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 2025-03-12.

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% 56%	112796
	Night	3 5% 2 4 3 3 3 3 5% 7% 61%	115040
Transparency	Day	24% 5% 10% 25% 25% 11%	112546
	Night	22% 5% 11% 27% 26% 10%	114881
Seeing	Day	10% 17% 34% 25% 12% 2	15858
	Night	6% 10% 38% 34% 11% 1	26074

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	4 3 7% 2 3 4 3 4 7% 63%	3638
	11th to 20th	Day	2 2 7% 5% 4 4 3 4 8% 60%	3962
	21st to end	Day	1 6% 3 7% 3 3 3 2 4 6% 63%	4510
February	1st to 10th	Day	1 6% 3 5% 3 2 3 3 5% 8% 62%	1800
	11th to 20th	Day	1 3 2 3 3 3 2 3 6% 8% 64%	1924
	21st to end	Day	5% 2 6% 3 3 3 4 5% 7% 63%	1650
March	1st to 10th	Day	1 6% 3 5% 3 3 3 2 4 8% 62%	3260
	11th to 20th	Day	3 13% 4 7% 4 3 3 4 5% 7% 47%	3502
	21st to end	Day	1 7% 3 5% 4 4 5% 4 7% 9% 50%	4023
April	1st to 10th	Day	2 6% 2 5% 5% 4 4 4 6% 8% 55%	2280
	11th to 20th	Day	5% 9% 3 6% 3 4 5% 4 5% 7% 49%	2251
	21st to end	Day	6% 8% 2 5% 4 4 5% 5% 6% 6% 47%	2280
May	1st to 10th	Day	7% 8% 4 5% 3 4 5% 5% 6% 7% 47%	3882
	11th to 20th	Day	8% 7% 3 5% 4 4 4 5% 7% 9% 45%	4352
	21st to end	Day	4 5% 2 4 3 4 5% 5% 7% 9% 52%	4825
June	1st to 10th	Day	4 5% 1 4 4 5% 6% 5% 8% 10% 49%	2660
	11th to 20th	Day	5% 4 1 4 3 4 5% 4 6% 8% 56%	2660
	21st to end	Day	4 4 2 5% 4 5% 6% 5% 8% 9% 49%	2660
July	1st to 10th	Day	5% 4 1 4 4 4 5% 5% 7% 8% 53%	4430
	11th to 20th	Day	5% 4 1 5% 5% 6% 7% 6% 8% 10% 44%	4430
	21st to end	Day	5% 5% 2 5% 5% 5% 5% 5% 7% 9% 48%	4533
August	1st to 10th	Day	6% 6% 3 6% 6% 6% 6% 5% 8% 9% 38%	4075
	11th to 20th	Day	4 3 1 4 4 5% 6% 6% 8% 10% 48%	3726
	21st to end	Day	4 5% 2 5% 4 5% 6% 6% 8% 10% 44%	4180
September	1st to 10th	Day	5% 5% 2 5% 4 4 4 4 6% 7% 54%	2280
	11th to 20th	Day	5% 4 1 4 3 4 3 3 6% 6% 60%	2278
	21st to end	Day	6% 4 1 3 3 3 3 2 4 5% 66%	2076
October	1st to 10th	Day	3 3 1 3 3 2 3 3 4 5% 70%	3170
	11th to 20th	Day	5% 4 1 4 3 3 4 4 6% 7% 60%	3150
	21st to end	Day	2 3 1 2 2 2 2 2 4 6% 73%	3416
November	1st to 10th	Day	1 3 2 4 2 2 2 2 4 7% 71%	1763
	11th to 20th	Day	1 2 2 4 2 2 2 2 4 6% 74%	1800
	21st to end	Day	1 4 2 4 3 2 2 3 4 8% 67%	1720
December	1st to 10th	Day	5% 1 3 2 2 2 2 3 6% 74%	2620
	11th to 20th	Day	1 2 2 2 2 2 3 3 5% 9% 69%	3026
	21st to end	Day	1 3 2 4 3 3 3 3 6% 8% 63%	4004
January	1st to 10th	Night	4 3 8% 3 3 3 3 4 7% 61%	6327
	11th to 20th	Night	1 2 1 4 4 4 4 3 5% 6% 67%	6046
	21st to end	Night	1 4 2 5% 3 3 3 3 4 5% 66%	6468
February	1st to 10th	Night	1 5% 2 5% 3 2 2 2 4 8% 67%	2600
	11th to 20th	Night	1 5% 3 6% 3 3 3 3 5% 7% 62%	2360
	21st to end	Night	1 5% 3 6% 2 3 2 3 4 7% 66%	1980
March	1st to 10th	Night	1 9% 3 5% 3 2 2 2 4 6% 61%	3822
	11th to 20th	Night	3 14% 3 5% 2 3 3 3 5% 7% 53%	3506
	21st to end	Night	1 7% 2 4 4 3 4 3 5% 7% 59%	3621
