A “regional tornado outbreak (is) possible Tuesday afternoon and evening in parts of the lower to middle Mississippi Valley,” the Storm Prediction Center warned Monday morning.
A level 4 out of 5, medium risk, for severe storms has been issued by the forecast center for Tuesday afternoon and evening. Moderate risk includes 1.5 million people from northeast Louisiana to southern Tennessee, including portions of the Memphis and Greenville metroplexes in Mississippi.
“Long track and/or significant tornadoes will be possible, with the most favorable corridor running from extreme northeast Louisiana to northeast through northwest Mississippi,” the forecast center pointed out.
Significant tornadoes are those with a magnitude of EF2 or higher that can result in winds of 111 miles per hour or more.
In addition to potentially significant tornadoes, hurricane-force gusts of up to 74 miles per hour and hail are also possible with Tuesday’s storms.
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On Sunday, the storm center warned of a “significant severe weather event” in parts of the lower Mississippi Valley.
Overall, severe storms threaten more than 25 million people Tuesday, from southeast Texas to Alabama and north to central Indiana, including Houston, New Orleans, Nashville, Baton Rouge, Shreveport, Little Rock and Jackson.
The storms are expected to begin late Tuesday afternoon and continue into the evening and into the early hours of the night.
Follow the storms as they develop here.
Nighttime tornadoes add an additional hazard
The system is likely to create tornadoes and damaging winds in the lower Mississippi Valley after dark Tuesday, which can be particularly dangerous.
“Unfortunately, it looks like the severe storm threat will continue into the evening and night hours Tuesday,” Bill Bunting, chief of forecasting operations at the Storm Prediction Center, told CNN Weather.
The time of day that a tornado occurs also makes a big difference in the death rate. Nocturnal tornadoes are more dangerous because many people are asleep, unaware that they need to find a safe place.
While the greater tornado danger for this particular event is during the daytime, there is still a possibility of some rotating storms in the evening hours.
Among the areas most at risk from overnight storms on Tuesday are southern Illinois down to Louisiana.
“Another challenge with nighttime tornadoes, particularly in the fall and winter, is that storms typically move very quickly, sometimes at 50 or 60 miles per hour,” Bunting said. “That means you need to make decisions quickly and take shelter based on the information contained in the severe thunderstorm or tornado warning, rather than waiting for the storm to come.”
Bunting pointed out that another concern will be the potential for flooding, thanks to heavy rains resulting from repeated rounds of thunderstorms.
Widespread precipitation is expected to fall in the 1 to 2 inch range, but could fall as much as 4 inches in some isolated locations.
Second severe weather season in November
While tornadoes can occur any month of the year in the United States, they most often occur in the spring, thanks to the clash of cold and hot air as the seasons change. The same merging of temperatures also occurs in the fall, which is why you’ll often see a secondary “severe season” later in the year.
“While severe storms occur less regularly in the fall and winter than in the spring/summer months, major severe weather outbreaks have occurred during this time of year,” Bunting noted. “Just think back to last December and the record number of tornadoes for the month and the tragic death toll.”
Earlier this month, a severe, medium-risk, Category 4 storm spawned dozens of tornadoes in Texas, Oklahoma, Louisiana and Arkansas, damaging scores of homes and businesses.
This is the first time two Level 4 risks have been issued anywhere in the US in the month of November.
“You can see that while the spring months are our busiest time climatologically, there is a secondary increase in tornado activity in November,” said the National Weather Service in New Orleans.
Texas, on average, sees the most tornadoes (7) in the month of November, followed by Alabama (6), Louisiana (5), and Mississippi (5).
“Heavy thunderstorms in the fall and winter can be extremely devastating and sometimes catch people off guard, as thunderstorms are less frequent in the cooler months,” Bunting added. “Now is the time to consider or develop a severe weather contingency plan for you and your family.”
Know where to go when storms hit and make sure flashlights are working and cell phones are fully charged in case you lose power.
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CNN meteorologists Allison Chinchar and Robert Shackelford contributed to this report.