Antelope Creek Heliophysics Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Antelope Creek Heliophysics 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	4 5% 2 5% 4 4 5% 4 6% 8% 54%	136127
	Night	4 5% 2 5% 3 3 4 3 5% 7% 59%	133358
Transparency	Day	25% 6% 10% 23% 25% 12%	131111
	Night	24% 5% 11% 25% 25% 10%	129378
Seeing	Day	7% 10% 30% 30% 17% 6%	17171
	Night	5% 5% 32% 39% 16% 2	27304

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% 3 5% 2 3 3 3 5% 9% 63%	3718
	11th to 20th	Day	1 2 1 4 4 5% 5% 4 6% 8% 60%	3878
	21st to end	Day	1 4 2 7% 4 3 3 3 5% 6% 62%	4609
February	1st to 10th	Day	1 6% 3 5% 5% 3 4 3 6% 7% 59%	1823
	11th to 20th	Day	1 3 2 5% 4 4 4 4 6% 9% 57%	1949
	21st to end	Day	1 5% 2 8% 4 3 4 3 5% 6% 58%	1650
March	1st to 10th	Day	1 4 2 5% 3 2 3 3 5% 7% 64%	4500
	11th to 20th	Day	3 9% 3 7% 4 4 4 3 6% 8% 50%	4898
	21st to end	Day	2 5% 3 5% 4 4 5% 4 6% 8% 54%	5854
April	1st to 10th	Day	3 6% 2 5% 3 4 4 5% 6% 9% 55%	2400
	11th to 20th	Day	6% 7% 3 6% 4 4 4 4 7% 8% 49%	2371
	21st to end	Day	6% 8% 2 5% 3 4 4 4 6% 9% 49%	2400
May	1st to 10th	Day	11% 8% 2 5% 3 4 4 4 6% 7% 47%	5716
	11th to 20th	Day	6% 6% 2 5% 3 4 5% 4 7% 9% 50%	6122
	21st to end	Day	6% 5% 2 5% 4 4 5% 5% 8% 9% 47%	6925
June	1st to 10th	Day	5% 4 2 5% 4 4 6% 6% 9% 9% 47%	2800
	11th to 20th	Day	4 3 1 4 4 4 5% 5% 8% 9% 54%	2800
	21st to end	Day	3 3 2 5% 5% 5% 6% 6% 9% 9% 49%	2800
July	1st to 10th	Day	3 3 1 4 3 4 5% 5% 7% 10% 53%	6339
	11th to 20th	Day	4 4 2 7% 5% 6% 6% 6% 8% 9% 43%	6340
	21st to end	Day	4 4 2 7% 6% 6% 6% 6% 7% 8% 44%	6750
August	1st to 10th	Day	7% 5% 2 6% 6% 5% 6% 6% 9% 10% 39%	5661
	11th to 20th	Day	3 3 1 5% 5% 5% 7% 5% 8% 10% 49%	5366
	21st to end	Day	8% 4 2 5% 4 5% 6% 5% 8% 8% 44%	5984
September	1st to 10th	Day	5% 3 2 4 3 5% 5% 4 7% 7% 56%	2400
	11th to 20th	Day	5% 3 1 4 3 4 4 5% 6% 7% 58%	2359
	21st to end	Day	4 4 1 5% 3 3 3 3 4 7% 64%	2200
October	1st to 10th	Day	4 4 1 3 1 2 2 2 4 5% 73%	3346
	11th to 20th	Day	4 5% 2 6% 3 3 3 3 4 6% 60%	3250
	21st to end	Day	3 3 1 3 2 2 2 3 4 6% 72%	3425
November	1st to 10th	Day	2 4 1 3 3 2 3 2 6% 7% 67%	1853
	11th to 20th	Day	1 3 1 3 3 2 3 3 5% 7% 69%	1890
	21st to end	Day	1 4 2 6% 3 3 3 3 5% 7% 63%	1853
December	1st to 10th	Day	1 4 2 3 3 2 3 3 4 6% 70%	2700
	11th to 20th	Day	1 3 1 3 3 2 3 3 4 8% 69%	3106
	21st to end	Day	1 4 2 5% 3 3 4 4 5% 7% 61%	4092
January	1st to 10th	Night	1 5% 3 7% 4 3 4 3 5% 8% 57%	6467
	11th to 20th	Night	1 3 2 4 4 4 4 3 5% 7% 64%	6367
	21st to end	Night	1 3 2 6% 4 3 3 3 4 6% 65%	6611
February	1st to 10th	Night	1 5% 2 6% 4 3 3 3 5% 8% 58%	2575
	11th to 20th	Night	1 6% 3 7% 4 3 4 4 6% 7% 54%	2338
	21st to end	Night	1 5% 2 6% 3 2 3 2 5% 4 66%	1980
March	1st to 10th	Night	1 5% 1 5% 3 4 4 3 5% 7% 63%	5374
	11th to 20th	Night	4 8% 2 5% 4 4 3 3 5% 6% 56%	5094