April	1st to 10th	Night	3 7% 2 4 3 2 3 3 5% 7% 62%	1900
	11th to 20th	Night	6% 10% 3 5% 2 3 3 3 4 6% 56%	1877
	21st to end	Night	7% 8% 2 4 3 3 3 3 6% 6% 55%	1900
May	1st to 10th	Night	7% 9% 2 3 2 3 3 3 4 6% 57%	3085
	11th to 20th	Night	10% 8% 2 4 3 3 3 4 5% 7% 50%	2549
	21st to end	Night	6% 6% 2 3 2 3 3 3 4 6% 61%	2762
June	1st to 10th	Night	6% 4 1 3 3 3 4 3 6% 10% 58%	1520
	11th to 20th	Night	4 3 1 3 2 2 3 3 6% 8% 65%	1520
	21st to end	Night	5% 3 1 3 4 4 5% 5% 7% 9% 54%	1520
July	1st to 10th	Night	8% 4 1 4 4 4 3 4 6% 7% 53%	2540
	11th to 20th	Night	4 4 1 3 3 3 5% 5% 8% 13% 51%	2540
	21st to end	Night	4 4 1 5% 4 4 5% 4 8% 9% 52%	3012
August	1st to 10th	Night	8% 5% 2 6% 5% 5% 6% 5% 9% 11% 38%	2863
	11th to 20th	Night	4 3 1 3 3 4 5% 6% 10% 13% 48%	3113
	21st to end	Night	4 5% 2 6% 4 6% 6% 5% 8% 11% 43%	3487
September	1st to 10th	Night	7% 5% 1 5% 4 4 4 4 7% 9% 50%	1900
	11th to 20th	Night	7% 4 1 3 2 3 3 2 5% 8% 62%	1900
	21st to end	Night	6% 5% 2 4 2 3 3 3 5% 5% 64%	2099
October	1st to 10th	Night	4 4 1 2 2 2 3 2 4 4 72%	3800
	11th to 20th	Night	5% 4 1 3 2 2 4 3 4 7% 65%	3778
	21st to end	Night	3 3 1 3 1 1 2 2 4 5% 74%	4120
November	1st to 10th	Night	2 3 1 3 2 2 2 2 4 7% 71%	2525
	11th to 20th	Night	3 2 3 3 2 3 2 4 4 75%	2600
	21st to end	Night	2 6% 2 3 2 3 2 3 4 6% 67%	2675
December	1st to 10th	Night	2 1 4 2 2 2 2 3 6% 76%	4570
	11th to 20th	Night	1 3 1 4 2 2 2 3 5% 7% 71%	5181
	21st to end	Night	1 5% 2 5% 3 3 4 3 5% 7% 61%	6974

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% 5% 8% 31% 28% 9%	3639
	11th to 20th	Day	22% 5% 8% 21% 32% 12%	3962
	21st to end	Day	23% 3 8% 27% 27% 13%	4510
February	1st to 10th	Day	20% 6% 11% 31% 22% 10%	1800
	11th to 20th	Day	18% 5% 9% 30% 31% 7%	1934
	21st to end	Day	20% 4 8% 23% 28% 17%	1650
March	1st to 10th	Day	20% 6% 6% 21% 36% 12%	3260
	11th to 20th	Day	34% 7% 9% 32% 16% 3	3502
	21st to end	Day	22% 7% 9% 38% 20% 4	4023
April	1st to 10th	Day	24% 6% 11% 24% 24% 12%	2280
	11th to 20th	Day	32% 6% 7% 25% 20% 10%	2254
	21st to end	Day	30% 8% 10% 25% 21% 6%	2280
May	1st to 10th	Day	30% 8% 10% 21% 17% 14%	3882
	11th to 20th	Day	31% 8% 15% 24% 15% 6%	4356
	21st to end	Day	22% 10% 10% 21% 23% 14%	4825
June	1st to 10th	Day	25% 8% 16% 21% 20% 10%	2660
	11th to 20th	Day	22% 5% 10% 18% 24% 20%	2660
	21st to end	Day	25% 6% 12% 21% 23% 12%	2660
July	1st to 10th	Day	26% 5% 9% 16% 24% 20%	4361
	11th to 20th	Day	31% 5% 12% 27% 16% 10%	4355
	21st to end	Day	29% 6% 13% 23% 13% 15%	4390
August	1st to 10th	Day	38% 7% 18% 21% 12% 5%	4061
	11th to 20th	Day	27% 6% 16% 17% 20% 14%	3762
	21st to end	Day	31% 4 16% 19% 24% 5%	4179
September	1st to 10th	Day	26% 5% 11% 20% 24% 14%	2280
	11th to 20th	Day	21% 4 11% 21% 27% 15%	2278
	21st to end	Day	21% 3 7% 22% 35% 12%	2076
