Atlanta State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atlanta State Park clear sky chart from 2005-11-06 to 2025-01-22.

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	14% 6% 2 6% 4 4 4 3 5% 7% 46%	105379
	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	104089
Transparency	Day	38% 4 9% 23% 20% 6%	109027
	Night	34% 4 9% 22% 23% 9%	108581
Seeing	Day	15% 9% 23% 26% 21% 5%	15443
	Night	15% 9% 25% 31% 18% 2	25365

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	18% 11% 2 5% 3 3 3 2 3 4 47%	2937
	11th to 20th	Day	17% 7% 2 4 2 2 2 2 4 5% 52%	2940
	21st to end	Day	23% 8% 2 6% 3 2 2 2 3 4 45%	3144
February	1st to 10th	Day	22% 9% 3 6% 4 4 3 3 3 4 40%	1710
	11th to 20th	Day	19% 9% 3 7% 4 3 3 2 4 5% 41%	1781
	21st to end	Day	24% 8% 2 6% 3 3 3 2 4 4 41%	1727
March	1st to 10th	Day	18% 11% 3 7% 4 3 3 3 4 6% 39%	3436
	11th to 20th	Day	18% 8% 2 6% 5% 4 4 4 6% 7% 38%	3480
	21st to end	Day	17% 8% 3 7% 4 4 4 3 4 6% 41%	3814
April	1st to 10th	Day	13% 6% 2 7% 4 4 3 4 5% 6% 45%	2161
	11th to 20th	Day	17% 7% 2 6% 3 4 4 3 5% 6% 45%	2254
	21st to end	Day	13% 5% 2 6% 5% 4 5% 3 5% 6% 45%	2280
May	1st to 10th	Day	21% 7% 2 6% 5% 4 4 4 4 7% 36%	3891
	11th to 20th	Day	15% 5% 2 6% 5% 4 4 3 5% 8% 44%	4082
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 5% 7% 35%	4477
June	1st to 10th	Day	7% 5% 3 6% 5% 5% 5% 4 7% 10% 44%	2470
	11th to 20th	Day	6% 4 2 5% 6% 5% 6% 5% 7% 9% 45%	2470
	21st to end	Day	5% 3 2 5% 4 5% 5% 4 7% 9% 50%	2470
July	1st to 10th	Day	9% 5% 2 7% 6% 6% 7% 5% 7% 10% 38%	4120
	11th to 20th	Day	6% 3 1 4 4 4 5% 4 6% 9% 55%	4120
	21st to end	Day	12% 8% 3 8% 5% 5% 5% 4 7% 8% 35%	4465
August	1st to 10th	Day	2 2 1 3 3 4 4 4 5% 7% 67%	4104
	11th to 20th	Day	6% 2 1 5% 4 4 5% 5% 8% 10% 51%	3884
	21st to end	Day	5% 4 2 6% 5% 4 6% 6% 8% 9% 44%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 5% 7% 49%	2266
	11th to 20th	Day	12% 4 2 5% 5% 4 5% 4 5% 7% 45%	2090
	21st to end	Day	8% 3 1 4 3 4 5% 3 6% 7% 56%	2079
October	1st to 10th	Day	7% 3 2 3 2 3 4 3 5% 6% 62%	1900
	11th to 20th	Day	14% 5% 1 4 3 2 3 3 3 6% 55%	1900
	21st to end	Day	17% 4 2 5% 3 3 3 2 3 4 54%	2090
November	1st to 10th	Day	14% 6% 2 6% 3 3 2 2 6% 6% 50%	1958
	11th to 20th	Day	10% 6% 2 5% 3 3 3 3 4 5% 55%	2000
	21st to end	Day	18% 6% 2 5% 4 2 4 2 4 5% 48%	1880
December	1st to 10th	Day	21% 6% 2 4 3 2 2 2 2 5% 51%	2940
	11th to 20th	Day	18% 9% 3 7% 3 3 4 3 3 4 43%	3391
	21st to end	Day	17% 9% 3 6% 4 3 3 2 4 5% 44%	4488
January	1st to 10th	Night	17% 8% 3 6% 3 2 3 3 3 5% 49%	4238
	11th to 20th	Night	18% 5% 1 4 3 2 2 2 3 4 56%	4250
	21st to end	Night	24% 10% 2 4 3 2 2 2 3 3 45%	4546
February	1st to 10th	Night	18% 8% 3 5% 3 3 3 2 4 5% 47%	2470
	11th to 20th	Night	20% 8% 3 5% 4 3 3 3 3 5% 44%	2299
	21st to end	Night	20% 6% 1 6% 3 3 2 2 3 5% 48%	1727
