-- Discussion containing changed information from previous version are highlighted. --
233
FXUS66 KMTR 220359
AFDMTR

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

...New UPDATE, MARINE...

.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.

&&

.UPDATE...
-- Changed Discussion --
Issued at 844 PM PDT Sat Sep 21 2024

Another calm night ahead with some low clouds moving inland with a
touch of fog and even some drizzle added in for that extra Bay
Area flavor in the forecast.

Not much to update in the near term tonight. There is still a lot
of interesting model shenanigans going on in the second half of
next week, which just means there is a fair amount of uncertainty
on how cool the cooling trend will be. Regardless, temperatures
still look to peak on Monday, with slight cooling on Tuesday.

-Murdock
-- End Changed Discussion --

&&

.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...
(00Z TAFS)
Issued at 427 PM PDT Sat Sep 21 2024

Currently VFR everywhere except SNS. The marine layer is at 1,500
feet and is expected to compress through the TAF period as high
pressure builds into place. High confidence in the blanket of
stratus offshore filtering inland, impacting all terminals tonight
in the form of IFR/LIFR ceilings/visibilities with the exception of
LVK which is expected to remain VFR. Widespread VFR will prevail by
tomorrow afternoon.

Vicinity of SFO...Currently VFR with northwesterly flow. Moderate
confidence on an IFR ceiling impacting the terminal overnight with
lower confidence on the exact onset. Winds will prevail out of the
west through the TAF period. VFR will prevail by late-morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with westerly flow at MRY and
MVFR with northwesterly flow at SNS as the terminal is just barely
under the influence of the stratus feed from the Monterey Bay. High
confidence in an early evening return of an LIFR ceiling for MRY with
SNS following suit and further deteriorating to LIFR.

&&

.MARINE...
-- Changed Discussion --
(Tonight through next Friday)
Issued at 844 PM PDT Sat Sep 21 2024

The pressure gradient between subtropical high pressure over the
Eastern Pacific Ocean and low pressure over the West Coast will
support strong northwesterly breezes and rough seas in the outer
waters through Monday. Northwesterly breezes decrease and seas
abate beginning Tuesday. Seas rebuild to become rough in the outer
waters towards the end of the forecast period.
-- End Changed Discussion --

&&

.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...Sarment
MARINE...Sarment

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