FXUS66 KMTR 200459
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
959 PM PDT Mon Oct 19 2026
...New AVIATION, MARINE...
.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 1235 PM PDT Mon Oct 19 2026
(This evening through Tuesday night)
Morning marine layer mixed out giving way to mostly sunny skies
this afternoon. Despite the increased insolation temperatures are
much colder than yesterday. Definitely a far cry from last weeks
heat. 24 hour trends this afternoon are 5 to 20 degrees colder
with highs still on track to top out in the 60s to 70s (80s
interior Central Coast).
Tonight through Tuesday afternoon will be the proverbial calm
before the "storm". If we take a broader view of the EPac and
West Coast one can see an active pattern with change in our
sensible weather literally on the horizon. A robust 150kt upper
level jet is diving southward from the Gulf of Alaska and rounding
the base of an upper level trough off the PacNW as we speak. The
cyclonic curvature of the jet is supporting upper level
divergence, which in turn promotes surface cyclongensis. Or in
this case, will further enhance the surface low already positioned
off the PacNW. This surface low an associated upper level low are
all upstream. In the meantime, it's a waiting game. Not expecting
a marine layer tonight due to increasing surface pressure
gradients and some marginal cold air advection. Don't be surprised
to see some radar echoes off the N Bay Coast either today through
Tuesday. These radar returns are elevated and tied to the upper
jet max rounding the base of the digging trough.
For Tuesday the upper level trough deepens enough and eventually
becomes cut-off from the mean flow. Any weather watchers know that
upper level lows are tricky and can lead to lower confidence on
timing/position since they're cut-off from the mean flow. For this
upper low, confidence begins to decrease as some hi-res guidance
begins to suggest two upper level vort maxes pivoting/rounding the
base of the upper trough. With two vort maxes focus of best
lift/dynamics becomes less certain. That being said, will carry a
chance of scattered showers over the coastal waters through
Tuesday afternoon. As for land locations, dry through Tuesday
afternoon with seasonably cool temps: 60s and 70s.
Tuesday night into Wednesday morning, enough moisture and lift
will be present with the nearby fully cut-off low to promote
showers moving onshore. Still best dynamics remain offshore, but a
few scout showers moving inland are plausible.
&&
.LONG TERM...
Issued at 130 PM PDT Mon Oct 19 2026
(Wednesday through next Sunday)
Wednesday will be an active day across the region as the upper
level low wobbles off the Central Coast before moving inland late
in the day. Solid upper level jet will fuel the main thrust with
this system. In fact, one could even argue a little bit of phasing
just offshore and through Point Conception during the day. As
such, expect precip chc to become more widespread across the
forecast area, but still main focus over the Central Coast. We've
been advertising a chance (15-20%) of thunderstorms over the
Central Coast waters and Central Coast. Current forecast keeps
the low chance in the forecast. Taking a closer look at dynamics
(still 48hrs out) this could end up being a lower CAPE high shear
environment. So what does that mean? Possible low topped cells
with some rotation. Given a solid lower level jet (under 850mb)
we'll see a higher shear environment for CA standards. Combine
the shear with some meager SFC and MU CAPE developed storms may
rotate. Predicted hodographs are also elongated implying a deeper
layer of shear. Greatest likelihood is near the Big Sur Coast
Wednesday from 12-18Z. SPC does at least have this region in a
general mention. Given the convective threat we'll be watching the
Timber and Plaskett burn areas. If a developed cell moves over
the right location it's within the realm of possibilities that a
threshold will be met for debris flows. Very low conf high impact
scenario, but wanted to at least mention it. The upper level low
slowly loses upper level jet support and ultimately becomes an
open wave late Wednesday into Thursday. As such, we'll keep precip
chances in the forecast through Thursday. Rainfall amounts from
Tuesday night through Thursday will generally be 0.05-0.25" and
0.25-0.75" Central Coast.
Drier weather returns by Thursday night as the now open wave moves
eastward. Behind the departing system some form of ridging
develops with a warming and drying trend heading into the
weekend. Not expecting the heat we just had, but a few degrees
above normal will be possible.
&&
.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...MM
LONG TERM....MM
AVIATION...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Mon Oct 19 22:30:03 PDT 2026
From the National Weather Service
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