Oil Capital Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oil Capital 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	12% 6% 2 5% 4 4 4 3 5% 7% 48%	127709
	Night	11% 5% 2 5% 3 3 3 3 5% 6% 53%	124593
Transparency	Day	35% 4 11% 26% 20% 5%	131347
	Night	31% 4 10% 26% 23% 7%	129018
Seeing	Day	13% 8% 25% 28% 20% 6%	17074
	Night	13% 8% 29% 34% 15% 1	27031

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% 10% 4 7% 3 4 4 4 4 4 44%	4167
	11th to 20th	Day	7% 5% 2 6% 4 3 4 3 4 5% 56%	4170
	21st to end	Day	19% 9% 2 5% 2 2 2 2 3 4 49%	4587
February	1st to 10th	Day	16% 10% 3 6% 5% 3 3 3 4 5% 42%	1800
	11th to 20th	Day	16% 7% 3 5% 4 4 4 3 5% 5% 44%	1877
	21st to end	Day	16% 7% 3 5% 4 3 3 3 5% 5% 46%	1710
March	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 4 4 53%	4936
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 7% 55%	4980
	21st to end	Day	13% 9% 3 7% 5% 5% 4 4 5% 7% 39%	5462
April	1st to 10th	Day	14% 6% 3 5% 4 4 4 4 5% 6% 45%	2225
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 45%	2374
	21st to end	Day	20% 8% 2 7% 4 3 3 3 5% 5% 40%	2529
May	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 39%	5862
	11th to 20th	Day	11% 6% 3 7% 4 5% 4 4 5% 7% 44%	5862
	21st to end	Day	18% 8% 3 7% 5% 4 5% 4 6% 7% 33%	6434
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 5% 8% 47%	2600
	11th to 20th	Day	9% 4 2 4 4 5% 5% 4 6% 9% 47%	2600
	21st to end	Day	5% 4 1 4 4 4 4 4 6% 8% 57%	2600
July	1st to 10th	Day	6% 5% 2 6% 4 5% 6% 6% 8% 11% 42%	5900
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 6% 10% 49%	5900
	21st to end	Day	4 3 1 4 4 3 4 4 6% 11% 55%	6422
August	1st to 10th	Day	4 3 1 4 3 3 4 4 6% 9% 59%	4234
	11th to 20th	Day	7% 4 1 5% 3 4 5% 4 6% 9% 51%	4171
	21st to end	Day	5% 4 1 5% 3 4 4 4 6% 8% 56%	4394
September	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 5% 7% 54%	2280
	11th to 20th	Day	11% 4 2 5% 4 4 5% 4 7% 7% 47%	2200
	21st to end	Day	8% 4 2 6% 3 4 4 4 5% 7% 55%	2200
October	1st to 10th	Day	9% 3 2 4 3 3 3 3 4 7% 60%	2050
	11th to 20th	Day	12% 4 1 2 3 2 2 2 4 4 63%	2000
	21st to end	Day	18% 5% 2 5% 2 2 2 2 3 5% 53%	2200
November	1st to 10th	Day	11% 4 2 4 3 2 2 2 4 7% 59%	2058
	11th to 20th	Day	12% 5% 2 4 2 3 4 3 4 5% 58%	1937
	21st to end	Day	16% 6% 1 4 3 2 3 3 5% 6% 52%	1890
December	1st to 10th	Day	12% 7% 2 5% 3 3 2 3 4 5% 54%	3030
	11th to 20th	Day	15% 7% 2 5% 3 3 3 2 4 6% 50%	3481
	21st to end	Day	21% 12% 4 6% 4 4 3 3 4 5% 35%	4587
January	1st to 10th	Night	15% 6% 3 7% 4 3 3 3 5% 5% 45%	6018
	11th to 20th	Night	7% 4 2 5% 3 4 4 3 4 5% 58%	6030
	21st to end	Night	19% 8% 3 5% 2 3 2 2 3 5% 48%	6633
February	1st to 10th	Night	16% 9% 2 6% 3 3 3 3 4 4 47%	2601
	11th to 20th	Night	16% 8% 3 6% 3 3 3 2 3 5% 49%	2428
	21st to end	Night	15% 6% 2 5% 3 4 4 3 4 4 50%	1918
