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 2024-11-12.

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	8% 5% 2 4 3 3 4 3 5% 7% 56%	101103
	Night	8% 4 2 4 3 3 3 3 5% 7% 59%	98193
Transparency	Day	27% 5% 9% 23% 25% 11%	104934
	Night	25% 5% 9% 22% 26% 14%	102489
Seeing	Day	9% 7% 23% 30% 23% 8%	15069
	Night	10% 7% 31% 37% 15% 1	24962

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	10% 5% 2 5% 3 2 3 2 4 4 60%	2847
	11th to 20th	Day	8% 6% 1 2 2 2 3 3 4 5% 62%	2850
	21st to end	Day	14% 7% 2 4 3 3 3 2 4 5% 52%	3309
February	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 5% 6% 52%	1900
	11th to 20th	Day	12% 8% 2 5% 3 3 3 2 4 5% 52%	1849
	21st to end	Day	15% 6% 2 4 2 2 3 2 3 5% 56%	1570
March	1st to 10th	Day	12% 6% 1 5% 3 3 3 3 5% 6% 52%	3302
	11th to 20th	Day	15% 6% 2 5% 4 3 4 4 5% 5% 47%	3480
	21st to end	Day	7% 5% 2 6% 5% 4 4 3 6% 8% 49%	3814
April	1st to 10th	Day	9% 6% 2 4 4 4 3 3 5% 7% 53%	2090
	11th to 20th	Day	11% 6% 2 5% 3 4 3 3 4 6% 53%	2195
	21st to end	Day	9% 5% 2 5% 4 3 3 2 4 6% 56%	2422
May	1st to 10th	Day	11% 6% 2 7% 5% 4 4 3 5% 6% 46%	4082
	11th to 20th	Day	12% 6% 2 6% 4 3 3 3 5% 6% 51%	4082
	21st to end	Day	11% 6% 2 6% 5% 5% 4 4 6% 7% 45%	4477
June	1st to 10th	Day	5% 3 1 4 3 3 5% 4 6% 8% 58%	2470
	11th to 20th	Day	4 3 1 3 4 3 5% 4 6% 8% 59%	2470
	21st to end	Day	6% 3 1 4 4 3 4 4 6% 8% 57%	2470
July	1st to 10th	Day	5% 3 1 4 4 4 5% 4 6% 7% 55%	4120
	11th to 20th	Day	3 2 1 3 3 3 4 3 5% 10% 63%	4120
	21st to end	Day	4 3 1 4 3 4 5% 4 7% 11% 55%	4465
August	1st to 10th	Day	1 1 1 2 3 3 3 3 4 7% 72%	4104
	11th to 20th	Day	4 2 1 3 3 3 3 3 5% 10% 62%	3737
	21st to end	Day	3 2 1 4 3 4 4 4 6% 9% 59%	4126
September	1st to 10th	Day	9% 5% 2 4 4 4 4 3 5% 6% 54%	2090
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 5% 7% 49%	2090
	21st to end	Day	7% 3 1 4 3 4 4 3 5% 6% 59%	2090
October	1st to 10th	Day	4 3 2 3 3 3 3 3 4 6% 65%	2090
	11th to 20th	Day	9% 3 1 3 2 2 3 2 5% 6% 65%	1980
	21st to end	Day	10% 4 1 4 2 2 3 2 3 4 65%	2090
November	1st to 10th	Day	10% 4 2 4 2 2 4 2 4 6% 59%	1887
	11th to 20th	Day	4 5% 2 3 2 3 3 2 4 7% 63%	1719
	21st to end	Day	12% 5% 2 5% 4 2 3 3 4 4 56%	1710
December	1st to 10th	Day	10% 7% 2 5% 2 3 3 3 4 5% 55%	1710
	11th to 20th	Day	10% 6% 2 5% 4 3 4 4 6% 6% 52%	2161
	21st to end	Day	11% 6% 2 4 3 3 3 2 4 3 58%	3135
January	1st to 10th	Night	13% 5% 2 3 2 2 2 2 3 6% 60%	4108
	11th to 20th	Night	10% 5% 1 4 2 2 2 2 3 4 66%	4120
	21st to end	Night	14% 7% 2 4 3 3 3 3 4 6% 52%	4372
February	1st to 10th	Night	11% 5% 2 5% 3 3 4 2 4 5% 56%	2280
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 5% 54%	2218
	21st to end	Night	12% 5% 2 3 4 3 3 3 4 4 57%	1884
March	1st to 10th	Night	9% 7% 2 6% 4 3 3 3 5% 6% 53%	3555
