All Weather News

Weather Rewind: June 29, 2012 Derecho Event

29 Jun 2013, 3:23 pm

On this date last year, a massive straight-line wind event occurred.  It lasted for much of the second half of the day and into the late night hours where it brought about a tremendous amount of damage along a 600 mile path that stretched from eastern Iowa to the East Coast near Delaware and Maryland.  Wind gusts were reported in excess of 80 mph and numerous severe thunderstorm warnings were popping up left and right with this system as it traveled towards the east at an incredible speed of around 60 mph!

This derecho was one of most well documented storms of its kind due a lot, in part, to the fact that it impacted several major metropolitan areas, from Columbus, OH to Pittsburgh, PA, to Washington, DC.  Winds were so strong, they toppled down trees like dominoes and power lines also fell.

After the storm came through, you can see where the power outages were.  The major metros were able to survive the storm but smaller towns and rural areas, where power lines are above ground, saw power knocked out easily.

Severe thunderstorm watches were issued earlier on in the day when forecasters knew of the potential of this kind of storm to form.  Once the event began in Iowa, warnings were issued when there was certainty of areas to be affected by the damaging winds.  And as this progressive-style derecho traveled eastward, warnings were added and subtracted.  You can clearly see where the bulk of the warnings were; right along the path of the storm.  The derecho is a long-lived, rapidly moving large bow-shaped cluster of thunderstorms, that fans out, creating a larger bow, as it travels, making its destructive winds more widespread.   There were a few tornado warnings that popped up and two tornadoes were confirmed.

Over 1100 wind reports came in from this derecho!  That is one massive wind outbreak.  Very high wind gusts, above 74 mph, are the black boxes above.  One report came in of a 91 mph gust in Fort Wayne, IN.  By the time the system made its way to the DC metro area, the airports recorded gusts as high as 71 mph.

Here are some other facts about the derecho:

Nearly $3 billion dollars in damage is just mind-blowing, and is rather excessive for a straight-line wind event.  Unfortunately, 28 people were lost with the derecho due to  falling trees and debris.

The Storm Prediction Center had issued a SLIGHT risk from Iowa to Maryland in the very early morning hours, which was eventually where the derecho moved through.  The red shaded area is a MODERATE risk for severe weather, and it was where some of the highest wind reports were eventually reported from.

This system rode around a large dome of heat that sat across the southeast and southern plains, baking the area, and the jet stream went up and over it.  There was “explosive” energy with this system!  The convective potential available energy, also know as CAPE, (which is a measure of the instability in the atmosphere)  was incredibly high, rather off the chart, even.  Most thunderstorms often have CAPE values that exceed 1000 J/Kg, and in extreme cases, above 5000.  But on this day last year, the CAPE values were above 6200 J/Kg.  Dew points were in the 70s and daytime high temps then were in the 90s and 100s in that area.  That is just an atmosphere super juiced and ready to explode, and all you would need is a trigger.

This is the sounding taken from the NWS Wilmington, OH office during the middle of the day.  Typically a sounding is taken early in the morning hours and in the evenings.  Only on a few occasions do they take a sounding during the middle of the day, such as in this case,  when they need the latest information on a potential storm system that was likely to happen.

It was an incredible day back then a year ago.  Typically, a derecho occurs in the upper Ohio River Valley about once a year.  Where the system ended, in the DelMarVa area, they see a derecho about once every 4 years.  Many folks in the east coast have never heard about a derecho.  So when the system hit DC, the media was all over it, and the term “derecho” was looked into heavily.

Here is a link showing how the system looked on radar.  Note, that they rewind the radar back at the end of the loop, the storm system didn’t back up.

Take care, and enjoy the rest of your weekend and the upcoming Independence Day holiday!

Meteorologist Addison Green (twitter: @agreenWNTV)

Leave a comment

Your email address will not be published. Required fields are marked *