A very broad and stacked ridge of subtropical high pressure built northward over most of the United States, bringing unseasonable heat and at times record high dewpoints to much of the Midwest. Central Indiana's far western and southwestern counties, as well as central and northern portions of the Indianapolis Metro Area, recorded excessive heat (Heat Index values greater than 110 degrees) on…
Every event with a place to put it; 37 filed by county or forecast zone are drawn at its center, in a lighter ring. 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 IND wrote it up.
A very broad and stacked ridge of subtropical high pressure built northward over most of the United States, bringing unseasonable heat and at times record high dewpoints to much of the Midwest. Central Indiana's far western and southwestern counties, as well as central and northern portions of the Indianapolis Metro Area, recorded excessive heat (Heat Index values greater than 110 degrees) on August 20th-21st before a relatively mild day on August 22nd brought only 105-109 degree maximum Heat Index values to the region's southwestern-most zones. August 23rd-25th then saw the region's most pronounced heat and humidity, with Excessive Heat criteria reached on the 23rd over western and northern counties, before the greatest expanse of Excessive Heat on the 24th which enveloped all but far-northeastern zones, with Excessive Heat continuing to persist through the 25th over most central and southern counties.
A cold frontal passage late on the 25th introduced milder conditions, but not before nearly all of the region had recorded at least three consecutive days with Heat Index values surpassing 105 degrees, with many locations observing at least one day with a Heat Index of 115 degrees or greater. Greatest Heat Index values were reported along the lower Wabash Valley, including 122 degrees at Terre Haute on both the 24th and 25th, while a Heat Index of 118 degrees was recorded as far north and east as Kokomo (on the 24th). Indianapolis' heat index officially peaked at 111 degrees on both the 24th and 25th. Highest temperatures occurred on the 25th, including 102 degrees at the Shoals 8 S (Martin County) and 100 degrees at the Farmersburg TV-2 (Sullivan County) COOP sites. Dewpoints amid Excessive Heat were most often in the upper 70s, although a broad swath of low 80s occurred along the entire Wabash Valley on the 23rd, before the Kokomo AWOS reported a dewpoint of 84 degrees on the 24th; Indianapolis' highest dewpoint was meanwhile 81 degrees - reached briefly on both the 24th and 25th.
Daily minimum temperatures trended from the upper 60s to mid-70s on the 21st and 22nd, to several reports of upper 70s on the mornings of the 24th and 25th, including a low of 81 degrees at the Rockville (Parke County) COOP station. Only two of the region's 39 counties (Henry and Randolph) did not reach Excessive Heat criteria, while two others (Brown and Delaware) only verified criteria for a few afternoon hours on a single day (the 24th).
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 Indianapolis, IN wrote its last area forecast discussion before the first event at Aug 20, 1:53 PM EST, 2 minutes earlier.
