Skyview Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyview Observatory clear sky chart from 2005-11-06 to 2024-10-24.

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 4 3 3 3 3 5% 7% 61%	100811
	Night	5% 4 1 4 3 3 3 3 5% 7% 62%	98163
Transparency	Day	24% 4 8% 21% 27% 16%	100579
	Night	21% 4 8% 21% 27% 17%	97985
Seeing	Day	7% 5% 23% 32% 25% 8%	15117
	Night	7% 6% 31% 40% 16% 1	25032

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	9% 6% 2 5% 3 3 3 2 4 6% 58%	2847
	11th to 20th	Day	3 2 2 4 2 3 2 3 4 5% 70%	2987
	21st to end	Day	6% 7% 2 6% 4 4 4 2 4 7% 54%	3487
February	1st to 10th	Day	5% 6% 2 4 2 3 3 3 4 6% 63%	1900
	11th to 20th	Day	7% 4 2 4 4 3 3 3 5% 6% 59%	1849
	21st to end	Day	5% 7% 3 4 3 2 3 3 4 5% 61%	1570
March	1st to 10th	Day	5% 5% 2 3 3 3 2 3 5% 6% 63%	3130
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 5% 5% 55%	3321
	21st to end	Day	4 4 2 5% 3 4 4 4 5% 8% 57%	4005
April	1st to 10th	Day	5% 3 1 4 2 3 3 3 4 6% 67%	2280
	11th to 20th	Day	8% 5% 2 4 3 2 2 3 4 6% 61%	2251
	21st to end	Day	4 3 1 4 3 3 3 3 5% 6% 66%	2280
May	1st to 10th	Day	8% 4 1 4 3 2 3 3 3 5% 63%	4046
	11th to 20th	Day	11% 4 1 4 3 2 3 3 5% 6% 57%	4082
	21st to end	Day	8% 4 1 4 3 3 4 3 5% 6% 60%	4489
June	1st to 10th	Day	4 4 2 4 3 3 4 3 5% 10% 58%	2470
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 7% 64%	2470
	21st to end	Day	3 2 1 3 3 3 4 4 6% 6% 63%	2470
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 4 6% 8% 48%	4120
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 9% 60%	4120
	21st to end	Day	4 3 1 4 3 4 4 4 6% 9% 58%	4348
August	1st to 10th	Day	2 2 1 3 2 3 3 3 6% 9% 67%	3784
	11th to 20th	Day	4 2 1 3 2 3 4 3 5% 8% 66%	3726
	21st to end	Day	6% 4 2 4 2 3 4 3 5% 7% 60%	4180
September	1st to 10th	Day	8% 5% 2 5% 4 4 3 3 5% 8% 52%	2263
	11th to 20th	Day	9% 5% 1 5% 4 4 5% 4 5% 8% 49%	2090
	21st to end	Day	9% 3 1 4 3 3 3 2 4 5% 64%	2090
October	1st to 10th	Day	6% 5% 2 4 3 2 3 2 4 5% 65%	2090
	11th to 20th	Day	8% 3 1 3 2 2 3 2 2 4 69%	2086
	21st to end	Day	7% 4 1 4 2 2 2 3 3 3 68%	1881
November	1st to 10th	Day	5% 3 1 3 2 3 3 2 4 5% 68%	1673
	11th to 20th	Day	2 3 1 3 3 3 3 3 5% 5% 69%	1710
	21st to end	Day	9% 5% 1 3 2 3 3 3 4 5% 62%	1710
December	1st to 10th	Day	7% 5% 2 4 3 4 3 3 5% 7% 59%	1710
	11th to 20th	Day	6% 5% 1 6% 4 3 3 3 5% 6% 59%	2161
	21st to end	Day	7% 5% 2 4 2 2 3 2 3 5% 66%	3135
January	1st to 10th	Night	4 6% 2 4 3 3 3 3 5% 6% 61%	4108
	11th to 20th	Night	3 2 1 3 2 2 3 3 4 7% 68%	4010
	21st to end	Night	5% 7% 3 5% 3 3 4 3 5% 7% 56%	4180
February	1st to 10th	Night	6% 5% 3 4 3 2 3 3 4 5% 63%	2280
	11th to 20th	Night	6% 4 2 5% 3 3 2 3 6% 6% 60%	2218
	21st to end	Night	5% 4 1 4 3 3 4 3 5% 6% 62%	1884
March	1st to 10th	Night	4 5% 2 4 3 3 3 2 4 5% 66%	3734
