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 2024-03-23.

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% 3 5% 5% 3 4 4 5% 7% 49%	79157
	Night	11% 5% 2 4 4 2 4 4 5% 7% 53%	80791
Transparency	Day	35% 5% 11% 25% 19% 4	78882
	Night	32% 5% 10% 26% 22% 5%	80586
Seeing	Day	13% 9% 28% 29% 17% 3	14560
	Night	13% 9% 33% 33% 12% 1	24638

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 6% 6% 3 5% 4 5% 6% 45%	2847
	11th to 20th	Day	9% 9% 2 4 6% 4 4 4 4 6% 47%	2850
	21st to end	Day	16% 13% 5% 5% 3 1 2 2 3 5% 45%	3135
February	1st to 10th	Day	13% 9% 4 5% 6% 3 3 4 4 6% 44%	1710
	11th to 20th	Day	11% 6% 3 6% 5% 2 4 4 4 6% 50%	1819
	21st to end	Day	11% 8% 3 5% 4 2 4 4 5% 6% 47%	1570
March	1st to 10th	Day	13% 6% 2 6% 5% 2 3 3 4 6% 50%	2083
	11th to 20th	Day	19% 7% 2 5% 4 2 3 3 4 5% 46%	2090
	21st to end	Day	16% 9% 4 6% 5% 3 4 4 5% 5% 39%	2200
April	1st to 10th	Day	10% 5% 2 5% 3 4 4 5% 5% 8% 49%	1980
	11th to 20th	Day	15% 6% 3 6% 4 3 4 4 5% 6% 44%	2155
	21st to end	Day	17% 6% 4 5% 6% 3 4 4 4 5% 42%	2340
May	1st to 10th	Day	17% 6% 3 6% 5% 3 4 4 5% 6% 41%	2340
	11th to 20th	Day	14% 5% 3 5% 5% 3 5% 5% 5% 7% 43%	2302
	21st to end	Day	15% 6% 3 6% 7% 3 5% 5% 5% 9% 35%	2531
June	1st to 10th	Day	6% 3 1 5% 5% 3 5% 6% 6% 9% 50%	2340
	11th to 20th	Day	7% 4 2 4 5% 3 5% 5% 6% 8% 50%	2340
	21st to end	Day	6% 2 2 3 3 2 4 5% 6% 9% 58%	2340
July	1st to 10th	Day	10% 4 2 4 5% 3 5% 6% 6% 10% 45%	2340
	11th to 20th	Day	4 2 2 3 4 2 4 5% 7% 10% 57%	2340
	21st to end	Day	6% 4 2 4 4 3 5% 7% 8% 10% 46%	2546
August	1st to 10th	Day	6% 3 2 4 5% 3 5% 5% 7% 10% 49%	2328
	11th to 20th	Day	8% 4 2 4 4 3 5% 5% 6% 9% 50%	2301
	21st to end	Day	6% 3 2 5% 5% 2 4 4 5% 8% 55%	2494
September	1st to 10th	Day	11% 5% 2 4 4 3 4 4 4 6% 54%	1987
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 5% 7% 48%	1980
	21st to end	Day	9% 3 1 4 3 3 4 3 4 7% 58%	1980
October	1st to 10th	Day	9% 4 2 4 5% 3 4 3 5% 7% 54%	1886
	11th to 20th	Day	10% 3 2 4 2 2 2 3 4 6% 63%	1800
	21st to end	Day	13% 6% 3 4 4 2 3 3 4 5% 55%	1980
November	1st to 10th	Day	8% 4 2 3 3 2 4 4 4 6% 61%	1797
	11th to 20th	Day	9% 5% 2 3 3 2 3 4 4 6% 60%	1710
	21st to end	Day	14% 4 2 4 4 2 3 3 3 6% 57%	1710
December	1st to 10th	Day	10% 6% 3 4 5% 2 3 4 6% 6% 51%	1710
	11th to 20th	Day	12% 7% 2 5% 6% 3 4 4 4 6% 47%	2161
	21st to end	Day	13% 9% 5% 9% 6% 4 4 4 5% 6% 34%	3135
January	1st to 10th	Night	11% 8% 2 6% 5% 3 3 4 4 6% 48%	4108
	11th to 20th	Night	8% 5% 2 5% 5% 2 4 4 4 6% 55%	4120
	21st to end	Night	19% 9% 3 4 3 2 2 3 3 4 49%	4532
February	1st to 10th	Night	13% 8% 3 5% 5% 3 4 4 4 6% 46%	2470
	11th to 20th	Night	12% 6% 3 5% 4 3 3 3 4 5% 52%	2264
	21st to end	Night	11% 6% 2 4 4 2 4 3 5% 7% 53%	1884
March	1st to 10th	Night	9% 5% 2 5% 5% 3 4 5% 5% 7% 51%	2095
