Golden
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Golden clear sky chart from 2005-11-06 to 2026-08-30.

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	4 5% 2 5% 4 4 5% 4 6% 8% 53%	152821
	Night	4 5% 2 5% 3 3 3 3 5% 7% 59%	146928
Transparency	Day	27% 6% 10% 22% 23% 11%	147774
	Night	24% 5% 10% 24% 26% 11%	142984
Seeing	Day	8% 9% 31% 32% 16% 4	18110
	Night	6% 6% 33% 40% 13% 2	28047

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	1 8% 2 5% 3 3 3 3 5% 6% 61%	4720
	11th to 20th	Day	1 3 2 6% 4 4 3 3 5% 7% 62%	4920
	21st to end	Day	1 4 2 6% 4 3 3 3 5% 7% 62%	5844
February	1st to 10th	Day	2 7% 3 7% 3 3 3 3 5% 7% 57%	1890
	11th to 20th	Day	1 5% 2 5% 4 4 4 4 6% 8% 57%	2012
	21st to end	Day	2 7% 2 5% 3 4 2 3 5% 6% 61%	1730
March	1st to 10th	Day	3 11% 3 4 2 3 3 3 5% 5% 59%	4600
	11th to 20th	Day	3 9% 3 6% 4 4 4 4 5% 8% 49%	5063
	21st to end	Day	3 8% 2 5% 4 4 5% 4 7% 8% 51%	5934
April	1st to 10th	Day	5% 7% 2 4 3 3 4 3 6% 8% 54%	2520
	11th to 20th	Day	8% 10% 2 6% 4 4 3 3 5% 7% 47%	2491
	21st to end	Day	9% 9% 2 5% 4 4 4 4 7% 8% 45%	2520
May	1st to 10th	Day	11% 8% 2 5% 4 4 5% 4 6% 7% 44%	7426
	11th to 20th	Day	10% 7% 2 5% 4 4 5% 5% 7% 7% 43%	8191
	21st to end	Day	6% 5% 2 5% 5% 5% 6% 5% 8% 10% 44%	9026
June	1st to 10th	Day	5% 4 1 4 4 5% 5% 5% 9% 10% 49%	2940
	11th to 20th	Day	6% 3 1 4 4 4 6% 5% 7% 9% 52%	2940
	21st to end	Day	5% 3 1 4 4 5% 6% 5% 8% 10% 49%	2940
July	1st to 10th	Day	3 3 1 4 4 4 6% 5% 7% 9% 54%	8249
	11th to 20th	Day	2 2 1 4 4 4 6% 5% 8% 10% 55%	8250
	21st to end	Day	4 3 2 6% 5% 6% 7% 5% 8% 9% 45%	8763
August	1st to 10th	Day	7% 3 2 5% 5% 7% 7% 6% 8% 10% 40%	5909
	11th to 20th	Day	2 3 1 4 4 5% 6% 5% 8% 9% 52%	5496
	21st to end	Day	6% 4 2 6% 5% 6% 5% 5% 8% 8% 44%	6093
September	1st to 10th	Day	5% 4 1 5% 3 3 4 4 6% 7% 59%	2400
	11th to 20th	Day	6% 4 1 3 4 3 4 4 5% 7% 58%	2385
	21st to end	Day	6% 5% 1 3 3 3 3 3 5% 6% 64%	2200
October	1st to 10th	Day	3 4 1 2 2 2 3 2 4 6% 72%	3275
	11th to 20th	Day	4 4 2 5% 3 4 4 3 6% 8% 57%	3250
	21st to end	Day	5% 6% 1 3 2 2 2 3 4 6% 66%	3434
November	1st to 10th	Day	2 5% 1 3 2 2 3 3 5% 7% 66%	1853
	11th to 20th	Day	2 5% 1 4 3 3 3 3 5% 7% 64%	1890
	21st to end	Day	3 5% 3 6% 3 2 2 3 5% 8% 60%	1769
December	1st to 10th	Day	1 3 1 6% 3 2 2 2 3 6% 70%	2700
	11th to 20th	Day	1 4 1 3 2 2 2 2 5% 7% 69%	3106
	21st to end	Day	2 5% 2 6% 4 4 5% 4 6% 8% 54%	4092
January	1st to 10th	Night	1 7% 4 7% 3 3 2 2 4 7% 60%	8201
	11th to 20th	Night	1 3 3 7% 4 4 3 2 3 6% 64%	8114
	21st to end	Night	2 5% 2 6% 4 3 4 3 4 5% 63%	8370
February	1st to 10th	Night	1 7% 2 5% 4 3 4 3 4 8% 58%	2730
	11th to 20th	Night	2 6% 3 6% 5% 3 4 3 5% 7% 56%	2493
	21st to end	Night	2 6% 2 6% 3 3 2 3 4 6% 62%	2076
March	1st to 10th	Night	3 10% 3 5% 3 3 3 3 4 7% 56%	5494
	11th to 20th	Night	5% 11% 2 4 3 3 3 3 5% 7% 55%	5138
