Copper Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Copper Mountain clear sky chart from 2005-11-06 to 2025-05-11.

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	3 7% 4 11% 6% 5% 4 3 5% 6% 45%	117917
	Night	1 5% 4 10% 5% 5% 4 3 5% 7% 51%	119942
Transparency	Day	38% 6% 11% 20% 19% 7%	117668
	Night	30% 7% 13% 24% 20% 6%	119781
Seeing	Day	17% 23% 29% 19% 9% 2	16159
	Night	9% 17% 30% 30% 13% 1	26339

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	3 6% 24% 9% 7% 3 2 3 5% 39%	3638
	11th to 20th	Day	5% 4 15% 11% 12% 6% 3 4 4 37%	3962
	21st to end	Day	5% 6% 17% 5% 6% 3 3 3 5% 47%	4510
February	1st to 10th	Day	5% 6% 18% 8% 6% 4 3 4 6% 39%	1800
	11th to 20th	Day	5% 6% 16% 8% 7% 4 3 4 6% 41%	1864
	21st to end	Day	5% 6% 18% 10% 5% 4 3 3 5% 41%	1650
March	1st to 10th	Day	6% 6% 19% 6% 3 3 2 3 4 49%	4633
	11th to 20th	Day	1 8% 8% 17% 7% 5% 4 3 5% 6% 37%	5000
	21st to end	Day	12% 9% 16% 7% 5% 3 3 4 5% 35%	5700
April	1st to 10th	Day	1 10% 5% 12% 6% 5% 5% 3 5% 6% 43%	2400
	11th to 20th	Day	1 15% 8% 14% 6% 4 4 3 4 6% 35%	2371
	21st to end	Day	2 15% 7% 11% 7% 5% 5% 3 5% 6% 33%	2400
May	1st to 10th	Day	2 15% 9% 14% 7% 5% 5% 5% 6% 6% 28%	4101
	11th to 20th	Day	4 12% 3 7% 5% 5% 6% 5% 7% 9% 37%	4390
	21st to end	Day	3 9% 3 6% 4 4 5% 5% 6% 9% 46%	4825
June	1st to 10th	Day	6% 7% 2 5% 5% 5% 5% 4 7% 9% 46%	2660
	11th to 20th	Day	7% 7% 2 5% 4 4 5% 4 5% 6% 51%	2660
	21st to end	Day	5% 6% 2 6% 5% 5% 5% 5% 7% 7% 49%	2660
July	1st to 10th	Day	7% 6% 2 6% 4 3 4 3 4 5% 56%	4430
	11th to 20th	Day	6% 5% 2 7% 6% 6% 6% 6% 8% 9% 38%	4430
	21st to end	Day	9% 6% 2 7% 6% 4 5% 4 5% 6% 46%	4531
August	1st to 10th	Day	11% 8% 2 8% 6% 6% 6% 5% 7% 8% 32%	4092
	11th to 20th	Day	8% 6% 2 9% 6% 5% 6% 4 6% 7% 40%	3815
	21st to end	Day	7% 5% 2 8% 6% 6% 6% 5% 6% 7% 41%	4180
September	1st to 10th	Day	9% 7% 3 5% 5% 4 4 3 4 5% 52%	2280
	11th to 20th	Day	8% 7% 2 6% 4 4 5% 3 4 5% 52%	2280
	21st to end	Day	6% 8% 2 5% 4 4 3 3 4 5% 57%	2052
October	1st to 10th	Day	3 5% 2 4 3 3 3 2 3 5% 68%	3170
	11th to 20th	Day	3 9% 2 6% 5% 5% 5% 3 6% 8% 48%	3150
	21st to end	Day	2 9% 3 8% 3 3 3 2 4 5% 60%	3438
November	1st to 10th	Day	7% 3 7% 5% 3 2 3 5% 5% 59%	1765
	11th to 20th	Day	7% 3 8% 5% 3 2 3 3 7% 58%	1800
	21st to end	Day	1 5% 4 10% 7% 3 2 2 4 5% 56%	1630
December	1st to 10th	Day	3 3 10% 9% 6% 2 2 3 6% 56%	2620
	11th to 20th	Day	5% 5% 12% 5% 3 2 2 4 7% 56%	3026
	21st to end	Day	8% 6% 16% 7% 4 4 3 5% 7% 41%	4004
January	1st to 10th	Night	2 4 22% 10% 6% 4 2 3 5% 42%	6327
	11th to 20th	Night	2 4 14% 12% 10% 7% 2 3 4 42%	6048
	21st to end	Night	4 4 16% 8% 6% 5% 3 4 5% 46%	6468
February	1st to 10th	Night	3 4 14% 9% 8% 4 4 5% 7% 42%	2600
	11th to 20th	Night	3 5% 15% 8% 6% 4 5% 6% 7% 42%	2421
	21st to end	Night	5% 4 14% 8% 6% 4 3 5% 6% 45%	1980
March	1st to 10th	Night	4 7% 18% 6% 5% 4 3 4 6% 44%	5242
