Wildfire in California, August 21 to 25, 2025

Area Forecast Discussion
National Weather Service San Francisco CA
140 PM PDT Thu Aug 21 2025

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

.KEY MESSAGES...
Updated at 1206 PM PDT Thu Aug 21 2025

 - A Heat Advisory is in effect for much of the Bay Area and
   Central Coast today for areas away from the ocean.

 - Heat advisories continue for many inland areas through
   Saturday.

 - Stay hydrated and avoid strenuous activities during the
   hottest part of the day.

&&

.SHORT TERM...
Issued at 1206 PM PDT Thu Aug 21 2025
(This evening through Friday)

On average temperatures are running about 5 degrees warmer than
this time yesterday. Weak offshore winds are bringing the heat all
the way to the Bay shore, though a sea breeze is helping relieve
to the immediate coast. For example temperatures in San Francisco
range from 62F at Ocean Beach to 87F in the Castro District. After
some misses yesterday triggered extensive edits to the maxT
forecast, things are looking more on track today. A couple daily
records will likely be challenged over the next couple hours.
Specifically 101 at Livermore and 92 at San Jose come to mind.
Tomorrow will bring similar heat to inland areas, although the
coastal areas will enjoy better onshore flow and somewhat cooler
temperatures.

Monsoon moisture is moving in from the south, and is
bringing some high clouds as proof. These should at least make
for a nice sunset after a warm day. As this moisture filters from
the upper to middle troposphere by Friday, it also brings a small
chance for a weak shower or even dry lightning tomorrow. The
limiting factor here is the depth of the moisture. Analyzing past
August monsoon pushes show that we really need moisture to extend
down to 700mb or lower for widespread thunderstorms to form. Most
guidance just keeps it too high. Even if we had the correct
moisture profile, we'd still need a trigger to realize the
potential energy, and we don't see an obvious sign of that. While
the chances are still very low, the best area appears to be in the
southern portion of our cwa. A RAP-13 point sounding from San
Benito Mountain brings the moisture all the way down to 700 mb,
which translates to a couple hundred J/kg of long, skinny CAPE
above a 10,000 ft LCL. With very dry air below the LCL, any rain
that falls will likely evaporate before it hit the ground. Again
the chance of this remains very small across the Bay Area and
Central Coast, but taller mountains across the State should be
able help the atmosphere realize some of this potential energy.

&&

.LONG TERM...
Issued at 1206 PM PDT Thu Aug 21 2025
(Friday night through next Wednesday)

As the ridge remains in place and 850 temperatures hover around
25C, inland areas will be slow to cool through the weekend. While
the peak of the event is either today or Friday, Saturday will
only bring marginal relief, and the Heat Advisory has been
extended through Saturday for much of the interior portions of the
Bay Area and Central Coast. A gradual cool-down will follow, with
more confidence in temperatures returning to normal by the middle
of next week as a weak 500 mb trough or cut-off low form in the
Eastern Pacific. We're also keeping one eye on the tropics as a
disturbance has moderate chance of forming and may push some
moisture into California by the end of the month. The uncertainty
with tropical systems this far out is very high, and this is just
one of many possibilities for now.

&&

.AVIATION...
(18Z TAFS)
Issued at 1029 AM PDT Thu Aug 21 2025

All TAF sites are currently VFR and are expected to remain so
through much of the forecast period. Onshore winds are forecast to
increase this afternoon before diminishing after sunset and more so
into Friday morning.

Vicinity of SFO...VFR. Northwest to west winds increase this
afternoon with gusts around or slightly above 22 knots. Wind speeds
ease after sunset and may become northeasterly early Friday morning.
Onshore winds increase once again by Friday afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Northwest to west winds increase this
afternoon before easing after sunset. There is low to moderate
confidence sub-IFR conditions return early Friday morning, yet
should be short in duration.

&&

.MARINE...
(Today through Tuesday)
Issued at 1029 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 until 9 PM PDT Saturday for CAZ504-510-513>518.

     Heat Advisory until 10 PM PDT this evening for CAZ506-508.

     Heat Advisory until 10 PM PDT Friday for CAZ512.

PZ...Small Craft Advisory until 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 to 9 PM PDT Friday for Pigeon Pt
     to Pt Pinos 0-10 nm.

     Small Craft Advisory until 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...Flynn
LONG TERM....Flynn
AVIATION...RGass
MARINE...RGass

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