Stone Mountain State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stone Mountain State Park clear sky chart from 2005-11-06 to 2025-07-21.

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	15% 6% 2 6% 4 4 5% 4 6% 8% 41%	120467
	Night	15% 6% 2 5% 4 3 4 3 5% 7% 46%	118668
Transparency	Day	38% 7% 12% 21% 17% 5%	124155
	Night	37% 6% 11% 21% 19% 6%	123117
Seeing	Day	19% 12% 23% 24% 16% 7%	16143
	Night	17% 8% 24% 30% 18% 3	26223

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	14% 5% 2 4 3 2 3 2 4 5% 56%	4056
	11th to 20th	Day	12% 5% 1 5% 3 3 3 3 3 4 57%	4060
	21st to end	Day	19% 5% 3 5% 3 3 3 3 4 4 49%	4466
February	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 6% 7% 42%	1800
	11th to 20th	Day	19% 8% 2 4 3 4 3 3 5% 7% 42%	1894
	21st to end	Day	19% 7% 2 4 4 3 5% 4 5% 6% 41%	1680
March	1st to 10th	Day	21% 7% 2 5% 3 3 4 4 5% 6% 41%	4935
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 5% 7% 53%	4980
	21st to end	Day	19% 6% 2 5% 3 3 3 3 4 6% 45%	5465
April	1st to 10th	Day	12% 5% 2 4 4 3 4 3 6% 8% 49%	2206
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 6% 7% 46%	2374
	21st to end	Day	15% 6% 2 5% 5% 5% 5% 4 5% 7% 42%	2595
May	1st to 10th	Day	13% 7% 2 7% 6% 6% 6% 5% 8% 9% 32%	5862
	11th to 20th	Day	23% 7% 2 7% 5% 5% 5% 4 7% 8% 28%	5861
	21st to end	Day	15% 5% 2 6% 5% 4 5% 4 7% 9% 38%	6433
June	1st to 10th	Day	12% 6% 2 6% 5% 6% 6% 5% 8% 10% 34%	2600
	11th to 20th	Day	9% 5% 2 7% 6% 6% 6% 5% 7% 11% 36%	2600
	21st to end	Day	8% 5% 2 6% 5% 6% 6% 6% 9% 11% 37%	2600
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 7% 6% 8% 10% 35%	4250
	11th to 20th	Day	9% 6% 2 7% 5% 7% 7% 7% 8% 10% 31%	4250
	21st to end	Day	15% 8% 3 10% 7% 8% 8% 6% 7% 8% 22%	4466
August	1st to 10th	Day	15% 8% 3 8% 5% 6% 6% 5% 8% 10% 26%	4104
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 8% 11% 34%	4044
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 6% 10% 49%	4286
September	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	2136
	11th to 20th	Day	18% 6% 2 6% 4 5% 4 3 6% 8% 37%	2090
	21st to end	Day	22% 7% 2 5% 4 4 5% 3 5% 6% 36%	2090
October	1st to 10th	Day	17% 4 2 5% 3 3 3 3 4 5% 52%	1968
	11th to 20th	Day	15% 4 2 4 3 3 4 2 4 5% 54%	1900
	21st to end	Day	15% 4 2 5% 3 2 3 2 4 5% 55%	2090
November	1st to 10th	Day	13% 5% 1 5% 3 3 3 3 4 6% 55%	1957
	11th to 20th	Day	13% 5% 1 4 3 3 4 3 5% 7% 54%	1800
	21st to end	Day	14% 5% 1 5% 4 3 2 3 5% 7% 51%	1800
December	1st to 10th	Day	15% 8% 2 5% 3 3 3 2 4 4 52%	2930
	11th to 20th	Day	18% 7% 2 4 3 3 3 3 5% 6% 45%	3373
	21st to end	Day	24% 5% 1 3 3 3 3 3 5% 7% 40%	4466
January	1st to 10th	Night	13% 6% 1 4 3 3 3 2 5% 4 56%	5889
	11th to 20th	Night	13% 5% 2 4 2 2 3 2 4 5% 57%	5900
	21st to end	Night	19% 6% 2 3 2 2 3 3 4 5% 51%	6490
February	1st to 10th	Night	14% 7% 2 4 4 5% 4 4 6% 7% 44%	2600
	11th to 20th	Night	21% 5% 2 5% 4 2 4 3 5% 6% 44%	2390
