Excessive Heat in Illinois, August 20 to 25, 2023

Name: Excessive Heat in Illinois, August 20 to 25, 2023
Start: 2023-08-20T13:00
End: 2023-08-25T20:00
Location: Illinois

August 20 to 25, 2023 · NWS ILX · 35 events in 35 counties and zones

A strong heat dome over the Midwest resulted in a six-day stretch of dangerous heat and humidity, which began on August 20 and continued through August 25. High temperatures were routinely above 90 degrees, while afternoon dewpoints were near 80 degrees, resulting in heat indices exceeding 110 degrees.

Where it happened

Every event with a place to put it; 35 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 35

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.

What happened

The episode as NWS ILX wrote it up.

What forecasters said that day

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 Aug 20, 11:03 AM CST, 1 hour 57 minutes earlier.

Area forecast discussion, Aug 20, 11:03 AM CST, 1 hour 57 minutes before

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1203 PM CDT Sun Aug 20 2023

.SYNOPSIS...
Issued at 1200 PM CDT Sun Aug 20 2023

Dangerously hot conditions are expected areawide starting today.
Maximum heat indices will range from 105 to 115 each afternoon
through at least Thursday. Stay safe in the heat by limiting
exposure outdoors and staying hydrated.

&&

.UPDATE...
Issued at 921 AM CDT Sun Aug 20 2023

Despite the fairly dry air noted in our morning sounding, the
high based ACCAS noted on satellite has managed to produce some
light showers and even a couple lightning strikes. Most are now in
a narrow east-west band just south of I-72, with a few sprinkles
as far north as Rantoul. Latest HRRR diminishes but not completely
eliminates these through midday. PoP's over the next few hours
have been updated, still mainly focusing on sprinkles, but
slightly higher with the narrow band.

Geelhart

&&

.DISCUSSION...
Issued at 335 AM CDT Sun Aug 20 2023

Key Points:

1) Dangerously hot conditions develops today and continue through at
least Thursday. Maximum afternoon heat indices will top out between
105 and 115. An Excessive Heat Warning goes into effect this
afternoon, continuing through Thursday evening.

2) Mostly dry weather is likely through much of the week.

A ~597 dm upper high centered over the central Plains states will
continue to build and lift northward over the next few days,
creating an omega block over the US. At the surface, high pressure
is situated over the Mid-Atlantic states with a surface trough/cold
front stretched from the Great Lakes Region southwestward toward
Missouri where a surface low is noted. The front will approach our
northwest counties tonight gradually sinking into the area overnight
into Monday, turning winds east-northeasterly and ushering in
slightly drier air over northern parts of the state. Presently, a
few widely scattered showers have been observed near and east of the
surface low which is where a 25-30 kt LLJ is overlaid. Although
forecast soundings are pretty dry in the low levels (cloud bases are
~15k ft), an EML with some instability may support an isolated
shower or sprinkle that could punch its way to the surface this
morning (10-15% chance).

Another surface low will develop and work into the northern Plains
states by Monday night/Tuesday, which will lift the aforementioned
cold front back northward as a warm front as the upper ridge
strengthens to near 600 dm and positions itself just west of
here. High temperatures today and Monday will peak in the low to
middle 90s with dewpoints surging into the middle to upper 70s as
they pool south of the front. Temperatures will increase by a few
degrees each day through midweek as deeper mixing comes into play.
High temperatures look to reach the middle to upper 90s by
Tuesday, with values possibly nearing 100 in spots by Thursday.
Dewpoints won't be quite as high by the Wednesday/Thursday
timeframe due to deeper mixing, but should still be "soupy" (low
to middle 70s). Heat indices today through Thursday look to range
from 105 to 115, with the highest values currently on Tuesday when
the warmest temperatures and highest dewpoints coincide. An
Excessive Heat Warning is in effect from this afternoon through
Thursday across the entire area, but may need to be expanded in
spots going into Friday (more on that below).

Moisture from (now) Hurricane Hilary will lift northward along the
western periphery of the upper ridge, merging with a shortwave over
the Pacific Northwest. This shortwave will get kicked east by
another shortwave then will track along the northern periphery of
the upper ridge as it flattens it out some. The shortwave will work
into the Great Lakes Region by late this week as ridging amplifies
over the High Plains/Intermountain West. A cold front tied to the
aforementioned system will work through the area on Friday, bringing
low end chances for precipitation and relief from the heat. Timing
differences still exist with the frontal passage, which may keep hot
and humid conditions present in parts of the area through much of
Friday too (most likely over the southern half of the CWA). Because
of this, the Excessive Heat Warning may need to be expanded into
Friday. Confidence remains too low to take any action on headline
expansion at this time though.

Much cooler temperatures filter in behind the front for the weekend
as surface high pressure sinks into the Great Lakes Region. Aside
from low chances (<15%) with the cold front passage late this week,
things look to stay pretty dry through day 7.

