FXUS66 KMTR 192354
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
454 PM PDT Sun Jul 19 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 148 PM PDT Sun Jul 19 2026
- Near or slightly below normal temperatures and higher humidity
through the first half of the upcoming week.
- The marine layer and mid to upper level cloud cover will
continue to help keep temperatures cooler under building high
pressure.
- Approximately 5% chance of elevated showers with isolated
thunderstorms Tuesday afternoon through Wednesday evening.
&&
.SHORT TERM...
Issued at 148 PM PDT Sun Jul 19 2026
(This evening through Monday night)
Marine layer stratus has retreated back to the coastline as of early
this afternoon. Increasing coverage of mid/high level clouds
streaming northeast out ahead of an upper level low over the EPAC
will continue this afternoon and tonight. Elevated showers can be
seen on radar approaching our southern outer marine zones and will
continue to remain well off shore for the remainder of today and
this evening. However, after midnight, elevated shower activity is
possible mainly for the Bay Area and the North Bay through mid-
morning Monday. Poor lapse rates and thermal instability will limit
the chances for thunderstorm activity. Along with the weak
instability, very dry air between 700mb-925mb will likely result in
little to no precipitation reaching the ground with only a trace to
a few hundredths where any rainfall is measured. Temperatures on
Monday will be similar to slightly cooler than todays values with
the increased cloud coverage.
Expecting a typical stratus intrusion tonight into early Monday
morning as onshore flow persists, with high clouds helping to limit
some of the radiational stratus cloud top cooling that will result
in less mist/drizzle coverage than we saw this morning, and mostly
confined to coastal areas.
&&
.LONG TERM...
Issued at 148 PM PDT Sun Jul 19 2026
(Tuesday through next Saturday)
Chances for another round of elevated showers with isolated
thunderstorms is trending upward. Not currently reflected in the
official forecast but subsequent updates may see increases in
coverage and intensity by Tuesday afternoon into Wednesday, mainly
across the North Bay and maybe as far south as the Bay Area. The
main source continues to be the moisture associated with what will
be the remnants of Elida moving north, well offshore of our area by
the end of the day Wednesday. Increasing lift, better thermal
instability and slightly improved mid-level lapse rates between 7-
7.5 C/km by late Tuesday afternoon into Tuesday night will provide
the best chances for elevated thunderstorms and potentially
impactful dry lightning. A similar pocket of dry air from 700mb-
925mb will continue to limit beneficial rainfall. A final wave of
elevated instability will move into the North Bay once again late
Wednesday afternoon into the evening hours with potentially
improved thermal instability, however less lift and weaker lapse
rates, with dry air in the mid-levels continuing to limit
precipitation reaching the ground. By Thursday into the weekend,
the increased mid-level moisture shifts north and we begin to see
drier air aloft with a gradual warming trend into the weekend.
However, onshore flow will persist will persist through the
extended forecast with typical no- sky-July conditions each night
and morning.
&&
.AVIATION...
(00Z TAFS)
Issued at 440 PM PDT Sun Jul 19 2026
VFR with IFR-LIFR stratus to return overnight. The marine layer is
expected to compress tonight which will lead both to lowered
ceiling heights and a smaller inland extent. Confidence in stratus
reaching SJC is slightly higher than it was this morning while
stratus chances for LVK remain minimal. Have kept higher chances
for IFR in at OAK/SFO with confidence increasing. Patchy fog is
possible along the coast tonight with LIFR CIGs and reductions in
visibility possible. Diurnally breezy onshore winds continue in
the afternoon/evening.
Vicinity of SFO...VFR with MVFR-IFR stratus to return overnight.
Moderate confidence of timing of stratus return. Satellite imagery
shows a less expansive stratus layer than last night which
increases confidence in a later stratus arrival (~07Z). MVFR CIGs
are the most likely scenario but cannot rule out patchy IFR CIGs
given the compressing of the marine layer. Conditions improve by
late morning with some potential for stratus to return again late
tomorrow evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR with stratus expected to build in
over the next few hours. IFR-LIFR CIGs are expected tonight with
CIGs to gradually lower early tomorrow morning. There is some
potential for fog and reductions in visibility due to the
compressing of the marine layer. Moderate confidence in clearing
between 17-19Z with a few models indicating stratus could linger
longer at MRY.
&&
.MARINE...
(Tonight through next Friday)
Issued at 440 PM PDT Sun Jul 19 2026
Gentle to moderate northwesterly breezes will persist through the
upcoming workweek with slight to moderate seas. As tropical
cyclone activity continues across the eastern Pacific, long period
southerly swell is forecast. Southerly swell heights are
anticipated to remain in the slight category but mixed seas may
result in hazardous boating conditions through the week.
Additionally, there are non-zero chances for high based showers
which could result in pockets of gusty outflow winds and
subsequent steep seas tonight through mid-week.
&&
.FIRE WEATHER...
Issued at 148 PM PDT Sun Jul 19 2026
Near to slightly cooler than normal temperatures will continue
through the week with typical diurnal intrusion of the marine layer
each night and retreat to the coast each morning as onshore flow
persists. However, above 1500-2000ft we'll see relatively weak
thermal belting the first half of the week with continued warm
overnights and poor RH recovery at higher elevations.
Guidance is trending toward an increasing potential for elevated
showers and isolated thunderstorms Tuesday afternoon through
Wednesday evening. Chances are below 5% in the official forecast but
may increase in subsequent updates tonight and Monday. The
primary concern is dry lightning strikes across the North Bay,
with lesser chances farther south into the Bay Area.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Bain
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Prepared by Boulder-Creek.com Weather at: Sun Jul 19 20:30:03 PDT 2026
From the National Weather Service
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