textproduct: Chicago

KEY MESSAGES

- Warm, breezy, and dry areawide today, with minor lakeshore cooling perhaps hanging on near the Lake Co. IL shore.

- More widespread showers and scattered thunderstorms with another cold front very late tonight into Friday.

- Seasonable and dry conditions over the weekend, then shower and thunderstorm chances return Monday.

DISCUSSION

Issued at 325 AM CDT Thu Apr 23 2026

Early this morning, conditions are largely quiet with light winds and temperatures throughout the 50s. A quasi-stationary frontal boundary is hanging out across the central CWA. As this gradually lifts northward, dewpoints will creep up ahead of the front and we could see some fog development toward daybreak, mainly near the Lake Michigan shoreline and around parts of northwest Indiana. We're already starting to see some pockets of 4-5 mile visibility mainly in the vicinity of the front. Any fog should burn away before mid-morning as we'll be warming quickly after sunrise. Today will be another warm one with afternoon temperatures forecast in the lower and middle 80s.

A line of thunderstorms has been going all night over the Dakotas along a cold front tied to a deep surface low over southern Saskatchewan. This front will cross into the Midwest this afternoon. A line of potentially severe thunderstorms is anticipated to develop out to our west along/ahead of the front this afternoon and evening. Convection will continue across northern IL through the night, though storms are expected to be on an overall weakening trend by then as the parameter space for strong-severe convection is notably lesser than farther upstream. A pool of low 60s dewpoints will advect in ahead of the line, but the unfavorable time of day will ensure that the boundary layer is generally stabilizing. Models maintain anywhere from 500-1000 J/kg of tall, skinny MUCAPE supported by deep layer moisture limiting entrainment and strong forced ascent along the line. The low level jet oriented along the line will see some nocturnal enhancement as it scoots east of the Mississippi and should offer some additional forcing as it noses into northern IL. But the LLJ will outpace the weakening mid- upper jet and effective shear (and orientation to the line) over northern IL is poor to marginal at best late tonight.

Forecast soundings, especially from CAMs, are in decent agreement on a layer of steeper lapse rates near and atop the freezing level. The NAM and NAM Nest are most bullish on these cooler mid level temps and this accounts for the notably higher CAPE values they're resolving. This could possibly enable some small hail formation, but does not appear supportive of severe hail. Additionally, the stronger low level wind field brought on by the LLJ and some drier sub-cloud air could offer strong to marginally damaging outflow winds. Both of these hazards will be most likely out toward and especially west of I-39 while parameter spacing wanes into Chicagoland later into the night. Storms are expected to approach the I-39 corridor around or shortly after midnight and continue across the CWA into early Friday.

The line of storms will outrun the cold front tonight and there's uncertainty on how quickly the front makes it across northern IL on Friday. A majority of guidance fires up additional showers and thunderstorms along the front for the late morning and afternoon. How much of our CWA actually sees any redevelopment into Friday is contingent on the progress of the front, so it's not quite clear. Areas near and east of I-55 are most favored to see additional precip during the day on Friday. The environment should be pretty worked over from the overnight activity and any additional convection into Friday should be sub-severe. Instances of heavy rain will be possible both tonight and tomorrow and deterministic QPF output favors at least localized splotches of around 0.5" through the end of Friday, though less is expected on a more widespread basis. So while not a sweeping concern, will need to keep an eye out for some localized flooding/ponding impacts given the added sensitivity from recent rains.

After the cold front moves away, high pressure over the Great Lakes should keep precip at bay through the weekend. Temperatures will be relatively cooler but comfortable with 60s and low 70s forecast on Saturday while 50s are expected near the lake. Similar conditions are progged for Sunday. Saturday should see mostly sunny skies while cloud cover will build during the day on Sunday ahead of our next regional storm system.

A fast-moving southern stream wave will move onshore near the Baja California coast over the weekend and quickly eject northeastward into the Plains. Speedy lee cyclogenesis is progged over the Plains early next week and the wave will continue to deepen as it lifts into the upper Midwest. Scattered showers and possible thunderstorms are anticipated to blossom east of the low during the day on Monday. Continued convection is anticipated as the front moves across later Monday and Monday night. There is a signal for potential strong or severe convection, but confidence is currently low. An EML plume looks to advect into the region ahead of wave and offer steeper mid level lapse rates for Monday. There's considerable spread regarding the quality of the low level airmass ahead of the front and the warmer solutions certainly look most supportive of deep, moist convection. Will keep an eye on the Monday-Monday night period through the weekend and see where guidance trends. Medium range guidance favors generally cooling, but seasonably appropriate temperatures during the week after Monday.

Doom

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1209 AM CDT Thu Apr 23 2026

Some modest vsby reductions in MIFG/BR will be possible tonight, with the greatest potential INVOF GYY where dewpoint depressions will be the lowest and low-level winds the weakest. Any BR/FG erodes quickly after sunrise as winds turn S/SSW and become gusty.

Gusts are then expected to ease after sunset, but may re-develop overnight, particularly at ORD/MDW as a low-level jet strengthens. Where gusts do not develop, LLWS will be possible, and some consideration may be given for introduction in future TAF issuances.

A line of weakening showers and embedded thunderstorms is expected to roll east across the region late overnight into Friday morning. While some timing differences remain, have introduced prevailing -SHRA mentions along with PROB30 groups for TSRA towards the tail end of the extended ORD/MDW TAFs. Depending on how robust storms are in eastern Iowa earlier in the evening, there could be a potential for strong NW wind gusts as an outflow boundary begins to push ahead of the line of incoming showers/storms.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

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