Napa, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

025
FXUS66 KMTR 200920
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
220 AM PDT Tue May 20 2025

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

.SYNOPSIS...
Issued at 203 AM PDT Tue May 20 2025

Strong and gusty northwesterly winds, above seasonal normal
temperatures, and hazardous marine conditions today. Elevated
fire weather conditions through Thursday.

&&

.SHORT TERM...
(Today and tonight)
Issued at 203 AM PDT Tue May 20 2025

Heights will ever so slightly fall today as a subtle upper-level
shortwave trough skirts the region, but temperatures will still
remain seasonably warm. High pressure over the Eastern Pacific
Ocean and low pressure over the Desert Southwest will support a
tight surface pressure gradient that will be conducive for
northwesterly flow that will be locally strong over the waters,
along the coastline, and through northwest/southeast oriented
valleys such as the Salinas and Santa Clara. The return of onshore
flow has allowed for cooler and moister conditions and
subsequently the reformation of the marine layer, albeit an
interesting looking one as offshore/downslope flow in the higher
terrain of the North Bay and Santa Cruz Mountains is resulting in
compressional warming that`s effectively wiping out the marine
layer in those spots. Elevated fire weather conditions will be
prevalent, primarily across the brush and grasses of the interior,
through Thursday as dry and gusty conditions continue.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 203 AM PDT Tue May 20 2025

A low amplitude upper-level shortwave ridge will nudge into the
region Wednesday, bringing the warmest conditions of the week with
temperatures of 10 degrees above normal. Global ensemble clusters
are all in agreement of heights falling through Friday due to an
upper-level shortwave trough, which will translate to
temperatures returning to seasonal normals by Friday as the brief,
gradual cooling trend brings temperatures down by 5 degrees each
day. Agreement in global ensemble clusters continues with heights
rebuilding Saturday as an upper-level shortwave ridge builds into
the West, kicking off another brief, gradual warming trend.
Oakland Museum (OAMC1) and San Francisco Downtown (SFOC1) will put
their daily minimum temperature records in jeopardy this week.
Oakland Museum (OAMC1): Wednesday (5/21), Saturday (5/24), Sunday
(5/25), and Monday (5/26), previous records of 49, 49, 49, and 50
degrees respectively set in 1986, 2011, 1980, and 2008
respectively, the official forecast is 51, 51, 51, and 53 degrees
respectively. San Francisco Downtown (SFOC1) on Friday (5/23) and
Sunday (5/25), previous records of 47 degrees set in 2010 and 1953
respectively, the official forecast is 50 degrees.

&&

.AVIATION...
(06Z TAFS)
Issued at 835 PM PDT Mon May 19 2025

It`s VFR over land except patches of stratus and fog /LIFR-IFR/
are developing along the immediate coastline. Late afternoon and
early evening satellite imagery showed standing waves within the
stratus and fog.

The ACV-SFO pressure gradient is 7.2 mb, the UKI-STS pressure
gradient is strong at 2.6 mb, the onshore gradient SFO-SAC is 2.7
mb. Pressure gradients initiate atmospheric motion; the overall
pressure pattern in recent days has favored gusty northwest winds
over the coastal waters and gusty west winds across the San
Francisco Bay, this is common during spring and even early summer
seasons. The marine layer varies in depth from several hundred
feet to locally up over 1500 feet e.g. Fort Ord profiler.

A general convergence of higher dewpoint air (water vapor) in
contact with chilly sea surface temps 50F-55F trapped beneath the
lower level temperature inversion ahead of overnight cooling both
due to temperature advection and radiative cooling to space favor
additional stratus and fog /LIFR-IFR/.

Vicinity of SFO...Strong west wind continuing through the evening,
with gusts 35-40 knots up through midnight. Increasing convergence
of stratus and fog on the ocean side of the peninsula will likely
advect on westerly wind reaching SFO late tonight and early Tuesday
morning, a dry surface based cold front will move southward along
the coast temporarily moving the stratus inland to the terminal
before drier post frontal air moves in for early return to VFR
Tuesday. West wind increasing to 20 to 30 knots with possibly higher
gusts Tuesday afternoon and evening. Current HREF output shows VFR
for Tuesday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...It`s currently VFR, however expect an
increasing probability of stratus with patchy fog /LIFR-IFR/ with
onshore winds 10 to 20 knots during the evening. Expect LIFR-IFR
in stratus, fog including possibly a few patches of late night
and/or morning drizzle tonight and Tuesday morning. Conditions
improving to VFR by late Tuesday morning and early afternoon.
Onshore winds 10 to 20 knots Tuesday afternoon and early evening.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 810 PM PDT Mon May 19 2025

Surface high pressure will result in widespread strong northerly
gale force gusts over the inner and outer waters through Tuesday.
Hazardous seas will persist Wednesday through Friday with strong
northwesterly winds occasionally near gale force gusts.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for SF
     Bay N of Bay Bridge.

     Small Craft Advisory until 9 PM PDT this evening for Mry Bay.

     Gale Warning until 9 PM PDT this evening for Pigeon Pt to Pt
     Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
     Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt
     Reyes to Pigeon Pt 0-10 nm.

     Gale Warning until 3 AM PDT Wednesday for Pt Arena to Pt Reyes
     10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...Canepa

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