textproduct: Chicago

KEY MESSAGES

- Strong to locally damaging non-thunderstorm wind gusts near and north of the Illinois and Kankakee Rivers through mid afternoon.

- There is a threat for severe weather later today, primarily between 4 and 11 PM this evening. The main threats are damaging winds and damaging hail.

- A transition toward a cooler and drier pattern will commence by midweek.

UPDATE

Issued at 109 PM CDT Mon Apr 27 2026

The rapidly advancing wake low winds have been intensifying with eastward extent into northeast Illinois, with observed gusts of 55-70 mph, including 49 kt at KDKB and 58 kt at KARR. Opted for a short-fused High Wind Warning for locations near and north of I-88/290, including the city of Chicago. The Wind Advisory issued earlier remains in effect southward to the IL and Kankakee River Valleys. The wind headlines are in effect until 4 PM for now. Will adjust as needed based on observational trends.

Castro

Previous Update Issued at 1215 PM CDT Mon Apr 27 2026

A Wind Advisory is in effect for locations near and north of the Illinois and Kankakee Rivers until 4 PM this afternoon due to strong wake low winds. Observed wind gusts west of the stratiform rain with embedded thunderstorms quickly advancing east have been in the 40-50+ mph range from the southeast, most recently 45 kt at DBQ and FEP. Forecast soundings and high resolution model output suggest brief localized gusts up to 60 mph are possible, which would enhance wind damage and power outage potential if/where this occurs.

The thunderstorm driven severe wind threat with the ongoing MCS will likely continue to focus just south of our far southern counties over the next 1-2 hours.

It's highly uncertain to what extent and how far north air mass recovery will occur later this afternoon into this evening regarding any renewed severe threat later on. This will be detailed with the full afternoon forecast issuance and discussion once we have a better handle on trends.

Castro

DISCUSSION

Issued at 247 AM CDT Mon Apr 27 2026

Early morning radar, satellite, and ASOS/AWOS observations depict a developing surface low in far southwestern Kansas with an associated broad warm frontal zone extending eastward through central Missouri and into far western Tennessee. Broad southwesterly flow continues to advect an EML plume across the central Plains, which with a developing low-level jet (some 50-60kt per regional VWPs) and the approach an unbalanced upper-level short-wavelengh trough propagating into the Southern Plains, is supporting an expansive region of elevated gravity wave associated convection (GWAC) across central Kansas at press time.

Owing to continued synoptic-scale ascent facilitated by the developing surface low and upper-level trough as well as a steady northeasterly feed of instability through the night, the expectation is for the ongoing elevated convection across central Kansas to coalesce into a bore-driven mesoscale convective system over the coming hours. The orientation of the low-level jet and instability axis would then guide the convective system through Kansas City, Missouri by daybreak and into central Illinois (along/south of I-80) by mid to late morning. With instability decreasing with eastward extent, the convective system should begin to weaken as it crosses the I-39 corridor in central Illinois. With that said, northeasterly- oriented deep-layer shear vectors will promote a broad stratiform precipitation region (perhaps with embedded thunder) on the northern side of the zone of active convection across northern Illinois/southern Wisconsin. The severe weather threat with the first batch of activity is currently thought to be low (call it a 5 to 15% chance at any given point) owing to meager instability. With that said, locally damaging winds cannot be ruled out particularly south of I-80 with any decaying convective element.

Outside the convection this morning, do have growing concern for a period of non-thunderstorm damaging winds mainly along/north of I-80 between noon and 3 PM along the backside of the decaying stratiform region this afternoon. CAM guidance has remained remarkably consistent in depicting rapid drying/subsidence along the backside of the stratiform region, which would support the development of a very tight pressure gradient behind the leading meso-high (a wake-low situation). The HRRR has long had the signal for nearly 24 hours now, including explicit wind gust output up to 75 mph in the most recent iteration. It's always tough to go all-in on these sorts of features given inherent dependencies on how convection evolves and a history of false alarms of such by CAM guidance. With that said, will give a very hearty warning to the incoming day shift to keep an eye out for even the slightest signs of wake low development to get lead time on what would probably be a short- fused High Wind Warning.

Attention then turns to the threat for severe weather this afternoon and evening. There is excellent agreement among deterministic and ensemble guidance that the upper-level shortwave currently propagating into the Central Plains will lift into the Great Lakes region this afternoon, allowing the aforementioned surface low to track from roughly Kansas City, MO this morning to near La Crosse, Wisconsin this evening. As the upper-level wave passes overhead, an associated 75kt 500mb speed max will arc directly across the Mississippi River as pressure falls in the central Great Lakes induce the rapid intensification of the 925- to 850mb wind field. The kinematic environment will thus become very supportive of organized convection by this evening.

