textproduct: Indianapolis

KEY MESSAGES

- Storm threat continues through tonight, with locally damaging winds and heavy rain possible, mainly across southern Central Indiana.

- Heat index values in excess of 100 possible today in southern portions of central Indiana

- Dry and milder weather early in the work week

- Additional storms possible mid week.

FORECAST UPDATE

Issued at 853 PM EDT Sun Aug 16 2026

A shortwave trough is evident in upper level water vapor channel imagery moving into Illinois now. Models show modest strengthening of low-level jet later tonight in response, along with increasing convergence with a weak front that will move southeast into the area. Although there was some degree of convective overturning with the earlier cold pool-driven MCS that traversed central Indiana, this should be replenished with persistent low- level southwesterly flow over the next few hours in a broader particularly moist regime. Enough instability will remain to support convection across Missouri and Illinois late into the night, with some increase in coverage expected. Convective intensity should be limited due to modest instability and marginal shear. However, much of the area has seen substantial rainfall lately with saturated ground making runoff of even modest amounts likely.

We adjusted precipitation probabilities slightly, mainly increasing in the north following trends we're now seeing in Illinois. Also, adjusted near-term temperatures in the wake of MCS. Despite temperature and dew point spreads being minimal, cloud cover should be widespread and persistent enough to limit the radiative component needed for patchy fog. Otherwise, minor adjustments were made to all other elements.

DISCUSSION (This evening through Sunday)

Issued at 146 PM EDT Sun Aug 16 2026

Surface analysis this afternoon shows low pressure in place over Ontario, with a weak trough of low pressure stretching south to eastern Indiana. Aloft, water vapor imagery continues to show a plume of tropical moisture stretching from the American southwest across the central Plains to the Great Lakes and Indiana. A convective cluster was found over western IL, moving east within the flow and has started to strengthen once again as daytime heating has lead to warm and unstable air flowing into the system. GOES19 shows cooling cloud tops here. Radar shows an area of scattered light showers associated with the trough, over SW Central Indiana, pushing east. Dew points across Central Indiana remained quite miserable, in the middle 70s.

This afternoon and Tonight...

Diurnal heating is leading to convection, mainly across the southern half of Central Indiana where the boundary is. SPC meso analysis suggests limited CIN across the area will be gone soon, leading to CAPE in excess of 3000 J/KG in place, able to fire storms. Thus best pops for the afternoon will remain mainly south of I-70. As heating is lost this evening, showers and storms will diminish.

Overnight, the HRRR suggests another nocturnal batch of thunderstorms to push across southern Central Indiana, due to embedded waves within in the flow aloft. Storms look to reach the Wabash by midnight, and exit the area by 6 AM. Fortunately, tracking of this system appears to follow the boundary across southern Central Indiana, keeping the rain soaked northern counties mainly dry. Thus will focus best overnight pops closest to the boundary, across southern Indiana, and mainly late tonight. Some low pops may still be needed across the northern forecast area, but any amounts should be minimal. High dew points will continue to remain across Central Indiana tonight. Lows should be near persistence.

Monday and Tuesday...

Dry, slightly cooler and slightly less humid weather is expected to arrive to start the work week. Through Tuesday, the upper flow becomes northwesterly and little in the way of forcing dynamics appear to pass. Subsidence and mid level drying begin settle across Indiana as the upper tropical plume flow shifts farther south. Meanwhile at the surface, high pressure over the plains builds east to Indiana through Tuesday. Forecast soundings show a dry column across Indiana for much of Monday and Tuesday. Thus clouds will exit on early monday morning with the departure of the overnight system, leading to mainly partly cloudy skies for the rest of Monday and Tuesday. Cooler NW winds will allow for dew points to fall into the 60s and highs will be cooler, only in the lower to middle 80s.

Wednesday and Thursday...

Dry weather will expected to start the day on Wednesday as high pressure will exiting the Ohio Valley to the east. Low pressure over the plains is expected to push a warm front into Indiana by late afternoon on Wednesday and Wednesday Night. Northwest flow looks to be in place aloft, and embedded short waves will be possible. On Thursday, models suggest this stationary front over Indiana, and for now, this will require pops starting on Wednesday afternoon, continuing through Thursday night.

Friday...

Surface high pressure is suggested to remain over Indiana on Friday, providing a cooler and drier NE flow. Models still do keep NW flow in place aloft with a trough approaching from the NW. However deep moisture will be more limited as NE winds allow for dew points to fall in to the 50s. Thus for now will try and use a dry forecast, but this could easily change given the flow aloft and the possibility of stronger forcing. Thus confidence is low.

Saturday And Sunday...

On Saturday, the models suggest building ridging aloft over the high plains, resulting in a more amplified pattern and troughing digging through the eastern Great Lakes and Appalachia. Upper support within the flow is shown to pass on Saturday, while the tail of a cold front moving across the Great Lakes will sweep across Indiana. Thus pops will be needed on Saturday. On Sunday the building ridge west of Indiana will create strong subsidence over the upper midwest, spilling southeast toward Indiana. This will create a surface high pressure system building across Indiana along with most likely dry weather.

AVIATION (00Z TAF Issuance)

Issued at 715 PM EDT Sun Aug 16 2026

Area of thunderstorms has cleared all sites with VFR cigs and somewhat variable post storm wind direction expected. CAMs still leaning towards another area of storms moving west to east across the area overnight. This may be taking shape from KGBG to KUIN as well as some activity well ahead of this. Given this same area will need some recovery after the first round, overall confidence on impacts are on the lower side. Timing in previous TAFs looks good, so will continue with a Prob30 for the southern 3 sites and introduce a Prob30 at KLAF who possibly has a shot as well, but not enough confidence for a predominate group. Some post frontal stratus could settle in into mid morning.

IND WATCHES/WARNINGS/ADVISORIES

None.