S. during the early morning hours of the 17th.
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 strong upper level low pressure system lifted northeast out of the southwest U.S. during the early morning hours of the 17th. The surface low was over South Dakota as a line of thunderstorms developed ahead of an advancing dry line that was south of the low. The atmosphere was moderately unstable with about 2000 J/kg as the storms developed in the evening. CAPE in the -10 to -30 C layer of the atmosphere was only about 400 J/kg with a freezing level around 13,000 feet. The lifted index was in the -4 to -5 C range as the storms approached with 40 to 45 kts of shear available. The LCL was quite low, around 750 meters. CAPE in the zero to 3 km layer was 50 to 100 J/kg. Precipitable water values were quite high, in the 1.25 to 1.5 inch range. For the most part, the thunderstorms were not severe and produced mainly heavy rainfall. Several reports of 2 to 3 inches of rainfall were received from southwest into north central Iowa. As the line advanced eastward, a small mesoscale vorticity maximum was observed riding north along the line. The thunderstorms became enhanced as it moved north with a line of damage extending from Clarke County north to Webster County. Eighty two cars of a railroad train were derailed by the winds, with two of them blown off into the nearby field. Numerous very large trees were downed and some farm buildings lost roofs. Reports of trees and power lines being blown down continued north as the vorticity maximum lifted north.
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 16, 10:58 PM CST, 1 hour 44 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 1158 PM CDT SAT MAY 16 2015 ...UPDATED AVIATION DISCUSSION... .SHORT TERM /TONIGHT/... ISSUED AT 324 PM CDT SAT MAY 16 2015 CONVECTIVE TRENDS WILL REMAIN THE PRIMARY CONCERN INTO THE NIGHT. THE CURRENT SITUATION HAS ISOLATED WEAK ELEVATED CONVECTION DRIFTING ACROSS ERN IA WHICH HAS BECOME MORE SURFACE BASED WITH TIME AS MLCAPES AND CINHS TRENDED MORE FAVORABLE. EFFECTIVE SHEAR AND CONVERGENCE ARE FAIRLY WEAK HOWEVER SO EXPECT PERSISTENCE OR EVEN A SLIGHT DOWNWARD TREND INTO THE EARLY EVENING HOURS. ATTENTION WILL THEN TURN UPSTREAM AND BECOMES MORE PROBLEMATIC. UNCAPPED 1500-2000 J/KG MLCAPES ARE IN PLACE AHEAD OF KS CONVECTION WITH INCREASED EFFECTIVE SHEAR FARTHER WEST LEADING TO THE POTENTIAL OF MORE ORGANIZATION. TRENDS ARE LEANING TOWARD THE POTENTIAL FOR MORE ROBUST SURFACE BASED POTENTIAL JUST WEST OF THE MO RIVER. MOST CONVECTION ALLOWING MODELS EXPAND AND DEVELOP THIS INTO WRN IA DURING THE EVENING WITH THE MEAN WIND. NAM ELEVATED CAPE LOOKS BELOW 1000 J/KG INTO THE NIGHT...SO WHILE INSTABILITY WILL NOT BE EXTREME BOTH SHALLOW AND DEEP SHEAR INCREASE WITH LOW LEVEL JET INCREASING TO 50KTS OR SO. MAIN THREATS WOULD BE HAIL AND WIND BUT CANNOT RULE OUT A QLCS TORNADO EITHER AS 0-1KM SHEAR INCREASES INTO THE NIGHT. SHEAR WILL CERTAINLY BE THERE...BUT QUESTION WILL BE HOW ROBUST