March	1st to 10th	Night	21% 9% 2 6% 3 3 4 3 4 6% 40%	3419
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 6% 6% 42%	3480
	21st to end	Night	14% 7% 2 6% 4 3 4 3 5% 6% 45%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 6% 51%	2019
	11th to 20th	Night	12% 5% 2 5% 4 4 3 3 5% 7% 48%	1875
	21st to end	Night	11% 5% 2 5% 3 4 3 3 4 8% 51%	1900
May	1st to 10th	Night	17% 6% 3 7% 5% 4 4 4 5% 7% 38%	2991
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 4 8% 46%	2823
	21st to end	Night	14% 5% 2 6% 5% 4 4 4 6% 8% 43%	3090
June	1st to 10th	Night	4 4 2 4 4 3 5% 4 7% 10% 55%	1710
	11th to 20th	Night	4 3 1 4 3 4 4 3 6% 8% 60%	1710
	21st to end	Night	4 3 1 3 3 3 4 3 6% 9% 59%	1710
July	1st to 10th	Night	8% 4 1 4 4 3 4 5% 7% 12% 48%	2850
	11th to 20th	Night	4 2 2 4 3 3 3 3 7% 12% 57%	2850
	21st to end	Night	10% 6% 2 7% 5% 4 5% 4 6% 8% 43%	3098
August	1st to 10th	Night	2 1 2 2 2 2 2 5% 8% 73%	2836
	11th to 20th	Night	4 2 1 3 3 3 4 4 8% 12% 58%	2947
	21st to end	Night	4 3 2 4 4 4 5% 5% 7% 9% 52%	3476
September	1st to 10th	Night	8% 3 1 4 3 4 4 4 5% 7% 56%	1909
	11th to 20th	Night	10% 4 2 4 4 4 5% 3 5% 7% 52%	2090
	21st to end	Night	7% 2 2 3 2 3 4 3 5% 7% 62%	2090
October	1st to 10th	Night	6% 3 1 4 3 3 2 2 4 6% 65%	2270
	11th to 20th	Night	12% 4 1 3 3 2 3 3 4 5% 61%	2280
	21st to end	Night	16% 5% 2 4 3 2 2 2 3 4 58%	2508
November	1st to 10th	Night	13% 5% 2 4 3 3 3 2 4 6% 56%	2340
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 6% 57%	2400
	21st to end	Night	15% 6% 2 5% 4 3 3 2 3 5% 52%	2515
December	1st to 10th	Night	17% 7% 2 5% 3 3 3 2 4 4 50%	4250
	11th to 20th	Night	15% 9% 2 7% 4 4 4 2 4 4 45%	4816
	21st to end	Night	15% 10% 3 6% 3 3 3 3 3 4 47%	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	45% 1 4 22% 23% 4	2938
	11th to 20th	Day	37% 2 7% 27% 23% 4	2940
	21st to end	Day	47% 1 4 17% 22% 10%	3144
February	1st to 10th	Day	50% 3 6% 16% 18% 7%	1710
	11th to 20th	Day	48% 3 5% 19% 18% 7%	1790
	21st to end	Day	48% 3 5% 15% 22% 8%	1727
March	1st to 10th	Day	49% 3 6% 14% 22% 7%	3436
	11th to 20th	Day	47% 3 7% 22% 17% 4	3480
	21st to end	Day	46% 3 8% 20% 21% 2	3814
April	1st to 10th	Day	41% 4 8% 22% 18% 8%	2161
	11th to 20th	Day	43% 4 7% 20% 19% 8%	2254
	21st to end	Day	39% 5% 9% 22% 21% 4	2280
May	1st to 10th	Day	50% 3 8% 25% 11% 3	3926
	11th to 20th	Day	40% 4 9% 24% 21% 1	4086
	21st to end	Day	49% 5% 12% 20% 10% 4	4489
June	1st to 10th	Day	36% 7% 13% 27% 16% 1	2470
	11th to 20th	Day	33% 7% 14% 24% 19% 3	2470
	21st to end	Day	29% 7% 13% 29% 20% 2	2470
July	1st to 10th	Day	40% 7% 20% 24% 9% 1	4056
	11th to 20th	Day	26% 5% 15% 35% 18% 1	4051
	21st to end	Day	46% 5% 13% 25% 10%	4325
August	1st to 10th	Day	16% 5% 14% 31% 26% 7%	4090
	11th to 20th	Day	28% 5% 18% 37% 11% 1	3923
	21st to end	Day	33% 7% 15% 28% 16% 1	4179
