North Georgia Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Georgia Astronomical Observatory clear sky chart from 2005-11-06 to 2025-08-05.

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 5% 4 6% 8% 40%	125516
	Night	15% 6% 2 5% 4 4 4 4 6% 7% 44%	122554
Transparency	Day	41% 5% 11% 20% 18% 6%	129291
	Night	39% 4 10% 20% 20% 6%	126847
Seeing	Day	20% 11% 22% 22% 16% 8%	15864
	Night	18% 10% 21% 28% 19% 4	25877

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% 7% 3 6% 3 3 3 3 4 4 47%	4056
	11th to 20th	Day	14% 6% 1 5% 3 3 3 2 3 4 56%	4060
	21st to end	Day	22% 7% 3 7% 4 3 3 2 4 4 42%	4558
February	1st to 10th	Day	19% 8% 2 5% 4 4 4 3 5% 7% 40%	2000
	11th to 20th	Day	24% 6% 2 4 3 3 3 3 5% 5% 41%	1948
	21st to end	Day	23% 6% 1 5% 4 4 3 3 5% 6% 39%	1650
March	1st to 10th	Day	23% 7% 2 6% 4 4 4 3 5% 6% 36%	4651
	11th to 20th	Day	12% 5% 2 6% 4 3 3 3 4 7% 52%	4980
	21st to end	Day	17% 5% 2 6% 4 4 4 3 4 5% 45%	5465
April	1st to 10th	Day	13% 5% 1 6% 4 5% 5% 4 6% 7% 43%	2245
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 6% 46%	2374
	21st to end	Day	13% 4 2 5% 4 4 4 4 6% 9% 45%	2586
May	1st to 10th	Day	16% 7% 3 7% 5% 4 4 4 7% 8% 35%	5862
	11th to 20th	Day	19% 8% 3 7% 6% 5% 5% 5% 7% 8% 27%	5861
	21st to end	Day	15% 6% 2 7% 5% 4 5% 4 6% 8% 37%	6433
June	1st to 10th	Day	11% 6% 2 8% 6% 6% 6% 5% 8% 10% 31%	2600
	11th to 20th	Day	6% 5% 2 6% 6% 6% 7% 6% 10% 12% 35%	2600
	21st to end	Day	7% 5% 2 6% 6% 6% 7% 5% 8% 12% 36%	2600
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 7% 5% 9% 11% 36%	5900
	11th to 20th	Day	7% 4 2 7% 6% 7% 8% 6% 10% 13% 29%	5900
	21st to end	Day	10% 7% 3 9% 7% 8% 8% 7% 9% 9% 23%	6424
August	1st to 10th	Day	8% 6% 2 6% 5% 5% 7% 6% 9% 10% 37%	4156
	11th to 20th	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 11% 40%	3862
	21st to end	Day	8% 5% 2 6% 4 5% 6% 4 6% 8% 47%	4180
September	1st to 10th	Day	12% 7% 3 7% 5% 5% 4 5% 7% 8% 39%	2090
	11th to 20th	Day	17% 6% 2 6% 5% 4 6% 5% 6% 7% 36%	2090
	21st to end	Day	15% 5% 1 6% 4 4 5% 4 6% 6% 44%	2090
October	1st to 10th	Day	13% 6% 2 4 3 3 3 3 5% 5% 54%	2090
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 4 6% 56%	1965
	21st to end	Day	15% 4 1 4 4 3 3 3 4 5% 55%	2090
November	1st to 10th	Day	15% 4 1 4 3 3 3 3 4 5% 55%	1781
	11th to 20th	Day	16% 5% 1 4 3 4 3 3 4 6% 53%	1800
	21st to end	Day	15% 6% 2 5% 4 3 4 3 4 7% 48%	1800
December	1st to 10th	Day	22% 5% 2 3 3 3 3 3 4 5% 48%	2930
	11th to 20th	Day	19% 8% 2 6% 4 4 4 3 4 4 41%	3373
	21st to end	Day	24% 5% 2 4 3 3 4 3 5% 7% 41%	4466
January	1st to 10th	Night	17% 6% 2 4 3 3 4 3 4 6% 49%	5889
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 5% 49%	5900
	21st to end	Night	20% 6% 2 6% 3 3 3 2 4 5% 46%	6380
February	1st to 10th	Night	16% 6% 2 5% 4 4 4 4 5% 6% 45%	2400
	11th to 20th	Night	23% 6% 2 5% 4 4 3 3 5% 4 41%	2338
	21st to end	Night	21% 5% 2 7% 3 4 4 3 5% 6% 40%	1980