	11th to 20th	Night	7% 5% 2 4 3 3 3 3 5% 8% 57%	3642
	21st to end	Night	4 4 2 5% 4 3 4 4 6% 7% 58%	3615
April	1st to 10th	Night	4 3 1 4 3 3 3 3 5% 6% 65%	1900
	11th to 20th	Night	6% 3 1 4 3 3 2 3 5% 7% 62%	1877
	21st to end	Night	4 3 1 4 3 3 3 3 4 7% 66%	1900
May	1st to 10th	Night	8% 4 1 3 3 2 2 2 3 5% 66%	2921
	11th to 20th	Night	7% 4 1 3 3 3 4 3 5% 6% 62%	2823
	21st to end	Night	7% 4 1 3 2 2 3 3 4 6% 65%	3098
June	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 11% 56%	1710
	11th to 20th	Night	2 2 1 2 3 2 4 4 7% 10% 63%	1710
	21st to end	Night	2 1 1 4 3 2 3 3 7% 9% 63%	1710
July	1st to 10th	Night	4 3 1 4 4 4 5% 5% 8% 10% 52%	2850
	11th to 20th	Night	3 2 1 3 4 3 4 4 8% 12% 55%	2850
	21st to end	Night	3 2 1 3 2 3 3 3 7% 11% 60%	3211
August	1st to 10th	Night	2 2 1 3 3 3 3 4 7% 11% 63%	3155
	11th to 20th	Night	3 2 1 4 3 4 5% 4 6% 8% 61%	3113
	21st to end	Night	4 2 1 3 3 2 3 3 5% 10% 63%	3487
September	1st to 10th	Night	7% 3 2 5% 4 3 4 4 5% 7% 56%	1915
	11th to 20th	Night	9% 4 2 4 3 4 4 3 6% 8% 53%	2090
	21st to end	Night	7% 3 1 4 3 2 3 3 4 6% 65%	2090
October	1st to 10th	Night	5% 4 1 4 3 2 3 3 4 5% 66%	2090
	11th to 20th	Night	9% 3 1 2 2 1 2 2 3 5% 71%	2090
	21st to end	Night	7% 4 1 3 2 2 2 2 3 5% 70%	2519
November	1st to 10th	Night	5% 3 1 2 2 2 2 3 4 6% 71%	2405
	11th to 20th	Night	2 3 1 3 2 2 3 2 5% 7% 70%	2470
	21st to end	Night	7% 5% 1 3 3 2 3 3 5% 6% 62%	2470
December	1st to 10th	Night	7% 4 1 3 2 3 3 3 5% 6% 62%	2470
	11th to 20th	Night	6% 5% 2 5% 3 3 3 3 5% 7% 59%	3036
	21st to end	Night	4 5% 2 5% 3 3 3 3 4 5% 63%	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% 3 4 20% 29% 14%	2848
	11th to 20th	Day	18% 3 6% 23% 36% 14%	2987
	21st to end	Day	31% 3 6% 18% 32% 10%	3487
February	1st to 10th	Day	24% 3 6% 20% 29% 19%	1900
	11th to 20th	Day	26% 3 5% 21% 26% 19%	1859
	21st to end	Day	27% 3 3 12% 34% 22%	1570
March	1st to 10th	Day	22% 2 4 11% 31% 30%	3130
	11th to 20th	Day	31% 4 6% 21% 27% 12%	3321
	21st to end	Day	24% 5% 6% 20% 28% 17%	4005
April	1st to 10th	Day	20% 3 5% 16% 29% 26%	2280
	11th to 20th	Day	26% 4 6% 15% 26% 24%	2254
	21st to end	Day	19% 4 7% 21% 31% 18%	2280
May	1st to 10th	Day	24% 5% 5% 15% 23% 28%	4046
	11th to 20th	Day	27% 5% 8% 19% 20% 21%	4086
	21st to end	Day	24% 5% 7% 16% 18% 29%	4489
June	1st to 10th	Day	21% 5% 15% 29% 19% 10%	2470
	11th to 20th	Day	20% 4 9% 21% 27% 18%	2470
	21st to end	Day	20% 6% 10% 27% 25% 12%	2470
July	1st to 10th	Day	31% 6% 12% 24% 19% 7%	4056
	11th to 20th	Day	20% 5% 12% 32% 26% 5%	4051
	21st to end	Day	21% 6% 12% 28% 28% 6%	4210
August	1st to 10th	Day	13% 4 12% 28% 31% 11%	3772
	11th to 20th	Day	16% 5% 10% 27% 31% 10%	3762
	21st to end	Day	24% 5% 12% 28% 26% 7%	4179
September	1st to 10th	Day	30% 5% 11% 19% 22% 12%	2263
