Flash Flood Warning 10, NWS Wilmington, OH

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
155 PM EDT Mon Jul 24 2023

.SYNOPSIS...
Temperatures will be heating up this week. A mid level
disturbance and weak surface low will generate showers and
thunderstorms this afternoon and evening. While a few afternoon
and evening storms cannot be ruled out later in the week, the
next better chance of showers and thunderstorms will hold off
Friday night and Saturday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Afternoon update following SPC Slight Risk 1630Z issuance...

Much of the area is now under a level 2 of 5 risk for severe
thunderstorms later this afternoon and into the evening hours.
Regional satellite analysis shows earlier thunderstorm activity
weakening with a suppressed cumulus field across much of
southwestern / southern Ohio. Across the I-70 corridor, cumulus
field is becoming more active as temperatures warm into the 80s.
The combination of the heating, rich low level moisture, and
6.5C lapse rates aloft, yield SBCAPE between 2500-3000 J/kg area
wide. Outside the earlier thunderstorm activity, DCAPE values
are over 1000 J/kg, indicating the potential for enhanced
thunderstorm downdrafts.

The specific timing and spacial coverage of thunderstorms is
still in question, however, confidence is increasing that much
of the area will experience thunderstorms today. Surface
convergence is increasing in western Ohio and east-central
Indiana, suggesting this is where thunderstorms are first going
to form between 2-4 pm. Ahead of an approaching shortwave, mean
flow (850-300mb) is primarily westerly, with the tendency to
become more northwesterly over the next few hours as the
shortwave nears. Initial storm motions support movement from
western Ohio into central Ohio with more organized thunderstorm
advancing southeastward into southwest Ohio and southern Ohio.
PoPs have been updated with this in mind.

Primary severe hazards are large hail and damaging wind, but
locally heavy rainfall is also a concern. While precipitable
water values are not overly high, the large pool of instability
over Indiana will provide the opportunity for multiple rounds
of thunderstorms over the same areas. At this time, the greatest
potential for this to occur is over portions of southeastern
Indiana, southwest Ohio, and portions of northern Kentucky south
of the tri-state.

Thunderstorm activity gradually shifts south and east out of
the area between midnight and 2 am. Calm winds and lingering low
level moisture support fog development overnight, especially in
the geographically foggier areas.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Trough axis shifts east of the area for Tuesday, with the
exiting shortwave providing thunderstorms chances to the east of
the region. This setup results in less favorable conditions for
showers and thunderstorms across the area, however, can't rule
out a stray shower or thunderstorm late in the afternoon.
Temperatures warm effectively into the mid and upper 80s setting
the stage for warmer conditions later this week.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Big picture: expecting quite a pattern change through the
period as the majority of the past few weeks has been dominated
by large areas of low pressure centered in Canada, keeping much
of the Midwest and eastern CONUS under northwesterly flow with
normal to slightly below normal average temperatures. As we head
into the extended period, a broad area of high pressure across
the southern US pushes northeast toward the Ohio Valley region,
allowing for height rises and a notable increase in
heat/humidity with the hottest temperatures of the summer so far
likely to arrive by week's end.

Breaking it down a bit further...

By Wednesday morning, the heat dome of high pressure continues
to be located over the southwestern US. In the east, a
persistent upper level trough stemming down from the Hudson Bay
will still be in place, but with a shortwave digging through the
larger flow. This shortwave will have an associated surface low
pressure system near the Nebraska/ Iowa border. As the
attendant surface boundary/ quasi warm front lifts north, the
ILN CWA will end up in an area with south/southwesterly flow,
which is marked by a notable increase in theta-e and PWATs
(rising to between 1.8 to 2+ inches). This all translates to
temperatures in the low 90s and dew points in the upper 60s/low
70s.

