textproduct: Chicago

KEY MESSAGES

- A couple of rounds of severe thunderstorms is possible between this afternoon and this evening. Damaging wind gusts are the biggest concern with storms.

- More severe weather is expected Thursday afternoon and evening. Damaging winds, large hail, and tornadoes will all be possible.

- Thursday will be another hot day with highs in the 80s and lower 90s and afternoon heat indices into the mid 90s.

- Friday and Saturday will be dry and noticeably cooler. A generally cool and at times wet pattern will develop next week.

DISCUSSION

Issued at 250 PM CDT Wed Jun 10 2026

Through Tonight...

Early this afternoon, we find a wave of strong to severe thunderstorms lifting northeast through north-central IL, now approaching the Fox Valley as of 230 PM. These storms are the result of a shortwave impulse pushing northeast through northwestern IL. We are safely uncapped and these storms are certainly surface- based and tapping into over 3,000 Joules of SBCAPE. However, the big lack of shear with rapidly growing updrafts have kept storms from being able to achieve much organization. The strongest storms thus far have been tracking closer to the wave itself while additional storms are going up farther south. This prompted an initial Severe Thunderstorm Watch to be issued across our northwest counties. This trend is expected to continue with most recent CAM guidance resolving the strongest convection through the rest of the afternoon favoring areas north of I-80 and especially up toward WI. A new downstream Watch is in the process of being drawn up as of this writing. These storms have a history of producing 70+ mph just west of our CWA and likely at least some small hail. Damaging winds will continue to be the biggest concern with storms this afternoon with locally destructive gusts possible. The tornado threat appears minimal this afternoon, especially if we're hardly seeing any signs of subtle rotation out to our west right now where/when the threat would conceptually be "maximized" around the CWA. Hail, likely sub-severe and non-damaging, is also a concern with these storms.

The storms have also been producing torrential rainfall with observations and MRMS reading over an inch in an hour in parts of north-central and northwest IL and instantaneous rates up to 3 to 4 inches per hour. If this were to continue, this could certainly lead to localized flooding or ponding issues, particularly in low-lying and more developed areas. Given that storms are moving along at around 45 mph and the heaviest rain is only lasting a handful of minutes over a given area, widespread flooding issues are not anticipated. This could change if additional upstream storms develop or convection clings onto any sort of outflow boundaries meandering about, but there's no sign of this occurring as of yet.

Looking to our next round, a second shortwave impulse/vort lobe will eject east across central IL this evening. It's expected to fire up additional storms across western portions of MO and IA later this afternoon and carry them east across the area during the evening along with the help of a modest low level jet nose pointing into west-central IL. Latest guidance is honing in on an eastward- propagating bowing MCS for a storm mode. Still some varying intensities among models with the strongest storms generally favored near and south of I-80 along the track of the wave where forcing will be strongest. Nonetheless, areas farther north are still very much in play for additional severe storms tonight. Most CAMs also depict a general weakening of the line with eastward extent across our area, which would make sense as storms become further removed from the better shear and kinematic forcing. The severe threat should exit the area to the east around midnight with some showers or non-severe storms possibly lingering behind for a couple of hours. Biggest concern with this second round will again be damaging wind gusts. High res camps favor these storms leaving behind a stalled outflow boundary which could possibly retrigger some additional showers or storms into the night, but this is not anticipated. Flash flooding appears to again be more of a localized concern, though it's worth mentioning that areas south of I-80 will be generally more sensitive to heavy rainfall given recent rain.

Thursday and Thursday Night...

An especially sharp shortwave impulse will quickly spin up east of the Colorado Rockies this evening and propagate northeastward through the night reaching our vicinity by tomorrow afternoon. The surface reflection will be a deepening center of low pressure. A frontal boundary stalling across northern IL or southern WI tonight will cling onto to this new circulation serving as its warm front. The advancement of the low will push the front farther north into Wisconsin reinforcing the high theta-e airmass for the day. We may have to keep an eye out for a sneaky morning setup in which showers and thunderstorms may attempt to develop along and overtop any stalled outflow/pseudo-front from tonight's storms, particularly south of I-80. The NAM is an outlier in showing some spotty light QPF while other camps remain dry owing to a lack of any additional forcing. While the potential appears low, felt it was still worth mentioning given that training and flash flooding would be a concern if storms do decide to go. Treated this with unmentionable PoPs (<15%) in the forecast. During the afternoon prior to the arrival of storms, temperatures are forecast to get back into the 80s and lower 90s with heat indices well into the 90s.

