textproduct: Indianapolis

KEY MESSAGES

- Multiple rounds of thunderstorms expected today, severe weather is possible this afternoon into tonight.

- Isolated Showers and thunderstorms possible on Tuesday, mainly across southern Indiana.

- Cooler temperatures expected Wednesday through Sunday.

DISCUSSION (Today through Sunday)

Issued at 330 AM EDT Mon Apr 27 2026

TODAY'S SEVERE WEATHER POTENTIAL

A potent vort max is ejecting out of the Rockies as of this writing. Lee cyclogenesis is ongoing over the high plains, with the resulting cyclone expected to move northeastward through sunrise. The system passes to our northwest this afternoon. Strong mass response should drive a potent southerly low-level jet (LLJ), which increases into the evening hours.

Flow at the surface may still be out of the east-southeast through this morning, as surface high pressure slides eastward. This may limit moisture return over Indiana, with some CAMs showing relatively dry conditions into this afternoon (RH as low as 45 percent). Winds gradually become more southerly through the day, allowing dew points to increase through the evening hours.

Two scenarios exist for convective evolution today. First, convection developing over Kansas (as of 3am) grows upscale into an MCS and propagates eastward through the night into the strengthening LLJ. Some CAM guidance like the HRRR show such a scenario, with the MCS arriving around 19z. Of particular interest is the relatively dry air mass over Indiana and whether this causes the approaching MCS to weaken. Also of interest is strong wind gusts shown by some CAMs within the anvil region of the MCS. This appears to be driven by strong evaporational cooling as rain falls into the dry low-level air mass. Momentum from the strengthening LLJ is then mixed downward, allowing for the strong wind gusts. Guidance also hints at a flooding threat on the southern margin of the MCS where training cell motions are most favored.

The second scenario is that there is no MCS, or it passes to our north, and thunderstorm development occurs over Illinois along the systems's trailing cold front. Such a scenario would allow instability to build up until explosive convective development occurs. Shear vectors slightly off boundary should allow for initially discrete convection, with shear magnitudes favoring supercells over Illinois. Upscale growth into a line then appears likely with eastward extent. Moisture advection ahead of the front should allow convection to sustain through Indiana and into Ohio. It is possible that the MCS from the first scenario does arrive and affects only part of our CWA with the cold frontal convection arriving later for those that did not see the MCS.

Given the potential for multiple rounds of convection, pin-pointing exact timing remains tricky. Additionally, keying in on which hazards are most likely and where is a challenge as each round of convection alters the environment ahead of the next round. That being said, all hazards are possible with today's severe weather given the amount of shear (40-60kt) and instability (1500-2500 J/Kg MLCAPE) expected. All hazards are possible especially with any supercell that develops. Supercells are most likely over Illinois, however, with upscale growth increasingly likely by the time things reach Indiana. Strong to damaging winds are favored with upscale growth or in scenarios that result in an dominant MCS. Given the strong LLJ and high amounts of SRH (200-300 m2s2) present within the warm sector, a QLCS tornado threat is possible as well.

TUESDAY ONWARD

A second shortwave ejecting from the Rockies closely behind Monday's may provide another chance at showers and storms. However, given the potency of Monday's system, much of the moist unstable air will have been swept away by the time the second system arrives. Sufficient moisture return may be possible for storms over the southern half of Indiana late Tuesday. Severe weather may again be possible should this occur, especially further south, but this depends on how quickly moisture and instability can advect back northward.

After Tuesday, persistent troughing aloft takes hold and cooler than average conditions are favored for the second half of the week and into the weekend. High temperatures in the 60s and lows in the 40s appear likely Wednesday through Saturday. Guidance is hinting at some lows into the 30s possible this weekend, which could mean frost potential.

AVIATION (06Z TAF Issuance)

Issued at 144 AM EDT Mon Apr 27 2026

Impacts:

- S-SE wind gusts 20 to 30 kt Monday - Scattered to numerous convection, mainly Monday evening - LLWS around 45kt Monday evening/night - MVFR ceilings Monday evening into early Tuesday

Discussion:

Tonight will be quiet with mainly high clouds moving through. Outside of convection, VFR conditions are expected through 00Z Tuesday, with a gradual lowering of ceilings occurring. Winds will increase Monday, with frequent gusts to around 25kt, with a potential for a few gusts near 30kt in the afternoon.

Uncertainty ramps up quickly Monday in terms of rain. There could be some weakening convection in the morning hours. Some convection may develop after 18Z depending on mesoscale features, but better odds of thunderstorms will occur after 22Z. Will use PROB30s, but when details become clearer, TEMPOs will be needed in later issuances.

Otherwise, MVFR ceilings are expected to develop as rain becomes more widespread and low-level moisture increases. These ceilings may persist into Tuesday morning. Additionally, a cold front is anticipated late Monday night with a wind shift to westerly behind the front. A period of low-level wind shear is likely ahead of the front as southerly flow increases.

IND WATCHES/WARNINGS/ADVISORIES

None.