textproduct: Indianapolis

KEY MESSAGES

- Occasion showers/t-storms today into next week, with greatest chances today through Friday night

- Localized ponding/flooding of low-lying areas will be possible where repeated rounds of downpours occur

- A few strong/severe storms are possible this weekend into early next week...with low confidence on exact details

FORECAST UPDATE

Issued at 904 AM EDT Thu Aug 6 2026

Surface analysis this morning shows a broad Bermuda high pressure system in place, providing warm, southerly gulf flow to Indiana and the Ohio Valley. A meso low was found near St. Louis, and this associated with a MCS cluster over MO and IL. This MCS was waning, with warming tops. Radar shows thunderstorms with this feature over Central IL, and a few showers had reached western Central Indiana. Aloft, a broad, shallow trough was in place across the northern half of the CONUS, with an axis near the Mississippi River. Dew points across Central Indiana were in the 60s.

Given our steering flow aloft, the decaying MCS should track ENE into central Indiana. However due to the warming tops and the unfavorable time of day, this system should continue to weaken upon approach. Pops will still be needed, particularly in the western parts of the forecast area as this system should continue to weaken upon arrival. HRRR shows limited precip reaching the area through the day, however at a minimum, some high clouds/convective debris clouds will pass through the day. These clouds may help to keep highs a bit cooler than persistence. Overall, ongoing forecast remains in good shape.

DISCUSSION (Today through Wednesday)

Issued at 400 AM EDT Thu Aug 6 2026

Today through Friday night...

Synoptic pattern through the next four 12-hour periods will feature a rather stagnant set-up between two broad and well- maintained upper level features...a trough over central/south- central Canada and a subtropical ridge across mainly the southern two-thirds of the CONUS, except through the OH/TN Valleys where heights will be more neutral courtesy of the southern end of the Canadian trough's axis. This will place central Indiana in a sort of saddle point...south of any sub-seasonal air, but north of any consistent above normal readings. Quasi-steady flow of small weaknesses curling around this axis, casually extending to the southeast of the Canadian trough will keep an overall disturbed pattern over the local region, amid precipitable water values of 1.70 inches or so per southerly flow around a Bermuda high ridging west into the Carolinas.

However, overall weak forcing will keep any scattered to briefly numerous showers occasional in nature. Generally isolated thunder will be sub-severe with greatest potential impact ponding of low- lying areas due to weak storm motion. Timing of higher chances/ coverage of convection will focus around early this morning from upper forcing...and then perhaps also mid/late afternoon if clouds can partially clear enough to facilitate better daytime heating... with both of these periods favored more west of Interstate 69. The diurnal uptick in clouds/showers Friday will most likely be for eastern/southeastern counties ahead of a more southern-tracking mini- vort coming up the Ohio Valley. A spatially larger-scale shift east of the quasi-stacked trough, across Indiana, could potentially bring several hours of scattered rain coverage around Friday night's early overnight...ahead of quieter weather to start the weekend.

Higher humidity will be the rule through the end of the workweek, with dewpoints nearing 75F Friday on southwest breezes gusting up to 15 mph. Cloudier skies to promote smaller diurnal temperature ranges from 66-72F in early mornings to a damp 81-86F during afternoons.

Saturday Through Sunday...

Synoptically, Saturday morning shows a quasi-stationary surface front across northern Indiana, situated along the southern edge of an elongated 500mb trough stretching across the Upper Great Lakes. Boundary layer moisture transport remains elevated ahead of the boundary, with ensemble means from the GEFS and EPS maintaining PWAT values near 1.8 to 2.0 inches, representing the 90th percentile for early August climatology. HREF probability-matched mean guidance indicates convective initiation by mid-to-late Saturday morning as low-level thermal advection and weak PVA associated with an embedded vorticity maximum traverse the region. Model soundings across central Indiana depict MLCAPE values rising to 1500-2500 J/kg during peak afternoon heating. Weak kinematic forcing, characterized by 0- 6km bulk shear of 15-20 kts, will preclude well-organized mesoscale convective systems, but slow cell motion along the quasi-stationary front presents a localized threat for training convection and flash flooding. Forecast soundings show a deep CAPE profile with freezing levels above 14,000 feet.

By Sunday, the surface boundary will continue to lift to the north further into the Great Lakes and have less overall impact on central Indiana weather. Aloft an upper-level ridge centered over the Central Plains will slowly strengthen with minor height rises across the area. 700-500mb temperatures will also warm a degree or two helping to build a mid-level cap with will help to suppress thunderstorm development. Mesoscale models including the HREF members suggest isolated High temperatures both days will range from the mid to upper 80s, with heat indices approaching the low to mid 90s.

Monday Through Wednesday...

The broad synoptic regime during the extended period will feature an amplified mid-level ridge across the South-Central Plains and an anchored longwave trough over the northeastern CONUS, establishing active west-northwesterly flow aloft over the Ohio Valley. Deterministic GFS and ECMWF runs, alongside GEFS and EPS cluster analyses, remain in general agreement regarding this large-scale pattern, though variance exists regarding the exact timing and magnitude of embedded shortwave troughs propagating around the northern periphery of the ridge.

There has been a slight trend for the jet stream to be further north into the Great Lakes which has led to lower rain chances across the Ohio Valley. That being said, the thermodynamic setup will maintain strong thermal instability, with diurnal CAPE values frequently exceeding 2000 J/kg. Lifting associated with shortwave disturbances traversing the broader trough, coupled with nocturnal LLJ strengthening (25-35 kts at 850mb), will foster potential for upstream MCS development over the Upper Midwest that could track southeastward into the CWA. Given the synoptic uncertainty inherent in timing northwest flow impulses at days 5 through 7, POPs will remain capped in the chance category (20-40%) throughout the week. Outside of convective active periods, subsidence beneath the ridge interface will promote warm and humid surface conditions, with high temperatures consistently reaching the upper 80s to low 90s and maximum afternoon heat indices nearing 100 degrees.

AVIATION (18Z TAF Issuance)

Issued at 1257 PM EDT Thu Aug 6 2026

Impacts:

- Mainly VFR this afternoon - MVFR Possible overnight, toward 071200Z

Discussion:

GOES19 continues to show a decaying convective MCS over IL and Indiana with a mid level cloud deck across the TAF sites. Radar shows decaying showers trying to progress east near the Wabash.

The decaying system is expected to continue to weaken and push across the TAF sites this afternoon, providing VFR Cigs. HRRR suggests enough clearing could be had for a pop up TSRA late this afternoon and early evening. Confidence is low for this, thus a VCTS mention will be used for now. Overnight, low dewpoint depressions and light winds will likely lead to fog and/or MVFR Stratus development around diurnal minimums.

IND WATCHES/WARNINGS/ADVISORIES

None.