A frontal boundary was draped across Iowa northwest and central Iowa, roughly in a southwest to northeast orientation, providing a focusing mechanism for storms to initiate. Primarily, bouts of heavy rainfall resulted from storms beginning the evening of the 6th and continuing on through much of the night across northern Iowa.
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.
A frontal boundary was draped across Iowa northwest and central Iowa, roughly in a southwest to northeast orientation, providing a focusing mechanism for storms to initiate. Primarily, bouts of heavy rainfall resulted from storms beginning the evening of the 6th and continuing on through much of the night across northern Iowa. Greatest rainfall amounts exceeded 5 inches in Pocahontas county, while the majority of rainfall reports fell within the 2 to 4 inch range.
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 Sep 6, 2:34 AM CST, 2 hours 26 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 334 AM CDT Tue Sep 6 2016 .SHORT TERM.../Today/ Issued at 334 AM CDT Tue Sep 6 2016 Main concerns today on temps/humidity and precip chances. Elongated area of low pressure remains in place off to the west/northwest of the CWA with the sfc trough axis/meandering frontal boundary slowly sinking into the northern CWA today. Majority of activity has stayed off to the west/northwest thus far tonight closer to the frontal boundary and expect it to stay that way through much of the morning. Push of stronger theta-e advection remains across far northern IA and southern MN. WAA in place across the CWA today, and increasing humidity with dewpoints already in the 70s across the state and expected to increase a bit more today with the strong southwesterly to southerly flow in the low levels. This will push highs into the mid 80s to around 90 across the CWA, and resultant heat indices into the 90s to around 100. Slightly cooler conditions expected in the furthest northern tiers near MN where clouds and potential precip to keep temps cooler in the lower to mid 80s. A few storms may clip the northern/northwestern portions of the CWA through mid-morning, but then expect the activity to mainly be across MN into the early afternoon hours. Otherwise as boundary slowly sinks southward and the potential for an outflow boundary across the northern CWA from the AM convection could see some redevelopment toward mid/late afternoon across the northern CWA. Thus backed off on pops across the central/southern CWA and kept the higher pops toward late afternoon for the north. Deep layer shear still decent at around 40 kts which is more than we have seen for much of the convective season. CAPE of around 2500 to 3000 J/kg expected, therefore the severe potential still exists across the north. Wind still looks like the main severe threat for northern IA given the low level shear profile not the best for tornadic activity, and the deep layer shear suggesting more multicellular activity across IA. Hail somewhat concern given the CAPE/shear, however freezing levels higher and PWATs exceptional for this time of year, therefore find that a secondary threat as well with heavy rain a factor. .LONG TERM.../Tonight through Monday/ Issued at 334 AM CDT Tue Sep 6 2016 A large western U.S. trough will dominate our weather through the work week. Several lobes of vorticity will round the base of this trough and move over Iowa and surrounding states. The first such wave will move through late Wednesday, the second late Thursday, then the third and strongest around Friday or Friday night. A nearly stationary low-level frontal boundary draped across southern Minnesota down to central Nebraska is providing a focus for convection early this morning and will likely do so again tonight, but further southeast into northern and western Iowa. 500 mb height changes will be largely neutral tonight and low-level flow and shear are weak, but there is sufficient instability to justify a slight risk in these areas as outlined by SPC. There is also a significant magnitude of atmospheric moisture and most forecast models indicate the development of