Bar-J Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bar-J Ranch clear sky chart from 2005-11-06 to 2026-07-16.

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 5% 2 5% 4 4 4 4 6% 8% 55%	146709
	Night	3 5% 2 4 3 3 3 3 5% 7% 61%	143486
Transparency	Day	25% 4 10% 25% 25% 12%	141670
	Night	22% 4 11% 27% 26% 10%	139535
Seeing	Day	11% 17% 34% 25% 11% 2	17796
	Night	7% 10% 38% 33% 11% 1	27811

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	5% 3 7% 3 3 4 3 4 6% 63%	4720
	11th to 20th	Day	2 2 5% 4 3 3 3 4 7% 68%	5160
	21st to end	Day	6% 2 6% 4 3 3 3 4 6% 64%	5844
February	1st to 10th	Day	1 6% 3 5% 3 2 3 3 5% 8% 63%	1890
	11th to 20th	Day	1 3 2 3 3 3 2 4 6% 8% 64%	2023
	21st to end	Day	4 2 5% 3 3 3 3 5% 7% 64%	1730
March	1st to 10th	Day	1 5% 3 4 3 2 3 3 4 8% 64%	4644
	11th to 20th	Day	2 9% 4 8% 5% 4 4 4 5% 7% 48%	5110
	21st to end	Day	1 5% 2 4 3 4 5% 4 7% 10% 54%	5889
April	1st to 10th	Day	2 6% 2 5% 5% 4 4 4 6% 8% 55%	2520
	11th to 20th	Day	5% 9% 3 6% 3 4 4 3 5% 7% 50%	2491
	21st to end	Day	6% 8% 2 5% 4 4 5% 4 6% 7% 48%	2520
May	1st to 10th	Day	9% 9% 3 5% 3 3 4 4 6% 8% 43%	7193
	11th to 20th	Day	5% 6% 2 5% 4 4 4 5% 7% 9% 49%	8130
	21st to end	Day	5% 6% 2 5% 4 4 5% 5% 6% 9% 50%	9026
June	1st to 10th	Day	4 4 1 4 4 5% 6% 5% 8% 10% 48%	2940
	11th to 20th	Day	4 3 1 4 3 4 5% 4 6% 8% 57%	2940
	21st to end	Day	3 4 2 4 3 5% 6% 4 7% 9% 52%	2940
July	1st to 10th	Day	3 3 1 4 4 4 5% 5% 7% 9% 56%	6479
	11th to 20th	Day	4 3 1 5% 5% 6% 7% 6% 9% 11% 43%	6411
	21st to end	Day	5% 5% 2 6% 5% 5% 6% 5% 7% 9% 44%	6522
August	1st to 10th	Day	5% 4 2 5% 5% 6% 7% 6% 8% 10% 41%	5762
	11th to 20th	Day	3 3 1 4 4 5% 6% 6% 8% 11% 48%	5366
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 6% 8% 10% 43%	5984
September	1st to 10th	Day	6% 5% 2 5% 4 4 4 4 6% 7% 54%	2400
	11th to 20th	Day	5% 4 1 5% 3 4 4 3 6% 7% 59%	2398
	21st to end	Day	6% 4 1 3 3 3 4 3 4 5% 64%	2185
October	1st to 10th	Day	3 3 1 3 3 2 3 3 3 5% 70%	3270
	11th to 20th	Day	5% 4 1 4 2 3 4 4 6% 7% 60%	3250
	21st to end	Day	2 3 1 2 2 2 3 2 4 6% 73%	3525
November	1st to 10th	Day	1 3 2 4 2 2 2 2 4 7% 72%	1853
	11th to 20th	Day	1 2 2 3 2 2 2 2 4 6% 73%	1890
	21st to end	Day	1 4 2 4 3 2 3 3 4 8% 66%	1806
December	1st to 10th	Day	5% 1 3 2 2 2 2 3 6% 74%	2700
	11th to 20th	Day	1 2 2 2 2 2 3 3 5% 9% 70%	3106
	21st to end	Day	1 3 2 4 3 3 3 3 6% 8% 64%	4092
January	1st to 10th	Night	5% 3 7% 3 3 3 3 4 7% 62%	8201
	11th to 20th	Night	1 1 3 3 3 3 3 4 6% 72%	7872
	21st to end	Night	1 4 2 5% 3 3 4 3 4 5% 67%	8370
February	1st to 10th	Night	1 5% 2 5% 3 2 2 2 3 7% 68%	2730
	11th to 20th	Night	1 5% 3 6% 3 3 3 3 4 7% 62%	2481
	21st to end	Night	1 5% 3 5% 2 2 2 3 4 6% 67%	2076
March	1st to 10th	Night	1 8% 3 5% 3 2 3 3 4 6% 62%	5449
	11th to 20th	Night	2 10% 2 4 2 3 3 3 5% 6% 59%	5110
