FXUS66 KMTR 190719
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1219 AM PDT Mon Oct 19 2026
...New SHORT TERM, LONG TERM...
.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
&&
.UPDATE...
Issued at 753 PM PDT Sun Oct 18 2026
The cooler weather has arrived! Across the Bay Area and Central
Coast, temperatures dropped 10-20 degrees within the last 24 hours
with some spots experiencing up to a 30 degree drop. Accompanied
with the lower temperatures is an increase in humidity. The marine
layer has reformed with a current depth around 1500-2000 feet.
Moderate, gusty onshore winds will help push stratus further inland
tonight. So, enjoy the stratus while you can because it won't last
long! Tomorrow, temperatures are expected to drop another 10-20
degrees with gusts around 20 mph. Breezier locations may experience
gusts up to 30-35 mph which gradually diminish Monday evening.
&&
.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...
(06Z TAFS)
Issued at 1001 PM PDT Sun Oct 18 2026
MVFR stratus is building into the valleys of the greater SF Bay Area
and patches around Monterey Bay with further expansion expected
overnight. Clearing times Monday morning and afternoon will be
rather late owing to an incoming trough that will lower temperatures
and expand the marine layer. Gentle to moderate onshore winds will
persist through Monday evening, when winds diminish and turn
southerly. Low confidence in the stratus extent and ceilings
beginning on Monday night owing to potential mixing out of the lower
layers as the trough approaches. Any rain chances from the incoming
trough come later on Tuesday, after the TAF period ends.
Vicinity of SFO... MVFR ceilings persist through Monday morning.
Moderate northwest winds will continue through Monday evening with
strong gusts expected in the afternoon and evening hours with a more
southerly component as the winds diminish Monday evening. Low
confidence for stratus returning to the terminal Monday night.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... MVFR ceilings at the terminals will clear
late Monday morning or early afternoon. Gentle to moderate northwest
winds prevail through Monday evening, with light southerly flow
developing Monday night.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 1001 PM PDT Sun Oct 18 2026
Moderate to fresh northwesterly breezes will prevail through
Monday, with hazardous conditions for small craft lingering at the
inner coastal waters south of Pigeon Point through Monday morning.
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 Monday, rebuilding to become rough Tuesday.
Light rain showers are expected Tuesday through Thursday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for
Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 9 AM PDT this morning for Pt Pinos to
Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...Navarrete
LONG TERM....Navarrete
AVIATION...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Mon Oct 19 02:30:04 PDT 2026
From the National Weather Service
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