A closed upper low lifted out to the west of Iowa with the surface low tracking northeast to near the Iowa-South Dakota border. A warm front extended southeast into Iowa and lifted north as the dry line pushed into western Iowa during the afternoon.
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 closed upper low lifted out to the west of Iowa with the surface low tracking northeast to near the Iowa-South Dakota border. A warm front extended southeast into Iowa and lifted north as the dry line pushed into western Iowa during the afternoon. The synoptic situation was fairly classic. The atmosphere was relatively unstable, though cloudiness limited that somewhat. CAPE values rose to 1500 to 2000 J/kg with a lifted index around -7 at the storms initiation. Downdraft CAPE was only 300 J/kg. There was 45 to 50 kts of effective shear however. CAPE in the -10 to -30 C layer was around 500 J/kg, with a freezing level around 12,000 feet. The parameters were favorable for potential tornado development with the LCL only 750 meters and 50 to 100 J/kg of CAPE in the zero to 3 km layer with steep lapse rates. Thunderstorms formed in an arc across western Iowa and quickly produced gusty winds and small hail. The cells tracked north as the line lifted northeast. Numerous reports of tornadoes were received. The reports were from the same tornado. Debris was reported with the tornado in Carroll County. Damage as done in the Lake City area of Calhoun County by a tornado, reported to be 1/4 mile wide by then. The tornado touched down northwest of Lidderdale and tracked northeast, striking the west side of Lake City. The tornado continued passing through rural Calhoun County and hit some power poles on the west side of Rockwell City before lifting about 2 miles north of Rockwell City in rural Calhoun County. Much of the damage included leaning power poles, tree damage and uprooted trees. In the town of Lake City, the roofing material was removed from the High School, and the roof was removed from a double-wide manufactured home and a warehouse building north of town. The tornado was of EF1 strength with winds of 100 MPH. The track was 23.5 miles long. Additional thunderstorms produced hail and high winds. An 80 MPH wind gust was reported west of Glidden, a machine shed was destroyed in Audubon County, and a weak shed was blown over in Cass County. Winds were measured at 65 MPH in Pocahontas. A strong storm moved through the Lake City area following the tornado and produced baseball size hail and destroyed a farm outbuilding west of Lidderdale.
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 10, 5:31 PM CST, 39 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 631 PM CDT SUN MAY 10 2015 .SHORT TERM /TONIGHT/... ISSUED AT 211 PM CDT SUN MAY 10 2015 STRONG TO SEVERE STORMS ONGOING AT TIME OF AFD ISSUANCE. LOW PRESSURE LOCATED OVER SE SOUTH DAKOTA MAIN SYNOPTIC SCALE DRIVER FOR SHORT TERM WX. WARM FRONT ATTACHED TO THIS LOW SERVES AS FOCUSING MECHANISM FOR AFTERNOON/EVENING SEVERE WX. COLD FRONT ATTACHED TO THIS LOW WILL SERVE AS FOCUSING MECHANISM FOR ROUND 2 OF STORMS TONIGHT. SYNOPTIC SCALE FORCING STRONGEST IN THE WESTERN PORTION OF OUR CWA. 30 KT LLJ PUSHING THROUGH FROM SW TO NE. ASCENT REGION OF 300 MB JET OVER NW CWA THROUGH 06Z MON PUSHING EASTWARD WITH THE LOW AND ITS ATTENDANT COLD FRONT. IN THE MESOSCALE...BEST TORNADO THREAT