COSMIC OBSERVATORY
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the COSMIC OBSERVATORY clear sky chart from 2005-11-06 to 2025-02-06.

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	12% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	108414
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	109813
Transparency	Day	39% 7% 11% 22% 16% 4	112064
	Night	37% 7% 12% 23% 18% 4	114302
Seeing	Day	17% 12% 24% 25% 16% 6%	15229
	Night	16% 8% 25% 34% 15% 2	25124

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	12% 7% 3 7% 4 4 4 3 4 5% 48%	4056
	11th to 20th	Day	11% 7% 3 8% 5% 4 3 3 4 5% 48%	4060
	21st to end	Day	14% 7% 3 6% 4 4 4 3 5% 5% 46%	4466
February	1st to 10th	Day	11% 8% 3 8% 5% 5% 5% 4 5% 6% 40%	1755
	11th to 20th	Day	14% 7% 2 7% 5% 4 4 4 5% 6% 42%	1663
	21st to end	Day	16% 8% 3 5% 4 4 5% 3 5% 6% 41%	1631
March	1st to 10th	Day	18% 9% 3 7% 4 5% 4 3 5% 6% 36%	3435
	11th to 20th	Day	9% 6% 2 6% 4 3 4 4 5% 6% 52%	3480
	21st to end	Day	14% 9% 3 7% 5% 5% 4 3 5% 5% 39%	3815
April	1st to 10th	Day	10% 6% 2 5% 5% 5% 5% 4 6% 6% 46%	2223
	11th to 20th	Day	13% 6% 2 6% 3 4 4 3 5% 7% 47%	2254
	21st to end	Day	15% 7% 3 6% 5% 4 5% 3 4 6% 43%	2357
May	1st to 10th	Day	17% 6% 3 8% 6% 6% 6% 4 6% 8% 30%	4082
	11th to 20th	Day	20% 7% 3 6% 4 5% 5% 3 4 7% 34%	4081
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 9% 40%	4653
June	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 5% 6% 9% 43%	2660
	11th to 20th	Day	9% 5% 2 6% 6% 6% 7% 5% 8% 10% 37%	2660
	21st to end	Day	7% 4 2 6% 5% 5% 5% 4 8% 11% 42%	2660
July	1st to 10th	Day	6% 4 2 8% 5% 5% 6% 5% 8% 10% 41%	4168
	11th to 20th	Day	8% 5% 2 6% 6% 6% 7% 5% 9% 12% 34%	4120
	21st to end	Day	11% 7% 3 9% 6% 6% 6% 5% 8% 10% 29%	4466
August	1st to 10th	Day	12% 5% 2 7% 5% 6% 6% 6% 9% 10% 31%	4104
	11th to 20th	Day	7% 5% 2 7% 5% 6% 7% 6% 9% 9% 37%	4019
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 7% 10% 46%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 5% 7% 46%	2280
	11th to 20th	Day	12% 7% 2 6% 4 4 5% 4 6% 8% 44%	2163
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 7% 37%	2046
October	1st to 10th	Day	15% 6% 2 5% 3 4 4 3 5% 8% 46%	1900
	11th to 20th	Day	14% 5% 2 5% 4 3 3 3 5% 6% 50%	1900
	21st to end	Day	13% 5% 2 4 4 3 4 3 5% 6% 51%	2090
November	1st to 10th	Day	11% 6% 2 4 2 4 3 3 5% 6% 54%	1957
	11th to 20th	Day	12% 6% 2 5% 4 3 3 4 5% 6% 50%	1760
	21st to end	Day	13% 5% 1 5% 3 4 4 3 5% 6% 49%	1600
December	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 4 7% 51%	2600
	11th to 20th	Day	18% 5% 2 5% 4 4 3 2 5% 7% 45%	2990
	21st to end	Day	16% 8% 3 6% 4 5% 5% 4 6% 8% 35%	4080
January	1st to 10th	Night	10% 7% 2 5% 4 4 4 4 5% 5% 51%	5889
	11th to 20th	Night	12% 8% 2 4 3 3 3 3 4 5% 53%	5900
	21st to end	Night	15% 8% 2 5% 3 3 3 2 4 5% 51%	6490
February	1st to 10th	Night	11% 9% 2 6% 4 4 5% 4 5% 6% 44%	2536