March	1st to 10th	Night	16% 7% 2 5% 4 3 3 2 4 4 50%	4919
	11th to 20th	Night	8% 4 2 4 3 3 3 2 4 6% 61%	4980
	21st to end	Night	13% 5% 2 5% 3 3 4 4 6% 8% 48%	5467
April	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 5% 5% 53%	2173
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 6% 52%	1975
	21st to end	Night	15% 7% 2 5% 4 4 3 3 4 6% 48%	1868
May	1st to 10th	Night	16% 7% 3 5% 4 4 4 3 4 6% 46%	4053
	11th to 20th	Night	13% 5% 2 6% 4 4 4 3 5% 8% 47%	4053
	21st to end	Night	15% 6% 2 5% 3 3 4 4 5% 7% 44%	4443
June	1st to 10th	Night	6% 4 2 4 4 5% 4 3 6% 8% 54%	1800
	11th to 20th	Night	4 4 1 4 4 4 4 5% 7% 8% 56%	1800
	21st to end	Night	3 3 1 2 3 3 3 3 5% 8% 65%	1800
July	1st to 10th	Night	6% 4 1 5% 4 4 5% 4 7% 11% 49%	4078
	11th to 20th	Night	4 3 1 4 4 3 4 3 6% 9% 59%	4077
	21st to end	Night	4 3 1 3 2 3 4 3 5% 11% 62%	4449
August	1st to 10th	Night	3 1 1 3 2 3 3 4 7% 9% 64%	2926
	11th to 20th	Night	5% 3 2 5% 4 4 5% 5% 6% 8% 54%	2888
	21st to end	Night	4 3 1 3 2 3 4 3 5% 8% 64%	3503
September	1st to 10th	Night	8% 4 2 5% 3 3 3 3 5% 7% 59%	2115
	11th to 20th	Night	9% 4 2 6% 4 3 4 4 5% 6% 53%	2200
	21st to end	Night	8% 4 2 5% 4 3 3 3 4 6% 59%	2200
October	1st to 10th	Night	7% 2 1 4 3 3 3 3 4 6% 64%	2328
	11th to 20th	Night	11% 4 1 4 3 3 3 2 4 5% 60%	2400
	21st to end	Night	15% 6% 1 4 2 3 3 2 4 5% 55%	2640
November	1st to 10th	Night	11% 5% 1 3 2 2 2 2 3 4 64%	2460
	11th to 20th	Night	9% 5% 2 4 3 3 3 2 3 5% 60%	2681
	21st to end	Night	14% 6% 2 4 3 2 3 2 4 5% 55%	2730
December	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 3 5% 57%	4380
	11th to 20th	Night	16% 5% 2 5% 3 3 3 2 3 4 54%	4946
	21st to end	Night	19% 9% 3 6% 4 3 3 3 4 5% 42%	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	44% 3 9% 25% 17% 2	4168
	11th to 20th	Day	30% 2 11% 27% 25% 5%	4170
	21st to end	Day	42% 1 6% 22% 24% 4	4587
February	1st to 10th	Day	46% 4 9% 22% 15% 3	1800
	11th to 20th	Day	42% 4 9% 25% 17% 3	1886
	21st to end	Day	41% 2 8% 22% 18% 9%	1710
March	1st to 10th	Day	35% 3 5% 21% 18% 17%	4936
	11th to 20th	Day	30% 3 10% 20% 21% 15%	4980
	21st to end	Day	45% 4 10% 30% 11% 1	5464
April	1st to 10th	Day	39% 5% 10% 23% 18% 5%	2225
	11th to 20th	Day	40% 5% 11% 23% 16% 6%	2374
	21st to end	Day	46% 4 9% 22% 17% 1	2529
May	1st to 10th	Day	46% 5% 10% 22% 16% 2	5900
	11th to 20th	Day	38% 5% 12% 22% 20% 3	5866
	21st to end	Day	48% 6% 12% 16% 15% 3	6447
June	1st to 10th	Day	33% 6% 14% 27% 17% 2	2600
	11th to 20th	Day	32% 6% 14% 29% 17% 2	2600
	21st to end	Day	25% 6% 13% 32% 19% 5%	2600
July	1st to 10th	Day	32% 7% 17% 29% 13% 2	5836
	11th to 20th	Day	29% 6% 13% 30% 20% 2	5831
	21st to end	Day	22% 6% 18% 38% 16%	6240
August	1st to 10th	Day	22% 5% 13% 29% 25% 5%	4220
	11th to 20th	Day	28% 7% 19% 27% 16% 2	4210
	21st to end	Day	25% 5% 12% 41% 12% 3	4393
