Sunday, April 06, 2008

the wedge...

The 'wedge' has been a popular topic as of late and anytime we talk about it we get lots of questions here in the weather department.

The wedge typically occurs during the winter and spring months here in Georgia... although it can actually happen any time of year. It takes a combination of our unique geography and a specific weather pattern to get the 'wedge.'

It happens when High Pressure settles over the NE United States. Because the flow around high pressure is clockwise it brings cool, maritime air into the southeastern U.S. (think about New England along the coast with sea fog and fog horns, etc). Because cool air is dense... when it gets pushed up against the Appalachian Mountains it can not go over the mountains so it gets pushed down the spine mountains into Georgia. You can see this in the graphic below.

Here is a weather chart from this past Friday morning when we were socked in with drizzle, fog, & cool temperatures. The arrows on the chart indicate the direction the wind is blowing from. Again, notice how the winds are blowing down the Appalachian Mountains. The other thing to note is the wide range in temperatures across Georgia. You go from 70s (in the morning!!) in south Georgia to 40s in NE Georgia. Needless to say, the wedge is one of the most difficult things to forecast.

In this picture from later Friday afternoon notice how the winds are shifting to out of the South instead of the East to NE. That is when the 'wedge' is retreating. This happens as the high pressure over the NE U.S. begins to move out into the Atlantic turning our winds to more of SE or South (think warm and tropical). Remember when temperatures soared to near 70 that afternoon? Those warmer temperatures helped allow for the development of the severe storms Friday afternoon/evening.

Well, guess what? It looks like the dreaded wedge weather pattern is again setting up for the early part of the week. I think the placement of the high over the NE U.S. is not ideal, but it is close enough to get some cooling, clouds, and drizzle over northern, and especially NE Georgia on Monday & Tuesday.

Have a great week... I promise the sun is up there somewhere!


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