textproduct: Indianapolis

KEY MESSAGES

- Warm and mostly dry through Thursday with temperatures well above normal.

- Moderate to heavy rain expected Thursday night into Friday.

- Chance of additional showers for southern areas Friday night into early Sunday.

- Dry and cooler weather expected next week with lows mainly in the 40s with upper 30s possibly in outlying areas Tuesday morning.

DISCUSSION (This evening through Tuesday)

Issued at 312 PM EDT Tue Sep 29 2026

Warm fall weather will be the rule through Thursday as upper ridging builds back over the SE CONUS and 850 mb temps rise to around 17 C. High temps will be in the 80s most areas Wednesday and areawide Thursday. A weak upper level disturbance located over OK/KS will rotate around the upper ridge and graze central Indiana during Wednesday. As a result sky cover has been increased to mostly cloudy for areas north of I-70. Steep mid level lapse rates will support elevated showers, but low levels will remain very dry, so only scattered sprinkles are expected from a mid level cloud ceiling. Winds will gradually increase on Wednesday as the pressure gradient steadily increases between surface high pressure over the srn Apps and low pressure over the central Plains. By Thursday, this gradient will increase sufficiently to support breezy conditions with south gusts near 20 mph during the afternoon.

Attention turns to the main forecast challenge/event during the period which is timing of arrival, duration and amounts of rainfall late Thursday into the weekend. Most model guidance suggests a fairly short period of strongest forcing/heaviest rainfall during the 06Z-18Z period Friday as a frontal boundary shifts southward through central Indiana. This shorter temporal rain threat than earlier forecasts advertised is due to several factors. The primary factors are the faster weakening of the mass fields with the remnant shortwave over the plains and a resultant increasing tendency for a stronger area of high pressure over the upper MS valley. The net result is stronger pressure rises supporting a greater southward displacement of the main baroclinic zone. As far as rainfall amounts, PWATs are still expected to be very high for early October, around 1.5 inches. Therefore, even with the shorter duration of rainfall, most areas will see between 0.75 to 1.25 inch QPF during this period. Even with a shorter duration of rainfall, these amounts are low enough that no hydro concerns are expected.

In the wake of this rainfall, there is still a few outlier models (AI based) showing a weak tropical surge attempting to make it up to Indiana Friday night into early Sunday. Low pops were kept for the outside chance of showers during this period across southern portions of central Indiana in closer proximity to the forcing/frontal boundary. The aforementioned reinforcing area of high pressure combined with stronger CAA (850 temps fall around 8 C from 18Z Sunday to 06Z Monday) should shift any threat for additional precip well south of the area.

The coldest night of the fall is expected Monday night as a 1030mb high pressure builds southward through the Great Lakes. Lows in the low-mid 40s are expected areawide with a few outlying locations possibly falling into upper 30s Tuesday morning. There will also likely be some areas of fog during this period with light winds and recent rainfall.

Looking further into the extended, expecting broad NW flow to maintain a fairly typical dry and benign fall pattern through much of next week into the following weekend with temps expected to be near or slightly below normal with highs in the mid 60s-mid 70s and lows in the 40s to lower 50s.

AVIATION (18Z TAF Issuance)

Issued at 100 PM EDT Tue Sep 29 2026

Impacts:

- None

Discussion:

VFR conditions will occur through the period. No fog is expected overnight with increasing high cloud cover. Winds will be light S-SW this afternoon become light S-SE overnight.

A grazing influence from a weak storm system currently over the southern Plains will provide for some SCT-BKN mid level clouds across the area Wednesday. There is some chance for light showers at KLAF, but confidence is too low to warrant any inclusion in the TAF at this time. Winds will become S-SW and increase to between 6-10 kts by midday with some gusts up to 15 kts possible during the afternoon.

IND WATCHES/WARNINGS/ADVISORIES

None.