106
FXUS66 KMTR 150449
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
949 PM PDT Sun Sep 14 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 139 PM PDT Sun Sep 14 2025

 - Warming trend with above normal temperatures through Wednesday

 - Showers and isolated storms are forecast Thursday and into next
   week

&&

.UPDATE...
Issued at 848 PM PDT Sun Sep 14 2025

The marine layer has compressed to around 1,000 feet according to
the latest sounding and vertical profilers. Time lapse videos
show the fog monster has moved across San Francisco, impacting
nearly everybody in the city, except the highest few floors on
the Salesforce Tower. As the high pressure ridge continues to
build, the marine layer will compress further over the next 24
hours. This will bring less extensive inland cloud coverage, but
could bring some fog to the coast and adjacent hills. On the other
hand, the current satellite loop reveals a significant pocket of
dry air north of Point Reyes, which will likely play a role in the
cloud coverage for the next several hours.

&&

.SHORT TERM...
Issued at 139 PM PDT Sun Sep 14 2025
(This evening through Tuesday)

The short term forecast period will be dominated by warm, though
quiescent, conditions across the Bay Area and Central Coast with a
potential for impactful heat. Further compression of the marine
layer, as evidenced by recent profiler and upper air observations,
will effectively limit the degree of onshore flow, except along
the immediate coast. In fact, guidance suggests weakly offshore
flow, which is ideal for MaxT`s overachieving, across our region
on Monday and Tuesday. Given the synoptic scale signal for
slightly offshore flow at 925mb (at or below 10 knots), I`ve
elected to incorporate more of the 50th NBM percentile for highs
as we kick of the work week. This will translate to areas of
Moderate to isolated regions of Major HeatRisk, especially across
the East Bay, Santa Lucia Range, and some interior regions of the
Central Coast. Overnight conditions do not appear that they`ll
spell any relief if you`re not a fan of the heat, as morning MinTs
through Wednesday will average between 5 to nearly 20 degrees
above normal. While the probability of an extreme heat event is
low, individuals should remain hydrated with plenty of water and
electrolytes, limit time outdoors during peak heating if possible,
and never leave children or pets unattended in vehicles. As far
as formal heat headlines, the areal coverage doesn`t appear to be
widespread enough to warrant products at this time. Regardless,
abide by the aforementioned heat safety protocols. The above
normal warmth during the day and nighttime hours will equate to
extended burn periods for some of the finer fuels (grasses/brush)
and this is discussed more in the fire weather section below.

&&

.LONG TERM...
Issued at 139 PM PDT Sun Sep 14 2025
(Wednesday through next Saturday)

The heat should subside some on Wednesday as reduced solar
insolation is anticipated thanks to more in the way of filtered
sunshine. There remains some uncertainty in Wednesday`s MaxT
forecast due to the expected increase in cloud cover. Southerly
flow, still technically offshore for most areas, will tend to
bring a warmer airmass, even to our largely coastal regime and
keep the marine layer confined (though it may be non-existent due
to these types of wind trajectories). We`ll refine this portion of
the forecast as we proceed through the next few days.

The main theme in the long term forecast period will be the
potential for impactful convection across the Bay Area and Central
Coast. The most probable time frame for thunderstorms, some dry,
Thursday and into Friday, though some high-based virga/showers may
get going as early as Wednesday across southern reaches of the
Central Coast. From a pattern recognition standpoint, there do
appear to be favorable ingredients needed for a hefty coverage of
convection. Moisture from the tropical cyclone in the eastern
Pacific (Mario) will gradually stream northward through mid-week,
with a more rapid surge Thursday. As is typical with these
setups, the moisture will be mostly confined to areas at or above
700mb (just under 10,000 ft AGL and above). In fact, EPS mean
probabilities of precipitable water (PW) values above 1" exceed
90%. Forecast PW percent of normal are anticipated to exceed 200%
across a large portion of the area by Thursday. Diffuse upper
troughing as manifest by a 2PVU anomaly should encourage broad
scale ascent across our portion of California. The ascent will be
quite modest, though potentially sufficient. So we have moisture
and modest, but potentially sufficient lift. The final question is
what about the instability? This is where the uncertainty is the
largest in the forecast as model progs during the late week period
suggest 700-500mb lapse rates of around 6 C/km. This is a little
on the marginal side, however, it`s quite possible that some of
the coarser guidance convective parametrization may be muting what
would otherwise be steeper mid- level lapse rates. Some of the
extended experimental higher resolution ensemble guidance does
illustrate a more convective simulated radar picture and this in
tandem with the overall synoptic background supports including
showers and 15-20% chance for isolated thunderstorms in the
forecast.

