A line of thunderstorms preceding a cold front dropped into north-central Illinois during the pre-dawn hours of July 15th. Several cells trained over the same locations, with Doppler radar rainfall estimates of 2 to 4 inches across southern Marshall County.
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The episode as NWS ILX wrote it up.
A line of thunderstorms preceding a cold front dropped into north-central Illinois during the pre-dawn hours of July 15th. Several cells trained over the same locations, with Doppler radar rainfall estimates of 2 to 4 inches across southern Marshall County. The heavy rainfall prompted the closure of several roads, including Illinois Route 17 between Lacon and Sparland.
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 Jul 15, 1:32 AM CST, 3 hours 15 minutes earlier.
Area Forecast Discussion National Weather Service Lincoln IL 232 AM CDT Thu Jul 15 2021 .SYNOPSIS... Issued at 232 AM CDT Thu Jul 15 2021 Shower and storms are expected today with an approaching cold front. Some of these storms could become strong to severe during the afternoon and evening hours. Temperatures will be seasonable for most, though cooler than normal temperatures will be present where showers and storms have already started spreading in this morning. && .SHORT TERM...(Today and tonight) ISSUED AT 232 AM CDT Thu Jul 15 2021 A potent upper shortwave trough is lifting into southern Ontario early this morning. It's associated surface low located over the northern Great Lakes Region has a cold front stretched southwest from there into the central Plains states. Showers and storms are occuring ahead of the cold front across eastern IA/northern IL within a region of a 40-50 kt LLJ and strong moisture transport. This will continue to drift east-southeast this morning, with activity already over our northwest counties as of 2 AM. A weakening trend should commence closer to sunrise as the LLJ wanes, with activity already becoming more ragged along the leading edge. Scattered showers and storms will sag southward through late morning into early afternoon as an upper trough swings into the middle Mississippi River Valley. A warm, moist airmass will be in place ahead of the front with dewpoints in the upper 60s to low 70s, which will lead to the development of around 1500-2000+ J/kg of instability. Bits of energy within the aforementioned wave will spread into IL this afternoon and evening, coinciding with the right entrance region of an upper-level jet. These two features will provide decent ascent for new development of storms ahead of the front this afternoon into evening. Modest deep layer shear of around 30 kts may allow any storms to become organized and pose a threat for at least some damaging wind gusts. Better directional shear will be displaced to our west nearest to the center of a surface low, displacing the better tornado threat west of here. With the steering flow expected to be mostly parallel to the front, the threat for heavy rain will also exist. Rainfall amounts look to range from around 1-2" today through tonight, though locally higher amounts will be possible in heavier storms or where storms repeat over the same area. A slight ERO is in place for areas north of I-70 for today and tonight. Shower and storm activity will continue tonight while gradually spreading southeast. The threat for severe weather will diminish into the overnight hours. && .LONG TERM...(Friday through Wednesday) ISSUED AT 232 AM CDT Thu Jul 15 2021 Come Friday morning the front is expected to be positioned smack dab across central portions of the state. The upper trough will continue swinging east across the area, cooling temperatures aloft and steepening lapse rates. At the surface a deepening area of low pressure will quickly lift northeast along the front from northern MO into central IL, reinvigorating shower and storm activity by the afternoon hours. Low 70 dewpoints to the south of the front will be in place, with moderate instability expected to build by the afternoon hours. With a surface low expected to be positioned across the area, shear with good turning will be present with about 25-30 kts forecast in the 0-3 km level, and about 15-20 kts of that being a 1 km and below. The threat for a few strong to severe storms looks possible across east-central and southeast IL Friday afternoon into early evening with damaging winds and perhaps even a tornado or two being the main threats. Similarly to today, heavy rainfall will also be of concern with PWATs of 1.5-2" and deep warm cloud depths. The surface low looks to quickly lift northeast into northern IN by Friday night as western CONUS ridging builds, pushing surface high pressure eastward into the Midwest. This will quickly put an end to any strong to severe storms by Friday evening. Upper ridging over the western CONUS amplifies later Friday into Saturday, with a 1022+ mb surface high looking to set up somewhere over MN/WI. This will act to push the frontal boundary further south of the area late Saturday into Sunday. Periodic shower and storm chances will remain possible mainly across southeast IL through the weekend before things look to dry out going into early next week. Temperatures look to be cooler than normal this weekend through early next week before they return to seasonable values by the middle of next week. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1151 PM CDT Wed Jul 14 2021 Storms active to the NW of our area should remain clear of the terminals until very late tonight near PIA. The MCV associated with that complex will shift eastward into northern IL overnight, dragging a surface boundary toward the IL river by sunrise. Scattered storms and MVFR ceilings could affect PIA toward 11z- 14z as the line of storms weakens into morning. The SW low level jet of 35-45KT could cause a period of LLWS at PIA late tonight as well, but confidence remains low on that occurrence. Better chances for showers and storms are expected mid-afternoon on Thursday, and VCTS was included to indicate storm potential after 21z. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && SYNOPSIS...NMB SHORT TERM...NMB LONG TERM...NMB AVIATION...Shimon
Hazardous Weather Outlook National Weather Service Lincoln IL 513 AM CDT Thu Jul 15 2021 ILZ027>031-037-038-042>046-049>057-061>063-066>068-072-073-161100- Champaign-Christian-Clark-Coles-Crawford-Cumberland-De Witt- Douglas-Edgar-Effingham-Jasper-Knox-Lawrence-Logan-Macon-Marshall- McLean-Morgan-Moultrie-Peoria-Piatt-Richland-Sangamon-Scott- Shelby-Stark-Tazewell-Vermilion-Woodford- 513 AM CDT Thu Jul 15 2021 This Hazardous Weather Outlook is for portions of central Illinois, east central Illinois, southeast Illinois and west central Illinois. .DAY ONE...TODAY AND TONIGHT... Strong to severe storms are possible this afternoon and tonight as a cold front slowly pushes into the area. Damaging winds will be the main threat; however, small hail and intense lightning will also be a threat. Heavy rainfall, possibly leading to flash flooding, will also be a concern. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY... Thunderstorms will continue through Saturday, with locally heavy rainfall and flash flooding still a threat. The severe weather threat is unknown at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this afternoon through tonight. ILZ036-040-041-047-048-161100- Cass-Fulton-Mason-Menard-Schuyler- 513 AM CDT Thu Jul 15 2021 This Hazardous Weather Outlook is for portions of central Illinois and west central Illinois. .DAY ONE...TODAY AND TONIGHT... Strong to severe storms are possible this afternoon and tonight as a cold front slowly pushes into the area. Damaging winds will be the main threat; however, small hail and intense lightning will also be a threat. Heavy rainfall, possibly leading to flash flooding, will also be a concern. Flooding will continue along the Illinois River from Havana and downstream. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY... Thunderstorms will continue through Saturday, with locally heavy rainfall and flash flooding still a threat. The severe weather threat is unknown at this time. Flooding will continue along the Illinois River, from Havana and downstream, for the next several days. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this afternoon through tonight. ILZ071-161100- Clay- 513 AM CDT Thu Jul 15 2021 This Hazardous Weather Outlook is for portions of southeast Illinois. .DAY ONE...TODAY AND TONIGHT... Strong to severe storms are possible tonight as a cold front slowly pushes into the area. Damaging winds will be the main threat; however, small hail and intense lightning will also be a threat. Heavy rainfall, possibly leading to flash flooding, will also be a concern. Flooding on the Little Wabash River around Clay City will continue. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY... Thunderstorms will continue through Saturday, with locally heavy rainfall and flash flooding still a threat. The severe weather threat is unknown at this time. Flooding on the Little Wabash River around Clay City will continue for the next several days. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed tonight. Auten
The Lincoln radar (KILX), 99 km away, was scanning. The volume nearest the first event began at 10:49 UTC.
2 flash flood. Local standard time, as filed.
Illinois Route 17 was closed between Lacon and Sparland due to water flowing across the road.
A culvert was washed out on Illinois Route 29 near Sparland, which swept a vehicle off the road. No injuries were reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2021Every state in 2021This day in weather historyWarnings in Illinois, July 2021
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: 966280, 966282.