textproduct: Indianapolis

KEY MESSAGES

- Mostly sunny early this week with warming temperatures.

- Patchy fog possible Monday and Tuesday mornings.

- Dry conditions persist through Wednesday, with the next chance for rain arriving Thursday and then continuing into the weekend.

FORECAST UPDATE

Issued at 956 AM EDT Mon Sep 28 2026

Based on webcams and recent obs widespread dense fog has ended across NW portions of central Indiana. Therefore will let the Dense Fog Advisory expire at 10 AM. In this area, patchy fog and low clouds remains but will end by noon.

Otherwise, temps are already warming slightly faster than current forecast and ahead of model guidance. Have bumped up highs by a degree for most areas, with near 80 expected in the Indy Metro this afternoon. Rest of short term forecast is on track. Watching potential for heavy rain event last week with frontal boundary/hurricane Polo remnants interacting. Stay tuned for afternoon forecast discussion for more details.

DISCUSSION (Today through Sunday)

Issued at 253 AM EDT Mon Sep 28 2026

A deep cut off upper-level low currently sits over the Mid-Atlantic with a split flow jet over the Plains. Ridging and surface high pressure prevail over Indiana. Large-scale subsidence will allow clear skies to continue today and tomorrow.

Temperatures will be modulated by boundary layer processes, with a large spread between highs and lows anticipated. Efficient mixing will allow highs to rise above normal into the mid/upper 70s. Lows however will be a bit below normal due to efficient radiative cooling, with values into the 40s.

Light winds from the surface high pressure should create good conditions for patchy fog during the overnights, especially this morning and Tuesday morning. The strong solar insolation will dissipate any fog quite quickly after sunrise. Dew points during the afternoon hours both today and tomorrow are expected to be below guidance, due to efficient boundary layer mixing.

An upper-level trough is moving on shore over southern California, which is expected to move eastward becoming cut off from the polar jet. The low then ingests moisture from Hurricane Polo, while inducing cyclogenesis over eastern Colorado. As suspected in previous updates, guidance has slowed the progression of the upper- low and resulting surface system. Rain chances now begin increasing on Thursday rather than Wednesday. Some members of guidance now show rain arriving as late as Friday.

Surface high pressure slides eastward on Wednesday, allowing winds to become southwesterly. With rainfall delayed a few days, warm air advection and partly sunny skies will bring much warmer temperatures to the region. Highs in the 80s appear likely both Wednesday and Thursday, with some locations over southern Indiana approaching 90. Friday appears cooler due to the aforementioned rainfall finally arriving, with highs in the 60s/low 70s. Should the system slow further, then these may be revised upward with future forecast updates.

Regardless, ensembles show a more progressive pattern developing with the upper-low and its associated cold front pushing eastward over weekend. Cooler than average temperatures follow, with lingering rain chances as the front moves eastward rather slowly. A secondary wave developing along the front is possible, and is shown by a few models. Model consensus diverges considerably so confidence in any one solution is low at this time.

Days 8-14: Ensemble guidance hints at large-scale troughing taking hold and persisting well into October. This would promote an extended period of cooler than normal temperatures.

AVIATION (18Z TAF Issuance)

Issued at 119 PM EDT Mon Sep 28 2026

Impacts:

- Patchy fog generating IFR conditions expected at KLAF early Tuesday morning, with MVFR conditions expected at KBMG early Tuesday morning

Discussion:

VFR conditions are expected for all the terminals this afternoon and evening as light N-NW winds prevail. As surface high pressure centered over the upper MS valley shifts SE, expect winds to become light NE and then light and variable overnight.

A signal exists for areas of patchy fog to develop across mainly northern portions of central Indiana towards daybreak Tuesday. With the ground gradually getting colder and drier, and low temps tonight not expected to be as low as last few nights, don't see the same ground fog development potential like we had the last few nights. As a result have backed off on IFR conditions at KBMG, with MVFR now expected. Have maintained tempo IFR vis conditions for the expected patchy fog at KLAF.

Winds will become light SE as high pressure shifts to the east of central Indiana by Tuesday morning. Any patchy fog at KLAF will be done no later than 12Z. Winds are expected to become southerly at KIND by early afternoon with speeds remaining under 10 kts.

IND WATCHES/WARNINGS/ADVISORIES

None.