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 2026-10-29.

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	10% 6% 2 5% 4 4 4 3 5% 7% 50%	149558
	Night	10% 5% 2 5% 3 3 3 3 5% 7% 55%	142911
Transparency	Day	33% 4 10% 27% 21% 5%	153223
	Night	30% 3 10% 27% 23% 6%	147313
Seeing	Day	13% 10% 29% 29% 16% 3	18228
	Night	12% 10% 34% 33% 11% 1	27996

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	12% 7% 2 7% 4 4 4 3 5% 6% 48%	5289
	11th to 20th	Day	6% 8% 2 6% 4 4 3 2 4 5% 57%	5310
	21st to end	Day	13% 10% 4 7% 3 3 2 2 3 4 50%	5812
February	1st to 10th	Day	13% 10% 3 6% 5% 3 3 3 4 6% 44%	1890
	11th to 20th	Day	11% 7% 2 6% 5% 3 4 2 4 6% 50%	2017
	21st to end	Day	11% 7% 3 6% 3 3 3 3 5% 6% 49%	1730
March	1st to 10th	Day	9% 6% 2 6% 3 3 3 2 4 5% 56%	5039
	11th to 20th	Day	9% 6% 2 5% 3 3 3 3 5% 6% 56%	5090
	21st to end	Day	10% 8% 3 7% 5% 4 5% 4 6% 7% 40%	5583
April	1st to 10th	Day	11% 6% 2 5% 3 4 4 4 5% 8% 49%	2310
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 45%	2520
	21st to end	Day	17% 7% 3 7% 5% 4 4 3 4 5% 41%	2730
May	1st to 10th	Day	18% 7% 2 6% 4 4 3 3 4 5% 44%	7617
	11th to 20th	Day	12% 5% 2 5% 3 3 4 3 5% 7% 51%	7627
	21st to end	Day	20% 7% 3 6% 5% 5% 4 3 4 6% 37%	8392
June	1st to 10th	Day	7% 4 1 6% 5% 4 5% 4 7% 9% 48%	2730
	11th to 20th	Day	7% 5% 2 5% 5% 5% 4 4 6% 8% 49%	2730
	21st to end	Day	7% 3 1 3 2 3 4 5% 7% 8% 56%	2730
July	1st to 10th	Day	6% 4 2 6% 4 5% 5% 5% 7% 9% 46%	7680
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 10% 52%	7680
	21st to end	Day	4 3 2 5% 4 5% 6% 5% 8% 11% 46%	8337
August	1st to 10th	Day	5% 3 1 4 4 4 4 4 6% 9% 58%	6014
	11th to 20th	Day	5% 3 1 4 3 4 5% 5% 6% 9% 56%	5948
	21st to end	Day	4 3 2 4 3 3 4 3 6% 8% 58%	6368
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 4 6% 55%	2317
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 4 5% 6% 50%	2310
	21st to end	Day	9% 4 2 6% 3 4 4 3 4 7% 55%	2310
October	1st to 10th	Day	8% 4 2 5% 4 3 3 2 5% 6% 57%	2200
	11th to 20th	Day	10% 3 1 4 2 2 2 2 4 5% 63%	2100
	21st to end	Day	14% 6% 2 4 3 3 3 3 4 5% 54%	2280
November	1st to 10th	Day	9% 5% 1 3 2 3 3 3 4 6% 61%	1990
	11th to 20th	Day	9% 5% 2 3 3 2 3 3 4 6% 59%	1890
	21st to end	Day	13% 4 2 4 3 2 3 2 3 7% 56%	1890
December	1st to 10th	Day	7% 6% 3 4 3 2 3 3 5% 5% 60%	3030
	11th to 20th	Day	8% 6% 2 5% 4 3 3 2 4 6% 57%	3481
	21st to end	Day	16% 10% 5% 9% 5% 4 4 3 4 5% 35%	4587
January	1st to 10th	Night	13% 7% 2 5% 4 3 3 3 4 6% 50%	7634
	11th to 20th	Night	5% 5% 2 5% 3 3 3 3 4 5% 62%	7680
	21st to end	Night	15% 8% 3 5% 3 3 3 3 4 4 50%	8402
February	1st to 10th	Night	13% 9% 3 5% 4 3 4 3 5% 5% 47%	2730
	11th to 20th	Night	12% 7% 3 5% 4 4 3 3 4 6% 51%	2508
	21st to end	Night	10% 6% 2 4 3 3 3 3 5% 6% 55%	2076
March	1st to 10th	Night	10% 7% 2 5% 4 3 3 3 3 5% 56%	5034
