Owl Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Owl Creek Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	10% 5% 2 5% 3 4 4 3 5% 7% 53%	127614
	Night	10% 5% 2 4 3 3 3 3 5% 6% 57%	124668
Transparency	Day	31% 5% 10% 25% 23% 7%	131318
	Night	27% 4 9% 24% 26% 9%	129027
Seeing	Day	12% 8% 25% 30% 20% 5%	16956
	Night	11% 9% 31% 34% 13% 1	26945

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 5% 3 3 3 3 4 6% 51%	4167
	11th to 20th	Day	6% 5% 2 4 2 2 2 2 3 5% 66%	4170
	21st to end	Day	16% 8% 2 5% 3 3 3 2 3 4 52%	4587
February	1st to 10th	Day	13% 8% 3 7% 4 3 3 3 4 6% 47%	1888
	11th to 20th	Day	13% 6% 2 6% 3 4 3 3 5% 6% 50%	1949
	21st to end	Day	15% 7% 2 5% 3 3 3 3 3 4 51%	1650
March	1st to 10th	Day	12% 6% 2 5% 3 3 3 2 4 6% 55%	4887
	11th to 20th	Day	8% 4 2 5% 4 4 4 3 4 6% 55%	4980
	21st to end	Day	13% 8% 3 6% 4 4 4 3 5% 8% 43%	5462
April	1st to 10th	Day	11% 6% 2 5% 4 4 4 3 4 7% 52%	2200
	11th to 20th	Day	14% 5% 2 5% 3 3 4 3 4 6% 50%	2334
	21st to end	Day	15% 6% 2 6% 3 4 4 3 5% 6% 46%	2600
May	1st to 10th	Day	18% 7% 3 6% 4 4 4 3 5% 6% 41%	5862
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 6% 50%	5862
	21st to end	Day	14% 6% 2 6% 4 5% 4 4 6% 7% 42%	6434
June	1st to 10th	Day	8% 4 2 5% 5% 4 4 4 7% 9% 47%	2600
	11th to 20th	Day	6% 4 1 5% 3 4 4 5% 7% 9% 52%	2600
	21st to end	Day	5% 3 1 3 4 4 4 4 5% 8% 59%	2600
July	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 5% 7% 8% 41%	5900
	11th to 20th	Day	5% 3 1 5% 4 4 4 4 5% 9% 57%	5900
	21st to end	Day	3 2 1 3 3 3 4 4 6% 8% 63%	6422
August	1st to 10th	Day	4 3 1 4 4 4 4 3 6% 8% 59%	4234
	11th to 20th	Day	5% 3 1 4 3 4 4 4 6% 9% 56%	4171
	21st to end	Day	3 3 1 4 3 4 4 4 5% 8% 61%	4311
September	1st to 10th	Day	9% 4 1 5% 3 4 3 4 5% 7% 56%	2200
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 6% 8% 49%	2200
	21st to end	Day	9% 3 1 4 4 3 4 3 4 6% 60%	2200
October	1st to 10th	Day	7% 3 2 4 3 3 3 3 4 5% 62%	2155
	11th to 20th	Day	10% 3 1 4 3 2 2 2 3 4 67%	2000
	21st to end	Day	13% 6% 2 4 2 2 3 2 3 4 58%	2200
November	1st to 10th	Day	9% 4 2 4 3 3 3 2 4 6% 60%	2011
	11th to 20th	Day	8% 4 1 3 3 2 2 2 4 6% 65%	1890
	21st to end	Day	13% 5% 1 4 2 3 3 2 4 5% 59%	1890
December	1st to 10th	Day	8% 8% 2 5% 2 3 4 3 4 6% 55%	3030
	11th to 20th	Day	12% 6% 2 4 2 3 3 2 4 5% 56%	3481
	21st to end	Day	19% 8% 2 5% 3 3 3 2 4 5% 46%	4587
January	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 4 5% 50%	6018
	11th to 20th	Night	4 3 1 3 3 2 3 2 4 6% 67%	6030
	21st to end	Night	16% 8% 2 4 2 2 3 3 3 4 51%	6633
February	1st to 10th	Night	12% 8% 3 4 4 3 3 3 4 5% 52%	2530
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 3 7% 51%	2338
	21st to end	Night	10% 7% 3 5% 3 4 3 3 4 5% 53%	1980
March	1st to 10th	Night	13% 6% 2 5% 3 3 3 2 4 6% 54%	4968
