Flash Flooding and Hail in Indiana, June 18 to 19, 2021

Area Forecast Discussion
National Weather Service Indianapolis IN
312 PM EDT Fri Jun 18 2021

.Short Term...(This Evening through Saturday Night)
Issued at 312 PM EDT Fri Jun 18 2021

Much of the forecast area remains free of rain in what has become an
increasing hot and humid afternoon for central Indiana. The only
convection has been limited to the vicinity of a remnant outflow
boundary over north central Indiana. Storms have struggled to
maintain intensity with LAPs soundings still highlighting hints of a
cap even across far northern sections of the forecast area. 19Z
temperatures ranged from the upper 80s to mid 90s with heat indices
over 100 degrees in parts of the region.

The threats for severe weather this evening and heavy rainfall and
flooding from this evening through the overnight remain primary
concerns in addition to the heat and humidity currently. Model
guidance has been less than stellar in handling the convection
throughout the day today and will be trending the forecast over the
next 12 hours heavily towards mesoanalysis in trying to key in on
some hints as to how the convection evolves over the next several
hours.

LAPs soundings show a highly unstable airmass above a low level cap
with MLCAPE values at 3000-4000 j/kg and mid level lapse rates that
continue to steepen and already are sitting at 7.5-8C/km. The cap is
keeping a lid on all of this at this point and with convective temps
currently at 93-95 degrees...expect little activity over much of the
forecast area through the next couple hours. Where things are likely
to start getting interesting will be by 22-23Z as the boundary layer
begins to cool. That combined with the approaching upper level wave
will help to bust the cap and open the door for rapid upscale
convective growth likely focused near the boundary just north of the
forecast area currently which may very well slip into our northern
counties by this evening. In addition...there is another subtle
boundary leftover from this morning that roughly extends as best can
tell from northwest to southeast.

There remains support for a supercellular storm mode early on with
all threats on the table including a few tornadoes. Once though the
storms grow into an MCS later this evening...damaging winds will
become the primary threat with the near dry adiabatic flow into the
mid levels suggesting efficient wind transport to the surface. As
the evening progresses into the overnight...the focus will shift
more to a heavy rain and enhanced flooding risk with the expansion
of a westerly low level jet into the region fueling an axis for
training and backbuilding convection. There continues to be
uncertainty with regards to exactly where the axis sets up as
outflow boundaries may shove the heaviest rainfall a bit further
south.

For now...have introduced a flash flood watch for a large swath of
the forecast area largely focused on the I-70 and I-74 corridors.
Confidence is highest in excessive rainfall from near the Indy metro
E/SE towards the Ohio border. While flash flood guidance is quite
high and the soils are dry...justification for the watch exists with
the potential for some locations to see 2-3 inches of rain...and
potentially higher...in a short time over the dry soils causing
increased runoff. May expand or adjust the watch later this evening
depending on if the axis of heaviest rainfall shifts further. But
confidence is moderate to high in impacts in the zone mentioned
above. The watch will begin at 00Z and extend through 14Z Saturday.

The rest of the forecast period for Saturday and Saturday night is
largely dependent on what transpires through tonight. It is
conceivable that convection could be shifted well south of the
region Saturday but the overnight storms with relatively quiet
conditions for much of Saturday and Saturday night. Considering the
leftover moist and unstable airmass...will maintain scattered
convection for much of this period but confidence is very low in
rain and storm coverage through this timeframe.

So to summarize:

1) Severe threat focused late afternoon and more likely during the
evening. Damaging winds remain primary threat...but large hail and a
few tornadoes possible as well

2) flooding concerns increase by late evening into the overnight.
Potential for training cells is high...axis of greatest concern
still yet to be determined.

3) storms will be prolific lightning producers. Something to keep in
mind for outdoor activities this evening even if storms are not
severe.

4) Stay Weather Aware this afternoon and tonight.

&&

.Long Term...(Sunday through Friday)
Issued at 312 PM EDT Fri Jun 18 2021

A more active pattern for weather will continue into the long term
period. Models are indicating that a boundary will likely linger
over the area Sunday as a tropical system coming out of the Gulf
will act to prevent the boundary from progressing forward. In
addition, highs are expected to be hot again getting into the
upper 80s to lower 90s so the daytime heating will lead to chance
PoPs for Sunday afternoon. Given the heat and ample moisture, some
higher CAPE and lapse rates will likely be in play so a few
storms could be strong to severe. With a lack of shear though,
organized storms are not expected through the day.

A trough and associated cold front will be advancing later in the
day Sunday which will help to finally push the boundary out of the
area. The front will then slowly push across the region for the
start of the week bringing the a line of rain and storms from Sunday
and lasting into Monday night. PWATs with this system look to be in
the 1.5 to 2 range, which will be above normal but not anywhere near
record for this time of year. Depending on how precipitation totals
pan out with the system today and tonight, the additional rain early
next week could lead to some flooding issues, but its still too soon
at this time to say for sure.

Towards midweek, surface high pressure and a cooler airmass will
move in behind the cold front. This will allow both a break in
precipitation and temperatures, as highs Tuesday and Wednesday are
expected to stay in the 70s, possibly into the low 80s on Wednesday.

Airflow will shift again to out of the S/Sw for the end of the week
providing more normal temperatures for this time of year. While the
long term models are a bit noisy for the end of next week, it does
look like there could be some upper short waves that could cause
more storms chances.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1254 PM EDT Fri Jun 18 2021

IMPACTS:

- VFR conditions through much of the rest of the afternoon
- Convection and increasing chances of temporary MVFR or worse
  flying conditions after 22Z
- Gusty SW winds and gusts through early evening
- Scattered severe storms mainly between 22Z and 04Z this evening
with wind gusts briefly at or in excess of 50 knots.
- Continued rain and storms overnight with periodic restrictions

DISCUSSION: The convection that tracked across northern portions of
central Indiana earlier this morning has moved away to the
east...leaving the region with mainly clear skies and gusty
southwest winds. Much of the rest of the afternoon will be dry
although a few storms may pass just north of KLAF over the next few
hours. Primary focus for robust convective development remains
aligned for the 22Z to 04Z timeframe when severe wind gusts and
possibly hail would be most likely with storms. Potential for
repeated rounds of convection overnight with heavy rainfall becoming
the primary threat. This will produce periodic restrictions at the
terminals through Saturday morning. Likely high impact to aviators
this evening through the overnight.

High uncertainty in additional showers and storms Saturday morning
but expect a decrease in coverage with potential that convection
shifts south of the terminals.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 8 PM EDT this evening through Saturday
morning for INZ035>037-039>049-051>057-062>065-071-072.

&&

Short Term...Ryan
Long Term...KH
Aviation...Ryan

Hazardous Weather Outlook
National Weather Service Indianapolis IN
410 AM EDT Fri Jun 18 2021

INZ021-028>031-035>049-051>057-060>065-067>072-191000-
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
410 AM EDT Fri Jun 18 2021

This hazardous weather outlook is for central Indiana.

.DAY ONE...Today and Tonight.

There is an ENHANCED RISK for severe thunderstorms this afternoon
and tonight. Severe storms are possible mainly after 300 PM. The
main severe threats will be damaging winds. An isolated tornado
and large hail will also be possible. Lightning is a threat from
any thunderstorm. Heavy rainfall and localized flooding will also
be possible mainly tonight.

Hot and humid conditions this afternoon and early evening. Max
heat indices will reach 100 to 105 degrees.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

More thunderstorms are possible at times from Saturday through
Monday night and again late next week. There is Marginal Risk for
severe weather Saturday afternoon and evening. Damaging winds,
large hail and isolated thunderstorms are possible.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be requested Friday afternoon and night
and or Saturday afternoon and night.

&&

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
938 AM EDT Fri Jun 18 2021

INZ042-049-181415-
Randolph-Henry-
938 AM EDT Fri Jun 18 2021

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHERN RANDOLPH AND
NORTHERN HENRY COUNTIES...

At 938 AM EDT, radar indicated strong thunderstorms were located
along a line extending from 7 miles south of Union City to near
Hagerstown to 9 miles southeast of Anderson. Movement was southeast
at 30 mph.

Winds in excess of 40 mph and penny size hail are possible with these
storms.

Locations impacted include...
New Castle, Lynn, Sulphur Springs, Mooreland, Mount Summit,
Losantville, Modoc, Springport, Blountsville and Summit Lake State
Park.

This includes Interstate 69 near mile marker 231.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 4000 8520 3988 8520 3987 8522 3988 8530
      4002 8558 4008 8558 4007 8518 4016 8481
      4001 8481
TIME...MOT...LOC 1338Z 296DEG 26KT 4010 8481 3997 8508 4000 8555

Ryan

Special Weather Statement
National Weather Service Indianapolis IN
210 PM EDT Fri Jun 18 2021

INZ021-181845-
Carroll-
210 PM EDT Fri Jun 18 2021

...A STRONG THUNDERSTORM WILL AFFECT CENTRAL CARROLL COUNTY...

At 209 PM EDT, a strong thunderstorm was located near Monticello,
moving east at 35 mph.

Winds in excess of 40 mph and nickel size hail are possible with this
storm.

Locations impacted include...
Delphi, Flora, Camden and Yeoman.

To report severe weather, contact your nearest law enforcement
agency. They can relay your report to the National Weather Service
office in Indianapolis.

LAT...LON 4070 8652 4069 8652 4069 8644 4049 8656
      4059 8677 4066 8677 4066 8676 4067 8674
      4068 8674 4068 8676 4069 8675 4070 8676
      4071 8676 4072 8675 4073 8676
TIME...MOT...LOC 1809Z 291DEG 32KT 4069 8680

AU/KH