textproduct: Chicago

KEY MESSAGES

- Showers likely late Friday into Friday night.

- Return to somewhat above average temperatures expected next week, though cooler temperatures expected near the lake.

DISCUSSION

Issued at 202 PM CDT Wed May 20 2026

High pressure over Lake Superior providing for northerly winds and a steady feed of rather chilly temperatures, especially near and just downwind of Lake Michigan. Thursday looks to be pretty similar to today, though with more mid-high level cloudiness northern CWA and with slightly less wind. While the winds won't be quite as gusty, they'll remain off the lake and keep temps in the 50s again near the lake. Southern CWA, where there should be a bit more sunshine, should see temps several degrees warmer than today, probably making a run at 70 degrees.

Shortwave trough over northern Mexico is progged to lift northeastward into the mid-Mississippi to lower Ohio valley regions Friday into Friday night. Associated sfc low is progged to track from central IL northeast into lower Michigan Friday night with the warm sector expected to remain south of most, if not all, of our CWA. Rain associated with this system is progged to begin spreading into our southern CWA during the afternoon, spreading north to the WI border early Friday evening. As mentioned in the previous AFD, instability is expected to remain well south of our CWA with seemingly very little threat of thunderstorms, so we're looking for primarily just a chilly rain.

Given the currently progged track of the sfc low, it is possible that our extreme southeast CWA could briefly poke into the warm sector Friday evening. Despite this, GFS and ECMWF forecast soundings exhibit little or no CAPE due to the rather cool low levels and warmer than average mid-level temps (-8 to -10C at 500mb). Opted to only retain the slight chance of thunderstorms Friday evening over the far southeast corner of our CWA and even there the chances appear meager.

Rain should end by or shortly after sunrise Saturday, but lingering cloud cover will likely keep temps from getting too warm. Winds off the lake will again keep it chilly near the lake. Fast on the heels of this southern stream shortwave will be a northern stream shortwave wave by Sunday. Warm air advection ahead of this wave should result in warmer temps Sunday, possibly right up to the lakefront. NBM pops were pretty low Sunday and didn't make any changes at this time, given some model variability in handling of this system as well as the progged weaker forcing and questionable moisture. This will be something we'll have to look at in coming days to see how models trend with that wave.

Medium range guidance is in pretty good agreement on a large scale pattern change over North America next week. Both EPS and GEFS develop high amplitude, high latitude upper ridging over central Canada south into the north central U.S. with a developing omega block pattern. Medium range guidance can struggle at times in dealing with blocking patterns, but the signal has been and continues to be pretty strong. This would likely result in warmer than average temperatures and likely drier than normal conditions locally. However, the northern displacement of the upper ridge would probably mean a surface high to our north as well, which would open to the door to winds off Lake Michigan and the typical spring/early summer "cooler near the lake" forecast for much of next week.

- Izzi

AVIATION /00Z TAFS THROUGH 06Z FRIDAY/

Issued at 626 PM CDT Wed May 20 2026

NE winds will prevail tonight, with gusts becoming less frequent through the evening. Winds will then veer E or even briefly SE late tonight and into Thursday morning. As this occurs, MVFR cigs may slosh westward across the terminals. Confidence remains a bit too low to warrant prevailing or TEMPO groups for MVFR cigs but will continue to monitor.

An increase in mid-level moisture is forecast to occur Thursday morning, particularly near RFD as a weak disturbance transits the area. Can't rule out the potential for a few sprinkles or even some showers, but chances remain too low for a precip mention given lingering sub-cloud dry air.

A secondary front/lake breeze will reinforce gusty NE winds Thursday afternoon before winds once again ease Thursday evening.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement through Thursday afternoon for ILZ006- ILZ103-ILZ104.

IN...Beach Hazards Statement through Thursday morning for INZ001.

Beach Hazards Statement through Thursday morning for INZ002.

LM...Small Craft Advisory until 1 PM CDT Thursday for the IL nearshore waters.

Small Craft Advisory until 7 AM CDT Thursday for the IN nearshore waters.