ROANOKE, Va. – March is about to come in like a roaring lion with rain and wind that could take out power and knock down trees.
A High Wind Watch goes in effect Thursday evening, but these potentially damaging winds won't be generated by thunderstorm's, but a large difference in pressure in a relatively small distance. Wind is all around us, but there are different ways it is generated.
These systems are driven and fueled by temperature and pressure differences. This is the type of system that will be generating our very strong wind gusts Thursday through Saturday. The greater the pressure difference, the stronger the wind with these storms. The winds in between the two increase. It can be completely sunny as the wind event is unfolding!
Thunderstorms can come in many shapes and sizes. Individual thunderstorm downburts, also know as microbursts can cause straight-line wind damage on an isolated scale.
Sometimes storms come in a line or clusters and have a system of downdrafts creating more widespread damage.
If the storms produce strong enough wind and produce straight-line wind damage over a large area, it will be classified as a derecho, like the one that blasted through the area in 2012. The image below from the National Weather Service in Blacksburg shows the derecho's history on the left. The blue markers on the top right all indicated wind damage reports.
Both the intensity and distance thresholds have to be met in order to be classified as a derecho. For example, straight-line winds from a line of storms could do as much damage as a derecho, but if it's contained to a small area, it won't be classified as one.
Tornadoes typically develop with isolated cells, but weaker ones can also develop in a line of storms given the proper environment, in this case wind shear. Tornadoes are violently rotating columns of air that extend from the cloud to the ground. Damage associated with tornadoes is scattered in all directions, rather than in one direction as in straight-line wind events. The debris is typically twisted from the turning winds.
Tropical storms and hurricanes are clusters of thunderstorms that organize and intensify over warm, open waters. The strongest hurricanes can produce winds of around 200 mph in the eye wall, the strongest part of the storm. These storms weaken with land interaction.