textproduct: Chicago

KEY MESSAGES

- Widely scattered showers and isolated storms are possible this evening through early Sunday afternoon (30-40% chance).

- Above normal temperatures are expected through early next week.

DISCUSSION

Issued at 226 AM CDT Sat May 23 2026

A surface low analyzed over southeastern Indiana is gradually moving northeastward toward southeastern Michigan and western Lake Erie. Moisture wrapping around the northern edge of the cyclonic flow is providing rain showers in northern Indiana. Meanwhile, bands of showers along the far outer edge are moving west over Lake Michigan toward Illinois. Coverage of showers through mid morning should be confined to counties adjacent to Lake Michigan, mostly isolated, and rain totals are expected to be a trace to locally a hundredth or two. Modeled instability is meager at best. So while the chance of lightning is "non-zero", it is not expected. As the surface low continues its eastward trajectory, showers will also move east over Michigan for drier conditions by mid morning. Winds are expected to be light and northerly before a lake breeze develops in the afternoon. High temperatures for inland areas are expected in the 70s, but the aforementioned lake breeze should limit heating near the lake shoreline to the 60s.

An upper level trough over the Central Plains will move east toward the western Great Lakes this evening through tomorrow, driving a surface front from west to east across the forecast area. Widely scattered showers out ahead of the front are expected to arrive near the west border of the forecast area early this evening. Model soundings show weak instability with these showers that could lead to an isolated thunderstorm. But the better instability, and better forcing in general, is expected farther west along the front which should not arrive until after sunset. After sunrise, instability will increase renewing the chances (20 percent) for thunder along and ahead of the front. There is some model disagreement on the exact placement of the front after sunrise, but the highest confidence in thunder development on Sunday is east of Interstate 55. Current guidance has the front exiting the area to the east during the afternoon with quieter conditions in its wake.

An upper level ridge is expected to grow Sunday night into Monday. As surface high pressure slides over central Illinois, southerly flow will advect a warmer air mass over the area. Temperatures are expected to climb above normal into the 80s both Monday and Tuesday.

Models are suggesting a 700 mb wave is expected to move northward out of Texas Tuesday night before phasing with a longer wave over the Intermountain west late in the week. The expectation is that this wave would send a front over the forecast area from south to north and provide another chance for rain Tuesday night into Wednesday. However, at this range there is still model disagreement on the progression of this wave as well as how it phases late in the week (potentially setting up a stagnant pattern) leading to low end PoPs through the end of the week, mainly south of Interstate 80. Persistent northeast winds late in the week are expected to help return high temperatures back to seasonal norms.

DK

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 655 AM CDT Sat May 23 2026

Key aviation forecast messages:

- A period of IFR CIGs through mid morning near Lake Michigan.

- Light northerly winds turning east behind a lake breeze this afternoon at ORD/MDW.

- Another round of showers possible this evening near RFD and late tonight into the Chicago area terminals (30% chance).

After holding off all night the IFR stratus has made an inland surge into ORD and MDW this morning which may linger through ~14-15Z before gradually lifting and scattering through midday.

Winds will be generally light north northeast near the lake early this morning then becoming light northerly to potentially variable through midday before a lake breeze turns winds easterly in the afternoon. Farther west near RFD prevailing light and variable winds will turn southwest to west late in the afternoon ahead of a potential line of gusty showers. Have introduced a PROB30 for these showers at RFD which are expected to then decrease in coverage with eastward extent toward Chicago.

Additional showers may develop near and ahead of an approaching cold front late tonight into early Saturday morning. Have introduced PROB30s for -SHRA at the Chicago area terminals to account for this. While lightning can't be ruled out with this activity the potential is too low to include with this update (20% chance).

Petr

LOT WATCHES/WARNINGS/ADVISORIES

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