An upper level vorticity maximum, the remnants of former tropical storm Don, moved into Iowa during the afternoon. Two areas of thunderstorms developed.
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The episode as NWS DMX wrote it up.
An upper level vorticity maximum, the remnants of former tropical storm Don, moved into Iowa during the afternoon. Two areas of thunderstorms developed. One was across southern Iowa, closer to the center of the system. Conditions were more favorable in this area with CAPE values around 4000 J/kg and lifted indices around -5 C. The freezing level was near 16,000 feet, limiting the production of hail. With precipitable water values around 2.2 inches over southern Iowa, the thunderstorms that formed produced heavy rainfall. Over northwest Lucas County, rainfall of 3 to 5 inches occurred in about 2 hours. Fortunately, antecedent soil conditions were very dry and the rain caused little problems. Over northeast Iowa, a small cluster of storms formed in the Waterloo area. Numerous reports of funnel clouds were received just north of the Waterloo Airport. Though they extended about half way to the ground, there was no circulation at ground level. The storms were clearly not supercells and the funnel clouds would have produced no more than landspouts.
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 Aug 4, 2:23 PM CST, 2 hours 17 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 323 PM CDT THU AUG 4 2011 .SHORT TERM /TONIGHT/... PRIMARY CONCERN TONIGHT WILL BE CONVECTIVE TRENDS. MCV FROM OVERNIGHT CONVECTION IS MOVING EASTWARD ACROSS MO...HOWEVER FORCING ASSOCIATED WITH LINGERING H85/H7 TROUGH FROM MCV INTO ERN NE WILL CONTINUE TO PRODUCE UVM ACROSS IA INTO AT LEAST THIS EVENING. AIRMASS IS CURRENTLY UNCAPPED WITH 1500 J/KG MLCAPE AND 100 PLUS J/KG 0-3KM CAPES. WITH WEAK MEAN WIND AND EFFECTIVE SHEAR...MEANDERING OUTFLOW BOUNDARIES IN THESE FAVORABLE THERMODYNAMIC CONDITIONS MAY PRODUCE A FEW FUNNEL CLOUDS OR MICROBURSTS IN COLLAPSING CELLS. WITH SLOW MOVEMENT AND PWS AT OR ABOVE 2 INCHES...LOCALLY HEAVY RAINS HAVE OCCURRED AND MAY CONTINUE. CONVECTION WILL STILL BE POSSIBLE...BUT LIKELY DIMINISH OVERNIGHT WITH LOSS OF HEATING. HAVE ALSO ADDED FOG MENTION OVER CENTRAL AND SOUTHERN AREAS. WITH LIGHT WINDS...SCATTERED RAINS...AND DEWPOINTS AOA 70F...FOG POSSIBLE. .LONG TERM /FRIDAY THROUGH THURSDAY/... WEAK SYSTEM EXPECTED TO BE EAST OF REGION LATER TONIGHT THOUGH WATER VAPOR IMAGERY SHOWS ANOTHER UPSTREAM SHORT WAVE IN SW COLORADO THIS AFTERNOON. MODELS HAVE BEEN HAVING DIFFICULTY WITH THE TRACK AND STRENGTH OF THIS FEATURE AS WELL...THOUGH IT LOOKS LIKE IT SHOULD IMPACT THE AREA TOMORROW AND HAVE INCREASED POP OVER THE AREA TO CHANCE VALUES OVER THE SOUTH FOR THE AFTERNOON HOURS ESPECIALLY. NEXT SYSTEM WILL BE THE NORTHERN STREAM SHORT WAVE APPROACHING FROM WESTERN MN BY LATE SAT AFTERNOON. WE CONTINUE TO BE OUTLOOKED FOR SVR CHANCES OVER THE WEST...THOUGH SOME UNCERTAINTIES REMAINS AS TO HOW