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 2025-05-26.

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 4 4 6% 8% 54%	118003
	Night	4 5% 2 5% 3 3 3 3 5% 7% 59%	120150
Transparency	Day	25% 7% 10% 23% 24% 10%	117747
	Night	24% 5% 10% 23% 26% 11%	119996
Seeing	Day	8% 10% 28% 33% 17% 4	16300
	Night	6% 10% 27% 39% 15% 2	26417

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 5% 7% 60%	3638
	11th to 20th	Day	1 3 2 7% 5% 5% 4 3 5% 8% 57%	3760
	21st to end	Day	1 4 2 7% 3 3 3 3 5% 7% 62%	4510
February	1st to 10th	Day	2 6% 4 7% 4 4 4 4 5% 6% 56%	1800
	11th to 20th	Day	1 4 3 5% 4 4 5% 3 5% 9% 56%	1911
	21st to end	Day	2 6% 3 7% 3 3 3 4 5% 5% 59%	1650
March	1st to 10th	Day	3 10% 3 5% 3 3 4 3 4 6% 57%	4500
	11th to 20th	Day	3 8% 3 6% 4 4 4 4 6% 8% 49%	4954
	21st to end	Day	3 7% 2 5% 4 4 5% 5% 7% 9% 49%	5806
April	1st to 10th	Day	5% 6% 2 4 3 3 3 4 6% 9% 54%	2400
	11th to 20th	Day	8% 9% 2 5% 3 4 4 3 6% 8% 47%	2371
	21st to end	Day	8% 8% 2 4 4 4 5% 4 8% 8% 45%	2400
May	1st to 10th	Day	9% 7% 2 7% 4 5% 5% 5% 7% 8% 39%	4139
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 10% 40%	4528
	21st to end	Day	5% 4 1 4 4 5% 5% 6% 8% 10% 49%	4897
June	1st to 10th	Day	4 3 2 4 4 5% 5% 6% 8% 10% 49%	2660
	11th to 20th	Day	5% 3 2 4 4 4 6% 6% 8% 8% 50%	2660
	21st to end	Day	3 3 1 4 4 5% 5% 6% 9% 10% 48%	2660
July	1st to 10th	Day	5% 4 1 4 4 4 5% 4 7% 8% 55%	4430
	11th to 20th	Day	3 2 1 4 4 6% 7% 6% 10% 11% 46%	4430
	21st to end	Day	4 3 1 5% 4 4 5% 4 6% 8% 55%	4711
August	1st to 10th	Day	9% 5% 2 5% 5% 6% 7% 6% 9% 10% 38%	4092
	11th to 20th	Day	3 3 1 4 4 5% 6% 5% 9% 10% 50%	3739
	21st to end	Day	3 4 2 4 4 4 5% 6% 8% 10% 50%	4180
September	1st to 10th	Day	4 4 1 4 4 4 4 4 5% 7% 60%	2280
	11th to 20th	Day	5% 4 1 4 3 3 4 3 5% 7% 60%	2266
	21st to end	Day	6% 4 2 4 2 3 3 3 4 5% 65%	2090
October	1st to 10th	Day	3 3 1 2 2 1 2 2 4 5% 75%	3174
	11th to 20th	Day	5% 4 2 4 3 3 4 3 6% 7% 60%	3150
	21st to end	Day	5% 6% 2 3 2 2 2 2 4 6% 67%	3324
November	1st to 10th	Day	2 5% 1 4 2 3 3 2 6% 7% 64%	1763
	11th to 20th	Day	2 5% 1 3 3 2 3 3 5% 8% 64%	1800
	21st to end	Day	2 6% 2 6% 2 3 3 4 4 8% 60%	1680
December	1st to 10th	Day	1 3 2 5% 2 2 3 2 4 6% 70%	2620
	11th to 20th	Day	1 4 2 3 2 3 2 2 4 7% 70%	3026
	21st to end	Day	2 5% 3 6% 5% 4 4 3 6% 8% 54%	4004
January	1st to 10th	Night	1 7% 4 7% 4 3 3 2 4 7% 57%	6327
	11th to 20th	Night	1 3 2 6% 4 4 4 3 5% 7% 62%	6250
	21st to end	Night	2 7% 2 7% 4 3 3 2 4 5% 60%	6468
February	1st to 10th	Night	1 8% 2 6% 4 3 4 3 4 8% 56%	2600
	11th to 20th	Night	1 7% 3 6% 5% 4 4 3 5% 7% 55%	2374
	21st to end	Night	2 7% 3 6% 3 3 3 2 5% 5% 60%	1980
March	1st to 10th	Night	3 10% 3 6% 3 3 3 3 4 6% 56%	5374
	11th to 20th	Night	5% 10% 2 4 3 3 3 3 4 7% 55%	5027
	21st to end	Night	7% 9% 3 4 3 2 3 3 5% 7% 53%	5152
