St Helena, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

021
FXUS66 KMTR 081647
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
947 AM PDT Tue Jul 8 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 118 AM PDT Tue Jul 8 2025

 - One more day of cool conditions before warmer temperatures
   return Wednesday through the weekend, with patchy Moderate
   HeatRisk across the Bay Area and Central Coast.

 - Localized elevated fire weather threat Wednesday through the
   weekend across the higher elevations.

 - Slight risk (20-40% probability) of extreme heat in the far
   interior portions of the Bay Area and Central Coast July 15-17.

&&

.UPDATE...
Issued at 926 AM PDT Tue Jul 8 2025

The marine layer was measured between 2,000 (OAK sounding) and
2,500 feet (Ft. Ord profiler) this morning. This allowed expansive
stratus coverage which is now beginning to slowly retreat out of
the inland valleys. While the clouds will gradually clear this
afternoon, the marine layer air will remain. As a result, temperatures
will be below normal today. Highs are expected in the mid 70s to
low 80s inland, with typical 60s along the coast.

&&

.SHORT TERM...
Issued at 118 AM PDT Tue Jul 8 2025
(Today and tonight)

Marine layer clouds blanket the coast and are expanding into the
inland valleys through the rest of the morning, with coastal drizzle
possible through the morning hours. Low temperatures hover in the
upper 40s to the middle 50s in the lower elevations, and up to the
lower 60s in the highest peaks. An upper level low pressure system
off the California coast continues to diminish and drift northwards,
but it will provide us one more day of temperatures cooler than
seasonal averages, with highs ranging from the middle 70s to lower
80s inland, up to the lower 90s in the warmest spots of southern
Monterey and San Benito counties, into the middle 60s to middle 70s
along the Bays, and into the upper 50s to the lower 60s along the
Pacific coast. The onshore winds this afternoon and evening will be
lighter than those seen yesterday, partially as a result of a
relaxing pressure gradient aloft from the weakening low, but gusts
around 20 mph are still possible through the gaps, passes, and the
Salinas Valley.

&&

.LONG TERM...
Issued at 118 AM PDT Tue Jul 8 2025
(Wednesday through Monday)

The dissipating upper level low will move inland near the California-
Oregon border and allow a ridge centered over the Desert Southwest
to expand into southern California, where heat products will go into
effect starting Wednesday morning. Our part of the state will still
experience a warming trend, with Wednesday`s highs rising to the 80s
inland with the warmest spots in southern Monterey and San Benito
counties reaching the upper 90s. Ensemble model cluster analysis has
begin homing in on the Bay Area and Central Coast seeing more zonal
flow as the heat peaks on Thursday and Friday, moderating the heat
impacts as the southern part of the state swelters. The inland
valleys see highs in the middle 80s to middle 90s on both days,
while the warmest interior locations see temperatures rising up to a
few degrees above 100. In terms of HeatRisk, patches of Moderate
HeatRisk are expected on Thursday and Friday across the interior
North Bay, East Bay, and South Bay, in addition to the Santa Lucia
mountains and the southern tip of San Benito County. Remember to
take frequent cooling breaks and drink plenty of water if
participating in outdoor activities on both days.

Temperatures for the upcoming weekend will cool slightly to the
lower 80s to lower 90s in the interior Bay Area with an shortwave
trough coming through the West Coast, while the interior Central
Coast remains rather warm with temperatures in the 90s. Winds remain
light and onshore through the weekend with locally breezier winds
through the gaps, passes, and the Salinas Valley. Further afield,
longer term outlooks show a lean towards temperatures above seasonal
averages into the third week of July.

Small fuels have effectively cured and large fuels are continuing to
cure across the region as the dry weather continues, with further
drying expected as the temperatures warm Wednesday through the
weekend. Localized fire weather threats are possible, particularly
in higher elevations above marine layer influence. Extreme caution
is advised if participating in outdoor activities involving open
flames and sparks, noting that most wildfires are started by human
activity. One less spark, one less wildfire!

&&

.AVIATION...
(18Z TAFS)
Issued at 946 AM PDT Tue Jul 8 2025

Currently a mixed bag of VFR-MVFR at the terminals with an early
improvement to VFR on tap. The marine layer is currently being
observed at 2,600 feet on the Fort Ord profiler. Just what happens
to it over the next 24-30 hours will be heavily dependent on the
upper-level pattern as broad upper-level ridging builds in from the
Desert Southwest while an upper-level trough swings through Northern
California, likely leading in a deepening marine layer from south to
north. For now greatest confidence is in widespread low-end MVFR
with the possibility for IFR ceilings, particularly at the coastal
terminals of HAF, MRY, and SNS.

Vicinity of SFO...Currently VFR with northeasterly flow. Westerly
flow will begin to prevail this afternoon once the sea breeze kicks
in. Moderate to high confidence on the return of sub-VFR ceilings to
the terminal tonight with ceilings likely being on the cusp of low-
end MVFR to IFR.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently MVFR and calm at both terminals
with high confidence in VFR being achieved shortly based on
satellite trends. Moderate to high confidence on the return of sub-
VFR ceilings to the terminals tonight. Uncertainty resides in the
ceiling height due to the fact that the terminals will likely begin
to be affected by the upper-level ridge which would subsequently
result in subsidence aloft, a compressed marine layer, and thus
relatively lower ceilings and visibilities. The key will be on if
this can happen tomorrow morning instead of tomorrow afternoon, if
so it is reasonable to believe that the terminals may be in the LIFR-
IFR category instead of low-end MVFR.

&&

.MARINE...
(Today through Sunday)
Issued at 926 AM PDT Tue Jul 8 2025

A gentle southerly breeze and moderate seas will prevail today.
Winds will strengthen and veer to become moderate and northerly by
Wednesday with further strengthening to become fresh to strong on
Thursday and into the weekend. Significant wave heights will be
rough to very rough Thursday through Saturday for the outer
waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM Wednesday to 3 AM PDT Thursday
     for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-
     10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Sarment
MARINE...Sarment

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