Tornadoes can occur anywhere. Mountains don't always shield us from tornado activity. Although this type of activity is limited, tornadoes can even occur on Mountain tops.
With the Appalachian Mountains somewhat protecting us from thunderstorms strong enough to produce tornadoes, it happens, and here's why.
This map shows elevation across the country. The Appalachian and Rocky Mountains are clearly evident.
The Appalachian Mountians are the oldest mountains in the country, at an age of about 480 million years. Since they are so old, they are also the lowest elevation mountains from millions of years of erosion. The average elevation of the Appalachian Mountians is only 3,000 to 6,000 feet. Still, completely obvious in parts of West Virginia.
The Appalachian Mountians are directly in the path of storms moving west to east, as they usually do in this region. When storms approach the mountianous areas, they often break down. With a stong enough system, storms are likely to redevelop on the east side of the mountain range. This coincides with the Shenandoah Valley and eastward.
Looking at the map above, this shows the number of reported tornadoes reported by the Storm Prediction Center form 1950 to 2011. The red colors showing the strongest tornadoes, the purple color showing the weakest.
Parts of West Virginia, the Shenandoah Valley and eastward, showing mostly purple, blue, and green colors. Meaning that stronger tonadoes are not common in this area.
There are obvious gaps where tornado covereage is limited. The Rocky Mountians allow a sharp western edge to tornado reports across the Great Plains. In West Virginia and western Virginia you can see a hole where tornado activity is limited.
These gaps coincide with the large mountain ranges in the country and the limits elevation puts on tornadogenesis.
So why are tornadoes less common at higher elevations? The golden rule when talking about higher elevations is, “the higher you go, the colder it gets.” This is true simply due to environmental lapse rates, or the change in temperature with height.
A normal change in temperature with height is about a 3 degree drop in temperature per thousand feet. Colder air at the surface is more stable, and so higher elevations are even colder, so even more stable.
A favorable tornado environment features warm and humid air to provide energy for the explosive thunderstorms capable of producing tornadoes. Warmer air being more unstable, and humidity to provide the moisture necessary for convection.
Despite the limited number of tornado reports in our area, there has definitely been tornado development in this region, as we've seen all too frequently in the past few years.
Shenandoah County had a tornado touch down in 2011. A mile-wide tornado struck Roanoke in April 1974. An EF3 tornado hit at more than 2,000 feet in Glade Spring in April 2011. A weaker tornado hit at Mt. Rogers National Park which sits at nearly 4,000 feet that same month.
So it is not impossible to see tornadogenesis in higher elevtaions, even though these cooler, more stable areas are not favorable.
The Appalacian Mountains shield us from a good amount of severe weather, but don't get too comfortable. Especially with the warm summer air appraoching us day by day, thunderstorms capable of producing destruction are on the horizon.
Information based on a study by Kathryn Prociv On March 14, 2013.
Scott, Doug (Ed). (2006). Guide to Mountains. Buffalo, NY:
Firefly Books, Ltd.Tornado History Project. Retrieved March 13, 2013, from http://www.tornadohistoryproject.com/