Crockett, California Weather Forecast Discussion

222
FXUS66 KMTR 252055
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
155 PM PDT Thu Sep 25 2025
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 151 PM PDT Thu Sep 25 2025
- 15% chance for thunderstorms in Southern Monterey and San
   Benito County through this afternoon
- Elevated fire weather risk Friday from wind and relative
   humidity
- Rain and thunderstorms return Monday
&&
.SHORT TERM...
Issued at 151 PM PDT Thu Sep 25 2025
(This evening through Saturday)
There remains a 15% chance for thunderstorms through the afternoon
in Southern Monterey and San Benito Counties as the cut-off low is
proving slow to exit the region. These thunderstorms will pose the
risk of lightning, locally heavy rainfall, small hail, and
erratic/gusty winds. It is difficult to say with certainty if the
marine layer will redevelop tonight as the temperature inversion has
been disrupted due to the recently active weather. If it does,
expect it to be patchy and shallow.
A northerly gradient (and thus northerly, drying winds) will develop
tonight as the cut-off low drifts southeastward to the Colorado
River Valley and high pressure noses in from the Eastern Pacific
Ocean. Minimum daytime relative humidity tomorrow afternoon will be
poor (25%-30%) for the interior with locally lower values of 15% in
Eastern Napa County as this region is within the periphery of
northerly winds down the Sacramento Valley. Fortunately, this threat
will be short-lived with at least moderate recovery (40%)
and the return of onshore flow expected tomorrow night.
Tomorrow, temperatures in the interior will be up to 10 degrees
above normal in the Bay Area and closer to normal in the Central
Coast. Fortunately, as we have just passed Autumnal Equinox and
transitioned from Summer to Autumn, the sun angle will continue to
lower until we reach the Winter Solstice (December 21, 2025). Why is
this important? Well, the lower sun angle will generally make the
heat feel less intense, which is great! Even though this is the
case, it is still important to increase hydration, seek shade during
the warmest parts of the day, and never leave children or pets in
vehicles. Overnight temperatures will cool off enough to open
windows for those of us who do not have air conditioning.
The upper-level shortwave ridge will quickly be broken down by an
upper-level shortwave trough - this will bring temperatures back
down to near normal on Saturday.
&&
.LONG TERM...
Issued at 151 PM PDT Thu Sep 25 2025
(Sunday through next Wednesday)
Global ensemble clusters are in good agreement that the region will
be under the influence of upper-level longwave troughing Sunday
through Tuesday. Just exactly how this takes shape is where it gets
a little fuzzy. There are going to be a slew of low pressure systems
and associated fronts in the Eastern Pacific Ocean by this weekend -
thus, a lot of moving parts. Right now the biggest variation
between the global models of ECMWF and GFS seems to be the timing
with the ECMWF providing an earlier initial arrival time (Monday
morning vs. Monday night). What seems to be certain is that these
systems are going to bring an influx of moisture with them. ECMWF
and GFS IVT (Vertically Integrated Water Vapor Transport) values are
in the 250-500 kg/ms range and our QPF forecast has trended higher
in the last 12 hours. The QPF presentation has taken the shape of
our typical northwesterly to southeasterly gradient with up to 2.00"
in the higher terrain of the North Bay with barely measurable
precipitation of 0.01" down in Southeastern Monterey County. There
is also a chance for thunderstorms during this time.
&&
.AVIATION...
(18Z TAFS)
Issued at 1056 AM PDT Thu Sep 25 2025
VFR conditions have returned to most TAF sites across the region,
all expect the immediate coast where IFR conditions persist at KHAF.
Onshore winds are forecast to increase late this morning or early
afternoon and prevail through sunset. Winds will become generally
less than 5 KT by early Friday morning before onshore winds increase
once again by Friday afternoon. Low confidence for IFR/MVFR ceilings
to develop this evening around the Bay Area terminals from around
01Z-05Z Friday, yet the latest runs of the HRRR are showing this.
Moderate confidence for sub-IFR conditions to return to the Monterey
Bay terminals late this evening and persist through Friday morning.
However, the HRRR is showing signs of clearing around 09Z Friday as
drier air advects inland on the back side of the exiting mid/upper
level cut-off low.
Vicinity of SFO...VFR. High confidence for onshore winds to increase
this afternoon with gusts to around or greater than 20 KT at KSFO.
Low confidence for IFR/MVFR ceilings to develop this evening around
the Bay Area terminals from around 01Z-05Z Friday, yet the latest
runs of the HRRR are showing signs of this occuring. There is a low
end potential for IFR/MVFR ceilings to return once again early
Friday morning, yet have left out of the current TAFs. Any low
ceilings that do develop Friday morning will clear out around 18Z-
19Z and give way to VFR conditions. Onshore winds are forecast to
increase once again by Friday afternoon.
SFO Bridge Approach...VFR. Low end potential for IFR/MVFR ceilings
over the approach early Friday morning between 10Z-18Z Friday.
Otherwise, similar to SFO.
Monterey Bay Terminals...VFR. Onshore winds are forecast by early
afternoon and will diminish after sunset. Moderate confidence for
sub-IFR conditions to return to the Monterey Bay terminals late this
evening and persist through Friday morning. However, the HRRR is
showing signs of clearing around 09Z Friday as drier air advects
inland on the back side of the exiting mid/upper level cut-off low.
Went more on the pessimistic side of things for the official TAFs.
&&
.MARINE...
(Today through Tuesday)
Issued at 1056 AM PDT Thu Sep 25 2025
An upper level low pressure system located across the Central
Coast this morning will move southeastward across the interior
this afternoon. North-northwesterly winds will return and become
gusty over the northern and outer waters later today through
Friday. This will also result in rough and steepening seas. Winds
will ease Saturday and then shift to light southerly on Sunday. A
strengthening low pressure system approaches the Pacific Northwest
bringing a cold front with rain to our coastal waters and bays
early next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 PM this evening to 9 PM PDT Friday
     for Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory until 9 PM PDT this evening for Pt Arena to
     Pt Reyes 10-60 NM.
Gale Warning from 9 PM this evening to 9 PM PDT Friday for Pt
     Arena to Pt Reyes 10-60 NM.
Small Craft Advisory from 9 PM this evening to 3 AM PDT Saturday
     for Pigeon Pt to Pt Pinos 10-60 NM.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...RGass
MARINE...RGass
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NWS MTR Office Area Forecast Discussion