Monte Sereno, California Weather Forecast Discussion

205
FXUS66 KMTR 180457
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
957 PM PDT Wed Sep 17 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 232 PM PDT Wed Sep 17 2025
- Showers with isolated to scattered thunderstorms as early as
   late tonight through Friday
- Cooler afternoon temperatures through late week
- Slight warm up for the weekend
&&
.UPDATE...
Issued at 813 PM PDT Wed Sep 17 2025
Quick update on conditions this evening. Current radar shows a
fairly persistent line of showers moving up the coast. Thus far,
nearly all observed lightning in our region have been over the
coastal waters. As these showers move northward tonight, they are
moving into an increasingly stable environment. Therefore, we
expect them to behave as we go into the nighttime hours. Overall
thinking is in line with the current forecast. No major changes
needed. However, one thing of note is that we are seeing some
wildly different run-to-run solutions among hi-res models. Timing
largely remains unchanged, but confidence has decreased in
thunderstorm placement and coverage Thursday afternoon/evening.
Through this evening shift, hourly updating hi-res models have
gradually shifted the center of circulation (of remnant Mario) to
the east. We`ll need to reassess what this means for us through
the night. Especially since this eastward shift appears to show a
bias with where the models are initializing the center of the low
(the observed position is further west than the models think it is
when they started their run). We should have a much better idea
of what our afternoon will look like by tomorrow morning.
Behringer
&&
.SHORT TERM...
Issued at 232 PM PDT Wed Sep 17 2025
(This evening through Thursday)
Upper level moisture is starting to spread across the Central Coast
this afternoon as remnants of Mario has arrived. There have been
showers and isolated thunderstorms south of the region earlier this
morning and rain showers along and off of the Big Sur coast early
this afternoon. Tonight into Thursday morning the potential
increases for isolated to scattered rain showers and isolated
thunderstorms as deeper moisture moves northward from the south.
Precipitable water values are forecast to reach from 1.00"-1.40"
across just about all of the region as we head into Thursday
morning. Thus, the potential for dry lightning almost ends entirely!
However, MUCAPE and lapse rates do increase through the day Thursday
suggesting the threat for embedded thunderstorms remain. CAMS
(convective-allowing models) also supports this.
From previous forecaster: "Any thunderstorm activity early Thursday
morning is expected to remain mostly offshore, but things get more
interesting by late morning into Thursday afternoon as the
environment becomes more favorable for scattered thunderstorms to
develop across the Central Coast into the South Bay. Given the near
record PWATs, MUCAPE values between 200-400 J/kg, moderate PVA, and
bulk shear up to 30kts by early Thursday afternoon, a few strong
thunderstorms can`t be ruled out especially along the Santa Lucia
and the Big Sur Coastline where terrain could also enhance lift at
times near the surface. The primary concern would be strong wind
gusts up to 50 MPH, cloud-to-ground lightning and brief downpours
given the high PWATs through early Thursday evening."
Afternoon temperatures on Thursday will cool to near or slightly
below seasonal averages as a result of the increased cloud cover and
the approaching trough.
&&
.LONG TERM...
Issued at 232 PM PDT Wed Sep 17 2025
(Thursday night through next Tuesday)
Isolated to scattered rain showers will linger into Friday late
afternoon or early evening before the deeper moisture shifts
eastward in response to an upper level trough approaching the coast.
Saturday will remain slightly below seasonal averages as far as
temperatures go. Temperatures warm by Sunday and Monday to above
average as a weak ridge of high pressure builds in from the east.
Unsettled weather returns by Monday night and will continue into
Tuesday as another round of tropical moisture advects northward.
Chances generally remain below 30%, but be sure to check back for
the latest forecast information.
&&
.AVIATION...
(06Z TAFS)
Issued at 957 PM PDT Wed Sep 17 2025
Main difference from 00Z TAFs was to adjust rain chances (decreasing
them) for airports across the Bay Area and shift higher potential
for rain showers further south over the Central Coast. Still some
uncertainty as to where showers and thunderstorms will set up
tomorrow so this is likely to be further refined in future TAF
issuances. Continuing to lean towards tropical moisture and showers
disrupting the marine layer tonight which will keep VFR conditions
at interior sites. For HAF, MRY, and SNS - delayed the arrival of
IFR conditions until later tonight which aligns better with  GFSLAMP
probabilistic guidance. Confidence remains on the lower side that
IFR CIGs will develop along the coast given the disruptions to the
marine layer from showers and tropical moisture. Elevated potential
for thunderstorms tomorrow continues with MRY and SNS the two most
likely to see thunderstorm activity. Winds look to pick up early
tomorrow morning and will remain breezy through the
afternoon/evening hours.
Vicinity of SFO...VFR through TAF period. Model guidance remains
more bullish as to the inland extent of IFR-MVFR stratus overnight
and shows some potential for CIGs between 12-16Z at SFO. Confidence
is low in that scenario with current thinking leaning towards
overcast high clouds and potentially a few low level clouds
developing early Thursday morning. Guidance has backed off on
showers in the vicinity of SFO early Thursday morning but remain
elevated during the afternoon and evening hours. Low confidence that
a thunderstorm will develop in the vicinity of SFO or directly
impact the airport.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Showers remain in the vicinity of MRY and
are expected to continue overnight. Showers will become more
widespread across the Central Coast by Thursday morning and continue
into the evening. Guidance suggests some potential for training
thunderstorms in the vicnity of MRY and SNS to begin late Thursday
evening and continue through early Friday morning. Model guidance
has not been consistent as to where these training thunderstorms
will set up so confidence is low to moderate in this outcome.
Adjusted the arrival of IFR CIGs tonight back by a few hours at MRY
and SNS with low to moderate confidence in timing of stratus
return.
&&
.MARINE...
(Tonight through next Tuesday)
Issued at 957 PM PDT Wed Sep 17 2025
Strong northerly winds continue over the outer waters through
Thursday before decreasing Friday into the weekend. Occasional
gale  force gusts and rough seas between 10 to 14 feet are
expected over  the far northern outer waters through early Friday.
Isolated  thunderstorms and showers continue over the southern
waters through  early Friday morning with storms to spread north
Thursday afternoon.  Mariners who encounter thunderstorms are
likely to experience gusty  outflow winds, locally rough seas, and
locally heavy rainfall.
&&
.FIRE WEATHER...
Issued at 813 PM PDT Wed Sep 17 2025
Threat for dry lightning is diminishing as deeper tropical
moisture moves in from the south. Thunderstorm chances are
uncertain Thursday afternoon across the Central Coast.
Thunderstorms that form over the Santa Lucia may experience dry
air entrainment due to strong offshore winds off the Gabilan
Range. Deep moisture will still be in place, so this isn`t a
typical "offshore wind event", but may be just enough to snub much
of the thunderstorm activity across the Central Coast. However,
this is all dependent on the track of the low and if it shifts
eastward. For the rest of the region, isolated thunderstorm
activity will spread northward through Thursday night into Friday
morning. Even though most thunderstorm cores will produce wetting
rain, there is always the chance of a stray strike or two outside
of the main core, in addition to gusty and erratic winds.
Behringer
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt
     Reyes 10-60 NM.
Small Craft Advisory until 9 AM PDT Thursday for Pigeon Pt to Pt
     Pinos 10-60 NM.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Kennedy
MARINE...Kennedy
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NWS MTR Office Area Forecast Discussion