textproduct: Indianapolis

KEY MESSAGES

- Heat Advisory through this evening for all of central Indiana except the far NE

- Isolated thunderstorm will be possible late this afternoon and evening.

- Not as warm and less humid on Sunday and Monday.

DISCUSSION (This evening through Saturday)

Issued at 153 PM EDT Sat Sep 5 2026

Surface analysis this afternoon shows a a weak, unorganized trough of low pressure stretching from OH, across Central Indiana to Illinois. Strong High pressure was found over Ontario and Quebec. Aloft, water vapor shows strong ridging in place over the plains, with NW flow spilling across the Great Lakes and into Indiana. Water Vapor also showed strong subsidence across the Great Lakes spilling south toward Indiana and Ohio. Dew points across Central Indiana were recovering to around 70.

Tonight...

Diurnal heating this afternoon along with the weak surface trough in place across the area will lead to Isolated thunderstorm development late this afternoon and this evening. CAMS suggest isolated convection, but all of this wanes after 03Z as heating is lost and more subsidence arrives. The main player through the overnight period will be the arrival of the high pressure system from the northeast. The strong subsidence aloft will allow the high to push south. The leading edge of this high will act as a pseudo cold front, pushing through trough further south. As the high arrives, winds are expected to become northerly, allowing lower dewpoints and cooler temperatures to arrive. Forecast soundings show a dry column overnight. Thus summing this all up, chances for showers and storms this evening, becoming mostly clear and cooler overnight.

Sunday and Monday...

The upper pattern will remain relatively the same, as strong ridging to the west is expected to slowly push east toward Indiana. This set up will allow any forcing dynamics to be pushed well to the north across the Great Lakes and Indiana will be protected. Meanwhile within the lower levels the cooler, Canadian high pressure system will sag south across the Great Lakes. This will allow for cooler and dry NE flow to spill across Central Indiana on Sunday and Monday. Forecast soundings each day show unreachable convective temperatures, a dry column and a strong mid level inversion in place. Thus, mostly sunny days and mostly clear nights will be expected, along with cooler highs in the mid 80s and less humidity.

Tuesday through Saturday...

A well defined new pattern aloft is suggested to take hold during this period.

The prominent and strong upper ridge that have been residing in the region will finally break down on Tuesday Night into Wednesday. This should allow for another day of heat on Tuesday before rain and storm chances return on Tuesday Night into Wednesday.

On Wednesday through Saturday, Pacific NW flow takes over across the northern plains, streaming to Indiana. A series of upper level short waves within that flow look to pass across Indiana during this time. Upper forcing with these waves look to pass at least once per day. Within the lower levels, best chances for rain look to be on Wednesday as a cold front passes, followed by Thursday Night through Saturday as a warm front arrives and Indiana looks to find itself within the warm sector of an approaching front. Temperatures look to be in the 80s, above normal for much of the week ahead. Tuesday will likely be the warmest day with highs around 90.

AVIATION (18Z TAF Issuance)

Issued at 1239 PM EDT Sat Sep 5 2026

Impacts:

- Isolated TSRA possible at IND and BMG from 23Z-02Z - Otherwise, mainly VFR

Discussion:

VFR conditions expected much of the TAF period as Indiana remains under the influence of strong high pressure over the east coast. Earlier convection has pushed a gust front across the TAF sites, reducing humidity briefly this afternoon, but the atmosphere should recover and be able to produce isolated storms late this afternoon and evening. HRRR suggests best chances will be in the eastern and southern parts of the forecast area. Hence have included mentions at IND and BMG. Confidence is high that there will be some isolated storms this evening, but confidence is low on overall timing/location.

Dry weather with VFR conditions is expected after 03Z as heating lost amid a dry forecast column.

IND WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT this evening for INZ028>030-035>037- 039-043>048-051>057-060>065-067>072.