Monday, October 1, 2012

Weather changes coming for Charlotte

It's raining, a stiff breeze is blowing out of the northeast, and the temperatures are locked in the lower 60s -- about 15 degrees below average.

Yes, autumn is here. But it won't be here for long.

A cold air wedge -- a Piedmont phenomena I've written about before ( -- has established itself today across much of North Carolina and South Carolina. It means we'll have a chilly, wet day, with temperatures probably not escaping the lower and middle 60s.

Computer models indicate there could be a break from the rain, lasting several hours, Monday afternoon and evening in the Charlotte region. But more rain will return later this evening.

Rainfall amounts won't be heavy, as most areas will get a half-inch or less.  This is exactly what the lawn doctor ordered for anyone who fertilized and seeded over the weekend.

These cold air wedge situations tend to be most common in autumn and spring, but they sometimes develop in the winter -- occasionally, with very important ramifications.  Many of our sleet and ice storm episodes happen during a cold air wedge, as warm, most air from the Gulf of Mexico or Atlantic is carried over a layer of cold air trapped near the surface.

We'll need to watch this pattern as we approach winter.  If we keep having cold air wedges, or if low pressure continues developing in the Gulf of Mexico and pushing up across the Southeast (as it is doing today, for the second time in recent weeks), then that could be a big hint about our winter weather pattern.

The cold air wedge is forecast to break down Tuesday, with the low pressure system moving north of the Carolinas, and the counter-clockwise flow of air eventually scouring away the layer of cold air near the surface. As that happens, a cold front will cross the region.

It's possible that a few strong thunderstorms could develop Tuesday as the front approaches, but those most likely would be south of Charlotte. Regardless, it'll be a lot warmer Tuesday, as the wedge dissipates. Highs are expected to reach the upper 70s.

That sets the stage for another big change, from Wednesday through Friday. We'll be back in some late-summer weather, with sunny to partly sunny skies and afternoon highs of 80 degrees or even a little warmer.

The next cold front will approach the region over the weekend, so the forecast for Saturday and Sunday is very iffy, at this point.  For now, the National Weather Service is going with partly cloudy and mid 70s Saturday, then low 70s with a small chance of rain Sunday.