The month of September in Atlanta experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 35% throughout the month. The clearest day of the month is September 21, with clear, mostly clear, or partly cloudy conditions 66% of the time.
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Atlanta, the chance of a wet day over the course of September is rapidly decreasing, starting the month at 31% and ending it at 23%. For reference, the year's highest daily chance of a wet day is 45% on July 9, and its lowest chance is 19% on October 29.
The average sliding 31-day rainfall during September in Atlanta is gradually increasing, starting the month at 3.0 inches, when it rarely exceeds 5.2 inches or falls below 1.1 inches, and ending the month at 3.4 inches, when it rarely exceeds 6.6 inches or falls below 0.9 inches. The highest average 31-day accumulation is 3.4 inches on September 23.
Over the course of September in Atlanta, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 0 minutes, implying an average daily decrease of 2 minutes, 4 seconds, and weekly decrease of 14 minutes, 25 seconds.
The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The growing season in Atlanta typically lasts for 8.0 months (243 days), from around March 19 to around November 17, rarely starting before February 24 or after April 8, and rarely ending before October 31 or after December 6.
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents.