Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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FXUS62 KTBW 291228
AFDTBW

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
728 AM EST Tue Nov 29 2016

.AVIATION...
Little if any low clouds this morning, but could still see some
areas of MVFR ceilings this morning with daytime heating getting
underway. Otherwise, VFR conditions are expected to prevail
through early tonight before the next chance of seeing some
MVFR/local IFR conditions after midnight. Southeast to south
winds will increase to 10 to 15 knots with higher gusts late this
morning through mid-afternoon then subside back to 10 knots or
less this evening.

&&

.Prev Discussion... /issued 308 AM EST Tue Nov 29 2016/

SYNOPSIS...
08Z water vapor and H4 RAP analysis shows a highly amplified upper
level pattern has evolved over the CONUS. The main player in the
synoptic pattern is longwave troughing extending form the inter-
mountain west through the entire mid-section of the country and
currently extending as far east as the Appalachians. The trough
has amplified bookend ridges over both the Pacific and Atlantic
seaboards. This large trough is anchored by a large cut- off low
spinning over the Dakotas/Minnesota. This large system has been
responsible for all kinds of inclement weather over the past 24
hours...from heavy snows in the north to severe weather in the MS
Valley. While one severe weather event is ending across the deep
south...another strong lobe of energy is poised to round the
bottom of the trough through the southern Plains/lower MS valley
later today and tonight...bringing another potential round of
severe thunderstorms to that region. We here in Florida remain
simply bystanders to all the inclement weather...as our region
remains within a much more benign pattern underneath deep layer
ridging. This ridging will continue to protect our region through
Wednesday...with generally dry and warm conditions.

At the surface...
Florida peninsula and eastern Gulf of Mexico resides within a
deep southeast to south flow pattern between a slow moving cold
front through the deep south...and sprawling high pressure over
the western Atlantic. Generally speaking...this synoptic pattern
will not change much of the next 24 hours. The continued southern
component to the low level flow will bring further increases with
respect to low level moisture. Temperatures early this morning
are very warm for the end of November...with most spots not
falling out of the 60s.

SHORT TERM (Today through Wednesday)...
Stacked ridging and a warm boundary layer will provide a mostly
dry day with well above normal temperatures. Temperatures will be
starting from a warm point...so given the expected efficient
diurnal mixing and insolation today...would expect most spots away
from the immediate coast to rise into the 80s this afternoon. The
immediate coast will be a bit more tricky in terms of temperatures
after about 18Z. Strong terrestrial heating should be sufficient
to turn winds a bit onshore at the immediate coast. This partial
flow off the cooler shelf waters should at least stop the diurnal
temperature rise...keeping temps in the 70s...or drop temps back
into the 70s for the majority of the afternoon. However...will not
have to go more than a couple miles inland to get right back into
the 80s.

The low level moisture is high...but its shallow. Borderline
conditions with the onshore convergence component to support a few
isolated shower along the I-75 corridor during the late
afternoon/early evening. A few convective allowing NWP members
support this...as does the NAM. Given the low level instability
potential...will add a few sprinkles/light showers to the forecast
after 20Z. Similar to Monday...most spots...even if they do see a
shower...with not even measure.

Another very warm night for the end of November coming up...as
southerly flow and low level moisture keeps low temperatures from
falling out of the lower/middle 60s. The gradient looks as though
it might be a bit weaker by the second half of tonight...and that
weaker BL mixing is likely to provide improved conditions for fog
formation during the late night hours. Have added areas of fog to
the grids away from the immediate coast...and will let the
day shift re-evaluate the SREF/NARRE guidance for dense fog
potential updates for the next forecast cycle.

Wednesday...More of the same for the daylight hours. Very warm and
mostly dry conditions will prevail for the majority of the day. We
will be watching a cold front slowly approach from the west across
the FL panhandle during the afternoon...with the mid/upper level
flow turning gradually more cyclonic over our northern Nature
Coast zones. However...the best synoptic forcing for deep ascent
is quickly lifting away from the northern Gulf coast by the end of
the day...and there is very good agreement among the reliable
guidance members that the low level convergent forcing and
moisture flux convergence along and ahead of the front will be
declining quickly after 18Z. Therefore...if this progs are
correct...we are likely only looking at a broken and decaying band
of narrow showers approaching Levy/Citrus county late in the
afternoon or evening. Allowed for a 20% PoP for Levy county after
21Z...but left rain mention out of remaining Nature Coast zones
for now...especially before dark.

