Blackhawk Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackhawk Ranch 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	3 4 2 4 3 4 4 4 6% 8% 58%	135920
	Night	4 5% 2 4 3 3 3 3 5% 7% 61%	133517
Transparency	Day	20% 7% 10% 21% 26% 15%	130933
	Night	21% 6% 10% 21% 27% 15%	129508
Seeing	Day	6% 10% 30% 31% 18% 5%	17030
	Night	6% 7% 36% 36% 13% 1	27172

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 7% 3 5% 2 2 3 2 4 8% 64%	3718
	11th to 20th	Day	1 3 2 4 2 4 4 2 4 7% 66%	4029
	21st to end	Day	2 7% 2 6% 2 2 3 3 5% 6% 63%	4609
February	1st to 10th	Day	1 4 3 5% 3 3 3 3 4 7% 63%	1874
	11th to 20th	Day	1 4 2 4 3 2 4 3 6% 8% 63%	1949
	21st to end	Day	1 5% 2 5% 3 3 3 3 4 7% 63%	1650
March	1st to 10th	Day	1 7% 3 3 2 3 2 2 4 5% 67%	4500
	11th to 20th	Day	4 9% 3 6% 4 3 4 4 5% 7% 52%	4904
	21st to end	Day	2 5% 1 3 3 3 4 4 6% 7% 62%	5851
April	1st to 10th	Day	3 5% 2 4 3 3 3 3 6% 8% 60%	2400
	11th to 20th	Day	5% 7% 2 5% 3 3 4 4 6% 7% 56%	2371
	21st to end	Day	6% 7% 2 4 3 3 4 4 6% 9% 53%	2400
May	1st to 10th	Day	9% 6% 2 4 3 3 4 4 6% 6% 54%	5596
	11th to 20th	Day	5% 4 2 4 3 4 4 3 7% 7% 58%	5946
	21st to end	Day	5% 3 1 3 3 3 4 4 6% 9% 58%	6925
June	1st to 10th	Day	4 3 1 4 4 5% 5% 6% 8% 10% 50%	2800
	11th to 20th	Day	3 2 1 3 2 3 5% 5% 8% 9% 58%	2800
	21st to end	Day	5% 3 2 4 4 5% 6% 5% 9% 10% 48%	2800
July	1st to 10th	Day	2 2 1 3 3 4 5% 5% 8% 11% 55%	6339
	11th to 20th	Day	2 2 1 4 4 6% 8% 6% 10% 11% 46%	6340
	21st to end	Day	4 3 1 6% 6% 7% 7% 7% 9% 9% 41%	6548
August	1st to 10th	Day	4 3 1 4 4 5% 6% 6% 10% 11% 45%	5548
	11th to 20th	Day	3 2 1 4 4 5% 6% 6% 10% 12% 47%	5366
	21st to end	Day	4 3 2 6% 5% 5% 6% 5% 8% 11% 44%	5984
September	1st to 10th	Day	6% 4 1 5% 4 4 5% 5% 7% 8% 54%	2400
	11th to 20th	Day	5% 3 1 3 3 3 4 4 6% 7% 60%	2352
	21st to end	Day	5% 3 1 5% 3 3 4 3 3 6% 64%	2200
October	1st to 10th	Day	3 3 1 2 2 2 3 2 4 5% 73%	3376
	11th to 20th	Day	3 3 1 3 2 2 3 3 6% 8% 65%	3250
	21st to end	Day	3 3 1 3 2 2 1 2 3 4 75%	3486
November	1st to 10th	Day	2 4 1 1 2 2 2 3 5% 6% 72%	1853
	11th to 20th	Day	1 4 1 4 3 2 2 2 4 7% 69%	1890
	21st to end	Day	3 6% 2 4 2 2 3 2 4 6% 66%	1890
December	1st to 10th	Day	3 1 3 1 2 2 2 3 5% 76%	2778
	11th to 20th	Day	1 3 1 3 2 2 3 3 5% 9% 70%	3106
	21st to end	Day	1 4 2 4 3 3 3 3 5% 7% 65%	4092
January	1st to 10th	Night	1 8% 3 7% 3 3 3 2 5% 7% 58%	6467
	11th to 20th	Night	1 4 2 5% 3 3 3 3 4 6% 67%	6202
	21st to end	Night	2 5% 2 6% 3 3 3 2 5% 6% 64%	6611
February	1st to 10th	Night	1 6% 2 6% 3 2 3 3 4 7% 62%	2524
	11th to 20th	Night	2 6% 3 6% 4 3 3 3 5% 7% 58%	2338
	21st to end	Night	1 6% 3 4 2 2 3 2 4 6% 68%	1980
March	1st to 10th	Night	2 8% 2 3 2 2 2 2 3 5% 68%	5374
	11th to 20th	Night	6% 8% 2 5% 3 3 3 3 5% 7% 57%	5088
	21st to end	Night	3 6% 1 5% 3 3 3 3 5% 6% 63%	5105
