textproduct: Indianapolis

KEY MESSAGES

- Clouds decreasing overnight

- Cooler and less humid on Monday

- Hot and humid conditions returning Tuesday and Wednesday with highs reaching the 90s

FORECAST UPDATE

Issued at 957 PM EDT Sun Sep 13 2026

Seasonably strong cold frontal zone passage so far today has lead to quick drop in humidity through PM hours on northerly breezes, with dewpoints at 915 PM EDT ranging from 50F at Lafayette to a fleeting 63F in Daviess County. Temperatures have displayed a parallel trend with seasonably mild mid-evening readings in the mid-60s to around 70F. Scattered mid/high decks arranged west-east across the region amid the lingering frontal zone will decrease by pre-dawn, although light breezes are expected to maintain while veering to NE through the overnight. Resultant cooling processes/advection to continue to drop readings...with lows bringing the first 50F in Greentown since late June, and upper 50s as far south as Crane.

Tonight will be the coolest overnight of the next week, with the axis of Canadian high pressure already tracking east into Ohio by Monday afternoon ahead of mid-week heat.

DISCUSSION (This evening through Sunday)

Issued at 134 PM EDT Sun Sep 13 2026

Overview.

A weak frontal boundary moving across Central Indiana will bring a brief chance of showers late this afternoon and early evening before high pressure brings cooler and less humid air on Monday. Hot and humid conditions will return quickly on Tuesday and Wednesday as an upper-level ridge builds across the Ohio Valley, driving high temperatures into the lower 90s. Occasional showers and storms are expected late Tuesday through the weekend with best chances Tuesday night and again on Thursday.

Tonight Through Tuesday.

The aforementioned surface cold front will drift through Central Indiana this evening and will exit to the southeast during the overnight hours. HREF guidance and HRRR show isolated to scattered showers along the baroclinic zone through sunset, diminishing rapidly as surface heating is lost and mid-level PVA departs. Moderate CAA in the 925-850mb layer behind the front will push lower dewpoint air across the region, while surface high pressure expanding from the Upper Midwest builds into the Ohio Valley. Efficient radiational cooling under clearing skies will drop Sunday night lows into the 50s across most locations. There may be some fog/low stratus across the Upper Wabash Valley but with the much drier air, confidence is low.

Surface high pressure across the region on Monday will result in broad-scale subsidence, light northerly flow, and pleasantly cool conditions. Model sounding profiles show a dry tropospheric column with low-level thermal mixing supporting daytime highs ranging from the mid 70s northeast to the lower 80s in the lower Wabash Valley. As the high shifts toward New England Monday night, return low-level southerly flow will initiate rapid moisture advection aloft. Mid- level height rises driven by an expanding 500mb ridge over the Tennessee Valley will take hold by Tuesday. Strong thermal advection at 850mb will lift daytime maximum temperatures into the upper 80s to lower 90s on Tuesday, while dewpoints rise back into the upper 60s.

Wednesday Through Sunday.

The synoptic pattern on Wednesday features a strong mid-level ridging over the southeastern states and Tennessee Valley, holding low-level baroclinicity and main storm tracks north over the Great Lakes. Continued S/SW surface flow and low-level WAA will maintain hot and muggy conditions across Central Indiana, with highs in the lower to mid 90s. There are some signs that a frontal system Tuesday night may sag south into central Indiana, but with the strength of the aforementioned ridge, confidence is fairly low as to how far south the front and associated rain threats will go. While diurnal MUCAPE values may exceed 1500 J/kg, weak mid-level capping and background subsidence will keep convective risks isolated and unorganized through Wednesday afternoon.

The next best chance for rain arrives late Wednesday night into Thursday as models show an upper trough ejecting out of the Plains toward the Upper Mississippi Valley. An advancing surface cold front will interact with an intensifying 40-50 kt 850mb LLJ, driving a deep plume of moisture northward with PWAT values surpassing 1.6 to 1.8 inches. Scattered showers and the potential for more organized thunderstorm clusters are likely at times Thursday into Friday along and ahead of the frontal boundary. Diurnal timing and cloud cover will determine peak instability, though shear profiles remain sufficient to support convective organization. As the front slowly pushes south by Sunday, post-frontal CAA and building surface high pressure to the north will lower high temperatures into the upper 70s to low 80s.

AVIATION (00Z TAF Issuance)

Issued at 546 PM EDT Sun Sep 13 2026

Impacts:

- VFR this TAF period

Discussion:

Post frontal high cloud from northern Indiana to central IL will push across the TAf sites this evening providing high VFR Cigs.

On Monday, forecast soundings show a dry column with unreachable convective temperatures as strong surface high pressure moves through Indiana and Ohio due to strong ridging aloft. Some high, passing CI will be possible through the day.

IND WATCHES/WARNINGS/ADVISORIES

None.