Atlanta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atlanta clear sky chart from 2005-11-06 to 2024-04-03.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 6% 3 5% 5% 3 5% 5% 6% 8% 42%	79253
	Night	13% 6% 2 5% 5% 3 4 5% 5% 8% 44%	80885
Transparency	Day	39% 7% 11% 19% 18% 5%	78976
	Night	38% 6% 10% 19% 20% 6%	80681
Seeing	Day	15% 8% 21% 22% 21% 13%	14015
	Night	15% 7% 22% 29% 22% 4	24159

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 9% 3 5% 5% 3 4 5% 5% 6% 38%	2836
	11th to 20th	Day	12% 6% 2 4 4 2 3 5% 4 6% 52%	2840
	21st to end	Day	26% 9% 2 4 4 2 3 3 4 4 39%	3281
February	1st to 10th	Day	15% 8% 3 6% 6% 3 4 5% 5% 6% 39%	1900
	11th to 20th	Day	20% 6% 3 5% 4 2 4 4 4 5% 41%	1848
	21st to end	Day	21% 7% 2 6% 5% 3 4 3 5% 6% 38%	1570
March	1st to 10th	Day	15% 6% 3 5% 5% 3 3 4 5% 6% 44%	1949
	11th to 20th	Day	17% 6% 3 6% 5% 3 4 5% 6% 7% 39%	2090
	21st to end	Day	15% 6% 2 5% 5% 3 5% 5% 6% 7% 40%	2299
April	1st to 10th	Day	12% 5% 2 4 5% 4 4 5% 5% 7% 46%	2059
	11th to 20th	Day	12% 6% 2 6% 6% 2 5% 4 4 7% 46%	2134
	21st to end	Day	9% 4 2 4 5% 3 4 4 5% 8% 51%	2290
May	1st to 10th	Day	9% 4 3 4 5% 2 4 4 5% 8% 51%	2340
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 6% 6% 9% 41%	2301
	21st to end	Day	9% 5% 2 6% 5% 3 5% 5% 6% 9% 45%	2531
June	1st to 10th	Day	9% 6% 3 7% 7% 4 6% 5% 7% 11% 35%	2340
	11th to 20th	Day	5% 4 2 4 6% 4 6% 6% 7% 12% 45%	2340
	21st to end	Day	6% 4 3 5% 7% 4 6% 8% 8% 10% 39%	2340
July	1st to 10th	Day	9% 5% 3 6% 7% 5% 9% 8% 8% 11% 29%	2340
	11th to 20th	Day	9% 5% 2 6% 6% 5% 7% 7% 9% 12% 31%	2340
	21st to end	Day	5% 5% 3 5% 8% 5% 8% 8% 9% 13% 31%	2547
August	1st to 10th	Day	7% 5% 2 6% 6% 5% 7% 9% 9% 12% 31%	2327
	11th to 20th	Day	12% 6% 3 6% 7% 4 6% 7% 8% 9% 33%	2142
	21st to end	Day	13% 7% 3 5% 6% 4 6% 6% 7% 11% 32%	2376
September	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 6% 6% 8% 41%	1990
	11th to 20th	Day	15% 5% 3 5% 5% 3 4 5% 7% 7% 42%	1980
	21st to end	Day	14% 5% 2 5% 5% 2 4 4 4 6% 50%	1980
October	1st to 10th	Day	12% 5% 2 4 3 3 3 4 4 5% 56%	1980
	11th to 20th	Day	11% 4 1 4 4 2 3 4 5% 8% 53%	1890
	21st to end	Day	14% 4 2 3 4 3 3 3 4 5% 54%	1980
November	1st to 10th	Day	12% 5% 2 5% 3 2 3 3 4 5% 56%	1686
	11th to 20th	Day	14% 5% 2 3 4 2 4 4 5% 5% 52%	1710
	21st to end	Day	13% 6% 3 5% 4 2 5% 4 5% 7% 46%	1710
December	1st to 10th	Day	19% 8% 3 5% 5% 3 4 5% 4 7% 37%	1710
	11th to 20th	Day	16% 7% 3 6% 5% 3 4 3 4 5% 43%	2153
	21st to end	Day	21% 8% 3 5% 5% 3 4 4 6% 6% 35%	3124
January	1st to 10th	Night	18% 7% 2 5% 4 3 4 4 5% 7% 40%	4109
	11th to 20th	Night	12% 8% 3 5% 5% 3 4 5% 5% 5% 46%	4120
	21st to end	Night	23% 11% 3 5% 3 2 3 3 3 4 40%	4372
February	1st to 10th	Night	17% 7% 3 5% 4 2 4 4 5% 7% 42%	2280
	11th to 20th	Night	20% 7% 3 5% 4 3 3 4 4 5% 42%	2218
	21st to end	Night	20% 7% 3 5% 5% 3 4 4 4 6% 40%	1884