	21st to end	Night	1 5% 2 4 3 3 3 3 5% 7% 63%	5313
April	1st to 10th	Night	2 7% 2 4 3 2 3 2 5% 7% 63%	2100
	11th to 20th	Night	6% 9% 3 4 2 3 3 2 4 6% 57%	2077
	21st to end	Night	7% 9% 2 4 3 3 3 3 5% 6% 55%	2100
May	1st to 10th	Night	8% 11% 2 4 3 3 4 3 5% 6% 50%	5737
	11th to 20th	Night	7% 7% 2 4 3 2 3 3 5% 7% 57%	4758
	21st to end	Night	11% 9% 2 4 2 3 3 2 4 6% 53%	5181
June	1st to 10th	Night	6% 4 1 3 3 3 4 3 6% 10% 57%	1680
	11th to 20th	Night	4 3 1 3 2 2 3 3 6% 8% 66%	1680
	21st to end	Night	5% 3 1 3 4 3 4 4 7% 8% 56%	1680
July	1st to 10th	Night	6% 4 1 4 3 4 4 5% 7% 8% 54%	3720
	11th to 20th	Night	4 4 1 4 3 4 6% 6% 10% 13% 46%	3680
	21st to end	Night	4 4 2 6% 4 5% 6% 5% 8% 9% 47%	4333
August	1st to 10th	Night	6% 4 1 5% 4 4 5% 4 7% 10% 49%	4049
	11th to 20th	Night	4 3 1 3 3 4 5% 5% 9% 12% 50%	4483
	21st to end	Night	7% 6% 2 7% 4 6% 5% 5% 7% 11% 41%	4993
September	1st to 10th	Night	7% 5% 1 5% 5% 4 4 4 7% 9% 50%	2000
	11th to 20th	Night	7% 4 1 3 2 3 3 3 5% 8% 60%	2000
	21st to end	Night	6% 5% 2 4 2 3 4 3 5% 5% 63%	2210
October	1st to 10th	Night	4 4 1 2 2 2 3 2 4 4 72%	3920
	11th to 20th	Night	5% 4 1 3 2 2 4 3 4 6% 65%	3898
	21st to end	Night	3 3 1 3 1 1 2 2 4 5% 74%	4252
November	1st to 10th	Night	1 3 1 3 2 2 2 2 4 7% 73%	2655
	11th to 20th	Night	3 1 3 3 2 3 2 4 5% 74%	2730
	21st to end	Night	2 6% 2 3 2 3 2 3 5% 6% 66%	2809
December	1st to 10th	Night	2 1 4 2 2 2 2 3 6% 76%	4710
	11th to 20th	Night	1 3 1 3 2 2 2 3 5% 7% 72%	5321
	21st to end	Night	1 5% 2 5% 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	21% 4 6% 31% 30% 7%	4723
	11th to 20th	Day	17% 4 7% 23% 35% 14%	5160
	21st to end	Day	22% 2 6% 26% 28% 16%	5844
February	1st to 10th	Day	20% 6% 10% 31% 24% 10%	1890
	11th to 20th	Day	18% 5% 9% 30% 30% 8%	2033
	21st to end	Day	20% 4 8% 23% 29% 17%	1730
March	1st to 10th	Day	19% 4 4 17% 35% 22%	4644
	11th to 20th	Day	34% 5% 6% 25% 24% 7%	5110
	21st to end	Day	21% 5% 7% 46% 18% 4	5889
April	1st to 10th	Day	25% 5% 10% 24% 24% 12%	2520
	11th to 20th	Day	30% 5% 7% 26% 21% 10%	2494
	21st to end	Day	29% 7% 10% 25% 22% 7%	2520
May	1st to 10th	Day	35% 4 10% 29% 14% 8%	7193
	11th to 20th	Day	30% 4 9% 23% 24% 10%	8134
	21st to end	Day	28% 5% 11% 23% 20% 12%	9027
June	1st to 10th	Day	26% 7% 15% 21% 21% 10%	2940
	11th to 20th	Day	22% 5% 9% 19% 24% 21%	2940
	21st to end	Day	23% 6% 12% 21% 23% 15%	2940
July	1st to 10th	Day	23% 3 7% 16% 26% 24%	6411
	11th to 20th	Day	30% 4 16% 27% 14% 9%	6336
	21st to end	Day	33% 4 16% 19% 15% 12%	6335
August	1st to 10th	Day	38% 7% 17% 21% 13% 5%	4191
	11th to 20th	Day	27% 6% 16% 18% 20% 13%	3882
	21st to end	Day	32% 4 16% 19% 23% 5%	4311
September	1st to 10th	Day	26% 5% 11% 22% 23% 13%	2400
	11th to 20th	Day	22% 4 11% 21% 28% 15%	2398
