Marine Weather and Tide Forecast for Olmsted, IL

DISCUSSION
Issued at 153 AM CDT Thu Jun 18 2026

Some showers and a few thunderstorms are finally developing and/or moving into the southern Illinois and southwest Indiana.
The existing activity moving in from the north appears to be elevated and is not severe, and the fresher development to its south will likely be elevated as well. The environment is still robust with 0-3km SRH 300-400J/kg and 0-1km SRH of 200-300J/kg.
With much of this apparent shear in the lowest kilometer, it is reasonable to assume that the existing convection is elevated and not tapping the greatest shear. However, with such a robust environment we cannot discount the severe risk. Tornadoes and damaging winds would still be the main concerns.

The Flash Flood Watch continues through 8 AM over southwest Indiana, as showers and thunderstorm finally begin to push into the Watch area. Confidence in widespread heavy rainfall is decreasing, but some localized flash flooding is still possible. The heaviest rain overnight is expected over northwest Kentucky, where 1-2" of rainfall is expected. Some isolated flooding issues cannot be ruled out there, as well.

These storms will progress eastward as they slowly develop farther south across the area through sunrise. The synoptic- scale cold front is back over northern Missouri at this time, and is not expected to push through the Quad State until this afternoon. Showers and thunderstorms will continue to be possible along and ahead of the cold front, even as the outflow boundary from overnight convection likely pushes south into Tennessee later this morning. MLCAPE could climb up to near 2000J/kg over the Bootheel and west Kentucky by early afternoon. Wind fields will be thoroughly muddled and the low-level and deep-layer shear will be weak. A stray strong to severe storm cannot be ruled out over southeast Missouri and west Kentucky this afternoon, but locally heavy rainfall and lightning will be the primary concerns with any storms today.

The cold front should clear the entire region by 00Z and that should bring an end to the thunderstorm threat. However, a few showers may linger into the evening along the Arkansas and Tennessee border regions.

Surface high pressure will keep the area dry and cooler Friday and likely Saturday as well. We still have some small PoPs in southeast Missouri Saturday, but the rest of the Quad State will definitely be dry. South winds will return Saturday into Saturday night as another storm system takes shape over the central Plains. Increasing south winds will bring dewpoints back to the lower 70s on Sunday and that will support a good chance of showers and thunderstorms by afternoon. Widespread convection is expected Sunday night as a cold front moves through the region. A few strong to severe storms cannot be ruled out Sunday and Sunday night. Heavy rainfall will also be a possibility.

The entire area should be dry by Monday afternoon and evening, and dry conditions are expected through mid-week.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
Issued at 1111 PM CDT Wed Jun 17 2026

Convection remains the primary flight concern this TAF period.
Storms are very slowly sagging southward ahead of a stalling cold front. Best chance for impacts will be EVV/OWB but can't rule it out completely anywhere. Prevailing VFR conditions with relatively light winds are forecast for Thursday.

PAH WATCHES/WARNINGS/ADVISORIES
IL...None.
MO...None.
IN...Flood Watch until 8 AM CDT /9 AM EDT/ this morning for INZ081- 082-085>088.
KY...None.