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 6% 43%	1948
March	1st to 10th	Night	21% 7% 2 5% 3 3 3 4 4 5% 44%	4918
	11th to 20th	Night	10% 3 1 4 3 3 4 3 5% 7% 57%	4980
	21st to end	Night	16% 5% 2 5% 4 3 4 4 6% 7% 44%	5467
April	1st to 10th	Night	13% 6% 2 4 4 4 3 3 6% 7% 46%	2192
	11th to 20th	Night	15% 5% 2 4 3 3 4 3 5% 7% 47%	1975
	21st to end	Night	15% 5% 2 5% 3 3 4 3 5% 7% 47%	1820
May	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 6% 9% 38%	4033
	11th to 20th	Night	22% 7% 2 6% 4 4 4 3 5% 8% 35%	4032
	21st to end	Night	19% 4 2 5% 4 3 3 3 6% 9% 41%	4421
June	1st to 10th	Night	11% 5% 2 4 5% 5% 5% 5% 8% 9% 42%	1800
	11th to 20th	Night	12% 6% 2 5% 3 4 5% 4 7% 10% 42%	1800
	21st to end	Night	8% 5% 2 5% 5% 4 5% 4 7% 12% 43%	1800
July	1st to 10th	Night	10% 5% 3 6% 5% 4 4 6% 8% 10% 38%	2930
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 5% 9% 11% 38%	2930
	21st to end	Night	13% 8% 3 9% 7% 6% 6% 5% 7% 9% 27%	3087
August	1st to 10th	Night	16% 8% 3 8% 5% 4 5% 5% 7% 10% 29%	2825
	11th to 20th	Night	12% 7% 2 8% 5% 5% 5% 4 7% 9% 37%	2785
	21st to end	Night	7% 4 1 4 4 4 4 4 6% 8% 52%	3338
September	1st to 10th	Night	12% 5% 2 6% 5% 4 4 4 6% 7% 45%	2040
	11th to 20th	Night	18% 7% 3 6% 4 3 4 3 5% 7% 39%	2090
	21st to end	Night	22% 6% 2 5% 4 4 5% 3 5% 5% 39%	2090
October	1st to 10th	Night	16% 6% 2 6% 3 2 3 3 4 6% 48%	2210
	11th to 20th	Night	16% 5% 1 4 3 3 3 3 4 6% 54%	2280
	21st to end	Night	15% 4 1 4 3 3 3 3 4 4 57%	2508
November	1st to 10th	Night	16% 5% 2 4 4 3 3 2 4 4 54%	2341
	11th to 20th	Night	15% 4 1 3 3 3 3 3 4 7% 54%	2597
	21st to end	Night	13% 5% 1 5% 3 2 4 4 5% 6% 52%	2600
December	1st to 10th	Night	13% 7% 2 6% 3 3 3 3 4 5% 52%	4250
	11th to 20th	Night	22% 8% 3 5% 3 3 3 3 3 5% 42%	4822
	21st to end	Night	23% 5% 1 4 3 3 3 3 5% 6% 43%	6490

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	31% 3 6% 20% 31% 8%	4057
	11th to 20th	Day	31% 3 5% 17% 34% 9%	4060
	21st to end	Day	39% 4 7% 22% 24% 5%	4466
February	1st to 10th	Day	39% 6% 11% 22% 18% 5%	1800
	11th to 20th	Day	42% 4 9% 20% 19% 5%	1904
	21st to end	Day	42% 6% 10% 17% 18% 6%	1680
March	1st to 10th	Day	43% 4 7% 19% 15% 12%	4935
	11th to 20th	Day	31% 5% 6% 20% 25% 13%	4980
	21st to end	Day	41% 4 8% 25% 17% 5%	5465
April	1st to 10th	Day	31% 6% 13% 23% 20% 6%	2206
	11th to 20th	Day	36% 6% 11% 20% 20% 7%	2374
	21st to end	Day	39% 7% 12% 23% 14% 3	2595
May	1st to 10th	Day	44% 10% 14% 19% 11% 1	5897
	11th to 20th	Day	51% 9% 11% 19% 8% 1	5865
	21st to end	Day	39% 9% 15% 19% 15% 3	6447
June	1st to 10th	Day	40% 10% 16% 23% 10% 1	2600
	11th to 20th	Day	38% 11% 16% 19% 14% 2	2600
	21st to end	Day	35% 12% 17% 20% 14% 1	2600
July	1st to 10th	Day	39% 13% 18% 18% 9% 3	4185
	11th to 20th	Day	41% 13% 23% 18% 5% 1	4181
	21st to end	Day	54% 12% 13% 15% 5% 1	4324
August	1st to 10th	Day	48% 11% 18% 18% 5%	4091
	11th to 20th	Day	39% 12% 20% 19% 8% 2	4083
