A significant severe thunderstorm outbreak with heavy rainfall has affected areas from the Southern Plains to the Great Lakes and Northeast, with historic flooding in parts of the Central Mississippi Valley. Significant rainfall amounts of over ten inches occurred over saturated soils of the Central Mississippi Valley and surrounding watersheds. The rainfall produced historic flooding on some rivers, and the Mississippi River itself is expected to approach record flood stage at Cape Girardeau over the coming days. Flood impacts have been locally severe and include reports of property damage, numerous road closures, evacuations and water rescues. A levee breach has forced evacuations near Pocahontas, Arkansas.
Meanwhile, the same weather system produced severe thunderstorms with reports of damaging straight-line wind gusts, hail and tornadoes from the Southern Plains to the Northeast. Severe weather reports include one EF-4 tornado just east of Dallas. Reports of downed trees and powerlines with light property damage are widespread, with localized severe damage due to significant tornadoes. Straight-line wind gusts were also reported in Southern and Central Ontario, Canada.
General Significant Flood Outlook; SOURCE: National Weather Service
Local Storm Reports April 28-May 1; SOURCE: NOAA, Storm Prediction Center
Confirmed Tornado Tracks April 28-May 1; EF-4 (Red), EF-3 (Orange), EF-2 (Yellow), EF-0 (Teal); SOURCE: NOAA, National Weather Service
Radar-estimated 30-day rainfall; ending 8AM EDT (12 UTC) May 1; SOURCE: NOAA, U.S. National Weather Service
Radar-estimated 7-day rainfall; ending 8AM EDT (12 UTC) May 1; SOURCE: NOAA, National Weather Service
Hydrograph; Black River at Pocahontas; SOURCE: NOAA, National Weather Service
Hydrograph; Meramac River near Eureka; SOURCE: NOAA, National Weather Service
Hydrograph; Mississippi River at St. Louis; SOURCE: NOAA, National Weather Service
Hydrograph; Mississippi River at Cape Girardeau; SOURCE: NOAA, National Weather Service
Hazard data illustrated in the CAT-i map was taken from GC AdvantagePoint®, Guy Carpenter’s web-based risk management platform. GC AdvantagePoint users can view impacted areas on any map as well as see how their portfolios were affected. Please contact your broker or cat modeling analyst for further information.
In the final days of April, a period of heavy rainfall affected areas of the Central Mississippi Valley and surrounding watersheds. This included daily rainfall amounts of at least three to four inches over a widespread area and locally higher amounts of 10 to 15 inches. This heavy rainfall overwhelmed local watersheds with saturated soils, following a period of 30-day rainfall amounts that well exceeded 200 to 300 percent of normal. As a result, historic flooding has been observed for river systems in Arkansas, Illinois and Missouri along with localized flash-flooding. The U.S. National Weather Service (NWS) maintains flood and flash-flood watches and warnings for areas under threat.
Historic flooding has been observed for several affected rivers to include the Illinois River in Oklahoma, the Black River in Arkansas, the Current River in Missouri and the Meramec River in Missouri. The Black River at Pocahontas reached record flood stage (record height of water level above reference) the evening of May 2 and is expected to lower from major to moderate flood stage before tomorrow morning. Levee breaches on the Black River near Pocahontas have caused significant flooding concerns for the surrounding area. The Meramec River near Eureka saw record flood stage on May 2, with a secondary peak expected this weekend before lowering from major to moderate flood stage early next week. The Mississippi River at Saint Louis is now at major flood stage and is expected to crest over the coming days before lowering to moderate flood stage late this weekend. Downstream, the Mississippi River at Cape Girardeau has already reached major flood stage and is expected to approach record flood stage over the weekend before lowering to moderate flood stage late next week.
The heavy rainfall was driven by strong upper-air mechanics, abundant moisture, a large upper-air disturbance to the west and aggressive circulation along a surface front crossing the area. An area of surface low pressure then developed along this front in the Southern Plains and crossed into the Great Lakes area during the first days of May. South and east of the frontal boundary, moist, unstable air together with wind shear produced widespread severe thunderstorms. These thunderstorms produced tornadoes, hail and straight-line (nontornadic) wind gusts with concentrations from the Southern Plains and Mississippi Valley to the Northeast. Significant tornado reports include confirmed EF-4, EF-3 and EF-2 tornadoes east of Dallas, and confirmed EF-2 tornadoes in Mississippi.
As another frontal system crossed the area yesterday, another round of rainfall further amplified the flood threat in the Central Mississippi Valley, and some residual rainfall is also expected today.
According to media reports, the heavy rainfall and flooding caused authorities to shut down traffic and urge residents to evacuate certain areas due to possible levee breaches in West Alton and Franklin County. At least five fatalities due to flooding have been reported by the media.
Reports indicate that Governor Eric Greitens declared a state of emergency for all of southern Missouri. The State Emergency Management Agency, the Missouri State Highway Patrol, the Missouri National Guard and Missouri’s Task Force 1 Rescue Unit have deployed resources to manage response and recovery efforts.
Flooding on the Meramec River forced Missouri transportation officials to close Interstate 55, along with other major routes including Interstate 44 on May 3. The state Department of Transportation says the roads will remain closed for the remainder of the week.
Media reports indicate approximately 200 homes have been impacted by the floods and another 1,500 are under threat. The historic Bruns Bridge built in 1888, was also destroyed by floodwaters.
Authorities urged residents to evacuate certain areas, according to media reports. The Governor of Arkansas, Asa Hutchinson, indicated that deployment of resources to support response efforts includes 108 National Guard members. There have been more than 500 evacuations and 25 guard vehicles are on standby for high-water rescues. At least six fatalities have been reported by the media.
Meanwhile, a levee failure in Pocahontas prompted a flood emergency on May 3 to impact a town of 6,500 residents. A mandatory evacuation order was issued May 2.
Several tornadoes struck east of Dallas in Eustace, Caney City and Canton on April 29, including one EF-4 and one EF-3. At least four fatalities have been reported by the media due to the tornadoes.
The town of Canton, with approximately 3,500 residents, sustained significant tornado damage. Many homes and businesses were destroyed including a car dealership, according to media reports.
Media reports indicate that the Governor of Mississippi, Phil Bryant, declared a state of emergency due to the severe storms. A confirmed EF-2 tornado affected the Durant area on April 30 causing downed trees and power lines. As many as 100 structures were damaged and more than 11,000 residents remained without power as of May 2. At least two fatalities have been reported by media.
One fatality was reported in Tennessee due to objects thrown by heavy winds, according to media reports.
Thunderstorms caused heavy rain and winds of up to 60 mph near central Oklahoma, causing flooding for several areas over the weekend.
Disaster declarations were made in Jackson and Franklin counties due to flood damage, according to media reports.
Sources: U.S. National Weather Service, U.S. Weather Prediction Center, U.S. Storm Prediction Center, Associated Press, Reuters, The Weather Channel
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