Wind River Special Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wind River Special Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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	3 4 2 5% 3 4 4 4 6% 8% 57%	117923
	Night	3 4 2 5% 3 3 3 3 6% 8% 60%	119636
Transparency	Day	21% 8% 14% 27% 22% 8%	117676
	Night	20% 7% 15% 29% 22% 7%	119473
Seeing	Day	8% 14% 30% 31% 14% 3	16303
	Night	5% 11% 37% 33% 12% 1	26550

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 2 7% 4 4 5% 4 6% 12% 52%	3638
	11th to 20th	Day	2 2 6% 6% 5% 4 4 7% 10% 54%	3990
	21st to end	Day	1 1 4 3 3 3 3 6% 8% 67%	4510
February	1st to 10th	Day	1 3 2 7% 5% 3 4 4 6% 10% 56%	1800
	11th to 20th	Day	4 2 6% 5% 3 5% 5% 6% 9% 55%	1755
	21st to end	Day	3 2 6% 3 3 5% 4 7% 8% 59%	1535
March	1st to 10th	Day	2 7% 3 5% 3 3 4 4 7% 9% 54%	4954
	11th to 20th	Day	1 7% 3 6% 4 3 4 2 5% 8% 57%	5000
	21st to end	Day	3 7% 2 6% 4 4 5% 5% 7% 12% 44%	5486
April	1st to 10th	Day	2 8% 2 6% 3 3 4 4 7% 11% 51%	2372
	11th to 20th	Day	3 7% 3 7% 4 4 5% 4 6% 10% 47%	2400
	21st to end	Day	7% 10% 3 6% 5% 4 5% 5% 7% 8% 40%	2537
May	1st to 10th	Day	7% 10% 3 7% 5% 5% 5% 4 7% 8% 39%	4110
	11th to 20th	Day	6% 6% 2 5% 3 3 4 4 6% 8% 54%	4374
	21st to end	Day	7% 5% 2 4 4 4 5% 5% 7% 10% 46%	4825
June	1st to 10th	Day	4 3 1 4 4 4 5% 6% 8% 12% 49%	2660
	11th to 20th	Day	5% 2 1 4 3 3 4 4 7% 9% 57%	2660
	21st to end	Day	2 2 1 3 3 3 4 4 7% 7% 65%	2660
July	1st to 10th	Day	2 1 1 3 2 3 4 4 7% 7% 67%	4430
	11th to 20th	Day	1 1 1 3 3 4 6% 5% 8% 9% 60%	4430
	21st to end	Day	3 3 1 4 4 5% 6% 5% 7% 8% 56%	4489
August	1st to 10th	Day	4 3 1 4 4 5% 5% 4 7% 8% 54%	4092
	11th to 20th	Day	2 2 1 4 4 5% 5% 4 5% 7% 60%	4028
	21st to end	Day	1 2 1 3 2 3 3 3 4 6% 71%	4346
September	1st to 10th	Day	3 3 1 4 3 4 4 4 5% 7% 63%	2280
	11th to 20th	Day	5% 3 1 3 3 2 3 2 5% 6% 66%	2181
	21st to end	Day	5% 3 1 4 3 3 3 4 3 6% 65%	2058
October	1st to 10th	Day	5% 5% 1 3 2 2 3 2 4 4 70%	3170
	11th to 20th	Day	4 4 1 3 2 2 3 3 4 7% 67%	3150
	21st to end	Day	3 5% 2 4 2 3 3 3 5% 8% 64%	3438
November	1st to 10th	Day	1 3 2 4 3 2 4 4 6% 9% 62%	1715
	11th to 20th	Day	2 1 4 2 3 3 3 6% 10% 65%	1600
	21st to end	Day	1 6% 2 5% 3 3 3 3 5% 8% 62%	1600
December	1st to 10th	Day	2 1 3 2 1 2 2 4 7% 75%	2620
	11th to 20th	Day	2 2 3 3 3 4 4 7% 11% 61%	3026
	21st to end	Day	1 5% 2 6% 4 4 4 4 7% 9% 54%	4004
January	1st to 10th	Night	4 3 7% 4 4 4 4 7% 10% 54%	6327
	11th to 20th	Night	2 2 6% 5% 6% 5% 4 7% 10% 53%	6020
	21st to end	Night	3 2 6% 3 3 3 2 5% 8% 64%	6468
February	1st to 10th	Night	1 4 2 6% 4 4 4 4 7% 9% 55%	2600
	11th to 20th	Night	1 4 2 6% 4 3 4 5% 6% 8% 57%	2532
	21st to end	Night	4 2 6% 3 3 3 4 5% 8% 60%	2091
March	1st to 10th	Night	2 10% 2 5% 3 3 4 3 5% 7% 56%	4940
	11th to 20th	Night	2 8% 3 5% 3 3 3 3 5% 8% 58%	5000
