862
FXUS66 KMTR 191757
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1057 AM PDT Thu Sep 19 2024

...New AVIATION...

.SYNOPSIS...
Issued at 239 AM PDT Thu Sep 19 2024

There is a slight chance of showers and even a couple rumbles of
thunder over southern Monterey County later this afternoon and
early evening, with the best chances farther inland you go into
higher elevations. Locations under the influence of the marine
layer along the coast will be in the 60s and low 70s. Interior
locations away from the marine layer will be in the 70s to low
80s. A warming trend for this weekend into the beginning of next
week remains on track.

&&

.UPDATE...
Issued at 907 AM PDT Thu Sep 19 2024

Showers and thunderstorms occurred and continue over the interior
Central Coast with rainfall amounts of 0.36" near Greenfield and
0.47" at Mustang Ridge in the past 12 hours. Those are just sites
that happened to be under the rainfall and up to 0.75" may have
occurred in areas without rain gauges. There remains the potential
for additional showers and thunderstorms through the afternoon
across this region, but current radar trends show this ongoing
convection diminishing. That said, the ongoing forecast remains on
track with no updates anticipated this morning.

&&

.SHORT TERM...
(Today and tonight)
Issued at 239 AM PDT Thu Sep 19 2024

A positively tilted upper level low currently situated offshore in
the vicinity of Big Sur will continue to track south along the
California coastline toward Los Angeles today and eventually begin
to move inland over San Diego by tomorrow afternoon and evening. The
best chance for showers and/or thunderstorms will be farther inland
where orographic upslope flow enhances an otherwise weak
thermodynamic environment for convection. Highs today will
generally be 5-10 degrees below normal, and slightly warmer
tomorrow.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 239 AM PDT Thu Sep 19 2024

The upper level trough moving across our area today and tomorrow
will eventually shift inland over SOCAL by tomorrow evening.
Increasing H50 heights and thickness values over the weekend will
result in temperatures rebounding back up above normal by the end of
the weekend into the beginning of next week. A weak upper level
disturbance interrupts the ridging pattern off the coast of central
California by late Sunday into early Monday morning, while the
northern extent of the ridging amplifies over the Pacific Northwest.
The net result is warmer than normal temperatures and increasing
heat risk concerns the farther inland and north you go for the
beginning of next week. The warming trend may result in the need for
a heat advisory for those locations as soon as Sunday, but more
likely Monday and Tuesday.

&&

.AVIATION...
(18Z TAFS)
Issued at 1057 AM PDT Thu Sep 19 2024

Mix of VFR and IFR-LIFR CIGs across the board. The upper level low
that disrupted the marine layer and brought light rain to our CWA
has moved to the south of us with a slightly more typical stratus
pattern expected tonight. Thunderstorm chances continue to decrease
along the Central Coast but a slight chance persists through the
afternoon. Moderate confidence that stratus will continue to clear
throughout the Bay Area with all sites to return to VFR by 20Z. Low
to moderate confidence in clearing across the Central Coast where
scattered convection continues across southern Monterey County.
Stratus is expected to return early this evening along the Central
Coast and by mid to late evening throughout the rest of the Bay
Area. Low to moderate confidence that MVFR CIGs will reach LVK
overnight with any ceilings that do develop expected to occur after
09Z. Clearing is expected by mid tomorrow morning with most sites
clearing 16-17Z.

Vicinity of SFO...Stratus is clearing out of SFO with northwesterly
winds to pick up over the next few hours. MVFR CIGs are expected to
prevail tonight with ensemble guidance suggesting some potential for
IFR CIGs to develop during the late evening/early morning hours,
however, confidence remains low on IFR development. Stratus is
expected to clear by mid morning with moderate northwest winds
between 12-15 knots expected.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Patchy IFR to LIFR CIGs continue with low
to moderate confidence that CIGs will fully clear around 20Z.
Scattered convection associated with the upper level low is still
located in southern Monterey County and is adding additional
uncertainty to time of stratus clearing at MRY and SNS this morning.
Current thinking is CIGs will at least temporarily clear out this
afternoon with a brief period of VFR conditions. Stratus will return
late this afternoon/early this evening between 00-03Z and persist
through the remainder of the TAF period with MVFR to IFR CIGs. A
slight chance (generally less than 10%) of thunderstorms continues
for SNS through this afternoon. Confidence is too low to include
VCTS in TAFs given that convection is weakening in southern Monterey
county and lightning probabilities are continuing to diminish.

&&

.MARINE...
(Today through Tuesday)
Issued at 907 AM PDT Thu Sep 19 2024

Moderate northwesterly winds continue over the majority of the
coastal waters. Northwesterly winds are expected to strengthen to
fresh to strong and seas will become rougher in the northern
outer waters through the day. Winds and seas remain elevated
through the weekend but ease into the next work week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 AM PDT
     Saturday for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Kennedy

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