'Dozens of tornadoes likely' into Tuesday night as week-long severe weather threat kicks off
AccuWeather meteorologists warn a severe weather outbreak is possible into Tuesday night; however, the risk for storms bringing hail, downpours and locally damaging winds across the nation will continue into late week.
AccuWeather’s Jon Porter and Geoff Cornish break down why May 21 could be a particularly dangerous day for areas around Chicago, St. Louis and Des Moines.
More severe weather looms as an energetic pattern in the upper levels of the atmosphere leads to numerous rounds of rain and thunderstorms across the nation this week. As energy emerges from the West into the Front Range and clashes with humid air spilling northward out of the Gulf of Mexico, robust thunderstorm activity will blossom across the Plains during the first half of the week.
The severe weather risk began on Monday night, as thunderstorms packing damaging wind gusts and hail moved through parts of the Plains and Midwest, from Colorado to southern Minnesota. Waterloo, Iowa, was among the hardest hit locations, with a wind gust of 70 mph recorded at the regional airport there.
Looming chances for a severe weather outbreak
Into Tuesday night, the environment will ripen across the Plains and Midwest, and AccuWeather meteorologists have designated a zone between northern Missouri and southern Wisconsin as an area at high risk for severe thunderstorms.
"We see the concern for dozens of tornadoes across parts of the central U.S. through Tuesday night, and some of this is going to be after dark," AccuWeather Chief Meteorologist Jon Porter said. "Whenever you have severe thunderstorms, especially destructive winds and a tornado threat after dark, that’s especially dangerous because tornadoes at night are two times more likely to produce fatalities than tornadoes that happen at other times of the day."
The volatility of the atmosphere was evidenced early Tuesday morning as severe thunderstorm and tornado warnings swept across western Iowa. The storms have packed an abundance of moisture, leading to flash flood dangers as well.
Wind shear, a term used by meteorologists, is the change in direction and speed of winds throughout the various levels of the atmosphere. Vertical wind shear is an influential factor in the development of damaging thunderstorms and tornadoes.
"Severe thunderstorms need wind shear to grow and thrive," AccuWeather Meteorologist Alex DaSilva said. DaSilva added that a strong mid-level jet stream with weaker surface winds can even enhance rotation in a storm, which increases the risk of tornado development. Warm and humid air combined with an unstable storm setting are also key ingredients to the formation of tornadoes.
Through Tuesday night, all of the prime ingredients will be in place for dangerous, quick-tracking storms to flourish from Missouri to Wisconsin.
"Several strong tornadoes will be possible across Iowa and into northwest Illinois and southwest Wisconsin," warned AccuWeather Senior Meteorologist Joseph Bauer.
“Our greatest concern is between perhaps about 10 p.m. and 1 a.m. local time, and our expectation is that we’re going to have a line of strong thunderstorms with damaging winds and the risk for embedded tornadoes that will move from the northwestern suburbs of Chicago and race into the city," Porter said, citing the Houston damaging wind event as even more reason for residents to be prepared for the potentially dangerous conditions.
Experts recommend that those located within a severe-risk area be aware of where they can take shelter and have multiple ways to receive alerts. As thunderstorms ramp up into the overnight hours, the heightened danger of nocturnal tornadoes will arise.
A broad sector of storms to span the nation by midweek
By midweek, the storm that will be responsible for severe weather Tuesday will travel northeastward into southern Canada, leaving a cold front sprawling from the eastern Great Lakes to Texas in its wake.
A widespread swath of the nation will be at risk for hail, downpours, locally damaging winds and isolated tornadoes. Cities like Dallas, Little Rock, St. Louis and Pittsburgh will be among some of the locations threatened by severe storms Wednesday and Wednesday night, placing roughly 51 million Americans at risk.
From Wednesday to Thursday, forecasters say a corridor from the Arklatex to the Mississippi, Tennessee and Ohio River valleys will pick up rounds of heavy rain in addition to severe weather hazards. Between 2-4 inches of rain can spread across this zone within a 48-hour period, along with locally higher amounts. The excessive rainfall outlook for the region can result in dangerous flash flooding, especially since much of the region has already experienced heavy rain over the last month.
By late week, storms can ramp up once again across portions of the Central states and Mississippi Valley. There will be some risk for severe weather from Wichita, Kansas to Oklahoma City, Dallas and Little Rock.
Localized damaging winds from Thursday to Thursday evening can reach speeds of 60-70 mph at times, with the strongest storms capable of producing the AccuWeather Local StormMax™ of 85 mph.
Farther to the east, major metro areas along the Northeast's Interstate 95 corridor can also face heavy, locally severe thunderstorms later Thursday, which will slice into building heat and humidity across the region.
AccuWeather forecasters say another broad zone of the Central states will be at risk for at least some severe weather at the end of the week, allowing for no rest for storm-fatigued residents.
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