textproduct: Chicago

KEY MESSAGES

- Isolated to widely scattered showers and thunderstorms will continue overnight, mainly along and south of a Rochelle to Joliet and Lafayette, IN line. No severe weather is expected.

- While there will be daily shower and thunderstorm chances through the upcoming week, expect plenty of dry hours. Outside of the convective chances, it will be very warm and humid (focused away from the lake until Tuesday).

UPDATE

Issued at 849 PM CDT Sat Jun 6 2026

No significant changes to the going forecast this evening, mainly minor tweaks to account for various boundaries (lake breeze, outflow and frontal) and their impacts on pop coverage and temps.

Early evening surface analysis depicts a composite frontal/lake breeze/outflow boundary stretching across the forecast area along a line from roughly Clinton, IA to south of Rochelle, then southeast through northeast Livingston county eventually to the Lafayette, IN vicinity. While little/no mid to upper level forcing is present, RAP mesoanalysis indicates ~2000 J/kg of MLCAPE remains along/south of the aforementioned boundary(ies) in our warm/humid summer-like air mass. Weak low-level convergence and modest southwest flow (10-15 kt in the 925-850 mb layer) feeding into the stalled baroclinic zone continues to produce isolated to widely-scattered showers and thunderstorms across the southwest half or so of the cwa at mid- evening. While mid-level short wave ridging is progged to continue to build overhead overnight, and low-level instability will decrease diurnally, weak short wave energy wrapping northward around the eastern periphery of the upper level low centered over the Southern Plains is expected to maintain this southwest low-level flow overnight which should allow isolated convection to continue along/south of the composite boundary. This will persist into Sunday as well, as the mid-level short wave nudges the mid-level ridge east and northeast of the forecast area and diurnal instability again increases.

Going forecast has this scenario handled fairly well, thus other than some tweaks to pops/temps this evening through the overnight hours based on the location of the composite boundaries, have not made significant changes (though did warm overnight mins south of the boundary where temps will likely remain near 70 degrees).

Ratzer

DISCUSSION

Issued at 307 PM CDT Sat Jun 6 2026

Through Sunday Night:

GOES visible satellite imagery this afternoon shows several regions of agitated cumulus in and near our forecast area. The most congested cumulus has generally been focused near the lake breeze and along a somewhat diffuse remnant outflow boundary from last night's convection that has been laid out across our far southern counties and into central Indiana, but deeper cumulus growth has also been noted within a couple of low-level confluence/convergence zones across the northern half of our forecast area. Synoptic-scale forcing remains fairly nebulous and pretty much limited to very modest isentropic upglide, but within moist and unstable summertime air masses like the one in place today, it typically does not take much for convection to get going, and that has been the case today. That said, the relative lack of large-scale ascent has kept convective coverage isolated to widely scattered thus far, and that should largely continue to remain the case through this evening.

Across our southern counties, RAP objective mesoanalysis depicts 2000-2500 J/kg of MLCAPE amidst 15-25 kts or so of deep- layer shear. This environment was just favorable enough to yield severe downburst winds and small hail in Benton County, IN with a tall storm that briefly pulsed up there a little while ago, and would not be surprised to see another instance or two of localized damaging winds and hail up to quarter size with any convective updraft cores that manage to pulse up towards the ~13 km AGL equilibrium levels south of I-80. Farther north, a more pronounced warm nose at around 600 mb may inhibit convective growth to a greater degree in the absence of stronger forcing for ascent, making it less likely for cells to grow tall enough to produce severe winds and hail there, in addition to reducing the overall likelihood of lightning. Lastly, could not entirely rule out a funnel cloud or even a landspout occurring somewhere as slow-moving cells develop along surface boundaries in this moist and unstable air mass. The latest RAP mesoanalysis depicts non-zero non-supercell tornado parameter values in a few spots, which supports this thinking.

A slight enhancement to the low-level jet this evening may allow for disorganized convection to fester across our southern counties for at least a few hours after sunset, and possibly well into the night. This convection should eventually diminish in coverage, though, as the attendant instability reservoir becomes increasingly depleted with time tonight. The resulting lull in convective activity should persist through at least mid-morning tomorrow before large-scale forcing increases toward midday as a closed-off upper-level low presently located over the southern Plains lifts northward toward our latitude and becomes sheared-out as it does so. Despite the weakening nature of the forcing associated with this disturbance, the persisting rich low-level moisture (surface dew points up to around 70F) and diurnal destabilization as surface air temperatures warm into the 80s will support another episode of convection in our forecast area into the afternoon hours. This time around, convective coverage looks to be greatest across the southwestern half or so of our CWA. Minimal deep-layer shear will also encourage tomorrow's convection to have a pulse-like character. Enough instability will be present to support a gusty wind and small hail threat with the strongest updrafts that pulse up, but subpar lapse rates and DCAPE should keep storms sub-severe.

Ogorek

Monday through Friday:

The aforementioned weakening mid-upper low/short-wave will continue to shear out Sunday night into Monday as it encounters robust ridging centered over the eastern Lakes by then. Nonetheless, weakly capped tropics- like airmass should support fairly widespread showers and at least scattered storms developing as early as midday Monday (unless debris cloudiness proves too detrimental to sufficient destabilization). Southeasterly synoptic flow and lake breeze reinforcement will keep IL shoreline locations in the 70s on Monday, while the rest of the area reaches the low- mid 80s.

Looking ahead at the rest of next workweek, there have been some guidance members with sufficiently strong mid-level ridging and low-level thermal ridging poking into the Great Lakes region for a few days of very warm (locally hot) and humid conditions. With that said, the more likely scenario is our area being on the precarious northwestern periphery of ridging centered near the East Coast. This should entail less capping and a continuation of shower and thunderstorm chances. By later in the week (Thursday or thereabouts), seasonably strong troughing from the north central US to central Canada could plausibly yield a pattern supportive of organized strong to severe convection into the region.

Note that the NBM depicted temperatures centered Tuesday through Friday (most notably on Wednesday and Thursday) are well outside of the ensemble spectrum due to likely spurious upward bias correction. Thus we will withhold from any heat messaging locally. It looks to be very warm and humid, but not hazardously so, per the current global ensemble guidance consensus.

Castro

AVIATION /06Z TAFS THROUGH 12Z MONDAY/

Issued at 1244 AM CDT Sun Jun 7 2026

Main Concern:

- Potential for TS into RFD area and the far western Chicago metro later this afternoon into this evening. Additional SHRA/TS may approach the terminals towards daybreak Tuesday.

Conditions at the main Chicago area terminals will likely be primarily quiet through most of the current TAF period. RFD area still has the highest chance for TS, where a PROB30 was maintained. May need to consider a PROB30 for DPA with later issuances. For ORD, MDW, and GYY, the most likely scenario is that the more stable marine layer conditions prevent TS into the vicinity. TS coverage does look high enough this afternoon-early evening west and southwest of Chicago for prolonged air space impacts. The next chance for TS looks to be towards and beyond the current ORD and MDW 30-hour TAF period, with no mention in this issuance.

Light easterly winds overnight/early this morning will increase to around 10 kt by the mid to late morning with speeds only gradually diminishing tonight/Sunday night. Outside of SHRA/TS, expect VFR conditions.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

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