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fxus62 ktbw 230749 
afdtbw

Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
249 am EST Tue Jan 23 2018

Synopsis...
08z water vapor and h4 rap analysis shows an amplified mid/upper
level pattern over the eastern half of the nation as a potent
trough/closed low feature migrates eastward over the MS/OH/TN
valleys. Well defined southern stream/subtropical jet is being
entrained into the large scale circulation of this trough...with a
deep train of moisture riding northeastward over the Gulf of Mexico
and Florida Peninsula. A subtle southern stream shortwave and
associated jet stream rapidly crossed the northern Gulf during
Monday and has been the driving force for large scale ascent to
support the widespread rainfall/storms over the NE Gulf of
Mexico/northern half of the Florida Peninsula early this morning. This
energy will start to exit off to our east...and will be taking the
best large scale mid/upper level forcing later this morning...but
not before another large area of rainfall seen on regional radar
over the eastern Gulf of Mexico moves toward the west-central Florida
coast during the next few hours leading up to dawn.

At the surface...surface cold front is slowly crossing the eastern
Gulf of Mexico...trailing southward all the way from parent low
pressure over the Great Lakes. Lingering upper level support to aid
the lower level focus along/ahead of the boundary is still forcing a
decent swath of rainfall with the front itself, but most guidance
members are indicating that as this upper support departs, we will
see this band of showers/rain become more and more disorganized and
broken on its approach and passage through our region today. There
has been some concern given the dewpoints in the lower 60s...and SSTs
in the 50s north of Englewood, that sea fog would be concern this
morning. So far, not seeing any significant visibility issues coming
off the Gulf, and the longer we go without seeing it, the less
likely it will be of widespread concern ahead of the front
today.

&&

Short term (today through wednesday)...
today...cold frontal boundary will approach this morning...
and then slowly move northwest to southeast across the forecast area this
afternoon and evening. As mentioned in the synopsis...the
upper dynamics supporting the widespread rainfall from
Tampa Bay northward and over the eastern Gulf early this
morning will be shifting away from the region by the
afternoon hours...leaving essentially only the lower level
focus along the front to force further showers. This front
is becoming increasingly stretched with time, and these
factors should result in an overall decrease in shower areal
coverage and organization along/ahead of the frontal
boundary by the second half of the day. Therefore, based on
the large area of rainfall approaching the coast now...and
the fact that most guidance members have not initialized
this area well...will be basing the next 6-9 hours of
forecasts off the last few runs of the rap/hrrr, which are
certainly the wettest solutions this morning. So...although
it is always still possible this area of rain rapidly
dissipates as it moves east...currently seeing no signs of
that trend yet off the long range ktpa tdwr...and no signs
of warming cloud tops in infrared satellite. Therefore, the safer
forecast is to go with widespread showers/storms ahead of
the front this morning moving ashore from the Gulf...but
still believe the midday/afternoon hours should generally
not end up being a washout for any part of the region. In
fact, several hires guidance members such as the past few
runs of the hrrr...suggest only isolated to widely scattered
light shower activity across the region by the time we
reach the afternoon. This scenario is definitely plausible
given the majority guidance trend toward drier forecasts,
and will be ramping down pops everywhere during the second
half the day...especially since even the rap becomes less
aggressive by this time. Over the Nature Coast the pops
would decrease anyway behind the frontal passage, but even
areas south of I-4 which will stay pre-frontal much of the
day, look to not see too much activity leftover for the
afternoon/early evening. Skies today (and beyond) are
expected to remain cloudy to mostly cloudy. We will likely
see the lower clouds scour out with time this afternoon to
the north of I-4...but the southern stream jet and
associated higher clouds will not be going
anywhere...resulting in skies staying partly to mostly cloudy
or at best highly filtered sunshine behind the front.