LONG TERM (Thursday through next Tuesday)...
The highly amplified pattern that we`ve seen over the past several
days will flatten out over the long term period. A closed upper low
sits over the western Great Lakes region with significant troughing
extending south through the central U.S. A little closer to home, an
upper level high sits over the Bahamas with ridging extending
southwest to northeast over the western Atlantic. This ridge will
slip eastward as the trough and upper low move northeast toward
Ontario by Thursday morning. By Friday night, the upper low has
moved over Nova Scotia and the upper ridge has flattened out over
the Caribbean. This zonal pattern will continue until late Monday
night when strong ridging builds back into the southeast U.S.

On the surface, ridging extends west southwest from a high pressure
center located near Bermuda. But, the main surface feature for the
eastern U.S. is a frontal boundary extending south along the
Appalachian Mountain chain from a low over the eastern Great Lakes.
Most of the dynamics of this low pressure system will remain well to
the north of Florida, but will still bring our highest chances of
rain through the period. We can expect 20-40 POPs over the northern
coastal waters and Nature Coast beginning late Wednesday with
coverage sinking south to Manatee County by Thursday morning. The
southern portion of the CWA should remain dry as the front moves
through. The front pushes south by Thursday evening, as high
pressure over the northern Gulf coast moves into the area bringing
clearing conditions through Saturday.

Models are in good agreement through late Saturday. At that time
they begin to diverge a bit with ECMWF developing a stronger low and
frontal boundary over southeast Texas and moving it up the Gulf
coast. GFS is hinting at a disturbance, but keeps it much weaker.
So, went with the more aggressive solution bringing 30-50 POPs into
the area on Sunday into early Monday. High pressure builds back in
on Tuesday once again bringing clearing conditions. Daytime highs
will be at or above normal on Thursday, then dropping down 3-5
degrees below normal on Friday, then warming back up once again to
average on Saturday and Sunday. With the passing of the frontal
boundary on Monday, temps will once again drop 3-6 degrees below
average through the middle of next week.


MARINE...
Flow will be from the southeast and south through Wednesday
between a slowly approaching front to our northwest and a large
region of Atlantic high pressure to our northeast. Winds over the
eastern Gulf of Mexico will be elevated at times...with cautionary
level winds ongoing this morning away from the immediate coast.
Winds are expected to briefly decrease this afternoon...but will
return to cautionary levels over the offshore waters tonight into
much of the day Wednesday. A cold front will shift south across
the forecast waters on Thursday...turning winds out of the north
and northeast. Another period of cautionary level winds from the
north will be possible behind this front during Thursday night and
Friday.

FIRE WEATHER...
No significant fire weather concerns through at least Thursday.
Low level moisture will continue to increase today and prevent any
critical levels of relative humidity from being reached. The
elevated moisture will linger through Wednesday. Only concern for
today will be the development of gusty southeast to south winds
during the later morning and afternoon hours. A cold front will
slip south through the region during Thursday. This front will
introduce a cooler and drier airmass to the region...however not
enough dry air is expected to arrive before sunset on Thursday to
cause any real fire weather hazards.

Fog Potential...
No significant fog concerns expected this morning. Increasing
potential for some areas of fog (possibly dense) after midnight
tonight into early Wednesday morning.

&&

.Preliminary Point Temps/PoPs...
TPA  82  67  81  69 /  10  10  10  20
FMY  85  66  83  67 /  10  10   0  10
GIF  85  65  85  66 /  10  10   0   0
SRQ  83  67  82  67 /  10  10  10  10
BKV  84  63  83  65 /   0  10  10  20
SPG  79  67  78  69 /  10  10  10  20

&&

.TBW WATCHES/WARNINGS/ADVISORIES...
FL...Beach Hazards Statement through Thursday evening for
     Coastal Sarasota.

Gulf waters...None.
&&

$$

AVIATION...69/Close
PREV DISCUSSION...Mroczka & Wynn



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