606
FXUS66 KMTR 241611
AFDMTR

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

...New UPDATE, MARINE...

.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.

&&

.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...
(12Z TAFS)
Issued at 413 AM PDT Mon Jun 24 2024

The marine layer is approximately 1000 feet deep. Radiative cooling
to space (loss of heat) overnight is assisting coastal stratus and
fog /LIFR-IFR/ redevelopment. Inland it`s a near high confidence
VFR forecast. The leading gradient of increasing precipitable
water (near 1") is slowly advancing northward over our forecast
area from southern California. With a northward progression of mid
level water vapor reaching our forecast area, convective parameters
for mid level convection will steadily increase today, however
700-500 mb thermal troughing is rather ill-defined today until
slightly more structured mid-level upward forcing arrives this
afternoon and/or evening. Not enough forecast confidence to place
convection in the 12z TAFs. Greater levels of water vapor above the
marine layer tonight and predawn Tuesday morning will slow radiative
cooling to space which may help limit areal coverage of stratus and
fog.

Vicinity of SFO...Moderate to high confidence VFR forecast for the
period. Northwest to west wind 5 to 12 knots through this morning,
increasing to 14 to 22 knots this afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...An eddy circulation has developed over
the northern Monterey Bay area, with stratus and fog caught up in
the circulation. IFR developing at KMRY and KSNS during the morning.
Stratus and fog /LIFR-IFR/ mixing out by late morning. Mid to late
afternoon and evening will need to keep an eye to the sky for potential
mid level convection, for now thunderstorm(s) not in current TAFs.

&&

.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.

&&

$$

UPDATE...RGass
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Canepa
MARINE...Kennedy

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