385
FXUS66 KMTR 220611
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1111 PM PDT Sat Sep 21 2024

...New AVIATION...

.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...
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

&&

.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...
(06Z TAFS)
Issued at 1111 PM PDT Sat Sep 21 2024

The marine layer depth currently varies from 900 feet to 1700 feet
per Bodega Bay, Fort Ord and Point Sur profilers. Coastal stratus
and fog /LIFR-IFR/ are redeveloping and will move inland tonight
and Sunday morning. Northerly and southerly pressure gradients
(and corresponding wind directions) juxtaposed over the coastal
waters within a stationary surface trough have eased since earlier
in the day; gradients were under-forecast by the meso-scale
models and with plenty of stratus/fog to our southeast along the
CA coast this may continue Sunday. Currently the 2.7 mb SFO-SAC
pressure gradient (onshore wind) is the predominating gradient
across the forecast area. Precipitable water on the Saturday
evening Oakland upper air sounding was a little above mid
September normal, however there still should be decent radiative
cooling tonight to daybreak Sunday helping with stratus and fog
development (favorable due to lengthening night time hours).

Stratus and fog /VLIFR-IFR/ mixes out back to the coastline and
bays late Sunday morning and afternoon. Elsewhere MVFR-VFR
conditions Sunday.

Vicinity of SFO...VFR except IFR ceiling is forecast 09z 18z Sunday.
Onshore wind 5 to 15 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...LIFR-IFR in stratus and fog tonight and
Sunday morning, conditions improving to MVFR-VFR by late Sunday
morning and early afternoon. Light and variable winds tonight and
Sunday morning becoming onshore 5 to 15 knots by late morning and
afternoon.

&&

.MARINE...
(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.

&&

.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...Canepa
MARINE...Sarment

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