September	1st to 10th	Day	30% 5% 10% 24% 22% 9%	2280
	11th to 20th	Day	32% 7% 10% 24% 21% 5%	2200
	21st to end	Day	29% 5% 9% 23% 28% 6%	2200
October	1st to 10th	Day	17% 2 8% 15% 42% 15%	3336
	11th to 20th	Day	16% 2 4 20% 42% 15%	3240
	21st to end	Day	29% 3 7% 27% 28% 7%	3538
November	1st to 10th	Day	28% 3 8% 26% 27% 8%	2058
	11th to 20th	Day	29% 2 7% 28% 24% 9%	1937
	21st to end	Day	35% 3 8% 26% 23% 5%	1890
December	1st to 10th	Day	34% 2 7% 34% 20% 1	3030
	11th to 20th	Day	37% 3 5% 26% 24% 4	3479
	21st to end	Day	54% 3 8% 22% 11% 3	4587
January	1st to 10th	Night	40% 3 10% 27% 16% 3	6018
	11th to 20th	Night	26% 4 13% 20% 33% 4	6030
	21st to end	Night	41% 2 8% 19% 27% 4	6633
February	1st to 10th	Night	41% 3 10% 24% 18% 4	2601
	11th to 20th	Night	40% 3 7% 25% 20% 5%	2429
	21st to end	Night	38% 3 7% 19% 23% 10%	1918
March	1st to 10th	Night	39% 3 6% 19% 20% 13%	4919
	11th to 20th	Night	26% 3 8% 23% 25% 15%	4980
	21st to end	Night	35% 4 12% 31% 16% 3	5467
April	1st to 10th	Night	34% 4 10% 22% 21% 9%	2173
	11th to 20th	Night	34% 3 10% 24% 20% 9%	1975
	21st to end	Night	38% 3 10% 25% 22% 2	1868
May	1st to 10th	Night	41% 5% 11% 20% 19% 3	4080
	11th to 20th	Night	36% 5% 12% 22% 19% 6%	4054
	21st to end	Night	39% 5% 14% 22% 15% 4	4452
June	1st to 10th	Night	26% 7% 15% 29% 19% 4	1800
	11th to 20th	Night	23% 7% 14% 31% 22% 3	1800
	21st to end	Night	18% 5% 13% 33% 25% 7%	1800
July	1st to 10th	Night	27% 7% 18% 29% 15% 4	4035
	11th to 20th	Night	21% 5% 12% 35% 24% 2	4026
	21st to end	Night	18% 4 16% 39% 22% 1	4320
August	1st to 10th	Night	16% 5% 14% 32% 28% 6%	2916
	11th to 20th	Night	26% 5% 17% 29% 20% 4	2915
	21st to end	Night	19% 4 11% 40% 22% 5%	3503
September	1st to 10th	Night	26% 4 9% 27% 23% 11%	2115
	11th to 20th	Night	31% 5% 10% 24% 23% 7%	2200
	21st to end	Night	27% 4 7% 26% 29% 7%	2200
October	1st to 10th	Night	14% 2 7% 14% 37% 26%	3809
	11th to 20th	Night	20% 2 5% 16% 37% 18%	3899
	21st to end	Night	29% 3 6% 26% 28% 9%	4252
November	1st to 10th	Night	27% 3 7% 24% 31% 9%	2460
	11th to 20th	Night	28% 3 7% 27% 26% 10%	2681
	21st to end	Night	33% 3 8% 24% 27% 6%	2730
December	1st to 10th	Night	32% 3 9% 35% 18% 3	4380
	11th to 20th	Night	36% 3 6% 24% 25% 7%	4947
	21st to end	Night	45% 3 8% 25% 14% 4	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	17% 13% 38% 26% 6%	330
	11th to 20th	Day	18% 20% 35% 21% 5% 1	330
	21st to end	Day	17% 12% 41% 21% 9% 1	363
February	1st to 10th	Day	29% 14% 33% 21% 3	300
	11th to 20th	Day	20% 19% 40% 18% 3	300
	21st to end	Day	22% 19% 39% 17% 3	249
March	1st to 10th	Day	23% 15% 34% 22% 5%	300
	11th to 20th	Day	20% 20% 39% 16% 5%	300
	21st to end	Day	22% 21% 36% 16% 4 1	330
April	1st to 10th	Day	18% 18% 36% 20% 7% 1	325
	11th to 20th	Day	20% 16% 37% 23% 4	492
	21st to end	Day	22% 15% 30% 23% 8% 1	629