LIES WITH THE WARM FRONT...WHICH SHOULD BE NEAR DES MOINES BY 23Z OR SO. BULK SHEAR VALUES APPROACH 50 KTS...HELICITY VALUES BETWEEN 100 AND 200 SUPPORT...LCL HEIGHTS OF 750M ALL SUPPORT TORNADOES WITH SUPERCELLS. FOR ROUND 2...TORNADO PARAMETERS WILL BE EAST OF CWA. DCAPE VALUES STILL LOOK TO BE IN THE 1000 J/KG RANGE. COUPLING THIS WITH GENERAL IA NOCTURNAL TRENDS...WOULD EXPECT DAMAGING WINDS TO BE BIGGEST THREAT. SATELLITE PICKING UP ON A VERY WELL-DEFINED CLEAR SLOT INTO NEBRASKA. EXPECTING THIS CLEAR SLOT TO COME IN BEHIND THE COLD FRONT FOR A FEW HOURS MON MORNING...AND THEN ST DECK TO RETURN TOWARDS THE END OF AND SLIGHTLY BEYOND THE END OF THE SHORT TERM FCST PERIOD. LOCATIONS THAT RECEIVE HEAVIER RAINFALL MAY EXPERIENCE PERIODS OF FOG MONDAY MORNING. .LONG TERM /MONDAY THROUGH SUNDAY/... ISSUED AT 211 PM CDT SUN MAY 10 2015 MAIN FORECAST CONCERN DEALT WITH TEMPERATURES THROUGH MID-WEEK AND WITH ADDITIONAL THUNDERSTORMS CHANCES BY THURSDAY INTO NEXT WEEKEND. LEANED TOWARD A BLEND OF THE GFS/ECMWF DUE TO UNCERTAINTY IN TIMING WITH SYSTEM ON THURSDAY. MONDAY THROUGH WEDNESDAY...STRONG CAA DEVELOPS THROUGHOUT THE DAY MONDAY WITH WINDS ATOP THE MIXED LAYER NEAR 35-40 KNOTS BY 21Z. CERTAINLY BORDERLINE WIND ADVISORY WEST OF INTERSTATE 35 AND INCREASED SUSTAINED WINDS/GUSTS DURING THE AFTERNOON HOURS TOMORROW. NO MAJOR CHANGES WITH ONGOING MAX TEMP FORECAST. MAY SEE A FEW SHOWERS DEVELOP ACROSS THE NORTH WITHIN THE CAA REGIME AND ENOUGH MOISTURE IN THE MID-LEVELS TO SQUEEZE OUT A FEW DROPS. LOW CONFIDENCE WITH ANY SIGNIFICANT PRECIP AMOUNTS AND ONLY LEFT SLIGHT POPS GOING. SURFACE HIGH PRESSURE BUILDS INTO THE REGION MONDAY NIGHT AND DOMINATES THE WEATHER PATTERN THROUGH THURSDAY. THURSDAY THROUGH SATURDAY...ZONAL FLOW ALOFT BEGINS TO TRANSITION TO SOUTHWEST FLOW BY THURSDAY. ECMWF IS ROUGHLY 12 HOURS QUICKER WITH NEXT 500MB SHORTWAVE TO CUT ACROSS THE STATE THURSDAY. GFS LAGS BEHIND AND BRINGS IT ACROSS BY LATE THURSDAY EVENING. TIMING OF THIS SHORTWAVE WILL DETERMINE SEVERE WITH THE ECMWF LEANING TOWARD HIGHER POTENTIAL FOR SEVERE. ANOTHER STRONG UPPER LOW PROJECTED VIA ECMWF/GFS LATE IN THE WEEKEND WITH THE GFS FURTHER NORTH AND THE ECMWF SLIGHTLY FASTER. STILL...THIS SYSTEM LOOKS TO BE THE NEXT BEST CHANCE FOR SEVERE WEATHER. && .AVIATION...11/00Z ISSUED AT 630 PM CDT SUN MAY 10 2015 MAIN CONCERNS OVERNIGHT WILL BE LINGERING THUNDER CHANCES AND WINDS ALONG WITH CIGS. HAVE TIMED STORMS TO PASS THROUGH AREA PRIOR TO 06Z WITH MOST OF THE STRONGER STORMS SOUTH OF US20. CIGS WILL VARY FROM VFR TO BRIEF IFR THROUGH 06Z...THEN MFVR TO VFR THROUGH THE REMAINDER OF PERIOD. AS STRONG LOW PULLS EAST...GUSTY WEST WINDS WILL DEVELOP WITH SUSTAINED 15-20KTS BECOMING GUSTS 30 KTS AFT 15Z MONDAY MOST AREAS./REV && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...KOTENBERG LONG TERM...PODRAZIK AVIATION...REV
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 449 PM CDT SUN MAY 10 2015 IAZ004-015-023-033-034-044>046-057-058-070-071-081-082-092-093- 112200- EMMET-PALO ALTO-POCAHONTAS-SAC-CALHOUN-CRAWFORD-CARROLL-GREENE- AUDUBON-GUTHRIE-CASS-ADAIR-ADAMS-UNION-TAYLOR-RINGGOLD- 449 PM CDT SUN MAY 10 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT ISOLATED TO SCATTERED STRONG TO SEVERE STORMS ARE EXPECTED ACROSS THE AREA THROUGH THIS EVENING WITH HAIL UP TO THE SIZE OF GOLF BALLS...DAMAGING WINDS TO 70 MPH AND AN ISOLATED TORNADO ARE ALL POSSIBLE. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY PERIODIC CHANCES FOR THUNDERSTORMS ARE EXPECTED BY THURSDAY AND THROUGH NEXT WEEKEND. A FEW SEVERE STORMS MAY OCCUR THROUGH THE PERIOD. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS EXPECTED THROUGH THIS EVENING. SEVERE WEATHER REPORTS ARE HIGHLY ENCOURAGED. IAZ024-035-036-047-048-059>061-072>075-083>086-094>097-112200- HUMBOLDT-WEBSTER-HAMILTON-BOONE-STORY-DALLAS-POLK-JASPER-MADISON- WARREN-MARION-MAHASKA-CLARKE-LUCAS-MONROE-WAPELLO-DECATUR-WAYNE- APPANOOSE-DAVIS- 449 PM CDT SUN MAY 10 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT ISOLATED TO SCATTERED STRONG THUNDERSTORMS WITH AN ISOLATED SEVERE THUNDERSTORM IS POSSIBLE ACROSS THE AREA THROUGH THIS EVENING WITH QUARTER SIZED HAIL...DAMAGING WINDS TO 60 MPH AND AN ISOLATED TORNADO ARE ALL POSSIBLE. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY PERIODIC CHANCES FOR THUNDERSTORMS ARE EXPECTED BY THURSDAY AND THROUGH NEXT WEEKEND. A FEW SEVERE STORMS MAY OCCUR THROUGH THE PERIOD. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS EXPECTED THROUGH THIS EVENING. SEVERE WEATHER REPORTS ARE HIGHLY ENCOURAGED. IAZ005>007-016-017-025>028-037>039-049-050-062-112200- KOSSUTH-WINNEBAGO-WORTH-HANCOCK-CERRO GORDO-WRIGHT-FRANKLIN- BUTLER-BREMER-HARDIN-GRUNDY-BLACK HAWK-MARSHALL-TAMA-POWESHIEK- 449 PM CDT SUN MAY 10 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT SCATTERED TO NUMEROUS THUNDERSTORMS WILL CONTINUE INTO THE EVENING HOURS. AN ISOLATED SEVERE STORMS IS POSSIBLE WITH HAIL UP TO HALF DOLLAR SIZED AND 60 MPH WINDS THE PRIMARY THREATS. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY PERIODIC CHANCES FOR THUNDERSTORMS ARE EXPECTED BY THURSDAY AND THROUGH NEXT WEEKEND. A FEW SEVERE STORMS MAY OCCUR THROUGH THE PERIOD. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED THROUGH THIS EVENING. SEVERE WEATHER REPORTS ARE HIGHLY ENCOURAGED. REV
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
135 PM CDT SUN MAY 10 2015
IAZ057-058-070-101900-
GUTHRIE IA-AUDUBON IA-CASS IA-
135 PM CDT SUN MAY 10 2015
AT 134 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 5
MILES EAST OF ATLANTIC...MOVING NORTHEAST AT 60 MPH.
WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH THIS STORM.
LOCATIONS IMPACTED INCLUDE...
ATLANTIC...AUDUBON...GUTHRIE CENTER...LAKE PANORAMA...ANITA...
EXIRA...BRAYTON...WIOTA...AUDUBON COUNTY AIRPORT...ATLANTIC MUNICIPAL
AIRPORT...ANITA MUNICIPAL AIRPORT AND LAKE ANITA STATE PARK.
A TORNADO WATCH REMAINS IN EFFECT UNTIL 900 PM CDT FOR SOUTHWESTERN
IOWA.
LAT...LON 4151 9505 4151 9504 4154 9504 4182 9495
4175 9444 4150 9468 4150 9470 4149 9470
4146 9472 4130 9488 4139 9509
TIME...MOT...LOC 1834Z 209DEG 53KT 4142 9492
HARDINGSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
255 PM CDT SUN MAY 10 2015
IAZ034-035-046-102030-
WEBSTER IA-CALHOUN IA-GREENE IA-
255 PM CDT SUN MAY 10 2015
AT 255 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 8
MILES NORTH OF JEFFERSON...MOVING NORTH AT 35 MPH.
HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.
LOCATIONS IMPACTED INCLUDE...
GOWRIE...DAYTON...CHURDAN...CALLENDER...FARNHAMVILLE...HARCOURT...
PATON AND DANA.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 15 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.
&&
A TORNADO WATCH REMAINS IN EFFECT UNTIL 900 PM CDT FOR WEST CENTRAL
IOWA.
