A sweltering moisture plume from Mexico will clash with Pacific gusts to plough the United States with a near 2,000-mile belt of hail-hurling tornadoes.
More than 60 million people in the path of the storm have in the past 24 hours been urged to “move to safe shelter”.
Volatile atmospheric conditions since spring threaten to push the seasonal tornado total to the 1,000 mark – well above the 626 average.
A raft of severe weather warnings is in force across the United States, including for flooding, severe thunderstorms and high winds.
Weather warnings across the US
NOAA
A spokesman for the National Weather Service said: “There is an increasing threat of severe weather and excessive rainfall as well as high winds over the northern Plains and upper Midwest.
“A persistent weather pattern will continue to send energetic and fast-moving weather systems onshore from the Pacific Ocean into the Northwest.
“Thunderstorms that erupt ahead of a potent cold front may contain damaging wind gusts, large hail, and a few tornadoes, from the central Plains to the Great Lakes, and especially over Iowa, where the Storm Prediction Centre has issued a Moderate Risk of severe thunderstorms.”
Severe weather since the end of winter has claimed several lives and caused billions of dollars of damage.
Heal could strike across multiple states
The Weather Channel
A “unique” mix of ingredients including dry winds and tropical moisture will create a “dangerous setup”.
AccuWeather chief meteorologist Jon Porter said: “Plentiful moisture from the Pacific Ocean is being drawn to the north and will combine with moisture from the Gulf of Mexico and a very potent spin in the atmosphere.
“The severe weather threat will push east on Wednesday, with the threat of hail and isolated tornadoes stretching more than 1,700 miles, from Austin, Texas, to Syracuse, New York.
“Individual storms will congeal into a line with damaging wind gusts and we expect some wind gusts to top 90 miles per hour.
“This is a dangerous setup.”
Accuweather meteorologists have urged people to keep up to date with forecasts and “move to safe shelter if faced with an immediate threat”.
The worst of the weather will strike through the middle of the week although forecasters warn of a “multi-day” event.
Giant hail, thunder, strong winds and flooding will be driven by a powerful low-pressure storm system sweeping the country.
The latest round of storms set in on Monday night which brought winds of more than 90mph in western Nebraska and “hail the size of softballs”, according to The Weather Channel.
Meteorologist Chris Dolce said: “Through the middle of the week, a dangerous, multi-day outbreak of severe weather will batter parts of the Plains and Midwest, and this will bring the risk of strong tornadoes, damaging hail and winds.”
Weather Channel meteorologist Danielle Banks added: “The multi-day severe weather threat will continue spreading across the Plains and the Midwest through the next couple of days.
“There are other threats on the table, including damaging winds, flash flooding from repeated rounds of heavy rain and very large hail.”
