This time, the cold air wedge does Charlotte a favor

The cold air wedge has done it again -- but this time, we should be thankful.

The wedge -- a pocket of cool, damp but relatively stable air that is pushed into the Carolinas Piedmont by high pressure systems over New England -- usually causes us plenty of problems. In winter, areas inside the wedge are prone to ice storms and snow.

In spring, the wedge often contributes to those chilly, rainy days. Does anyone remember the day before Easter?

A wedge of cool air was locked in place Monday across the northern half of North Carolina. While Charlotte was in the lower 80s on Monday afternoon, temperatures were 20 degrees cooler in Raleigh and Greensboro. Computer models, as they usually do, vastly underestimated the strength of the wedge. The models predicted the cool air would remain north of Charlotte.

It didn't. About 11 p.m. Monday, the wedge front pushed south of Charlotte. Dew point temperatures, which measure the level of humidity and instability in the atmosphere, dropped sharply. The wind shifted from south to northeast.

And at that moment, Charlotte was protected from the severe weather to the west.

As is often the case, the wedge of cool air was pushed up against the mountains. Cooler air sinks, and so it often is lodged against the mountains. That is why strong storms dumped several inches of rain overnight in Burke, Caldwell, McDowell and Catawba counties -- areas that were along, or just outside of, the cool air pocket.

So the big question is how long the cool air will remain in place?

Once again, the compute models predict the cooler and more stable air will retreat northward Tuesday. I enjoyed the comment from Justin Lane, a meteorologist at the National Weather Service's office in Greer, S.C. Talking about the predicted northward movement of the cooler air, he said, :"I don't have a lot of faith in that."

More likely, it will be late Tuesday night or early Wednesday before that happens.

Eventually, the severe thunderstorms probably will reach the Charlotte region. But the presence of the cool air wedge in Charlotte has prevented a couple inches of rain from falling overnight. That will decrease the overall storm total for the area and lessen the threat of flash flooding from whatever rain falls Tuesday night and Wednesday.