	11th to 20th	Night	7% 3 1 3 2 2 3 2 5% 7% 64%	5090
	21st to end	Night	10% 6% 2 5% 4 4 4 3 6% 7% 48%	5588
April	1st to 10th	Night	11% 5% 2 4 3 3 4 4 4 7% 53%	2310
	11th to 20th	Night	13% 5% 1 5% 3 3 3 2 4 7% 52%	2044
	21st to end	Night	16% 6% 3 4 3 3 2 3 5% 7% 48%	1890
May	1st to 10th	Night	16% 7% 2 5% 3 3 4 3 5% 6% 47%	5266
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 6% 8% 49%	5265
	21st to end	Night	18% 6% 2 4 3 3 4 3 5% 7% 45%	5793
June	1st to 10th	Night	6% 4 2 6% 4 3 3 3 6% 10% 52%	1890
	11th to 20th	Night	5% 3 1 4 3 4 4 4 7% 10% 53%	1890
	21st to end	Night	6% 3 1 3 3 3 3 3 6% 9% 60%	1890
July	1st to 10th	Night	4 3 1 5% 3 4 4 4 7% 10% 52%	5308
	11th to 20th	Night	4 4 1 5% 3 3 4 4 7% 10% 55%	5307
	21st to end	Night	4 2 1 5% 3 4 5% 5% 8% 11% 52%	5770
August	1st to 10th	Night	3 2 1 4 3 4 4 3 6% 8% 62%	4156
	11th to 20th	Night	3 3 1 4 3 4 5% 4 5% 8% 60%	4118
	21st to end	Night	3 2 1 4 2 3 3 3 5% 7% 66%	4757
September	1st to 10th	Night	10% 4 1 4 3 3 3 2 4 6% 60%	2298
	11th to 20th	Night	9% 5% 2 4 5% 4 4 3 5% 7% 53%	2310
	21st to end	Night	7% 4 2 5% 3 3 3 3 5% 6% 60%	2310
October	1st to 10th	Night	9% 4 2 4 3 3 3 3 4 6% 62%	2398
	11th to 20th	Night	11% 4 1 3 2 2 3 2 4 5% 63%	2520
	21st to end	Night	13% 4 2 4 2 3 3 3 4 5% 57%	2737
November	1st to 10th	Night	10% 4 1 3 2 2 2 2 4 5% 63%	2523
	11th to 20th	Night	10% 4 1 4 3 2 3 3 4 5% 61%	2730
	21st to end	Night	13% 6% 2 4 3 2 3 2 4 5% 56%	2730
December	1st to 10th	Night	6% 4 1 5% 3 3 3 2 4 6% 64%	4380
	11th to 20th	Night	9% 5% 2 6% 3 3 3 3 3 5% 58%	4946
	21st to end	Night	17% 8% 3 6% 4 3 4 3 4 6% 43%	6633

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	39% 3 8% 29% 19% 3	5290
	11th to 20th	Day	32% 2 9% 27% 23% 7%	5310
	21st to end	Day	41% 2 6% 22% 26% 3	5812
February	1st to 10th	Day	43% 3 10% 25% 15% 4	1890
	11th to 20th	Day	38% 3 11% 27% 17% 4	2027
	21st to end	Day	35% 3 6% 23% 22% 9%	1730
March	1st to 10th	Day	33% 2 4 21% 22% 17%	5039
	11th to 20th	Day	30% 3 8% 21% 22% 16%	5090
	21st to end	Day	42% 4 10% 30% 11% 1	5585
April	1st to 10th	Day	34% 5% 11% 25% 20% 5%	2310
	11th to 20th	Day	39% 5% 12% 21% 18% 5%	2520
	21st to end	Day	46% 5% 9% 24% 14% 2	2730
May	1st to 10th	Day	44% 3 8% 20% 23% 2	7655
	11th to 20th	Day	33% 5% 9% 24% 24% 5%	7631
	21st to end	Day	48% 5% 10% 17% 17% 2	8405
June	1st to 10th	Day	30% 7% 16% 26% 18% 2	2730
	11th to 20th	Day	31% 6% 12% 30% 17% 4	2730
	21st to end	Day	24% 5% 15% 28% 23% 5%	2730
July	1st to 10th	Day	33% 4 12% 30% 19% 3	7616
	11th to 20th	Day	29% 4 14% 28% 20% 6%	7611
	21st to end	Day	30% 3 17% 35% 14% 1	8155
August	1st to 10th	Day	24% 3 13% 26% 27% 7%	6000
	11th to 20th	Day	26% 3 17% 32% 21% 1	5987
	21st to end	Day	25% 3 18% 35% 16% 3	6367
September	1st to 10th	Day	32% 4 9% 25% 22% 8%	2317