September	1st to 10th	Day	36% 4 11% 20% 20% 10%	2266
	11th to 20th	Day	38% 6% 10% 21% 18% 7%	2090
	21st to end	Day	28% 5% 9% 22% 25% 11%	2079
October	1st to 10th	Day	14% 3 6% 13% 26% 38%	3160
	11th to 20th	Day	21% 2 3 17% 33% 24%	3140
	21st to end	Day	29% 2 4 24% 32% 8%	3428
November	1st to 10th	Day	36% 3 8% 20% 24% 9%	1958
	11th to 20th	Day	33% 3 7% 19% 27% 11%	2000
	21st to end	Day	41% 3 5% 17% 26% 8%	1880
December	1st to 10th	Day	41% 2 5% 26% 23% 5%	2940
	11th to 20th	Day	47% 2 4 17% 22% 7%	3389
	21st to end	Day	45% 3 4 20% 24% 4	4488
January	1st to 10th	Night	40% 2 4 17% 30% 6%	4238
	11th to 20th	Night	36% 2 7% 20% 28% 8%	4250
	21st to end	Night	47% 2 6% 16% 21% 9%	4546
February	1st to 10th	Night	41% 3 7% 20% 19% 10%	2470
	11th to 20th	Night	45% 3 5% 18% 21% 9%	2300
	21st to end	Night	42% 2 7% 16% 21% 12%	1727
March	1st to 10th	Night	49% 2 5% 15% 17% 11%	3419
	11th to 20th	Night	44% 3 8% 18% 19% 8%	3480
	21st to end	Night	40% 4 8% 20% 25% 3	3817
April	1st to 10th	Night	34% 4 10% 23% 19% 11%	2019
	11th to 20th	Night	37% 4 9% 20% 19% 11%	1875
	21st to end	Night	33% 4 9% 26% 24% 5%	1900
May	1st to 10th	Night	46% 5% 8% 24% 11% 6%	3021
	11th to 20th	Night	38% 4 11% 24% 20% 2	2824
	21st to end	Night	39% 6% 14% 23% 15% 3	3099
June	1st to 10th	Night	24% 6% 15% 32% 20% 3	1710
	11th to 20th	Night	23% 5% 14% 29% 23% 6%	1710
	21st to end	Night	21% 6% 15% 28% 26% 4	1710
July	1st to 10th	Night	28% 6% 21% 34% 10% 1	2805
	11th to 20th	Night	20% 4 15% 39% 19% 2	2796
	21st to end	Night	39% 5% 13% 30% 12% 1	2999
August	1st to 10th	Night	11% 4 15% 29% 36% 6%	2826
	11th to 20th	Night	19% 5% 19% 36% 18% 3	2974
	21st to end	Night	26% 6% 15% 25% 25% 2	3476
September	1st to 10th	Night	28% 6% 13% 21% 22% 11%	1909
	11th to 20th	Night	31% 5% 10% 23% 22% 9%	2090
	21st to end	Night	22% 5% 9% 23% 29% 13%	2090
October	1st to 10th	Night	14% 3 5% 15% 22% 42%	3790
	11th to 20th	Night	18% 2 4 15% 34% 28%	3779
	21st to end	Night	25% 2 4 21% 32% 17%	4120
November	1st to 10th	Night	33% 3 7% 18% 27% 12%	2340
	11th to 20th	Night	30% 3 8% 17% 28% 14%	2400
	21st to end	Night	37% 2 6% 20% 26% 9%	2515
December	1st to 10th	Night	39% 3 6% 21% 26% 5%	4250
	11th to 20th	Night	45% 3 7% 15% 21% 10%	4817
	21st to end	Night	43% 2 6% 19% 25% 5%	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	27% 17% 37% 15% 4	300
	11th to 20th	Day	26% 21% 36% 14% 2	300
	21st to end	Day	26% 24% 33% 12% 4	300
February	1st to 10th	Day	31% 17% 39% 9% 4 1	270
	11th to 20th	Day	33% 20% 36% 9% 1	270
	21st to end	Day	40% 24% 28% 6% 1	225
March	1st to 10th	Day	26% 17% 39% 15% 4	270
	11th to 20th	Day	26% 29% 34% 8% 3	270
	21st to end	Day	22% 25% 37% 12% 4	297
April	1st to 10th	Day	20% 18% 40% 16% 6%	341
	11th to 20th	Day	26% 16% 30% 19% 8% 1	452
	21st to end	Day	18% 16% 33% 23% 8% 2	460
