An isolated storm developed during the evening across central South Dakota and progressed into the James River valley north of Huron late in the evening. With an appreciable amount of DCAPE, the storm produced damaging wind before weakening.
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The episode as NWS FSD wrote it up.
An isolated storm developed during the evening across central South Dakota and progressed into the James River valley north of Huron late in the evening. With an appreciable amount of DCAPE, the storm produced damaging wind before weakening.
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 Aug 25, 10:01 PM CST, 11 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 1101 PM CDT Sat Aug 25 2018 .SHORT TERM...(This evening through Sunday) Issued at 400 PM CDT Sat Aug 25 2018 A rather complicated setup is occurring over the next several forecast periods beginning with tonight. In the near term, added a low pop for the Yankton vicinity late this afternoon just in case some of the activity in Nebraska sneaks northward before dissipating. At the moment, do not even have any thunder included as that may stay south of our area. Tonight, a short wave moves eastward across North Dakota and northern Minnesota along a boundary in the low levels. Thunderstorms should eventually get going in those areas to the north and interestingly, the latest ECMWF oozes that convection southeastward late tonight into the northern and eastern reaches of southwest MN. The various CAMs keep the convection north of our forecast area, but many times this summer they have done poorly in developing the activity southward as it builds into the low level jet. Therefore per the ECMWF, included some slight chance and chance pops in our northeast zones in case the southern end of the complex scrapes that area. With moist air and a south breeze, lows tonight will be very warm with readings about 65 to 70 degrees. On Sunday, a strong upper ridge of high pressure is centered over the lower MS valley. The models are in good agreement in bringing another short wave northeastward over the ridge into our southern zones. QG forcing shows this wave the best, especially in the 500- 300mb layer, and it does rapidly exit our southeast zones between 18Z and 00Z during the afternoon hours. There is a huge amount of model discrepancy with exact timing and placement of thunderstorm activity. In general however, the wave should primarily impact northwest IA and immediate adjacent locations, with a possible small second area of convection northwest of there in SD and the northern sections of southwest MN along a subtle mid level deformation. Due to the amount of cloud cover in our southeast zones, conditions are not overly unstable, with afternoon 0-1km ML CAPE roughly around 1000 J/kg, which is not very strong for this time of year. There is strong wind shear however, with veering profiles and 50 knots at 3km. 0-6km shear is forecast to be 50 to 55 knots. So therefore cannot rule some marginal severe storms during the daytime in our eastern zones, but again stability will be a limiting factor. With the increased cloud cover, highs should only reach the lower 80s in many parts of northwest IA. Conversely with warm 850mb temperatures and clearer skies, highs in our western zones will be in the lower 90s. It will also be quite breezy in the afternoon throughout the forecast area as the low level jet cranks up along with a tightening pressure gradient. .LONG TERM...(Sunday night through Saturday) Issued at 400 PM CDT Sat Aug 25 2018 At this time, Sunday night looks rather quiet as we appear to be in between waves. There is a strong short wave which moves across ND, stronger than tonight's short wave. However it appears too far north to affect our CWA. This wave does drag a surface wind shift into our forecast area however, which stalls roughly from Brookings SD to Tyndall SD late Sunday night and early Monday. On Monday afternoon, a complex of storms may develop east of our CWA along the eastern portions of this boundary with some frontal wave interaction. The question is how much of that will back build and impact our zones. It certainly is worth some slight chance and chance pops except for our western zones, so included chances generally east of the James River valley. On Monday night and Tuesday, the main upper level trough which resides over the intermountain west Sunday and Sunday night, will finally move across the plains. Therefore unsettled weather will continue along with a strong cold frontal push. After one more warm day on Monday, highs on Tuesday and Wednesday will be dramatically cooler with readings in the 70s. Due to the variances between the models with their respective solutions with the exact timing and placement of the cold frontal boundary and upper wave, it is very difficult to know where the highest chances for convection will