	11th to 20th	Night	17% 8% 2 5% 5% 3 4 4 5% 6% 41%	2403
	21st to end	Night	14% 8% 3 6% 5% 3 5% 3 6% 7% 41%	1819
March	1st to 10th	Night	20% 8% 3 7% 4 4 4 3 5% 6% 36%	3418
	11th to 20th	Night	9% 5% 2 7% 4 4 4 3 4 7% 51%	3480
	21st to end	Night	14% 7% 2 5% 4 4 3 2 4 6% 48%	3817
April	1st to 10th	Night	14% 8% 3 4 4 5% 4 4 6% 6% 44%	1956
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 7% 8% 46%	1875
	21st to end	Night	16% 5% 2 5% 4 4 4 4 5% 7% 45%	1838
May	1st to 10th	Night	18% 7% 3 7% 4 5% 5% 4 6% 7% 33%	2813
	11th to 20th	Night	22% 7% 2 7% 5% 5% 4 4 5% 6% 34%	2812
	21st to end	Night	11% 5% 2 5% 4 5% 5% 4 7% 10% 43%	2898
June	1st to 10th	Night	9% 5% 1 6% 4 4 5% 3 7% 11% 44%	1520
	11th to 20th	Night	9% 5% 2 7% 5% 4 5% 4 8% 9% 43%	1520
	21st to end	Night	8% 5% 1 5% 4 4 6% 5% 8% 10% 44%	1520
July	1st to 10th	Night	6% 4 2 6% 6% 5% 5% 5% 8% 11% 42%	2772
	11th to 20th	Night	7% 6% 3 8% 5% 6% 6% 5% 8% 9% 37%	2840
	21st to end	Night	8% 8% 3 9% 6% 6% 6% 4 8% 9% 31%	3087
August	1st to 10th	Night	14% 6% 3 6% 5% 5% 5% 5% 7% 10% 32%	2825
	11th to 20th	Night	9% 7% 2 8% 5% 7% 7% 5% 7% 8% 36%	2785
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 10% 46%	3467
September	1st to 10th	Night	12% 5% 2 6% 5% 4 4 4 5% 7% 47%	1900
	11th to 20th	Night	13% 5% 2 6% 4 5% 4 4 5% 7% 45%	2013
	21st to end	Night	21% 8% 2 5% 3 4 4 3 4 5% 41%	2133
October	1st to 10th	Night	16% 6% 2 5% 3 4 4 4 6% 7% 44%	2280
	11th to 20th	Night	13% 5% 1 6% 3 4 4 3 4 6% 51%	2280
	21st to end	Night	13% 4 1 5% 4 3 4 3 4 6% 52%	2508
November	1st to 10th	Night	11% 7% 2 5% 4 3 4 3 4 5% 53%	2341
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 5% 6% 49%	2635
	21st to end	Night	13% 5% 2 4 4 4 4 4 5% 6% 49%	2800
December	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 6% 51%	4580
	11th to 20th	Night	15% 8% 3 7% 4 4 4 4 4 6% 41%	5205
	21st to end	Night	15% 7% 2 6% 5% 5% 5% 5% 7% 8% 36%	6858

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	39% 4 5% 19% 24% 9%	4057
	11th to 20th	Day	39% 4 5% 17% 20% 14%	4060
	21st to end	Day	41% 4 7% 23% 21% 4	4466
February	1st to 10th	Day	44% 5% 11% 21% 16% 4	1755
	11th to 20th	Day	43% 5% 8% 21% 18% 4	1672
	21st to end	Day	43% 7% 12% 17% 17% 6%	1631
March	1st to 10th	Day	48% 6% 9% 19% 13% 5%	3435
	11th to 20th	Day	32% 5% 9% 25% 22% 7%	3480
	21st to end	Day	46% 7% 10% 19% 14% 4	3815
April	1st to 10th	Day	37% 7% 11% 20% 18% 7%	2223
	11th to 20th	Day	37% 6% 11% 21% 20% 5%	2254
	21st to end	Day	42% 6% 12% 22% 14% 4	2357
May	1st to 10th	Day	49% 9% 11% 20% 10% 1	4120
	11th to 20th	Day	49% 9% 11% 21% 9% 1	4085
	21st to end	Day	34% 12% 14% 20% 15% 4	4667
June	1st to 10th	Day	37% 9% 14% 24% 15% 1	2660
	11th to 20th	Day	39% 11% 15% 21% 13% 2	2660
	21st to end	Day	32% 12% 15% 26% 13% 1	2660
July	1st to 10th	Day	36% 10% 17% 20% 10% 6%	4103
	11th to 20th	Day	38% 12% 16% 26% 8% 1	4051
	21st to end	Day	47% 10% 10% 21% 11% 1	4324