	11th to 20th	Night	17% 5% 1 4 3 2 3 4 4 6% 50%	2090
	21st to end	Night	15% 7% 3 6% 5% 3 4 4 4 6% 44%	2200
April	1st to 10th	Night	10% 4 2 4 4 2 4 5% 4 7% 54%	1980
	11th to 20th	Night	14% 5% 2 4 4 2 3 3 4 7% 51%	1750
	21st to end	Night	15% 5% 3 4 3 2 3 4 5% 7% 50%	1620
May	1st to 10th	Night	15% 6% 2 4 4 2 4 4 5% 8% 46%	1620
	11th to 20th	Night	13% 4 2 5% 4 3 4 4 4 8% 49%	1593
	21st to end	Night	10% 5% 2 3 4 3 5% 6% 7% 10% 46%	1745
June	1st to 10th	Night	4 4 1 5% 5% 2 3 4 6% 9% 56%	1620
	11th to 20th	Night	5% 3 1 3 3 2 5% 5% 7% 11% 55%	1620
	21st to end	Night	5% 2 1 3 3 2 3 3 6% 10% 63%	1620
July	1st to 10th	Night	6% 3 1 3 4 3 4 6% 6% 10% 54%	1620
	11th to 20th	Night	3 2 1 3 4 2 4 4 6% 10% 62%	1620
	21st to end	Night	6% 2 2 5% 4 3 6% 6% 6% 11% 50%	1772
August	1st to 10th	Night	5% 2 2 3 5% 3 6% 5% 7% 10% 51%	1611
	11th to 20th	Night	5% 3 2 4 5% 3 4 6% 6% 8% 53%	1600
	21st to end	Night	4 2 2 3 3 3 3 4 6% 9% 61%	1862
September	1st to 10th	Night	11% 4 2 3 3 2 4 3 4 5% 60%	1969
	11th to 20th	Night	10% 5% 2 3 6% 3 4 4 4 7% 51%	1980
	21st to end	Night	7% 3 2 3 4 2 3 4 5% 6% 63%	1980
October	1st to 10th	Night	9% 4 2 4 4 2 3 3 4 6% 59%	2055
	11th to 20th	Night	11% 4 1 2 3 2 3 3 4 5% 62%	2160
	21st to end	Night	13% 4 2 3 3 2 3 4 4 5% 58%	2376
November	1st to 10th	Night	9% 3 2 3 3 2 3 3 4 5% 64%	2277
	11th to 20th	Night	10% 4 2 4 3 2 3 3 4 5% 60%	2470
	21st to end	Night	13% 5% 2 4 3 1 3 2 4 5% 57%	2470
December	1st to 10th	Night	11% 5% 2 4 4 2 4 4 4 7% 54%	2470
	11th to 20th	Night	10% 6% 3 5% 5% 3 4 3 4 5% 53%	3036
	21st to end	Night	16% 6% 3 5% 5% 3 4 4 5% 7% 43%	4532

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	40% 4 9% 26% 19% 2	2848
	11th to 20th	Day	38% 4 16% 24% 13% 5%	2850
	21st to end	Day	45% 3 9% 22% 21% 1	3135
February	1st to 10th	Day	43% 3 11% 24% 14% 4	1710
	11th to 20th	Day	37% 3 11% 28% 17% 4	1829
	21st to end	Day	38% 4 7% 24% 19% 9%	1570
March	1st to 10th	Day	37% 3 8% 22% 21% 8%	2083
	11th to 20th	Day	41% 4 9% 24% 17% 4	2090
	21st to end	Day	47% 6% 10% 23% 12% 3	2200
April	1st to 10th	Day	33% 5% 12% 26% 19% 5%	1980
	11th to 20th	Day	41% 5% 12% 22% 16% 4	2155
	21st to end	Day	45% 5% 9% 24% 15% 1	2340
May	1st to 10th	Day	44% 5% 10% 22% 17% 2	2340
	11th to 20th	Day	40% 6% 14% 24% 15% 1	2306
	21st to end	Day	44% 8% 14% 23% 9% 2	2531
June	1st to 10th	Day	29% 8% 17% 27% 18% 2	2340
	11th to 20th	Day	30% 7% 13% 30% 17% 4	2340
	21st to end	Day	22% 6% 14% 29% 24% 5%	2340
July	1st to 10th	Day	32% 8% 15% 27% 16% 3	2276
	11th to 20th	Day	21% 8% 14% 31% 23% 4	2271
	21st to end	Day	29% 7% 14% 30% 18% 1	2405
August	1st to 10th	Day	28% 7% 18% 27% 16% 3	2314
	11th to 20th	Day	29% 6% 15% 27% 22% 1	2301
	21st to end	Day	27% 6% 13% 26% 21% 8%	2494
September	1st to 10th	Day	33% 5% 8% 26% 21% 8%	1987
