Adams Ranch Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adams Ranch Dark Sky Site clear sky chart from 2005-11-06 to 2025-07-06.

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	11% 6% 2 6% 4 4 4 3 5% 7% 50%	120408
	Night	10% 5% 2 5% 3 3 3 3 5% 6% 54%	118639
Transparency	Day	34% 4 10% 25% 21% 5%	124115
	Night	30% 4 10% 27% 23% 7%	123062
Seeing	Day	13% 10% 29% 29% 16% 3	16408
	Night	13% 9% 33% 32% 11% 1	26291

By Month

Percentage Cloud Cover SE (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	14% 7% 2 7% 4 4 3 3 5% 5% 46%	4077
	11th to 20th	Day	7% 8% 2 7% 5% 4 3 3 4 5% 52%	4080
	21st to end	Day	13% 10% 4 6% 3 3 2 2 3 4 50%	4488
February	1st to 10th	Day	13% 10% 4 7% 5% 3 3 3 4 6% 43%	1800
	11th to 20th	Day	11% 7% 2 6% 5% 3 4 3 4 5% 50%	1918
	21st to end	Day	11% 8% 3 6% 4 3 3 3 5% 6% 48%	1650
March	1st to 10th	Day	9% 6% 2 6% 3 3 3 2 4 5% 57%	4929
	11th to 20th	Day	9% 6% 2 5% 3 3 3 3 5% 6% 56%	4980
	21st to end	Day	10% 8% 3 7% 5% 5% 5% 4 6% 7% 40%	5462
April	1st to 10th	Day	10% 6% 2 5% 3 4 4 4 5% 8% 49%	2200
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 45%	2399
	21st to end	Day	17% 7% 3 7% 5% 4 4 3 4 5% 42%	2600
May	1st to 10th	Day	19% 7% 2 6% 4 4 3 3 4 5% 42%	5862
	11th to 20th	Day	11% 5% 2 6% 3 3 4 4 5% 7% 50%	5862
	21st to end	Day	19% 7% 2 6% 5% 4 4 3 4 6% 39%	6434
June	1st to 10th	Day	6% 3 1 6% 5% 5% 5% 4 7% 9% 49%	2600
	11th to 20th	Day	7% 5% 2 5% 5% 5% 4 4 6% 8% 50%	2600
	21st to end	Day	6% 3 1 3 2 3 4 5% 7% 8% 57%	2600
July	1st to 10th	Day	10% 6% 3 6% 4 4 5% 4 6% 8% 45%	4186
	11th to 20th	Day	6% 4 2 5% 3 3 4 4 6% 9% 55%	4120
	21st to end	Day	5% 3 2 5% 5% 5% 5% 5% 8% 11% 46%	4465
August	1st to 10th	Day	6% 3 1 4 3 4 4 4 6% 10% 55%	4104
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 6% 9% 50%	4041
	21st to end	Day	5% 4 2 4 4 3 4 3 5% 8% 59%	4382
September	1st to 10th	Day	10% 5% 2 5% 3 5% 4 3 4 6% 54%	2097
	11th to 20th	Day	11% 5% 1 5% 4 4 4 4 5% 7% 49%	2090
	21st to end	Day	9% 4 1 5% 2 4 3 3 4 7% 57%	2090
October	1st to 10th	Day	8% 4 2 5% 4 4 3 3 5% 7% 55%	1990
	11th to 20th	Day	10% 3 2 4 2 2 2 2 4 5% 64%	1900
	21st to end	Day	13% 6% 2 4 3 3 3 3 4 4 56%	2090
November	1st to 10th	Day	9% 5% 1 3 3 3 3 3 4 6% 60%	1893
	11th to 20th	Day	9% 5% 2 3 3 2 3 3 4 6% 60%	1800
