CNN  — 

An outbreak of severe weather will threaten more than 40 million people this week from the southern Plains through the Southeast – with tornadoes, large hail, damaging winds and heavy rain all possible.

“The potential is there for significant severe weather,” said Meteorologist Jason Holmes at the National Weather Service (NWS) office in Birmingham, Alabama.

Long-track tornadoes are possible given the forecast weather pattern and environmental conditions, according to the NWS office in Mobile, Alabama.

Long-track tornadoes are possible, given the forecast weather pattern and environmental conditions, according to the National Weather Service (NWS) office in Mobile, Alabama.

These types of tornadoes are ones that consistently remain on the ground for an extended period of time, unlike a typical one which could be on the ground for just minutes.

There is also the risk for overnight tornadoes. Darkness makes it difficult to see a tornado on the ground, and it’s these kinds of tornadoes that are more dangerous and deadly.

The system that will be responsible for these strong storms is currently near the US west coast, but will make its trek through the Rocky Mountains and eject into the Plains by midweek, allowing for an atmospheric set-up conducive for dangerous storms to form.

“We’ve got increasingly warm and humid air over the Gulf of Mexico that will lift rapidly northward – those large scale conditions are quite favorable for severe storms. We think some of the smaller details that we often see on higher end days, especially with significant tornado potential, will also be in place,” said Bill Bunting, Chief of Forecast Operations at the Storm Prediction Center (SPC).

“This is a very strong system that we’ve been tracking the potential for severe storms as it develops and moves off to the northeast, from the Plains into the Ohio Valley,” Holmes told CNN.

Ahead of the storms, Alabama Gov. Kay Ivey issued a state of emergency for all 67 counties. Ivey urged residents to be prepared for the potential widespread severe weather event.

Timing out the storms

This next system will introduce the threat for thunderstorms as early as Tuesday evening for much of Kansas, Oklahoma and northeastern and central Texas.

The highest risk, however, will likely be during the overnight hours of Tuesday and continuing into Wednesday morning. An isolated tornado will be possible, but the main risks will be large hail and damaging winds.

There will also be a separate risk for a few strong storms across the South during the day Tuesday, including parts of Mississippi, Alabama and Georgia.

“Our real day of focus right now is Wednesday. We could see a fairly widespread severe weather threat and potentially some high-end severe thunderstorms,” said Bunting.

Wednesday into Wednesday night is forecast to be the most active day in terms of severe thunderstorms this week. There is currently an ‘Enhanced Risk’ for severe weather across eight states in the South, according to the SPC. An ‘Enhanced Risk’ is a level 3 out of 5 in terms of its potential severity. This includes states like Arkansas, Mississippi and Alabama.

Wednesday moderate severe outlook 2

The SPC said a “Moderate Risk” means “widespread severe storms are likely,” and all threats are possible in Wednesday’s set-up – tornadoes, large hail of at least golf ball size, and intense winds of at least 58 mph.

The ingredients for severe weather are looking so daunting that SPC is warning that an upgrade to a rare “High Risk” may be needed for Wednesday. High risk days are not used lightly – on average only occurring once or twice per year. In fact, there were no “High Risk” days in 2020. The last one was in May of 2019.

A morning round of showers and potentially thunderstorms are currently forecast to move through parts of the Gulf Coast states, but the main event will be ahead of the cold front Wednesday afternoon into Wednesday night. Near this cold front is where the most intense and tornadic storms could be.

During the afternoon hours, some of the states, especially in the “Moderate” or “Enhanced” risks, could see supercell thunderstorms develop. These types of storms are discrete, individual storms that are known for producing tornadoes. Not all of these storms will produce tornadoes, but given the favorable environment for tornadoes, it will be possible with some of them.

weather tornado threat wednesday 20210316

“With these discrete storms all modes of severe weather will be possible including some tornadoes, and perhaps a significant one,” the NWS office in Memphis said in Tuesday morning’s discussion.

There will then be a final line of storms along the cold front ramping up in the evening near the Mississippi River and tracking east through these southern states. The storms along this front will need to be monitored for tornadoes, damaging winds and large hail.

“This (overnight) wave of severe storms will likely have the higher potential for stronger long track tornadoes,” according to the NWS office in Birmingham.

There could be “potentially a few waves of severe weather, starting in the morning, then during the middle of the day, and then later in the evening as the cold front comes in,” said Holmes when discussing central Alabama’s forecast, a region currently in that “Enhanced Risk.”

By Thursday, the risk for strong to severe thunderstorms will shift toward the US east coast. The region from northern Florida through southern Virginia is currently being monitored by the SPC for this risk, but it is too early to know the exact timing and threat details.

Severe storms typical for South

Severe thunderstorms are not unusual for this part of the country and during this time of the year. Historically, strong tornadoes in mid-March have been most prevalent in northern Mississippi and Alabama, which aligns closely with this week’s forecast storms.

This graphic highlights the most probable areas for strong tornadoes (EF-2 or greater) during the mid-March time period. The darker shades means there is a greater chance for tornadoes based on history from 1982-2011.

“The details will play a significant role in just how bad things get and where the storms strike. I think what’s important is to know that it’s a typical early season, southeast US severe weather setup in the sense that storms will be fast-moving and they will continue after dark,” said Bunting.

“One dangerous aspect of tornadoes in the South is that they can occur in the middle of the night when people are sleeping unlike Tornado Alley storms that typically become less severe after sunset,” said CNN meteorologist Chad Myers.

Whenever severe weather threatens your area, it’s important to be prepared.

“It’s really important to heed the warning and not wait until you have visual confirmation (of the storm),” Bunting said. “This is the time for folks to have a plan in multiple ways to get the warnings.”

According to Holmes, it’s also important to know where to take shelter in the case a tornado warning gets issued. He says you need to go to the lowest floor of a sturdy building – not a mobile home – and to put as many walls as possible between you and the outdoors.

It’s also important to know where to take shelter in the case a tornado warning gets issued, Holmes said. He says you need to go to the lowest floor of a sturdy building – not a mobile home – and to put as many walls as possible between you and the outdoors.

Along with tornadoes, there will likely also be large hail and frequent lightning, so it’s important to stay inside during the storm.