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 2024-11-04.

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% 5% 5% 5% 4 6% 8% 40%	100996
	Night	15% 6% 2 6% 4 4 4 4 6% 7% 43%	97985
Transparency	Day	41% 5% 11% 19% 18% 6%	104815
	Night	39% 5% 10% 20% 20% 6%	102304
Seeing	Day	19% 11% 22% 23% 17% 8%	14891
	Night	18% 10% 21% 28% 19% 4	24902

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	20% 7% 4 7% 4 4 4 4 6% 5% 38%	2836
	11th to 20th	Day	17% 5% 2 5% 4 4 3 3 4 5% 49%	2840
	21st to end	Day	27% 6% 2 5% 3 3 3 2 4 3 42%	3188
February	1st to 10th	Day	20% 8% 2 5% 4 4 4 3 5% 7% 39%	1900
	11th to 20th	Day	24% 7% 2 4 3 3 3 3 5% 5% 41%	1848
	21st to end	Day	24% 6% 1 6% 4 4 3 3 5% 5% 38%	1570
March	1st to 10th	Day	27% 7% 2 5% 3 3 3 3 4 6% 36%	3235
	11th to 20th	Day	14% 5% 2 5% 4 3 4 3 4 6% 50%	3480
	21st to end	Day	18% 6% 2 7% 5% 4 4 3 5% 5% 41%	3815
April	1st to 10th	Day	13% 5% 1 6% 4 5% 5% 4 6% 7% 43%	2133
	11th to 20th	Day	13% 6% 2 7% 4 4 4 4 5% 6% 45%	2254
	21st to end	Day	12% 4 2 5% 4 4 5% 4 6% 8% 47%	2456
May	1st to 10th	Day	13% 7% 2 7% 5% 4 4 4 6% 8% 39%	4082
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 4 7% 10% 39%	4476
June	1st to 10th	Day	11% 6% 2 8% 6% 6% 6% 5% 8% 10% 31%	2470
	11th to 20th	Day	6% 5% 2 6% 6% 6% 7% 6% 9% 12% 36%	2470
	21st to end	Day	7% 5% 2 6% 6% 6% 7% 5% 8% 12% 35%	2470
July	1st to 10th	Day	8% 6% 3 8% 7% 7% 7% 6% 9% 12% 29%	4120
	11th to 20th	Day	9% 5% 2 8% 7% 7% 8% 6% 8% 10% 29%	4120
	21st to end	Day	11% 8% 3 10% 8% 8% 9% 7% 9% 8% 18%	4466
August	1st to 10th	Day	7% 7% 2 6% 5% 5% 7% 6% 9% 10% 38%	4104
	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	14% 5% 1 4 3 3 3 3 4 5% 56%	1718
	11th to 20th	Day	15% 5% 1 4 3 4 3 3 4 6% 53%	1710
	21st to end	Day	16% 6% 2 5% 4 3 4 3 4 7% 46%	1710
December	1st to 10th	Day	25% 6% 3 4 4 3 4 3 5% 6% 38%	1710
	11th to 20th	Day	18% 7% 2 5% 3 4 4 3 5% 5% 46%	2153
	21st to end	Day	23% 6% 2 5% 3 3 4 4 5% 7% 37%	3124
January	1st to 10th	Night	19% 7% 2 5% 4 3 4 3 5% 6% 41%	4109
	11th to 20th	Night	15% 8% 2 6% 4 3 4 4 5% 5% 44%	4120
	21st to end	Night	27% 7% 3 6% 3 3 3 2 3 4 39%	4464
February	1st to 10th	Night	16% 6% 2 5% 4 4 4 4 5% 6% 44%	2280
	11th to 20th	Night	22% 6% 2 6% 4 4 3 3 5% 4 41%	2218
	21st to end	Night	22% 5% 2 7% 4 4 5% 3 5% 5% 38%	1884
March	1st to 10th	Night	27% 7% 2 5% 4 4 4 3 4 5% 35%	3616
	11th to 20th	Night	11% 4 2 5% 3 3 4 4 7% 8% 50%	3480
	21st to end	Night	18% 7% 2 6% 5% 3 3 3 5% 6% 42%	3817
April	1st to 10th	Night	14% 4 1 4 3 4 4 4 5% 7% 49%	2062
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 5% 7% 48%	1875
	21st to end	Night	11% 5% 2 5% 3 4 3 3 5% 7% 52%	1721
May	1st to 10th	Night	13% 7% 3 6% 5% 4 5% 4 6% 8% 39%	2813
	11th to 20th	Night	18% 5% 2 6% 4 4 4 4 6% 8% 38%	2812
	21st to end	Night	8% 5% 2 5% 5% 4 5% 4 7% 11% 45%	3079
June	1st to 10th	Night	10% 6% 2 6% 7% 6% 6% 5% 8% 9% 35%	1710
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 6% 10% 12% 41%	1710
	21st to end	Night	7% 4 2 5% 5% 5% 5% 5% 9% 9% 44%	1710
