Cosmos Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cosmos Observatory clear sky chart from 2005-11-06 to 2024-03-08.

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	3 3 2 4 4 2 4 5% 6% 8% 60%	78760
	Night	3 3 1 3 4 2 4 4 5% 8% 62%	80861
Transparency	Day	21% 5% 9% 20% 27% 17%	78480
	Night	21% 5% 9% 21% 28% 16%	80663
Seeing	Day	9% 19% 29% 26% 14% 3	14170
	Night	6% 14% 30% 32% 16% 2	24441

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	1 5% 2 4 4 2 3 4 5% 7% 62%	2728
	11th to 20th	Day	2 3 1 2 3 1 2 4 4 5% 73%	2860
	21st to end	Day	3 6% 2 5% 4 3 4 5% 6% 8% 55%	3146
February	1st to 10th	Day	2 5% 3 4 3 2 3 4 5% 6% 63%	1779
	11th to 20th	Day	2 4 2 4 4 2 3 4 5% 8% 63%	1849
	21st to end	Day	1 5% 2 4 3 2 3 3 4 6% 65%	1570
March	1st to 10th	Day	1 4 1 3 3 2 4 4 6% 9% 63%	1918
	11th to 20th	Day	4 5% 3 4 4 2 3 3 5% 6% 61%	1980
	21st to end	Day	3 4 2 3 4 2 4 3 6% 7% 63%	2276
April	1st to 10th	Day	3 3 1 2 2 2 3 4 5% 9% 66%	2160
	11th to 20th	Day	4 4 2 4 4 2 3 4 5% 7% 62%	2131
	21st to end	Day	3 3 1 3 3 2 3 4 5% 8% 65%	2160
May	1st to 10th	Day	4 4 1 3 4 3 4 4 5% 7% 63%	2160
	11th to 20th	Day	5% 4 2 4 4 3 4 4 5% 8% 57%	2208
	21st to end	Day	4 3 1 3 3 2 4 4 6% 8% 62%	2724
June	1st to 10th	Day	2 2 1 3 4 2 5% 7% 6% 9% 60%	2520
	11th to 20th	Day	2 1 1 3 3 2 4 4 6% 6% 68%	2520
	21st to end	Day	5% 3 1 3 4 3 6% 6% 6% 7% 55%	2520
July	1st to 10th	Day	5% 3 2 6% 5% 4 8% 7% 8% 9% 43%	2520
	11th to 20th	Day	3 3 2 4 6% 4 6% 8% 9% 11% 44%	2368
	21st to end	Day	5% 4 2 5% 8% 5% 9% 8% 9% 10% 35%	2545
August	1st to 10th	Day	5% 3 2 4 6% 4 7% 7% 9% 11% 42%	2226
	11th to 20th	Day	6% 4 2 5% 6% 4 7% 8% 7% 11% 41%	2123
	21st to end	Day	4 4 2 5% 5% 5% 5% 6% 7% 10% 48%	2376
September	1st to 10th	Day	6% 4 2 5% 5% 4 5% 5% 6% 8% 50%	2160
	11th to 20th	Day	7% 3 2 3 4 2 5% 5% 5% 8% 56%	2156
	21st to end	Day	4 2 2 3 3 2 3 4 4 7% 68%	1980
October	1st to 10th	Day	8% 4 2 4 4 2 3 4 4 7% 58%	1806
	11th to 20th	Day	3 3 1 2 3 1 2 2 2 4 77%	1800
	21st to end	Day	4 3 1 3 2 2 2 3 4 4 72%	1980
November	1st to 10th	Day	2 2 1 2 2 1 3 3 4 8% 72%	1760
	11th to 20th	Day	1 3 2 3 1 1 3 3 6% 7% 70%	1710
	21st to end	Day	5% 4 2 2 3 2 3 4 4 6% 65%	1710
December	1st to 10th	Day	2 4 2 3 2 2 4 4 4 8% 65%	1611
	11th to 20th	Day	3 3 2 4 4 3 4 4 4 8% 61%	1926
	21st to end	Day	2 4 2 3 3 2 3 3 4 8% 66%	2794
January	1st to 10th	Night	1 5% 2 4 5% 3 4 4 5% 6% 61%	4256
	11th to 20th	Night	2 3 1 3 3 2 3 3 3 5% 71%	4110
	21st to end	Night	2 4 2 3 4 3 4 5% 6% 9% 58%	4521
February	1st to 10th	Night	2 5% 2 4 3 2 3 3 4 7% 65%	2399
	11th to 20th	Night	3 5% 1 3 3 2 3 3 4 8% 64%	2218
	21st to end	Night	2 5% 2 2 3 2 2 3 4 7% 68%	1884
March	1st to 10th	Night	1 3 2 3 4 2 3 4 4 7% 67%	2199
	11th to 20th	Night	3 5% 3 4 3 3 3 3 4 8% 60%	1980
