Conditions became moderately to highly unstable across eastern Nebraska and southwest Iowa by early afternoon on August 18th ahead of a weak slow moving cold front that was driven southeast by a weak upper level disturbance. Scattered super-cell thunderstorms developed by early afternoon near the northeast Nebraska and South Dakota border and tracked and developed southeast across eastern…
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 OAX wrote it up.
Conditions became moderately to highly unstable across eastern Nebraska and southwest Iowa by early afternoon on August 18th ahead of a weak slow moving cold front that was driven southeast by a weak upper level disturbance. Scattered super-cell thunderstorms developed by early afternoon near the northeast Nebraska and South Dakota border and tracked and developed southeast across eastern Nebraska and southwest Iowa through the afternoon and evening hours for a prolonged severe weather event across the area. Several of the storms produced very large destructive hail and very strong wind gusts which destroyed crops and caused property damage over large areas, notably Page county. As of the second week in September, State Farm Insurance stated it had processed around 6,600 homeowner and 5,200 auto claims in Iowa from the storm.
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 Omaha, NE wrote its last area forecast discussion before the first event at Aug 18, 9:49 AM CST, 3 hours 27 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 1049 AM CDT THU AUG 18 2011 .DISCUSSION... GOING FORECAST IN PRETTY GOOD SHAPE THIS MORNING. WILL BE UPDATING TO ADD IN SOME TIMING TO THE POPS TODAY AND TO ADJUST HOURLY TEMPERATURES FOR A FASTER DIURNAL RISE. 12Z UPPER AIR ANALYSIS INDICATED SEASONABLY STRONG MID LEVEL JET OF 80 KT FROM THE NORTHERN ROCKIES INTO THE MID MISSOURI RIVER VALLEY. NO SIGNIFICANT SHORTWAVE TROUGH WAS NOTED IN THIS FAST FLOW...BUT A SMALL WAVE APPEARED VISIBLE ASSOCIATED WITH SOME 20 M H5 HEIGHT FALLS OVER WY AT 12Z. LAPSE RATES WERE PRETTY DECENT ACROSS THE CENTRAL AND NORTHERN PLAINS WITH H5 TO H7 DELTA-T'S OF +20 TO +23 FOR MOST LOCATIONS THIS MORNING. THIS WAS CAPPING MOISTURE SEEN AT H85 WITH +15 C FROM THE LOWER MISSISSIPPI RIVER VALLEY TO THE MID MISSOURI RIVER VALLEY. THIS COMBINATION SHOULD LEAD TO MODERATE TO STRONG INSTABILITY BY MID AFTERNOON OVER THE CWA WITH 2500-3500 J/KG OF MLCAPE APPEARING QUIET REASONABLE. GIVEN THE LOW LEVEL S/SERLY FLOW BENEATH MID LEVEL WESTERLY WINDS OF 40 KT...SHOULD CREATE AROUND 35-40 KT OF EFFECTIVE SHEAR AS WELL. THUS ATMOSPHERE APPEAR SUPPORTIVE OF ORGANIZED DEEP MOIST CONVECTION TODAY. A COUPLE OF SCENARIOS ARE POSSIBLE TODAY FOR CONVECTIVE EVOLUTION. THE FIRST IS THE ELEVATED SHOWERS AND ISOLATED STORMS OVER SOUTH CENTRAL SODAK INCREASES IN AREAL COVERAGE AND INTENSITY AND TRACKS SOUTHEAST INTO EASTERN NEB/WRN IA EVENTUALLY BECOMING NEARLY SURFACED-BASED BY MID TO LATE AFTERNOON. THIS IS SUPPORTED BY LATEST 12Z NAM AND HRRR. THE SECOND OPTION IS FOR THIS ELEVATED ACTIVITY TO WEAKEN THROUGH THE MORNING AND SHIFT EASTWARD WITH THE SURFACE COLD FRONT LIGHTING