Sky Dancer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sky Dancer Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	9% 5% 2 4 3 3 4 3 5% 7% 56%	127224
	Night	8% 4 2 4 3 3 3 3 4 7% 59%	124430
Transparency	Day	27% 5% 9% 22% 25% 12%	131016
	Night	26% 4 9% 22% 25% 15%	128701
Seeing	Day	9% 7% 23% 30% 23% 8%	16565
	Night	10% 7% 31% 37% 15% 1	26533

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	11% 6% 3 5% 3 3 3 2 3 4 57%	4086
	11th to 20th	Day	6% 6% 1 2 2 2 3 3 4 5% 66%	4080
	21st to end	Day	18% 7% 2 4 3 3 3 2 4 4 51%	4746
February	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 6% 53%	2000
	11th to 20th	Day	12% 8% 2 6% 3 3 3 2 4 5% 52%	1949
	21st to end	Day	14% 6% 2 4 2 2 3 2 3 5% 56%	1650
March	1st to 10th	Day	12% 6% 1 4 3 3 3 3 4 6% 56%	4737
	11th to 20th	Day	11% 4 1 4 3 2 3 3 5% 5% 58%	4980
	21st to end	Day	7% 4 2 5% 4 4 4 3 6% 7% 55%	5462
April	1st to 10th	Day	9% 6% 2 5% 4 4 3 3 5% 7% 52%	2200
	11th to 20th	Day	11% 6% 2 5% 3 4 3 3 4 6% 53%	2312
	21st to end	Day	9% 5% 2 5% 4 3 3 3 4 6% 56%	2550
May	1st to 10th	Day	11% 6% 2 6% 4 4 4 3 5% 6% 49%	5862
	11th to 20th	Day	12% 6% 2 6% 4 3 3 3 5% 6% 51%	5862
	21st to end	Day	11% 6% 2 6% 5% 4 4 4 6% 7% 45%	6434
June	1st to 10th	Day	5% 3 1 4 3 3 5% 4 6% 8% 58%	2600
	11th to 20th	Day	4 3 2 4 4 3 5% 4 6% 8% 60%	2600
	21st to end	Day	5% 3 1 4 4 3 4 4 6% 8% 58%	2600
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	5900
	11th to 20th	Day	3 2 1 4 3 3 4 3 5% 10% 61%	5900
	21st to end	Day	3 2 1 3 3 3 4 4 6% 10% 60%	6422
August	1st to 10th	Day	1 1 1 2 3 3 3 3 4 7% 72%	4234
	11th to 20th	Day	4 2 1 3 3 3 3 3 5% 10% 62%	3857
	21st to end	Day	3 2 1 4 3 4 4 4 6% 9% 59%	4256
September	1st to 10th	Day	9% 5% 2 4 4 4 4 3 5% 6% 54%	2200
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 3 5% 7% 50%	2200
	21st to end	Day	7% 3 2 4 3 4 3 3 5% 7% 60%	2200
October	1st to 10th	Day	4 2 2 3 3 3 3 3 4 6% 66%	2200
	11th to 20th	Day	8% 3 1 3 2 2 3 2 5% 6% 66%	2084
	21st to end	Day	10% 4 1 4 2 2 3 2 3 4 65%	2200
November	1st to 10th	Day	10% 4 2 4 2 2 4 2 3 5% 61%	1983
	11th to 20th	Day	4 4 2 3 2 3 3 2 4 8% 65%	1890
	21st to end	Day	12% 5% 2 5% 4 3 3 3 4 4 55%	1890
December	1st to 10th	Day	13% 7% 3 5% 3 4 4 3 4 4 50%	3030
	11th to 20th	Day	9% 5% 2 5% 4 3 4 4 5% 5% 53%	3481
	21st to end	Day	11% 5% 2 4 3 3 2 2 3 4 61%	4587
January	1st to 10th	Night	13% 5% 2 4 2 2 2 2 3 5% 58%	5902
	11th to 20th	Night	7% 4 1 3 2 2 2 2 3 4 71%	5900
	21st to end	Night	17% 7% 2 5% 3 3 3 3 4 5% 48%	6260
February	1st to 10th	Night	11% 5% 2 4 3 3 3 2 4 5% 58%	2400
	11th to 20th	Night	13% 6% 2 6% 3 3 3 3 4 6% 53%	2338
	21st to end	Night	12% 5% 2 4 4 3 3 3 4 4 57%	1980
March	1st to 10th	Night	8% 7% 2 5% 3 3 3 3 5% 6% 56%	5111
	11th to 20th	Night	10% 4 1 4 2 3 3 3 5% 7% 58%	4980
	21st to end	Night	7% 5% 2 5% 4 4 4 3 5% 6% 57%	5467
April	1st to 10th	Night	7% 5% 1 4 3 3 3 3 6% 7% 57%	2200
	11th to 20th	Night	10% 4 2 5% 5% 3 3 3 6% 6% 53%	2033
	21st to end	Night	7% 5% 1 3 3 3 3 3 4 7% 61%	1847
May	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 4 6% 49%	4053
	11th to 20th	Night	7% 5% 3 7% 4 4 5% 3 5% 6% 52%	4053
	21st to end	Night	10% 4 2 4 4 3 4 4 6% 9% 49%	4443
June	1st to 10th	Night	3 3 1 4 3 3 3 4 6% 9% 62%	1800
	11th to 20th	Night	3 2 1 3 3 2 3 3 6% 9% 65%	1800
	21st to end	Night	3 3 1 4 3 3 3 3 5% 8% 64%	1800
July	1st to 10th	Night	9% 5% 2 6% 4 3 3 3 5% 9% 51%	4078
	11th to 20th	Night	2 1 1 2 2 2 3 3 5% 10% 70%	4077
	21st to end	Night	2 2 1 3 3 3 3 3 6% 10% 64%	4449
August	1st to 10th	Night	1 1 1 2 2 2 3 4 8% 76%	2926
	11th to 20th	Night	3 3 1 3 2 2 2 3 5% 9% 66%	3197
	21st to end	Night	3 2 1 4 3 3 3 4 6% 9% 63%	3651
September	1st to 10th	Night	7% 4 2 4 4 4 4 3 6% 8% 55%	2200
	11th to 20th	Night	10% 5% 1 5% 3 4 3 3 6% 8% 54%	2200
	21st to end	Night	7% 2 1 3 2 3 4 3 5% 7% 62%	2200
October	1st to 10th	Night	5% 3 1 3 2 2 3 2 4 7% 68%	2200
	11th to 20th	Night	8% 3 2 4 2 2 3 2 3 5% 66%	2295
	21st to end	Night	11% 4 1 3 2 2 3 2 3 5% 64%	2640
November	1st to 10th	Night	9% 4 1 4 2 3 3 3 3 5% 64%	2531
	11th to 20th	Night	5% 3 2 4 3 3 4 3 3 6% 65%	2730
	21st to end	Night	13% 4 2 4 3 3 3 2 4 6% 55%	2730
December	1st to 10th	Night	13% 4 2 5% 4 2 3 2 4 6% 55%	4380
	11th to 20th	Night	8% 6% 2 5% 4 3 4 3 5% 6% 54%	4946
	21st to end	Night	10% 5% 2 4 2 3 3 2 3 4 61%	6633

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	32% 2 5% 21% 27% 11%	4087
	11th to 20th	Day	22% 3 4 22% 36% 13%	4080
	21st to end	Day	37% 3 5% 14% 25% 17%	4746
February	1st to 10th	Day	33% 4 6% 16% 23% 19%	2000
	11th to 20th	Day	36% 4 7% 20% 20% 14%	1959
	21st to end	Day	33% 3 4 13% 27% 20%	1650
March	1st to 10th	Day	30% 4 6% 10% 25% 24%	4737
	11th to 20th	Day	28% 4 10% 11% 18% 28%	4980
	21st to end	Day	28% 6% 8% 20% 25% 13%	5464
April	1st to 10th	Day	32% 5% 9% 19% 19% 15%	2200
	11th to 20th	Day	32% 4 8% 18% 23% 15%	2312
	21st to end	Day	30% 5% 8% 18% 30% 9%	2550
May	1st to 10th	Day	35% 5% 9% 19% 22% 10%	5900
	11th to 20th	Day	35% 5% 7% 15% 29% 9%	5866
	21st to end	Day	36% 7% 11% 24% 15% 7%	6447
June	1st to 10th	Day	23% 8% 14% 30% 22% 4	2600
	11th to 20th	Day	21% 6% 13% 29% 23% 7%	2600
	21st to end	Day	23% 7% 12% 28% 22% 8%	2600
July	1st to 10th	Day	38% 7% 12% 30% 12% 1	5836
	11th to 20th	Day	18% 6% 18% 33% 22% 3	5831
	21st to end	Day	17% 7% 15% 36% 23% 2	6240
August	1st to 10th	Day	12% 5% 11% 31% 36% 5%	4220
	11th to 20th	Day	18% 5% 14% 34% 25% 4	3893
	21st to end	Day	20% 9% 16% 30% 22% 3	4255
September	1st to 10th	Day	31% 5% 9% 20% 25% 10%	2200
	11th to 20th	Day	32% 7% 9% 22% 24% 7%	2200
	21st to end	Day	24% 6% 8% 21% 27% 14%	2200
October	1st to 10th	Day	12% 3 6% 15% 34% 30%	3590
	11th to 20th	Day	16% 3 7% 22% 29% 23%	3376
	21st to end	Day	18% 3 4 23% 36% 15%	3538
November	1st to 10th	Day	27% 4 6% 20% 27% 15%	1983
	11th to 20th	Day	21% 3 8% 23% 28% 17%	1890
	21st to end	Day	33% 3 5% 20% 26% 14%	1890
December	1st to 10th	Day	37% 4 5% 17% 26% 10%	3030
	11th to 20th	Day	32% 5% 6% 13% 27% 16%	3479
	21st to end	Day	28% 3 4 22% 27% 17%	4587
January	1st to 10th	Night	31% 2 5% 20% 31% 11%	5902
	11th to 20th	Night	20% 2 4 18% 35% 22%	5900
	21st to end	Night	39% 4 4 13% 21% 18%	6260
February	1st to 10th	Night	30% 4 6% 16% 24% 20%	2400
	11th to 20th	Night	34% 4 7% 15% 24% 16%	2338
	21st to end	Night	31% 4 5% 14% 21% 24%	1980
March	1st to 10th	Night	29% 4 5% 15% 24% 22%	5111
	11th to 20th	Night	27% 4 9% 15% 16% 29%	4980
	21st to end	Night	28% 5% 8% 19% 27% 13%	5467
April	1st to 10th	Night	26% 5% 9% 20% 20% 19%	2200
	11th to 20th	Night	30% 6% 9% 17% 22% 16%	2033
	21st to end	Night	24% 5% 13% 22% 28% 9%	1847
May	1st to 10th	Night	36% 6% 7% 22% 18% 10%	4080
	11th to 20th	Night	32% 6% 11% 16% 20% 16%	4054
	21st to end	Night	30% 7% 13% 26% 15% 9%	4452
June	1st to 10th	Night	19% 7% 15% 33% 21% 4	1800
	11th to 20th	Night	16% 5% 15% 34% 22% 8%	1800
	21st to end	Night	19% 5% 12% 30% 27% 8%	1800
July	1st to 10th	Night	32% 6% 12% 33% 15% 2	4035
	11th to 20th	Night	12% 5% 15% 34% 31% 4	4026
	21st to end	Night	16% 6% 16% 35% 25% 2	4320
August	1st to 10th	Night	8% 4 10% 31% 41% 6%	2916
	11th to 20th	Night	15% 4 17% 37% 23% 4	3227
	21st to end	Night	18% 7% 21% 29% 22% 3	3651
September	1st to 10th	Night	26% 6% 10% 24% 23% 11%	2200
	11th to 20th	Night	28% 6% 12% 22% 22% 9%	2200
	21st to end	Night	21% 6% 8% 23% 25% 18%	2200
October	1st to 10th	Night	11% 3 6% 16% 30% 35%	3590
	11th to 20th	Night	15% 3 8% 19% 33% 23%	3729
	21st to end	Night	19% 3 4 21% 38% 15%	4252
November	1st to 10th	Night	25% 4 7% 20% 25% 19%	2531
	11th to 20th	Night	20% 5% 7% 23% 27% 19%	2730
	21st to end	Night	32% 3 6% 17% 27% 15%	2730
December	1st to 10th	Night	33% 4 5% 20% 25% 13%	4380
	11th to 20th	Night	32% 5% 6% 13% 28% 17%	4947
	21st to end	Night	28% 3 5% 21% 24% 19%	6633

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	13% 16% 42% 23% 5% 1	303
	11th to 20th	Day	15% 17% 30% 27% 10% 1	300
	21st to end	Day	15% 14% 39% 24% 8% 1	330
February	1st to 10th	Day	19% 14% 36% 24% 6%	300
	11th to 20th	Day	21% 14% 42% 20% 4	300
	21st to end	Day	21% 16% 39% 20% 4	249
March	1st to 10th	Day	17% 15% 39% 26% 4	300
	11th to 20th	Day	16% 15% 39% 23% 5% 1	300
	21st to end	Day	11% 15% 44% 25% 6%	330
April	1st to 10th	Day	13% 19% 39% 21% 8%	300
	11th to 20th	Day	14% 14% 47% 20% 5%	430
	21st to end	Day	12% 14% 42% 24% 8% 1	650
May	1st to 10th	Day	11% 10% 39% 32% 7%	703
	11th to 20th	Day	15% 7% 29% 32% 14% 3	725
	21st to end	Day	10% 5% 30% 37% 15% 3	789
June	1st to 10th	Day	5% 2 17% 42% 27% 6%	730
	11th to 20th	Day	3 2 18% 47% 25% 5%	730
	21st to end	Day	3 2 12% 36% 36% 11%	730
July	1st to 10th	Day	7% 1 7% 33% 39% 13%	721
	11th to 20th	Day	2 1 5% 34% 43% 14%	718
	21st to end	Day	2 1 6% 28% 46% 18%	794
August	1st to 10th	Day	2 4 32% 44% 18%	726
	11th to 20th	Day	7% 1 4 29% 40% 18%	528
	21st to end	Day	3 2 5% 27% 37% 27%	553
September	1st to 10th	Day	11% 1 6% 17% 40% 25%	330
	11th to 20th	Day	5% 1 7% 19% 47% 21%	330
	21st to end	Day	9% 2 6% 28% 35% 19%	330
October	1st to 10th	Day	3 1 12% 33% 33% 17%	330
	11th to 20th	Day	8% 5% 26% 34% 23% 4	330
	21st to end	Day	19% 7% 24% 28% 20% 2	363
November	1st to 10th	Day	14% 7% 29% 30% 15% 5%	330
	11th to 20th	Day	8% 12% 30% 33% 15% 3	330
	21st to end	Day	15% 15% 34% 24% 10% 2	330
December	1st to 10th	Day	14% 12% 35% 25% 13% 2	330
	11th to 20th	Day	8% 13% 42% 26% 10% 1	330
	21st to end	Day	17% 13% 33% 28% 8% 1	363
January	1st to 10th	Night	12% 9% 40% 33% 6%	1006
	11th to 20th	Night	14% 12% 34% 35% 6%	1000
	21st to end	Night	14% 11% 37% 31% 6%	1000
February	1st to 10th	Night	13% 10% 44% 28% 5%	800
	11th to 20th	Night	16% 12% 42% 27% 3	784
	21st to end	Night	17% 14% 44% 23% 3	660
March	1st to 10th	Night	14% 15% 40% 28% 3	693
	11th to 20th	Night	15% 9% 44% 28% 5%	600
	21st to end	Night	8% 12% 48% 28% 4	660
April	1st to 10th	Night	8% 13% 49% 27% 4	600
	11th to 20th	Night	10% 11% 49% 26% 3	593
	21st to end	Night	8% 10% 49% 26% 6%	600
May	1st to 10th	Night	10% 11% 43% 32% 4	600
	11th to 20th	Night	10% 5% 39% 35% 11% 1	591
	21st to end	Night	8% 4 37% 40% 10% 1	650
June	1st to 10th	Night	2 2 27% 49% 19% 1	600
	11th to 20th	Night	3 2 26% 55% 14%	600
	21st to end	Night	2 2 17% 53% 24% 2	600
July	1st to 10th	Night	8% 2 9% 49% 30% 3	585
	11th to 20th	Night	3 10% 55% 31% 1	582
	21st to end	Night	2 1 5% 52% 39% 2	657
August	1st to 10th	Night	1 6% 52% 38% 3	597
	11th to 20th	Night	6% 1 6% 46% 38% 4	594
	21st to end	Night	4 1 5% 42% 44% 3	660
September	1st to 10th	Night	7% 1 11% 45% 33% 4	600
	11th to 20th	Night	10% 1 9% 45% 34% 1	600
	21st to end	Night	9% 1 12% 44% 33% 2	600
October	1st to 10th	Night	5% 2 21% 44% 27% 1	600
	11th to 20th	Night	9% 4 29% 40% 17% 1	695
	21st to end	Night	12% 8% 30% 34% 15% 1	880
November	1st to 10th	Night	11% 4 32% 38% 14% 1	891
	11th to 20th	Night	6% 8% 34% 39% 12% 1	1050
	21st to end	Night	14% 8% 37% 30% 10% 1	1050
December	1st to 10th	Night	12% 8% 37% 36% 7%	1050
	11th to 20th	Night	14% 10% 34% 34% 7%	1050
	21st to end	Night	13% 9% 39% 30% 8%	1155

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