Candelas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Candelas clear sky chart from 2005-11-06 to 2026-09-29.

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	4 5% 2 5% 4 4 5% 4 6% 8% 54%	158002
	Night	4 5% 2 5% 3 3 3 3 5% 7% 59%	150994
Transparency	Day	26% 7% 10% 23% 24% 11%	152942
	Night	24% 5% 11% 23% 26% 11%	147063
Seeing	Day	8% 10% 28% 33% 17% 4	18230
	Night	6% 10% 27% 40% 15% 2	28145

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 7% 2 6% 3 3 3 3 4 7% 60%	4720
	11th to 20th	Day	1 3 2 6% 4 4 4 3 5% 7% 62%	4902
	21st to end	Day	1 3 2 7% 4 3 3 2 5% 7% 62%	5844
February	1st to 10th	Day	1 6% 3 7% 4 4 4 3 5% 6% 57%	1890
	11th to 20th	Day	1 4 3 4 4 4 5% 3 5% 9% 56%	2009
	21st to end	Day	1 6% 3 7% 3 3 3 3 5% 5% 61%	1730
March	1st to 10th	Day	3 10% 3 5% 2 3 4 3 4 6% 57%	4600
	11th to 20th	Day	3 8% 3 6% 4 4 4 4 6% 8% 50%	5063
	21st to end	Day	3 7% 2 5% 4 4 5% 5% 7% 9% 49%	5934
April	1st to 10th	Day	5% 6% 2 4 3 3 3 4 6% 9% 55%	2520
	11th to 20th	Day	8% 9% 2 5% 3 4 4 3 6% 8% 47%	2491
	21st to end	Day	8% 8% 3 4 4 4 5% 4 7% 8% 45%	2520
May	1st to 10th	Day	10% 7% 2 5% 4 4 5% 4 6% 7% 46%	7448
	11th to 20th	Day	10% 6% 2 6% 4 4 6% 5% 6% 8% 43%	8191
	21st to end	Day	6% 5% 2 5% 4 5% 6% 5% 8% 9% 45%	9026
June	1st to 10th	Day	4 3 2 4 4 5% 5% 6% 8% 10% 48%	2940
	11th to 20th	Day	5% 3 1 4 4 4 6% 5% 8% 8% 52%	2940
	21st to end	Day	4 3 1 4 4 5% 5% 6% 8% 10% 49%	2940
July	1st to 10th	Day	3 3 1 4 4 4 6% 4 7% 8% 57%	8249
	11th to 20th	Day	2 2 1 3 3 5% 5% 5% 8% 10% 55%	8250
	21st to end	Day	4 3 1 6% 5% 6% 6% 5% 8% 9% 46%	8782
August	1st to 10th	Day	6% 3 1 4 4 5% 6% 5% 8% 10% 48%	7549
	11th to 20th	Day	3 2 1 4 3 4 5% 5% 8% 10% 53%	7042
	21st to end	Day	5% 4 2 5% 4 5% 6% 6% 9% 11% 42%	7751
September	1st to 10th	Day	4 4 1 4 3 4 4 4 5% 7% 60%	2520
	11th to 20th	Day	4 4 1 5% 4 4 5% 4 5% 7% 58%	2504
	21st to end	Day	6% 4 2 4 2 3 3 3 5% 5% 63%	2288
October	1st to 10th	Day	3 3 1 2 2 1 2 2 4 5% 74%	3274
	11th to 20th	Day	5% 4 2 4 3 3 3 3 6% 7% 60%	3250
	21st to end	Day	5% 6% 2 3 2 2 2 2 4 6% 67%	3430
November	1st to 10th	Day	2 5% 1 4 2 3 3 2 6% 7% 65%	1853
	11th to 20th	Day	2 5% 1 3 3 2 3 3 5% 8% 64%	1890
	21st to end	Day	2 6% 2 6% 3 2 3 4 4 8% 60%	1764
December	1st to 10th	Day	1 3 2 5% 2 2 3 2 4 6% 70%	2700
	11th to 20th	Day	1 3 1 3 2 3 2 2 4 7% 70%	3106
	21st to end	Day	2 5% 3 6% 4 4 4 3 6% 8% 54%	4092
January	1st to 10th	Night	1 7% 3 7% 3 3 3 2 4 7% 60%	8201
	11th to 20th	Night	1 4 2 7% 4 3 3 3 4 6% 63%	8132
	21st to end	Night	1 5% 2 7% 4 3 3 3 4 5% 63%	8370
February	1st to 10th	Night	1 8% 2 6% 4 3 4 3 5% 8% 56%	2730
	11th to 20th	Night	1 7% 3 6% 5% 4 4 3 5% 7% 56%	2496
	21st to end	Night	2 7% 2 6% 3 3 3 2 5% 6% 61%	2076
March	1st to 10th	Night	3 10% 3 6% 3 3 3 3 4 6% 56%	5494
	11th to 20th	Night	5% 10% 2 4 3 3 3 3 4 7% 55%	5138
