What is a Derecho and The Southeast Derecho of April 4-5th, 2011
With all the talk about derechos today which frankly is a term that’s been around forever I thought I’d re-share this blog post from a few years back. These types of storms are hard to forecast though you usually know if the set-up is there. The problem is you usually don’t know if they will be classified as a derecho until they start or until they are over. Kinda similar to the F-scale which is a post event determination based on the exact definition below. I should also note no 2 events are ever the exact same and every event should be treated independent of the previous events. Plus remember it’s just a name for a type of storm. The impacts are damaging winds 60-100 mph, flash flooding, large hail and even tornadoes with these storms. That type of damage can come from severe storms even if they are not technically a derecho.
What’s a Derecho? (From the SPC about Derechos page)
A derecho (pronounced similar to “deh-REY-cho” in English, or pronounced phonetically as ““) is a widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms.
Although a derecho can produce destruction similar to that of a tornado, the damage typically occurs in one direction along a relatively straight path. As a result, the term “straight-line wind damage” sometimes is used to describe derecho damage.
By definition, if the swath of wind damage extends for more than 240 miles (about 400 kilometers), includes wind gusts of at least 58 mph (93 km/h) along most of its length, and several, well-separated 75 mph (121 km/h) or greater gusts, then the event may be classified as a derecho.
Click here to hear a pronunciation of the word “derecho.”
Because derecho is a Spanish word (see paragraph below), the plural term is “derechos.” In this case there is no letter “e” after the letter “o.”
What is the origin of the term “derecho”?
The word “derecho” was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, in a paper published in the American Meteorological Journal in 1888. A defining excerpt from this paper can be seen in this figure showing a derecho crossing Iowa on July 31, 1877. Dr. Hinrichs chose this terminology for thunderstorm induced straight-line winds as an analog to the word tornado. Derecho is a Spanish word which can be defined as “direct” or “straight ahead” while tornado is thought by some, including Dr. Hinrichs, to have been derived from the Spanish word “tornar” which means “to turn”. A web page about Dr. Gustavus Hinrichs’ background has been created by National Weather Service Science and Operations Officer Ray Wolf, and he provides more details about Dr. Hinrichs’ development of the term “derecho” in the late 1800s. He also mentions how the term “derecho” became more commonly used in the late 1900s.
Number of times a moderate or high intensity derecho has affected a point in the U.S. from 1980-2001 on the left. The map on the right is the times it’s happened in the cool season, September-April.
The Derecho of April 405th, 2011.
This severe weather outbreak will go down in the records books as one of the most widespread wind storms to affect the Carolinas since maybe hurricane Hugo in 1989. This event was what we call a derecho which is a term for a long-lived wind storm caused by a line of fast-moving thunderstorms. Sometimes it can also be referred to as a landcane due to the similarity of a fast-moving hurricane.
This was a fascinating event from a meteorological point of view. During the late evening Monday a surge of warm and moist air moved north ahead of this squall line. The temperature at 1am was still around 72° and the dewpoint surged to 60° after being in the upper 30s Monday morning. Aided by a very strong low-level Jetstream and strong mid level winds the thunderstorms were able to force intense winds down to the surface along the leading edge of the derecho.
Here was a look at the squall line as it approached from the west. Notice that there ware 2 larger bowing sections of the line separated by a notch where a meso vorticy was present. The location of the meso vorticy was where we had the tornado warnings because the signature on the velocity data of the Doppler radar. Even though no tornado has been confirmed to have touched down.
A Closer look at the line revels even smaller bowing segments within the line that match up well in the damage reports to areas of enhanced wind damage. Where winds were estimated at be 70-90mph.
As the derecho approached the Charlotte metro and the I-77 corridor around 2:00am you can see the smaller bowing segments still prevalent. One near South Charlotte lines up well with the power line damage at Hwy 51 and I-485.
The net result of this derecho was every single county that I cover all 22 of them in North & South Carolina was under a severe thunderstorm warning as the storm moved through. Along with the highest number of damage reports likely every received in a 24 hour period for our area.
