April 20th, 2016

U.S. Southern Plains Flooding

Posted at 1:18 PM ET

us-flood-plains-small In southeast Texas, a significant flood event has affected the Greater Houston Metro area as well as areas north and west. Heavy and persistent rainfall has produced catastrophic flooding, enabled by a slow-moving upper low and frontal boundary, together with available moisture. Record daily rainfall amounts were observed at Houston International Airport, with amounts of 15 to 18 inches reported north and west of the Houston area. National Weather Service flood and flash flood watches and warnings remain active for areas of the Southern Plains and Lower Mississippi Valley and some additional rainfall is expected with thunderstorms. Media reports indicate at least seven fatalities and first responders expect this number to rise. Reports indicate that over 1,000 homes have been inundated. Texas Governor Greg Abbott has declared a state of disaster in nine counties, enabling state resources to be used to respond to the emergency, according to media reports. It will take some time to fully assess the scope and severity of impacts of this event and our thoughts are with those lost and directly affected by this event.

Meteorological/Hydrological Summary

An extended period of widespread rainfall has affected areas of the Central and Southern Plains and the Lower Mississippi Valley. Embedded and slow-moving thunderstorm clusters produced excessive rainfall for some areas, with most severe effects over southeast Texas and parts of western Louisiana. This was enabled in the presence of moist, unstable air, a potent slow-moving upper-level low and a surface front. The mechanics and circulation of these features enabled an ongoing flow of moist air from the Gulf of Mexico to produce rainfall for an extended period of time. The movement of weather systems through the affected areas has been especially slow due to a meteorological blocking pattern over the continent (known as an “omega block”).

us-flood-plains-big

General outlook for significant flooding. Does not depict smaller flood areas. Source: 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.

Rainfall amounts reported by the U.S. National Weather Service (NWS) have exceeded five inches over areas of the Southern Plains, with amounts exceeding 15 inches north and west of the Houston Metro area. Rainfall rates of 3 to 4 inches per hour were reported in the area. A storm-total rainfall amount of 17.6 inches was reported by the NWS at Little Mound Creek at Mathis. A daily rainfall record of 9.92 inches was reported at Houston Intercontinental Airport on Monday. April 2016 is now the wettest month on record for this station. Shreveport, Louisiana experienced the second-wettest day on record on April 18.

The heavy rainfall intensities and amounts overwhelmed local drainage systems, especially in urban areas of the Greater Houston Metro area, resulting in significant flash flooding. Further north and west, excessive rainfall amounts quickly overwhelmed local watersheds to produce significant and widespread flooding. As the flood waters drain south and east, an ongoing significant flood threat continues to affect the Houston Metro area. The threat is amplified by ongoing rainfall and thunderstorm activity in the area. The National Weather Service maintains flood and flash-flood watches and warnings for areas under threat.

As the weather pattern begins to shift, the NWS expects that this will allow a cold front to clear the area to bring drier weather into Friday.

4-20-tx-ok-fl-radar-7-day-big

Radar-estimated seven-day rainfall. Ending  8 a.m. EDT April 20.

Source: NOAA, U.S. National Weather Service

4-20-tx-ok-fl-radar-24-hr-big

Radar-estimated 24-hour rainfall. Ending  8 a.m. EDT April 18.

Source: NOAA, U.S. National Weather Service 

Selected Unofficial Rainfall Amounts (Storm Total)

2 p.m. EDT April 15 through 4 a.m. EDT April 20

Source: NOAA/WPC  

Location Amount (inches)
   
TEXAS  
LITTLE MOUND CREEK AT MATHIS 17.6
CYPRESS CREEK AT SHARP RD 16.48
LANGHAM CREEK AT LONGENBAUGH RD 16.32
MONAVILLE 16.22
TRAILSIDE 15.72
CYPRESS CREEK AT KATY-HAWKIN 15.64
BEAR CREEK AT CLAY ROAD 15.08
SOUTH MAYDE CREEK 14.96
CYPRESS CREEK AT HUFFMEISTER RD 13.88
MILL CREEK NEAR BELLVILLE 13.23
HOUSTON INTERCONTINENTAL ARPT 9.92
AUSTIN 9.6 WNW 5.48
DALLAS 7.2 SW 5.04
   
OKLAHOMA  
FREDERICK MUNI ARPT 7.87
TIPTON 6.13
RINGLING 5.36
MEDICINE PARK 5.22
HOBART MUNI ARPT 5.03
OKLAHOMA CITY 4.69
GUTHRIE MUNI ARPT 4.14
TULSA/LLOYD JONES 4.12
FORT SILL AFB 3.95
   
LOUISIANA  
SHREVEPORT RGNL ARPT 6.7
BARKSDALE AFB/BOSSIER CITY 6.18
LAKE CHARLES MUNI ARPT 1.22
   
KANSAS  
ELKHART 1 N 6.52
HILL CITY MUNI ARPT 5.55
ROLLA 5.38
PLAINVILLE 4 WNW 5.31
DAMAR 1 NNW 5.28
DODGE CITY FORECAST OFFICE 5.15
PHILLIPSBURG AIRPORT 3.94
   
ARKANSAS  
FOUKE 5.3 ENE 4.48
BRADLEY 7.8 W 4.25
HOPE 12.2 S 3.88
TEXARKANA RGNL ARPT 2.77
   
NEBRASKA (Event Ended)  
RIVERDALE 6 N 6.25
KEARNEY 5.5
MCCOOK MUNI ARPT 5.37
CAMBRIDGE 4.91
MILLER 4.88
   
SOUTH DAKOTA (Event Ended)  
PORCUPINE 5 E 2.96
MARTIN 12 E 2.53
WANBLEE 11 ENE 2.5

 

Impacts

Media reports indicate at least seven reported fatalities due to flood-related incidents or vehicles caught in flood waters. Thousands of rescue efforts have been carried out and more are still underway for those trapped in homes and vehicles with rising waters. All reported fatalities were in the Houston area; four in Houston proper, two in Harris County and one in Waller County. State officials have urged residents to stay off roads due to dangerous conditions.

More than 6,300 customers were without power in the Houston area Tuesday afternoon according to media reports, down from over 100,000 on Monday according to CenterPoint Energy.

Approximately 20 inspection teams from city hall were in the field and at least 183 houses were reported damaged according to Houston Mayor Sylvester Turner.

More than 100 flights were cancelled Tuesday at Houston Intercontinental Airport and more than 1,000 flights were cancelled at major Texas airports on Monday due to the storms.

Sources: U.S. National Weather Service, U.S. Weather Prediction Center, FlightAware.com, Agence France Presse, Reuters, Associated Press.

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Guy Carpenter publishes CAT-i reports for major natural catastrophes worldwide. These reports cover catastrophes including worldwide tropical cyclones, earthquakes, major UK and European floods and any other natural event that is likely to incur a significant loss to the (re)insurance industry. Please email CAT.i@guycarp.com if you wish to be added to the free email distribution list.

Guy Carpenter compiles RISK-i reports for major technological or man-made events worldwide. These reports cover risks to property, transport and life including explosions, fires, crashes, engineering disasters and terrorist attacks that are likely to incur a significant loss to the (re)insurance industry. Please email RISK.i@guycarp.com if you wish to be added to the free email distribution list.

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