Marine Weather and Tide Forecast for Gurnee, IL

DISCUSSION
Issued at 326 PM CDT Mon Jun 16 2025

Through Tuesday Night:

Under the influence of an exiting sfc high pressure, mostly dry conditions have remained across the forecast area. This sfc high will continue to pull northeast into the New England State through this afternoon. As this high exits, winds have turned southeast to south. Winds should remain light behind the exiting high and under the slow moving upper low. Southerly winds will issue in some WAA which will increase temperatures and humidities through the evening.
Temperatures have already climbed into the low to mid 80s across northern Illinois. Immediate lake shore areas a likely to be cooler in the mid to upper 70s as cooler air is brought onshore.

The small chances for rain and a few storms remain for areas west and south of the Chicago Metro through the afternoon. These chances equate to roughly 10 to 15% or less for many areas. Southerly winds have brought up dewpoints across northern and northeastern Illinois, with the far southern and western portions of the forecast area bringing in some of the higher dewpoint from the south. Dewpoints in the low 60s are expected to be advected in which will create a moderately unstable environment for a few showers/storms to develop during peak heating. Coverage will be isolated as the wind profiles and lapse rates are pretty weak. As we loose diurnal heating this evening rain and storm chances will decrease and any ongoing convection will dissipate. Quiet conditions are expected across the forecast area through the overnight hours.

The next chance for rain come Tuesday morning along and ahead of an approaching cold front from the northwest. Any showers/storms that develop Tuesday morning will be along an outflow boundary that surges ahead of the main front. A few CAMs continue to hint at a few showers or storms developing to the north and west then moving into northern and northwestern Illinois. Confidence on this is low as many models have struggled with rain/storm timing and location over the last few runs which is why POPs have been capped at 20 % or less. Did lower the chances a bit from the previous run as the outflow is likely to be the main driver of low/mid level convergence.

The potential for rain and storms will increase heading into Tuesday evening and overnight. The high chance POPs (which top out around 80% for northern Illinois), will slowly expand southward heading into Wednesday. The driving force for more widespread rain and storms will be a shortwave trough moving east overtop of the warm and humid airmass at the sfc. By the time this shortwave moves into the area, diurnal heating will have brought up temps and made the environment that much more favorable for storms. Shear again looks to be the limiting factor here with values around 20 kts. Can't rule out a few stronger storms with the good CAPE and lapse rates, but main concerns with any stronger storms will be brief gusty winds and some hail. Storms will have to be pretty well organized to develop any severe hail and winds. So while the chances for stronger storms are low its non-zero. Will be keeping an eye on the mesoscale environment as this gets closer since a few runs of guidance try to develop an upstream MCS like structure. Should an MCS develop this would provide some better large scale structure to any storms that roll through.

Patterson

Wednesday through Monday:

Surface low pressure is expected to pivot through northern Illinois/southern Wisconsin throughout the day Wednesday. With much of northern Illinois and Indiana remaining in the warm sector of the low, thunderstorm chances remain elevated going into Wednesday morning. Confidence in storm mode remains low at this time, although MUCAPE of approximately 2000 J/kg and deep layer shear of 45 to 55 kt lends credence to strong to severe storm potential along a cold frontal feature progressing northwest to southeast by the afternoon hours. Timing and upstream convection will be key in determining the level of severity possible, with earlier overnight Tuesday storms yielding the potential of exhausting the environmental instability prior to the cold front. However, if the timing of cold front slows down and allows for more return flow, the atmosphere may reinvigorate and produce stronger storms, especially as the front nears eastern Illinois and northern Indiana. PWATs also remain high (1.7 to 2 inches) throughout Wednesday, leading to potential for localized flooding within training cells regardless of severity.

Wrap-around precipitation continues across northern and central Illinois into Wednesday night, but severe threat is expected to diminish quickly after the cold front propagates eastward out of the area. Expecting temperatures to recover Thursday with sunshine and light westerly winds.

Strong longwave pattern ridging then builds into the Upper Midwest going into Saturday, bringing high temperatures in the low to even mid-90s and dewpoints above 70 degrees as winds kick southwesterly and bring Gulf moisture into northern Illinois/Indiana. Confidence is increasing in increasing heat risk through the weekend into early next week, with heat indices in the afternoon exceeding 100 degrees each day. Concern remains that with the sufficient moisture, scattered diurnal thunderstorms or even overnight clusters may prevent sunshine from creating the heating necessary for the aforementioned heat indices. Regardless, trends are toward a very warm weekend.

MH

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
Issued at 1231 AM CDT Tue Jun 17 2025

Key Aviation Messages for the current TAF period:

- Chances for thunderstorms Tuesday afternoon and evening.

VFR conditions are expected through this morning as light southwest winds become westerly. A system will move through the region from west to east providing the next chance for showers and thunderstorms at area terminals in the afternoon and evening.
There is moderate confidence in the timing in the PROB30 group listed in the TAFs, though it should be noted that recent model runs are trending slightly later with arrival times. There is a nonzero chance for showers and storms to arrive as early as 19Z, but it was decided to leave that out of the TAF and handle that tactically should they materialize. Current expectations are for VFR cigs with these storms. Any reduction in flight rules to MVFR levels would be due to reduced vis from heavier downpours.
Nevertheless, if there is continuity in the next iteration of models, it would not be surprising to update the PROB30 to a TEMPO for the 12Z forecast.

Lower confidence on the end time for showers/storms at terminals, but it is looking like there could be break at area terminals behind the storms and into Wednesday morning. While conditions will remain VFR and winds are expected to be light through the overnight, there is lower confidence in wind directions and they could very well be light enough to be variable.

DK

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