If you are like me, you were probably looking forward to the predicted sunny skies this afternoon, which obviously didn’t happen. The moist air left over from Saturday’s rain remained in place as the slow moving cold front that brought the rain stalled across south Georgia. This kept the clouds in place and kept the temperatures cooler than expected.

If you were hoping for bright April skies this week, it looks like that won’t happen either, and there is a possibility of rain affecting the upcoming Masters Tournament in Augusta this weekend. For the first part of the week, we’ll see another wedge keep temperatures cooler than normal, with a good chance of fog and drizzle in northeast Georgia.

The wedge moves out on Wednesday, leaving us with a pleasant day for the first round of the Masters on Thursday, but setting us up for a chance of showers and thunderstorms through the weekend. Right now, it looks like the greatest chance of rain is in the western part of the state, but golfers could see rain on Friday and Saturday. The storm system moves out Saturday night, leaving better weather for Sunday.

The week of the 13th promises to be interesting, at least by the early forecasts. There’s a good possibility that cold Canadian air will make one last stand, with a chance of a very late freeze for the first part of the week. Both the 6-10 and 8-14 day outlooks are calling for colder than normal temperatures, and Accuweather is calling for lows in the mid 30s a week from Monday and Tuesday. If you were planning to get your annuals out this week, it might be a good idea to hold off until the forecast becomes clearer as the week wears on.

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It looks like things could get fairly nasty Wednesday Night and into Thursday for much of the Atlanta area north of Interstate 20, and especially for the northeast counties, including Gwinnett.  An incoming low pressure system in the Gulf of Mexico will bring precipitation to Georgia beginning Wednesday morning.  Meanwhile, the high currently over the eastern part of Kentucky will move northeast, running into the Appalachians, and causing a ‘wedge’, or cold air damming to affect northeast Georgia.

What happens is that the colder air gets trapped on the western edge of the mountains, and the approaching lower pressure, warmer air slides above the colder, heavier air. You can tell when we’re in a CAD situation when the wind comes from the east, and it doesn’t warm up much during the day.

The presence of warm air above cooler closer to the ground tends to favor the formation of sleet or freezing rain, since the warm air layer will melt any snow as it passes through, while the cold air close to the ground will either re-freeze the precipitation, or cause freezing when the water hits the surface.

In the last day, forecasters have increased the total amount of expected precipitation from the storm to almost an inch, while dropping the low temperature Wednesday night, especially in the northeast counties most affected by the wedge.

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Depending on where you were, you may have been disappointed with the Thanksgiving Day rainfall totals. Here in Lawrenceville, I recorded .15 inches for the storm, which is less than many other areas did. Looking at the radar as the storm passed over the Atlanta metro area, most of the rainfall seemed to be to the north of Georgia 316, and that’s borne out by some of the precipitation reports:

Athens: 1.17 inches (they really needed it)
Gainesville: .46 inches
Johns Creek: .93 inches
Alpharetta: 1.09 inches
Rome: .87 inches
Atlanta: .16 inches

The good news is that we’re due for some more rain before the month ends, and then at the beginning of December. Cooler air is beginning to filter into the state from northwest to southeast, and Friday should be a sunny, if cool, day for shopping or golf. (Someone told me that the day after Thanksgiving is one of the biggest days for golf - the ladies go shopping and the men to golfing.)

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With the Dog Days of summer ready to begin tomorrow, it’s time to take a look at what we had in June, and what to look forward to as the hottest part of the summer begins.

June actually ended up having close to normal rainfall in Georgia, largely because of the effects of Tropical Storm Barry in the southeastern part of the state. Up here in North Georgia, Atlanta was just about at normal June rainfall with 3.66 inches of rain. With 4.7 inches, Columbus had more than an inch of above-normal rain. Macon saw 4.69 inches of rain, or 1.15 inches more than normal. Athens continued its deficit, with 2.17 inches, or 1.77 inches below normal. And finally here in South Gwinnett, my rain gauge recorded 5.03 inches, including over two inches from the thunderstorms that rolled through on June 28th.

The map above shows total estimated rainfall for Georgia in June. Areas in green and yellow, including most of the northwest part of the state, were short of rain.

The month ended up being warmer than normal for most of the state Mean temperatures include Atlanta at 79.5 degrees, 2.7 degrees above normal; Gainesville at 77.9 degrees, or 3.3 degrees above normal, and Athens at 78.5, 2.2 degrees above normal. Here in Lawrenceville, I was at the low end of the scale, at 76.5 degrees mean for the month. Part of the reason for that may be that I had more rain than normal, which tends to keep things a bit cooler.

July is likely to be warmer than normal as well, with the Weather Service estimating a 40% chance of above normal temperatures for all but the southernmost portions of Georgia. It may be that most of that heat will be towards the second half of the month, though, with the medium range outlook from the 8th to the 16th calling for normal to below normal temperatures.

On the rainfall side, the Weather Service doesn’t make a firm call one way or another, however it looks like we’re likely to see continued wet weather in the short term, or until the massive storm that is flooding much of Texas and Oklahoma finally goes away.

Today was the first time since July 10th, 2005 that a day in July didn’t go above 80 degrees (at least in my records). While the clouds kept the temperatures down, the main reason for the cooler weather is a phenomenon we normally see in the wintertime: cold air damming, otherwise known as the wedge. High pressure air in the mid-Atlantic states flows down the side of the Appalachian mountains, while low pressure air moves in from the southwest. Because high pressure air is heavier than low pressure, it becomes trapped underneath the low pressure system, and keeps the temperatures down (and the humidity up).

The good news is that the drier air will be moving in over the next few days, and we will, with any luck, have very nice, cooler than normal weather for Independence Day.

There’s a reasonable chance that metro Atlanta might get its first wintry weather Wednesday night and into Thursday, but the forecast is tricky, and a lot of what will happen will depend on exactly how conditions set up.

During the day Wednesday, North Georgia will be under control of a high pressure system located over Virginia. This will make for a chilly day again. Meanwhile, a low pressure system is moving east. It’s the same one that has brought freezing rain to Texas earlier this week. Whether we get a major winter event depends on how these two systems interact.

As the warm, moist air moves into Georgia, it will meet the colder air. Since the colder air is heavier than the warmer air, it will remain below the warm air. This effect is called Cold Air Damming, or popularly, ‘the wedge’. The possible effect is that instead of temperatures rising with the incoming rainfall, it will remain cold enough at the surface to cause sleet or freezing rain.

Below is the Weather Service graphical forecast for 7 AM on Thursday:

You can see that below Macon, there will be heavier precipitation, and it will be all rainfall. There’s an area north of that that may see heavier icing, since it will be in the more active part of the rainy sector, while also under the influence of the wedge. North of a line from Columbus to Athens, including Gwinnett County, freezing rain is also predicted.

So what happens on Thursday morning is a function of how strong a wedge develops, and how fast the precipitation moves. Since the ground is warm because of the springlike weather we saw before today, there isn’t likely to be any accumulation on the ground. However, if we do get freezing rain, it will affect trees and power lines, and things could turn nasty. If it’s too cold, we get sleet, which won’t be a problem. And, if the wedge is weak, we may get all rain as temperatures close to the surface remain above 32 degrees.

Stay tuned…