MUCH DAYTIME HEATING WILL INFLUENCE THE EVOLUTION OF THE STORMS AS THEY MOVE THROUGH. WESTERLY FLOW INCREASES ALOFT WITH BEST WINDS OVER THE NORTH. FOR NOW...GFS HAS THE NORTHEAST BETTER PEGGED FOR SFC CONVERGENCE AND SUPPORT FROM ALOFT. HAVE INCLUDED POP FOR THE ENTIRE AREA THROUGH THE NIGHT HOURS AND THEN FIRST REAL SHOT OF DEW POINT CLEARING AIRMASS DRIVING SOUTHEAST INTO THE AREA OVER THE NORTHEAST SECTIONS ESPECIALLY. THE AIRMASS OVER THE SOUTHWEST THIRD MAY NOT REALIZE THE DRYING AS MUCH...WITH THE RIDGE HOLDING ON OVER THAT PORTION OF THE FORECAST AREA. THE PATTERN HAS SHIFTED TO A MORE PROGRESSIVE WNW FLOW WITH MORE ENERGY EXPECTED TO CROSS THE PLAINS NEXT WEEK. THIS SHOULD ENHANCE OUR CHANCES FOR RAIN ALONG WITH SOME QUICK CHANGES IN AIRMASS OVER THE AREA. WITH ANOTHER FRONT APPROACHING ON TUESDAY...TEMPS SHOULD SHOOT UP ON MONDAY BRIEFLY BEFORE WE SEE ANOTHER COOLER AIRMASS ENTERING THE PICTURE BY TUESDAY. A CANADIAN HIGH PRESSURE SYSTEM SHOULD SETTLE INTO THE REGION FOR WED AND THURSDAY PRIOR TO ANOTHER SYSTEM LATE IN THE PERIOD. FOR NOW...HAVE HELD OFF ON ANY PRECIP LATE DUE TO TIMING UNCERTAINTIES. SOME ADJUSTMENTS TO POP WILL UNDOUBTEDLY NEED TO BE MADE NEXT WEEK...BUT THE GOOD NEWS IS THAT THE NW FLOW SHOULD CONTINUE TO SUPPRESS THE TEMPERATURES FOR AT LEAST THROUGH THE EXTENDED. && .AVIATION...04/18Z INITIAL CONCERN WILL BE SLOW MOVING CONVECTION CURRENTLY AFFECTING CENTRAL IA BUT AVOIDING MOST SITES FOR THE TIME BEING...THUS NOTHING MORE THAN VCSH WORDING AT KFOD/KDSM/KALO. ONLY CARRIED IN THE BODY AT KOTM WHERE ISOLATED SOUTH CENTRAL SHOWERS MAY BUILD IN DAYTIME HEATING AS THEY WORK EASTWARD. NEXT ITEM OF CONCERN WILL BE FOG DEVELOPMENT OVERNIGHT. WITH LINGERING LOW LEVEL MOISTURE FUELED BY ADDITIONAL SCT CONVECTION...FEEL AT LEAST MVFR FOG DEVELOPMENT A GOOD BET. IFR/LIFR POSSIBLE AS WELL BUT HAVE ONLY GONE DOWN TO IFR UNTIL TRENDS BECOME MORE CLEAR. CONDITIONS SHOULD IMPROVE FRI MORNING...BUT MVFR CIGS MAY LINGER AFTER FOG LIFTS. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE && SHORT TERM/AVIATION...SMALL LONG TERM...REV
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 342 PM CDT THU AUG 4 2011 IAZ070>075-081>086-092>097-051100- CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 342 PM CDT THU AUG 4 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND SOUTHERN IOWA. .DAY ONE...THIS AFTERNOON AND TONIGHT SCATTERED SLOW MOVING THUNDERSTORMS ARE EXPECTED TONIGHT... ESPECIALLY DURING THE EVENING HOURS. LOCALLY HEAVY RAINS ARE POSSIBLE. A FEW STORMS MAY ALSO BE SEVERE WITH LARGE HAIL OR DAMAGING WINDS. AFTER THE PRECIPITATION DIMINISHES OVERNIGHT...FOG MAY FORM AND BE LOCALLY DENSE. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY ADDITIONAL THUNDERSTORM CHANCES ARE POSSIBLE FRIDAY...AND AGAIN LATE MONDAY AND TUESDAY. THERE IS A SLIGHT RISK FOR SEVERE WEATHER WITH THE ACTIVITY LATE SATURDAY. AT THIS TIME LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS. .SPOTTER INFORMATION STATEMENT... OUTSIDE OF A LOW POTENTIAL LATE SATURDAY...SPOTTER ACTIVATION IS NOT ANTICIPATED. IAZ035>039-044>050-057>062-051100- WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE- BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER- POWESHIEK- 342 PM CDT THU AUG 4 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...THIS AFTERNOON AND TONIGHT AN ISOLATED THUNDERSTORM IS POSSIBLE EARLY THIS EVENING. SEVERE WEATHER AND HEAVY RAINS ARE NOT ANTICIPATED. AFTER THE PRECIPITATION DIMINISHES OVERNIGHT...FOG MAY FORM AND BE LOCALLY DENSE. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY ADDITIONAL THUNDERSTORM CHANCES ARE POSSIBLE FRIDAY...AND AGAIN LATE MONDAY AND TUESDAY. THERE IS A SLIGHT RISK FOR SEVERE WEATHER WITH THE ACTIVITY LATE SATURDAY. AT THIS TIME LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS. .SPOTTER INFORMATION STATEMENT... OUTSIDE OF A LOW POTENTIAL LATE SATURDAY...SPOTTER ACTIVATION IS NOT ANTICIPATED. IAZ004>007-015>017-023>028-033-034-051100- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN- 342 PM CDT THU AUG 4 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHERN IOWA. .DAY ONE...THIS AFTERNOON AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY ADDITIONAL THUNDERSTORM CHANCES ARE POSSIBLE FRIDAY...AND AGAIN LATE MONDAY AND TUESDAY. THERE IS A SLIGHT RISK FOR SEVERE WEATHER WITH THE ACTIVITY LATE SATURDAY. AT THIS TIME LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS. .SPOTTER INFORMATION STATEMENT... OUTSIDE OF A LOW POTENTIAL LATE SATURDAY...SPOTTER ACTIVATION IS NOT ANTICIPATED. SMALL
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 245 PM CDT THU AUG 4 2011 IAZ070>075-081>086-092>097-050000- CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- INCLUDING THE CITIES OF...ATLANTIC...GREENFIELD...WINTERSET... INDIANOLA...KNOXVILLE...OSKALOOSA...CORNING...CRESTON...OSCEOLA... CHARITON...ALBIA...OTTUMWA...BEDFORD...MOUNT AYR...LEON... CORYDON...CENTERVILLE...BLOOMFIELD 245 PM CDT THU AUG 4 2011 ...CONDITIONS ARE FAVORABLE FOR FUNNEL CLOUDS... CURRENT ATMOSPHERIC CONDITIONS SUPPORT THE DEVELOPMENT OF FUNNEL CLOUDS FROM SOUTH OF INTERSTATE 80 TO THE MISSOURI BORDER. USUALLY...THESE FUNNEL CLOUDS CAN FORM FROM SHOWERS AND WEAK THUNDERSTORMS. THESE FUNNELS ARE NORMALLY BRIEF...DROP ONLY A FEW HUNDRED FEET FROM THE CLOUD BASE...AND RARELY BECOME A TORNADO OR CAUSE DAMAGE. HOWEVER...IF ONE IS SPOTTED...PLEASE REPORT IT IMMEDIATELY TO LOCAL LAW ENFORCEMENT FOR RELAY TO THE NATIONAL WEATHER SERVICE. IF A TORNADO WARNING WOULD BECOME NECESSARY... TAKE APPROPRIATE ACTION. SMALL
The Des Moines radar (KDMX), 144 km away, was scanning. The volume nearest the first event began at 22:37 UTC.
1 funnel cloud. Local standard time, as filed.
Rope funnel cloud reaching about half way to the ground, reported by multiple trained spotters and the observer at the Waterloo Airport. The funnel cloud lasted about 10 minutes before dissipating.
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: 319213.