	21st to end	Day	21% 3 6% 23% 34% 12%	2185
October	1st to 10th	Day	17% 3 6% 18% 35% 21%	3270
	11th to 20th	Day	22% 1 6% 34% 26% 11%	3250
	21st to end	Day	14% 2 4 24% 42% 14%	3525
November	1st to 10th	Day	13% 3 9% 24% 38% 14%	1853
	11th to 20th	Day	13% 3 5% 35% 33% 10%	1890
	21st to end	Day	18% 3 8% 29% 31% 11%	1806
December	1st to 10th	Day	14% 3 9% 34% 30% 10%	2700
	11th to 20th	Day	13% 3 9% 32% 34% 9%	3104
	21st to end	Day	16% 4 8% 30% 31% 11%	4092
January	1st to 10th	Night	24% 3 5% 33% 30% 4	8202
	11th to 20th	Night	14% 3 9% 27% 29% 17%	7872
	21st to end	Night	22% 3 10% 24% 27% 15%	8370
February	1st to 10th	Night	19% 4 11% 33% 26% 8%	2730
	11th to 20th	Night	23% 4 10% 29% 27% 6%	2481
	21st to end	Night	19% 3 7% 28% 31% 13%	2076
March	1st to 10th	Night	22% 2 5% 19% 37% 14%	5449
	11th to 20th	Night	26% 4 8% 23% 29% 10%	5110
	21st to end	Night	21% 4 9% 42% 21% 2	5313
April	1st to 10th	Night	20% 6% 11% 28% 27% 8%	2100
	11th to 20th	Night	28% 4 9% 26% 23% 9%	2077
	21st to end	Night	29% 4 13% 27% 20% 7%	2100
May	1st to 10th	Night	34% 3 13% 31% 13% 7%	5735
	11th to 20th	Night	27% 4 11% 28% 19% 10%	4759
	21st to end	Night	32% 4 14% 18% 19% 12%	5182
June	1st to 10th	Night	21% 6% 20% 23% 16% 13%	1680
	11th to 20th	Night	17% 5% 11% 23% 23% 21%	1680
	21st to end	Night	24% 6% 13% 22% 19% 16%	1680
July	1st to 10th	Night	26% 4 9% 19% 27% 15%	3680
	11th to 20th	Night	26% 4 23% 29% 12% 5%	3632
	21st to end	Night	30% 6% 21% 20% 12% 11%	4209
August	1st to 10th	Night	35% 9% 25% 16% 9% 6%	2944
	11th to 20th	Night	24% 7% 26% 19% 16% 8%	3243
	21st to end	Night	32% 7% 17% 25% 17% 3	3597
September	1st to 10th	Night	29% 7% 11% 23% 20% 9%	2000
	11th to 20th	Night	22% 4 12% 22% 25% 14%	2000
	21st to end	Night	22% 4 9% 25% 31% 10%	2210
October	1st to 10th	Night	17% 3 7% 22% 32% 18%	3920
	11th to 20th	Night	21% 2 9% 30% 29% 9%	3898
	21st to end	Night	14% 2 5% 27% 37% 15%	4252
November	1st to 10th	Night	13% 3 10% 29% 34% 11%	2655
	11th to 20th	Night	14% 3 7% 34% 33% 10%	2730
	21st to end	Night	18% 3 10% 27% 32% 10%	2809
December	1st to 10th	Night	13% 3 8% 34% 34% 8%	4710
	11th to 20th	Night	13% 4 8% 29% 39% 8%	5322
	21st to end	Night	21% 5% 10% 26% 32% 7%	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	11% 20% 39% 21% 8%	330
	11th to 20th	Day	12% 19% 42% 24% 2 1	330
	21st to end	Day	6% 18% 47% 22% 6% 1	363
February	1st to 10th	Day	15% 24% 43% 16% 2 1	330
	11th to 20th	Day	12% 27% 45% 13% 3 1	330
	21st to end	Day	16% 25% 42% 14% 3	273
March	1st to 10th	Day	14% 25% 38% 19% 4	348
	11th to 20th	Day	17% 25% 36% 18% 5%	540
	21st to end	Day	17% 32% 36% 12% 3	594
April	1st to 10th	Day	16% 30% 33% 15% 5% 1	540
	11th to 20th	Day	24% 30% 31% 11% 2 1	532
	21st to end	Day	19% 30% 31% 16% 4 1	540