	21st to end	Day	13% 4 2 4 3 2 2 2 3 6% 58%	1800
December	1st to 10th	Day	7% 6% 3 4 3 2 3 3 5% 5% 60%	2940
	11th to 20th	Day	9% 6% 2 5% 4 3 3 2 3 6% 57%	3391
	21st to end	Day	16% 11% 5% 9% 5% 4 4 3 4 5% 34%	4488
January	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 4 6% 48%	5888
	11th to 20th	Night	6% 5% 2 5% 4 4 3 3 5% 6% 58%	5900
	21st to end	Night	15% 8% 3 5% 2 3 2 2 4 4 52%	6490
February	1st to 10th	Night	13% 9% 3 5% 4 3 4 3 5% 5% 46%	2600
	11th to 20th	Night	12% 7% 3 5% 4 4 3 3 4 5% 51%	2386
	21st to end	Night	10% 6% 2 4 3 3 4 3 5% 6% 54%	1980
March	1st to 10th	Night	10% 7% 2 5% 4 3 3 3 3 5% 56%	4924
	11th to 20th	Night	8% 3 1 3 2 2 3 2 5% 6% 64%	4980
	21st to end	Night	10% 6% 2 5% 4 5% 4 3 6% 7% 47%	5467
April	1st to 10th	Night	11% 5% 2 4 3 3 4 4 4 7% 53%	2200
	11th to 20th	Night	14% 5% 1 5% 3 3 3 2 4 7% 52%	1945
	21st to end	Night	15% 6% 3 4 3 3 2 3 5% 7% 49%	1800
May	1st to 10th	Night	18% 8% 2 5% 3 3 3 2 4 6% 46%	4053
	11th to 20th	Night	13% 5% 2 5% 3 4 3 3 5% 8% 50%	4053
	21st to end	Night	16% 5% 2 4 3 3 4 3 5% 7% 49%	4443
June	1st to 10th	Night	5% 4 2 6% 4 3 3 3 6% 10% 53%	1800
	11th to 20th	Night	5% 3 1 4 3 4 5% 4 7% 10% 54%	1800
	21st to end	Night	5% 3 1 4 3 3 3 2 6% 9% 62%	1800
July	1st to 10th	Night	6% 4 1 5% 4 4 4 4 6% 9% 52%	2895
	11th to 20th	Night	3 2 1 4 3 4 3 3 7% 10% 60%	2850
	21st to end	Night	5% 2 1 4 3 4 5% 5% 8% 11% 51%	3098
August	1st to 10th	Night	3 2 1 4 3 4 4 4 7% 9% 59%	2836
	11th to 20th	Night	4 4 1 5% 4 4 6% 4 7% 9% 52%	2798
	21st to end	Night	3 2 2 3 3 3 3 3 5% 7% 66%	3280
September	1st to 10th	Night	10% 4 1 4 3 3 3 2 4 6% 60%	2079
	11th to 20th	Night	10% 5% 2 4 5% 4 4 3 5% 7% 52%	2090
	21st to end	Night	7% 3 1 4 3 3 3 3 5% 6% 62%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 2 4 6% 60%	2170
	11th to 20th	Night	10% 4 1 3 2 2 3 2 4 5% 63%	2280
	21st to end	Night	12% 4 2 4 2 3 3 3 4 5% 58%	2508
November	1st to 10th	Night	10% 4 1 3 3 3 2 2 4 5% 63%	2400
	11th to 20th	Night	10% 4 1 4 3 2 3 3 4 5% 60%	2600
	21st to end	Night	13% 6% 2 4 3 2 3 2 4 5% 58%	2600
December	1st to 10th	Night	6% 4 1 5% 3 3 3 2 4 6% 64%	4250
	11th to 20th	Night	9% 5% 2 6% 3 3 3 3 3 4 58%	4816
	21st to end	Night	17% 8% 3 6% 4 3 4 3 4 6% 43%	6490

