Hardscrabble Journal

Thermal Air Inversion

Hardscrabble escaped frost damage again. We’ve had more close calls this April than I care to remember. Many Virginia vineyards have not been as fortunate. We have been lucky, as luck always seems to play some role in life. However, a major factor in selecting this site for a vineyard was just for this reason: frost mitigation.

In the early 1980s I worked at a vineyard on the Shenandoah Valley floor. Spring frost damage was always an issue. At the same time, some colleagues had started a vineyard at a higher elevation in the Blue Ridge Mountains. They never had to worry about frost. This was my valuable lesson in thermal air inversions.

During most cold spring mornings, the coldest air pools in the lowest areas. These frost pockets can be as much as 10°F colder than ground located a few hundred feet higher in elevation. This is because cold air is heavier than warm air. In these foothills, when the nights are still, the air separates with the coldest air flowing to the lowest point. The relatively warm air is pushed to a higher elevation. This elevation zone is the “sweet spot”. This is where vineyards and orchards are best located.

So how does one know exactly where these sweet spots are? Ancestral knowledge helps. At the turn of the last century, this area was one of the largest fruit producing regions in the United States. Back then the growers learned exactly where the thermal zones were, and avoided planting either too low (frost pockets), or too high (very high elevations are too far above any thermal zones). One hundred years ago Hardscrabble was an apple orchard. In fact, the entire east side of the Blue Ridge in Virginia, from Loudon County to well south of Charlottesville was in orchards.

Many vineyards are now replacing them, but too many vineyards did not take lessons from history. They planted too low.

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Linden Vineyards / Learn More / Latest at Linden | Journal: April 22, 2020