NMA

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1203 PM CDT Sun Aug 20 2023

Showers and isolated thunder that has been occurring near KCMI are
finally shifting more southeast, though a stray shower is still
possible for another hour or two. Otherwise, main feature of note
will be winds shifting to the east-northeast. A weak boundary is
sinking south and should be past a KSPI-KCMI line by mid
afternoon. Once that passes, winds should stay east-northeast
through midday Monday.

VFR conditions expected to prevail through the period.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 10 PM CDT Thursday for ILZ027>031-
036>038-040>057-061>063-066>068-071>073.

&&

Hazardous weather outlook, Aug 20, 10:35 AM CST, 2 hours 25 minutes before

Hazardous Weather Outlook
National Weather Service Lincoln IL
1135 AM CDT Sun Aug 20 2023

ILZ027>031-036>038-040>043-047>053-211100-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler-
Mason-Logan-De Witt-Cass-Menard-Scott-Morgan-Sangamon-Christian-
Macon-
1135 AM CDT Sun Aug 20 2023

This Hazardous Weather Outlook is for central Illinois and west
central Illinois.

.DAY ONE...This afternoon and tonight.

Dangerous heat builds into the area today with peak heat index
values of 100 to 110 degrees, locally higher west of the Illinois
River.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Dangerous heat will persist through at least Thursday. Peak daily
heat index values of 105 to 115 degrees are likely each day.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated through tonight.

ILZ044>046-054>057-061>063-066>068-071>073-211100-
Piatt-Champaign-Vermilion-Moultrie-Douglas-Coles-Edgar-Shelby-
Cumberland-Clark-Effingham-Jasper-Crawford-Clay-Richland-Lawrence-
1135 AM CDT Sun Aug 20 2023

This Hazardous Weather Outlook is for east central Illinois and
southeast Illinois.

.DAY ONE...This afternoon and tonight.

Isolated thunderstorms will occur through midday, though severe
weather is not likely.

Dangerous heat builds into the area today with peak heat index
values of 100 to 110 degrees this afternoon.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Dangerous heat will persist through at least Thursday. Peak daily
heat index values of 105 to 115 degrees are likely each day.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated through tonight.

Geelhart

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

35 excessive heat. Local standard time, as filed.

Excessive Heat, Peoria

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Peoria forecast zone
Reported by: ASOS
Coordinates: 40.788, -89.760 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. Peoria International Airport (KPIA) recorded a peak heat index of 121 degrees on Wednesday, August 23, which was the highest ever recorded at the airport. Records date back to 1948. The Peoria Airport also set record warm low temperatures of 77 and 78 degrees on August 23 and August 24, respectively.

Excessive Heat, Knox

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Knox forecast zone
Reported by: AWOS
Coordinates: 40.932, -90.213 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. The Galesburg Airport (KGBG) recorded a heat index over 110 degrees each day, with a maximum heat index of 128 degrees on Wednesday, August 23.

Excessive Heat, Champaign

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Champaign forecast zone
Reported by: ASOS
Coordinates: 40.140, -88.199 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. Willard Airport (KCMI) recorded a maximum heat index of 116 degrees on August 24. Also on August 24, the AWOS at the Rantoul Airport recorded a maximum heat index of 117 degrees.

Excessive Heat, Christian

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Christian forecast zone
Reported by: AWOS
Coordinates: 39.546, -89.277 (the zone’s center; the record gives no point)

Excessive Heat, Clay

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Clay forecast zone
Reported by: AWOS
Coordinates: 38.754, -88.490 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. The Flora Airport (KFOA) recorded a heat index over 110 degrees each day, including a maximum heat index of 119 degrees on August 24.

Excessive Heat, Coles

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Coles forecast zone
Reported by: ASOS
Coordinates: 39.520, -88.222 (the zone’s center; the record gives no point)

Excessive Heat, Crawford

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Crawford forecast zone
Reported by: AWOS
Coordinates: 39.003, -87.760 (the zone’s center; the record gives no point)

Excessive Heat, Effingham

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Effingham forecast zone
Reported by: AWOS
Coordinates: 39.060, -88.590 (the zone’s center; the record gives no point)

Excessive Heat, Lawrence

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Lawrence forecast zone
Reported by: ASOS
Coordinates: 38.720, -87.727 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. The Lawrenceville Airport (KLWV) recorded a maximum heat index of 121 degrees on both August 24 and August 25. The AWOS at the Mount Carmel Airport (KAJG) recorded a maximum heat index of 119 degrees on August 25.

Excessive Heat, Logan

When: August 20, 1:00 PM CST to 8:00 PM CST
Where: Logan forecast zone
Reported by: AWOS
Coordinates: 40.125, -89.367 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. The Logan County Airport (KAAA) recorded a maximum heat index of 120 degrees on August 23. Additionally, the National Weather Service in Lincoln recorded a record warm low temperature of 77 degrees on August 24.

Excessive Heat, Macon

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Macon forecast zone
Reported by: ASOS
Coordinates: 39.860, -88.962 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. The Decatur Airport (KDEC) recorded a heat index over 110 degrees each day during the heat wave, with a maximum heat index of 119 degrees on August 21.

