Area Forecast Discussion
Issued by NWS Jackson, KY

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712
FXUS63 KJKL 221348 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
948 AM EDT Sun Oct 22 2017

.UPDATE...
Issued at 948 AM EDT SUN OCT 22 2017

Now that fog has dissipated across the area, a zone update has
been issued to remove mention of fog from the forecast. The latest
update also included the current obs and trends.

UPDATE Issued at 718 AM EDT SUN OCT 22 2017

Seeing typical morning valley fog that will lift and dissipate by
mid morning. Higher clouds have thinned considerably but another
upstream band has yet to push through. Update required some minor
tweaks to the hourly grids for current trends and obs. No update
to the zone package at this time.

&&

.SHORT TERM...(Today through Monday)
Issued at 450 AM EDT SUN OCT 22 2017

Ridging aloft and at the surface will yield to a storm system
coming together over the Midwest and Ohio Valley region during the
next 36 to 48 hours. Previous model runs advertised digging,
amplifying northern stream energy lifting a southern stream
disturbance up out of the deep south and through the Ohio Valley
region with little if any phasing. Most recent runs however show
more phasing, resulting in a slightly slower overall evolution of
the storm system through our area. This has slowed the onset of
precipitation into our area just a bit, now more solidly into
the Monday morning time frame.

At the surface, low pressure will ride north out of the Gulf of
Mexico and into the Ohio Valley by Monday. Ample gulf moisture
will be pulled up into the area as this wave of low pressure
phases with an incoming cold frontal boundary which will be moving
into the mid Mississippi Valley later today. This will result in
a good soaking rain for our forecast area, with between one and
two inches possible across most of the area for the event.

Until then we have one last day of fair and pleasantly warm
weather as temperatures climb close to the 80 degree mark later
today. Trends suggest a little subsidence ahead of the approaching
system to our west, which may help scour our the thicker high
level cloud cover as the day progresses. While this may allow for
a little better heating it will be offset with lowering heights.
Thus afternoon highs may end up being very similar to
yesterday`s, possibly a degree or two warmer overall. Rainfall
will overspread the area from the southwest late tonight, reaching
our far southwestern zones during the predawn time frame, and the
heart of our CWA closer to dawn. For Monday, rain cooled highs
will only manage to climb into the mid and upper 60s.

.LONG TERM...(Monday night through Saturday)
Issued at 413 AM EDT SUN OCT 22 2017

The extended forecast begins on Monday night with a deepening longwave
trough digging southeast into the OH Valley. This, exhibiting a
rather amplified upper level pattern beginning the extended. A
closed 500MB low develops and lifts northeast out of the area as
precip associated with the low exits eastern Kentucky by Tuesday
morning. Given the lack of instability apparent in the GFS model
sounding, rainfall Monday night and through the day on Tuesday
will be more showery precip with no thunder expected.`As some of
the coldest air of the season so far advects into the region, a
secondary wave behind the front will push in from the northwest
with another chance of showers expected in northeast and eastern
Kentucky Tuesday night and into the day on Wednesday.

With coldest part of the fall like airmass reaching the area on
Wednesday, the 0 degree 850MB isotherm will dip into eastern
Kentucky. In fact. highs on Wednesday will barely make it out of the
40s for highs in some parts. With lows Thursday morning dipping
into the mid 30s and dew points dropping into the low 30s,
widespread frost will be an impact to vegetation.

The upper level pattern begins to shift to a more progressive flow
as brief ridging will keep eastern Kentucky dry for Thursday and
much of Friday. The pattern then begins to amplify again as a
second trough digs south as another front pushes southeast through
the OH Valley. At this point, the front seems to be lacking the
instability so will keep thunder out of the forecast at this point
as well. However, another good soaking rain looks to be on tap for
next weekend with another shot of cold air, possibly colder than
the last.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 718 AM EDT SUN OCT 22 2017

VFR conditions are expected through the forecast. However, CIGS
and VSBYS will begin to drop just beyond the end of the forecast
window, by around dawn as rain showers begin to overspread the
area. Still picking up our typical valley fog on the regional
satellite but nothing is affecting any of our terminals. High
clouds have thinned out considerably but another upstream band
has yet to push through. Light southeast winds along the
ridgetops will veer through the morning, becoming southerly and
increasing to around 10 kts.

&&

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

$$

UPDATE...AR
SHORT TERM...RAY
LONG TERM...SHALLENBERGER
AVIATION...RAY



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