Special Weather Statement, NWS Indianapolis, IN

Area Forecast Discussion
National Weather Service Indianapolis IN
637 AM EDT Tue Aug 10 2021

...Updated Aviation Discussion...

.Short Term...(Today through Wednesday)
Issued at 256 AM EDT Tue Aug 10 2021

...HOT AND HUMID WITH CHANCES FOR STRONG TO SEVERE STORMS...

Today

Early this morning, an upper trough was moving through Lower
Michigan, with near zonal flow across central Indiana. Thunderstorms
were across northern Illinois into northern Indiana, moving east.
Additional convection was across southern Missouri.

During the day today, central Indiana will remain in near zonal flow
aloft. Large scale forcing should be weak, and 850mb winds diminish.
It appears that development of convection will likely depend on any
weak impulses in the upper flow or perhaps remnant outflow from
current convection to the north, if it can make it down here.

Forcing causing the convection in southern Missouri should move east
and keep that forcing south of the area.

Strong instability will build today with dewpoints in the mid to
upper 70s common during the afternoon. However, mid level
temperatures will be warm (10-11.5 C), which will provide some
capping. Precipitable water values will be near 2 inches.

With only weak forcing and some capping, will only go with chance
PoPs today. Given the strong instability, any storm that does
develop will have the possibility of becoming severe, with damaging
winds being the primary threat. Any storm could produce heavy rain.

It looks like there will be enough sunshine to push temperatures
into the upper 80s and lower 90s. Combined with the aforementioned
dewpoints, heat indices will be in the upper 90s to near 105
degrees. The highest dewpoints are expected in the Wabash Valley, so
will continue the Heat Advisory as is.

Tonight

Diurnal convection may continue into the evening. During the night,
850mb winds increase some. and some upper energy will be moving
through the near zonal flow aloft. These may be enough to generate
additional thunderstorms during the night. Instability will remain
high, so severe storms remain possible. Questions in the upper
energy timing and strength will keep PoPs in the chance category.

Wednesday

On Wednesday, any thunderstorm complex that may develop or lingering
scattered thunderstorms from tonight will be waning, perhaps leaving
behind some clouds. In the afternoon, mid level temperatures cool
some and an approaching upper jet could bring some forcing. Will
continue with chance PoPs on Wednesday. Once again, strong
instability could develop, especially if morning cloud cover is low.
Thus, severe storms will once again be possible.

Assuming there is no significant cloudiness Wednesday morning,
temperatures on Wednesday will be in the 90s most locations, with
heat indices topping out once again in the upper 90s to around 105.
However, given the uncertainties in cloud cover, will not issue an
advisory at this time.

&&

.Long Term...(Wednesday night through Monday)
Issued at 256 AM EDT Tue Aug 10 2021

By Wednesday night, dry weather looks to be in place for much of
central Indiana as the upper level jet and associated weak forcing is
mostly north of the forecast area.  Can't rule out an isolated
shower or storm across the far northern counties, but with little to
no flow aloft, don't expect any precipitation across the area. Much
of the same is expected for Thursday, although the 850mb jet does
look to be marginally stronger.  The big question will be if
temperatures warm enough to overcome the weak cap at 850mb with
temperatures between 22-24C across the forecast area.  Do think at
least a few stronger updrafts should break the cap and when they do,
steep lapse rates aloft result in 3500-4500 J/kg of CAPE which will
be more than enough for strong to possibly severe storms. Thursday
still looks to be the warmest day of the week with highs in the low
90s across the area.

With the loss of daytime heating, don't expect any additional
convection during the overnight hours barring an MCS moving in from
the northwest where the jet aloft remains strong. A seasonably
strong surface cold front then looks to pass through the area on
Friday bringing relief from the heat and another round of strong to
severe thunderstorms to the area.  High pressure then looks to build
across the area Saturday and Sunday with dry and cooler weather
expected. Going into early next week, isolated to scattered diurnal
convection is possible across the southern counties which where the
ridge and cap aloft looks to be weakest, but expect that the more
widespread convection will remain south of the forecast area where
the aforementioned surface front looks to have stalled.