	11th to 20th	Night	7% 3 1 3 2 3 3 3 4 7% 64%	4980
	21st to end	Night	12% 6% 2 5% 4 4 3 3 6% 8% 48%	5467
April	1st to 10th	Night	11% 5% 2 4 3 3 3 3 5% 6% 55%	2200
	11th to 20th	Night	12% 4 2 4 3 2 2 3 4 6% 57%	2011
	21st to end	Night	13% 5% 1 4 3 3 4 4 5% 7% 52%	1800
May	1st to 10th	Night	17% 7% 2 5% 4 3 3 2 4 6% 47%	4053
	11th to 20th	Night	10% 3 2 4 3 3 4 4 6% 9% 54%	4053
	21st to end	Night	11% 5% 2 5% 3 3 4 3 6% 7% 52%	4443
June	1st to 10th	Night	6% 3 1 4 3 3 4 4 5% 10% 57%	1800
	11th to 20th	Night	5% 3 2 4 3 2 4 3 5% 10% 59%	1800
	21st to end	Night	3 2 1 2 2 2 4 3 6% 8% 67%	1800
July	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 4 6% 10% 47%	4078
	11th to 20th	Night	3 2 1 3 2 3 4 3 6% 10% 63%	4077
	21st to end	Night	3 2 1 3 2 2 3 3 5% 9% 68%	4449
August	1st to 10th	Night	1 1 1 3 3 3 4 3 6% 8% 67%	2926
	11th to 20th	Night	3 2 1 3 3 3 4 4 7% 9% 59%	2888
	21st to end	Night	3 2 1 3 2 3 3 3 5% 9% 66%	3560
September	1st to 10th	Night	8% 4 2 4 3 3 4 3 5% 6% 59%	2200
	11th to 20th	Night	10% 5% 2 5% 4 3 4 3 5% 7% 53%	2200
	21st to end	Night	7% 3 1 3 3 3 3 3 5% 7% 62%	2200
October	1st to 10th	Night	7% 3 2 3 3 3 4 2 4 6% 65%	2225
	11th to 20th	Night	9% 4 1 4 3 3 3 2 3 4 65%	2400
	21st to end	Night	14% 4 2 3 2 2 3 2 4 5% 60%	2640
November	1st to 10th	Night	9% 4 1 3 2 2 3 3 3 5% 65%	2502
	11th to 20th	Night	6% 4 2 4 3 3 4 2 4 5% 64%	2730
	21st to end	Night	12% 5% 1 3 3 3 3 3 3 6% 58%	2730
December	1st to 10th	Night	7% 6% 2 4 2 2 3 2 4 6% 63%	4380
	11th to 20th	Night	13% 5% 2 5% 3 3 2 2 3 4 58%	4946
	21st to end	Night	17% 7% 2 4 3 2 3 2 4 4 52%	6633

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	36% 3 10% 26% 22% 3	4168
	11th to 20th	Day	24% 2 9% 21% 37% 6%	4170
	21st to end	Day	39% 2 5% 19% 28% 8%	4587
February	1st to 10th	Day	39% 4 8% 21% 22% 6%	1888
	11th to 20th	Day	37% 3 7% 27% 20% 6%	1959
	21st to end	Day	39% 3 5% 15% 27% 11%	1650
March	1st to 10th	Day	33% 2 6% 16% 21% 23%	4887
	11th to 20th	Day	31% 4 7% 19% 21% 18%	4980
	21st to end	Day	40% 4 10% 25% 18% 3	5464
April	1st to 10th	Day	34% 4 9% 22% 21% 9%	2200
	11th to 20th	Day	36% 5% 9% 22% 21% 8%	2334
	21st to end	Day	39% 6% 9% 24% 19% 4	2600
May	1st to 10th	Day	44% 6% 11% 20% 15% 4	5900
	11th to 20th	Day	34% 6% 11% 21% 23% 5%	5866
	21st to end	Day	40% 7% 11% 21% 14% 6%	6447
June	1st to 10th	Day	31% 8% 16% 27% 15% 3	2600
	11th to 20th	Day	26% 8% 14% 28% 21% 3	2600
	21st to end	Day	23% 7% 15% 27% 23% 6%	2600
July	1st to 10th	Day	36% 8% 15% 25% 14% 2	5836
	11th to 20th	Day	24% 5% 12% 31% 25% 3	5831
	21st to end	Day	18% 6% 16% 36% 23% 1	6240
August	1st to 10th	Day	22% 6% 11% 26% 26% 9%	4220
	11th to 20th	Day	23% 7% 15% 34% 18% 3	4210
	21st to end	Day	21% 7% 12% 43% 14% 3	4310
September	1st to 10th	Day	28% 5% 11% 23% 23% 11%	2200
