Area Forecast Discussion
Issued by NWS Wilmington, OH

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414
FXUS61 KILN 210200
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
1000 PM EDT Tue Aug 20 2019

.SYNOPSIS...
Several mid/upper level disturbances will move east through the
region through Thursday, with a slow-moving surface frontal
boundary drifting south during this time period. With seasonably
warm and humid conditions persisting through Thursday night,
periods of scattered showers and storms will be possible before
drier conditions filter in area-wide for the upcoming weekend.
Slightly below normal temperatures are expected for this weekend
with generally drier and sunnier conditions. A few isolated
storms may be possible by late Sunday afternoon.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Subsidence has taken hold of the ILN CWA behind the widespread
convective activity this afternoon, with the entire forecast
area currently clear of any precipitation. In fact, much of the
CWA is clear of any low clouds. Attention overnight will turn to
a shortwave currently moving eastward along the IN/MI border,
which at the very least appears likely to produce an increase in
clouds, as satellite imagery currently supports. Earlier
NAM/GFS projections of more widespread precipitation overnight
appear unlikely to occur, but even recent HRRR runs do suggest
some scattered showers in the northern half of the forecast
area, so some PoPs will be kept in overnight.

Current conditions and recent RAP/HRRR runs also support lower
temperatures this evening, especially with the clearing that
should be observed for the first segment of the overnight
period. Min temps were lowered by a couple degrees, with values
now expected to reach the middle to upper 60s. This is still
fairly warm, and the surface Tds in the upper 60s to around 70
would suggest that temperatures will not be able to fall too
much further than that. The possibility of fog is also worth
mentioning, but for now it appears that in a general sense, this
should be limited to MVFR-type visibilities.

Previous discussion >
A corridor of isolated to scattered thunderstorms have
developed in a moderately to highly unstable environment
entrenched across the heart of the ILN FA. This activity
continues to blossom out ahead of a slowly-decaying MCS with
attendant MCV noted on mosaic radar further to the north/west in
north-central IL.

For the rest of the afternoon, the corridor of scattered storms
currently approximately coincident with the I-75 corridor will
continue to drift east-northeast as additional isolated to
scattered activity develops ahead of the decaying complex
tracking south-southeast through central/southern Indiana. While
the MCS-generated convection is generally moving into a
favorably unstable environment characterized by MLCAPE in excess
of 2500j/kg and DCAPE of 1000-1200j/kg, the leading edge
continues to push further away from the MCV itself --
essentially outrunning the source that has kept it going for
this long. Nevertheless, this activity is likely to trend a bit
further south of southeast through mid/late afternoon -- likely
grazing and impacting only the Tri-State area and points
south/west of this particular area. Elsewhere, any isolated to
scattered activity will be more pulsy/airmass-driven opposed to
along the leading edge of a cohesive line/MCS. It is the pulsy
type activity that will likely pose the greatest strong/damaging
wind risk through early evening -- especially coincident with an
environment that will support downward acceleration of healthier
cores. Even with this said -- the highly unstable environment,
with good instability aloft, will also support instances of
large hail with the better/stronger cores.

The best coverage of storms will gradually shift from western
OH/eastern IN/northern KY from mid-afternoon through central OH
and northeast KY by early this evening. There seems to be
fairly good agreement in the short-term hi-res CAMs showing a
downtick in convection near/past sunset as the environment
becomes worked over and subsidence behind the main MCS
overspreads the ILN FA. Feel pretty confident in a trend toward
drier conditions by/past sunset this evening, with just a few
isolated showers possible past this time period as some midlevel
energy continues to propagate through the mean northwest flow in
the area. However, as previously mentioned, subsidence behind
the main MCS structure diving south-southwest through central
KY could be enough to stifle additional isolated shower activity
further north in an environment that will be fairly used up by
late evening into the overnight.

Highs for today have reached into the lower 90s but have likely
already plateaued due to the overspreading of
clouds/precipitation through the remainder of the local area
over the next several hours.

Some light fog will be possible late overnight with the nearly
saturated low level environment. However, the pressure gradient
will not completely relax -- lending itself to some uncertainty
in exactly where and how widespread any fog development will be.
Therefore, have not included in the official fcst although
certainly observational trends will be monitored closely to see
if this may eventually be warranted.

Lows tonight will bottom out in the upper 60s and lower 70s
area-wide.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
After any fog/stratus lifts/dissipates by late morning on
Wednesday, anticipate some diurnally-enhanced Cu to develop in
the region.

Although the frontal boundary will still be stretched in an E-W
fashion across the northern Ohio Valley on Wednesday, the
absence of any focused mid/upper level disturbance and/or source
for forcing is likely to keep an diurnally-driven activity to
mainly isolated in nature. The approach of a disturbance by late
evening may help spread some higher chance PoPs into the far
western ILN FA by late evening into the overnight hours --
especially as we near the end of the short term period by
Thursday morning. However, with a relatively strong cap in
place, anticipate that coverage will be far less than is the
case today.

Scattered showers and isolated thunderstorms will be on the
increase from the west towards sunrise Thursday as more S/W
energy ejects east through west-central and central Ohio Valley.

Highs on Wednesday will again top out around 90 degrees near the
Ohio River and mainly mid to upper 80s near/north of the I-70
corridor. Heat indices south of the I-70 corridor will again be
in the mid/upper 90s. Lows Wednesday night will fall into the
mid/upper 60s in the north to lower 70s south of the Ohio River.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Period begins with a cold front around the Ohio River. The front
will provide convergence and lift in the southern part of the fa,
giving the best PoPs around and south of the Ohio River. Went will
likely PoPs in the far south.

The front will continue to sag south Thursday night into Friday.
This will keep chance PoPs in the region for Friday.

By Saturday, high pressure will be settling in across the Great
Lakes. This will bring cooler and drier conditions.

On Sunday, an inverted trof will bring increasing humidity back into
the region along with a chance of thunderstorms to northern Kentucky
and the Scioto Valley.

Thunderstorm chances will increase Monday and Tuesday as
heat and instability increases.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Chances for thunderstorms this evening have diminished, leaving
just a few showers left in the area. The main concern overnight
will be the development of MVFR visibilities and MVFR/IFR
ceilings. The lowered ceilings appear most likely to develop at
KDAY (where IFR is quite possible) and KILN/KCMH/KLCK (where
MVFR is most likely). Some visibility restrictions are possible
at all TAF sites, though IFR visibilities appear generally
unlikely as of now.

Any visibility or ceiling restrictions should improve by 15Z,
with quiet conditions expected heading into the afternoon, and
WSW winds generally at or below 10 knots. A chance of pop-up
showers and storms is in the forecast for late afternoon, but
this will be handled with a VCSH for now, as storm coverage
should be fairly light.

OUTLOOK...Thunderstorms will remain possible at times through
Friday afternoon.

&&

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

&&

$$
SYNOPSIS...KC
NEAR TERM...KC/Hatzos
SHORT TERM...KC
LONG TERM...Sites
AVIATION...Hatzos



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