Thunderstorms and tornadoes are a complicated recipe. But this is one batch that’s been continually whipped up in the past few weeks.
As states from Missouri to North Carolina examine the wreckage of tornadoes and floods, NewsFeed thought we’d look at why the Midwest and South have been pummeled time and time again the past few weeks.
1. Warm Temps in the South
The first ingredient is a warm start to spring for the southern United States. For the past few weeks we’ve seen pleasant temperatures in the Gulf States, ranging from the 60s to the 80s. This warm, unstable moisture flows north from the Equator and through the Gulf of Mexico, lingering over the Midwest and Southern U.S.
(More on TIME.com: See photos of the 240 tornadoes that pummeled the South last week)
2. Cold Air from the Rockies
Cold air streams down from Canada and into the Rockies in the U.S. The current dovetails around the base of the mountains in Colorado and New Mexico, heading up toward the Midwestern states. This pocket of chilly air hangs over states like Oklahoma, Kansas and Missouri.
3. Mix Well
When the cold low-pressure system meets with the humid air, it draws all the moisture up to high altitudes. This is the process by which clouds are formed – and where storms and thunderstorms come from. The saturated cloud brings driving torrents of rain, the falling droplets create major wind currents, and the major pressure changes produce thunder and lightning. This may sound like a common thunderstorm. But “the biggest, baddest, strongest storms can produce tornadoes,” KELO-TV meteorologist Tony Barlow tells NewsFeed.
4. Spin into Tornado
As the cold current continually sucks up the warm air, winds from all levels of the atmosphere swirl the newly minted cloud around. Called wind shear, the multilevel winds propel updrafts and downdrafts, Barlow says. The swirling winds form funnel clouds, which can intake so much warm air from the ground that the cloud actually touches down, causing the immense destruction at the surface.
(More on TIME.com: See photos of rising rivers threatening Midwest towns)
5. Spread Eastward
The Earth’s rotation, coupled with wind currents flowing across the country from east to west, help to propel the storm, which has formed a bowing arc across the Midwest. The system slices east, bringing the pressure system with it, a system that slowly dissipates as it reaches the cool Atlantic states.
Combine this with the remnants of winter in northern states and Canada, causing ice jams that block rivers and massive snowmelts that leave an unfathomable amount of excess water, and this recipe is one that could leave major damage. Though many of us are wishing the tornadoes and wicked weather would end, know this: May is typically the most active month for twisters.