Convection percolated along a warm front across the area through the morning. By afternoon, storms re-strengthened as as daytime heating helped enhance instability.
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 DMX wrote it up.
Convection percolated along a warm front across the area through the morning. By afternoon, storms re-strengthened as as daytime heating helped enhance instability. Despite good instability with MLCAPE over nearing 2000 J/kg, lapse rates were modest and speed shear was weak. Despite this, directional shear was good and when combined with instability for brief stretching, allowed for a number of weak and short-lived tornadoes to develop. While 13 tornadoes occurred, they were confined to two small areas in Iowa where storms trained, resulting in several storms over the same locations. In addition, the training storms made for pockets of heavy rain with three to four inches or more of rain. This did result in flash flooding in Pocahontas County with impacts to homes and businesses.
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 Des Moines, IA wrote its last area forecast discussion before the first event at May 12, 5:40 PM CST, 10 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 640 PM CDT Fri May 12 2023 ...Updated for the 00z Aviation Discussion... .DISCUSSION.../Tonight through Friday/ Issued at 305 PM CDT Fri May 12 2023 Key Messages: -Severe Weather in Southwest Iowa This Evening, Threat Diminishing As Storms Track East -More Severe Weather Possible in North Central Iowa Tomorrow -Cooler Sunday and Monday with Quieter Weather to Start Next Week A surface low in western Nebraska continues to creep north and east and its associated warm front will be the focal point for convection this afternoon and evening. This convection has already begun to initiate in east central Nebraska and will slowly track north and east towards southwest IA this evening. According to the SPC mesoanalysis page, the southwest IA/eastern NE area is primed with high amounts of surface based instability, with widespread values from 2000 to 3000 J/kg. In addition to the instability, there will be a fair amount of 30 to 40 kt bulk wind shear in the effective inflow layer. This, in addition to curved hodographs and effective SRH in the 100 to 200 range, indicates supercellular development which could produce large hail, gusty winds and a few tornadoes. As storms congeal into a line along the boundary, they may also be capable of producing QLCS tornadoes. As mentioned in the previous discussion, 30 to 35 kts of line normal 0 to 3km shear and strong 0 to 3km CAPE of 200+ J/kg will help promote vorticity stretching in any surface based storms. However, the catch to this severe threat is the "surface based" part. The ingredients present suggest a tornado threat, which will be true in eastern Nebraska and far southwest IA. However, as storms start to make their way into our CWA, they will begin to outrun the surface boundary into relatively cooler air. Similarly, the timing for storms entering Iowa will be around and after sunset, so the surface will be cooling and an inversion will begin to set in. When this happens, the storms will become elevated and lose some of their larger-scale kinematic support. Therefore, the severe threat in our CWA will likely be confined to our southwestern counties this evening with a diminishing threat further north and east into central IA. However, some elevated instability will still be in place through the night and short range guidance continues to indicate a branch of this convection persisting throughout our area in the overnight hours. Looking ahead to Saturday, the surface front will have made its way further north in Iowa and will again light up with convection in the afternoon as the boundary layer mixes, surface flow picks up and instability increases. This severe threat will impact a larger area of our CWA, as indicated by the Slight Risk (level 2 out of 5) of severe weather issued by the SPC earlier today in north central Iowa. Tomorrow's storms may look similar to those out in central Nebraska today where stout surface based instability will combine with large amounts of shear/vorticity along the surface boundary, allowing for tornadoes to develop along it. However, while our setup will be similar to that in Nebraska's today, they wont be identical. While there will be good veering of winds with height along the boundary, the associated low pressure is weakening and flow will be slightly weaker. This will make it slightly more difficult to spin up a tornado than what they are seeing out west where flow around the low pressure is stronger. Regardless, strong 0 to 3km CAPE will attempt to compensate for this weaker flow and tornadoes will remain possible along the boundary in central Iowa tomorrow. Hail will also be a threat tomorrow, especially with elongated hodographs and moderate instability. A secondary threat tomorrow will be training storms in northern Iowa along the surface boundary bringing some locally heavy rainfall to these areas. Flooding does not appear to be a risk at the moment with rivers near normal flow and fairly dry conditions, however, some localized impacts remain possible. After the storms on Saturday, the surface low will make it's way overhead bringing cooler temperatures to the state on Sunday. Highs will be in the 60s and 70s Sunday and Monday but quickly rebound to the 70s and 80s by mid-week. The passage of this low will also mark the start of a quieter and drier period through the beginning of next week as an upper level ridge develops over much of the US. && .AVIATION.../For the 00Z TAFS through 00Z Saturday evening/ Issued at 640 PM CDT Fri May 12 2023 Main aviation concerns will be timing the arrival of showers and storms as they move from Nebraska into Iowa and weaken overnight along with lowering ceilings. Have timed a prevailing group for SHRA/VCTS for western terminals and will adjust eastern terminals at 6z issuance. After showers and/or storms end, will have some lingering MVFR and perhaps higher end IFR in a few places into Saturday morning with some clearing at the southern sites. Additional showers and storms are expected to develop in the afternoon over at least northern Iowa and have handled that with VCSH mention. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && DISCUSSION...Dodson AVIATION...Ansorge
Hazardous Weather Outlook National Weather Service Des Moines IA 309 PM CDT Fri May 12 2023 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-132015- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene- Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper- Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union- Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne- Appanoose-Davis- 309 PM CDT Fri May 12 2023 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight A few strong to severe storms will be possible this evening and tonight, mainly west of Interstate 35. Primary threats will be for large hail and damaging winds. Tornado threat remains low. .DAYS TWO THROUGH SEVEN...Saturday through Thursday Another chance for strong to severe storms arrives on Saturday, mainly across the NE half of the state during the afternoon and evening, with a primary threat for a few tornadoes. Large hail and damaging winds possible too. .SPOTTER INFORMATION STATEMENT... Spotters may be needed at times late Friday through Saturday. CURTIS
The Des Moines radar (KDMX), 155 km away, was scanning. The volume nearest the first event began at 23:48 UTC.
