Published: March 24,2017
A progressive weather pattern with the likelihood of multiple embedded rounds of strong to severe storms is kicking off across the southern tier of the country.
The active pattern began Thursday as an energetic disturbance pushed through the jet stream and sparked a low-pressure system east of the central Rockies.
This first system will have strong wind shear and a deep surge of Gulf moisture, which will bring a chance of severe weather to the mid and lower Mississippi Valley through Saturday.
(FORECAST: Severe Weather Kicks Off in the Plains, South Late Week)
Sunday-MondayA second system will develop Sunday as a "lee cyclone," a cyclone that develops downwind of a major mountain range – the southern Rockies, in this case.
Deep southerly winds will bring moist air northward into the southern Plains. By late Sunday, a dry line is expected to push east, a lifting agent to spark severe storms during the afternoon and evening hours.
Some of these could be supercells with large hail, damaging winds, and, perhaps, tornadoes.
(MORE: The Different Types of Tornadoes)
Any severe storms that materialize will spark from the north-central Texas to Oklahoma and progress eastward toward the Ark-La-Tex region.
Sunday's Thunderstorm Forecast
(MORE: Tornadoes in the Southeast May Be Influenced by Mountainous Terrain)
Monday's Thunderstorm Forecast
...and More Next WeekUnfortunately, this severe threat will persist into much of next week, if not into next weekend.
The reason for this is the jet-stream pattern will feature two more prominent, strong southward plunges, or troughs, carving into the West, then pivoting into the Plains states.
Add changing wind speed and direction with height - wind shear - and you have the ingredients for severe t-storms.
While it is too soon to go into details on the threat, here's a general outlook on when and where severe weather may be a concern from the middle of the week into next weekend.
- Tuesday: Central/southern Plains
- Wednesday: Similar to Tuesday; may spread as far east as Lower Mississippi Valley
- Thursday: Deep South; Lower Mississippi Valley
- Next Saturday (April 1): Central/southern Plains
- Next Sunday (April 2): Ozarks, Ark-La-Tex region
Spring Season Ramp-Up UnderwayOverall, severe weather chances begin to climb east of the Rockies as spring progresses and air steadily gets warmer and moister. That said, this year has already been very active with several rounds of severe storms and tornadoes starting in January.
(MORE: With More Than 300 Tornadoes, It's the Most Active Start to a Year Since 2008)
The jet stream that has allowed plunges of colder air into large sections of the country during the winter remains active into the spring months. The jet stream provides wind shear and a secondary source of lift for storms to organize into possible severe weather.
These conditions are increasingly more supportive for severe storms.
Chances for severe weather begin to climb in parts of the mid-South and southern Plains toward the end of March.Climatologically, as we move into April, the number of tornadoes increases, and the threat zone expands farther north as conditions become more favorable for severe weather.
For instance, the average number of tornadoes per year quadruples from three to 12 tornadoes in Illinois from March into April as favorable ingredients reach the Midwest. Similar changes occur in portions of the central Plains.
Generally, moisture and heat are able to penetrate farther north into portions of the Plains, Ohio Valley and Midwest, expanding the areal extent to which severe weather – including tornadoes – can fester. But as we've already seen in 2017, severe weather season can get off to an earlier start in those regions.
Average number of tornadoes in March and April, 1989-2013.
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