April	1st to 10th	Night	3 4 1 3 2 3 3 3 5% 6% 66%	2000
	11th to 20th	Night	5% 6% 3 4 2 3 2 2 5% 7% 61%	1977
	21st to end	Night	8% 7% 2 3 3 3 3 3 5% 6% 58%	2000
May	1st to 10th	Night	9% 6% 2 4 3 2 3 2 4 6% 58%	4368
	11th to 20th	Night	7% 3 1 4 2 3 3 3 5% 7% 61%	3953
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 6% 59%	3972
June	1st to 10th	Night	5% 4 1 4 3 3 3 5% 7% 10% 57%	1600
	11th to 20th	Night	3 2 1 2 3 3 3 3 8% 9% 63%	1600
	21st to end	Night	6% 4 2 5% 3 3 5% 5% 7% 10% 50%	1600
July	1st to 10th	Night	6% 3 1 4 3 4 5% 5% 7% 9% 53%	3640
	11th to 20th	Night	4 2 1 5% 4 5% 5% 6% 9% 11% 48%	3640
	21st to end	Night	5% 4 2 6% 5% 6% 7% 6% 9% 11% 42%	4307
August	1st to 10th	Night	4 4 2 6% 5% 5% 5% 5% 7% 9% 48%	4263
	11th to 20th	Night	4 3 1 4 3 4 5% 5% 9% 15% 46%	4483
	21st to end	Night	5% 4 2 6% 5% 5% 6% 6% 9% 11% 39%	4993
September	1st to 10th	Night	5% 5% 1 3 3 4 4 4 8% 9% 55%	2000
	11th to 20th	Night	6% 3 1 3 2 2 3 3 5% 8% 65%	2046
	21st to end	Night	5% 4 1 3 3 3 3 3 5% 6% 65%	2200
October	1st to 10th	Night	4 3 1 2 2 2 2 2 3 5% 73%	3806
	11th to 20th	Night	5% 3 1 3 2 2 3 3 4 6% 66%	3898
	21st to end	Night	3 4 2 3 2 2 2 2 3 4 75%	4280
November	1st to 10th	Night	3 3 1 3 2 1 2 3 4 5% 73%	2665
	11th to 20th	Night	1 3 2 4 1 2 2 2 3 5% 75%	2730
	21st to end	Night	3 6% 2 4 2 2 2 3 5% 7% 66%	2730
December	1st to 10th	Night	4 2 3 2 2 2 2 4 6% 72%	4628
	11th to 20th	Night	1 3 1 3 2 3 3 3 4 8% 69%	5321
	21st to end	Night	2 5% 2 4 3 3 4 3 5% 7% 62%	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	18% 5% 7% 27% 31% 12%	3719
	11th to 20th	Day	17% 5% 7% 19% 34% 17%	4029
	21st to end	Day	21% 5% 8% 19% 34% 13%	4609
February	1st to 10th	Day	21% 4 8% 26% 26% 15%	1874
	11th to 20th	Day	18% 5% 8% 25% 31% 12%	1959
	21st to end	Day	20% 4 6% 18% 28% 23%	1650
March	1st to 10th	Day	18% 4 5% 12% 33% 26%	4500
	11th to 20th	Day	26% 8% 7% 16% 30% 13%	4904
	21st to end	Day	17% 5% 9% 34% 28% 6%	5851
April	1st to 10th	Day	20% 6% 9% 23% 24% 17%	2400
	11th to 20th	Day	25% 6% 10% 22% 21% 16%	2374
	21st to end	Day	24% 7% 12% 22% 26% 9%	2400
May	1st to 10th	Day	26% 7% 11% 22% 21% 13%	5596
	11th to 20th	Day	20% 8% 12% 14% 23% 23%	5950
	21st to end	Day	18% 8% 13% 21% 18% 22%	6926
June	1st to 10th	Day	22% 10% 16% 21% 19% 12%	2800
	11th to 20th	Day	16% 8% 12% 16% 23% 24%	2800
	21st to end	Day	25% 9% 13% 20% 18% 16%	2800
July	1st to 10th	Day	17% 9% 12% 18% 25% 18%	6271
	11th to 20th	Day	22% 11% 16% 27% 19% 5%	6265
	21st to end	Day	30% 11% 14% 19% 17% 8%	6360
August	1st to 10th	Day	28% 13% 20% 22% 12% 5%	4032
	11th to 20th	Day	22% 11% 16% 20% 17% 14%	3882
	21st to end	Day	25% 10% 16% 24% 19% 6%	4311
September	1st to 10th	Day	25% 6% 11% 25% 22% 12%	2400
	11th to 20th	Day	20% 7% 11% 18% 25% 19%	2352
	21st to end	Day	21% 5% 7% 18% 33% 16%	2200
