156
FXUS63 KIND 020726
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
326 AM EDT Wed Apr 2 2025

.KEY MESSAGES...

- Severe weather mainly this evening into the early overnight

- Flood Watch this evening 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 (Today and tonight)...
Issued at 303 AM EDT Wed Apr 2 2025

SYNOPTIC OVERVIEW...

An upper level low will move northeast into Minnesota into tonight.
Southwest flow aloft will continue across central Indiana. A potent
upper level jet will be northwest of the area, with the right
entrance region influencing central Indiana.

At the surface, low pressure will move into Wisconsin, first
bringing a warm front through the area early today, followed by a
cold front tonight.

Strong southwest winds aloft will pump in very high moisture for
this time of year, with integrated water vapor transport values as
well as precipitable water values near climatological maxima for
early April.

Some showers and storms will accompany the warm front this morning,
especially north. More widespread convection will develop ahead of
the cold front and perhaps along it as well later this afternoon and
tonight.

NON-THUNDERSTORM WIND THREAT...

Mixing after the warm frontal passage will tap into some of the
stronger winds aloft today, especially this afternoon. Wind gusts
near 50 mph are possible. Sustained winds over 30 mph are likely at
times as well. Will continue the Wind Advisory.

SEVERE WEATHER THREAT...

Parameters this morning for convection with the warm front aren`t
that great, so do not expect severe storms with these.

The wind fields will produce strong shear across the entire area
this afternoon and evening. Even with cloud cover around, the strong
southwest flow will bring in warmth and moisture, increasing the
instability across central Indiana.

The combination of strong shear and good instability will lead to
the potential for severe storms this afternoon and tonight. All
modes of severe weather are possible. Straight line winds from the
convection of over 70 mph are possible given the strong wind fields
in place.

However, forecast soundings show a cap across the area for much of
the afternoon. Convection will have a hard time initiating with this
in place, until better forcing arrives and the cap erodes. This will
likely keep any coverage of convection low for much of the afternoon
hours.

Widespread convection will move in, especially after 22-23Z and
continue into the night. Multiple models are showing more than 1
line of convection, with some isolated convection ahead of/in-
between the lines. The solo storms may be able to tap into the
shear/instability and become supercellular and produce large hail as
well as tornadoes if the storms form.

Otherwise, damaging straight line winds will be likely with the
lines of convection, with perhaps some meso-vorticies producing
tornadoes within the lines.

POSSIBLE SCENARIOS FOR SEVERE...

1) The afternoon remains pretty quiet with the cap in place. Next,
better forcing from the larger system will create a stronger line
impacting the northern forecast area. To the south, another line
would form in the better parameter space, impacting the southern
forecast area. The central forecast area could see strong to severe
individual storms or, on the other hand, weaker storms with the
other lines dominating.

2) The cap is weaker than forecast this afternoon and individual
storms develop and become severe/potentially supercellular. Lines of
severe convection would then follow this evening.

HEAVY RAIN/FLOODING CONCERNS...

As noted above, near climatological maximum moisture will be around
for the storms to work with. Multiple lines of storms could lead to
heavy rain amounts. At the moment, it appears that 1.5 to 2 inches
of rain is possible through 12Z Thursday across the south, with 0.75
to 1.25 inches north.

HREF Local Probability Matched Means for 24 QPF show the possibility
of local amounts of over 3 inches south.

Thus feel the Flood Watch begin time looks good given the above
potential.

&&

.LONG TERM (Thursday through Tuesday)...
Issued at 326 AM EDT Wed Apr 2 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.

After Wednesday night, several more rounds of rain are expected
through Sunday, which could bring anywhere from 4 to almost 9 inches
of rainfall during that timeframe, with highest amounts expected
across the south, and thus the potential for significant flooding by
the weekend. The glimmer of good news is that all of this rain is
expected over 4 to 5 days instead of 1 or 2, but still a concerning
amount for what will quickly become a saturated ground.

Models continue to lack agreement on exactly where the swath of
showers and storms will set up day to day for the latter part of the
week, particularly how far north storms get Thursday and Friday.
Confidence grows Friday night into Saturday with better agreement
that the boundary and moisture surge will shift northward into
Central Indiana. With this late week surge comes the higher concern
for a flooding threat. Parts of our forecast area will likely have
creeks and rivers overrunning their banks as well as roads flooded
out. Before trying to travel, check for road closures and NEVER
drive around barricades or into flood waters.

Temperatures are expected to be above normal through Saturday. The
stationary front will finally move off to the east sometime during
the day Sunday, after which cooler, slightly below normal
temperatures, will settle in for the remainder of the forecast
period.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 112 AM EDT Wed Apr 2 2025

Impacts:

- Non-convective LLWS at most sites through about 12Z

- Early TSRA at KLAF with -SHRA at KIND. Scattered convection
  this afternoon then widespread convection this evening

- Southeast winds becoming strong southerly after warm front
  passage early this morning. Afternoon gusts near 40kt

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

Discussion:

A low level jet will bring LLWS conditions for the first quarter of
the period, then as mixing takes place behind a warm front some of
those winds will mix down to the surface.

Some convection mainly near KLAF with the warm front. Widespread
convection developing around 22-24Z and persisting into the night.


&&

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

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

&&

$$

SHORT TERM...50
LONG TERM...KF
AVIATION...50