	21st to end	Night	6% 10% 3 5% 3 2 3 3 5% 7% 53%	5266
April	1st to 10th	Night	5% 7% 2 4 2 3 4 3 5% 7% 58%	2100
	11th to 20th	Night	9% 9% 2 4 3 3 4 3 5% 6% 53%	2077
	21st to end	Night	12% 8% 3 6% 3 3 3 3 3 7% 50%	2100
May	1st to 10th	Night	14% 8% 2 5% 3 3 4 3 5% 7% 46%	5504
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 7% 50%	4701
	21st to end	Night	8% 6% 2 5% 3 3 4 3 4 6% 55%	5181
June	1st to 10th	Night	5% 3 1 3 3 3 3 4 5% 9% 61%	1680
	11th to 20th	Night	6% 3 2 2 3 3 3 5% 8% 65%	1680
	21st to end	Night	4 2 1 3 2 3 3 4 7% 9% 61%	1680
July	1st to 10th	Night	2 2 1 2 2 3 3 3 5% 8% 68%	4740
	11th to 20th	Night	3 2 1 3 3 3 4 4 7% 10% 61%	4740
	21st to end	Night	3 2 1 4 4 5% 6% 6% 9% 11% 49%	5329
August	1st to 10th	Night	5% 4 1 4 3 4 5% 4 8% 9% 53%	4123
	11th to 20th	Night	3 2 1 3 3 4 4 4 8% 11% 58%	4571
	21st to end	Night	5% 4 2 6% 5% 5% 5% 5% 7% 8% 49%	5083
September	1st to 10th	Night	6% 3 1 4 3 4 4 3 5% 7% 62%	2000
	11th to 20th	Night	7% 2 1 2 3 2 2 3 4 8% 65%	2015
	21st to end	Night	7% 3 2 3 3 3 3 2 4 4 65%	2200
October	1st to 10th	Night	4 4 1 2 1 2 2 2 3 4 75%	3911
	11th to 20th	Night	5% 4 1 4 2 3 2 2 4 7% 66%	3898
	21st to end	Night	5% 6% 2 3 2 2 2 2 3 5% 67%	4333
November	1st to 10th	Night	2 4 1 3 3 2 3 3 4 7% 69%	2665
	11th to 20th	Night	2 6% 1 4 3 2 2 2 3 6% 67%	2730
	21st to end	Night	3 7% 2 5% 3 2 3 3 4 7% 62%	2846
December	1st to 10th	Night	1 4 2 4 2 2 2 2 3 6% 73%	4710
	11th to 20th	Night	1 4 2 4 2 2 2 2 4 8% 68%	5321
	21st to end	Night	3 6% 2 6% 3 4 5% 4 5% 8% 54%	7128

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	24% 5% 7% 31% 24% 10%	4723
	11th to 20th	Day	21% 4 10% 27% 28% 10%	4920
	21st to end	Day	23% 5% 7% 26% 27% 13%	5844
February	1st to 10th	Day	27% 5% 11% 26% 22% 9%	1890
	11th to 20th	Day	23% 6% 10% 28% 26% 7%	2022
	21st to end	Day	22% 5% 9% 21% 29% 13%	1730
March	1st to 10th	Day	26% 6% 6% 18% 29% 15%	4600
	11th to 20th	Day	30% 10% 10% 19% 26% 5%	5063
	21st to end	Day	26% 8% 12% 34% 16% 3	5934
April	1st to 10th	Day	26% 6% 13% 25% 21% 9%	2520
	11th to 20th	Day	33% 9% 12% 18% 20% 9%	2494
	21st to end	Day	33% 9% 13% 23% 19% 3	2520
May	1st to 10th	Day	35% 7% 12% 25% 17% 4	7426
	11th to 20th	Day	35% 8% 10% 19% 20% 8%	8195
	21st to end	Day	31% 8% 16% 23% 17% 6%	9027
June	1st to 10th	Day	26% 11% 16% 21% 18% 8%	2940
	11th to 20th	Day	25% 9% 11% 18% 21% 15%	2940
	21st to end	Day	26% 8% 12% 19% 22% 12%	2940
July	1st to 10th	Day	24% 4 5% 15% 30% 21%	8181
	11th to 20th	Day	23% 4 10% 19% 21% 22%	8175
	21st to end	Day	33% 5% 14% 21% 15% 11%	8568
August	1st to 10th	Day	38% 8% 13% 20% 15% 6%	4338
	11th to 20th	Day	29% 6% 15% 17% 21% 13%	4012
	21st to end	Day	29% 6% 12% 19% 23% 11%	4420
September	1st to 10th	Day	23% 6% 9% 21% 25% 16%	2400
	11th to 20th	Day	22% 7% 10% 20% 27% 14%	2385
