Southern Appalachian Tornado Hole Gets Hit Again
The "tornado hole" of the southern Appalachians (shown below) has been unusually active this month. There's no mystery to why this happens; mountains disrupt thunderstorm circulations moving over them, and dry out storms as elevation decreases.
But this April, there have been five tornadoes already in this area: two in Pulaski, Virginia April 8th (I pass this town's sign every summer on the way to Mom's house) and one in Surry County, North Carolina (only a couple dozen miles northeast of my Mom's house) April 5th.
The National Weather Service has more details on both the Pulaski and Surry twisters; you can see damage photos from Pulaski on this website and read a news story about it here.
Given the extremely small number of tornadoes in that area historically, this month's outbreak is especially impressive. But why? Yes, the mountains will tend to disrupt the storms, but it's still possible to have tornadoes at elevation. Yet it's not nearly as likely now as later in the season (according to the SPC graph for this area, shown below):
Here's the answer. The ingredients in this Spring's tornado outbreaks are unusually conducive to storms, especially early in the season, so when weather systems have moved over the mountains this month, tornadoes dropped. Unfortunately, this is likely to happen again tonight and tomorrow; here is a map showing all tornado reports this month, with today's tornado risk (then tomorrow's severe weather risk) overlaid:
