124
FXUS63 KIND 040654
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
254 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.

&&

.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 diuranl 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 stregthen
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.

Not 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 breif period following the elevated frontal passage

The more prolific rainfall is expected to arrive shortly after
sundown this evening as the LLJ stregthens and pushes highly
anomolous moisture along the WCB into the Ohio Valley. Strong
isentropic lift along with a deep CAPE profile should allow for very
effecient 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 effecient 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 buancy above the surface inversion and
shallowness of the surface inversion isolated severe wind gusts
within wet microbursts and/or more organzized 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 caviate 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 futher 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, with some potential for a greater risk
as confidence in the conditions becomes clearer later today.

&&

.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 (06Z TAF Issuance)...
Issued at 119 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

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.

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.

&&

$$

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