A very unstable airmass generated by temperatures into the 90s and dew point readings in the 70s was in place as a cold front pushed through during the late afternoon. An isolated storm developed, feeding off the instability to briefly produce large hail.
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 FSD wrote it up.
A very unstable airmass generated by temperatures into the 90s and dew point readings in the 70s was in place as a cold front pushed through during the late afternoon. An isolated storm developed, feeding off the instability to briefly produce large hail.
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 Sioux Falls, SD wrote its last area forecast discussion before the first event at Jul 4, 2:01 PM CST, 2 hours 55 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 301 PM CDT Wed Jul 4 2018 .SHORT TERM...(This evening through Thursday) Issued at 259 PM CDT Wed Jul 4 2018 The 4th of July has certainly been an interesting day weatherwise. Early morning MCV tracking across the CWA forced severe convection over the eastern portions of the forecast area, with continued weak synoptic lift trailing across the Missouri River valley for much of the day. The end result has been a general stabilization of the atmosphere north of this convection, along with cooler temperatures than expected. Generally, model guidance has proven fairly useless today with poor initializations across the board, with only the RAP and the afternoon runs of the HRRR providing some value. This afternoon and tonight: The greatest severe weather risks are going to be focused along or south of the Missouri River this afternoon, as a shortwave tracks northward into the area. Latest mesoanalysis suggests MLCAPE values approaching 2000 J/KG south of the CWA, but overall marginal shear. Now that the MCV has moved far enough to the east, we should begin to see 850 mb flow focus itself across north central Nebraska, where new convection should form quickly along a convergence axis between Oneill and Ainsworth. If short term guidance is correct, this should relieve some of the pressure on ongoing convection in Charles Mix and Bon Homme counties. A small scale MCS cluster may develop and move across northern Nebraska into the evening. Further north, not as impressed with rain or convection risks through the evening festivities. It's certainly possible the developed stratiform region of convection further south could clip the I-90 areas, but those chances are lower now. The only other area to watch will be with a frontal boundary dropping southward this evening. Convergence is minimal, but could see an isolated shower or storm form on this boundary as it moves south this evening. While most models are NOT indicating this potential, I do see some concern for redevelopment of convection after midnight south of I- 90 as the 850 mb boundary remains planted in the area. There could be just enough convergence and enhancement of the LLJ to produce a linger band of moderate rains between Sioux Falls and Sioux City. Will bump up the QPF amounts in this area, but must stress this is low confidence on occurring. Thursday-Thursday night: High pressure will bring cooler temperatures and drier air southward on Thursday. The 850 MB boundary will fail to clear the CWA however, and this certainly could bring the potential for a few daybreak showers and storms into Friday morning. Later shifts may need to add this potential into the forecast. .LONG TERM...(Thursday night through Wednesday) Issued at 259 PM CDT Wed Jul 4 2018 Friday-Sunday: Mid-level height rises will bring an increase in temperatures and humidity back into the region for this weekend. A growing 597DM ridge overhead should suppress convection this weekend. A lone precipitation chance could present itself late Sunday evening over northern South Dakota and western Minnesota along a poorly defined front. Next week: Medium range guidance seems to suggest that we'll continue to grow a mid-level ridge over the region, again keeping precipitation chances on the lower end. Temperatures will trend above average, with rather oppressive humidity settling into the region. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1216 PM CDT Wed Jul 4 2018 Scattered convection for the most part should miss the terminals today. Very uncertain forecast into this evening, so would rather not pin down any prevailing TSRA at this point and will keep skies VFR. A surface boundary should drift southwards after midnight, turning winds to the north in most areas. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Heat Advisory until 8 PM CDT this evening for SDZ068>071. MN...None. IA...Heat Advisory until 8 PM CDT this evening for IAZ031-032. NE...Heat Advisory until 8 PM CDT this evening for NEZ013-014. && SHORT TERM...Dux LONG TERM...Dux AVIATION...Dux
Hazardous Weather Outlook National Weather Service Sioux Falls SD 331 PM CDT Wed Jul 4 2018 IAZ001>003-MNZ071-072-080-081-089-090-097-098-SDZ038>040-050- 052>067-052045- Lyon IA-Osceola-Dickinson-Lincoln MN-Lyon MN-Murray-Cottonwood- Nobles-Jackson-Pipestone-Rock-Beadle-Kingsbury-Brookings-Gregory- Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson- McCook-Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Lincoln SD- 331 PM CDT Wed Jul 4 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, southwest Minnesota, central South Dakota, east central South Dakota, south central South Dakota, and southeast South Dakota. .DAY ONE...This Afternoon and Tonight Isolated thunderstorms could be possible later this evening, however most will stay dry. Severe storms are not anticipated. Moderate to major flooding continues on several rivers and streams. For specific river details, visit https://water.weather.gov. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday No active weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated. IAZ012>014-020>022-031-032-NEZ013-014-SDZ068>071-052045- Sioux-O'Brien-Clay IA-Plymouth-Cherokee-Buena Vista-Woodbury-Ida- Dixon-Dakota-Bon Homme-Yankton-Clay SD-Union- 331 PM CDT Wed Jul 4 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, northeast Nebraska, and southeast South Dakota. .DAY ONE...This Afternoon and Tonight Scattered thunderstorms will continue this afternoon into the evening. The severe weather risk has lessened this evening, but a few strong storms may develop from Vermillion to Sioux City and Storm Lake early this evening. The main risks will be damaging winds and locally heavy rainfall. There is a chance that a few thunderstorms could redevelop after midnight tonight. These storms could produce locally heavy rains across areas south of Interstate 90 between Sioux Falls and Sioux City. Moderate to major flooding continues on several rivers and streams. For specific river details, visit https://water.weather.gov. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday No active weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
157 PM CDT WED JUL 4 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1135 AM TSTM WND DMG SPENCER 43.15N 95.15W
07/04/2018 CLAY IA TRAINED SPOTTER
LARGE TREES UPROOTED.
&&
KJHPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
201 PM CDT WED JUL 4 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1050 AM TSTM WND DMG LAKE PARK 43.45N 95.33W
07/04/2018 DICKINSON IA EMERGENCY MNGR
CORRECTS TIME OF PREVIOUS REPORT FROM LAKE
PARK. TREE DOWN. 3 INCHES OF RAIN FELL.
&&
KJHPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
203 PM CDT WED JUL 4 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1055 AM TSTM WND DMG 3 NW LAKE PARK 43.48N 95.37W
07/04/2018 DICKINSON IA EMERGENCY MNGR
CORRECTS TIME OF PREVIOUS TSTM WND DMG
REPORT FROM 3 NW LAKE PARK. SMALL TREE
BRANCHES DOWN. 2 INCHES OF RAIN IN 20
MINUTES.
&&
KJHThe Sioux Falls radar (KFSD), 120 km away, was scanning. The volume nearest the first event began at 22:54 UTC.
2 thunderstorm wind. Local standard time, as filed.
A power line was knocked down by thunderstorm wind.
Several three inch diameter tree limbs broken by thunderstorm wind gusts.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2018Every state in 2018This day in weather historyWarnings in Iowa, July 2018
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: 773085, 773086.