October	1st to 10th	Day	12% 4 7% 15% 36% 26%	3376
	11th to 20th	Day	16% 5% 8% 24% 31% 16%	3250
	21st to end	Day	14% 3 4 15% 40% 23%	3486
November	1st to 10th	Day	12% 3 7% 21% 33% 23%	1853
	11th to 20th	Day	16% 4 6% 25% 33% 16%	1890
	21st to end	Day	21% 3 6% 19% 32% 20%	1890
December	1st to 10th	Day	12% 3 7% 23% 42% 13%	2778
	11th to 20th	Day	13% 4 7% 22% 36% 19%	3104
	21st to end	Day	17% 6% 8% 24% 29% 16%	4092
January	1st to 10th	Night	25% 5% 6% 25% 30% 9%	6467
	11th to 20th	Night	17% 6% 7% 23% 31% 16%	6202
	21st to end	Night	19% 7% 9% 22% 30% 13%	6611
February	1st to 10th	Night	22% 4 8% 26% 25% 16%	2524
	11th to 20th	Night	24% 4 9% 26% 24% 12%	2338
	21st to end	Night	19% 3 6% 18% 36% 19%	1980
March	1st to 10th	Night	20% 3 4 12% 35% 26%	5374
	11th to 20th	Night	26% 7% 8% 14% 28% 18%	5088
	21st to end	Night	20% 6% 8% 34% 26% 7%	5105
April	1st to 10th	Night	18% 4 11% 24% 28% 15%	2000
	11th to 20th	Night	22% 5% 12% 22% 23% 15%	1977
	21st to end	Night	26% 6% 13% 23% 22% 10%	2000
May	1st to 10th	Night	27% 5% 10% 23% 18% 16%	4365
	11th to 20th	Night	20% 7% 9% 20% 26% 18%	3954
	21st to end	Night	23% 9% 13% 16% 17% 23%	3972
June	1st to 10th	Night	21% 9% 15% 23% 16% 16%	1600
	11th to 20th	Night	15% 7% 11% 19% 24% 24%	1600
	21st to end	Night	25% 9% 12% 18% 20% 15%	1600
July	1st to 10th	Night	24% 9% 17% 18% 19% 13%	3600
	11th to 20th	Night	26% 11% 21% 27% 13% 3	3592
	21st to end	Night	31% 11% 16% 18% 18% 7%	4183
August	1st to 10th	Night	39% 11% 18% 17% 11% 5%	3103
	11th to 20th	Night	24% 10% 21% 22% 15% 8%	3243
	21st to end	Night	28% 11% 18% 25% 14% 5%	3597
September	1st to 10th	Night	23% 8% 11% 26% 23% 10%	2000
	11th to 20th	Night	17% 6% 10% 20% 26% 20%	2046
	21st to end	Night	19% 6% 9% 18% 32% 16%	2200
October	1st to 10th	Night	14% 4 8% 17% 35% 22%	3806
	11th to 20th	Night	18% 4 9% 22% 30% 17%	3898
	21st to end	Night	15% 3 5% 19% 37% 21%	4280
November	1st to 10th	Night	14% 3 7% 22% 33% 21%	2665
	11th to 20th	Night	14% 2 5% 26% 36% 17%	2730
	21st to end	Night	19% 4 7% 21% 30% 19%	2730
December	1st to 10th	Night	14% 3 6% 27% 37% 11%	4628
	11th to 20th	Night	14% 4 6% 20% 41% 16%	5322
	21st to end	Night	19% 6% 9% 23% 29% 14%	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	7% 14% 37% 30% 9% 2	330
	11th to 20th	Day	8% 13% 40% 29% 7% 3	330
	21st to end	Day	6% 10% 39% 30% 12% 2	363
February	1st to 10th	Day	5% 18% 50% 22% 5% 1	300
	11th to 20th	Day	6% 13% 50% 23% 7%	300
	21st to end	Day	9% 20% 39% 29% 3	249
March	1st to 10th	Day	5% 20% 36% 27% 11%	300
	11th to 20th	Day	11% 18% 34% 27% 10% 1	456
	21st to end	Day	11% 24% 36% 22% 6%	550
April	1st to 10th	Day	7% 22% 38% 24% 6% 1	500
	11th to 20th	Day	11% 22% 42% 19% 4 2	492
	21st to end	Day	11% 22% 37% 23% 6% 1	500
May	1st to 10th	Day	11% 14% 39% 25% 9% 2	568
