Marine Weather and Tide Forecast for Chillicothe, IL

UPDATE
Issued at 904 PM CDT Thu May 15 2025

Severe convection that fired along a dryline across the Illinois River Valley earlier has advanced eastward toward I-57 and dissipated significantly as of 02z/9pm. One remaining cell over Vermilion County will drift eastward and push into Indiana prior to 10pm. The Tornado Watch has been cleared for all locations along/west of a Bloomington to Taylorville line and the rest of it may be cancelled prior to 10pm if trends continue. The rest of the night will be quiet with skies clearing from west to east.
Overnight lows will drop into the upper 50s and lower 60s.

Barnes

DISCUSSION
Issued at 134 PM CDT Thu May 15 2025

An upper level trough evident in water vapor satellite imagery across the Northern Plains/Upper Midwest early this afternoon is slated to drift east-southeast into our area by tomorrow night.
Ahead of that feature, several disturbances will offer central and southeast IL active weather, while behind it the pattern turns benign for the upcoming weekend. At some point early next work week, thunderstorm chances will return with the approach of another trough lifting out of the Great Plains.

***** SEVERE WEATHER RISK THIS EVENING *****

The most imminent forecast concern is the prospect of severe weather this evening. Unfortunately, this remains a conditional risk as a capping inversion continues to prevent the realization of abundant mid level instability. If and when that cap breaks, the hellacious severe weather parameter space characterized by 3000-4000 J/kg MLCAPE and 40-50 kt EBWD will prove ample for explosive convective development, as well as the longevity of storms that do fire. Given relatively weak forcing along the dry line (vs the stronger forcing we would expect along a true cold front) and a large component of the shear oriented normal to that boundary, we'd expect a discrete storm mode with large to significant hail being the primary risk; entrainment CAPE, or ECAPE (a parameter closely tied to potential hail size), values from RAP/HRRR forecast soundings are in excess of 3000 J/kg across our eastern counties this evening. Prolific mid level dry air and PWATs nearing record values will favor efficient evaporational cooling and hence strong downward momentum in thunderstorm downdrafts for severe winds as well, with DCAPE values on the RAP's most recent mesoanalysis between 1300-1500 J/kg. While LCLs are higher than ideal for tornadogenesis, increasing the difficulty for surface convergence to connect to thunderstorm mesocyclones, we certainly don't want to downplay that threat because of the anticipated strength and longevity of those mesocyclones. Thankfully, the relatively fast storm motion will confine the risk to just a few hours this evening, with storms quickly sailing into the Hoosier State; at this time, we're most concerned about the 6-10pm timeframe, though again it's not entirely plain when the cap will vanish.

***** SEVERE WEATHER RISK FRIDAY AFTERNOON-EVENING *****

After our glancing blow with severe storms this evening, all attention turns to the set up for tomorrow. Deterministic guidance is in agreement another shortwave will soar into the Prairie State during the afternoon, but precisely how far northwest moisture returns ahead of the attendant incoming dry line/prefrontal trough will dictate destabilization and hence storm intensity along that boundary during the afternoon and evening. The magnitude and northward extent of that moisture return itself will also be conditional on if/where storms form this evening, how far south they push the effective boundary, and whether convection initiates further south during the early afternoon as a few of the CAMs are indicating. In any case, even the more bullish guidance suggests instability will be at least marginally lower tomorrow compared to today, but that comes at the expense of a weaker cap and slightly stronger forcing for ascent.
Once again, all severe hazards will be in play tomorrow, with perhaps a higher risk for tornadoes and damaging straight-line winds given (1) slightly lower LCLs and (2) more mid level dry air with the encroaching upper trough. The CAMs comprising the 15.12z HRRR seem to be converging on roughly the I-55 corridor for convective initiation, though there are some discrepancies with the NAMNest firing storms west of the IL River and the ARW igniting those updrafts nearer I-57. Storm motion will once again be quickly towards the northeast, with the convective threat shifting out of the area after around 8-9pm.

