Spring is rapidly building towards its annual tornado crescendo in May.
The polar vortex, which suppressed tornadic conditions as it enhanced those for winter storms, has retreated far enough north to let warm, humid air from the Gulf of Mexico invade much of the plains and midwest. Yet the jet stream is still strong enough to produce a mid-level flow of dry air from the west.
These are the ideal conditions for thunderstorms, hail, and tornadoes.
Special Circumstance In The Jet Stream: A Cutoff Low
Normally waves move from west to east in the jet stream at around 25 miles per hour, carrying cyclones and cold fronts with them. However, it is possible for a wave to ‘cut off,’ forming a low pressure eddy which moves very slowly. Aardvark will become a cutoff low as it crosses the Rockies and could affect the plains, midwest, south, and east coast for the next week.
Favorable Conditions For Tornado Development
Any process that lifts warm, humid air can create unstable conditions and severe weather. Upslope flow, daytime heating, and cold fronts are the most common causes of instability in the atmosphere. When air rises, it cools, and moisture condenses (cold air holds less water vapor than warm). If the lifting is powerful enough, thunderstorms form.
When the lifting is accompanied by wind shear — a change of wind speed or direction with height — a spinning column of air, a tornado, can form.
The Central U.S. Is The Most Favorable Place In The World For Tornado Formation
The unique position of the central United States makes it ground zero for tornadoes. Warm, humid air streams north from the Gulf of Mexico; dry air, its moisture squeezed out by the mountains, moves east from the Rockies. The air is conditionally unstable, which means that any lifting of the air will result in a general overturning, with strong up- and downdrafts; thunderstorms with strong winds and hail result. Vertical wind shear can add the turning that leads to tornado formation.
Aardvark Advances East — But Takes His Sweet Time
Because the jet stream will create a cutoff low, Aardvark will amble eastward, affecting Texas, Oklahoma, and Kansas on Sunday, and only reaching the east coast on Thursday. At this time, the greatest threats are in the following areas:
- Sunday: Storms will hit Arkansas, Missouri and parts of the ten surrounding states. Large cities facing the greatest threat are Omaha, St. Louis, Kansas City, and Little Rock.
- Monday: Storms will hit from The Mississippi Valley east to the western Appalachians. New Orleans, Nashville, and Atlanta could see tornadoes.
- Tuesday: Storms will hit from Louisiana to the Carolinas, with Atlanta in the center of activity.
- Wednesday: Storms will hit the Carolinas, Virginia, and Georgia.
- Thursday: The severe weather threat will diminish, but storms could still hit the eastern Carolinas and northern peninsula Florida.
These are the latest forecasts as of Sunday morning. This is a large and dangerous weather system. Those living in all potentially affected areas should be prepared to react to weather warnings and watches issued by the National Weather Service (NWS). The NWS bases these warnings and watches on real-time data, including doppler radar, which can often detect a forming tornado.
What Will Follow Aardvark? Beaver, of course. But First, A Respite From Severe Storms
The next outbreak of severe weather this spring or summer will be called Beaver. Once Aardvark clears the coast, dry air will cover the eastern United States, so Beaver will have to wait her turn. The next upper level trough in the jet stream could impact the south and midwest in about ten days, but it is not likely to be as powerful as Aardvark.