While there are 100s of pictures and video of the damage which can been seen on wcnc.com. The most impressive damage I saw from this storm was a 120 foot Duke power transmission tower in Gaston county completely leveled. According to Duke power this was the first time this has occurred in about 20 years and the last time was due to a tornado. Duke also at the peak of the damage had more that 260,00 people without power the most since the 2002 December ice storm. Most of the power crews who have been around for many years compared this damage to a smaller version of Hurricane Hugo.
Biggest severe weather outbreak ever?
Lots of questions about this statement since this was the most reports ever received by the Storm Prediction Center. Due to the way technology & communication have advanced as well as population density it’s more likely that the numbers have been inflated. Either way this was the most reports received since 2000 and even after filtering repeat reports would likely put this #3 since 2000.
No matter the final number many meteorologists will be studying this event to see what made it such a prolific wind producer. I’ll continue to pull data and be on the look out for my colleagues case studies on this derecho. It’s will most likely end up in this list of other memorable derecho events in the U.S. from the SPC site about derechos.
NOTEWORTHY DERECHOS IN RECENT DECADES
What are some of the more significant derechos that have occurred in North America?
Many significant derechos (i.e., those that have caused severe damage and/or casualties), have occurred over North America during the last few decades. Most of these affected the United States and Canada. Listed below is a selection of some of the more noteworthy events in recent years; the list is not all-inclusive. Information provided in the links includes a map of the area affected, and a description of the storm’s impact.
Holiday weekend events
The human impact of the following events was enhanced by their occurrence on summer holiday weekends, causing many to be caught out-of-doors during the sudden onset of high winds…
July 4, 1969…………….”The Ohio Fireworks Derecho”….MI, OH, PA, WV
July 4, 1977…………….”The Independence Day Derecho of 1977″….ND, MN, WI, MI, OH
July 4-5, 1980…………”The ‘More Trees Down’ Derecho”….NE, IA, MO, IL, WI, IN, MI, OH, PA, WV, VA, MD
Sept. 7, 1998………….”The Syracuse Derecho of Labor Day 1998″….NY, PA, VT, MA, NH
Sept. 7, 1998 …………”The New York City Derecho of Labor Day 1998″….MI, OH, WV, PA, NJ, NY, CT
July 4-5, 1999…………”The Boundary Waters-Canadian Derecho”….ND, MN, ON, QB, NH, VT, ME
The derechos of mid-July 1995
The mid-July 1995 derechos were noteworthy for both their intensity and range…
Series Overview……….Montana to New England
July 12-13, 1995……..”The Right Turn Derecho”….MT, ND, MN, WI, MI, ON, OH, PA, WV
July 14-15, 1995……..”The Ontario-Adirondacks Derecho”….MI, ON, NY, VT, NH, MA, CT, RI
Two well-documented, classic events over the eastern United States…
April 9, 1991……………”The West Virginia Derecho of 1991″….AR,TN, MS, AL, KY, IN, OH, WV, VA, MD, PA
March 12-13, 1993….”The Storm of the Century Derecho”….FL, Cuba
“Southward burst” is a term coined by Porter et al. in a 1955 paper (see reference here) to describe a progressive-type squall line that surges rapidly southward rather than east…
May 4-5, 1989…………”The Texas Derecho of 1989″….TX, OK, LA
May 27-28, 2001……..”The People Chaser Derecho”….KS, OK, TX
Other noteworthy events
June 7, 1982…………..”The Kansas City Derecho of 1982″….KS, MO, IL
July 19, 1983…………..”The I-94 Derecho”….ND, MN, IA, WI, MI, IL, IN
May 17, 1986………….”The Texas Boaters’ Derecho”…..TX
July 28-29, 1986……..”The Supercell Transition Derecho”….IA, MO, IL
July 7-8, 1991………….”The Southern Great Lakes Derecho of 1991″….SD, IA, MN, WI, MI, IN, OH, ON, NY, PA
May 30-31, 1998……..”The Southern Great Lakes Derecho of 1998″….MN, IA, WI, MI, ON, NY
June 29, 1998………….”The Corn Belt Derecho of 1998″….NE, IA, IL, IN, KY
July 22, 2003……………”The Mid-South Derecho of 2003″….AR, TN, MS, AL, GA, SC
May 8, 2009……………..”The ‘Super Derecho’ of May 2009″….KS, MO, AR, IL, IN, KY, TN, VA, WV, NC