March	1st to 10th	Night	23% 7% 2 5% 4 4 5% 4 5% 6% 35%	5200
	11th to 20th	Night	11% 4 1 4 3 3 4 4 6% 8% 52%	4980
	21st to end	Night	16% 7% 2 6% 4 3 3 3 4 6% 44%	5467
April	1st to 10th	Night	14% 4 2 4 3 4 4 4 5% 7% 49%	2170
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 5% 7% 50%	1975
	21st to end	Night	12% 6% 3 6% 3 3 3 3 5% 6% 50%	1811
May	1st to 10th	Night	13% 7% 3 7% 5% 5% 5% 4 7% 8% 36%	4033
	11th to 20th	Night	23% 6% 2 6% 4 5% 5% 4 7% 8% 30%	4032
	21st to end	Night	14% 5% 2 5% 5% 4 5% 4 6% 9% 41%	4421
June	1st to 10th	Night	10% 6% 2 6% 7% 6% 6% 5% 8% 9% 35%	1800
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 6% 9% 12% 40%	1800
	21st to end	Night	7% 4 2 5% 5% 5% 5% 5% 9% 10% 45%	1800
July	1st to 10th	Night	9% 7% 3 7% 6% 5% 6% 5% 8% 10% 34%	4058
	11th to 20th	Night	7% 5% 2 7% 6% 5% 7% 5% 10% 11% 35%	4057
	21st to end	Night	12% 8% 4 8% 5% 5% 6% 5% 8% 9% 30%	4427
August	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 5% 8% 11% 38%	2861
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 6% 9% 45%	2963
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 9% 50%	3476
September	1st to 10th	Night	10% 6% 3 7% 5% 4 5% 4 7% 8% 42%	2070
	11th to 20th	Night	16% 6% 2 5% 5% 4 4 4 6% 7% 40%	2090
	21st to end	Night	15% 5% 1 6% 3 3 4 3 5% 7% 48%	2090
October	1st to 10th	Night	14% 5% 1 4 2 3 3 2 3 6% 56%	2090
	11th to 20th	Night	13% 4 2 5% 3 3 3 3 4 6% 55%	2213
	21st to end	Night	14% 4 1 4 3 3 3 3 4 6% 56%	2508
November	1st to 10th	Night	14% 5% 2 4 3 2 2 2 4 6% 54%	2513
	11th to 20th	Night	16% 5% 2 3 3 3 3 3 5% 5% 53%	2600
	21st to end	Night	17% 5% 2 5% 3 4 4 4 5% 7% 46%	2600
December	1st to 10th	Night	18% 6% 2 5% 3 3 3 3 4 5% 49%	4250
	11th to 20th	Night	22% 5% 2 5% 3 3 4 3 4 5% 43%	4822
	21st to end	Night	24% 5% 1 5% 3 3 4 3 5% 5% 40%	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	42% 3 3 20% 24% 8%	4057
	11th to 20th	Day	34% 3 4 17% 31% 11%	4060
	21st to end	Day	48% 2 3 17% 21% 9%	4558
February	1st to 10th	Day	44% 4 7% 20% 20% 5%	2000
	11th to 20th	Day	46% 3 5% 19% 20% 7%	1958
	21st to end	Day	47% 3 6% 15% 21% 8%	1650
March	1st to 10th	Day	50% 2 6% 13% 21% 9%	4651
	11th to 20th	Day	34% 3 5% 15% 24% 19%	4980
	21st to end	Day	43% 3 6% 23% 20% 5%	5465
April	1st to 10th	Day	39% 5% 10% 21% 20% 6%	2245
	11th to 20th	Day	38% 4 8% 19% 24% 8%	2374
	21st to end	Day	35% 5% 12% 27% 18% 4	2586
May	1st to 10th	Day	46% 4 14% 20% 14% 2	5897
	11th to 20th	Day	53% 5% 14% 18% 9% 1	5865
	21st to end	Day	43% 6% 11% 21% 17% 2	6447
June	1st to 10th	Day	44% 8% 18% 20% 8% 2	2600
	11th to 20th	Day	37% 8% 19% 23% 11% 2	2600
	21st to end	Day	38% 9% 17% 20% 13% 3	2600
July	1st to 10th	Day	40% 7% 20% 25% 7% 1	5835
	11th to 20th	Day	43% 8% 30% 15% 3 1	5831
	21st to end	Day	54% 8% 17% 17% 5%	6240
August	1st to 10th	Day	38% 6% 14% 32% 10%	4143
	11th to 20th	Day	37% 6% 20% 20% 14% 3	3901