	21st to end	Night	3 4 1 3 3 2 3 3 5% 7% 66%	2080
April	1st to 10th	Night	3 3 1 2 2 2 3 3 4 8% 69%	1800
	11th to 20th	Night	4 4 2 3 3 2 4 3 4 6% 65%	1777
	21st to end	Night	3 3 1 3 3 2 4 3 5% 6% 68%	1800
May	1st to 10th	Night	3 3 1 3 3 2 4 3 5% 7% 66%	1800
	11th to 20th	Night	6% 4 2 5% 4 3 5% 4 6% 6% 55%	1681
	21st to end	Night	5% 2 1 2 4 2 3 4 5% 7% 65%	1552
June	1st to 10th	Night	3 3 2 3 4 3 5% 6% 7% 10% 54%	1440
	11th to 20th	Night	2 2 1 2 2 2 4 4 5% 7% 69%	1440
	21st to end	Night	6% 3 2 3 5% 4 5% 5% 6% 10% 52%	1440
July	1st to 10th	Night	5% 5% 2 4 7% 4 6% 6% 7% 8% 46%	1440
	11th to 20th	Night	3 3 1 4 5% 4 5% 8% 9% 13% 45%	1587
	21st to end	Night	5% 4 3 4 5% 4 6% 8% 9% 12% 40%	1773
August	1st to 10th	Night	4 3 2 4 7% 5% 6% 9% 8% 12% 41%	1708
	11th to 20th	Night	4 4 3 4 7% 4 7% 7% 8% 12% 41%	1778
	21st to end	Night	4 3 1 4 5% 4 5% 6% 8% 13% 46%	1980
September	1st to 10th	Night	5% 3 2 3 6% 3 4 6% 8% 7% 52%	1800
	11th to 20th	Night	6% 5% 1 4 4 3 4 5% 5% 8% 56%	1804
	21st to end	Night	5% 3 1 3 4 2 3 4 5% 6% 64%	1980
October	1st to 10th	Night	9% 4 2 3 3 2 3 3 4 5% 61%	2150
	11th to 20th	Night	3 2 1 2 2 1 2 2 3 5% 77%	2160
	21st to end	Night	4 3 1 2 3 2 2 2 4 5% 72%	2376
November	1st to 10th	Night	2 3 1 2 2 1 2 3 4 5% 76%	2297
	11th to 20th	Night	1 2 1 2 2 2 3 4 4 6% 74%	2470
	21st to end	Night	5% 4 2 2 2 2 3 4 4 6% 65%	2470
December	1st to 10th	Night	3 3 1 3 3 2 3 3 5% 8% 66%	2567
	11th to 20th	Night	3 3 2 3 4 3 4 5% 5% 8% 62%	3271
	21st to end	Night	3 4 1 3 4 2 3 3 5% 6% 65%	4873

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	21% 3 7% 25% 34% 9%	2729
	11th to 20th	Day	12% 4 8% 31% 37% 7%	2860
	21st to end	Day	25% 5% 9% 20% 32% 10%	3146
February	1st to 10th	Day	21% 3 7% 21% 32% 15%	1779
	11th to 20th	Day	20% 3 7% 23% 28% 19%	1859
	21st to end	Day	18% 3 5% 16% 35% 23%	1570
March	1st to 10th	Day	18% 3 6% 20% 33% 20%	1918
	11th to 20th	Day	24% 3 7% 17% 33% 16%	1980
	21st to end	Day	20% 3 6% 21% 33% 15%	2276
April	1st to 10th	Day	16% 3 6% 21% 33% 21%	2160
	11th to 20th	Day	21% 4 6% 19% 29% 22%	2134
	21st to end	Day	17% 3 8% 22% 35% 15%	2160
May	1st to 10th	Day	20% 4 6% 18% 29% 23%	2160
	11th to 20th	Day	26% 6% 10% 19% 23% 17%	2212
	21st to end	Day	19% 6% 8% 18% 23% 27%	2724
June	1st to 10th	Day	17% 7% 12% 20% 22% 21%	2520
	11th to 20th	Day	15% 4 8% 13% 22% 38%	2520
	21st to end	Day	25% 6% 11% 17% 21% 20%	2520
July	1st to 10th	Day	31% 10% 15% 15% 15% 14%	2451
	11th to 20th	Day	26% 11% 16% 25% 15% 8%	2297
	21st to end	Day	35% 13% 18% 24% 9% 1	2404
August	1st to 10th	Day	29% 10% 18% 20% 12% 9%	2211
	11th to 20th	Day	33% 10% 12% 21% 15% 9%	2123
	21st to end	Day	26% 10% 15% 21% 22% 5%	2376
September	1st to 10th	Day	29% 7% 11% 20% 23% 10%	2160
	11th to 20th	Day	25% 6% 9% 20% 22% 19%	2156