THE MCS IS BY THE TIME IT REACHES IA. WHATEVER REACHES US SHOULD PERSIST INTO THE NIGHT IN SOME FORM HOWEVER WITH PERSISTENT STRONG LOW LEVEL MOISTURE TRANSPORT. .LONG TERM /SUNDAY THROUGH SATURDAY/... ISSUED AT 324 PM CDT SAT MAY 16 2015 MAIN FORECAST CONCERN WILL BE WITH PRECIPITATION CHANCES FOR BEGINNING OF PERIOD. EXPECT LINGERING PRECIPITATION FROM OVERNIGHT TO BE ONGOING IN THE NORTH AND EAST...THOUGH EXPECT PRECIPITATION TO BECOME MORE SCATTERED THROUGH THE MORNING HOURS. UPPER LEVEL LOW WILL CONTINUE TO LIFT NORTHEAST FROM NEBRASKA THROUGH THE DAY SUNDAY...REACHING NORTHERN MINNESOTA BY LATE IN THE DAY. CONCERN WILL BECOME PLACEMENT OF BOUNDARY ACROSS CENTRAL IOWA...MODELS ARE IN GOOD AGREEMENT WITH TIMING AND PLACEMENT OF SYSTEM...WITH BOUNDARY PUSHING EAST QUICKLY AFTER 18Z. NEAR BOUNDARY COULD SEE POTENTIAL FOR SEVERE THUNDERSTORMS WITH MODELS INDICATING CAPE VALUES OF NEAR/OVER 2000 J/KG...INCREASING TO THE EAST. SHEAR VALUES WILL SUFFICIENT TO SUPPORT THUNDERSTORMS WHICH DEVELOP WITH BULK SHEAR OF NEAR 40KTS. THIS COULD LEAD TO A WINDOW OF SEVERE POTENTIAL IN THE AFTERNOON EAST OF INTERSTATE 35...BEFORE QUICKLY PUSHING EASTWARD OUT OF CWA. HOWEVER...STILL SOME UNCERTAINTY IF THESE PARAMETERS WILL BE ABLE TO BE REALIZED WITH LINGERING PRECIPITATION AND CLOUDS FROM OVERNIGHT CONVECTION...WITH CONDITIONS BEING MORE FAVORABLE TO THE EAST OF THE CWA. WINDS WILL BE STRONG AND GUSTY TOMORROW WITH GOOD SOUTHERLY FLOW AND MIXING. TOP OF MIXED LAYER WINDS IN THE NORTH ARE NEAR 40KTS...AND MAY BE NEAR ADVISORY CRITERIA AT TIMES IN THE NORTH. HOWEVER...AGAIN WITH EXPECTED LINGERING PRECIPITATION/CLOUDS IN THE NORTH MAY HELP LIMIT MIXING. BEHIND BOUNDARY ANOTHER ROUND OF COOLER AIR WILL PUSH IN AS LOW MOVES EAST. NAM IS MOST AGGRESSIVE WITH THE COOLING...AND FEEL IT IS TOO AGGRESSIVE GIVEN TIME OF YEAR...AND HAVE KEPT TEMPERATURES NEAR GOING...TRENDING TOWARDS GFS. COLDEST NIGHT WILL BE MONDAY NIGHT...WITH DRY AIR AND HIGH PRESSURE WORKING SOUTH MAY BE TOO WARM ON LOWS...WHICH COULD DROP READINGS TO NEAR FREEZING IN THE NORTH. HOWEVER...WINDS WILL REMAIN UP WHICH SHOULD HELP LIMIT COOLING SOMEWHAT. NEXT CHANCES FOR PRECIPITATION WILL COME TUESDAY AS SYSTEM LIFTS NORTH FROM FOUR CORNERS REGION. HOWEVER...WITH HIGH PRESSURE IN PLACE ACROSS THE NORTHERN PLAINS HAVE KEPT PRECIPITATION CHANCES TO THE SOUTH AND MAY BE TOO AGGRESSIVE. ANOTHER ROUND OF PRECIPITATION CHANCES COMES FOR THE WEEKEND AS LOW PRESSURE SYSTEM COMES ONSHORE IN SOUTHERN CALIFORNIA AND PUSHES HIGH EAST FOR VERY END OF PERIOD. ATTM MODELS ARE IN GOOD AGREEMENT WITH THE TIMING AND PLACEMENT OF THIS SYSTEM..THOUGH GFS IS A BIT MORE AGGRESSIVE AND HAVE JUST KEPT CHANCES POPS ATTM. && .AVIATION...17/06Z ISSUED AT 1153 PM CDT SAT MAY 16 2015 OUT AHEAD OF THE SHOWERS AND STORMS CONDITIONS SHOULD REMAIN VFR. MOST AREAS WITHIN THE SHOWERS AND STORMS WILL SEE AT LEAST PERIODS OF MVFR OR BORDERLINE VFR CIGS. WITH SLOW PROGRESSION OF SHOWERS EASTWARD AND WEAKENING...HAVE HANDLED PRECIP AT MCW...ALO..AND OTM WITH VCSH. SUNDAY WILL BE HIGHLIGHTED BY RAPIDLY INCREASING WINDS WITH SUSTAINED TO AROUND 20KTS AND GUSTS TOWARDS 30KTS OR MORE. WAS NOT CONFIDENT ENOUGH TO PUT PREVAILING 30KT PLUS GUSTS. STORMS...ESPECIALLY IN THE EAST...MAY FIRE UP LATER IN THE AFTERNOON SUNDAY TOO...BUT HAVE KEPT THOSE OUT OF TAFS FOR THE TIME BEING. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...SMALL LONG TERM...AWB AVIATION...CURTIS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 405 PM CDT SAT MAY 16 2015 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-172115- 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- 405 PM CDT SAT MAY 16 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...THIS AFTERNOON AND TONIGHT SCATTERED THUNDERSTORMS ARE EXPECTED THIS AFTERNOON...WITH STORMS MOVING EAST ACROSS THE AREA TONIGHT. SOME STORMS MAY BE SEVERE IN THE WEST WITH HIGH WINDS AND HAIL THE MAIN THREAT. AN ISOLATED TORNADO IS POSSIBLE. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THERE IS A CHANCE FOR THUNDERSTORMS SUNDAY MORNING AND AGAIN THE AFTERNOON. SOME STORMS MAY BE SEVERE WITH HIGH WINDS AND HAIL THE MAIN THREAT...AN ISOLATED TORNADO WILL ALSO BE POSSIBLE. THE BEST CHANCES FOR SEVERE WEATHER WILL BE IN THE AFTERNOON AND EAST OF INTERSTATE 35. SCATTERED THUNDERSTORMS ARE EXPECTED TUESDAY NIGHT INTO WEDNESDAY NIGHT...AND AGAIN FRIDAY. THE LIKELIHOOD OF SEVERE WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED LATE TODAY INTO TONIGHT...MAINLY WEST OF U.S. HIGHWAY 169 AWB
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 756 PM CDT SAT MAY 16 2015 IAZ004-005-015-023-024-034-035-045-046-057-058-070-071-081-082- 092-093-170300- EMMET-KOSSUTH-PALO ALTO-POCAHONTAS-HUMBOLDT-CALHOUN-WEBSTER- CARROLL-GREENE-AUDUBON-GUTHRIE-CASS-ADAIR-ADAMS-UNION-TAYLOR- RINGGOLD- INCLUDING THE CITIES OF...ESTHERVILLE...ALGONA...EMMETSBURG... POCAHONTAS...LAURENS...ROLFE...FONDA...GILMORE CITY...HUMBOLDT... ROCKWELL CITY...MANSON...LAKE CITY...POMEROY...FORT DODGE... CARROLL...JEFFERSON...AUDUBON...EXIRA...GUTHRIE CENTER...PANORA... BAYARD...CASEY...ATLANTIC...GREENFIELD...STUART...ADAIR... FONTANELLE...CORNING...CRESTON...BEDFORD...LENOX...NEW MARKET... MOUNT AYR 756 PM CDT SAT MAY 16 2015 ...LINE OF THUNDERSTORMS WITH GUSTY WINDS AND HAIL POSSIBLE... A LINE OF THUNDERSTORMS IS MOVING NORTHEAST THROUGH THE REGION THIS EVENING. THE STORMS WILL BRING BRIEF HEAVY RAINFALL UP TO ONE HALF TO THREE QUARTERS OF AN INCH. ALONG WITH THE RAINFALL...THERE IS A POTENTIAL OF WIND GUSTS NEAR 50 MPH WITH A FEW OF THE STORMS THIS EVENING ALONG WITH SOME HAIL UP TO DIME SIZE. THE STORMS ARE EXPECTED TO CONTINUE ACROSS THE AREA FOR UNTIL ABOUT 10 PM CDT BEFORE SLOWLY MOVING EAST OF THE REGION. REV
