Bosque Farms Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bosque Farms Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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 3 1 3 3 3 3 3 5% 7% 65%	117818
	Night	4 4 1 4 3 3 4 3 5% 7% 61%	120362
Transparency	Day	17% 5% 9% 20% 29% 20%	117581
	Night	21% 5% 9% 19% 28% 19%	120188
Seeing	Day	5% 8% 21% 31% 26% 9%	15610
	Night	5% 5% 25% 43% 21% 1	25903

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	3 8% 2 4 2 3 3 3 5% 7% 60%	4098
	11th to 20th	Day	2 4 1 2 2 2 3 3 4 7% 70%	4100
	21st to end	Day	3 5% 2 5% 3 3 3 4 5% 6% 61%	4510
February	1st to 10th	Day	3 5% 2 4 3 2 4 4 4 6% 64%	1800
	11th to 20th	Day	3 4 2 4 3 3 4 3 6% 6% 61%	1947
	21st to end	Day	3 4 2 3 2 2 4 3 5% 5% 67%	1650
March	1st to 10th	Day	2 3 1 3 3 2 3 3 5% 6% 68%	4882
	11th to 20th	Day	4 4 2 5% 4 4 3 3 5% 7% 59%	5000
	21st to end	Day	2 4 1 4 3 3 3 4 6% 7% 63%	5587
April	1st to 10th	Day	3 2 1 3 3 3 3 3 5% 6% 68%	2400
	11th to 20th	Day	4 3 1 3 2 3 3 3 4 5% 68%	2371
	21st to end	Day	2 2 1 2 2 2 3 3 5% 6% 72%	2400
May	1st to 10th	Day	2 2 1 2 2 2 3 3 4 6% 75%	3920
	11th to 20th	Day	3 3 1 3 3 3 4 4 6% 8% 63%	4032
	21st to end	Day	1 1 1 2 1 1 2 2 4 5% 80%	4730
June	1st to 10th	Day	2 2 1 3 3 3 3 4 6% 10% 65%	2660
	11th to 20th	Day	2 2 1 3 2 2 2 2 5% 6% 74%	2660
	21st to end	Day	4 3 1 3 3 4 4 4 7% 8% 59%	2659
July	1st to 10th	Day	2 2 1 2 3 4 4 4 7% 9% 61%	4110
	11th to 20th	Day	2 2 1 2 3 3 4 4 9% 12% 58%	4110
	21st to end	Day	3 2 1 4 4 5% 6% 6% 9% 12% 49%	4454
August	1st to 10th	Day	2 2 1 3 3 4 6% 5% 8% 12% 55%	4014
	11th to 20th	Day	2 2 1 3 3 4 4 4 7% 10% 63%	3726
	21st to end	Day	3 3 1 4 4 5% 6% 5% 9% 11% 49%	4180
September	1st to 10th	Day	4 3 2 4 4 4 4 4 6% 7% 57%	2280
	11th to 20th	Day	5% 2 1 3 4 3 4 3 7% 8% 61%	2280
	21st to end	Day	3 2 1 3 3 2 3 3 4 5% 73%	2038
October	1st to 10th	Day	3 1 1 2 2 2 2 2 4 4 77%	3170
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 6% 71%	3150
	21st to end	Day	2 1 1 1 1 1 2 2 3 5% 81%	3438
November	1st to 10th	Day	3 2 1 3 2 2 2 2 4 8% 72%	1959
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 5% 73%	1835
	21st to end	Day	4 4 1 3 3 3 4 3 4 5% 66%	1800
December	1st to 10th	Day	3 3 1 2 2 2 2 2 3 5% 76%	2657
	11th to 20th	Day	2 3 1 4 3 3 3 2 4 7% 67%	3026
	21st to end	Day	3 4 1 3 2 3 3 2 4 7% 68%	4185
January	1st to 10th	Night	3 9% 2 5% 3 3 4 4 5% 6% 56%	5867
	11th to 20th	Night	3 4 1 3 2 2 3 3 4 6% 70%	5880
	21st to end	Night	5% 5% 2 5% 3 4 4 4 5% 7% 56%	6468
February	1st to 10th	Night	3 5% 2 4 3 3 3 2 3 5% 67%	2600
	11th to 20th	Night	5% 6% 2 3 3 3 3 3 5% 7% 59%	2338
	21st to end	Night	4 4 2 4 2 2 3 2 4 5% 67%	1980
March	1st to 10th	Night	5% 5% 1 4 3 3 4 3 4 5% 64%	4993
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 4 5% 55%	5000