UP FROM NE SODAK INTO N-CNTRL NEB BY LATE AFTERNOON AND THEN MAKING IT INTO THE FA AFTER 22Z. THIS IS MORE SUPPORTED BY RECENT RUC AND GFS RUNS. ATTM IS HARD TO SAY WHICH WILL WORK OUT TODAY...BUT THE LONGER THE ACTIVITY GOES IN SE SODAK...THE BETTER THE CHANCE THAT THIS ACTIVITY EVENTUALLY BECOMES NEAR SURFACE-BASED AND TURN SE. WITH CURRENT UPDATE WILL REMOVE MORNING POPS FROM CENTRAL AND SOUTHERN FA AND CONT CHC POPS IN THE NORTH. WILL INCREASE POPS INTO THE LIKELY CAT THIS AFTERNOON IN NORTHEAST NEB. HAIL AND WIND CONTINUE TO LOOK TO BE THE MAIN THREATS WITH WEAKER LOW LEVEL WIND SHEAR LIMITING TORNADO THREAT. NEW ZFP/GRIDS ARE ALREADY OUT. BOUSTEAD && .PREV DISCUSSION... /ISSUED 312 AM CDT THU AUG 18 2011/ DISCUSSION... MAIN CHALLENGE WITH THIS FORECAST PACKAGE DEALS WITH THE POTENTIAL FOR SEVERE CONVECTION LATE THIS AFTERNOON THROUGH THE OVERNIGHT HOURS. TODAY - TONIGHT: A ZONE OF STRONG UPPER LEVEL FLOW AROUND 80 TO 90 KTS IS ROUNDING THE TOP OF THE SOUTHWESTERN RIDGE. THERE ALSO APPEARS TO BE A WAVE MOVING INTO THE NORTHERN ROCKIES BASED ON AIRCRAFT DATA AND WATER VAPOR IMAGERY. THIS WAVE SHOULD MAKE IT INTO THE CENTRAL/NORTHERN PLAINS THIS AFTERNOON AND HELP TRIGGER CONVECTION IN WHAT SHOULD BE A FAVORABLE ENVIRONMENT FOR SEVERE THUNDERSTORMS. THE NAM AND THE GFS BOTH INDICATE A SURFACE WAVE IN NORTHERN NEBRASKA/SOUTHERN SOUTH DAKOTA WHICH WILL HELP TO NOT ONLY INITIATE CONVECTION BUT ALSO TO BACK SURFACE WINDS AND LOCALLY ENHANCE HELICITY VALUES. THIS SHOULD OCCUR IN WHAT MAY BE EXTREME INSTABILITY WITH CAPE VALUES RANGING FROM 3K J/KG TO 4K J/KG. THE STRONG UPPER LEVEL FLOW WILL ALSO LEAD TO FAVORABLE SHEAR ON THE ORDER OF 40 TO 50 KTS. ONGOING MESOANALYSIS WILL NEED TO BE DONE TO DETERMINE THE LOCATION OF THE SURFACE WAVE THROUGHOUT THE DAY BUT LATEST MODELS INITIATE CONVECTION ALONG/EAST OF THE WAVE TO THE WEST/NORTHWEST OF THE CWA. GIVEN CAPE/SHEAR COMBINATIONS IN THIS AREA SEVERE CONVECTION SEEMS LIKELY WITH THE INITIAL STORMS LIKELY TO BE SUPER-CELLULAR. STORMS SHOULD THEN GROW UPSCALE AS COLD POOLS MERGE WITH THE END RESULT BEING ONE OR MORE STRONG TO SEVERE CONVECTIVE SYSTEMS/BOWS. GIVEN THE NORTHWEST FLOW ALOFT ANY CONVECTIVE SYSTEM SHOULD TRACK TO THE SOUTHEAST ACROSS EASTERN NEBRASKA/WESTERN IOWA AND INTO NORTHWESTERN MISSOURI. THIS TRACK WILL ALSO CORRESPOND TO AN AXIS OF HIGHER THETA-E AIR SO STORMS SHOULD BE ABLE TO MAINTAIN THEMSELVES EASILY ACROSS THE CWA. FRIDAY: WE SHOULD BE IN THE WAKE OF ANY SYSTEM FOR FRIDAY WITH ANOTHER BRIEF BREAK FROM THE ACTIVE WEATHER. NORTHEASTERLY SURFACE FLOW SHOULD HELP KEEP THE REGION DRY WITH TEMPERATURES IN THE MID TO UPPER 80S PREVAILING. TEMPERATURES COULD BE A BIT COOLER DEPENDING ON HOW THICK THE CLOUD COVER IS IN THE WAKE OF THE CONVECTIVE SYSTEM. FRIDAY NIGHT - SATURDAY: A BOUNDARY IS EXPECTED TO BE DRAPED ACROSS KANSAS OR OKLAHOMA BY FRIDAY EVENING. AS ISENTROPIC ASCENT OVERRIDES THIS BOUNDARY WIDESPREAD SHOWER AND THUNDERSTORM ACTIVITY IS EXPECTED TO DEVELOP ACROSS NORTHERN KANSAS AND SHOULD MOVE INTO SOUTHERN PORTIONS OF NEBRASKA. HAVE ARRANGED THE HIGHEST POPS IN FAR SOUTHERN/SOUTHEAST NEBRASKA AND