textproduct: Indianapolis

KEY MESSAGES

- Isolated/scattered showers and a few t-storms are possible late tonight...and again Saturday afternoon, mainly east.

- Cooler and less humid weather expected Sunday through Tuesday with highs mainly in the 70s to near 80.

- Areas of late night/early morning fog will occur Saturday and Sunday nights.

- Dry weather expected Monday and Tuesday with increasing chances for rain and storms mid-late next week.

FORECAST UPDATE

Issued at 959 PM EDT Fri Aug 21 2026

Fair conditions will continue this evening amid weak surface high pressure departing under increasing clouds coming off upstream convection. Approaching supporting wave will bring increasing chances of RWs and embedded isolated thunder...granted any cells are expected to be weaker than present activity over northern Illinois, with possibly a stray strong/marginally severe wind gust near/west of Lafayette during the early overnight. Otherwise widely scattered showers to cross much of the region while overall dissipating into pre-dawn hours. Although better chances of modest regeneration across northern counties which will be closer to vort support...and low-moderate chances of a few additional showers towards dawn near the cold front entering the CWA's northwestern corner.

Cannot rule out patchy visibility reductions from fog. Tonight will be the last period with overall light, if not variable winds. Low temperatures to display a modest range given overnight cloud cover, from low 60s near Muncie to 66 in Vincennes.

DISCUSSION (This evening through Friday)

Issued at 318 PM EDT Fri Aug 21 2026

Late this Afternoon...

Elevated showers over northern Indiana are indicative of a weak lead shortwave. An instability axis extends across far eastern portions of the forecast area northward into NE Indiana. Recent convective development in NE Indiana was occurring in a zone of modest low level convergence. There is a small chance that an isolated shower or TS will develop in extreme northeastern zones before activity weakens around sunset.

Tonight and Saturday...

Vigorous convective development will continue to the northwest of central Indiana across parts of southern WI/far northern IL and eastern IA the remainder of the afternoon into the evening. This activity is forming in a broad convergence zone ahead of a seasonably strong shortwave trough and within a moderate to strong instability axis with MLCAPE values from 2000-3000 J/KG. TS activity in several lines will develop develop S-SE towards central Indiana overnight. However, instability decreases markedly with SE extent, with MUCAPE under 1000 J/KG across all of central Indiana overnight. Time of day combined with minimal instability suggests that the severe weather threat is close to zero across the forecast area. Well south of any precip and/or convective clouds overnight, patchy fog is expected across southern portions of central Indiana where light winds and mostly clear skies will prevail.

The weak cold front associated with this progressive system will push across the region Saturday morning. There is some indications that a secondary shear induced mid level vorticity max will move through the region on Saturday afternoon. With residual instability, a few lower topped showers/TS will be possible behind the main cold front but ahead of this mid level feature/surface convergence boundary during the afternoon, mainly over eastern zones. Have maintained pops in these regions. Would not be overly surprised with some renegade showers across western zones where some instability remains, but for the sake of consistency will leave out of the forecast.

Saturday night through Sunday...

In the wake of the shortwave/cold front Saturday surface high pressure will gradually build southward through the northern/central plains into the upper MS valley. Broad NW low level flow will support some lake enhanced clouds and showers Saturday evening and again during Sunday afternoon in far northern areas mainly during the period when daytime heating/convective overturning is maximized. A stout mid level inversion noted on forecast soundings should limit convective cloud depth and only a slight chance of showers is currently forecast.

Sunday night through Tuesday...

Broad area of surface high pressure will push SE into the Ohio Valley through the period, providing for much drier conditions, with dewpts falling into the 50s. As a result most areas will see low temperatures in the 50s Sunday night. Light winds and mostly clear skies will lead to another night with areas of fog Sunday night. A weak system in the NW flow aloft is expected to move across the MO/mid-MS valleys Monday into Tuesday. At present the only expected effect from this system will be increasing mid-high clouds. This should limit fog chances Monday night and keep high temperatures in the 70s most areas Monday and Tuesday.

Wednesday through Friday...

Another upper wave/surface cold front will move through during the period. Confidence in timing is very low considering the system is currently off the west coast, so for now will only have some low PoPs. Seasonable temperatures are expected with increasing humidity with increasing SW flow in the low levels.

AVIATION (06Z TAF Issuance)

Issued at 106 AM EDT Sat Aug 22 2026

Impacts:

- Isolated/scattered -SHRA/TSRA possible through 13-15Z - Low chance for brief fog at outlying sites this morning - WNW winds gusting up to 20-25KT Saturday afternoon/late day

Discussion:

Scattered convection and isolated thunder will be possible through 13-15Z as a disturbance moves across the region. Low confidence on MVFR from convection...with also a brief window of potential MVFR from fog at terminals outside of KIND, towards dawn. It does appear increasingly likely brief MVFR ceilings are possible at KLAF between 12-16Z so added a TEMPO group.

Overall light/variable flow tonight will yield to stronger post- frontal flow Saturday midday-afternoon, with winds veering slightly within 270-320 degrees, occasionally gusting up to 20-25KT through late afternoon. Morning cloud cover could limit diurnal mixing and peak gusts slightly.

IND WATCHES/WARNINGS/ADVISORIES

None.