textproduct: Chicago

KEY MESSAGES

- A period of rain showers and breezy southwesterly winds are expected today.

- Showers and scattered thunderstorms are likely late Monday into Tuesday. A few storms Monday night could be strong to severe with threats for hail and strong winds (mainly south of I-80).

- Outside of a brief warmup today into Monday, near to below normal temperatures are favored through next weekend with occasional chances for rain showers.

DISCUSSION

Issued at 303 AM CDT Sun May 3 2026

A fairly tame upper-level shortwave trough is evident in GOES water vapor imagery early this morning over southern Minnesota. This shortwave will proceed southeastward through the remainder of the morning and arrive in northern Illinois a bit after sunrise, accompanied by some rain showers. The earlier 00Z MPX, DVN, and ILX RAOBs all sampled a notable wedge of dry air below 700 mb in the air mass downstream of the shortwave, and the forcing provided by the shortwave alone won't be enough to substantially alter this dry low-level air. However, low- to mid-level frontogenesis and isentropic lift will create a focused zone of enhanced ascent that should induce enough hydrometeor mass for more appreciable top-down saturation to be realized, making it more likely for measurable rainfall to be observed across a corridor or two of our forecast area. That said, the dry sub-cloud air and relatively short duration of the precipitation will largely keep rainfall totals under a tenth of an inch, with some areas likely to not see any measurable rainfall too.

After these showers depart this afternoon (possibly as early as the late morning across our western and far northern counties), already breezy southwesterly winds -- induced by a compressed pressure gradient between the cold frontal surface trough and a ~1020 mb surface high centered over the southeastern CONUS -- will pick up even further as mixing heights rise into stronger 750-850 mb flow. This will likely result in a period of 30-40 mph gusts prior to this stronger low-level flow advancing off to the east and the onset of nocturnal boundary layer stabilization. These winds will help usher in more seasonable temperatures for early May into our area with today's high temperatures expected to range from the low 60s to near 70F.

The southwesterly breezes will continue into Monday as a deeper surface low associated with a more pronounced upper-level trough dives southeastward from the Canadian Prairies towards Lake Superior. Continued warm air advection off of these winds will propel temperatures well into the 70s south of another inbound cold front. The aggressively-mixed HRRR and RAP actually both have a good chunk of the area climbing above 80F tomorrow, and this outcome appears to be conceivable given the tendency for temperatures to overperform in these breezy warm air advection regimes with deep mixing and mostly clear skies. That said, would like to see how much dew points mix out and how temperatures commensurately perform in the upstream source region for Monday's air mass before fully biting on this more extreme/outlying forecast solution.

An influx of better (though still far from stellar) low-level moisture will accompany the arrival of the warmer temperatures on Monday, making conditions more favorable for showers and thunderstorms to occur. There appear to be two main areas/forcing mechanisms that we'll need to monitor for convection late Monday afternoon and evening. One area will be along the aforementioned cold front. There is fairly good agreement amongst the 00Z HREF members that convection will bubble within a narrow axis of meager MLCAPE along the cold front while it is in Iowa and Wisconsin during the afternoon. However, the front likely won't reach our northern counties until around sunset, by which point, the already limited instability will be on a downward trend, putting into question how long this frontal convection will be able to sustain itself into our forecast area during the evening.

Additionally, a southwest-northeast oriented low-level jet centered just to our south/southeast and juxtaposed by better low-level moisture and instability will likely try to force convection in or near our southern counties as it strengthens during the evening. Eventually, the cold front will encounter the slightly higher dew points across our southern CWA and cross paths with the low-level jet, but this likely won't happen until late in the evening or during the early overnight hours -- by which point, the available instability coincident with the better moisture will have likely dwindled quite a bit. If storms are able to occur in our area while sufficient instability remains, then 30-40 kts of deep-layer shear would support the potential for some degree of storm organization and an attendant threat for hail and strong to locally damaging winds. This would primarily be the case with any storms near the low-level jet in the southern half of our CWA, but the early evening cold frontal convection may still produce some gusty outflow winds in our northern counties prior to petering out.

All that said, while some finer-scale forecast details remain uncertain (particularly with respect to the threat for severe weather), confidence in showers and thunderstorms occurring in our area on Monday night has increased with pretty much every forecast model resolving at least scattered convection in our forecast area in spite of the somewhat limited moisture. PoPs for Monday night have been brought up into the "likely" range in response. With the frontal zone not expected to clear our area all that quickly and more abundant large-scale forcing expected to arrive on the scene, showers and storms will likely continue into the daytime on Tuesday with the greatest coverage/chances focused in our southern counties, which will be closer to the surface front. The extended period of rainfall (including some potential for training convection with locally heavier rainfall rates late Monday night/early Tuesday morning) may give us some things to monitor on the hydrologic front, but at this time, think that any hydrologic issues that arise would be more of the nuisance variety and fairly limited in scope.

Aggregate troughing and northwest flow over the Great Lakes and Midwest will then be the theme for the synoptic upper-level pattern for the latter half of the week and into next weekend. This will favor the persistence of near to below normal temperatures and should allow for additional periodic opportunities for rain showers in the coming days as more disturbances embedded within the mean longwave troughing and northwesterly flow aloft dive into the region.

Ogorek

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 551 AM CDT Sun May 3 2026

- Strong and gusty south-southwest winds are expected today, especially this afternoon.

Scattered showers will move across the region this morning in association with an upper level disturbance. Anticipate virga initially as showers encounter dry air in the low levels, but reasonably confident that most TAF sites will see a brief shower or two this morning, so have converted the PROB30 to a TEMPO. Even during any -SHRA that occurs, I'd expect conditions to remain VFR.

South-southwest winds and gusts will gradually increase this morning, with peak magnitude of winds/gusts expected this afternoon. During the afternoon prevailing gusts over 30kt are likely with a few rogue gusts approaching 40kt possible, especially if with any more prominent breaks in the cloudiness. Winds will begin to ease prior to sunset with gusts likely abating by around sunset. Light south-southwest winds expected by mid-late evening through the overnight.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 7 PM CDT this evening for the IL and IN nearshore waters.