Marine Weather and Tide Forecast for Jacksonville, IL

DISCUSSION
Issued at 223 PM CDT Tue Jul 15 2025

Severe Weather Risk on Wednesday

As a frontal boundary currently draped across the Upper Midwest into the Plains sags southeastward, it will interact with a highly unstable and weakly sheared environment to trigger scattered strong to severe thunderstorms across mainly north-central Illinois Wednesday afternoon and evening. Given surface dewpoints rising into the middle to perhaps upper 70s, HRRR mean SBCAPEs reach 2500-3000J/kg by peak heating. Deep-layer wind shear has been absent for the past couple of days: however, as a short-wave trough ejecting E/NE out of the Rockies approaches, 0-6km bulk shear is progged to increase to 20-30kt...with even higher values in excess of 40kt focused further north across central/southern Wisconsin. 12z HRRR shows a high probability (40-60% chance) of SBCAPEs exceeding 2000J/kg and 0-6km greater than 20kt along/north of a Macomb to Bloomington line where SPC has highlighted a Slight Risk for severe. CAMs still exhibit some timing and areal coverage differences: however, based on latest water vapor imagery showing the position of the short-wave, think the earlier models such as the HRRR and NSSL WRF are more on target rather than the slower NAM. As such, think a broken line of thunderstorms will develop ahead of the slowly approaching cold front across eastern Iowa/northwestern Illinois toward midday....then will advance eastward across locations mainly along/north of I-72 during the afternoon. Given severe weather parameters, think damaging wind gusts in excess of 60mph will be the primary severe weather risk.
Further north where shear will be stronger, the chances for large hail and a few tornadoes increase across far northern Illinois into southern Wisconsin.

Additional Storm Chances over the Weekend

The cold front will settle southward through central Illinois on Thursday...triggering additional showers and thunderstorms. Based on the position of the frontal boundary, the greatest rain chances on Thursday will materialize along/south of I-72 during the afternoon, although the chance for severe weather will remain low.

The front will sink south of the region Thursday night into Friday, setting up a period of slightly cooler/drier weather.
After that, the boundary will lift back northward and become stationary within the quasi-zonal upper flow pattern over the weekend. As individual short-wave troughs track eastward through the zonal flow and interact with the boundary, scattered thunderstorms will occur from time to time Friday night through Monday. It is still too early to pinpoint any severe weather risks during that time: however, it appears likely that a few locations will see locally heavy rainfall. While the NBM is forecasting widespread copious rainfall amounts, think this may be a bit overdone due to questions regarding timing of the waves and exact areal coverage of the corresponding convection. The 00z Jul 15 LREF seems to have a much more reasonable handle on the potential rainfall...showing a 70-100% chance of greater than 1 inch tonight through next Tuesday...and a 30-50% chance of more than 2 inches.
After that, ridging will build over the Midwest and summertime heat and humidity will return in earnest next week. The latest NBM guidance suggests high temperatures reaching the lower 90s and heat index values exceeding 100 degrees across the board by next Tuesday.

Barnes

AVIATION
(For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1255 PM CDT Tue Jul 15 2025

1740z/1240pm radar shows widely scattered convection developing across central Illinois...with the highest concentration focusing along/east of I-57. Based on radar trends and latest RAP/HRRR output, have opted to maintain PROB30 for thunder at all sites except KPIA through 23z/00z. After that, storm coverage will steadily decrease through the evening, followed by dry conditions overnight into Wednesday morning. Given ample boundary layer moisture and corresponding low LCLs, cloud bases were 1500-2500ft upon initial development this morning. Bases have mostly improved to low VFR as of midday, with MVFR lingering at just KDEC. Since the atmosphere will be unchanged, think the same process will unfold Wednesday morning, with SCT-BKN clouds at around 2500ft forming by 15z. Any scattered convection will hold off until afternoon. Winds will initially be S/SE at less than 10kt this afternoon, then will veer to SW and increase to around 10kt Wednesday morning.

Barnes

ILX WATCHES/WARNINGS/ADVISORIES
None.