Flash Flood Warning 3, NWS Indianapolis, IN

Area Forecast Discussion
National Weather Service Indianapolis IN
912 PM EDT Wed Apr 2 2025

.KEY MESSAGES...

- Severe weather likely late today and this evening into the early
  overnight. Tornadoes, widespread damaging winds are likely with
  large hail and flash flooding possible as well

- Flood Watch this evening through Sunday morning with 4 rounds of
  moderate to heavy rain and total rainfall potentially as high as 6-9
  inches

- Wind Advisory through 1 am tonight with wind gusts to 50 mph
  expected

- Widespread, significant river flooding expected late week into
  next week.

&&

.FORECAST UPDATE...
Issued at 912 PM EDT Wed Apr 2 2025

High confidence for storms the next several hours as the convective
complex across Central Indiana currently stretches from west of
Lebanon to western Hendricks county and to points southwest near
Linton and Vincennes. HRRR suggest this line of storms will make
steady progress eastward across Central Indiana through the next 2-3
hours, exiting Indiana by 100AM. Strong low level jet remains in
place ahead of the line feeding the storms. Thus severe storms will
continue to be expected through the early morning hours as the
storms depart. Some storms may have the capability of producing 70-
80 mph winds.

Overnight, after 200am, dry weather will return as high pressure
builds across Indiana from the west. High clouds will lead to just
partly cloudy skies with westerly winds.

&&

.MESOSCALE UPDATE...
Issued at 912 PM EDT Wed Apr 2 2025

Weak echoes on KVWX from near Vincennes south-southwestward to near
Paducah, Kentucky, appear to be a shallow convective process within
a deep/moist (but capped) PBL, per model soundings. Some glaciation
is seen in Day Cloud Phase RGB satellite imagery, but small anvils
are orphaned quickly. Large scale ascent is minimal for this to
change in the short term, thus capping should continue to suppress
deeper more organized convection for the next few hours, at least
for central Indiana.

&&

.SHORT TERM (This Evening through Thursday)...
Issued at 152 PM EDT Wed Apr 2 2025

A strong mid-latitude cyclone is taking shape over the Midwest
currently, with a broad warm sector setting up across Indiana. The
system's warm front passed through early this morning with a round
of elevated convection. Winds are now out of the south and
temperatures have climbed into the low 70s as of 1pm, dew points are
near 60F. Continued warm moist advection is expected as we head into
the afternoon hours.

Given the strength of the mid-latitude cyclone, a tight MSLP
gradient has become established over Indiana. Very gusty gradient
winds are developing with gusts already to 45mph at IND, and up to
52mph near Vincennes. High-resolution guidance suggests continued
gusts 45 to 55 mph are likely at times this afternoon.

These strong southerly winds will allow moisture to advect
northward, setting the stage for our convective threat later this
afternoon and evening.

SEVERE WEATHER POTENTIAL AND HAZARDS

Thunderstorms are ongoing along a cold front across Illinois and
Missouri as of this writing, with eastward propagation expected
through the afternoon hours. Ahead of the line, strong southerly
flow is promoting rapid moisture advection which will help
destabilize the atmosphere, especially in the lower levels. Thick
cirrus from the upstream convection could limit diurnal heating
somewhat...but instability from advection alone will likely be more
than enough to compensate.

Our primary hazard will depend on storm mode, which is a bit tricky
today. Shear vectors are roughly parallel with the initiating
boundary, in this case the system's cold front...so a linear mode is
preferred. However, there may be enough forcing to overcome weak CIN
within the open warm sector to promote a few discrete cells near and
just ahead of the front / ongoing line of storms.

Model soundings show steep lapse rates with moisture through the
column. Additionally, long curved hodographs indicate large amounts
of wind shear especially in the lower levels. Should a discrete cell
form then it could easily become a supercell with all hazards
possible, including tornadoes and large hail. Tornado potential will
depend on the quality of low-level moisture and near-ground lapse
rates. That being said, mesoscale trends will need to be monitored
very closely as the event unfolds.

As mentioned above, our most likely storm mode will be linear. In
this case, strong damaging winds, potentially significant (over
75mph), are the most likely hazard. A QLCS tornado or two is
possible as well, especially within line breaks, due to the large
amounts of low-level shear present. It is also possible that a mixed
mode occurs where we begin with a few discrete cells before upscale
growth transitions everything into a line.

Lastly, flash flooding is possible as some storm training is
possible. Some of the higher-resolution model runs are depicting 2-4
inches of rain in isolated swaths.

THURSDAY

The cold front mentioned above looks to cross the state during the
night tonight, settling across the Ohio River by around sunrise.
North of the front, cooler temperatures and diminished winds are
expected.