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 6% 7% 49%	3480
	21st to end	Night	7% 5% 2 6% 5% 4 4 4 6% 7% 51%	3817
April	1st to 10th	Night	6% 4 1 5% 4 3 3 3 6% 7% 57%	2090
	11th to 20th	Night	9% 4 2 5% 5% 3 3 3 6% 7% 53%	1930
	21st to end	Night	8% 5% 1 3 2 3 3 3 4 7% 61%	1755
May	1st to 10th	Night	15% 8% 2 5% 3 3 4 3 4 7% 47%	2823
	11th to 20th	Night	8% 6% 3 6% 3 3 4 3 4 6% 53%	2823
	21st to end	Night	9% 4 1 4 4 3 4 4 6% 8% 53%	3090
June	1st to 10th	Night	3 3 1 3 3 3 3 4 5% 9% 63%	1710
	11th to 20th	Night	3 2 1 3 3 2 3 3 6% 9% 65%	1710
	21st to end	Night	3 3 1 4 3 3 3 3 6% 8% 63%	1710
July	1st to 10th	Night	4 3 1 4 3 3 2 3 4 8% 65%	2850
	11th to 20th	Night	2 1 1 2 2 2 2 2 5% 10% 71%	2850
	21st to end	Night	3 3 1 3 3 3 3 3 6% 10% 62%	3098
August	1st to 10th	Night	1 1 1 2 2 2 3 4 8% 76%	2836
	11th to 20th	Night	3 3 1 3 2 2 2 3 5% 9% 67%	3098
	21st to end	Night	3 2 1 4 3 3 3 4 6% 9% 63%	3539
September	1st to 10th	Night	7% 4 2 3 4 4 4 3 6% 8% 55%	2090
	11th to 20th	Night	10% 5% 1 5% 3 4 3 3 6% 8% 53%	2090
	21st to end	Night	7% 2 1 3 2 3 4 3 5% 7% 62%	2090
October	1st to 10th	Night	5% 3 1 3 2 2 3 2 3 6% 68%	2090
	11th to 20th	Night	8% 3 2 4 2 3 3 2 3 5% 65%	2180
	21st to end	Night	11% 5% 1 3 2 2 3 2 3 5% 63%	2508
November	1st to 10th	Night	9% 5% 1 4 2 3 3 3 3 5% 62%	2407
	11th to 20th	Night	5% 3 2 4 3 3 4 3 3 6% 64%	2484
	21st to end	Night	14% 4 2 4 3 3 3 2 4 6% 55%	2470
December	1st to 10th	Night	9% 3 2 4 4 2 4 3 4 7% 57%	2470
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 5% 6% 53%	3036
	21st to end	Night	11% 6% 2 4 3 3 3 3 4 4 58%	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	29% 2 5% 15% 33% 16%	2848
	11th to 20th	Day	25% 4 5% 20% 33% 14%	2850
	21st to end	Day	36% 3 6% 15% 29% 12%	3309
February	1st to 10th	Day	33% 4 6% 17% 23% 17%	1900
	11th to 20th	Day	36% 4 6% 19% 21% 14%	1859
	21st to end	Day	33% 3 4 13% 27% 20%	1570
March	1st to 10th	Day	32% 5% 5% 11% 28% 18%	3302
	11th to 20th	Day	38% 6% 15% 14% 19% 8%	3480
	21st to end	Day	32% 7% 10% 18% 23% 10%	3814
April	1st to 10th	Day	31% 5% 9% 20% 19% 15%	2090
	11th to 20th	Day	33% 4 8% 18% 22% 14%	2195
	21st to end	Day	31% 5% 8% 18% 30% 9%	2422
May	1st to 10th	Day	38% 5% 9% 18% 19% 10%	4120
	11th to 20th	Day	35% 5% 9% 19% 29% 4	4086
	21st to end	Day	36% 8% 13% 22% 14% 8%	4489
June	1st to 10th	Day	23% 8% 14% 30% 21% 4	2470
	11th to 20th	Day	21% 7% 13% 29% 22% 7%	2470
	21st to end	Day	24% 7% 11% 27% 23% 8%	2470
July	1st to 10th	Day	26% 7% 13% 38% 15% 1	4056
	11th to 20th	Day	17% 5% 15% 35% 26% 3	4051
	21st to end	Day	20% 7% 14% 37% 20% 2	4325
August	1st to 10th	Day	12% 5% 10% 31% 37% 5%	4090
	11th to 20th	Day	19% 5% 13% 34% 25% 4	3773
	21st to end	Day	20% 9% 16% 30% 22% 3	4125
September	1st to 10th	Day	31% 5% 9% 20% 24% 10%	2090
