textproduct: Chicago

KEY MESSAGES

- Rain showers will likely pass through the area tonight. Isolated thunderstorms and locally gusty winds may also be observed in a few areas this evening.

- There is potential for heavy rainfall and thunderstorms in the region on Sunday, though whether these threats will materialize here locally remains uncertain.

DISCUSSION

Issued at 316 AM CDT Fri Jun 19 2026

Today through Saturday:

The daytime hours today will be dry and will feature plenty of sunshine courtesy of a ~1016 mb surface high drifting just to the southwest of our area. Today's high temperatures should end up being a few degrees warmer compared to yesterday with mid- upper 70s temperatures advertised across most of our forecast area in our official gridded forecast database, though would not be surprised to see a few 80 degree readings here and there based on some of the latest bias-corrected temperature guidance output. That said, temperatures within a few miles of the lakeshore in Illinois and slightly farther inland in northwest Indiana will remain a bit cooler this afternoon behind a lake breeze.

This evening, a well-defined upper-level shortwave diving into the Dakotas from Saskatchewan early this morning will reach our longitude. The shortwave may be in a somewhat weakening state as it begins to shear out, but coupled with modest low to mid- level frontogenesis and cold frontal/outflow-driven forcing at the surface, there should be enough forcing for ascent present for rain showers to spread into northern Illinois and northwest Indiana from the northwest as this wave arrives. Mid-level lapse rates will be far from exceptional, but should nevertheless be steep enough to support some potential for charge separation and isolated lightning strikes within any deeper convective updrafts/wherever lift is maximized. Surface dew point depressions on the order of 20-30 degrees and 50+ kts of mid- level flow could also support gusty winds in excess of 30 mph with any deeper convective elements or immediately behind any consolidated gust fronts this evening, but the lack of more appreciable instability should preclude a threat for stronger wind gusts from materializing.

While a few showers may still be ongoing near the lingering frontal zone in our southern counties come sunrise Saturday morning, conditions are expected to dry out across the entirety of our forecast area by midday. High temperatures tomorrow look to be fairly similar, if not a smidge warmer, compared to today's highs, though post-frontal onshore flow should keep some of our northwest Indiana locales a bit cooler relative to elsewhere.

Sunday:

The most notable upper-level disturbance progged to track through our region over the next seven days will eject eastward out of the central Rockies on Saturday and reach our neck of the woods on Sunday, accompanied by an attendant surface low. Ensemble guidance over the past few days has struggled to get a good handle on how this ejecting shortwave disturbance and associated surface low will evolve, and this theme has continued with the latest 00Z ensemble suite. The existing and persisting ensemble variance can partly be explained by slight differences in the configuration of various influencing synoptic-scale features this weekend, but it is also a likely byproduct of the extensive coverage of convection that is expected across the central Plains on Saturday and what effects that may have in modulating the main synoptic wave and surface low. Because of the role that this central Plains convection may play in dictating the strength and track of the shortwave and surface low, their ultimate evolution will likely not be truly known until Saturday night at the earliest, once observational trends with the Plains convection have become apparent (and even then, there's no guarantee that the system's track and strength will become obvious). Despite the existing uncertainties, there is fair agreement across the ensemble suite that this system will track over or close enough to our area for at least part, and quite possibly all, of our CWA to see rain from it on Sunday, so made no changes to the 70-90% PoPs delivered by the NBM.

Model guidance generally favors precipitable water values peaking anywhere between 1.25" and 2" here, which raises concern for notable rainfall rates that could bring about some potential for flooding. Whether such a threat for flooding will ultimately materialize here, though, appears to be contingent upon either 1.) a relatively strong surface low developing and tracking across or just south of our forecast area and inducing a robust deformation band on its northern flank that steadily pumps out rainfall at a good clip as it persists over the same areas for a few hours, and/or 2.) the surface low tracking far enough to the north for the associated warm front, richer boundary layer moisture (70+ degree dew points), and greater instability to enter our forecast area, allowing for convectively-driven torrential rainfall rates to occur with any thunderstorms that develop near and south of the front. Will also note that the latter scenario would also introduce a potential for severe weather for at least our southern counties on Sunday. The envelope of the latest ensemble and deterministic forecast guidance shows mixed support for both of these scenarios, but there are also several advertised outcomes with relatively weak surface lows and more southerly surface low tracks that would make this a relative non-event for our area with fairly insignificant rainfall totals and little to no thunderstorm activity north of I-74. The bottom line right now though is that, while a great deal of uncertainty remains, Sunday continues to be a day to monitor for potential weather impacts in our area, so stay tuned for forecast updates.

Monday through Thursday:

After the Sunday system clears the region, quieter and drier conditions should settle into the area for the beginning of the upcoming work week. However, there remains a signal for another upper-level disturbance embedded within northwesterly flow aloft to bring another round of precipitation to the area sometime in the late Tuesday through Wednesday time frame. Global ensemble meteograms are otherwise in relatively good alignment on temperatures remaining near to below normal for this time of year through at least the middle of the upcoming week.

Ogorek

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 554 AM CDT Fri Jun 19 2026

There are no significant aviation weather concerns anticipated through the period.

West-northwest winds will prevail at most terminals through the period as surface high pressure shifts eastward across the Lower Missouri Valley today. The only exception to this being at KGYY, where winds look to turn north-northeasterly off the lake for a period this afternoon in association with a lake breeze. It appears unlikely that this lake breeze will shift far enough inland to impact ORD and MDW. Diurnal mixing of the boundary layer may result in some gustiness up to near 20 kt this afternoon, but any gustiness will quickly abate into early this evening. Otherwise, expect VFR conditions to prevail today.

The next weather impulse will track southeastward into the western Great Lakes into this evening. As it does, we should see an increase in VFR cloud cover and a chance (~50%) for a period of light showers this evening. The only change for the 12z TAFs was to transition the PROB30 mention to a tempo group for a few hours this evening. The threat of lightning continues to look low with this activity.

KJB

LOT WATCHES/WARNINGS/ADVISORIES

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