	11th to 20th	Day	33% 6% 10% 27% 20% 4	2310
	21st to end	Day	31% 4 9% 22% 28% 6%	2310
October	1st to 10th	Day	22% 3 6% 17% 41% 11%	3512
	11th to 20th	Day	17% 2 4 29% 35% 13%	3340
	21st to end	Day	27% 2 7% 29% 28% 7%	3618
November	1st to 10th	Day	26% 4 8% 28% 27% 7%	1990
	11th to 20th	Day	27% 3 9% 27% 27% 7%	1890
	21st to end	Day	31% 3 9% 27% 25% 5%	1890
December	1st to 10th	Day	28% 3 6% 40% 22% 1	3030
	11th to 20th	Day	31% 2 6% 32% 25% 4	3479
	21st to end	Day	52% 3 6% 25% 12% 2	4587
January	1st to 10th	Night	37% 2 8% 29% 21% 3	7635
	11th to 20th	Night	26% 3 8% 26% 29% 8%	7680
	21st to end	Night	39% 2 7% 22% 26% 4	8402
February	1st to 10th	Night	40% 4 10% 23% 17% 6%	2730
	11th to 20th	Night	37% 4 10% 27% 18% 5%	2508
	21st to end	Night	31% 4 8% 22% 25% 11%	2076
March	1st to 10th	Night	33% 3 5% 21% 24% 12%	5034
	11th to 20th	Night	22% 2 6% 22% 29% 18%	5090
	21st to end	Night	36% 4 10% 34% 14% 2	5588
April	1st to 10th	Night	31% 5% 11% 23% 22% 8%	2310
	11th to 20th	Night	34% 4 12% 22% 21% 7%	2044
	21st to end	Night	36% 5% 12% 25% 19% 4	1890
May	1st to 10th	Night	40% 4 12% 19% 22% 3	5293
	11th to 20th	Night	35% 4 10% 24% 21% 6%	5266
	21st to end	Night	40% 5% 13% 23% 16% 3	5805
June	1st to 10th	Night	27% 7% 18% 28% 16% 3	1890
	11th to 20th	Night	25% 6% 16% 31% 19% 3	1890
	21st to end	Night	22% 4 16% 29% 23% 6%	1890
July	1st to 10th	Night	26% 3 15% 35% 18% 3	5265
	11th to 20th	Night	25% 4 13% 32% 21% 5%	5256
	21st to end	Night	24% 3 17% 40% 14% 1	5641
August	1st to 10th	Night	20% 3 10% 27% 31% 9%	4146
	11th to 20th	Night	24% 3 15% 29% 26% 2	4145
	21st to end	Night	19% 4 14% 38% 22% 4	4757
September	1st to 10th	Night	27% 4 9% 26% 24% 10%	2298
	11th to 20th	Night	32% 5% 10% 25% 23% 5%	2310
	21st to end	Night	26% 3 10% 25% 29% 7%	2310
October	1st to 10th	Night	18% 2 6% 14% 43% 17%	3853
	11th to 20th	Night	19% 3 4 21% 36% 17%	4019
	21st to end	Night	26% 3 6% 27% 31% 8%	4349
November	1st to 10th	Night	24% 3 8% 27% 30% 8%	2523
	11th to 20th	Night	27% 2 8% 28% 28% 7%	2730
	21st to end	Night	32% 2 8% 25% 26% 7%	2730
December	1st to 10th	Night	24% 2 10% 41% 20% 2	4380
	11th to 20th	Night	31% 2 6% 28% 26% 6%	4947
	21st to end	Night	43% 4 7% 28% 15% 4	6633

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	17% 14% 38% 24% 5% 1	330
	11th to 20th	Day	20% 19% 39% 18% 4	330
	21st to end	Day	17% 12% 44% 23% 4 1	363
February	1st to 10th	Day	17% 19% 41% 18% 4 1	330
	11th to 20th	Day	19% 16% 45% 16% 4	330
	21st to end	Day	16% 22% 42% 18% 2	273
March	1st to 10th	Day	19% 20% 38% 19% 3	330
	11th to 20th	Day	20% 21% 36% 19% 3 1	330
	21st to end	Day	21% 20% 39% 15% 3 1	363
April	1st to 10th	Day	20% 21% 36% 19% 4	330
	11th to 20th	Day	20% 18% 42% 17% 3	558
	21st to end	Day	22% 18% 35% 17% 7% 1	750
