textproduct: Chicago

KEY MESSAGES

- Another round of showers and thunderstorms on Tuesday, some of which could be strong to severe mainly during the afternoon hours. - Summer-like warmth and breezy winds will prevail through Tuesday, then cooler temperatures and dry conditions will return for the middle of the week.

- Milder weather returns heading into the weekend, though with at least intermittent shower/thunderstorm potential.

DISCUSSION

Issued at 244 PM CDT Mon May 18 2026

Through Tonight...

Convection and associated MCV responsible for this morning's severe weather has moved into Lower Michigan. Air mass in the wake of this wave is substantially more stable and combined with modest height rises in its wake should prevent any renewed convective development this afternoon or evening.

Severe convection currently developing over the central Plains is likely to congeal into a large QLCS that will move toward the mid-Mississippi Valley tonight. Most intense convection is likely to focus farther southwest across Missouri, likely intercepting the low level jet and orphaning the convection farther north across Iowa. This should result in convection over Iowa diminishing as it moves eastward into northern IL with some guidance suggesting very little shower activity would actually make it into our CWA. Have reflected this trend in pop grids, but opted to maintain at least chance pops given the inherent uncertainties in forecasting convective evolution.

Pressure field is recovering in the wake of the morning convection which has allowed winds to pick and become rather gusty from the southwest. Gustiness of the winds will generally tend to abate by sunset, except perhaps remaining somewhat gusty tonight in the urban heat island of Chicago.

-Izzi

Tuesday...

Convectively induced vorticity maximum will slide through northeast Illinois into early Tuesday, well outpacing the cold front, and therefore we may have some showers hanging on into the area, but confidence is medium-high that thunderstorm coverage will be on the lower side. Any lingering MCS cold pool footprint and residual cloudiness will likely delay destabilization into midday Tuesday, though additional storm development appears somewhat probable across the southeast half of the forecast area Tuesday afternoon/evening as the cold front finally pushes through the forecast area. Southwesterly flow ahead of the front will maintain mid to possibly upper 60s dewpoints and support MLCAPE approaching 1500 J/Kg. Stronger mid-level flow on the southeastern periphery of the Model guidance would support some additional vorticity maximum riding along the front, and flow to the southeast of the mid level trough across the northern Great Lakes will likely support enough storm development and some organization for a hail/wind threat during this time. This would be favored along and southeast of I-55, with short term ensemble guidance suggesting the window for much of NE IL and NW IN being fairly limited in the mid to late afternoon. For the Chicago metro area the picture is also a bit muddled for precipitation chances. High res guidance is mostly dry for the area, whereas global guidance and NAM/RAP does bring some shower activity across Chicagoland along the front in the early afternoon.

KMD

Wednesday onward...

Following the cold front, surface high pressure is progged to build east into the western Great Lakes region Wednesday and Thursday. Dry, but breezy and cooler weather is expected both days, with temps mainly in the 60s, but only in the 50s near Lake Michigan with northeast-east flow off the lake. Nighttime lows in the 40s are expected. The high then drifts off to the east Thursday night, with the upper level pattern favoring a series of mid-level disturbances tracking through the area Friday into the weekend. This will support milder temperatures, but also some occasional shower/thunderstorm chances into the holiday weekend.

Ratzer

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 109 PM CDT Mon May 18 2026

Wind field has been substantially altered by storms this morning, but will revert back to a south-southwest direction early this afternoon. Pressure gradient is baggier in the wake of the storms than originally forecast, so gustiness of the winds may be slower to develop today than indicated in the TAFs.

Showers and storms that develop over the central Plains today will move east and likely reach northern Illinois in a quickly decaying state late tonight/early Tuesday morning. Confidence is low in whether this activity will reach the terminals, so opted to just hang onto a PROB30 in the TAFs.

Finally, confidence in winds Tuesday is on the lower end of the spectrum. There is a chance wind fields could be altered by diminishing storms, which could play havoc on directions and speeds. However, if wind fields aren't significantly altered, then winds will likely be even stronger than indicated in the TAFs.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

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