Yountville, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

808
FXUS66 KMTR 080444
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
944 PM PDT Wed May 7 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 133 PM PDT Wed May 7 2025

A dynamic weather pattern will bring a warming trend through
Saturday, followed by a sharp cool-down through Monday.

&&

.UPDATE...
Issued at 905 PM PDT Wed May 7 2025

Most locations cooled today with a deep marine layer and
persistent onshore winds keeping temps in the 60s near the coast
and bays with 70s inland and 80s confined to the warmest interior
areas of the Central Coast. Evening satellite shows low clouds
spreading inland in a more traditional pattern with nw winds
returning to the coastal waters. Tonight we once again see low
stratus pushing through the Petaluma gap, across the Golden Gate
and down over the Monterey Peninsula in a more typical NW regime
versus yesterday when the southerly surge was still influencing
things. The 00z Oakland sounding shows an inversion height in
excess of 3000 feet so expect widespread stratus intrusion
overnight with the 2.5mb SFO-Sac gradient. If anything the marine
layer should begin to compress by morning as high pressure to our
south begins to nose northward which could lead to some fog for
the coastal slopes and hills. Warming trend should ensue Thursday
and peak Friday for the Bay Area with interior Monterey/San Benito
staying warm to locally hot through Saturday. Heat impacts look
pretty short lived with a potent dry cold front/upper trough
impacting the North Bay as early as Saturday evening. Much cooler
all areas Sunday with breezy NW winds. Breezy and cool Monday with
a slight chance of showers.

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 133 PM PDT Wed May 7 2025

A disturbance in the ridge is moving through today, and the tail
end of a weak cold front is draped across northern California.
Marine layer stratus is mixing out, but the cooler humid air
remains across much of the Bay Area and lower elevations of the
Central Coast. Broadly speaking, temperatures are roughly 5-10
degrees cooler than this time yesterday, while the relative
humidity is 10 to 20% higher. The cold front will meander south
while dissipating over the next 24 hours, with little impact
outside of the deeper marine layer. For Thursday expect similar
stratus coverage in the morning before mostly clearing out by mid
day. The ridge will rebuild, allowing a warming trend to begin.
High temperatures Thursday will reach the mid 80s to lower 90s
in the typical warm spots, with comfortable temperatures in the
upper 60s to mid 70s along the coast.

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 133 PM PDT Wed May 7 2025

The ridge continues to build through Saturday, allowing
temperatures to climb well above normal. Friday and Saturday are
the peak of the warm snap. This sentence may be a little
confusing, but there is a 90% chance that the observed 850mb temp
from the Oakland sounding will reach the 90th percentile of
sounding observations for this time of year. The air mass will be
even warmer over the interior Central Coast, where the 850
temperature has a good chance of exceed 20C. A strong ridge will
keep the marine layer compressed to around 500 feet or less, but
onshore winds will still bring relief to the immediate coast where
temperatures will stay in the upper 60s to mid 70s.
Interestingly, while the uncertainty isn`t incredibly high, the
deterministic NBM output has been consistently in the coolest 25th
percentile of the probabilistic envelope. Given the warm air mass
compared to climatology, and comparing analog days around this
time of year, the warmer ensemble mean solution seems more
reasonable. Even with this warmer solution, bias corrected MOS
data is warmer than our forecast blend at Paso Robles, which is
just outside of our forecast area, but serves as a good
approximation for some of our warmer spots in the southern Salinas
Valley. This new temperature forecast brings more widespread
moderate HeatRisk to the southern Salinas Valley, which may now
need a Heat Advisory for Friday. The rest of the area is broadly
under minor HeatRisk, which is still a concern for those extremely
susceptible to heat related illness.

After the warm snap, a strong cold front will bring temperatures
crashing back down starting Sunday. While there is significant
timing and intensity uncertainty, it is clear that a major trough
will usher in a much cooler air mass to start next week and
temperatures could swing as much as 15 degrees below normal by
Monday. It`s not clear how long this cold air will remain
entrenched, as the probabilistic guidance and cluster analysis
really start to diverge with different solutions beyond Monday.
The exact pattern evolution will also have a significant impact on
the wind speed and direction. Notably, an inside slider type
pattern shows up in one of the clusters, which would bring us
offshore winds if it comes to fruition. In addition to the cool-
down, the cold front and possible post frontal showers could bring
some light rain early next week. The NBM isn`t showing much QPF,
but the ECMWF ensemble mean brings a respectable 2/10ths to area.

&&

.AVIATION...
(06Z TAFS)
Issued at 944 PM PDT Wed May 7 2025

MVFR-IFR stratus is building in the coastal regions. The interior
remains VFR for now, as stratus expands inland through the night,
with the inland stratus mixing out late Thursday morning, with
patchy stratus remaining over the immediate coast. Light and
variable winds continue overnight before breezy onshore flow resumes
Thursday afternoon. With a developing ridge and warming
temperatures, not expecting much inland stratus development Thursday
night.

Vicinity of SFO... VFR through the next few hours. Models remain
split over the potential development of stratus later tonight, but
most guidance points to an MVFR ceiling developing overnight,
although there`s low to moderate confidence about timing. Stratus
should dissipate late Thursday morning. Breezy northwesterly winds
should dissipate in the early overnight hours before resuming on
Thursday afternoon, with very low chances of stratus Thursday night.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... MVFR-IFR stratus through the night with
light drainage winds. Stratus dissipates Thursday morning with
breezy northwest flow resuming in the afternoon. Developing ridge
over the region translates to increased uncertainty over coastal
stratus Thursday night. Some model data indicates possible
development of fog, but confidence is not high enough to note
ceilings in the TAFs at this time.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 944 PM PDT Wed May 7 2025

Moderate to fresh northwest winds continue across the coastal
waters through Saturday, with widespread fresh to strong gusts.
Winds turn to the west on Sunday before northwest flow resumes
next Tuesday. Moderate seas continue through the end of the
forecast  period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM to 9 PM PDT Thursday for Pt Arena
     to Pt Reyes 0-10 nm.

     Small Craft Advisory until 9 PM PDT Thursday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...DialH

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