Scattered severe thunderstorms moved across parts of northern Illinois during the late evening of May 14th. Additional thunderstorms produced heavy rain and localized flash flooding during the late evening of May 14th into the morning of May 15th.
Every event with a place to put it. Tap one for its entry below.
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.
Scattered severe thunderstorms moved across parts of northern Illinois during the late evening of May 14th. Additional thunderstorms produced heavy rain and localized flash flooding during the late evening of May 14th into the morning of May 15th. Some of the highest 48 hour rainfall totals ending Friday morning May 15th included: 4.75 inches near Sycamore; 4.71 inches near Park Ridge; 4.69 inches in St. Charles; 4.61 inches two miles west of Elgin; 4.35 inches in De Kalb; 4.26 inches at Chicago O'Hare Airport (ORD); 4.22 inches in Cortland; 4.14 inches in Waukegan; 3.98 inches in Kankakee; 3.94 inches in Harwood Heights; 3.86 inches in Dixon and 3.72 inches in Cary.
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 May 14, 7:15 PM CST, 1 hour 15 minutes earlier.
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
815 PM CDT Thu May 14 2020
.MESOSCALE DISCUSSION...
815 PM CDT
Convective trends early this evening have generally matched
expectations with gradual organization to the mature, deep
convection in Iowa as it moves eastward and scattered development
ahead of this. The severe threat is primarily through 12-1 a.m.
and the flash flood threat through 3 a.m. The threat area for both
still remains mainly I-88 and south, though may be honing in on
the I-80 corridor and just south of that.
Early this evening finds warm and muggy conditions over the area,
with the effective surface warm front draped across our southern
CWA and gradually diminishing instability further north. Above
that, the southerly low-level jet around 30 kt sampled on the 00Z
DVN and ILX soundings has been gradually increasing and will
continue to. The convective cluster/developing complex in
southeast Iowa has been gradually becoming more organized and is
associated with a low amplitude short wave impulse/MCV. Ahead of
this, moistening around 850 mb as sampled on the 00Z DVN sounding
is assisting in a pseudo-warm advection wing arc of convection
into the southern CWA. This has gradually been maturing on GOES-16
meso satellite and radar imagery. The 00Z ILX sounding sampled
40-45 kt of mid-level flow and mid-level lapse rates near 8 C/km,
so not surprised to see some of these already exhibit some
supercell characteristics. Coupled with a lower freezing level of
11-12kft, this could certainly exhibit a hail and wind threat, and
this is why we recently expanded the Severe Thunderstorm Watch
into the far southern and southwestern Chicago suburbs and points
to the immediate south/southwest. Will also have to watch along
the effective front for a temporary tornado threat -- primarily
Livingston and southern LaSalle Counties.
The warm advection-driven convection in the southern CWA is
potentially pointing where a targeted flash flood risk may
develop. This convection is in a zone of diminishing Corfidi
vectors and rooted along the 850 mb front -- a favored synoptic-
to-mesoscale place to be for training cells. Individual storm
motions have slowed to under 30 mph. These storms are tapping into
precipitable waters of 1.4-1.6 inches pooled along that boundary
per analysis. So they themselves will have heavy rainfall, and
then as the cluster/complex of storms currently in southeast Iowa
moves into the CWA that would provide several more hours of heavy
rainfall over the same area. Convection-allowing models (CAMs) are
struggling with an overall evolution of this, and observationally
with the convective behavior, leaning toward a slightly further
south evolution of the heaviest rain threat -- again toward I-80.
How far north/south of that is still too uncertain to say, and
certainly there will be convection for most of the CWA late this
evening into overnight. Will be considering a possible slight
southward expansion of the Flash Flood Watch for Newton, Jasper,
Ford, and Iroquois Counties depending on behavior the next 1-2
hours.
With the amalgamation of cold pools and a gradual inching
southward of the most unstable CAPE, convection still looks to
progress southeastward with a tad more haste after 2 a.m. The
flooding threat certainly may continue beyond that though, which
lines up well with the Watch through daybreak.
MTF
&&
.SHORT TERM...
249 PM CDT
Through Friday...
