The frontal system that moved through the region yesterday brought widespread heavy rain over the Upper Chattahoochee River Basin upstream of Lake Lanier, Georgia. A narrow band of rainfall in the 6 to 8 inch range was reported. However, even more important is the widesread nature of this rain event. At least 3 inches of rain covered the entire basin, with a basin average likely close to 4 inches. This amount of rain, covering the entire basin, will result in significant, and welcome, inflows into Lake Lanier.
Here is a USGS streamflow hydrograph of a feeder tributary (Chattahoochee River Near Cornemia, GA) into Lake Lanier. Note that the flow increased from a base flow around 200 cfs, to nearly 10,000 cfs.