	11th to 20th	Day	32% 5% 9% 23% 24% 7%	2090
	21st to end	Day	24% 3 7% 19% 34% 14%	2090
October	1st to 10th	Day	24% 4 9% 21% 25% 17%	2090
	11th to 20th	Day	22% 2 5% 15% 30% 26%	2086
	21st to end	Day	22% 3 4 20% 31% 19%	1881
November	1st to 10th	Day	19% 3 6% 18% 32% 22%	1673
	11th to 20th	Day	18% 3 5% 21% 36% 18%	1710
	21st to end	Day	25% 3 5% 16% 31% 21%	1710
December	1st to 10th	Day	26% 2 6% 24% 28% 13%	1710
	11th to 20th	Day	26% 3 7% 20% 26% 17%	2159
	21st to end	Day	23% 2 6% 19% 33% 17%	3135
January	1st to 10th	Night	23% 4 6% 25% 30% 12%	4108
	11th to 20th	Night	16% 3 12% 21% 35% 12%	4010
	21st to end	Night	27% 5% 7% 20% 29% 12%	4180
February	1st to 10th	Night	25% 3 6% 16% 29% 22%	2280
	11th to 20th	Night	26% 3 6% 19% 25% 22%	2218
	21st to end	Night	23% 4 4 14% 26% 29%	1884
March	1st to 10th	Night	22% 3 4 12% 25% 34%	3734
	11th to 20th	Night	26% 4 9% 22% 21% 18%	3642
	21st to end	Night	23% 5% 7% 25% 23% 18%	3615
April	1st to 10th	Night	20% 4 7% 16% 27% 27%	1900
	11th to 20th	Night	22% 3 9% 18% 25% 23%	1877
	21st to end	Night	19% 4 9% 21% 27% 19%	1900
May	1st to 10th	Night	21% 4 7% 20% 17% 30%	2921
	11th to 20th	Night	21% 7% 10% 19% 20% 22%	2824
	21st to end	Night	21% 6% 9% 14% 14% 36%	3099
June	1st to 10th	Night	20% 7% 16% 28% 18% 10%	1710
	11th to 20th	Night	16% 5% 13% 23% 27% 17%	1710
	21st to end	Night	15% 6% 14% 29% 21% 15%	1710
July	1st to 10th	Night	24% 7% 13% 35% 18% 3	2805
	11th to 20th	Night	19% 5% 12% 27% 30% 6%	2796
	21st to end	Night	17% 5% 12% 28% 33% 5%	3110
August	1st to 10th	Night	15% 4 10% 28% 32% 11%	3144
	11th to 20th	Night	20% 5% 9% 25% 32% 9%	3143
	21st to end	Night	18% 4 15% 28% 28% 6%	3487
September	1st to 10th	Night	27% 6% 10% 20% 26% 11%	1915
	11th to 20th	Night	28% 5% 13% 19% 27% 8%	2090
	21st to end	Night	22% 3 7% 21% 30% 17%	2090
October	1st to 10th	Night	21% 5% 10% 20% 22% 22%	2090
	11th to 20th	Night	19% 3 5% 17% 30% 26%	2090
	21st to end	Night	19% 3 5% 18% 33% 22%	2519
November	1st to 10th	Night	16% 2 6% 21% 33% 21%	2405
	11th to 20th	Night	15% 2 6% 20% 37% 20%	2470
	21st to end	Night	23% 3 5% 16% 34% 20%	2470
December	1st to 10th	Night	24% 2 6% 22% 28% 18%	2470
	11th to 20th	Night	26% 3 5% 19% 30% 17%	3037
	21st to end	Night	23% 3 4 19% 33% 17%	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	12% 10% 30% 31% 14% 2	270
	11th to 20th	Day	7% 13% 34% 33% 12% 2	270
	21st to end	Day	7% 8% 35% 32% 17% 1	297
February	1st to 10th	Day	9% 8% 38% 34% 10% 1	270
	11th to 20th	Day	8% 11% 40% 31% 10% 1	270
	21st to end	Day	9% 14% 45% 26% 6% 1	225
March	1st to 10th	Day	8% 7% 39% 34% 12%	270
	11th to 20th	Day	15% 7% 31% 32% 13% 2	270
	21st to end	Day	7% 13% 41% 29% 9% 1	411
April	1st to 10th	Day	8% 12% 45% 25% 9% 1	460
	11th to 20th	Day	11% 10% 45% 28% 5% 1	452
