Special Weather Statement, NWS Wilmington, OH

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
124 PM EDT Wed Aug 11 2021

.SYNOPSIS...
Hot and humid conditions continue through Friday along with periodic
chances for showers and thunderstorms. A cold front will move
through the area of Friday bringing cooler, drier air for the
weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The weather pattern today will feature very warm and humid
conditions that will lead to heat indicies in the 95-100 degree
range. The areas where heat indicies will be closer to 100 look
to primarily be more towards the Tri-state as dewpoints will be
a degree or two higher further west, and fewer debris clouds
currently exist in our southwestern. Meanwhile, ongoing
convection just north of the CWA is spreading a fair amount of
low-level clouds in portions of central and west-central Ohio,
which may keep the heat index closer to 95 during the peak of
daytime heating. Continued to handle the heat index values with
an SPS for today as criteria for a Heat Advisory will be
limited.

Alongside the excessive heat, the other main feature to be aware
of today will be a strengthening MCS that is currently moving
through north-central Illinois. Radar currently indicates winds
in excess of 60 mph for the northern part of the MCS, with a few
spots potentially in excess of 70 mph. The HRRR has begun to
pick up on this system, pushing the southern tier of this MCS
into our northern counties by the early to mid afternoon.
However, the latest 12z NAM 3K weakens this system substantially
by the time it pushes into Indiana, leaving little to no
precipitation for our counties. CAMs once again offer widely
varying solutions in this weakly forced environment - but this
system will be the main feature to monitor as we progress
through the late morning and early afternoon hours. If it holds
together, a number of our northern counties could end up
observing strong to severe straight-line winds. The time range
we would be most concerned about would be from roughly 2-7 PM.
And while hail cannot be completely ruled out, winds would be
the primary threat from this system. There is definitely no
shortage in the amount of instability today, and while there is
slightly better shear today from a southward digging trough, the
best shear continues to remain north of our CWA which may
partially hinder the organization/intensity of the MCS as it
approaches. Have updated the grids to reflect the better chance
for afternoon storms across our northern half of the fa.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
A broad mid and upper level trough will remain just north of the
area overnight tonight into Thursday. This results in lack of any
clear upper level forcing for precipitation. Current CAM guidance
suggests diurnal convection today is likely to die off during the
early evening resulting in dry conditions overnight. There is a
slight chance that outflow from left over diurnal thunderstorm
complexes could lead to a shower or two, but left the forecast
without chances of rain by late overnight. Forecast lows are in the
middle 70s.

Thursday will feature the same uncertainty as the past few days in
regards to precipitation and heat. One one hand, heat headlines may
be needed if there is no convection or convective debris are in the
area. But, there is once again the chance for showers and
thunderstorms in the afternoon due to a highly unstable atmosphere
being in place. Synoptically speaking, the best chance for storms
will likely be along and north of I-70 closer to the longwave upper
level trough. However, CAMS are suggesting the possibility of
thunderstorm complexes forming near the Ohio River Thursday
afternoon. Due to this uncertainty, have included at least slight
chance of showers/storms everywhere in the afternoon. Also, have
elected to hold off on heat headline issuance for now due to only
moderate probability of occurrence thanks to the possibility of
thunderstorms. Any storms that do form could be strong and pose a
damaging wind threat. Forecast high are in the lower to middle
90s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
An unsettled pattern will remain in place through Friday, with ample
heat and humidity coinciding with episodic chances for showers and
storms through Friday night before relief in the form of a cold
front moves through by this upcoming weekend.

Aloft, flow is largely zonal across the OH Vly for the start of the
period, with an elongated high stretched from near Bermuda to TN and
an unseasonably deep/strong longwave trof axis centered over south-
central Canada dipping into the upper Midwest/Great Lakes. Expect
that the aforementioned cold front /finally/ drifts south into the
Great Lakes/OH Vly regions Friday evening/night, signaling the end
to the stagnant/muggy/stormy pattern for the upcoming weekend before
more seasonable warmth and humidity once again gradually return
early next week.

