Area Forecast Discussion
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FXUS62 KKEY 121934

Area Forecast Discussion
National Weather Service Key West FL
234 PM EST Mon Nov 12 2018

.DISCUSSION...In the middle and upper levels( 700-200 mb), latest
available GOES-R satellite imagery overlaid with model streamline
analysis as of 200 pm continues to depict a burgeoning trough
across the Western CONUS with its positively tilted axis oriented
from Minnesota to Northern New Mexico. Downstream of that, low
amplitude ridging encompasses much of the Central and Eastern
CONUS, including Gulf of Mexico, the Florida Peninsula, and the
Florida Keys. An approximate 100 knot jet at 250 mb is in between
these two features and is evident from Central Texas northeast to
across Central New England and offshore where is accelerates to
about 150 knots.

At the surface and in the lower to mid levels(Surface to 700 mb),
latest available GOES-R satellite imagery overlaid with marine
and land surface observations and surface analysis, as of 200 pm,
detail a 1042 mb plus arctic high over the Northeastern Montana building
southeastwards. To the east, there is a 1031 mb high center just
southeast of New England. Well south of that, the decaying
western end of a stationary front reaches across South Florida
fron the high latitude North Central Atlantic.

.CURRENTLY...As of 200 pm, skies are mostly sunny across the
islands and surrounding waters. Radar and satellite imagery are
only supportive of some sprinkles at best as dry air has
infiltrated from the mid levels. Temperatures across the Keys are
in the lower to middle 80s and its muggy with dewpoints in the
lower to mid 70s. C-man stations along the Florida Reef and Smith
Shoal Light are recording east to southeast winds near 15 knots.
Island platforms are near 15 knots.

.SHORT TERM...Tonight thru Thursday evening, large scale models
agree that cooler and breezy weather will eventually get into the
Keys and surrounding waters by Thursday evening. Until that time,
surface ridging off of the Northeast coast will scoot away as a
weaker pressure pattern takes hold with ridging across the Florida
Peninsula tonight through tomorrow night. As this unfolds the
larger polar trough will be migrating east across the CONUS and
the Gulf of Mexico. As it does that it will swing a cold front
eastward across the Gulf beginning tonight through Thursday,
eventually moving slowly thru the Keys from west to east by later
in the day and early Thursday evening. In advance of the front,
forecast soundings are indicating decent lower to middle level
moisture combined with some minor instability beginning tomorrow
night until the FROPA. Given trends, will maintain a low chance,
30% for showers tonight and Tuesday, with a medium chance for
showers with a slight chance of thunderstorms Tuesday night thru
Thursday, 40%. High and low temperatures outside of showers will
continue to be several degrees above normal with dewpoints
typical of earlier in the fall, in the 70s.

.Extended...Thursday Night through Monday, the cold frontal
boundary should be through the Keys, in the case of both the ECMWF
and GFS by early Thursday night. Local winds will be slower to
increase behind the front, becoming northwest to north. Also, Given
some moisture in the lower levels, typical of an anafrontal
structure, a low chance for showers remains in the grids Thursday
night, 30%. During Friday and Friday night, drier air moves in.
The 1000-850 mb cold thickness advection on north winds will
allow for breezy to windy conditions with highs now a few degrees
below normal, reaching mid 70s and lows in the 60s, with dewpoints
in the 50s.

Slow modification will occur as winds veer to northeast and
decrease during Saturday and Saturday Night. At this time we have
near breezy conditions as MSLP gradient not that strong.
confidence in the wind forecast does remain low, as winds could
be stronger. High and lower temperatures will be near normal, with
dewpoints in the mid 60s thru this period.


.MARINE...SCEC conditions have winded down for now. Winds and seas
will let down by late tonight thru Thursday afternoon. Winds and
seas will increase by Thursday evening, with SCEC and SCA
headlines across all water Thursday Night, and SCA conditions on
all waters during Friday. SCEC and SCA conditions expected Friday
Night. Winds and seas may come down a bit for the weekend, but
this is less certain then usual attm.


.AVIATION...VFR conditions will prevail at both KEYW and KMTH
through this  afternoon and evening. Low level cloud coverage
will generally be FEW, though cannot rule out a brief period of
MVFR ceilings if an isolated shower passes over the terminal.
Gusty east-southeast winds will remain in the 10 to 15 knot range
at both terminals through late this afternoon before diminishing
below 10 kt in the 21-00z timeframe.


Key West  86  78  85  78 / 10 30 30 40
Marathon  87  78  85  78 / 10 30 30 40




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

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