A large and unseasonably warm system brought showers and thunderstorms to the state. Over an inch of rain fell across much of Iowa.
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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.
A large and unseasonably warm system brought showers and thunderstorms to the state. Over an inch of rain fell across much of Iowa. In northern Iowa, this was on top of a snowpack of two to four inches. The quick rain on top of frozen group resulted in runoff sufficient to send the Winnebago River at Mason City into minor river flooding. The river exceeded minor flood stage and quickly crested the morning of February 27th before falling back below flood stage the morning of February 28th.
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 Feb 27, 3:23 AM CST, 1 hour 7 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 323 AM CST Mon Feb 27 2023 .DISCUSSION.../Today through Sunday/ Issued at 323 AM CST Mon Feb 27 2023 Key messaging highlights: * Moderate rains diminishing by mid morning * Breezy conditions central and south today * Light rain or snow chances late Tue, and again Thu night As expected, widespread light to moderate rain is in progress early this morning, driven mainly by kinematic forcing from upper level diffluence and cyclonic differential vorticity advection ahead of the noted KS PV anomaly, and plenty of moisture transport. The baroclinicity isn't too strong with what is left mainly to our north, but the kinematic support and 50-70kts of 300K moisture laden flow more than make up for that. There is some frontogenetic support around 700mb northeast on the nose of elevated instability, but that forcing should exit soon. The severe weather potential looks minimal this morning. There are 500-1000 j/kg elevated CAPEs rooted around 1km but effective shear is weak and hodographs above that point are not too impressive. The inversion is currently saving us from bad things (QLCS tornadoes) with 0-1km SRH and streamwise ingest very impressive. There does appear to be a brief inflection where convection may be rooted lower southeast 11-12z or so, roughly aligned with recent convective development in northeast KS, but that window appears small and the proximity of the upper low creates unfavorable hodographs and winds aloft for much organization. The current small linear feature on radar will likely exit the forecast area before this occurs with 09z obs still showing 48-50F T/Td downstream. Precip amounts may end up within previous 1-2" expectations, but likely not the high end of that range. There will be little in the way of locally higher amounts with more stratiform precip and stronger convective elements lacking for the most part. The precipitation should diminish later this morning and end altogether with gusty winds becoming the main weather story. Advisory criteria winds are not anticipated, but shallow mixing will likely produce 30-40 mph gusts central and south before diminishing into sunset. Our pattern will transition to fast, zonal flow into the middle of the week with a short wave into the Mid MO Valley late Tuesday bringing chances for light rain or light snow into at least the evening, mainly north. The forcing and deeper moisture do not really phase too well however so this precip window seems a little disjointed right now. Later in the week a trough will deepen through the southern Plains and likely track through the Mid MS Valley. 00Z EC and GFS deterministic solutions keep nearly all the precip to our south, where a substantial precip event will likely occur. However both ensembles do suggest more of a northern trend is still in play. Mean precip appears overly weighted by several high end members, but the more tempered median output still suggests chances as well southeast. The outlook for next weekend currently looks dry with warmer temperatures, as the pattern goes back to either fast zonal flow or weak ridging. && .AVIATION.../For the 06Z TAFS through 06Z Monday night/ Issued at 1141 PM CST Sun Feb 26 2023 LIFR cigs expected to persist overnight with moderate rain. High confidence in thunderstorms for southern terminals overnight. Low confidence in thunderstorms at KOTM after 12z, but left out of TAF. Accompanying fog will reduce vsbys. Low pressure will pass over area after 10z, quickly turning winds to northwesterly within a few hours. Winds will then become gusty reaching 30 kts at times in the afternoon hours. IFR/LIFR cigs expected to prevail through the TAF period with improvement possible near the end of the TAF period. && .HYDROLOGY... Issued at 323 AM CST Mon Feb 27 2023 There has been little change in river flooding expectations, but confidence remains low due previous QPF going into river forecasts possibly a bit high, but on the other side frost still enhancing runoff, even this far south. Our evening frost depth observation noted the top three inches thawed, but still five inches of frozen ground from three to eight inches. This will all be re-evaluated by RFCs with the morning model runs, but expectations are still for plenty of within bank rises, Action to nearly Flood Stage rises at several locations mainly north, and one or two possibly getting just to Flood Stage including at Black Hawk Cr/Hudson where a Flood Watch for minor flooding remains in effect. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && DISCUSSION...Small AVIATION...Small/Jimenez HYDROLOGY...Small
Hazardous Weather Outlook National Weather Service Des Moines IA 320 AM CST Mon Feb 27 2023 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-280930- 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- 320 AM CST Mon Feb 27 2023 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Isolated thunderstorms will occur early this morning, mainly over the southern and eastern half of Iowa. The probability of severe weather is low. Unseasonably high rainfall accumulations will lead to ponding water and modest rises on area streams and rivers early this week. Strong northwest winds will develop during the day today, with gusts to 30 to 40 mph expected by the afternoon. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed. Lee
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
River entered flood state at 430am LST on the 27th of February, crested at 11.24 ft at 630am LST on February 27th, and fell below flood stage at 430am LST on February 28th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2023Every state in 2023This day in weather historyWarnings in Iowa, February 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: 1081129.