	21st to end	Night	4 3 1 4 3 3 4 3 5% 6% 64%	5381
April	1st to 10th	Night	3 3 2 4 3 2 3 3 5% 6% 66%	2000
	11th to 20th	Night	5% 3 1 4 4 2 3 3 4 6% 65%	1977
	21st to end	Night	5% 3 1 3 3 2 3 3 4 6% 67%	2000
May	1st to 10th	Night	5% 3 2 4 3 3 3 3 4 5% 66%	3270
	11th to 20th	Night	6% 4 2 5% 4 5% 5% 4 6% 7% 53%	3088
	21st to end	Night	3 2 1 3 2 2 3 2 3 4 74%	2968
June	1st to 10th	Night	3 2 1 4 4 5% 5% 4 6% 8% 56%	1520
	11th to 20th	Night	2 2 1 4 2 3 3 4 6% 7% 67%	1520
	21st to end	Night	4 4 1 6% 4 4 5% 5% 7% 9% 50%	1520
July	1st to 10th	Night	2 3 2 5% 4 5% 6% 5% 7% 8% 53%	2852
	11th to 20th	Night	3 3 2 6% 4 6% 6% 6% 8% 13% 44%	2860
	21st to end	Night	5% 4 2 7% 6% 7% 6% 6% 10% 12% 34%	3109
August	1st to 10th	Night	2 3 2 7% 6% 8% 7% 5% 10% 13% 36%	2922
	11th to 20th	Night	4 3 2 6% 5% 6% 6% 6% 9% 12% 42%	3113
	21st to end	Night	4 3 2 7% 6% 7% 9% 7% 10% 11% 34%	3487
September	1st to 10th	Night	4 4 1 5% 6% 4 5% 4 6% 10% 50%	1900
	11th to 20th	Night	5% 4 2 4 3 4 4 4 6% 8% 57%	1900
	21st to end	Night	4 3 1 3 2 3 3 3 3 6% 69%	2137
October	1st to 10th	Night	3 3 1 2 2 2 2 2 4 6% 74%	3800
	11th to 20th	Night	5% 3 2 5% 3 4 3 3 4 5% 63%	3778
	21st to end	Night	2 2 1 2 2 1 2 2 3 6% 78%	4120
November	1st to 10th	Night	3 2 1 2 2 2 2 2 4 5% 75%	2340
	11th to 20th	Night	2 3 2 2 2 2 3 4 5% 75%	2542
	21st to end	Night	7% 4 2 3 3 2 3 2 4 5% 65%	2600
December	1st to 10th	Night	3 2 1 2 2 2 3 2 5% 7% 72%	4530
	11th to 20th	Night	3 2 1 3 2 3 3 3 5% 9% 67%	5181
	21st to end	Night	4 5% 1 3 3 3 3 2 4 6% 67%	6821

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	23% 3 8% 31% 30% 4	4099
	11th to 20th	Day	15% 4 9% 27% 29% 15%	4100
	21st to end	Day	23% 5% 8% 20% 31% 14%	4510
February	1st to 10th	Day	20% 4 9% 24% 29% 15%	1800
	11th to 20th	Day	22% 4 9% 23% 29% 13%	1957
	21st to end	Day	18% 3 6% 17% 32% 24%	1650
March	1st to 10th	Day	16% 3 6% 12% 33% 30%	4882
	11th to 20th	Day	19% 8% 8% 19% 27% 20%	5000
	21st to end	Day	19% 2 8% 18% 39% 14%	5587
April	1st to 10th	Day	16% 3 8% 14% 35% 24%	2400
	11th to 20th	Day	17% 3 7% 14% 29% 29%	2374
	21st to end	Day	14% 3 7% 16% 36% 24%	2400
May	1st to 10th	Day	10% 2 8% 12% 33% 34%	3920
	11th to 20th	Day	18% 4 10% 16% 32% 20%	4035
	21st to end	Day	7% 2 5% 10% 19% 56%	4730
June	1st to 10th	Day	15% 4 10% 17% 25% 29%	2660
	11th to 20th	Day	12% 3 6% 9% 21% 49%	2660
	21st to end	Day	21% 4 12% 16% 21% 26%	2659
July	1st to 10th	Day	17% 6% 12% 14% 21% 30%	4046
	11th to 20th	Day	14% 8% 16% 30% 24% 7%	4041
	21st to end	Day	22% 9% 18% 34% 16% 2	4314
August	1st to 10th	Day	17% 9% 18% 28% 19% 9%	4000
	11th to 20th	Day	15% 7% 12% 24% 27% 16%	3762
	21st to end	Day	24% 10% 17% 23% 20% 6%	4179
September	1st to 10th	Day	24% 6% 10% 20% 25% 15%	2280