May	1st to 10th	Day	17% 25% 35% 17% 6% 1	590
	11th to 20th	Day	14% 18% 31% 26% 10% 1	775
	21st to end	Day	13% 16% 30% 27% 14%	844
June	1st to 10th	Day	7% 12% 33% 31% 14% 3	780
	11th to 20th	Day	7% 14% 37% 28% 11% 2	780
	21st to end	Day	6% 17% 32% 27% 16% 2	780
July	1st to 10th	Day	7% 8% 24% 33% 23% 4	771
	11th to 20th	Day	6% 3 24% 35% 27% 5%	744
	21st to end	Day	8% 5% 22% 37% 23% 5%	631
August	1st to 10th	Day	10% 6% 29% 36% 14% 5%	527
	11th to 20th	Day	6% 8% 32% 31% 17% 5%	517
	21st to end	Day	10% 7% 32% 32% 16% 3	583
September	1st to 10th	Day	7% 9% 30% 31% 18% 5%	530
	11th to 20th	Day	6% 11% 40% 27% 12% 3	528
	21st to end	Day	10% 9% 24% 33% 20% 4	330
October	1st to 10th	Day	8% 14% 28% 25% 20% 5%	330
	11th to 20th	Day	12% 18% 30% 24% 14% 1	330
	21st to end	Day	13% 18% 33% 25% 10% 1	363
November	1st to 10th	Day	11% 16% 39% 23% 11% 1	330
	11th to 20th	Day	12% 14% 42% 25% 6% 2	330
	21st to end	Day	9% 16% 46% 23% 5%	330
December	1st to 10th	Day	10% 21% 42% 20% 7%	330
	11th to 20th	Day	10% 19% 48% 15% 7% 1	330
	21st to end	Day	14% 25% 41% 16% 4 1	363
January	1st to 10th	Night	5% 16% 46% 26% 6% 1	1050
	11th to 20th	Night	4 17% 49% 23% 6%	919
	21st to end	Night	2 12% 53% 27% 5%	924
February	1st to 10th	Night	5% 13% 59% 22% 2	840
	11th to 20th	Night	6% 16% 53% 22% 3	824
	21st to end	Night	4 18% 57% 21% 1	692
March	1st to 10th	Night	5% 16% 50% 26% 4	840
	11th to 20th	Night	8% 13% 43% 31% 6%	840
	21st to end	Night	6% 13% 50% 28% 3	795
April	1st to 10th	Night	7% 15% 44% 31% 3	630
	11th to 20th	Night	12% 16% 38% 29% 5%	623
	21st to end	Night	11% 13% 38% 32% 6%	630
May	1st to 10th	Night	14% 10% 31% 37% 7% 1	630
	11th to 20th	Night	12% 9% 29% 39% 11%	621
	21st to end	Night	14% 7% 30% 35% 14%	683
June	1st to 10th	Night	7% 6% 24% 45% 16% 2	630
	11th to 20th	Night	5% 5% 30% 48% 12% 1	630
	21st to end	Night	7% 4 23% 43% 23%	630
July	1st to 10th	Night	8% 3 15% 43% 29% 3	615
	11th to 20th	Night	6% 1 10% 47% 34% 3	597
	21st to end	Night	7% 2 9% 40% 39% 2	657
August	1st to 10th	Night	9% 2 14% 42% 32% 2	597
	11th to 20th	Night	7% 1 13% 50% 26% 2	594
	21st to end	Night	7% 2 15% 46% 28% 2	660
September	1st to 10th	Night	7% 2 15% 50% 24% 3	600
	11th to 20th	Night	10% 3 22% 45% 20% 1	600
	21st to end	Night	8% 6% 24% 46% 15% 1	610
October	1st to 10th	Night	8% 5% 35% 39% 12% 1	800
	11th to 20th	Night	5% 6% 40% 38% 12%	800
	21st to end	Night	7% 8% 41% 34% 10% 1	880
November	1st to 10th	Night	3 11% 47% 31% 7%	1015
	11th to 20th	Night	4 15% 47% 27% 6%	1050
	21st to end	Night	6% 12% 45% 32% 4	1050
December	1st to 10th	Night	4 14% 49% 30% 3	1050
	11th to 20th	Night	4 14% 54% 23% 5%	1050
	21st to end	Night	6% 19% 50% 22% 3	1155

Page generated at 2026-07-13 01:14:51. Version ac07

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