	21st to end	Day	17% 4 6% 22% 33% 18%	1980
October	1st to 10th	Day	27% 4 8% 17% 26% 18%	1806
	11th to 20th	Day	14% 2 4 14% 33% 34%	1800
	21st to end	Day	17% 3 5% 19% 36% 21%	1980
November	1st to 10th	Day	12% 3 5% 19% 40% 21%	1760
	11th to 20th	Day	14% 2 6% 23% 39% 15%	1710
	21st to end	Day	20% 3 4 18% 32% 23%	1710
December	1st to 10th	Day	18% 3 9% 29% 28% 13%	1611
	11th to 20th	Day	21% 3 9% 22% 29% 15%	1924
	21st to end	Day	17% 2 6% 19% 33% 22%	2794
January	1st to 10th	Night	22% 3 8% 24% 33% 10%	4256
	11th to 20th	Night	17% 4 7% 30% 32% 12%	4110
	21st to end	Night	20% 5% 10% 24% 32% 9%	4521
February	1st to 10th	Night	19% 3 9% 23% 30% 16%	2399
	11th to 20th	Night	19% 4 7% 23% 29% 17%	2218
	21st to end	Night	17% 3 4 17% 34% 25%	1884
March	1st to 10th	Night	17% 3 6% 23% 31% 20%	2199
	11th to 20th	Night	23% 3 7% 20% 32% 15%	1980
	21st to end	Night	17% 4 8% 20% 34% 16%	2080
April	1st to 10th	Night	16% 3 6% 20% 33% 22%	1800
	11th to 20th	Night	20% 4 6% 18% 29% 23%	1777
	21st to end	Night	16% 4 8% 22% 34% 16%	1800
May	1st to 10th	Night	19% 5% 7% 17% 31% 22%	1800
	11th to 20th	Night	27% 6% 11% 19% 20% 16%	1682
	21st to end	Night	19% 6% 11% 16% 21% 28%	1552
June	1st to 10th	Night	22% 8% 16% 16% 18% 20%	1440
	11th to 20th	Night	15% 3 9% 16% 19% 37%	1440
	21st to end	Night	27% 6% 14% 17% 17% 20%	1440
July	1st to 10th	Night	34% 9% 13% 19% 13% 12%	1400
	11th to 20th	Night	23% 11% 22% 23% 13% 8%	1535
	21st to end	Night	32% 11% 27% 21% 7% 2	1674
August	1st to 10th	Night	30% 10% 21% 18% 11% 8%	1699
	11th to 20th	Night	31% 10% 18% 22% 12% 6%	1778
	21st to end	Night	26% 8% 18% 26% 15% 7%	1980
September	1st to 10th	Night	27% 7% 16% 23% 19% 9%	1800
	11th to 20th	Night	27% 5% 10% 18% 22% 17%	1804
	21st to end	Night	20% 4 9% 19% 31% 18%	1980
October	1st to 10th	Night	25% 5% 7% 19% 21% 22%	2150
	11th to 20th	Night	14% 2 4 14% 33% 33%	2160
	21st to end	Night	16% 2 6% 19% 35% 21%	2376
November	1st to 10th	Night	12% 2 5% 21% 38% 21%	2297
	11th to 20th	Night	12% 3 5% 22% 40% 17%	2470
	21st to end	Night	20% 3 6% 18% 30% 23%	2470
December	1st to 10th	Night	18% 3 8% 28% 29% 13%	2567
	11th to 20th	Night	21% 4 7% 22% 32% 15%	3272
	21st to end	Night	19% 3 7% 23% 31% 17%	4873

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	15% 27% 33% 18% 7%	270
	11th to 20th	Day	16% 31% 30% 18% 5% 1	270
	21st to end	Day	3 25% 40% 20% 9% 2	297
February	1st to 10th	Day	9% 36% 33% 19% 3	270
	11th to 20th	Day	9% 40% 31% 17% 4	270
	21st to end	Day	21% 38% 28% 11% 2	225
March	1st to 10th	Day	10% 37% 32% 16% 5%	309
	11th to 20th	Day	17% 29% 31% 17% 5% 1	420
	21st to end	Day	17% 36% 33% 11% 3 1	462
April	1st to 10th	Day	11% 33% 37% 13% 5% 1	420
	11th to 20th	Day	13% 37% 34% 14% 2	412
	21st to end	Day	12% 33% 37% 15% 3	420
