603
FXUS63 KIND 281356
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
956 AM EDT Tue Apr 28 2026

.KEY MESSAGES...

- Showers and thunderstorms expected late Tuesday. Severe
  potential very low.

- Flooding threat continues across southern Indiana after multiple
  rounds of heavy rainfall.

- Cooler temperatures expected Wednesday through Sunday.

- Frost possible this weekend.

&&

.FORECAST UPDATE...
Issued at 955 AM EDT Tue Apr 28 2026

Quiet a different airmass over Indiana compared to just 12 hours ago
as severe storms were barreling through the state. Latest satellite
imagery and observations show west-northwest flow over the region
this morning behind the cold front pushing east through Ohio
extending from a departing low in Ontario. Widespread low clouds and
stratus remain overhead as near surface moisture is trapped under a
developing subsidence inversion around 1 km agl. Upstream
observations indicate that clouds will likely stick around through
the day, keeping temperatures near or below guidance for highs.
Temperatures may struggle to get out of the 50s in portions of North
Central Indiana where more widespread cloud cover persists. Expect
mid to upper 60s further south, with low 70s possible in far
southwestern portions of the region where a bit more sunshine is
expected.

&&

.DISCUSSION (Today through Monday)...
Issued at 309 AM EDT Tue Apr 28 2026

A potent vort max and associated surface cyclone are now passing to
our north. Though thunderstorm activity has ended across Indiana,
winds remain out of the south. The system`s cold front lags quite a
bit behind the rain, and is located to our west over Illinois. High-
resolution guidance brings the front through around 12z with only a
subtle drop in temperatures.

Guidance is hinting at lingering low-level cloud cover through much
of the day today. Should these clouds persist through the afternoon
hours, then high temperatures may be well-below blended guidance. We
will trend lower than the blend, but not as low as some high-res
models suggest (highs in the upper 50s to low 60s). The cold front
may stall out over our southern counties, allowing temperatures to
be warmer than further north. Highs into the low 70s are more likely
closer to the Ohio River.

TONIGHT`S THUNDERSTORM CHANCES

Zooming out a bit, a subtle mid-level vort max ejects out of the
Rockies today. Another round of surface cyclogenesis is anticipated,
this time to our south along the stalled-out front. A coupled jet,
vorticity advection, and broad isentropic lift should allow for
widespread shower activity late Tuesday into Tuesday night.
Isentropic lift is centered around 700mb, and there are hints that
some elevated instability develops ahead of the approaching vort max
allowing for thunderstorm potential. At the surface, however, winds
look to become northerly as low pressure develops to our south. This
will prevent warm buoyant surface air from lifting northward. As
such, most if not all convection will be elevated.

As for severe potential, there appears to be enough shear for
organized thunderstorms but it is displaced from the best
instability which remains to our south. The threat appears very low,
but marginally severe hail cannot be ruled out. Again, the best
chance of this occurring (less than 10 percent) is across our
southern counties.

WEDNESDAY ONWARD

Ensemble guidance remains in good agreement showing a persistent
troughing pattern developing over the Great Lakes and northeastern
US. Global teleconnections add weight to this idea, with the Pacific
North American pattern trending positive and both the Arctic
Oscillation and North Atlantic Oscillation trending negative. All of
these favor anomalous ridging over the western US with troughing
over the east.

Such a pattern typically brings northwesterly flow aloft and cooler
than normal temperatures. Deterministic guidance shows just that,
with much cooler weather taking hold by Wednesday and continuing
into the weekend. In fact, troughing may become deep enough that
multiple days with nightly lows in the upper 30s to low 40s are
likely. Should a period of ideal radiative cooling occur, then low
temperatures well into the 30s with frost is possible. The best
chance of this scenario occurring appears to be over the weekend as
surface high pressure develops overhead.

Temperatures may rebound a bit early next week but cooler
than average conditions are still favored.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 635 AM EDT Tue Apr 28 2026

Impacts:

- MVFR/IFR ceilings this morning, persisting into the afternoon at
  LAF
- Showers and possibly a thunderstorm tonight

Discussion:

Widespread stratus persists across central Indiana after rain and
thunderstorms last night. Ceilings have been as low as 600ft agl,
but have risen slowly over the past few hours. Stratus is expected
to diminish this morning from HUF to IND southward, persisting into
the afternoon at LAF. MVFR ceilings return with rain/storms tonight.

Rain showers appear likely as a system approaches from the west.
Thunder is possible, but not as likely as rain, so a PROB30 group
has been included for TSRA. Showers/storms continue into tonight
ending by around 12z.

Surface winds become northwesterly today, slowly turning northerly
this evening. Speeds around 10kt are likely through morning,
diminishing this evening into tonight.


&&

.HYDROLOGY...
Issued at 324 PM EDT Mon Apr 27 2026

Precipitable water values are forecast to be increasing to
over 1.5 inches until around 6z or thereafter. While a morning
sounding launched from IU Bloomington showed a distinct and deep dry
layer in the mid levels, advection of deep moisture is occurring and
should make for more efficient rain processes. The current
convective line has taken on a more southwest to northeast
orientation, and the back edge of this is becoming more WSW to ENE.
Several different ensemble members are showing the potential for 3
hour rainfall amounts approaching/exceeding 3 inches along the I-70
corridor and this has resulted in a highlight from the urban rain
rate dashboard for Indianapolis. HREF has LPMM bullseyes of 5 to 7
inches by Tuesday morning embedded in a larger area 3 to 5 inches
over an area along I-70 and southward over much of western Indiana
eastward to about I-65. WOFS runs are highlighting similar high
rainfall amounts with high probabilities of over 3 inches in 3
hours, again along I-70. Training of cells over the same area could
increase with time as a boundary stalls out and low level jet ramps
up perpendicular to the boundary similar to surface flow, but the
mid level flow is more oriented along the boundary. Last couple of
HRRR runs have bounced back and forth with the precip amounts in
excess of 3-4+ inches, with the 17z run trending higher again and
further north, but majority of factors including current satellite
and radar trends are favoring the areas along I-70 and southward.
May include a tier of counties north of there to account for
uncertainty. On most guidance, southern tier of counties miss out on
the heavy rain amounts, so may keep the flood watch relatively
small.

Fast responding creeks and streams can be expected to see quick and
significant rises, and if the higher amounts pan out in a particular
basin locally significant and impactful flash flooding could be the
table. On the main stem rivers, streamflows are low and have room
for water so anything more than minor lowland river flooding
developing would be pretty localized.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...CM
AVIATION...Eckhoff
DISCUSSION...Eckhoff
HYDROLOGY...CP