An early uptick in severe thunderstorm activity is likely over the central and southeastern United States in the coming weeks as a volatile weather pattern sets up across the Lower 48 states. The upcoming pattern shift will cleave the nation in two, with lingering cold across the west while spring settles into the east.
Throughout the region in between, dangerous thunderstorms, flooding rains and sharp temperature swings are in store.
The severe thunderstorm risk looks to ramp up by the middle of next week, National Oceanic and Atmospheric Administration’s Storm Prediction Center warned Friday, stating that an “increase in organized severe potential appears possible, perhaps as soon as [Wednesday].” This first round of storminess could shift into the southeast by Thursday or Friday as renewed storm threats develop to the west.
Meanwhile, more rain is in sight for the already waterlogged Deep South and southeast, where many cities just wrapped up their wettest meteorological winter on record. The soakers look to continue as potential flood concerns arise deeper into spring.
The ingredients for repeated rounds of severe weather
The pattern takes hold beginning next week as an upper level bowling ball of cold air, known as an upper level low, digs south over the southwest. This will bring dreary skies and unsettled weather to Southern California. For example, San Diego may struggle to climb above 60 degrees late next week, with sporadic rain and gloomy weather.
Las Vegas, where the average high for this time of year is 70 degrees, will see temperatures peak in the upper 50s.
Meanwhile, high pressure will build into the east, bringing a welcome surge of warmth and mildness. That will provide the needed fuel for potentially severe thunderstorms over the Plains, Ozarks and the Mississippi and Tennessee valleys.
The pattern also favors an active jet stream slicing across the nation’s midsection from southwest to northeast. The jet stream is a narrow corridor of swiftly moving air in the upper atmosphere. It weaves across the boundary between cold and warm air masses, and is also the conveyor belt along which storms propagate.
The jet stream will also enhance the amount of wind shear in the atmosphere for thunderstorms to tap into. Shear describes a change in wind speed or direction with height, and sufficient amounts of shear can cause thunderstorms to rotate. Storms with a persistent rotating updraft, known as supercells, can produce large hail and tornadoes.
Severe thunderstorms are possible by Wednesday over portions of the southern Plains and eventually the southeast, according to the Storm Prediction Center.
Other NOAA forecasters have also keyed into a broad area from the Gulf Coast and Lower Mississippi River Valley north through the Ozarks that could bear watching late next week into the weekend of March 21 and 22.
“Model guidance indicates surface low development over the Great Plains with moist, southerly flow ahead over the Great Plains and the Mississippi Valley to increase the risk of heavy precipitation, high winds, and severe weather across the region,” they wrote in a technical discussion posted online Friday.
The exact magnitude and nature of the threats will come into clearer focus as we approach the date, but it’s a reminder to everyone in the central and eastern United States that tornado season is fast approaching. Preparations such as cleaning out tornado shelters and making sure you have a working NOAA weather radio or other way to get warnings even at night should be made this weekend to get ready for next week’s storms.
The storms could hit at a time when schools are already closed and staffing at Weather Service forecast offices could be stretched thin due to the novel coronavirus pandemic.
Flooding concerns keep rising
Flooding may also prove problematic, especially in the Deep South and southeast. Some parts of Alabama have seen two-and-a-half feet of rain since the start of the year. It’s been a top five wettest start to the year on record for many, with little end in sight.
And as more storm systems roll across the mid-south, parts of the Interstate 20 corridor over Mississippi, Alabama and Georgia may be in for renewed rounds of wet weather.
“We’re still looking at an above-average flood potential for the spring of 2020,” said Chelly Amin, the hydrology program manager at the National Weather Service in Huntsville, Ala. “We’ve had more than our fair share of rain during this period. Any additional rainfall is going to convert to runoff.”
Some weather models indicate another six inches or more of rain is possible over parts of northern Georgia, Alabama, Mississippi, Arkansas and Oklahoma through the end of March. The placement and persistence of projected flood threats lends credence to an anticipated soggy, stagnant pattern.
“Any of these kind of storm systems that move through, especially if they slow down and stall, can be the worst-case scenario for us,” Amin said. “This allows multiple waves of heavy rain. In the [Climate Prediction Center’s] eight-to-14-day outlook, we have the bull’s eye right over us [in northern Alabama] and Nashville.”
Amin did note that the upcoming “bloom season” could help, with thirstier plants drawing more water into their roots.
“We’re ready for the rain to stop,” Amin said. “I’m tired of the rain.”
But she emphasizes that, in addition to the rain, severe weather season also looms over the Deep South and southeast.
“We are heading into our spring severe weather season, too. March, April and May is our prime severe season, with a secondary peak in the fall. April has the highest number of tornadoes here for the Huntsville office,” she said.
“Aside from the flooding threat, people are going to have to pay attention to multiple [hazards] as we head into the spring,” she said.