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000
FXUS66 KMTR 240844
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
144 AM PDT Wed Apr 24 2024

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

.SYNOPSIS...
Issued at 1228 AM PDT Wed Apr 24 2024

A deep marine layer and expansive cloud coverage will keep
temperatures cool through Thursday before a cold front brings
strong wind on Friday. Clearer skies and slightly warmer
temperatures are expected this weekend.

&&

.SHORT TERM...
(Today through Friday)
Issued at 1228 AM PDT Wed Apr 24 2024

Stratus coverage is quite expansive early this morning due to a
deep marine layer. Some light drizzle is possible along windward
facing slopes this morning, although there hasn`t been any
measurable precipitation so far. The cloud cover will keep
morning temperatures near normal, with high temperatures 5-10
degrees below normal this afternoon.

The weather pattern is fairly dynamic over the next few days. A
persistent low pressure system off the coast of San Francisco
will finally weaken and open up into a trough late today, bringing
the return of NW flow. The supporting upper-level cut-off low
will evacuate to the east on Thursday, allowing a small amplitude
ridge to become established. This high pressure will squish the
marine layer from around 4,000 ft on Wednesday to around 1,500 ft
on Thursday. This change will bring lower, but less expansive
cloud coverage and the potential for morning fog. This regime
won`t last long as a new cold front and associated trough move
will move through on Friday.

&&

.LONG TERM...
(Friday through Tuesday)
Issued at 1228 AM PDT Wed Apr 24 2024

The Weather Prediction Center forecasts the cold front to move
through Friday morning, with a slight chance for light rain on
either side. The biggest impact from this system will be strong NW
wind behind the front. Our official forecast has gale force wind
gusts along the coast of Sonoma, Marin, and Big Sur on Friday
afternoon and evening. NBM probabilities are above 95% of
confirming the previous sentence. All of this has led me to
strongly consider a wind advisory. While there is still some
uncertainty if the threshold will be hit between Marin and
Monterey counties (roughly a 30% chance), I`d rather have the
advisory out with as much lead time as possible to allow the Rocky
Creek slip-out repair crew time to secure the crane for high
winds. The downside of the early issuance is that the coverage
may need to be expanded over the next 24 hours if the rest of the
coast or inland areas start trending higher in the guidance.

Winds will remain strong through the night Friday before gradually
decreasing through the weekend. The cold front will also usher in
a dryer airmass with much less cloud coverage expected this
weekend, especially for inland areas. This will allow
temperatures to return to normal through the weekend and into
early next week.

Some super long range guidance is starting to hint at a potential
storm during the first weekend in May. While there have been some
aggressive deterministic runs lately, the current ECMWF and GEFS
ensemble means both keep the total precipitation under 1/2" at San
Francisco. Even that would be a lot for May, however, which
typically averages about 1/2" for the entire month. The Climate
Prediction Center is also taking note of this and showing
slightly wetter than normal conditions in the 8-14 day outlook
(May 1-7). This is just something to keep an eye on for now.

&&

.AVIATION...
(06Z TAFS)
Issued at 1117 PM PDT Tue Apr 23 2024

At this hour, most terminals are VFR but low to mid level clouds
just above the threshold of MVFR CIGs continue to linger over
area terminals. Through the night, cloud cover is expected to
increase, with CIGs lowering to just meet MVFR conditions for most
terminals in the early to mid morning of Wednesday. Cloud CIGs
are at greater altitudes than in previous nights thanks to the
movement of a trough through the region, providing ample lift and
rise. Towards the later morning, CIGs are expected to lift to
usher in VFR conditions, though clouds around 4000-5000` will
persist. Winds out of the W/SW predominantly this afternoon and
breezy between 10-15 knots for most terminals. Terminals near
coastal gaps are likely to see stronger gusts nearing 20 knots. In
the late evening, winds ease below 10 knots and generally become
more westerly. Low clouds return beyond the current TAF period to
bring MVFR conditions once more.


Vicinity of SFO...Currently VFR despite the presence of clouds, but
expected to become MVFR as CIGs lower. Hi-res models show KSFO
seemingly waffling in and out of MVFR CIGs in the mid morning up
until sunrise, with the greatest chances of achieving MVFR around
45% near 14Z. Confidence on MVFR CIG development is low-moderate, so
this will be something that is watched closely through the night.
However, into the late morning and afternoon, high confidence for
VFR CIGs. Winds initially out of the SW and breezy near 12 knots and
gusting up to 20, eventually turning to become more westerly into
the late evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR conditions persist through at least the
mid morning of Wednesday, but are expected to become MVFR around 15Z
as CIGs lower. Clearing to VFR expected again into the late morning
and lasting through the remainder of the TAF period. Winds SW in the
afternoon and breezy around 15 knots. Gusts around 20 knots are
likely in the later afternoon. Winds ease into the late night to
below 10 knots.

&&

.MARINE...
(Tonight through next Monday)
Issued at 902 PM PDT Tue Apr 23 2024

A weak low pressure system off the coast will continue to bring
light to moderate southerly winds over the coastal waters. As
this system begin to weaken tonight, northwest flow will return
over the waters ushering in calmer conditions. Moderate swells
will persist through the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...AC
MARINE...CW

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