April	1st to 10th	Night	4 7% 2 4 3 3 3 4 5% 7% 57%	2000
	11th to 20th	Night	10% 7% 2 4 3 4 4 2 5% 6% 52%	1977
	21st to end	Night	11% 8% 3 5% 4 3 3 3 5% 7% 49%	2000
May	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 7% 7% 46%	3047
	11th to 20th	Night	10% 6% 2 5% 3 4 4 3 6% 9% 48%	2597
	21st to end	Night	7% 4 1 4 3 3 4 3 4 7% 59%	2806
June	1st to 10th	Night	5% 3 1 3 3 3 4 4 6% 9% 59%	1520
	11th to 20th	Night	5% 3 1 3 2 3 3 3 6% 7% 64%	1520
	21st to end	Night	4 2 1 3 3 3 4 4 7% 9% 60%	1520
July	1st to 10th	Night	4 2 1 3 2 4 4 4 5% 8% 62%	2540
	11th to 20th	Night	2 2 1 4 3 4 4 5% 7% 11% 58%	2540
	21st to end	Night	3 2 1 4 3 3 4 4 7% 9% 59%	2848
August	1st to 10th	Night	7% 4 2 5% 3 4 5% 5% 8% 10% 46%	2847
	11th to 20th	Night	3 2 1 2 3 4 5% 5% 8% 12% 57%	3100
	21st to end	Night	2 2 1 4 3 4 5% 5% 8% 10% 55%	3487
September	1st to 10th	Night	7% 3 1 4 3 4 4 3 5% 6% 61%	1900
	11th to 20th	Night	7% 3 1 3 2 2 3 2 4 8% 66%	1914
	21st to end	Night	6% 3 1 4 3 3 4 2 4 5% 65%	2090
October	1st to 10th	Night	4 3 1 2 1 2 2 2 3 4 76%	3792
	11th to 20th	Night	5% 4 1 4 3 3 2 3 4 7% 65%	3778
	21st to end	Night	5% 6% 2 3 2 2 3 2 3 6% 66%	4200
November	1st to 10th	Night	3 5% 2 3 2 2 3 3 5% 7% 66%	2535
	11th to 20th	Night	2 5% 2 5% 2 2 3 2 4 5% 67%	2600
	21st to end	Night	3 7% 2 5% 2 2 3 3 5% 6% 62%	2715
December	1st to 10th	Night	1 3 2 4 2 2 2 2 4 5% 74%	4570
	11th to 20th	Night	1 4 2 4 3 3 3 2 5% 9% 66%	5181
	21st to end	Night	3 8% 3 6% 4 4 4 3 5% 7% 53%	6974

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	23% 5% 10% 32% 21% 10%	3639
	11th to 20th	Day	25% 5% 11% 22% 26% 11%	3760
	21st to end	Day	23% 6% 8% 27% 24% 13%	4510
February	1st to 10th	Day	28% 5% 11% 26% 20% 10%	1800
	11th to 20th	Day	24% 6% 9% 27% 26% 7%	1921
	21st to end	Day	25% 5% 9% 20% 27% 13%	1650
March	1st to 10th	Day	27% 4 6% 19% 29% 14%	4500
	11th to 20th	Day	30% 9% 9% 22% 26% 5%	4954
	21st to end	Day	26% 10% 11% 34% 17% 3	5806
April	1st to 10th	Day	26% 7% 12% 25% 22% 9%	2400
	11th to 20th	Day	34% 8% 11% 20% 19% 8%	2374
	21st to end	Day	32% 9% 13% 23% 20% 2	2400
May	1st to 10th	Day	35% 11% 12% 22% 14% 6%	4139
	11th to 20th	Day	33% 11% 15% 23% 15% 2	4532
	21st to end	Day	24% 10% 14% 24% 20% 6%	4897
June	1st to 10th	Day	26% 12% 15% 23% 17% 8%	2660
	11th to 20th	Day	25% 11% 12% 17% 22% 14%	2660
	21st to end	Day	26% 8% 13% 19% 23% 11%	2660
July	1st to 10th	Day	24% 7% 8% 15% 30% 16%	4361
	11th to 20th	Day	25% 9% 11% 21% 22% 12%	4355
	21st to end	Day	26% 8% 10% 18% 21% 18%	4562
August	1st to 10th	Day	36% 10% 14% 19% 15% 6%	4078
	11th to 20th	Day	26% 8% 14% 16% 21% 14%	3775
	21st to end	Day	26% 7% 11% 19% 25% 12%	4179
September	1st to 10th	Day	23% 6% 8% 20% 25% 18%	2280
	11th to 20th	Day	22% 7% 9% 19% 28% 15%	2266
	21st to end	Day	21% 5% 7% 19% 36% 12%	2090
