Despite threats of 4-5 inches of rain along the I-85 corridor due to the remnants of Hurricane Ida, it appears that most of the Atlanta area only received in the neighborhood of 2-3 inches of precipitation. Here in Lawrenceville, I’ve recorded 1.87 inches since the rain started early this morning. In Alpharetta, they recorded 3.11 inches, and in Johns Creek, the Atlanta Athletic Club measured 2.98 inches.

Other Georgia locations received much more rain. Pine Mountain was reporting 5.48 inches of rainfall today, while Columbus recorded 5.01 inches. These two areas seem to be the hardest hit, and from glancing at the radar this afternoon, it seems that Alabama got the most rain. Gainesville recorded 2.44 inches, while Marietta saw 2.77 inches. The official Atlanta rain gauge at Hartsfield Airport recorded 2.71 inches.

The rain did cause some area rivers to reach flood stage. Big Creek in Alpharetta is flooding, as is Pew Creek in Gwinnett County, Peachtree Creek in Atlanta, and the Nickajack Creek in Cobb county. Suwanee Creek is expected to experience minor flooding tomorrow morning.

There’s still more rain to come before Ida bids Georgia farewell (and her remnants cause problems in the Delmarva peninsula). But, looking at the radar now, it seems like the forecasters should have picked I-59 in Alabama as the worst hit area, rather then the I-85 corridor.

I hope you enjoyed the beautiful weather today, with highs eight degrees above normal. In fact, the last week is the first time we’ve gone seven days without any rain since the middle of August. That’s about to change.

The map to the right tells the story. A combination of a cold front, a low pressure system now over Texas, and Hurricane Ida will bring as much as four inches of rain to north Georgia beginning Monday night through Wednesday morning.

Much will depend on Ida’s exact path. While the official forecast from the Hurricane Center takes her path over extreme south Georgia, the GFS and Canadian models are much further north, passing over the Atlanta area. Over the past few forecast updates, the Hurricane Center has brought Ida’s path further north.

The Weather Service has issued a flash flood watch for much of North Georgia from Tuesday morning through Wednesday morning. Despite the lack of rain over the last week, the ground is still extremely wet, and any rain over two inches or so could trigger yet more flooding.

Now that September is over, we can look back at a month that will be remembered for plenty of rain. Of course, it all depended on where you were: Gwinnett, Cobb and Douglas counties received far more precipitation than did the official measuring station at Hartsfield Airport. Still, it was the fifth wettest September on record in Atlanta, with 8.94 inches, or 219% of normal. It was the third wettest September in Macon with 10.68 inches, or 328% of normal, and the fourth wettest in Athens, with 9.86 inches, or 279% of normal rainfall.

At my house in Lawrenceville, I recorded 16.28 inches of rain, or 427% of normal rain. Gainesville reported 12.10 inches of rain, or 275% of normal, and Peachtree DeKalb airport had 15.74 inches of precipitation, or 420% of normal. The image above graphically displays the month’s rainfall. Click on it to enlarge.

Cooler than normal temperatures early in the month were balanced out with warmer than normal temperatures later on, ending up with a more or less normal average temperature for September. Atlanta’s mean temperature was 73.4 degrees, two tenths of a degree above normal. In Gainesville, the average of 71.0 degrees was 0.7 degrees cooler than normal, and in Athens, temperatures were half a degree above normal, with 73.1.

By now, even the most cynical will have to admit that the drought that plagued Georgia from 2006-2008 is finally over. A recent study by Columbia University indicated the drought wasn’t caused by global warming, and in fact wasn’t that unusual. The study says that the drought appeared more serious this time because of the Atlanta region’s growing population. While there was enough water for the region during similar droughts in the 1950s, not enough additional water storage was available to meet needs this time.

Weather-wise, the rainfall that caused the record-breaking flooding in metro Atlanta is now over. Of course, it’s going to take a while for roads to be rebuilt, and damage to homes to be repaired, but the last few days of dry weather has allowed river levels to recede and land to dry out.

The US Geological Survey declared the flooding a 500 year flood, according to an article in the AJC. Basing their data on river flow gauges, the USGS said there is only a 1/2 of one percent chance of a flood of the magnitude we saw this week. That doesn’t mean it will be another 500 years before we see this much rain, it’s just that the odds are very slim.

The weather service reports nine record river flows in the area, including Suwanee Creek cresting at 14.3 feet, more than two feet above the previous record. Additionally there were five top 5 record flows at other river gauges. Lake Lanier rose by about three feet due to all the rain.

Here are some rainfall totals from Monday, September 14th at 8 AM through Tuesday, September 22nd at 8 AM:

Satellite image taken Monday morning, September 21. Blues and Reds show the location of the heaviest rainfall when the image was taken.

You can see the full list as reported by the weather service and cooperative stations here.

One of the major causes of all the rain was a low pressure system west of Georgia being blocked by a high pressure system to our north. Even after the storms passed, the blocking pattern remained, which caused the continuing high humidity and 10 degree above average low temperatures over the past few days. This weekend, a cold front will finally push the whole system away, and give us cooler temperatures with low humidity, and a chance to dry out wet crawl spaces.

The weather service has reported 24 hour rainfall totals for North Georgia ending at 8 AM on Monday, September 21st. Here are some highlights:

Athens: .65 inches
Atlanta: .87 inches
Canton: 3.95 inches
Carrollton: 7.66 inches
Cartersville: 1.68 inches
Cleveland: 3.68 inches
Chamblee: 4.28 inches
Cumming: 1.80 inches
Doraville: 5.37 inches
Gainesville: .82 inches
Lafayette: 7.20 inches
Marietta: 3.54 inches
Rome: 2.61 inches
Sautee: 5.18 inches
West Point: 4.33 inches

If you think we had plenty of rain over the last six days, it looks like day seven is the one to beat them all. As of 6:50 this morning, my rain gauge is reporting 5.84 inches of precipitation fell…this morning. The AJC is reporting that Spaghetti Junction is closed because of heavy rain (both I-85 and I-285). In Gwinnett, two feet of water is blocking the intersection of Scenic Highway and Sugarloaf Parkway, and there is additional flooding in downtown Lawrenceville. The weather service is reporting 7 inches of rain in Lilburn, over 3 inches in downtown Atlanta, and 9 inches in southwest Atlanta.

So, that brings the total rainfall for the last week to 12.57 inches. In Atlanta, 3.72 inches of rain fell on Saturday, breaking a record. I’m sure there will be more records set today. Flash flood warnings are in effect until later this morning, with flood warnings until

And if you’re wondering about Lake Lanier, it’s rising rapidly as well. After being fairly stable until the weekend, the runoff and excessive rain has cause the lake’s level to rise by a foot since Sunday morning, and I imagine it will continue to go up. The current level is 1065.81 feet.

The latest drought report, as of July 14th, lists just over one third of the state of Georgia as being abnormally dry, including metro Atlanta and Gwinnett. This is despite the one to three inches of rain that fell on Sunday. While this may seem ominous, keep in mind that a year ago over half the state was in a severe drought.

The other bit of good news is that the drought outlook isn’t calling for any drought to develop east of the Mississippi River through October. There’s a better than even chance for precipitation tonight and tomorrow, and both the 6-10 and 8-14 day precipitation outlooks for Georgia are calling for wetter then normal weather.

In addition, both the one month and three month outlooks for August and August through October are calling for equal chances of above and below normal temperature and precipitation.

You may have noticed that it’s been a bit cooler than normal so far this April. As of this afternoon, the mean temperature for the month at Hartsfield Airport is 56.3 degrees, which is 3.6 degrees less than normal. Here in Lawrenceville, the mean is 56.4 degrees, not varying by much. Except on March 9th and 10th–when it barely made 80, we haven’t seen 80 degrees yet this year.

Normal temperatures for April 16th are a high of 73 and a low of 50. For the past few days, the highs have been in the mid-60s, with lows in the 40s. Much of the country has had a cooler than normal April, as you can see from the map below, which shows departure from normal temperatures for the first fourteen days of April:

It looks like we’ll have one more week of cool temperatures, before we start seeing 80 degrees by the end of next week. If you’re a fan of spring flowers like me, the positive side to the cool weather is that mother nature’s show lasts longer than normal. I remember in years past when a warm spell in late March brought out everything at once, and it was gone in a week. Not this year.

Today, the Climate Prediction Center updated its long-term outlooks for drought, May and the early part of the summer. North Georgia has mostly recovered from the drought, with only five percent of the state in moderate drought, and another two percent abnormally dry. The dry area includes the northeast portion of the state, but not metro Atlanta. Compare this to a year ago, when 54% of Georgia was experiencing drought conditions. Lake Lanier continues to improve as well, measuring 1062.76 feet above sea level, or over a foot above where it was a week ago.

