Wake low moves through the Tennessee Valley Monday, produces 43 mph wind gust

A wake low has moved through the Tennessee Valley, and in its wake, winds gusted as high as 43 mph.

What is a wake low? 

Recall that low pressure systems are areas of rising air, and high pressure systems are areas of sinking air.

When large swaths of heavy rain move through a region, the rain produces a column of subsiding, or sinking, air towards the surface. This causes a vacuum behind back edge of the rain to, and air begins to rise to fill its place. The resulting vacuum/rising air is the low pressure system, and it is generated in the wake of the rain — hence the term, “wake low”.

Because the atmosphere is trying to resolve a perturbation within the system, air will continue to vacillate up and down (in the vertical) as well as from west to east (in the horizontal) while it tries to come back to equilibrium. It’s for this reason why you may also hear a wake low referred to as a gravity wave. With that said, there are many types of gravity waves, and wake lows are a large, dynamic example.

Wake low schematic cross section (Source: Johnson, R. H., and P. J. Hamilton, 1988)

Wake low schematic cross section (Source: Johnson, R. H., and P. J. Hamilton, 1988)

Wake lows can produce very gusty winds

Wake lows are mesoscale systems, which means they can be about a state-wide. The tight pressure gradient that sets up between the meso-high within the rain and the wake low can produce intense, damaging winds within an hour or two across an entire state — all without having any rain detected on radar. This is why wake lows should be taken seriously: They can cause considerable wind damage but without any thunderstorms present, and hence with little to no warning, since they cannot be tracked on radar.

Below are examples of the wind gusts and power outages reported from the wake low that moved through the Tennessee Valley Monday.