textproduct: Chicago

KEY MESSAGES

- Thunderstorms with torrential rainfall may continue across areas southwest of the Chicago metro this morning.

- A low pressure system is expected to bring showers and thunderstorms with locally torrential rain and potential flooding late tonight into Saturday morning for portions of northern Illinois.

- A stormy pattern is expected to remain in place through the weekend.

DISCUSSION

Issued at 334 AM CDT Fri Aug 14 2026

Ongoing significant rainfall and potential flooding over far southern portions of the CWA should subside soon. However, continued weak low-level isentropic ascent combined with sufficient elevated instability may foster continued development across the southwest CWA through at least daybreak before the existing modest LLJ veers and decays. Will need to monitor if any MCV develops within ongoing convection over central Iowa. This would reinvigorate scattered convection with locally heavy rain late this morning into the afternoon across, with the most likely MCV track favoring western portions of the CWA.

A robust convective complex currently over south-central Nebraska is significantly enhancing a mid-level wave across the central Great Plains. Based on latest guidance, the vast amount of convection is expected to turn this wave into a warm core low through this morning. This wave/low will drift along a broader ridge through tonight, with latest trajectories favoring a track over or slightly north of the forecast area late tonight into Saturday morning. Given high-end PWAT values of 2.3" to possibly upward of 2.5" and expected slow forward motion of the wave, significant rainfall rates of over 2" per hour are possible near and along the track of the associated surface wave. Additionally, strong southeast winds of advisory caliber (at least 45mph) cannot be ruled out along the southern periphery of the track. A Flood Watch may be needed for areas roughly around and north of I-80 for late tonight and Saturday morning. Will also need to monitor a threat for elevated convective linear elements capable of transporting corridors of damaging wind to the surface ahead of the wave.

Another wave expected to become convectively enhanced in the lee of the central Rockies tonight will track north of the area late Saturday night, dragging a cold front with showers across the CWA sometime during the daytime hours on Sunday. Thunderstorm chances will be dictated by the expected timing of the front, with a later arrival in the afternoon supporting higher coverage of storms and a marginal damaging wind risk.

High pressure will build southward over the area early next week, supporting seasonable temperatures and a decent chance of a dry stretch Monday and Tuesday. Another stronger wave and cold front will bring chances of showers and storms on Wednesday, with the front expected to stall well south of the area late in the week.

Kluber

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 659 AM CDT Fri Aug 14 2026

Key aviation forecast messages:

- Lingering MVFR to near IFR VSBYs and CIGs through mid morning.

- 30% chance for SHRA developing ahead of approaching system this evening.

- SHRA and TSRA likely sometime late tonight into Saturday AM, lower confidence on onset timing.

Showers from the overnight period have focused mainly south of I-80 this morning other than some shallow showers that have developed over the lake near UGN. Residual MVFR to near IFR CIGs and VSBYs will very gradually improve through mid morning with most areas returning to VFR to midday.

While a stray shower can't be ruled out through the afternoon the majority of the day is expected to remain dry at the terminals. Winds will mainly be out of the east to northeast around 5-10 kt.

A disturbance moving across Nebraska will bring our next potential for widespread showers and thunderstorms sometime late tonight into Saturday morning. Out ahead of this feature there is guidance that attempts to develop showers and isolated thunderstorms ahead of this feature which could move into the terminals during the evening. Have introduced PROB30 groups to account for this potential for now. Confidence in SHRA/TSRA then increases late tonight. Have maintained PROB30 groups for TS mainly due to lower confidence in onset timing, but prevailing or TEMPO TS or VCTS will likely be needed with later updates.

Petr

LOT WATCHES/WARNINGS/ADVISORIES

IL...Flood Watch until 10 AM CDT this morning for ILZ010-ILZ019- ILZ021-ILZ023-ILZ032-ILZ033-ILZ039.

IN...Flood Watch until 10 AM CDT /11 AM EDT/ this morning for INZ010-INZ011-INZ019.

LM...None.