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 2026-09-14.

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 8% 4 10% 6% 5% 5% 4 5% 6% 44%	157890
	Night	1 5% 3 9% 5% 4 4 3 5% 7% 52%	150812
Transparency	Day	39% 5% 10% 20% 19% 7%	152816
	Night	30% 6% 14% 25% 20% 6%	146895
Seeing	Day	18% 23% 29% 19% 9% 2	18106
	Night	9% 17% 31% 30% 12% 1	28065

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 5% 8% 21% 9% 6% 3 2 3 4 39%	4720
	11th to 20th	Day	4 4 13% 9% 9% 5% 2 3 5% 45%	5160
	21st to end	Day	4 7% 18% 4 6% 3 2 3 4 47%	5844
February	1st to 10th	Day	5% 6% 18% 7% 6% 4 3 4 6% 40%	1890
	11th to 20th	Day	5% 6% 17% 8% 8% 4 2 4 6% 41%	1960
	21st to end	Day	5% 6% 17% 9% 5% 4 3 3 5% 43%	1730
March	1st to 10th	Day	6% 6% 18% 6% 3 3 2 3 4 49%	4736
	11th to 20th	Day	1 7% 8% 16% 7% 5% 4 3 5% 6% 38%	5110
	21st to end	Day	12% 9% 16% 7% 5% 3 3 4 5% 35%	5826
April	1st to 10th	Day	1 10% 5% 11% 6% 5% 4 3 5% 6% 43%	2520
	11th to 20th	Day	1 15% 8% 14% 6% 4 4 2 4 7% 36%	2491
	21st to end	Day	2 16% 8% 11% 7% 5% 5% 3 5% 6% 33%	2520
May	1st to 10th	Day	2 16% 8% 11% 5% 5% 5% 4 5% 6% 33%	7376
	11th to 20th	Day	3 15% 4 7% 5% 5% 6% 4 6% 7% 38%	8191
	21st to end	Day	3 9% 3 6% 5% 6% 6% 5% 7% 8% 41%	9026
June	1st to 10th	Day	6% 7% 2 5% 5% 5% 5% 4 7% 9% 45%	2940
	11th to 20th	Day	6% 6% 2 5% 4 4 5% 4 5% 6% 53%	2940
	21st to end	Day	5% 6% 1 6% 5% 4 5% 5% 7% 7% 50%	2940
July	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 6% 6% 52%	8249
	11th to 20th	Day	6% 4 2 7% 6% 6% 6% 6% 7% 8% 41%	8250
	21st to end	Day	10% 6% 2 8% 6% 6% 6% 4 6% 7% 37%	8463
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	7549
	11th to 20th	Day	9% 6% 2 8% 6% 6% 6% 4 6% 7% 38%	7170
	21st to end	Day	9% 6% 2 9% 7% 7% 6% 5% 7% 8% 34%	7751
September	1st to 10th	Day	8% 7% 3 5% 5% 4 4 3 4 6% 51%	2520
	11th to 20th	Day	8% 7% 2 6% 5% 4 5% 3 5% 5% 50%	2437
	21st to end	Day	6% 8% 2 5% 4 4 3 3 4 5% 56%	2159
October	1st to 10th	Day	3 5% 2 4 3 3 3 2 3 4 68%	3270
	11th to 20th	Day	3 9% 2 6% 5% 5% 5% 3 6% 8% 48%	3250
	21st to end	Day	2 9% 3 8% 3 3 3 2 4 5% 60%	3548
November	1st to 10th	Day	7% 3 7% 4 3 3 3 5% 5% 60%	1855
	11th to 20th	Day	7% 3 7% 5% 3 3 3 3 8% 57%	1890
	21st to end	Day	1 6% 4 11% 6% 3 2 2 4 5% 55%	1711
December	1st to 10th	Day	3 3 11% 9% 6% 2 2 2 6% 55%	2700
	11th to 20th	Day	4 5% 12% 5% 3 2 2 4 7% 56%	3106
	21st to end	Day	8% 6% 16% 7% 4 3 3 5% 7% 42%	4092
January	1st to 10th	Night	4 4 20% 8% 5% 3 2 3 6% 43%	8201
	11th to 20th	Night	2 5% 14% 10% 8% 5% 2 3 4 48%	7874
	21st to end	Night	3 5% 17% 7% 5% 5% 3 4 5% 47%	8370
February	1st to 10th	Night	3 4 14% 9% 8% 4 4 5% 7% 44%	2730
	11th to 20th	Night	4 4 15% 8% 6% 4 4 6% 8% 41%	2545
	21st to end	Night	5% 4 14% 8% 6% 4 3 4 6% 45%	2076
March	1st to 10th	Night	4 6% 17% 6% 5% 4 3 4 6% 44%	5359
