textproduct: Chicago

KEY MESSAGES

- Scattered thunderstorms Tuesday with a level 1 for severe weather, mainly in the afternoon/early evening.

- Severe thunderstorms Wednesday into Wednesday evening with a level 3 for severe weather, with all hazards possible, large hail, damaging winds and tornadoes.

- Torrential rainfall and localized flash flooding possible Wednesday.

- Possible high waves and dangerous swimming conditions at Indiana Lake Michigan beaches Thursday.

DISCUSSION

Issued at 225 AM CDT Mon Jun 15 2026

Dry and quiet conditions are expected today with below normal temps topping out in the mid 70s. Westerly winds will gust into the 20 mph range.

An upper level trough and associated cold front will move across the area Tuesday bringing showers and scattered thunderstorms. There remains some timing differences with activity possibly into the western cwa Tuesday morning and then strengthening into the afternoon as it moves across the eastern cwa, likely exiting the cwa early Tuesday evening. The Day 2 outlook maintains a level 1 risk for severe weather with moisture/dewpoints being the limiting factor given current model trends. The NAM does have a narrow axis of dewpoints in the lower/mid 60s ahead of the front across northern IN by 00z and if this were to materialize, there may be a bit higher severe threat in the far eastern cwa. Prevailing southwest winds ahead of the cold front may gust into the 30 mph range on Tuesday.

Another stronger upper level trough and associated surface low will move across the Great Lakes region Wednesday bringing the threat of severe thunderstorms across much of the region, though there remains quite a bit of uncertainty for the local area. There could be ongoing convection midday Wednesday with perhaps widespread coverage. While there is a chance this could limit how far north the warm front is able to lift later Wednesday afternoon into Wednesday evening, the deepening low pressure that is likely to be north of the area and the strong wind field may allow the warm front to lift back north through at least the I-80 corridor and much of the guidance generally supports the warm front lifting back through at least part of the local area. Despite these uncertainties, all severe hazards will be possible Wednesday into Wednesday evening, large hail, damaging winds and tornadoes, some possibly strong.

Precipitable water values on Wednesday are forecast to be in the 1.5 to 2 inch range across much of the area and the past few operational runs of the GFS show precipitable water values across the southern cwa into the 2.25 inch range. Current forecast qpf amounts for this time period are around 2 inches for most of the area and if these materialize, combined with the wet ground and elevated river/creek levels, torrential rain will lead to localized flash flooding. Too early for a flood watch but that will need to be considered as Wednesday approaches.

Prevailing south/southeast winds outside convection Wednesday may gust into the 30-35 mph range and then shift southwest south of the warm front. Northwest winds behind the cold front may also gust into the 30 mph range Wednesday night into Thursday, but will be dependent on the strengthen/deepening of the system as it departs. Wind directions may allow for high waves and dangerous swimming conditions for Indiana Lake Michigan beaches Thursday.

Quite a bit of uncertainty for the end of the week into next weekend regarding precip chances. There appears to be a few weak waves in northwest flow that may allow for some afternoon showers and thunderstorms Friday and Saturday. And then maybe a more organized system in the Sunday time frame, which the ECMWF appears to be fairly consistent with. Temperatures look to remain slightly below normal through the period. cms

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 623 AM CDT Mon Jun 15 2026

Forecast concerns include...

Chance of thunderstorms Tuesday morning. Gusty southwest winds Tuesday.

Light southwest winds to start will become more west/southwest by mid morning and increase into the 10-12kt range with gusts into the 15-20kt by late morning. Winds will diminish under 10kt with sunset and turn southwest. Speeds and gusts will slowly begin to increase toward daybreak Tuesday morning and continue to increase Tuesday morning with gusts into the mid 20kt range.

There will be a chance for showers and thunderstorms Tuesday morning, mainly after daybreak through mid morning. There remains uncertainty for both timing and location though there are some trends in guidance that if thunderstorms occur, this would be the time period. Despite the low confidence, opted to include prob thunder mention in the new 30 hour ORD/MDW tafs. cms

LOT WATCHES/WARNINGS/ADVISORIES

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