Marine Weather and Tide Forecast for Winthrop Harbor, IL

DISCUSSION
Issued at 242 PM CDT Mon Jun 8 2026

Through Tuesday Night:

Early this afternoon, water vapor imagery showcases a midlevel shortwave perturbation spinning over far eastern IA. A plume of heavy showers with embedded thunderstorms recently exited the area to the northeast after leaving behind anywhere from a half an inch to an inch of rain around parts of the CWA this morning.
The heavy rain rates and lowered visibilities were made possible by a deeply saturated, generally warm profile with PWATS of nearly 2". The forcing was provided by a northward progressing warm front which has now lifted into southern WI. In the wake of this front, we've seen a hiatus in precip coverage although dewpoints continue to climb, now largely getting into the middle 70s pushing PWATs above that 2" mark. Additional storms are now entering the CWA from the southwest as of around 2 PM, driven by a vort lobe/secondary warm frontal feature lifting through IL extending east from the low center. Heavy rain rates have been observed across central IL recently, a couple as high as three to four inches per hour.

This plume will continue advancing northward through northern IL and northwest IN through the afternoon, and we expect the heavy rain rates to continue as it does with torrential downpours and flash flooding our biggest concerns with this afternoon activity. Forecast soundings for this afternoon are very reminiscent of a tropical environment exhibiting very weak deep layer shear and 1,500 to 2,000 Joules of tall, skinny CAPE.
The weak shear should make it difficult for storms to organize all that well and greatly limits the overall severe potential, but is supportive of water-loaded updrafts and furthers concerns for localized flooding. These concerns prompted us to issue a Hydrologic Outlook our IL counties to highlight the flash flood potential. With impacts looking more likely on a localized basis vs more widespread, opted to hold off on issuing a Flood Watch, but near-term trends will continue to be monitored closely for any reconsideration. Wet downdrafts will also be possible and strong, likely non-damaging wind gusts are on the table.
Finally, strong low level vorticity extending from the low and some low level shear could lead to the development of some funnel clouds, particularly in our south and west. An SPS was recently issued for these areas for the possibility of funnel clouds.

This main plume and the flood concerns should push out of the CWA during the early evening as the vort lobe does. The low center will scoot from far NW IL across southern WI tonight into tomorrow. Forcing and instability will wane after dusk, but plenty of low-mid level moisture and transient forcing will be present to keep chances for isolated to widely scattered showers going through the night.

With the sheared out low still working across the region, lighter rain or drizzle could remain into Tuesday morning with mostly cloudy skies likely to start the day. A warmer air mass out over the Plains will be allowed to translate east into the Midwest behind this current wave. Afternoon highs are forecast to push into the middle and upper 80s, including up to the lakefront. Dewpoints still hanging out in the lower 70s will result afternoon heat indices into the lower 90s. We'll destabilize nicely during the day, however a big lack of forcing should inhibit most convection and largely dry conditions are anticipated.

A storm system developing off the lee of the Rockies today will mature through tomorrow and is expected to track northeastward into the middle of the week. As the eastern edge of the upper trough moves over the region, an EML will spread east into our region late. Guidance favors an MCS forming well out to our west during the day on Tuesday and continue into the night on the nose of the nocturnal LLJ. Most camps steer this system to our north and leave us largely dry or with only isolated activity during the night, but some (namely the Euro) bring storms across our CWA late tomorrow night into early Wednesday as a warm front may stall in the area. If storms were to occur, damaging winds and potentially some hail would be the biggest concerns.

Wednesday and Wednesday Night:

Any lingering thunderstorms at daybreak Wednesday should end by mid-morning as low-level capping increases at the base of the EML plume and the low-level jet weakens. A largely dry day will then set the stage for temperatures to warm to the upper 80s to lower 90s (heat indices in the mid to upper 90s).

Wednesday evening, an upper-level shortwave embedded in the aggregate troughing will lift into the Upper Mississippi River Valley leading to the development of severe thunderstorms across Minnesota and Wisconsin. A separate region of thunderstorm development may take place in central and eastern Iowa tied to a secondary, more subtle, 500mb wave. Assuming this occurs, convection may try to continue eastward across the Mississippi River and across northern Illinois/northwestern Indiana during the evening and overnight hours. However, do wonder if thunderstorms would tend to struggle into northern Illinois given (1) the upper-level jet and associated region of deep- layer shear will be displaced northwest of our area and (2) the terminus of the low-level jet will be focused into Wisconsin.
With that said, any development of a deep cold pool would sustain a threat for outflow-driven convection well into the nighttime hours given an expansive reservoir of instability across the region. In all, will watch the Wednesday night timeframe for a threat for severe weather in the general region.

Thursday:

The forecast for Thursday carries quite a bit of uncertainty.
In the wake of the lead shortwave responsible for thunderstorms Wednesday evening, a few individual models are hinting at a trailing subtle secondary wave moving through the central Plains during the overnight hours into early Thursday morning. In such a scenario, initial elevated convection in the Nebraska/Kansas/Iowa region may evolve into a forward- propagating MCS that would be encouraged to roll toward northern Illinois after daybreak. Confidence in this scenario is rather low.

Assuming there isn't an MCS rolling into the area during the morning, Thursday should be another warm and humid day with highs in the 80s and heat indices remaining in the 90s. A strong upper-level shortwave and associated cold front is then expected to swing into the Midwest during the afternoon and evening hours. This time frame looks to be the most concerning for an episode of severe weather in our local area with an overlap of strong low-and deep-layer shear, steep mid-level lapse rates, and moisture-laden instability profiles. A mix of supercells and bowing segments certainly seems realistic with a threat for all hazards.

Friday Onward:

In the wake of the cold front, Friday and Saturday should be noticeably cooler and less humid. Ensemble mean highs from the EPS and GEFS range from the upper 70s to lower 80s with overnight lows in the mid to upper 60s. Am quite confused as to why NBM guidance putting chances for showers and thunderstorms in the forecast for our area Friday night into Saturday given a large surface high pressure system will be moving through the area in the wake of the cold frontal passage. Ensemble guidance supports temperatures trending below average (highs in the low to mid 70s) and a return of rain chances next week as aggregate troughing develops over the northern United States in some fashion.

Doom/Borchardt

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
Issued at 1259 AM CDT Tue Jun 9 2026

Main Concerns:

- Occasional +RA at MDW and GYY early this morning

- Low CIGs until mid to late morning

- Early evening lake breeze wind shift at near lake terminals

- Low (20%) chance for a few TS in the area this afternoon-early evening and again late tonight/Tuesday night-early Wednesday

Areas of heavy rain primarily confined to locations south and east of downtown Chicago as of this writing will result in occasional VSBY down to 1SM or possibly lower. CIGs have finally trended lower across the area, with a period of IFR (temporary LIFR in a few spots) and 2-4SM VSBY expected until steady improvement this morning.

A mostly quieter day is in store, though still can't rule out a few isolated PM SHRA/TS. A late arriving lake breeze boundary could serve as one possible focus area. Timing of the northeasterly wind shift (from westerly) currently looks to be in the ~00-01z timeframe, though confidence is only medium. TS may develop over the area in the pre-dawn hours of Wednesday, with low confidence and thus no mention in the 06z TAFs.

Castro

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...None.