&&

.Aviation...(12Z TAF Issuance)
Issued at 637 AM EDT Tue Aug 10 2021

IMPACTS:
- Scattered convection, mainly this afternoon and tonight
- Winds generally from 200-230 degrees at 9-14 kt

DISCUSSION:

VFR conditions are expected through the period outside of
convection.

Scattered convection will continue through the period, mainly this
afternoon and tonight. Based on latest radar trends, will include a
VC mention at the southern sites this morning. Otherwise, added VCTS
for the most likely time this afternoon, but left mention out for
tonight as confidence is lower as to what time it could occur. MVFR
and worse are possible with convection, including strong winds.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM this afternoon to 8 PM EDT this evening
for INZ021-028-029-035-043-044-051-060-067.

&&

Short Term...50
Long Term...White
Aviation...50

Hazardous Weather Outlook
National Weather Service Indianapolis IN
356 AM EDT Tue Aug 10 2021

INZ021-028>031-035>049-051>057-060>065-067>072-110800-
Carroll-Warren-Tippecanoe-Clinton-Howard-Fountain-Montgomery-Boone-
Tipton-Hamilton-Madison-Delaware-Randolph-Vermillion-Parke-Putnam-
Hendricks-Marion-Hancock-Henry-Vigo-Clay-Owen-Morgan-Johnson-Shelby-
Rush-Sullivan-Greene-Monroe-Brown-Bartholomew-Decatur-Knox-Daviess-
Martin-Lawrence-Jackson-Jennings-
Including the cities of Delphi, Flora, Williamsport, West Lebanon,
Lafayette, West Lafayette, Frankfort, Kokomo, Attica, Covington,
Veedersburg, Crawfordsville, Lebanon, Zionsville, Tipton, Fishers,
Carmel, Noblesville, Anderson, Muncie, Winchester, Clinton, Newport,
Rockville, Greencastle, Plainfield, Brownsburg, Danville,
Indianapolis, Greenfield, New Castle, Terre Haute, Brazil,
Clay City, Spencer, Martinsville, Mooresville, Greenwood, Franklin,
Shelbyville, Rushville, Sullivan, Linton, Bloomfield, Bloomington,
Nashville, Columbus, Greensburg, Vincennes, Washington, Loogootee,
Shoals, Bedford, Mitchell, Seymour, Brownstown, and North Vernon
356 AM EDT Tue Aug 10 2021

This hazardous weather outlook is for central Indiana.

.DAY ONE...Today and Tonight.

Thunderstorms are possible through tonight. Some storms may become
severe this afternoon and tonight.

The primary severe threat will be damaging winds. Lightning, gusty
winds, and heavy rainfall are possible with any storm. Storm motion
will be generally from the west at around 25 mph.

Heat indices will peak in the upper 90s to near 105 degrees this
afternoon, with the highest values in the Wabash Valley.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Thunderstorms are possible over all or parts of the area Wednesday
through Saturday, and again on Monday. Some of the storms on Wednesday
and Thursday could become strong to severe, with damaging winds and
large hail the primary severe threats.

Locally heavy rain is possible with any storm.

Peak heat indices will remain in the upper 90s to around 105 degrees
for most locations through Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible at times today into Thursday.

&&

More information, along with other weather, hydrological and climate
information can be found at http://weather.gov/ind

Special Weather Statement
National Weather Service Indianapolis IN
832 AM EDT Tue Aug 10 2021

INZ065-072-101300-
Decatur IN-Jennings IN-
832 AM EDT Tue Aug 10 2021

...A strong thunderstorm will impact portions of Decatur and
northeastern Jennings Counties through 900 AM EDT...

At 831 AM EDT, Doppler radar was tracking a strong thunderstorm 9
miles south of Greensburg, or 16 miles west of Batesville, moving
east at 30 mph.

HAZARD...Winds in excess of 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This storm will remain over mainly rural areas of Decatur and
northeastern Jennings Counties, including the following locations...
Newpoint, Westport, Millhousen and Letts.

This includes Interstate 74 between mile markers 132 and 144.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3920 8544 3912 8544 3913 8569 3915 8569
      3937 8557 3937 8530 3927 8530
TIME...MOT...LOC 1231Z 260DEG 24KT 3921 8550

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

CP