textproduct: Chicago

KEY MESSAGES

- Showers and storms are expected this afternoon/evening with the highest coverage southwest of the Chicago Metro, some capable of torrential downpours and gusty winds.

- An additional round of showers and storms are expected areawide tomorrow.

- Heat and humidity increase mid-week with heat indices in the mid to upper 90s.

- Low chances for showers and storms Tuesday and Wednesday, but there is a chance that Thursday could be the next threat for severe weather.

DISCUSSION

Issued at 233 PM CDT Sun Jun 7 2026

SPC mesoanalysis depicts a stout theta-e gradient along a surface stationary front from northwest Illinois through Gary, Indiana. Luckily for the Chicago Metro, most of the activity this afternoon and evening should be along and southwest of this boundary. Storm motions are incredibly slow (to the north- northeast at 10 to 15 mph). While wet microbursts producing locally gusty winds are possible, the main hazard this afternoon is becoming a hydro concern. Instantaneous rain rates on MRMS for storms closer to the Mississippi River (where the better forcing is located) have had isolated storms producing over 2 inch per hour rates! For now, the higher rain totals have remained west of the area, but the threat for localized torrential downpours this afternoon and evening keeps the threat for flash flooding prevalent.

An upper level trough over the central Plains is expected to slowly move east through the overnight and over northern Illinois on Monday. This should eventually kick the aforementioned stationary front northeastward and produce widespread showers and storms across the forecast area tomorrow. With the wave being more progressive in nature, the threat for flooding concerns is somewhat lower than this afternoon. But given the amount of moisture available and how efficient the rain should be produced, flooding concerns remain elevated tomorrow. Additionally, there will remain a threat for wet microbursts producing localized gusty winds. With high CAPE, weak shear, and ample ambient vorticity, a funnel cloud or two cannot be completely ruled out, particularly in the afternoon when the trough axis is overhead.

Weak ridging will grow on Tuesday from the west. Lingering showers and some isolated storms are possible in the morning, mainly east of I-55. While some afternoon summertime pop-up showers are possible, with weak forcing, the forecast for Tuesday and Wednesday is trending drier. More impactfully, this ridge will drive flow back to southwesterly and advect in a much warmer, and muggy, airmass. 850 mb temperatures are expected to increase to and potentially in excess of 20C. Surface temperatures are expected to climb above normal into the mid to upper 80s and even the low 90s. With forecasted dew points in the 70s, heat indices are expected to climb into the mid to upper 90s each day.

That ridge axis is expected to slide eastward over the area on Wendesday as the next long wave trough sets up over the northern Plains. An upper level low is expected to deepen Wednesday night over Manitoba with a strengthening 100 knot upper level jet embedded in the trough. A reflected surface low over southern Canada is expected to develop with a cold front draped southward down the Plains. There is a lot of model uncertainty on storm development along the front on Wednesday. There is a non-zero chance that a MCS develops and arrives in northwest Illinois overnight, it would arrive in a less than favorable time of day. Models are showing a little better consistency with showers and storms developing with the better forcing with the front on Thursday. With strong low level flow, a stout upper level jet for synoptic forcing, and MUCAPE values 2000-3000 J/kg, an eastward propagating squall line may develop with strong to possibly even severe storms Thursday. Lastly, there is also a little uncertainty on temperatures for Thursday due to the front. It could set up as another hot and humid day at first, but the timing of the front may impact max temps.

Quasi-zonal flow aloft is expected to develop behind the frontal passage on Thursday. Temperatures should become slightly more muted at the end of the week. Another upper level wave may pass over on Saturday providing another chance for showers and storms over the weekend, but low confidence in timing and strength at this distance.

DK

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 106 AM CDT Mon Jun 8 2026

Main Concerns:

- Periods of SHRA and TS, with TS most favored from the afternoon through the early evening.

- Low CIGs and reduced VSBY tonight/Monday night

In the overnight-morning period, showers will be possible at just about any point (considering that SHRA are developing overhead as of this writing), so opted for a broad brushed VCSH. TS chance has diminished to <20%, though can't rule out a period of higher rainfall rates and reduced VSBY until sunrise or just after.

Daytime heating and an upper disturbance shifting over the area this afternoon should translate to SHRA and at least VCTS and/or convective cloud tops >25kft. Given some lingering uncertainty regarding timing of direct TS impacts, maintained a longer PROB30 window in the TAFs. Any heavy showers or storms passing overhead will result in low VSBY, potentially down around 1SM. While TS can't be ruled out later in the evening and overnight, coverage should be limited by then. As a weak surface low pressure tracks across northwest IL overnight, light southerly winds and very moist conditions will probably support BR and/or drizzle amidst on and off showers. CIGs will likely build down to IFR and potentially even LIFR with time.

East-southeast winds through this morning will become south- southeast with occasional gustiness by early this afternoon.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.