Forecasters miffed 'cuz we didn't have the lift!

There are many parameters meteorologists look at when trying to determine heavy rain potential.

Obviously, the amount of water vapor present is critical and we refer to this as precipitable water, or the total amount of water vapor present in a column of air from the surface to very high up in the atmosphere.

Another key is the amount of wind shear, or changes in the wind with height.

If the winds are blowing from the same direction through a great depth of the atmosphere, showers and storms will align themselves in such a way that multiple cells will repeatedly pass over the same location, resulting in excessive rainfall.

But none of this amounts to a hill of beans if there isn't a process in place to initiate upward motion in the atmosphere.

And to further complicate matters, this upward motion operates on different scales.

One is called the synoptic scale, where systems that affect multiple states at a time create large scale upward motion, which can lead to widespread precipitation, especially in the cool part of the year.

The more difficult scale to predict is called the mesoscale, where very small scale features can dump multiple inches of rain on one location, while leaving areas just a few miles away bone dry.

This scale of motion in the atmosphere is challenging to observe, let alone predict.

Early this week we had plenty of moisture present, along with a large scale system (trough in the upper atmosphere), and the consensus among many meteorologists was that the stage was set for widespread heavy rainfall.

So what was missing?

Well first, the atmosphere was not all that terribly unstable, which means showers and thunderstorms had a harder time than usual getting started, and the largest amount of lift generated by the upper trough was in eastern North Carolina, and thus the most widespread activity was near the coast as opposed to inland parts of North Ccarolina.

One analogy to explain why summertime forecasting is so difficult is this: imagine a ball at the top of a hill that isn't moving.

That ball will represent a parcel of air in the atmosphere.

As long as nothing pushes the ball, it remains stationary.

Stormy weather on tap this evening

But just the slightest shove, and the ball begins to move faster and faster down the hill.

Instability can be described as an object accelerating away from its initial location never to return to its starting point.

We didn't have much of that Monday and Tuesday, making it even more difficult for showers and storms to get going.

So the devil was in the details, as usual. yet another reason why during the summertime in North Carolina, you should never cancel your plans to do something outside.

You may just luck out, just like many did the first two days of this week!