textproduct: Indianapolis

KEY MESSAGES

- Potential for showers/storms late tonight/early tomorrow morning, better chances in the afternoon and evening

- Dry and quiet this weekend

- Strong to severe storms likely Monday into Monday night

DISCUSSION (This evening through Thursday)

Issued at 113 PM EDT Thu Apr 23 2026

Overview.

An active and progressive spring pattern continues across the Ohio Valley as a series of shortwave troughs traverse the mean flow. The first of these features will impact central Indiana tonight through Friday evening as a surface cold front interacts with a modestly unstable airmass bringing rain and the potential for a few strong to severe storms. After a brief period of quiet weather through the weekend, a more potent, negatively-tilted synoptic system is forecast to eject from the Four Corners region into the Great Plains by late Sunday. This system will bring a significant threat for organized severe storms and heavy rainfall to the region on Monday and Monday night as it brings a powerful LLJ and rich boundary layer moisture into the region.

Rest of Today Through Saturday.

The primary forecast challenge through the next 24 hours revolves around the timing and convective evolution of an approaching surface cold front currently across the Upper Midwest. Mid-level water vapor imagery reveals a compact shortwave trough pivoting across the Great Lakes, which will provide the large-scale ascent to maintain ongoing convection across Iowa as it moves to the southeast. As it nears central Indiana the storm complex will exit the area of better elevated instability and weak shear due to a weaker LLJ. Surface- based instability will continue to wane with nocturnal cooling, especially towards daybreak Friday as the line approaches. Timing currently looks to be either just before daybreak in the scenario where the line is stronger with a more robust cold pool, or the more likely scenario of after daybreak with an overall weaker and less organized complex of showers.

As we transition into Friday, the surface front will likely be bisecting the forecast area by midday. Model consensus, including recent HRRR and RAP runs, indicates a window for destabilization ahead of the boundary as clearing skies allow temperatures to climb into the mid-70s. However, there is some uncertainty regarding the impact of remnant debris clouds from the overnight activity. If sufficient diabatic heating occurs, SBCAPE could reach 2000 J/kg by 18Z-20Z. Given the frontal forcing and steepening mid-level lapse rates approaching 7.0 C/km, a second round of more organized convection is possible, especially further east towards Ohio. The primary risk with this Friday afternoon activity would be damaging wind gusts and large hail. By Friday night, some ensemble guidance suggests an MCV currently over the Central Plains may track along the departing front, which could keep rain chances elevated for the southern tier of counties through Saturday morning.

Sunday Through Thursday.

Attention then shifts to the significant synoptic event unfolding for Monday. Recent global model guidance, including the 12Z GFS and ECMWF, has shown remarkable consistency in depicting a vigorous, negatively-tilted mid-level wave ejections out of the Southwest. This feature is expected to induce rapid surface cyclogenesis over the Central Plains by Sunday night, with the resulting sub-995mb surface low tracking toward the Upper Mississippi Valley by Monday afternoon. This will result in a significant northward surge of Gulf moisture, with dewpoints expected to reach the mid 60s as far north as the I-70 corridor.

Scientifically, the Monday setup is particularly concerning due to the coupling of strong kinematics and significant instability. Guidance indicates a 55-65 kt LLJ will be in place across central Indiana by Monday afternoon, which will not only provide intense low- level moisture transport but also contribute to enlarged, curved low- level hodographs. 0-1 km SRH values exceeding 250 m2/s2 are currently being modeled, which would be more than sufficient for a tornado threat if storms can remain discrete. CAPE values in the 2000-3000 J/kg range appear plausible given the WAA regime. While some global models show a faster progression with a QLCS along the cold front, the potential for pre-frontal supercells within the open warm sector cannot be ruled out, especially given the degree of forcing from the approaching shortwave.

Furthermore, the high PWAT values approaching 1.5 to 1.7 inches, which is near the 90th percentile for late April, will introduce a risk for flash flooding. The orientation of the LLJ relative to the advancing front suggests the possibility of training cells or back- building convection during the Monday night period. As the primary surface low moves into the Great Lakes by Tuesday, a powerful cold front will sweep through the Ohio Valley, effectively shunting the moisture south and ushering in a much cooler, drier airmass for the middle of next week. In the wake of this system, GEFS and EPS means show a period of high-pressure dominance with temperatures returning to near or slightly below seasonal norms.

AVIATION (18Z TAF Issuance)

Issued at 113 PM EDT Thu Apr 23 2026

Impacts:

- Wind gusts around 20kt this afternoon

Discussion:

VFR conditions generally expected outside of convective activity. Tonight will see scattered TSRA/RA chances at KLAF and KIND after 10Z, with temporary MVFR cigs/vsbys possible in heavier cells. Additional convection is possible during the daytime hours, but confidence on timing is too low to mention in the TAF at this time. Winds will remain gusty out of the southwest at 10-15 kts with gusts to 25 kts through 00Z. A frontal passage on Friday will shift winds to the northwest towards the late afternoon.

IND WATCHES/WARNINGS/ADVISORIES

None.