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August 14, 2014

Geography plays a role in storm tracks

Geography, topography, and urban landscapes can affect the tracks and strength of thunderstorms.

Reader Question:

When I read your fascinating article about the Piedmont trough, I realized that you should research a local saying about Pittsboro and Chatham County!

I was born in 1940, and since childhood I have heard that Pittsboro is "located in the dry forks."  This referred to Pittsboro's not receiving rain when surrounding areas did.  I thought it was just an old wives' tale, until Doppler images verified it!  Huge bands of moisture sweep toward Pittsboro--only to separate and move north and south of Circle City or to disappear altogether.

Please research the science behind this oral tradition!

Rebekah

Thank you for the question, Rebekah. I searched for a reference to the dry forks area online, but I could not find anything pertaining to the weather in the Pittsboro area. That's not to say that there isn't an oral tradition or even something to that tradition. It only shows that no one has done an official scientific study or review of it, or if someone has, it's not easy to find.

Still, looking at the question in a broader light, geography, topography, and even urban landscapes can affect storm tracks as well as the strength of storms. In the case of cities, a study was done at Purdue University that showed a majority of storms change their characteristics as they pass through urban areas - a solid line of storms may split into smaller cells as it crosses the city. Once the thunderstorms make it to the other side, they realign and often strengthen. Many of my colleagues and I call this the "beltline effect."

Topography can play a role as well. As systems rise over higher terrain, orographic lift (rising air caused by an increase in elevation) can cause rain showers. Coming down from higher elevations, the energy available for storms can increase, which is why we see may systems increase in strength as they come down from the mountains and cross into the piedmont and coastal plain.

Pittsboro sits on the edge of a narrow geographic area called the Deep River Basin that runs from southern Granville County down through Anson County. It is a low point of elevation in the center of the state. My best guess is that the combination of geography and landscape of Pittsboro is having some effect on the storms there.

Note: If one of my more scholarly readers has studied this particular area, I would welcome input.

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