Update: Another Great Midwest Flood of 1993 This Summer? There Are Still Concerning Signs

Jonathan Erdman
Published: June 7, 2019

Much of the Midwest and Plains have received a record-soaking since last summer that has primed the area in a way similar to the Great Flood of 1993 and dramatically increased the chance for another potential major summer flood event there.

Flooding already smashed records in parts of the nation's heartland this spring.

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In March, rapid snowmelt and heavy rain led to record flooding in Nebraska, Iowa and other Midwest states, including the destruction of a dam.

On April 30, a temporary levee protecting Davenport, Iowa, failed, sending water pouring into downtown buildings. Three days later, the Mississippi River at nearby Rock Island, Illinois, ticked above its previous record crest from 1993, buoyed by recent heavy rain and water from melted snow upstream.

Heavy rain in parts of the Plains and Midwest in May drove the Mississippi River to its highest level since 1993 at Hannibal, Missouri; Alton, Illinois; and St. Louis.

The mention of 1993 probably caught your attention, particularly if you lived in the Mississippi and Missouri valleys at the time.

The Midwest flood of 1993, also known as The Great Flood of 1993, was arguably the nation's most widespread, destructive flood of record since the Great Flood of 1927 on the Mississippi River.

Nearly 150 major rivers and tributaries flooded from Illinois to Kansas to the Dakotas, inundating at least 15 million acres of farmland and submerging at least 75 towns, according to a summary by NOAA's Lee Larson. Some rivers stayed above flood stage for 200 days.

At least 787 levees either failed or were overtopped. Tens of thousands were evacuated, some permanently. At least 10,000 homes were damaged or destroyed. NOAA estimated damages of $37.3 billion (2019 dollars) from the flood, making it the nation's costliest non-tropical inland flood.

In several locations along the Mississippi River, the longevity of flooding this year already set records that dated to the Great Flood of 1927, the worst in modern history in the lower Mississippi River.

To be clear: We're not predicting a repeat of the massive 1993 flood this summer. We can't determine if, where or how severe summer flooding may be in the Midwest.

But the conditions that could create an exceptional summer flood in some places exceed those that led to the Great Flood of 1993.

Conditions Primed For Summer Flooding

The seeds of a major flood are sown days, weeks and even months in advance.

While a procession of summer thunderstorm clusters ultimately triggered the massive 1993 flood, a wet fall, snowy winter and wet spring beforehand laid the foundation for that event.

What's worrisome this year is that many parts of the upper Mississippi and Missouri valleys have an even wetter floor for potential summer flooding than in the months prior to summer 1993.

According to data compiled by NOAA's National Centers for Environmental Information, seven of nine Plains and upper Midwest states had a wetter fall in 2018 than 1992.

The map above shows the difference in statewide precipitation in fall (September-November) 2018 compared to the same period in 1992. A positive/negative precipitation difference (in inches) indicates the state had a wetter or drier fall in 2018 than 1992.
(Data: NOAA/NCEI; Graphic: Infogram)

Kansas, Iowa, Wisconsin and Illinois had wet September-November periods both in 2018 and 1992, but owa had its third-wettest Fall on record in 2018.

Eight of nine states were wetter this winter than in 1992-93. The only exception was Kansas, which was only slightly less wet in winter 2018-19 than its second-wettest winter in 1992-93.

The map above shows the difference in statewide precipitation in winter (December-February) 2018-19 compared to the same period in 1992-93. A positive/negative precipitation difference (in inches) indicates the state had a wetter or drier winter in 2018-19 than 1992-93.
(Data: NOAA/NCEI; Graphic: Infogram)

Seven of those nine states had a top-10-wettest winter in 2018-19, headed by Wisconsin's wettest December-February in records dating to 1895.

This showed up particularly well in seasonal snowfall. Parts of the upper Mississippi and Missouri valleys picked up 30 inches or more of snow in 2018-19 than they did in 1992-93. Eau Claire, Wisconsin, even smashed a seasonal snowfall record with just shy of 100 inches.

Plotted above is the difference in seasonal snowfall (in inches) in 2018-19 compared to 1992-93, prior to the Midwest flood of 1993. A positive/negative value indicated 2018-19 picked up more/less snowfall than 1992-93.

The beat continued into spring, again among the top 10 wettest on record for almost every Midwestern state and much wetter than spring 1993, particularly in an arc from South Dakota to Kansas to Missouri and Illinois.

