541
FXUS63 KIND 020210
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1010 PM EDT Tue Apr 1 2025

.KEY MESSAGES...

- Severe weather Wednesday evening into the early overnight

- Flood Watch Wednesday to Sunday with 4 rounds of moderate to heavy
  rain and total QPF potentially as high as 6-8 inches

- Wind Advisory 8AM to 1AM with wind gusts to 50 mph expected

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

&&

.FORECAST UPDATE...
Issued at 1010 PM EDT Tue Apr 1 2025

Much of the forecast has remained similar on the latest update.
There have been slight increases in precipitation chances early
tonight, with trends pushing precipitation onset closer to 12-2AM
EDT over NW central Indiana. Outside of this, most of central
Indiana should remain dry until near dawn. Temperatures are still
expected to remain fairly stagnant overnight within modest WAA and
extensive upper level cloud cover.

Grid updates are out

&&

.SHORT TERM (This Evening through Wednesday Night)...
Issued at 250 PM EDT Tue Apr 1 2025

Tonight.

Quiet weather is expected to continue for much of the night with
some elevated convection across the northwestern portions of the
forecast area. The main uncertainty for tonight will be the southern
extent of these elevated showers/storms with the severe threat
looking minimal with small hail being the most likely threat.
Temperatures won`t be quite as cool tonight as the surface winds
become easterly before transitioning to southerly by daybreak.

Wednesday and Wednesday Night.

The threat for severe weather returns Wednesday as a low pressure
system tracks across the Upper Midwest. Any remaining convection
from the overnight will quickly exit with dry weather for much of
the day. There doesn`t look to be much clearing through the day but
strong southerly flow will help bring temperatures into the mid to
upper 70s for much of the forecast area. There remains some
uncertainty as to the timing of the evening convection, but general
model consensus brings things in after 6PM with the greatest threat
through 12AM. There is an increasing threat in discrete convection
out ahead of the more organized line which will be able to tap into
very favorable low level dynamics with plenty of near surface shear.
This potential pushes confidence in the tornado threat higher which
lines up well with the latest SPC day 2 outlook which upgraded
portions of southern Indiana into a Moderate risk with a hatched 15%
tornado risk. If discrete cells do not end up forming ahead of the
line, the wind threat will become the primary threat with QLCS
tornadoes being a secondary threat.

The secondary concern with this first part of the system will be
flash flooding followed by areal and river flooding that will be
discussed further in the long term section below. There looks to be
decent forward progression with the convection across central
Indiana but the southern end of the line may end up training with
some signals for upshear propagation which could bring pockets of
heavier rain. The first round Wednesday into Wednesday night looks
to end up around 1.5-2.5 inches but the HREF max hints at some of
the pockets of heavier rain where localized amounts could be as high
as 4 inches, but most models keep those extreme amounts south of the
forecast area.

In addition to the convection/flooding threat, gusty gradient winds
will also be a concern throughout the day as model soundings show
lapse rates should be steep enough to allow for the mixing down of
gusts up to 50 mph at times.

&&

.LONG TERM (Thursday through Tuesday)...
Issued at 250 PM EDT Tue Apr 1 2025

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

An active and exceptionally wet pattern will continue through the
weekend as a frontal boundary becomes quasi-stationary across the
Ohio Valley. A highly amplified 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 a deep southwest flow that will draw a rich fetch of moisture
from both the equatorial Pacific and the Gulf. The setup in tandem
with a stagnant frontal boundary and sharp baroclinic zone that will
further promote strong lift and convergence is one that is
historically supportive of a prolonged risk for heavy rainfall and
flooding for the Ohio Valley and central Indiana.

Thursday through Sunday

The initial threat for heavy rainfall will come with the frontal
passage Wednesday night and confidence has increased in the boundary
shifting south of the Ohio River by Thursday morning. This would
take the heavier rain south of the forecast area prior to daybreak
Thursday and leave much of the forecast area in a general lull for
much of the day Thursday before lighter showers return back north
during the afternoon. The second wave of heavier rainfall and storms
will setup within the Ohio Valley Thursday night likely clipping the
far southern portion of the forecast area. The focus for heaviest
rainfall amounts will align closer to the Ohio River but potential
exists for up to an inch across the southern row of counties in the
forecast area with lighter amounts further north. More than
anything...this wave of rainfall is likely to serve as a predecessor
rain event with rainfall Wednesday night for the higher impact rain
set for Friday night and Saturday.

Rainfall coverage will diminish again on Friday leaving cloudy skies
and a cool...damp easterly flow across much of central Indiana. As a
closed upper low kicks out of the southwest U S and the ridge subtly
retrogrades off the southeast coast...the front will shift north
back into the forecast area and set the stage for the third wave of
rainfall poised to arrive Friday night as surface waves ride 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
most if not all of the forecast area all night and into Saturday
morning.

Rainfall coverage and rates may diminish briefly Saturday morning
but the arrival of a stronger surface wave into the region by late
Saturday will trigger 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. Low level profiles remain ideal for heavy...efficient
rainfall to impact the forecast area before transitioning to lighter
and more scattered rain early Sunday as the trailing upper level
trough moves in from the west. Temperatures may struggle to climb
out of the 40s on Sunday with a stiff northerly wind and periodic
light showers making for a miserable end to the weekend.

Rainfall Amounts and Flooding

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

- Wednesday evening/night
- Thursday Night
- Friday Night/Saturday Morning
- Saturday Afternoon/Night

Widespread rainfall amount of 3 to 6 inches are likely across the
forecast area by Sunday with highest amounts south. The potential
for up to 8 inches may sneak up into far southern portions of the
forecast area. These rainfall amounts could produce significant
flooding...especially along rivers...creeks and streams and within
poor drainage areas. This has the potential to be near the top of
the list for highest impact heavy rain/flooding events for central
Indiana in the last 15 years.

A reminder that the Flood Watch will go into effect for all but
the northwest part of central Indiana at 00Z Thursday and run
through 12Z Sunday.

Monday and Tuesday

Other than a small threat for a few light areas of precipitation
Monday...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 631 PM EDT Tue Apr 1 2025

Impacts:

- Non-convective LLWS 05Z-12Z

- Low threat for TSRA at LAF and HUF after 09z with a better
  chance for all the terminals Wednesday afternoon, including
  the potential for severe wind gusts, large hail and nearby
  tornadoes

- Winds 170-200 degrees gusting to 40kts in between thunderstorms
  with higher winds possible in thunderstorms

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

Discussion:

A low level jet will bring low level wind shear to the terminals
overnight and convection and potential MVFR and worse conditions
will roll in during the morning with better chances for convection,
including strong to severe thunderstorms, Wednesday afternoon and
evening.

Winds will become SSW and gust to 40 knots Wednesday in between
thunderstorms and higher in strong to severe thunderstorms.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 8 AM Wednesday to 1 AM EDT Thursday for
INZ021-028>031-035>049-051>057-060>065-067>072.

Flood Watch from Wednesday evening through Sunday morning for
INZ037-039>042-045>049-051>057-060>065-067>072.

&&

$$

UPDATE...Updike
SHORT TERM...White
LONG TERM...Ryan
AVIATION...MK