Cottageville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cottageville Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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 7% 5% 5% 5% 4 6% 8% 39%	126873
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	123505
Transparency	Day	40% 7% 13% 17% 16% 6%	130519
	Night	37% 7% 13% 18% 18% 7%	127928
Seeing	Day	14% 11% 26% 25% 16% 7%	16906
	Night	13% 9% 25% 31% 18% 3	26962

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	13% 4 2 5% 3 3 3 3 5% 6% 53%	4056
	11th to 20th	Day	14% 6% 2 5% 3 3 3 2 4 7% 52%	4060
	21st to end	Day	14% 8% 3 6% 4 3 3 3 5% 7% 44%	4466
February	1st to 10th	Day	15% 6% 3 4 3 5% 4 5% 6% 7% 42%	1800
	11th to 20th	Day	19% 6% 2 5% 3 3 3 3 5% 7% 43%	1943
	21st to end	Day	14% 7% 3 6% 4 3 4 3 5% 5% 47%	1772
March	1st to 10th	Day	21% 9% 3 6% 4 4 4 3 5% 5% 37%	4935
	11th to 20th	Day	9% 4 2 4 4 4 3 4 5% 7% 54%	4980
	21st to end	Day	13% 6% 2 6% 4 4 4 4 4 4 48%	5465
April	1st to 10th	Day	9% 4 2 5% 4 4 5% 4 6% 7% 51%	2200
	11th to 20th	Day	10% 5% 2 6% 4 5% 4 4 5% 7% 48%	2369
	21st to end	Day	7% 4 2 4 4 4 5% 4 6% 9% 51%	2410
May	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 36%	5862
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 9% 33%	5861
	21st to end	Day	8% 5% 2 6% 5% 6% 5% 5% 7% 8% 41%	6433
June	1st to 10th	Day	11% 6% 3 8% 7% 6% 7% 6% 8% 9% 29%	2600
	11th to 20th	Day	7% 5% 2 6% 6% 6% 8% 5% 8% 12% 33%	2600
	21st to end	Day	7% 4 2 7% 7% 9% 7% 7% 8% 12% 31%	2600
July	1st to 10th	Day	11% 8% 3 11% 7% 7% 8% 7% 9% 9% 20%	5900
	11th to 20th	Day	4 4 2 9% 7% 8% 9% 8% 10% 14% 25%	5900
	21st to end	Day	6% 6% 3 9% 7% 8% 8% 7% 9% 13% 25%	6424
August	1st to 10th	Day	22% 8% 3 9% 6% 7% 6% 6% 8% 9% 17%	4234
	11th to 20th	Day	7% 6% 3 8% 7% 7% 8% 6% 9% 11% 27%	4108
	21st to end	Day	8% 7% 3 10% 6% 6% 6% 5% 7% 10% 31%	4312
September	1st to 10th	Day	10% 6% 2 8% 6% 6% 6% 5% 7% 9% 34%	2236
	11th to 20th	Day	14% 7% 3 7% 6% 5% 6% 5% 6% 7% 34%	2200
	21st to end	Day	15% 6% 3 7% 5% 4 5% 4 6% 7% 37%	2200
October	1st to 10th	Day	12% 7% 2 8% 4 4 6% 3 5% 7% 42%	2060
	11th to 20th	Day	10% 4 1 5% 3 4 3 2 5% 6% 57%	2000
	21st to end	Day	10% 5% 2 5% 3 3 4 3 4 5% 56%	2200
November	1st to 10th	Day	11% 5% 1 4 4 3 3 4 5% 6% 53%	2057
	11th to 20th	Day	12% 8% 2 5% 2 3 4 2 3 6% 51%	2061
	21st to end	Day	14% 6% 2 4 4 3 4 3 4 7% 50%	1800
December	1st to 10th	Day	8% 4 2 6% 4 4 4 4 6% 6% 53%	2930
	11th to 20th	Day	14% 6% 3 6% 3 3 4 3 5% 7% 48%	3373
	21st to end	Day	19% 9% 2 5% 3 3 3 3 4 6% 42%	4466
January	1st to 10th	Night	10% 5% 2 4 3 3 4 3 4 5% 56%	5889
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 6% 7% 43%	5900
	21st to end	Night	14% 8% 3 7% 4 3 3 3 5% 6% 45%	6490
February	1st to 10th	Night	15% 7% 2 5% 5% 4 4 4 5% 6% 44%	2600
	11th to 20th	Night	17% 7% 2 5% 4 4 4 3 5% 5% 43%	2338
	21st to end	Night	12% 7% 3 5% 4 4 4 3 6% 7% 44%	1855
March	1st to 10th	Night	18% 10% 3 7% 4 4 4 3 4 6% 38%	4918
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 6% 9% 52%	4980
	21st to end	Night	13% 5% 2 4 3 3 4 3 5% 7% 50%	5467
April	1st to 10th	Night	10% 5% 2 5% 5% 4 4 4 5% 7% 50%	2200
	11th to 20th	Night	11% 4 2 5% 4 4 3 4 5% 8% 51%	1977
	21st to end	Night	8% 4 2 5% 4 4 4 5% 5% 8% 53%	2000
May	1st to 10th	Night	6% 6% 2 6% 5% 4 4 4 7% 10% 45%	4038
	11th to 20th	Night	14% 7% 2 4 4 4 5% 4 6% 10% 39%	4032
	21st to end	Night	10% 5% 2 6% 4 4 5% 5% 6% 9% 44%	4421
June	1st to 10th	Night	9% 6% 4 7% 5% 4 6% 5% 8% 12% 34%	1800
	11th to 20th	Night	6% 6% 2 6% 4 6% 6% 5% 8% 12% 39%	1800
	21st to end	Night	6% 4 2 6% 5% 6% 6% 6% 10% 13% 36%	1800
July	1st to 10th	Night	10% 7% 3 8% 7% 6% 7% 5% 8% 10% 29%	4058
	11th to 20th	Night	5% 5% 3 7% 6% 6% 7% 6% 9% 14% 32%	4057
	21st to end	Night	7% 7% 3 9% 6% 7% 7% 6% 8% 11% 28%	4427
August	1st to 10th	Night	19% 8% 3 6% 5% 4 5% 6% 8% 13% 24%	2915
	11th to 20th	Night	7% 6% 2 8% 6% 6% 6% 6% 9% 11% 34%	2906
	21st to end	Night	6% 5% 2 7% 5% 5% 6% 5% 7% 9% 43%	3586
September	1st to 10th	Night	9% 5% 2 7% 5% 5% 5% 4 7% 10% 40%	2159
	11th to 20th	Night	9% 7% 2 8% 6% 5% 5% 5% 7% 9% 38%	2200
	21st to end	Night	15% 7% 3 6% 4 4 5% 4 7% 7% 39%	2200
October	1st to 10th	Night	13% 6% 2 6% 3 4 4 3 5% 6% 48%	2339
	11th to 20th	Night	12% 4 1 4 3 3 3 2 5% 6% 58%	2400
	21st to end	Night	10% 6% 2 5% 3 3 3 3 4 5% 56%	2640
November	1st to 10th	Night	11% 5% 2 5% 3 3 3 4 5% 5% 54%	2461
	11th to 20th	Night	14% 7% 2 4 3 3 3 2 5% 5% 52%	2490
	21st to end	Night	11% 6% 2 7% 4 4 4 3 6% 7% 47%	2600
December	1st to 10th	Night	10% 6% 3 5% 3 3 3 2 4 6% 56%	4250
	11th to 20th	Night	17% 8% 3 7% 4 3 3 3 4 4 44%	4822
	21st to end	Night	17% 7% 3 6% 4 3 4 3 5% 6% 43%	6490

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	31% 6% 6% 17% 31% 9%	4057
	11th to 20th	Day	34% 4 6% 16% 30% 11%	4060
	21st to end	Day	40% 4 6% 19% 19% 11%	4466
February	1st to 10th	Day	39% 6% 9% 20% 19% 6%	1800
	11th to 20th	Day	42% 4 7% 16% 22% 9%	1953
	21st to end	Day	39% 4 9% 18% 19% 11%	1772
March	1st to 10th	Day	49% 4 7% 11% 18% 10%	4935
	11th to 20th	Day	29% 5% 10% 16% 22% 19%	4980
	21st to end	Day	39% 4 9% 16% 21% 12%	5465
April	1st to 10th	Day	31% 6% 12% 21% 21% 9%	2200
	11th to 20th	Day	35% 4 9% 22% 18% 12%	2369
	21st to end	Day	28% 6% 12% 28% 21% 5%	2410
May	1st to 10th	Day	39% 7% 18% 23% 10% 3	5897
	11th to 20th	Day	45% 7% 17% 18% 12% 1	5865
	21st to end	Day	36% 7% 15% 19% 20% 2	6447
June	1st to 10th	Day	47% 10% 17% 16% 11%	2600
	11th to 20th	Day	39% 10% 21% 22% 7% 1	2600
	21st to end	Day	40% 13% 21% 17% 8% 1	2600
July	1st to 10th	Day	54% 11% 20% 12% 3 1	5835
	11th to 20th	Day	43% 15% 32% 9% 2	5831
	21st to end	Day	45% 13% 19% 19% 3	6240
August	1st to 10th	Day	60% 9% 19% 10% 2	4221
	11th to 20th	Day	45% 12% 17% 18% 8%	4147
	21st to end	Day	45% 9% 14% 26% 5% 1	4312
September	1st to 10th	Day	44% 9% 15% 14% 14% 4	2236
	11th to 20th	Day	46% 9% 11% 18% 13% 3	2200
	21st to end	Day	45% 6% 13% 18% 13% 4	2200
October	1st to 10th	Day	42% 5% 8% 12% 25% 7%	3359
	11th to 20th	Day	19% 3 5% 13% 32% 28%	3240
	21st to end	Day	25% 4 6% 16% 36% 12%	3538
November	1st to 10th	Day	32% 5% 9% 17% 25% 13%	2057
	11th to 20th	Day	36% 4 7% 17% 24% 13%	2061
	21st to end	Day	35% 4 8% 22% 22% 9%	1800
December	1st to 10th	Day	31% 5% 10% 18% 23% 13%	2930
	11th to 20th	Day	37% 4 10% 21% 22% 6%	3370
	21st to end	Day	44% 4 7% 21% 21% 3	4466
January	1st to 10th	Night	29% 5% 7% 15% 35% 9%	5889
	11th to 20th	Night	39% 5% 6% 16% 27% 7%	5900
	21st to end	Night	41% 5% 7% 12% 24% 11%	6490
February	1st to 10th	Night	41% 4 9% 19% 19% 8%	2600
	11th to 20th	Night	42% 5% 9% 14% 20% 10%	2339
	21st to end	Night	39% 5% 11% 18% 16% 12%	1855
March	1st to 10th	Night	48% 5% 7% 13% 18% 10%	4918
	11th to 20th	Night	29% 5% 9% 13% 27% 17%	4980
	21st to end	Night	34% 4 12% 19% 20% 12%	5467
April	1st to 10th	Night	33% 6% 12% 20% 20% 9%	2200
	11th to 20th	Night	31% 5% 9% 23% 20% 12%	1977
	21st to end	Night	28% 6% 13% 26% 21% 5%	2000
May	1st to 10th	Night	33% 7% 21% 27% 10% 2	4065
	11th to 20th	Night	39% 8% 21% 19% 12% 1	4033
	21st to end	Night	35% 7% 16% 24% 17% 2	4429
June	1st to 10th	Night	39% 10% 21% 19% 10%	1800
	11th to 20th	Night	34% 12% 22% 24% 7% 1	1800
	21st to end	Night	33% 15% 25% 21% 5% 1	1800
July	1st to 10th	Night	47% 10% 24% 15% 3 1	4015
	11th to 20th	Night	38% 15% 35% 10% 3	4006
	21st to end	Night	45% 13% 21% 19% 3	4297
August	1st to 10th	Night	50% 12% 25% 11% 2	2904
	11th to 20th	Night	39% 13% 21% 21% 6%	2933
	21st to end	Night	34% 10% 17% 34% 5%	3586
September	1st to 10th	Night	37% 11% 19% 19% 11% 4	2159
	11th to 20th	Night	40% 11% 15% 19% 13% 2	2200
	21st to end	Night	42% 8% 15% 19% 14% 2	2200
October	1st to 10th	Night	37% 5% 9% 18% 25% 7%	3820
	11th to 20th	Night	17% 4 5% 13% 25% 35%	3899
	21st to end	Night	25% 4 6% 19% 30% 16%	4252
November	1st to 10th	Night	32% 4 9% 16% 25% 14%	2461
	11th to 20th	Night	36% 3 7% 17% 25% 12%	2490
	21st to end	Night	36% 4 9% 17% 23% 10%	2600
December	1st to 10th	Night	31% 4 8% 14% 30% 12%	4250
	11th to 20th	Night	44% 4 10% 15% 20% 7%	4824
	21st to end	Night	41% 5% 8% 20% 24% 3	6490

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	18% 25% 43% 11% 2	300
	11th to 20th	Day	19% 19% 40% 16% 6% 1	300
	21st to end	Day	28% 27% 34% 9% 2	330
February	1st to 10th	Day	20% 22% 39% 17% 2	300
	11th to 20th	Day	32% 25% 34% 7% 2	300
	21st to end	Day	19% 21% 40% 17% 4	371
March	1st to 10th	Day	22% 18% 33% 20% 7%	500
	11th to 20th	Day	16% 23% 36% 17% 6% 1	500
	21st to end	Day	17% 20% 38% 17% 8% 1	550
April	1st to 10th	Day	17% 21% 35% 19% 8% 1	500
	11th to 20th	Day	12% 18% 30% 22% 12% 5%	492
