textproduct: Chicago

KEY MESSAGES

- Showers and thunderstorms are expected through midday, with highest chances along and east of I-55. Primary concern is downpours leading to ponding in poor drainage areas.

- Above normal temperatures through the early part of the week, though cooler near Lake Michigan.

DISCUSSION

Issued at 226 AM CDT Sun May 24 2026

Festering showers continue to bubble up west of the forecast area, closer to a surface front analyzed along or just west of the Mississippi River. With weaker forcing, coverage is a little lacking leading to more isolated to localized clusters developing. A few lightning strikes may be possible, but with limited instability, confidence low. Some of these showers may continue into the area west of the Fox Valley through the next couple of hours.

The previously mentioned front is expected to sweep across the area through the early morning, exiting to the east around midday. Coverage of showers along and ahead of the front is expected to increase closer to daybreak along the better forcing with the arrival of a mid level wave. Southerly winds will advect in an almost tropical air mass with precipitable water amounts north of 1.50 inches. With slow storm motions (around 20 mph or less) nearly parallel to the front, the primary threat is for downpours and even localized torrential rainfall. Widespread flash flooding is not expected, but with intense rain rates (locally greater than an inch per hour) and possible training there is a chance that there could be localized ponding in poor drainage areas. Additionally, model soundings depicting tall, skinny CAPE allows for the potential for some embedded thunder as the front moves through, though higher coverage of storms is expected along and east of I-55 after daybreak.

Drier conditions are expected in the afternoon in the wake of the front through Tuesday. Models are suggesting a weak 700 mb wave moving across Iowa into lower southern Wisconsin late on Monday. Given its projected track away from northern Illinois, PoPs were kept dry and just something to monitor. Otherwise, upper level ridging and surface high pressure will grow today through Tuesday driving not just dry conditions but warm, above normal temperatures. Lake breezes will help keep cooler conditions cooler near the lake shoreline, but temperatures well into the 80s can be expected farther inland.

Models are suggesting that by Wednesday morning, a near Omega blocking pattern will set up in the mid-to-upper levels. Ensembles are still suggesting that a weak 700 mb wave will move northward from the Gulf to the mid Mississippi River Valley. This could provide the next chances for rain and storms, but models noticeably keep the better chances farther south compared to 24 hours prior. As the stagnant pattern remains toward the end of the week, conditions are looking dry and seasonable beyond Thursday.

DK

AVIATION /06Z TAFS THROUGH 12Z MONDAY/

Issued at 1257 AM CDT Sun May 24 2026

Key aviation forecast messages:

- Period of SHRA with embedded TS expected early this morning at the Chicago area terminals.

- Associated IFR to LIFR CIGs expected with the SHRA, lowest near the lake, with IFR to near LIFR VSBYs.

While spotty showers will remain possible west of I-55 through the rest of the overnight hours, expecting most areas to stay dry through ~9Z. Thereafter model guidance has remained consistent in a quick expansion of shower coverage into the Chicago metro, though with slightly slower onset and end times. Have accordingly shifted the timing by about an hour later for most sites. While confidence in thunderstorm coverage is on the lower side, isolated embedded non-severe thunderstorms will be possible and have accordingly maintained TEMPOs for TSRA. Any showers/storms that develop will also be efficient rain producers with rainfall rates >=1"/hr possible. The increased low-level moisture will also likely lead to quickly lowering ceilings to IFR and potentially LIFR, lowest near the lakeshore and under the heaviest showers. Showers and any isolated embedded storms are expected to end from west to east from mid morning through midday.

Light and variable winds are expected prior to the expansion of shower coverage early this morning. Directions will settle into a prevailing northwest direction in the wake of the showers/storms initially with the potential for a weak lake breeze turning winds east at the Chicago terminals during the mid to late afternoon.

Similar to yesterday, given increased low-level moisture in the wake of this morning's showers and storms, we will have to monitor fog and low ceiling trends over Lake Michigan into the evening and early overnight hours in case it happens to ooze inland again.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

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