another nocturnal low- level jet and associated enhanced moisture transport, so there is some threat of heavy rainfall. However, steering flow will keep discrete cells moving at a good clip and the weak low-level flow will ensure progressive outflow boundaries somewhat mitigating a training threat. In addition, the antecedent conditions indicate that it will be very difficult for even heavy rainfall to result in significant impacts, especially falling in our flatter areas and not expected to be widespread in nature. Therefore no flood watches have been issued at this time. On Wednesday afternoon and evening as the aforementioned first shortwave rounds the base of the western U.S. trough it will kick off more thunderstorms across Iowa, with the surface front continuing to provide a focus mechanism. Synoptic forcing for ascent will be stronger during this time, but instability may be somewhat limited despite the peak heating time frame, depending on the degree of convective overturning from overnight and morning storms. The mid-level trough moving through will then cause the surface front to surge eastward and clear our area out by Thursday morning. A surface high pressure area will move quickly by on Thursday, providing sunny and cooler weather, however the second shortwave trough will then approach around Thursday evening. The GFS keeps any significant convection associated with this feature tied to the surface front will to our south across Missouri. However, the ECMWF and NAM retreat the boundary northward across Iowa and also develop storms northwest of the front, which is reasonable given the strong forcing associated with the shortwave. Confidence in these details is somewhat dependent on the evolution of the first system on Wednesday, but still feel 40-50 POPs are justified for Thursday evening/night. The third and most powerful vorticity maximum rounding the 500 mb trough will finally push it eastward and break the blocking pattern toward the end of the work week. This will cause what appears to be a true autumnal cold front to surge across Iowa around Friday night. Ahead of and along the front thunderstorms will be likely, especially if the timing lines up around peak heating on Friday afternoon/evening. It appears that instability may be somewhat seasonally limited, but the strong forcing associated with the mid/upper trough as well as robust flow fields would seem to support some severe weather threat, primarily in the form of straight-line winds. We will be monitoring this potential during the coming week. From Friday night through early next week, including the entire weekend, cool and mostly clear conditions are forecast. Meanwhile another western U.S. trough will rebuild by Monday and there are indications of another round of thunderstorms and strong frontal passage somewhere around next Tuesday. && .AVIATION.../For the 06Z TAFS through 06Z Tuesday night/ Issued at 1140 PM CDT Mon Sep 5 2016 Overall little change to previous package. Thunder chances increase toward 12z over the north with additional chances aft 16-18z over the north. Hires models now slowing the majority of the convection start until 21-00z north and potentially over the south after 00z or later. Confidence on the evolution remains low. Once storms become more widespread...chances for some severe and low vsby very possible due to heavy rainfall. Winds will be SW with gusts to 25 mph. Brief period of llws over the north through 11z north sites. /rev && .DMX WATCHES/WARNINGS/ADVISORIES...None. && SHORT TERM...Beerends LONG TERM...Lee AVIATION...rev