July	1st to 10th	Night	12% 8% 3 8% 7% 5% 6% 5% 7% 9% 30%	2840
	11th to 20th	Night	7% 5% 2 6% 6% 5% 7% 6% 10% 11% 35%	2840
	21st to end	Night	13% 8% 4 9% 5% 6% 6% 6% 9% 10% 23%	3087
August	1st to 10th	Night	8% 6% 3 7% 5% 5% 5% 5% 8% 11% 38%	2825
	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 3 3 2 2 3 4 6% 56%	2429
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 5% 5% 53%	2470
	21st to end	Night	17% 5% 2 5% 4 4 4 4 5% 7% 44%	2470
December	1st to 10th	Night	21% 7% 2 6% 4 3 4 3 5% 6% 39%	2470
	11th to 20th	Night	18% 5% 2 5% 3 3 3 3 5% 5% 48%	3042
	21st to end	Night	23% 6% 2 6% 4 4 5% 4 6% 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	47% 4 5% 17% 21% 7%	2837
	11th to 20th	Day	38% 4 6% 19% 25% 8%	2840
	21st to end	Day	47% 3 4 17% 22% 7%	3188
February	1st to 10th	Day	45% 4 7% 18% 21% 5%	1900
	11th to 20th	Day	45% 3 5% 19% 20% 7%	1858
	21st to end	Day	48% 3 6% 15% 19% 8%	1570
March	1st to 10th	Day	50% 3 8% 14% 15% 10%	3235
	11th to 20th	Day	36% 4 6% 18% 24% 11%	3480
	21st to end	Day	45% 4 7% 19% 21% 4	3815
April	1st to 10th	Day	38% 5% 10% 21% 20% 6%	2133
	11th to 20th	Day	39% 4 8% 17% 24% 8%	2254
	21st to end	Day	33% 6% 11% 27% 19% 4	2456
May	1st to 10th	Day	42% 5% 13% 20% 17% 3	4120
	11th to 20th	Day	48% 6% 11% 22% 12% 1	4085
	21st to end	Day	37% 8% 14% 22% 18% 1	4489
June	1st to 10th	Day	44% 8% 18% 20% 8% 2	2470
	11th to 20th	Day	36% 9% 19% 24% 11% 2	2470
	21st to end	Day	39% 9% 17% 19% 13% 3	2470
July	1st to 10th	Day	44% 9% 22% 19% 5% 1	4055
	11th to 20th	Day	46% 8% 23% 16% 4 2	4051
	21st to end	Day	59% 11% 15% 11% 5%	4324
August	1st to 10th	Day	37% 6% 14% 32% 10%	4091
	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	31% 3 7% 16% 32% 11%	1718
	11th to 20th	Day	34% 3 6% 20% 26% 11%	1710
	21st to end	Day	38% 4 7% 17% 27% 7%	1710
December	1st to 10th	Day	48% 4 6% 18% 18% 6%	1710
	11th to 20th	Day	42% 3 6% 16% 25% 9%	2150
	21st to end	Day	44% 5% 7% 19% 22% 4	3124
January	1st to 10th	Night	42% 4 5% 15% 27% 6%	4109
	11th to 20th	Night	40% 5% 7% 19% 19% 10%	4120
	21st to end	Night	49% 3 4 14% 23% 7%	4464
February	1st to 10th	Night	41% 3 8% 19% 21% 7%	2280
	11th to 20th	Night	47% 3 4 18% 21% 7%	2219
	21st to end	Night	47% 5% 6% 15% 19% 8%	1884
March	1st to 10th	Night	51% 4 7% 15% 16% 7%	3616
	11th to 20th	Night	31% 5% 9% 19% 25% 11%	3480
	21st to end	Night	44% 3 7% 21% 18% 7%	3817
April	1st to 10th	Night	34% 4 11% 20% 25% 6%	2062
	11th to 20th	Night	36% 3 7% 23% 21% 10%	1875
	21st to end	Night	32% 5% 12% 28% 20% 3	1721
May	1st to 10th	Night	41% 6% 15% 22% 15% 1	2840
	11th to 20th	Night	43% 7% 13% 24% 12%	2813
	21st to end	Night	31% 7% 16% 28% 16% 2	3087
June	1st to 10th	Night	41% 10% 17% 20% 11% 2	1710
	11th to 20th	Night	30% 9% 23% 24% 13% 1	1710
	21st to end	Night	34% 9% 18% 22% 14% 4	1710
July	1st to 10th	Night	49% 8% 18% 19% 6%	2795
	11th to 20th	Night	39% 10% 24% 21% 5% 2	2786
	21st to end	Night	53% 12% 16% 13% 4 1	2988
August	1st to 10th	Night	38% 6% 20% 29% 7%	2814
