Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 280807

National Weather Service Wilmington OH
407 AM EDT Wed Jul 28 2021

Humidity and storm chances commence late Wednesday and continue
into Thursday ahead of a cold front. Below normal temperatures
and low relative humidities arrive behind the cold front Friday
into the weekend.


Surface high pressure remains over the region this morning,
however, it slowly drifts southward throughout the day in
response to a weak front moving in from the north. Have
maintained the potential for scattered showers and thunderstorms
along and north of I-70.

Another hot day is in store. While some upper level clouds and
scattered cumulus are expected today, abundant sunshine favors
temperatures quickly rising into the upper 80s and lower 90s
this afternoon. Higher dewpoints advecting in from the west
present the potential for heat indices to reach the low to mid
90s area wide and perhaps mid to upper 90s across the broad tri-
state area.

Attention then shifts to the Great Lakes region where
thunderstorm development is anticipated late in the afternoon
and through the evening hours, potentially entering the local
area overnight through Thursday morning.


By this evening, a shortwave feature moving through the upper
Midwest will have initiated convection across parts of Wisconsin
and eastern Minnesota. Throughout the evening and early
overnight hours, the convection is expected to consolidate into
a severe mesoscale convective system resulting in widespread
wind damage potential for portions of southern Wisconsin and
southern Michigan. As the complex continues southeastward toward
the local forecast area, there is great uncertainty as to what
the intensity will be during the early morning hours. The
complex will likely be arriving to west-central/central Ohio
during the convective minimum hours due to temperatures cooling
through the overnight. However, forecast soundings still
indicate instability due to steeper mid-level lapse rates and
building surface moisture. Broad, mid-level ascent associated
with the shortwave and strong deep-layer shear will be co-
located with this complex so it is difficult to have high
confidence that it completely dissipates upon arrival. The
majority of the CAMs suggest a weakening scenario, but there are
too many factors supporting the complex to suggest there will
be no severe weather threat early Thursday morning. This
potential has been appropriately highlighted by a Day 1 Marginal
Risk and will continue to be mentioned in the HWO.

The following few hours after sunrise are critical to the both
the heat related threats and the severe weather threats for
Thursday afternoon and evening. As the thunderstorm complex
moves into the area, late morning heating and continued moisture
advection from the west results in rapid destabilization across
the Ohio Valley. Investigating the synoptic layout suggests the
shortwave trough has now moved off to the east with fast moving
northwesterly flow in its wake. At the surface, a low pressure
is expected somewhere in the eastern Great Lakes/northeast US
with a surface cold front stretched southwestward into the Ohio
Valley. Since the shortwave is now off to the east, the forcing
for new convection will be directly dependent on the progress of
the front through the developing instability. The forecast is
currently presented to show the morning thunderstorms weakening
enough to allow new thunderstorms to develop by early afternoon
along the I-70 corridor. These will then spread southward
through the southern half of the forecast area toward the Ohio
River by evening. While damaging winds will be the most likely
dominant threat during the late afternoon and early evening,
large hail and even a tornado or two are possible as storms
initially develop. This threat is currently characterized by an
SPC Slight Risk. It should be noted that western portions of the
area may end up with more instability, but due to the
displacement of the stronger ascent to the east, more scattered
storm coverage is possible. Much of this forecast is dependent
on forcing to be strong enough along the front.

As the initial wave of thunderstorms/rain/cloud cover moves
into the area Thursday morning, the exact location of this
activity will play a key role in how quickly temperatures warm.
If the activity is much less widespread or decays fairly
quickly, parts of the tri-state area may require a heat advisory
as dewpoints in the low to mid 70s are expected. This potential
remains noted in the HWO.


Will hang on to chance pops into Thursday night with the
highest pops across our south in the evening and then decreasing
overnight as the cold front moves through. Surface high
pressure and a cooler and drier airmass will settle into the
region behind the front on Friday. Northwest flow will persist
aloft and short wave energy dropping down through it over the
weekend will help develop a broader upper level trough over the
eastern US through early next week. An associated weak cold
front will move through the area over the weekend, leading to
some lower end chances for pcpn. Otherwise, expect dry
conditions through much of the long term period. Temperatures
will be below seasonal normals with afternoon highs mostly in
the upper 70s to lower 80s each day.


Only changes for the 06Z TAF were to limit the threat for VCTS
for the northern TAF sites due to low coverage. Otherwise, VFR
conditions will prevail this TAF period with just some
valley/shallow fog development over the next few hours. There
will be the potential for river valley fog at KLUK overnight. In
addition have some tempo fog mention in at KILN. Wednesday
afternoon and evening, there will be some cu and high clouds
possible. In addition KDAY, KCMH, and KLCK will also have the
potential for thunderstorm development. Have limited this
potential to VCSH for now due to low coverage and low confidence
of occurrence.

.OUTLOOK... Thunderstorms will be possible Thursday into
Thursday night. Wind gusts will be possible on Thursday.




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