	11th to 20th	Day	33% 7% 9% 21% 24% 7%	2090
	21st to end	Day	24% 6% 8% 20% 28% 14%	2090
October	1st to 10th	Day	13% 3 6% 14% 34% 31%	3480
	11th to 20th	Day	16% 3 7% 21% 29% 23%	3272
	21st to end	Day	18% 3 4 24% 36% 15%	3428
November	1st to 10th	Day	28% 5% 6% 21% 25% 15%	1887
	11th to 20th	Day	22% 4 8% 23% 28% 16%	1719
	21st to end	Day	34% 3 5% 20% 25% 15%	1710
December	1st to 10th	Day	33% 4 6% 18% 27% 11%	1710
	11th to 20th	Day	33% 4 8% 15% 25% 15%	2159
	21st to end	Day	32% 3 4 19% 26% 16%	3135
January	1st to 10th	Night	28% 2 4 16% 34% 15%	4108
	11th to 20th	Night	25% 2 4 19% 30% 21%	4120
	21st to end	Night	36% 4 5% 16% 25% 15%	4372
February	1st to 10th	Night	31% 5% 6% 16% 24% 18%	2280
	11th to 20th	Night	33% 4 7% 15% 25% 17%	2218
	21st to end	Night	31% 4 5% 14% 22% 23%	1884
March	1st to 10th	Night	33% 4 6% 13% 25% 18%	3555
	11th to 20th	Night	33% 5% 12% 21% 17% 10%	3480
	21st to end	Night	31% 6% 10% 20% 26% 7%	3817
April	1st to 10th	Night	26% 5% 9% 21% 20% 19%	2090
	11th to 20th	Night	30% 6% 9% 18% 21% 16%	1930
	21st to end	Night	23% 5% 12% 22% 29% 9%	1755
May	1st to 10th	Night	39% 6% 7% 20% 18% 10%	2850
	11th to 20th	Night	30% 7% 12% 20% 23% 8%	2824
	21st to end	Night	27% 8% 13% 28% 17% 7%	3099
June	1st to 10th	Night	19% 7% 15% 34% 21% 4	1710
	11th to 20th	Night	15% 5% 15% 34% 23% 8%	1710
	21st to end	Night	19% 5% 11% 29% 27% 8%	1710
July	1st to 10th	Night	19% 6% 12% 42% 18% 3	2805
	11th to 20th	Night	10% 4 12% 39% 31% 5%	2796
	21st to end	Night	18% 6% 14% 38% 23% 1	2999
August	1st to 10th	Night	8% 4 10% 31% 41% 6%	2826
	11th to 20th	Night	16% 4 16% 36% 24% 4	3128
	21st to end	Night	17% 7% 22% 29% 22% 3	3539
September	1st to 10th	Night	26% 6% 10% 24% 22% 12%	2090
	11th to 20th	Night	29% 6% 13% 21% 22% 9%	2090
	21st to end	Night	21% 6% 8% 23% 25% 18%	2090
October	1st to 10th	Night	11% 3 6% 16% 29% 36%	3480
	11th to 20th	Night	16% 3 8% 18% 32% 23%	3614
	21st to end	Night	19% 3 4 21% 38% 15%	4120
November	1st to 10th	Night	26% 4 7% 20% 24% 19%	2407
	11th to 20th	Night	21% 5% 7% 23% 27% 18%	2484
	21st to end	Night	33% 3 6% 16% 27% 16%	2470
December	1st to 10th	Night	27% 4 7% 21% 26% 14%	2470
	11th to 20th	Night	32% 4 5% 15% 26% 17%	3037
	21st to end	Night	31% 3 4 16% 25% 20%	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	11% 16% 42% 24% 6% 1	270
	11th to 20th	Day	15% 17% 29% 27% 10% 1	270
	21st to end	Day	14% 13% 38% 25% 8% 1	297
February	1st to 10th	Day	19% 15% 36% 24% 6%	270
	11th to 20th	Day	21% 13% 41% 20% 4	270
	21st to end	Day	22% 16% 42% 17% 2	225
March	1st to 10th	Day	15% 16% 39% 27% 4	270
	11th to 20th	Day	16% 14% 40% 23% 6% 1	270
	21st to end	Day	11% 15% 44% 23% 6%	297
April	1st to 10th	Day	13% 18% 41% 21% 7%	270
	11th to 20th	Day	14% 13% 46% 21% 5%	393
