Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 281740
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1240 PM EST Tue Feb 28 2017

.UPDATE...

UPDATE Issued at 1130 AM EST TUE FEB 28 2017

Updated the forecast to issue a flash flood watch.  Made only
minor adjustments to temperatures for today with high temperatures
in the 60s expected. A couple rounds of showers and thunderstorms
will move across the area today. There will be a brief lull this
evening before another round of thunderstorms moves towards the
region late in the overnight.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 254 AM EST TUE FEB 28 2017

Broad mid/upper level flow remains out of the southwest this
morning. An embedded shortwave is noted on water vapor imagery,
pushing east/northeast across the mid Mississippi region this
morning. This is already helping to spark some shower and storm
activity off to our west this morning across western Kentucky and
western Tennessee. Hi-res models continue to have this activity
expanding as it moves east this morning with showers a sure bet
for the area by late morning into the early afternoon hours. For
this reason, will continue with categorical pops. Instability will
remain all elevated through the day, so no severe threat
anticipated with this early activity. As the shortwave exits to
the northeast this evening, it looks more likely we will see a
lull in shower/storm activity through the evening hours. Southwest
flow will continue into tonight with temperatures holding steady
or even coming up a few degrees overnight. This will keep lows
tonight near 60 or higher.

A shortwave trough will push across the great lakes on Wednesday
with a surface low tracking across the southern lakes. This low
pressure will drag a strong cold front east across Kentucky during
the day. Still lots of uncertainty with the speed of this front as
it crosses the area on Wednesday with the 00z NAM maintaining its
slower solution, while the 00z GFS maintains the faster solution.
The other differences in the models stem around the surface
instability available with this system. NAM continues to be plenty
unstable during the afternoon, while the GFS remains very meager
with its instability. ECMWF remains in between the two, but
continues to lean towards the GFS solution. While instability is
still in question, the amount of shear is certainly not.
Strong/deep layer unidirectional flow remains in place through the
day Wednesday. This would support a damaging wind threat if storms
can get going. For this reason, SPC has expanded the enhanced risk
of severe storms across eastern Kentucky this morning. Despite the
expansion, confidence hasn`t increased all that much, as we will
also have a good deal of cloud cover potentially limiting
instability. With the shear being so strong, its possible it may
overwhelm whatever instability is there also limiting storm
organization. Either way, this is a tricky forecast surrounding
the severe weather threat. Its best to stay updated on the latest
changes as we head through the day today. At this point, it
certainly looks like it could go either way with the severe threat
on Wednesday. Despite the uncertainty in severe chances,
measurable rain is a good bet with the frontal passage, so will
maintain categorical pops again. PW`s will also be quite high
across the area today through Wednesday and could lead to some
heavy rain at times and potential for localized flooding. As
mentioned in earlier discussions, the PW`s will be near the 99th
percentile for this time of year, so certainly well above normal.
Temperatures will spike around midday Wednesday before the frontal
passage brings quickly falling temperatures through the late
afternoon and evening hours.

.LONG TERM...(Wednesday night through Monday)
Issued at 437 AM EST TUE FEB 28 2017

A cold front will be exiting southeast of the area as the period
starts. The GFS and ECMWF have it far enough away that precip is
already finished. The NAM is slower, and still has some showers
in southeast KY Wednesday evening. With the GFS and ECMWF in
better agreement at a longer time range, prefer to give them more
credence. Have used mainly 20-30% POP in the southeast part of the
area to allow some minimal weighting for the NAM.

Much colder air arriving behind the front will limit the diurnal
temperatures rise on Thursday, even with clouds breaking up.
Another cold front is expected late Thursday night as a weak, fast
moving storm system sweeps by to our north. Moisture will be very
limited, but forecast soundings in the NAM and GFS show some
potential for snow showers with the arrival of the colder air, and
a 20% POP was carried in our northern and eastern counties late
Thursday night into Friday morning. Canadian high pressure with
the cold air mass then builds in on Friday, and holds on with fair
but cool weather into the weekend.

The high shifts to our southeast by Saturday night, and warm air
advection returns. This is followed by moisture advection Sunday
night and Monday, well in advance of the next cold front, and
along with it another potential for showers.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 1220 PM EST TUE FEB 28 2017

MVFR, local IFR, conditions can be expected through the remainder
of the afternoon hours as showers and embedded thunderstorms move
east across the terminals. As a focused low level jet moves east
by late afternoon, precipitation will wane with MVFR ceilings
lingering.

For tonight, region will be firmly in a warm sector as a warm
front lifts north to the southern Great Lakes. Another strong low
level jet will develop overnight. However, the moist, convergent
flow will be more focused to the northwest of the terminals, so
mainly dry weather is expected. With the strong low level jet,
LLWS was added to the terminals. Ceilings should rise back to VFR
between 03Z and 06Z.

On Wednesday, potent low pressure and a cold front will sweep east
through the Great Lakes and Ohio Valley. There is a good
likelihood of showers and thunderstorms along or just ahead of
the front. Models suggest precipitation may arrive to the
northwest terminals between 15Z and 18Z.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Wednesday afternoon for KYZ044-050>052-
060-104-106.

&&

$$

UPDATE...
SHORT TERM...KAS
LONG TERM...HAL
AVIATION...



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