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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 211422

Area Forecast Discussion
National Weather Service Key West FL
922 AM EST Sun Jan 21 2018

.DISCUSSION...In the middle and upper levels(700-200 mb), latest
available satelitte imager overlaid with model streamline analysis
as of 900 am, depict the next developing middle and upper trough
and associated cold core low developing over the Central Rockies.
Yet downstream of that, middle and upper height rises continue
across the Central and Eastern CONUS. Closer to South Florida and
the Keys, the axis of a shortwave trough is moving to the east,
with height rises ensuing across the Keys.

At the surface and in the lower to middle levels,(700-200 mb),
latest available satelitte imager overlaid with marine and land
surface observations and analysis as of 900 am detail a 1026-1028
mb surface ridge axis of an anticyclone oriented from North
Georgia east southeast into the Western Atlantic along the 30th
parallel. Farther to the south, there is a middle level trough 
between 500-700 mb from East Central Florida to SW Florida. As a 
result, the 12Z sounding at KEY illustrated fresh to strong east 
to southeast flow aoa FL004 just off the surface to about 925 MB. 
A weak, 2 degree C inversion was evident from about 1011 mb to 
1002 mb, but a stronger inversion, 3.5-4.0 degree C is in place 
from 921 to 905 mb, indicative of stratocumulus. Above that, there
is a moist layer between 680 up to about 600 mb, which is 
evidenced by a thick canopy of altocumulus aoa FL120-FL150. 
Overall, however, the lower to mid troposphere was fairly dry with
PWAT at 1.09 inches.

.CURRENTLY...As of 900 am, skies are mostly cloudy owing to the
aforementioned lower and middle cloud decks. Temperatures across
the island chain are in the upper 60s to lower 70s, with dewpoints
that have risen into the lower to mid 60s. Hence, on the radar, 
none of the altocumulus are producing any measurable 
precipitation. C-man stations along the Florida Reef are recording
east to southeast winds between 15 and 20 knots. Ship reports 
indicate winds are greater than 20 knots in the Straits. However 
winds across the islands and in the shallower cooler waters are 
decoupled and only between 10 and 15 mph. 

.SHORT TERM...Rest of day and this evening, a near breezy more 
east to even southeasterly flow across the islands will allow
temperatures to return to seasonal levels this afternoon, into the
middle 70s with comfortable levels of humidity, mid to hi 60s
dewpoints returning. Forecast soundings will continue to hold
middle level cloudiness in place, so partly to mostly cloudy
conditions will prevail through the end of the day. But it will
continue to be dry below 700 mb, so the clouds will have a hard
time delivering anything other than a sprinkle. 


.MARINE...Rest of today and this evening, the 1025 mb surface
ridge oriented from North Florida into the Western Atlantic will 
drive the overall MSLP gradient across the islands and surrounding
waters. Winds will be lighter across the cooler Florida Bay and 
shallower Nearshore Gulf waters inside the five fathom line. 
Elsewhere, SCEC conditions will continue across the Hawk Channel, 
offshore Gulf waters, and Florida Straits waters. Winds will pick
again this evening, and a SCA will likely be issued for the 
Atlantic waters, and possibly for Hawk Channel and the SE Gulf of 
Mexico waters. Will revisit for the afternoon package


.AVIATION...Rest of the day, thru 24Z, VFR conditions will 
prevail at both the KEYW & KMTH island terminals. Surface winds 
will average 12-14 knots from between 100-120 degrees with gusts 
to between 16 and 20 knots. Expect only a few-sct clouds aoa 
FL025-030, with broken to overcast AC aoa FL100-150. 


On this date in Florida Keys weather history, in 1877, the high 
temperature in Key West was 86 degrees. This set the daily record 
for maximum temperature measured in Key West on January 21st, a 
record which still stands 141 years later. Temperature records at 
Key West date back to 1872.




Upper Air/Data Collection......DR/MCL/DAF

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