	21st to end	Day	21% 6% 7% 20% 33% 13%	2200
October	1st to 10th	Day	15% 4 7% 15% 35% 24%	3275
	11th to 20th	Day	26% 3 8% 26% 30% 8%	3250
	21st to end	Day	21% 3 5% 24% 36% 11%	3434
November	1st to 10th	Day	18% 4 10% 24% 30% 15%	1853
	11th to 20th	Day	19% 4 9% 26% 32% 10%	1890
	21st to end	Day	24% 4 10% 22% 28% 12%	1769
December	1st to 10th	Day	17% 4 8% 33% 28% 10%	2700
	11th to 20th	Day	15% 3 9% 29% 33% 11%	3104
	21st to end	Day	25% 6% 8% 24% 28% 9%	4092
January	1st to 10th	Night	26% 3 6% 29% 27% 8%	8202
	11th to 20th	Night	21% 4 9% 25% 25% 17%	8114
	21st to end	Night	24% 4 8% 22% 28% 13%	8370
February	1st to 10th	Night	25% 5% 11% 26% 26% 7%	2730
	11th to 20th	Night	29% 4 10% 26% 23% 8%	2493
	21st to end	Night	24% 4 7% 23% 27% 16%	2076
March	1st to 10th	Night	27% 5% 7% 16% 34% 11%	5494
	11th to 20th	Night	28% 6% 10% 15% 26% 15%	5138
	21st to end	Night	30% 5% 10% 33% 19% 3	5266
April	1st to 10th	Night	25% 6% 13% 23% 23% 10%	2100
	11th to 20th	Night	31% 6% 11% 22% 21% 9%	2077
	21st to end	Night	35% 6% 11% 23% 20% 5%	2100
May	1st to 10th	Night	36% 6% 13% 25% 15% 5%	5502
	11th to 20th	Night	33% 7% 11% 24% 19% 7%	4702
	21st to end	Night	29% 5% 18% 24% 18% 5%	5182
June	1st to 10th	Night	19% 8% 18% 30% 16% 9%	1680
	11th to 20th	Night	18% 6% 14% 20% 24% 19%	1680
	21st to end	Night	18% 7% 12% 25% 26% 12%	1680
July	1st to 10th	Night	16% 4 8% 18% 41% 13%	4700
	11th to 20th	Night	19% 4 13% 24% 23% 17%	4692
	21st to end	Night	27% 5% 19% 23% 16% 10%	5212
August	1st to 10th	Night	31% 6% 16% 22% 18% 6%	3018
	11th to 20th	Night	20% 6% 21% 22% 20% 10%	3331
	21st to end	Night	25% 6% 15% 22% 26% 6%	3687
September	1st to 10th	Night	23% 5% 11% 22% 24% 16%	2000
	11th to 20th	Night	18% 5% 11% 23% 27% 15%	2015
	21st to end	Night	23% 4 8% 21% 31% 13%	2200
October	1st to 10th	Night	15% 4 6% 19% 30% 25%	3911
	11th to 20th	Night	21% 2 8% 26% 32% 10%	3898
	21st to end	Night	21% 3 5% 22% 35% 14%	4333
November	1st to 10th	Night	17% 5% 10% 24% 30% 16%	2665
	11th to 20th	Night	19% 4 8% 26% 34% 10%	2730
	21st to end	Night	23% 4 9% 22% 30% 11%	2846
December	1st to 10th	Night	16% 3 8% 30% 35% 9%	4710
	11th to 20th	Night	17% 4 7% 29% 36% 8%	5322
	21st to end	Night	27% 6% 9% 22% 25% 11%	7128

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	7% 9% 31% 40% 11% 2	330
	11th to 20th	Day	8% 12% 41% 32% 7% 1	330
	21st to end	Day	5% 12% 46% 28% 8% 1	363
February	1st to 10th	Day	5% 18% 48% 23% 5% 1	330
	11th to 20th	Day	4 11% 46% 34% 4 1	330
	21st to end	Day	5% 15% 47% 30% 3	273
March	1st to 10th	Day	4 13% 44% 28% 10% 1	330
	11th to 20th	Day	10% 19% 35% 28% 7% 1	519
	21st to end	Day	11% 21% 36% 25% 6% 1	594
April	1st to 10th	Day	11% 19% 36% 26% 7% 1	540
	11th to 20th	Day	14% 23% 36% 20% 5% 1	532
	21st to end	Day	15% 16% 34% 25% 9% 1	540
