000
FXUS66 KMTR 190417
AFDMTR

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

...New UPDATE, 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...
(00Z TAFS)
Issued at 445 PM PDT Thu Apr 18 2024

VFR through the remainder of the day with the exception of KMRY
where the stratus straddling the coast, has moved over into the
terminal causing MVFR conditions. The remainder terminals will start
to see flight conditions lowering into MVFR/IFR tonight (with the
exception of KSJC and KLVK, where VFR is expected to prevail)into
the early morning hours, with low to moderate confidence of LIFR
conditions in North Bay and Monterey Bay. Most terminals start to
improve to VFR near 16-17Z. Moderate to breezy winds are expected to
diminish overnight and rebuild Friday morning.

Vicinity of SFO...VFR through the remainder of today with possible
MVFR conditions near 13Z but moderate confidence on ceiling height.
If conditions remain dry, there is a chance for VFR through the TAF
period. Breezy onshore winds will start to diminish to light winds
tonight before becoming breezy again Friday afternoon.

SFO Approach Bridge...Similar to SFO.

Monterey Bay Terminals...VFR with breezy onshore winds. Moderate
confidence that IFR/LIFR conditions will return tonight into early
Friday morning. VFR will prevail after 17Z. Light variable winds
overnight before rebuilding Friday morning.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 827 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.
&&

$$

UPDATE...Canepa
SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...SO
MARINE...SO

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