445
FXUS66 KMTR 220029
AFDMTR

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

...New AVIATION, MARINE...

.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...
(00Z TAFS)
Issued at 528 PM PDT Thu Aug 21 2025

Widespread VFR lasts into the night. Expect moderate to breezy wind
to last into the evening and early night before reducing. Stratus
struggles to form overnight, LIFR CIGs look to build at HAF with
only spotty LIFR CIG coverage expected around OAK and the Monterey
Bay terminals. Low clouds look to erode in the mid morning with
widespread VFR expected by Friday afternoon as moderate to breezy
winds return.

Vicinity of SFO...VFR through the TAF period. Breezy to gusty winds
linger into the early night before winds reduce and gusts cut off.
Winds stay moderate and westerly through the night and into Friday
afternoon. Expect winds to into the mid afternoon with gust peaking
around 25 kts. These winds and gusts last though the evening before
gusts ease and wind become more moderate into Friday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR lasts into the early morning. Winds
reduce and become light in the mid evening and stay light through
the night. Spotty LIFR CIGS and reductions in visibilities look to
affect the terminals early Friday morning but exit in the mid
morning. Expect moderate winds to build again for Friday
afternoon.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 528 PM PDT Thu Aug 21 2025

A moderate to strong northwesterly breeze will persist through
Friday, with locally stronger gusts 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. Winds 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 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory until 3 AM PDT Friday for Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt
     to Pt Pinos 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 3 AM PDT Saturday 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.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Murdock
MARINE...RGass

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