textproduct: Chicago

KEY MESSAGES

- Chances for showers and storms persist into this evening south of I-80.

- Drier and warmer conditions are expected into early next with cooler conditions near Lake Michigan.

DISCUSSION

Issued at 237 PM CDT Fri Jul 10 2026

Early this afternoon, a surface frontal boundary remains draped from west-to-east across my southern CWA from southern Lasalle county through Newton and Jasper counties in IN. Diurnal heating of the very moist low-level airmass (surface dew points in the low to mid 70s) through the morning has eroded convective inhibition, resulting in isolated shower and thunderstorm development along and near the boundary. This activity is expected to persist on a widely scattered basis this afternoon into this evening, particularly south to well south of I-80. Severe weather is not anticipated with these storms, owing to the poor deep layer shear. However, some locally gusty winds up to 40 mph will be possible with the strongest cells. Also, cannot 100% rule out the possibility for a brief landspout type tornado with the convection right along the the surface boundary. Otherwise, the slow eastward motion of 10-15 mph will result in some locally heavy rainfall.

The surface frontal boundary will sag southward into downstate IL tonight and on Saturday as a slow moving convectively enhanced mid-level impulse shifts east-southeastward from the Mid-Missouri Valley out across the Mid-Mississippi Valley. This track is expected to push the primarily focus for showers and thunderstorms on Saturday south of our area. Accordingly, our current forecast thus only mentions a low (20%) chance for areas as far north as around the U.S. 24 corridor. Elsewhere, partly cloudy skies are expected, with inland temperatures topping out in the mid 80s. Cooler conditions (mid to upper 70s) are again anticipated along the Lake Michigan shore, owing to the persistent onshore northeasterly winds.

Temperatures will begin to warm Sunday back into the upper 80s (mainly inland locations) on Sunday in response to the building of a large and anomalous mid/upper- level ridge. This upper- level ridge/high is forecast to peak in amplitude Monday into Tuesday, when 500 mb heights peak around 600 DAM across the Dakotas. For reference, this is nearly 3 standard deviations from normal! Across our area high temperatures are expected to be into the low 90s, particularly inland from the lake. Closer to the lake, the potential for daily lake breeze development through the week suggests that cooler afternoon conditions (80s) will result. Fortunately, the hot inland temperatures do not look to be accompanied by significantly high dewpoints/RH. Accordingly, peak afternoon heat indices next week do not look to get out of the 90s.

Our rain and storm chances look to remain rather minimal Sunday through at least early next week as this large expansive ridge dominates across the northern Plains into the Upper Midwest. However, later next week (Thursday into Friday) there are signs in the ensemble guidance that an anomalous trough/low digging into eastern Canada will flatten the ridge across the Great Lakes region. As this occurs, our area may become better positioned for experiencing more episodes of showers and thunderstorms later next week.

KJB

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/

Issued at 601 PM CDT Fri Jul 10 2026

With a surface high pressure system expected to remain parked along the Ontario and Quebec borders tonight and tomorrow, generally northeasterly winds will prevail at all terminals through the TAF period. Will be watching to see if winds at ORD/MDW slip north to even northwesterly overnight, though speeds would be less than 5 kt should that occur and turn back northeasterly after daybreak. Broken high clouds will prevail.

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES

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