The definition of a bow echo is relatively straightforward. It is a convective system that resembles the shape of an archer’s bow. They produce straight-line wind damage and once in a while will spin up a tornado. Let’s take a look at one using RadarScope.
On Sunday, November 5, 2017, there were multiple severe storms from Illinois to Pennsylvania. A few tornadoes were spotted, and rain caused flooding. There was also a lot of wind damage. In the image below, you can see a classic bow echo moving through western Pennsylvania. Looking at the loop, you can see the storm is bowing out from just north of Ross Township up towards Oil City. The bow becomes more pronounced by the end of this loop and is visible in both reflectivity and velocity data.
Taking a look at a still image and using the Inspector tool shows the velocity at over 70 mph in some areas. While this is not at ground level, it is also not far from the radar. The speed at the ground may be less, but shouldn’t be a lot less due to the lower height of the beam. You will also notice that the reflectivity amount is not a very high number. A bow echo doesn’t need high amounts of rain or hail as the prevalent damage is caused by wind.
The Storm Prediction Center’s Storm Reports show over 100 wind reports. Delving deeper, most are for downed trees and power lines in the area the bow traveled. Roof damage is also mentioned. One report, a telling sign, states “a ton of trees laid down flat in one direction at golf course.” An aerial shot of the area would show the majority of tree damage to be caused by straight-line winds and fall patterns of those trees to be to the southeast, the direction the bow echo was traveling.
Bow echoes can be very dangerous due to the increased speed of the wind at the edge of the line of these storms. Next time you see a line of thunderstorms heading your way and the part near you starts bowing out, quickly put away anything that may blow away and then get inside and stay away from the windows on the exposed side of your house. And as always, keep your phone charged so that you can continue to watch the storm using RadarScope.