-- Discussion containing changed information from previous version are highlighted. --
443
FXUS66 KMTR 210340
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
840 PM PDT Mon May 20 2024

...New UPDATE...

.SYNOPSIS...
Issued at 1224 PM PDT Mon May 20 2024

Typical summer-like pattern to persist throughout the first half of
the week. Temperatures are forecast to dip below seasonal averages
by the upcoming weekend as an upper level trough impacts the
region.

&&

.UPDATE...
-- Changed Discussion --
Issued at 841 PM PDT Mon May 20 2024

Pleasant day around the Bay Area and Central Coast as it turned
out to be one of the sunnier days out of the last week (yesterday
was pretty sunny too). Despite the ample sunshine, temperatures
struggled to reach seasonal values. Highs topped out in the upper
60s to lower 80s inland, but much cooler at the coast with highs
in the upper 50s to 60s.

As the sun set, some patchy stratus began to form around Monterey
Bay, Big Sur coast and SF Peninsula coast. This patchy stratus
will fill in a little more and up the Salinas Valley, but much
less coverage than a few days ago. What`s the reason? Developing
offshore flow and drier air. Latest large-scale pressure gradient
(SFO-WMC) has finally flipped offshore. Not expecting a strong
offshore push, but offshore nonetheless. Obs over the North Bay
interior mts already showing NE flow with lower RH. The offshore
flow will also lead to milder temperatures in the hills tonight.

No update needed this evening. As noted below Tuesday will be the
warmest day over the next few days. Warmest temperatures will be
across the interior and away from any marine influence. Speaking
of marine influence, the very persistent gusty NW winds has led to
some impressive upwelling along the North Bay coast. Current SSTs
are in the upper 40s to lower 50s.

MM
-- End Changed Discussion --

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 1224 PM PDT Mon May 20 2024

Weak offshore flow aloft is resulting in dry weather conditions this
afternoon with minimum relative humidity values between 15-35% for
inland areas and those higher up in elevation. Meanwhile, the coast
continues to experience onshore flow with higher humidity. Humidity
increases overnight in all but the highest elevations with lows
generally in the mid-to-upper 40`s to low-to-mid 50`s.

RH values will be even lower tomorrow as offshore flow aloft
persists and will drive drier conditions even closer to the coast.
As such, tomorrow will be the warmest day of the week with mid 80`s
across the interior and 60`s to lower 70`s near the coast. People
who are incredibly sensitive to heat should take precautions while
outdoors and remember to drink plenty of water.

&&

.LONG TERM...
(Tuesday night through next Sunday)
Issued at 1224 PM PDT Mon May 20 2024

By late week, temperatures cool to near seasonal averages across the
interior but coastal locations will still be slightly cooler due to
onshore flow. By this upcoming weekend, temperatures region-wide
drop below average as a mid/upper level trough more directly impacts
the region. This systems looks fairly dry with ensemble guidance
indicating very low chances of accumulating precipitation with it
Friday into Saturday morning. If any precipitation does fall it will
be light and not very impactful. Guidance from the Climate
Prediction Center indicates slightly below average temperatures and
slightly above average precipitation through the end of the month.

&&

.AVIATION...
(00Z TAFS)
Issued at 419 PM PDT Mon May 20 2024

Generally VFR conditions for the interior through the night, with
moderate confidence (40-66% probability) of MVFR stratus
developing early Tuesday morning around Monterey Bay and a lower
confidence (20-30% probability) of further development elsewhere
on the coast south of the Golden Gate.

Vicinity of SFO... VFR through the TAF period. Breezy and gusty west-
northwest winds with gusts up to around 25 knots diminishing by
about 04Z this evening, and resuming Tuesday afternoon with
similar speeds. Probability of gusts above 35 knots is near zero.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Breezy northwest winds will diminish in
the evening. Model output shows a moderate confidence (40-65%
probability) of MVFR stratus around the region early Tuesday
morning, with the period of highest probability from 09-16Z.

&&

.MARINE...
(Today through Saturday)
Issued at 907 AM PDT Mon May 20 2024

Strong and gusty northwest winds persist over the coastal waters
through Thursday. Expect hazardous conditions and steeper wind
waves during the week. Winds look to ease later in the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt
     Reyes 0-10 nm.

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

     Small Craft Advisory from 3 PM Tuesday to 3 PM PDT Wednesday for
     Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning until 3 PM PDT Wednesday for Pt Arena to Pt Reyes
     10-60 NM.

     Gale Warning until 3 AM PDT Wednesday for Pigeon Pt to Pt Pinos
     10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...MHeinlein
MARINE...DialH

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