An upper level disturbance combined with the return flow of warmer and more unstable air and fueled a thunderstorm complex that dropped down the Missouri River Vally during the mid to late morning hours of July 12th. The storms produced mainly strong winds.
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The episode as NWS OAX wrote it up.
An upper level disturbance combined with the return flow of warmer and more unstable air and fueled a thunderstorm complex that dropped down the Missouri River Vally during the mid to late morning hours of July 12th. The storms produced mainly strong winds.
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 Jul 12, 1:55 AM CST, 7 hours 35 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 255 AM CDT SUN JUL 12 2009 .DISCUSSION... MODELS IN GENERAL NOT DOING VERY WELL WITH SUBTLE FEATURES...AND ALSO NOT IN AGREEMENT WITH ONE ANOTHER. THE NAM DOES NOT PICK UP ON THE SOUTHERN MCS THAT HAS MOVED OUT OF NORTHWEST KANSAS...AND HAS THE NORTHERN MCS TOO FAR NORTH INTO SOUTH DAKOTA. MEANWHILE...THE GFS SEEMS TO PERHAPS A SLIGHTLY BETTER HANDLE ON INITIAL CONVECTION AND DOES MOVES THE SOUTHERN MCS EASTWARD ALONG THE KS/NE BORDER THIS MORNING...AND DOESNT REALLY ALLOW THE NORTHERN MCS TO PROPAGATE EASTWARD AT ALL AS IT RUNS INTO LESS FAVORABLE INSTABILITY. THUS...WILL HAVE SOME MORNING CHANCES IN THE FORECAST FOR THE REMNANTS OF EITHER MCS TO AFFECT THE CWFA...BUT MOSTLY FOR SOUTHWESTERN CWFA...ALTHOUGH THE REMAINS OF THE MCS ACROSS CENTRAL NEBRASKA COULD ALSO AFFECT US THIS MORNING. FOR THIS AFTERNOON...LOOKING AT WATER VAPOR IMAGERY...IT APPEARS THERE MAY BE ANOTHER IMPULSE MOVING OUT OF THE 4 CORNERS REGION...AND ALSO A WAVE MOVING INTO THE NORTHERN PLAINS WHICH IS HELPING TO TRIGGER CONVECTION IN THE BLACK HILLS EARLY THIS MORNING. THE COMBINATION OF THESE TWO WAVES SHOULD TRIGGER ADDITIONAL ACTIVITY THIS AFTERNOON...BUT UNCERTAIN OF THE AMOUNT OF INSTABILITY THAT WE CAN ATTAIN GIVEN THE CONVECTIVE DEBRIS CLOUDINESS MOVING OVER THE CWFA EARLY THIS MORNING. NEVERTHELESS...WILL HAVE 30/40 POPS FOR THIS AFTERNOON...AND WILL LINGER A CHANCE INTO THE EVENING WITH GREATEST POPS BOTH NORTH AND SOUTH... ALTHOUGH HAVE KEPT THE FORECAST DRY AFTER MIDNIGHT TONIGHT AS ACTIVITY CONTINUES TO PUSH INTO THE LOWER MISSOURI RIVER VALLEY. REGARDING SEVERE POTENTIAL...IT WILL BE HIGHLY DEPENDENT ON HOW MUCH CLEARING WE CAN ACHIEVE THIS AFTERNOON...BUT HAVE MY DOUBTS...ALTHOUGH A SLIGHT RISK STILL SEEMS REASONABLE. KEPT MONDAY DRY FOR NOW...BUT DID BRING IN THE NEXT CHANCE FOR STORMS MONDAY NIGHT AND TUESDAY AS A COLD FRONT BEGINS TO PUSH INTO THE REGION. MONDAY NIGHT WOULD BE PREFRONTAL ACTIVITY WITH A POSSIBLE MCS ROLLING IN FROM THE NORTHWEST...THEN HAVE A CONTINUED THREAT ALONG/AHEAD OF THE FRONT THAT PUSHES THROUGH DURING THE DAY TUESDAY. BEYOND THEN...NORTHWEST FLOW PREVAILS. WEDNESDAY LOOKS DRY FOR SURE...AND POSSIBLY EVEN INTO THURSDAY...ALTHOUGH THE 00Z GFS IS INDICATING THE NEXT WAVE COULD BE ROLLING THROUGH THE AREA ABOUT 12 HOURS EARLIER THAN