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FXUS63 KJKL 222249
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
649 PM EDT Sat Sep 22 2018

.UPDATE...
Issued at 649 PM EDT SAT SEP 22 2018

Updated to remove thunder as storms in the south have quickly
diminished and instability is non-existent at this point. Also
raised pops tonight to max them out with rain expected to become
widespread through the overnight hours north of the stalled
frontal boundary. Rainfall amounts are in question as the rates
haven't been that impressive upstream at this point, but with the
watch already out, no plans to do anything with it.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 320 PM EDT SAT SEP 22 2018

18z sfc analysis shows the stalled cold front across the area.
This is serving as a focus for additional shower and stray
thunderstorm development this afternoon. Temperatures vary
starkly across this boundary with mid 60s found northwest to the
low 80s in the far southeast. Similarly, dewpoints range from the
upper 50s northwest to the lower 70s in the south. Under an
overcast sky winds are generally from the northwest at 5 to 10
mph.

The models are in good agreement aloft with the broader details
through the short term portion of the forecast. They all depict
impulses moving east generally along the Ohio River between
weakening ridging to the southeast and troughing to the
northwest. This train of energy looks to keep some upper level
influence in our forecast through the short term and beyond.
Given the agreement do favor a blended solution with a strong lean
toward the aggregate CAMs scenarios when it comes to PoPs and QPF
through Sunday.

Sensible weather will feature the start of a very wet period for
Kentucky. This is as a result of a stalled frontal boundary
over the area, decent moisture in the column, and the interaction
with shortwave energy aloft. As a result of these ingredients,
and some beefy forecast rainfall totals from the CAMs, have
hoisted a flash flood watch - in conjunction with LMK and RLX -
for all but our Tennessee border counties from 10 PM tonight
through 10 pm Sunday evening. Temperatures will be rather steady
state through the period as well with fall-like readings to the
north and summer still seen in the south. There will also be a
very small diurnal range along and north of the front. With
periods of rain and convection there will also be areas of fog
around during the night.

Used the CONSShort and ShortBlend as the starting point for most
of the grids - though did use the WPC guidance for the QPF. While
we did not deviate much with the temperatures and dewpoints did
adjust PoPs higher for much of the flood watch time frame.

.LONG TERM...(Monday through Saturday)
Issued at 304 PM EDT SAT SEP 22 2018

Longwave troughing will be the topic for the extended portion of the
forecast. This troughing will begin to deepen across Central Canada
at the start of the period, with much of the U.S. quickly becoming
involved within the troughing pattern to some degree, especially as
high pressure ridging sits off both the West and Southeast coasts.
Kentucky will find itself in the southwest to northeast flow of this
upper level troughing, with the upper level ridge located to our
southeast. This will result in return S to SW flow across the region
at the start of the period Monday, and continuing through at least
mid week as the upper level pattern slowly transitions eastward.
Several shortwaves will pass through this pattern as well,
correlating to low pressure centers at the surface. These low
pressure centers will also have cold fronts that will extend to the
southeast. The first of these fronts is expected to move across
Kentucky Wednesday into Wednesday evening. Winds will increase from
the south ahead of the front and then become more northerly just
after the frontal passage. The axis of the trough will move across
the Ohio Valley Thursday night into Friday morning with a surface
low pressure system pulling another reinforcing cold front across
the region during this time as well. Behind this cold front and
trough axis, we will find ourselves in dampening northwest flow, as
a ridge begins to build back in from the south.

With the combination of southerly flow through midweek, multiple
upper level waves, and surface frontal features for the second half
of the week, expect precip chances to continue through much of the
forecast. Best rain chances will be Monday through Wednesday
evening, lessoning after the passage of the first cold front. Low
end chances will then remain in place through Friday, at which point
the drier airmass moving behind the secondary cold front will cut
off any remaining precip chances. While instability is not great,
the presence of two fairly progressive fronts was enough to keep
some slight chance thunder mention during much of the week,
especially during the daytime hours. High temperatures will be near
seasonable normals through much of the period (mid 70s). The
exception will be Tuesday, when strong southerly flow ahead of the
first cold front will help boost temperatures into the low 80s
across the CWA. Overnight lows, however, will remain above normal,
as ongoing cloud cover will keep us insulated and prevent
radiational cooling. Temperatures will cool behind the cold front on
Friday, but will begin to rise again heading into the weekend as the
ridge builds in from the south.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 150 PM EDT SAT SEP 22 2018

A surface cold front across the area will keep showers and
potential thunderstorms in the forecast through the first part of
the evening. A brief lull in the shower activity will be possible
for a time this evening, before increasing in areal coverage once
again towards dawn. Consequently, any increase in ceilings this
evening will fall once again late staying low into Sunday
morning. Winds will average around 5 kts out of the northeast
through the period.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 10 PM EDT this evening through Sunday
evening for KYZ044-050>052-058>060-068-069-079-080-104-106>120.

&&

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...JMW
AVIATION...GREIF
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