	21st to end	Night	3 7% 2 5% 3 3 4 3 5% 7% 57%	5104
April	1st to 10th	Night	3 5% 1 4 3 3 4 3 5% 8% 61%	2000
	11th to 20th	Night	6% 9% 2 5% 2 4 3 4 5% 7% 53%	1977
	21st to end	Night	7% 7% 2 5% 3 4 4 3 5% 8% 52%	2000
May	1st to 10th	Night	11% 7% 2 4 3 3 3 3 4 7% 53%	4264
	11th to 20th	Night	6% 7% 2 4 3 4 4 4 6% 9% 52%	3776
	21st to end	Night	8% 6% 2 5% 4 4 4 4 5% 7% 52%	3972
June	1st to 10th	Night	6% 4 2 4 2 3 3 4 7% 10% 56%	1600
	11th to 20th	Night	4 3 1 3 3 3 3 3 6% 9% 63%	1600
	21st to end	Night	4 4 1 5% 4 3 5% 5% 7% 8% 53%	1600
July	1st to 10th	Night	4 4 1 5% 4 5% 5% 4 6% 7% 54%	3640
	11th to 20th	Night	3 4 2 5% 5% 5% 5% 6% 8% 12% 46%	3640
	21st to end	Night	4 5% 2 5% 4 4 5% 5% 8% 9% 48%	4119
August	1st to 10th	Night	8% 5% 2 4 4 4 5% 4 8% 10% 46%	4148
	11th to 20th	Night	4 4 1 5% 4 5% 5% 5% 8% 11% 49%	4483
	21st to end	Night	8% 5% 2 6% 4 5% 5% 5% 8% 10% 43%	4993
September	1st to 10th	Night	5% 4 2 5% 4 5% 6% 4 7% 8% 53%	2000
	11th to 20th	Night	7% 4 1 4 3 3 3 3 4 7% 62%	2040
	21st to end	Night	5% 4 2 4 3 3 3 3 4 6% 64%	2200
October	1st to 10th	Night	5% 4 1 2 2 2 2 2 3 5% 72%	3839
	11th to 20th	Night	7% 5% 1 4 3 3 3 3 5% 6% 60%	3898
	21st to end	Night	3 3 2 3 2 2 2 2 3 6% 71%	4343
November	1st to 10th	Night	2 4 1 3 2 3 3 2 5% 7% 67%	2665
	11th to 20th	Night	1 2 2 3 3 2 3 3 5% 5% 71%	2730
	21st to end	Night	2 4 2 5% 3 3 2 3 5% 6% 64%	2762
December	1st to 10th	Night	2 1 4 3 2 2 2 3 5% 75%	4710
	11th to 20th	Night	1 3 2 4 3 3 3 3 5% 10% 65%	5321
	21st to end	Night	2 5% 2 5% 3 3 4 3 5% 7% 61%	7128

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	19% 3 7% 34% 27% 10%	3719
	11th to 20th	Day	23% 4 10% 22% 30% 12%	3878
	21st to end	Day	24% 3 7% 26% 28% 13%	4609
February	1st to 10th	Day	25% 3 10% 27% 23% 11%	1823
	11th to 20th	Day	24% 5% 7% 27% 28% 8%	1959
	21st to end	Day	25% 3 7% 20% 25% 19%	1650
March	1st to 10th	Day	18% 4 7% 16% 34% 22%	4500
	11th to 20th	Day	30% 5% 8% 22% 27% 8%	4898
	21st to end	Day	24% 6% 10% 38% 19% 3	5854
April	1st to 10th	Day	24% 6% 12% 25% 23% 11%	2400
	11th to 20th	Day	30% 6% 10% 23% 19% 11%	2374
	21st to end	Day	31% 6% 11% 26% 22% 5%	2400
May	1st to 10th	Day	33% 6% 11% 25% 17% 9%	5716
	11th to 20th	Day	26% 8% 10% 20% 26% 11%	6126
	21st to end	Day	26% 9% 14% 22% 21% 7%	6926
June	1st to 10th	Day	27% 9% 14% 24% 17% 10%	2800
	11th to 20th	Day	21% 7% 12% 17% 25% 18%	2800
	21st to end	Day	27% 7% 11% 19% 22% 13%	2800
July	1st to 10th	Day	23% 6% 11% 18% 26% 16%	6271
	11th to 20th	Day	30% 8% 13% 24% 16% 9%	6265
	21st to end	Day	31% 8% 12% 16% 18% 14%	6555
August	1st to 10th	Day	36% 9% 15% 23% 11% 5%	4123
	11th to 20th	Day	27% 9% 12% 19% 20% 14%	3882
	21st to end	Day	28% 7% 13% 20% 26% 7%	4311
September	1st to 10th	Day	23% 6% 10% 22% 25% 15%	2400
	11th to 20th	Day	21% 6% 9% 18% 29% 18%	2359