Lingering showers and thunderstorms have diminished in coverage and
exited to the east of the area this afternoon. Meanwhile, dew points
have surged into the low to mid 60s across the area. The extensive
cloud cover has limited surface warming somewhat, but current
satellite trends suggest the cirrus beginning to thin which should
help temperatures warm up into the low 70s across much of the area.
An east-west oriented boundary has set up across southern Iowa
into northern IL, combined with strengthening low level jet will
set the stage for potential severe weather and heavy rain this
evening and overnight.
The primary corridor for severe weather has shifted south mainly
along and south of I-80 where the better instability will be.
Conditions are not as favorable as once thought thanks to the
continued precip through the morning and early afternoon hours which
has prevented the surface boundary from lifting as far north. In
general, expecting things to begin in multi-cell clusters this
evening and transition to a more linear mode and track off to the
east. Primary severe weather threats will be strong winds on the
leading edge of this line. Some hail may be possible with the
stronger storms, especially at the onset and a QLCS tornado threat
cannot be entirely ruled out.
Of greater concern with this system is the potential for training
thunderstorms resulting in flash flooding. The upwind Corfidi
vectors for propagation into the inflow are light and even
oriented to the northeast which suggests that redevelopment
behind the leading edge of the line is possible resulting in heavy
rain falling over the same areas for multiple hours. Current
thinking and trends is that this will favor along and near the
I-80 corridor. Have fielded a Flash Flood Watch to account for the
potential for heavy rain. Wherever this ultimately sets up could
see locally heavy rain amounts of 3-4+ inches of rain when this is
all said and done. If the cold pool ends up being stronger it may
be able to help push this out of the area more quickly reducing
the flooding potential, but current thinking is this will be
limited in its influence.
Once overnight showers and thunderstorms move out Friday morning a
mostly quiet day between systems. Temperatures are expected in the
70s, (60s closest to the lake). A lake breeze is expected to develop
in the afternoon which will lead to quick cooling behind it.
Aside from the severe weather and flooding threat, dense marine fog
is expected across southern Lake Michigan through late morning
tomorrow.
Petr
&&
.LONG TERM...
154 PM CDT
Friday Night through Thursday...
Things look more tranquil to start of the the long term portion of
the forecast on Friday night as shortwave ridging briefly builds
in overhead northeasterly winds develop in the wake of our
departing storm system. Can't rule out a few showers developing
across our far southern counties through the overnight hours, but
think things look mainly dry. Persistent east to northeasterly
winds on Saturday look to hold lakeside temperatures down towards
60 degrees or so, but a notable temperature gradient may set up
inland and for areas south of I-80 should cloud cover hold off
through the afternoon with some mid and even upper 70s not out the
question.
Warm advection will really get cranking Saturday afternoon and
evening in advance of our next weather maker which looks to be a
rather stout shortwave. Will commensurately ramp PoPs up through
Saturday night and Sunday in advance of this system. With the
latest multi-model consensus supporting this disturbance arriving
during the overnight and early-morning hours, currently
anticipate the severe threat remaining on the lower end of the
spectrum with an overall dearth of surface-based instability
present although things do look impressive upstairs from a
kinematic standpoint. Should this system slow down, the severe
threat would increase owing to the potential for diurnal gains in
instability.
This disturbance peels east of the region through the day on
Sunday although conditions may remain somewhat unsettled even
into Monday as the core of the cold upper-low looks like it may
take its time fully clearing the area to the east. We'll also have
to keep an eye on a period of potentially gustier onshore winds
which may develop on the backside of this departing low. Still
some uncertainty regarding the magnitude of the developing onshore
flow with things-- as they stand right now--looking like waves
may flirt with Lakeshore Advisory criteria into Monday and Monday
evening.
Guidance today continues to trend towards developing a rather
blocky upper air pattern into the middle of next week with the
potential for persistent east or northeasterly surface winds to
keep temperatures on the cooler side. Always some volatility with
these types of set ups, but have trended things cooler in line
with the most recent blended guidance into the middle and end of
the week as a result.
Carlaw
&&
.AVIATION...
For the 00Z TAFs...
