Area Forecast Discussion
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FXUS62 KKEY 050248

Area Forecast Discussion
National Weather Service Key West FL
948 PM EST Sun Dec 4 2016

.DISCUSSION...In the middle and upper levels(700-200 mb), latest
available IR satelitte imagery overlaid with model streamline
analysis as of 900 pm depict deep low amplitude troughing across the
entire Central and Western Conus, with a developing cold middle and upper
level low pressure system in the Rio Grande Region of Northern Old
Mexico. This feature trails a sharp trough axis well to the SW into
the Eastern Tropical Pacific to near 17 North 115 West. A deep middle
and upper southwest flow flanks the eastern side of this trough,
transporting some middle level PVA lobes at 500 mb up from SW Mexico
northeastward, with one decent lobe of vorticity and associated
lightning now crossing Pinar Del Rio Cuba just SW of the Florida

At the surface and in the lower to middle levels,(Surface to 700 mb),
latest available marine and land surface observation and analysis
overlaid with IR satelitte imagery as of 900 pm detail the center of
1025 mb surface ridging located over NE North Carolina. Well to the
SW of that, an area of low pressure is deepening along a cold front
in the Western Gulf Of Mexico. The 00Z evening sounding illustrated a
veering lower to middle level troposphere with some moisture below
800 mb with dry air above that and total columnar PWAT at 1.51
inches. Only weak directional and speed shear was evident.

.CURRENTLY...As of 900 pm. skies are mostly cloudy owing to lower
cumulus advecting from the SE and middle altocumulus from the SW
associated with an approaching middle level disturbance over Western
Cuba. Temperatures and humidity levels are not comfortable for this
time of year across the islands, averaging in the Upper 70s with
dewpoints in the middle 70s. Key West radar detects a broken band of
showers over the far SW Florida Straits attm. C-man stations along
the Florida Reef are recording SE winds between 15 and 20 knots, near
15 knots at Smith Shoal Light and in Florida Bay, and near 15 mph
over the Keys.

.SHORT TERM...Overnight, middle level height falls expected across SE
Gulf Of Mexico and South Florida and the Florida Keys. This will
occur as the aforementioned strong closed middle and upper level low
pressure system moves NE across the Lone Star State. 00Z GFS
initializes well the 500 mb vorticity now over Pinar Del Rio,
bringing it NE overnight, reaching near the Lower Keys by daybreak.
In the lower levels, model forecast soundings illustrate good lower
level confluence, with PWAT rising to between 1.85 inches per ECMWF
and 2.00 inches per 12Z GFS. As such, will raise shower chances into
the scattered coverage arena and add isolated thunderstorms. This
action was already performed on an earlier evening update.


.MARINE...The surface ridge over NE North Carolina and the developing
low over the Western Gulf will continue to drive near breezy to
breezy conditions across all waters overnight, with SCA conditions
continuing across the Florida Straits.


.AVIATION...VFR is expected to prevail at EYW & MTH through the next
24 hours, though some brief MVFR ceilings are not out of the
question early this morning, with the greatest potential between
8-16z. Increasing moisture out of the south will bring the
opportunity for vicinity showers. Expect moderate breezes out of the
ESE to continue.


GM...Small Craft Advisory overnight GMZ052>055- 072>075.



Data Collection......DR

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