	21st to end	Day	12% 15% 42% 23% 8% 1	602
May	1st to 10th	Day	11% 11% 39% 32% 7%	653
	11th to 20th	Day	15% 7% 28% 32% 16% 3	675
	21st to end	Day	10% 5% 30% 36% 15% 3	734
June	1st to 10th	Day	5% 2 17% 42% 28% 7%	680
	11th to 20th	Day	3 1 19% 47% 25% 5%	680
	21st to end	Day	3 2 12% 36% 36% 12%	680
July	1st to 10th	Day	6% 1 7% 33% 40% 13%	671
	11th to 20th	Day	2 1 4 34% 44% 15%	668
	21st to end	Day	2 1 6% 28% 47% 18%	739
August	1st to 10th	Day	2 4 32% 44% 19%	676
	11th to 20th	Day	7% 1 5% 28% 41% 18%	488
	21st to end	Day	3 1 5% 27% 37% 27%	511
September	1st to 10th	Day	12% 1 6% 15% 41% 26%	300
	11th to 20th	Day	5% 1 7% 19% 46% 22%	300
	21st to end	Day	10% 2 5% 28% 36% 19%	300
October	1st to 10th	Day	4 1 13% 34% 33% 15%	300
	11th to 20th	Day	8% 5% 27% 34% 23% 2	300
	21st to end	Day	19% 7% 24% 28% 20% 2	330
November	1st to 10th	Day	16% 7% 30% 30% 13% 5%	300
	11th to 20th	Day	8% 12% 30% 33% 14% 3	273
	21st to end	Day	16% 16% 33% 24% 9% 1	270
December	1st to 10th	Day	14% 11% 34% 25% 14% 2	270
	11th to 20th	Day	10% 14% 42% 27% 8%	270
	21st to end	Day	19% 14% 34% 27% 6%	297
January	1st to 10th	Night	12% 8% 41% 33% 6%	950
	11th to 20th	Night	14% 11% 33% 35% 7%	950
	21st to end	Night	14% 11% 37% 32% 6%	950
February	1st to 10th	Night	13% 11% 44% 27% 5%	760
	11th to 20th	Night	15% 12% 42% 27% 3	744
	21st to end	Night	17% 13% 46% 22% 3	628
March	1st to 10th	Night	14% 14% 41% 28% 4	659
	11th to 20th	Night	15% 8% 44% 28% 5%	570
	21st to end	Night	7% 13% 48% 27% 4	627
April	1st to 10th	Night	8% 12% 50% 27% 4	570
	11th to 20th	Night	10% 11% 49% 26% 3	563
	21st to end	Night	8% 10% 50% 26% 6%	570
May	1st to 10th	Night	10% 11% 44% 30% 4	570
	11th to 20th	Night	11% 4 38% 35% 12% 1	561
	21st to end	Night	7% 4 37% 40% 10% 1	617
June	1st to 10th	Night	2 2 25% 50% 20% 1	570
	11th to 20th	Night	3 2 26% 55% 14%	570
	21st to end	Night	2 2 18% 52% 25% 2	570
July	1st to 10th	Night	6% 1 9% 51% 29% 3	555
	11th to 20th	Night	3 10% 55% 31% 1	552
	21st to end	Night	2 1 5% 52% 39% 2	624
August	1st to 10th	Night	1 6% 53% 38% 3	567
	11th to 20th	Night	6% 1 7% 46% 37% 4	564
	21st to end	Night	4 6% 43% 44% 4	627
September	1st to 10th	Night	7% 1 10% 44% 34% 4	570
	11th to 20th	Night	11% 1 9% 43% 35% 1	570
	21st to end	Night	9% 1 12% 43% 34% 2	570
October	1st to 10th	Night	5% 2 22% 44% 26% 1	570
	11th to 20th	Night	10% 4 29% 41% 16% 1	660
	21st to end	Night	13% 8% 31% 33% 15% 1	836
November	1st to 10th	Night	11% 4 32% 37% 15% 1	847
	11th to 20th	Night	6% 8% 34% 39% 12% 1	956
	21st to end	Night	15% 8% 38% 29% 9% 1	950
December	1st to 10th	Night	11% 9% 35% 37% 7%	950
	11th to 20th	Night	15% 10% 34% 35% 6%	950
	21st to end	Night	13% 10% 40% 30% 7%	1045

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