	11th to 20th	Night	5% 6% 16% 4 3 3 3 4 7% 49%	5000
	21st to end	Night	1 11% 8% 16% 6% 4 4 3 5% 5% 37%	5265
April	1st to 10th	Night	6% 3 9% 6% 4 5% 4 5% 8% 50%	2000
	11th to 20th	Night	1 10% 5% 10% 5% 4 5% 4 6% 6% 44%	1977
	21st to end	Night	2 11% 4 8% 4 3 4 3 4 7% 50%	2000
May	1st to 10th	Night	2 10% 6% 9% 4 4 4 4 7% 7% 43%	3083
	11th to 20th	Night	2 9% 2 8% 4 6% 5% 5% 9% 8% 40%	2521
	21st to end	Night	2 8% 2 5% 4 4 4 3 5% 7% 55%	2762
June	1st to 10th	Night	3 3 1 3 3 3 4 3 7% 9% 60%	1520
	11th to 20th	Night	3 4 1 3 3 3 4 3 5% 6% 65%	1520
	21st to end	Night	2 4 1 4 3 2 3 4 7% 9% 62%	1520
July	1st to 10th	Night	4 3 1 4 4 4 4 3 5% 7% 60%	2540
	11th to 20th	Night	2 3 1 3 3 4 6% 5% 8% 11% 54%	2540
	21st to end	Night	3 3 1 4 3 4 5% 5% 7% 8% 58%	3028
August	1st to 10th	Night	4 4 1 6% 5% 4 6% 5% 9% 11% 44%	2847
	11th to 20th	Night	3 3 1 4 3 4 4 5% 8% 10% 55%	3022
	21st to end	Night	3 3 1 4 4 5% 7% 6% 7% 11% 50%	3487
September	1st to 10th	Night	4 4 2 4 3 4 4 3 7% 8% 58%	1900
	11th to 20th	Night	3 4 1 4 4 3 3 3 5% 7% 62%	1900
	21st to end	Night	3 5% 1 5% 3 3 3 3 6% 7% 62%	2125
October	1st to 10th	Night	1 3 1 3 2 2 2 2 3 5% 74%	3800
	11th to 20th	Night	1 4 2 4 3 3 4 3 6% 8% 62%	3778
	21st to end	Night	2 6% 2 7% 2 2 2 2 4 6% 66%	4120
November	1st to 10th	Night	4 3 6% 4 3 4 2 4 6% 64%	2511
	11th to 20th	Night	4 4 9% 4 3 3 3 4 7% 59%	2600
	21st to end	Night	4 4 9% 5% 4 4 3 5% 7% 54%	2765
December	1st to 10th	Night	2 2 7% 5% 6% 3 3 3 5% 63%	4570
	11th to 20th	Night	3 3 10% 6% 4 4 3 5% 7% 55%	5181
	21st to end	Night	8% 5% 16% 7% 5% 5% 4 5% 7% 38%	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	42% 8% 10% 19% 16% 5%	3639
	11th to 20th	Day	48% 7% 12% 12% 17% 4	3962
	21st to end	Day	38% 6% 10% 18% 19% 9%	4510
February	1st to 10th	Day	45% 6% 15% 15% 13% 5%	1800
	11th to 20th	Day	42% 5% 11% 20% 16% 5%	1873
	21st to end	Day	44% 4 12% 17% 17% 7%	1650
March	1st to 10th	Day	38% 4 7% 18% 22% 11%	4633
	11th to 20th	Day	44% 7% 10% 24% 13% 2	5000
	21st to end	Day	49% 5% 13% 23% 9% 1	5700
April	1st to 10th	Day	41% 5% 13% 21% 15% 5%	2400
	11th to 20th	Day	49% 5% 11% 17% 15% 2	2374
	21st to end	Day	49% 6% 9% 23% 11% 1	2400
May	1st to 10th	Day	50% 8% 11% 16% 13% 1	4101
	11th to 20th	Day	36% 10% 15% 24% 14% 1	4394
	21st to end	Day	30% 8% 12% 23% 23% 4	4825
June	1st to 10th	Day	32% 8% 13% 24% 18% 5%	2660
	11th to 20th	Day	32% 5% 10% 19% 23% 12%	2660
	21st to end	Day	32% 6% 9% 19% 24% 10%	2660
July	1st to 10th	Day	30% 5% 7% 10% 23% 25%	4361
	11th to 20th	Day	38% 7% 11% 20% 17% 9%	4355
	21st to end	Day	38% 6% 9% 14% 16% 17%	4388
August	1st to 10th	Day	48% 6% 14% 13% 15% 4	4078
	11th to 20th	Day	43% 6% 11% 13% 19% 7%	3853
	21st to end	Day	40% 6% 10% 17% 21% 7%	4179
September	1st to 10th	Day	35% 5% 8% 15% 26% 11%	2280
