Prunedale, California Weather Forecast Discussion

543
FXUS66 KMTR 162353
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
453 PM PDT Tue Sep 16 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 130 PM PDT Tue Sep 16 2025
- Above normal temperatures with Moderate HeatRisk persists today
   and Wednesday
- Isolated to scattered thunderstorms Thursday into early Friday
- Additional rain chances return early next week
&&
.SHORT TERM...
Issued at 123 PM PDT Tue Sep 16 2025
(This evening through Wednesday)
Near term - compressed marine layer lingering along the immediate
coast this afternoon is wreaking havoc on max temps at the
shoreline. The onshore flow and lingering clouds are resulting in
a slower rise in temps and cooler 24 hour trends. The forecast
has been updated to reflect this. Once you move inland and away
from the marine influence temperatures soar with 90s and a few
100s - or about 5 to 15 degrees warmer than Monday afternoon.
Tonight into Wednesday: the marine layer lurking along the coast
will come inland slowly with patchy dense fog along the immediate
coast. It will be compressed again so we`ll need to monitor vsby
for another Dense Fog Advisory. Expect another night of active
thermal belts with mild and dry conditions above the marine layer.
The big item of note tonight will be the influx of tropical
moisture along the SoCal and Central California coast. Let`s take
a look at the complex upper level longwave pattern. A few notable
features: ridge of high pressure lingering over CA/PacNW(bringing
the hot wx), an upper level low/trough approaching from the NW,
to the south there is a weak upper low spinning west of the
Channel Island, and even farther south is TD Mario just west of
Baja. Over the next 12-18 hrs the ridge will ease eastward as the
two lows inch closer to the CA coast. This upper level flow
pattern will help to usher Mario tropical moisture northward. The
timing of the moisture has varied as of late and even the latest
guidance is still struggling. Latest satellite imagery already has
the leading edge of higher PWAT near Pt Conception. That being
said, current forecast will bring moisture north overnight into
early Wednesday, but primarily over the coastal waters. As
moisture surges northward instability increases over the Central
Coast coastal waters. Therefore, will have a mention of
thunderstorms. There was concern of dry lightning, but given the
westward track of the initial push will not have a mention over
land. Shift this scenario farther east and now we`re dealing with
a higher impact scenario with dry lightning over the Santa Lucia
range. Nocturnal convection over the coastal waters is not that
unusual either. For the rest of Wednesday: if there are storms
over the waters would not be surprised if the fade early in the
day before firing again in the afternoon. One final day of
moderate to isolated major HeatRisk with temps in the 90s to near
100 across the interior. One potential bust scenario are high
clouds impacting insolation, but for now will lean toward the mild
airmass yielding hot temps.
&&
.LONG TERM...
Issued at 233 PM PDT Tue Sep 16 2025
(Wednesday night through next Monday)
Wednesday day was just a preview of tropical moisture. The main
push of high PWAT air will occur Wednesday night into Thursday
morning. This push will initially impact Paso Robles and south
before reaching southern Monterey/San Benito by Thursday morning.
Given the PWAT signature on profiles will lean toward wetter
storms mitigating dry lightning concerns. MUCAPE and lapse rates
do increase through the day Thursday suggesting the threat for
embedded tstorms remain. CAMS also keeps this idea going through
the day. Additional lift maybe enhanced from a weak shortwave
moving in from the west. Showers and thunderstorms will spread
south to north through the day on Thursday. By Thursday evening
the convective threat ends, but showers will linger for Friday and
even into Saturday. Rainfall amounts are problematic for two
reason: tropical nature and convective bullseyes. A few hundredths
to a tenth or two is a good start, but local jackpots up to one
half to three quarters of an inch are possible.
Drier and cooler weather finally return Sunday. The dry period
will be short lived as additional rainfall chances return Monday.
&&
.AVIATION...
(00Z TAFS)
Issued at 453 PM PDT Tue Sep 16 2025
Currently VFR at most airports with IFR-LIFR CIGs expected along the
coast tonight. Satellite shows stratus pushing back inland into the
Monterey Peninsula with IFR-LIFR conditions and fog to develop by
late evening/overnight. Confidence is low that stratus will reach
the Bay Area given the marine layer is currently at a depth of ~800
ft. Guidance shows some potential for stratus to temporarily clip
OAK but confidence was to low to include in the TAF at this time
with a tempo being considered for stratus in the next TAF issuance.
Otherwise, low level clouds clear by late tomorrow morning with high
level clouds expected across the region as upper level moisture
moves in from the south.
Vicinity of SFO...VFR through the TAF period. Moderate to high
confidence that SFO will stay VFR tonight. The majority of guidance
suggests stratus will not develop within the SF Bay region but a few
models show some patchy stratus developing on the eastern portions
of the bay (impacting OAK). Current thinking is that the marine
layer is too shallow for stratus to push into the SF Bay which will
keep SFO clear through the TAF period. Breezy onshore winds gusting
around 25 knots continue through this evening and are expected to
redevelop again tomorrow afternoon and evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...IFR-LIFR  conditions and fog overnight. The
marine layer remains around 800 ft which will help compress ceilings
tonight. The main debate is around the arrival time of stratus
tonight - the inherited TAF had a later arrival (3-5Z) but current
satellite imagery suggests stratus is already approaching as of 00Z.
Bumped stratus arrival up to 02Z/03Z at MRY and SNS which is faster
than the majority of the models - confidence is low to moderate in
this timing. Looking at conditions improving around 16/17Z tomorrow
morning but this may need to be pushed back by 1-2 hours depending
on how fast it is able to clear.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 453 PM PDT Tue Sep 16 2025
A gentle to moderate northerly breeze will prevail through
Wednesday  morning, increasing to become fresh to strong for the
northern outer  waters Wednesday night into Thursday. Gale force
gusts will be  possible Thursday across the northern outer waters.
Moderate seas  will prevail tonight, building to become rough for
the outer waters  Wednesday through Friday. Isolated thunderstorms
are possible  Wednesday night and Thursday with isolated rain
showers lingering  through Saturday.
&&
.FIRE WEATHER...
Issued at 225 PM PDT Tue Sep 16 2025
- Near critical fire weather conditions through Wednesday
- Threat for dry lightning has diminished, but didn`t completely
   go away.
Near critical fire weather conditions continue into Wednesday due
to hot, dry, and afternoon breezy onshore winds. Tuesday afternoon
featured interior temps of a hot 101 and a crispy 11% at Arroyo
Seco. Expect another repeat away from the coast on Wednesday.
Don`t expect much relief tonight either as thermal belts will be
very pronounced with mild and dry conditions over the higher
elevations. Overnight humidity recovery will be moderate to poor
over the highest peaks. Still have concerns regarding low
confidence high impact scenario as tropical moisture brings a
chance for elevated/high- based thunderstorms. After assessing the
latest guidance and coordinating with other offices and fire
partners decided to NOT issue any Fire Weather watch at this time.
The initial threat for dry lightning is decreasing with focus
over the ocean on Wednesday and Wednesday night. If the threat
shifts east we`ll have to re-evaluate. Once convection chances
increase over land Thursday enough moisture should be present
that storms will be wetter vs drier.
MM
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM Wednesday to 3 AM PDT Thursday
     for Pt Arena to Pt Reyes 10-60 NM.
Gale Watch from late Wednesday night through Thursday afternoon
     for Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Kennedy
MARINE...RGass
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NWS MTR Office Area Forecast Discussion