A stationary front that had been over southern Iowa began to lift north as a warm front on the morning of the 17th. The atmosphere had become more unstable during the morning with CAPE increasing to 1000 to 2000 J/kg.
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The episode as NWS DMX wrote it up.
A stationary front that had been over southern Iowa began to lift north as a warm front on the morning of the 17th. The atmosphere had become more unstable during the morning with CAPE increasing to 1000 to 2000 J/kg. Precipitable water values increased to about 1.4 inches by late morning. The atmosphere exhibited very little shear. Thunderstorms developed during the morning and tracked slowly north. The storms produced very heavy rainfall of 2 to 6 inches in a short period of time, under 3 hours. Flash flooding occurred in Winnebago County north of the Forest City area where a gravel road was washed out.
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 17, 3:01 AM CST, 1 hour 29 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 401 AM CDT FRI MAY 17 2013 .SHORT TERM.../TODAY /... ISSUED AT 400 AM CDT FRI MAY 17 2013 CONVECTION ONGOING ACROSS THE NORTH ON THE NOSE OF 850MB THETA-E ADVECTION IN ADVANCE OF A WEAKENING SHORTWAVE TROUGH LIFTING THROUGH THE WEAK UPPER LEVEL RIDGE. OVERALL WEAK SHEAR AND OK INSTABILITY...SO SEVERE THREAT IS LIMITED. HOWEVER DUAL-POL ANALYSIS CONTINUES TO INDICATE SOME SMALL HAIL WITHIN THE STRONGER STORMS AND MAIN THREAT OF STORMS TO BE HEAVY RAIN ESPECIALLY WITH CELLS NOW TRAINING SOME WITH EASTERLY MOVEMENT. EXPECT CHANCE FOR PRECIP TO CONTINUE LINGER INTO THE MORNING ACROSS THE NORTHERN CWA...WITH FORCING WEAKENING TOWARD LATE MORNING INTO THE AFTERNOON HOURS. ENERGY ROTATING AROUND A WEAK UPPER LEVEL SYSTEM MOVING THROUGH MISSOURI. MAY SEE SOME SHOWER/THUNDERSTORM DEVELOPMENT WITH THIS SYSTEM TOWARD THIS AFTERNOON...WITH STORMS LIFTING NORTHWARD INTO THE FAR SOUTHEASTERN CWA. OVERALL THOUGH BEST CHANCES FOR PRECIP TODAY...WILL BE WITH THE LINGERING CONVECTION THIS MORNING. AIR MASS ALOFT AGAIN SIMILAR TO PREVIOUS DAYS...SO STICK NEAR PERSISTENCE WITH MAX TEMPS EXCEPT KEPT THE NORTH A BIT COOLER WITH CLOUDS/PRECIP CHANCES. .LONG TERM.../TONIGHT THROUGH THURSDAY/... ISSUED AT 400 AM CDT FRI MAY 17 2013 UPPER LEVEL RIDGE BUILDING INTO THE CENTRAL PLAINS WILL BRING AN END TO PRECIPITATION CHANCES TONIGHT INTO SATURDAY AS THE WARM SECTOR SPREADS ACROSS THE STATE. THE RIDGE WILL SHIFT EAST SATURDAY NIGHT AS A VIGOROUS UPPER LEVEL SYSTEM DIVES INTO THE NORTHERN HIGH PLAINS. THIS WILL CREATE AN ACTIVE SOUTHWEST FLOW ACROSS THE STATE. STRONG MOISTURE TRANSPORT WILL LIFT INTO SOUTHWEST IOWA AS THE LOW LEVEL JET INCREASES ACROSS EASTERN KANSAS AND POINTS INTO THE STATE. A GOOD ELEVATED MIXED LAYER WILL BE IN PLACE WITH A FAIR AMOUNT OF DRY AIR TO OVERCOME AND THIS MAY LIMIT OVERALL COVERAGE BUT STILL SOME STORMS SHOULD DEVELOP AND WILL BRING THE THREAT FOR LARGE HAIL AND HEAVY RAIN GIVEN INCREASING PWATS TO 1.5 INCHES AND STORM MOVEMENT AT 25 TO 30 KTS TO THE NORTHEAST. THE BEST SEVERE WEATHER THREAT THROUGH THE PERIOD WILL BE ON SUNDAY AS A STRONG UPPER WAVE ROTATES AROUND THE DEVELOPING CLOSED LOW TO THE WEST. THE GREATEST THREAT WILL BE DURING THE AFTERNOON AND EVENING. THE SURFACE LOW IS EXPECTED TO BE OVER EASTERN NEBRASKA TO FAR WEST CENTRAL IOWA WITH THE WARM FRONT EXTENDING INTO SOUTHERN OR CENTRAL IOWA. CONDITIONS CONTINUE TO LOOK FAVORABLE FOR SUPERCELLULAR DEVELOPMENT WITH VERY LARGE HAIL EXPECTED. TORNADO THREAT STILL LOOKS FAVORABLE ACROSS THE SOUTHWEST HALF WITH INCREASING CONFIDENCE THAT THE SFC WINDS WILL BACK LEADING TO INCREASED LOW LEVEL SHEAR. THE MID LEVEL FLOW IS NOT REAL STRONG AND COULD BE A LIMITING FACTOR HOWEVER LATEST FORECAST MODELS SOUNDINGS SUGGEST LCLS WILL BE LOWER THAN PREVIOUSLY EXPECTED. HEAVY RAIN WILL REMAIN A THREAT WITH PWATS UP TO 1.75 INCHES AND