Flooding occurred along portions of the Rock River due to an ice jam.
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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 LOT wrote it up.
Flooding occurred along portions of the Rock River due to an ice jam.
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 Chicago, IL wrote its last area forecast discussion before the first event at Jan 21, 5:25 AM CST, 35 minutes earlier.
Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 525 AM CST Tue Jan 21 2020 .SHORT TERM... 405 AM CST Today and Tonight... Quiet weather has settled across the area early this morning, and will persist through tonight. Only minor concerns early this morning are the potential for a little patchy fog to develop prior to sunrise west of the Chicago metro area, and some lingering lake-induced cloudiness over parts northwest Indiana. Early morning GOES water vapor imagery shows a digging upper trough moving away from the region across the Tennessee Valley and Southern Appalachians. Strong mid-level height rises, on the order of 100-120 meters at 500 mb, were occurring within the upper level ridge developing in the wake of the departing trough. This deep subsidence was evident at the surface in the form of 1041 mb high pressure centered just south of the Quad Cities. Diminishing winds and generally clear skies are the result of this large scale sinking air, and have allowed temperatures to drop into the single digits and low teens across much of the forecast area early this morning. The exception to this has been across Porter and Jasper counties in northwest Indiana, where continued north- northwesterly low level winds have maintained lake-induced cloud cover through the night. This low level flow will back more westerly this morning however, as the surface anticyclone continues to drift southeast toward the lower Ohio Valley, and will result in clearing skies for the remainder of our northwest Indiana counties with the loss of onshore winds. Some high resolution model guidance, (HRRR, RAP and LAMP) had earlier been depicting the development of fog across parts of north central IL west of Chicago early this morning, though recent trends in these hourly run guidance has been less aggressive. GOES-16 nighttime microphysics imagery has shown some patchy fog/low stratus development across parts of western IL, where some weak warm advection was developing above the surface. It's not completely out of the question that some of this could develop into north central IL by sunrise, though the guidance trends suggest this may be a fairly low probability occurrence. Have maintained a mention however, of some patchy fog generally north of the I-88 corridor west and northwest of Chicago early this morning. Otherwise, with the surface high moving south of the area today, surface winds will back to the southwest through this afternoon. Warm advection aloft, and a good amount of sunshine should allow temps to moderate into the mid 20s to around 30 today. Tightening surface pressure gradient will maintain persistent south winds tonight, which along with a gradual increase in high cloud cover overnight should help keep min temps in the teens to low 20s. Ratzer && .LONG TERM... 405 AM CST Wednesday through Monday... Longer term forecast continues to focus on the expected development and evolution of a deep closed upper low across the region, and the likelihood of a prolonged period of light to moderate precipitation across the forecast area from late Wednesday through Saturday. While medium-range guidance remains in decent overall agreement with the general pattern, there remains considerable spread in the details of the evolution of the closing off of the upper low, and the exact track of the low across the Midwest. This lends an overall lower confidence to the details of the forecast, including precipitation type and amounts. On Wednesday, the initially open trough will be propagating eastward across the Plains, while a northern stream disturbance tracks well north of the region across Ontario. A surface cold front trails from this northern stream wave into the Plains, with guidance in overall good agreement in lifting a small amplitude shortwave northeast along this baroclinic zone on the forward periphery of the Plains upper trough. This induces enhanced southwesterly flow into the region Wednesday and Wednesday night, as this lead disturbance propagates across the area. Low levels are initially quite dry, seen in large dew point depressions below roughly 600 mb in forecast soundings. While the strongest moisture advection remains mainly west of the forecast area initially, persistent 30-35 kt 850 flow is indicative of warm advection, and isentropic progs in the 295-305 K layer depict increasing isentropic ascent and moistening. Saturation develops from the mid-levels downward Wednesday evening/night, with light precipitation eventually reaching the surface and spreading eastward with time through Thursday morning. Forecast soundings from various models depict thermal profiles mainly supportive of all snow, though the GFS continues to be warmest with a subtle +0.5 to +1.0 degree warm nose between 900-850 