SkyStar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SkyStar Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	6% 4 1 3 2 2 3 2 4 6% 67%	100873
	Night	6% 6% 2 4 2 3 3 2 4 5% 63%	98373
Transparency	Day	18% 4 5% 16% 26% 31%	100643
	Night	22% 5% 5% 15% 23% 30%	98194
Seeing	Day	8% 11% 29% 33% 13% 5%	15703
	Night	8% 4 14% 32% 33% 9%	26047

By Month

Percentage Cloud Cover SW (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% 1 4 2 2 2 3 3 5% 63%	2858
	11th to 20th	Day	9% 5% 2 4 2 3 4 3 5% 8% 55%	2998
	21st to end	Day	16% 7% 1 4 3 3 3 3 5% 7% 47%	3498
February	1st to 10th	Day	11% 5% 1 4 3 3 3 3 4 5% 57%	1900
	11th to 20th	Day	10% 7% 2 4 3 3 3 3 5% 6% 54%	1850
	21st to end	Day	13% 9% 3 5% 3 3 4 3 4 6% 46%	1570
March	1st to 10th	Day	15% 7% 2 4 3 3 4 5% 8% 9% 39%	3138
	11th to 20th	Day	7% 5% 2 5% 3 3 5% 3 5% 7% 55%	3356
	21st to end	Day	12% 8% 2 4 3 3 3 3 5% 6% 50%	3979
April	1st to 10th	Day	8% 7% 2 5% 3 3 3 3 5% 7% 56%	2280
	11th to 20th	Day	5% 4 1 3 3 3 3 3 4 5% 65%	2249
	21st to end	Day	8% 5% 2 2 2 2 2 2 4 7% 64%	2280
May	1st to 10th	Day	6% 4 1 3 1 2 2 2 2 5% 73%	4017
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 6% 76%	4071
	21st to end	Day	3 4 1 3 2 2 2 2 4 6% 71%	4477
June	1st to 10th	Day	3 3 1 2 2 2 2 2 4 6% 73%	2470
	11th to 20th	Day	1 2 1 1 2 1 2 1 3 4 81%	2470
	21st to end	Day	1 2 1 1 2 2 1 1 4 3 82%	2470
July	1st to 10th	Day	1 1 1 1 1 1 1 2 4 86%	4110
	11th to 20th	Day	1 1 1 1 1 2 2 2 4 6% 78%	4110
	21st to end	Day	1 1 1 2 2 2 2 5% 5% 79%	4303
August	1st to 10th	Day	1 1 2 1 1 2 2 4 6% 79%	3783
	11th to 20th	Day	1 1 1 2 1 1 2 1 2 4 84%	3724
	21st to end	Day	1 1 1 1 1 2 2 2 4 85%	4180
September	1st to 10th	Day	2 2 1 2 2 3 2 2 4 5% 76%	2247
	11th to 20th	Day	2 2 2 1 1 1 1 2 3 84%	2090
	21st to end	Day	2 2 1 2 2 2 2 2 3 4 79%	2090
October	1st to 10th	Day	4 4 1 3 2 2 3 2 4 5% 69%	2090
	11th to 20th	Day	5% 4 1 3 2 2 2 2 3 4 73%	2090
	21st to end	Day	4 3 1 3 1 2 2 2 3 5% 74%	2006
November	1st to 10th	Day	6% 4 1 3 3 2 2 2 4 6% 67%	1674
	11th to 20th	Day	4 4 1 3 3 3 3 2 4 5% 67%	1710
	21st to end	Day	8% 6% 2 3 3 3 3 4 5% 7% 57%	1710
December	1st to 10th	Day	9% 5% 2 5% 3 4 3 3 5% 7% 56%	1710
	11th to 20th	Day	13% 7% 2 5% 4 4 4 4 6% 7% 44%	2169
	21st to end	Day	12% 8% 2 6% 6% 6% 4 4 5% 5% 42%	3146
January	1st to 10th	Night	7% 7% 2 4 3 3 3 2 3 5% 61%	4097
	11th to 20th	Night	8% 7% 2 5% 4 4 3 3 5% 8% 51%	3972
	21st to end	Night	18% 8% 2 4 2 3 3 3 4 5% 48%	4180
February	1st to 10th	Night	10% 7% 1 5% 2 2 4 3 5% 4 57%	2280
	11th to 20th	Night	10% 9% 2 3 4 3 4 2 3 4 55%	2218
	21st to end	Night	11% 11% 2 5% 3 3 4 3 4 6% 48%	1884
March	1st to 10th	Night	15% 19% 3 6% 4 3 3 2 4 6% 36%	3736
	11th to 20th	Night	8% 9% 2 3 3 3 4 3 5% 7% 54%	3624