	21st to end	Night	7% 9% 3 4 3 3 3 3 5% 7% 53%	5266
April	1st to 10th	Night	4 7% 2 4 3 3 4 3 5% 7% 58%	2100
	11th to 20th	Night	9% 8% 2 4 3 3 4 3 5% 6% 52%	2077
	21st to end	Night	11% 7% 2 5% 4 3 3 3 5% 7% 48%	2100
May	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 5% 6% 46%	5483
	11th to 20th	Night	10% 7% 2 5% 3 3 4 3 5% 7% 49%	4701
	21st to end	Night	9% 5% 2 5% 3 3 4 3 4 6% 55%	5181
June	1st to 10th	Night	5% 3 1 4 3 3 4 4 6% 9% 59%	1680
	11th to 20th	Night	5% 3 1 3 2 3 3 3 5% 7% 65%	1680
	21st to end	Night	4 3 1 3 3 3 4 4 7% 8% 61%	1680
July	1st to 10th	Night	2 2 1 3 2 3 3 4 6% 7% 67%	4740
	11th to 20th	Night	3 2 1 3 2 3 3 4 6% 10% 62%	4740
	21st to end	Night	4 3 1 4 3 4 6% 5% 9% 11% 50%	5323
August	1st to 10th	Night	5% 3 1 4 3 3 4 4 7% 8% 58%	5273
	11th to 20th	Night	3 2 1 3 3 4 5% 4 7% 11% 57%	5814
	21st to end	Night	5% 3 2 5% 3 5% 5% 5% 8% 12% 48%	6465
September	1st to 10th	Night	6% 3 1 4 3 4 3 3 5% 6% 62%	2100
	11th to 20th	Night	7% 3 1 3 2 2 3 3 4 8% 64%	2116
	21st to end	Night	7% 3 1 4 3 3 4 3 4 5% 63%	2288
October	1st to 10th	Night	5% 3 1 2 1 2 2 2 3 4 75%	3912
	11th to 20th	Night	5% 4 1 4 3 2 2 3 4 7% 65%	3898
	21st to end	Night	5% 6% 2 3 2 2 3 2 3 5% 66%	4335
November	1st to 10th	Night	2 4 2 3 2 2 3 2 5% 7% 68%	2665
	11th to 20th	Night	2 5% 2 5% 2 2 3 2 4 6% 66%	2730
	21st to end	Night	3 7% 2 5% 2 2 3 2 5% 7% 62%	2851
December	1st to 10th	Night	1 3 2 4 2 2 2 2 4 5% 73%	4710
	11th to 20th	Night	1 4 1 4 3 2 2 2 5% 9% 67%	5321
	21st to end	Night	3 7% 2 6% 4 4 4 3 5% 7% 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% 8% 30% 23% 10%	4723
	11th to 20th	Day	21% 4 10% 26% 28% 11%	4902
	21st to end	Day	22% 5% 6% 27% 26% 13%	5844
February	1st to 10th	Day	27% 5% 11% 26% 21% 10%	1890
	11th to 20th	Day	24% 6% 9% 27% 26% 8%	2019
	21st to end	Day	24% 5% 9% 21% 28% 14%	1730
March	1st to 10th	Day	27% 4 6% 18% 30% 14%	4600
	11th to 20th	Day	30% 9% 9% 22% 26% 5%	5063
	21st to end	Day	26% 10% 11% 34% 17% 3	5934
April	1st to 10th	Day	26% 7% 11% 25% 22% 9%	2520
	11th to 20th	Day	33% 8% 10% 20% 20% 9%	2494
	21st to end	Day	33% 9% 13% 22% 20% 3	2520
May	1st to 10th	Day	34% 8% 11% 26% 17% 4	7448
	11th to 20th	Day	34% 8% 10% 20% 19% 8%	8195
	21st to end	Day	30% 9% 15% 23% 18% 6%	9027
June	1st to 10th	Day	26% 11% 15% 22% 18% 8%	2940
	11th to 20th	Day	24% 10% 11% 17% 23% 15%	2940
	21st to end	Day	25% 8% 13% 19% 23% 12%	2940
July	1st to 10th	Day	22% 7% 6% 15% 30% 21%	8181
	11th to 20th	Day	20% 7% 10% 19% 21% 22%	8175
	21st to end	Day	31% 8% 13% 20% 16% 12%	8586
August	1st to 10th	Day	30% 8% 11% 18% 18% 16%	5978
	11th to 20th	Day	26% 8% 15% 21% 20% 10%	5546
	21st to end	Day	26% 8% 16% 23% 19% 8%	6078
September	1st to 10th	Day	22% 6% 8% 21% 25% 17%	2520
	11th to 20th	Day	23% 7% 9% 20% 27% 14%	2504
