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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KMTR 230255
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
755 PM PDT Mon Apr 22 2024

...New UPDATE...

.SYNOPSIS...
Issued at 118 AM PDT Mon Apr 22 2024

Warm inland temperatures expected through today before cooler,
unsettled weather returns Tuesday and continues through late week.
Light rain chances for Thursday night and into Friday.

&&

.UPDATE...
-- Changed Discussion --
Issued at 748 PM PDT Mon Apr 22 2024

The southerly wind reversal is in full effect this evening with
low stratus clouds banked along the shoreline and spilling inland
around the Monterey Bay, along the North Bay Coast, and through
the Golden Gate. Inland stratus intrusion will continue overnight
with most lower elevations covered given the deepening marine
layer. There should be enough moisture for some coastal drizzle as
well, especially along south/west facing slopes. This is all well
captured via the going forecast, so no changes are necessary this
evening.
-- End Changed Discussion --

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 256 PM PDT Mon Apr 22 2024

Primarily sunny across inland areas with clouds lingering along the
coastline and the Central Coast. Looking at satellite shows the
southerly surge of stratus in action with stratus extending
northwards from southern California to the North Bay coastline. As
of 2PM, inland temperatures are in the upper 60`s to low 80`s while
temperatures are in the low to mid 60`s along the coast. Widespread
stratus will move inland by late this evening/overnight throughout
the majority of the Bay Area. HREF guidance suggests that cloud
coverage will be patchier in nature throughout the Santa Clara
Valley. Monday night into Tuesday, orographic lifting will help to
generate light drizzle across coastal regions with precipitation
accumulations of a few hundredths of an inch expected.

An upper level disturbance will approach the coast beginning Tuesday
and lead to a pattern shift from above normal temperatures to below
normal temperatures. While Monday`s highs were 5 to 10 degrees above
normal, Tuesday`s highs are forecast to be, on average, 5 to 15
degrees below normal. High temperatures along the coast will linger
in the upper 50`s to low 60`s while highs inland will stay in the
60`s with a few areas potentially reaching the low 70`s.

&&

.LONG TERM...
(Tuesday night through next Sunday)
Issued at 256 PM PDT Mon Apr 22 2024

Cooler, unsettled conditions will continue through Friday as an
upper level disturbance moves inland. High temperatures throughout
the work week will stay in the 60`s inland and in the upper 50`s to
low 60`s along the coastline. Low temperatures will stay in the mid
40`s to low 50`s with a few locations in mountainous terrain
dropping into the low 40`s. Guidance continues to indicate some
light precipitation is likely Thursday into Friday but confidence
remains mixed as to how much precipitation will actually occur. The
most recent run of the ECMWF shows light, scattered showers moving
over the Bay Area with amounts generally receiving less than 0.15 to
0.25 inches.

Temperatures will gradually start to rise and become closer to
normal towards the end of the weekend with highs returning to the
upper 60`s to low 70`s.

&&

.AVIATION...
(00Z TAFS)
Issued at 512 PM PDT Mon Apr 22 2024

Moderate to strong southerly pressure gradients (southerly winds)
3.7 mb SMX-SFO and 2.8 mb SBA-SFO are coupled to a moderate onshore
gradient (onshore wind) 3.3 mb SFO-SAC. The surface winds are also
coupling to (mainly dry) cyclonic flow surface and aloft over the
coastal and offshore waters; today`s weather is a complex mix of
warm season stratus, fog and southerly surge and larger scale cool
season low pressure system dynamics.

Robust surface to lower level cool air advection will deepen the
marine layer and fully weaken/mix out the marine layer temperature
inversion tonight. Stratus will move inland, cool air advection
and upsloping flow resulting in patchy drizzle. Radiative warming
returning Tuesday will result in plenty of mixing with sufficiently
drier air resulting in VFR conditions Tuesday.

Vicinity of SFO...VFR, low confidence southwest wind maintains in to
the evening. Coastal pressure gradient SNS-SJC is strong at 2.8 mb
and if it holds it may influence the wind direction at both SJC and
SFO in the evening once the current wind pattern diminishes, meaning
it may bring about a stronger southerly wind component to 210 degrees.
It`s a complex forecast and the mesoscale models are having trouble
keeping up with the pattern, observations are very helpful. VFR-MVFR
tonight and Tuesday morning the wind direction likely holding close
to 210 degrees until late Tuesday afternoon/early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus is tightly spun up with clockwise
wind flow around the Monterey Bay per satellite imagery, a result
of the southerly surge, marine layer deepening with incoming surface
to lower level cool air advection. As mentioned above surface pressure
gradient SNS-SJC has steepened to 2.8 mb and SMX-SFO, SBA-SFO pressure
gradients are at least moderate in strength. Surface to lower level
cool air advection will continue to deepen the marine layer eventually
fully weakening the marine layer temperature inversion tonight. Patchy
coastal drizzle possible tonight and Tuesday morning. VFR-MVFR tonight
and Tuesday.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 423 PM PDT Mon Apr 22 2024

Southerly flow will persist into Tuesday over the coastal waters.
Locally stronger winds will be possible through the Golden Gate
into the West Delta Monday evening and Tuesday afternoon.
Additionally, stronger southerly winds near Point Sur will develop
Tuesday afternoon. Starting Wednesday, winds turn once more to
become moderate and northerly. Light southerly swell continues to
move through the waters for much of the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of
     Bay Bridge.

&&

$$

UPDATE...SPM
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Canepa
MARINE...MM

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