Penngrove, California Weather Forecast Discussion

798
FXUS66 KMTR 162149
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
249 PM PDT Tue Sep 16 2025
...New KEY MESSAGES, SHORT TERM, LONG TERM, FIRE WEATHER...
.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...
(18Z TAFS)
Issued at 1046 AM PDT Tue Sep 16 2025
VFR conditions have returned to most sites away from the immediate
coast with KHAF still seeing LIFR ceilings/visibilities that should
scattered out by 22Z. Onshore winds will increase this afternoon
before easing after sunset and more so into Wednesday morning. High
confidence of VFR conditions prevailing through the TAF period for
the Bay Area terminals and LIFR conditions for the Monterey Bay
terminals (and KHAF).
Vicinity of SFO...VFR. High confidence for onshore winds to increase
this afternoon before easing into early Wednesday morning. High
confidence for VFR conditions to prevail through the TAF period with
increasing onshore winds once again Wednesday afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR. Onshore winds increase this afternoon
before easing after sunset. High confidence for LIFR conditions to
return to the region late evening and continue through about 16Z
Wednesday.
&&
.MARINE...
(Today through Sunday)
Issued at 1046 AM PDT Tue Sep 16 2025
A gentle to moderate northerly breeze will prevail today,
increasing to become fresh to strong for the northern outer waters
Wednesday night into Thursday. Moderate seas will prevail today,
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...RGass
MARINE...RGass
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NWS MTR Office Area Forecast Discussion