	11th to 20th	Day	33% 6% 10% 22% 22% 7%	2200
	21st to end	Day	26% 4 9% 24% 29% 9%	2200
October	1st to 10th	Day	16% 3 6% 14% 42% 19%	3506
	11th to 20th	Day	18% 2 6% 23% 33% 17%	3240
	21st to end	Day	25% 3 7% 28% 30% 8%	3538
November	1st to 10th	Day	27% 3 8% 22% 30% 10%	2011
	11th to 20th	Day	23% 2 8% 26% 31% 11%	1890
	21st to end	Day	31% 2 6% 24% 28% 9%	1890
December	1st to 10th	Day	31% 3 8% 33% 22% 3	3030
	11th to 20th	Day	32% 3 5% 20% 30% 10%	3479
	21st to end	Day	42% 2 7% 24% 20% 5%	4587
January	1st to 10th	Night	37% 3 7% 27% 22% 4	6018
	11th to 20th	Night	20% 3 12% 19% 34% 12%	6030
	21st to end	Night	37% 3 6% 17% 28% 9%	6633
February	1st to 10th	Night	36% 4 8% 20% 25% 7%	2530
	11th to 20th	Night	35% 4 7% 23% 23% 7%	2338
	21st to end	Night	35% 4 6% 16% 25% 15%	1980
March	1st to 10th	Night	33% 3 6% 16% 24% 19%	4968
	11th to 20th	Night	23% 3 7% 23% 19% 26%	4980
	21st to end	Night	34% 4 12% 21% 26% 3	5467
April	1st to 10th	Night	30% 4 10% 22% 21% 14%	2200
	11th to 20th	Night	29% 4 11% 24% 20% 12%	2011
	21st to end	Night	32% 6% 10% 26% 22% 4	1800
May	1st to 10th	Night	39% 6% 13% 19% 17% 5%	4080
	11th to 20th	Night	27% 6% 13% 24% 20% 10%	4054
	21st to end	Night	30% 6% 16% 21% 19% 7%	4452
June	1st to 10th	Night	22% 8% 15% 31% 20% 4	1800
	11th to 20th	Night	22% 6% 15% 28% 25% 5%	1800
	21st to end	Night	16% 5% 13% 29% 30% 7%	1800
July	1st to 10th	Night	31% 7% 16% 28% 15% 3	4035
	11th to 20th	Night	16% 5% 12% 36% 27% 3	4026
	21st to end	Night	15% 4 14% 37% 27% 2	4320
August	1st to 10th	Night	14% 5% 11% 26% 35% 9%	2916
	11th to 20th	Night	19% 6% 11% 36% 24% 4	2915
	21st to end	Night	16% 4 13% 42% 20% 4	3560
September	1st to 10th	Night	26% 5% 9% 22% 26% 12%	2200
	11th to 20th	Night	32% 5% 8% 22% 24% 9%	2200
	21st to end	Night	23% 3 7% 26% 30% 11%	2200
October	1st to 10th	Night	15% 3 7% 14% 38% 23%	3641
	11th to 20th	Night	18% 2 5% 18% 38% 20%	3899
	21st to end	Night	23% 3 5% 30% 29% 10%	4252
November	1st to 10th	Night	24% 3 7% 23% 31% 13%	2502
	11th to 20th	Night	25% 3 7% 24% 29% 12%	2730
	21st to end	Night	30% 3 7% 21% 29% 10%	2730
December	1st to 10th	Night	25% 3 6% 33% 27% 5%	4380
	11th to 20th	Night	32% 2 5% 20% 30% 11%	4947
	21st to end	Night	37% 3 6% 24% 22% 7%	6633

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% 12% 38% 25% 7%	330
	11th to 20th	Day	16% 22% 33% 22% 6% 1	330
	21st to end	Day	16% 13% 37% 26% 8% 1	363
February	1st to 10th	Day	22% 15% 38% 20% 5%	300
	11th to 20th	Day	18% 21% 40% 18% 2	300
	21st to end	Day	25% 16% 37% 17% 4 1	249
March	1st to 10th	Day	17% 20% 38% 20% 6%	300
	11th to 20th	Day	20% 20% 40% 13% 7% 1	300
	21st to end	Day	18% 18% 39% 20% 5%	330
April	1st to 10th	Day	17% 24% 29% 24% 7%	300
	11th to 20th	Day	18% 20% 41% 18% 3	452
	21st to end	Day	19% 14% 35% 23% 7% 2	700