Aviation concerns include:
* Period of thunderstorms expected to develop by mid-evening and
persisting past midnight before diminishing.
* IFR/low MVFR ceilings likely with storms and lingering
afterwards into early Friday morning.
* Winds generally southwest winds until shifting to northwest with
cold frontal passage early Friday morning, with northeast lake
breeze winds expected Friday afternoon/evening.
Outflow from convection earlier in the day had pushed the
effective warm frontal boundary well south of the terminals across
southern IL. However, decreasing cloudiness this afternoon has
allowed some warming and destabilization of the airmass north of
this boundary, allowing it to mix back northward late this
afternoon. A mid-level disturbance will track east along and just
north of this warm front from IA into northern IL and northwest
IN this evening/overnight, with an area of thunderstorms currently
over central/eastern expected to expand eastward across the
terminals during the mid-late evening hours. Thunderstorm coverage
should diminish after midnight (1-2 am) across the terminals,
though showers will likely linger for several hours into early
Friday morning before sliding off to the southeast with the
passage of a cold front.
Patchy MVFR ceilings have scattered late this afternoon as better
mixing has developed northward into the area, though a rather
moist boundary layer will likely support low MVFR and IFR ceilings
to develops as precipitation spreads across the area with the
storms. Guidance maintains IFR ceilings through most of the
overnight hours before a gradual improvement through MVFR occurs
behind the cold front Friday morning.
Surface winds are initially south-southwest ahead of the cluster
of storms this evening, and may back slightly as weak surface low
pressure approaches. Some variability in direction is possible as
the complex of showers/storms moves through. Cold frontal passage
looks to occur 12-13Z Friday morning for the Chicago terminals,
with a shift to northwest winds, and an expected lake breeze
should produce a shift to northeast winds for the afternoon and
evening hours.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch...ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-
ILZ107-ILZ108 until 7 AM Friday.
IN...Flash Flood Watch...INZ001-INZ002 until 7 AM Friday.
LM...Dense Fog Advisory...IL nearshore waters until 7 AM Friday.
&&
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www.youtube.com/NWSChicagoHazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
326 PM CDT Thu May 14 2020
ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-152030-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
326 PM CDT Thu May 14 2020 /426 PM EDT Thu May 14 2020/
This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.
.DAY ONE...Tonight.
Weather hazards expected...
Significant Thunderstorm Risk...with an associated:
Elevated hail risk...up to ping pong ball sized.
Elevated damaging wind risk...up to 65 mph.
Limited Tornado Risk
Significant Flooding Risk.
DISCUSSION...
Thunderstorms are expected to redevelop later this afternoon and
evening, and some of these could be severe, capable of producing
some instances of damaging winds and large hail. The most likely
time of any potential severe thunderstorms is roughly between 6 pm
and 11 pm. The main severe threat appears to be near and south of
I-80.
In addition to the risk for severe weather, there is a threat for
several rounds of thunderstorms to produce locally very heavy
rainfall this evening and overnight with rainfall totals in
excess of three inches possible. A Flash Flood Watch is in effect
for locales near and south of I-88 and north of a Chatsworth to
DeMotte, Indiana line.
.DAYS TWO THROUGH SEVEN...Friday through Wednesday.
Saturday...
Limited Flooding Risk.
Limited Thunderstorm Risk.
Sunday...
Limited Thunderstorm Risk.
.SPOTTER INFORMATION STATEMENT...
Spotters may be needed tonight mainly south of I-80.
GENERAL STORM MOTION OF THE DAY:
Moving toward the east northeast at 35 to 40 mph.
LMZ740>745-152030-
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-
326 PM CDT Thu May 14 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...Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Elevated hail risk...up to ping pong ball size.
Elevated thunderstorm wind gust risk...up to 60 kts.
Elevated Fog Risk.
.DAYS TWO THROUGH SEVEN...Friday through Wednesday.
Friday...
Limited Thunderstorm Risk.
Saturday and Sunday...
Hazardous conditions for small craft are likely.
Limited Thunderstorm Risk.
Monday...
Hazardous conditions for small craft are likely.
