Summer Midwest flooding could rival 1993 as most expensive in history

Heavy rains this summer could trigger floods that would rival America's most expensive flood disaster of all-time, said NOAA in a press release yesterday. The most expensive flood in America occurred in 1993, when torrential summer rains caused a $25 billion flood along the Missouri River and surrounding regions of the Upper Midwest. Record 100-year flooding has already occurred along many stretches of the Missouri, Souris, James, North Platte, and other rivers in the Upper Midwest over the past month. With rivers running high and soils completely saturated this summer, just a small amount of rain could trigger more flooding, including areas that have already seen major to record flooding. "The sponge is fully saturated--there is nowhere for any additional water to go," said Jack Hayes, Ph.D., director of NOAA's National Weather Service. "While unusual for this time of year, all signs point to the flood threat continuing through summer."

Throughout the rest of the summer, the highest flood risk areas include:

- North Central U.S. including Souris River (North Dakota) and Red River of the North (border of North Dakota and Minnesota), Minnesota River (Minnesota), Upper Mississippi River (Minnesota and Iowa), and Des Moines River (Iowa)
- Lower Missouri River from Gavin’s Point (Nebraska and South Dakota border) downstream along the border of Nebraska and Iowa, continuing through the borders of Kansas and Missouri then through Missouri to the Mississippi River
- Tributaries to the Lower Missouri including the James and Big Sioux Rivers in North Dakota
- Lower Ohio River Valley including the White, Wabash and lower Ohio River
- East of Rockies: North Platte River in Colorado, Wyoming and Nebraska and Yellowstone River in Wyoming and Montana
- West of Rockies: Utah and Colorado

The latest 3-month precipitation forecast from NOAA's Climate Prediction Center (Figure 1) show an above average chance of heavy rains over much of the Upper Midwest this summer.


Figure 1. Precipitation forecast for July-August-September as issued by NOAA's Climate Prediction Center. Above average chances of heavy precipitation (green colors) are expected over much of the Upper Midwest.

June 2011 was highest single month of runoff in Missouri River Basin since 1898
The Army Corps of Engineers announced this week that runoff into the Missouri River Basin above Souix City, Iowa during June was the highest single runoff month since records began in 1898. June 2011 runoff into the Missouri River Basin above Sioux City was 13.8 million acre feet (maf.) The previous record was 13.2 maf in April of 1952; May of this year now holds the record for 3rd greatest runoff, 10.5 maf. The May and June combined runoff totaled 24.3 maf, just short of the normal total annual runoff for the entire basin which is 24.8 maf. Four federal levees and 11 non-federal levees have breached or overtopped across Iowa, Kansas, Nebraska and Missouri so far this year along the Missouri River.


Figure 2. Flood heights were rising rapidly on the Yellowstone River the night of the pipeline disaster on July 1, 2011. A few hours after the disaster, the river crested just below moderate flood stage of 14' in Billings, about twenty miles downstream from where the pipeline broke in Laurel, Montana. This was the 3rd highest flood on record at this location, with records extending back to 1904. Image credit: NWS.

Oil spill in Yellowstone River likely influenced by flooding
An Exxon Mobil oil pipeline under the Yellowstone River burst on Friday night, spilling at least 42,000 gallons of oil into the river. The prevailing theory among officials and the company is that the raging Yellowstone eroded the riverbed and exposed the line to damaging rocks or debris. The river was rising rapidly the night of the break, and crested at 13.95', the third highest flood in recorded history. Records extend back to 1904 at the site. Crude has been reported as far as 240 miles downstream, although most appears to be concentrated in the first 25 miles. The Yellowstone is a tributary of the Missouri River.


Figure 3. Morning satellite image of 96L and the tropical wave approaching South America.

Invest 96L in the Atlantic little threat
An area of disturbed weather in the Gulf of Mexico centered just west of the Florida Keys has been labeled Invest 96L by NHC this morning. The disturbance is under high wind shear, about 20 - 25 knots, and the latest SHIPS model forecast predicts the shear will be 15 - 25 knots over the next two days as 96L moves slowly northwards towards the Florida Panhandle. The high shear should keep any development slow. Water vapor satellite images show that 96L is located on the east side of an upper-level low pressure system centered a few hundred miles south of New Orleans. This upper level low is pumping dry, stable air into the west side of 96L, which will retard development. There is no sign of a surface circulation in 96L, and none of the reliable computer models is developing it. NHC is giving 96L a 10% chance of developing into a tropical depression by Saturday.

The other area of note is a tropical wave about 600 miles east of the southernmost Lesser Antilles Islands. This wave is under 10 - 20 knots of wind shear, and may show some modest development before moving ashore over the northern coast of South America on Saturday. NHC is giving this disturbance a 10% chance of developing into a tropical depression by Saturday. The disturbance is too close to the Equator to leverage Earth's spin much, which will slow any possible development.

Jeff Masters