Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 211920

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
220 PM EST Tue Feb 21 2017

19Z water vapor and H4 RAP analysis shows a well-define
trough/closed low feature slowly migrating eastward along
the northern Gulf coast and western/central Gulf of Mexico.
This feature will be the main weather maker for our region
during the next 24 to 36 hours...however...we will not begin
to feel any significant impacts over the FL peninsula until
Wednesday morning...impacts over the coastal waters of the
eastern Gulf will begin overnight.

Currently...The Florida peninsula is still under sharp large
scale ridging...but we have come to the end of our time
under this feature. Synoptic height falls associated with
the approach of the trough will commence shortly and
continue into the overnight hours. Upper level diffluence
ahead of the trough as been forcing abundant upper level
clouds to spread overhead today...and this will
continue...keeping the sun hidden or filtered for the
remainder of the daylight hours. Regardless of the loss of
diurnal heating...the potential of the column is quite
high...and many spots have reached the middle 70s to lower
80s already this afternoon.


.SHORT TERM (This evening through Wednesday)...
As mentioned in the synopsis...synoptic height falls are
about to get underway as strong troughing approaches from
the west. This will begin to set the stage for Wednesday`s
forecast...but until that time...we can continue to enjoy a
dry and warm forecast this afternoon and through the evening

During the second half of the overnight hours...GFS/ECMWF in
good agreement showing the trough/closed low pivoting east
and southeast into the eastern Gulf of Mexico. Both global
models show an impressive swath of deep layer Qvector
convergence in phase with the deep moisture crossing the
eastern Gulf and arriving along the Florida west coast by
12Z. In addition to this synoptic support for lift...the
whole process will be aided by a coincident region of highly
diffluent flow in the mid/upper levels. This combination
will lead to impressive large scale omega fields spreading
onshore and inland through the morning hours. Given this
setup...anticipate a large area of rain/embedded thunder to
approach the Florida west coast after midnight...arriving
along much of the Florida west coast within a few hours
either side of sunrise. Potential exists for sct showers
even a few hours ahead of this given the deep layer cyclonic
flow...especially over the Nature Coast. However...the bulk
of the strongest lift appears slated for the morning through
first half of the afternoon. While it appears everyone is
going to get wet...this system does not look to have a large
potential for flooding. The strongest synoptic forcing
remains progressive...and therefore...heavy rainfall
potential may be short-lived...while the high rain chances
in general last longer. Can never rule out very localized
heavier downpours...especially given the defined FGEN
banding below 700mb shown by the GFS pivoting onshore
between 12-15Z.

Some indications of a dry-slot feature attempting to pivot
into the SW FL coast...perhaps up to the Tampa Bay area
after mid-afternoon. If this was to occur...then the
steadier rainfall would likely come to an end for this
region after 20Z. Have dropped PoPs somewhat second half of
afternoon over the suncoast for this potential.
However...can not drop PoPs altogether given the large scale
cyclonic flow and arriving cold temps aloft...that will
likely keep at least sct showers/isolated storms in the
forecast through Wednesday evening.

Enough cold air under the upper low may arrive by Wednesday
afternoon to support a few enhanced updrafts...and some
potential for small hail associated with any stronger
storms. Generally for strong updrafts is
limited...and the threat of severe weather low.
However...will not be shocked to see a few small hail


.MID/LONG TERM (Wednesday Night through next Tuesday)...
An area of low pressure will be centered over the area at
the start of the mid term forecast period. This low will
slowly move east during the day Thursday with rain chances
and cloud cover diminishing as the day progresses.
Sufficient lift should remain in place through the aftn
hours however so will maintain PoPs in the 30- 40 range for
the majority of the area through the afternoon.

As the low continues to move away Friday, mostly sunny skies and dry
conditions can be expected Friday and into next week. Highs in the
lower 80s can be expected to end the work-week. As we get into the
weekend, a cold front will begin to approach the area late
Saturday/early Sunday. Moisture and upper-level support will be very
limited so no precip expected with this front but it will help bring
in some slightly cooler and drier air to the area for Sunday. As is
usually the case around here however, the "cool-down" will be short-
lived and aftn highs will once again top out in the low to mid 80s
by the time we start next week.


.AVIATION (21/12Z through 23/00Z)...
No significant aviation concerns through the evening hours
under plenty of passing mid/high level clouds. Aviation
concerns do not look to materialize until late tonight...and
especially Wednesday morning. Expect several bands of rain
with embedded storms to move onshore during this period and
impact all terminals of west- central and southwest Florida.
Much of Wednesday after 12Z has the potential to be
prevailing VFR with periods of IFR both in CIG and
VIS...especially during the morning and early afternoon


High pressure shifts east of the region this evening in
response to the approach of a weak area of low pressure
from the north-central Gulf of Mexico. This low will shift
across the forecast waters during Wednesday...reaching the
Atlantic on Thursday. The low moving directly through the
waters will make for highly variable and changeable winds
the next 24-36 hours...although generally remaining at or
below 15 knots. A brief periods of cautionary level winds is
possible... although confidence in exact location and
timing is low. Winds will shift to the north and northeast
by Friday and become light as the system moves away. A cold
front looks to cross the Gulf during the upcoming
weekend...with a period of cautionary or advisory level
winds to follow.


.Fire Weather...
No fire weather concerns the next couple of days. Relative
humidity values will remain well above critical levels with
high chances for widespread wetting rain during Wednesday.
Rain chances will diminish by Thursday...and certainly by
Friday...however...ERC values are likely to be low after
the wetting rainfall.

Fog Potential...No significant areas of fog are expected the
next several days.


.Preliminary Point Temps/PoPs...
TPA  65  71  61  77 /  40 100  50  30
FMY  65  72  59  78 /  40 100  40  40
GIF  63  72  60  79 /  10  90  60  40
SRQ  64  71  59  74 /  50 100  40  30
BKV  63  72  59  79 /  30  90  60  30
SPG  65  71  62  75 /  50 100  40  30


Gulf waters...None.



MID TERM/LONG TERM/DECISION SUPPORT...McKaughan is the U.S. government's official web portal to all federal, state and local government web resources and services.