March	1st to 10th	Night	14% 7% 3 4 4 3 4 4 4 6% 48%	2229
	11th to 20th	Night	14% 7% 2 4 5% 3 3 5% 5% 8% 44%	2090
	21st to end	Night	12% 6% 2 6% 4 2 6% 4 5% 6% 46%	2299
April	1st to 10th	Night	11% 5% 2 4 5% 3 5% 5% 5% 8% 47%	1960
	11th to 20th	Night	14% 5% 2 4 4 2 4 4 5% 7% 49%	1775
	21st to end	Night	9% 5% 2 4 4 3 4 4 5% 8% 53%	1668
May	1st to 10th	Night	9% 4 2 5% 5% 3 4 5% 5% 7% 51%	1620
	11th to 20th	Night	8% 6% 2 5% 6% 4 6% 5% 6% 8% 43%	1592
	21st to end	Night	8% 6% 3 6% 6% 3 4 5% 6% 8% 45%	1744
June	1st to 10th	Night	7% 5% 2 5% 6% 4 7% 6% 9% 14% 37%	1620
	11th to 20th	Night	4 3 1 5% 6% 4 5% 5% 8% 13% 46%	1620
	21st to end	Night	5% 4 1 4 6% 3 6% 7% 8% 11% 43%	1620
July	1st to 10th	Night	7% 5% 3 6% 6% 5% 6% 7% 7% 12% 35%	1620
	11th to 20th	Night	5% 4 2 6% 7% 4 7% 8% 8% 14% 34%	1620
	21st to end	Night	6% 5% 3 5% 7% 5% 7% 8% 8% 12% 34%	1771
August	1st to 10th	Night	6% 5% 2 6% 7% 4 7% 7% 9% 12% 35%	1611
	11th to 20th	Night	9% 5% 3 5% 6% 4 6% 6% 9% 10% 38%	1755
	21st to end	Night	12% 6% 3 6% 7% 5% 4 6% 7% 9% 36%	1980
September	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 6% 7% 10% 43%	1951
	11th to 20th	Night	12% 6% 3 5% 5% 3 4 5% 6% 8% 44%	1980
	21st to end	Night	12% 5% 2 5% 4 3 4 4 5% 7% 49%	1980
October	1st to 10th	Night	10% 5% 3 4 3 2 4 4 4 6% 55%	1980
	11th to 20th	Night	10% 5% 2 4 4 2 3 3 4 6% 56%	2069
	21st to end	Night	13% 4 2 4 4 2 3 4 4 5% 56%	2376
November	1st to 10th	Night	12% 4 1 4 4 2 3 3 4 6% 57%	2388
	11th to 20th	Night	13% 5% 2 4 3 2 3 4 4 6% 54%	2470
	21st to end	Night	15% 6% 2 4 4 2 4 4 5% 6% 47%	2470
December	1st to 10th	Night	16% 6% 2 6% 5% 3 5% 3 5% 7% 41%	2470
	11th to 20th	Night	17% 8% 3 4 4 2 3 3 4 5% 48%	3042
	21st to end	Night	19% 9% 3 6% 5% 4 4 5% 5% 7% 34%	4532

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	45% 5% 8% 15% 21% 6%	2837
	11th to 20th	Day	33% 4 8% 24% 24% 6%	2840
	21st to end	Day	49% 3 5% 17% 20% 6%	3281
February	1st to 10th	Day	46% 4 8% 16% 21% 4	1900
	11th to 20th	Day	46% 4 6% 18% 20% 6%	1858
	21st to end	Day	47% 4 8% 14% 19% 8%	1570
March	1st to 10th	Day	41% 4 9% 16% 21% 9%	1949
	11th to 20th	Day	45% 6% 11% 16% 18% 6%	2090
	21st to end	Day	42% 5% 11% 21% 17% 4	2299
April	1st to 10th	Day	37% 6% 9% 22% 19% 6%	2059
	11th to 20th	Day	38% 5% 7% 20% 23% 7%	2134
	21st to end	Day	31% 7% 10% 26% 24% 2	2290
May	1st to 10th	Day	31% 6% 13% 23% 24% 3	2340
	11th to 20th	Day	39% 9% 16% 21% 13% 2	2305
	21st to end	Day	35% 7% 12% 27% 18% 1	2531
June	1st to 10th	Day	43% 9% 15% 22% 11% 1	2340
	11th to 20th	Day	29% 11% 20% 26% 13% 1	2340
	21st to end	Day	35% 12% 17% 22% 12% 2	2340
July	1st to 10th	Day	42% 14% 18% 17% 8% 2	2275
	11th to 20th	Day	40% 13% 19% 17% 8% 2	2271
	21st to end	Day	38% 14% 20% 19% 8%	2405
August	1st to 10th	Day	39% 16% 19% 22% 5%	2314
	11th to 20th	Day	43% 13% 16% 17% 9% 2	2142
