Area Forecast Discussion
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FXUS62 KKEY 212005

Area Forecast Discussion
National Weather Service Key West FL
305 PM 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 200 pm, depict the next developing middle and upper trough
and associated cold core low developing over the Central Plains.
Yet downstream of that, middle and upper height rises continue
from the Mississippi Valley eastward to the Seaboard. Closer to
South Florida and the Keys, the axis of a middle level shortwave
trough continues to move to the east of the Bahamas, 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 200 pm detail a near 1025 mb
surface ridge axis of an anticyclone oriented from North Florida
eastward along the 30th parallel to near 70W. As such, middle
level altocumulus has begun to become more scattered over the Keys
and surrounding waters.

.CURRENTLY...As of 200 pm, skies are partly to mostly cloudy
across the islands and surrounding waters, owing to some lower
level cumulus/stratocumulus, but mostly to the aforementioned
altocumulus. Temperatures have reached the middle 70s with
dewpoints risen into the middle 60s. C-man stations along the Reef
are recording northeast to east winds 15 to 20 knots, with island
sensors generally 10 to 15 mph.

.SHORT TERM...Tonight thru Wednesday, Continued moderation in
temperatures and humidity levels are expected thru the middle of
the upcoming workweek. Temperatures reached climo values today and
will become a few degrees above that thru Tuesday afternoon, with
highs in the upper 70s tomorrow and near 80 on Tuesday. The
surface ridge across Northern Florida will remain in place aoa
1025 mb, allowing for near breezy conditions on east to southeast
winds across the islands and less over the cooler shallower
waters, but breezy to winds conditions tonight across the deeper
waters tonight and at least during tomorrow. Winds will let down a
bit more tomorrow night thru Tuesday night. The next continental
ridge will begin to influence to weather during Wednesday, with
the stronger breezes coming in for late Wednesday. Both 12Z ECMWF
& GFS model forecast soundings do illustrate PWAT increasing to
between 1.25 and 1.5 inches beginning tonight and during Monday.
Have inserted a dime pop in the grids for these two periods, but
then increase to around 1.50 inches Monday thru Wednesday.
Therefore, given weaker low level convergence ahead of the next
boundary Wednesday night, have isolated showers, 20% in the grids
for Monday night thru Wednesday.


.LONG TERM...Wednesday Night thru Sunday, Middle level height
rises will occur in combination with very strong surface ridging,
near 1030 mb plus setting up from Thursday and Friday,
intensifying to 1035 mb plus by Saturday and Saturday Night ahead
of the next front which may move in Sunday. As a result, breezy to
windy conditions are expected across the islands thru the entire
period, with hi and low temperatures near to above normal as well
as only a slight chance, 10%, for showers through the entire
period given just enough boundary level moisture and strong
surface convergence available.


.MARINE...SCA for increasing winds across GMZ033-034-
 042>044-052>055-072>075 tonight. Looks possible that there will
be SCA conditions across 052>055-072>075, with SCEC conditions
across those waters tomorrow night. Winds and seas will let down a
bit Tuesday thru Wednesday, before SCEC conditions return across
portions of waters Wednesday Night, and SCA conditions likely
across almost all waters Thursday thru Friday.


.AVIATION...Tonight, VFR conditions expected at both the KEYW and
KMTH Int`l airports. Some cloudiness will remain between
FL100-150 feet. Surface winds will become 100 degrees aoa 12-14
knots with gusts near 20 knots


Key West  69  78  70  78 / 10 10 20 20
Marathon  69  79  70  79 / 10 10 20 20


GM...Small Craft Advisory until 5 AM EST Monday for GMZ033-034-




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