Area Forecast Discussion National Weather Service Indianapolis IN 253 PM EDT Sun Aug 20 2023 .Short Term...(This evening through Monday) Issued at 250 PM EDT Sun Aug 20 2023 - Mostly Clear, Warm, with fog overnight - Mostly Sunny and Hot on Monday Surface analysis early this afternoon shows a large area of high pressure centered over the middle Atlantic States. A weak trough of low pressure was found stretching from the northern Great Lakes across Central IN and Central IL to Central MO. This was resulting in a warm southerly surface flow across Central Indiana. Some cloud coverage was noted ahead of this trough over southern IN and and southern IL, pushing southward within the flow aloft. Otherwise, GOES16 shows partly cloudy skies across Central Indiana with more sunshine found in the wake of the trough where subsidence was in play. The bigger story was found aloft where a large area of high pressure was found over the plains, extending its influence from the high plains through the Ohio Valley to the southeastern states. This high was steering any forcing dynamics across the northern plains to the eastern Great Lakes and northeastern United States. Temperatures this afternoon were quickly climbing into the upper 80s as the clouds depart to the south. Dew points have also risen into the lower 70s, resulting in humid conditions. Tonight... A ridge axis extending east from the high pressure system centered over the plains is expected to settle across Central Indiana. This will result in continued subsidence overnight. Mostly clear skies and light to calm winds will be expected as the broad surface high pressure system reorganizes across the region. Since dewpoints have increased somewhat, dew point depressions overnight look to fall to 1-3F. This will result in fog formation aided by calm to light winds. Thus mostly clear with patchy fog late looks to be the ongoing forecast. Given the warm and humid air mass in place, lows in the lower 70s will be expected. Monday... A hot day will be in store. After morning fog burns off due to daytime heating, plentiful sunshine and very warm temperatures will be expected. The previously mentioned ridge axis associated with the broad high pressure will remain over Indiana, providing subsidence. Forecast soundings show a dry column through the day. 850mb temps look a bit cooler amid the surface flow having an easterly component. However mixing within the lower levels still suggests that highs in the lower 90s will be possible. This seems quite reasonable given the warmer start expected and a full day of sunshine. The ongoing Heat Advisory looks to be on the mark as highest heat index values look to be reached mainly along and west of an LAF-IND- GEZ-Greensburg line. At this time no changes will be made to the ongoing heat advisory. && .Long Term...(Monday night through Sunday) Issued at 250 PM EDT Sun Aug 20 2023 An anomalously strong H500 ridge currently resides over the central CONUS. Guidance is nearly unanimous regarding its position, intensity, and subsequent evolution. Currently located over Kansas City with 500mb heights near 600dm, the ridge is modeled to remain in place over the next several days while intensifying slightly to around 602dm. This is roughly 3-4 sigma above the climatological mean for this time of year. Blended guidance continues to show high temperatures in the mid to upper 90s this week, but this may be a bit overdone. Over-mixing in a few members has pulled the blend temps up too much. Furthermore, wet ground may slightly limit temperatures. Therefore, will nudge temperatures downward a bit especially Tuesday where easterly to northeasterly surface winds are anticipated. Highs may fail to reach 90 Monday and Tuesday from Indianapolis northeastward as a weak backdoor cold front brings in some cooler air. Locations further south and west may avoid effects from this front and advisory-level heat/heat indices are likely. Some low clouds are possible at times, like today, as model soundings continue to show abundant moisture below a strong subsidence inversion through Tuesday. The hottest temperatures this week are likely Wednesday through Friday as winds switch to westerly and warm air advection resumes. There are some hints that a round of elevated convection may occur as the warm air advection commences, potentially impacting our northeastern counties. As of right now, the chances seem quite low and mainly outside our CWA. Regardless, very hot temperatures are still expected. Combined with high humidity (which may be too low in guidance due to the over-mixing problem) heat indices of 105 to 110 should be quite common. Occasional ground fog may occur during the overnights, especially near rivers, low-points, and over corn fields. Some hazy skies from distant wildfires is also possible. By the end of the week, guidance weakens the ridge and retreats it westward. concurrently, a trough and associated cold front may allow storm chances to return by Friday followed by cooler temperatures over the weekend. Guidance is in fairly good agreement with this, but begins to diverge significantly after Saturday. Nevertheless, forecast confidence is fairly high through the long range. && .Aviation...