textproduct: Chicago

KEY MESSAGES

- Seasonable and dry conditions over the weekend, but colder near the Lake Michigan shore.

- Severe thunderstorms Monday along with heavy rain and possible localized flooding.

DISCUSSION

Issued at 237 PM CDT Fri Apr 24 2026

Stratiform rain associated with a passing mid-level wave is now confined almost exclusively east of I-57, and will gradually end from west to east through the afternoon. Thunderstorm potential remains quite low, with the only focus in the far southeast CWA where cloud tops may become barely sufficient for a lightning strike late this afternoon. Farther west, a cold front entering the western CWA will track across the remainder of the area through mid-evening. Abundant cloud cover and slight low-level dry air advection has limited cumulus growth and will likely prevent new precip generation during the remainder of the day.

High pressure drifting eastward across the northern Great Lakes this weekend will promote dry and mostly clear conditions. Temps will be seasonable to seasonably warm well inland. Persistent east to northeast winds will lead to substantially cooler conditions with high in the upper 40s Saturday and mid 50s Sunday along the Lake Michigan shore. Cannot rule out some lake-induced fog or low stratus along the shore each morning as well.

Focus then turns to a potential severe weather event over and west of the area on Monday as deep troughing ejects northeastward over the central Great Plains. Impressive mid and upper-level dynamics shifting between the MO/MS River valleys Monday afternoon should quickly erode a modestly strong cap and force discrete convection around the I-35 corridor. Convection would likely congeal with eastward extend across the MS River, favoring primarily a QLCS set-up over some or all of our area late Monday afternoon and especially Monday evening. The intensity of convection with eastward extent, however, remains somewhat in question due to 1) the ability for less- pronounced forcing farther east to erode the cap and 2) amount of low-level moisture advection as flow remains backed and nearly parallel to a notable moisture gradient. Obviously we are still a few days out to hone in on more details, but conditional on a more favorable thermodynamic farther east, discrete supercells with all severe hazards are a possibility over or particularly south and west of the forecast area, followed by a damaging wind threat with embedded QLCS tornadoes. Will also need to monitor for a flooding threat, especially north of I-88 where river flooding is ongoing, if convection becomes more widespread and/or slower moving.

Behind Monday's system, a transition to longwave troughing over the eastern Great Lakes and eastern Ontario/Quebec will favor a cooler (still seasonable) end to April with perhaps a couple chances for showers later in the week.

Kluber

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1224 PM CDT Fri Apr 24 2026

Key messages:

- A few showers possible at the eastern terminals this afternoon.

- West-northwest winds this afternoon shift north- northeasterly late this evening and overnight.

- Potential (20-30% chance) for a period of IFR to low MVFR CIGS late tonight through around daybreak Saturday morning.

Some patchy areas of MVFR CIGs continue to shift across the area early this afternoon in advance of a cold front shifting into the area. These are expected to be short lived early this afternoon, with generally VFR conditions anticipated this afternoon and evening. Otherwise, there is an area of rain currently working its way northeastward across east central IL into northwestern IN in advance of this front early this afternoon. While a few of these showers may make shift across the eastern terminals for a period this afternoon, their duration is expected to remain rather short.

West-northwesterly winds setting up in the wake of the cold frontal boundary this afternoon will shift north-northeasterly late this evening and overnight. This may promote some IFR CIGs developing inland off the lake across portions of northeastern IL and northwestern IN for a period overnight. However, due to low confidence on the extent of IFR CIGs, we continue to only mention a scattered deck around 600 feet. Any low clouds that move in off the lake should improve by mid morning on Saturday. Accordingly, VFR conditions are expected during the day Saturday, with breezy east-northeasterly winds.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

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