October	1st to 10th	Day	17% 3 6% 18% 35% 22%	3170
	11th to 20th	Day	22% 1 6% 34% 26% 10%	3150
	21st to end	Day	14% 2 4 24% 42% 15%	3416
November	1st to 10th	Day	13% 3 9% 23% 38% 14%	1763
	11th to 20th	Day	13% 4 6% 34% 33% 10%	1800
	21st to end	Day	18% 3 8% 28% 32% 12%	1720
December	1st to 10th	Day	14% 3 9% 34% 30% 10%	2620
	11th to 20th	Day	13% 3 9% 32% 34% 9%	3024
	21st to end	Day	17% 4 8% 30% 31% 10%	4004
January	1st to 10th	Night	24% 4 7% 30% 30% 6%	6327
	11th to 20th	Night	17% 4 8% 26% 30% 15%	6046
	21st to end	Night	21% 3 11% 27% 24% 13%	6468
February	1st to 10th	Night	19% 4 11% 33% 24% 9%	2600
	11th to 20th	Night	23% 5% 10% 29% 27% 5%	2360
	21st to end	Night	20% 3 7% 27% 30% 13%	1980
March	1st to 10th	Night	22% 4 7% 24% 37% 6%	3822
	11th to 20th	Night	31% 6% 12% 31% 18% 3	3506
	21st to end	Night	23% 6% 12% 36% 22% 2	3621
April	1st to 10th	Night	20% 6% 11% 27% 27% 9%	1900
	11th to 20th	Night	29% 5% 9% 27% 21% 9%	1877
	21st to end	Night	29% 5% 14% 27% 19% 6%	1900
May	1st to 10th	Night	26% 6% 12% 24% 19% 13%	3085
	11th to 20th	Night	32% 7% 17% 25% 11% 9%	2550
	21st to end	Night	21% 7% 14% 21% 26% 11%	2762
June	1st to 10th	Night	21% 7% 20% 23% 16% 13%	1520
	11th to 20th	Night	17% 5% 12% 22% 23% 21%	1520
	21st to end	Night	24% 7% 14% 22% 20% 13%	1520
July	1st to 10th	Night	28% 6% 9% 20% 22% 15%	2500
	11th to 20th	Night	22% 5% 20% 33% 14% 6%	2492
	21st to end	Night	26% 7% 19% 24% 9% 15%	2918
August	1st to 10th	Night	36% 9% 25% 16% 8% 6%	2854
	11th to 20th	Night	24% 8% 26% 18% 16% 8%	3143
	21st to end	Night	31% 7% 17% 25% 17% 3	3487
September	1st to 10th	Night	28% 8% 12% 23% 20% 10%	1900
	11th to 20th	Night	21% 4 13% 21% 25% 15%	1900
	21st to end	Night	21% 4 9% 25% 31% 10%	2099
October	1st to 10th	Night	17% 3 7% 22% 33% 18%	3800
	11th to 20th	Night	21% 2 9% 31% 29% 9%	3778
	21st to end	Night	14% 2 5% 26% 37% 15%	4120
November	1st to 10th	Night	14% 3 10% 29% 33% 11%	2525
	11th to 20th	Night	14% 3 7% 32% 33% 11%	2600
	21st to end	Night	18% 3 10% 26% 33% 10%	2675
December	1st to 10th	Night	13% 3 8% 34% 34% 8%	4570
	11th to 20th	Night	13% 4 8% 29% 38% 8%	5182
	21st to end	Night	21% 5% 10% 25% 31% 7%	6974

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	10% 19% 40% 22% 9%	300
	11th to 20th	Day	10% 20% 43% 25% 2 1	300
	21st to end	Day	5% 17% 47% 24% 6% 1	330
February	1st to 10th	Day	15% 26% 42% 16% 1 1	300
	11th to 20th	Day	10% 28% 46% 13% 3 1	300
	21st to end	Day	15% 25% 43% 14% 3	249
March	1st to 10th	Day	12% 25% 38% 20% 5%	317
	11th to 20th	Day	15% 24% 37% 18% 5%	465
	21st to end	Day	17% 32% 36% 13% 3	506
April	1st to 10th	Day	16% 31% 33% 16% 4	460
	11th to 20th	Day	23% 30% 33% 12% 2	452
	21st to end	Day	16% 31% 31% 17% 4	460
