Area Forecast Discussion

KEY MESSAGES

- High temperatures around 90 degrees coupled with humid conditions are expected again today so a heat advisory has been issued for the area. If venturing outside, be sure to take breaks and stay hydrated.

- Chances for severe weather exist again tonight. Damaging wind, hail, heavy rain, and a few tornadoes are possible with this severe weather threat. - Next chances for showers and storms return Saturday night with another cool frontal passage, bringing cooler temperatures into low/mid 70s to lower 80s along with decreased humidity across the area Sunday and Monday.

- A moderate swim risk exists along the southeast Lake Michigan shoreline today and Friday as waves reach 2 to 4 feet. Breaking waves and currents are expected. Stay away from dangerous areas like piers, breakwalls, and river outlets. Always have a flotation device with you in the water.

DISCUSSION

Issued at 337 AM EDT Thu Jun 11 2026

A shortwave rounds the base of the mid level trough in the west and approaches the area this afternoon and tonight. As it does so, the outflow boundary from yesterday's storms situated across our areas serves as a dividing line between higher and lower dew points than 70 degrees. The GFS even keeps the better 850 mb airmass south of that boundary. The daytime appears to be enough to push the boundary farther north to allow for another warm and humid airmass that does two things:

#1, it makes for another day where a heat advisory could be necessary as heat indices exceed 100 degrees east of I-69 and other areas have heat indices surpass the mid 90s. There's some question how high dew points get west of IN-15 (The HRRR/RAP/NAM get to 75 degrees) and there's also some question about when that boundary lifts northward to allow warmer temps into the area. Given this is now the second day of such heat indices as well as the information above, thought it prudent to issue another heat advisory across the area.

#2 is that we have a very unstable airmass across the area with the NAM showing greater than 4000 J/kg of SBCAPE so the atmosphere is expected to have plenty of instability in the warm sector. The one interesting thing is that the NAM still shows the outflow boundary across the area as late as late afternoon. This could be interesting for surface based cells if that remains the case as this tends to be more conducive to rotating cells if they can become rooted to the boundary. There is some question about if cells can erupt out in front of the main squall line and if that does happen perhaps that could eat away at the heat and instability for storms as well as for the heat advisory. NAM and HRRR bufkit soundings indicate we're capped in the morning. We finally get the warmer 700 mb airmass (and better 7+ C/km mid level lapse rates) after 18z and this could help with hail and damaging wind potential. That thermal boundary is north into MI by the time the cold front arrives according to the NAM. 30+ kts of effective shear arrive with the cold front, but 200 to 400 units of effective helicity arrive in areas west of IN-15 by late afternoon. This would help with embedded circulations within the squall line and make this more of a QLCS. Given the lack of pre- frontal cells forecast as well as the progressive nature of the squall line, would think there would be a lower chance for flooding, but the atmosphere is so moist with the 70 degree dew points and 850 mb dew points above 10C that it cannot be completely taken off the table with this convective environment. The squall line looks like it should be through the area by 3 to 4 am.

Friday looks drier (50 degree dew points) and cooler (highs around 80 degrees), but as the wave that causes our Thursday night storms pushes northeastward, another wave dives southward from Canada and picks up some moisture from our south and west. As the plume swings through Saturday night, dew points in the upper 60s allow for MUCAPE values between 1500 and 2000 J/kg. Storms are likely elevated at this point given the formation of a low level inversion on NAM and GFS soundings, but mid level lapse rates could reach 6.5 C/km for a period so perhaps some hail could form. We could probably also eek out some heavy rain given the moist profiles. I'm initially skeptical of a damaging wind threat with this, but things could change. SPC has put the area in a marginal risk of severe weather for this period.

The upper low still remains across eastern Canada during the next work week and so while we look drier and a little cooler, it doesn't look like another prolonged dry period. In fact, there's some model confluence on rain by Tuesday.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 623 AM EDT Thu Jun 11 2026

Another warm and humid day that starts with some scattered to broken low cloudiness around. Otherwise, we'll be waiting until likely after 00z for our chance for thunderstorms to arrive to the area. These look to be intense with enough moisture in the atmospheric column to produce IFR conditions or worse so will put that into a prevailing group as confidence is at least medium that it comes through at SBN. This is expected to have damaging wind with it and may have embedded tornadic circulations. This moves through the area by 7 or 8z. There's lesser confidence downstream at FWA so have gone with low MVFR there. Drier conditions follow this system for Friday. We'll also have some gusty winds to 25 kts ahead of the line this afternoon.

IWX WATCHES / WARNINGS / ADVISORIES

IN...Heat Advisory from noon EDT /11 AM CDT/ today to 8 PM EDT /7 PM CDT/ this evening for INZ005>009-012>015-017-018-020- 022>027-032>034-103-104-116-203-204-216. OH...Heat Advisory from noon today to 8 PM EDT this evening for OHZ001-002-004-005-015-016-024-025. MI...Heat Advisory from noon today to 8 PM EDT this evening for MIZ078>081-177-277. MARINE...Small Craft Advisory from 5 PM this afternoon to 5 AM EDT Friday for LMZ043-046.