textproduct: Indianapolis

KEY MESSAGES

- A few showers and possibly a stray TS far S-SE areas ending this evening.

- Heavy rain and severe storms are possible Sunday afternoon into early Monday.

- Flooding threat both river and non-river will increase with heavy rain on already saturated soils in some areas.

- Below normal temperatures will continue for much of the period.

- Transition to multiple heavy rain events is possible going into the week of 4th of July.

DISCUSSION (This evening through Saturday)

Issued at 342 PM EDT Sat Jun 20 2026

Rest of this afternoon...

Weak surface confluence zone associated with slight T/TD gradient will continue to shift south of I-70 over the next few hours. As a result modest convergence and steep 0-3 KM lapse rates and residual moisture in the 850-700mb layer will support some scattered light showers. Recent ACARS soundings from KIND continue to support presence of mid level inversion centered between 3-4 KM on the backside of departing shortwave trough. Some indications are that sufficient moistening and cooling from transport and lift below this inversion may allow for just enough erosion to support an isolated TS across far S-SE zones this afternoon with between 750- 1000 J/KG potentially being realized. As a result have continued to carry slight chance of TS in these areas until 00Z.

Tonight....

Fairly quiet conditions are expected as weak area of high pressure moves into the region. Winds will become light and variable with increasing mid-high level clouds preventing any concerns for patchy fog formation.

Sunday into Monday...

Lee cyclogenesis over the High Plains currently ongoing will help in the development of an MCS over the central High Plains this evening. This MCS will move into the lower plains/MO valley overnight supported by a progressive mid level shortwave trough and 35-45 kt low level jet. Exact morphology of this system into Sunday morning remains somewhat uncertain. Recent ensemble guidance suggest that at the very least the remnant MCV will move into Indiana during the late afternoon. Increasing clouds and light showers are expected to develop during the late morning on the leading WAA wing of the MCS/MCV. As a result, instability is expected to be more limited across areas north of I-70 and as a result severe TS threat. Therefore, current indications are that the best threat for severe TS will occur south of I-70 and may be a combination of reinvigoration of ongoing convective line late Sunday morning over the MS valley and/or combination of redevelopment of convection along the MCV trough axis/remnant outflow boundary during the late afternoon.

As a result of the uncertainties in the morphology of convection Sunday morning/afternoon, storm mode is equally uncertain. With the surface low attendant to the shortwave trough likely enhanced by diabatic effects of tonight/s MCS, there is the potential for isolated tornadoes, especially considering the 200-300 0-1 KM SRH noted on forecast soundings owing to relatively strong low level jet. Proximity of south/central Indiana to the track of the surface- 850 mb low also would support a tornado threat with any cellular activity per pattern recognition. However if a more linear mode remains in place/intensifies during the afternoon/evening into southern/central Indiana, then damaging winds will likely be the primary threat, with isolated embedded tornadoes still possible within the line given the aforementioned low level shear profiles. The main limiting factor for a more substantial severe threat will be relatively marginal instability /per June standards/ with forecast soundings suggesting between 1000-1500 J/KG of SB/MU CAPE and mid level lapse rates near 6 C/KM.

QPF forecasts remain bullish for the most part, with average QPF around 2 inches, with some areas near I-70 expected to receive locally over 3 inches, owing to the proximity of expected synoptic/mesoscale differential heating/baroclinic zone and 30-40 kts low level jet impinging on this boundary. Have maintained the Flood Watch for most of central Indiana, except the far NE. PWAT values remain around 1.8 inches, near the 90th percentile, and storm training effects will likely be the main instigator for any flash flood threat. Much of central Indiana along and 50 miles either side of the I-70 corridor has a Moderate Risk for Flash Flood per the WPC day 2 outlook and this seems very reasonable given aforementioned synoptic pattern as well as antecedent high soil moisture levels for much of the area.

Tuesday through Thursday...

Broad long wave trough will remain anchored over the eastern Canadian provinces. In the wake of the early week shortwave, surface high pressure will build southward through the Great Lakes on Tuesday leading to another day of below normal temps in the 70s and relatively dry airmass. Several SE moved shortwave troughs in NW flow will be capable of producing scattered precip Wednesday and Thursday.

Friday into 4th of July week...

Exceptional agreement exists in the medium range model guidance. With the EPS, GEFS, AIFS all showing a very strong trough developing over the intermountain west late next week into next weekend. As a result, downstream riding will intensify over the plains supported by near record heat. On the northern periphery of the ridge, remnant W-NW flow combined with moderate to high instability will set the stage for one or more severe MCS events in the corn belt region potentially starting next Saturday in central Indiana and going into the 4th of July week. Stay tuned on the timing and intensity of these events.

AVIATION (18Z TAF Issuance)

Issued at 130 PM EDT Sat Jun 20 2026

Impacts:

- Gusty winds this afternoon around 20 kts

- Showers developing midday.

- Scattered thunderstorms expected late Sunday afternoon near IND.

Discussion:

Isolated showers are still possible this afternoon, but should remain well south-southeast of KIND/KBMG. Otherwise, the only sensible weather concern this afternoon is some wind gusts up around 20 kts from the West to WNW as a weak boundary moves south through the terminals. Scattered to BKN VFR ceilings will gradually diminish with loss of heating as will the wind gusts around 23Z.

Overnight, mid level clouds will begin to increase ahead of a storm system over the plains. Weak surface high pressure will lead to light and variable winds and VFR conditions.

On Sunday, expecting winds to become SE with some gust possible as high as 15 kts by midday ahead of a developing low pressure area over MO. Associated with this low pressure area, expecting a complex of thunderstorms, gradually weakening to move into central Indiana towards midday. VCSH will be carried at most TAF sites by midday. Renewed convective development is expected to develop over IL during the afternoon with the potential for some of that to move into KIND towards late afternoon so have PROB30 in the forecast to account for this potential.

IND WATCHES/WARNINGS/ADVISORIES

Flood Watch from Sunday afternoon through Monday morning for INZ028>030-035>037-039-043>048-051>057-060>065-067>072.