TAPERED CHANCES ACROSS THE REMAINDER OF CWA. WHILE THE FOCUS IS EXPECTED TO BE ACROSS NORTHERN KANSAS AND SOUTHERN NEBRASKA...THE ENTIRE REGION SHOULD BE IN A FAVORABLE/DIFFLUENT REGION OF THE UPPER JET SO COULD SEE MORE ISOLATED TO SCATTERED SHOWER AND THUNDERSTORM ACTIVITY NORTH OF THE MAIN FOCUS. SUNDAY - WEDNESDAY: FEW CHANGES WERE MADE TO THIS PERIOD BUT WITH THE SOUTHWESTERN RIDGE EXPANDING DID INCREASE TEMPERATURES A FEW DEGREES THROUGH TUESDAY. THE AREA SHOULD REMAIN IN NORTHWEST FLOW ALOFT BUT WITH THE JET SHIFTED NORTH OF THE REGION PRECIPITATION CHANCES LOOK TOO LOW AT THIS POINT TO MENTION. CDB AVIATION... FOR THE 06Z TAFS... WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE THROUGH EARLY MORNING ACROSS THE REGION. THE BULK OF THE TSRA ACTIVITY SHOULD STAY NORTH AND EAST OF THE TERMINALS...BUT A FEW STORMS AFFECTING THE TAF SITES CAN NOT BE RULED OUT. CIGS/VIS WILL GENERALLY BE VFR...THOUGH A FEW INSTANCES OF MVFR WILL BE POSSIBLE. LATER TODAY...WINDS WILL TURN SOUTHEAST AHEAD OF AN APPROACHING STORM SYSTEM. TSRA WILL BE POSSIBLE AT THE TERMINALS DURING THE AFTERNOON AND ESPECIALLY EVENING HOURS...WITH A FEW STRONG STORMS POSSIBLE. IFR CONDITIONS CAN BE EXPECTED WITHIN ANY TSRA. BOXELL && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && 99
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 1135 AM CDT THU AUG 18 2011 IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034- 042>045-050>053-065>068-078-088>093-190645- MONONA-HARRISON-SHELBY-POTTAWATTAMIE-MILLS-MONTGOMERY-FREMONT- PAGE-KNOX-CEDAR-THURSTON-ANTELOPE-PIERCE-WAYNE-BOONE-MADISON- STANTON-CUMING-BURT-PLATTE-COLFAX-DODGE-WASHINGTON-BUTLER- SAUNDERS-DOUGLAS-SARPY-SEWARD-LANCASTER-CASS-OTOE-SALINE- JEFFERSON-GAGE-JOHNSON-NEMAHA-PAWNEE-RICHARDSON- 1135 AM CDT THU AUG 18 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST IOWA...WEST CENTRAL IOWA...EAST CENTRAL NEBRASKA...NORTHEAST NEBRASKA AND SOUTHEAST NEBRASKA. .DAY ONE...THIS AFTERNOON AND TONIGHT THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS ACROSS THE ENTIRE AREA THIS AFTERNOON AND TONIGHT. THE MOST LIKELY TIME FOR SEVERE WEATHER WILL BE AFTER 1 PM IN NORTHEAST NEBRASKA...AND AFTER 3 PM IN EAST CENTRAL AND SOUTHEAST NEBRASKA...AS WELL AS WESTERN IOWA. THE MOST LIKELY THREAT FROM THESE STORMS WILL BE LARGE HAIL AND DAMAGING WINDS. THUNDERSTORMS ARE EXPECTED TO DEVELOP AND MOVE INTO NORTHEAST NEBRASKA EARLY THIS AFTERNOON. THESE THUNDERSTORMS WILL CONTINUE TO MOVE SOUTHEAST ACROSS THE AREA THIS AFTERNOON. ADDITIONAL THUNDERSTORM DEVELOPMENT IS LIKELY IN SOUTH DAKOTA AND THIS ACTIVITY MAY MOVE INTO THE REGION THIS EVENING AND OVERNIGHT. WITH SUFFICIENT MOISTURE IN PLACE ACROSS THE AREA...THE ATMOSPHERE IS EXPECTED TO BECOME STRONGLY UNSTABLE THIS AFTERNOON. THIS...ALONG WITH SEASONABLY STRONG WIND SHEAR...WILL ALLOW FOR ORGANIZED THUNDERSTORMS...INCLUDING A COUPLE OF SUPERCELLS. LARGE HAIL AND DAMAGING WINDS WILL BE THE MAIN THREAT WITH THESE THUNDERSTORMS. MINOR TO MODERATE FLOODING CONTINUES ALONG THE MISSOURI RIVER. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY ANOTHER ROUND OF THUNDERSTORMS IS FORECAST FROM FRIDAY EVENING THROUGH SATURDAY ACROSS MAINLY SOUTHEASTERN NEBRASKA. SEVERE THUNDERSTORMS ARE NOT EXPECTED. ADDITIONAL SMALL CHANCES FOR THUNDERSTORMS WILL PERSIST INTO MONDAY BUT AGAIN...SEVERE STORMS ARE NOT EXPECTED WITH THIS ACTIVITY MINOR TO MODERATE FLOODING WILL CONTINUE ALONG THE MISSOURI RIVER FOR THE NEXT SEVERAL WEEKS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING. BOUSTEAD
