US: Adverse weather forecast across portions of northern and southern regions through at least early May 22 /update 5

Event

Thunderstorms with rounds of strong winds, hail, and possible tornados are forecast to occur across portions of the northern and southern US through at least early May 22. The affected area includes eastern Montana, northern and eastern Wyoming, eastern Colorado, far western and eastern Oklahoma, far western and far eastern Kansas, western and far eastern Nebraska, western and northern South Dakota, North Dakota, Minnesota, northwestern Wisconsin, Iowa, western Missouri, western Arkansas, far eastern Texas, Louisiana, and far southwestern Mississippi. As of May 20, officials maintain a state of emergency in Louisiana in response to the severe weather. Additionally, at least four people have died 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 southeastern Montana, far southwestern North Dakota, far western South Dakota, far eastern Wyoming, western Nebraska, and far northeastern Colorado for May 20 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 US. As a result, the Weather Prediction Center (WPC) has issued a "Moderate Risk" for excessive rainfall for portions of southwestern Louisiana, where the heaviest rainfall is forecast. A "Slight Risk" for excessive rainfall is in place for portions of far eastern Texas, western, central, and southern Louisiana, far southwestern Arkansas, and far southeastern Oklahoma.

Additionally, flood and flash flood watches and warnings are in place across portions of far eastern Texas, far southeastern Oklahoma, southwestern and central Arkansas, western and southern Louisiana, and far southern Mississippi. 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 22. 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, and I-35 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 22. 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