Carlaw
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www.youtube.com/nwschicagoSpecial Weather Statement
National Weather Service Chicago/Romeoville
808 PM CDT Thu May 14 2020
ILZ019-032-150130-
Livingston IL-La Salle IL-
808 PM CDT Thu May 14 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN LIVINGSTON AND
SOUTHWESTERN LA SALLE COUNTIES UNTIL 830 PM CDT...
At 807 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles north of Cullom to near Flanagan to
near Roanoke. Movement was northeast at 35 mph.
Penny size hail and wind gusts up to 45 mph will be possible with
these storms.
Locations impacted include...
Streator, Pontiac, Dwight, Flanagan, Wenona, Odell, Cornell, Rutland,
Long Point, Campus, Dana and Emington.
Including the following interstate...
I-55 between mile markers 197 and 217.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
A Severe Thunderstorm Watch remains in effect until 100 AM CDT for
central and north central Illinois.
LAT...LON 4093 8893 4093 8905 4109 8905 4110 8857
4111 8826 4094 8825 4082 8893
TIME...MOT...LOC 0107Z 232DEG 28KT 4096 8831 4087 8895 4082 8928
BirkSpecial Weather Statement
National Weather Service Chicago/Romeoville
909 PM CDT Thu May 14 2020
ILZ021-032-150245-
Grundy IL-Livingston IL-
909 PM CDT Thu May 14 2020
...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN LIVINGSTON AND SOUTHERN
GRUNDY COUNTIES UNTIL 945 PM CDT...
At 909 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles west of Odell, or 9 miles north of Pontiac, moving east at 40
mph.
Penny size hail and wind gusts up to 50 mph will be possible with
this storm.
Locations impacted include...
Streator, Dwight, Flanagan, Odell, South Wilmington, Cornell, Campus,
Emington and East Brooklyn.
Including the following interstate...
I-55 between mile markers 199 and 225.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
A Severe Thunderstorm Watch remains in effect until 100 AM CDT for
central, north central and northeastern Illinois.
LAT...LON 4088 8887 4109 8886 4111 8875 4111 8859
4113 8858 4118 8826 4096 8825
TIME...MOT...LOC 0209Z 247DEG 37KT 4102 8867
BirkSpecial Weather Statement
National Weather Service Chicago/Romeoville
921 PM CDT Thu May 14 2020
ILZ023-033-039-150245-
Iroquois IL-Kankakee IL-Ford IL-
921 PM CDT Thu May 14 2020
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN KANKAKEE...NORTH
CENTRAL FORD AND NORTHWESTERN IROQUOIS COUNTIES UNTIL 945 PM CDT...
At 920 PM CDT, Doppler radar was tracking a strong thunderstorm near
Herscher, or 15 miles east of Dwight, moving east at 30 mph.
Half inch hail and wind gusts up to 50 mph will be possible with this
storm.
Locations impacted include...
Kankakee, Bourbonnais, Bradley, Herscher, Clifton, Chebanse,
Bonfield, Buckingham, Cabery, Kempton, Reddick, Irwin and Union Hill.
Including the following interstate...
I-57 between mile markers 296 and 308.
This includes... Kankakee County Fairgrounds and Speedway.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
A Severe Thunderstorm Watch remains in effect until 100 AM CDT for
northeastern Illinois.
LAT...LON 4111 8825 4112 8824 4114 8824 4118 8788
4093 8781 4089 8824
TIME...MOT...LOC 0220Z 252DEG 25KT 4101 8816
BirkThe Chicago radar (KLOT), 89 km away, was scanning. The volume nearest the first event began at 02:29 UTC.
17 flash flood, 13 thunderstorm wind, 3 flood, 1 heavy rain, 1 lightning. Local standard time, as filed.
Multiple roads were flooded in northwest Livingston County.
Flooding was reported across most roads in the Herscher area including flood waters across all of Route 115, which was closed during the peak of the heavy rain. Horse Creek was 90% full at 9000 W Road and well over its banks at 10000 W Road. Pilot Drive was also flooded. Storm total rainfall of 4.10 inches was reported in Herscher.
Trees and power lines were blown down along River Road, west of Momence.
Utility poles were damaged northeast of Momence.