	21st to end	Night	3 7% 3 7% 4 3 4 3 5% 10% 50%	5489
April	1st to 10th	Night	2 7% 2 4 3 3 3 4 6% 8% 57%	2026
	11th to 20th	Night	4 9% 3 6% 4 3 4 3 6% 9% 49%	1945
	21st to end	Night	7% 8% 2 7% 5% 4 4 4 6% 8% 46%	1759
May	1st to 10th	Night	9% 10% 3 6% 4 3 4 4 6% 8% 42%	2860
	11th to 20th	Night	7% 6% 2 5% 3 3 3 3 5% 6% 55%	2531
	21st to end	Night	10% 5% 1 4 2 3 3 4 5% 10% 53%	2762
June	1st to 10th	Night	4 3 2 3 3 3 4 4 7% 10% 58%	1520
	11th to 20th	Night	5% 4 1 3 3 3 4 3 5% 8% 61%	1520
	21st to end	Night	2 2 1 3 3 3 3 3 5% 8% 69%	1520
July	1st to 10th	Night	3 2 1 2 2 2 3 4 6% 7% 68%	2540
	11th to 20th	Night	1 2 2 2 2 3 6% 9% 72%	2540
	21st to end	Night	2 1 1 2 2 2 3 4 7% 10% 67%	3070
August	1st to 10th	Night	6% 4 1 3 2 2 3 3 4 6% 64%	2847
	11th to 20th	Night	2 2 1 3 3 4 5% 4 6% 8% 61%	2811
	21st to end	Night	2 1 1 2 2 2 3 3 4 7% 74%	3320
September	1st to 10th	Night	3 2 1 2 2 2 3 3 5% 6% 71%	1900
	11th to 20th	Night	4 3 1 4 3 2 4 2 5% 7% 65%	1995
	21st to end	Night	6% 3 1 2 2 2 2 2 4 6% 69%	2121
October	1st to 10th	Night	5% 4 1 3 2 2 2 2 3 4 72%	3800
	11th to 20th	Night	5% 5% 1 5% 3 3 3 3 4 6% 61%	3778
	21st to end	Night	4 6% 2 5% 3 3 4 3 5% 7% 58%	4120
November	1st to 10th	Night	1 3 1 3 2 3 4 4 7% 9% 63%	2559
	11th to 20th	Night	1 3 1 4 3 3 3 3 6% 10% 64%	2800
	21st to end	Night	1 4 2 4 4 4 3 3 6% 10% 60%	2800
December	1st to 10th	Night	2 1 3 2 2 3 2 4 8% 73%	4570
	11th to 20th	Night	1 2 1 3 3 3 4 4 6% 11% 64%	5181
	21st to end	Night	1 4 3 5% 3 3 4 4 7% 10% 58%	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	21% 7% 21% 28% 21% 1	3639
	11th to 20th	Day	19% 10% 19% 26% 23% 2	3990
	21st to end	Day	12% 7% 20% 33% 21% 7%	4510
February	1st to 10th	Day	22% 7% 23% 29% 16% 3	1800
	11th to 20th	Day	23% 8% 20% 31% 14% 4	1764
	21st to end	Day	20% 9% 17% 31% 19% 4	1535
March	1st to 10th	Day	21% 8% 12% 34% 16% 8%	4954
	11th to 20th	Day	21% 9% 15% 30% 24% 1	5000
	21st to end	Day	28% 9% 22% 33% 7% 1	5486
April	1st to 10th	Day	27% 8% 20% 29% 14% 3	2372
	11th to 20th	Day	30% 8% 19% 30% 12% 1	2403
	21st to end	Day	39% 9% 14% 28% 10%	2537
May	1st to 10th	Day	36% 11% 13% 24% 11% 5%	4110
	11th to 20th	Day	26% 8% 14% 30% 16% 5%	4378
	21st to end	Day	27% 10% 15% 29% 17% 2	4825
June	1st to 10th	Day	23% 12% 20% 24% 16% 4	2660
	11th to 20th	Day	20% 8% 15% 22% 24% 11%	2660
	21st to end	Day	14% 8% 9% 27% 28% 15%	2660
July	1st to 10th	Day	13% 6% 8% 19% 33% 21%	4361
	11th to 20th	Day	15% 7% 8% 17% 25% 28%	4355
	21st to end	Day	21% 7% 7% 17% 34% 14%	4347
August	1st to 10th	Day	22% 8% 10% 22% 22% 16%	4078
	11th to 20th	Day	20% 6% 8% 20% 32% 13%	4067
	21st to end	Day	13% 5% 6% 18% 41% 17%	4345
September	1st to 10th	Day	20% 6% 9% 17% 32% 17%	2280
	11th to 20th	Day	20% 4 9% 26% 30% 11%	2181