	21st to end	Day	21% 4 7% 20% 34% 15%	2200
October	1st to 10th	Day	15% 3 7% 15% 39% 22%	3346
	11th to 20th	Day	24% 4 8% 21% 32% 12%	3250
	21st to end	Day	15% 2 6% 22% 38% 18%	3425
November	1st to 10th	Day	17% 2 8% 24% 31% 18%	1853
	11th to 20th	Day	16% 3 5% 29% 34% 12%	1890
	21st to end	Day	21% 3 7% 23% 29% 17%	1853
December	1st to 10th	Day	16% 4 7% 29% 34% 10%	2700
	11th to 20th	Day	16% 3 5% 31% 32% 13%	3104
	21st to end	Day	20% 4 10% 26% 28% 12%	4092
January	1st to 10th	Night	26% 4 6% 31% 26% 7%	6467
	11th to 20th	Night	21% 3 9% 25% 26% 15%	6367
	21st to end	Night	22% 4 10% 25% 27% 13%	6611
February	1st to 10th	Night	26% 3 9% 26% 25% 10%	2575
	11th to 20th	Night	29% 4 9% 28% 22% 8%	2338
	21st to end	Night	22% 3 5% 26% 27% 17%	1980
March	1st to 10th	Night	20% 3 8% 16% 38% 15%	5374
	11th to 20th	Night	28% 5% 10% 17% 29% 11%	5094
	21st to end	Night	26% 6% 11% 33% 21% 3	5104
April	1st to 10th	Night	23% 5% 12% 25% 25% 11%	2000
	11th to 20th	Night	29% 6% 11% 25% 20% 9%	1977
	21st to end	Night	30% 6% 13% 26% 19% 6%	2000
May	1st to 10th	Night	32% 6% 14% 30% 12% 7%	4261
	11th to 20th	Night	28% 7% 14% 23% 18% 10%	3777
	21st to end	Night	31% 7% 16% 23% 17% 6%	3972
June	1st to 10th	Night	24% 7% 21% 25% 15% 9%	1600
	11th to 20th	Night	18% 7% 14% 23% 20% 18%	1600
	21st to end	Night	26% 7% 11% 22% 22% 12%	1600
July	1st to 10th	Night	28% 6% 11% 21% 28% 6%	3600
	11th to 20th	Night	28% 8% 19% 26% 15% 5%	3592
	21st to end	Night	30% 9% 15% 19% 16% 11%	4002
August	1st to 10th	Night	39% 9% 18% 19% 10% 5%	3010
	11th to 20th	Night	30% 8% 17% 21% 19% 5%	3243
	21st to end	Night	27% 9% 18% 25% 17% 4	3597
September	1st to 10th	Night	27% 6% 11% 22% 23% 11%	2000
	11th to 20th	Night	21% 5% 9% 24% 26% 15%	2040
	21st to end	Night	23% 4 8% 22% 31% 12%	2200
October	1st to 10th	Night	17% 4 7% 20% 36% 17%	3839
	11th to 20th	Night	25% 3 7% 27% 28% 10%	3898
	21st to end	Night	17% 3 6% 25% 32% 16%	4343
November	1st to 10th	Night	17% 4 8% 25% 30% 16%	2665
	11th to 20th	Night	16% 3 7% 28% 33% 13%	2730
	21st to end	Night	21% 3 9% 24% 30% 13%	2762
December	1st to 10th	Night	14% 3 7% 33% 33% 10%	4710
	11th to 20th	Night	18% 3 6% 27% 36% 10%	5322
	21st to end	Night	24% 3 10% 23% 27% 12%	7128

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	5% 9% 35% 36% 12% 4	330
	11th to 20th	Day	5% 12% 36% 35% 9% 3	330
	21st to end	Day	4 11% 36% 34% 13% 2	363
February	1st to 10th	Day	5% 15% 48% 25% 6% 2	300
	11th to 20th	Day	2 15% 46% 27% 10% 1	300
	21st to end	Day	2 16% 47% 28% 7% 1	249
March	1st to 10th	Day	2 16% 37% 32% 10% 3	300
	11th to 20th	Day	8% 18% 40% 21% 10% 3	450
	21st to end	Day	10% 22% 40% 20% 6% 2	550
April	1st to 10th	Day	10% 19% 40% 24% 7% 2	500
	11th to 20th	Day	11% 23% 38% 20% 6% 2	492
	21st to end	Day	13% 18% 34% 26% 7% 2	500