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	41% 3 9% 26% 17% 3	4078
	11th to 20th	Day	36% 3 11% 21% 23% 6%	4080
	21st to end	Day	41% 2 6% 21% 27% 3	4488
February	1st to 10th	Day	44% 3 11% 24% 15% 4	1800
	11th to 20th	Day	38% 3 11% 27% 17% 4	1928
	21st to end	Day	37% 4 6% 24% 21% 9%	1650
March	1st to 10th	Day	32% 2 4 21% 22% 17%	4929
	11th to 20th	Day	30% 4 8% 21% 22% 16%	4980
	21st to end	Day	43% 5% 10% 30% 11% 1	5464
April	1st to 10th	Day	34% 5% 11% 24% 20% 6%	2200
	11th to 20th	Day	40% 5% 11% 22% 18% 5%	2399
	21st to end	Day	45% 5% 9% 24% 14% 2	2600
May	1st to 10th	Day	46% 4 9% 19% 20% 3	5900
	11th to 20th	Day	33% 6% 9% 22% 23% 6%	5866
	21st to end	Day	46% 6% 9% 18% 19% 3	6447
June	1st to 10th	Day	29% 7% 16% 26% 18% 2	2600
	11th to 20th	Day	31% 6% 12% 30% 18% 4	2600
	21st to end	Day	22% 5% 15% 29% 24% 5%	2600
July	1st to 10th	Day	36% 5% 11% 24% 19% 4	4122
	11th to 20th	Day	26% 5% 11% 34% 23% 2	4051
	21st to end	Day	29% 5% 17% 32% 16% 1	4325
August	1st to 10th	Day	25% 4 15% 27% 23% 5%	4090
	11th to 20th	Day	31% 4 20% 24% 19% 1	4080
	21st to end	Day	24% 4 14% 37% 16% 5%	4381
September	1st to 10th	Day	32% 5% 8% 24% 22% 9%	2097
	11th to 20th	Day	33% 6% 10% 25% 21% 4	2090
	21st to end	Day	28% 4 9% 22% 30% 7%	2090
October	1st to 10th	Day	22% 3 6% 17% 41% 11%	3302
	11th to 20th	Day	16% 2 4 29% 35% 14%	3140
	21st to end	Day	26% 2 7% 29% 28% 8%	3428
November	1st to 10th	Day	27% 4 9% 27% 26% 7%	1893
	11th to 20th	Day	27% 3 9% 27% 27% 8%	1800
	21st to end	Day	30% 3 9% 27% 26% 5%	1800
December	1st to 10th	Day	28% 3 6% 40% 22% 1	2940
	11th to 20th	Day	31% 2 6% 32% 25% 4	3389
	21st to end	Day	53% 3 7% 24% 11% 2	4488
January	1st to 10th	Night	38% 3 9% 32% 15% 4	5888
	11th to 20th	Night	28% 3 10% 24% 28% 7%	5900
	21st to end	Night	38% 2 7% 21% 27% 5%	6490
February	1st to 10th	Night	41% 4 10% 22% 17% 5%	2600
	11th to 20th	Night	37% 4 9% 27% 19% 5%	2386
	21st to end	Night	32% 4 8% 22% 24% 11%	1980
March	1st to 10th	Night	33% 3 5% 22% 24% 12%	4924
	11th to 20th	Night	22% 2 6% 22% 29% 18%	4980
	21st to end	Night	36% 4 10% 34% 14% 2	5467
April	1st to 10th	Night	31% 5% 11% 22% 22% 9%	2200
	11th to 20th	Night	34% 4 12% 23% 21% 7%	1945
	21st to end	Night	35% 5% 12% 24% 20% 4	1800
May	1st to 10th	Night	41% 5% 12% 19% 20% 3	4080
	11th to 20th	Night	34% 5% 10% 24% 20% 7%	4054
	21st to end	Night	36% 6% 12% 24% 18% 4	4452
June	1st to 10th	Night	26% 7% 17% 29% 17% 4	1800
	11th to 20th	Night	24% 6% 16% 32% 20% 3	1800
	21st to end	Night	20% 4 16% 29% 24% 6%	1800
July	1st to 10th	Night	28% 4 14% 29% 19% 4	2850
	11th to 20th	Night	20% 4 10% 36% 27% 3	2796
	21st to end	Night	25% 4 18% 35% 16% 2	2999
August	1st to 10th	Night	21% 4 13% 31% 23% 8%	2826
	11th to 20th	Night	28% 5% 18% 25% 22% 2	2825
	21st to end	Night	19% 5% 12% 39% 20% 5%	3280
September	1st to 10th	Night	27% 4 9% 27% 23% 10%	2079
	11th to 20th	Night	32% 5% 10% 22% 25% 6%	2090
	21st to end	Night	24% 3 9% 26% 31% 8%	2090
October	1st to 10th	Night	18% 3 6% 14% 42% 17%	3625
	11th to 20th	Night	18% 3 3 22% 37% 17%	3779
	21st to end	Night	25% 3 6% 27% 31% 8%	4120
November	1st to 10th	Night	25% 3 8% 27% 29% 8%	2400
	11th to 20th	Night	28% 3 8% 26% 28% 7%	2600
	21st to end	Night	31% 2 9% 24% 27% 7%	2600
December	1st to 10th	Night	24% 2 10% 41% 21% 2	4250
	11th to 20th	Night	32% 2 6% 28% 26% 6%	4817
	21st to end	Night	43% 4 7% 28% 15% 4	6490