	21st to end	Day	29% 8% 17% 33% 11% 2	4286
September	1st to 10th	Day	37% 11% 12% 20% 17% 4	2136
	11th to 20th	Day	42% 8% 12% 20% 16% 2	2090
	21st to end	Day	48% 5% 10% 18% 16% 3	2090
October	1st to 10th	Day	29% 6% 7% 20% 27% 10%	3267
	11th to 20th	Day	23% 3 5% 24% 25% 20%	3140
	21st to end	Day	27% 5% 8% 25% 19% 16%	3428
November	1st to 10th	Day	31% 5% 8% 22% 26% 7%	1957
	11th to 20th	Day	31% 4 9% 23% 27% 7%	1800
	21st to end	Day	34% 4 8% 23% 27% 4	1800
December	1st to 10th	Day	36% 4 7% 20% 26% 7%	2930
	11th to 20th	Day	39% 4 11% 18% 21% 6%	3370
	21st to end	Day	42% 4 12% 25% 14% 2	4466
January	1st to 10th	Night	29% 4 7% 20% 28% 11%	5889
	11th to 20th	Night	30% 4 6% 18% 33% 9%	5900
	21st to end	Night	36% 4 6% 22% 26% 6%	6490
February	1st to 10th	Night	39% 4 11% 23% 19% 4	2600
	11th to 20th	Night	42% 5% 9% 20% 18% 7%	2391
	21st to end	Night	41% 5% 11% 19% 19% 6%	1948
March	1st to 10th	Night	41% 5% 6% 18% 20% 9%	4918
	11th to 20th	Night	26% 5% 7% 21% 25% 16%	4980
	21st to end	Night	38% 5% 9% 27% 16% 5%	5467
April	1st to 10th	Night	37% 5% 11% 21% 21% 5%	2192
	11th to 20th	Night	35% 6% 10% 22% 20% 7%	1975
	21st to end	Night	36% 6% 12% 27% 16% 3	1820
May	1st to 10th	Night	42% 10% 15% 21% 12% 1	4060
	11th to 20th	Night	48% 8% 14% 20% 9%	4033
	21st to end	Night	38% 8% 13% 26% 11% 2	4429
June	1st to 10th	Night	36% 11% 16% 24% 12% 2	1800
	11th to 20th	Night	36% 9% 18% 23% 13% 1	1800
	21st to end	Night	33% 11% 17% 22% 13% 4	1800
July	1st to 10th	Night	39% 13% 16% 19% 11% 2	2885
	11th to 20th	Night	37% 12% 25% 20% 5% 2	2876
	21st to end	Night	51% 12% 14% 17% 5%	2988
August	1st to 10th	Night	48% 10% 19% 17% 5%	2814
	11th to 20th	Night	41% 12% 19% 18% 10% 1	2812
	21st to end	Night	28% 10% 14% 37% 9% 3	3338
September	1st to 10th	Night	37% 8% 15% 20% 15% 5%	2040
	11th to 20th	Night	44% 7% 11% 18% 18% 1	2090
	21st to end	Night	46% 7% 10% 18% 17% 3	2090
October	1st to 10th	Night	35% 6% 7% 18% 23% 11%	3691
	11th to 20th	Night	22% 3 7% 25% 28% 16%	3779
	21st to end	Night	26% 4 6% 23% 25% 15%	4120
November	1st to 10th	Night	34% 4 8% 21% 23% 8%	2341
	11th to 20th	Night	31% 4 9% 21% 26% 9%	2597
	21st to end	Night	33% 4 8% 25% 26% 5%	2600
December	1st to 10th	Night	35% 5% 8% 21% 28% 4	4250
	11th to 20th	Night	46% 4 8% 17% 17% 8%	4824
	21st to end	Night	40% 4 15% 22% 17% 1	6490

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	26% 29% 30% 12% 4	300
	11th to 20th	Day	29% 22% 32% 16% 1	300
	21st to end	Day	24% 28% 33% 11% 3	330
February	1st to 10th	Day	22% 23% 33% 18% 3	300
	11th to 20th	Day	36% 25% 29% 10%	300
	21st to end	Day	27% 24% 34% 13% 2	279
March	1st to 10th	Day	23% 20% 30% 20% 6% 1	500
	11th to 20th	Day	23% 22% 31% 18% 6% 1	500
	21st to end	Day	25% 17% 34% 18% 5% 1	550
April	1st to 10th	Day	20% 20% 30% 20% 9% 1	500
	11th to 20th	Day	19% 16% 27% 23% 12% 3	492
	21st to end	Day	19% 14% 27% 26% 11% 4	500
