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.

- Flash flood threat across southern Indiana with multiple rounds of heavy rainfall.

MESOSCALE UPDATE

Issued at 1002 PM EDT Mon Apr 27 2026

Surface analysis shows the outflow boundary remains over far southern portions of Indiana. A wake low/meso-high earlier this evening has lead to fairly strong E-SE low level flow in near surface layer. This combined with increasing 1-2 KM LLJ, has aided in strong low level shear recent KIND VWP showing between 350-450 M2/S2 of 0-1 KM SRH.

Recent KIND ACARS sounding confirms with RAP mesoanalysis that around 200-300 J/KG of MLCINH exists over most of central Indiana which is limiting the threat for QLCS tornadoes except in brief instances where meso-vortices can be maintained either with cell mergers or within bowing segments of the line. Steep mid level lapse rates from 7-7.5 C/KM along with extremely strong effective bulk shear of 60-70 kts will continue the threat for severe hail.

Damaging wind gusts from 60-70 mph will continue to be the primary threat especially in bowing segments that are perpendicular to the deep shear vector. The damaging wind threat will reach the Indy metro by 11 PM. Further south, rainfall accumulations from 3-5 inches have lead to flash flooding potential. Increasing heavy rainfall with the convective line will support additional threat for heavy rainfall and localized flash flooding south of I-70 through the early AM period.

DISCUSSION (This evening through Monday)

Issued at 158 PM EDT Mon Apr 27 2026

Surface analysis late early this morning shows deepening low pressure over IA and MN, with a cold front extending south across IA to Central MO and NE OK. An area of strong convection had developed within the warm sector, over IL and was pushing east toward Indiana. Cloud tops continue to show steady state or slightly cooling tops. However the strongest echos were now pushing into a more stable area of air as showers have been falling in the Wabash Valley. Expected progression of the storms will be to the east, but conditions across Indiana were less favorable for convection. A better area for storms was found across southern Central Indiana with more access to instability there. Aloft, water vapor shows a moderate short wave over the Dakotas with a southwest flow of air ahead of this wave spreading across Illinois and Indiana amid weak diffluence aloft.

Tonight...

SEVERE WEATHER THREAT REMAINS TONIGHT.

Models show the upper wave progressing across the region, continuing to spread forcing dynamics across Indiana through the evening, Caveats have come into play. Namely, the cloud cover across Central Indiana from convection upstream have not allowed for peak heating. CAPE across the area remains limited this afternoon and the convection is expected to spread across Indiana in a decaying state late this afternoon. This will further diminish our severe weather threat. Later this evening, HRRR suggests more development over southern Illinois, pushing east into SW central Indiana. Confidence is higher for these storms to be strong to severe, perhaps impacting Vincennes, Sullivan, Linton, Washington and Shoals. Damaging straight line winds will continue to be the main threat, again an isolated QLCS tornado.

After a rainy evening, upper forcing is shown to end toward 05Z. Forecast soundings show drying and subsidence as the upper trough axis exits to the northeast. Lower level cloud cover should remain through the night, as lower level moisture remains trapped underneath an inversion.

Thus overall, high confidence for rain and storms this evening, with best chances across the southern and southwest parts of the forecast area. This will be followed by cloudy skies tonight. Little overall change in the air mass will result in lows only in the upper 50s as dew points are expected to remain in the 50s.

Tuesday...

Dry weather is expected on Tuesday as the upper flow is nearly zonal, with little in the way of forcing dynamics passing across Indiana. Forecast soundings continue to show a dry column with subsidence ongoing with the departure of the previous wave. At the surface, high pressure over the northern plains will continue to spill southeast toward Indiana. Thus after morning clouds, some afternoon sunshine should become available. Highs will reach the upper 60s to around 70.

Tuesday Night and Wednesday...

Showers and Thunderstorms will be expected during this time, particularly on late Tuesday Night into Wednesday. Models show another subtle short wave within the broader cyclonic flow aloft pushing across our region on late Tuesday night into Wednesday. A weak area of surface low pressure is expected to ride this wave, pushing across KY, and placing Indiana on the NW side of the low. Forecast soundings show the arrival of deep saturation late Tuesday Night into Wednesday with pwats as high as 1.7 inches. Thus confidence is high for another round of rain showers on at this time. Rain showers will exit by Wednesday afternoon as the upper forcing and surface low departs. northerly surface winds in the wake of the this system will allow for cooler temperatures on Wednesday, with highs only in the lower to middle 60s.

Thursday Through Monday...

Indiana/s weather during this period will be controlled mainly by a strong area of upper level low pressure over Ontario and Quebec. This feature is suggested to rotate waves within this flow across Indiana, mainly on Friday and again on Monday. The upper flow during this time will be mainly a northwest fetch spilling toward Indiana from Central Canada, providing mainly dry and cool air, due to the low to the northwest. It is only when the weak waves pass that enough forcing will be present to result in shower or storm chances.

Through this period within the lower levels surface high pressure looks to be anchored over the plains states, keeping mainly westerly or northwesterly flow in place across Indiana. Models suggest a poorly organized cold front to pass on Friday, but this system lacks access to deeper gulf moisture. A weak area of low pressure is suggested to pass across Indiana on Monday, again associated with the upper level feature.

Thus will try to contain pop chances to just Friday and Monday, with mainly dry and cool weather expected on Thursday, Saturday and Sunday.

As no intrusions of arctic or tropical air are expected, look for temperatures to be near or below typical seasonal lows.

AVIATION (00Z TAF Issuance)

Issued at 813 PM EDT Mon Apr 27 2026

Impacts:

- S-SE wind gusts 20 to 35 kt with higher gusts in TSRA - Scattered storms across area through the evening - Next line of storms to move through TAF sites around 02-05z - MVFR ceilings overnight into early Tuesday

Discussion:

Non-thunderstorm stronger wind gusts will persist early in the period with gusts around 35kt possible. Scattered convection will be ahead of the main line of convection, and the main line is expected to move through in the 02Z-05Z time frame. Gusts over 45kt, hail, and IFR/worse conditions are possible in the convection.

Overnight, MVFR ceilings will develop and persist into Tuesday morning. Winds will become west into Tuesday.

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

Flood Watch until 2 AM EDT Tuesday for INZ043>047-051>055- 060>063-067>070.