Nocturnal elevated thunderstorms developed due a strong low-level jet and steep mid-level lapse rates, with some spotty large hail in far southeast South Dakota. Farther north and east, storms weakened but developed a large stratiform region of rain, under which the strong synoptic flow was allowed to accelerate with areas of damaging wind gusts well away from storm updrafts.
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The episode as NWS FSD wrote it up.
Nocturnal elevated thunderstorms developed due a strong low-level jet and steep mid-level lapse rates, with some spotty large hail in far southeast South Dakota. Farther north and east, storms weakened but developed a large stratiform region of rain, under which the strong synoptic flow was allowed to accelerate with areas of damaging wind gusts well away from storm updrafts.
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 Apr 15, 9:36 PM CST, 5 hours 9 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Sioux Falls SD 1036 PM CDT Mon Apr 15 2024 .KEY MESSAGES... - High confidence in rainfall arriving tonight and continuing through Wednesday morning. Widespread amounts between 1.0 to 2.5 inches are expected, with isolated pockets of 3+ inches also possible. - Rainfall rates could exceed 1 inch per hour at times, which may result in isolated to scattered flash flooding in urban and low lying areas. - Isolated to scattered severe thunderstorms will be possible tonight and Tuesday afternoon. The greatest threat with the strongest storms will be large hail. - More precipitation chances (30%-70%) return Wednesday night into Thursday mostly south of I-90. - The breezy conditions will continue along with more seasonal conditions from the midweek into the weekend. && .DISCUSSION... Issued at 251 PM CDT Mon Apr 15 2024 CURRENT: Dry and breezy conditions continue across the region, with latest observations showing southeasterly winds gusting between 25 to 35 MPH and temperatures in the 70s. Relative humidity values have plummeted quite a bit this morning, with values largely in the teens to lower 20s. As such, the Red Flag warning remains in good shape and will remain valid until 8 PM. TONIGHT: Sfc warm front and low pressure lift northeastward across Nebraska this evening, causing showers and storms to return to the forecast. Similar to days past, latest CAMs continue to slow the arrival time ever so slightly, with most supporting initiation along the Missouri River near/shortly after 7 PM. With a stout LLJ overhead, have ample bulk layer shear (40+ kts) to work with in addition to increasing low level moisture. However, latest soundings still show a decent cap in place, suggesting that most if not all of these storms will remain elevated in nature. Near 03Z, should see MLCAPE approach 1000-1500 J/kg along the MO River Valley, with mid level lapse rates between 7.5-8 degC/km, and DCAPE values near 1000 J/kg. Thus, as highlighted in SPC's Latest Day 1 Outlook, expect large hail (2+) to be the primary hazard initially - especially in the Enhanced Risk (Level 3 of 5). As storms grow further upscale, upper level forcing begins to wane, so would expect hail size to lessen to the size of ping pong balls or smaller. Damaging winds in excess of 50+ MPH and an isolated tornado or two also remain possible. Given that these storms look to take place during the evening and overnight period, we strongly encourage you to have a way to receive warnings in the event that storms become severe! TUESDAY: Widespread rain chances (>80%) are expected heading into Tuesday and the aforementioned sfc low moves over NE/SD border. Easterly winds are expected to remain breezy during this time, especially along and east of the James River, with gusts between 30 to 45 MPH still possible. May even see some locations east of I-29 approach 50 MPH at times as the SPG tightens overhead. For now, have opted to forgo any wind headlines. Will allow the coming shifts to evaluate model trends and issue as necessary - so continue to monitor for updates. Sfc low pressure moves overhead by Tuesday afternoon, resulting in some lulls in precipitation thanks to the dry-slot. While tomorrow's severe weather threat remains highly conditional on if we can destabilize again after the morning convection - latest CAMs do show another line of convection across NW Iowa and SW Minnesota during the afternoon as the triple point lifts over the SD/IA border. With the current dynamics in place, would expected elevated hailers to be the primary hazard again, with damaging wind gusts and isolated tornadoes being a secondary threat. Lastly, in regard to rainfall totals, expect widespread amounts between 1 to 2.5 inches across our area, with isolated pockets of 3+ inches also possible. WPC's latest Day 1 Outlook has introduced a Slight Risk (Level 2 of 4) to portions of our area, mainly along and north of the MO River Valley to I-90. As such, could see rainfall rates exceed 1 inch per hour at times, which may result in isolated to scattered flash flooding in urban and low lying areas. Ponding would be expected in areas elsewhere. River rises are also expected with locations most at risk of approaching flood stage being smaller streams/creeks and the upper Little Sioux River between Milford and Spencer. WEDNESDAY - THURSDAY: Heading into the extended period, any lingering precipitation chances will continue to