16 tornado, 11 heavy rain, 1 hail, 1 flash flood. Local standard time, as filed.
A 24 hour total of 6.90 inches of rain, with 3.5 inches of that occurring in the last one hour.
Storm Chaser has video of the weak tornado passing across rural portions of Warren county. Some minor tree damage occurred. This tornado then proceeded into Marion county.
This tornado entered into Marion county from Warren county. The tornado was captured on video by several storm chasers. Some minor tree damage occurred with this tornado as it remained in rural Marion county.
Over three inches of rain with standing water and street flooding in town.
Brief tornado captured on video by a storm chaser northeast of Schaller. Tornado remained in open crop field with no impacts to damage indicators, hence the EFU rating.
Storm total of 4.22 inches.
Storm total of 3.28 inches.
Brief tornado captured on imagery and reported by a storm chaser. Tornado did not impact any damage indicators, hence the EFU rating.
Report from KNIA radio of quarter inch hail occurring at their studio.
Another brief tornado which produced minor damage to an outbuilding and a hoop building. The tornado was captured on video by a storm chaser.
Tornado was captured on video by storm chasers. Some minor EF0 tree damage occurred with this tornado prior to lifting northwest of Harvey.
Intermittent tornado with well developed funnel on video from storm chaser. No damage indicators were impacted, hence the EFU rating.
Brief tornado reported by storm chaser southwest of Fonda. No damage indicators were impacted, therefore the EFU rating.
Brief tornado east of Scranton captured by storm chaser. Tornado remained in open fields with no impact to damage indicators, hence the EFU rating.
Storm total of 4.67 inches.
Storm total of 3.30 inches thus far, rain still falling.
Storm total of 4.25 inches.
Storm total of 4.95 inches.
Storm total of 2.96 inches.
Storm total of 4.67 inches.
Storm total of 2.69 inch of rain thus far, rain still falling.
Brief tornado reported by storm chaser. No damage indicators were impacted, hence the EFU rating.
Tornado developed east of Pomeroy and moved north passing into Pocahontas county shortly after forming. The tornado remained in open fields in Calhoun county and did not impact any damage indicators, hence the EFU rating for this portion of the path.
Tornado developed east of Pomeroy and moved north from Calhoun into Pocahontas county. Upon entering Pocahontas county, the tornado produced some damage to grain bins and an outbuilding. The remainder of the path was over open cropland.
Brief tornado caught on video northwest of Pocahontas. It appears no damage indicators were impacted, hence the EFU rating.
A brief tornado occurred north of Highway 5 captured by many chasers. There was some tree damage produced by the tornado before dissipating.
A brief tornado was sighted by law enforcement passing across open farmland. No damage indicators were impacted, hence the EFU rating.
Brief tornado that remained in open cropland. No damage indicators were impacted, hence the EFU rating.
Delayed report of extensive flooding in town. Water up against some homes and businesses in town. Time estimated.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2023Every state in 2023This day in weather historyThe tornado archive for Iowa, 2023Warnings in Iowa, May 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: 1092796, 1090046, 1090049, 1092795, 1090053, 1092799, 1092800, 1090056, 1092794, 1090058, 1090061, 1090069, 1090071, 1090073, 1092805, 1092798, 1092801, 1092802, 1092803, 1092804, 1092797, 1090075, 1090077, 1090079, 1090080, 1090081, 1090083, 1090084, 1092806.