August	1st to 10th	Day	44% 12% 16% 21% 7%	4091
	11th to 20th	Day	38% 10% 12% 27% 13% 1	4058
	21st to end	Day	32% 10% 17% 27% 13% 1	4180
September	1st to 10th	Day	38% 9% 12% 18% 19% 5%	2280
	11th to 20th	Day	38% 7% 8% 26% 19% 3	2163
	21st to end	Day	47% 6% 10% 19% 16% 3	2046
October	1st to 10th	Day	32% 6% 8% 20% 28% 6%	3160
	11th to 20th	Day	25% 4 9% 28% 22% 12%	3140
	21st to end	Day	22% 4 9% 30% 23% 11%	3428
November	1st to 10th	Day	31% 5% 9% 26% 25% 5%	1957
	11th to 20th	Day	34% 5% 10% 20% 23% 8%	1760
	21st to end	Day	36% 4 9% 25% 22% 3	1600
December	1st to 10th	Day	34% 5% 10% 24% 20% 6%	2600
	11th to 20th	Day	40% 4 12% 22% 17% 5%	2986
	21st to end	Day	45% 7% 13% 19% 15% 1	4080
January	1st to 10th	Night	33% 5% 8% 21% 26% 7%	5889
	11th to 20th	Night	34% 5% 6% 22% 23% 11%	5900
	21st to end	Night	37% 4 7% 26% 22% 5%	6490
February	1st to 10th	Night	39% 6% 12% 25% 16% 2	2536
	11th to 20th	Night	43% 5% 9% 21% 17% 6%	2405
	21st to end	Night	42% 6% 13% 21% 14% 6%	1819
March	1st to 10th	Night	47% 6% 9% 22% 13% 3	3418
	11th to 20th	Night	30% 6% 8% 25% 27% 4	3480
	21st to end	Night	38% 5% 11% 22% 19% 4	3817
April	1st to 10th	Night	39% 6% 11% 20% 19% 5%	1956
	11th to 20th	Night	33% 7% 15% 21% 20% 5%	1875
	21st to end	Night	38% 6% 13% 26% 15% 3	1838
May	1st to 10th	Night	48% 10% 11% 20% 10% 2	2840
	11th to 20th	Night	48% 8% 11% 23% 9% 1	2813
	21st to end	Night	33% 10% 18% 26% 10% 3	2905
June	1st to 10th	Night	33% 10% 16% 27% 13% 1	1520
	11th to 20th	Night	35% 11% 15% 25% 12% 2	1520
	21st to end	Night	30% 12% 17% 22% 17% 2	1520
July	1st to 10th	Night	34% 11% 23% 17% 13% 2	2727
	11th to 20th	Night	38% 12% 18% 22% 9% 1	2786
	21st to end	Night	45% 10% 17% 19% 9%	2988
August	1st to 10th	Night	43% 11% 17% 22% 6% 1	2814
	11th to 20th	Night	41% 9% 14% 23% 12%	2812
	21st to end	Night	33% 8% 17% 30% 10% 2	3467
September	1st to 10th	Night	35% 8% 14% 21% 17% 4	1900
	11th to 20th	Night	37% 7% 9% 27% 18% 3	2013
	21st to end	Night	45% 6% 9% 20% 17% 2	2133
October	1st to 10th	Night	41% 5% 10% 20% 20% 4	3800
	11th to 20th	Night	25% 5% 11% 21% 30% 8%	3779
	21st to end	Night	21% 4 10% 30% 28% 7%	4120
November	1st to 10th	Night	34% 5% 9% 23% 23% 6%	2341
	11th to 20th	Night	35% 5% 9% 22% 23% 6%	2635
	21st to end	Night	35% 5% 11% 24% 21% 4	2800
December	1st to 10th	Night	32% 6% 10% 26% 22% 3	4580
	11th to 20th	Night	44% 4 11% 18% 16% 6%	5208
	21st to end	Night	41% 7% 12% 22% 16% 1	6858

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% 29% 28% 17% 4 1	300
	11th to 20th	Day	23% 29% 28% 18% 2	300
	21st to end	Day	22% 26% 32% 16% 3 1	330
February	1st to 10th	Day	22% 24% 34% 15% 4	285
	11th to 20th	Day	30% 27% 34% 7% 1	270
	21st to end	Day	27% 19% 34% 16% 4	343
March	1st to 10th	Day	18% 23% 30% 22% 6%	460
	11th to 20th	Day	18% 23% 32% 19% 6% 2	460
	21st to end	Day	20% 18% 31% 23% 8% 1	506
April	1st to 10th	Day	20% 23% 27% 22% 8% 1	460