	11th to 20th	Night	6% 6% 16% 4 3 2 3 4 7% 50%	5110
	21st to end	Night	1 11% 8% 16% 6% 4 4 3 5% 5% 38%	5381
April	1st to 10th	Night	6% 3 9% 6% 4 5% 4 5% 8% 50%	2100
	11th to 20th	Night	1 10% 5% 10% 5% 4 5% 3 6% 6% 45%	2077
	21st to end	Night	2 11% 4 8% 4 3 4 3 4 7% 49%	2100
May	1st to 10th	Night	1 13% 5% 7% 4 4 4 4 6% 7% 44%	5552
	11th to 20th	Night	2 10% 4 6% 3 4 4 5% 7% 7% 48%	4701
	21st to end	Night	2 7% 2 5% 4 4 4 3 5% 8% 56%	5181
June	1st to 10th	Night	3 4 1 3 3 3 4 3 7% 9% 60%	1680
	11th to 20th	Night	3 4 1 3 3 3 3 3 5% 5% 67%	1680
	21st to end	Night	2 4 1 4 3 3 3 4 6% 8% 63%	1680
July	1st to 10th	Night	3 2 1 3 3 4 4 4 6% 7% 63%	4740
	11th to 20th	Night	1 2 1 3 3 3 5% 5% 8% 11% 59%	4740
	21st to end	Night	3 3 1 5% 3 4 5% 6% 9% 12% 49%	5642
August	1st to 10th	Night	3 3 1 4 3 3 4 4 7% 9% 58%	5273
	11th to 20th	Night	3 3 1 4 3 4 4 4 8% 10% 56%	5684
	21st to end	Night	5% 4 1 4 4 5% 7% 6% 9% 13% 41%	6465
September	1st to 10th	Night	4 4 2 4 3 4 4 3 6% 8% 58%	2100
	11th to 20th	Night	3 4 1 4 4 3 3 3 5% 8% 62%	2030
	21st to end	Night	3 5% 1 5% 3 3 3 3 6% 7% 62%	2238
October	1st to 10th	Night	1 3 1 3 2 2 2 2 3 5% 74%	3920
	11th to 20th	Night	1 4 2 4 3 3 4 3 6% 8% 62%	3898
	21st to end	Night	1 6% 2 7% 2 2 2 2 4 6% 66%	4252
November	1st to 10th	Night	5% 3 6% 4 3 3 2 4 6% 65%	2640
	11th to 20th	Night	4 4 9% 4 3 3 3 4 7% 59%	2730
	21st to end	Night	4 4 9% 5% 4 4 3 5% 7% 54%	2904
December	1st to 10th	Night	2 2 8% 5% 6% 3 3 3 5% 62%	4710
	11th to 20th	Night	3 3 10% 5% 4 4 3 5% 7% 55%	5321
	21st to end	Night	8% 5% 16% 7% 5% 5% 4 5% 7% 39%	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	45% 6% 8% 23% 13% 4	4723
	11th to 20th	Day	42% 5% 13% 18% 16% 6%	5160
	21st to end	Day	40% 5% 8% 19% 20% 9%	5844
February	1st to 10th	Day	44% 6% 14% 17% 14% 5%	1890
	11th to 20th	Day	43% 5% 11% 20% 16% 5%	1969
	21st to end	Day	43% 4 11% 18% 18% 7%	1730
March	1st to 10th	Day	38% 4 7% 18% 22% 11%	4736
	11th to 20th	Day	44% 7% 10% 24% 14% 2	5110
	21st to end	Day	48% 5% 13% 24% 9% 1	5826
April	1st to 10th	Day	41% 5% 12% 21% 16% 5%	2520
	11th to 20th	Day	48% 5% 11% 17% 16% 3	2494
	21st to end	Day	50% 6% 9% 23% 11% 2	2520
May	1st to 10th	Day	48% 5% 9% 20% 16% 2	7376
	11th to 20th	Day	41% 6% 9% 22% 19% 2	8195
	21st to end	Day	37% 5% 12% 23% 20% 3	9027
June	1st to 10th	Day	33% 7% 12% 23% 19% 5%	2940
	11th to 20th	Day	30% 5% 9% 18% 25% 13%	2940
	21st to end	Day	31% 6% 9% 18% 25% 12%	2940
July	1st to 10th	Day	31% 5% 5% 10% 26% 25%	8181
	11th to 20th	Day	38% 5% 10% 20% 17% 10%	8175
	21st to end	Day	45% 5% 15% 12% 14% 9%	8276
August	1st to 10th	Day	39% 5% 11% 14% 19% 13%	5978
	11th to 20th	Day	46% 7% 15% 14% 14% 5%	5652
	21st to end	Day	44% 4 16% 17% 15% 5%	6078
September	1st to 10th	Day	35% 5% 8% 17% 25% 10%	2520
	11th to 20th	Day	36% 4 10% 18% 23% 8%	2437
	21st to end	Day	31% 4 8% 24% 27% 6%	2159
October	1st to 10th	Day	22% 4 5% 25% 36% 9%	3270
	11th to 20th	Day	34% 3 9% 31% 19% 5%	3250
	21st to end	Day	28% 3 6% 31% 28% 4	3548
November	1st to 10th	Day	25% 6% 13% 23% 30% 4	1855
	11th to 20th	Day	25% 5% 16% 28% 20% 6%	1890
	21st to end	Day	32% 4 10% 28% 18% 8%	1711
December	1st to 10th	Day	33% 4 9% 33% 17% 5%	2700
	11th to 20th	Day	29% 4 15% 30% 20% 1	3104
	21st to end	Day	38% 8% 10% 17% 23% 5%	4092
January	1st to 10th	Night	41% 6% 9% 26% 14% 4	8202
	11th to 20th	Night	39% 5% 12% 21% 17% 7%	7874
	21st to end	Night	35% 7% 9% 17% 22% 10%	8370
February	1st to 10th	Night	37% 7% 14% 22% 17% 4	2730
	11th to 20th	Night	38% 6% 14% 22% 17% 3	2546
	21st to end	Night	37% 5% 12% 19% 20% 7%	2076
March	1st to 10th	Night	38% 6% 9% 17% 23% 8%	5359
	11th to 20th	Night	32% 8% 10% 21% 26% 2	5110
	21st to end	Night	44% 7% 18% 24% 7% 1	5381
April	1st to 10th	Night	31% 8% 14% 25% 19% 4	2100
	11th to 20th	Night	36% 6% 14% 25% 17% 2	2077
	21st to end	Night	33% 7% 15% 29% 15% 1	2100
May	1st to 10th	Night	36% 6% 13% 31% 14% 1	5550
	11th to 20th	Night	31% 6% 14% 32% 17%	4702
	21st to end	Night	25% 5% 16% 30% 22% 1	5182
June	1st to 10th	Night	19% 8% 17% 30% 21% 5%	1680
	11th to 20th	Night	19% 5% 12% 22% 28% 14%	1680
	21st to end	Night	18% 7% 13% 22% 27% 14%	1680
July	1st to 10th	Night	20% 4 7% 15% 33% 21%	4700
	11th to 20th	Night	19% 4 17% 34% 20% 6%	4692
	21st to end	Night	25% 8% 26% 22% 11% 8%	5517
August	1st to 10th	Night	25% 5% 19% 20% 22% 9%	4168
	11th to 20th	Night	25% 8% 29% 19% 13% 6%	4478
	21st to end	Night	30% 7% 29% 15% 16% 3	5069
September	1st to 10th	Night	23% 6% 14% 23% 26% 8%	2100
	11th to 20th	Night	22% 6% 14% 25% 24% 9%	2030
	21st to end	Night	22% 6% 11% 32% 25% 5%	2238
October	1st to 10th	Night	14% 4 8% 30% 35% 8%	3920
	11th to 20th	Night	20% 3 11% 42% 19% 4	3898
	21st to end	Night	21% 3 8% 31% 31% 5%	4252
November	1st to 10th	Night	22% 6% 13% 27% 27% 5%	2640
	11th to 20th	Night	24% 5% 14% 29% 21% 6%	2730
	21st to end	Night	29% 4 12% 28% 20% 7%	2904
December	1st to 10th	Night	26% 5% 10% 35% 20% 4	4710
	11th to 20th	Night	27% 5% 12% 29% 24% 2	5322
	21st to end	Night	41% 8% 10% 18% 18% 5%	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	24% 28% 21% 19% 7% 1	330
	11th to 20th	Day	25% 27% 28% 16% 2 1	330
	21st to end	Day	20% 31% 31% 13% 4 1	363
February	1st to 10th	Day	31% 34% 24% 8% 2 1	330
	11th to 20th	Day	30% 35% 23% 10% 2	330
	21st to end	Day	33% 31% 23% 13%	273
March	1st to 10th	Day	24% 30% 27% 15% 3	388
	11th to 20th	Day	23% 29% 31% 13% 3 1	540
	21st to end	Day	18% 40% 31% 9% 2	594
April	1st to 10th	Day	21% 36% 31% 9% 2 1	540
	11th to 20th	Day	28% 34% 26% 9% 2	532
	21st to end	Day	19% 36% 32% 9% 3 1	540
May	1st to 10th	Day	20% 32% 30% 13% 4 1	582
	11th to 20th	Day	17% 20% 33% 21% 8% 2	775
	21st to end	Day	16% 20% 30% 23% 9% 2	844
June	1st to 10th	Day	12% 17% 30% 23% 17% 2	780
	11th to 20th	Day	12% 21% 34% 21% 10% 2	780
	21st to end	Day	11% 19% 31% 22% 15% 2	780
July	1st to 10th	Day	10% 9% 28% 29% 20% 3	771
	11th to 20th	Day	9% 8% 26% 30% 21% 5%	768
	21st to end	Day	13% 11% 27% 28% 17% 4	676
August	1st to 10th	Day	16% 15% 33% 23% 10% 3	567
	11th to 20th	Day	12% 9% 34% 27% 14% 5%	557
	21st to end	Day	12% 12% 33% 28% 12% 4	627
September	1st to 10th	Day	15% 14% 31% 24% 12% 5%	570
	11th to 20th	Day	13% 19% 35% 22% 9% 2	543
	21st to end	Day	13% 19% 29% 21% 13% 4	360
October	1st to 10th	Day	16% 19% 27% 20% 15% 3	330
	11th to 20th	Day	20% 29% 25% 16% 9% 2	330
	21st to end	Day	21% 28% 27% 17% 6% 1	363
November	1st to 10th	Day	22% 32% 25% 14% 6% 1	330
	11th to 20th	Day	22% 29% 29% 13% 5% 2	330
	21st to end	Day	14% 30% 35% 16% 4	330
December	1st to 10th	Day	27% 26% 26% 13% 7% 1	330
	11th to 20th	Day	24% 29% 29% 12% 5%	330
	21st to end	Day	28% 28% 28% 10% 5%	363
January	1st to 10th	Night	14% 25% 29% 22% 9% 2	1050
	11th to 20th	Night	15% 23% 33% 21% 7% 1	921
	21st to end	Night	9% 22% 42% 20% 6% 1	924
February	1st to 10th	Night	13% 25% 39% 18% 5%	840
	11th to 20th	Night	12% 29% 34% 21% 4	824
	21st to end	Night	13% 28% 37% 20% 2	692
March	1st to 10th	Night	10% 21% 37% 26% 5%	840
	11th to 20th	Night	9% 19% 36% 28% 7%	840
	21st to end	Night	8% 23% 42% 23% 3	824
April	1st to 10th	Night	8% 23% 41% 25% 3	630
	11th to 20th	Night	10% 23% 33% 27% 6%	623
	21st to end	Night	9% 19% 37% 27% 7% 1	630
May	1st to 10th	Night	10% 12% 40% 29% 9%	630
	11th to 20th	Night	9% 8% 33% 35% 14% 1	621
	21st to end	Night	7% 13% 31% 33% 14% 1	683
June	1st to 10th	Night	5% 6% 28% 40% 20% 1	630
	11th to 20th	Night	6% 10% 31% 42% 10% 1	630
	21st to end	Night	4 6% 24% 40% 25% 1	630
July	1st to 10th	Night	5% 3 17% 41% 31% 2	615
	11th to 20th	Night	3 1 12% 45% 35% 4	612
	21st to end	Night	6% 2 12% 39% 38% 3	690
August	1st to 10th	Night	8% 1 15% 44% 30% 2	627
	11th to 20th	Night	4 3 16% 46% 28% 3	624
	21st to end	Night	7% 2 16% 43% 30% 3	693
September	1st to 10th	Night	4 3 19% 48% 23% 3	630
	11th to 20th	Night	5% 4 23% 44% 22% 3	609
	21st to end	Night	6% 9% 23% 38% 21% 4	668
October	1st to 10th	Night	5% 13% 33% 33% 14% 4	800
	11th to 20th	Night	9% 20% 29% 28% 13% 2	800
	21st to end	Night	9% 18% 33% 29% 9% 2	880
November	1st to 10th	Night	8% 22% 34% 28% 8% 1	1000
	11th to 20th	Night	11% 26% 33% 24% 5% 2	1050
	21st to end	Night	9% 20% 35% 29% 7%	1050
December	1st to 10th	Night	11% 26% 36% 22% 5%	1050
	11th to 20th	Night	13% 27% 32% 21% 6%	1050
	21st to end	Night	16% 24% 35% 20% 4 1	1155

Page generated at 2026-09-11 02:11:56. Version ac07

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