textproduct: Chicago

KEY MESSAGES

- After a relatively cool Wednesday, temperatures will trend upward through the weekend and into early next week.

- Chances for periodic showers and storms will return to the area Thursday night and last through early next week. Some storms may be severe, particularly Saturday through Tuesday.

DISCUSSION

Issued at 1234 PM CDT Wed May 13 2026

Regional satellite imagery early this afternoon shows expansive cyclonic flow across the Great Lakes associated with a surface low pressure system moving across southern Ontario. The passage of an upper-level shortwave embedded within the parent trough over southern Lake Michigan allowed for a lake breeze to shift well inland this afternoon, which is leading to a gradient in temperatures ranging from the lower 60s west of I-39 to upper 40s along the shore. When combined with blustery north to northwesterly winds, it feels more like March than May outside (though the largely sunny skies are welcome).

Tonight, a surface high pressure system will quickly move into the region causing surface winds to become nearly calm and skies to clear. Temperatures will hence be poised to plummet overnight with lows expected to bottom out in the upper 30s to lower 40s. Patchy frost may develop in the typical cold spots by daybreak.

The surface high pressure system will only slowly shift away from the region throughout the day on Thursday, leading to fairly calm winds. Mostly sunny skies and a gradual increase in low-level warm air advection will help highs rise into the upper 60s to lower 70s. The exception will be along the Lake Michigan shoreline where a lake breeze will hold temperatures in the low to mid 50s.

Thursday night onward:

Toward the end of the week, the upper-level pattern will transition from predominantly upper-level cyclonic flow across the northern United States to zonal and eventually southwesterly flow. The net result will be a gradual warming and moistening trend leading to more seasonable to above-average temperatures and periodic shots of showers and storms. Note that some storms could be severe in the general region, particularly Saturday through Tuesday. Ensemble guidance suggests a break in the warm and stormy pattern toward the middle of next week.

Borchardt

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/

Issued at 633 PM CDT Wed May 13 2026

VFR conditions are forecast through the period. Any lingering mid-high clouds will gradually erode with sunset along with winds becoming light and variable as surface high pressure settles into the region. Winds return to a light northeast direction near the lake late Thursday morning then turn east behind a reinforcing lake breeze. Light and variable winds continue for inland areas for much of the day before settling into a prevailing light SSW to SSE direction late in the afternoon. Increasing high clouds are then expected toward the end of the period as our next weather system approaches the area.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 1 AM CDT Thursday for the IN nearshore waters.