push to the northeast with the surface low by Wednesday morning. Quieter conditions will temporarily return from the late morning onwards as a mid- level ridge moves into the region. However, northwesterly surface winds will increase as the SPG tightens with gusts between 30-40 mph expected. This along with lingering cold air advection aloft will lead to a slightly cooler conditions compared to the previous day with highs expected to peak in the mid to upper 50s and lower 60s. Otherwise, more precipitation chances (30%-70%) will likely return from Wednesday afternoon into Thursday as a weak mid-level wave interacts with a developing surface low over Nebraska and Kansas. While the better rain chances will certainly be south of I-90, most ensemble guidance continues to show the highest confidence (50%-80%) along and south of the Hwy-18 corridor with at least a tenth of QPF or greater expected at time. Nonetheless, the precipitation chances will likely continue into the early afternoon hours on Thursday before pushing southeastwards with the cold front. FRIDAY - SUNDAY: Looking into the start of the weekend, much quieter conditions return as broad troughing continues to progress across the northern plains. Northwesterly surface flow along with lingering cold air advection (CAA) aloft will continue to gradually decrease our overall temperatures through Saturday with daily highs sitting in the upper 40s to low 50s across the area. Things could potentially begin to trend warmer from Saturday night onwards as a surface high builds in behind a departing shortwave. A switch to southerly flow along with increased warm air advection (WAA) aloft will lead to a gradual increase in temperatures with highs gradually increasing from the mid to upper 50s on Sunday to the low to mid 60s by Monday. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1025 PM CDT Mon Apr 15 2024 Scattered convection is expected to begin to develop as mid-lvl moisture and deep lift finally arrives to the area. Some of this convection may bring a risk for small hail at times, though the biggest risk will be heavy rain. Ceilings will remain VFR through daybreak, but then may begin to fall as the upper low approaches mid-morning. Periods of visibility in heavy rain may be reduced to 2-3 miles at times. The upper low crosses the Tri-State area by mid-day, producing a wide array of winds throughout the area. Scattered showers may redevelop in the afternoon with a high probability of MVFR or locally lower ceilings at times into the evening. && .FIRE WEATHER... Issued at 251 PM CDT Mon Apr 15 2024 Red Flag conditions continue across the region, with latest observations showing temperatures in the mid to upper 70s with southeasterly winds gusting between 35 to 45 MPH. Relative humidity values as a result have plummeted into the teens to lower 20s. Thus, believe the current headline remain in good shape and will remain valid until 8 PM. We strongly encourage you to exercise caution with any activity that may cause a spark, as fires can spread quickly under these conditions! && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && DISCUSSION...SST/Gumbs AVIATION...Dux FIRE WEATHER...SST
Hazardous Weather Outlook National Weather Service Sioux Falls SD 706 PM CDT Mon Apr 15 2024 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-170015- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson- Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-Brookings-Gregory- Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook- Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton- Union- 706 PM CDT Mon Apr 15 2024 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...Tonight. Elevated fire danger will persist through the evening hours as humidity slowly increases along with persistent gusty southeast winds gusting to 35-40 mph. A strong low pressure system will begin to impact the area this evening. Showers and thunderstorms are possible, with those counties along the Missouri River at the highest risk for severe weather. The most likely threat from these storms are large hail up to 1.5 inches and damaging wind gusts. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Showers and thunderstorms progress northeastward Tuesday morning, bringing more chances for strong to severe thunderstorms. A secondary line of thunderstorms is possible late Tuesday morning. This line is expected to impact areas east of I-29. The greatest threat with these storms are again large hail up to 1.5 inches, damaging wind gusts, and a low chance for a tornado or two. A widespread half inch to two inches of rain is expected by Wednesday, along with isolated amounts of 2+ inches. Be sure to continue to monitor the forecast for updates. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
Preliminary Local Storm Report
National Weather Service Sioux Falls SD
341 AM CDT Tue Apr 16 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0207 AM Hail 1 SE Elk Point 42.67N 96.67W
04/16/2024 E1.25 Inch Union SD Public
Report from mPING: Half Dollar (1.25 in.).
&&The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
Wake low winds were periodically sustained around 40 mph and gusted as high as 64 mph at Iowa Road Weather Information System site RSYI4 near Sibley.
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, April 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: 1178016.