	11th to 20th	Day	9% 11% 33% 29% 16% 3	725
	21st to end	Day	6% 11% 33% 32% 14% 3	789
June	1st to 10th	Day	5% 8% 25% 33% 23% 6%	730
	11th to 20th	Day	4 6% 31% 35% 20% 4	730
	21st to end	Day	5% 5% 29% 34% 22% 5%	730
July	1st to 10th	Day	5% 3 19% 33% 32% 7%	721
	11th to 20th	Day	3 1 11% 36% 36% 13%	718
	21st to end	Day	4 2 12% 31% 36% 15%	644
August	1st to 10th	Day	5% 2 19% 38% 27% 9%	527
	11th to 20th	Day	3 3 20% 33% 31% 9%	517
	21st to end	Day	4 3 18% 42% 27% 6%	583
September	1st to 10th	Day	6% 3 19% 39% 25% 8%	530
	11th to 20th	Day	5% 2 26% 38% 23% 5%	482
	21st to end	Day	8% 5% 23% 30% 27% 6%	330
October	1st to 10th	Day	7% 11% 25% 25% 24% 8%	330
	11th to 20th	Day	3 13% 33% 31% 15% 5%	330
	21st to end	Day	7% 11% 30% 32% 18% 2	363
November	1st to 10th	Day	5% 13% 34% 29% 17% 2	330
	11th to 20th	Day	5% 10% 33% 33% 15% 4	330
	21st to end	Day	8% 12% 34% 31% 13% 3	330
December	1st to 10th	Day	5% 15% 38% 26% 14% 3	330
	11th to 20th	Day	5% 11% 41% 34% 7% 2	330
	21st to end	Day	8% 16% 42% 28% 6% 1	363
January	1st to 10th	Night	4 10% 42% 34% 9% 2	1050
	11th to 20th	Night	5% 9% 43% 31% 10% 2	928
	21st to end	Night	4 8% 44% 34% 9% 1	924
February	1st to 10th	Night	4 10% 50% 30% 6%	800
	11th to 20th	Night	5% 13% 51% 25% 6%	784
	21st to end	Night	5% 14% 50% 27% 3	660
March	1st to 10th	Night	6% 12% 48% 28% 6% 1	800
	11th to 20th	Night	7% 10% 40% 36% 7% 1	800
	21st to end	Night	7% 12% 48% 28% 4 1	716
April	1st to 10th	Night	5% 11% 54% 27% 3	600
	11th to 20th	Night	9% 12% 41% 33% 5%	593
	21st to end	Night	12% 9% 40% 32% 7%	600
May	1st to 10th	Night	10% 7% 40% 35% 8% 1	600
	11th to 20th	Night	13% 5% 32% 35% 13% 1	591
	21st to end	Night	9% 7% 38% 34% 11% 1	650
June	1st to 10th	Night	5% 5% 33% 37% 19% 1	600
	11th to 20th	Night	3 4 37% 43% 12% 1	600
	21st to end	Night	5% 5% 27% 42% 21% 1	600
July	1st to 10th	Night	5% 3 20% 41% 28% 2	585
	11th to 20th	Night	5% 1 14% 45% 33% 2	582
	21st to end	Night	5% 2 11% 37% 42% 3	657
August	1st to 10th	Night	6% 2 11% 43% 34% 4	597
	11th to 20th	Night	8% 1 12% 49% 28% 2	594
	21st to end	Night	5% 2 16% 47% 28% 3	660
September	1st to 10th	Night	6% 3 16% 49% 23% 3	600
	11th to 20th	Night	7% 3 25% 48% 15% 3	600
	21st to end	Night	7% 5% 26% 44% 16% 3	600
October	1st to 10th	Night	8% 3 33% 39% 14% 2	725
	11th to 20th	Night	3 5% 35% 40% 15% 3	800
	21st to end	Night	7% 6% 33% 37% 15% 3	896
November	1st to 10th	Night	4 7% 37% 39% 12% 1	1025
	11th to 20th	Night	3 8% 38% 40% 10% 1	1050
	21st to end	Night	5% 10% 35% 38% 11% 1	1050
December	1st to 10th	Night	3 9% 45% 32% 9% 2	1050
	11th to 20th	Night	3 10% 44% 34% 7%	1050
	21st to end	Night	5% 12% 44% 33% 5% 1	1155

Page generated at 2026-01-28 23:21:46. Version ac07

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