FXUS66 KMTR 191210
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
510 AM PDT Mon Oct 19 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 753 PM PDT Sun Oct 18 2026
- Cooling trend continues through the end of the week
- Beneficial light rain showers expected mid-week
- Thunderstorms possible mid-week across southern Central Coast
&&
.SHORT TERM...
Issued at 1218 AM PDT Mon Oct 19 2026
(Today and tonight)
As the upper-level trough nears the West coast, it pushes southward
until it finally settles a few hundred miles west-southwest of San
Francisco by Tuesday. In the meantime, as the trough center
approaches our immediate coastline, the marine layer deepens to
around 2000 feet overnight accompanied with a gentle to moderate
onshore flow up to 10-20 mph through Monday afternoon. Another
drastic drop in temperatures due to enhanced cold air advection
occurs on Monday with widespread maximum temperatures in the mid 50s
to low 70s. The far interior Central Coast will remain in the 70s
however. By Monday evening, winds gradually ease and become variable
through Tuesday.
The upper-level trough becomes fully cut-off from the main jet
stream by Tuesday. As a result, a cooler and more humid air mass
gets ushered into the Central Coast and Bay Area. Ensemble Euro and
GFS members continue to forecast precipitable water (PWAT) values
around 0.80-0.85 inches by Tuesday evening, exceeding the 75th
percentile for this time of year. To put into perspective, the most
recent 00Z OAK sounding measured PWAT at 0.56 inches which falls
within the seasonal norm. An increased moisture content supports the
initiation of light rain (mainly offshore) while suppressing the
redevelopment of the marine layer.
&&
.LONG TERM...
Issued at 1218 AM PDT Mon Oct 19 2026
(Tuesday through Sunday)
Light rain showers migrate onshore Tuesday evening impacting the
Central Coast first and gradually making their way through the rest
of the Bay Area. As a result, the marine layer is not expected to
redevelop in the next few days. The rain-producing system propagates
eastward toward land on Wednesday, thereby allowing for widespread
showers to persist through Thursday. The North Bay will likely see
lower rainfall totals compared to the rest of the Bay Area. Given
its proximity to the center of the cut-off 500 mb low, the Central
Coast will likely experience the highest rainfall amounts as well as
the greatest potential for thunderstorm development (<20%),
particularly along the Santa Lucia Range and Sierra de Salinas.
Ensemble Euro and GFS members forecast PWAT values to rise above the
90th percentile on Wednesday. According to deterministic European
model, most unstable CAPE continues to trend upwards generally
around 100-300 J/kg with a few spots exceeding 500-800 J/kg. The
moisture and instability is available to support thunderstorm
development. The alignment of these elements with orographic lift
will be sufficient to result in some "wet" thunderstorms, which is
why the greatest potential resides over the Central Coast higher
terrain. While the winds are expected to remain light and variable
through the event, any thunderstorm development can result in gusty
and erratic winds. This event will be the first test to the Timber
and Plaskett fire burn scars as the soil in these areas cannot
absorb much moisture. If rainfall rates exceed their thresholds, the
water will slip right off the surface resulting in burn scar debris
flows, which may lead to flash flooding. If your home is downslope
of these burn scars, now is the time to prepare for the possibility
of an emergency.
By Thursday night, the cut-off low is well to our East with rainfall
chances rapidly diminishing. The usual diurnal onshore wind pattern
returns briefly on Friday with a persistent troughing pattern
through the remainder of the forecast period, resulting in near to
slightly below seasonal temperatures.
&&
.AVIATION...
(12Z TAFS)
Issued at 507 AM PDT Mon Oct 19 2026
The marine layer is here, blanketing much of the region with stratus
and MVFR ceilings. Expect the stratus to slowly trim back this
morning, with coastal communities seeing clouds cling into the early
afternoon. After that, VFR conditions should prevail for much of the
region. Models try to hint some MVFR cigs trying to sneak back in
tonight, but with a 20-40% probability opted to not lock in any BKN
or OVC cigs.
Vicinity of SFO...Stratus engulfs the SF Bay this morning, with MVFR
cigs being reported at SFO and surrounding stations. These
conditions should hold through mid morning, with clearing expected
by late morning or early afternoon. After that look for onshore to
pick up in the afternoon and linger through the early evening hours
with gusts up to 20-24kt. The marine layer is expected to mix out
completely today, which should make the return of stratus difficult
tonight. Opted to keep the hint of some lower cigs tonight, but
confidence is low in any stratus development around the region.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...The stratus has been most interesting
around the Monterey Bay this morning as it has played peek-a-boo
with the terminals for a few hours. But alas, it appears to have
finally filled in leaving us with MVFR cigs. These should clear by
late morning or early afternoon if it remains pesky. Then, we should
have VFR conditions through the early evening. Both the HREF and
HRRR hint at stratus trying to make an appearance before clearing by
early Tuesday morning. Medium confidence in the forecast.
&&
.MARINE...
(Today through Saturday)
Issued at 507 AM PDT Mon Oct 19 2026
Moderate to fresh northwesterly breezes will prevail today, with
hazardous conditions for small craft lingering at the inner
coastal waters south of Point Pinos through this afternoon. Winds
will diminish and back to a gentle southerly breeze Tuesday and
Wednesday before returning to moderate to fresh northerly breezes
Thursday. Rough seas across the outer waters will subside to
become moderate but will rebuild briefly to become rough Tuesday.
Light rain showers are expected Tuesday through Thursday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
evening for Mry Bay.
Small Craft Advisory until 3 PM PDT this afternoon for Pt Pinos
to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...Navarrete
LONG TERM....Navarrete
AVIATION...KR
MARINE...KR
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Prepared by Boulder-Creek.com Weather at: Mon Oct 19 08:30:03 PDT 2026
From the National Weather Service
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