A “regional tornado outbreak (is) possible Tuesday afternoon and evening across parts of the Lower to Mid-Mississippi Valley,” the Storm Prediction Center warned Monday morning.
A Level 4 of 5, moderate risk, for severe storms has been issued by the prediction center for Tuesday afternoon and evening. The moderate risk encompasses 1.8 million people from northeastern Louisiana to southern Tennessee, including portions of the Memphis metroplex and Greenville in Mississippi.
“Long-track and/or significant tornadoes will be possible, with the most favorable corridor located from far northeast Louisiana northeastward across northwest Mississippi,” the prediction center emphasized.
Long-track tornadoes are tornadoes which stay on the ground far longer than a typical tornado and can cause much more damage. Significant tornadoes are those with EF2 strength or higher, which can result in winds of 111 mph or more.
In addition to potentially significant tornadoes, hurricane-force wind gusts up to 74 mph and hail will also be possible with Tuesday’s storms.
On Sunday, the storm center began warning for a “significant severe-weather event” across parts of the lower Mississippi River Valley.
In total, more than 25 million people are under the threat of severe storms on Tuesday from southeastern Texas to Alabama and northward to central Indiana, including Houston, New Orleans, Nashville, Baton Rouge, Shreveport, Little Rock, and Jackson.
The reason for the severe weather outbreak is a strong cold front, which will dig across the Mid-South from the Plains Tuesday. The cold air will be met with much warmer, humid air currently in place across the South. The clash in airmasses will be one of the reasons for the potential of monster storms.
Storms are expected to begin in the late afternoon on Tuesday and continue through the evening and into the early overnight hours.
This is the second Level 4 of 5 threat to be issued this month, according to CNN meteorologist Taylor Ward. This is also the first time on record that there have been two Level 4 threats in November since the storm center started using its five-tier system of severe storm risk categories in 2014, Ward said. The previous threat was on November 4 when there were 62 tornado reports across Texas, Oklahoma, Arkansas and Louisiana, according to the prediction center.
Those tornados killed two, injured dozens and damaged hundreds of homes and businesses, Ward said.
Nighttime tornadoes add an extra danger
The system is likely to spawn tornadoes and damaging winds across the lower Mississippi River Valley after dark Tuesday, which can be particularly dangerous.
“Unfortunately, it does appear that the severe storm threat will continue into the evening and overnight hours on Tuesday,” Bill Bunting, chief of forecast operations at the Storm Prediction Center, told CNN Weather.
The time of day when a tornado occurs also makes a big difference in the fatality rate. Nocturnal tornadoes are more dangerous because many people are asleep and unaware they need to be seeking a safe location.
While the greater tornado threat for this particular event exists during the day, there is still the possibility for a few rotating storms through the evening hours.
The areas most at risk for nocturnal storms Tuesday include southern Illinois down through Louisiana.
“Another challenge with nighttime tornadoes, especially in the fall and winter, is that storms typically move very quickly, at times 50 or 60 mph,” Bunting said. “This means that you must make decisions quickly and take shelter based on information contained in the severe thunderstorm or tornado warning, and not wait until the storm arrives.”
Bunting pointed out another concern will be the potential for flooding, thanks to heavy rainfall resulting from repeated rounds of thunderstorms.
Widespread rainfall is expected to fall in the 1 to 2 inch range, but some isolated locations could see up to 4 inches.
Second ‘severe weather season’ in November
While tornadoes in the US can happen in any month of the year, they are most common in the spring time thanks to the clash of cold and hot air as the seasons change. The same merging of temperatures also occurs in the autumn, which is why you will often see a secondary “severe season” later in the year.
“While severe storms occur with less regularity in the fall and winter than during the spring/summer months, major severe weather outbreaks have occurred during this time of the year,” Bunting noted. “One only has to think back to last December and the record number of tornadoes for the month and the tragically high number of deaths.”
“You can see that while the spring months are our busiest time climatologically, there is a secondary increase in tornado activity in November,” the National Weather Service in New Orleans said.
Texas sees the most tornadoes (7) in the month of November on average, followed by Alabama (6), Louisiana (5), and Mississippi (5).
“Severe thunderstorms in the fall and winter can be extremely impactful, and may sometimes catch people off guard as thunderstorms tend to occur less frequently during the cooler months,” Bunting added. “Now is the time to revisit, or develop, a severe weather emergency plan for you and your family.”
Know where you will go if severe weather hits, and make sure flashlights work and cell phones are fully charged in case you lose power.
CNN Meteorologists Allison Chinchar, Robert Shackelford, and Jennifer Gray contributed to this report.