May	1st to 10th	Day	17% 13% 38% 25% 7% 1	753
	11th to 20th	Day	16% 13% 34% 25% 11% 2	775
	21st to end	Day	18% 10% 29% 25% 15% 3	844
June	1st to 10th	Day	8% 5% 25% 37% 20% 4	780
	11th to 20th	Day	9% 4 29% 39% 16% 2	780
	21st to end	Day	6% 4 29% 40% 18% 2	780
July	1st to 10th	Day	9% 2 18% 34% 29% 7%	771
	11th to 20th	Day	3 2 14% 42% 32% 6%	768
	21st to end	Day	6% 2 13% 40% 31% 8%	849
August	1st to 10th	Day	6% 2 18% 42% 27% 4	776
	11th to 20th	Day	8% 2 17% 39% 30% 5%	765
	21st to end	Day	8% 1 12% 37% 34% 8%	763
September	1st to 10th	Day	10% 3 14% 32% 35% 7%	367
	11th to 20th	Day	6% 3 20% 40% 25% 7%	360
	21st to end	Day	14% 4 25% 35% 18% 6%	360
October	1st to 10th	Day	9% 6% 26% 33% 21% 6%	360
	11th to 20th	Day	10% 10% 41% 28% 10% 1	360
	21st to end	Day	23% 9% 33% 27% 7% 2	387
November	1st to 10th	Day	15% 10% 39% 23% 11% 2	330
	11th to 20th	Day	15% 12% 40% 22% 10% 1	330
	21st to end	Day	18% 15% 38% 23% 5% 1	330
December	1st to 10th	Day	12% 14% 43% 22% 7% 2	330
	11th to 20th	Day	16% 17% 37% 23% 6% 1	330
	21st to end	Day	14% 22% 39% 21% 3	363
January	1st to 10th	Night	13% 12% 40% 30% 6%	1050
	11th to 20th	Night	14% 14% 42% 25% 5%	1050
	21st to end	Night	14% 13% 40% 28% 5%	1155
February	1st to 10th	Night	17% 14% 40% 26% 3	1050
	11th to 20th	Night	17% 16% 39% 25% 3	874
	21st to end	Night	14% 14% 41% 27% 3	692
March	1st to 10th	Night	14% 15% 38% 29% 4	635
	11th to 20th	Night	20% 12% 36% 28% 4	630
	21st to end	Night	16% 14% 43% 23% 4 1	693
April	1st to 10th	Night	15% 17% 39% 24% 5%	630
	11th to 20th	Night	16% 18% 39% 23% 4	623
	21st to end	Night	18% 14% 40% 22% 6% 1	630
May	1st to 10th	Night	18% 9% 38% 28% 7%	630
	11th to 20th	Night	15% 7% 32% 33% 13%	621
	21st to end	Night	14% 6% 30% 33% 15% 2	683
June	1st to 10th	Night	6% 4 29% 40% 21%	630
	11th to 20th	Night	6% 3 33% 43% 14%	630
	21st to end	Night	7% 2 36% 41% 13%	630
July	1st to 10th	Night	6% 1 19% 46% 26% 3	615
	11th to 20th	Night	3 2 19% 47% 26% 2	612
	21st to end	Night	5% 1 13% 50% 29% 2	690
August	1st to 10th	Night	4 1 21% 49% 24% 1	627
	11th to 20th	Night	6% 1 19% 47% 26% 1	624
	21st to end	Night	5% 1 14% 41% 36% 2	693
September	1st to 10th	Night	11% 2 17% 43% 25% 2	630
	11th to 20th	Night	11% 2 23% 41% 20% 3	630
	21st to end	Night	8% 5% 23% 43% 18% 3	630
October	1st to 10th	Night	10% 4 30% 33% 21% 2	718
	11th to 20th	Night	13% 8% 41% 30% 9%	840
	21st to end	Night	15% 12% 34% 28% 10%	913
November	1st to 10th	Night	11% 8% 40% 30% 10% 1	883
	11th to 20th	Night	12% 13% 38% 30% 8% 1	1050
	21st to end	Night	17% 13% 32% 30% 7%	1050
December	1st to 10th	Night	13% 13% 39% 29% 6%	1050
	11th to 20th	Night	17% 12% 38% 29% 5%	1050
	21st to end	Night	15% 15% 37% 29% 4	1155

Page generated at 2026-10-26 03:37:47. Version ac07

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