If you've ever taken a Spanish class, you know the word "derecho" means right, when talking about directions.
What is a Derecho?
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In a way, that definition applies to the weather term, "derecho." Storm systems most often moved from west to east (left to right) in the Northern Hemisphere.
This is a widespread windstorm that produces damage along a swath of at least 240 miles.
A widespread storm that moved through Oklahoma and Texas Sunday night and Monday morning sparked my interest in writing this story.
From the damage reports collected by the Storm Prediction Center, it appears as though this cluster of storms was responsible for damage along a swath of more than 400 miles.
How does it form?
In the Eastern U.S., they usually form on the northern edge of high pressure.
In the summer months, especially, these domes of high pressure create large areas of widespread heat. To the north, the air is cooler. In between, the wind increases and creates a railroad track for these storm systems.
Let's take this down to a smaller scale now.
Ahead of the storm that happened in Oklahoma and Texas, the air was very hot. The heat index in Dallas reached nearly 105 degrees Sunday afternoon.
Behind the main line, the air is now cooled by the rain. This temperature difference causes the air to rush from west to east.
This is what causes your wind damage that is able to sustain itself for miles and miles.
When and where do derechos happen most?
This time of year is when you expect these to happen more often. On average, 63% of derechos happen between May and July.
One of the more prominent ones in the Mid-Atlantic was the one that happened on June 29, 2012. It produced wind speeds of 80 to 100 mph in Virginia, as it moved into air that reached temperatures of 100° and higher.
Statistically, these happen an average of once every four years here in North Carolina. They happen more often in the Upper Midwest, Great Lakes and down toward the Ozarks.
These storm clusters can pose a challenge to forecasting, which I covered in a separate Facebook post Sunday afternoon.
What does it look like (sometimes)?
Shelf clouds are fairly common on the leading edge of any thunderstorm, though they are often captured in advance of a derecho.
Below are two examples what a shelf cloud looks like, as warm and moist air rises above rain-cooled air on the leading edge of a thunderstorm.
This was a picture we showed Sunday morning, following a storm that happened in Louisburg Saturday evening.
Thanks to Roni-Leigh Hefner for sending us this picture through Report It.
Dwayne Reaves caught another great glimpse of a shelf cloud in Roxboro Saturday.
Have questions about the weather and how it works?
Send me an email with the subject line 'Ask the Meteorologist:' to cmichaels@pugongyingbo.com.