	21st to end	Day	44% 11% 15% 17% 10% 2	2376
September	1st to 10th	Day	38% 9% 14% 18% 16% 4	1990
	11th to 20th	Day	39% 9% 11% 18% 22% 2	1980
	21st to end	Day	36% 4 10% 20% 23% 6%	1980
October	1st to 10th	Day	32% 5% 9% 19% 28% 7%	1980
	11th to 20th	Day	30% 4 9% 23% 26% 8%	1890
	21st to end	Day	33% 4 6% 17% 30% 10%	1980
November	1st to 10th	Day	31% 4 8% 14% 31% 10%	1686
	11th to 20th	Day	33% 4 7% 18% 27% 10%	1710
	21st to end	Day	38% 5% 8% 18% 24% 7%	1710
December	1st to 10th	Day	46% 5% 6% 19% 17% 6%	1710
	11th to 20th	Day	44% 4 6% 15% 24% 7%	2150
	21st to end	Day	45% 6% 9% 18% 19% 3	3124
January	1st to 10th	Night	42% 5% 7% 16% 25% 6%	4109
	11th to 20th	Night	39% 4 7% 22% 21% 8%	4120
	21st to end	Night	49% 3 4 12% 25% 6%	4372
February	1st to 10th	Night	42% 4 9% 17% 20% 9%	2280
	11th to 20th	Night	44% 4 5% 16% 21% 8%	2219
	21st to end	Night	45% 4 8% 15% 17% 10%	1884
March	1st to 10th	Night	38% 4 9% 18% 20% 12%	2229
	11th to 20th	Night	38% 6% 11% 16% 21% 7%	2090
	21st to end	Night	38% 5% 9% 21% 21% 5%	2299
April	1st to 10th	Night	35% 5% 10% 20% 23% 8%	1960
	11th to 20th	Night	34% 3 7% 21% 23% 10%	1775
	21st to end	Night	29% 6% 10% 28% 21% 6%	1668
May	1st to 10th	Night	30% 7% 12% 23% 22% 4	1620
	11th to 20th	Night	37% 8% 17% 21% 16% 2	1593
	21st to end	Night	34% 9% 11% 24% 19% 3	1745
June	1st to 10th	Night	36% 12% 17% 21% 13% 1	1620
	11th to 20th	Night	27% 10% 22% 27% 13% 2	1620
	21st to end	Night	31% 12% 20% 20% 14% 3	1620
July	1st to 10th	Night	39% 12% 20% 19% 9% 2	1575
	11th to 20th	Night	34% 16% 23% 16% 10% 3	1566
	21st to end	Night	36% 13% 23% 18% 8% 2	1672
August	1st to 10th	Night	37% 14% 18% 24% 6% 1	1600
	11th to 20th	Night	37% 12% 19% 18% 12% 2	1755
	21st to end	Night	43% 11% 16% 17% 11% 3	1980
September	1st to 10th	Night	34% 11% 17% 18% 17% 5%	1951
	11th to 20th	Night	37% 8% 12% 20% 19% 3	1980
	21st to end	Night	34% 7% 12% 18% 21% 9%	1980
October	1st to 10th	Night	30% 6% 11% 18% 27% 8%	1980
	11th to 20th	Night	30% 5% 7% 22% 27% 10%	2069
	21st to end	Night	30% 3 6% 17% 31% 13%	2376
November	1st to 10th	Night	31% 3 7% 17% 28% 13%	2388
	11th to 20th	Night	33% 4 6% 17% 28% 13%	2470
	21st to end	Night	37% 4 7% 18% 26% 8%	2470
December	1st to 10th	Night	43% 6% 8% 19% 19% 6%	2470
	11th to 20th	Night	39% 4 8% 14% 29% 7%	3044
	21st to end	Night	49% 4 8% 19% 17% 3	4532

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	22% 20% 36% 18% 3	270
	11th to 20th	Day	24% 19% 32% 16% 7% 2	270
	21st to end	Day	24% 21% 36% 13% 5% 1	297
February	1st to 10th	Day	20% 20% 35% 20% 6%	270
	11th to 20th	Day	34% 17% 31% 16% 3	270
	21st to end	Day	28% 17% 38% 15% 3	225
March	1st to 10th	Day	24% 15% 30% 24% 7% 1	319
	11th to 20th	Day	20% 14% 31% 25% 8% 1	460
	21st to end	Day	19% 14% 33% 25% 8% 1	506
April	1st to 10th	Day	18% 14% 28% 21% 18% 1	428
	11th to 20th	Day	14% 13% 29% 23% 18% 3	412
