The Story And News Behind This Past Weekend’s Derecho (June 29-July 1)

This past weekend we saw a massive line of storms impact large areas of the country from Iowa to Maryland in what is known as a Derecho. What is a Derecho? The best way to define this weather feature is by describing a large mass of t-storms combining together to form an elongated region of storms which can create intense surface winds that can blow in excess of 60mph reaching well into the 100 plus mph range. These winds are also known as straight line winds.

What happens is, as these thunderstorms begin to develop, they form a line east to west or north to south and rapidly move across a region which can be thousands of miles in length. This past weekend’s Derecho formed in Iowa and lasted all the way into Maryland leaving in its trail plenty of damage reports. The storms created winds in excess of 60mph with many places seeing winds in the range of 80-100mph. Sometimes these types of storms can mislead people to believe that a tornado has just hit their area.

The best way that these storms can be identified is by the damage path that they create; they will leave a straight line in their destruction path as with a tornado the damage path shows signs of turning in towards the middle and not in straight line. This past weekend’s storms have left many people in the dark which is combining with the extensive heat leading to very serious situations for many places with the combination of the heat and no power.

So how common are these Derecho features? In the United States they are more common than you may think. The most common time of the year to see these is during the summer when the interaction of cold air from the north runs into the very warm heated surfaces and moisture that is in place in the Northern Plains. These Derecho’s can occur anywhere from the Northern Plains, Mid-Atlantic and even the Southeast United States.

A special feature with the Derecho is the type of clouds that usher in the storm. The first type of cloud that will approach an area is known as a shelf cloud or gust front. This type of cloud usually moves through the air in a horizontal pattern but also will show signs of having a vertical roll to it as it moves through the area. What happens is as this cloud reaches the area the winds will rapidly increase creating damaging winds that can topple trees and even tip over unsecured mobile homes and tractor trailers. Also with this feature it is common to see large damage paths extending for miles on end, like what happened this past weekend with damage being reported from Iowa all the way east into Maryland.

The two types of weather features on a surface map that these Derechos form along are known as the squall line ahead of a cold front and also along the stationary boundary. This past weekend’s storms formed along a stationary front and rode the stationary front all the way from west to east.

Image Caption: Above image shows a rough outline of the storm tracks.