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	18% 14% 37% 24% 6% 1	300
	11th to 20th	Day	20% 18% 39% 19% 3	300
	21st to end	Day	17% 13% 44% 22% 4 1	330
February	1st to 10th	Day	19% 20% 38% 18% 3 1	300
	11th to 20th	Day	19% 17% 44% 16% 4	300
	21st to end	Day	17% 22% 41% 18% 2	249
March	1st to 10th	Day	18% 20% 38% 20% 4	300
	11th to 20th	Day	20% 21% 37% 18% 3 1	300
	21st to end	Day	22% 21% 37% 16% 3 1	330
April	1st to 10th	Day	20% 20% 37% 18% 4	300
	11th to 20th	Day	20% 17% 41% 18% 3	517
	21st to end	Day	21% 17% 35% 18% 7% 1	700
May	1st to 10th	Day	17% 12% 38% 25% 8% 1	703
	11th to 20th	Day	15% 12% 33% 26% 11% 3	725
	21st to end	Day	18% 10% 30% 24% 15% 3	789
June	1st to 10th	Day	7% 5% 25% 38% 21% 4	730
	11th to 20th	Day	8% 4 28% 40% 17% 2	730
	21st to end	Day	5% 4 28% 42% 19% 2	730
July	1st to 10th	Day	10% 2 16% 35% 30% 7%	697
	11th to 20th	Day	3 2 15% 42% 33% 6%	668
	21st to end	Day	7% 1 12% 39% 32% 9%	739
August	1st to 10th	Day	7% 2 16% 42% 29% 5%	676
	11th to 20th	Day	9% 2 17% 37% 31% 5%	665
	21st to end	Day	6% 1 12% 36% 35% 9%	663
September	1st to 10th	Day	10% 3 14% 32% 34% 7%	307
	11th to 20th	Day	6% 2 19% 39% 26% 8%	300
	21st to end	Day	14% 3 25% 35% 17% 5%	300
October	1st to 10th	Day	9% 7% 28% 29% 21% 5%	300
	11th to 20th	Day	8% 9% 44% 29% 9%	300
	21st to end	Day	22% 10% 35% 26% 6% 2	330
November	1st to 10th	Day	16% 10% 37% 24% 11% 2	300
	11th to 20th	Day	16% 13% 38% 22% 10% 1	300
	21st to end	Day	17% 15% 39% 22% 6% 1	300
December	1st to 10th	Day	12% 13% 43% 22% 8% 2	300
	11th to 20th	Day	16% 17% 37% 23% 6% 1	300
	21st to end	Day	15% 23% 39% 21% 2	330
January	1st to 10th	Night	13% 12% 39% 30% 6%	1000
	11th to 20th	Night	15% 13% 41% 26% 5%	1000
	21st to end	Night	13% 13% 40% 29% 5%	1100
February	1st to 10th	Night	18% 14% 39% 25% 3	1000
	11th to 20th	Night	17% 16% 39% 25% 3	832
	21st to end	Night	15% 14% 40% 28% 3	660
March	1st to 10th	Night	14% 14% 39% 30% 4	605
	11th to 20th	Night	21% 11% 36% 29% 4	600
	21st to end	Night	17% 14% 42% 23% 4 1	660
April	1st to 10th	Night	15% 17% 39% 24% 5%	600
	11th to 20th	Night	16% 17% 39% 24% 4	593
	21st to end	Night	18% 13% 40% 23% 6% 1	600
May	1st to 10th	Night	18% 8% 39% 28% 7%	600
	11th to 20th	Night	14% 7% 32% 34% 13% 1	591
	21st to end	Night	13% 6% 31% 33% 15% 2	650
June	1st to 10th	Night	6% 4 28% 41% 22%	600
	11th to 20th	Night	6% 3 32% 44% 15%	600
	21st to end	Night	6% 2 36% 43% 13%	600
July	1st to 10th	Night	6% 1 18% 46% 26% 3	570
	11th to 20th	Night	3 2 19% 47% 26% 3	552
	21st to end	Night	5% 1 13% 48% 30% 3	624
August	1st to 10th	Night	5% 1 18% 49% 26% 1	567
	11th to 20th	Night	6% 1 19% 47% 25% 1	564
	21st to end	Night	5% 1 14% 40% 39% 2	627
September	1st to 10th	Night	12% 2 18% 41% 26% 2	570
	11th to 20th	Night	11% 2 24% 39% 20% 4	570
	21st to end	Night	8% 5% 23% 42% 18% 3	570
October	1st to 10th	Night	11% 4 31% 32% 20% 2	650
	11th to 20th	Night	13% 8% 41% 30% 9%	760
	21st to end	Night	14% 12% 35% 28% 11%	836
November	1st to 10th	Night	11% 8% 40% 30% 10% 1	840
	11th to 20th	Night	12% 13% 37% 30% 8% 1	1000
	21st to end	Night	17% 12% 33% 31% 7%	1000
December	1st to 10th	Night	13% 13% 39% 29% 6%	1000
	11th to 20th	Night	17% 12% 37% 30% 5%	1000
	21st to end	Night	15% 15% 37% 29% 4	1100

Page generated at 2025-07-03 00:30:12. Version ac07

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