	21st to end	Day	7% 13% 31% 26% 15% 7%	500
May	1st to 10th	Day	9% 17% 34% 22% 13% 6%	503
	11th to 20th	Day	12% 7% 32% 25% 17% 7%	527
	21st to end	Day	12% 6% 23% 30% 19% 10%	573
June	1st to 10th	Day	12% 5% 24% 32% 18% 9%	530
	11th to 20th	Day	8% 4 19% 30% 25% 13%	530
	21st to end	Day	7% 3 18% 34% 25% 13%	530
July	1st to 10th	Day	8% 4 12% 30% 31% 16%	525
	11th to 20th	Day	7% 1 10% 32% 33% 17%	524
	21st to end	Day	5% 3 13% 36% 31% 12%	576
August	1st to 10th	Day	15% 4 14% 28% 25% 14%	526
	11th to 20th	Day	9% 3 10% 31% 30% 17%	519
	21st to end	Day	14% 3 15% 29% 25% 14%	583
September	1st to 10th	Day	11% 3 18% 29% 26% 12%	530
	11th to 20th	Day	16% 5% 17% 35% 20% 7%	530
	21st to end	Day	19% 1 21% 31% 20% 8%	530
October	1st to 10th	Day	16% 7% 26% 27% 15% 8%	530
	11th to 20th	Day	12% 7% 24% 33% 18% 6%	530
	21st to end	Day	14% 8% 26% 31% 17% 4	583
November	1st to 10th	Day	17% 8% 32% 24% 16% 2	535
	11th to 20th	Day	18% 14% 36% 20% 10% 2	519
	21st to end	Day	14% 16% 36% 25% 7%	300
December	1st to 10th	Day	17% 20% 36% 21% 5% 1	300
	11th to 20th	Day	20% 19% 37% 17% 6% 1	300
	21st to end	Day	26% 17% 34% 16% 6% 1	330
January	1st to 10th	Night	15% 17% 34% 28% 6%	800
	11th to 20th	Night	17% 15% 32% 28% 8%	800
	21st to end	Night	19% 17% 36% 25% 3	880
February	1st to 10th	Night	18% 14% 35% 28% 5%	800
	11th to 20th	Night	21% 17% 34% 24% 3	783
	21st to end	Night	16% 17% 37% 25% 4	660
March	1st to 10th	Night	15% 14% 37% 27% 7%	800
	11th to 20th	Night	16% 15% 36% 28% 7%	800
	21st to end	Night	14% 16% 34% 28% 7%	880
April	1st to 10th	Night	12% 16% 36% 29% 7% 1	800
	11th to 20th	Night	13% 12% 32% 29% 13% 1	791
	21st to end	Night	10% 11% 31% 35% 13%	800
May	1st to 10th	Night	6% 8% 29% 39% 17% 1	605
	11th to 20th	Night	11% 5% 28% 35% 19% 2	591
	21st to end	Night	11% 2 18% 36% 28% 4	650
June	1st to 10th	Night	10% 2 21% 42% 22% 4	600
	11th to 20th	Night	9% 3 11% 38% 31% 9%	600
	21st to end	Night	5% 2 14% 40% 33% 7%	600
July	1st to 10th	Night	8% 2 11% 39% 34% 7%	585
	11th to 20th	Night	8% 1 6% 35% 42% 7%	582
	21st to end	Night	5% 3 7% 40% 38% 6%	657
August	1st to 10th	Night	11% 3 6% 34% 38% 8%	597
	11th to 20th	Night	7% 2 9% 31% 40% 11%	612
	21st to end	Night	12% 3 12% 30% 32% 11%	880
September	1st to 10th	Night	9% 2 13% 33% 37% 6%	800
	11th to 20th	Night	13% 3 13% 36% 30% 6%	800
	21st to end	Night	19% 3 14% 32% 28% 5%	800
October	1st to 10th	Night	17% 4 22% 31% 22% 5%	800
	11th to 20th	Night	13% 6% 23% 33% 22% 3	800
	21st to end	Night	12% 8% 25% 32% 20% 2	880
November	1st to 10th	Night	12% 8% 26% 33% 17% 2	820
	11th to 20th	Night	16% 11% 29% 29% 14% 1	829
	21st to end	Night	14% 11% 29% 28% 17% 1	800
December	1st to 10th	Night	17% 12% 30% 31% 10%	800
	11th to 20th	Night	19% 12% 28% 29% 12% 1	800
	21st to end	Night	21% 12% 31% 28% 9%	880

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