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA 1223 PM CDT THU AUG 18 2011 NEZ011-181815- KNOX NE- 1223 PM CDT THU AUG 18 2011 ...SPECIAL WEATHER STATEMENT FOR CENTRAL KNOX COUNTY UNTIL 115 PM CDT... AT 1219 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS WERE TRACKING A STRONG THUNDERSTORM 7 MILES NORTHWEST OF NIOBRARA...OR 35 MILES WEST OF YANKTON...MOVING SOUTHEAST AT 30 MPH. HAIL UP TO THE SIZE OF NICKELS AND WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM. LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE... NIOBRARA... VERDIGRE... CENTER... WINNETOON... BAZILE MILLS... THIS STORM MAY INTENSIFY. MONITOR LOCAL RADIO AND TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE. BOUSTEAD
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
1238 PM CDT THU AUG 18 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1238 PM HAIL NIOBRARA 42.75N 98.03W
08/18/2011 E0.88 INCH KNOX NE TRAINED SPOTTER
NICKEL SIZE HAIL
&&
MILLERPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
1255 PM CDT THU AUG 18 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1245 PM HAIL NIOBRARA 42.75N 98.03W
08/18/2011 E1.00 INCH KNOX NE TRAINED SPOTTER
QUARTER SIZE HAIL...AND LOTS OF IT.
&&
MILLERPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
113 PM CDT THU AUG 18 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0113 PM TSTM WND GST BLOOMFIELD 42.60N 97.65W
08/18/2011 E60 MPH KNOX NE FIRE DEPT/RESCUE
50 TO 60 MPH IN BLOOMFIELD.
&&
JBPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
120 PM CDT THU AUG 18 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0110 PM HAIL 6 ENE BLOOMFIELD 42.63N 97.54W
08/18/2011 E4.25 INCH KNOX NE LAW ENFORCEMENT
HAIL UP TO SOFTBALL SIZE
&&
JBRANDThe Omaha radar (KOAX), 106 km away, was scanning. The volume nearest the first event began at 19:17 UTC.
20 hail, 12 thunderstorm wind. Local standard time, as filed.
The public estimated that thunderstorm wind gusts reached around 60 mph.
Thunderstorm winds were measured at 65 mph a few miles northwest of Harlan. The winds flattened grain bins in the area and a couple of outbuildings were destroyed. A thousand gallon propane tank was moved around 10 feet by the winds.
Nickel-size hail fell along with thunderstorm wind gusts estimated at around 50 mph.
Hail up to quarter-size lasted for around 10 minutes.
Hail up to baseball-size which was accompanied by thunderstorm wind gusts estimated at around 60 mph caused extensive damage to homes and vehicles in the Council Bluffs area. Iowa Western Community College had at least a million dollars worth of damage to buildings, mainly to roofs, windows and siding, according to the college's vice president of marketing and public relations.
