Area Forecast Discussion
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FXUS62 KKEY 240221

Area Forecast Discussion
National Weather Service Key West FL
921 PM EST Thu Nov 23 2017

.DISCUSSION...In the middle and upper levels(700-200 mb) latest
available IR imagery overlaid with available model streamline
analysis as of 900 pm depict a well defined narrow full
latitudinal positively tilted trough axis from Eastern Canada down
to the Bay of Campeche. The Florida Keys are beneath the lower
right side of the trough, beneath 75 knot southwesterlies at 250
mb, but with marginal moisture despite some weak middle level

At the surface and in the lower to middle levels(Surface-700 mb),
latest IR imagery overlaid with marine and land surface
observations and analysis as of 900 pm detail a cold front draped
southwest to near Cancun from weak 1009 mb low pressure analyzed
near Orlando. As such scattered showers and thunderstorms have
developed in situ along boundaries late this afternoon and into
the evening. Though velocity signatures have been nothing to write
home about, some of these have exhibited weak rotation and this
resulted in the issuances of several marine warnings, but
available ground platforms couldn`t get to sample these stronger
winds near the ground as of yet. Now as of 900 pm, winds in the
lowest 3 KFT per the VAD profiler have veered into the Northwest,
while they remain strong southwest above that all the way up into
the mid and upper atmosphere.

.CURRENTLY...As of 900 am, skies are mostly cloudy across the
islands and all surrounding waters, with radar detecting numerous
showers with embedded scattered thunderstorms across the Florida
Straits mostly south of the Lower Florida Keys and points
westward. Temperatures outside of shower activity are in the
middle to upper 70s with dewpoints in the 60s to near 70, except
near 70 in the rain cooled air, especially in the Lower Keys.
C-man stations outside of the convection along the Reef are
recording west to northwest winds near 10 knots., with island
sensors 5 to 10 mph.

.SHORT TERM...Weak 1008 mb surface low should continue moving
northeast overnight as the main mid and upper trough axis slides
towards Florida during Friday. Available model forecast soundings
do indicate that low level winds surface to 3kft should again
back again to southwest during the next few hours and given good
speed shear with moderate amounts of moisture, numerous showers
and scattered thunderstorms will continue to develop in situ
through the overnight period. Will still maintain low likely
coverage overnight, 60% as columnar PWAT for both models still
near 1.75 per soundings and is adequate for this coverage.

During Friday, despite the main trough axis finally moving over
the Keys, consensus is that the middle levels dry out in the deep
unstable cyclonic flow somewhat, with PWAT back to between 1.25
and 1.50 inches, hence have reduced shower coverage back to
mid range scattered, 40%, with isolated thunder. Then by Friday
night the surface front will move thru shutting off any chances
for rain and bringing in drier and cooler air. Excellent weather
rolls in in time for the shopping weekend.


.MARINE...Gentle to moderate breezes overnight and Friday, except
in the presence of stronger showers and isolated storms, where
some local gusts near 30 plus knots are probable.


.AVIATION...Scattered to numerous showers and scattered storms
will impact either/both terminals thru the overnight hours. For
now will leave VCSH in TAF and amend for lower MVFR/IFR conditions
when activity is immanent to impact the terminals. Improving VFR
cigs will predominate during Friday with less of a chance of short
mvfr/ifr in showers.




Upper Air/Data Collection......DR

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