textproduct: Indianapolis

KEY MESSAGES

- Hot and humid conditions today; heat index values above 105 over western central Indiana

- A thunderstorm complex is possible this afternoon with damaging winds and heavy rainfall the primary threats. Additional thunderstorms are possible overnight but confidence is low

- Rain free Tuesday-Thursday amid near to slightly below normal temperatures/humidity.

FORECAST UPDATE

Issued at 1023 AM EDT Mon Jul 27 2026

Only minor updates this morning mainly concerning fog coverage and cloud cover. Also trimmed PoPs back a bit as upstream convection has weakened somewhat. Satellite still shows some unstable altocumulus northwest of Lafayette, which some high-res guidance wants to develop further. Will need to monitor this area over the next few hours as atmospheric instability is high and sufficient shear is present for strong thunderstorm potential. Actually getting convection to initiate is the biggest hurdle through the morning. CAM guidance can struggle greatly in low forcing situations with high instability. Therefore, run-to-run consistency is likely to be very poor and model uncertainty will be high. Take individual model runs with a grain of salt through this afternoon. Confidence is likely to improve this evening as a more defined area of forcing arrives from the north in the form of a potent short wave. This short wave is expected to bring additional convective chances into tonight.

DISCUSSION (Today through Sunday)

Issued at 225 AM EDT Mon Jul 27 2026

Today through Tonight

An upper level ridge will continue to build eastward within modest westerly WAA. This WAA within the lower levels will continue to push temperatures and dew points well above normal building deep instability across the region. MUCAPE values will exceed 3000 J/kg by noon, with values likely pushing above 4000 J/KG towards the middle of the afternoon through the evening. Shear will also be plentiful as the jet stream remains aloft, with 35-50kt of effective shear. The combination of high instability and plentiful bulk shear will lead to a potent airmass, but the source of upward motion to initiate these thunderstorms is still a bit of an enigma. There is building confidence on a convective complex initiating along a weak shortwave early this morning over the upper Great Lakes region, with a majority of the CAMs pushing this complex southward into the Ohio Valley this afternoon. The primary threat with this thunderstorm complex will be wind gusts of 60-80MPH, but small hail and an isolated tornado cannot be completely ruled out.

Even with this additional confidence in general timing, specifics on timing and location remain fairly uncertain within the previously mentioned window due to somewhat ambiguous storm motions. Unlike strongly forced events, storm motion will greatly depend on the placement of any developing cold pools and its relation to the ongoing thermodynamic parameters. This could lead to a storm motion range from 340 degrees to potentially 20 degrees over the course of this event. Also, CAMs notoriously struggle with translation speed and longevity of these thermodynamically induced convective complexes due to underestimating cold pool density and interaction within the ongoing environment. This is a lot of information to say, be very hesitant on taking any CAM reflectivity output verbatim this afternoon, and thus confidence in thunderstorm passage for any specific location will likely have to wait until 3-6 hours ahead of arrival.

After this first convective threat this afternoon, additional thunderstorms are expected to develop along and ahead of a diffuse frontal boundary between 01-08Z. As with the first round, confidence is fairly low on any specifics, but the overall atmospheric parameters will remain potent enough for an additional severe threat with wind once again being the primary threat. This time, greatest confidence will shift towards NE portions of the area, as this portion looks to have slightly greater surface confluence and therefor a greater confidence in convective forcing.

The temperature forecast today will also be fickle and will greatly depend on thunderstorm timing and location. The WAA previously mentioned will push a very humid airmass into the region with dew points likely nearing 80 and temperatures pushing into the low 90s. This combination will likely lead to a prolonged period of heat index values above 100 and a few hours between 105-110. For this reason, a Heat Advisory has been issued. The current ending time for the advisory will be 01Z, but this could be canceled early depending on cooling impacts from afternoon convection. As stated, a frontal passage is expected overnight into tuesday morning. The front is not strong, but will still push temperatures back towards seasonal for the coming week.

Tuesday through Sunday...

Strengthening hot and humid upper subtropical ridge over western North America...will be offset partially by progression of smaller weaknesses plunging from north-central CONUS to Ohio Valley...which will likely result in slightly below-normal warmth and humidity across central Indiana through at least Thursday morning. First cool front progged to push south across the region around dawn Tuesday, with northerly gusts actually up to 20-25 mph for many locations...only allowing low to mid-80s for central/northern counties, and noticeably lower humidity for all by late evening.

Tuesday night to Wednesday night to host most pleasant conditions, as weak but amplified surface high pressure builds south from James Bay into much of the Midwest...and ridge axis' alignment near the Wabash Valley maintaining lower dewpoints and readings for most of the region into early Thursday...with highs Wednesday around 80-85F amid more September-like breezes...flanked by consecutive overnights with lows around 60F.

Late work week to transition warmer and touch more humid as upper ridge tries to build east across central US...which will at least push the surface high out of the region, returning light southerly breezes and perhaps a few afternoon showers/t-storms for Friday- Saturday. Low confidence in any 90s returning late in the period as next northern mini-wave plunges/slows down across the Midwest during the weekend, with accompanying clouds...and what should eventually be a flip back to northerly winds and only low-chances of convective showers by the very end of the long term, with near normal ranges in the 60s/80s.

AVIATION (12Z TAF Issuance)

Issued at 623 AM EDT Mon Jul 27 2026

Impacts:

- Fog could linger for the first hour of the TAF. Prevailing MVFR with tempo IFR to LIFR

- Storm complexes may impact the area this afternoon and again late this evening into the overnight.

- Non-thunderstorm gusts out of the south this afternoon up to 18kt

Discussion:

Low lying fog is expected for the first hour at KLAF and KHUF, this should clear quickly after 13Z. Some lingering MVFR clouds are possible early, but should become scattered by 15Z, with occasional wind gusts to 15-18kt this afternoon.

Still a fairly uncertain thunderstorm forecast ahead, but confidence is growing is a organized line arriving this afternoon between 18-22Z. Additional thunderstorms are possible overnight at KLAF and KIND, but confidence in occurrence is low. A frontal passage overnight will shift winds from the SW to NW with winds remaining below 10kt.

IND WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 9 PM EDT this evening for INZ028-029-035>037- 043>047-051>055-060>064-067>071.