	21st to end	Day	14% 9% 24% 25% 22% 6%	420
May	1st to 10th	Day	12% 9% 27% 26% 19% 8%	423
	11th to 20th	Day	12% 3 19% 25% 25% 16%	447
	21st to end	Day	13% 4 13% 24% 26% 21%	485
June	1st to 10th	Day	13% 3 12% 24% 30% 18%	450
	11th to 20th	Day	7% 2 11% 24% 22% 34%	450
	21st to end	Day	10% 1 11% 25% 27% 25%	450
July	1st to 10th	Day	8% 2 7% 16% 34% 33%	445
	11th to 20th	Day	8% 2 7% 14% 30% 39%	444
	21st to end	Day	6% 1 7% 14% 40% 32%	488
August	1st to 10th	Day	11% 2 12% 21% 25% 30%	446
	11th to 20th	Day	10% 2 9% 18% 34% 27%	439
	21st to end	Day	16% 1 8% 22% 28% 25%	495
September	1st to 10th	Day	10% 2 12% 22% 31% 24%	450
	11th to 20th	Day	15% 3 11% 21% 33% 17%	450
	21st to end	Day	15% 2 15% 19% 35% 13%	450
October	1st to 10th	Day	17% 3 17% 32% 21% 11%	450
	11th to 20th	Day	12% 9% 22% 24% 25% 8%	450
	21st to end	Day	18% 7% 20% 28% 22% 5%	495
November	1st to 10th	Day	19% 7% 27% 25% 18% 5%	284
	11th to 20th	Day	16% 14% 34% 24% 9% 2	270
	21st to end	Day	10% 14% 36% 26% 12% 2	270
December	1st to 10th	Day	26% 16% 33% 16% 9%	270
	11th to 20th	Day	22% 17% 29% 23% 8% 1	270
	21st to end	Day	30% 13% 32% 18% 6% 1	297
January	1st to 10th	Night	23% 15% 34% 23% 5% 1	760
	11th to 20th	Night	20% 15% 31% 26% 8%	760
	21st to end	Night	21% 14% 34% 27% 4	836
February	1st to 10th	Night	20% 11% 31% 32% 6%	760
	11th to 20th	Night	23% 12% 38% 25% 2	743
	21st to end	Night	22% 15% 35% 25% 3	628
March	1st to 10th	Night	18% 11% 34% 31% 6%	760
	11th to 20th	Night	17% 9% 36% 27% 11%	760
	21st to end	Night	16% 13% 27% 33% 11%	836
April	1st to 10th	Night	14% 10% 30% 32% 14%	686
	11th to 20th	Night	17% 9% 27% 29% 16% 1	533
	21st to end	Night	11% 6% 24% 36% 21% 1	540
May	1st to 10th	Night	10% 6% 24% 34% 25% 1	540
	11th to 20th	Night	11% 2 20% 35% 27% 5%	531
	21st to end	Night	11% 1 13% 31% 36% 8%	584
June	1st to 10th	Night	8% 1 11% 36% 37% 6%	540
	11th to 20th	Night	4 2 11% 27% 40% 16%	540
	21st to end	Night	6% 1 8% 31% 44% 10%	540
July	1st to 10th	Night	9% 2 6% 22% 45% 16%	525
	11th to 20th	Night	8% 1 5% 17% 52% 17%	522
	21st to end	Night	7% 1 6% 26% 45% 15%	591
August	1st to 10th	Night	7% 1 7% 23% 47% 14%	537
	11th to 20th	Night	11% 1 7% 26% 46% 9%	534
	21st to end	Night	14% 2 8% 24% 41% 11%	594
September	1st to 10th	Night	9% 1 9% 25% 45% 12%	691
	11th to 20th	Night	15% 2 10% 27% 41% 6%	720
	21st to end	Night	14% 1 13% 30% 38% 3	720
October	1st to 10th	Night	11% 4 17% 34% 26% 8%	720
	11th to 20th	Night	13% 6% 24% 31% 22% 4	720
	21st to end	Night	15% 6% 21% 35% 21% 3	792
November	1st to 10th	Night	15% 7% 21% 34% 21% 2	740
	11th to 20th	Night	16% 9% 30% 29% 15% 1	760
	21st to end	Night	17% 8% 28% 33% 13% 1	760
December	1st to 10th	Night	19% 10% 29% 31% 10% 1	760
	11th to 20th	Night	22% 8% 31% 28% 11%	760
	21st to end	Night	27% 12% 27% 28% 8%	836

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