Thunderstorm wind gusts estimated at around 60 mph accompanied hail that reached up to baseball-size in the Council Bluffs area. The wind driven hail caused extensive damage to homes, vehicles and trees around town.
Hail, some as large as around softball-size, was accompanied by thunderstorm winds estimated at 60 mph or stronger. The hail and strong winds caused considerable home and vehicle damage in the Mineola area, especially on the east side of the structures. It was reported that almost every home in town lost at least one window. Bicyclists on a weekly jaunt on a local trail were hit by the wind and hail with several sustaining minor injuries due to the wind driven hail.
Hail, some as large as softball-size, was accompanied by thunderstorm winds estimated at 60 mph or stronger. The hail and strong winds caused considerable home and vehicle damage in the Mineola area, especially on the east side of the structures. Bicyclists on a weekly jaunt on a local trail were hit by the wind and hail with several sustaining minor injuries due to the wind driven hail.
A thunderstorm wind gust of 64 mph was measured at the Red Oak Awos. The strong winds severely damaged a hanger at the Red Oak airport and dropped some trees onto homes in the region.
Hail up to baseball-size was accompanied by thunderstorm wind gusts estimated at around 70 mph around the Stanton area. Some crops north of Stanton were destroyed and vehicle and home damage was noted across the area.
Hail up to baseball-size was accompanied by thunderstorm wind gusts estimated at around 70 mph around the Stanton area. Some crops north of Stanton were destroyed and vehicle and home damage was noted across the area.
Thunderstorm wind gusts estimated at over 60 mph severely damaged some grain bins in the Villisca area and caused widespread tree damage as well. Some of the fallen trees damaged homes and vehicles and the winds were accompanied by hail at least golf ball-size which also damaged vehicles and homes.
Hail at least up to golf ball-size was accompanied by thunderstorm wind gusts estimated at over 60 mph. The winds and hail caused extensive tree, vehicle and home damage in the area.
Thunderstorm wind gusts estimated at around 70 mph and at least one inch hail caused extensive damage in a swath from Shambaugh through College Springs, Coin and into the Braddyville area. Numerous north or east facing windows and siding across these areas were broken out or damaged, power lines and trees were downed and crop damage was extensive. More than 80 power poles were snapped from Highway 2 to south of Coin, and the downed poles and lines essentially closed off the south or east routes in or out of town. Some residents claimed it was the worst storm that they had ever witnessed.
Hail at least 1 inch in diameter was accompanied by thunderstorm wind gusts estimated at around 70 mph. The wind driven hail caused extensive damage in a swath from Shambaugh through College Springs and into the Braddyville area. Numerous north or east facing windows and siding were broken out or damaged, power lines and trees were downed and crop damage was extensive. More than 80 power poles were snapped from Highway 2 to south of Coin. Some residents claimed it was the worst storm they had ever witnessed.
Near the intersection of Highway 30 and I29.
The hail lasted for around 15 minutes.
Pea to quarter-size hail was reported by the public in the Glenwood area. The hail was accompanied by wind gusts estimated at 60 mph or stronger.
Pea to quarter-size hail was accompanied by wind gusts estimated at 60 mph or stronger. Trees and large tree limbs were downed in the area and some vehicle and home damage was noted.
Thunderstorm wind gusts estimated at around 70 mph caused extensive tree and property damage in the Sidney area. The county Chief Deputy reported that there was a tree down on about every block. Pieces of a roof of an auto parts store blew off and damaged several vehicles in the area and a grocery store lost several windows. A barn collapsed from the winds as well. Power poles were snapped and the power was lost across a large part of the area.
Thunderstorm wind gusts estimated at around 60 mph downed several trees in the Shenandoah area.
Thunderstorm wind gusts were measured at 58 mph by the Awos in Clarinda.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2011Every state in 2011This day in weather historyWarnings in Iowa, August 2011
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: 326009, 326013, 326015, 326016, 326030, 326017, 326035, 342761, 326019, 334980, 334981, 326021, 326040, 326041, 334993, 334997, 335050, 326044, 326047, 326055, 342768, 326056, 326057, 326058, 326060, 326061, 334985, 326064, 334632, 326065, 334629, 326068.