379
FXUS66 KMTR 211724
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1024 AM PDT Wed May 21 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 111 AM PDT Wed May 21 2025

Above seasonal normal temperatures and hazardous marine conditions
today. Elevated fire weather conditions through Thursday.

&&

.SHORT TERM...
(Today and tonight)
Issued at 111 AM PDT Wed May 21 2025

Conditions are warmer and drier than they were this time last night,
but only in the higher terrain. Why? Well, last night there was a
shallow marine layer that impacted coastal areas while tonight the
region is clear and winds are calm, allowing for maximal radiational
cooling. A low amplitude upper-level shortwave ridge will trek
across the region today, bringing the warmest conditions of the
week. Temperatures will be 10 degrees above normal with
widespread minor HeatRisk and areas of moderate HeatRisk for the
Interior Bay Area and Central Coast. Elevated fire weather
conditions will continue through tomorrow for the Interior Bay
Area and Central Coast as dry conditions (poor daytime relative
humidity of 15-25%, overnight relative humidity recovery of 30-50%
in the higher terrain) and moderate to strong onshore winds
continue. The threat is primarily in the finer, flashier fuels of
brush and grass as recent offshore flow and warm conditions
continue to cure them.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 111 AM PDT Wed May 21 2025

The lack of a longwave pattern over the region is evident in the
extended forecast. An upper-level shortwave trough will skirt the
region Thursday, causing temperatures to return to seasonal normals.
A second, deeper upper-level shortwave trough will dig into the
region Friday, bringing the coolest conditions of the week. An upper-
level longwave ridge builds into the West Saturday which will bring
temperatures up to 5 degrees above normal. Global ensemble
clusters show an Omega Block, the combination of two cutoff lows
with one blocking high sandwiched between them, developing by
Sunday. By nature, this will lead to uncertainty and low
confidence in the progression of the longwave pattern into early
next week as these features have very weak forcing and thus can
be persistent.

&&

.AVIATION...
(18Z TAFS)
Issued at 1023 AM PDT Wed May 21 2025

VFR conditions have returned all TAF sites and look to persist
through the remainder of the afternoon and evening. Onshore winds
will increase by late morning or early afternoon before easing into
the night. There is moderate confidence for low clouds to return to
the Monterey Bay terminals early Thursday morning. Elsewhere, VFR
conditions are likely to persist through the TAF period.

Vicinity of SFO...Onshore winds are forecast to increase this
afternoon with gusts up to 30 kt. Winds are forecast to ease into
the night potentially becoming variable early Thursday morning.
Onshore winds will return by Thursday afternoon. VFR conditions are
likely through the TAF period.

SFO Bridge Approach...Weaker wind speeds, otherwise similar to SFO.

Monterey Bay Terminals...Onshore winds increase this afternoon
before easing after sunset. There is moderate confidence for low
clouds to return early Thursday morning resulting in IFR/LIFR
conditions by around 06Z - 09Z

&&

.MARINE...
(Today through Monday)
Issued at 1023 AM PDT Wed May 21 2025

Hazardous marine conditions continue today as strong northwesterly
breezes with near gale to gale force gusts and rough to very
rough seas persist. Winds will slowly diminish and seas will
slowly abate tonight with fresh northwesterly breezes with strong
gusts and moderate to rough seas prevailing Thursday through
Sunday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay.

     Small Craft Advisory until 3 AM PDT Thursday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt
     Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning until 3 PM PDT this afternoon for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT
     Thursday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...RGass
MARINE...RGass

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