899
FXUS66 KMTR 212025
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
125 PM PDT Sat Sep 21 2024

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 124 PM PDT Sat Sep 21 2024

Gradual warming continues through the rest of the weekend with
temperatures near or slightly below seasonal averages. Even warmer
temperatures expected Monday and Tuesday with moderate HeatRisk
possible inland.

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 124 PM PDT Sat Sep 21 2024

Warmer temperatures are starting to make their way into the interior
regions, with temperatures generally running 5 to 10 or occasionally
15 degrees above those at the same time yesterday. The stratus deck
has pared back to the immediate coast, as the marine layer has
gradually compressed with observations from the Fort Ord profiler
showing a marine layer depth around 1500 feet today compared to
nearly 2000-2200 feet this time yesterday. Overnight stratus is
expected to develop into the coastal valleys although the interior
East Bay and the Morgan Hill-Hollister corridor are expected to
remain clear.

Today`s temperatures should be warmer than yesterday`s, although the
extensive stratus coverage this morning led me to bump down the high
temperature forecast in the interior valleys by a few degrees. The
current forecast shows high temperatures today ranging from the 80s
across the inland valleys, to the 70s and low 80s near the Bayshore,
and the low to mid 60s along the Pacific coast.

Even warmer temperatures are forecast on Sunday, although some
uncertainty continues into this period. A shortwave trough begins to
develop off the coast of California through the day, interrupting
the expanding upper level high over this part of the region and
moderating the warming trend. As of time of writing, the inland
valleys are expected to reach into the low to mid 90s on Sunday,
with temperatures in the Bayshore up to the mid 70s to mid 80s and
the Pacific coast rising to the mid to upper 60s. Low temperatures
remain in the 50s across the lower elevations, up to the mid 60s
along the thermal belts.

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 124 PM PDT Sat Sep 21 2024

The upper level disturbance builds ever so slightly into the
beginning of the upcoming work week, migrating further offshore
through the next couple days with a potential window for the
development of a closed low, before the pulse is absorbed into the
polar jet mid week. The interaction between this upper level
disturbance and the upper level ridge pushing into the northwestern
United States will dominate our weather pattern for the next several
days. In particular, the positioning of the low off the California
coast will result in light offshore flow during the overnight and
morning hours, although onshore flow should dominate the afternoon
and evening hours. Temperatures are expected to peak on Monday and
Tuesday, when moderate HeatRisk is possible in the interior regions.
Highs in the inland valleys are expected to rise into the mid to
upper 90s on those days. Of note, the extent of heat-related impacts
is correlated to how cold it gets overnight, with significant
uncertainty across the thermal belts, but also near San Francisco
Bay. For example, the reasonable range of low temperatures near San
Francisco International Airport is around 15 degrees.

From the midweek onward, persistent upper level troughing should
moderate temperatures to near the seasonal average through the end
of the week.

&&

.AVIATION...
(18Z TAFS)
Issued at 1119 AM PDT Sat Sep 21 2024

Stratus has cleared from most area terminals this morning, leaving
behind VFR in its wake. VFR will persist through the early evening
today with W/NW breezy winds at area terminals this afternoon.
Stratus begins to return in the early portion of the evening for
Monterey Bay tonight, but later for most other terminals. However,
stratus is likely to bring IFR CIGs overnight for the majority of
terminals. Late morning clearing to VFR on Sunday expected.

Vicinity of SFO...VFR lasts through the early morning of Sunday,
though confidence on this is only moderate. Some models indicate a
return of stratus prior to midnight, though at this time, higher
confidence is placed in stratus bringing MVFR CIGs beyond midnight
for KSFO. Otherwise, breezy NW winds return this afternoon, but
settle and become light into the late evening.

SFO Bridge Approach...Clear through the day today. Low coastal
clouds are likely to filter into the SF Bay overnight bringing low
CIGs.

Monterey Bay Terminals...IFR CIGs are expected to clear soon, with
VFR lasting through the late afternoon today. Stratus will make an
early return, bringing IFR CIGs once more towards the 00-02Z Sunday
window. In the overnight, CIGs are expected to lower to become LIFR,
with some reduction in visibility as fog develops.

&&

.MARINE...
(Today through Thursday)
Issued at 1119 AM PDT Sat Sep 21 2024

Fresh to moderate northwest winds continue, with strong gusts over
the far northern outer waters through Monday. Seas will be
moderate, continuing to build and remain rough in the outer
waters with significant wave heights up to 12 feet. Winds
decrease and seas abate beginning Tuesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...AC
MARINE...AC

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