Numerous streets and underpasses were flooded in Bradley.
Multiple reports of flash flooding were received from the Momence area, including two feet of water over 4000 N Road, northwest of Momence. Storm total rainfall of 4.07 inches was reported in Momence.
Rainfall of 1.10 inches was measured in 10 minutes.
Tree damage was reported in the Woodhaven Lakes area.
Part of a roof was uplifted in Sublette.
Over ten tall wooden utility poles were blown down, just west of Interstate 39.
Flooding was reported at Route 26 and Route 30 as well as on residential Streets in Amboy.
Numerous trees were blown down or snapped off in Paw Paw including along Chicago Road, Chapman Street and Maple Street.
Tree damage was reported just north of Leland.
A large tree limb was snapped off.
Trees and power lines were blown down.
Large tree limbs were blown down.
Tree damage was reported north of Hinckley.
Numerous reports of flooding were received from Huntley, Lakewood and Algonquin.
Route 64 at 1st street was impassible due to flood waters.
Water and crop debris from fields was reported over the road at Perry and Somonauk Roads.
A healthy one foot diameter tree limb was blown down from a maple tree.
Route 25 was closed due to flooding near Gilberts Street.
Heavy rain fell across much of northern Cook County, which caused flooding in many areas. In Elk Grove Village, water was up to doorways in a town home complex near Beisner Road. Nearby retention ponds were overflowing. North of Roselle, a retention pond was overflowing near Marion Street and Arthur Avenue. Street flooding was reported in Hanover Park with 1 to 2 feet of water on Barrington Road. Street flooding was reported in Bartlett. Near Des Plaines, Central Road was closed between Route 45 and Deerlove Road due to flooding. Near Schiller Park, Irving Park Road was flooded near O'Hare Airport with numerous cars flooded. Lawrence Avenue was closed near Interstate 294 due to a flooded underpass. In Northlake, Grand Avenue was closed due to flooding near Interstate 294. Near Golf, Route 58 was closed due to flooding at Route 43. Numerous streets were flooded on the north side of Chicago including at Devon Avenue and Milwaukee. Interstate 94 was briefly closed due to flooding. Multiple water rescues occurred between Interstate 90 at Touhy Avenue. One family waited on the top of their car near Pratt Avenue until firefighters arrived.
Lake Shore Drive was flooded in numerous locations including underpasses.
Klein Creek exceeded bankfull stage in Carol Stream. Flooding was reported on many streets in Carol Stream. Flood waters were nearing a structure near Kuhn Road and Munson Drive. Rainfall of 5.67 inches was measured in Carol Stream over a 36 hour period on the morning of May 15th.
Lightning struck the WSR-88D radar at the National Weather Service office in Romeoville. A computer and other electronics were damaged.
Route 53 was closed near Butterfield Road and Park Boulevard due to flooding from the East Branch DuPage River.
In Elmhurst, 1 to 2 feet of flood waters were reported on Interstate 290. North Avenue was closed at Interstate 290 due to flooding. Some interchange ramps were also closed.
Multiple intersections were flooded and closed around Zion including on Route 173 and on Wadsworth Road.
Route 41 near Route 132 was closed due to flooding.
Flooding was reported on 47th street at a railroad underpass with a water rescued reported.
Route 30 was closed due to flooding of an underpass near Highland Park Drive.
Heavy rain caused flooding across many areas of northern Cook County during the early morning of May 15th which slowly receded through mid to late morning.
An 18 year old woman attempted to cross a flooded pedestrian bridge in the Winfield Mounds Forest Preserve and was swept away. A witness said water from the West Branch DuPage River was waist deep over the bridge. The woman's body was found several days later.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Flood, Du Page | 2020-05-15 | 18 | Female | In Water | Direct |
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, May 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: 892461, 892478, 892443, 892759, 892476, 892477, 892474, 892444, 892445, 892446, 892479, 892449, 892447, 892448, 892450, 892458, 892460, 892473, 892471, 892472, 892451, 884748, 892775, 892779, 894150, 892776, 894151, 892771, 892772, 892773, 892774, 892786, 892788, 892789, 892770.