Sunday, October 13, 2013

What is a Derecho ?


This graphic is simply a guide. My farm has seen a derecho annually for the last several years. If I were going to construct this map, I would extend the every two year delineation to encompass most of Virginia, to the East.
   This graphic is the work product of the US Government.

  I went through a fair bit of my adult life never having heard of a derecho, and thankfully, never having been afflicted in any way by one.  In the last few years though, I have not only heard the word, but lived through several of these on our Virginia farm.  Derecho is a Spanish word, which is pronounced də-reh-choh.    A derecho is a type of thunderstorm in which severe straight line winds with severe thunderstorms pass over a land area.  A derecho brings with it a number of hazards.  There is potential for lightning strike of persons and buildings. This can also create difficulties for your home electrical box and for the electrical box of outbuildings, even if they were grounded correctly and even if they have lightning arrestors.  Next, there is potential for winds so severe that tornadic damage to buildings and fencing can occur.  Often people who have endured a derecho think that a tornado came through. The difference is that these are straight line winds, but straight line winds can do great damage which can be similar to that of tornadoes in terms of the total level of destruction.  They may deliver torrential rains which can cause zero visibility leading to chain reaction accidents on highways and individual accidents on secondary roads.  They can result in flash flooding.  A derecho can make it difficult to see where the wet road ends and the lake beside it begins.   A derecho travels quickly and has severe sustained winds. They are capable of doing the same level of damage on land as is a hurricane.  There are different varieties of derechos. Sometimes there is clear view of something called a shelf cloud.

This cloud preceded a derecho.  (Picture: )

  This is a link to other shelf clouds.  Please review these so that you would recognize this phenomenon in advance.

              A derecho most often occurs during warmer months when a cold front and a pre-existing warm air mass meet. The storm which is created produces a wind shear which has resulted in plane crashes.  They can occur at night as well as during daylight hours. The derecho which last graced my Virginia county took out eighty year old oak trees, thirty year old Virginia pines, and shredded a house flag.   Nearby it pulled the roof of a barn and tore the roof of a conventional new house.  These storms can be very dangerous because unlike hurricanes where we usually have some notice, a derecho can come on quickly during your work day leaving you potentially unprepared until such a storm is upon you.

               It is therefore important to have some contact with either internet based weather media during the day, or have a weather notification sent to your phone while you are out or working.  Be alert to the advent of cold fronts intruding on your area when it has been warm, especially during June, July, and August.  Derechos can however, occur at any time of the year.  Become alert to potential derecho weather BEFORE the National Weather Service tells you that one may be coming today.

              Of course, make sure that your ordinary preparedness supplies are ready.   A derecho can afflict a fairly wide long area and emergency help can be tied up for awhile.  You need to have your emergency radio, good first aid kit, emergency food and water, and your own shelter alternatives for people and animals. They can be devastating to the electrical grid doing damage which cannot be repaired for weeks from a simple standpoint of procuring repair materials to the area and getting sufficient manpower hours to repair such a level of electrical system devastation in a timely manner.

              Derechos can occur in many places in the world. The US, Canada, Europe, South America have all seen derechos.  Remember that a tornado is a twisted wind, whereas a derecho brings straight and severe winds with wind shear.  Remember that , the Great North American Derecho of June, 2012 took out the power for 3.7 million families in the US Mid-Atlantic Region during a heat wave.   Consider it a not so pleasant sibling of the tornado.

Read More About This Phenomenon At:


Sunnybrook Farm said...

We have had two in the last two years in Franklin county, I suspect they hit you up north. We live in a house that has survived 200+ years down in a hollow. The derecho winds seem to pass over us for the most part but trees on the ridge get hit. The surrounding area gets raked badly and we lost a firefighter in the first one. Other than a bad ice storm, these have become our big weather issue to be prepared for. Power loss is the big problem for us and mainly concerning frozen foods.

JaneofVirginia said...

Our house is also in what might be considered a protected region, however other portions of our farm and our large border trees have taken a beating in the last few years. These can be tough to prepare for because although we are attuned to "Tornado Warning" or "Tornado Watch", we are not always alerted so quickly to coming derechos. It also takes time to retrieve alpacas or horses from outlying fields to secure them in a barn for a bad storm. Two of our dogs who were on patrol stayed out for the last one. They were fine but we couldn't find them when it was time for everyone to come in. We can survive with no power here for awhile, but it is cheaper and much more convenient to have local power restored to us quickly. Ice storms have also been particularly bad here in the last four years.

Gorges Smythe said...

We've always had bad weather events, but I can remember a time when we didn't feel that we had to give them Spanish names to be politically correct or make them sound more impressive. :-)

JaneofVirginia said...

Gorges, It IS interesting that I could raise five children and live on the Earth this long, and have never heard the word until the last couple of years.

Linda said...

Gorges, This is not a new term!

Jane, I think it is used more in print than in spoken language here in the South.

Our weather forecaster in Birmingham, Jerry Tracey, is brilliant. He does warn of straight line winds all the time. I can guarantee you we have more than one every two years.

I can prepare my mind for a tornado and know pretty much the signs of one coming without a forecast. But, straight-line winds or a derecho? It is not an easy thing to discern. Often, the forecasters are less sure of them than tornados.

JaneofVirginia said...

Linda, You raise interesting points. Here they mention "severe straight line winds with possible wind shear" fairly often. It's only in the past few years that in Virginia they have warned of potential for a derecho. Interestingly, when they do, we see tornado like damage, although when the federal weather people come out to assess damage, they assure the people who are now missing a roof, a barn, or even a house, that it wasn't a tornado. Over the last few years we have seen a lot more tornado and derecho activity than we did in the 1980s and 1990s.
I first heard the term derecho from Colorado meteorologists about seven years ago. I actually mention derechos in the book "Rational Preparedness".
Thanks for your post, Linda.

BBC said...

I drove though a couple of them when long haul trucking, lots of fun.

JaneofVirginia said...

I'll bet it was quite interesting.

BBC said...

Would have been more interesting if the truck had tipped over, I've seen that happen a number of times.

JaneofVirginia said...

Certainly possible. A derecho here pulled up an entire row of hundred year old oaks lining an entranceway. People in the area were shocked that this had not been the work of a tornado.