A strong negatively tilted trough lifted northward through the Western Plains during the afternoon and evening of May 6. While instability was not intense with around 1000 J/kg MLCAPE, a very strong low-level jet produced a considerable amount of boundary parallel deep-layer shear to entice a quick linear upscale growth, but the southwest-oriented shear in the 0-3km layer also led to brief…
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The episode as NWS FSD wrote it up.
A strong negatively tilted trough lifted northward through the Western Plains during the afternoon and evening of May 6. While instability was not intense with around 1000 J/kg MLCAPE, a very strong low-level jet produced a considerable amount of boundary parallel deep-layer shear to entice a quick linear upscale growth, but the southwest-oriented shear in the 0-3km layer also led to brief mesovortices with enhanced wind corridors in segments which became oriented more northwest to southeast.
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 May 6, 6:13 PM CST, 12 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Sioux Falls SD 713 PM CDT Mon May 6 2024 .KEY MESSAGES... - Lines of showers and thunderstorms will move across the forecast area this evening. While an isolated stronger storm is still possible, the risk of severe weather appears to be decreasing. - Periodic rain chances continue for much of the upcoming week into next weekend with the focus on Wednesday. Highs in the 60s to 70s are expected. && .UPDATE... Issued at 713 PM CDT Mon May 6 2024 Still seeing isolated gusts over 40 mph as of 7 PM, but overall expect winds to be on a downward trend through this evening, and thus have allowed the Wind Advisory to expire. That said, with a fairly stout low level jet still over the area, cannot rule out isolated stronger gusts with the showers and thunderstorms moving across the area. While these isolated gusts may be marginally severe (60 MPH), instability across much of our forecast area seems to be lacking given general downtrend in storm intensity as the line of storms in eastern Nebraska moves northeast. Area of greatest concern at this point would seem to be portions of the Highway 20 corridor (Sioux City) and perhaps into Storm Lake. && .DISCUSSION... Issued at 250 PM CDT Mon May 6 2024 Rest of Afternoon and Evening: At a large scale, pronounced mid/upper low is evident on WV imagery across the northern Rockies with surface low deepening across western SD. A warm front is lifting through central NE with a narrow warm sector before a quickly approaching dryline/cold front is crashing eastward. These features will all lift east or northeast into the evening and overnight hours and provide for thunderstorm chances. Severe Storms: Forecast soundings show a ribbon of modest elevated instability lifting from roughly 850:800 mb around 1000 J/kg with higher values as you go south. Surface parcels would obtain closer to 50o J/kg if they can overcome a modest inversion, although current thinking is this may be tough given persistent cloud cover thus far. A robust and dynamic wind field through the entire atmospheric column is helping to drive deep layer shear of 40-50 kts however effective shear for elevated parcels looses a good chunk of the lower directional and speed shear. If a surface parcel can be realized, nearly 30 kts of 0-1 km shear exists with a well curved elongated low level hodograph. With the above stated, well forced dynamics should result in increasing coverage of storms through the 654second half of the afternoon with likely a rapid transition to linear mode. Damaging wind gusts up to 60-70 mph seems the most likely threat with a 50 to 55 kt LLJ at 850 mb. Even less organized convection may be able to tap into this higher momentum air, especially while the boundary layer remains mixed during the daylight hours. Hail would be a secondary risk although again, elevated parcels lack a better effective shear profile. Any tornado threat would be conditional on realizing surface parcels and at this time seems low but should be monitored given the low level wind field. Any more organized bowing segment that can orient from northwest to southeast would also need to be monitored with 0-3 km shear vectors out of the SW AOA 30 kts Heavy Rain: PWATs around 1.25, and near the top of climatology, should provide for a period of heavy rain with the passage of the line of thunderstorms but with a warm cloud layer generally less than 10 kft and the progressive nature of any thunderstorms, any flash flooding threat should remain isolated and probably confined to urban areas. QPF amounts near and east of I-29 are a bit either side of 1-1.5 inches with HREF PMM suggesting pockets of up to 2-2.5 inches, more likely across NW IA. Given saturated soils as of late, renewed issues with ponding of water and river rises will be the more likely impact. Synoptic Wind: Aforementioned deepening surface low to the west will continue to provide for Advisory level wind gusts (45 mph or higher) into the early evening before decreasing BL mixing should result in a decreasing trend closer to sunset. Tonight: After storms exit to our east toward the midnight hour, the remainder of the overnight looks fairly benign. Tuesday and Wednesday: Vorticity ribbons pivot off the filling upper low into midweek. This will bring occasional rain chances with Wednesday currently appearing to be the focus as the main lobe shifts east. With the main upper low overhead, Wednesday would be a timeframe to monitor for slow moving storms capable of locally heavy rain as well at least some potential for low topped funnels. Thursday through Sunday: Transition to upper level northwest flow on the backside of the upper level trough will bring seasonal temperatures for the second half of the week with perhaps a few low chances for a light shower. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 713 PM CDT Mon May 6 2024 Lines of showers and thunderstorms will rotate across the forecast area through this evening. The thunderstorms are expected to push east of the I-29 corridor by 03Z-05Z, and east of the Highway 71 corridor by 05Z-07Z, though an area of showers may linger across southwest Minnesota into the pre-dawn hours of Tuesday. MVFR ceilings and MVFR-locally IFR visibility are expected with the showers and thunderstorms, becoming predominantly VFR behind the lingering showers. Additional stratocu will spread over the region from the northwest on Tuesday. While this is currently expected to be VFR, a brief period of MVFR ceilings is possible. Spotty light showers or an isolated thunderstorm is possible Tuesday afternoon, but chances are too low to include in the TAF at this time. The strongest of the southeasterly gusty winds should diminish with sunset, though occasional gusts over 30kt are still possible this evening. Speeds diminish further as a trough axis slides east behind the showers tonight. Southwest to west winds behind the trough will again increase after daybreak Tuesday with gusts 25-30kt common in most areas, perhaps up to 35kt near/west of the James River Valley. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && UPDATE... DISCUSSION...Kalin AVIATION...JH
Hazardous Weather Outlook National Weather Service Sioux Falls SD 205 PM CDT Mon May 6 2024 IAZ003-MNZ071-072-080-081-089-090-097-098-SDZ038>040-054>056-071915- Dickinson-Lincoln-Lyon-Murray-Cottonwood-Nobles-Jackson-Pipestone- Rock-Beadle-Kingsbury-Brookings-Miner-Lake-Moody- 205 PM CDT Mon May 6 2024 This Hazardous Weather Outlook is for northwest Iowa, southwest Minnesota and east central South Dakota. .DAY ONE...This afternoon and tonight. Thunderstorms will increase in coverage by late afternoon into the evening hours. These storms are expected to form into a line as they move eastward toward the I-29 corridor by early to mid evening. Damaging wind gusts to around 60 mph are expected to be the primary threat with a secondary risk of hail up to the size of quarters. Locally heavy rain is also possible. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Scattered showers and thunderstorms are possible Wednesday. Some of these storms may contain small hail, along with a potential for weak funnels. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Any severe weather reports are appreciated. IAZ001-002-012>014-020>022-031-032-NEZ013-014-SDZ050-052-053-057>071- 071915- Lyon-Osceola-Sioux-O'Brien-Clay-Plymouth-Cherokee-Buena Vista- Woodbury-Ida-Dixon-Dakota-Gregory-Jerauld-Sanborn-Brule-Aurora- Davison-Hanson-McCook-Minnehaha-Charles Mix-Douglas-Hutchinson- Turner-Lincoln-Bon Homme-Yankton-Union- 205 PM CDT Mon May 6 2024 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, northeast Nebraska, central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...This afternoon and tonight. Thunderstorms will increase in coverage by late afternoon into the evening hours. These storms are expected to form into a line as they move eastward toward the I-29 corridor by early to mid evening. Damaging wind gusts up to 70 mph are expected to be the primary threat with a secondary risk of hail up to the size of quarters. While not likely, a tornado cannot be ruled out. Locally heavy rain is also possible. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Scattered showers and thunderstorms are possible Wednesday. Some of these storms may contain small hail, along with a potential for weak funnels. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Any severe weather reports are appreciated.
Preliminary Local Storm Report
National Weather Service Sioux Falls SD
227 PM CDT Mon May 6 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1243 PM Non-Tstm Wnd Gst 2 NNW Huron 44.39N 98.23W
05/06/2024 M51 MPH Beadle SD ASOS
ASOS station KHON Huron Regional Airport.
&&The Sioux Falls radar (KFSD), 84 km away, was scanning. The volume nearest the first event began at 00:24 UTC.
3 thunderstorm wind. Local standard time, as filed.
Thunderstorm wind gust was measured by Iowa mesonet station RSYI4 near Sibley.
Significant roof damage to outbuildings was caused by thunderstorm wind gusts.
Part of the roof of the new car wash in Sutherland was ripped off by thunderstorm winds. Several homes also had large tree branches land on the roof.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2024Every state in 2024This day in weather historyWarnings in Iowa, May 2024
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: 1178093, 1178092, 1178090.