A slow-moving upper-level disturbance interacting with a weak area of low pressure brought widespread rain and a few thunderstorms to central Illinois during the early morning of September 22nd. Due to the slow-moving nature of the showers, rainfall amounts exceeded 3 inches in a swatch from southeastern Logan and northwestern Macon counties northward across DeWitt and McLean counties.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS ILX wrote it up.
A slow-moving upper-level disturbance interacting with a weak area of low pressure brought widespread rain and a few thunderstorms to central Illinois during the early morning of September 22nd. Due to the slow-moving nature of the showers, rainfall amounts exceeded 3 inches in a swatch from southeastern Logan and northwestern Macon counties northward across DeWitt and McLean counties. A localized spot in southeastern Logan County near the town of Chestnut picked up more than 9 inches of rain, leading to flash flooding and the closure of a state highway.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Lincoln, IL wrote its last area forecast discussion before the first event at Sep 22, 1:25 AM CST, 35 minutes earlier.
Area Forecast Discussion National Weather Service Lincoln IL 225 AM CDT Fri Sep 22 2023 .SYNOPSIS... Issued at 215 AM CDT Fri Sep 22 2023 Scattered showers will continue today. The best chance for rain is west of I-55 during the morning. Locally heavy rainfall over one inch is possible. Showers will diminish in coverage into the afternoon. Saturday will be dry, with above normal temperatures as highs climb into the 80s. Next week looks mostly dry with highs in the 70s. && .DISCUSSION... Issued at 215 AM CDT Fri Sep 22 2023 ---------- Key Messages ------------ 1. Scattered showers are likely (60-70%), especially west of I-55, through Friday morning, then coverage should diminish during the afternoon. 2. Drier weather is expected during the day Saturday, then light rain is possible mainly west of I-55 on Sunday. 3. Seasonable temperatures and mostly dry weather is expected next week. ------------------------------------ An unsettled pattern exists both locally and across the CONUS. From the synoptic perspective, a deep, closed upper low was over the Intermountain West, while Potential Tropical Cyclone (PTC) Sixteen was located off the southeastern US coast. Closer to home, a weak upper low has led to periods of showers over the last 36 hours. ** FRIDAY ** LLJ forcing has contributed to renewed scattered shower development during the pre-dawn hours of Fri morning, and the environment remains supportive of locally heavy rainfall/isolated flash flooding. Forecast soundings from the NAM check several boxes in that regard: a deep warm cloud layer (greater than 10kft), PWAT values around the 90th percentile for this time of year (1.50"), and skinny CAPE profiles (with less than 1000 J/kg of CAPE). If the modeled conditions weren't convincing enough, the environment has already shown what it's capable of, as training storms produced observed reports of 3-4" of rain across southeastern Logan County late Thursday evening (with unconfirmed radar estimates as high as 8 inches). Thus far, with the LLJ development, cell motion has been sufficient to mitigate any flood threat, as showers have exhibited a steady NNE motion rather than sitting over the same areas. Showers are likely to continue, primarily west of I-55, through Friday morning before coverage starts to decrease into the afternoon. The latest HREF suggests areas west of I-55 could see greater than 1" of rainfall through Fri eve, with localized pockets of over 3", which certainly seems plausible based on the forecast soundings. 3-hr flash flood guidance (FFG) west of I-55 is anywhere from 2.5-3", while 6-hr FFG is generally over 3.5". Based on that FFG and the modeled rainfall totals from the CAMs, expect flash flood issues will be relatively sparse, primarily limited to any heavy rain over urban areas or localized instances of very heavy rainfall exceeding 3". ** SATURDAY INTO NEXT WEEK ** Sat should provide an area-wide reprieve from the shower activity. While the upper low currently over the Intermountain West ejects onto the Plains, PTC-16 will move towards the Mid-Atlantic and impede the progression of an upper ridge over central IL. With ridging in place and the Plains low pressure system/associated fronts firmly west of the area, dry conditions should prevail through the daytime hours. Above normal temperatures are expected, with highs into the 80s, along