May	1st to 10th	Day	17% 10% 35% 29% 9% 1	703
	11th to 20th	Day	15% 11% 29% 29% 12% 4	725
	21st to end	Day	14% 8% 30% 24% 18% 6%	789
June	1st to 10th	Day	8% 4 18% 34% 28% 7%	730
	11th to 20th	Day	9% 2 19% 40% 24% 6%	730
	21st to end	Day	3 2 18% 41% 31% 5%	730
July	1st to 10th	Day	8% 1 11% 33% 34% 14%	721
	11th to 20th	Day	3 2 12% 36% 38% 10%	718
	21st to end	Day	6% 2 6% 31% 39% 16%	794
August	1st to 10th	Day	6% 1 9% 41% 36% 8%	726
	11th to 20th	Day	10% 1 11% 31% 36% 11%	715
	21st to end	Day	8% 1 8% 28% 39% 15%	639
September	1st to 10th	Day	8% 2 10% 29% 40% 13%	410
	11th to 20th	Day	5% 2 13% 36% 33% 12%	330
	21st to end	Day	9% 5% 15% 30% 29% 10%	330
October	1st to 10th	Day	8% 3 26% 32% 20% 11%	330
	11th to 20th	Day	9% 10% 34% 30% 15% 1	330
	21st to end	Day	24% 10% 28% 24% 12% 1	363
November	1st to 10th	Day	15% 9% 38% 24% 12% 2	330
	11th to 20th	Day	15% 9% 36% 25% 12% 2	330
	21st to end	Day	21% 13% 34% 23% 8% 1	330
December	1st to 10th	Day	17% 13% 39% 21% 9% 2	330
	11th to 20th	Day	21% 13% 37% 22% 5% 1	330
	21st to end	Day	18% 18% 34% 24% 6%	363
January	1st to 10th	Night	15% 12% 36% 31% 5%	1050
	11th to 20th	Night	15% 15% 38% 28% 4	1050
	21st to end	Night	15% 12% 37% 32% 4	1155
February	1st to 10th	Night	21% 12% 35% 27% 4	1001
	11th to 20th	Night	20% 16% 35% 26% 3	874
	21st to end	Night	17% 13% 41% 27% 3	598
March	1st to 10th	Night	18% 11% 36% 31% 4	600
	11th to 20th	Night	17% 11% 37% 30% 5%	600
	21st to end	Night	16% 10% 42% 25% 6%	660
April	1st to 10th	Night	15% 12% 40% 29% 4	600
	11th to 20th	Night	16% 10% 38% 28% 7%	593
	21st to end	Night	17% 9% 39% 28% 7% 1	600
May	1st to 10th	Night	14% 8% 35% 36% 8% 1	600
	11th to 20th	Night	13% 6% 29% 37% 15% 1	591
	21st to end	Night	11% 6% 29% 33% 20% 2	650
June	1st to 10th	Night	8% 3 18% 40% 30% 2	600
	11th to 20th	Night	5% 3 20% 48% 23% 2	600
	21st to end	Night	3 2 18% 51% 24% 2	600
July	1st to 10th	Night	5% 1 9% 45% 36% 3	585
	11th to 20th	Night	2 1 10% 44% 38% 4	582
	21st to end	Night	4 1 6% 40% 45% 3	657
August	1st to 10th	Night	3 1 9% 46% 39% 2	597
	11th to 20th	Night	6% 2 9% 40% 40% 3	594
	21st to end	Night	4 2 9% 39% 41% 5%	660
September	1st to 10th	Night	9% 2 10% 41% 37% 2	600
	11th to 20th	Night	11% 2 13% 43% 27% 4	600
	21st to end	Night	9% 3 17% 41% 27% 3	600
October	1st to 10th	Night	8% 2 23% 38% 26% 3	728
	11th to 20th	Night	12% 8% 32% 36% 12%	800
	21st to end	Night	17% 9% 30% 32% 11% 1	880
November	1st to 10th	Night	12% 7% 35% 34% 12% 1	820
	11th to 20th	Night	11% 11% 34% 35% 9%	1001
	21st to end	Night	17% 12% 34% 28% 9%	1050
December	1st to 10th	Night	16% 11% 35% 32% 6%	1050
	11th to 20th	Night	19% 10% 35% 30% 6%	1050
	21st to end	Night	18% 11% 36% 29% 5%	1155

Page generated at 2026-01-29 00:21:47. Version ac07

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