Wind exists in all levels of the atmosphere, but most notably at the surface and in the upper levels. While we’re used to hearing about the surface winds associated with storms, fronts, and more gradual changes in the weather, we might not pay as much attention to those upper level winds, which are referred to as the jet stream. Within the jet stream, there are areas of faster wind, called jet streaks, where the wind speeds reach 50 knots or greater. If we think of the jet stream as a highway, we can think of a jet streak as a superhighway, moving air through the upper atmosphere very efficiently.
Every highway has on and off ramps, and a jet streak is no exception. The air coming up from the ground level over a surface low becomes part of the jet stream and can enter the jet streak at a point we call the right entrance. Beneath the right entrance, down at the earth’s surface, we are more likely to get thunderstorms. An even better area for storms to form is below the “off ramp” of the jet streak, which is called the left exit.
On Wednesday, the frontal system that blew through North Carolina was aligned with the left exit of a jet streak. That alignment, which could cause the lift and rotation necessary to create tornadic activity, was a large part of the reason a tornado watch was issued in December – something that might be considered out of the ordinary. Most of North Carolina dodged a bullet on Wednesday because the system moved through the state so quickly that it didn’t have time to intensify until it hit the coastal area, where it did produce a weak, short-lived tornado in Carteret County.