National Weather Service Raw Text Product

484 
FXUS63 KIND 011850
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
250 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.

&&

.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 (18Z TAF Issuance)...
Issued at 1251 PM EDT Tue Apr 1 2025

Impacts:

- Non-convective LLWS tonight
- Low threat for TSRA at LAF and HUF tonight
- Southerly wind gusts to 40kts after 17Z tomorrow

Discussion:

VFR conditions expected through much of the early portions of the 
TAF period with cirrus clouds moving in through the evening. A 
strong LLJ combined with weaker surface winds will bring periods of 
LLWS from 06Z to 12Z. Isolated TSRA at HUF and LAF late tonight, but 
confidence is low. Cigs will then begin to fall during the daytime 
hours with MVFR cigs by 17Z. Additional thunderstorms expected 
tomorrow afternoon, but storms are more likely to occur after the 
end of the current TAF period. Easterly winds will become more 
southerly after 12Z with gusts to 40kts after 17Z.

&&

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

&&

$$

SHORT TERM...White
LONG TERM...Ryan
AVIATION...White