PREVIOUSLY THOUGHT. GIVEN LOW CONFIDENCE THAT FAR OUT...DECIDED TO NOT MAKE ANY CHANGES AND WILL LET THE DAY SHIFT TAKE A BETTER LOOK. REGARDING TEMPERATURE TRENDS...DID NOT STRAY TOO FAR FROM GUIDANCE EARLY...ALTHOUGH MOS DIFFERENCES INCREASE QUITE A BIT BY TUESDAY WHEN THE COLD FRONT MOVES IN...THUS TRIED TO BLEND A LITTLE MORE THEN TO ACCOUNT FOR TIMING DIFFERENCES AMONGST THE MODELS. && .AVIATION... FOR TAF SITES KOFK/KOMA/KLNK FORECAST VALID THROUGH 13/06Z. SOMEWHAT DIFFICULT AVIATION FORECAST THIS MORNING WITH REMAINS OF CONVECTION MOVING THROUGH THE REGION...AS WELL AS NEW CLOUD DEVELOPMENT AND POSSIBLY THUNDERSTORM DEVELOPMENT IN THIS WEATHER PATTERN. GIVEN THE RECENT GROWTH TRENDS OF THE CONVECTIVE CLUSTER IN SOUTH CENTRAL NEBRASKA...WILL PLAN ON THOSE SHOWERS AND STORMS AND ASSOCIATED IFR CIGS REACHING KLNK AROUND SUNRISE. KOMA AND KOFK WILL HAVE LOWER CHANCES OF THUNDERSTORM ACTIVITY...BUT CERTAINLY HIGH ENOUGH TO MENTION IN THE TAFS. ALSO EXPECT CIGS OF 020-040 TO DEVELOP IN KOMA AND KOFK BY SUNRISE. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && DEWALD/NIETFELD
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 515 AM CDT SUN JUL 12 2009 IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034- 042>045-050>053-065>068-078-088>093-130015- 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- 515 AM CDT SUN JUL 12 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN NEBRASKA AND SOUTHWEST IOWA. .DAY ONE...TODAY AND TONIGHT SCATTERED THUNDERSTORMS WILL MOVE THROUGH PORTIONS OF SOUTHEAST NEBRASKA EARLY THIS MORNING...MAINLY SOUTH OF INTERSTATE 80 AND ESPECIALLY NEAR THE KANSAS BORDER. THESE STORMS COULD CONTAIN GUSTY WINDS UP TO 30 OR 40 MPH AND POSSIBLY SOME SMALL HAIL. OTHERWISE...ADDITIONAL THUNDERSTORMS WILL BE POSSIBLE LATER THIS AFTERNOON AND EVENING AS ANOTHER WEATHER IMPULSE MOVES INTO THE AREA. IF THE CLOUDS THIS MORNING CAN BREAK UP ENOUGH TO ALLOW ENOUGH INSTABILITY TO DEVELOP...A FEW SEVERE STORMS MAY BE POSSIBLE WITH LARGE HAIL AND DAMAGING WINDS THE PRIMARY HAZARDS. THUNDERSTORM CHANCES SHOULD PUSH SOUTH AND EAST OUT OF THE AREA BY MIDNIGHT. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY MORE THUNDERSTORMS ARE POSSIBLE MONDAY NIGHT THROUGH TUESDAY NIGHT AS A COLD FRONT BEGINS TO MOVE THROUGH THE AREA. SOME SEVERE STORMS MAY BE POSSIBLE WITH THIS ACTIVITY ALSO. .SPOTTER INFORMATION STATEMENT... STORM SPOTTER ACTIVATION MAY BE NEEDED IN SOME AREAS THIS AFTERNOON AND EVENING ACROSS THE OUTLOOK AREA. DEWALD
The Omaha radar (KOAX), 88 km away, was scanning. The volume nearest the first event began at 15:30 UTC.
2 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds estimated at 60 mph downed a few trees and power lines from west of Harlan into town.
Thunderstorm winds estimated at close to 60 mph downed a large tree branch in the area.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2009Every state in 2009This day in weather historyWarnings in Iowa, July 2009
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: 171140, 171142.