Wednesday, May 22, 2013

Tornadoes & Oklahoma

Our part of the world is not a part of "Tornado Alley", the swath of real estate across the South and the Southern Plains where tornadoes most commonly develop.  Oklahoma is one of the hubs of severe weather nationally and tornadoes are a way of life in this part of the world.

The Oklahoma City area, in particular, is one of the most severe weather prone areas on earth according to climatology, with an average year featuring 56 tornadoes within 140 miles of Oklahoma City.  This is not even including the average of 629 hail reports EACH year in this part of the world.

Difference between Philadelphia (left) and Oklahoma City (right) in terms of severe weather events  between 1980 & 2006. Source: NOAA.

Oklahoma may arguably be the nation's severe weather capital in concentration of severe weather outbreaks, due in large part to its geographic location in the Plains.   Moist air is easily accessible from the Gulf of Mexico. This clashes with dry air advancing in off of the Rockies, leading to the development of a moisture boundary known as a dry line.  The dry line separates the humid heat that bubbles north from the Gulf with the dry heat of New Mexico and West Texas, typically the firing line for the nastiest of storms.  The high numbers that are to the east of the dry line/warm front on the graphic below signify "CAPE" -- convective available potential energy -- the amount of juice in the atmosphere for storms to fire.  The higher the number, the more ripe the environment.

Adding to this a strong batch of winds in the mid atmosphere and a cold air push from the north and the stage is set for a severe weather outbreak in the Plains.  Such events occur more frequently in the Plains, thanks in large part to the infusion of dry air to create a sharp boundary upon which storms can develop.

While severe weather certainly does occur here, the general threat levels for severe weather are much lower than it is across the Plains and South at this time of the year.  Our peak for severe is typically from late June into July as the temperature differential between inland and the Atlantic Ocean lessens (thanks to the Atlantic's warming trend that carries into the summer).  However, our risk for severe is not on the order of what Oklahomans typically deal with each May.