883 
FXUS63 KIND 041637
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1237 PM 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 (18Z TAF Issuance)...
Issued at 1235 PM EDT Fri Apr 4 2025

Impacts:

- VFR conditions expected to deteriorate to MVFR or worse this 
period 

- Rain arrives this afternoon with isolated thunderstorms. 

- More TSRA overnight; IFR VIS within TSRA.

Discussion:

Rain showers over southern IL and southern Indiana associated with a 
warm front will surge northward this afternoon, bringing 
precipitation and a return to MVFR or worse conditions to the TAF 
sites.

MVFR to IFR Cigs are expected through the evening and overnight 
hours as the warm front settles across Central Indiana. Another 
round of showers and storms will be expected overnight as another 
upper level weather disturbance passes across Indiana. Thunderstorms 
will be a bit more likely with this round as forecast soundings show 
some elevated instability. Some of these storms may produce heavy 
rain. Used a time window with tempo periods for this in the TAFs.

Another brief dry spell is expected early Saturday morning as the 
wave departs, however isolated stray light showers cannot be ruled 
out.  More rain and continued MVFR conditions will return by 
Saturday afternoon as yet another wave arrives.

&&

.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...Puma