A Week of Storms in USA – Flash Floods in South Dakota, Wisconsin, Texas and Arizona

Short lived but intense storms bringing high levels of rainfall have been a feature of the weather across parts of the USA over the last few days.

Earlier this week the remnants of Tropical Storm Erika brought heavy rainfall to South Carolina and Florida, with severe flooding reported in Charleston and North Charleston, where around 100 families had to be evacuated.

Elsewhere in the USA, storms accompanied by intense rainfall have caused flash floods in Wisconsin, Arizona, Texas and South Dakota, where 0.71″ (18 mm) of rain fell in 5 minutes in Sioux Falls on Thursday 27 August, 2015.

South Dakota

Bringing back memories of the summer storms of 2004, Sioux Falls in South Dakota, was bit by a series of thunderstorms, described by National Weather Service meteorologists as “train echoes”.

A remarkable feature of the storms was just how much fell in a short space of time. Sioux Fall National Weather Service said that 2.73″ (69mm)  of rain fell within 25 minutes at Sertoma Park. The same gauge recorded 0.71″ of rain within 5 minutes.

sioux falls rainfall
Image: NWS Sioux Falls
south dakota rainfall totals
Rainfall totals for Sioux Falls Area for 27 August 2015. Image: NWS Sioux Falls

Extensive street flooding was reported and Sioux Falls police issued a “no travel advisory”. Boats were needed to help stranded residents and drivers. Some residents had to evacuate their homes and the Red Cross opened a shelter for those displaced.

In 2004, Sioux Falls was hit by summer thunderstorms that caused major flooding throughout the city and sparked concerns about the storm drainage system in flood-prone areas. The storms last week were one of the biggest tests faced by the city’s new storm drainage system that had undergone a $65 million upgrade.

A Sioux Falls officials said that investment into the city’s waste water system had paid off. In particular the new monitoring technology enabled the water authority to track the flow of the storm water in the system, to see where attention was required and where storm might need to be held or diverted.

Wisconsin

Parts of Chippewa County in western Wisconsin saw over 5 inches of rain during the evening of Wednesday 02 September 2015, prompting the National Weather Service to issue flood warnings for areas around north Dunn and north-west Chippewa counties. Street flooding was reported in both areas, causing problems for traffic. Some flooding was also reported in Dunn County.

At 14:30 yesterday, 02 September 2015, NWS said that “heavy rain, with rates to 2-3 inches per hour, is moving through Chippewa Falls”. They stressed that drivers should avoid flooded roads.

Texas

Local media reported that Brownsville in South Texas experienced 3 feet deep flood water after a storm on Monday, 31 August, 2015 dumped high levels of rain in a short space of time. At the height of the storm, the rain was reportedly falling at a rate of 2 to 3 inches per hour.

On Monday, NWS Brownsville said the thunderstorm had dumped 3-5″ of rain and caused widespread flooding in the Brownsville area. Unofficial weather watchers reported 6.02″ (152 mm) of rain near Rancho Viejo for the 31 August 2015. Further rainfall is expected, but NWS Brownsville say they aren’t “expecting the “craziness” like Monday”.

Street flooding caused problems for drivers, and some were forced to abandon their vehicles. There were also reports of evacuations but no reports of casualties. The heavy rain also caused flooding in the Mexican city of Matamoros, just across the border from Brownsville.

Arizona

Flash flooding and strong monsoon storms hit the Phoenix area late on Monday 31 August 2015. Several roads were flooded and several cars reported stranded. Firefighters were needed to carry out flood rescues for around 10 people stranded in their vehicles, including a mother and a 1 month old baby.

The storms forced Phoenix airport to close at around 7pm, but it was able to re-open just 2 hours later. The storms also brought down power lines and caused power outages to over 50,000 homes.

NWS Phoenix said that “scattered thunderstorms developed to the south and west of the Phoenix metro area during the late afternoon hours of 31 August 2015.”

The initial storms were particularly strong, but they intensified rapidly as they moved into the west valley, and “several locations saw heavy rainfall with gauges reporting over an inch of rain north and west of Sky Harbor Airport.” NWS Phoenix said yesterday that they are expecting further storm activity around Thursday or Friday this week.