textproduct: Indianapolis

KEY MESSAGES

- Cooler weather will continue through the week, with afternoon temperatures staying below seasonal averages

- Drizzle and light rain showers through tonight.

- Persistent mostly cloudy skies will begin to break towards Friday

DISCUSSION (Today through Tuesday)

Issued at 309 AM EDT Wed Sep 23 2026

Strong surface high pressure remains in place over southeastern Canada. East-northeasterly flow and moisture advection continues from the Mid-Atlantic states westward towards Indiana. Widespread stratus has been in place since yesterday.

Aloft, an upper-level low is advancing into Indiana from the west. This feature has allowed the surface wind field to gain cyclonic curvature. Combined with steepening lapse rates aloft, this has lead to broad lift within the stratus deck. Drizzle has developed across most of the region as of 3am this morning.

Today and Tonight

Drizzle should continue into the morning hours, before diurnal mixing causes it to diminish somewhat. Light rain showers may become the more dominant precipitation mechanism. As such, slight to chance PoPs will be carried today. Precipitation chances increase this evening into tonight as the upper low settles in. Drizzle may once again become more prominent during the overnight hours.

Ceilings will be low today, with cloud bases only 500 to 1000 feet above ground level. Diurnal mixing may allow this to rise to between 1500 to 2500 feet. Overcast skies are expected through tonight.

These clouds should keep temperatures suppressed as we've seen in previous days. We will go below guidance with highs only climbing into the low to mid 60s. Lows however will be on the warmer side of guidance, due to the insulating effect of the low clouds.

Thursday

Things begin to change on Thursday as the upper-level low continues southeastward. After it departs, surface high pressure to our north once again becomes the dominant feature. Broad subsidence and low- level dry air advection will help dissipate the stratus. This may take most of the day, unfortunately, so we are still expecting mostly cloud skies.

Temperatures a bit warmer than Wednesday are likely, given breaks in the clouds and less rain/drizzle. Highs in the 60s are still the most probable outcome. As for lows, a more dramatic difference is in store for Thursday night. With clearing skies, light winds, efficient radiational cooling is anticipated. This should help temperatures drop to the coolest values we've seen since spring. Lows in the 40s to low 50s are likely across most of the region by Friday morning. Patchy fog may be possible as well.

Friday Through Tuesday.

Increasing subsidence aloft along with weak upper level flow will keep cloud cover at bay Friday into the weekend bringing temperatures closer to normal for this time of the year. Dry air advection continues, with min RH values dropping below 40 percent across south central Indiana which combined with the drier conditions of late, may need to be monitored for a low-end fire danger. Near calm winds will help to limit that threat.

Looking further into early next week, temperatures in the lower 80s look to return as the surface flow gradually gains a more southerly component along with gradually increasing rain chances towards late Tuesday ahead of the next system.

AVIATION (06Z TAF Issuance)

Issued at 141 AM EDT Wed Sep 23 2026

Impacts:

- MVFR/IFR ceilings through the forecast period. - Patchy drizzle this morning, light rain showers and drizzle into Wednesday night.

Discussion:

Strong surface high pressure remains in place over southeastern Canada, providing northeasterly winds between 8-12kt across central Indiana. Moisture advection from the east has allowed extensive cloud cover to develop and persist since Tuesday.

An upper-level low is arriving from the west and this has allowed the surface wind field to gain cyclonic curvature. The primary effect this will have is to cause the stratus layer to thicken and for patchy drizzle to develop. We have already seen drizzle over most of the region since midnight. Patchy drizzle should continue into the morning hours Wednesday.

Drizzle diminishes later this morning as diurnal mixing intensifies. However, this may allow for light rain showers to develop during the afternoon. Showers and renewed drizzle then continue into tonight, potentially through 12z Thursday.

Winds remain out of the northeast through the TAF period around 10kt, decreasing a bit after 00z.

IND WATCHES/WARNINGS/ADVISORIES

None.