The map above shows the difference in statewide precipitation in spring (March-May) 2019 compared to the same period in 1993. A positive/negative precipitation difference (in inches) indicates the state had a wetter or drier spring in 2019 than 1993.
(Data: NOAA/NCEI; Graphic: Infogram)

NOAA's U.S. climate report found the 12-month period ending in May 2019 was the single wettest 12-month period in U.S. history, according to Bob Henson, meteorologist and climate expert at Weather Underground. It was a record wet June-May in 18 states, including Iowa, Kansas, Nebraska, South Dakota and Wisconsin.

Where We Stand Now

The upshot of this is that there is little capacity to absorb heavy rain right now.

An expansive area of the Midwest and Plains are in the 99th percentile for soil moisture relative to early-June averages, according to an analysis by NOAA's Climate Prediction Center.

Being in the 99th percentile is great if it's your son or daughter's test scores, but in this case, it's dangerous: Any significant rain in these areas won't soak into the soil, but will instead runoff quickly into creeks and rivers.

Analysis of soil-moisture content percentiles on June 5, 2019. Areas in the darkest green contour have soil moisture in the top-1 percent of historical values for June 5.
(NOAA/Climate Prediction Center)

And on top of that, those rivers have little capacity right now.

At the time of this article, just under 250 river gauges were reporting levels at least above flood stage, primarily in the Mississippi River Basin, but also in stretches of the Missouri River, Arkansas River and other tributaries.

This map shows river and stream gauges above flood stage (black triangles), those in the 99th percentile for streamflow (in blue) and those at least in the 95th percentile (in teal) on June 7, 2019.
(NOAA, USGS)

The Wild Card: Summer's Thunderstorm Clusters

The massive 1993 flood was ultimately produced by a relentless summer parade of torrential rain-producing thunderstorm clusters over the same areas in the Plains and Midwest.

An area of Kansas, eastern Nebraska, Iowa, southern Minnesota, western Wisconsin, Illinois and Missouri picked up 20 inches or more of rain from June through August that year. Some parts of Iowa measured up to 38 inches of rain.

One location in Worth County, Missouri, picked up 30.3 inches of rain in July 1993 alone, according to a NOAA NCEI report.

These thunderstorm clusters, known to meteorologists as mesoscale convective systems, are common in the summer in the Midwest. Any one of these clusters is capable of producing heavy rain over a period of a few hours.

But in summer 1993, a persistent weather pattern locked in place, generating a seemingly endless barrage of these thunderstorm clusters. According to the aforementioned NOAA summary, measurable rain fell every day between late June and late July in parts of the upper Mississippi Basin.

The dominant weather pattern triggering the Midwest flood of 1993 included an unusually strong, persistent jet-stream dip over the West and a waffling frontal boundary in the nation's midsection, igniting clusters of thunderstorms in the Plains and Midwest.

So if summer conditions in 1993 ultimately caused the Great Flood, what can we say about conditions this summer?

Long-range outlooks of summer precipitation are notoriously challenging, as precipitation bullseyes are often dictated by thunderstorm clusters, not to mention tropical cyclones near the Gulf and East coasts.

NOAA's Climate Prediction Center has the highest odds of above-average precipitation through August in an area from the Rockies to the Plains, including parts of the Mississippi Valley.

Precipitation outlook through August, issued by NOAA's Climate Prediction Center on May 16, 2019. Darker green/brown contours indicate increasing chances of above/below-average precipitation during that time.
(NOAA/Climate Prediction Center )

Given the highly saturated conditions currently in place, if a stagnant, persistent weather pattern with a jet-stream dip or slow-moving low pressure aloft in the West sets up this summer, similar to what occurred in late May, major summer flash flooding and river flooding is possible in parts of the nation's midsection.

Whether this pattern sets up, how long it persists, where the thunderstorm clusters track and how severe the resulting flooding remains to be seen.

Weather Underground's Bob Henson noted the wet soil could also enhance rainfall produced by those thunderstorms over that wet ground in a positive feedback.

Even if this summer's flooding doesn't come close to 1993's magnitude, there have been other notable flood events in recent years that may be similar to the type that may take place in 2019.

In 2011, for example, record-high water on the Souris River flooded 4,000 homes in Minot, North Dakota, and numerous levees were breached along the Missouri River, flooding farmland and stretches of Interstate 29 in Iowa.

June 2008 was the flood of record in Cedar Rapids, Iowa, after a levee broke, putting much of downtown underwater. A stretch of land between man-made Lake Delton, Wisconsin, and the Wisconsin River eroded, emptying the lake.

Flooding this summer hopefully won't reach the high bar set by 1993, but there is little wiggle room for rain after a historic 12-month stretch of rain and snow.


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