Marine Weather and Tide Forecast for Winthrop Harbor, IL

MESOSCALE
Issued at 821 PM CDT Wed Jun 10 2026

While we have had decent instability recoveries upstream of the area, the harsh environment across northeast Illinois has now shown its hand in a significant decaying trend in the depth of storm cores and strength of the winds speeds. Running a quick loop of the radar shows the southeastward surging higher reflectivity echoes which are steering into a slightly less worked over environment south of the I-80 and more so south of highway 24 corridor. A notable decrease in lightning trends suggests the severe threat is significantly diminished.

This line of storms has had some longer staying power than expected earlier, with recent wind gusts to 40 to 45 mph in Morris given a bit more appreciable low level shear, with gusts to 35 mph or so as far north as the I-88 corridor. There is also bit better instability south of a Streator to Kankakee to Rensselaer line. Therefore a severe thunderstorm watch for isolated damaging wind gusts is in effect until late evening mainly south of I-80. We will continue to assess this threat through the evening hours as additional cells develop ahead of the main line as to how far north the severe threat will be.

These storms continue to dump decent rain with an increasing low level jet and storms laying out more east to west, a flooding threat does continue as these storms fall over somewhat saturated ground from recent rains, which may be the more immediate concern in the near term.

KMD

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 /00Z TAFS THROUGH 06Z FRIDAY/
Issued at 642 PM CDT Wed Jun 10 2026

Aviation forecast concerns for the 00Z TAFs:

- Another round of TSRA expected this evening, though likely not as strong as storms earlier this afternoon especially for CHI metro.

- Chance (~30 percent) of late morning/midday storms along the IL/WI border (RFD mainly), then strong/severe storms likely for all sites Thursday late afternoon/evening.

- Breezy south winds ahead of late Thursday storms, with gusts around 30 kt possible.

Initial strong/severe squall line which impacted the terminals this afternoon has moved east of the area. Another line of TSRA has developed across eastern IA, however, and was approaching the Mississippi River at issuance time. Large footprint of cool, stable outflow air from earlier storms was in place across much of northern IL, though a developing low-level jet and steep mid-level lapse rates will likely allow current IA storms to continue to propagate eastward across the terminals this evening. These storms may tend to be slightly more elevated (storm inflow source from above the more stable boundary layer), which may decrease surface wind gust potential somewhat especially with eastward extent - though confidence in this is rather low. Have included TEMPO mentions at all sites for these storms, starting at 01Z for RFD, 02Z for most of the Chicago sites. Storms and a period of trailing stratiform rain should exit to the east by late evening/midnight.

Moist low-level air mass will linger overnight (and into Thursday), and may support development of patchy MVFR ceilings into Thursday morning, though confidence on extent/location is low at this time. On Thursday, surface low pressure is forecast to lift northeast across IA into WI through the afternoon/evening hours, supporting strengthening south winds across the area. Wind gusts around 30 kts (potentially higher)
appear likely during the afternoon hours.

There remains some model support for another cluster of thunderstorms to track across northwest IL into southern WI late Thursday morning/midday. Have maintained a PROB30 for TS at RFD for this, with lower confidence of it affecting the Chicago metro sites. Higher confidence persists for another line of strong/severe thunderstorms ahead of a cold front late Thursday afternoon/evening.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES
IL...Flood Watch until 4 AM CDT Thursday for ILZ010-ILZ011-ILZ012- ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039- ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Flood Watch until 4 AM CDT /5 AM EDT/ Thursday for INZ001- INZ002-INZ010-INZ011-INZ019.

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