In my post discussing June severe weather two weeks ago, I suggested nicknaming June “the month of the derecho” with last year’s derecho fresh in mind.  Then came the line(s) of storms last week that the National Weather Service’s Storm Prediction Center (SPC) pronounced a “low-end derecho”.  Perhaps “month of the derecho” is an apt description…

CWG’s Ian Livingston wrote a great piece last week on the meteorological set-up of last week’s severe weather event, with a nice discussion on whether or not the storm lived up to the hype.

As a meteorologist and geographer, I was not only interested in examining the meteorological setup as outlined by Ian, but also in comparing this year’s so-called derecho event with the June 2012 version in terms of power, size and spatial extent.

Source: NWS NOAA Storm Prediction Center

(Disclaimer: In this article I analyze the entire June 12-13 event – which includes two rounds of storms or a derecho series – based on the diagram to the right, from SPC.)

First, some quick facts:

Peak winds:

Peak winds from the 2012 event were substantially stronger than the 2013 event, with a number of 80 mph or greater gusts reported.

Number of states impacted:

2012: 12

2013: 18

Number of severe thunderstorm and tornado warnings issued:

2012: 199

2013: 295

Number of wind and tornado reports (filtered storm reports from the Storm Prediction Center):

2012: 951 (*2 tornado reports)

2013: 991 (*11 tornado reports)

Distance covered, lifetime, and average speed:

2012: 700 miles/12 hours/average forward speed of 65 mph

2013: 1,100 miles/ 18 hours/average forward speed of 47 mph (combining the two derecho series)

Derecho maps:

Warning coverage:

June 29, 2012

You may recall this map from my June severe weather climatology post of the June 29, 2012 derecho event. Warning data courtesy of the Iowa Environmental Mesonet. Map by Kathryn Prociv

June 13, 2013

June 12-13, 2013 low-end derecho event. Warning data courtesy of the Iowa Environmental Mesonet. Map by Kathryn Prociv

In comparing the two maps, notice the warnings associated with June 13, 2013 are more disjointed than 2012, but they are more widespread covering a larger area and half a dozen more states than June 29, 2012.

Now watch what happens when I overlay the two:

Overlay of the June 2012 and June 2013 derecho event warnings. Warning data courtesy of the Iowa Environmental Mesonet. Map by Kathryn Prociv

The similarity of the general tracks of the two events is striking.  It is not uncommon for derecho events to begin in the upper Midwest and track southeastward, and this map certainly lends credence to that general pattern.

Storm reports:

The total number of local storm reports from the two events were fairly similar, with both events boasting more than 900 reports.  The local storm reports differ, however, in two ways:

1) June 13, 2013 produced more tornadoes than June 29, 2012, with tornadoes reported in Maryland, Georgia, and Tennessee (as opposed to tornadoes reported just in Ohio in 2012).

2) June 12-13, 2013 led to more local reports of wind damage  and spanned across six more states than 2012, concentrated in the southeast region impacting South Carolina, Georgia, Tennessee, and Alabama.

Overlay of the June 2012 and June 2013 derecho storm reports. Warning data courtesy of the Iowa Environmental Mesonet. Map by Kathryn Prociv

*A second glimpse at the map provides an interesting tidbit: if you do not like severe weather, move to central and eastern West Virginia!  There is a notable absence of storm reports in that region from both derecho events.


Whereas the June 12-13, 2013 event was larger, traveled farther, impacted more states, and spawned more tornadoes, the June 29, 2012 event featured overall stronger wind gusts and traveled faster.  Due to the severity and impact of the incredible derecho from last June 29, 2012, this class of storms went from  technical weather jargon to a household word.

There is no doubt these are powerful and impressive storm systems, and for two years running the month of June continues to be “the month of the derecho.”

(Note: although SPC classified the June 12-13th event as a low-end derecho, the event did not come close to meeting derecho criteria in the D.C. area)