The threat of severe storms and flooding comes just in time for Super Tuesday, when hundreds of thousands will be heading to the polls to vote in presidential primaries.
Severe thunderstorms are a possibility Tuesday in parts of Arkansas, Tennessee and Texas, all of which are holding primaries, before spreading to the Southeast on Wednesday and/or Thursday. The stormy, wet pattern may continue into the first few weeks of March.
Timing and location
“An active week of thunderstorms and heavy rain is likely next week from the Arklatex region across the southeast states and Tennessee Valley regions,” wrote Bill Bunting, acting director of the Storm Prediction Center, in an email to The Washington Post.
Tuesday should offer the first risk of severe weather. If the system moves through earlier in the day, Arkansas, Louisiana and East Texas would see a severe-weather threat before dark.
Timing is a source of uncertainty. Some models — including the European model — are trending slower with the timing of the storms’ needed triggering mechanism.
That would put places such as extreme southeastern Oklahoma, East Texas and possibly just east of the Interstate 35 corridor in the zone to watch Tuesday.
A slower timing could also delay storms until very late Tuesday or even overnight into Wednesday farther east and favor a lesser severe-weather risk over Arkansas and Louisiana because of a lack of sunshine and cooler surface temperatures.
Thereafter, additional storminess is possible Wednesday or Thursday over portions of the Interstate 20 corridor in the Southeast, including in Mississippi, Alabama and Georgia. There is an outside chance a subtle severe threat could even snake its way up the Mid-Atlantic.
“The specific details on timing and location of the threats will become clearer over the next several days, and it’s important for people in these areas to monitor the latest forecasts,” wrote Bunting.
Hazards and impacts
Two upper-air disturbances will merge into one larger “trough” as they move east. One will ride down the California coast while the other dives south over the Northern Tier states.
Watch one, visible as a bowling ball of cold air at the mid-levels of the atmosphere, be re-energized and eventually consolidate with another surge of cold from the north:
That “phasing” of the systems and overlap of their fierce jet-stream energy could brew a storm system ripe for severe weather.
Broadly, the setup favors a squall line of severe storms with perhaps some supercells, or rotating thunderstorms, mixed in. Damaging winds, large hail and isolated tornadoes are all on the table as potential threats where severe storms do occur.
Determining the exact risk and location of specific hazards more than four days in advance, however, is impossible.
In any case, the system will scoop plenty of warm, moist air north ahead of us. That will probably lead to sufficient fuel for at least some severe storms. We can look at a parameter called CAPE, or convective available potential energy, to diagnose regions that could be juicy enough for dangerous storms:
It is important to note that, while specific impacts remain unclear, there is never a bad time to review your severe-weather plan.
To the north of the storms, a shield of heavy rain is possible somewhere over the southern Tennessee Valley or northern Dixie Alley, but in the Southeast that setup is uncertain. Where training — or the repeated movement of downpours over the same areas — occurs, two to three inches or more are possible.
Thunderstorms and rain will approach the East Coast into Thursday.
Heavy rain potential
Heavy rain along a slow-moving cold front associated with the storm system will lead to impressive rain totals in spots. A few locales may pick up more than four inches. That could set the stage for potential flooding.
“There are several signals that are increasing our confidence in heavy rain into next week,” said Alex Lamers, warning coordination meteorologist at the Weather Prediction Center.
“When we’re considering the potential for flash flooding, you’re looking at many components,” Lamers explained. “Where it will fall, how much will fall, the actual rainfall rates … but it’s also to consider hydrologic aspects as well — so how river and stream levels are currently, what soil moisture conditions are like, even things like the characteristics of the basins the rain may be falling in.”
Lamers said soil moistures are running anomalously high in the wake of an exceptionally wet winter.
“There are large sections over much of the interior Southeast [that] have all seen precipitation at least 50 percent above average,” Lamers said.
As of Thursday, vast swaths of the Southeast were at their 95th percentile for soil moisture. This comes on the heels of impressive flooding across much of the South. The Pearl River in Jackson, Miss., recorded its third-highest flood crest barely two weeks ago, while a week earlier, a rare “high risk” of rainfall was issued amid an anticipated widespread flash flood event.
Significant flooding occurred across much of Alabama, Tennessee and into Georgia. Numerous high-water rescues occurred near Tuscaloosa, Ala., on Feb. 9 after nearly eight inches of water swamped the city.
This time around, atmospheric moisture values could approach record levels for the start of March — a clear signal for incoming heavy rain.
It has been an incredibly wet start to the year for much of the Southeast. With only a couple of days left in the season, which encompasses December, January and February, a number of cities in the Southeast are on tap to conclude their wettest meteorological winter on record.
Among them is Starkville, Miss., where records date back 114 years. Since Dec. 1, 31.34 inches have fallen; the average during the same period is roughly half that — a hair over 16 inches.
Tuscaloosa, Ala., and Beesemer, Ala., have both picked up more than 28 inches, with winter 2019-2020 claiming the top spot. Birmingham, Ala., will wrap up its second-wettest meteorological winter at 26.17 inches since the start of December.
Columbus, Ga., and Columbia, S.C., and Spartanburg, S.C., are all in line to wind up with their wettest winter on record as well.
A wet pattern looks to continue at least through the first week or two of March. The majority of days will be dry, but a persistent storm track will continue to steer periods of moisture-loaded storminess through the region.
“At the very least, we’re definitely expecting it to continue into next week,” Lamers said.
Overall, the pattern also appears favorable for an active March punctuated with several bouts of severe weather. With cold air banked to the west and warmth favored in the east, the eventual clash of the seasons — and the release of Mother Nature’s pent-up volatility — is inevitable.