textproduct: Chicago

KEY MESSAGES

- Additional rounds of showers and thunderstorms Monday through Tuesday, some of which could be severe at times.

- Summer-like warmth and breezy winds at times will prevail through Tuesday before cooler temperatures return for the middle of the week.

DISCUSSION

Issued at 130 PM CDT Sun May 17 2026

A robust convectively-augmented MCV continues to pivot north out of southern Wisconsin and away from our region early this afternoon. Modest large scale height rises will develop over the local region which will promote precip-free conditions across the area the rest of the afternoon. The one exception might be across our far northwest where some lingering glancing ascent co-located with cooler mid-level temperatures may support some lingering spotty sprinkles.

In advance of our next weather-maker, tonight will feature warm and somewhat humid conditions. With a tightening surface pressure gradient and only modest decoupling, should see at least intermittent gusty southerly breezes through the night.

Expansive strong to severe convection is expected to develop later this afternoon and evening across the central and northern Great Plains along an eastward-advancing cold front. Given the strong nature of low-level forcing with the front, it's not surprising that there's good model agreement suggesting upscale growth into one or two expansive MCSs through the evening hours. While some timing discrepancies remain, there's a general consensus for this activity to approach our forecast area just prior to daybreak Monday morning. Deep layer shear over the local area is not forecast to be particularly robust, and generally oriented from southwest to northeast, roughly parallel to the progged MCS(s). This overall is not favorable-- combined with the time of day and nocturnally-stabilized boundary layer--for robust convective sustenance.

At this time, it appears the most probable scenario is for a decaying thunderstorm complex, potentially with lingering strong gusty outflow and maybe some cores with a small hail potential, to push into the region through Monday morning. In this scenario, expansive cloud cover, trailing stratiform rain, and some embedded thunderstorms may linger well into Monday afternoon across the northwest half of the CWA (roughly NW of I-55). This would obviously significantly reduce the subsequent afternoon severe weather threat across this area.

If this morning complex doesn't just surge through the entire forecast region (which remains a potential), muted insolation, with the bulk of the anvil blow off likely streaming northeast as opposed to easterly, may facilitate destabilization through midday and into the afternoon south and east of I-55. This could support gradually-increasing storm organization and intensification. That said, progged shear profiles still aren't anything spectacular with the main mid/upper jet cores still relegated well to the west. Given this, it seems like the locally greatest threat for strong-severe storms exists across the eastern half of the CWA from about midday through the afternoon. In this scenario, deeper boundary layer mixing would also promote increasing southwesterly wind gusts, possibly pushing 40 mph. If the overnight complex fizzles prior to reaching our area, the severe threat would likely increase across more of the region, although this currently looks like a lower potential at this time based on the latest multi-model consensus.

Today's guidance paints a similar picture/evolution to things for Monday night into Tuesday as the main cold front will sweep west to east through the region Tuesday afternoon. Once again, a potential for mainly sub-severe morning convection exists, followed by a threat for more robust storm development on the advancing cold front midday into the afternoon. While deep layer shear is forecast to be a bit more significant than Monday, instability could once again be muted significantly by morning convection.

In the wake of the cold front, breezy northwesterly winds will develop Tuesday/Tuesday night before turning north/northeasterly on Wednesday as high pressure builds into the region. A period of tranquil weather is in store until the end of the week and next weekend when the next series of disturbances will bring additional chances of showers and perhaps some thunderstorms to the area.

Carlaw

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1232 PM CDT Sun May 17 2026

Key messages for the 18Z TAF period:

* A system of showers and thunderstorms likely Monday morning. Associated periods of MVFR possible.

Southerly winds early this afternoon are expected to favor west of south (190-200) around Chicago with higher confidence in SSW after about 20Z. Gusts between 20 and 25 kt will occasionally reach near 30 kt for the mid and late afternoon. A low level jet just off the deck and weak decoupling should allow at least occasional near 20 kt gusts to persist through the evening and overnight. A signal exists for direction to get squirrelly for a brief period during the morning coincident with the rain potential, but predominantly SSW is anticipated during the day on Monday.

A system of showers and possible embedded thunderstorms will traverse the area Monday morning. Precip and thunder coverage are both fairly uncertain. While prevailing VFR is favored, periods of MVFR will be possible with the rain. Stronger signal for MVFR exists up at RFD. Rain should push east of Chicagoland by early afternoon.

Doom

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 10 PM CDT this evening for Wilmette Harbor IL to Michigan City IN.