textproduct: Indianapolis

KEY MESSAGES

- Scattered showers and thunderstorms pushing northward, through the afternoon. Potential for severe winds and hail this evening into tonight.

- Cooler and rainy on Tuesday. Heavier rain late Tuesday could lead to localized flooding.

- Largely below normal this upcoming week, with multiple chances for additional rain.

MESOSCALE UPDATE

Issued at 1038 PM EDT Mon May 4 2026

Main focus for this evening's update/mesoscale discussion will be on the severe threat during the overnight hours across Central Indiana.

Strong upper level divergence over the region in this split flow pattern in addition to an approaching surface cold front from the north create more than enough lift for precipitation development tonight. A strengthening 45-50 kt LLJ ahead of the front will work to sustain upstream convection and help induce convective development across Illinois early this evening. Despite a good set up aloft, poor moisture return northward has resulted in 20-25+ degree dew point depressions across Indiana today. ACARs soundings look more like an inverted Vs with high LCLs nearing 700mb and steep mid to upper lapse rates above it around 8-8.5C/Km. While not the best environment for severe weather, this unique set up for Indiana in May can support multi and discrete cells capable of producing some strong winds and hail.

Radar over Illinois has shown a lot of convective development over the past hour in response to mass upper level divergence on top of a strong low level jet. The environment west of Indiana is a bit more conducive for these storms with better lapse rates, slightly higher dew points, and CAPE of 500-1000+ J/kg. Observations and soundings show little to no CAPE over Indiana this evening and it will be a struggle for the atmosphere to destabilize through the overnight hours. While there are a many convective parameters favoring a threat for damaging winds and hail from these high based storms, the lack of CAPE over Indiana may significantly decrease the overall severe threat as storms approach the IL/IN border.

Currently watching a cluster of storms in Central Illinois producing quarter size hail at times. Expect these storms to weaken over the next few hours as they make their way along the I-74 and I-70 corridors. Best chance for any hail will be in Western Indiana in the 11pm to 1am timeframe. The strong wind threat (gusts up to 50mph) may persist throughout the night as steeper low level lapse rates within a fairly dry boundary layer will be conducive for stronger winds to mix to the surface under any shower or storm. Still, confidence remains low in severe gusts at or above 60 mph as the storms weaken.

The first round of storms will make its way into Central Indiana from the west in the 11PM to 1AM timeframe. At the same time, watching a cluster of thunderstorms and bowing segments along the cold front in Northern Illinois sagging southeastward. CAMs shows both of these areas of storms combining during the overnight hours as they weaken. Northwestern portions of Central Indiana including Lafayette may have a better strong wind threat as a bowing segment near Bloomington, IL heads in that direction over the next couple hours. OVerall, not too concerned with the severe threat for Central Indiana tonight. Would not be surprised to see an isolated damaging wind gust or large hail report, but for the most part everything should remain below severe limits. With that said, gusty winds, small hail, and lightning can be threats with any of these storms.

DISCUSSION (This evening through Monday)

Issued at 325 PM EDT Mon May 4 2026

This afternoon, scattered showers with isolated lightning are slowly pushing northward. Winds aloft are sitting around 50-55 mph, with gusts up to 50 mph periodically mixing down to the ground within stronger showers. Outside of the rain, gusts of 20-35 mph are also mixing down and these winds are expected to continue into the early overnight hours.

More showers and storms are expected to arrive this evening, ahead of a cold front that will be pushing from NW to SE through from tonight through early Wednesday morning. There is the potential for severe storms this evening to tonight ahead of the front as winds aloft and instability increase, potentially enough to overcome the limited moisture at that time. Main threats will be damaging winds as well as hail. The tor threat doesn't look great, but it is non- zero. The severe threat is expected to come to an end within a few hours after midnight, but scattered showers and storms will continue. Models show an additional surge of moisture from the S/SW to arrive Tuesday afternoon into the overnight hours then prompting localized flooding concerns, particularly across our south. In total with this system, 1-2 inches are forecasted through Wednesday morning, but locally higher amounts, again mainly in the south, can't be ruled out.

Also with the front, cooler temperatures arrive tomorrow and last through much of the rest of the work week. Rain should come to an end by Wednesday morning or midday, exiting to the SE.

Overall upper pattern remains unchanged for Thursday and on. Models suggest the upper low that provided the cold front remaining over eastern Canada, keeping the continued cyclonic flow in place aloft over much of the eastern 1/2 of the country including Indiana. This will keep a steady stream of below normal temperatures in place across Indiana from Thursday through the weekend. Meanwhile at the surface, a series of weak highs and lows will look to pass. High pressure is expected to push across the area on THursday, before a weak trough passes on Friday. Another high arrives for Saturday followed by a slightly more organized low on Sunday. Given the cyclonic flow in place aloft, and forecast soundings suggest cold air aloft with steep lapse rates available each day, daily convection cannot be ruled out and for the moment, additional support appears available on Friday and Sunday. Thus daily chances for rain will be expected in the forecast, however, this will be mainly due to daily diurnal chances and the passing of the trough and low on Friday and Sunday respectively. Overall, high confidence of periodic showers during this period, but low confidence on specific timing.

AVIATION (00Z TAF Issuance)

Issued at 757 PM EDT Mon May 4 2026

Impacts:

- Widely scattered strong storms possible near KHUF and KBMG 02-05z timeframe - Main line of storms from the NW moves through Central IN 04z-09z - Gusty SW winds of 20-25 kt into the overnight hours, higher winds likely in thunderstorms - Another round of widespread rain after 12z persisting most of Tuesday. TSRA may be along leading edge during late morning hours. - Low MVFR to IFR ceilings starting early to mid morning and persisting through the day

Discussion:

An active night for aviation weather expected over Central Indiana. Satellite and radar show a cluster of storms developing in west central Illinois and also a line of storms along a cold front in Northern Illinois and Iowa. The cluster of strong to severe storms may near KHUF and KBMG in the 02-04z timeframe if they can hold together after sunset with hail, winds, and lightning all being threats. Higher confidence exists in the line associated with the cold front which will push southeast through Central Indiana around the 04z-09z timeframe. Cloud bases should be fairly high, so there is a good chance that cigs remain VFR with brief periods of MVFR or worse vis in heavier rain. Erratic wind speeds and directions likely.

Expect wind gusts to remain elevated at 20-25 kts even after sunset and ahead of the approaching front. Gusts may become more sporadic after sunset however confidence remains high enough to keep them in the TAF. Expect a wind shift to the north behind the front.

Widespread rain develops over Central Indiana, impacting all TAF sites during the mid to late morning hours and persists through much of the day. There may be a brief period of lightning on the leading edge of this rainfall before the environment stabilizes and the lightning threat diminishes during the afternoon. Ceilings are expected to drop to MVFR around and after 12z and eventually to IFR as a cold front moves through from NW to SE. Visibilities should also drop to MVFR within the rain as well.

IND WATCHES/WARNINGS/ADVISORIES

None.