The drought outlook through July show no signs of drought redeveloping, and calls for improvement in the corner of the state where drought still exists. The precipitation outlook, both for May and for May through July calls for equal chances of above or below normal rainfall for most of the United States. Above normal precipitation is likely for Minnesota and the Dakotas, while it is likely to be drier than normal in Utah and Idaho.

The temperature outlook for May and for May-July calls for equal chances of above or below normal temperatures east of the Mississippi, with warmer than normal weather in most of the southwest, and cooler temperatures in the same Minnesota-Dakotas area that is going to be wetter than normal.

The Climate Predication Center notes that we are entering a neutral period, neither in El Nino nor in La Nina sea surface temperatures. With neutral conditions, there are fewer reliable signals of what weather conditions will be, compared to either a La Nina or El Nino state.

The Atlanta area is forecast to get some of the wettest weather in quite some time beginning early Wednesday and lasting through Saturday night.

To the right is the Hydrometeorological Prediction Center’s forecast for rainfall over the next five days. As you can see, much of the northern part of the state could receive between four and five inches of rain.

The weather situation is similar to what we had back in Mid-December, when a stationary front was stalled just south of the Atlanta area. That rain episode added about a foot to the level of Lake Lanier. Depending on exactly where the rain falls, we could see a similar rise in lake levels this time. Lake Lanier is presently at 1059.14 feet above sea level.

One difference between the storm in December and the one this week is the possibility of thunderstorms. While it’s too early to issue any watches or warnings, you might want to keep an eye out for the possibility of severe weather through the weekend.

The good news is that after this storm clears out Saturday night, we’re in for some pleasant weather to begin the week.

The rain last week raised the water level of Lake Lanier about a foot, which likely means that Atlanta’s water supply won’t reach a record low in 2008. As usual, the mainstream media issued stories which said that the rain is good, but the drought isn’t over yet, we’ve got a long way to go, etc. &ct.

Now comes the Southeast River Forecast Center with the best estimate (PDF) I’ve seen for what it will take to get Lake Lanier to full pool — or 1071 feet above sea level, about 20 feet higher than where it is today.

Surprisingly, it’s only 10% above normal rainfall for a year.

The forecast center measured annual precipitation against Lake Lanier’s level since the lake began to fill back in 1952.  It determined that, on average, 60 inches of rain fell in the lake’s drainage basin per year, providing about 1.36 million acre feet of water.  Using those figures, and accounting for the fact that the Corps of Engineers has restricted the outflow from Lanier over the past year, the Forecast Center says,

Lake Lanier’s pool was at 1054 feet msl at the beginning of this water year (1.37 million acre-ft). To get to full pool at elevation 1071 feet msl, an additional 585,000 acre-ft of inflow is needed. However, this assumes no outflow. If we apply the annual average outflow of last year for this year (1070 cfs), 775,000 acre-ft are released downstream. So the total inflow volume needed to fill the reservoir and sustain a release similar to last year is 1.36 million acre-ft.
…[T]his would put the total annual precipitation at around 65 inches (following the lower end of the trend). This is only about 10% above normal.

Of course, part of the equation depends on when the water comes. If we get a lot of excessive rain in the winter, it will count more than if we get it in the summer, since the heat and absorption by plants prior to the water reaching the lake will be higher in the summer months. The calculations used in the analysis are based on rain during the water year, which starts on October 1, and there has already been six inches of rainfall. That means there are only 59 inches to go.

I listened to Lieutenant Governor Casey Cagle (who is clearly running to become governor in 2010) addressing the Gwinnett Chamber’s monthly meeting this afternoon. He dumped most of the problems with metro Atlanta’s water supply on the Corps of Engineers favoring mussels in Apalachicola Bay over the water needs of Georgia. He also offered an innovative idea for increasing the water available to metro Atlanta. He estimated 10% of the lake’s capacity had been lost due to silt (something I’m not going to argue with). By dredging the lake, Cagle says we could not only expand the lake’s capacity to hold more water, we could recycle and resell any valuable materials that were dredged up.

In my mind, Cagle’s plan will only work if Georgia gets some formal rights to the lake’s water. Based on court decisons and the official use plan for the lake, we aren’t there yet.