Tonight/Wednesday... weak cold front settles south of Fort Myers by
midnight...shifting winds to the north for all areas, and allowing a
drier/ and somewhat cooler low level airmass to filter down all the
way to South Florida overnight. May still see a residual isolated
shower from Highlands County to Charlotte/Lee counties through
midnight, but the second half of the night looks rain-free for all
zones. The impact of this cold front on the airmass will certainly
be "lower level". While winds near the surface will be from the
north and northeast...only a short ways above the surface these
winds will veer southeast and then all the way to SW at only about
850mb (~5kt). This veering of winds with height is indicative of
warm air advection above the surface, which will support keeping
lower/mid level clouds in the forecast into Wednesday over the
southern half of the region. From the I-4 corridor northward...the
lower level clouds will be mostly scoured out still, but the high
level cirrus remain...keeping any sunshine highly filtered.

Wednesday afternoon/evening...another strong piece of shortwave
energy is forecast to quickly pass through the Tennessee
Valley/deep south. It will be this energy that pushes a
secondary cold front down through the region Wednesday
afternoon and night. This front will have a much greater
influence on our atmospheric column...and allow a deeper
layer of dry air to arrive overhead (and more sun potential)
Thursday and Friday.

&&

Long term (wednesday night - tuesday)...
upper level ridging extends over the Bahamas westward over southern
Florida and into the Gulf Mexico. Farther north, troughing extends
south from the Great Lakes region, but should not really impact the
local area through the week. As the trough moves northeast, the
ridging will further build into the area by the end of the week.
This pattern will hold until the beginning of next week when another
trough moves over the northern U.S., But will not really impact the
area as a predominant zonal flow remains over the southeast Continental U.S..
on the surface, high pressure to the west ridges east keeping dry
and sunny conditions over the area through the end of the week. The
next weather system is expected to develop in the eastern Gulf of
Mexico on Sunday and will move eastward producing our highest rain
chances through the long term period. A 50-70 percent chance of
showers can be expected on Sunday. High pressure will build into the
area once again early next week bringing pleasant weather back to
the region.

&&

Aviation (23/06z through 24/12z)...
occasional light showers moving over ktpa/kpie/ksrq should
become more concentrated before sunrise with occasional MVFR
cigs/vis. Kpie is seeing some sea fog move off the Bay with
IFR visibility at times, and will keep in forecast during
next several hours. Further south...rain chances will be
much lower...although some patchy fog is possible late. The
degree of clouds suggests the mav may be a bit aggressive
with fog at kpgd/kfmy/krsw and have not gone below MVFR.
Broad band of MVFR ceilings and occasional showers should settle
southward across the region during Tuesday. Have gone with
prevailing MVFR much of the day for the I-4 corridor
terminals...with a later arrival during the afternoon for
the terminals closer to Fort Myers. Much of Tuesday night is
looking VFR for Tampa Bay/I-4 terminals well behind a cold
front...however...further south...lingering moisture could
still result in a period of MVFR/IFR visibility during the
second half of the overnight.

&&

Marine...
a cold front will drop slowly southward across the eastern
Gulf of Mexico today and this evening. Periods of cautionary
level winds from the north and northeast are in the forecast
behind this front from later today through much of the week.
The prevailing northeasterly flow through the week behind
the front will keep the largest waves offshore. Mariners
today should be aware that pockets of dense sea fog may be
encountered until the frontal passage later today or this
evening.

&&

Fire weather...
no significant fire weather concerns are expected through
the middle of the week as relative humidity values remain
above critical levels and most areas see a wetting rainfall
today. Drier and somewhat cooler air will arrive for
Wednesday and Thursday behind a cold front, but nothing
compared to the airmass we experienced last week. The next
significant rain potential after today will not arrive until
the second half of the weekend...at the earliest.

Fog potential...no significant areas of fog or reduced
visibility are anticipated during the next several days
behind the cold front.

&&

Preliminary point temps/pops...
tpa 73 52 67 48 / 80 0 10 0
fmy 78 59 73 52 / 60 10 10 10
gif 78 52 70 48 / 70 0 10 0
srq 71 54 67 50 / 80 10 10 0
bkv 74 46 67 42 / 70 0 0 0
spg 73 52 67 49 / 80 10 10 0

&&

Tbw watches/warnings/advisories...
Florida...none.
Gulf waters...none.

&&

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