	21st to end	Day	35% 6% 13% 26% 19% 2	4179
September	1st to 10th	Day	41% 8% 13% 17% 18% 3	2090
	11th to 20th	Day	46% 6% 10% 17% 20% 1	2090
	21st to end	Day	39% 5% 11% 17% 22% 6%	2090
October	1st to 10th	Day	27% 3 6% 14% 40% 11%	3480
	11th to 20th	Day	20% 2 5% 17% 28% 28%	3244
	21st to end	Day	31% 2 4 21% 28% 14%	3428
November	1st to 10th	Day	33% 3 6% 16% 31% 10%	1781
	11th to 20th	Day	34% 3 6% 20% 27% 11%	1800
	21st to end	Day	37% 4 7% 17% 28% 7%	1800
December	1st to 10th	Day	41% 2 4 16% 27% 9%	2930
	11th to 20th	Day	49% 2 5% 16% 21% 8%	3370
	21st to end	Day	42% 4 7% 26% 18% 3	4466
January	1st to 10th	Night	37% 3 5% 17% 30% 7%	5889
	11th to 20th	Night	38% 3 5% 18% 27% 10%	5900
	21st to end	Night	43% 2 3 16% 27% 9%	6380
February	1st to 10th	Night	41% 3 8% 20% 21% 7%	2400
	11th to 20th	Night	47% 3 5% 18% 21% 7%	2339
	21st to end	Night	45% 4 6% 16% 20% 8%	1980
March	1st to 10th	Night	50% 3 5% 14% 21% 7%	5200
	11th to 20th	Night	30% 3 7% 17% 27% 16%	4980
	21st to end	Night	42% 2 6% 23% 19% 7%	5467
April	1st to 10th	Night	35% 4 11% 20% 24% 6%	2170
	11th to 20th	Night	35% 3 7% 24% 22% 10%	1975
	21st to end	Night	34% 5% 12% 27% 20% 3	1811
May	1st to 10th	Night	45% 5% 17% 21% 12% 1	4060
	11th to 20th	Night	51% 5% 16% 18% 8%	4033
	21st to end	Night	38% 6% 14% 26% 14% 2	4429
June	1st to 10th	Night	41% 10% 17% 20% 11% 2	1800
	11th to 20th	Night	32% 9% 22% 23% 13% 1	1800
	21st to end	Night	33% 9% 19% 23% 13% 4	1800
July	1st to 10th	Night	45% 7% 16% 24% 7%	4015
	11th to 20th	Night	41% 10% 27% 18% 4 1	4006
	21st to end	Night	49% 9% 18% 18% 5% 1	4297
August	1st to 10th	Night	39% 6% 20% 28% 6%	2850
	11th to 20th	Night	37% 6% 17% 23% 16% 1	2990
	21st to end	Night	32% 5% 14% 25% 22% 2	3476
September	1st to 10th	Night	38% 8% 15% 19% 16% 4	2070
	11th to 20th	Night	41% 7% 12% 19% 19% 2	2090
	21st to end	Night	36% 6% 12% 20% 19% 8%	2090
October	1st to 10th	Night	28% 2 9% 15% 35% 11%	3480
	11th to 20th	Night	19% 3 5% 18% 32% 23%	3673
	21st to end	Night	27% 2 4 23% 28% 16%	4120
November	1st to 10th	Night	32% 4 7% 20% 26% 12%	2513
	11th to 20th	Night	34% 3 5% 19% 27% 12%	2600
	21st to end	Night	38% 4 5% 21% 24% 8%	2600
December	1st to 10th	Night	40% 2 4 18% 29% 7%	4250
	11th to 20th	Night	44% 3 6% 18% 22% 7%	4824
	21st to end	Night	45% 3 6% 26% 17% 2	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	30% 27% 34% 7% 2	300
	11th to 20th	Day	30% 23% 29% 13% 4 1	300
	21st to end	Day	28% 26% 33% 9% 3	330
February	1st to 10th	Day	27% 22% 33% 17% 2	300
	11th to 20th	Day	45% 19% 28% 8%	300
	21st to end	Day	37% 20% 32% 9% 2	249
March	1st to 10th	Day	29% 17% 30% 17% 6%	367
	11th to 20th	Day	28% 19% 28% 19% 5% 1	500
	21st to end	Day	25% 17% 35% 17% 5% 1	550
April	1st to 10th	Day	25% 14% 29% 22% 9% 1	500
	11th to 20th	Day	15% 18% 35% 20% 11% 1	492
	21st to end	Day	21% 12% 25% 24% 14% 4	500