October	1st to 10th	Day	14% 4 6% 15% 36% 26%	3174
	11th to 20th	Day	22% 4 9% 26% 30% 8%	3150
	21st to end	Day	20% 3 5% 23% 36% 13%	3324
November	1st to 10th	Day	19% 4 10% 24% 29% 14%	1763
	11th to 20th	Day	18% 5% 9% 25% 33% 10%	1800
	21st to end	Day	23% 4 9% 22% 29% 13%	1680
December	1st to 10th	Day	16% 4 7% 34% 29% 10%	2620
	11th to 20th	Day	15% 4 8% 31% 33% 10%	3024
	21st to end	Day	26% 4 10% 23% 27% 9%	4004
January	1st to 10th	Night	27% 4 8% 28% 26% 9%	6327
	11th to 20th	Night	21% 5% 10% 24% 23% 17%	6250
	21st to end	Night	26% 5% 9% 22% 25% 13%	6468
February	1st to 10th	Night	27% 4 11% 26% 24% 8%	2600
	11th to 20th	Night	29% 4 10% 26% 23% 8%	2374
	21st to end	Night	25% 3 7% 22% 27% 15%	1980
March	1st to 10th	Night	28% 4 7% 16% 33% 12%	5374
	11th to 20th	Night	29% 5% 10% 15% 26% 15%	5027
	21st to end	Night	30% 4 11% 33% 20% 3	5152
April	1st to 10th	Night	26% 6% 11% 23% 24% 10%	2000
	11th to 20th	Night	33% 6% 11% 22% 21% 8%	1977
	21st to end	Night	35% 6% 10% 24% 21% 4	2000
May	1st to 10th	Night	32% 10% 13% 22% 15% 10%	3047
	11th to 20th	Night	31% 10% 16% 22% 19% 2	2598
	21st to end	Night	22% 8% 19% 23% 20% 7%	2806
June	1st to 10th	Night	20% 7% 18% 31% 15% 9%	1520
	11th to 20th	Night	19% 6% 14% 19% 23% 19%	1520
	21st to end	Night	18% 7% 13% 23% 27% 12%	1520
July	1st to 10th	Night	20% 7% 11% 19% 31% 13%	2500
	11th to 20th	Night	19% 8% 15% 26% 22% 10%	2492
	21st to end	Night	19% 7% 13% 25% 20% 16%	2759
August	1st to 10th	Night	32% 7% 16% 22% 18% 5%	2838
	11th to 20th	Night	19% 7% 21% 20% 22% 11%	3130
	21st to end	Night	23% 7% 13% 22% 28% 7%	3487
September	1st to 10th	Night	23% 5% 9% 22% 23% 18%	1900
	11th to 20th	Night	18% 4 11% 23% 27% 17%	1914
	21st to end	Night	22% 5% 7% 20% 32% 14%	2090
October	1st to 10th	Night	14% 4 6% 19% 30% 26%	3792
	11th to 20th	Night	21% 3 8% 25% 32% 10%	3778
	21st to end	Night	22% 3 5% 21% 35% 14%	4200
November	1st to 10th	Night	18% 5% 9% 24% 29% 15%	2535
	11th to 20th	Night	20% 4 8% 25% 34% 10%	2600
	21st to end	Night	23% 4 9% 22% 31% 12%	2715
December	1st to 10th	Night	15% 3 7% 28% 37% 8%	4570
	11th to 20th	Night	17% 4 7% 29% 36% 7%	5182
	21st to end	Night	28% 4 10% 22% 25% 11%	6974

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	5% 12% 28% 42% 10% 3	300
	11th to 20th	Day	6% 15% 36% 36% 6% 1	300
	21st to end	Day	3 15% 38% 34% 8% 2	330
February	1st to 10th	Day	5% 26% 41% 24% 2 2	300
	11th to 20th	Day	5% 15% 46% 29% 5% 1	300
	21st to end	Day	7% 16% 41% 34% 2	249
March	1st to 10th	Day	4 14% 40% 32% 9% 1	300
	11th to 20th	Day	12% 18% 31% 29% 8% 1	480
	21st to end	Day	13% 20% 36% 24% 7% 1	550
April	1st to 10th	Day	11% 21% 32% 26% 9% 1	500
	11th to 20th	Day	13% 24% 33% 24% 5% 1	492
	21st to end	Day	15% 13% 34% 26% 10% 1	500
May	1st to 10th	Day	15% 11% 31% 31% 9% 2	622
