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This article is from the Encyclopedia of North Carolina edited by William S. Powell. Copyright © 2006 by the University of North Carolina Press. Used by permission of the publisher. For personal use and not for further distribution. Please submit permission requests for other use directly to the publisher.

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Isothermal Belt

by Paul L. McCraw, 2006

The isothermal belt is a zone in western North Carolina, primarily in Rutherford and Polk Counties, in which temperature inversion resulting in milder temperature contributes to longer growing seasons than in the immediate surrounding region. The phenomenon usually occurs on the southern slopes of mountains and foothills protected from frost and freezing temperatures by higher mountains to the north and northwest. The temperature inversion, possible at any time, usually develops in the early spring. The condition is advantageous for tender plant life and early blooming trees as well as for the cultivation of fruit, especially apples and grapes.

In 1858 Silas McDowell of Franklin coined the name "isothermal belt" based on the concept of the isotherm, a line on a weather map linking all points that have an identical mean temperature for a given time. Since then the term has been widely used and modified by scientists and area residents to sometimes exaggerate the advantages of the area. The names of Thermal City in Rutherford County and Isothermal Community College, which serves Rutherford and Polk Counties, are derived from this term.


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If ever we return to normal, I plan to buy a small house in N.C. so I can escape the hot, humid summers in the Lowcountry of S.C., which have become unbearable now that I'm in my 80's. I really like the small, historic city of Rutherfordton, but friends warn me that the summers there aren't so cool because it's in the Thermal Belt. Do you agree with their assessment? If so, any ideas as to where I should look for an area that doesn't require AC in the summer, or at least only occasionally. I'd love to find a little house after the first of the year so I can have it ready for next summer......P.S.....I must confess that N.C.'s magazine, OUR STATE, has really influenced my choice of possible states to spend the summer!


It can get scorching hot in Rutherfordton, and Polk in the summers though it hasn't been out of the mid 90s in a few years. Also the humidity is very high unless you live somewhere near Lake Lure or near North/Western Polk near the Henderson county border. Henderson county is where the temperatures tend to milder during the summer and where most of the really good apples are grown in NC. Saluda, NC is a compromise of the climate types. You get the earlier springs with a normal moutain fall, but with a cooler summer, up to a 10 degree difference, for most of the other parts of the counties. Its on the Polk/Henderson county line. Other places like it exist, but they are either very
expensive i.e. Lake Lure/Golden Valley or very rural i.e. Whitehouse/Thermal City/Golden Valley. Saluda was also historically a place where people from Charleston for the summer in the 1800s. As for the tradeoffs to living in Saluda well, I live in Rutherfordton near the Polk county line, and our first frost for 2020 didn't come until November 26, Saluda had it's first frost late September.

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