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000
FXUS66 KMTR 190614
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1114 PM PDT Thu Apr 18 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 142 PM PDT Thu Apr 18 2024

A touch cooler Friday as a weak system moves through. Chance for
light drizzle for coastal areas the next couple of days. Temperatures
rebound late weekend and early next week. Chance for light rain
enters the forecast mid next week.

&&

.UPDATE...
Issued at 917 PM PDT Thu Apr 18 2024

Meso-scale models did a good job verifying a return of coastal
stratus earlier today, however have since only picked up approx
50% of the full extent of the southerly SMX-SFO, SBA-SFO pressure
gradients. Similarly it`s true also regarding the ACV-SFO pressure
gradient, the NAM typically is 1 mb too low between these two
locations anyhow. The ACV-SFO, SMX-SFO and SFO-SAC pressure
gradients have been/are similar in strength indicating general
north-south convergence and onshore directed winds. The Fort Ord
profiler shows the marine layer depth increasing to 1700 feet, the
Bodega Bay profiler showing the depth steady near 1,000 feet. At
and below the marine layer temperature inversion, sea surface
temperatures, air temperatures and dew point temperatures (including
above the marine temperature inversion where it`s clear for nocturnal
radiative cooling) remain conducive to night and morning stratus and
fog development and with lower level cooling and gentle upslope
flow, a few patches of coastal drizzle will likely continue. Daytime
surface warming and mixing will erode the stratus and fog back close
to the coastline. A greater push of cooler maritime air is forecast
to reach far inland Tuesday.

On the other side of things, surface based convective potential
over southeastern San Benito county quickly blossomed up to a
thunderstorm with echo tops to 36 thousand feet during the late
afternoon. Once formed the thunderstorm almost as quickly dissipated,
but quite likely produced a decent downpour and possibly small hail;
e.g. vertically integrated liquid approached but just stayed below
low end double digits.

Current forecast looks good, please see below for more details.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 142 PM PDT Thu Apr 18 2024

Increased cloud cover today along coastal areas south of SF as the
marine layer deepens ahead of the approaching weak trough. Still
looking like a progressive, open wave, this system will scoot
through rather quickly Friday, bringing additional cloud cover and
a slight chance for drizzle along coastal locations and higher
elevations of the East Bay Friday and Saturday mornings. The other
impact from this system will be the breezy NW winds that develop
along the coast as the system departs. Generally looking at gusts
of 25-30 mph along the immediate coast Saturday afternoon into
Sunday afternoon.

&&

.LONG TERM...
(Saturday night through next Wednesday)
Issued at 142 PM PDT Thu Apr 18 2024

By Sunday, ridging dominates the pattern once again with temps
warming back into near 80 for inland areas and 60s to near 70
along the coast. Similar picture into Monday as well. Tuesday
brings some changes. Ensemble guidance continues to advertise
anomalous troughing over the EPac/West Coast during the mid-to-
late next week period, hinting at a pattern that promotes above
average precip and below average temperatures. Average precip for
the second half of April for our region is roughly a half inch,
give or take a few tenths depending on if you`re coastal or
inland. What we`re expecting next week is generally on the order
of a trace to a few tenths here and there. Longer terms guidance
does show the pattern continuing into next weekend, where there
could be additional light rainfall, bringing us into that
ballpark of slightly above normal. The main caveat with this
forecast is that while there is moderate to high confidence in the
overall pattern, the confidence in widespread measurable rainfall
is low. In fact, in a grouping of 100 different models, roughly 24
of them advertise any measurable precip for us at all through next
weekend. The answer to the question of next week being widespread
light rain or just some increased cloudiness and drizzle will
need further refinement in future forecasts. For now, plan on the
latter half of next week being cool and damp.

&&

.AVIATION...
(06Z TAFS)
Issued at 1114 PM PDT Thu Apr 18 2024

A mix of predominantly LIFR and IFR conditions through the night
tonight and the late morning of Friday. North Bay and Monterey Bay
terminals are likely to see LIFR conditions persisting through the
overnight hours and into the late morning as a result of fog and low
stratus CIGs. Sinking, drier air aloft is likely helping to lower
and squash CIGs down to around 1400 feet currently per the Bodega
Bay profiler, and 1800 feet per the Ft. Ord profiler. Expect these
CIGs to lower progressively through the night and into the morning
hours. Terminals in the SF Bay region are more likely to see MVFR
conditions per model suggestions, though confidence on this is only
moderate, given the low CIGs elsewhere. A drop into IFR CIGs for SF
Bay terminals overnight is not out of the question. Decent onshore
flow overnight will also be a factor in helping advect stratus
inland, leading to robust cloud coverage through at least the late
morning of Friday. In the early afternoon, as things heat up, clouds
should begin to mix out bringing a return of VFR conditions and
breezy to moderate onshore winds.


Vicinity of SFO...SFO in particular overnight appears to remain the
odd one out, as it is likely to remain in VFR territory, with good
agreement among numerous models. Despite good onshore flow overnight
around 6-7 knots, given the fact that the stratus deck currently
sits around 1400` and is expected to lower, stratus may not be able
to rise above and advect through the San Bruno gap, keeping
conditions clear and VFR locally at SFO terminal. Additionally, any
stratus that fills over the bay waters will be likely kept just on
the periphery of the SFO vicinity as good overnight flow out of
the west helps keep any stratus over the bay away and pushed more
towards the KOAK side. KOAK conversely will likely see IFR
conditions last through the nighttime as good overnight onshore
flow helps push stratus through the Golden Gate gap and into the
SF bay. Late clearing is expected at KOAK with VFR returning in
the late morning to early afternoon.

SFO Bridge Approach...IFR-LIFR conditions are likely as robust
stratus coverage develops overnight over the SF bay waters thanks to
good onshore flow. Clearing expected into the very late morning to
early afternoon of Friday to VFR.

Monterey Bay Terminals...IFR/LIFR through much of the night as a
result of very low CIGs. Stratus is expected to continue to lower
through the night. Some reductions in visibility are possible as
CIGs lower and the air reaches saturation near the ground, leading
to mist and fog development. However, confidence on mist and fog
development is not as strong as confidence in CIGs lowering. This
will be something to watch closely overnight. VFR returns in the
early afternoon though a FEW-SCT low clouds may linger, with winds
onshore and around 10 knots. Stratus makes an early return in the
evening of Friday.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 1114 PM PDT Thu Apr 18 2024

Expect light to moderate winds into the weekend before breezy to
gusty northerly winds arrive Saturday afternoon that will increase
hazardous conditions over the waters. Wave heights will start to
build heading into the late weekend before diminishing by mid-
week. Another moderate period northwest swell arrives over the
weekend as well as another light, longer period (18 seconds)
southerly swell.

&&

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

$$

SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...AC
MARINE...SO

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