May	1st to 10th	Day	8% 31% 40% 17% 3 1	423
	11th to 20th	Day	8% 16% 38% 26% 9% 2	526
	21st to end	Day	7% 15% 38% 28% 10% 1	679
June	1st to 10th	Day	4 9% 28% 35% 21% 4	630
	11th to 20th	Day	5% 11% 27% 35% 19% 2	630
	21st to end	Day	7% 8% 25% 33% 23% 4	630
July	1st to 10th	Day	6% 2 17% 35% 33% 7%	621
	11th to 20th	Day	6% 1 11% 38% 36% 9%	470
	21st to end	Day	6% 1 8% 33% 41% 10%	487
August	1st to 10th	Day	5% 3 17% 38% 32% 6%	447
	11th to 20th	Day	4 4 22% 40% 24% 6%	437
	21st to end	Day	4 2 22% 40% 24% 7%	495
September	1st to 10th	Day	7% 3 22% 43% 21% 5%	450
	11th to 20th	Day	4 6% 33% 37% 16% 4	446
	21st to end	Day	6% 13% 29% 29% 18% 4	270
October	1st to 10th	Day	11% 17% 30% 22% 16% 4	270
	11th to 20th	Day	10% 19% 33% 25% 11% 3	270
	21st to end	Day	13% 19% 33% 21% 11% 3	297
November	1st to 10th	Day	9% 33% 33% 18% 6% 1	270
	11th to 20th	Day	6% 20% 39% 25% 9% 2	270
	21st to end	Day	14% 27% 30% 18% 10% 1	270
December	1st to 10th	Day	11% 29% 31% 21% 7% 1	270
	11th to 20th	Day	8% 33% 38% 17% 4	270
	21st to end	Day	16% 36% 31% 13% 4	297
January	1st to 10th	Night	4 22% 34% 27% 11% 1	854
	11th to 20th	Night	7% 20% 37% 26% 9% 2	760
	21st to end	Night	5% 20% 38% 27% 10%	836
February	1st to 10th	Night	6% 22% 39% 28% 6%	760
	11th to 20th	Night	7% 25% 38% 25% 6%	744
	21st to end	Night	8% 26% 45% 19% 2	628
March	1st to 10th	Night	5% 23% 38% 27% 6% 1	750
	11th to 20th	Night	8% 18% 30% 34% 10%	720
	21st to end	Night	5% 21% 39% 28% 6%	694
April	1st to 10th	Night	6% 23% 39% 27% 5%	540
	11th to 20th	Night	8% 19% 35% 31% 6%	533
	21st to end	Night	6% 20% 37% 30% 6% 1	540
May	1st to 10th	Night	4 15% 36% 35% 10%	540
	11th to 20th	Night	7% 10% 31% 36% 16% 1	531
	21st to end	Night	5% 11% 35% 37% 11% 1	584
June	1st to 10th	Night	3 6% 24% 45% 21%	540
	11th to 20th	Night	3 5% 30% 44% 17% 1	540
	21st to end	Night	6% 3 21% 41% 28% 1	540
July	1st to 10th	Night	8% 2 7% 43% 36% 4	525
	11th to 20th	Night	3 1 6% 34% 50% 5%	522
	21st to end	Night	6% 1 6% 29% 50% 7%	591
August	1st to 10th	Night	6% 1 7% 31% 46% 8%	537
	11th to 20th	Night	4 2 10% 39% 40% 4	534
	21st to end	Night	4 1 9% 42% 38% 6%	594
September	1st to 10th	Night	5% 3 14% 41% 33% 4	540
	11th to 20th	Night	8% 3 13% 47% 26% 2	540
	21st to end	Night	6% 5% 23% 42% 22% 2	540
October	1st to 10th	Night	8% 7% 23% 42% 18% 2	710
	11th to 20th	Night	5% 10% 32% 37% 13% 3	720
	21st to end	Night	6% 13% 31% 30% 17% 3	792
November	1st to 10th	Night	4 12% 34% 34% 13% 2	817
	11th to 20th	Night	3 16% 36% 33% 11% 2	950
	21st to end	Night	7% 18% 34% 28% 11% 2	950
December	1st to 10th	Night	7% 21% 36% 28% 7% 1	950
	11th to 20th	Night	5% 25% 36% 24% 8%	950
	21st to end	Night	9% 24% 40% 23% 4	1045

Page generated at 2024-03-05 05:24:00. Version ac07

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