An unstable airmass was in place over northern Iowa with an outflow boundary draped across the north central counties into southwest Minnesota. This boundary served as a focusing mechanism for thunderstorm development.
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.
An unstable airmass was in place over northern Iowa with an outflow boundary draped across the north central counties into southwest Minnesota. This boundary served as a focusing mechanism for thunderstorm development. The freezing level was relatively low at around 11,500 feet. CAPE available in the -10 to -30 layer of the atmosphere was between 200 and 400 J/kg. The atmosphere became unstable with afternoon highs in the upper 70s to low 80s and dewpoint temperatures in the mid 60s. CAPE was around 2000 J/kg with a lifted index of -4 C. The shear was quite weak with only 25 kts of shear available. Precipitable water increased to 1.4 inches. The LCL had lowered to 1000 meters by later afternoon. Isolated thunderstorms formed along the old outflow boundary. They moved very slowly and dumped copious amounts of rain. A report of 5 inches in one hour was received from north of Emmetsburg in Palo Alto County resulting in flash flooding in the city. There were numerous reports of half inch to three quarter inch diameter hail and 1 inch diameter hail falling west of Emmetsburg. As the thunderstorm continued to the southwest, hail of 1 to 1.75 inch diameter fell with the largest being golf ball size hail that fell west-southwest of Curlew.
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, 2:59 PM CST, 1 hour 28 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 359 PM CDT FRI MAY 17 2013 .SHORT TERM.../TONIGHT/ ISSUED AT 354 PM CDT FRI MAY 17 2013 AREAS OF SHOWERS AND THUNDERSTORMS WHICH HAVE DEVELOPED ACROSS PORTIONS OF NORTHERN CWA ALONG WEAK BOUNDARY WILL PERSIST THROUGH THE EVENING HOURS...AS SYSTEM CONTINUES TO PUSH SLOWLY EASTWARD. ANTICIPATE DEVELOPMENT TO TAPER OFF AFTER PEAK HEATING...BUT WILL CONTINUE TO SEE ISOLATED THUNDERSTORMS. VERY LIMITED SHEAR WITH STORMS...AND DO NOT ANTICIPATE SEVERE WEATHER...THOUGH A STORM MAY BRIEFLY PRODUCE HAIL OR GUSTY WINDS. IN ADDITION...STORMS HAVE BEEN EFFICIENT RAINFALL PRODUCERS...AND MAY SEE A RISK FOR FLASH FLOODING ACROSS THE NORTH WERE SOILS ARE SATURATED...IF STORMS TRAIN OR MOVE SLOWLY ACROSS THE REGION. WILL NOT PUT OUT A FLASH FLOOD WATCH GIVEN THE ISOLATED NATURE OF STORMS. PRECIPITATION CHANCES WILL DIMINISH THROUGH 06Z AS SYSTEM LIFTS NORTHEAST. OVERNIGHT LOWS AGAIN ARE TRICKY WITH CLOUD COVER. HAVE DROPPED TEMPERATURES A FEW DEGREES ACROSS THE NORTHEAST WHERE HIGH TEMPERATURES WERE COOLER WITH CLOUD COVER. SOME STRONGER WAA BEGINS TO PUSH INTO THE WEST LATE IN THE OVERNIGHT...AND MAY SEE SLIGHTLY WARMER TEMPERATURES THERE...HOWEVER HAVE KEPT TEMPS BELOW GUIDANCE THERE. .LONG TERM.../SATURDAY THROUGH FRIDAY/ ISSUED AT 354 PM CDT FRI MAY 17 2013 PRIMARY CONCERN REMAINS PRECIP TRENDS THROUGH THE PERIOD...ESPECIALLY SUNDAY INTO MONDAY. THE WEEKEND WILL BEGIN FAIRLY TRANQUIL HOWEVER WITH WARM AND HUMID WEATHER AS IA IS INFLUENCED BY THE WARM SECTOR. THETA-E ADVECTION WILL SPREAD SW- NE INTO SAT NIGHT HOWEVER INCREASING OUR CHANCES FOR CONVECTION.,.WHICH LOOKS LIKE IT WILL LINGER INTO AT LEAST SUNDAY MORNING. STEEP LAPSE RATES AND SOME FORM OF AN ELEVATED MIXED LAYER EARLY MAY KEEP THE CONVECTION QUITE ELEVATED INITIALLY...HOWEVER SOUNDINGS SHOW THE COLUMN MOISTENING TOWARD DAYBREAK. MORE FAVORABLE CAPE/CIN PARCELS LOWER IN SOUNDINGS LEADING TO CONVECTION POTENTIALLY BEING ROOTED LOWER INTO SUNDAY. ESTIMATED EFFECTIVE SHEAR IS NOT GREAT AT THIS POINT...BUT WOULD STILL BE SUFFICIENT FOR LOW END SEVERE THREAT CONSIDERING MUCAPES APPROACHING 2000 J/KG AT TIMES. THIS LEADS INTO LATER SUNDAY WHERE SOME QUESTIONS ABOUT SURFACE BASED EVENT COMING TOGETHER STILL EXIST. THETA-E ADVECTION STILL LINGERS INTO IA BY MIDDAY LEADING TO QUESTIONS RAISED YESTERDAY REGARDING RECOVERY TIME BETWEEN ELEVATED CONVECTION AND PEAK HEATING SURFACE BASED POTENTIAL. MODELS ARE STILL IN SOME DISAGREEMENT WITH REGARD TO PLACEMENT OF SURFACE FEATURES AS WELL...ON BOTH THE SYNOPTIC AND MESOSCALE. 