	11th to 20th	Day	19% 7% 10% 16% 26% 22%	2280
	21st to end	Day	14% 4 6% 20% 32% 24%	2038
October	1st to 10th	Day	12% 3 6% 13% 29% 36%	3170
	11th to 20th	Day	13% 4 6% 16% 35% 27%	3150
	21st to end	Day	9% 2 4 20% 40% 25%	3438
November	1st to 10th	Day	13% 3 6% 21% 39% 18%	1959
	11th to 20th	Day	15% 3 6% 23% 40% 13%	1835
	21st to end	Day	21% 4 5% 22% 34% 14%	1800
December	1st to 10th	Day	13% 4 6% 32% 31% 14%	2657
	11th to 20th	Day	19% 4 7% 35% 30% 5%	3024
	21st to end	Day	17% 3 11% 27% 32% 10%	4185
January	1st to 10th	Night	25% 4 9% 26% 30% 5%	5867
	11th to 20th	Night	16% 4 7% 26% 33% 14%	5880
	21st to end	Night	25% 5% 8% 18% 29% 15%	6468
February	1st to 10th	Night	20% 3 10% 20% 31% 15%	2600
	11th to 20th	Night	25% 3 8% 21% 27% 15%	2338
	21st to end	Night	19% 3 4 16% 32% 24%	1980
March	1st to 10th	Night	20% 3 6% 11% 34% 26%	4993
	11th to 20th	Night	26% 6% 7% 17% 27% 17%	5000
	21st to end	Night	19% 3 10% 16% 37% 16%	5381
April	1st to 10th	Night	18% 3 6% 13% 35% 25%	2000
	11th to 20th	Night	20% 3 7% 13% 24% 33%	1977
	21st to end	Night	18% 4 9% 12% 32% 25%	2000
May	1st to 10th	Night	17% 2 10% 9% 29% 32%	3270
	11th to 20th	Night	23% 5% 13% 15% 23% 22%	3089
	21st to end	Night	11% 2 7% 10% 14% 57%	2968
June	1st to 10th	Night	23% 5% 11% 14% 19% 28%	1520
	11th to 20th	Night	16% 3 7% 11% 19% 45%	1520
	21st to end	Night	28% 7% 12% 12% 15% 26%	1520
July	1st to 10th	Night	26% 8% 13% 15% 12% 27%	2807
	11th to 20th	Night	27% 8% 18% 25% 16% 5%	2806
	21st to end	Night	34% 12% 16% 27% 8% 2	3011
August	1st to 10th	Night	32% 12% 16% 20% 13% 7%	2913
	11th to 20th	Night	27% 10% 15% 17% 16% 14%	3143
	21st to end	Night	35% 13% 17% 18% 12% 5%	3487
September	1st to 10th	Night	27% 8% 12% 19% 20% 14%	1900
	11th to 20th	Night	24% 6% 12% 15% 20% 23%	1900
	21st to end	Night	19% 3 7% 14% 31% 26%	2137
October	1st to 10th	Night	14% 3 6% 11% 28% 37%	3800
	11th to 20th	Night	21% 5% 6% 13% 25% 30%	3778
	21st to end	Night	11% 2 4 19% 40% 25%	4120
November	1st to 10th	Night	13% 2 5% 20% 40% 19%	2340
	11th to 20th	Night	14% 3 5% 19% 39% 21%	2542
	21st to end	Night	23% 3 6% 17% 35% 16%	2600
December	1st to 10th	Night	13% 3 7% 31% 32% 14%	4530
	11th to 20th	Night	16% 3 7% 31% 35% 8%	5182
	21st to end	Night	18% 3 8% 30% 32% 9%	6821

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	6% 6% 24% 46% 17% 1	300
	11th to 20th	Day	11% 7% 24% 37% 19% 3	300
	21st to end	Day	2 6% 27% 40% 21% 3	330
February	1st to 10th	Day	3 11% 31% 34% 20% 1	300
	11th to 20th	Day	8% 11% 27% 45% 9%	300
	21st to end	Day	8% 14% 31% 35% 11% 1	249
March	1st to 10th	Day	6% 17% 33% 29% 13% 2	465
	11th to 20th	Day	10% 19% 27% 28% 15% 1	500
	21st to end	Day	9% 23% 31% 23% 13% 1	550
April	1st to 10th	Day	7% 18% 32% 27% 12% 3	500
	11th to 20th	Day	8% 20% 33% 28% 9% 2	492
