Area Forecast Discussion
Issued by NWS Key West, FL

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FXUS62 KKEY 111504
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
1104 AM EDT Sun Apr 11 2021

.DISCUSSION...
Currently - It`s the calm before the storm this morning. Overnight
activity has long since diminished and dissipated. It was quite an
impressive, yet decaying squall line that came through overnight.
Strongest winds were reported at Long Key C-MAN station which
registered a 42 knot, or 48 mph wind gust.

Today so far, we`ve had fair weather cu and strato-cu streaming
in from the south. We have more low level moisture today than
this time yesterday. Yesterday there was hardly a cloud in the sky
and today they are proliferating. Taking a look at this morning`s
12Z RAOB we have a PWat of 1.52 compared to 1.24 inches 24 hours
ago. As a side note, this PWat value places it between the 75th
and 90th percentile. Instability is also definitely higher today
with a MLCAPE of close to 2000 J/kg. Meanwhile, cu is developing a
lot sooner over Cuba this morning and starting to look agitated.

I mention all of this because another squall line/MCS is currently
across the eastern Gulf of Mexico and sliding southeast towards
our area. The atmosphere is better primed today for strong to
marginally severe weather later this afternoon and evening.
Convective allowing models (CAMs) are showing this squall line/MCS
shifting southeast towards our area, arriving in the late
afternoon at the earliest. At the same time, CAMs are hinting at
boundaries being ejected from Cuba in the late afternoon ahead of
this squall line. The difference in today vs yesterday is the
upper level trough associated with this surface feature will pass
relatively close to our area. Yesterday`s line was far removed
from the upper level support by the time it reached us. With that
said, we will still be slightly displaced from the main upper
level forcing and therefore coverage and intensity will be
limited. Best chances may favor the Upper Keys with the initial
convection and then slide south across the Middle and Lower Keys.
However, will maintain likely chances for the evening and taper
back to chances after midnight. Any thunderstorms that push across
the area will have a wind threat as the main impact.

Thereafter, we may have a reverse cloud line situation for Monday
but otherwise, generally dry conditions will return towards
midweek.

&&

.MARINE...
Generally moderate southerly breezes prevail across all waters
this morning. Winds should slacken and become more southwest by
this afternoon. Continuing to monitor for inclement weather as a
line of strong showers and thunderstorms are sliding southeast
across the eastern Gulf of Mexico and Florida Peninsula. Current
timing would arrive in our waters by the late afternoon and early
evening. The main threat would be strong gusty winds and higher
seas in the vicinity of thunderstorms.

From synopsis: A very weak front will ease into the
Keys Monday night, briefly swinging winds around the compass,
before settling to gentle to moderate easterly flow by Tuesday.
Light to gentle breezes are forecast for the middle and later part
of the week.

&&

.AVIATION...
VFR conditions will prevail at both island terminals through at
least 22z this evening. Thereafter, showers and thunderstorms are
expected to develop and push across the island chain from the north,
continuing through much of the overnight hours. VCTS has been
included in the TAFs for now, with TEMPOS and a more refined period
of prevailing convective conditions expected to added to the 18z TAF
issuance. South to southwest will be sustained near 10 knots with
occasional gusts 15 to 20 knots.

&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  84  75  83  74 / 50 60 30 -
Marathon  84  75  85  73 / 50 60 30 -

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...LIW
Aviation/Nowcasts....BT
Data Acquisition.....JAM

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