Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 191039

Area Forecast Discussion
National Weather Service Wilmington OH
639 AM EDT Sat Aug 19 2017

A few showers and thunderstorms will be possible today as a
weather system shifts through the Great Lakes. Skies will clear
tonight as strong high pressure builds into the Ohio Valley,
bringing several days of quiet weather. Temperatures will remain
seasonable for mid August with highs in the 80s and lows in the
60s. A strong cold front will shift through the area on Tuesday
evening with more showers and storms, before a much cooler and
drier airmass moves in for the middle and end of next week.


Spent a great deal of time on today`s forecast given potential
rain/thunderstorm chances and less-than-desired confidence on
how things will evolve.

At mid/upper level shortwave trough was crossing
Lake Michigan with seasonably strong southwesterly mid level
flow downstream over the Ohio Valley. 50-60m height falls
/500mb/ were accompanying the trough and an area of
thunderstorms had recently developed immediately downstream of
the strongest PVA with the wave across northern Indiana with a
trajectory towards northwest Ohio. Slowly thickening cirrus was
spreading across the ILN forecast area, with mid cloud back
along the mid-level trough axis.

Using an amalgam of the most recent high resolution and
convective allowing guidance and expected path of strongest
height falls and synotpic forcing with the shortwave trough,
expect area of storms over northern Indiana to track mainly east
and perhaps brush far northern counties through sunrise hours as
it weakens. Further south, modest low-mid level warm advection
and moisture transport will continue to support a few showers
from southern/central Indiana...and these should move across
southeast Indiana/southwest Ohio in the hours just after sunrise
with weakening toward mid-late morning. Thunder will be
possible with this activity owing to weak elevated instability,
but expect it to be isolated.

By early afternoon, main shortwave energy will be pushing
through northeast Ohio and pulling away from area. With lack of
a respectable surface reflection of this system, boundary layer
convergence will be hard to come by, but what semblance of a
cold frontal structure that does eventually organize will focus
its boundary layer convergence over central Ohio around
17Z...sinking slowly south/east through the afternoon. The
result of this forcing should be a slowly organizing band of
sct/bkn storms feasting on peak diurnal destabilization /MUCAPE
around 1250 J/kg/ amidst modest effective shear /25-30kt/ which
support some brief storm organization and severity. Expect
highest threat area to be Scioto River Valley of central/south-
central Ohio where a few gusty storms are likely before
instability quickly is shunted south/east as the deeper
northwesterly flow spreads in as the wave departs. Will continue
to mention a few strong/severe storm possibilities in central
Ohio mainly between noon and 4 PM which lines up well with new
SWODY1 with likely a better focus of marginal severe threat east
of the ILN area once storms exit and become a little better
organized. There is considerable uncertainty how far west any
afternoon development will occur. It`s possible some isolated
updrafts may form as far west as ILN/CVG/DAY immediately
along/ahead of the mid level trough axis ~18z, but convective
allowing guidance is underwhelming and erratic on the likelihood
of meaningful updrafts that far west. Overall, highest rain
chances in central Ohio during the early-mid afternoon with much
less chance further south/west.


This will be a period of relatively quiet weather as the wave
from this afternoon shifts rapidly east bringing an end to any
early evening shower and thunderstorm threat. Should see clouds
dissipate quickly as good subsidence moves in.

Perhaps a little fog later tonight especially in the valleys as
good radiational cooling signature develops as 1020mb surface
high moves across Ohio with light flow and residual 60s

Sunday to feature plenty of sun per forecast soundings from
19.00Z NAM/GFS. Most recent NAM runs however have been a little
more robust on low level moisture suggesting some deeper cumulus
is possible in the afternoon. But either way there should be
ample sunshine with highs well into the 80s on light winds.

Weak shortwave energy deamplifying as it crosses the Great Lakes
Sunday night shouldn`t have much of an impact on an expected
clear/mostly clear night.

During this entire period, a bias-corrected MOS blend with minor
adjustments should perform quite well given rather
quiet/unchanging airmass, and this yields highs slightly above
normal and lows around normal.


Models remain in good agreement showing a broad area of surface
high pressure centered over the Mid-Atlantic region with its
influence stretching westward into the eastern Ohio Valley on
Monday. With the displacement of the high from the immediate
area and increasing low level warmth and moisture, a very
isolated afternoon shower/storm cannot be completely ruled out
Monday -- particularly across the northwestern third or so of
the FA. This being said, even with sufficient instability, there
is not any notable forcing mechanism to initiate such activity
(either at the surface or aloft), so maintained a dry fcst for

The main item of interest for Monday will be the sky condition for
eclipse viewing. In addition to development of an afternoon Cu
field, do think there will be some thin cirrus streaming into
western parts of the area by Monday afternoon. There continues to be
some model variability on both the extent and thickness of such
cirrus, but anticipate it to be fairly thin in nature given current

Monday will likely be the warmest day of the week with lack of
widespread dense cloud cover and the nudging of midlevel ridging
into the Ohio Valley (particularly evident on ECMWF solutions).
Highs in the upper 80s to around 90 degrees are expected area-wide.

Past Monday afternoon, attention will turn to the next system that
will impact the area on Tuesday. Model solutions continue to be in
remarkable agreement with the broad-scale features of Tuesday/s
system, including the general timing. 00Z solutions came in a bit
faster than previous runs, showing precipitation entering
northwestern parts of the FA as early as late Tuesday morning. This
initial activity would be isolated to scattered in nature, but
expect fairly substantial destabilization in the pre-frontal
environment Tuesday afternoon and evening. Although wind profiles
will be nearly unidirectional (WSW at sfc to W aloft) in nature,
wind field magnitudes should be sufficient to support scattered to
widespread thunderstorm development ahead of and/or along the
advancing cold front. With this in mind, did maintain likely PoPs
Tuesday afternoon and evening, but shifted time frame ahead by
several hours. Pcpn should end from NNW to SSE very early Wednesday

The front will bring a big change in airmass to the region, with
amplified upper-level troughing situated across the eastern third of
the country by Wednesday. The coolest day of the week may end up
being Thursday as a disturbance rotates around the broader-scale
trough and unseasonably cool temperatures aloft filter into the
region. Would not be entirely surprised to see near-record cool
temperatures at some point late this week. However, some airmass
modification is anticipated for Friday into next weekend.


Elevated showers falling out of a 8-10kft altocumulus deck are
spreading across Indiana and western Ohio as of 11Z. While
perhaps hitting a TAF site with sprinkles or light showers
through about 14Z or so, these are not expected to have impact
and conditions should remain VFR as they pass. As the mid deck
begins to break up this afternoon, would expect a diurnally
forced cumulus layer especially in central Ohio where
convergence ahead of a weak cold front will be maximized. Still
expecting a few showers/isolated storms to develop around 17-19Z
in central Ohio which could impact the central Ohio terminals
with MVFR conditions. Still a great deal of uncertainty on any
updrafts further west/southwest along the front where
convergence is less but at peak heating. This would include
ILN/CVG/LUK but not enough confidence to put anything in these
terminals yet. Any showers should shift quickly east and leave
the area under diminishing clouds by late afternoon/evening.
Expect a clear night tonight with river valley fog for KLUK and
some light fog for central Ohio /LCK and CMH/ closer to the
center of the high pressure system where winds will be lightest.

OUTLOOK...Thunderstorms are likely on Tuesday into Tuesday




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