textproduct: Chicago

KEY MESSAGES

- Storm system to bring chances for showers and thunderstorms late Monday night through Tuesday. A few storms could be strong to severe, especially Tuesday afternoon/evening.

- Stormy weather pattern expected to persist into through Saturday.

DISCUSSION

Issued at 328 AM CDT Mon Mar 30 2026

Through Wednesday night:

The surface high that brought us the pleasant weather over the weekend is now moving off the eastern seaboard which will allow the shortwave trough traversing the TX/OK panhandles and the deeper trough over the Mountain West to take hold of our weather. The first of these features to arrive will be the TX/OK panhandle shortwave which will eject out of the southern Plains today and in the process allow for the development of a weak surface low in the central Plains. Attached to the low will be a warm front (signs of which can already be seen in recent observations in southern NE and eastern MO) that will lift through northern IL and northwest IN this afternoon. Moisture ahead of the front will be limited as dew points are currently in the 30s and only look to improve into the lower 40s prior to the front's arrival. Therefore, dry conditions are expected to prevail through this afternoon. What the front will bring us is another round of breezy southwest winds (gusting 20-30 mph) and unseasonably warm temperatures in the mid to upper 70s. In fact, the initial concern about the front getting hung up around the lake no longer appears to be a concern as the stronger winds should push it into WI so even those along the IL shore will see these warm 70 degree temperatures.

Tonight is where the forecast will start to turn more active with the shortwave beginning to pivot into the area late this evening as a low-level jet begins to develop aloft. The combination of forcing from these features does look to generate some isolated to widely scattered showers and thunderstorms along the warm front which is expected to be stalled in northeast IA and southern WI. Recent forecast soundings across northern IL and northwest IN continue to show a decently capped atmosphere due to a layer of dry air aloft which should keep the bulk of any showers/storms north of the warm front in WI. However, a slug of mid-level moisture is expected to be advected into the area on the low-level jet which will be attempting to erode some of the cap. Thus, there remains a 20-30% chance for an isolated shower/storm to develop across northern IL, mainly near and north of I-88, overnight. If any storms do materialize they will be in the presence of 40-45 kts of effective shear which may allow a few of them to become strong to possibly severe with a threat of hail and locally gusty winds. The shortwave and any associated showers/storms that develop tonight will pivot into Lower MI by Tuesday morning which should give us a brief break in the active weather through at least midday. Though, the northern stream shortwave will be moving into the northern Great Lakes and will start to push the stalled front back south as a cold front. Guidance continues to be in good agreement that the cold front will move through the area late Tuesday afternoon and evening and bring with it a better coverage of showers and thunderstorms. Given the later frontal arrival temperatures on Tuesday are forecast to warm into the mid to upper 70s (lower 80s possible south of I-80) areawide. With dew points expected to be in the upper 50s to near 60 by this point, the warm and "humid" air mass looks to generate around 1000-1500 J/kg of MLCAPE which in the presence of 40-45 kts of shear should allow for some of the storms to become severe. Since wind profiles continue to look unidirectional the main threat with any severe storms will be large hail and gusty to damaging winds. However, if surface winds back ahead of the front then a low-end (<2% chance) tornado threat could materialize, especially east of I-57.

Showers and thunderstorms will gradually taper from north to south Tuesday night as the front pushes southward into central IL and IN. In the wake of the front, temperatures will cool into the upper 30s and lower 40s by Wednesday morning and don't look to improve much on Wednesday due to persistent northeast winds. While the daytime hours on Wednesday do look to be mostly dry, there continues to be a lot of uncertainty as to how quickly the next shortwave trough will arrive. Previous forecast runs had the next wave holding off until late Thursday but recent forecast trends continue to be faster with the trough and thus rain chances do look to return sooner. At the present time it appears the next wave will begin to arrive Wednesday night and lift the frontal zone back north as it does so resulting in widespread showers developing across northern IL and northwest IN. Forecast soundings during this period do show some modestly steep lapse rates aloft which could support some isolated rumbles of thunder Wednesday night (especially south of I-80) but it does seem like the better thunder potential should hold off until the warm sector arrives sometime on Thursday.

Yack

Thursday through Sunday:

A very active weather pattern is favored to persist across the Midwest into the Great Lakes region through Saturday. Within this pattern, ensemble guidance favors the increasing potential for two additional storm systems to track northeastward through the western Great Lakes. While questions remain regarding the actual track and timing of both systems, there is an increasing signal supporting additional periods of showers and thunderstorms, particularly Thursday with the first system, and then again sometime Friday night into Saturday with the second system. The strong dynamic environment with each system, along with the nearly unabated access to deep moisture from the Gulf does add some concern for the occurrence of locally heavy rainfall and potential flooding. Accordingly, this is something that will need to be monitored over the next few days, along with any potential threat for strong to severe thunderstorms.

Following the second system slated to track across our region on Saturday, another push of colder air is anticipated for the second half of the weekend. Accordingly, a cooler day is anticipated for Easter Sunday, with highs likely only in the 40s to low 50s.

KJB

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 633 AM CDT Mon Mar 30 2026

Key messages:

- Gusty south-southeast winds of 20-25 kt expected this afternoon into this evening.

- Period of LLWS likely (60%+ chance) mid to late this evening through early Tuesday morning.

- Chance for a period of showers and thunderstorms tonight, mainly after midnight. South-southwesterly winds will increase and become gusty up to 20 to 25 kt again for this afternoon. While surface gusts may become more sporadic for period after sunset early this evening, it does appear we may continue to have at least some periodic gustiness to the winds tonight. However, of more concern is the increased threat for a few hour period of LLWS mid to late this evening through early Tuesday morning as a southwesterly low- level jet quickly intensifies. Considering peak speeds within this low-level jet could reach 55-60 kt at only about 2,000 ft AGL late this evening, we have opted to include a formal mention of LLWS in the TAFs after 02Z this evening. It appears this threat should wane prior to daybreak Tuesday morning.

The other forecast element we continue to monitor for the area is the threat for a period of scattered showers and thunderstorms tonight and again later Tuesday. While the highest potential for thunderstorms impacting the terminals continues to be with the cold frontal passage Tuesday afternoon and evening, there also continues to be 20-30% chance for scattered showers and storms ahead of the system late tonight (after 04Z Tuesday at RFD and after 06z at the Chicago terminals) into Tuesday morning. Confidence with the coverage and timing of these showers and storms continues to be on the low side. In spite of this, we have opted to include a PROB30 mention for showers later tonight at the Chicago area terminals, and a PROB30 for TS at RFD after 04z this evening. The timing and chances will likely need to be refined with later TAF updates as forecast confidence increases.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 7 AM Tuesday to 7 PM CDT Wednesday for the IL and IN nearshore waters.