	11th to 20th	Day	35% 5% 10% 18% 24% 8%	2280
	21st to end	Day	30% 4 8% 25% 28% 5%	2052
October	1st to 10th	Day	21% 4 5% 25% 36% 9%	3170
	11th to 20th	Day	34% 3 9% 32% 18% 4	3150
	21st to end	Day	29% 3 6% 31% 28% 3	3438
November	1st to 10th	Day	25% 7% 13% 22% 29% 4	1765
	11th to 20th	Day	25% 5% 16% 26% 21% 7%	1800
	21st to end	Day	30% 4 11% 28% 18% 9%	1630
December	1st to 10th	Day	32% 4 9% 33% 17% 5%	2620
	11th to 20th	Day	29% 5% 16% 29% 20% 1	3024
	21st to end	Day	39% 8% 9% 17% 22% 5%	4004
January	1st to 10th	Night	41% 7% 10% 20% 16% 5%	6327
	11th to 20th	Night	43% 7% 12% 16% 16% 7%	6048
	21st to end	Night	34% 9% 10% 17% 21% 10%	6468
February	1st to 10th	Night	38% 8% 14% 21% 16% 4	2600
	11th to 20th	Night	38% 7% 14% 22% 17% 3	2422
	21st to end	Night	37% 5% 13% 19% 18% 7%	1980
March	1st to 10th	Night	38% 6% 9% 17% 22% 8%	5242
	11th to 20th	Night	32% 9% 10% 21% 26% 2	5000
	21st to end	Night	45% 7% 18% 23% 6% 1	5265
April	1st to 10th	Night	30% 9% 14% 25% 18% 4	2000
	11th to 20th	Night	36% 7% 14% 25% 16% 2	1977
	21st to end	Night	33% 7% 16% 29% 14%	2000
May	1st to 10th	Night	33% 9% 15% 27% 14% 2	3083
	11th to 20th	Night	31% 11% 18% 26% 14%	2522
	21st to end	Night	22% 8% 15% 28% 23% 3	2762
June	1st to 10th	Night	18% 8% 19% 29% 20% 5%	1520
	11th to 20th	Night	20% 6% 13% 21% 26% 14%	1520
	21st to end	Night	18% 7% 14% 23% 26% 12%	1520
July	1st to 10th	Night	24% 6% 10% 18% 20% 21%	2500
	11th to 20th	Night	22% 6% 16% 33% 16% 8%	2492
	21st to end	Night	21% 8% 17% 28% 11% 15%	2933
August	1st to 10th	Night	31% 7% 24% 20% 12% 4	2838
	11th to 20th	Night	24% 7% 26% 16% 18% 9%	3050
	21st to end	Night	28% 7% 19% 19% 23% 4	3487
September	1st to 10th	Night	23% 6% 14% 21% 27% 8%	1900
	11th to 20th	Night	22% 6% 14% 24% 24% 10%	1900
	21st to end	Night	21% 6% 11% 32% 25% 4	2125
October	1st to 10th	Night	14% 4 8% 30% 36% 8%	3800
	11th to 20th	Night	20% 3 11% 43% 18% 4	3778
	21st to end	Night	21% 3 8% 31% 31% 5%	4120
November	1st to 10th	Night	22% 6% 13% 27% 26% 5%	2511
	11th to 20th	Night	25% 5% 14% 28% 22% 6%	2600
	21st to end	Night	28% 5% 12% 28% 21% 7%	2765
December	1st to 10th	Night	25% 5% 10% 36% 20% 4	4570
	11th to 20th	Night	28% 5% 12% 29% 25% 2	5182
	21st to end	Night	42% 8% 10% 17% 18% 5%	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	21% 28% 21% 21% 8% 1	300
	11th to 20th	Day	23% 27% 30% 17% 2 1	300
	21st to end	Day	16% 32% 32% 15% 5% 1	330
February	1st to 10th	Day	30% 35% 25% 8% 1 1	300
	11th to 20th	Day	29% 34% 24% 11% 2	300
	21st to end	Day	31% 31% 23% 14%	249
March	1st to 10th	Day	24% 30% 26% 16% 3	355
	11th to 20th	Day	20% 29% 33% 14% 3 1	500
	21st to end	Day	18% 40% 31% 9% 2	550
April	1st to 10th	Day	21% 37% 29% 9% 2 1	500
	11th to 20th	Day	27% 35% 26% 10% 2	492
	21st to end	Day	18% 36% 33% 9% 3 1	500
May	1st to 10th	Day	20% 32% 29% 14% 5% 1	540
	11th to 20th	Day	15% 20% 32% 22% 9% 2	676
	21st to end	Day	16% 21% 28% 23% 10% 2	734
June	1st to 10th	Day	10% 17% 28% 24% 18% 2	680
	11th to 20th	Day	12% 19% 34% 22% 11% 2	680
	21st to end	Day	8% 18% 31% 24% 17% 2	680
July	1st to 10th	Day	10% 10% 26% 28% 22% 4	671
	11th to 20th	Day	9% 9% 25% 30% 21% 6%	668
	21st to end	Day	12% 11% 28% 27% 17% 5%	582
August	1st to 10th	Day	17% 14% 30% 25% 11% 3	487
	11th to 20th	Day	11% 10% 35% 26% 14% 5%	477
	21st to end	Day	11% 12% 32% 29% 12% 4	539
September	1st to 10th	Day	14% 14% 29% 25% 12% 6%	490
	11th to 20th	Day	12% 18% 34% 23% 10% 2	490
	21st to end	Day	13% 19% 28% 22% 14% 4	329
October	1st to 10th	Day	15% 19% 26% 21% 16% 3	300
	11th to 20th	Day	16% 29% 26% 17% 10% 2	300
	21st to end	Day	21% 28% 26% 17% 6% 1	330
November	1st to 10th	Day	22% 31% 25% 15% 6% 1	300
	11th to 20th	Day	23% 28% 28% 14% 5% 2	300
	21st to end	Day	12% 31% 35% 17% 4	300
December	1st to 10th	Day	22% 27% 28% 14% 8% 1	300
	11th to 20th	Day	22% 29% 31% 13% 4	300
	21st to end	Day	25% 29% 28% 12% 6%	330
January	1st to 10th	Night	13% 25% 29% 23% 9% 2	1000
	11th to 20th	Night	15% 22% 33% 21% 7% 1	877
	21st to end	Night	8% 22% 42% 21% 6% 1	880
February	1st to 10th	Night	13% 25% 38% 18% 5%	800
	11th to 20th	Night	11% 29% 34% 22% 4	784
	21st to end	Night	12% 27% 38% 20% 2	660
March	1st to 10th	Night	10% 21% 36% 27% 6%	800
	11th to 20th	Night	6% 18% 38% 30% 8%	800
	21st to end	Night	8% 23% 41% 24% 4	785
April	1st to 10th	Night	7% 23% 41% 25% 4	600
	11th to 20th	Night	10% 23% 32% 28% 6%	593
	21st to end	Night	9% 19% 36% 28% 7% 1	600
May	1st to 10th	Night	9% 12% 40% 29% 9% 1	600
	11th to 20th	Night	8% 7% 31% 37% 15% 1	563
	21st to end	Night	7% 13% 29% 34% 16% 1	617
June	1st to 10th	Night	4 6% 27% 40% 21% 1	570
	11th to 20th	Night	5% 10% 30% 43% 11% 1	570
	21st to end	Night	3 5% 22% 42% 28% 1	570
July	1st to 10th	Night	6% 3 14% 41% 34% 2	555
	11th to 20th	Night	3 1 10% 44% 38% 4	552
	21st to end	Night	6% 2 11% 38% 41% 3	624
August	1st to 10th	Night	8% 1 12% 44% 33% 2	567
	11th to 20th	Night	5% 2 15% 45% 29% 4	564
	21st to end	Night	7% 2 14% 42% 33% 3	627
September	1st to 10th	Night	4 3 15% 49% 25% 4	570
	11th to 20th	Night	5% 4 21% 44% 23% 3	570
	21st to end	Night	6% 9% 23% 38% 21% 4	634
October	1st to 10th	Night	4 13% 31% 34% 14% 4	760
	11th to 20th	Night	8% 19% 29% 29% 13% 2	760
	21st to end	Night	9% 17% 33% 29% 10% 2	836
November	1st to 10th	Night	7% 21% 33% 29% 8% 1	951
	11th to 20th	Night	11% 26% 33% 24% 5% 2	1000
	21st to end	Night	8% 20% 35% 29% 7%	1000
December	1st to 10th	Night	9% 26% 37% 22% 6%	1000
	11th to 20th	Night	12% 27% 33% 21% 7%	1000
	21st to end	Night	15% 24% 35% 21% 4 1	1100

Page generated at 2025-05-08 07:33:57. Version ac07

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