Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 200520
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
120 AM EDT Thu Apr 20 2017

.UPDATE...
Issued at 1133 PM EDT WED APR 19 2017

The last of the showers and storms look like they are finally
winding down. Will hold onto some isolated POPs for another hour
or so matching the radar trends, with the rest of the night
looking quiet. Clouds are much less prevalent tonight, compared to
last several nights, so have played up the fog more, especially
with pockets of locally heavy rainfall having occurred earlier.
Lows will range from the mid 50s in the cooler spots, to around
60, where light southerly winds keep things a bit more mixed.
Updates have been sent.

UPDATE Issued at 755 PM EDT WED APR 19 2017

Mainly freshened up the hourly temperatures and dew points over
the next few hours, as localized storms have cooled off places,
including JKL. POPs were already in good shape, with a gradual
diminishment expected through midnight. Only made a few minor
adjustments to these based on the current radar trends.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 433 PM EDT WED APR 19 2017

Scattered showers and thunderstorms have fired across the area
this afternoon. These storms are not quick builders, the likely
result of slight height rises and relatively weak instability to
feed off of. Activity is expected to gradually die down through
the late afternoon and early evening as sunset approaches. We will
probably see some patchy fog develop through the overnight where
precipitation has fallen late this afternoon and/or this evening.
Added a mention of fog to the zones, particularly in the valleys.

Otherwise, focus turns to a cold front that will drop into the
region by late Thursday night into Friday. There is still
considerable uncertainty with the details of this system. The GFS
and NAM manage to take the boundary considerably further south
than the ECMWF. This lowers confidence a bit with respect to
sensible weather. Ramped up pops Thursday night as the front
approaches but stayed close to model blends and guidance.

For sensible weather, expect showers and thunderstorms to
gradually die off through sunset. Skies will partially clear
allowing for some reasonable radiative cooling. Preferred the
inherited cooler valley temps over the warmer blends and model
guidance for tonight. This will favor some patchy valley fog,
which might tend to become more dense at times where late
afternoon and evening precip occurs. Clouds will be on the
increase late Thursday afternoon and gradually brought pops back
into the picture late in the day. Showers and thunderstorms
increase in coverage Thursday night with the cold front dropping
into the area. Temperatures will climb to around 80 for much of
the area Thursday.

.LONG TERM...(Friday through Wednesday)
Issued at 433 PM EDT WED APR 19 2017

Overall, there is good model agreement during the period. At the
onset, a cold front will have entered KY from the northwest, and
will be draped across the southeastern CWA as of Friday morning. It
is expected to bring at least scattered showers and thunderstorms,
especially east of the front, along the southeastern CWA where moist
and warm southerly flow will still be occurring. The front will sag
just southeast of KY during the day Friday, and remain in close
enough proximity for an ongoing potential of precip on Friday,
including some continuing thunder chances near the TN and VA
borders. Loss of remaining instability overnight will cut off
thunder chances by Friday night.

Meanwhile, low pressure will be taking shape over the southern
plains on Friday as well. This will be in response to an upper level
wave (emanating from the upper low currently off the Pacific
Northwest coast) moving southeast toward that region. The low
pressure system will track eastward and draw the frontal boundary
back north as a warm front toward far southern KY Friday night and
Saturday. The GFS has remained further south with the eventual low
track since yesterday, and is similar to the ECMWF which has
remained nearly steady. This track takes the low near the KY/TN
border, resulting in a wet start to the weekend, with a temperature
contrast across the JKL forecast area. Rain is a good bet everywhere
on Saturday. Thunderstorms will also be possible near the passing
low, with surface based instability possible in far southern KY, and
elevated instability further north. Heavy rainfall could be a
concern, with 6 hour QPF values between 0.75 and 1 inch, and
locally higher amounts possible. Latest trends show highest rainfall
occurring along the far eastern KY border Sunday night. Significant
rain should then pull out with the departing low by Sunday, but some
light rain could linger. Ridging at all levels then builds in on
Sunday night and brings decreasing clouds, with fair weather lasting
through the rest of the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 120 AM EDT THU APR 20 2017

TAF sites are starting off the period VFR and should generally
remain that way through the TAF period. The caveat will be the
more valley sites could see fog, but right now will lean toward
LOZ for MVFR VIS potential and leave out at other sites. Outside
of TAF sites would think anywhere that saw convection and places
that saw showers would have the chance of seeing fog through mid
morning. While the convection this afternoon will be isolated in
a weakly forced environment will mention VCTS for all the TAF
sites. Winds will remain light out of the south to start the
period, but deeper mixing into a modest LLJ could provide gusts of
15 to 20 knots through the afternoon. The better gusts would
likely be in the Bluegrass and Lake Cumberland regions.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GEOGERIAN
SHORT TERM...RAY
LONG TERM...JMW
AVIATION...DJ



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