Some of the more recent guidance has suggested a potential lull in
convective activity across the region Thursday night without a
midlevel impulse rippling through the midlevel flow during this
time. While this trend is encouraging, it should be taken with a
rather large grain of salt as many times these weak forcing/large
instby (even nocturnal) scenarios waffle back and forth many times
and are handled rather poorly even by the more-skilled hi-res short-
term guidance offered by the HRRR/RAP/ARW/NSSL-WRF, etc. These
environments so often times get modulated quite significantly by
small-scale features, such as outflows, MCVs, cold pools, etc. which
both increase or decrease the environment's capability of producing
widespread convection on a smaller temporal scale. By Friday, the
large-scale forcing, characterized by slightly stronger deep-layer
flow and increased LL convergence along the slowly-propagating
frontal boundary will provide the best chance for convection in a
widespread manner. There are still some model differences in the
timing of the boundary shifting south through the ILN FA, with some
guidance pointing more toward a Friday evening progression to/south
of the OH Rvr. Nevertheless, even without the details known at this
point, from an ingredients-based perspective and considering the
overall setup, do feel that strong to severe storms will be likely
Friday afternoon/evening, which could last into the nighttime,
depending on the timing of things. The large-scale ascent and decent
LL convergence will promote widespread convection amidst a highly
unstable environment. Will likely see the maintenance of 15% severe
probs for Day 3 by SPC, with damaging winds, large hail, and
torrential downpours/localized flooding being the primary threats.
Will continue mention in the HWO.

It should be mentioned, too, that any convective activity Friday
afternoon through early Friday night will be capable of
producing torrential rainfall rates and localized flooding.
There is the potential that one or more complexes of storms
produce a flooding threat that is more than just isolated in
nature should the propagation of such complex(es) result in
training or backbuilding of convection, but the details of such
potential will only come into focus as we get closer to the end
of the week.

High confidence continues in a return to more mild temperatures and
lower humidity for the latter part of Saturday through Monday with
dry conditions, especially north of the OH Rvr. A somewhat messy
midlevel flow pattern may set up early next week, with
weak/meandering midlevel lows/disturbances amidst a /very/ broad
midlevel pressure pattern. This suggests a return to diurnally-
driven pulse storm chances by Monday and/or Tuesday with near normal
temperatures and a return to slightly more humid conditions.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are likely to prevail through the taf period,
with the only exception being if a shower or storm were to move
over a taf site. For the rest of this afternoon, KDAY/KCMH/KLCK
would likely have the best chances at observing a passing shower
or storm, but uncertainty still remains high, so just left a
VCSH in through the evening. The forecast will trend drier for
tonight, which may even persist into much of Thursday based on
latest guidance.

Southwesterly winds will remain around 10-15 kts sustained today
with gusts near 20 kts. Winds will be very similar for Thursday
with no major change in direction or magnitude.

OUTLOOK... The threat for thunderstorms will continue through
Friday.

&&

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

&&

SYNOPSIS...Campbell
NEAR TERM...Clark
SHORT TERM...Campbell
LONG TERM...KC
AVIATION...Clark

Hazardous Weather Outlook
National Weather Service Wilmington OH
302 PM EDT Wed Aug 11 2021

INZ050-058-059-066-073>075-080-KYZ089>100-OHZ060>065-070>074-077>082-
088-121915-
Wayne-Fayette IN-Union IN-Franklin IN-Ripley-Dearborn-Ohio-
Switzerland-Carroll-Gallatin-Boone-Kenton-Campbell-Owen-Grant-
Pendleton-Bracken-Robertson-Mason-Lewis-Preble-Montgomery-Greene-
Fayette OH-Pickaway-Fairfield-Butler-Warren-Clinton-Ross-Hocking-
Hamilton-Clermont-Brown-Highland-Adams-Pike-Scioto-
302 PM EDT Wed Aug 11 2021

...HEAT ADVISORY IN EFFECT FROM NOON TO 8 PM EDT THURSDAY...

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

.DAY ONE...This afternoon and tonight.

Isolated strong storms are possible this afternoon and evening.
Storms will be capable of producing gusty winds and locally heavy
rainfall.

The heat index will reach between 95 and 100 this afternoon.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Strong to severe storms are possible Thursday and Friday with
damaging winds being the main threat. Locally heavy rain is also
possible with the strongest storms.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Heat Advisory.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

OHZ026-034-035-042>046-051>056-121915-
Hardin-Mercer-Auglaize-Darke-Shelby-Logan-Union OH-Delaware-Miami-
Champaign-Clark-Madison-Franklin OH-Licking-
302 PM EDT Wed Aug 11 2021

...HEAT ADVISORY IN EFFECT FROM NOON TO 8 PM EDT THURSDAY...

This Hazardous Weather Outlook is for Central Ohio and West Central
Ohio.

.DAY ONE...This afternoon and tonight.

A line of strong to severe thunderstorms are expected this afternoon
and evening. Damaging winds will be the primary threat with these
storms. Locally heavy rain is also expected.

The heat index will reach between 95 and 100 this afternoon.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Strong to severe storms are possible Thursday and Friday with
damaging winds being the main threat. Locally heavy rain is also
possible with the strongest storms.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Heat Advisory.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed for this afternoon into this
evening.