	11th to 20th	Day	34% 6% 10% 24% 21% 4	1980
	21st to end	Day	27% 5% 9% 23% 30% 7%	1980
October	1st to 10th	Day	30% 5% 10% 23% 27% 4	1886
	11th to 20th	Day	26% 3 7% 26% 30% 8%	1800
	21st to end	Day	34% 4 9% 25% 20% 8%	1980
November	1st to 10th	Day	26% 4 9% 28% 27% 7%	1797
	11th to 20th	Day	27% 3 9% 27% 28% 6%	1710
	21st to end	Day	31% 3 9% 26% 26% 5%	1710
December	1st to 10th	Day	35% 4 9% 32% 18% 2	1710
	11th to 20th	Day	39% 4 7% 26% 21% 4	2159
	21st to end	Day	50% 5% 8% 22% 12% 2	3135
January	1st to 10th	Night	37% 4 8% 30% 18% 3	4108
	11th to 20th	Night	31% 4 14% 25% 22% 3	4120
	21st to end	Night	42% 3 9% 23% 20% 3	4532
February	1st to 10th	Night	41% 4 11% 21% 18% 5%	2470
	11th to 20th	Night	36% 4 9% 27% 19% 5%	2264
	21st to end	Night	33% 4 8% 22% 22% 11%	1884
March	1st to 10th	Night	34% 4 8% 23% 22% 10%	2095
	11th to 20th	Night	36% 4 11% 23% 20% 6%	2090
	21st to end	Night	42% 5% 10% 24% 16% 3	2200
April	1st to 10th	Night	30% 5% 12% 23% 22% 8%	1980
	11th to 20th	Night	35% 4 12% 23% 19% 7%	1750
	21st to end	Night	35% 5% 11% 24% 21% 4	1620
May	1st to 10th	Night	38% 6% 13% 22% 18% 4	1620
	11th to 20th	Night	35% 5% 14% 27% 17% 2	1594
	21st to end	Night	32% 9% 17% 27% 13% 1	1746
June	1st to 10th	Night	25% 7% 17% 31% 16% 3	1620
	11th to 20th	Night	23% 6% 16% 32% 19% 3	1620
	21st to end	Night	19% 4 16% 30% 25% 7%	1620
July	1st to 10th	Night	25% 6% 13% 32% 20% 4	1575
	11th to 20th	Night	18% 5% 14% 29% 29% 5%	1566
	21st to end	Night	27% 6% 12% 33% 20% 2	1673
August	1st to 10th	Night	25% 6% 13% 35% 17% 4	1601
	11th to 20th	Night	27% 7% 11% 26% 26% 4	1600
	21st to end	Night	21% 7% 12% 28% 24% 8%	1862
September	1st to 10th	Night	28% 4 9% 27% 22% 10%	1969
	11th to 20th	Night	33% 5% 11% 20% 25% 6%	1980
	21st to end	Night	23% 4 9% 26% 31% 8%	1980
October	1st to 10th	Night	28% 4 11% 22% 25% 11%	2055
	11th to 20th	Night	26% 4 6% 23% 31% 10%	2160
	21st to end	Night	30% 4 7% 22% 27% 9%	2376
November	1st to 10th	Night	23% 3 9% 27% 29% 8%	2277
	11th to 20th	Night	28% 3 8% 27% 28% 6%	2470
	21st to end	Night	32% 2 8% 23% 27% 7%	2470
December	1st to 10th	Night	31% 4 11% 28% 22% 3	2470
	11th to 20th	Night	35% 4 7% 26% 24% 5%	3037
	21st to end	Night	40% 5% 8% 26% 17% 4	4532

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% 15% 36% 24% 6% 1	270
	11th to 20th	Day	22% 18% 37% 20% 3	270
	21st to end	Day	17% 13% 43% 22% 4 1	297
February	1st to 10th	Day	18% 20% 38% 20% 3 1	270
	11th to 20th	Day	18% 16% 45% 17% 4	270
	21st to end	Day	19% 24% 40% 16% 1	225
March	1st to 10th	Day	18% 20% 37% 21% 3	270
	11th to 20th	Day	20% 20% 36% 20% 3 1	270
	21st to end	Day	26% 19% 34% 18% 3	270
April	1st to 10th	Day	17% 20% 40% 19% 5%	240
	11th to 20th	Day	20% 16% 41% 19% 4	433
	21st to end	Day	21% 17% 36% 18% 8% 1	600