Looking at this setup through a severe weather lens.. the more
robust vertical wind field/best forcing aloft seems to be near
northwestern Indiana and decay slightly as it travels to the
Ohio Valley. However, it does appear a LLJ will be rounding the
base of the shortwave and that areas of 30-35 kt sfc-500 bulk
shear move into our western counties /sometime/ between
Wednesday late afternoon/evening and Thursday early morning.
Obviously, depending on time of day, this could certainly
support organized convection. CAMs have not begun to really
resolve this time frame yet... will be interested to see what
kind of signal they produce, given the more forced convection
(compared to what we've been experiencing).

As the shortwave moves east of the region by Thursday, flow
aloft becomes more zonal in nature with the area of high
pressure to our southwest expanding northward into the Ohio
Valley. Height rises with this shift will keep hot and sticky
conditions in place for the remainder of the week and into the
first half of the weekend. Heat index values are likely to rise
into the upper 90s during the afternoons with muggy conditions.

As the CWA sits on the northern periphery of the ridge,
occasional shortwaves moving through the pattern will allow for
continued chances for rounds of showers and storms, which will
provide brief respites from the heat where rain falls.

Looking near the end of the period, there are some hints that
the larger pattern will begin to break up with an upper level
trough to our north sagging southeastward and driving more
northwesterly flow toward the Great Lakes region.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Confidence has increased in thunderstorm coverage this afternoon
and evening so have added TEMPO groups at area TAF sites.
Locally strong winds are expected in thunderstorm activity, with
these details provided through amendments as confidence
increases.

Clearing skies and light winds and a moist environment will
lead to fog development overnight. After morning fog clear, VFR
restrictions are forecast with winds less than 10 knots.

OUTLOOK...No significant weather expected.

&&

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

&&

SYNOPSIS...AR
NEAR TERM...McGinnis
SHORT TERM...McGinnis
LONG TERM...CA
AVIATION...McGinnis

Hazardous Weather Outlook
National Weather Service Wilmington OH
126 PM EDT Mon Jul 24 2023

INZ050-058-059-066-KYZ098-OHZ026-034-035-042>046-051>056-060>062-070-
251730-
Wayne-Fayette IN-Union IN-Franklin IN-Robertson-Hardin-Mercer-
Auglaize-Darke-Shelby-Logan-Union OH-Delaware-Miami-Champaign-Clark-
Madison-Franklin OH-Licking-Preble-Montgomery-Greene-Butler-
126 PM EDT Mon Jul 24 2023

This Hazardous Weather Outlook is for East Central Indiana,
Southeast Indiana, Northern Kentucky, Central Ohio, Southwest Ohio
and West Central Ohio.

.DAY ONE...This afternoon and tonight.

Thunderstorms are expected this afternoon and into this evening.
Some strong to severe storms are possible with damaging winds and
large hail the primary threats. Where multiple rounds of
thunderstorms occur, locally heavy rainfall may lead to a localized
flash flooding.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

A few strong to severe storms are possible Wednesday night.

The heat index will approach 100 on Wednesday, Thursday, and Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

INZ073>075-080-KYZ089>097-099-100-OHZ063>065-071>074-077>082-088-
251730-
Ripley-Dearborn-Ohio-Switzerland-Carroll-Gallatin-Boone-Kenton-
Campbell-Owen-Grant-Pendleton-Bracken-Mason-Lewis-Fayette OH-
Pickaway-Fairfield-Warren-Clinton-Ross-Hocking-Hamilton-Clermont-
Brown-Highland-Adams-Pike-Scioto-
126 PM EDT Mon Jul 24 2023

This Hazardous Weather Outlook is for Southeast Indiana, Northeast
Kentucky, Northern Kentucky, Central Ohio, South Central Ohio and
Southwest Ohio.

.DAY ONE...This afternoon and tonight.

Thunderstorms are expected this afternoon and into this evening.
Some strong to severe storms are possible with damaging winds and
large hail the primary threats. Where multiple rounds of
thunderstorms occur, locally heavy rainfall may lead to a localized
flash flooding.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

The heat index will approach 100 on Wednesday, Thursday, and Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

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