May	1st to 10th	Day	19% 11% 37% 25% 8% 1	537
	11th to 20th	Day	14% 7% 31% 31% 14% 3	675
	21st to end	Day	12% 8% 26% 34% 16% 4	734
June	1st to 10th	Day	8% 4 15% 38% 29% 7%	680
	11th to 20th	Day	5% 3 17% 41% 29% 5%	680
	21st to end	Day	6% 2 16% 34% 32% 10%	680
July	1st to 10th	Day	8% 2 13% 31% 36% 10%	671
	11th to 20th	Day	4 2 8% 36% 39% 10%	668
	21st to end	Day	8% 1 8% 33% 38% 11%	739
August	1st to 10th	Day	4 1 7% 30% 47% 11%	676
	11th to 20th	Day	10% 1 6% 34% 38% 11%	573
	21st to end	Day	9% 2 5% 25% 42% 18%	539
September	1st to 10th	Day	9% 1 9% 30% 39% 11%	476
	11th to 20th	Day	6% 4 15% 28% 35% 13%	300
	21st to end	Day	9% 4 17% 36% 27% 7%	300
October	1st to 10th	Day	6% 2 26% 43% 19% 4	300
	11th to 20th	Day	13% 7% 34% 31% 13% 3	300
	21st to end	Day	25% 12% 31% 19% 11% 2	330
November	1st to 10th	Day	20% 9% 32% 27% 11% 1	300
	11th to 20th	Day	13% 16% 39% 24% 8%	300
	21st to end	Day	21% 20% 31% 20% 6% 1	300
December	1st to 10th	Day	21% 16% 39% 16% 6% 2	300
	11th to 20th	Day	26% 20% 34% 15% 5% 1	300
	21st to end	Day	24% 21% 37% 14% 3 1	330
January	1st to 10th	Night	23% 14% 32% 26% 5%	1000
	11th to 20th	Night	23% 16% 32% 24% 5%	1000
	21st to end	Night	23% 15% 33% 26% 3	1051
February	1st to 10th	Night	23% 15% 36% 22% 5%	950
	11th to 20th	Night	26% 15% 36% 20% 3	825
	21st to end	Night	25% 19% 34% 21% 2	471
March	1st to 10th	Night	24% 11% 35% 25% 5%	570
	11th to 20th	Night	20% 15% 31% 29% 5% 1	570
	21st to end	Night	18% 12% 39% 25% 6%	627
April	1st to 10th	Night	14% 14% 38% 27% 7%	570
	11th to 20th	Night	14% 15% 35% 25% 10%	563
	21st to end	Night	13% 12% 36% 31% 8% 1	570
May	1st to 10th	Night	11% 9% 36% 33% 11% 1	570
	11th to 20th	Night	12% 5% 33% 32% 17% 2	561
	21st to end	Night	10% 5% 25% 36% 21% 3	617
June	1st to 10th	Night	5% 2 12% 40% 38% 4	570
	11th to 20th	Night	5% 2 16% 42% 32% 3	570
	21st to end	Night	4 2 12% 38% 36% 8%	570
July	1st to 10th	Night	6% 1 7% 36% 43% 7%	555
	11th to 20th	Night	4 7% 35% 47% 6%	552
	21st to end	Night	4 2 7% 34% 44% 9%	624
August	1st to 10th	Night	4 1 6% 37% 45% 7%	567
	11th to 20th	Night	7% 1 7% 42% 37% 7%	564
	21st to end	Night	7% 1 5% 37% 42% 8%	627
September	1st to 10th	Night	9% 1 8% 32% 42% 7%	570
	11th to 20th	Night	10% 2 11% 35% 38% 3	570
	21st to end	Night	9% 2 11% 39% 34% 4	570
October	1st to 10th	Night	7% 3 15% 42% 28% 5%	750
	11th to 20th	Night	13% 7% 24% 36% 19% 1	760
	21st to end	Night	17% 8% 28% 28% 18% 2	836
November	1st to 10th	Night	14% 7% 27% 36% 14% 1	780
	11th to 20th	Night	12% 11% 30% 36% 10% 1	800
	21st to end	Night	17% 15% 31% 26% 11% 1	915
December	1st to 10th	Night	21% 11% 32% 31% 6%	1000
	11th to 20th	Night	21% 12% 31% 30% 6%	1000
	21st to end	Night	23% 15% 31% 26% 5%	1100

Page generated at 2025-01-19 02:06:49. Version ac07

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