Marine Weather and Tide Forecast for Gurnee, IL

DISCUSSION
Issued at 237 PM CDT Mon May 12 2025

Through Tuesday Night:

Water vapor satellite imagery is showing the upper level low in the Lower Mississippi Valley slowly lifting northward and warping longitudinally. It is projected to continue to track northeastward along a Memphis to Indianapolis line. This track will keep the better forcing and instability well east of the forecast area. That being said, models are suggesting a lobe of higher vorticity to pivot around the low this evening and through the overnight with a slug of higher moisture content.
However, guidance is all over the place on whether the showers will be focused more around Interstate 39 and Fox Valley corridor, while others bring it into the Chicago Metro. While the expectation is for the moisture to move from southeast to northwest (along the cyclonic track), there is lower confidence on exact coverage of showers. Additionally lapse rates aloft are fairly marginal around only 6C/km, so the risk for thunder developing was capped at a slight chance

Shower coverage overnight will be monitored, but with cloud cover building in temperatures should only cool into the low to mid 60s. Model soundings are projecting a stout inversion over the area. Winds will diminish, but remain around 5 to 10 mph.
Combine that with the warmer temperatures, and the chance for fog on land is low. However, with the cooler lake, the temperature difference could be enough to have some patchy fog over the water and potentially along the immediate shoreline.

The upper level low continues its molasses speed journey northeastward on Tuesday. Being on the backside of the low, flow aloft will become weaker. The better coverage for showers tomorrow will be during the day time hours around the I-39 corridor and down south of Interstate 80 later in the day, as a lobe of vorticity rotates around the low. While there is a chance for showers and storms, there will be many hours and areas that will remain dry. Again, instability does not look fantastic tomorrow, but as these showers and storms pulse, some lightning, brief downpours and locally erratic winds (as a storm would collapse) cannot be completely ruled out. Chances for showers and storms diminish into Tuesday night. Lastly, the forecast tempered high temperatures tomorrow. There is a chance that localized western parts will touch 80, but with the increasing cloud cover, the expectation is for more widespread 70s across much of the forecast area (60s along the lake shoreline).

DK

Wednesday through Monday:

The forecast in the long term picks up on Wednesday when mild southerly low level flow will overspread the region ahead of developing Plains storm system. This should allow for afternoon temperatures to reach the lower 80s around most of the area. A bit of an onshore component to the wind will keep conditions notably cooler near the IL lakeshore. While forecast soundings are rather dry, a few isolated diurnally-driven showers could pop up in the afternoon, but a majority of the CWA will be staying dry. Efficient warm advection will continue into Thursday ahead of the system and afternoon highs are forecast around 90 degrees area-wide. Conditions will again be a few to several degrees cooler near the lake, especially along the IL northshore.

The big focus in this forecast package is a potential for severe weather on Thursday associated with that Plains system.
During the day on Thursday, a digging upper trough will eject from the central Plains up into MN and an associated strengthening surface low will follow suit. Extending southeast of the low track will be a heavily occluded cold front that will be moving across our area during the afternoon and evening.
It's along and just out ahead of this front that we see the possibility of severe weather, but it'll be very sensitive environment with a clear bust potential. An impressive thermodynamic field will overspread the region ahead of the boundary with models resolving anywhere from 2,500 to 3,500 Joules of MLCAPE atop our CWA during the afternoon and early evening. Surface highs around 90 beneath cold advection aloft will provide steep lapse rates on the order of 8-9 K/km through the mid levels and near dry-adiabatic through the boundary layer. Shear profiles are also more than sufficient to support organized, severe convection. However, a capping inversion, only modest forcing, and tons of dry air all put a damper on this potential. There are disagreements in how much CIN is maintained ahead of the front, but anything appreciable may be difficult to overcome in this setup. Quick surface pressure falls will generate modest dynamic forcing in the low levels which may help chip away at the cap, but the far better deep layer forcing will be displaced to the north and west nearer to the low track.
Convergence and forcing for ascent along the front itself appear pretty meager as well. CIN should generally lessen through the daytime with diurnal heating, so it's possible that storms may have an easier time going up with eastward extent across our CWA This will be especially true if the earlier solutions (namely GFS) can verify. Finally, possibly the biggest wrench in this potential is the copious amounts of dry air.
Forecast soundings exhibit a typical "inverted-v" boundary layer and it's possible that just enough moisture will gather beneath the inversion to saturate and realize the explosive instability. Deep mixing through a dry boundary layer will make this difficult though. Guidance is struggling with this potential based off of splotchy and inconsistent PoP and QPF output. If storms develop, all hazards will be on the table but the biggest concern looks to be damaging wind gusts as the steep lapse rates amid such dry air should be very supportive of strong convective downdrafts. The seemingly best chance at seeing storms on Thursday is across our north where slightly better moisture and forcing will be found, but it's possible the whole area stays quiet. More details will come into focus over the next couple of days as more guidance becomes available.

The upper low will track across far northern WI on Friday and an enhanced low level wind field on the southern flank of the low will extend over our area. Deep and very efficient boundary layer mixing should lead to gusty, if not outright strong winds out of the southwest during the day. And with very dry low level air, there are quickly-growing concerns regarding fire weather on Friday, possibly a considerable threat. This morning's 12Z Euro, for instance, resolves 40 to 50 mph gusts during the day while mixing surface RHs down to 15 to 20%. If something like this were to verify, we'd be talking about extreme fire weather concerns for Friday. Following Thursday, temperatures should be on a general cooling trend through the weekend but will remain warm. The upper low still hanging out to our north will allow for continued warm advection aloft and we should largely see lower 80s on Friday with highs in the 70s forecast through the weekend.

Doom

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
Issued at 652 PM CDT Mon May 12 2025

Forecast concerns include...

Chance of showers, possibly a thunderstorm tonight.
Chance of showers, possibly a thunderstorm Tuesday afternoon.
Ifr/low mvfr cigs overnight/Tuesday morning.
Possible ifr cigs/vis Tuesday evening.

Scattered showers and thunderstorms currently over east central IL are expected to move northwest, but remain south of the terminals this evening. Additional showers are possible overnight for the terminals but confidence is low. While many areas will remain dry, maintained prob mention for now.
Scattered showers and a few thunderstorms are again possible Tuesday afternoon into Tuesday evening, with the best chances southwest of the Chicago terminals and kept the tafs dry for this time period for now.

Guidance is in fair agreement with cigs lowering to low mvfr or ifr overnight and then quickly lifting through mvfr Tuesday morning. Previous forecast had these trends handled well. Only concern is for the potential for lifr cigs and confidence is low.

Fog is expected to develop over Lake Michigan tonight into Tuesday morning. Some of this fog and associated lower cigs may drift inland a short distance on Tuesday but after sunset Tuesday evening, models steadily spread this inland. Have cigs lowering for the new 30hr ORD/MDW taf. Lower conditions are possible and trends will need to be monitored.

East/southeast winds are expected through the period. cms

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