-- Discussion containing changed information from previous version are highlighted. --
980
FXUS66 KMTR 241020
AFDMTR

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

...New 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.

&&

.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...
(06Z TAFS)
Issued at 1159 PM PDT Sun Jun 23 2024

The marine layer is approximately 1000 feet deep. The Sunday
evening Oakland upper air sounding showed the precipitable water
was 0.48" which is a dry troposphere for late June, near the 10th
percentile. The lack of water vapor will allow for good longwave
radiative cooling to space (loss of heat) overnight assisting
coastal stratus and fog /LIFR-IFR/ redevelopment. Inland it`s a
near high confidence VFR forecast. To the south near the
Monterey/San Luis Obispo county line the leading gradient of
increasing precipitable water (near 1") is slowly advancing
northward from southern California, the Sunday evening Vandenberg
upper air sounding showed water vapor mostly focused near 12000
feet agl; additionally positive convective potential at this level
was met with convective inhibition i.e. no thunderstorm development
noted along the more immediate coast. A slow northward progression
of mid level water vapor will reach our forecast area, convective
parameters for mid level convection steadily increase late tonight
and Monday, however 700-500 mb thermal troughing is rather ill-defined
tonight and Monday until perhaps slightly more structured for mid-
level upward forcing Monday afternoon and/or evening. For the time
being, decided to leave out convection in the 06z TAFs.

Vicinity of SFO...Moderate to high confidence VFR forecast for the
period. Northwest to west wind 5 to 12 knots through Monday morning,
increasing to 14 to 22 knots Monday 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. KWVI has reported IFR ceiling. High resolution
model output show gradually increasing surface to near surface
humidity overnight, increasing the chances IFR develop at KMRY and
KSNS overnight. Stratus and fog /LIFR-IFR/ mixing out by late Monday
morning. Mid to late Monday 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...
-- Changed Discussion --
(Today through Saturday)
Issued at 320 AM PDT Mon Jun 24 2024

Hazardous conditions for small crafts persist across the northern
coastal waters through early week. Fresh to strong northwest
winds continue over the northern coastal waters. Fresh gusts
remain possible over the southern 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.
-- End Changed Discussion --

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 4 AM PDT early this morning for
     CAZ506.

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...Canepa
MARINE...Canepa

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