321
FXUS63 KIND 041410
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1010 AM EDT Fri Apr 4 2025

.KEY MESSAGES...

- Flood Watch through Sunday morning with rounds of moderate to
  heavy rain and total rainfall potentially as high as 6 to 8 inches
  in localized areas

- Some strong to severe storms possible again Tonight; Severe wind
  gusts and large hail are the primary threats

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

&&

.FORECAST UPDATE...
Issued at 1009 AM EDT Fri Apr 4 2025

High confidence for flooding over the next several days for Central
Indiana; however lower confidence exists in exact areas that may see
heaviest rainfall.

No changes on the overall weather pattern capable of producing long
periods of heavy rain and flooding. A surface boundary across
Kentucky is slated to shift northward later today into Central
Indiana as a wave rides along it. A strong low level jet will
continue to pump copious amounts of moisture over this
boundary...strengthening later tonight which will also increase
severe weather chances.

Watching where exactly this boundary sets up as a narrow area of
higher rainfall amounts and an increased flash flooding will likely
develop. Guidance over the past several runs has been more
consistent in showing this area setting up across North Central
Indiana. Widespread 1.5+ inches of rain is likely through Saturday
morning, with a swath of 2-4+ inches setting up along this boundary.
A shift in as little as 10-20 miles of this boundary will have
significant impacts on the forecast as that could mean the
difference between flash flooding in the Indy Metro vs areas further
north, which would have vastly different impacts. This will be a
detail to closely focus on tonight.

South of this boundary, severe weather chances increase for later
tonight as a quasi-warm sector forms. Forecasting soundings continue
to keep convection elevated above a surface inversion...keeping the
damaging wind threat relatively isolated. If the surface warms more
than what guidance shows, allowing storms to become surface based,
the damaging wind threat would significantly increase. Best chance
for this happening is in Southern Indiana where better warm air
advection is located. Still the main threat with storms tonight will
be heavy rainfall, flash flooding from repeated rounds of storms and
lightning. Hail and damaging winds are more secondary threats as
confidence remains lower on the extent of this threat due to stable
surface conditions.

&&

.SHORT TERM (Today and tonight)...
Issued at 253 AM EDT Fri Apr 4 2025

Through this Morning:

The cold front has stalled out near the KY/IN border leading to
widespread showers and thunderstorms along and just north of the
boundary as warm moist air lifts above. Currently, these showers and
storms are now south of central Indiana, but a few of these cells
may sneak over the CWA boundary at times early this morning. Steep
mid level lapse rates north of the boundary could allow for a few
stronger updrafts and small to marginally severe hail to develop.
This looks like a very low threat at this time for central Indiana,
but non-zero nonetheless.

Elsewhere, widespread stratus at about 5000ft remained strong, and
is expected to maintain itself through the overnight and morning
hours. This thick stratus layer will inhibit diurnal cooling
significantly, with overnight temperatures remaining in the low 50s
to upper 40s.

This Afternoon through Tonight:

The deep trough over the Western CONUS that has been creating this
highly active pattern will continue a slow progression eastward
today. A new area of upper level diffluence is expected to
strengthen this morning through the afternoon ahead of this
trough, and downstream of a phasing jet streak. In return, this
will create a broad area of low level pressure depletion, and
eventually another low pressure system over the lower to mid
Mississippi Valley this afternoon. The low is expected to push NE
within strong WAA nearing the western Ohio Valley overnight. This
WAA push should be greatest in the 900-750mb layer this evening,
pushing a elevated warm sector over the northern Ohio Valley. This
isn`t a true warm sector as the surface based boundary will lag
behind, keeping mostly all the buoyancy above the surface layer.

Now that the synoptic pattern has been discerned, how will that
impact conditions here in central Indiana? Initially, this will lead
to a suppressed cloud layer and light rainshowers this afternoon as
the 900-750mb warm front lifts northward. Within this elevated
frontal boundary a modest 0.3-0.6" is expected over a 6-8hr period.
Once the elevated frontal zone is north of a location, clouds should
lift some with a slight warm-up into the upper 50s to low 60s this
evening into the overnight. Showers should become more isolated for
a brief period following the elevated frontal passage

The more prolific rainfall is expected to arrive shortly after
sundown this evening as the LLJ strengthens and pushes highly
anomalous moisture along the WCB into the Ohio Valley. Strong
isentropic lift along with a deep CAPE profile should allow for very
efficient rainfall processes with average rainfall rates around
1- 2"/6hr. Areas along and south of I-69 corridor are expected to
have the most prolonged exposure to these higher precipitation
rates with additional overnight rainfall of around 2" likely
(isolated to scattered higher amounts are expected given the
convective nature).