(18Z TAF Issuance) Issued at 1243 PM EDT Sun Aug 20 2023 Impacts: - VFR this afternoon. - IFR conditions possible near dawn Discussion: Clouds and sprinkles associated with the weak surface trough will continue to sag southward, exiting the TAF sites early this afternoon. This will lead to a quick return to VFR conditions as subsidence associated with the large high builds across the region by mid afternoon. Models suggest dew point depressions of 1-2F at the rural TAF sites near daybreak. Clear skies and light wind will provide good radiational cooling conditions. Thus some fog formation near diurnal lows will be possible. This could result in a few hours of IFR conditions, and for the moment, we have used TEMPO groups to account for this. As heating resumes on Monday morning, any fog will quickly burn off leading to a return to VFR under the large and warm area of high pressure. && .IND WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 8 AM Wednesday to midnight EDT Thursday night for INZ021-030-031-038-040>042-049-057-065. Heat Advisory until midnight EDT Thursday night for INZ028-029- 035>037-039-043>048-051>056-060>064-067>072. && Short Term...Puma Long Term...Eckhoff Aviation...Puma
Hazardous Weather Outlook National Weather Service Indianapolis IN 312 AM EDT Sun Aug 20 2023 INZ021-028>031-035>049-051>057-060>065-067>072-210715- Carroll-Warren-Tippecanoe-Clinton-Howard-Fountain-Montgomery-Boone- Tipton-Hamilton-Madison-Delaware-Randolph-Vermillion-Parke-Putnam- Hendricks-Marion-Hancock-Henry-Vigo-Clay-Owen-Morgan-Johnson-Shelby- Rush-Sullivan-Greene-Monroe-Brown-Bartholomew-Decatur-Knox-Daviess- Martin-Lawrence-Jackson-Jennings- Including the cities of Delphi, Flora, Williamsport, West Lebanon, Lafayette, West Lafayette, Frankfort, Kokomo, Attica, Covington, Veedersburg, Crawfordsville, Lebanon, Zionsville, Tipton, Fishers, Carmel, Noblesville, Anderson, Muncie, Winchester, Union City, Farmland, Parker City, Clinton, Fairview Park, Rockville, Montezuma, Rosedale, Greencastle, Plainfield, Brownsburg, Danville, Indianapolis, Greenfield, New Castle, Terre Haute, Brazil, Spencer, Gosport, Martinsville, Mooresville, Greenwood, Franklin, Shelbyville, Rushville, Sullivan, Carlisle, Shelburn, Farmersburg, Linton, Bloomfield, Jasonville, Worthington, Bloomington, Nashville, Columbus, Greensburg, Vincennes, Washington, Loogootee, Shoals, Bedford, Mitchell, Seymour, and North Vernon 312 AM EDT Sun Aug 20 2023 This hazardous weather outlook is for central Indiana. .DAY ONE...Today and Tonight. Heat index values around or just above 100 degrees are expected today across western and southern Indiana. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Dangerous heat is expected through the upcoming week with multiple days of heat index values between 100 and 110 degrees. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated. && More information, along with other weather, hydrological and climate information can be found at http://weather.gov/ind
The national radar mosaic for the moment the first event began.
37 excessive heat. Local standard time, as filed.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 20th over south-central portions of Hamilton County. Heat index values were from measured temperature and dewpoint at the UMP AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 20th within downtown and northeastern portions of Marion County. Heat index values were from measured temperature and dewpoint at both the IND and EYE ASOS and nearby UMP AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st. Heat index values are estimated from combination of observed maximum temperatures at the Vincennes 5 NE COOP station and estimated dewpoints from proximity to nearby LWV ASOS and DCY and AJG AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st for essentially all of Sullivan County. Heat index values were estimated from reported maximum temperature at Farmersburg TV-2 COOP station and dewpoint data from the RSV AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st for essentially all of Vigo County. Heat index values were from measured temperature and dewpoint at the HUF ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st. Heat index values were from measured temperature and dewpoint at the DCY AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st over mainly western portions of Clay County. Heat index values were estimated from measured temperature and dewpoint at the nearby HUF ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st over the western half of Greene County. Heat index values were estimated from measured temperature and dewpoint at both the the BMG ASOS and RSV AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 21st over the southwestern half of Martin County. Heat index values were estimated from reported maximum temperature at the Shoals 8 S COOP station and dewpoint at the nearby DCY AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st over mainly central and southwestern portions of Parke County. Heat index values were estimated from reported maximum temperature at the Rockville COOP station and dewpoint at the nearby HUF ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the early afternoon of August 21st. Heat index values were estimated from measured temperature and dewpoint at the nearby HUF ASOS and DNV AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were from