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Showers and Thunderstorms for the Eastern Third of the Country; Fire Weather Concerns; Flooding Issues for the Great Lakes Region

Showers and thunderstorms will continue along and ahead of a cold front for the eastern third of the country. The rainfall for the Great Lakes region could prolong the ongoing flooding. Much cooler weather will filter in behind this cold front along and east of the Rockies. Where the rain is needed, the Southern High Plains, critical fire weather concerns through this weekend. Read More >

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975
FXUS66 KMTR 181139
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
439 AM PDT Sat Apr 18 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1134 PM PDT Fri Apr 17 2026

- Seasonably warm temperatures expected through the weekend

- Cooler temperatures with minor flooding possible in the North
Bay Monday, mostly beneficial rain for the remainder of our
area


&&

.SHORT TERM...
Issued at 1223 AM PDT Sat Apr 18 2026
(Today and tonight)

A progressive upper level ridge axis will shift east across our area
this morning, while temperatures inland climb into the upper 70s to
low 80s. Locations most likely to reach or exceed 80 will be in the
interior valleys of the South Bay and Central Coast where there will
be plenty of sunshine and light winds. Coastal locations will be
only slightly warmer than Friday with weak onshore flow during the
day out ahead of the developing offshore disturbance. Even with the
ridge exiting to the east, overnight lows into Sunday will be more
mild than we`ve seen the last few nights with increasing mid/high
level cloud cover insulating some of todays heat.

&&

.LONG TERM...
Issued at 1223 AM PDT Sat Apr 18 2026
(Sunday through Friday)

Sunday will be a nice transition day as the pattern changes for the
first half of next week. Overall, consensus is improving but the
timing of the first ejecting wave of the developing upper low is
still in question. What we do know is that deep onshore flow will at
least bring a return of stratus along our entire Pacific Coast
Sunday night. Our official forecast has slight chance PoPs over the
North Bay late Sunday evening but any rainfall initially would be
measured in the hundredths. By sunrise Monday morning we may see
more impactful rain over the North Bay coastal ranges then shift
into the interior valleys. The slow moving system with notable
longitudinal orientation out ahead initially will see areas of
showers training over the North Bay. The WPC does have much of
Sonoma County in a Day 4 Excessive Rain Outlook on Monday. The
second wave approaches the coast overnight Monday into Tuesday as
the associated trough becomes negatively tilted providing added
lift and increasing baroclinic instability by late morning/early
afternoon for any showers/storms moving onshore. The system will
be slow to move onshore initially, but once inland it will eject
east quickly. Attm, the pattern indicates another disturbance
splitting off the back side with an inside slider trajectory for
the second half of next week.

&&

.AVIATION...
(12Z TAFS)
Issued at 439 AM PDT Sat Apr 18 2026

It`s VFR except for patchy low clouds and fog /IFR-LIFR/. VFR
prevails today with diurnal mixing then a few areas of low clouds
and fog /IFR-LIFR/ redevelop tonight and Sunday morning.

Vicinity of SFO...VFR. Light and variable wind, possibly becoming
light northeast this morning. Currently there is a 0.4 mb OAK-SFO
pressure gradient. Otherwise a west wind redevelops by 21z and
increases to 15 to 20 knots. West wind 10 knots tonight becoming
a light west wind Sunday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR today, then a few areas of coastal
low clouds and fog /IFR-LIFR/ develop tonight and Sunday morning.
Southeast cool air drainage winds 5 to 10 knots this morning
becoming west to northwest 10 to 15 knots by noon or early
afternoon. West wind 5 to 10 knots diminishing to light and
variable winds tonight and Sunday morning.

&&

.MARINE...
(Today through Thursday)
Issued at 428 AM PDT Sat Apr 18 2026

Northwest winds will continue to diminish today. Winds shift to
southerly Sunday ahead of an incoming low pressure system and cold
front. Winds will strengthen ahead of the cold front Monday
through Tuesday with localized strong gusts expected. Expect
moderate seas, rain and a slight chance to chance of thunderstorms
Monday night and Tuesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Canepa
MARINE...Canepa

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