May	1st to 10th	Day	14% 16% 34% 25% 8% 3	623
	11th to 20th	Day	12% 11% 28% 31% 14% 4	725
	21st to end	Day	9% 12% 29% 28% 18% 4	789
June	1st to 10th	Day	6% 9% 23% 32% 23% 7%	730
	11th to 20th	Day	6% 9% 27% 32% 21% 5%	730
	21st to end	Day	4 7% 26% 33% 22% 7%	730
July	1st to 10th	Day	6% 5% 19% 31% 29% 10%	721
	11th to 20th	Day	5% 3 15% 32% 34% 12%	718
	21st to end	Day	7% 3 12% 30% 33% 14%	729
August	1st to 10th	Day	8% 2 20% 35% 27% 7%	527
	11th to 20th	Day	4 6% 20% 35% 21% 13%	517
	21st to end	Day	7% 4 22% 38% 20% 10%	583
September	1st to 10th	Day	7% 4 26% 34% 19% 10%	530
	11th to 20th	Day	5% 7% 30% 29% 21% 8%	489
	21st to end	Day	9% 8% 18% 28% 24% 12%	330
October	1st to 10th	Day	8% 12% 20% 28% 24% 9%	330
	11th to 20th	Day	2 11% 36% 30% 15% 6%	330
	21st to end	Day	6% 12% 33% 29% 17% 3	363
November	1st to 10th	Day	6% 11% 36% 28% 14% 5%	330
	11th to 20th	Day	3 7% 36% 35% 15% 3	330
	21st to end	Day	5% 12% 34% 32% 13% 4	330
December	1st to 10th	Day	3 11% 41% 29% 13% 4	330
	11th to 20th	Day	5% 8% 40% 31% 15% 1	330
	21st to end	Day	3 12% 42% 33% 8% 2	363
January	1st to 10th	Night	3 6% 40% 36% 12% 4	1050
	11th to 20th	Night	3 7% 43% 35% 10% 2	1002
	21st to end	Night	2 6% 38% 43% 10% 1	924
February	1st to 10th	Night	3 5% 52% 33% 6% 1	800
	11th to 20th	Night	3 6% 47% 35% 8% 1	784
	21st to end	Night	3 7% 51% 34% 5%	660
March	1st to 10th	Night	3 6% 45% 35% 9% 1	800
	11th to 20th	Night	8% 7% 34% 40% 11% 1	800
	21st to end	Night	5% 9% 43% 35% 7%	715
April	1st to 10th	Night	7% 10% 42% 36% 5%	600
	11th to 20th	Night	13% 12% 33% 34% 7% 1	593
	21st to end	Night	11% 9% 33% 37% 9% 1	600
May	1st to 10th	Night	11% 9% 29% 37% 13% 1	600
	11th to 20th	Night	12% 6% 25% 42% 14% 2	591
	21st to end	Night	10% 6% 30% 35% 16% 2	650
June	1st to 10th	Night	7% 5% 20% 43% 22% 3	600
	11th to 20th	Night	4 4 25% 50% 17% 1	600
	21st to end	Night	5% 3 20% 47% 23% 2	600
July	1st to 10th	Night	6% 3 13% 42% 33% 2	585
	11th to 20th	Night	4 2 8% 43% 39% 4	582
	21st to end	Night	6% 2 9% 37% 42% 4	657
August	1st to 10th	Night	7% 3 10% 39% 38% 3	597
	11th to 20th	Night	6% 1 9% 48% 32% 3	594
	21st to end	Night	6% 1 9% 45% 35% 4	660
September	1st to 10th	Night	5% 3 11% 47% 28% 6%	600
	11th to 20th	Night	9% 3 15% 47% 22% 4	600
	21st to end	Night	8% 3 20% 44% 22% 3	600
October	1st to 10th	Night	10% 4 24% 41% 18% 3	745
	11th to 20th	Night	4 4 31% 39% 18% 4	800
	21st to end	Night	6% 6% 32% 37% 16% 3	935
November	1st to 10th	Night	4 4 35% 42% 14% 2	1025
	11th to 20th	Night	2 6% 37% 44% 10% 2	1050
	21st to end	Night	5% 7% 34% 40% 12% 2	1050
December	1st to 10th	Night	2 6% 41% 39% 11% 1	1050
	11th to 20th	Night	3 6% 42% 37% 11% 2	1050
	21st to end	Night	4 8% 45% 34% 8% 1	1155

Page generated at 2026-01-28 23:21:43. Version ac07

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