFR conditions returning along the Central
Coast overnight. The marine layer remains compressed to
approximately 1000 feet this morning with little change expected
during the TAF period. Stratus should stay confined directly along
the coast and Central Coast regions with mid-level moisture bringing
scattered to broken mid-level and upper level clouds this
afternoon/overnight. Slight chance of thunderstorms continues along
the Central Coast but confidence remains low that thunderstorms will
impact either MRY or SNS. Onshore west to northwest flow continues
for most airports except for STS and APC where more southerly to
southwesterly winds are expected to prevail. Moderate winds between
10 to 18 knots are expected this afternoon before lighter, more
variable winds return overnight.

Vicinity of SFO...VFR through the TAF period. Moderate confidence
that stratus will not reach SFO with the more compressed marine
layer keeping stratus directly confined along the coastline.
Moderate west to northwest winds continue through the afternoon and
evening before weakening overnight. Ensemble guidance indicated
slight potential for gusts between 20 to 25 knots this afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR becoming IFR overnight. Moderate
onshore flow persists through the afternoon/evening before lighter,
variable winds return overnight. Low to moderate confidence that
broken to overcast IFR CIGs will develop overnight with model
consistency increasing after 08-11Z for both MRY and SNS. A slight
chance of thunderstorms in the vicinity of MRY and SNS remains
possible but confidence is still too low to include in TAFs. Will
continue to monitor for any thunderstorms that do develop and update
as needed.
-- End Changed Discussion --

&&

.MARINE...
(Today through Saturday)
Issued at 910 AM PDT Mon Jun 24 2024

Hazardous conditions for small crafts persist across the northern
coastal waters through early week. Fresh to strong north to
northwest winds continue over the northern coastal waters.
Moderate northwest winds continue over the southern coastal waters
with the occasional fresh gust possible over the outer waters.
Significant wave heights over the northern waters will build to
10-11 feet through today before wave heights abate below 10 feet
by Tuesday. Widespread fresh to strong winds are expected to
return over the coastal waters by late week with wave heights
gradually building to 10 feet across portions of the northern
coastal waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Tuesday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Kennedy
MARINE...Kennedy

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