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 907 PM CDT SAT MAY 16 2015 IAZ058-071-081-082-092-093-170415- GUTHRIE-ADAIR-ADAMS-UNION-TAYLOR-RINGGOLD- INCLUDING THE CITIES OF...GUTHRIE CENTER...PANORA...BAYARD... CASEY...GREENFIELD...STUART...ADAIR...FONTANELLE...CORNING... CRESTON...BEDFORD...LENOX...NEW MARKET...MOUNT AYR 907 PM CDT SAT MAY 16 2015 ...HEAVY RAINFALL WITH PONDING/STANDING WATER POSSIBLE... A SLOW EASTWARD PROGRESSING LINE OF STORMS WILL CONTINUE THROUGH THE EVENING. STORMS WITHIN THE LINE ARE MOVING NORTHWARD AND AREAS MAY SEE MULTIPLE STORMS PASS OVER. THE STORMS MAY CONTAIN HEAVY RAINFALL AND LOCAL TOTALS MAY REACH OR EXCEED ONE AND A HALF INCHES. AS A RESULT...ROADSIDE DITCHES AND LOW LYING AREAS MAY EXPERIENCE PONDING WATER...AND ROADS MAY BECOME COVERED BY STANDING WATER...ESPECIALLY IN URBAN AREAS. CURTIS
The national radar mosaic for the moment the first event began.
13 thunderstorm wind, 5 tornado, 3 heavy rain. Local standard time, as filed.
Many large branches were down in town and several car ports flipped.
Measured at the Leon road weather information system.
Trees were reported down on houses in town and power was out. Relayed by KCCI TV.
Trees and grain bins were blown down.
Around 82 train cars were blown over. Several very large trees were uprooted in a narrow corridor. Many branches were snapped and several farm buildings lost roofs.
Farm buildings were damaged or destroyed in the 1675 to 1700 blocks of Highway 34. A 2 X 10 was driven into the ground.
A wooden barn was completely destroyed along 180th Ave.
This tornado affected several farmsteads along its path. Damage was mostly to trees and storage silos, with damage to outbuildings caused by flying debris from these sources. The tornado path became intermittent for the latter portion of its life as it tracked northward.
This short-lived tornado damaged a few trees along its path.
Tree damage was reported.
This short-lived tornado tracked northwest and damaged several farmsteads. A horse trailer was thrown 40 yards into a pine tree, flipping a parked car along the way. Damage was otherwise contained to outbuilding roofs and trees.
This intermittent tornado tracked northwest during its short life and damaged several groves of trees.
Tree damage reported with tree tops snapped, a flag pole was bent and heavy outdoor objects were moved.
Several 8 inch diameter tree limbs were damaged. Minor tree damage was reported within a block or two radius of this location.
This brief tornado only damaged trees near the North Raccoon River.
Minor tree damage was reported and shingles were torn from roofs.
Multiple large trees over 12 inches in diameter were blown down throughout town.
Rainfall of 3.23 inches for the 24 hour period ending at 6 AM. End time is based on Radar.
Strong winds caused tree and power line damage west of Ogden.
Rainfall of 1.93 inches for the 24 hour period ending at 6:30 AM. End time is based on Radar.
Rainfall of 2.30 for the 24 hour period ending at 6 AM. End time is based on Radar and relayed by KCCI TV.
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: 566380, 568026, 566377, 566374, 566379, 566382, 566394, 575674, 575679, 566375, 575680, 575681, 566396, 566447, 575682, 566381, 566376, 566371, 566448, 566373, 566372.