May	1st to 10th	Day	17% 13% 37% 24% 8% 1	603
	11th to 20th	Day	16% 11% 34% 26% 11% 2	625
	21st to end	Day	17% 9% 30% 24% 16% 4	679
June	1st to 10th	Day	7% 3 23% 39% 23% 5%	630
	11th to 20th	Day	8% 4 28% 41% 17% 2	630
	21st to end	Day	5% 4 27% 41% 20% 3	630
July	1st to 10th	Day	10% 2 14% 34% 32% 8%	621
	11th to 20th	Day	2 2 14% 41% 34% 6%	618
	21st to end	Day	7% 1 11% 40% 32% 8%	684
August	1st to 10th	Day	7% 2 15% 43% 29% 5%	626
	11th to 20th	Day	9% 1 16% 36% 33% 5%	615
	21st to end	Day	7% 1 11% 36% 35% 10%	613
September	1st to 10th	Day	11% 2 14% 30% 35% 7%	277
	11th to 20th	Day	6% 3 19% 37% 26% 9%	270
	21st to end	Day	13% 4 25% 36% 17% 5%	270
October	1st to 10th	Day	10% 8% 28% 29% 19% 6%	270
	11th to 20th	Day	9% 9% 47% 27% 8%	270
	21st to end	Day	24% 10% 33% 25% 6% 2	297
November	1st to 10th	Day	14% 10% 37% 26% 11% 2	270
	11th to 20th	Day	15% 13% 39% 23% 10% 1	270
	21st to end	Day	19% 15% 36% 24% 5% 1	270
December	1st to 10th	Day	13% 14% 40% 23% 9% 2	270
	11th to 20th	Day	18% 16% 34% 24% 6% 1	270
	21st to end	Day	14% 24% 39% 20% 2	297
January	1st to 10th	Night	13% 12% 39% 31% 6%	950
	11th to 20th	Night	15% 13% 40% 26% 5%	950
	21st to end	Night	13% 13% 39% 30% 5%	1045
February	1st to 10th	Night	17% 14% 39% 26% 3	950
	11th to 20th	Night	16% 15% 39% 26% 4	790
	21st to end	Night	16% 14% 40% 27% 3	628
March	1st to 10th	Night	13% 14% 39% 30% 4	575
	11th to 20th	Night	21% 11% 35% 29% 4	570
	21st to end	Night	18% 13% 41% 23% 4 1	600
April	1st to 10th	Night	14% 17% 40% 24% 5%	540
	11th to 20th	Night	16% 16% 38% 26% 5%	533
	21st to end	Night	18% 13% 39% 22% 6% 1	540
May	1st to 10th	Night	18% 8% 39% 28% 7%	540
	11th to 20th	Night	15% 7% 32% 34% 12% 1	531
	21st to end	Night	13% 5% 31% 33% 16% 2	584
June	1st to 10th	Night	4 4 27% 41% 24%	540
	11th to 20th	Night	5% 3 33% 44% 14%	540
	21st to end	Night	6% 1 35% 43% 15%	540
July	1st to 10th	Night	6% 1 17% 46% 28% 3	525
	11th to 20th	Night	3 2 18% 48% 27% 3	522
	21st to end	Night	5% 1 12% 50% 29% 3	591
August	1st to 10th	Night	5% 1 18% 49% 26% 1	537
	11th to 20th	Night	6% 1 18% 48% 26% 1	534
	21st to end	Night	5% 1 14% 38% 40% 2	594
September	1st to 10th	Night	12% 2 18% 41% 25% 2	540
	11th to 20th	Night	12% 3 22% 39% 20% 4	540
	21st to end	Night	8% 5% 24% 42% 18% 3	540
October	1st to 10th	Night	11% 4 31% 30% 21% 2	615
	11th to 20th	Night	13% 8% 41% 29% 9%	720
	21st to end	Night	14% 12% 34% 28% 11%	792
November	1st to 10th	Night	10% 7% 41% 30% 11% 1	797
	11th to 20th	Night	12% 13% 36% 30% 8% 1	950
	21st to end	Night	17% 12% 32% 31% 7%	950
December	1st to 10th	Night	13% 12% 38% 30% 7%	950
	11th to 20th	Night	17% 12% 36% 31% 5%	950
	21st to end	Night	15% 15% 37% 29% 4	1045

Page generated at 2024-03-19 22:31:03. Version ac07

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