textproduct: Indianapolis

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.

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.