	21st to end	Day	22% 5% 7% 20% 34% 12%	2288
October	1st to 10th	Day	14% 4 6% 15% 36% 25%	3274
	11th to 20th	Day	22% 4 9% 25% 31% 8%	3250
	21st to end	Day	20% 3 5% 23% 37% 12%	3430
November	1st to 10th	Day	18% 4 9% 24% 30% 14%	1853
	11th to 20th	Day	18% 5% 8% 25% 34% 10%	1890
	21st to end	Day	24% 4 10% 23% 28% 13%	1764
December	1st to 10th	Day	17% 4 7% 34% 29% 10%	2700
	11th to 20th	Day	14% 4 8% 31% 33% 11%	3104
	21st to end	Day	26% 4 10% 23% 28% 9%	4092
January	1st to 10th	Night	26% 3 6% 29% 27% 9%	8202
	11th to 20th	Night	22% 4 9% 23% 26% 16%	8132
	21st to end	Night	24% 4 9% 22% 28% 13%	8370
February	1st to 10th	Night	26% 4 10% 26% 26% 7%	2730
	11th to 20th	Night	28% 4 11% 26% 23% 9%	2496
	21st to end	Night	24% 3 6% 22% 27% 16%	2076
March	1st to 10th	Night	28% 4 7% 16% 33% 12%	5494
	11th to 20th	Night	29% 5% 10% 15% 26% 16%	5138
	21st to end	Night	30% 4 10% 33% 20% 3	5266
April	1st to 10th	Night	26% 6% 12% 23% 24% 10%	2100
	11th to 20th	Night	32% 6% 10% 22% 21% 9%	2077
	21st to end	Night	35% 6% 10% 24% 21% 5%	2100
May	1st to 10th	Night	37% 7% 12% 24% 15% 5%	5481
	11th to 20th	Night	33% 6% 12% 23% 19% 7%	4702
	21st to end	Night	29% 7% 17% 25% 18% 5%	5182
June	1st to 10th	Night	21% 7% 17% 31% 16% 9%	1680
	11th to 20th	Night	18% 6% 13% 20% 24% 20%	1680
	21st to end	Night	18% 6% 12% 23% 27% 13%	1680
July	1st to 10th	Night	16% 5% 7% 19% 40% 13%	4700
	11th to 20th	Night	17% 6% 13% 23% 23% 17%	4692
	21st to end	Night	26% 7% 18% 22% 16% 11%	5207
August	1st to 10th	Night	26% 5% 12% 22% 25% 10%	4168
	11th to 20th	Night	21% 8% 23% 23% 17% 8%	4586
	21st to end	Night	22% 7% 21% 26% 19% 5%	5069
September	1st to 10th	Night	23% 5% 9% 22% 25% 16%	2100
	11th to 20th	Night	20% 4 11% 24% 26% 16%	2116
	21st to end	Night	24% 5% 7% 20% 31% 13%	2288
October	1st to 10th	Night	15% 4 6% 19% 31% 26%	3912
	11th to 20th	Night	21% 3 8% 25% 32% 11%	3898
	21st to end	Night	22% 3 5% 21% 36% 14%	4335
November	1st to 10th	Night	17% 5% 9% 24% 30% 15%	2665
	11th to 20th	Night	19% 4 7% 26% 34% 10%	2730
	21st to end	Night	23% 4 9% 22% 30% 12%	2851
December	1st to 10th	Night	16% 3 7% 29% 37% 8%	4710
	11th to 20th	Night	17% 3 7% 29% 36% 8%	5322
	21st to end	Night	28% 4 10% 22% 26% 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	6% 13% 28% 41% 9% 2	330
	11th to 20th	Day	6% 17% 36% 34% 6% 1	330
	21st to end	Day	3 17% 39% 33% 7% 1	363
February	1st to 10th	Day	5% 26% 41% 24% 3 2	330
	11th to 20th	Day	5% 14% 44% 32% 4 1	330
	21st to end	Day	7% 19% 39% 33% 2	273
March	1st to 10th	Day	5% 14% 39% 33% 8% 1	330
	11th to 20th	Day	11% 20% 33% 28% 8% 1	519
	21st to end	Day	12% 19% 37% 24% 7% 1	594
April	1st to 10th	Day	11% 21% 31% 27% 9% 1	540
	11th to 20th	Day	13% 23% 34% 24% 5% 1	532
	21st to end	Day	15% 13% 35% 27% 9% 1	540
