Area Forecast Discussion

KEY MESSAGES

- Isolated to scattered showers and thunderstorms are possible this weekend over central IL, mainly north of I-70. A few storms could have the potential to become strong to severe, posing a risk for locally heavy rain of 1-2 inches, large hail and damaging winds.

- More widespread showers and thunderstorms are expected over central and southeast IL Sunday night through Monday night.

- Expect a warm and muggy conditions today with feel-like temperatures climbing into the lower 90s this afternoon.

- A stronger warming trend arrives Tuesday through Friday, pushing afternoon heat index values 95 to 105 degrees.

DISCUSSION

Issued at 330 AM CDT Sat Jun 6 2026

Radar mosaic shows scattered showers/thunderstorms over northern parts of IL/IN into southern Iowa and northern MO. Over IL this developing convection was north of a Macomb to Peoria to Kankakee line and tracking eastward. This convection aided by a WSW 25-40 kt low level jet (strongest winds ne of central IL over southern Great Lakes) and tropical PW values of 1.4-1.7 inches over much of IL. Unstable air mass over northern IL with MLCAPES of 1800-2500 j/kg from I-74 north. Bulk Shear values were less than 25 kts over central IL and 30-45 kts from I-80 north, over northern IL. The 08Z/3 am surface map shows a cold front over southeast WI into northern Iowa and southeast Nebraska. SW winds and increasing clouds giving mild temps in the low to mid 70s (warmest from I-55 west). Dewpoints were in the lower to mid 60s in east central and southeast IL and upper 60s to near 70F from Highway 51 west.

The 06Z and 07Z HRRR show scattered convection north of Peoria and lifting through early this morning and mostly existing CWA by mid morning as low level jets pushes further ne of central IL. A few strong cells with gusty winds along with locally heavy rainfall possible early this morning with this convection mainly north of PIA and BMI next few hours. Otherwise an outflow boundary lingering over northern CWA to see scattered convection develop near it during this afternoon in unstable air mass (but weak wind shear), especially during mid to late afternoon initially north of a Rushville to Lincoln to Paris line. But convection chances to shift further south into central IL during this evening but generally staying north of I-70 into tonight. SPC Day1 outlook has marginal risk of severe storms this afternoon/evening north of an Effingham to Robinson line for damaging winds and large hail. The HREF LPMM also shows a few pockets of 1-2 inches north of I-74 early this morning and north of highway 36 this afternoon/evening. Muggy today with very warm highs in the upper 80s with afternoon heat indices in the lower 90s. Lows overnight in the upper 60s, with se IL around 70F.

The main synoptic front will move into northern IL this afternoon/evening, and remain north of central IL on Sunday. Best convection chances tonight into Sunday will be over northern CWA closer to this front and over the MS river valley late Sunday afternoon as system wx system approaches from west Texas. The weak cutoff 500 mb low over west Texas to open up into a mid level trof as it moves over IA/MO overnight Sunday night and into IL Monday afternoon. Deeper tropical moisture to lift into IL ahead of this system Sunday night and Monday, with more widespread convection moving eastward over IL during Sunday night and continues Monday before diminishing from the west overnight Monday night into Tue morning. NBM has 70-90% chance of over 1 inch of rain over CWA Sunday night thru Monday night. Highs Sunday mid to upper 80s and low to mid 80s Monday. Chances of showers and thunderstorms lingers on Tue and Tue night especially in eastern IL.

Upper level ridging into IL Tue/Wed to return higher heat and humidity to the area during mid/late week. Highs Tue in the upper 80s to around 90F and 90-95F Wed-Fri (warmest over the IL river valley). Dewpoints in the low to mid 70s to give afternoon heat indices of 95-105F from Tue thru Friday. This will be our longest heat wave so far this season and be weather aware of this high heat and humidity. The ECMWF and GFS models showing a frontal boundary pushing se into IL Thu night and to bring more chances of convection. Though most days upcoming week we have at least slight chances of convection in tropical airmass.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1241 PM CDT Sat Jun 6 2026

MVFR ceilings in spots to start the period should lift here shortly, with VFR conditions largely expected the remainder of the period. A couple periods of showers and storms may impact the terminals this afternoon (KPIA, KBMI, KCMI) and Sunday morning. Confidence in timing and exact placement of storms remains low, so PROB30 groups remain in place to cover this probability. West-southwest winds with speeds between 10-15 kts will become light tonight as they back to the south-southeast by morning.

ILX WATCHES / WARNINGS / ADVISORIES

None.