***** GUSTY WINDS TODAY AND ESPECIALLY TOMORROW ****

Outside of thunderstorms, it'll be seasonably breezy this afternoon as south winds gust 20-30 mph, sporadically higher especially near/west of I-55 where deeper mixing and steeper low level lapse rates will materialize behind a dry line into the early evening.
Tomorrow will be even windier with some potential for gusts to kiss Wind Advisory criteria (45 mph). Confidence in that is too low at this point, with Bufkit soundings mixing technique suggesting a high degree of uncertainty in the depth of mixing, and also variability between models. In general, top of channel winds are running around 30-35 kt, though there could be a brief period where deeper mixing allows us to tap into the 40-45+ kt winds around 850-900mb during the afternoon-evening. Winds ahead of the frontal boundary crossing the region will be from the south-southwest, while behind it they'll blow from the west. Just noticing the 10-40% deficit in soil moisture north of roughly I-72 and observed 0.25 2-inch soil moisture (wfv) at SPI, one wonders whether these winds will result in a risk for blowing dust, especially (1) if the stronger winds come to fruition and (2) in the vicinity of any ongoing agricultural activities.

***** DRY AND COOLER OVER THE WEEKEND *****

The upper trough will shift east and surface high pressure build into the region in its wake Friday night into Saturday, giving us a dry and seasonably cool weekend with daily highs in the low to mid 70s. The next opportunity for precipitation will arrive Monday into Tuesday of next week as another system lifts out of the Central Plains. A lot remains unclear about that system, including its arrival time and warmth/moisture return ahead of it, which suggests vast uncertainty surrounding both precipitation amounts and any severe weather potential.

Bumgardner

AVIATION
(For the 00z TAFs through 00z Friday Evening)
Issued at 638 PM CDT Thu May 15 2025

2330z radar imagery shows a broken line of convection along a KPIA to KSPI line. Based on radar trends and timing tools, have included thunder at all terminals this evening. Thunder will pass just east of KPIA/KSPI shortly after 00z, then will impact KBMI/KDEC by around 01z and KCMI by 02z. Have included wind gusts to 45kt and hail as the storms pass. Once the activity shifts east of the TAF sites, partly to mostly clear skies will prevail tonight into Friday morning...before clusters of thunderstorms develop and track along or just south of I-72 Friday afternoon.
Based on 18z HRRR output, have included a PROB30 group for thunder at KSPI/KDEC/KCMI between 20z Fri and 00z Sat. Winds will initially be S/SW with gusts of 25-35kt early this evening, with the winds decreasing to 10-15kt by late evening through the overnight hours. S/SW winds will once again increase on Friday, with forecast soundings suggesting gusts over 30kt.

Barnes

FIRE WEATHER
Issued at 134 PM CDT Thu May 15 2025

Behind the dry line this afternoon, various high res guidance, most notably the RAP/HRRR, advertise dewpoints dropping sufficiently to bring RH values into the 20s mainly west of I-55. Combining this with southwesterly winds gusting 25-30 mph will increase the risk for erratic fire behavior, so we'd recommend limiting (or at least using extra precautions with) any burning activities during the latter portion of this afternoon into the evening. Tomorrow, the risk appears to be even higher as the residual dry airmass across our northwest counties combines with even stronger southerly wind gusts (35-45 mph) from the late morning into the afternoon. While confidence was too low to issue on this shift due to model variability, a Red Flag Watch/Warning may become necessary.

Bumgardner

CLIMATE
Issued at 727 PM CDT Wed May 14 2025

Record temperatures for Thursday and Friday:

Location Thu Record Thu Record Fri Record . High Warm Low High



CLIMATE
Issued at 727 PM CDT Wed May 14 2025

Record temperatures for Thursday and Friday:

Location Thu Record Thu Record Fri Record . High Warm Low High



ILX WATCHES/WARNINGS/ADVISORIES
None.