	11th to 20th	Day	17% 14% 28% 24% 13% 4	452
	21st to end	Day	21% 15% 30% 21% 11% 3	460
May	1st to 10th	Day	19% 17% 25% 24% 11% 5%	463
	11th to 20th	Day	21% 10% 26% 23% 15% 4	487
	21st to end	Day	16% 7% 19% 28% 20% 10%	529
June	1st to 10th	Day	12% 7% 23% 29% 21% 7%	490
	11th to 20th	Day	11% 7% 22% 30% 20% 11%	490
	21st to end	Day	8% 5% 22% 38% 20% 7%	490
July	1st to 10th	Day	10% 4 15% 30% 28% 13%	485
	11th to 20th	Day	5% 2 13% 36% 31% 13%	484
	21st to end	Day	12% 3 13% 34% 27% 12%	532
August	1st to 10th	Day	12% 6% 15% 28% 26% 14%	486
	11th to 20th	Day	13% 4 14% 30% 25% 14%	479
	21st to end	Day	11% 2 10% 30% 28% 18%	539
September	1st to 10th	Day	13% 7% 15% 24% 25% 16%	490
	11th to 20th	Day	14% 4 15% 25% 30% 12%	490
	21st to end	Day	28% 8% 17% 23% 19% 5%	490
October	1st to 10th	Day	20% 7% 16% 29% 23% 6%	490
	11th to 20th	Day	13% 13% 25% 28% 18% 4	490
	21st to end	Day	15% 12% 30% 28% 12% 3	539
November	1st to 10th	Day	17% 7% 29% 31% 14% 3	495
	11th to 20th	Day	17% 15% 30% 25% 12% 2	318
	21st to end	Day	17% 20% 32% 23% 8% 2	200
December	1st to 10th	Day	20% 19% 34% 21% 6% 2	200
	11th to 20th	Day	25% 15% 30% 20% 9% 2	200
	21st to end	Day	21% 17% 33% 19% 9% 1	247
January	1st to 10th	Night	18% 16% 36% 26% 4	800
	11th to 20th	Night	19% 14% 31% 32% 4	800
	21st to end	Night	17% 11% 42% 27% 3	880
February	1st to 10th	Night	17% 12% 35% 33% 3	781
	11th to 20th	Night	23% 16% 37% 22% 1	743
	21st to end	Night	22% 13% 37% 25% 3	628
March	1st to 10th	Night	17% 12% 37% 30% 4	760
	11th to 20th	Night	20% 15% 33% 25% 7% 1	760
	21st to end	Night	20% 10% 32% 31% 6% 1	836
April	1st to 10th	Night	17% 17% 31% 28% 7%	760
	11th to 20th	Night	14% 11% 32% 31% 12% 1	751
	21st to end	Night	18% 7% 29% 36% 9% 1	698
May	1st to 10th	Night	18% 7% 23% 34% 17% 1	570
	11th to 20th	Night	19% 4 23% 36% 17% 2	561
	21st to end	Night	14% 3 15% 39% 27% 2	513
June	1st to 10th	Night	9% 2 17% 47% 23% 2	380
	11th to 20th	Night	9% 3 14% 45% 27% 2	380
	21st to end	Night	8% 2 13% 49% 25% 2	380
July	1st to 10th	Night	12% 2 8% 36% 36% 6%	513
	11th to 20th	Night	5% 1 9% 37% 43% 5%	552
	21st to end	Night	8% 3 7% 41% 36% 5%	624
August	1st to 10th	Night	11% 2 8% 40% 35% 4	567
	11th to 20th	Night	13% 3 8% 38% 35% 3	564
	21st to end	Night	13% 2 10% 36% 35% 5%	827
September	1st to 10th	Night	14% 3 11% 34% 32% 6%	760
	11th to 20th	Night	14% 4 11% 35% 31% 5%	760
	21st to end	Night	24% 5% 17% 31% 22% 2	760
October	1st to 10th	Night	18% 6% 18% 31% 24% 4	760
	11th to 20th	Night	16% 7% 26% 34% 16% 1	760
	21st to end	Night	15% 9% 25% 36% 14% 2	836
November	1st to 10th	Night	15% 7% 22% 41% 13% 2	780
	11th to 20th	Night	15% 12% 25% 37% 10% 1	800
	21st to end	Night	15% 11% 30% 34% 9% 1	800
December	1st to 10th	Night	19% 9% 33% 33% 6%	800
	11th to 20th	Night	16% 10% 32% 36% 6%	800
	21st to end	Night	17% 11% 29% 39% 5%	880

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