As mentioned previously, the near surface frontal boundary will lag
behind, with most (if not all) of central Indiana remaining in a
"quasi-warm sector". This quasi-warm sector will have strong low
level SW WAA, but will not have any surface based instability due to
the surface inversion remaining intact, keeping these storms rooted
above the boundary layer. Elevated storms are less efficient at
producing severe wind gusts, and thus will lower the coverage of
severe wind gusts within thunderstorms. With that said, given the
strong LLJ, strong buoyancy above the surface inversion and
shallowness of the surface inversion isolated severe wind gusts
within wet microbursts and/or more organized clusters will be
possible. These steep mid level lapse rates will also allow for an
isolated severe hail threat within the stronger updrafts tonight.
There was a caveat earlier with the mention of "most" of central
Indiana will remain in the quasi-warm sector. This is due to the
close proximity of the near surface boundary and the chance for it
to reach the southern portions of central Indiana. If this does
occur, the severe wind risk and isolated tornado risk will
increase, thus this area of greater uncertainty has been highlight
by the slight (level 2) risk by SPC.

FLOOD POTENTIAL

1 to 3 inches across most of the CWA over the last 36 hours has led
to heavily saturated soils and already rising river levels. An
additional 0.3-0.6" this afternoon will only further saturate the
area prior to the expected heavy rainfall tonight. This has led
to an increasing concern in flash flooding for central Indiana,
especially for those along and south of the I-69 corridor where an
additional 2" or more of rain is expected to fall. For this
reason a slight risk for excessive rainfall risk has been issued
by WPC for most of S/E central Indiana. As heavy rain continues
into Saturday morning, the excessive rain threat will continue to
increase leading the a moderate risk for tomorrow.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 253 AM EDT Fri Apr 4 2025

Saturday and Sunday

Rainfall coverage and rates should diminish briefly again Saturday
morning before the arrival of an additional surface wave into the
region late Saturday This should result in the final round of
moderate to heavy rainfall for central Indiana with the frontal
boundary shifting back to the southeast of the region later Saturday
night. This last round of rain doesn`t look quite as potent with
PWAT values, while still anomalous, fall closer towards climatology.
Also, this wave will be backed by some CAA, pushing is quicker
eastward, limiting the amount of training convection over central
Indiana. Although rainfall amounts/rates are expected to be less on
Saturday, the shear amount of prior rainfall in combination will
continue the ongoing flooding concerns as even an inch of rain cloud
lead further impacts. Regardless of how much rain falls on Saturday,
river flooding this weekend through most of next week is expected to
be significant, especially over the southern Wabash and White Rivers.

Temperatures may struggle to climb out of the 40s on Sunday with a
stiff northerly wind and periodic light showers moving through the
area. Some models are hinting at snow mixing into these light
showers, but given the thermal profile of low 40s over low 30s,
wetbulbing to 35 and therefor snow chances looks unlikely.  T Monday
through Wednesday

Monday Onward:

After the wet and mild regime, a deep upper level trough will
overspread the eastern half of the country next week with high
confidence in cooler than normal conditions developing. Highs
through the first half of next week will only range from the mid 40s
to mid 50s with those temperatures subtly modifying later next week.
There will be a few opportunities for mainly light precipitation as
well as multiple weak waves aloft swing through the region. Cannot
rule out a few snowflakes mixing in with rain at times.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 632 AM EDT Fri Apr 4 2025

Impacts:

- MVFR to IFR ceilings 18Z onward with the arrival of SHRA

- Occasional gusts to 20kt overnight at KIND, KHUF and KBMG

- TSRA at KHUF, KIND and KBMG overnight; IFR VIS within TSRA

Discussion:

A brief dry period will begin shortly and continue through the
morning and into the afternoon. Within this dry period, ceilings
will remain around 5000ft with a NE to eventually east wind below
10kt. Light rain may stick around at KBMG for a few hours this
morning

This afternoon, another wave will arrive, pushing a frontal boundary
northward into central Indiana. Along the boundary MVFR and
eventually IFR ceilings will develop with light showers. This should
eventually pass north of all TAF sites by 00-02Z tonight with
ceilings lifting to between 1500-2500ft, but there is less
confidence in MVFR returning at KLAF.

After the boundary passes, heavier showers and scattered
thunderstorms are expected to pass through deteriorating conditions
further. These heavier showers and thunderstorms are expected to
continue through at least 08Z tonight


&&

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

&&

$$

UPDATE...CM
SHORT TERM...Updike
LONG TERM...Ryan/Updike
AVIATION...Updike