Area Forecast Discussion

KEY MESSAGES

- Severe storms likely through this evening (highest threat between 5 and 10 PM). All hazards (tornadoes, destructive winds, significant hail) are possible across the entire area.

- After a dry and cooler day on Friday, there is another threat for severe weather late Saturday.

MESOSCALE

Issued at 222 PM CDT Thu Jun 11 2026

Quick update on latest thinking regarding today's severe threat. The 18z sounding from ILX has shown an impressive EML (elevated mixed layer) has advected into the area. This is resulting in MUCH steeper 700-400 mb lapse rates, however at the base of those steeper lapse rates there's been about a 2C+ warming in/near 700mb. That warming near 700mb and resultant convection inhibition combined with weaker large scale ascent (for now) has prevented the convection near the tail end of the morning MCS from becoming rooted in the boundary layer and taking off. This bodes well for reducing the chances for discrete convection in the open warm sector across central IL.

HRRR continues to lose that convection much more quickly than what is actually happening, however the WOFS (Warn-on Forecast System) hangs onto that convection and the lingering footprint of the cold pool longer than the HRRR. It too, loses that convection quickly, perhaps a bit too quickly, but generally depicts that the northern extent of the very concerning tornado environment later this afternoon would be a farther south. It wouldn't be shocking to see that northern extent shift a bit farther south in later runs as WOFS initializes from current radar.

Farther west, the low level response the sfc cyclone lifting northeast has been quite impressive with northward surge of low level moisture. Cloud cover and precipitation is preventing boundary layer temps from warming in this area resulting in very weak low level lapse rates. Farther south, across far northeast Missouri some breaks in the cloud cover have allowed temps to warm into the low to mid 80s, resulting stronger low level CAPE. Satellite trends suggest that some partial clearing will overspread much of northern IL this afternoon. This combined with increasing southerly flow in the synoptic response to the deepening low lifting north in Iowa should result in the outflow boundary/southern extent of outflow from the morning convection gradually lifting north and perhaps mixing out a bit this afternoon.

It still seems like there will be a gradient between stronger low level CAPE and weaker low level destabilization somewhere in our CWA. Latest WOFS has the northern extent of that better low instability and resultant very favorable tornado environment getting as far north as roughly to an Ottawa to Chicago line by later this afternoon. While the exactly how far north the more concerning environment gets is lower confidence (ultimately may not be a sharp line rather more of a gradient), but the general idea of significant tornado threat increasing near/south of I-55 and I-80 seems reasonable.

There is a dramatic increase in low and deep layer shear comparing ILX's VWP to DVN's VWP. The unseasonably strong shear noted on DVN's VWP is expected to spread eastward across our CWA as the afternoon progresses. Storm mode may tend to favor linear by the time the convection reaches our CWA, but given the very strong low level shear, QLCS tornadoes and perhaps even tornadic supercells embedded within the QLCS will be a threat. This threat will likely be more prolific where the stronger boundary layer heating leads to stronger low level CAPE, but even farther north the strong shear will support a QLCS tornado threat.

Finally, any discrete supercell within the warm sector later this afternoon (especially southern CWA) will be in an exceptionally favorable environment for strong tornadoes. While linear storm mode is most likely, there is still some chance for discrete supercell development in the warm sector, so we will be watching that closely. If the remnant outflow boundary from this morning's MCS doesn't mix out, then it would be a potential source for enhanced low level vorticity and a zone we'd watch for a locally higher tornado threat (both supercellular and QLCS).

- Izzi

DISCUSSION

Issued at 242 PM CDT Thu Jun 11 2026

Broad mid and upper-level cyclonic flow will persist across the northern United States through the period. While this will maintain periodic opportunities for showers and thunderstorms into next week, we will experience a brief break in pattern for Friday. On Friday, a much less humid airmass shifting overhead on westerly winds in the wake of this evenings cold frontal passage will support a more comfortable weather day with temperatures topping out around 80 under mainly sunny skies.

Humidity values will be back on the increase again for Saturday as the low-level flow turns south-southwesterly in advance of the next approaching surface cold front dropping southward from the Upper Midwest. As the front shifts into our area late Saturday into Saturday night, a narrow corridor of slightly better low-level moisture return preceding it may support the development of some scattered showers and thunderstorms. Should these materialize, we will also have to monitor the potential for some more organized storms into Saturday evening, particularly given the presence of strong deep layer flow. While not looking to be a major severe weather event at this time, we certainly cannot rule out the threat for a few stronger storms to become capable of producing instances of damaging winds and hail. Accordingly, the SPC Day 3 outlook continues to highlight our area in a level 1 of 5 severe weather threat for late Saturday.

A push of much cooler and dry weather is anticipated for the second half of the weekend into early next week following the cold frontal passage Saturday night. Interestingly, this airmass looks to hold daytime highs in the 70s (lows in the low to mid 50s) early next week. Conditions then look to turn more active again (return of showers and thunderstorms) mid to late next week as an enhanced northwesterly upper-level flow pattern sets up across the central part of the country.

KJB

AVIATION /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 634 PM CDT Thu Jun 11 2026

Key Messages:

- Strong storms impact the terminals through 02-03Z this evening. Brief period of gusty winds in excess of 45 kt and torrential downpours may accompany these storms.

- Winds shift westerly and gradually abate mid to late this evening following a cold frontal passage.

The main aviation weather concern revolves around the strong thunderstorms that will impact the terminals through 02-03Z this evening. Very heavy rainfall will accompany these storms, which will likely result in a short (hour or less) period of sub mile VSBYs. Also, a period of strong, potentially damaging wind gusts (in excess of 45 kt) may accompany this line of storms. Fortunately, the line of storms will quickly shift east of the terminals after 02-03z this evening as a cold front shifts across the area. Winds will shift westerly following this frontal passage, with speeds expected to ease overnight.

Quieter weather is expected overnight and through the day Friday, with mainly clear skies and westerly winds.

KJB

LOT WATCHES / WARNINGS / ADVISORIES

IL...Flood Watch until 11 PM CDT this evening for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

IN...Flood Watch until 11 PM CDT /midnight EDT/ this evening for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 10 PM CDT this evening for the IL and IN nearshore waters.