Zooming back out a bit, guidance is showing a deepening trough over
the Rockies with a subtle wave ejecting eastward early Thursday.
This wave then rides the front allowing it to lift northward a bit.
Showers and thunderstorms expand in coverage through the day as
lifting arrives ahead of the wave.

Our flooding threat increases substantially later Thursday and into
the weekend. Though Thursday's risk depends on how much rain we see
across the region today. More details in the long range discussion
below.

&&

.LONG TERM (Thursday Night through Wednesday)...
Issued at 223 PM EDT Wed Apr 2 2025

...MULTIPLE ROUNDS OF HEAVY RAIN THROUGH SUNDAY MORNING...
...SIGNIFICANT FLOODING POSSIBLE...

High confidences concerns for significant flooding across the Ohio
Valley as multiple rounds of moderate to heavy rainfall will impact
the region into Sunday. The frontal boundary that will pass through
the forecast area tonight will becomes quasi-stationary across the
Ohio Valley on Thursday. A highly amplified and blocky upper level
pattern across the country anchored by a deep trough over the
Intermountain West and a strong ridge off the southeast US coast
will place the Ohio Valley within deep southwest flow that will draw
a rich fetch of moisture from both the equatorial Pacific and the
Gulf. Additionally the sharp baroclinic zone that will align north
of the stagnant frontal boundary will further promote strong lift
and convergence with a strong upper jet supporting divergence aloft.
This setup is historically supportive of a prolonged risk for heavy
rainfall and flooding for the Ohio Valley and central Indiana.

Thursday Night through Sunday

The second wave of heavier rainfall and storms for Thursday night
(with tonight being the first) has trended further north into the
forecast area with recent model runs as the boundary is likely to
become nearly stationary just south of the Ohio River. Rain showers
will return as north as early as Thursday afternoon but the
widespread heavier rainfall rates will focus Thursday night. A
strong mid level deformation axis north of the surface front will
lend its weight to enhancing rainfall across the forecast area with
growing confidence in a widespread 1 to 2 inches by Friday morning.
In addition to the rainfall received later today and tonight...these
amounts will lead to exacerbating flooding concerns while only
serving to magnify the impacts from the third and fourth waves of
heavier rainfall set to impact the region Friday night through early
Sunday.

Rainfall coverage will briefly diminish on Friday morning leaving
cloudy skies and a cool...damp easterly flow across much of central
Indiana. The front will shift further north into the region Friday
afternoon with the third wave of rainfall poised to arrive late day
into Friday night as surface waves ride along the boundary. Precip
efficiency levels should be excellent as deep convergence up through
700mb aligns with the axis of highest precip water values above the
climatological max and near 300% of normal for early April. This
will support widespread heavy rainfall over the entire forecast area
all night and into Saturday morning. Additional rainfall amounts of
1 to 3 inches look likely.

Rainfall coverage and rates may diminish briefly again Saturday
morning before the arrival of a stronger surface wave into the
region by late Saturday triggers the fourth and final wave of
rainfall into the Ohio Valley for Saturday afternoon and night with
the frontal boundary shifting back to the southeast of the region as
the night progresses. Despite slightly lower PWAT values...low level
profiles remain ideal for heavy...efficient rainfall to impact the
forecast area for several hours before transitioning to lighter and
more scattered rain late Saturday night as the trailing upper level
trough moves in from the west. Flooding concerns will be maximized
by Friday night and Saturday as even a small amount of rain is
likely to initiate or worsen ongoing flooding.

Temperatures may struggle to climb out of the 40s on Sunday with a
stiff northerly wind and periodic light showers and maybe a
few snowflakes making for a miserable end to the weekend.

Rainfall Amounts and Flooding

To reiterate the four primary waves of rainfall will come...

- This Evening/Early Overnight
- Thursday Night
- Friday Late Day/Friday Night
- Saturday Afternoon/Night

Widespread rainfall amount of 4 to 7 inches are likely across the
forecast area later today through Sunday with highest amounts south.
The potential for up to 8-9 inches may sneak up into far southern
portions of the forecast area as well. These rainfall amounts will
produce significant flooding...especially along rivers...creeks and
streams and within poor drainage areas. High confidence exists that
the heavy rainfall anticipated through Sunday could be one of the
highest impact flooding events for central Indiana over the last 15
years.

A reminder that the Flood Watch will go into effect for the entire
forecast area at 00Z tonight and run through 12Z Sunday and now
covers all of central Indiana.

Monday through Wednesday

Other than a small threat for a few light areas of precipitation
Monday into Tuesday...the pattern will shift to a cooler and drier
regime that likely extends out for much of next week as deep
troughing develops across the eastern part of the country. Highs by
Monday and Tuesday will only range from the mid 40s to mid 50s with
those temperatures persisting out through later next week.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 605 PM EDT Wed Apr 2 2025

Impacts:

- Thunderstorms this evening. Some Severe.