be. So pops are pretty broad brushed Monday and Tuesday. The weather looks quiet Tuesday night and Wednesday. There may be a few storms Wednesday night and early Thursday in the central portions of our CWA along a strengthening low level jet and warm air advection, coupled with elevated instability. Although pops are low for any given location, if storms do develop this type of scenario can produce locally heavy downpours for brief periods of time, so something to watch for in the future. Further out, there is model consensus in bringing a strong short wave through our area Thursday night. So overall the pattern is quite active over the next week with periodic waves moving rapidly eastward across a quasi zonal flow. In addition, temperatures will begin to warm again late next week into widespread upper 70s to upper 80s from Thursday through Saturday. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 1057 PM CDT Sat Aug 25 2018 Thunderstorms will be possible leading up to 06z for KHON and the surrounding area, with gusts to 40 kt possible. After 06z, light winds are expected in the forecast area. During the morning hours into Sunday afternoon, scattered thunderstorms are possible along the I-29 corridor, including KFSD and KSUX. These are not expected to be strong, but gusty and variable winds are possible under storm cores. South winds will be breezy throughout the day, gusting in the 20 to 25 kt range. Winds lighten after sunset on Sunday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && SHORT TERM...MJ LONG TERM...MJ AVIATION...VandenBoogart
Hazardous Weather Outlook National Weather Service Sioux Falls SD 607 AM CDT Sat Aug 25 2018 MNZ072-080-081-090-261115- Lyon MN-Murray-Cottonwood-Jackson- 607 AM CDT Sat Aug 25 2018 This Hazardous Weather Outlook is for portions of southwest Minnesota. .DAY ONE...Today and Tonight Areas of dense fog will prevail through early morning, with visibility to around one quarter mile. An isolated thunderstorm will be possible late tonight around Marshall, but no severe storms are expected. .DAYS TWO THROUGH SEVEN...Sunday through Friday Spotty thunderstorms will be possible Sunday, but in general chances will remain quite low until Monday afternoon and evening. Storms late Monday could be severe. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today and tonight. IAZ001>003-012>014-MNZ071-089-097-098-SDZ038>040-053>056-060>062- 067-261115- Lyon IA-Osceola-Dickinson-Sioux-O'Brien-Clay IA-Lincoln MN-Nobles- Pipestone-Rock-Beadle-Kingsbury-Brookings-Sanborn-Miner-Lake- Moody-Hanson-McCook-Minnehaha-Lincoln SD- 607 AM CDT Sat Aug 25 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, southwest Minnesota, east central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight Patchy fog is expected to linger through around 9 am this morning. Fog will be most concentrated against eastern slopes of the James and Big Sioux river valleys and through lower elevations across northwest Iowa, and could briefly drop visibility to a half mile or less. .DAYS TWO THROUGH SEVEN...Sunday through Friday Spotty thunderstorms will be possible Sunday mainly east of Interstate 29, but in general chances will remain quite low until Monday afternoon and evening. A severe storms will be possible across northwest Iowa and southwest Minnesota late Monday. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today and tonight. IAZ020>022-031-032-NEZ013-014-SDZ050-052-057>059-063>066-068>071- 261115- Plymouth-Cherokee-Buena Vista-Woodbury-Ida-Dixon-Dakota-Gregory- Jerauld-Brule-Aurora-Davison-Charles Mix-Douglas-Hutchinson- Turner-Bon Homme-Yankton-Clay SD-Union- 607 AM CDT Sat Aug 25 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, northeast Nebraska, central South Dakota, south central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight Patchy fog will continue through early morning. A few locations could briefly find visibilities less than a mile. Isolated thunderstorms will be possible tonight toward south central South Dakota. While unlikely, any storm that manages to develop could produce gusty wind. .DAYS TWO THROUGH SEVEN...Sunday through Friday In general, the risk of thunderstorms will remain quite low until increasing on Monday night. A few storms Monday night could be strong. Very warm and humid conditions will bring heat index values on Sunday and Monday into the mid to upper 90s. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today and tonight.
The Aberdeen radar (KABR), 92 km away, was scanning. The volume nearest the first event began at 04:12 UTC.
1 thunderstorm wind. Local standard time, as filed.
Tree branches up to two inches in diameter were broken from trees.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in South Dakota in 2018Every state in 2018This day in weather historyWarnings in South Dakota, August 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: 780611.