Marine Weather and Tide Forecast for Olmsted, IL

DISCUSSION
Issued at 135 PM CST Fri Mar 6 2026

It is feeling more like early May rather than early March, as temperatures this afternoon have soared well into the 70s (and even the 80s in the KY Pennyrile and southwest IN). Dew point temperatures have also climbed into the lower to middle 60s. The driver of this warmth and humidity is surface low pressure that is deepening across the central Great Plains this afternoon.
Thunderstorms will erupt along an associated dry line across the southern/central Plains and grow upscale into an MCS that will march through our region Saturday morning, mainly between 10 and 18z.

The MCS will likely be in a weakening mode with mostly elevated convection due to a stable layer inversion and limited instability. On the other hand, the latest CAM guidance indicates about 250-750 J/kg of SBCAPE will be present, along with about 100-200 m2/s2 of 0-1 km SRH. Forecast hodographs look to be elongated in the 0-3 km layer as well. However, lapse rates will be weak to modest, around 5-6C/km in the mid-levels.
Still thinking that a few strong/severe level wind gusts will the the main threat, and some trees in soggy soils could be uprooted with sub-severe level gusts. Cannot completely rule out a brief tornado, but confidence is this is very low. This line of thunderstorms will exit the region by late morning or early afternoon.

Additional development may fire near the Ohio River during the mid-afternoon along the surface cold front, but whether this activity would reach severe levels would be highly conditional on how widespread and intense the morning convection is.
Rainfall amounts will range from 0.25-0.75" due to the progressive nature of the line of storms, which will keep flooding concerns low. Following the passage of the cold front, quiet and cooler conditions are expected on Sunday as high pressure becomes centered across the Ohio Valley.

Temperatures will again warm to near-record levels and humidity values will jump as the surface high shifts east of the area.
Southerly return flow will again yield high temperatures in the middle to upper 70s and dew point temperatures around 60 degrees Monday. Another, potentially deeper/stronger, H5 trough and surface low will organize over the southern Great Plains Monday into Tuesday morning. The surface low will deepen quickly as it moves NE from the southern/central Great Plains Tuesday morning into the Great Lakes by Wednesday afternoon.

The associated surface warm front will lift through the forecast area Monday afternoon and evening, kicking off scattered shower and thunderstorm development. Some of these storms could produce heavy rain and flooding issues Monday night. A complex of thunderstorms will develop Tuesday afternoon and evening in central MO and northern AR and move through the area from west to east through Wednesday morning. These storms will pose both a risk of severe thunderstorms and more heavy rain and flooding issues.

Right now, SPC has placed much of southeast MO into its Day 5 outlook for a slight risk of severe thunderstorms. Expecting some severe probabilities to be extended eastward with later updates. Additionally, the risk of training convection along the warm front followed by one or more rounds of heavy rain from thunderstorms will create the potential for flash flooding, especially Tuesday afternoon and night. The latest NBM QPF has a broad brush of 1.75-2.25" across the region during the Tuesday- Wednesday period. These amounts will likely fluctuate given we are still five days out. However, it is possible that corridors of significantly high rainfall could occur as well, enhancing the flash flood potential (and prolong/worsen ongoing main stem river flooding).

For the latter half of next week, it appears a few days of cooler, but seasonably mild weather is in store as the active zonal H5 flow pattern shifts north of the area. Ensemble guidance does show a pretty strong pressure gradient with high pressure over the southeast CONUS, so gusty winds may be something to watch Thursday and beyond.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
Issued at 1122 AM CST Fri Mar 6 2026

Widespread diurnal CU will continue to spread from south to north through this afternoon. Cloud bases will initially around 2500-3500ft, but will gradually lift as boundary layer mixing continues. The best chances of seeing brief MVFR restrictions will be at CGI and PAH through 22z. Between roughly 09-15z, a decaying line of showers and thunderstorms will move through the region, with TEMPO periods of MVFR/IFR vsbys and cigs. Outside of thunderstorms, winds will be steady from the S-SW at 10-15 kts with gusts up to 20-25 kts possible.

PAH WATCHES/WARNINGS/ADVISORIES
IL...None.
MO...None.
IN...None.
KY...None.