216
FXUS66 KMTR 190602
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1102 PM PDT Sun Aug 18 2024

...New AVIATION...

.SYNOPSIS...
Issued at 1246 PM PDT Sun Aug 18 2024

Temperatures at or slightly below seasonal averages continue through
the next week, along with breezy onshore flow and early morning
stratus. A passing disturbance to the north will result in a few
isolated showers north of the Golden Gate Friday.

&&

.SHORT TERM...
Issued at 115 PM PDT Sun Aug 18 2024
(This evening through Monday)

Current situation: After some morning clouds/fog mostly sunny
skies prevail across the region. The exceptions are some patchy
clouds piling along the coast and a few afternoon cumulus popping
over the S Gabilan Range. Despite some afternoon sunshine
temperatures are struggling to reach seasonal average. Highs will
ultimately top out in the upper 50s to 60s along the coast and
60s to lower 80s inland, which is 5 to 15 degrees below average.
Weak onshore flow is resulting in some breezy winds along the
coast and inland gaps/passes with gusts 20-25 mph.

The bigger picture: Longwave wave pattern over the CONUS has some
Omega Block vibes too it. An upper low parked over the PacNW,
upper ridge over the Plains, and an upper low over New England.
The upper low part of the Omega Block has some perturbations
flowing through it resulting in active weather over the PacNW
(recent lightning near Seattle). So what does this mean for us in
CA? Repetitive weather in the near term. A mixed version of the
marine layer with some stratus, patchy fog, and possibly some
drizzle. Additionally, below normal temperatures will persist
despite meager warming on Monday. Highs will be in the 60s to
mid 70s coast and 80s to lower 90s inland.

&&

.LONG TERM...
Issued at 135 PM PDT Sun Aug 18 2024
(Monday night through next Saturday)

The ridge portion of the quasi-Omega block nudges westward on
Tuesday leading to a additional few degrees of warming. The
building 500 mb heights will help to compress the marine layer a
little. Warmest inland locations will soar into the upper 80s/90s
with far S interior locations making a run for 100 degrees
(40-60% chc).

The flexing upper ridge quickly retreats eastward Wednesday as an
embedded shortwave trough rounds the base of the PacNW upper low.
Temps will begin to trend cooler as the marine layer redevelops.
Had added some light drizzle back to the forecast for Wednesday
night into Thursday.  Coastal fog will also be an issue again.

The second half of the week into next weekend becomes more active
as the upstream upper low final gets kicked. Decent agreement
among ensembles and cluster analysis (minor diff on timing/depth)
with an upper low dropping into CA late Thursday and Friday.
Deterministic agreement is a different story with a wide variety
of outcomes. Following the ensemble approach temperatures cool
further Thursday and moreso Friday. EFI shows below seasonal
averages through the period as well. The wrinkle in the forecast
will be precip. Latest guidance does bring some scattered showers
into the North Bay Friday, but nothing south of the Golden Gate.
While there is some instability, think best chance for actual
thunder will be north of the forecast area. Therefore, will keep
with a low chc (15-20%) for showers. Not expecting much in the
way of accumulation.

Drier weather returns next weekend with a warming trend.

&&

.AVIATION...
(06Z TAFS)
Issued at 1045 PM PDT Sun Aug 18 2024

Narrow band of low stratus clouds continue to track south along
the coast line from Bodega Bay south to the South Bay, then
farther south down to Big Sur. VFR will prevail for inland
terminals but a tricky forecast for locations near the water.
An influx of drier low level air just above the marine layer is
helping to maintain VFR but once radiational cooling accelerates,
low clouds will develop, but the timing and precise location of
where that will occur, amounts to a low confidence forecast.

Vicinity of SFO...Winds have eased across the Bay Area with a
narrow band of stratus occasionally meandering far enough inland
to produce MVFR ceilings, but VFR is expected to prevail through
the overnight with low ceilings reemerging around sunrise Monday
morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with radiational cooling
helping to increase probability of IFR ceilings developing during
the overnight and persisting into at least mid-Monday morning.
Onshore winds will continue with 5 to 15 knots with a few gusts
to 20 knots with newly arriving air mass from the northwest.

&&

.MARINE...
(Tonight through next Friday)
Issued at 450 PM PDT Sun Aug 18 2024

Surface high pressure over the offshore waters will result in
northwest winds this week. An upper level low pressure system from
Alaska will dig southward reaching the Pacific Northwest and far
northern California late this week.

&&

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

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...JM
MARINE...Canepa

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