	21st to end	Day	8% 16% 32% 29% 13% 3	500
May	1st to 10th	Day	4 14% 35% 28% 16% 3	503
	11th to 20th	Day	4 12% 30% 30% 18% 6%	528
	21st to end	Day	4 11% 27% 34% 21% 3	658
June	1st to 10th	Day	2 4 18% 36% 32% 8%	680
	11th to 20th	Day	2 5% 17% 35% 34% 6%	680
	21st to end	Day	4 3 14% 35% 36% 8%	679
July	1st to 10th	Day	2 1 12% 31% 34% 20%	486
	11th to 20th	Day	3 5% 19% 37% 35%	484
	21st to end	Day	2 1 4 21% 37% 35%	531
August	1st to 10th	Day	3 1 6% 24% 41% 25%	487
	11th to 20th	Day	3 1 7% 25% 43% 22%	477
	21st to end	Day	4 1 6% 27% 40% 22%	539
September	1st to 10th	Day	5% 1 12% 26% 39% 17%	490
	11th to 20th	Day	3 1 14% 35% 36% 10%	490
	21st to end	Day	3 7% 14% 27% 35% 14%	352
October	1st to 10th	Day	5% 4 18% 28% 30% 16%	300
	11th to 20th	Day	6% 7% 15% 31% 30% 12%	300
	21st to end	Day	7% 8% 14% 29% 32% 9%	330
November	1st to 10th	Day	7% 8% 22% 37% 24% 2	300
	11th to 20th	Day	2 6% 15% 43% 28% 6%	300
	21st to end	Day	8% 10% 25% 33% 18% 6%	300
December	1st to 10th	Day	6% 5% 26% 37% 20% 6%	300
	11th to 20th	Day	3 7% 28% 39% 19% 4	300
	21st to end	Day	12% 8% 25% 39% 14% 3	330
January	1st to 10th	Night	5% 3 28% 47% 16% 1	800
	11th to 20th	Night	7% 5% 31% 44% 13% 1	800
	21st to end	Night	6% 5% 30% 41% 16% 1	880
February	1st to 10th	Night	5% 7% 33% 42% 13% 1	800
	11th to 20th	Night	8% 8% 35% 42% 7%	784
	21st to end	Night	6% 9% 41% 40% 4	660
March	1st to 10th	Night	6% 9% 36% 39% 10%	800
	11th to 20th	Night	7% 9% 32% 40% 12%	800
	21st to end	Night	6% 12% 32% 41% 9%	836
April	1st to 10th	Night	5% 10% 41% 38% 7%	600
	11th to 20th	Night	5% 13% 37% 37% 8%	593
	21st to end	Night	6% 11% 37% 39% 6% 1	600
May	1st to 10th	Night	5% 7% 36% 43% 9%	600
	11th to 20th	Night	6% 6% 31% 39% 16% 1	591
	21st to end	Night	3 6% 32% 45% 13%	634
June	1st to 10th	Night	3 4 22% 52% 18% 1	570
	11th to 20th	Night	3 3 24% 50% 20%	570
	21st to end	Night	4 2 18% 46% 28% 2	570
July	1st to 10th	Night	3 1 13% 43% 37% 3	555
	11th to 20th	Night	3 1 7% 34% 52% 3	552
	21st to end	Night	4 1 7% 29% 52% 6%	624
August	1st to 10th	Night	3 1 5% 31% 53% 7%	567
	11th to 20th	Night	4 1 7% 41% 43% 5%	564
	21st to end	Night	3 7% 37% 50% 4	627
September	1st to 10th	Night	5% 10% 46% 37% 1	570
	11th to 20th	Night	5% 2 13% 46% 32% 2	570
	21st to end	Night	4 1 17% 44% 32% 1	670
October	1st to 10th	Night	6% 3 20% 47% 23% 1	760
	11th to 20th	Night	4 5% 18% 52% 19% 2	760
	21st to end	Night	5% 4 22% 43% 24% 3	836
November	1st to 10th	Night	3 3 22% 49% 22% 1	780
	11th to 20th	Night	2 4 25% 47% 20% 2	942
	21st to end	Night	8% 7% 23% 38% 22% 2	1000
December	1st to 10th	Night	7% 4 26% 46% 17% 1	1000
	11th to 20th	Night	7% 6% 26% 46% 15% 1	1000
	21st to end	Night	8% 6% 27% 48% 11%	1038

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