mb in our southern cwa Wednesday night. Have generally favored the consensus of the in the similar NAM/CMC and ECMWF in keeping the profile cold enough for just snow. This would support some minor accumulations mainly west of Chicago and the I-55 corridor by Thursday morning. While the initial short wave lifts northeast of the area Thursday morning, the upper trough to our west deepens during the day as additional energy digs into it across the Plains. This results in somewhat weak but persistent forcing for ascent during the day, which looks to maintain the threat of continued light precip. Thermal profiles become marginal for snow near the surface during the day with marginal diurnal/warm advection warming into the 30s, making p-type likely a mix of rain/snow. Forcing then strengthens Thursday night and Friday as the low closes off and tracks eastward into the lower Ohio Valley. The GFS remains farthest north with the track of the mid-level circulation and resulting surface low, though the NAM and CMC have trended slightly north of their previous runs. As mentioned previously, this lowers confidence particularly in precip type Thursday night into Friday, with the profile already somewhat marginal, especially across south/southeastern parts of the cwa where low level southeast flow will provide the most warming. Surface temps will generally be close to freezing, suggesting the potential for snow/rain or freezing rain into early Friday. Northwest parts of the cwa will have a better potential for remaining primarily snow with some continued accumulation, though even there we may see a snow/rain mix during the day Friday. The upper low will then slowly drift east of the region through Saturday, with the column eventually cooling enough for precip to change over/end as some light snow. Low level thermal details will undoubtedly come into clearer focus as models narrow in on a solution over the next couple of days. High pressure then builds into the region Sunday/Monday, though with temperatures still fairly mild and above average given the lack of cold air with the closed off nature of the departing storm. Ratzer && .AVIATION... For the 12Z TAFs... 525 AM...No forecast concerns today as high pressure moves across the area this morning. Light westerly winds will become southwest this morning with speeds increasing to 10kts. Speeds will remain around 10kts this evening and may increase some overnight but especially Wednesday morning when gusts to 20kts will be possible. Some light fog will be possible this morning mainly west of the Chicago terminals. Skc to start with increasing high clouds later today into tonight. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && Visit us at weather.gov/chicago Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSChicago www.twitter.com/NWSChicago www.youtube.com/NWSChicago
Hazardous Weather Outlook National Weather Service Chicago/Romeoville IL 426 AM CST Tue Jan 21 2020 ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 221030- Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-Cook- La Salle-Kendall-Grundy-Will-Kankakee-Livingston-Iroquois-Ford- Lake IN-Porter-Newton-Jasper-Benton- 426 AM CST Tue Jan 21 2020 /526 AM EST Tue Jan 21 2020/ This Hazardous Weather Outlook is for portions of North Central Illinois...Northeast Illinois and Northwest Indiana. .DAY ONE...Today and Tonight. Weather hazards expected... Limited Excessive cold Risk this morning. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Thursday and Friday... Limited Ice Accumulation Risk. Limited Snow Risk. DISCUSSION: A slow moving storm system will affect the area from Wednesday night into Saturday. Precipitation is expected to be mainly light, though with accumulating light snow at times. There is also the potential for a period of mixed precipitation which could produce light ice accumulations, particularly Thursday night into early Friday morning. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be necessary through tonight. LMZ740>745-221030- Winthrop Harbor to Wilmette Harbor IL- Wilmette Harbor to Northerly Island IL- Northerly Island to Calumet Harbor IL- Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN- Burns Harbor to Michigan City IN- 426 AM CST Tue Jan 21 2020 This Hazardous Weather Outlook is for portions of the Illinois nearshore waters of Lake Michigan and the Indiana nearshore waters of Lake Michigan. .DAY ONE...Today and Tonight. Weather hazards expected... Hazardous conditions for small craft. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Wednesday... Hazardous conditions for small craft are likely. Ratzer Visit us at http://weather.gov/chicago Follow us on Facebook, Twitter, and Youtube at: www.facebook.com/nwschicago www.twitter.com/nwschicago www.youtube.com/nwschicago
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
An ice jam on the Rock River caused flooding between Grand Detour and Dixon. Flooding was also reported in an agricultural area due to backwater on Pine Creek.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2020Every state in 2020This day in weather historyWarnings in Illinois, January 2020
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: 872608.