textproduct: Indianapolis

KEY MESSAGES

- Spotty showers and possibly a rumble of thunder this afternoon and evening

- Below normal temps to continue through the weekend with frost likely Saturday and Sunday

- Slow warm up with rain returning early next week, potential for heavy rain at times

DISCUSSION (This evening through Thursday)

Issued at 127 PM EDT Thu Apr 30 2026

Overview.

Central Indiana will experience a persistent period of below-normal temperatures through the upcoming weekend as a deep upper-level trough remains anchored over southeast Canada. While scattered light showers and isolated rumbles of thunder are possible through this evening, the primary focus shifts toward a significant frost threat for Saturday and Sunday mornings as surface high pressure settles over the region. Looking into next week, a transition to a more active and humid pattern is expected as the synoptic flow shifts, bringing an increasing threat of heavy rainfall by midweek.

This Evening through Saturday Night.

The current mesoscale environment is defined by a lingering northwesterly flow behind a departing frontal boundary, with high- resolution model guidance such as the HRRR and NAM indicating a weak shortwave ripple moving along the broader cyclonic flow. While low- level moisture is limited, a narrow window of mid-level saturation and modest lapse rates around 7 C/km will support spotty showers and perhaps a few isolated thunderstorms late this evening, though instability remains too meager for any severe concern. As the shortwave exits, residual mid-level moisture will keep clouds across the area through near daybreak which will keep temperatures slightly more mild with lows in the low to mid 40s. Friday will be dry and seasonably cool, but by Saturday morning, the proximity of a surface high-pressure ridge will promote better radiational cooling conditions. With areas of frost expected along and north of the I-74 corridor with a low-end potential for a freeze near Muncie and areas to the northeast. Radiational cooling becomes most favorable on Sunday morning as the axis of the surface high pressure moves directly over central Indiana, resulting in nearly calm winds and clear skies. This setup will allow the boundary layer to decouple efficiently, with high confidence in widespread frost as temperatures bottom out in the lower 30s across most of the forecast area with the main uncertainty being the timing of the shift to stronger southerly flow which could advect just enough warm air to limit frost formation.

Sunday through Thursday.

Another dry day is expected for Sunday with southerly flow gradually strengthening ahead of the pattern shift for early next week. Transitioning into Monday and Tuesday, the high pressure departs to the east, allowing for a slow warming trend as low-level flow turns southerly and begins to draw moisture from the Gulf of Mexico. Broad ensemble runs, including the GEFS and ECMWF, highlight a deepening longwave trough over the Central Plains by Wednesday, which will significantly increase precipitable water (PWAT) values toward 1.40 to 1.60 inches. This surge in moisture, combined with a quasi- stationary frontal boundary draped across the Ohio Valley, creates a notable threat for heavy rain and training convection toward the end of the period. Current probabilistic guidance suggests a 20-30% chance of rainfall totals exceeding 2 inches in some basins, necessitating a close watch on river levels and potential flash flooding concerns for the middle of next week.

AVIATION (18Z TAF Issuance)

Issued at 127 PM EDT Thu Apr 30 2026

Impacts:

- Showers tonight at times, a rumble of thunder possible - MVFR cigs after 06Z, IFR possible towards 10Z - Isolated gusts to 20kts towards LAF this afternoon

Discussion:

VFR conditions with mostly clear skies expected through the remainder of the day with only an isolated gust towards 20kts possible at times. Rain chances begin to increase after 00Z with best chances from 04Z to 09Z. As the rain arrives, cigs will drop to MVFR with IFR possible towards 10Z. Vsbys will generally remain MVFR during showers, but a rumble of thunder or two will be possible along with brief IFR vsbys. Any showers should end by 12Z with cigs becoming VFR shortly after. WInds will remain northwesterly to westerly through the period at 7-13kts outside of the isolated gusts this afternoon.

IND WATCHES/WARNINGS/ADVISORIES

None.