	21st to end	Day	21% 5% 10% 26% 32% 7%	2058
October	1st to 10th	Day	19% 4 7% 20% 28% 21%	3170
	11th to 20th	Day	17% 5% 11% 35% 23% 9%	3150
	21st to end	Day	19% 5% 12% 35% 25% 3	3438
November	1st to 10th	Day	17% 10% 17% 28% 23% 5%	1715
	11th to 20th	Day	14% 7% 21% 31% 22% 5%	1600
	21st to end	Day	21% 7% 17% 29% 22% 5%	1600
December	1st to 10th	Day	10% 5% 16% 38% 26% 5%	2620
	11th to 20th	Day	14% 9% 30% 29% 16% 2	3024
	21st to end	Day	23% 8% 11% 31% 22% 5%	4004
January	1st to 10th	Night	20% 9% 20% 30% 21% 1	6327
	11th to 20th	Night	21% 9% 21% 26% 20% 3	6020
	21st to end	Night	17% 6% 17% 35% 21% 3	6468
February	1st to 10th	Night	22% 8% 19% 33% 14% 4	2600
	11th to 20th	Night	22% 9% 18% 30% 18% 3	2533
	21st to end	Night	21% 7% 16% 30% 22% 4	2091
March	1st to 10th	Night	25% 8% 10% 29% 19% 9%	4940
	11th to 20th	Night	23% 7% 16% 32% 21% 1	5000
	21st to end	Night	27% 9% 19% 35% 8% 1	5489
April	1st to 10th	Night	23% 10% 20% 28% 15% 4	2026
	11th to 20th	Night	30% 9% 19% 26% 15% 2	1945
	21st to end	Night	32% 10% 15% 30% 12%	1759
May	1st to 10th	Night	36% 10% 11% 24% 16% 4	2860
	11th to 20th	Night	26% 9% 14% 31% 13% 7%	2532
	21st to end	Night	23% 10% 14% 37% 14% 2	2762
June	1st to 10th	Night	21% 9% 23% 25% 19% 3	1520
	11th to 20th	Night	20% 7% 12% 21% 26% 14%	1520
	21st to end	Night	14% 6% 9% 23% 30% 19%	1520
July	1st to 10th	Night	13% 5% 9% 21% 35% 17%	2500
	11th to 20th	Night	8% 4 6% 20% 34% 28%	2492
	21st to end	Night	10% 4 8% 24% 33% 21%	2974
August	1st to 10th	Night	20% 5% 8% 23% 28% 16%	2838
	11th to 20th	Night	18% 7% 8% 25% 29% 14%	2838
	21st to end	Night	10% 5% 7% 22% 31% 25%	3320
September	1st to 10th	Night	13% 6% 8% 19% 36% 18%	1900
	11th to 20th	Night	19% 6% 8% 27% 29% 11%	1995
	21st to end	Night	19% 4 9% 30% 31% 7%	2121
October	1st to 10th	Night	18% 4 6% 25% 32% 15%	3800
	11th to 20th	Night	24% 5% 10% 31% 26% 5%	3778
	21st to end	Night	22% 7% 12% 30% 20% 8%	4120
November	1st to 10th	Night	15% 11% 18% 29% 23% 5%	2559
	11th to 20th	Night	16% 7% 19% 35% 20% 4	2800
	21st to end	Night	19% 8% 16% 32% 20% 5%	2800
December	1st to 10th	Night	11% 5% 18% 36% 26% 3	4570
	11th to 20th	Night	14% 7% 24% 37% 16% 1	5182
	21st to end	Night	19% 8% 14% 32% 20% 7%	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	7% 17% 29% 32% 13% 2	300
	11th to 20th	Day	7% 19% 35% 24% 14% 2	300
	21st to end	Day	6% 16% 40% 24% 11% 3	330
February	1st to 10th	Day	10% 27% 42% 16% 5% 1	300
	11th to 20th	Day	7% 20% 43% 23% 8% 1	300
	21st to end	Day	9% 20% 37% 25% 9%	259
March	1st to 10th	Day	6% 22% 36% 29% 6% 1	500
	11th to 20th	Day	7% 21% 34% 28% 9% 1	500
	21st to end	Day	12% 20% 32% 27% 9% 1	550
April	1st to 10th	Day	10% 24% 31% 26% 8% 1	500
	11th to 20th	Day	11% 21% 34% 26% 8%	492
	21st to end	Day	14% 18% 26% 27% 13% 2	481