	21st to end	Day	7% 11% 38% 33% 10% 2	460
May	1st to 10th	Day	6% 8% 38% 35% 12% 2	605
	11th to 20th	Day	13% 5% 30% 31% 17% 4	675
	21st to end	Day	8% 7% 31% 34% 18% 2	734
June	1st to 10th	Day	5% 3 16% 44% 28% 4	680
	11th to 20th	Day	5% 2 23% 41% 24% 5%	680
	21st to end	Day	3 1 13% 39% 36% 9%	680
July	1st to 10th	Day	5% 2 5% 33% 37% 18%	671
	11th to 20th	Day	3 1 3 31% 45% 16%	668
	21st to end	Day	3 3 26% 48% 20%	670
August	1st to 10th	Day	2 1 4 31% 43% 18%	487
	11th to 20th	Day	5% 2 5% 28% 39% 21%	477
	21st to end	Day	6% 1 4 25% 40% 24%	539
September	1st to 10th	Day	8% 1 5% 32% 36% 18%	473
	11th to 20th	Day	1 2 5% 35% 42% 16%	300
	21st to end	Day	12% 2 10% 23% 39% 14%	300
October	1st to 10th	Day	10% 2 14% 35% 30% 9%	300
	11th to 20th	Day	8% 3 21% 37% 25% 6%	300
	21st to end	Day	14% 4 25% 26% 25% 6%	306
November	1st to 10th	Day	13% 4 24% 33% 23% 3	270
	11th to 20th	Day	5% 9% 23% 36% 21% 6%	270
	21st to end	Day	16% 10% 34% 25% 13% 3	270
December	1st to 10th	Day	10% 5% 35% 31% 18% 1	270
	11th to 20th	Day	7% 9% 30% 41% 13% 1	270
	21st to end	Day	10% 8% 44% 27% 9% 1	297
January	1st to 10th	Night	7% 8% 35% 40% 9% 1	950
	11th to 20th	Night	6% 7% 37% 38% 10% 1	879
	21st to end	Night	6% 7% 38% 39% 9%	836
February	1st to 10th	Night	9% 7% 43% 32% 8% 1	760
	11th to 20th	Night	8% 9% 44% 33% 6% 1	744
	21st to end	Night	8% 11% 47% 32% 3	628
March	1st to 10th	Night	8% 11% 41% 35% 5%	760
	11th to 20th	Night	10% 11% 41% 31% 6%	667
	21st to end	Night	5% 12% 48% 30% 4	627
April	1st to 10th	Night	5% 11% 48% 32% 3	570
	11th to 20th	Night	6% 9% 54% 28% 3	563
	21st to end	Night	6% 8% 51% 30% 4	570
May	1st to 10th	Night	6% 5% 49% 37% 3	570
	11th to 20th	Night	8% 5% 35% 38% 13% 1	561
	21st to end	Night	9% 4 40% 38% 9%	617
June	1st to 10th	Night	4 2 31% 51% 12%	570
	11th to 20th	Night	2 2 39% 46% 10%	570
	21st to end	Night	3 1 23% 52% 21%	570
July	1st to 10th	Night	5% 1 10% 48% 34% 3	555
	11th to 20th	Night	3 1 6% 50% 39% 1	552
	21st to end	Night	2 1 4 44% 48% 2	624
August	1st to 10th	Night	2 1 7% 47% 42% 2	567
	11th to 20th	Night	4 1 6% 47% 40% 2	564
	21st to end	Night	4 5% 44% 44% 2	627
September	1st to 10th	Night	8% 1 8% 46% 35% 2	570
	11th to 20th	Night	11% 1 11% 48% 28% 1	570
	21st to end	Night	8% 2 18% 40% 30% 2	570
October	1st to 10th	Night	6% 2 25% 46% 21% 1	570
	11th to 20th	Night	10% 4 29% 43% 13% 1	570
	21st to end	Night	10% 5% 27% 36% 20% 2	911
November	1st to 10th	Night	7% 4 27% 45% 16% 1	925
	11th to 20th	Night	4 6% 31% 42% 15% 2	950
	21st to end	Night	10% 7% 30% 38% 14% 1	950
December	1st to 10th	Night	9% 7% 33% 41% 10% 1	950
	11th to 20th	Night	10% 7% 39% 35% 9%	950
	21st to end	Night	10% 8% 37% 36% 9% 1	1045

Page generated at 2024-10-21 01:19:59. Version ac07

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