with southeasterly winds. Winds could become a little breezy (gusts up to 25 mph) northwest of the IL River. By Sun, an occluded sfc low will be positioned over the northern Plains, with a triple point/warm front located southwest of the ILX CWA. Despite the front being out of the area, it will be close enough to warrant a chance of precip in the forecast. Given that any such precip will be north of the warm front, instability looks low, with only a few hundred J/kg of CAPE present. Severe weather is not expected, although a rumble of thunder can't be ruled out. Rain chances decrease with eastward extent, such that there is less than a 10% chance of rain east of a Bloomington-to- Shelbyville line. On Sun, both low pressure systems start to weaken/fill, while upper ridging and sfc high pressure strengthen near the James Bay in Canada. This pattern should result in easterly sfc flow across IL by early next week, resulting in dry and seasonable conditions to be favored. Typical conditions for late September include highs in the low 70s and lows near 50. Can't completely rule out a few rain chances next week, as guidance differs in the evolution of the two weakening upper lows. There are hints that the wave over the northern Plains meanders southeast towards the TN Valley, which could lead to additional shower chances locally. The NBM keeps occasional low-end precip chances (15%) in the forecast next week, which seems reasonable given uncertainty about the upper pattern evolution and the potential presence of a weak disturbance aloft. Erwin && .AVIATION... (For the 06z TAFs through 06z Friday Night) Issued at 1145 PM CDT Thu Sep 21 2023 Scattered showers and a few storms are expected to increase in coverage again, mainly along/west of I-55 late this evening and overnight in response to a weak low level jet over the region. Showers will continue through the morning, then become increasingly isolated through the afternoon. There could be some brief visibility reduction due to fog late tonight, mainly at PIA to BMI but confidence remains too low to include in the TAF. Outside of this and any temporary vsby reduction in precip, VFR conditions and a modest SE breeze will prevail through the period. Deubelbeiss && .ILX WATCHES/WARNINGS/ADVISORIES... None. &&
Hazardous Weather Outlook National Weather Service Lincoln IL 305 PM CDT Thu Sep 21 2023 ILZ027>031-036>038-040>055-061-221100- Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler- Mason-Logan-De Witt-Piatt-Champaign-Vermilion-Cass-Menard-Scott- Morgan-Sangamon-Christian-Macon-Moultrie-Douglas-Shelby- 305 PM CDT Thu Sep 21 2023 This Hazardous Weather Outlook is for central Illinois, east central Illinois and west central Illinois. .DAY ONE...Tonight. Showers and a few thunderstorms will continue across the area tonight. Severe weather is not expected: however, a few pockets of locally heavy rainfall will be possible. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Showers and a few thunderstorms will be possible on Friday. Severe weather is not expected. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated tonight. ILZ056-057-062-063-066>068-071>073-221100- Coles-Edgar-Cumberland-Clark-Effingham-Jasper-Crawford-Clay-Richland- Lawrence- 305 PM CDT Thu Sep 21 2023 This Hazardous Weather Outlook is for east central Illinois and southeast Illinois. .DAY ONE...Tonight. Showers and a few thunderstorms will continue across the area tonight. Severe weather is not expected: however, a few pockets of locally heavy rainfall will be possible. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated tonight. Barnes
Preliminary Local Storm Report
National Weather Service Lincoln IL
903 PM CDT Thu Sep 21 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0900 PM Rain Mount Pulaski 40.01N 89.28W
09/21/2023 M3.31 inch Logan IL CO-OP Observer
Since 6am.
&&Preliminary Local Storm Report
National Weather Service Lincoln IL
1007 PM CDT Thu Sep 21 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0954 PM Rain 2 NW Downs 40.42N 88.90W
09/21/2023 E3.33 inch McLean IL Broadcast Media
&&The Lincoln radar (KILX), 13 km away, was scanning. The volume nearest the first event began at 07:59 UTC.
1 flash flood. Local standard time, as filed.
A portion of Route 54 between Mount Pulaski and Chestnut was closed due to water flowing across the road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2023Every state in 2023This day in weather historyWarnings in Illinois, September 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1131365.