Technical NOAA Weather Discussion

FXUS66 KMTR 181721
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1021 AM PDT Mon May 18 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1147 PM PDT Sun May 17 2026

 - Breezy to windy conditions, especially across the North, East,
   and South Bay Mountains and the Santa Cruz Mountains through
   today

 - Hazardous beach conditions through this morning

 - Hazardous marine conditions expected through today

 - Elevated fire weather concerns continue through today across 
   the interior with low humidities and strong gusts

&&

.UPDATE...
Issued at 842 AM PDT Mon May 18 2026

Gusty offshore winds continue through this morning with winds
gradually easing this afternoon/evening. The Wind Advisory remains
on track to expire at 11AM PDT across the higher elevations.
Notably, the current hourly temperatures are running 6-7 degrees
above what the current forecast has. This is likely due to the
stronger offshore (NE) winds bringing in warmer and drier air,
with some additional warming from downsloping occurring at the
base of the mountains. Bumped temperatures up using the NBM90th
percentile to better account for the already warmer temperatures
observed this morning. This puts the interior into the 80s to low
90s today with the coast staying in the 70s. Winds don't look to 
switch onshore again until after peak heating (3/4PM) so would not
expect much marine influence on today's high temperatures outside
of the direct coastline.

&&

.SHORT TERM...
Issued at 1147 PM PDT Sun May 17 2026
(Tonight through Monday)

An upper level low pressure system digs into the tri-state area of 
CO, UT, and WY by late Monday morning. We remain under the influence 
of the broader trough associated with it, leading to breezy offshore 
flow. North to northeast winds pick up tonight across the Santa Cruz 
Mountains, the interior North Bay Mountains, and the Eastern Santa 
Clara and East Bay Hills. Sustained wind speeds of 15 to 30 mph 
along with gusts up to 50 mph, though localized gusts up to 60 mph 
are expected for favored ridges, gaps, and passes. These winds will 
usher in drier air to the region as well, keeping the fire weather 
threat elevated for interior Bay Area and Central Coast locations. 
In terms of more every day hazards from the winds, impacts include, 
but are not limited to difficult driving, especially for high profile 
vehicles, downed tree limbs, the potential for power outages, and 
the possibility of loose or unsecured items being blown around. 

Winds begin to ease late Monday morning into the afternoon and will 
continue to decrease into the evening and overnight hours. Offshore 
winds should bring some warmer temperatures to the region, the 90s 
for the interior Bay Area valleys, the 60s to low 70s along the 
coast, and the mid 70s to low 80s for the Central Coast Valleys. 

&&

.LONG TERM...
Issued at 1147 PM PDT Sun May 17 2026
(Tuesday through next Sunday)

Upper level troughing looks to hold just west of the Desert 
Southwest and into southern CA Tuesday into Wednesday, leaving us 
with teetering between quasi-zonal and barely trough-y. Weak 
offshore lingers at least over the interior mountain ranges through 
Tuesday into Wednesday, with onshore flow trying to make a diurnally 
driven push each afternoon/evening. During this time high pressure 
just to the west of us (over the eastern Pacific) builds, pushing 
towards the coast mid week. The upper level trough begins to meander 
south to southwest of southern California late week. This should 
bring a return of onshore flow to the region and perhaps the marine 
layer. Current guidance suggests we could see a 500ft marine layer 
return by Wednesday, with a 1000-1200ft marine layer by Thursday and 
Friday. Will need to keep an eye on this as it will affect how 
temperatures pan out.

&&

.AVIATION...
(18Z TAFS)
Issued at 1021 AM PDT Mon May 18 2026

VFR conditions prevail through the TAF period. Breezy and gusty 
northeast winds will gradually diminish through the next couple of 
hours as an onshore push returns to the coastal regions this 
afternoon, with the coastal breeze continuing through the evening. 
Breezy winds will continue across the interior mountains of the Bay 
Area through the night, with northeast winds spreading across the 
interior valleys Tuesday morning towards the end of the 24-hour TAF 
period. Beyond that, Tuesday's coastal breezes look to be stronger 
than today's.

Vicinity of SFO... VFR conditions through the TAF period. Breezy and 
gusty northeast winds will turn more northwesterly through the 
afternoon, before diminishing through the evening and remaining 
light overnight through Tuesday morning. West-northwest winds will 
resume on Tuesday afternoon.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR conditions through the TAF period. 
Breezy northwest winds will develop imminently and continue into the 
evening. Winds remain light overnight before resuming Tuesday 
afternoon after the end of the TAF period.

&&

.MARINE...
(Today through Saturday)
Issued at 1021 AM PDT Mon May 18 2026

Winds continue to diminish throughout the marine environment, but
moderate to rough seas and moderate to fresh northwest breezes
will still offer hazardous conditions for small craft into the mid
weak before easing for most zones. Fresh to strong northwest
breezes will remain hazardous for small craft into the late week
for the northern outer zone.

&&

.FIRE WEATHER...
Issued at 449 AM PDT Mon May 18 2026

Strong and gusty north to northeast winds continue to affect the 
region. Expect peak gusts greater than 30 mph for most areas, 
with around 45 to 55 mph along through gaps and passes, and across
higher terrain. These winds will begin to reduce in the late
morning but remain breezy until the late night. Daytime humidity 
retentions loos to stay around 10- 25% across the interior regions
and higher peaks, with limited overnight humidity recoveries. 
Humidities will be slow to recover into the work week as a light 
offshore flow will continue to affect the district.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 11 AM PDT this morning for CAZ504-512-514-
     515.

     Coastal Flood Advisory until 3 AM PDT Tuesday for CAZ506.

PZ...Small Craft Advisory until 3 PM PDT this afternoon for SF Bay N 
     of Bay Bridge.

     Small Craft Advisory until 9 PM PDT this evening for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PDT Tuesday for Pt Arena to Pt 
     Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

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

     Small Craft Advisory until 9 AM PDT Tuesday for Pigeon Pt to Pt 
     Pinos 10-60 NM.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Mon May 18 12:30:03 PDT 2026
From the National Weather Service