Meanwhile, increasing isentropic ascent atop the (what will be outflow-reinforced) warm front will set the stage for festering convection from eastern Missouri into central Illinois during the afternoon hours. Even with increasing synoptic southwesterly flow, a steady feed of cool outflow from the festering convection will likely impede the northeastward progression of the warm front, and hence, instability, into area area by early evening. Heavy cloud cover throughout the day will also hamper the ability for low-level lapse rates to steepen and surface temperatures to warm, with highs only poised to make it into the upper 60s to perhaps locally 70. Nevertheless, cooling mid- level temperatures (by virtue of synoptic-scale ascent and the continued advection of an EML plume via southwesterly mid-level flow) will nevertheless support the development of elevated instability throughout the afternoon.

Even with a lack of surface-based instability, we still do expect the rapid development and expansion of convection across our area this afternoon as the arrival of the upper-level shortwave interacts with the elevated instability axis. Accordingly, we continue to see a threat for severe weather this afternoon and evening in our local area mainly in the form of locally damaging winds and hail. The inability for the surface- based instability axis to make it into our area should relegate the (what will be a higher-end) tornado threat south of our area across central and southern Illinois, but tracking the exact location of the warm front will be important in case it does sneak into our area. So, today still looks active, just not necessarily what initially looked like a very concerning scenario in our local area. In collaboration with SPC, the Level 3/5 threat area has been adjusted southward to be closer to the expected position of the outflow-reinforce warm front this afternoon.

In spite of the most likely outcome outlined above, do still feel the need to discuss the low-probability scenario in which the surface-based instability does make it into our area. Should convection across central Nebraska fail to coalesce into a bore-driven MCS (as it has struggled to do so thus far and instead remain as GWAC), or the convective footprint into central Illinois is minimized by early afternoon (so no outflow to counteract southwesterly flow), the safeguard of festering convection limiting the northeastward-movement of the warm front would fail to materialize. In such a scenario, the warm front would be able to lift into at least northwestern Illinois, leading to a narrow zone where surface-based instability would overlap with an intense kinematic environment. Should this occur, a band of supercells with a threat for all hazards including tornadoes would materialize near the Mississippi River with upscale growth into an intense squall line thereafter. Would have to think that instability would still decrease with eastward extent toward Lake Michigan... though there would still a more pronounced threat for an all-hazard severe weather event. Most guidance does not support this outcome at this point in time, though it does remain completely realistic provided a lot of dominoes fall in the wrong direction.

Tuesday onward:

The upper-level pattern will undergo a substantial pattern shift through the rest of the week with predominant aggregate troughing along the US/Canadian border. As a result, the expectation is for cooler and drier conditions to prevail with highs in the 60s and overnight lows in the upper 30s to lower 40s. We can easily envision a threat for frost by the weekend. Thereafter, long-range ensembles advertise warming trend during the first week of May.

Borchardt

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1236 PM CDT Mon Apr 27 2026

Key Aviation Messages for the current TAF period:

- Strong and gusty winds through most of the TAF period. Strongest winds out of the southeast this afternoon in excess of 40 knots.

- Another round of showers and storms possible this evening.

A line of showers and storms is currently moving east-northeast over Illinois. This line is expected to be out over Lake Michigan after 1830Z, with a period of dry VFR conditions after the rain ends.

More notably, in the wake of the area of convection, a small scale low pressure area will increase winds out of the southeast this afternoon. Strongest wind gusts in the TAF were listed at 40 kt, but obs to the west have already recorded around 45 kt.

Winds will turn to the south as the low moves east later tonight. Models have consistently shown another line of showers and storms that could develop this evening. With lower confidence in development behind the low, KRFD was converted down to a PROB30. However, the TEMPO for the Chicago terminals were adjusted for timing, with chances for it to linger around KMDW and KGYY for longer.

As the threat for showers and storms diminish, drier conditions are expected overnight, but there is a chance for lingering MVFR cigs. Winds will turn to the southwest and eventually west with gusts 20 to 25 knots. Breezy conditions are expected to remain through much of Tuesday, becoming VFR in the afternoon. Models are hinting at a weak lake breeze development tomorrow afternoon, but not with enough confidence to introduce it into the TAF presently.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory until 4 PM CDT this afternoon for ILZ003-ILZ004- ILZ008-ILZ010-ILZ019-ILZ020-ILZ021-ILZ023-ILZ105-ILZ106- ILZ107-ILZ108.

High Wind Warning until 4 PM CDT this afternoon for ILZ005- ILZ006-ILZ011-ILZ012-ILZ013-ILZ103-ILZ104.

IN...Wind Advisory until 4 PM CDT this afternoon for INZ001-INZ002.

LM...Gale Warning until 7 PM CDT this evening for the IL and IN nearshore waters.

Small Craft Advisory from 7 PM this evening to 10 AM CDT Tuesday for the IL and IN nearshore waters.