	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	31% 4 7% 19% 26% 12%	2429
	11th to 20th	Night	33% 3 6% 20% 26% 13%	2470
	21st to end	Night	39% 4 5% 20% 23% 7%	2470
December	1st to 10th	Night	46% 4 7% 19% 18% 6%	2470
	11th to 20th	Night	37% 4 7% 18% 27% 7%	3044
	21st to end	Night	47% 5% 7% 19% 18% 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	29% 26% 35% 8% 2	270
	11th to 20th	Day	31% 21% 30% 14% 4	270
	21st to end	Day	28% 27% 33% 9% 3	297
February	1st to 10th	Day	29% 22% 31% 16% 2	270
	11th to 20th	Day	43% 20% 28% 9%	270
	21st to end	Day	40% 20% 33% 6% 1	225
March	1st to 10th	Day	27% 17% 31% 18% 7%	333
	11th to 20th	Day	28% 19% 29% 19% 5% 1	460
	21st to end	Day	24% 17% 34% 18% 6% 1	506
April	1st to 10th	Day	25% 14% 28% 22% 10% 1	460
	11th to 20th	Day	15% 19% 34% 20% 11% 2	452
	21st to end	Day	20% 13% 26% 23% 14% 4	460
May	1st to 10th	Day	19% 12% 29% 22% 12% 7%	463
	11th to 20th	Day	18% 8% 20% 28% 16% 10%	487
	21st to end	Day	16% 7% 19% 29% 17% 12%	529
June	1st to 10th	Day	15% 6% 19% 29% 20% 12%	490
	11th to 20th	Day	9% 3 18% 26% 24% 20%	490
	21st to end	Day	10% 6% 20% 29% 22% 14%	490
July	1st to 10th	Day	12% 4 9% 25% 30% 21%	485
	11th to 20th	Day	11% 2 8% 23% 34% 22%	484
	21st to end	Day	8% 3 8% 26% 33% 23%	532
August	1st to 10th	Day	16% 5% 14% 22% 24% 19%	486
	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	23% 10% 26% 26% 13% 3	298
	11th to 20th	Day	19% 20% 36% 21% 3 1	270
	21st to end	Day	16% 18% 39% 18% 9% 1	270
December	1st to 10th	Day	35% 18% 26% 17% 3 1	270
	11th to 20th	Day	28% 17% 33% 18% 4	270
	21st to end	Day	36% 17% 29% 13% 4 1	297
January	1st to 10th	Night	28% 20% 25% 22% 5%	760
	11th to 20th	Night	24% 18% 28% 24% 7%	760
	21st to end	Night	23% 18% 33% 23% 2	836
February	1st to 10th	Night	20% 15% 32% 27% 7%	760
	11th to 20th	Night	28% 18% 29% 22% 2	743
	21st to end	Night	25% 17% 35% 20% 3	628
March	1st to 10th	Night	23% 15% 32% 26% 5%	760
	11th to 20th	Night	19% 15% 33% 24% 8% 1	760
	21st to end	Night	22% 14% 27% 28% 9%	836
April	1st to 10th	Night	18% 16% 28% 27% 10% 1	732
	11th to 20th	Night	16% 13% 26% 29% 15% 1	563
	21st to end	Night	14% 7% 25% 32% 21% 1	570
May	1st to 10th	Night	13% 12% 19% 33% 21% 2	570
	11th to 20th	Night	16% 7% 16% 34% 24% 4	561
	21st to end	Night	16% 2 12% 31% 32% 7%	617
June	1st to 10th	Night	12% 3 12% 36% 30% 6%	570
	11th to 20th	Night	8% 1 15% 29% 34% 13%	570
	21st to end	Night	8% 2 8% 38% 35% 9%	570
July	1st to 10th	Night	12% 3 5% 27% 44% 10%	555
	11th to 20th	Night	10% 4 5% 22% 45% 14%	552
	21st to end	Night	8% 3 9% 23% 45% 12%	624
August	1st to 10th	Night	14% 2 7% 24% 39% 15%	567
	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% 19% 2	755
	11th to 20th	Night	18% 12% 28% 29% 12% 1	760
	21st to end	Night	21% 14% 25% 27% 13% 1	760
December	1st to 10th	Night	25% 16% 24% 27% 7% 1	760
	11th to 20th	Night	22% 13% 28% 28% 8% 1	760
	21st to end	Night	31% 12% 25% 27% 6%	836

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