May	1st to 10th	Day	15% 11% 32% 31% 9% 2	668
	11th to 20th	Day	18% 7% 26% 31% 15% 3	775
	21st to end	Day	10% 7% 27% 32% 20% 4	844
June	1st to 10th	Day	6% 6% 21% 36% 24% 7%	780
	11th to 20th	Day	6% 5% 29% 38% 17% 5%	780
	21st to end	Day	6% 5% 26% 38% 19% 7%	780
July	1st to 10th	Day	8% 2 16% 37% 30% 8%	771
	11th to 20th	Day	5% 2 15% 36% 33% 10%	768
	21st to end	Day	6% 4 13% 32% 35% 10%	788
August	1st to 10th	Day	8% 3 22% 37% 23% 8%	567
	11th to 20th	Day	4 4 22% 35% 27% 7%	557
	21st to end	Day	7% 4 20% 39% 24% 7%	627
September	1st to 10th	Day	6% 3 22% 38% 25% 7%	570
	11th to 20th	Day	6% 4 25% 38% 22% 5%	554
	21st to end	Day	9% 3 25% 30% 25% 7%	354
October	1st to 10th	Day	10% 7% 24% 30% 23% 7%	330
	11th to 20th	Day	4 13% 28% 39% 13% 3	330
	21st to end	Day	6% 13% 34% 35% 11% 1	363
November	1st to 10th	Day	5% 10% 33% 32% 17% 2	330
	11th to 20th	Day	8% 14% 25% 42% 9% 2	330
	21st to end	Day	7% 12% 37% 34% 9% 1	330
December	1st to 10th	Day	7% 18% 35% 30% 9% 2	330
	11th to 20th	Day	5% 21% 38% 30% 6% 1	330
	21st to end	Day	6% 18% 35% 33% 8% 1	363
January	1st to 10th	Night	3 18% 33% 36% 9% 2	1050
	11th to 20th	Night	2 24% 38% 26% 8% 2	1010
	21st to end	Night	5% 16% 35% 36% 6% 1	924
February	1st to 10th	Night	4 19% 40% 32% 5%	840
	11th to 20th	Night	4 17% 37% 36% 6%	824
	21st to end	Night	5% 16% 40% 36% 3	692
March	1st to 10th	Night	4 14% 36% 39% 7% 1	840
	11th to 20th	Night	9% 12% 29% 39% 11% 1	840
	21st to end	Night	9% 12% 34% 40% 4 1	774
April	1st to 10th	Night	8% 11% 36% 39% 6%	630
	11th to 20th	Night	12% 9% 34% 35% 9% 1	623
	21st to end	Night	15% 6% 32% 34% 11% 1	630
May	1st to 10th	Night	13% 8% 27% 40% 12% 1	630
	11th to 20th	Night	18% 4 17% 44% 14% 3	621
	21st to end	Night	10% 4 23% 40% 20% 2	683
June	1st to 10th	Night	6% 3 17% 46% 24% 4	630
	11th to 20th	Night	6% 3 21% 50% 19% 2	630
	21st to end	Night	4 2 17% 46% 28% 3	630
July	1st to 10th	Night	7% 2 11% 38% 38% 4	615
	11th to 20th	Night	2 1 8% 42% 41% 6%	612
	21st to end	Night	7% 1 4 39% 42% 6%	690
August	1st to 10th	Night	6% 1 9% 43% 37% 4	627
	11th to 20th	Night	4 1 8% 47% 34% 5%	624
	21st to end	Night	4 1 9% 45% 33% 8%	693
September	1st to 10th	Night	6% 3 10% 45% 30% 6%	630
	11th to 20th	Night	7% 3 16% 48% 21% 6%	630
	21st to end	Night	8% 3 19% 46% 20% 5%	624
October	1st to 10th	Night	10% 5% 21% 44% 16% 4	792
	11th to 20th	Night	6% 7% 26% 45% 14% 2	800
	21st to end	Night	8% 10% 32% 38% 10% 2	927
November	1st to 10th	Night	4 11% 30% 43% 12% 1	1025
	11th to 20th	Night	5% 15% 34% 38% 6% 1	1050
	21st to end	Night	6% 10% 33% 42% 8%	1050
December	1st to 10th	Night	3 18% 32% 39% 7%	1050
	11th to 20th	Night	3 17% 38% 35% 6% 1	1050
	21st to end	Night	5% 17% 34% 35% 7% 1	1155

Page generated at 2026-09-26 02:18:44. Version ac07

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