12Z GFS AND ECMWF FAVOR A SURFACE LOW BEING CENTERED OVER ERN NE...WHILE 12Z NAM SUGGESTS LOWER PRESSURE FROM NE INTO MN ALONG INVERTED TROUGH. NAM ALSO SHOW FRONT ENHANCED BY OUTLOW ACROSS MO. THIS OUTFLOW FROM EARLIER CONVECTION COULD VERY WELL AFFECT NORTHWARD EXTENT OF THERMODYNAMIC RECOVERY AND WHERE LOCALIZED 0-1KM SHEAR AND TORNADO THREAT IS ENHANCED. EVEN WITH THESE QUESTIONS IT STILL APPEARS THAT CURRENT SPC DAY 3 OUTLOOK HAS FAVORED AREA IN PLACE WHICH IS ON THE NOSE OF THE UPPER LEVEL JET AND POTENTIAL FOR BETTER DEEP SHEAR. LOOKED AT SLU CIPS 12Z ANALOGS TO SEE IF THEY OFFERED ANY INSIGHT...BUT 60HR FORECAST UTILIZES THE NAM AS A BASELINE WHICH MAY BE TOO FAR NORTH WITH SURFACE FEATURES. 00Z GFS ANALOGS MAY BE TOO FAR NORTH AS WELL...AS GFS HAS NOW TRENDED CLOSER TO PREVIOUS ERN NE ECMWF SOLUTIONS. SITUATION CHANGES SOMEWHAT MONDAY WITH LOWER DEWPOINTS DROPPING INSTABILITY SOMEWHAT AS WELL. SOUNDINGS APPEAR WELL MIXED WITH LITTLE CINH HOWEVER SO STILL EXPECT CONVECTION TO DEVELOP DIURNALLY. DAMAGING WINDS POTENTIAL MAY BE SOMEWHAT HIGHER DUE TO STRONGER MIXED LAYER WINDS AND BETTER DCAPES AS LOW LAYERS DRY OUT SOMEWHAT. SYSTEM THEN OCCLUDES INTO TUE AND IS IN NO HURRY TO DEPART. MID/LATE MAY SOLAR HEATING NEAR THIS UPPER LOW WILL KEEP POTENTIAL FOR MAINLY DIURNALLY BASED CONVECTION IN THE FORECAST TO SOME EXTENT UNTIL THU WHEN SYSTEM FINALLY OPENS UP AND EXITS. && .AVIATION...17/18Z ISSUED AT 1217 PM CDT FRI MAY 17 2013 CEILINGS WILL REMAIN PRIMARILY VFR...WITH ISOLATED THUNDERSTORMS BETWEEN18-00Z WHICH MAY BRING LOWER MVFR CEILINGS TO SITES...ESPECIALLY NORTHERN SITES KFOD/KMCW/KDSM. HOWEVER...IMPACT WILL BE BRIEF. HAVE INCLUDED MENTION OF VCTS...WITH ISOLATED NATURE OF STORMS. CEILINGS WILL BE LIFTING AS SYSTEM PUSHES FURTHER EAST WITH WINDS BECOMING MORE SOUTHERLY AND LIGHT OVERNIGHT. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...AWB LONG TERM...SMALL AVIATION...AWB
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 327 PM CDT FRI MAY 17 2013 IAZ070>075-081>086-092>097-182030- CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 327 PM CDT FRI MAY 17 2013 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...THIS AFTERNOON 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>028-033>039-044>050-057>062-182030- 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- 327 PM CDT FRI MAY 17 2013 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...THIS AFTERNOON AND TONIGHT SCATTERED THUNDERSTORMS ARE POSSIBLE TODAY THROUGH THIS 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. AWB
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1201 PM CDT FRI MAY 17 2013
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1158 AM HEAVY RAIN 3 W FOREST CITY 43.26N 93.70W
05/17/2013 M4.75 INCH HANCOCK IA PUBLIC
1158 AM HEAVY RAIN 1 W JOICE 43.36N 93.48W
05/17/2013 M3.50 INCH WORTH IA PUBLIC
1158 AM HEAVY RAIN LAKOTA 43.38N 94.09W
05/17/2013 M6.00 INCH KOSSUTH IA 911 CALL CENTER
1158 AM HEAVY RAIN FOREST CITY 43.26N 93.64W
05/17/2013 M2.20 INCH WINNEBAGO IA PUBLIC
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1226 PM CDT FRI MAY 17 2013
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1210 PM HEAVY RAIN KENSETT 43.35N 93.21W
05/17/2013 E3.50 INCH WORTH IA EMERGENCY MNGR
&&
AWBSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
517 PM CDT FRI MAY 17 2013
IAZ015-172245-
PALO ALTO-
517 PM CDT FRI MAY 17 2013
...THUNDERSTORMS PRODUCING VERY HEAVY RAIN AND HAIL...
AT 513 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM OVER CENTRAL PALO ALTO COUNTY...MOVING SOUTH AT 5
MPH.
PENNY SIZE HAIL...WINDS GREATER THAN 30 MPH...VERY HEAVY
DOWNPOURS...ARE POSSIBLE WITH THIS STORM.
LOCATIONS IMPACTED INCLUDE...
RURAL PALO ALTO COUNTY AT 530 PM CDT
GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW
AROUND. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THIS STORM HAS
PASSED.The national radar mosaic for the moment the first event began.
7 hail, 2 heavy rain, 1 flash flood. Local standard time, as filed.
Public reported heavy rainfall along with nickel to quarter size hailstones.
Several inches of water flowing over the road in Emmetsburg at Lawler and Main.
Rainfall in the past hour of 1.25 inches.
Rainfall in the past hour of 5.00 inches. Relayed by KICD radio.
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: 440184, 440282, 440183, 440283, 440185, 440284, 440186, 440285, 440286, 440287.