142
FXUS66 KMTR 200041
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
541 PM PDT Tue Aug 19 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 245 PM PDT Mon Aug 18 2025

 - Heat Advisory Thu - Fri across much of the interior

 - Moderate HeatRisk extends into Saturday

 - See Heat Safety tips below

&&

.SHORT TERM...
Issued at 1233 PM PDT Tue Aug 19 2025
(This evening through Wednesday)

Another nice day with comfortable temperatures and clear skies.
Strong wind gusts will arrive along the coast and Bayshore this
evening before calming overnight. A warming trend starts in
earnest Wednesday in response to building high pressure from the
SE. Near normal temperatures today will increase to about 5-10
degrees above normal by Wednesday afternoon.

&&

.LONG TERM...
Issued at 1233 PM PDT Tue Aug 19 2025
(Wednesday night through next Monday)

While the max temperature only climbs another couple degrees from
Wednesday to Thursday, warmer overnight lows and the multi-day
duration will bring more widespread moderate HeatRisk by Thursday.
In response we issued a Heat Advisory for much of the interior
from Thursday-Friday when max temperatures will broadly range
from the low to upper 90s. Some portion of the advisory may need
to be extended into Saturday, but better onshore flow will start
to cool things off a bit by the weekend.

I was a little surprised to see that this is our first
Heat Advisory of the Summer. Would you believe that we had 23 days
under a Heat Advisory and 9 days under an Excessive Heat Warning
by this time last year? We did have a few in May this year, but
broadly speaking it`s been cooler than normal since then. We are
only talking about 5-10 degrees above climatology this week, but
most people aren`t acclimated to a normal summer, and it may feel
worse than that.

Outside of the heat, there is a plume of monsoonal moisture
expected to push through from the Gulf of California Friday-
Saturday. ECMWF brings the PW between 150-200% of normal. Model
soundings show most of this moisture anomaly will be above 700
mb. This moisture combined with a conditionally unstable 7 C/km
lapse rate between 700-500 mb, means there is a possibility for
elevated convection Fri-Sat. Most model guidance keeps any
thunderstorms confined to southern California and the higher
terrain along the Sierra where the landscape acts as a natural
lifting mechanism. Despite the lack of model support, we have a
small possibility for elevated convection in our cwa as well. With
dry air below the moisture plume, this brings a chance for dry
lightning (when all the rain evaporates before hitting the
ground). Dry lightning storms are notorious for igniting
wildfires. It will be interesting to see how the higher resolution
CAMs resolve this scenario over the next few days.

Heat Safety Tips:

Heat is the number 1 weather related killer in the United States.
Follow these tips to protect yourself, your loved ones, and your
animals.

-Stay inside in an air conditioned environment between 10am and 7pm.
-Suspend unnecessary outdoor activities during moderate heat, but
 if you must be outdoors, take frequent breaks in the shade or AC
 and drink cool water.
-Know the signs and symptoms of Heat Exhaustion vs. Heat Stroke!
Heat Stroke can be deadly if not treated immediately by a medical
professional. Call 911 if you suspect someone is suffering from Heat
Stroke.
-Wear a life jacket, swim near a lifeguard, and check conditions
 before entering the water if going to a river or ocean to cool
 off. Beware of cold water shock.
-Use a cool and damp towel on your body if you do not have AC and
are feeling hot. Or, take a cool shower or bath.
-Do not leave kids or pets in a parked car.
-Ensure pets and livestock have access to shade and water.

&&

.AVIATION...
(00Z TAFS)
Issued at 540 PM PDT Tue Aug 19 2025

Widespread VFR lasts through the mid evening before IFR CIGs begin
to rebuild along the coast and affect HAF. Winds stay moderate into
the evening before beginning to reduce in most areas and become light
overnight. Cloud cover builds around the Monterey Bay later into the
night with IFR CIGs then turning to LIFR with some pockets of fog
into early Wednesday there and at HAF. Additionally APC and OAK look
to be affected by spotty IFR CIGs in the early to mid morning. Cloud
cover across the region begins to erode in the mid morning with
Widespread VFR expected for Wednesday afternoon with moderate winds
rebuilding and lasting into that evening.

Vicinity of SFO...VFR through the TAF period. Moderate winds with
infrequent gusts linger into the late evening and early night before
reducing. Moderate west winds return Wednesday afternoon and look to
last into that night.

SFO Bridge Approach...Expect some moments of passing IFR-level
clouds between 12z to 17z, otherwise similar to SFO.

Monterey Bay Terminals...VFR lasts into the night. Expect winds to
reduce in the mid evening as stratus and an otter eddy builds in the
Monterey Bay. This eddy looks to cause some moments of pushing and
pulling of stratus around the bay through the night, but CIGs look
to be fairly consistent at MRY after 6z and SNS after 10z. IFR CIGS
and reduced visibility look to affect MRY into Wednesday morning,
with only moments of lowering CIGs affecting SNS. Cloud cover erodes
in the late morning, bringing back VFR by noon.

&&

.MARINE...
(Tonight through next Monday)
Issued at 540 PM PDT Tue Aug 19 2025

Moderate seas will continue tonight and become rough by Wednesday
with moderate to strong northwesterly breezes, especially across
the outer waters and coastal jet regions near Point Sure and Point
Reyes. Expect widespread hazardous conditions for small craft
tonight through early Thursday morning.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory from 10 AM Thursday to 10 PM PDT Friday for CAZ504-
     510-512>518.

PZ...Small Craft Advisory until 9 PM PDT this evening for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm-
     SF Bay N of Bay Bridge.

     Small Craft Advisory until 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...Flynn
LONG TERM....Flynn
AVIATION...Murdock
MARINE...JM

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea