Technical NOAA Weather Discussion

FXUS66 KMTR 121143
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
443 AM PDT Sun Jul 12 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1230 AM PDT Sun Jul 12 2026

 - Warmer and drier conditions continue through midweek with
   Moderate HeatRisk returning across the region

 - Coastal Flood Advisory for up to 1.7 feet of inundation above 
   ground level is possible in low-lying areas near shorelines and
   tidal waterways

 - Potential for thunderstorms and elevated fire weather concerns
   continue today and tomorrow

&&

.SHORT TERM...
Issued at 1230 AM PDT Sun Jul 12 2026
(Today and tonight)

Monsoonal moisture has started to make its way into the Bay Area and 
Central Coast. ACARS soundings all show a distinct moistening of the 
mid to upper levels of the atmosphere at MRY, SJC, SFO, and OAK. 
This correlates with the influx of mid and high level clouds moving 
over the region. Radar currently (as of midnight) shows a few 
showers moving into the coastal waters and across the interior 
Central Coast. NBM guidance does not show showers reaching the area 
until late Sunday morning. This increases confidence in the high 
resolution models (HRRR, NAM) that have consistently showed showers 
starting Saturday night into Sunday morning before becoming more 
widespread Sunday into Monday. NBM guidance shows a 5% chance of 
scattered thunderstorms on Sunday with high resolution guidance 
suggesting thunderstorm potential will increase starting early this 
morning. The overall confidence that high based thunderstorms 
(compared to high based showers) will develop today and tomorrow 
remains low given a lack of forecast instability in the models. The 
NAM shows the most instability across the region but keeps it 
limited to a few hundred J/kg of MUCAPE. While the overall 
thunderstorm risk is low, that does not mean we won't see any 
thunderstorms develop today or tomorrow. It often takes just a few 
hundred J/kg of MUCAPE for a thunderstorm to develop here. This is a 
low probability, high impact scenario wherein if a thunderstorm 
develops, fire starts will be more likely given how dry the fuels 
are. Another aspect of this is how much precipitation will reach the 
surface. Given the high based nature of these storms any 
precipitation that falls is likely to evaporate before it reaches 
the ground (virga). Models do support some light rain making it to 
the ground but this peaks at a few hundredths of an inch. To sum it 
up, shower activity associated with the monsoonal moisture surge 
will increase over the next day and a low potential for dry 
thunderstorms to develop remains on the table.

Temperatures remain in the upper 80s to low 90s across the interior 
today with the far interior Central Coast peaking in the upper 90s 
to low 100s. Coastal areas and the SF Bay shoreline will see 
temperatures peaking in the 70s to low 80s. Conditions may feel more 
humid during the day due to the influx of monsoonal moisture across 
the region. Temperatures drop into the 60s across the lower 
elevations Sunday night and remain in the 70s across the higher 
elevations. Widespread Moderate HeatRisk is expected across the 
higher elevations today with patchy Moderate HeatRisk across the 
urban portions of the Bay Area.

&&

.LONG TERM...
Issued at 1230 AM PDT Sun Jul 12 2026
(Monday through Saturday)

Beyond Monday's thunderstorm chances (discussed in Short Term), shower
and thunderstorm potential will dissipate Tuesday with most 
models suggesting the monsoonal moisture surge will diminish 
across our CWA. ECMWF guidance suggests enough moisture may linger
during the day on Tuesday to see an isolated shower or two across
the higher terrain but confidence is low in that scenario. 
Another round of monsoonal moisture, potentially bringing showers
back to the region, is possible Friday into next weekend. The 
forecast remains in flux with regards to a second moisture surge 
so stay up to date on the forecast this week.

Outside of shower potential, upper level ridging will continue to 
dominate the western United States with the center of the high 
located over the Intermountain West. Temperatures warm into the 
upper 80s to 90s across the interior with low 100s possible across 
the usual hotspots (far interior East Bay, interior Central Coast) 
Tuesday and Wednesday. Coastal areas will stay in the 60s to 70s 
with low 80s possible along the SF Bay shoreline. Widespread 
Moderate HeatRisk is expected across the higher elevations and most 
of the interior Bay Area. If you are spending significant periods of 
time outdoors, make sure to listen to your body, take breaks in the 
shade, and drink plenty of water. Cooler temperatures return 
Thursday into the weekend as upper level ridging weakens and shifts 
eastward while a deep upper level trough pushes into the PNW.&&

&&

.AVIATION...
(12Z TAFS)
Issued at 439 AM PDT Sun Jul 12 2026

Marine layer is compressed and primarily confined to the coast. 
Elevated showers are more widespread than expected despite building 
high pressure at the surface, with rainfall evaporating before 
hitting the ground. Some gusty erratic outflow winds can be expected 
in vicinity of these weak bands. Otherwise VFR is expected for all 
terminals except KHAF and KMRY until early Monday morning.

Vicinity of SFO...VFR is expected to prevail through the forecast period 
with a slight chance of MVFR/IFR ceilings early Monday morning. 
Gusty erratic winds are possible in vicinity of the elevated 
showers through the morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR should prevail especially at KSNS, KMRY 
may see-saw between VFR/MVFR ceilings through sunrise into mid-
morning at times, otherwise expect VFR through the remainder of 
the day, with a chance of MVFR/IFR ceilings returning after 
sunset. 

&&

.MARINE...
(Today through Friday)
Issued at 439 AM PDT Sun Jul 12 2026

Hazardous conditions over the northerly outer waters continue
with moderate to fresh winds. Otherwise, expect light to moderate
north-northwest winds with moderate northwest swell. Winds and
seas build by the middle of next week.

&&

.FIRE WEATHER...
Issued at 439 AM PDT Sun Jul 12 2026

Warm and dry conditions persist through much of the upcoming 
week, especially away from the coastal marine influences which are
forecast to persist. This will increase fire weather concerns as 
fuels rapidly dry out due to low humidities. Fire weather concerns
further increase later tonight into Monday as a surge of 
monsoonal moisture advects northward around the western periphery 
of the high pressure over the Desert Southwest and Intermountain 
West. If thunderstorms are able to develop, dry lightning and 
gusty, erratic outflow winds would be the main hazards. The 
limiting factor is the lack of instability over our region those 
days. Thus, we will continue to closely monitor these conditions 
through the weekend. Given the combination of the potential for 
dry lightning and rapidly drying fuels, it is important to stay up
to date on the forecast as it evolves.

&&

.BEACHES...
Issued at 439 AM PDT Sun Jul 12 2026

A Coastal Flood Advisory is in effect for minor high tide 
flooding through Thursday July 16th. The combination of a perigean
spring tide (lunar perigee on 7/13 and new moon on 7/14) enhanced
by 3-6 inches of additional water from thermal expansion and 
accumulated sea level rise since the tidal datum was established 
(1983-2001) will bring high tides up to 1.7 feet above normal. 
This will lead to minor flooding of parking lots, parks and roads 
with isolated closures expected. For context, in June we reached 
2.0 feet above normal and in January we reached 2.5 feet above 
normal.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 4 AM PDT Thursday for CAZ006-506-
     508.

     Coastal Flood Advisory until 4 AM PDT Wednesday for CAZ505-509-
     529-530.

PZ...Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...JM
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Sun Jul 12 08:30:03 PDT 2026
From the National Weather Service