Boyes Springs, California Weather Forecast Discussion

375
FXUS66 KMTR 190022
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
522 PM PDT Thu Sep 18 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 304 AM PDT Thu Sep 18 2025
- Showers with isolated thunderstorms today into Friday
- Cooler temperatures today and Friday, with a weekend warm up
- Rainfall chances increase again for the beginning of next week
&&
.SHORT TERM...
Issued at 209 PM PDT Thu Sep 18 2025
(This evening through Friday)
The richer and juicier tropical air has finally arrived into the
Central Coast and continues to push northward this afternoon.
ACARs soundings out of SJC show the influx of upper level
moisture. However, its impact isn`t panning out as advertised on
some of the guidance the last few days. We`ve mentioned how low
confidence and how nuanced the forecast would be and that is still
the case even as events unfold. Showers and thunderstorms have
been most prolific for our area over the ocean and that was well
advertised. Where the forecast is suffering is over land. Rainfall
amounts over the land have been slashed from previous forecast as
the focus for most precip this afternoon through Friday is either
over the ocean or east of the forecast area. Rainfall amounts are
still forecast to be highest over the Central Coast, but for the
Bay Area not expecting much with only a few hundredths to a tenth.
So what`s happening? We have a few things at play. For one, the
moisture continues to surge north, but ACARS still indicate a
rather robust dry layer still hanging around. While the radar
shows echoes over land they`re evaporating before reaching the
ground. This will ultimately change later this afternoon and this
evening as the column becomes more saturated. Starting to see this
trend with a few gages finally showing a few tips in
Monterey/Carmel and East Bay Hills. Second, a weak surface low has
remained west of Monterey Bay and continues to drift northward.
This explains the better convection over the ocean. Third, the
Mario left over circulation is trending eastward focusing the
forcing to the Central Valley. Fourth, the northward movement of
the initial moisture was slightly delayed. As such, it`s now
battling the approaching upper level trough seen on water vapor
to the northwest. The upper trough may also be helping to push the
Mario circulation eastward as well.
All that being, still expecting some showers and isolated
thunderstorms across portions of the Central Coast and Bay Area
through Friday. The convective threat has decreased, but cannot
rule out an isolated rumble or two. Will still feel muggy given
the higher dew points and tropical nature. Would not be surprise
to near record moisture on the Oakland sounding this evening.
&&
.LONG TERM...
Issued at 239 PM PDT Thu Sep 18 2025
(Friday night through next Wednesday)
Friday night into Saturday is looking much drier than previous
forecast. There may be one or two lingering showers early Friday
due to wrap around moisture with the departing circulation.
Over the weekend the approaching upper trough deepens enough at
500 to eventually become cut-off. The upper low meanders off the
coast before moving to SoCal early next week. As the trough/and
low move through there is a sliver of upper level moisture/lift
Saturday into Sunday. Maybe some cu building on the hills.
Forecast is dry for now as precip seems more likely over the
Sierra and mt ranges north of here.
Early next week gets interesting once again as the upper low that
meandered to SoCal pulls in some higher PWAT air and moves
northward to the forecast area. This feature will bring rain
chances, possibly thunderstorms, back to the forecast area
Tuesday/Wednesday.
&&
.AVIATION...
(00Z TAFS)
Issued at 521 PM PDT Thu Sep 18 2025
Currently VFR at all sites except HAF where IFR conditions continue.
Low confidence in stratus forecast tonight due to tropical moisture
and passing showers disrupting the marine layer. Guidance is more
bullish with MVFR-IFR CIGs extending across the interior but
confidence is low in that scenario. Expect some lowering of cloud
bases overnight but they should stay few to scattered in the lower
levels. Temporary lowering of ceiling heights and visibilities is
possible if a shower drifts over an airport. Precipitation is taking
a more easterly route (avoiding the Bay Area and northern portions
of the Central Coast) with scattered showers most likely to impact
MRY and SNS. Thunderstorm chances are diminishing but a low chance
(confidence too low to include in TAF) will remain through this
evening.
Vicinity of SFO...VFR through TAF period. Guidance pushes for MVFR-
IFR CIGs to develop overnight but confidence is low in that outcome
due to passing showers and tropical moisture. If CIGs do lower it is
more likely to occur after 12Z. Winds pick up during the
afternoon/evening and peak around 14-15 knots.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Currently VFR with potential for scattered
showers and a low chance of thunderstorms through this evening. The
bulk of the showers remain south of MRY/SNS and are expected to pass
into the Central Valley (away from MRY and SNS). Thunderstorms are
not included in the TAF at this time due to low confidence in one
impacting either airport. Confidence is low that MVFR-IFR CIGs will
develop early this evening at either airport. CIG arrival time may
need to be adjusted to later this evening/overnight depending on
arrival of stratus. Low to moderate confidence in CIGs improving
around 18-19Z with skies to clear by late tomorrow morning/early
afternoon.
&&
.MARINE...
(Tonight through next Wednesday)
Issued at 521 PM PDT Thu Sep 18 2025
Breezy northwesterly winds and rough seas will prevail over the
northern outer waters tonight. Isolated rain showers with embedded
thunderstorms remain possible into tonight which will pose the
risk of locally heavy rainfall and erratic outflow gusts.
Conditions  improve Friday as winds diminish, seas abate, and
unsettled weather exits the region.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Friday for Pt Arena to Pt
     Reyes 10-60 NM.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Kennedy
MARINE...Canepa
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NWS MTR Office Area Forecast Discussion