Severe weather in the US at the start of spring storm season. by Dan Corbett
Severe weather in the US at the start of spring storm season.
In many parts of the world spring means flowers in bloom and milder temperatures but in Tornado alley in the US it also means the beginning of the storm season. The storm season has certainly gone off with a bang as severe thunderstorms moved across parts of the southern US over the past day or so.
Some of the more intense storms brought golf ball sized hail and spawned damaging tornados.
One tornado in northwestern Mississippi tore the roof off a car factory, and hail the size of golf balls rained down from eastern Oklahoma to southern Georgia. Trees were blown down in many parts of the southeastern US in the stronger wind gusts.
All of this severe weather is a result of a weather system moving across the southeastern US and quite a contrast of air masses. Warm and humid air moving up ahead of a weather front interacts with cooler, drier air from the north. This interaction helped ignite the strong thunderstorms. It is the stronger thunderstorms that grow large enough to spawn tornados.
Strong to severe thunderstorms are like big wind machines. Warm humid air feeds into them at the bottom and cooler, drier air comes in aloft. The mixing, condensing and interaction of the air masses helps create all the cloud and rain as the storm continues to grow.
In the storm tremendous updrafts and downdrafts develop. It is these updrafts that help create hail which are concentric layers of ice that freeze as the raindrops are pushed high into the thunderstorm.
The winds continue to strengthen in the storm and eventually start rotating high up in the thunderstorm cloud. The tremendous updrafts and downdrafts then twist, this rotating column of air then begins to descend in the cloud. When it can be seen at the bottom of the cloud it is know as a funnel cloud. It is called a tornado when it touches the ground.
Tornados can last just seconds or they can last hours and are rated in size and strength by the Fujita scale. A small F0 might do minimal damage but a larger F5 could be a mile wide and have winds over 300 mph.
The peak area for severe weather and tornados shifts north thru the spring and early summer as the upper level winds (jet stream)
|
|
