textproduct: Chicago

KEY MESSAGES

- An unseasonably warm and humid pattern arriving today will persist through the workweek. This pattern will be accompanied by periodic shower and thunderstorm chances.

- While there may be some threat for severe weather on Monday night, Tuesday PM and Wednesday PM are the timeframes of greatest concern for severe storms.

- It will also be frequently breezy to windy this week, particularly today with gusts up to 40-45 mph.

DISCUSSION

Issued at 339 AM CDT Sun Apr 12 2026

Synopsis:

Western and High Plains troughing will result in fairly amplified downstream ridging through most of the upcoming week, resulting in late spring to early summer-like temperatures. While plenty of dry time can be expected, there will be multiple opportunities for convection.

Through Tonight:

A strong warm front will surge north today as mid 990s mb surface low pressure tracks towards the Arrowhead region of Minnesota. The warm frontal passage this morning will usher in the advertised unseasonable warmth and humidity. Dew points off to our south and southwest are well into the 50s and even 60s, which is what can be expected locally. Despite extensive mid and high level cloud cover, it does appear that mixing will be deep enough to tap into robust southwesterly gradient flow, yielding gusts up to 40-45 mph this afternoon. Confidence isn't quite there for a wind advisory with this issuance, though a short-fused advisory can't be ruled out on the day shift.

A remnant subtle impulse/MCV approaching the mid MS Valley early this morning may be able to generate some showers into northwest and far north central IL this morning after daybreak. After this wave lifts north, attention will turn to a stronger subtropical impulse approaching the mid and upper MS Valley by early this evening (a bit slower than previous forecast cycles with this feature). Forecast soundings continue to be unimpressive from a thermodynamic perspective this afternoon, with modest to weak mid-level lapse rates and modest ELs.

As forcing begins to overspread the area from the southwest this afternoon, any leading edge convection for the first couple/few hours may be capable of generating lightning. This would be conditional upon a few updrafts overcoming an overall warm profile and warm layers aloft with no assist from low-level convergence (given unidirectional SW low-level flow). Maintained some 20-30% t- storm probs, though it's possible even these are too bullish in light of recent guidance trends. Rain/shower coverage will become more widespread from northwest to southeast late this afternoon into this evening, and then generally push southeast of most of the area by early Monday. There may be another window for potential isolated embedded storms overnight near and south of I-88. Well above normal precipitable water values and deep moist profiles with unusually high freezing levels could very well result in periodic downpours, though limited thunderstorm coverage should tend to keep rates and amounts in check.

Monday through Saturday:

During the upcoming workweek, the prevailing mid and upper level pattern will tend to focus ejecting short-wave energy and corresponding stronger large scale forcing to the north and northwest of our area. This lowers confidence in specific details, with more subtle impulses and/or MCVs playing a larger role. On Monday morning, any convection from overnight lingering past sunrise in our southeast should quickly come to an end. In the afternoon, height rises, pronounced capping, and dry mid-level air will likely suppress renewed convective development. Monday should have similar to slightly warmer highs than today, and southwest winds will gust up to 25-30 mph from the afternoon into the early evening.

Monday night is the first period of interest for organized convection, and it continues to appears rather conditional on this note, being tied to a sufficiently far south MCS propagation across the upper MS Valley towards the western Lakes. If this impulse ends up farther north (as favored my a majority of the guidance), chances for storms and any threat for severe weather (wind and hail) will commensurately decrease. On the other hand, in the presence of sufficient forcing, very steep modeled mid-level lapse rates support the level 1-2/5 severe threat north of I-80.

Tuesday and Wednesday continue to look synoptically supportive for the SPC outlooked severe threats, along with a threat for flooding due to anomalously high column moisture. However, as alluded to earlier, unknown (at this time) mesoscale details can be expected to modulate the relative threat into our area. Neutral height tendencies on Tuesday afternoon and evening, but good upper jet support, 7C/km or greater mid-level lapse rates, and the possible presence of the warm frontal boundary near or just north of the area may lend to concern for supercellular storm mode. This setup may yield a threat for all severe hazards somewhere in the region, though possibly relatively higher threat just to our west/NW.

On Wednesday PM into Wednesday evening, large scale forcing will uptick with a stronger and farther south short-wave trough ejection, and the approaching cold front providing enhanced low-level convergence. The parent surface low tracking fairly far northwest and not quite as steep mid-level lapse rates may relegate the primary severe threat (if one materializes locally) to damaging winds. There eventually should be a quieter (but still unseasonably warm) period later in the workweek, though confidence is low in specifics. A stronger cold front will then move across the area Friday night into/through Saturday, with additional showers and storms, followed by a sharp cool-down to close out the weekend.

Castro

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 649 AM CDT Sun Apr 12 2026

Main Concerns:

- Strong southwest winds today (LLWS to start the morning).

- A chance for thunderstorms this afternoon then showers will bring occasional downpours and reduced VSBY this evening.

- Lower CIGs should develop this evening/tonight and may then persist into/through Monday morning.

Isolated to scattered showers over far northern IL (in VC of RFD) will shift northeast later this morning. The next disturbance, associated with showers and some embedded TS over the central and southern Plains, will approach this afternoon. Widely scattered SHRA and perhaps isolated TS may develop as early as the early to mid afternoon across northern Illinois. The TS potential will be tied to how much instability can be realized, which is a low confidence item. Maintained PROB30 mention in the TAFs due to the uncertainty. Widespread SHRA this evening may result in 2-3SM VSBY at times. CIGs will drop to MVFR this evening, with IFR possible in spots, particularly at RFD. 3-6SM BR may also develop after the rain ends, especially at RFD, DPA, and GYY.

Current breezy south-southwest winds will steadily increase and peak this afternoon when frequent 30-35 kt gusts are expected from a ~210-230 deg direction. Forecast soundings suggest the potential for 35-40 kt gusts at times, which will be assessed for subsequent updates. Southwest winds will diminish as rain becomes widespread this evening.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until noon CDT today for the IL and IN nearshore waters.

Small Craft Advisory from 9 PM this evening to 4 AM CDT Monday for the IL and IN nearshore waters.

Gale Warning from noon today to 9 PM CDT this evening for the IL and IN nearshore waters.