Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 220148

Area Forecast Discussion
National Weather Service Wilmington OH
948 PM EDT Fri Jul 21 2017

Multiple disturbances are expected to bring several rounds of
showers and thunderstorms to the region through the weekend and
into early Monday. High pressure and dry conditions are then
expected for Tuesday. More disturbances in northwesterly flow
aloft will cross the region later in the week.


A very humid air mass remains in place over the ILN CWA, with
the 00Z KILN sounding indicating an unstable and uncapped
environment. Forcing has been the missing factor through most of
the day, though a few isolated storm clusters developed near
Cincinnati, and a weak boundary (part of a tailing boundary from
an earlier MCV) is now starting to ignite near Wilmington.
Nonetheless, with overall support for organized ascent rather
weak, and no shear to speak of, activity through the first half
of the overnight is not expected to be more than intermittently
strong (and unlikely to be severe).

A much different scenario is expected for the second half of the
overnight period, as an environment much more favorable for
organized storms gradually advects to the ESE out of northern
Illinois. The thermodynamic environment over the ILN CWA (and
downstream of existing convection) will be entering its usual
min, which may lead to some storms becoming elevated with time,
as indicated by RAP/HRRR soundings. What these storms will bring
is their own source of forcing (low level convergence ahead of
another developing MCV) and shear (increasing 30-35 knot
westerly 850mb flow). These factors should help the storms stay
strong to severe, at least for portions of the line/MCS/cluster,
even as the storms make it into the ILN CWA somewhere in the
3AM-6AM time frame. Current storm trajectories, storm-level
flow, and recent HRRR runs would suggest the greatest threat for
strong storms will be in the northern third of the forecast
area. Nonetheless, eventual propagation toward instability will
likely lead to more of the area being impacted in some way. PoPs
have been increased and re-focused in terms of timing and
placement, based on this latest forecast information.

Finally, added some fog to the forecast for the areas where
heavy rains occurred from Cincinnati southeastward.

Previous discussion >
Apparent temperatures were expected to remain
at or over 100 in the southwest, which had me extend the current
advisory into the overnight hours as the eastern portion of it
drops off later today.

Upstream thunderstorm complex west of Indianapolis and a shower
complex underneath the MCV northeast of Indy will work into the
CWA later this afternoon into this evening. Expect convection to
be possible almost anywhere this evening but with a higher
propensity southwest of a Richmond/Lebanon/Georgetown line.

Overnight should see convection from this evening waning, but
another upper level disturbance will ride southeast in the mean
flow and cross northern Ohio. Storms from this will primarily
affect the I-70 corridor and northward, with isolated activity
possible elsewhere late overnight.

Confidence in the occurrence and/or placement of these storm
clusters is low. Forecast will be dynamically updated as storms
fire and a better timing and areal extent of them are able to be
extrapolated in both time and space. With this being said,
forecast is probably too low on pops overnight in the northern
CWA where it was limited to chance category.


Saturday had me bring another tier of counties into the heat
advisory fold as unusually warm dewpoints solidly in the middle
70s combine with temperatures in the low 90s to push apparent
temperatures over the 100 degree mark.

Storms that are present in the morning should be focused north
of and along the I-70 corridor, but a few models are indicating
some isolated activity popping south of it just before daybreak.

The outflow boundary that lays out along the I-70 corridor later
in the day is expected to be a focus for a second round of
development, given an added boost by a continued feed of moist
and unstable air on southerly winds. Storms will fire along a
w-e oriented line and then move south in the evening.

Any storm in the next few days will have a higher potential for
damaging winds and especially very heavy rainfall. The tornado
and large hail threat appear to be negligible at this moment in

Storms will weaken and diminish as they move south to the Ohio
River on Saturday night. Dewpoints will remain in the middle 70s
until the airmass changes beyond the short term period.


A weak trof/boundary is forecast to push through the region on
Sunday. This feature may be entering our far eastern/southeast
zones by peak heating which would bring the highest PoPs to these
locations. All in all, just have slight chance/chance of
showers/storms. SPC has a slight risk for severe storms. There could
be an isolated severe during the afternoon due to diurnal heating.

For the period Sunday night into Monday night, mid level trough will
dig southeast across the Great Lakes/eastern Canada. As this occurs,
a cold front will move slowly southeast through our region. With the
lack of strong low level forcing and upper level support, the
chances for showers/storms appears low and should affect our
eastern/southern zones in the afternoon on Monday. Skies should
become at least partly cloudy Monday night as high pressure builds
into the region from the north with a drying and stabilizing air

High pressure should remain over the region through at least Tuesday
into Tuesday night with dry weather expected.

As the high moves east on Wednesday, return flow and increasing
moisture may lead to a small chance of showers and thunderstorms.

Models indicate that the next frontal boundary to affect our region
will be during the Thursday/Friday time frame. Differences are seen
in the timing, so a broad brush forecast has been used with a chance
of showers and thunderstorms.

Temperatures will cool back down to more July normals Tuesday
through Friday.


While VFR conditions will prevail through the evening, an area
of thunderstorms will move through the Cincinnati area over the
next hour or two, possibly bringing MVFR/IFR TSRA conditions to
the CVG/LUK TAF sites. Some MVFR visibilities are possible with
an area of rain moving into CMH/LCK as well.

Later in the overnight period, a larger complex of thunderstorms
is expected to move into the region, affecting the northern four
TAF sites near daybreak. These storms have now been specifically
included in the TAFs, and future forecasts may need to forecast
further reduced conditions (lower ceilings / higher winds) with
the storms. It is most likely that these storms will remain
north of Cincinnati. Outside of the storms, some MVFR
visibilities are also possible at the Columbus airports.

After a break in the activity through late morning and early
afternoon, additional thunderstorm development will be possible
going into the afternoon and evening. Southwest winds will
increase to around 10-15 knots.

OUTLOOK...Thunderstorms will be possible again from Saturday
night through Sunday, and then again on Wednesday.


OH...Heat Advisory from 1 PM to 7 PM EDT Saturday for OHZ070-071.
     Heat Advisory until 7 PM EDT Saturday for OHZ077-078.
KY...Heat Advisory until 7 PM EDT Saturday for KYZ089>096.
IN...Heat Advisory from 1 PM to 7 PM EDT Saturday for INZ066.
     Heat Advisory until 7 PM EDT Saturday for INZ073>075-080.


NEAR TERM...Franks/Hatzos
LONG TERM...Hickman
AVIATION...Hatzos is the U.S. government's official web portal to all federal, state and local government web resources and services.