textproduct: Indianapolis

KEY MESSAGES

- Mainly cloudy and cool through midweek

- Dry and seasonable late week into the weekend with gradually warming temperatures

FORECAST UPDATE

Issued at 912 PM EDT Mon Sep 21 2026

Surface analysis this evening shows strong, Canadian high pressure in place over Ontario and Quebec. This high was influencing the weather across the Great lakes and south to the Ohio River. Cool and dry northeasterly flow was in place across Indiana, along with a moderate pressure gradient. GOES19 shows abundant cloud cover across Central Indiana and the region. The high to the north was resulting in a cool NW dirty flow.

Overnight, very little change in the overall forecast. Clouds will remain across the area amid the continued easterly flow. Forecast soundings continue to indicate saturation within the lower levels with a trapping inversion aloft. Thus cloudy skies will persist through the night. The clouds and winds will keep temperatures from falling too much as they reach the mid and upper 50s.

DISCUSSION (This Evening through Monday)

Issued at 220 PM EDT Mon Sep 21 2026

Much cooler air has overspread the region in the wake of the frontal passage late Sunday. Cloudy and breezy conditions are expected through Wednesday as an upper low moves slowly through the area. This feature will cutoff over the mid Atlantic by late week...with much drier air being pulled south into the Ohio Valley through the weekend.

Rest of Today through Wednesday Night

In the wake of the morning rain...a damp and dreary airmass remains across central Indiana under a thick stratus deck and with breezy northeast winds. 18Z temperatures were much cooler than what has been experienced over the last several days with much of central Indiana in the 60s.

There remain a few light showers or sprinkles over the southeast half of the forecast area but the overall trend since the morning has been for rainfall coverage to decrease extensively as the frontal boundary that moved through the area Sunday afternoon and evening has now moved well south into the Tennessee Valley.A few light showers remain possible for the next few hours before departing. Abundant moisture persists through the boundary layer trapped beneath a stout inversion. Model soundings show the inversion weakening slightly this evening which may be just enough to allow for a brief period with breaks in the stratus deck. As the inversion strengthens overnight however...expect the stratus deck to thicken back up with ceilings lowering again into Tuesday morning. Cannot entirely rule out a few sprinkles tonight but low confidence in this occurring.

Clouds will remain on Tuesday as an upper low pivots into the region from the northwest. The upper low will bring isolated light showers across the far northeast portion of the forecast area otherwise expect a continuation of weather today with thick stratus and cool N/NE flow. The upper low will be slow to shift east of the area as it becomes cutoff from the mean flow aloft well to the north of the region. This will keep an abundance of clouds over most of the forecast area through Wednesday as well with again a low chance for a few showers across our northeast counties. More substantial breaks in the clouds should come Wednesday night as ridging aloft slowly spreads into the Ohio Valley from the west.

Temps...highs will not get out of the 60s this afternoon for much of the forecast area...the coolest day since May 23. Expect similar temperatures both Tuesday and Wednesday with highs ranging from the mid 60s northeast to the lower 70s southwest. Lows will be in the 50s.

Thursday through Sunday

The aforementioned upper low will settle over the Mid Atlantic region during the second half of the week. Cool E/NE flow and at least some lingering cloud cover on the back side of the developing cutoff low will maintain below normal temperatures Thursday with highs ranging from the upper 60s to the mid 70s from northeast to southwest. Ridging aloft will gradually shift into the Ohio Valley with an axis of deepening subsidence advecting into the region from the north. Under mainly clear skies...temperatures will recover back to late September normals with highs warming into the mid and upper 70s by Sunday and perhaps into the lower 80s over parts of the forecast area by Monday. The coolest night since the Spring comes Friday night as lows in the mid and upper 40s will be common...with temperatures recovering into the 50s for lows by the end of the weekend.

AVIATION (00Z TAF Issuance)

Issued at 545 PM EDT Mon Sep 21 2026

Impacts:

- Mainly MVFR Cigs this period. - Periods of IFR possible at BMG.

Discussion:

Cool, Canadian high pressure north of Central Indiana will continue to provide a dirty NE flow of cooler air to the TAF sites. Forecast soundings through the period keep saturated lower levels in place with a trapping inversion aloft.

With little change in the pattern over the next 24-30 hours, MVFR cigs will remain. A moderate pressure gradient across the area will keep wind speeds around 10 knts. This will keep mixing going overnight and should help to prevent fog.

IND WATCHES/WARNINGS/ADVISORIES

None.