textproduct: Chicago

KEY MESSAGES

- Dry conditions with a warming trend through Thursday.

- Strong cold front will bring another abrupt end to unseasonable warmth late Thursday/Thursday evening.

- Thunderstorms are possible Thursday afternoon and evening.

DISCUSSION

Issued at 230 AM CDT Mon Mar 23 2026

The large and powerful upper level ridge that's been responsible for the recent record demolishing heat continues to be the dominant feature across the U.S. and is progged to remain so through the week. Our current chilly weather is a result of a transient shortwave trough over the Great Lakes and New England, which caused the mega-upper ridge to retrograde west a bit. A powerful 160kt+ jet over the eastern Pacific should help push the upper ridging back eastward toward the Mississippi Valley over the next few days, which will result in a substantial warming trend.

Through Wednesday, our weather should be pretty tranquil. Today will remain seasonably cool with an afternoon lake breeze keeping temps even chillier close to Lake Michigan. Surface high pressure will move east of the region and allow southerly winds to develop and pull in much milder air Tuesday and especially Wednesday. The proximity of the strong Pacific jet stream looks to good deal of high level cloudiness on Tuesday and Wednesday, so didn't stray from NBM forecast highs. If we end up with more sunshine, then temps could be several degrees or more warmer than NBM for highs Tues & Wed.

Thursday's pattern looks much more like mid-summer than late March, except for the strength of the mid-upper level flow. Tightening geopotential heights between an amplifying northern stream shortwave trough and the powerhouse upper ridge will result in a strong mid-upper level jet streak developing over the Great Lakes. At the surface, a fast moving surface low is expected to race eastward across the region Thursday allowing a trailing cold front to move southward across in its wake. Not surprisingly, there is still considerable spread on exact track of this sfc low and placement/movement of the boundary. Ahead of the front, strong southwesterly winds should allow for widespread 80F+ temps again. Currently looks like our southern CWA will be on the warm side of this front Thursday with less confidence north of I-80, where spread of potential high temp outcomes Thursday is very large.

Above the southerly flow at the sfc, there will be a deep westerly flow aloft which will advect an impressive early season elevated mixed layer (EML) east into the region. Steep mid level lapse rates associated with this EML will help bolster instability, but strong capping at the base of the EML raises big doubts about whether the cap will be breached in our area. The strongest synoptic scale ascent looks to be east of our area by afternoon with frontal forcing not looking terribly strong either given the veered sfc flow ahead of the front. Question becomes will surface heating and modest frontal forcing be enough to break a potentially strong cap, something we may not have a good handle on until event gets closer. If the cap is breached, very strong shear and strong instability for late March would set the stage for severe thunderstorms. Still a lot of uncertainty this far out, but Thursday will bear watching.

Digging upper trough should allow for another brief, but potent shot of cold air to spill into the area Friday before temps slowly moderate heading into next weekend.

- Izzi

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1248 PM CDT Mon Mar 23 2026

There are no significant aviation forecast concerns for the current TAF period.

Winds will continue to gradually diminish through the remainder of the day, eventually shifting easterly as an increasingly defined lake breeze works its way inland. Winds should settle under 10 kts and remain primarily east-of-south tonight, but will pick up a bit again while becoming more south-southwesterly towards daybreak, then more or less remain that way through most of the daytime tomorrow.

VFR conditions will prevail through the TAF period with a lower-end chance (~10-15%) that one or more of our TAF sites observes a few flurries or sprinkles tomorrow morning.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 3 PM CDT this afternoon for the IL nearshore waters.

Small Craft Advisory until 9 PM CDT this evening for the IN nearshore waters.