textproduct: Chicago

KEY MESSAGES

- Showers and thunderstorms with locally heavy rainfall tonight. Amounts may exceed an inch and a half in some areas, particularly across northwestern IL, where new rises on area rivers and creeks may result.

- Warmer, but more active weather pattern with periods of storms returns late in the weekend through early next week.

- A threat for severe thunderstorms exists Tuesday and Wednesday of next week.

DISCUSSION

Issued at 209 PM CDT Thu Apr 9 2026

A west-to-east oriented surface boundary has stalled across the southern CWA (south of I-80) this afternoon. A few isolated to widely scattered showers and storms may develop in it's vicinity this afternoon. In fact, there has already been some hints at this across western IL. However, limited low-level moisture is expected to curtail the threat of a higher coverage of storms through late this afternoon. Accordingly, we expect most areas will remain dry and mild through the remainder of the day, with temperatures remaining in the 60s to the low to mid 70s (warmest south).

As we head into this evening, a strengthening southwesterly low- level jet will promote increasing moisture advection and convergence right into the low/mid-level baroclinic zone north of the stationary front into IA/western IL. This, in addition to the associated strengthening frontogenetic ageostrophic circulation will support the increasing coverage of showers this evening, particularly across northwestern parts of the area (from the west- northwest Chicago suburbs westward across the Rockford metro area). There will also be a threat for embedded non-severe thunderstorms and locally heavy rainfall with this activity given the strongly forced ascent and rapidly moistening profile (Precipitable water values up around 1.1"). Given the high soil moisture and high river levels from previous heavy rain in the past week, this heavy rain (which could exceed 1.5" in some areas of northwestern IL) may result in at least some localized hydro issues. Accordingly, to highlight this potential, we have issued an ESF (Hydro outlook) north of I-80.

The focus for these showers and storms will gradually sag south- southeastward with the frontal zone overnight into early Friday morning. Accordingly, a gradual end in the rain is expected from north-northwest to south-southeast late tonight through Friday morning. Thereafter, dry weather is anticipated for the remainder of the day Friday as a seasonably strong surface high begins to build in from the northwest. Northerly winds in advance of this surface high will result in a cooler day across the area on Friday. As is typical this time of year, onshore north- northeasterly flow will result in the coolest conditions (in the low to mid 40s) near the Lake Michigan shore. Conversely, areas farther inland should warm into the low to mid 50s north, and closer to 60 far south. However, if cloud cover ends up remaining more substantial during the afternoon, conditions could end up a couple of degrees cooler than those currently advertised.

Global models/ensembles remain in good agreement with the upper level pattern becoming more amplified this weekend as a deep upper trough and closed low develops over the West Coast and downstream ridging builds across the eastern CONUS. Locally, the surface high pressure over the area Friday night will progress eastward towards New England on Saturday. As this occurs, surface winds will turn southeasterly during the day. While temperatures will moderate back into the 60s for areas inland from the northeastern IL Lake Michigan shore, the persistent onshore wind component into northeastern IL will keep temperatures there several degrees cooler Saturday afternoon. Broad warm/moist advection, tapping low-level moisture from the western Gulf, then ramps up Saturday night into Sunday downstream of surface low pressure which lifts from the Plains into the upper Midwest. Accordingly, there will be some low chances (30-40%) for showers and storms Saturday night into Sunday amidst milder conditions, though the better chances for showers and storms look to come later Sunday into Sunday evening.

Even warmer (70s/80s temps), more humid (dewpoints into the 60s) and more active weather is expected for at least the first half of next week. During this period, a series of mid-level short wave disturbances riding the fast southwest flow downstream of the western CONUS upper trough look to take aim on our region. Of particular forecast interest as we head into this emerging pattern early next week, is the threat for a couple of episodes of severe weather in our near our general region. This is still several days away, so questions remain on the finer scale details. However, in spite of this, there is enough of a larger scale signal to support the SPC highlighting much of our area in a threat area for severe thunderstorms next Tuesday and Wednesday. Stay tuned!

KJB

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/

Issued at 1217 PM CDT Thu Apr 9 2026

Generally westerly winds and SCT VFR cigs will prevail through the afternoon and evening hours. A few gusts in excess of 20 kt may occur at DPA/MDW/ORD this evening.

After dark, an upper-level wave will propagate into the Great Lakes atop a northward-moving frontal boundary. Winds will shift northeasterly and cigs will trend downward through MVFR and into IFR as showers increase in coverage overnight. There should be a 2 to 3 hour window at each terminal overnight with steady rain with prevailing visibility of 2 to 4 miles. A lightning strike or two cannot be ruled out through the overnight hours, particularly with westward extent.

While shower coverage will taper toward daybreak, cigs will take longer to improve upward back into MVFR. Winds should remain northeasterly at ORD/MDW/GYY while trending northerly at DPA and northwesterly at RFD toward the end of the TAF period.

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES

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