	21st to end	Night	10% 15% 2 5% 4 3 3 3 6% 7% 42%	3657
April	1st to 10th	Night	8% 10% 1 5% 3 2 3 3 5% 7% 52%	1900
	11th to 20th	Night	7% 8% 2 5% 3 3 3 2 4 5% 59%	1879
	21st to end	Night	8% 9% 2 4 2 3 3 3 3 7% 57%	1900
May	1st to 10th	Night	3 9% 1 4 2 2 2 1 3 4 69%	2942
	11th to 20th	Night	2 6% 3 5% 2 3 3 2 3 5% 65%	2834
	21st to end	Night	3 10% 2 5% 3 3 3 2 4 5% 61%	3110
June	1st to 10th	Night	2 5% 2 4 3 3 2 2 4 7% 66%	1710
	11th to 20th	Night	1 4 1 1 3 2 2 1 2 6% 76%	1710
	21st to end	Night	1 3 2 1 2 2 1 3 4 80%	1710
July	1st to 10th	Night	1 1 1 1 1 1 2 4 88%	2860
	11th to 20th	Night	1 1 1 2 1 3 5% 84%	2860
	21st to end	Night	1 1 1 2 1 2 2 2 3 5% 81%	3260
August	1st to 10th	Night	1 1 1 1 1 1 2 3 6% 82%	3166
	11th to 20th	Night	1 1 1 1 1 2 2 3 5% 85%	3126
	21st to end	Night	1 1 1 1 1 1 1 2 3 89%	3498
September	1st to 10th	Night	1 2 1 3 2 3 3 2 4 5% 76%	1931
	11th to 20th	Night	2 4 1 3 1 2 1 1 2 3 80%	2090
	21st to end	Night	3 3 1 2 2 1 2 2 2 3 80%	2090
October	1st to 10th	Night	5% 4 1 3 2 3 2 3 4 5% 68%	2090
	11th to 20th	Night	6% 5% 1 3 2 2 2 2 2 5% 70%	2090
	21st to end	Night	5% 4 1 3 2 2 3 2 3 5% 70%	2586
November	1st to 10th	Night	6% 5% 1 3 2 2 2 2 3 5% 68%	2411
	11th to 20th	Night	4 5% 2 3 2 3 3 2 4 5% 67%	2470
	21st to end	Night	8% 6% 2 4 4 3 4 4 5% 6% 55%	2470
December	1st to 10th	Night	9% 6% 2 4 4 3 3 4 5% 5% 54%	2470
	11th to 20th	Night	13% 8% 2 5% 4 4 4 3 7% 6% 43%	3041
	21st to end	Night	11% 9% 3 7% 4 4 4 4 5% 6% 44%	4521

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	23% 5% 5% 16% 30% 21%	2859
	11th to 20th	Day	27% 6% 8% 23% 22% 15%	2998
	21st to end	Day	34% 7% 7% 12% 23% 17%	3498
February	1st to 10th	Day	29% 4 5% 13% 21% 29%	1900
	11th to 20th	Day	30% 4 6% 13% 25% 22%	1860
	21st to end	Day	38% 5% 5% 12% 20% 19%	1570
March	1st to 10th	Day	32% 7% 7% 19% 18% 16%	3138
	11th to 20th	Day	22% 9% 12% 23% 22% 13%	3356
	21st to end	Day	31% 6% 8% 26% 20% 8%	3979
April	1st to 10th	Day	28% 4 7% 22% 24% 14%	2280
	11th to 20th	Day	20% 4 7% 19% 28% 22%	2252
	21st to end	Day	19% 4 6% 21% 34% 16%	2280
May	1st to 10th	Day	15% 3 5% 18% 38% 21%	4017
	11th to 20th	Day	9% 3 4 22% 35% 27%	4074
	21st to end	Day	12% 3 5% 20% 43% 17%	4477
June	1st to 10th	Day	12% 3 5% 22% 33% 26%	2470
	11th to 20th	Day	9% 2 4 13% 25% 48%	2470
	21st to end	Day	9% 2 2 8% 22% 57%	2470
July	1st to 10th	Day	6% 2 3 6% 13% 72%	4046
	11th to 20th	Day	8% 4 5% 12% 34% 36%	4041
	21st to end	Day	8% 5% 7% 22% 24% 35%	4168
August	1st to 10th	Day	8% 3 6% 16% 39% 28%	3770
	11th to 20th	Day	7% 2 4 12% 25% 49%	3760
	21st to end	Day	7% 2 3 8% 23% 58%	4179
September	1st to 10th	Day	12% 4 5% 10% 29% 39%	2247
	11th to 20th	Day	7% 1 2 9% 33% 47%	2090
	21st to end	Day	11% 3 4 10% 29% 44%	2090
October	1st to 10th	Day	18% 3 5% 14% 24% 35%	2090
