May began on a wet note as overnight rains ending early on the 1st brought precipitation to most of the HSA. The heaviest amounts were over the Iowa/Cedar basin where Hampton  had 1.73", Tripoli 1.24",  Shell Rock 1.20", Iowa Falls 1.10" and  Popejoy 1.02". Amounts close to an inch were also observed over the southwest, where Blockton picked up 0.95".  Forecasts of additional heavy rain during the overnight of May 1-2 prompted the issuance of a Flood Potential Outlook (ESF), for the especially for rivers in the southwest and south central parts of the HSA. Extremely heavy rainfall was observed during the overnight hours of May 1-2 , but not exactly in the areas forecast the previous afternoon. Repeat convection across parts of Sac and Calhoun counties, in the upper Raccoon River basin produced some extraordinary rainfall accumulations. WSR-88D radar indicated over 12" of rain may have fallen, while several unofficial reports of over 8" were received by the NWS. The highest amounts fell along the Sac and Calhoun county line between the towns of Yetter and Lytton, where best estimates from radar, satellite and gages suggest that at least 9 inches of rain fell. Typically, the highest official rainfall report was substantially lower, with Rockwell City (RKWI4) reporting 4.60", although the Data Collection Platform (DCP) at Sac City (SCRI4) measured over 6 inches in 10 hours. Flash flooding occurred along Camp Creek , east of Yetter, where moving water covered county road D53 and swept two motorists off the road. Both were rescued or escaped from their vehicles, narrowly averting tragedy. Flash Flood Warnings for Sac and Calhoun counties were issued well in advance of the most severe flooding. The heaviest rainfall was concentrated in the North Raccoon River basin, which led to moderate flooding along this river from Jefferson to Perry. Initial crest forecasts were for near record levels at Perry, based on the combination of runoff and heavy quantitative precipitation forecasts (QPF). Fortunately, the QPF failed to verify and the crest was quite a bit (more than 6 feet) lower than initially forecast.  Further south, contributions from the Middle and South Forks of the Raccoon were quite low, so only minor flooding was observed several days later along the mainstem Raccoon from Van Meter to Des Moines.  Also of concern at this time was the increasing inflow to Saylorville Reservoir in response to the heavy spring snowmelt runoff and rainfall in the upper Des Moines River basin. The river gage at Stratford reached its 9th highest level on record at 21.28 feet on the 6th, with a flow of about 27,550 cubic feet per second (cfs) into the reservoir. As of May 10th  the pool elevation had reached over 877 feet, which was the highest level since the Floods of 1993 (892 feet). The flood control elevation of the reservoir is 890 feet and the U.S. Army Corps of Engineers was making efforts to release enough water to draw down the pool elevation. Releases are increased above an 875 foot pool elevation and again after 884 feet. The reservoir eventually crested at 878.80 feet on the 13th and by months end had only fallen to 877.88 feet due to the wet weather all month.  Fortunately, with all the flooding that occurred, it was early enough in the year that agricultural damage was minimal.  Most of the flood waters spread into agricultural lands as opposed to flooding in urban areas.

Flood in BLACK HAWK, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in BUTLER, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in CALHOUN, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in CARROLL, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in CERRO GORDO, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in DALLAS, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in EMMET, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in FRANKLIN, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in GREENE, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in GRUNDY, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in GUTHRIE, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in HAMILTON, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in HANCOCK, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in HARDIN, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in HUMBOLDT, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in KOSSUTH, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in MARSHALL, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in PALO ALTO, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in POCAHONTAS, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in POLK, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in SAC, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in STORY, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in WEBSTER, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in WINNEBAGO, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in WORTH, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.

Flood in WRIGHT, IOWA
From 01-MAY-01 00:00:00 to 09-MAY-01 18:00:00 (CST)
Property damage: 75K
Reported by: OFFICIAL NWS OBS.