US: Adverse weather forecast across portions of central and southern regions through at least early May 21 /update 4

Event

Thunderstorms with rounds of strong winds, hail, and possible tornados are forecast to occur across portions of the central and southern US through at least early May 21. The affected area includes southern North Dakota, western and central South Dakota, southeastern Montana, eastern Wyoming, western and southeastern Nebraska, eastern Colorado, Kansas, Oklahoma, Texas, Louisiana, Arkansas, far southwestern Mississippi, western Missouri, Iowa, southeastern Minnesota, far northwestern Illinois, and western Wisconsin. As of May 18, a state of emergency has been issued in Louisiana in response to the severe weather. Additionally, at least two people have died and at least one person is missing in Louisiana as a result of the ongoing flooding.

The Storm Prediction Center (SPC) has issued a "Slight Risk" (Level 2 on a 5-tier scale) forecast for severe weather for portions of far southern Texas, northeastern Wyoming, far southeastern Montana, southwestern South Dakota, far northeastern Colorado, and western Nebraska for May 19 to early May 21. However, storms in this region are not forecast to be widespread or long-lived. Isolated intense storms are possible, which may contain hail, damaging winds, and a few tornadoes.

Heavy rainfall and flooding will be the main threat for the southern and central US. As a result, the Weather Prediction Center (WPC) has issued a "Moderate Risk" for excessive rainfall for portions of southern and far eastern Texas and southern Louisiana, where the heaviest rainfall is forecast. A "Slight Risk" for excessive rainfall is in place for portions of eastern Texas, western and southern Louisiana, western Arkansas, eastern Oklahoma, eastern Kansas, and far western Missouri.

Additionally, flood and flash flood watches and warnings are in place across portions of eastern and southern Texas, far southeastern Oklahoma, southwestern Arkansas, western and southern Louisiana, and far southwestern Mississippi. Severe thunderstorm watches and warnings are in effect for far southern Texas. Officials could update and possibly extend the coverage of the relevant weather alerts over the coming days.

Hazardous Conditions
The storms will be capable of producing heavy downpours, damaging winds, hail, and tornadoes across the affected area through at least early May 21. Should sustained heavy rainfall occur, it could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed or a lack of stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where the soil has become saturated by heavy rainfall. Disruptions to electricity and telecommunications services are possible where significant flooding, landslides, or strong winds impact utility networks.

Transport
Floodwaters and debris flows could render some bridges, rail networks, or roadways impassable, impacting overland travel around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways including the I-10, I-20, I-30, I-35, and I-45 corridors. Authorities could temporarily close some low-lying routes that become inundated by floodwaters.

Severe weather could also trigger intermittent flight delays and cancellations at regional airports, though these are unlikely to be severe or prolonged. Flooding could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track inundation. Localized business disruptions may occur in low-lying areas.

Advice

Confirm flights. Monitor local media for updated emergency and weather information. Seek updated information on weather and road conditions before driving or routing shipments through areas where severe weather is forecast. Plan accordingly for potential delivery delays if routing shipments by truck through the affected area through at least May 21. Do not attempt to drive through flooded areas. Review contingency plans and be prepared to move quickly to shelter if tornado warnings are issued. Charge battery-powered devices in the case of prolonged electricity outages.

Resources

NWS Tornado (Twitter)
US National Weather Service (NWS)
US Road Conditions