Excessive Heat, Marshall

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Marshall forecast zone
Reported by: AWOS
Coordinates: 41.033, -89.345 (the zone’s center; the record gives no point)

Excessive Heat, Mason

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Mason forecast zone
Reported by: Mesonet
Coordinates: 40.240, -89.917 (the zone’s center; the record gives no point)

A prolonged stretch of dangerous heat and humidity occurred across the Midwest. Peak afternoon heat indices were near or over 110 degrees each day, and heat indices remained above 80 degrees overnight. A mesonet station two miles southeast of Topeka and a mesonet station in Snicarte both recorded maximum heat indices of 120 degrees on August 23.

Excessive Heat, McLean

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: McLean forecast zone
Reported by: AWOS
Coordinates: 40.491, -88.847 (the zone’s center; the record gives no point)

Excessive Heat, Morgan

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Morgan forecast zone
Reported by: AWOS
Coordinates: 39.716, -90.201 (the zone’s center; the record gives no point)

Excessive Heat, Richland

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Richland forecast zone
Reported by: Mesonet
Coordinates: 38.712, -88.085 (the zone’s center; the record gives no point)

Excessive Heat, Sangamon

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Sangamon forecast zone
Reported by: ASOS
Coordinates: 39.758, -89.659 (the zone’s center; the record gives no point)

Excessive Heat, Tazewell

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Tazewell forecast zone
Reported by: Mesonet
Coordinates: 40.508, -89.513 (the zone’s center; the record gives no point)

Excessive Heat, Vermilion

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Vermilion forecast zone
Reported by: AWOS
Coordinates: 40.183, -87.733 (the zone’s center; the record gives no point)

Excessive Heat, Cass

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Cass forecast zone
Reported by: Mesonet
Coordinates: 39.974, -90.247 (the zone’s center; the record gives no point)

Excessive Heat, Clark

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Clark forecast zone
Reported by: Mesonet
Coordinates: 39.334, -87.788 (the zone’s center; the record gives no point)

Excessive Heat, De Witt

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: De Witt forecast zone
Reported by: Mesonet
Coordinates: 40.175, -88.904 (the zone’s center; the record gives no point)

Excessive Heat, Douglas

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Douglas forecast zone
Reported by: Mesonet
Coordinates: 39.770, -88.217 (the zone’s center; the record gives no point)

Excessive Heat, Fulton

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Fulton forecast zone
Reported by: Mesonet
Coordinates: 40.473, -90.207 (the zone’s center; the record gives no point)

Excessive Heat, Jasper

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Jasper forecast zone
Reported by: Mesonet
Coordinates: 39.010, -88.154 (the zone’s center; the record gives no point)

Excessive Heat, Menard

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Menard forecast zone
Reported by: Mesonet
Coordinates: 40.027, -89.802 (the zone’s center; the record gives no point)

Excessive Heat, Moultrie

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Moultrie forecast zone
Reported by: Mesonet
Coordinates: 39.642, -88.619 (the zone’s center; the record gives no point)

Excessive Heat, Schuyler

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Schuyler forecast zone
Reported by: Mesonet
Coordinates: 40.158, -90.615 (the zone’s center; the record gives no point)

Excessive Heat, Scott

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Scott forecast zone
Reported by: Mesonet
Coordinates: 39.644, -90.475 (the zone’s center; the record gives no point)

Excessive Heat, Shelby

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Shelby forecast zone
Reported by: Mesonet
Coordinates: 39.391, -88.805 (the zone’s center; the record gives no point)

Excessive Heat, Stark

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Stark forecast zone
Reported by: Mesonet
Coordinates: 41.093, -89.797 (the zone’s center; the record gives no point)

Excessive Heat, Woodford

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Woodford forecast zone
Reported by: Mesonet
Coordinates: 40.788, -89.211 (the zone’s center; the record gives no point)

Excessive Heat, Cumberland

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Cumberland forecast zone
Reported by: Mesonet
Coordinates: 39.273, -88.240 (the zone’s center; the record gives no point)

Excessive Heat, Edgar

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Edgar forecast zone
Reported by: Mesonet
Coordinates: 39.679, -87.746 (the zone’s center; the record gives no point)

Excessive Heat, Piatt

When: August 20, 1:00 PM CST to August 25, 8:00 PM CST
Where: Piatt forecast zone
Reported by: Mesonet
Coordinates: 40.010, -88.591 (the zone’s center; the record gives no point)

What these are

Excessive Heat: Heat at or above the local excessive heat warning criteria, or heat that caused deaths.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Illinois in 2023 Every state in 2023 This day in weather history Warnings in Illinois, August 2023

Sources

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: 1121988, 1121998, 1122018, 1122022, 1122028, 1122033, 1122037, 1122041, 1122047, 1122050, 1122053, 1122056, 1122058, 1122060, 1122062, 1122066, 1122070, 1122074, 1122078, 1122117, 1122118, 1122119, 1122120, 1122121, 1122122, 1122124, 1122125, 1122128, 1122134, 1122135, 1122137, 1122139, 1122140, 1122141, 1122143.