582
FXUS66 KMTR 220939
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
239 AM PDT Thu May 22 2025

...New SYNOPSIS, SHORT TERM, LONG TERM, MARINE, FIRE WEATHER...

.SYNOPSIS...
Issued at 238 AM PDT Thu May 22 2025

Elevated fire weather conditions remain the primary concern today as
warm, dry, and windy conditions continue.

&&

.SHORT TERM...
(Today and tonight)
Issued at 238 AM PDT Thu May 22 2025

The marine layer is being observed at 800 feet by the Fort Ord
profiler with satellite just starting to show some stratus forming
over Tomales Bay and along the San Francisco Peninsula Coast.
Despite this, the 00Z KOAK sounding revealed a LowRH (surface-850
mb) value of 25%, a MidRH (850mb-650mb) value of 9%, and a
precipitable water value of 0.45 inches which is slightly above the
10th percentile of 0.42 inches for 00Z May 22nd. An upper-level
shortwave trough will skirt the region today, bringing temperatures
back down to seasonal normals. Of more impact will be the strong
onshore winds that it brings with gusts of 25-35 mph expected over
the waters, along the immediate coastline, through
northwest/southeast oriented valleys, and in the higher terrain.
These winds in conjunction with poor relative humidity (both
overnight recovery and daytime minimum) will continue to support
elevated fire weather conditions.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 238 AM PDT Thu May 22 2025

An approaching second, deeper upper-level shortwave trough will
deepen the marine layer and finally ease fire weather concerns for
the time being as excellent relative humidity recovery (70%+)
returns to all but the highest terrain of the Central Coast.
Sensibly, temperatures will drop to 5 degrees below normal, dubbing
tomorrow the coolest day of the week. Heights will begin to build
and temperatures rebound to seasonal normals Saturday as a
positively tilted upper-level longwave ridge builds into the West.
Due to the orientation of the upper-level pattern, the warmest day
for the Bay Area will be Saturday with the Central Coast having to
wait until Sunday to achieve that feat. The unofficial start of
Summer (Memorial Day) will feel anything but with below normal
temperatures brought to you by a dry cold front. The previously
mentioned upper-level longwave ridge will build and broaden across
the Western two-thirds of CONUS with an upper-level shortwave trough
likely to undercut it, resulting in split flow and unimpactful
weather for our region Tuesday and Wednesday.

&&

.AVIATION...
(06Z TAFS)
Issued at 937 PM PDT Wed May 21 2025

It`s VFR except for haze nearer the coastline is resulting in
areas MVFR visibilities. Similar to late last night and earlier
this morning a few patches of stratus and/or fog /IFR/ may develop
tonight and Thursday morning. Otherwise VFR Thursday. Expect gusty
afternoon and evening west to northwest winds Thursday.

Vicinity of SFO...VFR tonight through Thursday then stratus /IFR/
returns beginning 10z early Friday morning. West wind 10 to 15
knots tonight and Thursday morning, west wind increasing to 25 to
32 knots Thursday afternoon to mid evening, easing to 15 knots
late Thursday night/Friday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the evening, then increasing
probability of stratus and/or fog /IFR/ developing tonight and
Thursday morning. VFR returning late Thursday morning. Onshore
winds 10 to 20 knots this evening, decreasing to 5 to 10 knots
tonight and Thursday morning. Wind increasing to 10 to 20 knots
Thursday afternoon and early evening.

&&

.MARINE...
(Today through Tuesday)
Issued at 238 AM PDT Thu May 22 2025

Widespread hazardous marine conditions continue today as strong
northwesterly breezes with near gale to gale force gusts and rough
seas persist. Fresh to strong northwesterly breezes and moderate
to  rough seas will prevail Friday through Monday.

&&

.FIRE WEATHER...
Issued at 238 AM PDT Thu May 22 2025

The combination of poor daytime relative humidity of 15-25% and
onshore winds with gusts of 25-35 mph along the immediate coastline,
in northwest/southeast oriented valleys, and in the higher terrain
will continue to support elevated fire weather conditions today. The
greatest period of concern is today in cured grass areas. Remain
fire wise and do not be the reason for fire starts.

Sarment

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for SF Bay N of Bay
     Bridge.

     Small Craft Advisory from 9 AM this morning to 3 AM PDT Friday
     for Mry Bay.

     Small Craft Advisory until 3 AM PDT Friday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory until 3 PM PDT this afternoon for Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

     Gale Warning from 3 PM this afternoon to 9 PM PDT this evening
     for Pt Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...Sarment

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea