Severe Thunderstorm Warning 159, NWS Indianapolis, IN

Area Forecast Discussion
National Weather Service Indianapolis IN
247 PM EDT Mon May 18 2026

.KEY MESSAGES...

- Severe storms possible this afternoon and again Tuesday
  afternoon and evening with damaging winds the primary threat

- Heavy rain and some flooding are possible into the evening and
  again Tuesday

- Highs in the 80s Tuesday

- Storms will end Wednesday as the front shifts south, but unsettled
  weather likely returns late this week into the holiday weekend

&&

.DISCUSSION (This evening through Monday)...
Issued at 246 PM EDT Mon May 18 2026

Rest of This Afternoon and Tonight...

Please see the latest Mesoscale Discussion section for details on
the current convective situation.

Thunderstorms will continue to move east this afternoon, with faster
movement across the northern forecast area. To the south, the cold
pool is having a harder time moving south, and showers and storms
continue to develop as the low level jet impinges upon it.

Later this afternoon into early evening, some additional upper
energy will produce additional showers and thunderstorms. Will
continue high PoPs this afternoon into early evening, especially
southwest where the regeneration of storms will continue along the
cold pool boundary.

This regeneration of showers and storms in the southwest may lead to
flooding, so will continue the Flood Watch. May have to adjust the
location of the watch if the area of regeneration shifts.

The main threat for severe will be out ahead of the initial line of
storms into the afternoon. Damaging winds will be the primary threat.

Coverage of rain will diminish this evening into the overnight as
most forcing exits. However, some weak upper energy may keep the
threat for a few showers around northwest.

Went cooler than guidance for lows given the rain cooled air.

Tuesday...

Uncertainty remains on how convection will develop on Tuesday with
the surface cold front moving in. There may be cloud cover in the
morning from upstream convection which would help limit instability.
Some CAMs limit coverage to the southeast forecast area, while
larger scale models bring rain to all areas Tuesday into Tuesday
night.

Given the strength of the front and the plentiful moisture, went
likely PoPs all areas at some point Tuesday afternoon and evening.
The severe threat will depend on how well the instability is able to
build. Damaging winds will be the primary severe threat. Given
today's rainfall and the plentiful moisture Tuesday, heavy rain and
flooding will remain a threat for Tuesday as well.

Highs on Tuesday could reach the middle and upper 80s if morning
clouds are thin enough and rain holds off long enough.

Wednesday and Thursday...

Some rain may linger Wednesday morning in the south, so kept some
low PoPs there. There remains some uncertainty on how far south the
front will then settle and thus how fast it returns north. GFS seems
aggressive with returning rain on Thursday, so will keep most of the
area dry through the daytime Thursday. Rain chances begin to spread
north Thursday night.

Much cooler air will return for this period with highs in the upper
60s to around 70 and lows in the middle 40s to lower 50s.

Friday through Memorial Day...

A northern stream upper trough will move into the central USA while
a southern stream smaller upper wave moves into the area. These will
help bring the surface front northward back into the area into
Saturday. Decent moisture will move back north with it, so will have
likely or higher PoPs Friday into Friday night.

Upper energy may interact with the lingering front to produce some
rain on Saturday, so will keep PoPs around.

A couple of upper troughs will bring more rain chances Sunday into
Memorial Day. There remains some decent uncertainty on timing and
strength, so will broadbrush PoPs and keep them under the likely
category until uncertainty improves.

With the surface front having lifted north, warmer air will return,
with perhaps 80s again by the latter half of the holiday weekend.
However, confidence isn't high in these given the uncertainty in
rain coverage Sunday into Memorial Day.

&&

.MESOSCALE UPDATE...
Issued at 1244 PM EDT Mon May 18 2026

Thunderstorms are developing along the Indiana Illinois state line.
These storms have been loosely organized so far, but an outflow
boundary from convection further upstream is impinging from the
west. This outflow boundary may allow storms to consolidate into a
more coherent line as they progress deeper into Indiana.

A recent sounding from Purdue University shows modest lapse rates
between 6-7 C/Km, with a moist profile to about 500 mb.
Additionally, modest shear is also present (20-25 knots) with messy
hodographs centered around the mean storm motion. As such, little in
the way of storm relative upper-level outflow appears
likely...storms should behave more like single cells to multicell
clusters until they become influenced by the outflow boundary or
their own outflow.

Once storms consolidate on the outflow boundary, they should still
be relatively 'pulsey' in nature but more organized than in the open
warm sector. The primary threat today appears to be strong wind
gusts, as enough moisture loading within mature updrafts is possible
for wet microbursts. Additionally, cold pool dynamics such as rear-
inflow jet surges are also possible which may produce strong to
damaging wind gusts. Given a mean shear vector towards the
northeast, cold pools that orient in a NW to SE direction pose the
greatest threat for severe wind gusts.

Hail is possible but given only modest lapse rates, high moisture
content, and the lack of long straight hodographs it does not appear
to be all that likely. Tornado potential also appears low, given the
outflow dominant nature of storms today. A brief QLCS spin up cannot
be ruled out, however.

Another threat, likely replacing wind as the primary hazard later
this evening, is the potential for flooding and flash flooding. High-
resolution guidance shows the cold pool settling in a SW to NE
fashion across central Indiana. This may allow for repeated rounds
of storms into tonight. As mentioned above, moisture content in the
profile is high and freezing levels are near 15,000 feet. With a
warm cloud layer over 10,000 feet in thickness, warm rain processes
should lead to efficient rainfall production today. As such, various
CAMs are showing pockets of very heavy rainfall totals between 3 to
5 inches. HREF ensemble mean shows a large area of 1 to 2 inches.
Because of this potential, a Flood Watch has been issued for for
western portions of the area. As cold pools become more defined,
this may need to be trimmed or expanded.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 114 PM EDT Mon May 18 2026

Impacts:

- Showers and storms at times into this evening

- Peak wind gusts this afternoon at 25 to 30kts

Discussion:

Initial area of convection impacting the western sites at the moment
will continue to move east and will impact the other sites early in
the period. Additional development will continue into the evening,
so there will be periods of showers and storms through about 03Z.
IFR and worse are possible in convection.

While additional convection may pop up overnight, better chances for
convection return closer to 18Z Tuesday.

Gusty winds will continue this afternoon, and near LLWS conditions
are possible tonight.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 11 PM EDT this evening for INZ043>045-051>054-
060>062-067.

&&

AVIATION...50
DISCUSSION...50
MESOSCALE...Eckhoff

Hazardous Weather Outlook
National Weather Service Indianapolis IN
419 PM EDT Mon May 18 2026

INZ021-028>031-035>049-051>057-060>065-067>072-192030-
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-
419 PM EDT Mon May 18 2026

This hazardous weather outlook is for central Indiana.

.DAY ONE...Through Tonight.

Thunderstorms continue across much of the area into the evening.
Isolated severe storms are possible mainly south and east of
Indianapolis, with damaging winds as the primary threat.

Torrential rainfall producing localized flooding is also possible,
focused especially across the southwest half of central Indiana.

The severe threat should end by 700 PM with flooding remaining
possible this evening.

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

Scattered severe storms are possible again Tuesday afternoon and
evening. Damaging winds and large hail will be the primary threats
with localized flooding possible.

Additional chances for thunderstorms return Friday into the holiday
weekend.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report any heavy rain, flooding, or strong
winds into this evening. Spotters may be activated again on Tuesday.

&&

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

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