May	1st to 10th	Day	12% 21% 26% 26% 12% 3	463
	11th to 20th	Day	15% 10% 23% 33% 14% 5%	661
	21st to end	Day	14% 9% 22% 31% 19% 5%	734
June	1st to 10th	Day	6% 11% 26% 30% 21% 6%	680
	11th to 20th	Day	7% 14% 33% 32% 13% 2	680
	21st to end	Day	4 8% 30% 36% 18% 4	680
July	1st to 10th	Day	3 6% 22% 38% 24% 7%	671
	11th to 20th	Day	1 7% 26% 41% 22% 3	668
	21st to end	Day	5% 6% 26% 35% 24% 5%	553
August	1st to 10th	Day	6% 3 28% 38% 20% 5%	487
	11th to 20th	Day	4 4 32% 35% 19% 6%	477
	21st to end	Day	3 8% 26% 39% 19% 6%	539
September	1st to 10th	Day	6% 6% 27% 39% 17% 6%	490
	11th to 20th	Day	6% 11% 29% 32% 17% 4	490
	21st to end	Day	7% 11% 25% 34% 18% 4	458
October	1st to 10th	Day	10% 10% 22% 36% 17% 5%	300
	11th to 20th	Day	11% 16% 25% 25% 16% 7%	300
	21st to end	Day	7% 17% 40% 26% 8% 1	330
November	1st to 10th	Day	7% 17% 40% 29% 6% 2	300
	11th to 20th	Day	9% 17% 34% 30% 9% 1	300
	21st to end	Day	6% 22% 35% 25% 10% 2	300
December	1st to 10th	Day	8% 19% 39% 24% 8% 2	300
	11th to 20th	Day	4 24% 42% 21% 9% 1	300
	21st to end	Day	7% 17% 40% 23% 11% 2	330
January	1st to 10th	Night	4 19% 40% 28% 8% 1	1000
	11th to 20th	Night	3 20% 47% 18% 10% 2	862
	21st to end	Night	3 18% 46% 26% 6% 2	880
February	1st to 10th	Night	3 22% 45% 23% 7%	800
	11th to 20th	Night	3 16% 47% 24% 8% 2	784
	21st to end	Night	4 17% 51% 20% 7% 1	660
March	1st to 10th	Night	4 13% 46% 30% 7% 1	800
	11th to 20th	Night	3 12% 42% 34% 9% 1	800
	21st to end	Night	6% 11% 41% 35% 6% 1	880
April	1st to 10th	Night	7% 13% 42% 30% 7%	626
	11th to 20th	Night	7% 13% 42% 33% 6%	593
	21st to end	Night	10% 12% 31% 36% 10% 1	587
May	1st to 10th	Night	15% 9% 25% 34% 15% 1	570
	11th to 20th	Night	15% 7% 22% 37% 18% 1	561
	21st to end	Night	14% 6% 23% 36% 20% 1	617
June	1st to 10th	Night	5% 7% 27% 37% 22% 2	570
	11th to 20th	Night	7% 9% 35% 38% 11%	570
	21st to end	Night	2 4 26% 47% 20% 1	570
July	1st to 10th	Night	2 2 18% 48% 28% 2	555
	11th to 20th	Night	1 2 23% 55% 18% 1	552
	21st to end	Night	2 2 17% 54% 23% 2	624
August	1st to 10th	Night	5% 1 15% 53% 26% 1	567
	11th to 20th	Night	3 2 17% 52% 25% 1	564
	21st to end	Night	3 2 22% 50% 22% 1	627
September	1st to 10th	Night	4 3 22% 48% 22% 1	570
	11th to 20th	Night	6% 4 26% 44% 16% 3	665
	21st to end	Night	9% 4 29% 36% 18% 4	760
October	1st to 10th	Night	11% 8% 29% 35% 15% 2	760
	11th to 20th	Night	8% 11% 34% 31% 13% 2	760
	21st to end	Night	5% 12% 45% 27% 8% 2	836
November	1st to 10th	Night	3 14% 49% 27% 6% 1	880
	11th to 20th	Night	4 15% 51% 24% 5% 1	1000
	21st to end	Night	3 14% 49% 26% 7% 1	1000
December	1st to 10th	Night	4 18% 46% 25% 6% 1	1000
	11th to 20th	Night	4 17% 49% 24% 7%	1000
	21st to end	Night	3 18% 46% 24% 7% 2	1100

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