324
FXUS66 KMTR 211141
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
441 AM PDT Thu Aug 21 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 1216 PM PDT Wed Aug 20 2025

 - A Heat Advisory is in effect through Friday for much of the
   interior Bay Area and through Saturday for interior Central
   Coast.

 - Temperatures will remain above normal through the weekend.

 - Elevated fire weather conditions across the interior into the
   weekend.

&&

.SHORT TERM...
Issued at 215 AM PDT Thu Aug 21 2025
(Today and tonight)

Pretty quiet overnight with mostly clear skies. Satellite imagery
shows less stratus, but still seeing a patch or two near Monterey
Bay and SF Peninsula. Other item of note on the satellite is the
broad area of upper level clouds streaming in from the south.
More on that later.

Temperatures will be the big weather impact over the next 24
hours. Wednesday`s interior warmth was only a preview of what we
can expect the next few days. The 4-corners ridge that scorched
the Desert SW will make its presence known today across a large
portion of the forecast area. If you`re near the coast onshore
flow will keep temperatures in check thanks to some natural AC off
the ocean, but temps will still be above seasonal average. Away
from the coast the well above normal 850mb temps (forecast to be
above 90th percentile) will yield temperatures in the 90s to lower
100s. Could see a few records fall at our climate sites today.
The warmer air aloft has already arrived, as noted by current
temps in the 80s for the hills. A mild start to the day combined
with daytime interior heat HeatRisk values will be in the Moderate
to Major category today. As such, Heat Advisories will go into
effect for interior locations and the SF Bay Shoreline. Tonight
will feature another night with active thermal belts and mild
temps in the hills with little relief.

&&

.LONG TERM...
Issued at 303 AM PDT Thu Aug 21 2025
(Friday through Wednesday)

A slight adjustment has been made for the Friday forecast.
Temperatures near the coast will be within a few degrees of
Thursday`s max temps, but interior locations will warm a few more
degrees as 850mb temperatures make a run at record values.In some
cases, Friday will actually be the hottest day of this round of
heat. Saturday will be a transition day as the ridge begins to
ease its grip. While temps begin to cool on Saturday far interior
locations are still in the triple digits, especially interior
Central Coast. Therefore, extended the Heat Advisory for interior
Monterey/San Benito counties with HeatRisk staying in the
Moderate to Major with a few pockets of Extreme. This blends well
with our neighboring counties. Temperatures will remain above
seasonal average into next week, but do expect a gradual cooldown
Sunday through Wednesday. Temperatures will drop 3 to 5 degrees
each day, which will lower HeatRisk concerns each day too.

Now for the wrinkle and wildcard in the forecast. The high clouds
currently streaming in from the south is upper level monsoonal
moisture wrapping around the ridge of high pressure. Models
continue to vary on details with the monsoonal moisture and its
impacts. However, most show solid upper level moisture, decent
lapse rates from 700-500mb, MUCAPE (some CAMS are very high),
critical modified Total-totals, and classic inverted V point
soundings. One piece of the puzzle is a more pronounced lifting
mechanism or trigger. After coordinating with neighboring offices
will continue to advertise this as a non-zero chance for
thunderstorms. Given the profile developed storms would have a
higher chance to be dry. The threat for convection still remains
focused on Friday and Saturday over the Central Coast.

&&

.AVIATION...
(12Z TAFS)
Issued at 441 AM PDT Thu Aug 21 2025

Patchy coastal stratus and fog /IFR-LIFR/ continues this morning
and redevelops tonight and Friday morning otherwise it`s VFR.

Vicinity of SFO...VFR. Northwest to west wind 5 knots increasing
to 16 to 22 knots this afternoon to mid evening, then west wind 10
knots shifting to light northeast Friday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Patchy coastal stratus and fog /IFR-LIFR/
this morning and tonight to Friday morning otherwise VFR. Mainly
onshore winds 5 to 15 knots.

&&

.MARINE...
(Today through Tuesday)
Issued at 215 AM PDT Thu Aug 21 2025

Breezy to gusty northwest winds will prevail through Friday
morning, especially across the outer waters and coastal jet
regions near  Point Sur and Point Reyes. This will result in
widespread hazardous conditions for small craft. Wind and seas
will gradually ease Friday  afternoon and evening, leading to
calmer conditions over the weekend and well into the next work
week.

&&

.FIRE WEATHER...
Issued at 305 AM PDT Thu Aug 21 2025

Will continue to carry a headline in the forecast through the
weekend for elevated fire weather concerns due to hot/dry
conditions day/night with daily sea breeze winds. Critical
humidity values will be reached afternoon with little to no
relief at night. Winds don`t appear to be strong enough for an
extended period of time to warrant a Red Flag. ERC charts will be
responding to the warm up. In addition, we are monitoring a surge
of monsoonal moisture set to arrive on Friday through the weekend,
which will bring a very low, but non-zero, chance for elevated
convection across the Central Coast. Greatest concern for any
developed storm would be dry lightning.

MM

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 10 AM this morning to 10 PM PDT Friday for
     CAZ504-510-512>515.

     Heat Advisory from 10 AM this morning to 10 PM PDT this evening
     for CAZ506-508.

     Heat Advisory from 10 AM this morning to 9 PM PDT Saturday for
     CAZ516>518.

PZ...Small Craft Advisory from 3 PM to 9 PM PDT Friday for Pigeon Pt
     to Pt Pinos 0-10 nm-SF Bay N of Bay Bridge.

     Small Craft Advisory from 3 PM this afternoon to 9 AM PDT Friday
     for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10
     nm.

     Small Craft Advisory from 3 PM this afternoon to 9 PM PDT Friday
     for Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

     Small Craft Advisory until 9 AM PDT Friday for Pigeon Pt to Pt
     Pinos 10-60 NM.

&&

$$

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

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