measured temperature and dewpoint at the TYQ AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were from estimated from reported maximum temperatures at the Spencer COOP station and dewpoint data from the nearby BMG ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were from measured temperature and dewpoint at the GPC AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were estimated from reported maximum temperatures at the Columbus COOP station and dewpoint data from the nearby GEZ ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were estimated from measured temperature and dewpoint at the HLB AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd. Heat index values were estimated from reported maximum temperature at the nearby Perrysville 4 WNW COOP station and dewpoint data at the LAF ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th over most of Hancock County. Heat index values were estimated and interpolated from measured temperature and dewpoint at the MQJ and UMP AWOS and reported maximum temperatures from the Greenfield COOP station.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were estimated from reported maximum temperatures at the Seymour 1 WSW COOP station and dewpoint data from the nearby BFR AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th over mainly western portions of Jennings County. Heat index values were estimated and interpolated from reported maximum temperatures from the North Vernon 2 ESE COOP station and dewpoint data from the nearby HLB and IMS AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th over most of Johnson County. Heat index values were from reported maximum temperature at the Franklin WWTP COOP station and dewpoint data from the IND and GEZ ASOS and the HFY AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were interpolate from data reported by the nearby Hardin Ridge RAWS station.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd over far western portions of Madison County. Heat index values were estiamted and interpolated from measured temperature and dewpoint at both the nearby UMP AWOS and MIE ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were from measured temperature and dewpoint at the BMG ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd to the west and north of Crawfordsville. Heat index values were estimated and interpolated given temperature and dewpoint data from the nearby LAF ASOS and reported maximum temperature from the Crawfordsville 6 SE COOP station.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were estimated from reported maximum temperature at the Martinsville 2 SW COOP station and dewpoint data from the nearby IND ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were from measured temperature and dewpoint at the GEZ ASOS as well as maximum temperatures from the Shelbyville COOP station.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd. Heat index values were estimated from reported maximum temperature from the Tipton 5 SW COOP station and dewpoint data from the OKK AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd over essentially all of Howard County. Heat index values were from measured temperature and dewpoint at the OKK AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd. Heat index values were from measured temperature and dewpoint at the LAF ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd. Heat index values were from measured temperature and dewpoint at the MCX AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 24th. Heat index values were estimated from proximity to nearby ASOS at both IND and EYE.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd. Heat index values were estimated from measured temperature and dewpoint at both the LAF ASOS and DNV AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees on the afternoon of August 23rd over northern and central portions of Clinton County. Heat index values were from measured temperature and dewpoint at the FKR AWOS.
Criteria was reached from maximum heat index values exceeding 110 degrees briefly on the afternoon of August 24th. Heat index values were estimated from measured temperature and dewpoint at the BMG ASOS, and reported maximum temperatures at the nearby Columbus and Oolitic COOP stations.
Criteria was reached from maximum heat index values exceeding 110 degrees only on the afternoon of August 24th, over central and western portions of Delaware County. Heat index values were from measured temperature and dewpoint at the MIE ASOS.
Criteria was reached from maximum heat index values exceeding 110 degrees briefly on the afternoon of August 24th. Heat index values were estimated from reported maximum temperature at the Rushville COOP station and dewpoint data from the GEZ ASOS and HLB AWOS.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Indiana in 2023Every state in 2023This day in weather historyWarnings in Indiana, August 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: 1138496, 1138513, 1138508, 1138543, 1138556, 1138487, 1138483, 1138495, 1138514, 1138530, 1138553, 1138480, 1138528, 1138531, 1138479, 1138488, 1138490, 1138498, 1138501, 1138502, 1138505, 1138511, 1138512, 1138519, 1138523, 1138527, 1138538, 1138551, 1138500, 1138547, 1138482, 1138499, 1138557, 1138486, 1138481, 1138489, 1138533.