Technical NOAA Weather Discussion

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