Marine Weather and Tide Forecast for Chillicothe, IL

UPDATE
Issued at 839 PM CDT Wed Jul 9 2025

Extended coverage of isolated showers for the evening given more widespread than expected coverage in radar obs, however latest trends suggest coverage will be near zero by 9 pm. Otherwise, main feature of concern overnight is potential for fog by morning. High pressure ridging across the area at the surface suggests mostly clear skies should continue, allowing good radiational cooling and light winds, so model guidance depicting patchy to widespread fog in most models appears on track. Followed model consensus of first development in east-central to northeast IL around 3 AM, spreading southwestward to areas northeast of a Galesburg-Springfield- Lawrenceville line by sunrise. Otherwise, lows in the mid to upper 60s look on track for tonight.

37

DISCUSSION
Issued at 144 PM CDT Wed Jul 9 2025

Weak surface ridging is in place across central Illinois this afternoon which is resulting in generally fair weather across the region. While an afternoon or evening isolated pop-up shower or storm cannot be completely ruled out today, most of the area will be dry through tonight. By Thursday, surface ridge axis will inch east into Indiana with a bit of a mixed picture on convective chances through the day. Dew points will creep back up into the lower 70s for much of the area contributing to moderate instability across the region. GFS advertises around 1500 J/kg MLCAPE which will be weakly capped (generally less than 30 J/kg MLCIN). Despite the atmosphere primed for thunderstorms, synoptic scale forcing will be well west of the area with eastern portions of Illinois still under the influence of the surface ridge. Still, some of the CAMs suggest a convectively induced vort max will move into portions of central Illinois Thursday late afternoon/evening and could serve as the focus for some scattered storm development. Should this occur, a few stronger storms will be possible with damaging downburst winds and locally heavy rain due to slow storm motions the primary concerns. Week flow aloft and weak deep layer shear will keep the threat for a more organized severe threat low.

On Friday, a more robust trough is progged to move east along the Canada/US border while a southern stream wave lifts from the central Great Plains into the Upper Midwest. A deepening surface low over the Upper Midwest will lift a warm front across central Illinois through the day. Temperatures will warm to around 90 degrees within a broad warm sector while dew points further climb into the mid 70s. Strong instability will result with MLCAPE values exceeding 3000 J/kg expected by Friday afternoon and evening. Mid level warm air advection could drive some showers and storms during the day Friday, but the main concern will be Friday evening as storms grow upscale over the mid Missouri Valley in response to a developing low level jet. These storms will congeal into a line and move east along the instability gradient into portions of Illinois late in the evening and overnight. While there will be a gradually diminishing severe threat with time through the overnight hours, it's possible that some of these storms could reach and maintain severe levels as they push into the state. Uncertainty in some of the placement/timing details remains which keeps the SPC D3 marginal risk right on our doorstep for the time being.

Depending on the evolution of storms Friday night and placement of remnant outflow boundaries Saturday (impacting the location of the effective cold front), there will be some potential for additional strong to severe storms over the weekend. Areas further north in the state will be less warm with highs back in the lower to mid 80s, but closer to the effective front across the southern half of the state temps will continue to run warmer with highs near 90F.

Deubelbeiss

AVIATION
(For the 06z TAFs through 06z Thursday Night)
Issued at 1227 AM CDT Thu Jul 10 2025

Main concern in the short term is with potential for stratus/fog in the KPIA-KCMI corridor, along a weak surface boundary.
Visibility at KPNT has dropped below 3 miles recently, and HRRR probabilities of ceilings below 500 feet are 50-60% just north of the boundary by 10Z. Will keep this corridor at SCT003 for now and watch trends closely as we get toward sunrise. However, MVFR visibility is not out of the question, and have maintained that potential in the new TAF set.

Getting into the afternoon, some concerns for scattered showers and storms, some of which depends on leftover features from storms that will be moving across Iowa later tonight. Kept the PROB30 mention in at all sites, though confidence wanes the further south and east you get.

Geelhart

ILX WATCHES/WARNINGS/ADVISORIES
None.