Guidance is in solid agreement on a strongly forced line of convection moving east across the area along the storm's cold front. An initial, pre-frontal push of some severe storms will be possible as well in the late morning and early afternoon ahead of the front. Solutions which track the low center nearer to northern IL are most excited about this initial push impacting our area, and favor northwestern portions of the CWA. The primary push of storms is slated for the mid-afternoon through mid-evening. The storm's warm sector will feature 3,000 to 4,000+ Joules of uncapped SBCAPE and over 50kt of effective shear. An all hazards severe event appears to be in the cards with damaging to destructive winds, hail, and tornadoes all possible. Given a great deal of low level instability, prime environment for deep, persistent updrafts, and long, curved low level hodographs ahead of the front, a few strong (EF2+) tornadoes are on the table. With PWATs hanging out above 1.5" tomorrow, more torrential downpours and flash flooding will be possible. Given the progressive nature of the storms among other factors, widespread impactful flooding does not look likely, but rather on a more localized basis. Any areas that receive a good amount of rain or any flooding today and tonight will be especially vulnerable to flooding issues tomorrow. SPC has maintained their level 3 of 5 Enhanced Risk over the area.

Doom

Friday onward:

A break in the hot and stormy pattern is expected Friday and Saturday as a surface high pressure system works through the region. Highs on Friday should top off in the upper 70s (locally 80), and lows Friday night should fall into the lower 60s. Ensemble guidance than depicts the development of expansive troughing across the northern United States next week. While the main reservoir of hot and humid air would get shunted well south of our area, a parade of shortwaves may lead to periodic opportunities for showers and thunderstorms across our region through next week.

Borchardt

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 1236 PM CDT Wed Jun 10 2026

Key Aviation Messages for the current TAF period:

- Three rounds of strong to severe storms is expected to impact regional terminals through the TAF window.

A very active period of weather impacting regional terminals over the course of the next 36 hours. Currently, conditions are VFR with southwest wind gusts 20 to 25 knots. However,...

Round 1 (this afternoon): A complex of showers and storms currently (at the time this discussion was published) over eastern Iowa is expected to move over northern Illinois, sending a line of strong to severe storms across the state impacting regional terminals. The primary concern during this window is for strong and damaging winds and downpours that reduce vis down to IFR conditions. Adjusted the TEMPO to account for the earlier than expected arrival time and narrow down the window for the line to pass over TAF sites.

Round 2 (this evening through midnight): There is lower confidence in whether or not VFR showers may linger between Rounds 1 and 2, but the thinking is that there could be a break in the weather for a bit. But after 00Z, a surface boundary will pass over northern Illinois for an additional line of showers and thunderstorms at area terminals. While the severe risk is lower than Round 1, it remains non- zero, with the main hazards still being damaging winds and heavy rain. With models coming into better agreement with this window, the PROB30 was converted to a TEMPO with timing adjusted to a slightly later arrival. Lastly, the VRB wind direction was kept in the TEMPO to account for a brief pressure drop behind the line which may cause winds to become squirrelly for a time.

While timing for Round 2 may be adjusted in later TAF packages, there is higher confidence in VFR and drier conditions developing once this line exits to the east-southeast through the rest of the morning and early afternoon.

Round 3 (late tomorrow afternoon): A cold front is expected to move across northern Illinois tomorrow bringing another round of strong to severe storms over the region. All severe hazards (damaging winds, hail, flash flooding, and tornadoes) is on the table with storms tomorrow. The primary window for this event may be after 00Z, but confidence in its arrival as early as 23Z was high enough for mention in the Chicago terminal TAFs.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 9 PM CDT this evening for the IL and IN nearshore waters.