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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 191751
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
151 PM EDT Tue Sep 19 2017

.SYNOPSIS...
A weak upper level disturbance will move through the area,
offering a chance of showers and thunderstorms today into
Wednesday. Drier conditions are expected for the end of the week
into the weekend as upper level ridging builds into the Ohio
Valley. Above normal temperatures will continue into the
upcoming weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Showers and thunderstorms continue to push in from the east this
morning with PWATs around 1.70" (near max observed values for
this time of year). This area of showers and thunderstorms is
thanks to a shortwave pushing east through the region this
morning. Overall, high res guidance shows a weakening trend of
the complex this afternoon as LLJ convergence weakens and
vorticity advection wanes. Have made minor adjustments to the
forecast this morning due to current trends, but overall
thinking remains unchanged. New zones already out.

Prev Discussion->
Showers and thunderstorms have developed across portions of
IL and IN ahead of a mid level shortwave over the Mid MS VLY.
As this s/w moves east into the Ohio Valley scattered convection
will develop across ILN/s FA. Marginal instability develops
durg the day, so embedded thunderstorms will will also be
possible, mainly during the late morning into this afternoon.
The best coverage of showers and embedded thunderstorms will
occur across the western counties. Precipitable water values
increase with values up to 1.75 inches this afternoon. This high
pw is close to record values for this time of year. Therefore,
locally heavy rain will be possible in storms. Although clouds
and pcpn will mute temperatures some today, warm conditions are
expected to continue with highs from the upper 70s northwest to
the lower 80s southeast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
As mid level shortwave weakens and instability is lost expect to
see showers and embedded thunderstorms end early this evening.
Expect some decrease in clouds with partly cloudy skies
overnight. Light winds, low level moisture should lead to the
development of patchy fog overnight. Expect lows in the lower
and middle 60s.

A few showers and perhaps a thunderstorm will be possible
across the eastern counties early Wednesday as the weak s/w
departs the area. Otherwise, mid level ridge builds across the
west. This ridge will offer dry weather conditions and warm
temperatures. Expect highs on Wednesday 7 to 10 degrees above
normal, and generally in the lower and middle 80s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
High pressure at the surface and aloft will dominate the weather
through the period. Dry air and subsidence in the circulation around
the high should keep any precipitation from occurring, and cloud
cover will probably be lower than normal as well, suggesting ample
sunshine.

Geopotential heights will be well above average for late September.
Models indicate a 5900 meter 500 mb high lifting gradually across
the Ohio Valley to the Great Lakes. This warm regime will allow high
temperatures to reach the mid 80s, about 10 degrees above normal.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Mid level shortwave continues to slowly push east across the
TAF sites this afternoon and can clearly be seen on water vapor.
As the shortwave has slowly weakened this afternoon and lapse
rates remain pitiful lightning has quickly decreased in
coverage. Therefore have gone ahead and pulled thunder from the
TAF sites even though an isolated strike can`t be ruled out.
This evening the shortwave will slowly exit east with showers
coming to an end from west to east.

Overnight into Wednesday morning winds will quickly decouple
thanks to the weak pressure gradient and with dewpoint
depressions close to zero degrees fog looks likely. The main
catch remains how much leftover cloud debris will be across the
area. Overall have trended TAFs downward with visibilities and
also brought in some cigs as well. Latest HRRR and NAM is also
hinting at some MVFR/ IFR ceilings forming overnight which
could delay fog formation as well. For now confidence is higher
in fog formation compared to MVFR/ IFR ceiling formation.
During the day Wednesday some weak shower and thunderstorm
formation will be possible, but given that the TAF sites are on
the back side of the shortwave have kept mention of
precipitation out.

OUTLOOK...No significant weather is expected at this time.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...Haines/AR
NEAR TERM...Haines/AR
SHORT TERM...AR
LONG TERM...Coniglio
AVIATION...Haines