FXUS66 KMTR 200708
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1208 AM PDT Tue Oct 20 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1200 PM PDT Mon Oct 19 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
&&
.UPDATE...
Issued at 829 PM PDT Mon Oct 19 2026
If you stepped outside today, you probably noticed multiple cloud
layers present. The mix of high, mid, and low-level clouds are
usually a sign of an incoming frontal system due to the interactions
between the different air masses. In our case, a cool/dry air mass
is getting replaced with a colder/moist air mass. Multiple cloud
layers will continue to dominant the skies through Tuesday before
the arrival of the first rain shower.
In other news, another drastic drop in temperature was observed
today. Tomorrow, they are expected to remain stable in the mid 50s
to 70s through the remainder of the work week.
Navarrete
&&
.SHORT TERM...
Issued at 1203 AM PDT Tue Oct 20 2026
(Today through Wednesday)
The low pressure system is already making its presence known as it
nears our coast. Not only were there various cloud layers present on
Monday, but some measurable rainfall has been observed in
Northern California nearby Eureka (as of 10 PM PDT Monday). Given
that the center of the low is still to our northwest, these
rainbands are not expected to impact us just yet...
Overnight, the upper-level trough continues to dig southward along
the coast and becomes fully cut-off from the main airflow by
Tuesday. During the day, calm conditions are expected with below
normal temperatures and infrequent wind gusts up to 20-25 mph.
Later tonight, the cut-off low begins to slowly propagate
eastward with the first few rainbands possibly impacting the
southern Central Coast first. Through the overnight hours, these
rainbands begin to make their way across the rest of the Central
Coast and Bay Area.
Rain chances increase Wednesday with the North and East Bay less
likely to experience wetting rain (>0.10 inch) during the event.
Chances for wetting rain increase towards the Central Coast where
the center of the cut-off low is expected to enhance moisture
transport onshore. The eastern portion of the system is forecast to
have stronger wind speeds than the western portion, likely due to a
tighter pressure gradient downstream as well as a surge in momentum
flux from the subtropical jet stream. This roughly coincides with
where the most moisture, instability, and lift can be found. As a
result, thunderstorm potential (<20%) remains the greatest along the
Central Coast. The exact timing is uncertain, though model guidance
is suggesting the highest probabilities are during Wednesday
afternoon. Most unstable CAPE has trended slightly downward compared
to yesterday, though it is still highlighting the Big Sur Coastline.
The latest SPC convective outlook has upgraded Central and Southern
California to a marginal severe thunderstorm risk, just south of the
Monterey County border... Even though we are not included in the
marginal severe risk, this is too close to comfort considering the
proximity to the Timber and Plaskett fire burn scars. As the event
draws closer, this will be an area of special interest not only for
the potential of debris flows if rainfall thresholds are met, but
also gusty and erratic winds that may result from low-topped
thunderstorms.
&&
.LONG TERM...
Issued at 1203 AM PDT Tue Oct 20 2026
(Wednesday night through Monday)
Overnight, the center of the low gradually moves across the region
resulting in diminishing rainfall chances, though the Central Coast
still remains with a 60-80%. Lingering rain showers persist through
Thursday as the system continues its eastward track. Across the Bay
Area, 20-40% rain chances persist with a 40-60% chance across the
Central Coast.
By Friday, the trough center will be east of our area as high
pressure gradually builds in its wake with a mean northerly wind
flow. To balance out the recent disturbance, a slightly warmer and
drier air mass settles over the region this weekend with seasonal
temperatures in the 60s and 70s.
&&
.AVIATION...
(06Z TAFS)
Issued at 959 PM PDT Mon Oct 19 2026
Generally VFR ceilings with increasing high cloud cover throughout
the TAF period. Low confidence for any stratus development tonight
owing to a combination of incoming high clouds and a mixing out of
the lower layers. Light to gentle onshore winds will back to a more
south to southeast flow through the night, with gentle to moderate
onshore winds possible late Tuesday afternoon. Chances for rain will
arrive Wednesday after the end of the 24-hour TAF period.
Vicinity of SFO... VFR with high clouds through the TAF period.
Moderate west winds with strong gusts linger, becoming a light
southeast flow overnight, with a moderate west wind developing late
Tuesday afternoon. Low confidence in shower chances coming in early
Wednesday morning before the end of the TAF period, increased
confidence in rain impacts after the TAF period ends.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... Some stratus has developed across the
region with ceilings right at the edge of MVFR-VFR criteria,
expected to dissipate Tuesday morning with high clouds persisting
through the TAF period. Light drainage winds persist overnight into
Tuesday morning, with a burst of moderate onshore flow during the
afternoon.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 959 PM PDT Mon Oct 19 2026
Moderate northwesterly breezes will diminish through the night and
back to a gentle southerly breeze Tuesday morning. Moderate
northerly breezes will prevail Wednesday, increasing to become
fresh to strong Thursday into Friday. Moderate seas will prevail
with rough seas across the outer waters Tuesday and Friday. Rain
showers with a chance of thunderstorms are expected late Tuesday
through Thursday, especially south of Pigeon Point.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Navarrete
LONG TERM....Navarrete
AVIATION...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Tue Oct 20 04:30:04 PDT 2026
From the National Weather Service
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