	11th to 20th	Day	17% 2 3 10% 26% 42%	2090
	21st to end	Day	14% 3 3 11% 23% 46%	2006
November	1st to 10th	Day	20% 3 4 14% 23% 37%	1674
	11th to 20th	Day	19% 3 6% 10% 24% 39%	1710
	21st to end	Day	26% 4 5% 11% 23% 32%	1710
December	1st to 10th	Day	28% 4 6% 14% 18% 29%	1710
	11th to 20th	Day	36% 7% 9% 12% 18% 18%	2168
	21st to end	Day	39% 7% 6% 17% 18% 13%	3146
January	1st to 10th	Night	24% 5% 5% 14% 27% 24%	4097
	11th to 20th	Night	30% 6% 8% 20% 20% 16%	3972
	21st to end	Night	36% 6% 6% 9% 24% 18%	4180
February	1st to 10th	Night	29% 4 5% 12% 21% 29%	2280
	11th to 20th	Night	33% 5% 4 10% 22% 26%	2219
	21st to end	Night	37% 4 5% 13% 20% 22%	1884
March	1st to 10th	Night	43% 10% 6% 11% 16% 14%	3736
	11th to 20th	Night	25% 8% 9% 22% 22% 13%	3624
	21st to end	Night	37% 10% 8% 15% 20% 10%	3657
April	1st to 10th	Night	31% 5% 7% 19% 22% 17%	1900
	11th to 20th	Night	25% 4 8% 17% 22% 23%	1879
	21st to end	Night	27% 3 7% 20% 24% 19%	1900
May	1st to 10th	Night	18% 4 5% 17% 35% 21%	2942
	11th to 20th	Night	14% 7% 6% 29% 24% 19%	2835
	21st to end	Night	18% 5% 6% 24% 26% 22%	3110
June	1st to 10th	Night	15% 4 8% 20% 26% 27%	1710
	11th to 20th	Night	11% 2 3 17% 20% 48%	1710
	21st to end	Night	9% 2 3 9% 21% 55%	1710
July	1st to 10th	Night	4 1 2 8% 13% 72%	2815
	11th to 20th	Night	5% 3 5% 13% 37% 36%	2806
	21st to end	Night	8% 3 5% 22% 27% 35%	3158
August	1st to 10th	Night	5% 3 5% 19% 39% 29%	3156
	11th to 20th	Night	5% 2 3 18% 22% 50%	3156
	21st to end	Night	5% 2 2 9% 18% 65%	3498
September	1st to 10th	Night	11% 4 4 15% 25% 42%	1931
	11th to 20th	Night	12% 2 3 9% 27% 47%	2090
	21st to end	Night	11% 2 4 10% 31% 42%	2090
October	1st to 10th	Night	20% 3 5% 15% 21% 35%	2090
	11th to 20th	Night	18% 3 4 13% 23% 40%	2090
	21st to end	Night	18% 3 5% 10% 19% 46%	2586
November	1st to 10th	Night	21% 3 4 11% 24% 37%	2411
	11th to 20th	Night	20% 3 4 12% 20% 40%	2470
	21st to end	Night	29% 5% 5% 12% 18% 31%	2470
December	1st to 10th	Night	30% 5% 6% 11% 19% 28%	2470
	11th to 20th	Night	37% 7% 7% 12% 18% 19%	3041
	21st to end	Night	37% 8% 6% 18% 18% 14%	4521

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	21% 11% 25% 31% 11% 1	270
	11th to 20th	Day	14% 12% 26% 38% 9% 1	356
	21st to end	Day	15% 19% 33% 25% 7% 2	506
February	1st to 10th	Day	16% 16% 34% 23% 8% 3	460
	11th to 20th	Day	15% 19% 33% 25% 8%	455
	21st to end	Day	19% 24% 31% 20% 7%	382
March	1st to 10th	Day	17% 21% 37% 18% 6% 1	460
	11th to 20th	Day	15% 18% 33% 24% 7% 2	460
	21st to end	Day	14% 23% 35% 21% 6%	506
April	1st to 10th	Day	12% 17% 33% 25% 10% 3	460
	11th to 20th	Day	8% 23% 39% 19% 10% 2	452
	21st to end	Day	10% 16% 32% 25% 12% 5%	460
May	1st to 10th	Day	13% 15% 35% 24% 11% 3	463
	11th to 20th	Day	7% 13% 37% 30% 10% 4	488
