Area Forecast Discussion
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FXUS62 KKEY 130815

Area Forecast Discussion
National Weather Service Key West FL
315 AM EST Wed Dec 13 2017

As of 300 am, a dry cold front knocking on our doorstep with a
thin ribbon of clouds along the boundary moving southeast across
the island chain. Temperatures range from the low 60s in the
Upper Keys, to near 70 in the Lower Keys. Dew points have dropped
from upper 50s to the mid-50s in the past hour. A few very light
showers formed in the Gulf Waters and crossed the Middle and Lower
Keys, delivering at most a trace of rain. A shallow inversion had
flow decoupled across the island chain, but northerly winds have
since picked up to 10-15 knots. Winds are beginning to increase
across our coastal waters, with CMAN and Weatherflow sites
reporting 15 to 20 knot winds out of the northwest.

The advancing cold front will bring a refreshing mass of dry
continental air to the island chain early this morning, allowing
temperatures to plummet before sunrise, and causing dew points to
drop back into the 40s/near 50 as cold air advection continues
throughout the day. The boundary layer will become decoupled as
the front sweeps the island chain, and northerly flow will
increase to moderate/fresh breezes early today. This afternoon, a
surface ridge over the western gulf will migrate to South Florida,
firmly planting itself across the Florida Keys until early Friday
morning. As a result, expect breezy winds to become light this
afternoon, and near calm through tomorrow night, allowing ideal
conditions for a radiational cooling event under nearly cloudless
skies tomorrow night. How cold will it get? So far, the official
forecast remains below most guidance, mirroring conditions
experienced earlier this week in the low 50s... though a few
colder spots across the island chain may experience a brief dip
into the Upper 40s.


The upper level pattern will remain broadly cyclonic across the
Upper Midwest, Ohio River Valley, and Northeast, and quasi-zonal
across the Southeast Thursday through Saturday, with mid-level
ridging building across the western Atlantic this weekend. Rising
heights and a return to easterly flow will moderate temperatures
and dew points back into the 70s late this weekend, with
afternoon highs reaching near 80 degrees Sunday through Tuesday.
Rain chances will remain very low through early next week.


A passing cold front will keep moderate to fresh breezes out of
the north in place until late morning. A high pressure ridge
shifts to the Keys this afternoon, decreasing flow to gentle
breezes this afternoon. A Small Craft Advisory will remain in
place for all coastal waters adjacent to the Florida Keys until
winds decrease later today.

Until 12z/14th, VFR conditions will prevail at the Key West and
Marathon terminals. Northwest winds of around 10 knots with
occasional gusts of 15 knots will turn north to northeast and
increase to 10 to 15 knots with gusts near 20 knots between 10z and
17th. Thereafter, winds will abate significantly and become light
and variable overnight.


In 1962, the daily record low temperature of 46 degrees was recorded
in Key West. Temperature records have been kept since 1872.


Key West  54  71  59  75 / -  -  -  -
Marathon  53  70  58  75 / -  -  -  -


GM...Small Craft Advisory until 11 AM EST this morning for GMZ031>035-




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