- Southwest wind gusts 40 to 45 knots this evening. Severe
gusts in excess of 55 Knts with storms.

- MVFR and worse conditions possible at times and especially in
  thunderstorms

- Rain returns Thursday evening

Discussion:

Radar shows a strong squall line stretching from NE IL across
Central IL to SE MO and Arkansas. HRRR suggests this line of storms
will push across Central Indiana within the 00Z-05Z time frame.
Ahead of the line VFR Conditions with strong gusts to 40 knts will
be possible.

As the line passes severe gusts, heavy rain and MVFR or worse cigs
will be possible.

The line will exit overnight leading to a quick return to VFR after
06Z. Here, forecast soundings show drying and subsidence within the
column in the wake of the convective line as surface high pressure
builds across the area from the plains states.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Sunday morning for INZ021-028>031-035>049-
051>057-060>065-067>072.

Wind Advisory until 1 AM EDT Thursday for INZ021-028>031-035>049-
051>057-060>065-067>072.

&&

MESOSCALE...BRB
UPDATE...Puma
SHORT TERM...Eckhoff
LONG TERM...Ryan
AVIATION...Puma

Hazardous Weather Outlook
National Weather Service Indianapolis IN
253 PM EDT Wed Apr 2 2025

INZ021-028>031-035>049-051>057-060>065-067>072-031000-
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-
253 PM EDT Wed Apr 2 2025

This hazardous weather outlook is for central Indiana.

.DAY ONE...Through Tonight.

Numerous thunderstorms and heavy rain will develop late this
afternoon into tonight. Severe weather is expected. Tornadoes and
widespread damaging winds are likely with large hail and flash
flooding possible as well.

The main timeframe for severe weather will be from 5 pm through 1 am.

Outside of thunderstorms, windy conditions are expected, with gusts
up to 50 to 55 mph possible into this evening.

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

Additional thunderstorms are possible at times Thursday into
Saturday. Some severe storms cannot be ruled out through Friday,
especially south of Interstate 70. Present indications are that
damaging winds would be the primary severe threat.

More rounds of heavy rain Thursday through Saturday night will lead
to additional flooding or prolonging existing flooding. Significant
river flooding is expected to develop late this week and into the
weekend.

Lightning is a threat from any storm.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to send reports in this evening into tonight.

&&

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

Ryan

Preliminary Local Storm Report
National Weather Service Indianapolis IN
1028 PM EDT Wed Apr 2 2025

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

0925 PM     Hail             6 SE Beech Grove        39.66N 86.01W
04/02/2025  M0.25 Inch       Marion             IN   Public

            Time estimated from radar.

&&

BH

Preliminary Local Storm Report
National Weather Service Indianapolis IN
1040 PM EDT Wed Apr 2 2025

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

0930 PM     Tstm Wnd Gst     2 W Homecroft           39.68N 86.17W
04/02/2025  M80 MPH          Marion             IN   Public

            Unknown number of tree branches down. Winds
            shaking house considerably. Time estimated
            from radar.

&&

BH

Preliminary Local Storm Report
National Weather Service Indianapolis IN
1043 PM EDT Wed Apr 2 2025

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

1039 PM     Hail             4 NW Mitchell           38.79N 86.51W
04/02/2025  E0.75 Inch       Lawrence           IN   Public

            Report from mPING: Dime (0.75 in.).

&&

BH

Preliminary Local Storm Report
National Weather Service Indianapolis IN
1047 PM EDT Wed Apr 2 2025

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

0910 PM     Tstm Wnd Dmg     2 ENE Brownsburg        39.85N 86.35W
04/02/2025                   Hendricks          IN   NWS Employee

            Damage to Hession Farms Inc. Time estimated
            from radar.

&&

BH

Preliminary Local Storm Report
National Weather Service Indianapolis IN
1049 PM EDT Wed Apr 2 2025

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

1044 PM     Flood            1 W Silverville         38.86N 86.68W
04/02/2025                   Lawrence           IN   Public

            Report from mPING: River/Creek overflowing;
            Cropland/Yard/Basement Flooding.

&&

BH

Preliminary Local Storm Report
National Weather Service Indianapolis IN
1103 PM EDT Wed Apr 2 2025

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

0930 PM     Tstm Wnd Dmg     3 W Meridian Hills      39.89N 86.22W
04/02/2025                   Marion             IN   Amateur Radio

            Aluminum siding blown off a house and a
            12-inch diameter tree was split in
            half...suspected lightning strike. Time
            estimated from radar.

&&

BH