May	1st to 10th	Day	20% 12% 29% 22% 11% 6%	503
	11th to 20th	Day	19% 8% 21% 27% 16% 9%	527
	21st to end	Day	19% 8% 19% 27% 16% 12%	573
June	1st to 10th	Day	15% 6% 20% 28% 20% 11%	530
	11th to 20th	Day	10% 3 18% 26% 25% 19%	530
	21st to end	Day	10% 5% 18% 29% 23% 14%	530
July	1st to 10th	Day	11% 3 9% 26% 30% 20%	525
	11th to 20th	Day	10% 2 8% 23% 35% 23%	524
	21st to end	Day	8% 2 8% 26% 33% 23%	576
August	1st to 10th	Day	18% 5% 13% 22% 24% 19%	502
	11th to 20th	Day	14% 4 11% 26% 29% 16%	479
	21st to end	Day	17% 2 9% 24% 31% 17%	539
September	1st to 10th	Day	11% 4 13% 32% 28% 12%	490
	11th to 20th	Day	20% 5% 11% 25% 30% 9%	490
	21st to end	Day	17% 4 20% 24% 27% 8%	490
October	1st to 10th	Day	18% 4 22% 29% 19% 8%	490
	11th to 20th	Day	14% 11% 24% 30% 17% 4	490
	21st to end	Day	19% 9% 26% 27% 16% 3	539
November	1st to 10th	Day	24% 10% 27% 25% 12% 3	319
	11th to 20th	Day	21% 19% 36% 20% 3 1	300
	21st to end	Day	17% 18% 38% 17% 8% 1	300
December	1st to 10th	Day	34% 20% 27% 16% 3 1	300
	11th to 20th	Day	30% 16% 32% 18% 4	300
	21st to end	Day	35% 16% 28% 15% 4 2	330
January	1st to 10th	Night	27% 21% 26% 21% 5%	800
	11th to 20th	Night	24% 18% 29% 23% 7%	800
	21st to end	Night	23% 17% 35% 23% 2	880
February	1st to 10th	Night	20% 14% 32% 28% 7%	800
	11th to 20th	Night	28% 19% 29% 22% 2	783
	21st to end	Night	24% 17% 36% 21% 3	660
March	1st to 10th	Night	23% 15% 32% 25% 5%	800
	11th to 20th	Night	19% 15% 34% 24% 7% 1	800
	21st to end	Night	22% 14% 27% 29% 8%	880
April	1st to 10th	Night	18% 16% 28% 27% 10% 1	770
	11th to 20th	Night	16% 12% 26% 30% 15% 1	593
	21st to end	Night	15% 7% 25% 32% 20% 1	600
May	1st to 10th	Night	14% 11% 19% 34% 21% 2	600
	11th to 20th	Night	17% 6% 16% 34% 23% 4	591
	21st to end	Night	16% 2 13% 31% 30% 6%	650
June	1st to 10th	Night	11% 3 12% 38% 30% 6%	600
	11th to 20th	Night	9% 1 14% 29% 34% 13%	600
	21st to end	Night	8% 2 8% 37% 37% 9%	600
July	1st to 10th	Night	11% 2 5% 26% 45% 10%	585
	11th to 20th	Night	10% 4 5% 22% 46% 14%	582
	21st to end	Night	9% 2 8% 23% 46% 12%	657
August	1st to 10th	Night	15% 2 6% 24% 39% 15%	579
	11th to 20th	Night	15% 1 9% 26% 40% 9%	564
	21st to end	Night	18% 2 6% 26% 39% 9%	627
September	1st to 10th	Night	11% 4 11% 28% 36% 9%	740
	11th to 20th	Night	18% 3 13% 29% 33% 4	760
	21st to end	Night	18% 4 13% 35% 29% 3	760
October	1st to 10th	Night	17% 5% 18% 32% 22% 6%	760
	11th to 20th	Night	14% 9% 21% 34% 20% 2	760
	21st to end	Night	17% 10% 19% 34% 18% 2	836
November	1st to 10th	Night	17% 8% 24% 30% 18% 2	780
	11th to 20th	Night	19% 11% 27% 30% 12% 1	800
	21st to end	Night	21% 14% 26% 27% 12% 1	800
December	1st to 10th	Night	25% 16% 25% 26% 7% 1	800
	11th to 20th	Night	22% 13% 27% 29% 8% 1	800
	21st to end	Night	31% 12% 25% 27% 6%	880

Page generated at 2025-08-02 01:32:24. Version ac07

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