May	1st to 10th	Day	15% 13% 31% 29% 9% 2	664
	11th to 20th	Day	17% 7% 29% 30% 14% 3	775
	21st to end	Day	9% 7% 30% 32% 17% 4	844
June	1st to 10th	Day	6% 5% 25% 35% 23% 6%	780
	11th to 20th	Day	6% 7% 30% 36% 17% 5%	780
	21st to end	Day	6% 5% 29% 35% 18% 6%	780
July	1st to 10th	Day	6% 3 20% 33% 30% 8%	771
	11th to 20th	Day	5% 1 17% 34% 34% 10%	768
	21st to end	Day	6% 2 16% 33% 35% 8%	782
August	1st to 10th	Day	6% 4 24% 34% 23% 8%	567
	11th to 20th	Day	5% 3 22% 37% 24% 8%	557
	21st to end	Day	7% 3 22% 38% 22% 8%	620
September	1st to 10th	Day	6% 4 22% 38% 23% 7%	530
	11th to 20th	Day	6% 4 29% 35% 23% 4	515
	21st to end	Day	8% 5% 28% 30% 23% 6%	330
October	1st to 10th	Day	10% 5% 27% 30% 23% 5%	330
	11th to 20th	Day	5% 11% 31% 41% 9% 4	330
	21st to end	Day	8% 12% 35% 31% 12% 2	363
November	1st to 10th	Day	6% 8% 38% 31% 15% 2	330
	11th to 20th	Day	7% 11% 28% 42% 9% 2	330
	21st to end	Day	6% 11% 38% 35% 9% 2	330
December	1st to 10th	Day	5% 14% 38% 31% 10% 2	330
	11th to 20th	Day	5% 12% 42% 35% 6% 1	330
	21st to end	Day	5% 10% 46% 31% 6% 1	363
January	1st to 10th	Night	3 11% 41% 34% 9% 2	1050
	11th to 20th	Night	3 13% 47% 28% 8% 1	1005
	21st to end	Night	4 10% 44% 36% 6%	924
February	1st to 10th	Night	5% 10% 48% 31% 4	840
	11th to 20th	Night	4 10% 48% 34% 5%	824
	21st to end	Night	5% 9% 48% 35% 2	692
March	1st to 10th	Night	4 8% 44% 37% 7%	840
	11th to 20th	Night	9% 6% 39% 37% 9% 1	840
	21st to end	Night	10% 8% 43% 34% 4 1	774
April	1st to 10th	Night	10% 9% 41% 36% 5%	630
	11th to 20th	Night	12% 10% 37% 33% 8%	623
	21st to end	Night	14% 7% 36% 34% 9% 1	630
May	1st to 10th	Night	15% 5% 30% 37% 11% 1	630
	11th to 20th	Night	16% 4 22% 45% 12% 2	621
	21st to end	Night	10% 4 25% 40% 19% 2	683
June	1st to 10th	Night	6% 3 19% 48% 22% 3	630
	11th to 20th	Night	7% 2 26% 50% 14% 2	630
	21st to end	Night	4 2 19% 47% 26% 1	630
July	1st to 10th	Night	5% 2 14% 42% 34% 3	615
	11th to 20th	Night	2 1 11% 46% 36% 3	612
	21st to end	Night	6% 1 7% 45% 36% 4	690
August	1st to 10th	Night	5% 2 12% 46% 33% 2	627
	11th to 20th	Night	5% 1 12% 52% 27% 3	624
	21st to end	Night	5% 2 11% 49% 30% 3	687
September	1st to 10th	Night	6% 2 15% 49% 24% 6%	600
	11th to 20th	Night	8% 2 19% 47% 20% 5%	600
	21st to end	Night	7% 3 22% 46% 18% 4	600
October	1st to 10th	Night	11% 3 26% 42% 15% 3	791
	11th to 20th	Night	5% 4 31% 46% 12% 2	800
	21st to end	Night	9% 6% 34% 38% 11% 2	925
November	1st to 10th	Night	4 5% 38% 41% 11% 1	1025
	11th to 20th	Night	5% 10% 39% 40% 5% 1	1050
	21st to end	Night	6% 6% 38% 41% 8%	1050
December	1st to 10th	Night	3 10% 41% 40% 6%	1050
	11th to 20th	Night	4 8% 48% 33% 6% 1	1050
	21st to end	Night	5% 10% 44% 33% 6% 1	1155

Page generated at 2026-08-27 02:07:10. Version ac07

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