FXUS66 KMTR 181703
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1003 AM PDT Wed Mar 18 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 149 PM PDT Tue Mar 17 2026

 - Early season, long duration heat wave bringing record-breaking
   temperatures and Moderate HeatRisk continues through at least 
   Friday

 - Elevated potential for grass fires through the week due to 
   warm and dry conditions with periods of moderate offshore winds

 - Gradual cooling trend begins this weekend

&&

.UPDATE...
Issued at 841 AM PDT Wed Mar 18 2026

On track to break more records once again this afternoon and through 
Friday (see CLIMATE below). The Heat Advisory remains in effect 
through 8 PM Friday before cooling is looking more likely for this 
upcoming weekend. No updates are anticipated to the ongoing forecast 
at this time.  

RGass

&&

.SHORT TERM...
Issued at 121 AM PDT Wed Mar 18 2026
(Today and tonight)

Yesterday broke numerous daily max temperature records, and even 
a few monthly records. Most notably, 93 degrees at Redwood City 
broke the monthly record of 90 degrees set just the day prior. 
The earliest 93 degree day on record is April 9th. Temperatures
are cooling nicely overnight in the North Bay and interior
valleys, but higher elevations and even some coastal areas are 
still in the mid 60s. Downtown San Francisco was still 70 degrees
at midnight.

The ridge axis has moved east of us, and will be centered over the
SE California desert today, before moving into Arizona tomorrow. 
While the distance to the center of the ridge is increasing, the 
strength of the high pressure is also increasing. This 
combination will keep our 500 mb heights and 850 mb temperatures 
fairly consistent at around 5910 m and 20 C. Both higher than 
we've recorded in March outside of the last couple days.

As such, today will be very similar to yesterday for inland 
areas, though there will be slightly more marine influence along 
the immediate coast. The current satellite shows a bank of low 
stratus off the coast of Pt. Reyes moving south. These clouds will
probably not make landfall, but they are a sign that boundary 
layer averaged winds have shifted from offshore yesterday to 
onshore this morning. Offshore winds still dominate above the very
shallow boundary layer, however. The compression from the high 
pressure will keep this more humid air confined to the coast while
the rest of the area gets another dry, hot afternoon.

&&

.LONG TERM...
Issued at 121 AM PDT Wed Mar 18 2026
(Thursday through Tuesday)

Rinse and repeat through Friday. Expect record breaking heat each
afternoon as the ridge of high pressure stalls over the desert SW.
Confidence is increasing that the heat wave will start to break on
Saturday. Our latest forecast has temperatures dropping around 
10 degrees on Saturday, and another 5 on Sunday. That would bring
us back into the 70s for most inland areas and 60s along the
coast to start next week. By the way, that's still 5-15 degrees 
above normal for this time of year. As the ridge breaks down there
is good chance for stronger winds this weekend, which will bring 
some additional relief to the hot temperatures, but also brings some
enhanced fire weather conditions for fine dead fuels. The next
chance for any rain is around the end of the month or early April,
but the ensemble members diverge spectacularly by that point, and
it's just as likely that another dry heatwave moves in.

&&

.AVIATION...
(18Z TAFS)
Issued at 1003 AM PDT Wed Mar 18 2026

Quiet weather continues with high pressure holding and mainly 
offshore winds being observed this morning. Diurnally driven onshore 
winds are expected for areas near the coast or around the Bay later 
this afternoon and evening and will become offshore or light and 
variable overnight. VFR conditions will prevail, though there could 
be some pockets of haze. 

Vicinity of SFO...No major changes, light and variable winds, will 
become onshore this afternoon and evening. Winds may peak at KSFO 
around 10-15kt after 23Z. Wind weaken late in the evening, with 
light and variable winds expected overnight and into Thursday 
morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Quiet weather with offshore flow continuing 
this morning. Winds will gradually become onshore by the afternoon, 
with winds becoming weakly offshore or variable by the evening and 
overnight hours. VFR conditions continue.  

&&

.MARINE...
(Today through Monday)
Issued at 411 AM PDT Wed Mar 18 2026

Moderate northwest breezes persist across the outer waters, with
gentle breezes over the inner waters. Strengthening northwest
winds and hazardous seas will likely return to the coastal waters
late  this week and weekend.

&&

.CLIMATE...
Issued at 421 AM PDT Wed Mar 18 2026

The following are the record high temperatures at the long term
sites for March 18th, 19th and 20th.

Location             Mar 18      Mar 19      Mar 20      

Santa Rosa         84 in 2010  83 in 2004  84 in 2004
San Rafael         80 in 1996  81 in 1964  82 in 1960
Kentfield          89 in 1914  83 in 1996  82 in 2001
Napa               87 in 1914  86 in 1914  86 in 2004
Richmond           78 in 1996  80 in 1996  81 in 2004
Livermore          86 in 2004  82 in 2015  87 in 1915
San Francisco      86 in 1914  80 in 2010  78 in 2004
SFO Airport        77 in 2004  78 in 2010  78 in 2004
Redwood City       84 in 2004  81 in 2010  82 in 2004
Half Moon Bay      75 in 1978  79 in 2010  75 in 2010
Oakland Museum     81 in 2004  81 in 1984  78 in 2001
San Jose           87 in 1914  82 in 1988  78 in 2004
Salinas Airport    84 in 1960  87 in 1997  80 in 1934

The following are the record high temperatures at the long term
sites for the entire month of March.

Location 		 

Santa Rosa       91 on March 16, 2004
San Rafael       88 on March 25, 1952
Kentfield        91 on March 28, 1923
Napa             92 on March 17, 1914
Richmond         87 on March 31, 2021
Livermore        90 on March 25 and 26, 2025
San Francisco    87 on March 11, 2005
SFO Airport      85 on March 25, 1952 and March 17, 2026
Redwood City     93 on March 17, 2026
Half Moon Bay    83 on March 31, 2000 and March 17, 2004
Oakland Museum   89 on March 17, 2026
San Jose         89 on March 14, 2015
Salinas Airport  92 on March 14, 2015 and March 17, 2026

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Friday for CAZ006-502>506-508>510-
     512>518-528>530.

PZ...None.
&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...KR
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Wed Mar 18 10:30:02 PDT 2026