May	1st to 10th	Day	13% 12% 36% 31% 7% 1	703
	11th to 20th	Day	15% 9% 34% 26% 14% 2	725
	21st to end	Day	13% 8% 32% 29% 14% 4	789
June	1st to 10th	Day	9% 4 19% 38% 24% 6%	730
	11th to 20th	Day	7% 2 24% 41% 22% 4	730
	21st to end	Day	4 2 17% 42% 29% 7%	730
July	1st to 10th	Day	6% 2 12% 35% 34% 12%	721
	11th to 20th	Day	3 1 10% 39% 38% 9%	718
	21st to end	Day	5% 1 6% 32% 41% 15%	794
August	1st to 10th	Day	5% 2 7% 38% 40% 8%	726
	11th to 20th	Day	8% 2 9% 36% 36% 9%	715
	21st to end	Day	5% 1 9% 33% 36% 16%	595
September	1st to 10th	Day	9% 2 7% 32% 35% 16%	330
	11th to 20th	Day	6% 3 10% 32% 35% 15%	330
	21st to end	Day	15% 3 13% 32% 27% 10%	330
October	1st to 10th	Day	6% 4 25% 35% 22% 9%	330
	11th to 20th	Day	10% 9% 29% 35% 15% 2	330
	21st to end	Day	24% 10% 26% 24% 13% 2	363
November	1st to 10th	Day	15% 8% 37% 26% 12% 2	330
	11th to 20th	Day	15% 9% 35% 28% 12% 2	330
	21st to end	Day	19% 11% 38% 22% 8% 2	330
December	1st to 10th	Day	12% 14% 40% 24% 10% 1	330
	11th to 20th	Day	16% 13% 38% 25% 7%	330
	21st to end	Day	18% 16% 37% 22% 6% 1	363
January	1st to 10th	Night	13% 12% 40% 28% 7%	1050
	11th to 20th	Night	12% 14% 37% 31% 5%	1050
	21st to end	Night	12% 11% 39% 33% 5%	1155
February	1st to 10th	Night	17% 13% 40% 26% 4	930
	11th to 20th	Night	16% 16% 39% 25% 4	784
	21st to end	Night	15% 17% 40% 25% 3	660
March	1st to 10th	Night	15% 16% 34% 31% 4	625
	11th to 20th	Night	16% 15% 38% 28% 4	600
	21st to end	Night	15% 13% 44% 23% 5%	660
April	1st to 10th	Night	14% 16% 42% 24% 4	600
	11th to 20th	Night	14% 12% 45% 23% 5%	593
	21st to end	Night	14% 12% 40% 28% 6% 1	600
May	1st to 10th	Night	10% 8% 44% 31% 7%	600
	11th to 20th	Night	12% 7% 37% 29% 14% 1	591
	21st to end	Night	8% 6% 34% 37% 15% 2	650
June	1st to 10th	Night	5% 4 23% 44% 22% 3	600
	11th to 20th	Night	6% 3 26% 52% 14%	600
	21st to end	Night	3 1 22% 50% 21% 3	600
July	1st to 10th	Night	6% 1 12% 45% 33% 3	585
	11th to 20th	Night	2 1 12% 50% 33% 2	582
	21st to end	Night	3 7% 51% 36% 2	657
August	1st to 10th	Night	1 1 9% 54% 32% 3	597
	11th to 20th	Night	5% 1 10% 46% 35% 4	594
	21st to end	Night	3 1 8% 46% 37% 5%	660
September	1st to 10th	Night	9% 2 11% 45% 32% 2	600
	11th to 20th	Night	12% 2 16% 38% 30% 3	600
	21st to end	Night	8% 2 19% 45% 22% 4	600
October	1st to 10th	Night	8% 3 28% 38% 22% 2	625
	11th to 20th	Night	11% 8% 34% 34% 13% 1	800
	21st to end	Night	17% 10% 30% 31% 12% 1	880
November	1st to 10th	Night	10% 8% 37% 32% 12% 1	862
	11th to 20th	Night	8% 12% 33% 36% 10%	1050
	21st to end	Night	15% 11% 38% 28% 9%	1050
December	1st to 10th	Night	13% 10% 38% 32% 7%	1050
	11th to 20th	Night	17% 10% 38% 29% 6%	1050
	21st to end	Night	16% 12% 38% 29% 6%	1155

Page generated at 2026-01-29 00:21:43. Version ac07

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