The only thing that the extreme weather of Friday night has to do with us is that the storms originated, just south and east of our area.  As a weather geek, I just had to blog about this.  If you have been following the news you may have heard to Friday nights event being referred to as a  ”severe wind event”, which it was, but an event like this has a special name.

It is called a Derecho.  A Derecho is a widespread and long-lived, violent convectively induced straight-line windstorm that is associated with a fast-moving band of severe thunderstorms usually taking the form of a bow echo.  To put this into perspective, if you recall what happend in the Kenyon/Wanamingo area a couple of weeks, that was a microburst.  Microbursts form as rain falls through dry air in the mid-levels of the atmosphere.  As the rain falls through that air the air is cooled and in turn becomes more dense.  This new rain cooled air falls to the ground at great speeds and once that air hits the ground it has no where to go but out.  If the downburst is strong enough it can cause extreme damage as it did a few weeks ago in our area.

Microburts are on a pretty small scale, less than about 2 or 3 miles.  Imagine now that you have a family of thunderstorms in a line producing that same damage (or worse) as we saw in Kenyon and Wanamingo.  That’s what places saw Friday night, and reports out of some states is that power may not be restored for a week because of how heavy the damage is.

This is why there is a separate name for an event like this.  These are the storm reports compiled by the Storm Prediction Center from yesterday as the dangerous storm moved from west to east.

Storm Reports from Friday nights Derecho (SPC)

Here is a radar reflectivity image of what the bow echo looked like as moved out of Indiana and into western Ohio.

Radar image of Derecho

Here are the line of storms as they moved through Maryland and northern Virginia.

Tis the season for Derechos, but an event like this is definitely not common.

Posted under severe weather