	21st to end	Day	9% 14% 33% 29% 12% 4	529
June	1st to 10th	Day	3 7% 29% 37% 17% 7%	490
	11th to 20th	Day	2 7% 33% 34% 18% 7%	490
	21st to end	Day	1 5% 30% 35% 21% 8%	490
July	1st to 10th	Day	2 1 18% 49% 18% 12%	486
	11th to 20th	Day	2 17% 46% 20% 15%	484
	21st to end	Day	2 1 11% 52% 19% 15%	531
August	1st to 10th	Day	2 1 23% 43% 17% 13%	487
	11th to 20th	Day	2 1 19% 45% 18% 15%	477
	21st to end	Day	1 2 20% 50% 16% 12%	539
September	1st to 10th	Day	3 2 27% 46% 14% 8%	490
	11th to 20th	Day	4 5% 35% 36% 15% 5%	490
	21st to end	Day	3 10% 29% 36% 16% 6%	490
October	1st to 10th	Day	5% 10% 32% 34% 16% 2	490
	11th to 20th	Day	5% 12% 33% 35% 13% 2	490
	21st to end	Day	6% 10% 28% 36% 16% 3	425
November	1st to 10th	Day	9% 11% 24% 39% 15% 3	270
	11th to 20th	Day	7% 10% 30% 36% 16% 1	270
	21st to end	Day	13% 14% 33% 26% 12% 3	270
December	1st to 10th	Day	9% 14% 31% 31% 16%	270
	11th to 20th	Day	7% 11% 31% 33% 14% 2	270
	21st to end	Day	21% 18% 24% 26% 9% 2	297
January	1st to 10th	Night	10% 7% 21% 32% 21% 8%	760
	11th to 20th	Night	9% 6% 22% 35% 21% 6%	760
	21st to end	Night	15% 8% 19% 35% 20% 3	836
February	1st to 10th	Night	13% 7% 21% 30% 22% 6%	760
	11th to 20th	Night	13% 8% 18% 34% 21% 6%	744
	21st to end	Night	16% 9% 20% 34% 18% 3	628
March	1st to 10th	Night	16% 9% 23% 33% 18% 2	760
	11th to 20th	Night	13% 6% 17% 35% 22% 7%	760
	21st to end	Night	11% 8% 17% 36% 23% 4	836
April	1st to 10th	Night	12% 5% 18% 36% 24% 5%	760
	11th to 20th	Night	10% 8% 17% 36% 24% 5%	751
	21st to end	Night	10% 5% 17% 31% 29% 7%	760
May	1st to 10th	Night	7% 7% 18% 34% 30% 4	626
	11th to 20th	Night	5% 5% 16% 35% 31% 8%	561
	21st to end	Night	7% 6% 19% 33% 30% 4	617
June	1st to 10th	Night	2 2 14% 39% 35% 7%	570
	11th to 20th	Night	3 2 9% 41% 40% 5%	570
	21st to end	Night	2 1 7% 35% 49% 6%	570
July	1st to 10th	Night	1 3 25% 60% 11%	555
	11th to 20th	Night	1 1 23% 62% 12%	552
	21st to end	Night	2 1 2 18% 60% 17%	713
August	1st to 10th	Night	1 3 22% 54% 19%	756
	11th to 20th	Night	2 2 16% 57% 23%	752
	21st to end	Night	2 2 17% 56% 24%	836
September	1st to 10th	Night	1 1 5% 22% 57% 14%	760
	11th to 20th	Night	2 3 7% 31% 47% 10%	760
	21st to end	Night	3 1 10% 34% 38% 13%	760
October	1st to 10th	Night	7% 3 9% 40% 35% 6%	760
	11th to 20th	Night	7% 4 13% 38% 29% 10%	760
	21st to end	Night	6% 2 16% 35% 27% 14%	836
November	1st to 10th	Night	8% 3 14% 39% 27% 9%	742
	11th to 20th	Night	6% 3 17% 37% 27% 11%	760
	21st to end	Night	11% 6% 18% 34% 24% 8%	760
December	1st to 10th	Night	12% 5% 21% 33% 22% 7%	760
	11th to 20th	Night	16% 6% 21% 34% 18% 5%	760
	21st to end	Night	14% 7% 21% 32% 19% 6%	836

Page generated at 2024-10-29 08:20:48. Version ac07

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