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 522 AM CDT TUE SEP 6 2016 IAZ004>007-015>017-023>028-033>039-044>048-057-058-071100- 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-AUDUBON-GUTHRIE- 522 AM CDT TUE SEP 6 2016 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS ARE LIKELY AT INTERVALS TODAY AND TONIGHT. SEVERE WEATHER MAY BE POSSIBLE AT TIMES...WITH LARGE HAIL AND STRONG WINDS THE PRIMARY THREATS. A FEW AREAS OF HEAVY RAINFALL ARE ALSO EXPECTED AND MAY LEAD TO LOCALIZED FLASH FLOODING. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THUNDERSTORMS WILL REMAIN LIKELY ON WEDNESDAY BEFORE ENDING WEDNESDAY NIGHT. A FEW OF THESE STORMS COULD BE STRONG TO SEVERE WITH GUSTY WINDS THE PRIMARY THREAT. ADDITIONAL THUNDERSTORMS ARE FORECAST BETWEEN THURSDAY NIGHT AND FRIDAY NIGHT...AND AGAIN AROUND NEXT MONDAY. THE SEVERE WEATHER THREAT IS UNCERTAIN AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED TUESDAY AFTERNOON THROUGH WEDNESDAY. IAZ060-071100- POLK- 522 AM CDT TUE SEP 6 2016 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT HEAT INDEX VALUES WILL TOP OUT AROUND 100 DEGREES THIS AFTERNOON. THUNDERSTORM CHANCES WILL RETURN TO THE FORECAST TONIGHT. A FEW STORMS COULD BE STRONG TO SEVERE WITH GUSTY WINDS THE PRIMARY THREAT. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THUNDERSTORMS WILL REMAIN LIKELY ON WEDNESDAY BEFORE ENDING WEDNESDAY NIGHT. A FEW OF THESE STORMS COULD BE STRONG TO SEVERE WITH GUSTY WINDS THE PRIMARY THREAT. ADDITIONAL THUNDERSTORMS ARE FORECAST BETWEEN THURSDAY NIGHT AND FRIDAY NIGHT...AND AGAIN AROUND NEXT MONDAY. THE SEVERE WEATHER THREAT IS UNCERTAIN AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT ANTICIPATED. IAZ049-050-059-061-062-070>075-081>086-092>097-071100- MARSHALL-TAMA-DALLAS-JASPER-POWESHIEK-CASS-ADAIR-MADISON-WARREN- MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR- RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 522 AM CDT TUE SEP 6 2016 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT THUNDERSTORM CHANCES WILL RETURN TO THE FORECAST TONIGHT. A FEW STORMS COULD BE STRONG TO SEVERE WITH GUSTY WINDS THE PRIMARY THREAT. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THUNDERSTORMS WILL REMAIN LIKELY ON WEDNESDAY BEFORE ENDING WEDNESDAY NIGHT. A FEW OF THESE STORMS COULD BE STRONG TO SEVERE WITH GUSTY WINDS THE PRIMARY THREAT. ADDITIONAL THUNDERSTORMS ARE FORECAST BETWEEN THURSDAY NIGHT AND FRIDAY NIGHT...AND AGAIN AROUND NEXT MONDAY. THE SEVERE WEATHER THREAT IS UNCERTAIN AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT ANTICIPATED. LEE
The national radar mosaic for the moment the first event began.
17 heavy rain, 1 flood. Local standard time, as filed.
CoCoRaHS observer reported heavy rainfall of 2.34 inches over the last 24 hours. Most of which came down in the evening and overnight.
Algona AWOS measured 2.98 inches of heavy rainfall over the last 24 hours.
Mason City ASOS measured 2.87 inches of heavy rainfall over the last 24 hours.
Forest City AWOS measured 2.08 inches of heavy rainfall over the last 24 hours.
Trained spotter measured 1.98 inches of heavy rainfall over the last 24 hours.
CoCoRaHS observer reported heavy rainfall of 2.02 inches over the last 24 hours.
CoCoRaHS observer reported heavy rainfall of 3.46 inches over the last 24 hours.
Coop observer reported heavy rainfall of 2.68 inches over the last 24 hours.
Coop observer reported heavy rainfall of 2.70 inches over the last 24 hours.
CoCoRaHS observer reported heavy rainfall of 2.15 inches over the last 24 hours.
Trained spotter reported heavy rainfall of 2.70 inches over the past 24 hours.
Trained spotter reported heavy rainfall of 3.06 inches of rain since Tuesday evening. Spring Creek reported to be rising over bank full.
Public reported storm total heavy rainfall of 3.50 inches since Tuesday night.
Trained spotter reported heavy rainfall of 2.42 inches storm total since Tuesday night.
Public reported heavy rainfall of 4.20 inches.
Public reported an estimated 5.7 inches of heavy rainfall about 2 miles north of Plover.
Public reported storm total heavy rainfall of 4.5 inches since Tuesday night.
Public reported water, a couple inches deep, gradually overflowing from field across 200th Ave, just north of the 200th St and 200th Ave intersection. Roughly 1 mile north of St. Benedict.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2016Every state in 2016This day in weather historyWarnings in Iowa, September 2016
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: 657998, 658000, 658001, 658003, 658004, 658005, 658006, 658007, 658008, 658009, 658015, 657997, 658013, 658010, 658011, 657999, 658012, 658014.