	11th to 20th	Day	18% 7% 26% 30% 16% 3	725
	21st to end	Day	11% 7% 28% 31% 19% 4	760
June	1st to 10th	Day	6% 6% 21% 34% 26% 7%	680
	11th to 20th	Day	6% 5% 29% 38% 18% 5%	680
	21st to end	Day	6% 5% 26% 37% 20% 7%	680
July	1st to 10th	Day	8% 2 15% 37% 29% 9%	671
	11th to 20th	Day	5% 2 16% 36% 32% 9%	668
	21st to end	Day	6% 4 13% 33% 34% 10%	684
August	1st to 10th	Day	9% 3 22% 33% 25% 8%	487
	11th to 20th	Day	4 4 25% 37% 24% 6%	477
	21st to end	Day	6% 4 21% 39% 23% 6%	539
September	1st to 10th	Day	6% 3 21% 37% 25% 7%	490
	11th to 20th	Day	6% 4 25% 36% 24% 5%	476
	21st to end	Day	8% 3 28% 29% 24% 7%	300
October	1st to 10th	Day	10% 6% 23% 30% 23% 7%	300
	11th to 20th	Day	4 11% 28% 39% 15% 3	300
	21st to end	Day	6% 14% 33% 34% 11% 2	330
November	1st to 10th	Day	6% 9% 34% 32% 18% 2	300
	11th to 20th	Day	9% 15% 24% 42% 9% 2	300
	21st to end	Day	8% 12% 35% 34% 9% 1	300
December	1st to 10th	Day	7% 15% 34% 31% 10% 2	300
	11th to 20th	Day	5% 18% 39% 32% 5%	300
	21st to end	Day	6% 18% 35% 31% 8% 1	330
January	1st to 10th	Night	3 19% 32% 36% 9% 2	1000
	11th to 20th	Night	2 24% 37% 27% 9% 2	962
	21st to end	Night	5% 16% 34% 37% 7% 1	880
February	1st to 10th	Night	4 20% 39% 32% 5% 1	800
	11th to 20th	Night	4 17% 36% 36% 6%	784
	21st to end	Night	5% 16% 39% 37% 3	660
March	1st to 10th	Night	4 14% 35% 39% 7% 1	800
	11th to 20th	Night	9% 11% 28% 40% 11% 1	800
	21st to end	Night	9% 12% 34% 39% 4 1	737
April	1st to 10th	Night	8% 12% 37% 38% 6%	600
	11th to 20th	Night	12% 10% 33% 35% 9% 1	593
	21st to end	Night	16% 6% 32% 34% 12% 1	600
May	1st to 10th	Night	13% 8% 27% 40% 12% 1	600
	11th to 20th	Night	18% 4 18% 43% 14% 3	591
	21st to end	Night	10% 4 23% 39% 21% 2	634
June	1st to 10th	Night	6% 2 16% 46% 25% 5%	570
	11th to 20th	Night	6% 3 20% 49% 19% 2	570
	21st to end	Night	4 2 16% 45% 30% 3	570
July	1st to 10th	Night	7% 2 10% 35% 41% 5%	555
	11th to 20th	Night	2 1 9% 41% 41% 6%	552
	21st to end	Night	7% 1 5% 37% 43% 7%	624
August	1st to 10th	Night	6% 2 8% 41% 40% 4	567
	11th to 20th	Night	5% 1 9% 47% 33% 5%	564
	21st to end	Night	4 1 9% 44% 33% 9%	627
September	1st to 10th	Night	6% 3 10% 43% 31% 7%	570
	11th to 20th	Night	7% 3 15% 46% 22% 6%	570
	21st to end	Night	7% 3 20% 45% 20% 5%	570
October	1st to 10th	Night	10% 5% 21% 44% 16% 4	752
	11th to 20th	Night	5% 7% 25% 46% 15% 2	760
	21st to end	Night	9% 10% 31% 37% 11% 2	880
November	1st to 10th	Night	4 10% 29% 43% 12% 1	975
	11th to 20th	Night	6% 16% 33% 39% 6% 1	1000
	21st to end	Night	6% 11% 33% 42% 9%	1000
December	1st to 10th	Night	3 18% 31% 40% 8%	1000
	11th to 20th	Night	3 16% 38% 36% 6% 1	1000
	21st to end	Night	5% 18% 33% 35% 7% 1	1100

Page generated at 2025-05-23 07:21:00. Version ac07

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