textproduct: Indianapolis

KEY MESSAGES

- Dry through today but upper level smoke will be over the area

- Growing concern for numerous strong to severe thunderstorms with heavy rainfall late Monday night into Tuesday

- Noticeably cooler and less humid for the second half of the week

FORECAST UPDATE

Issued at 900 AM EDT Mon Jul 20 2026

Surface analysis early this morning shows high pressure over NY and PA while a frontal boundary was found over MN and SD, sagging SE. This was resulting in SE surface flow across Indiana. A convective cluster was found over SE MN. GOES19 shows high cloud associated with this drifting SE into NW Indiana. Otherwise, skies were clear across Central Indiana, although haze was present in most observations. Aloft the upper flow continued to be dominated by high pressure in place across the central Rockies, which was allowing a stream of Pacific moisture to flow across the NW CONUS across the northern plains and diving southeastward toward the Ohio Valley.

Ongoing forecast remains in good shape. The surface high will continue to drift east this afternoon as the frontal boundary to the northwest approaches. Forecast soundings remain dry through the day as we remain under the influence of of the departing high pressure systems. However, diurnal CU is expected to develop this afternoon leading to partly cloudy skies with continued haze. Thus only minor adjustments will be needed to the ongoing forecast.

One caveat to watch, the convective cluster over MN will drift SE today, and could reach NW parts of Central Indiana this evening. Will need to monitor progression through the day to determine if pops will need to be added.

DISCUSSION (Today through Sunday)

Issued at 307 AM EDT Mon Jul 20 2026

Hazy conditions from Canadian wildfire smoke is expected again today, although should be at least somewhat less dense than what central Indiana saw yesterday. High pressure across the area will maintain dry conditions throughout the day and expecting highs in the 80s again.

The surface high will push off to the east late in the day and into the overnight hours, with return flow, out of the SW, developing on the backside. This will help to push more of the smoke out of the area.

A low developing across central Canada will track north of the Great Lakes, with the associated cold front tracking across the the region tonight and into tomorrow. Confidence continues to increase in an MCS developing to our northwest and diving towards the region tonight due to this feature.

While there remain differences with respect to the actual evolution and track of a convective cluster, the presence of a surface wave along the boundary will promote an enhancement of speed and directional shear in addition to higher SRH values across the lower Great Lakes. Timing will be a factor in whether severe convection will make it into the forecast area and if so how far, but the greatest risk from an MCS moving into the region will be damaging winds especially if a mature cold pool develops. The orientation and strength of the low level jet in tandem with a rapid influx of deep moisture and PWATS near 2 inches supports heavy rainfall and flooding concerns as well and this may end up being the main impact with the potential of a late night/predawn timing early Tuesday. Rainfall rates will be efficient with the freezing level near 15kft. Still details to be worked out but potential for impactful convection late tonight and early Tuesday continues to grow.

The timing and extent of the overnight/early morning convection will have a direct impact on what takes place during the day Tuesday with the cold front across the area. In the wake of the convective cluster, significant uncertainty exists regarding the degree of destabilization as there is potential for an extended period with leftover cloud debris limiting heating. Considering the kinematic environment, any redeveloping convection along the front would carry an inherent severe risk. The most likely scenario however is that the greatest potential for severe weather will be to the southeast of the forecast area Tuesday afternoon and evening. All hazards will be possible with this redevelopment, but damaging winds pose the greatest threat. Any convection will depart central Indiana late Tuesday evening as broad surface high pressure takes over with a cooler and drier airmass.

The surface high is expected to persist through the end of the week allowing for growing confidence in high temperatures to range from the mid 70s to low 80s and lows down into the 50s for a couple of nights. The cooldown won't last long as models show the high exiting and returning surface flow from the south to southwest with temperatures likely returning to near to above normal.

AVIATION (18Z TAF Issuance)

Issued at 1254 PM EDT Mon Jul 20 2026

Impacts:

- Smoke/Haze continues this afternoon.

- Showers with some thunderstorms expected overnight into Tuesday morning. MVFR conditions possible.

Discussion:

High pressure east of Indiana continues to provide subsidence and haze across the TAF sites. Some afternoon CU is expected to develop given expected inverted V soundings. Overall this will result in some MVFR visibilities this afternoon and evening.

Any CU is expected to diminish after sunset.

An upper wave and cold front is expected to arrive from the northwest across Indiana late tonight and into Tuesday. This feature will have sufficient moisture and instability overnight to generate some showers and storms. HRRR projects arrival and passage during a 09Z-14Z window, thus have used VCSH/VCTS and some tempo groups during that time. Any TSRA that strikes a TAF site may produce MVFR/IFR conditions.

In the wake of the storms after 14Z...VFR conditions will return along with NW surface flow.

IND WATCHES/WARNINGS/ADVISORIES

None.