LAT...LON 4239 9440 4232 9400 4221 9411 4221 9416
4216 9416 4202 9430 4216 9458
TIME...MOT...LOC 1955Z 201DEG 32KT 4214 9438
HARDINGSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 408 PM CDT SUN MAY 10 2015 IAZ035-036-047-102200- WEBSTER IA-BOONE IA-HAMILTON IA- 408 PM CDT SUN MAY 10 2015 ...WINDS TO 50 MPH AND SMALL HAIL POSSIBLE... AT 408 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 10 MILES NORTH OF OGDEN...OR 10 MILES NORTHWEST OF BOONE...MOVING NORTHWEST AT 40 MPH. WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... FORT DODGE...WEBSTER CITY...DAYTON...STRATFORD...COALVILLE...OTHO... STANHOPE...LEHIGH...DUNCOMBE...HARCOURT...BOXHOLM...PILOT MOUND... FRASER...DOLLIVER MEMORIAL STATE PARK...WOODMAN HOLLOW STATE PARK... LIZARD CREEK STATE RECREATION AREA...BRUSHY CREEK ST RECREATION AREA AND WEBSTER CITY MUNICIPAL AIRPORT. THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE. LAT...LON 4219 9378 4210 9408 4253 9431 4254 9377 TIME...MOT...LOC 2108Z 153DEG 36KT 4218 9400 KOTENBERG
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 442 PM CDT SUN MAY 10 2015 IAZ005-016-017-024>026-102230- FRANKLIN IA-WRIGHT IA-CERRO GORDO IA-HUMBOLDT IA-KOSSUTH IA- HANCOCK IA- 442 PM CDT SUN MAY 10 2015 ...STRENGTHENING STORM MAY PRODUCE DIME TO NICKEL HAIL AND WINDS TO 50 MPH... AT 441 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 6 MILES NORTHEAST OF BIG WALL LAKE...OR 7 MILES EAST OF CLARION... MOVING NORTH AT 45 MPH. NICKEL SIZE HAIL AND WIND GUSTS OF 50 TO 55 MPH WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... CLARION...EAGLE GROVE...BELMOND...ELM LAKE...KANAWHA...GOLDFIELD... DOWS...KLEMME...THORNTON...WESLEY...CORWITH...LU VERNE...MESERVEY... RENWICK...THOR...ALEXANDER...SWALEDALE...ROWAN...GOODELL AND HARDY. PRECAUTIONARY/PREPAREDNESS ACTIONS... THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE. TO REPORT SEVERE WEATHER...CONTACT YOUR NEAREST LAW ENFORCEMENT AGENCY. THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE OFFICE IN DES MOINES . && LAT...LON 4308 9328 4263 9344 4266 9405 4309 9413 TIME...MOT...LOC 2141Z 186DEG 38KT 4270 9358 KOTENBERG
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
710 PM CDT SUN MAY 10 2015
IAZ070-110100-
CASS IA-
710 PM CDT SUN MAY 10 2015
...STRONG THUNDERSTORM MOVING ACROSS CASS COUNTY...
AT 708 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 5
MILES EAST OF GRISWOLD...OR 9 MILES SOUTH OF ATLANTIC...MOVING
NORTHEAST AT 40 MPH.
DIME SIZE HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.
THIS STRONG THUNDERSTORM WILL BE NEAR...
ATLANTIC AROUND 725 PM CDT.
OTHER LOCATIONS IMPACTED BY THIS STORM INCLUDE LEWIS...ATLANTIC
MUNICIPAL AIRPORT...GRISWOLD PARK...ANITA...WIOTA...ANITA MUNICIPAL
AIRPORT...LAKE ANITA STATE PARK AND COLD SPRINGS STATE PARK.
LAT...LON 4151 9503 4150 9470 4149 9470 4116 9503
4120 9516 4123 9516
TIME...MOT...LOC 0008Z 202DEG 37KT 4126 9504
BOKSAThe Des Moines radar (KDMX), 103 km away, was scanning. The volume nearest the first event began at 00:02 UTC.
5 thunderstorm wind, 3 tornado, 1 hail. Local standard time, as filed.
Debris on the ground. Tornado continued into Calhoun County.
A small shed was blown over.
Tornado moved from Carroll County into Calhoun County. It moved across the western side of Lake City, doing EF1 damage to houses and the high school. It remained in rural areas of Calhoun County for the remainder of it's path, broadening as it went along. The tornado lifted shortly before crossing Highway 20.
A machine shed on a farm was destroyed.
This was a broad and brief tornado that caused little to no damage. Reported by a spotter and likely track found in satellite data.
A wind gust of 65 MPH as measured by a hand-held anemometer.
Power lines and poles were down just south of Van Meter near 360th and R Ave.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2015Every state in 2015This day in weather historyThe tornado archive for Iowa, 2015Warnings in Iowa, May 2015
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: 565904, 566516, 565905, 565755, 566652, 565757, 565754, 565758, 565759.