May	1st to 10th	Day	15% 27% 34% 17% 6% 1	506
	11th to 20th	Day	12% 16% 32% 28% 10% 1	675
	21st to end	Day	12% 16% 30% 27% 15%	734
June	1st to 10th	Day	6% 12% 32% 32% 14% 4	680
	11th to 20th	Day	7% 13% 37% 30% 11% 3	680
	21st to end	Day	4 15% 32% 29% 17% 3	680
July	1st to 10th	Day	7% 8% 24% 32% 25% 3	671
	11th to 20th	Day	6% 3 23% 35% 28% 5%	668
	21st to end	Day	8% 5% 21% 37% 24% 5%	584
August	1st to 10th	Day	11% 6% 26% 38% 15% 5%	487
	11th to 20th	Day	6% 8% 33% 31% 18% 4	477
	21st to end	Day	9% 7% 31% 32% 17% 3	539
September	1st to 10th	Day	7% 9% 30% 32% 18% 4	490
	11th to 20th	Day	7% 11% 40% 28% 12% 2	488
	21st to end	Day	10% 10% 23% 33% 20% 4	300
October	1st to 10th	Day	8% 13% 28% 25% 22% 5%	300
	11th to 20th	Day	10% 17% 31% 26% 15% 1	300
	21st to end	Day	13% 18% 32% 24% 11% 2	330
November	1st to 10th	Day	10% 17% 38% 23% 11% 1	300
	11th to 20th	Day	11% 14% 42% 24% 7% 2	300
	21st to end	Day	9% 16% 46% 23% 6%	300
December	1st to 10th	Day	9% 18% 43% 22% 8%	300
	11th to 20th	Day	8% 19% 51% 16% 6%	300
	21st to end	Day	12% 25% 41% 17% 5% 1	330
January	1st to 10th	Night	4 15% 46% 27% 6% 1	1000
	11th to 20th	Night	4 17% 49% 23% 6%	875
	21st to end	Night	3 11% 52% 29% 5%	880
February	1st to 10th	Night	5% 12% 58% 22% 2	800
	11th to 20th	Night	5% 16% 53% 23% 3	784
	21st to end	Night	3 17% 57% 22% 1	660
March	1st to 10th	Night	5% 16% 49% 27% 4	800
	11th to 20th	Night	6% 11% 42% 34% 7%	766
	21st to end	Night	6% 13% 48% 29% 3	719
April	1st to 10th	Night	7% 16% 43% 31% 3	570
	11th to 20th	Night	12% 15% 36% 31% 6%	563
	21st to end	Night	10% 12% 38% 34% 6%	570
May	1st to 10th	Night	13% 11% 32% 36% 7% 1	570
	11th to 20th	Night	12% 8% 28% 40% 12% 1	561
	21st to end	Night	12% 7% 30% 36% 14%	617
June	1st to 10th	Night	7% 5% 24% 44% 18% 2	570
	11th to 20th	Night	4 5% 30% 48% 13% 1	570
	21st to end	Night	6% 3 20% 46% 25% 1	570
July	1st to 10th	Night	8% 3 13% 42% 31% 3	555
	11th to 20th	Night	6% 1 10% 45% 35% 3	552
	21st to end	Night	7% 2 8% 39% 41% 2	624
August	1st to 10th	Night	9% 2 12% 42% 33% 2	567
	11th to 20th	Night	7% 1 13% 50% 26% 2	564
	21st to end	Night	6% 2 15% 46% 30% 2	627
September	1st to 10th	Night	7% 2 14% 49% 25% 3	570
	11th to 20th	Night	9% 2 22% 45% 21% 1	570
	21st to end	Night	8% 6% 23% 46% 16% 1	579
October	1st to 10th	Night	7% 5% 34% 40% 12% 1	760
	11th to 20th	Night	4 5% 39% 39% 13%	760
	21st to end	Night	7% 8% 40% 34% 11% 1	836
November	1st to 10th	Night	4 11% 45% 32% 8%	965
	11th to 20th	Night	4 15% 46% 28% 7%	1000
	21st to end	Night	6% 12% 45% 33% 4	1000
December	1st to 10th	Night	3 13% 49% 31% 4	1000
	11th to 20th	Night	3 15% 54% 23% 5%	1000
	21st to end	Night	5% 18% 51% 23% 3	1100

Page generated at 2025-03-09 06:08:45. Version ac07

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