Special Weather Statement
National Weather Service Wilmington OH
1045 AM EDT Wed Aug 11 2021

INZ050-058-059-066-073>075-080-KYZ089>100-OHZ026-034-035-042>046-
051>056-060>065-070>074-077>082-088-120000-
Wayne-Fayette IN-Union IN-Franklin IN-Ripley-Dearborn-Ohio-
Switzerland-Carroll-Gallatin-Boone-Kenton-Campbell-Owen-Grant-
Pendleton-Bracken-Robertson-Mason-Lewis-Hardin-Mercer-Auglaize-
Darke-Shelby-Logan-Union OH-Delaware-Miami-Champaign-Clark-
Madison-Franklin OH-Licking-Preble-Montgomery-Greene-Fayette OH-
Pickaway-Fairfield-Butler-Warren-Clinton-Ross-Hocking-Hamilton-
Clermont-Brown-Highland-Adams-Pike-Scioto-
Including the cities of Richmond, Connersville, Liberty,
West College Corner, Brookville, Batesville, Milan, Versailles,
Lawrenceburg, Aurora, Rising Sun, Vevay, Carrollton, Warsaw,
Florence, Burlington, Oakbrook, Covington, Erlanger,
Independence, Newport, Alexandria, Owenton, Williamstown,
Crittenden, Dry Ridge, Falmouth, Butler, Augusta, Brooksville,
Mount Olivet, Maysville, Vanceburg, Tollesboro, Kenton, Ada,
Celina, Coldwater, Wapakoneta, St. Marys, Greenville, Sidney,
Bellefontaine, Marysville, Delaware, Troy, Piqua, Tipp City,
Urbana, Springfield, London, West Jefferson, Plain City,
Columbus, Newark, Eaton, Camden, Dayton, Kettering, Beavercreek,
Fairborn, Xenia, Washington Court House, Circleville, Lancaster,
Pickerington, Hamilton, Middletown, Fairfield, Oxford, Mason,
Lebanon, Springboro, Wilmington, Blanchester, Chillicothe, Logan,
Cincinnati, Milford, Georgetown, Mount Orab, Hillsboro,
Greenfield, West Union, Peebles, Waverly, Piketon, Portsmouth,
and Wheelersburg
1045 AM EDT Wed Aug 11 2021

A combination of hot temperatures and high humidity will likely
result in the heat index reaching between 95 and 100 this
afternoon into the early evening.

If you have to be outdoors, please take the necessary precautions
to protect yourself from heat related illnesses. Drink plenty of fluids,
stay in an air-conditioned room, stay out of the sun, and check up
on relatives and neighbors. Young children and pets should never be
left unattended in vehicles under any circumstances.

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE WILMINGTON OH
334 PM EDT WED AUG 11 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0330 PM     TSTM WND DMG     3 WSW ST. HENRY         40.41N 84.69W
08/11/2021                   MERCER             OH   EMERGENCY MNGR

            A TREE WAS BLOWN DOWN ON TOWNSHIP LINE ROAD.

&&

JOHNF

Special Weather Statement
National Weather Service Wilmington OH
352 PM EDT Wed Aug 11 2021

OHZ044-045-052-112015-
Champaign OH-Logan OH-Union OH-
352 PM EDT Wed Aug 11 2021

...STRONG THUNDERSTORMS WILL IMPACT PORTIONS OF NORTHERN CHAMPAIGN,
LOGAN COUNTIES IN WEST CENTRAL OHIO AND NORTHWESTERN UNION COUNTIES
IN CENTRAL OHIO THROUGH 415 PM EDT...

At 352 PM EDT, strong thunderstorms were reported along a line
extending from Bellefontaine to De Graff, moving east at 50 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Bellefontaine, Urbana, St. Paris, West Liberty, North Lewisburg, De
Graff, West Mansfield, Quincy, Rushsylvania, Woodstock, Valley Hi,
Zanesfield, Cable, Raymond, New Jerusalem, Broadway, Mcmorran, Kiser
Lake State Park, Millerstown and Pottersburg.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a sturdy building.

Residents in these areas should remain alert. If these storms become
stronger, then a warning may be needed.

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
central and west central Ohio.

To report hazardous weather conditions, go to our website at
weather.gov/iln and submit your report via social media, when you can
do so safely.

&&

LAT...LON 4023 8349 4016 8350 4010 8403 4040 8400
      4048 8352 4050 8351 4050 8327
TIME...MOT...LOC 1952Z 264DEG 42KT 4043 8375 4023 8397

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

Hatzos