Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 230803

National Weather Service Jackson KY
403 AM EDT Wed Aug 23 2017

.SHORT TERM...(Today through Thursday)
Issued at 358 AM EDT WED AUG 23 2017

A cold front is currently tracking eastward across Kentucky. Based
on latest IR imagery, there is a defined edge to the cloud cover
along and ahead of the frontal boundary verses the drying/clear
skies behind. Most pre-frontal precip has now moved out of the
CWA, with just a few lingering showers right along the VA border.
These showers should continue to exit over the next couple of
hours. The cold front should make it through the CWA and exit just
to our SE by dawn or just thereafter.

In the wake of the cold front, a large area of high pressure will
begin moving in from our northwest, encompassing much of the
north-central Conus. Meanwhile, aloft, a large upper level low
over eastern Quebec will result in longwave troughing across much
of the eastern Conus, including the Ohio Valley. This will produce
deep NW flow across the region, pulling in a cooler Canadian airmass.
Our position to the east of the surface high will promote
northerly flow at the surface, with NW flow aloft. All in all,
this will do two things: Promote dry (much less humid) conditions
across the region, as well as below normal temperatures. Highs
today will be in the upper 70s across much of the CWA with very
little humidity.

This pattern will remain in place through the rest of the short
term portion of the forecast. Radiational cooling and continued
weak northerly flow overnight will allow temps to drop into the
50s for lows, with lowest temps in the valleys. A near-surface
inversion will also set up overnight, which will trap lingering
moisture (generally in the valleys) and promote valley fog overnight.
Once fog lifts and dissipates Thursday, similar conditions to
today will be in place. However, the northerly flow will actually
intensify a bit, so temps on Thursday will only reach the mid and
upper 70s across the CWA.

.LONG TERM...(Thursday night through Tuesday)
Issued at 403 AM EDT WED AUG 23 2017

The long wave pattern will be amplifying through early next week,
as ridging sharpens up west of the Rockies, while troughing is
found across the eastern half of the CONUS. The model agreement is
decent through the first half of the weekend, but confidence then
decreases into early next week, as questions revolve around the
eventual outcome of the tropical system Harvey. The ECMWF has
been slower to eject this feature out of the western Gulf, while
the operational GFS has been more progressive. Most of the GFS
ensemble members are slower as well, so did favor this solution a
bit more than the blended guidance reflected into early next week.

Drier and cooler weather will prevail across eastern Kentucky
through Saturday, as high pressure controls to our north. An
inverted trough will then nose in from the southwest by Sunday and
into early next week, bringing a diurnal increase in POPs, but did
stay just a bit under the blended guidance numbers.

Temperatures will average below normal through the period, with
highs mainly in the mid to upper 70s, with lows in the mid to
upper 50s.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)

A cold front is continuing southeast, and will be crossing eastern
Kentucky through the overnight. Pre-frontal convection is now
confined to the far SE CWA along the VA border and will continue
exiting SE of the state over the next few hours. As we lose
instability, expect any remaining convection to be in the form of
rain. There is some residual low clouds and fog across some of
the TAF sites in the immediate aftermath of the precip, with
conditions ranging from VFR to VLIFR across eastern Kentucky.
However, strong dry air advection is in place, so do not expect
these cigs or fog to persist more than a couple of hours. That
being said, this will be something to monitor in case further
updates need to be made to keep it in for a longer duration.
Regardless, by daybreak tomorrow, high pressure will be in full
swing with VFR conditions in play through the remainder of the TAF
period. Winds will be light and variable, and a few fair weather
diurnal CU (between 4 and 6k) will be possible during the
afternoon hours.

A cold front is swinging south across eastern Kentucky tonight
with a period of showers and thunderstorms. The convection will
bring reductions in visibility and ceilings through midnight. As
the front passes later tonight, some lower cigs could develop late
bringing ceilings back into the MVFR category and possibly even
IFR late. Look for the low clouds to dissipate by midday on
Wednesday. VFR conditions then follow for quite some time. Winds
will be light and variable through the period, outside of any
storms this evening.




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