RIGHT MOVER SUPERCELL MOTIONS OF 20 TO 30 KTS. COULD CERTAINLY DEVELOP INTO A VOLATILE SITUATION. THE DRY SLOT WILL THEN LIFT SOUTHWEST TO NORTHEAST SUNDAY NIGHT AND INTO A PORTION OF MONDAY. A FEW SEVERE STORMS ARE POSSIBLE YET MONDAY BY THE PRIMARY SHOW WILL BE SUNDAY. THE UPPER LOW WILL SLOWLY FILL AND ROTATE THROUGH THE AREA THROUGH MID WEEK AND WILL KEEP PRECIPITATION CHANCES IN THE FORECAST. UPPER RIDGE FINALLY SHIFTS INTO THE REGION TOWARD THE END OF THE PERIOD AND BRING DRIER WEATHER AND WARMER TEMPERATURES. && .AVIATION...17/06Z ISSUED AT 1154 PM CDT THU MAY 16 2013 SHOWERS AND A FEW THUNDERSTORMS WILL PERSIST ACROSS NORTHERN IOWA AND POSSIBLY AFFECT KMCW DURING THE EARLY MORNING HOURS...BUT THE PROBABILITY IS LOW AND EVEN IF A STORM DOES PASS OVER THE TERMINAL CONDITIONS WOULD EITHER REMAIN VFR OR GO BELOW ONLY VERY BRIEFLY. THUS HAVE HANDLED IT WITH ONLY A VCSH IN THE 06Z TAFS. OTHERWISE...LIGHT WINDS AND VFR CIGS EXPECTED AT ALL TERMINALS THROUGH THE TAF PERIOD. LIGHT BR MAY DEVELOP LATE TONIGHT...MAINLY AT KDSM/KOTM...BUT CONFIDENCE IS TOO LOW FOR INCLUSION IN THE TAFS AT THIS TIME. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...BEERENDS LONG TERM...DONAVON AVIATION...LEE
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 453 AM CDT FRI MAY 17 2013 IAZ033>039-044>050-057>062-070>075-081>086-092>097-181000- 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- 453 AM CDT FRI MAY 17 2013 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND SOUTH CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY PERIODS OF THUNDERSTORMS ARE FORECAST SATURDAY NIGHT THROUGH TUESDAY. THERE IS A THREAT FOR SEVERE WEATHER SATURDAY NIGHT THROUGH MONDAY WITH THE MOST SIGNIFICANT POTENTIAL SUNDAY AFTERNOON AND EVENING. VERY LARGE HAIL...DAMAGING WINDS AND A FEW TORNADOES ARE POSSIBLE SUNDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED SUNDAY AFTERNOON AND EVENING. IAZ004>007-015>017-023>028-181000- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER- 453 AM CDT FRI MAY 17 2013 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT SCATTERED THUNDERSTORMS ARE POSSIBLE TODAY THROUGH EARLY EVENING. THE PRIMARY THREAT IS HEAVY RAINFALL THAT COULD PRODUCE LOCAL FLASH FLOODING. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY PERIODS OF THUNDERSTORMS ARE FORECAST LATE SATURDAY NIGHT THROUGH TUESDAY. THERE IS A THREAT FOR SEVERE WEATHER SATURDAY NIGHT THROUGH MONDAY WITH THE MOST SIGNIFICANT POTENTIAL SUNDAY AFTERNOON AND EVENING. LARGE HAIL...DAMAGING WINDS AND AN ISOLATED TORNADO ARE POSSIBLE SUNDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED SUNDAY AFTERNOON AND EVENING.
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 201 AM CDT FRI MAY 17 2013 IAZ005-170730- KOSSUTH- 201 AM CDT FRI MAY 17 2013 ...NICKEL HAIL AND HEAVY RAIN POSSIBLE... AT 157 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER CENTRAL KOSSUTH COUNTY...MOVING NORTHEAST AT 15 MPH. NICKEL SIZE HAIL...WINDS GREATER THAN 30 MPH...BRIEF HEAVY DOWNPOURS...ARE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... BURT... BANCROFT... TITONKA... GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW AROUND. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THIS STORM HAS PASSED. BEERENDS
The Minneapolis radar (KMPX), 171 km away, was scanning. The volume nearest the first event began at 10:28 UTC.
5 heavy rain, 1 flash flood. Local standard time, as filed.
A gravel road was washed out at the intersection of 150th and 380th.
Rainfall of 4.75 inches recorded.
Rainfall of 6.00 inches recorded.
Rainfall of 2.20 inches recorded.
Rainfall of 3.50 inches recorded.
Rainfall of 3.50 inches recorded.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2013Every state in 2013This day in weather historyWarnings in Iowa, May 2013
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: 440177, 440178, 440179, 440180, 440181, 440182.