May	1st to 10th	Day	17% 16% 31% 21% 11% 4	503
	11th to 20th	Day	20% 8% 25% 25% 16% 7%	527
	21st to end	Day	21% 6% 19% 25% 18% 11%	573
June	1st to 10th	Day	12% 6% 19% 34% 20% 9%	530
	11th to 20th	Day	11% 6% 18% 25% 29% 11%	530
	21st to end	Day	10% 3 19% 33% 24% 11%	530
July	1st to 10th	Day	11% 3 11% 27% 31% 17%	525
	11th to 20th	Day	8% 2 12% 27% 33% 18%	524
	21st to end	Day	13% 3 11% 28% 28% 16%	532
August	1st to 10th	Day	17% 3 18% 23% 20% 18%	486
	11th to 20th	Day	13% 2 12% 31% 25% 17%	479
	21st to end	Day	10% 2 9% 27% 31% 20%	539
September	1st to 10th	Day	14% 2 14% 24% 31% 15%	490
	11th to 20th	Day	18% 5% 13% 21% 31% 12%	490
	21st to end	Day	25% 7% 18% 27% 17% 5%	490
October	1st to 10th	Day	21% 6% 15% 27% 25% 6%	490
	11th to 20th	Day	14% 13% 23% 27% 20% 3	490
	21st to end	Day	19% 9% 23% 32% 14% 3	539
November	1st to 10th	Day	21% 10% 25% 27% 13% 3	495
	11th to 20th	Day	16% 21% 30% 24% 7% 1	300
	21st to end	Day	16% 21% 30% 25% 8% 1	300
December	1st to 10th	Day	27% 21% 31% 17% 4	300
	11th to 20th	Day	22% 17% 33% 22% 6%	300
	21st to end	Day	28% 16% 29% 21% 5% 1	330
January	1st to 10th	Night	18% 16% 36% 25% 5%	800
	11th to 20th	Night	20% 12% 35% 30% 3	800
	21st to end	Night	19% 10% 41% 27% 3	880
February	1st to 10th	Night	18% 13% 33% 33% 3	800
	11th to 20th	Night	24% 15% 37% 22% 2	783
	21st to end	Night	17% 15% 39% 27% 2	660
March	1st to 10th	Night	18% 13% 35% 30% 5%	800
	11th to 20th	Night	19% 13% 35% 26% 6% 1	800
	21st to end	Night	19% 13% 34% 28% 6%	880
April	1st to 10th	Night	17% 15% 32% 28% 8%	800
	11th to 20th	Night	17% 13% 29% 30% 11% 1	791
	21st to end	Night	17% 7% 28% 35% 13%	620
May	1st to 10th	Night	15% 10% 27% 32% 16% 1	600
	11th to 20th	Night	19% 7% 18% 34% 20% 2	591
	21st to end	Night	20% 2 13% 29% 31% 5%	650
June	1st to 10th	Night	12% 2 13% 40% 31% 4	600
	11th to 20th	Night	13% 3 13% 31% 36% 5%	600
	21st to end	Night	8% 2 10% 35% 41% 4	600
July	1st to 10th	Night	10% 2 8% 27% 46% 7%	585
	11th to 20th	Night	9% 1 5% 28% 48% 9%	582
	21st to end	Night	9% 1 7% 29% 45% 8%	624
August	1st to 10th	Night	16% 2 8% 28% 39% 7%	567
	11th to 20th	Night	14% 3 7% 31% 38% 8%	564
	21st to end	Night	12% 2 7% 27% 42% 10%	750
September	1st to 10th	Night	13% 3 9% 29% 38% 9%	760
	11th to 20th	Night	19% 3 13% 24% 34% 6%	760
	21st to end	Night	24% 4 15% 30% 24% 2	760
October	1st to 10th	Night	19% 5% 18% 27% 25% 6%	760
	11th to 20th	Night	18% 6% 24% 32% 18% 3	760
	21st to end	Night	16% 10% 19% 38% 15% 2	836
November	1st to 10th	Night	18% 8% 21% 36% 15% 2	780
	11th to 20th	Night	16% 10% 26% 36% 11% 1	800
	21st to end	Night	15% 10% 30% 33% 11% 1	800
December	1st to 10th	Night	22% 10% 32% 29% 8%	800
	11th to 20th	Night	20% 8% 33% 31% 7%	800
	21st to end	Night	26% 12% 24% 33% 5%	880

Page generated at 2025-07-18 01:10:02. Version ac07

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