Currently QPF is largely anticipated to remain under one-tenth of
an inch, however, with the greater PW values forecast, there`s
around a 10-20% chance that wetting rain may occur. Regardless,
rain amounts will not be very high with this system and as a
result, I`ve inserted "dry" storms into the forecast. We`ll need
to monitor this potential over the next several days and if it
does appear that more numerous dry thunderstorms are more
probable, Fire Weather Watches may be needed. Uncertainty
increases with regard to how quickly instability wanes on Friday
and into the weekend. At this time, the forecast will mention
showers, however, the potential for thunderstorms is around 10%.

&&

.AVIATION...
(06Z TAFS)
Issued at 949 PM PDT Sun Sep 14 2025

Winds have reduced through the evening and low clouds have filled
around HAF and around the bays. Status coverage increases and moves
inland into the night becoming nearly widespread into Monday
morning. Pockets of fog look to affect STS and HAF in the early to
mid morning. Cloud cover will be slow to erode on Monday, but nearly
widespread VFR is expected into the afternoon. The exception, being
HAF, which sees CIGS rise from LIFR to MVFR levels, but don`t clear.
Moderate to breezy winds arrive Monday afternoon and last into that
evening. Cloud cover looks to stay mostly along the coast into
Monday night, eventually filling over MRY and SNS.

Vicinity of SFO...Inconsistent CIGs affect SFO into the late night
before persistent CIGs fill over SFO into the Monday morning. These
CIGs erode into the late morning and breezy west winds build Monday
afternoon. Expect these winds to reduce in the mid evening, becoming
light for Monday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...MVFR/IFR CIGs are building around the the
bay with winds expected to reduce in the mid evening. CIGs fall to
IFR levels across the area into the late night with winds becoming
light and variable into the late night. Moments of IFR CIGS and
reduced visibilities look to affect the terminals into the morning.
CIGs erode into Monday afternoon as moderate west winds build. These
winds reduce into Monday evening as CIGs build around the bay again,
affecting MRY in the mid evening.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 949 PM PDT Sun Sep 14 2025

Winds are reducing across the waters and will continue to do so
into Monday afternoon leading to widespread light winds into
Monday evening. Moderate seas persist, especially offshore and
will subside through midweek before building again late week.

&&

.FIRE WEATHER...
Issued at 139 PM PDT Sun Sep 14 2025

The fire weather threat will elevate this week for a few reasons.
1) Despite last weeks precipitation, our area has NOT had a season
ending rainfall event. 2) While Energy Release Components (ERCs)
have rebounded significantly, the above normal MaxTs and MinTs
will serve to rapidly cure some of the finer fuels and
subsequently ERC values will support some fire spread. The above
normal warmth will also translate to poor overnight humidity
recovery (RH below 35%) across the Mayacamas, Santa Cruz
Mountains, as well as the Diablo, Santa Lucia, and Galiban Ranges
this week. Afternoon RH will also fall into the 20-35% range for
most areas, except along the immediate coast. 3) There is an
opportunity for isolated thunderstorms as early as Thursday and
into Friday. The areas with the greatest chances (around 20-25%)
for isolated thunderstorms, are across the Central Coast, Eastern
Santa Clara Hills, and East Bay. At this time, rain amounts are
anticipated to remain largely below one-tenth of an inch and as a
result, ignitions due to dry lightning may transpire Thursday and
into Friday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Monday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 PM PDT Monday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Murdock
MARINE...Murdock

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