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 2026-08-30.

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 4 3 4 4 4 6% 9% 57%	153279
	Night	3 4 2 5% 3 3 4 3 6% 8% 60%	146560
Transparency	Day	20% 8% 14% 28% 22% 8%	148063
	Night	20% 7% 14% 30% 22% 8%	142785
Seeing	Day	8% 14% 30% 31% 14% 3	18256
	Night	5% 12% 37% 33% 12% 1	28288

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 6% 4 4 4 4 6% 11% 54%	4720
	11th to 20th	Day	2 1 5% 5% 4 3 4 7% 10% 59%	5202
	21st to end	Day	1 1 4 4 4 4 3 6% 8% 66%	5844
February	1st to 10th	Day	3 2 7% 4 3 4 4 6% 10% 56%	1890
	11th to 20th	Day	3 2 6% 5% 3 5% 4 7% 9% 55%	1845
	21st to end	Day	3 2 6% 2 3 4 4 7% 8% 60%	1609
March	1st to 10th	Day	2 7% 3 5% 3 3 3 4 7% 9% 54%	5064
	11th to 20th	Day	1 7% 3 6% 4 3 4 2 5% 8% 57%	5110
	21st to end	Day	3 7% 2 6% 4 4 5% 4 7% 12% 44%	5607
April	1st to 10th	Day	2 7% 2 5% 3 3 4 4 7% 11% 50%	2491
	11th to 20th	Day	3 7% 3 6% 4 4 4 4 6% 10% 47%	2521
	21st to end	Day	6% 10% 3 7% 5% 5% 5% 5% 6% 8% 39%	2730
May	1st to 10th	Day	6% 8% 2 6% 3 4 4 3 6% 8% 49%	7626
	11th to 20th	Day	5% 6% 2 4 3 4 4 4 6% 8% 52%	8150
	21st to end	Day	6% 5% 2 5% 4 4 5% 5% 8% 11% 44%	9026
June	1st to 10th	Day	4 3 1 4 4 4 5% 6% 7% 11% 51%	2940
	11th to 20th	Day	4 2 1 4 3 3 4 5% 7% 9% 58%	2940
	21st to end	Day	2 2 1 3 3 3 4 4 7% 8% 64%	2940
July	1st to 10th	Day	1 1 1 3 3 4 5% 5% 8% 8% 62%	8249
	11th to 20th	Day	1 1 1 2 3 4 5% 5% 8% 9% 62%	8250
	21st to end	Day	2 3 1 4 4 5% 6% 5% 8% 9% 53%	8367
August	1st to 10th	Day	3 2 1 4 4 5% 5% 4 7% 8% 57%	5909
	11th to 20th	Day	2 2 1 4 4 5% 6% 5% 6% 8% 58%	5928
	21st to end	Day	3 2 1 4 3 4 4 4 5% 8% 62%	6330
September	1st to 10th	Day	3 3 1 3 3 4 4 4 5% 7% 63%	2400
	11th to 20th	Day	5% 3 1 3 3 3 4 2 5% 6% 65%	2296
	21st to end	Day	5% 3 1 4 3 3 3 4 4 6% 64%	2166
October	1st to 10th	Day	5% 5% 1 3 2 2 3 2 3 4 69%	3270
	11th to 20th	Day	4 4 1 3 2 2 3 3 4 7% 66%	3250
	21st to end	Day	3 5% 1 4 2 3 3 3 5% 8% 65%	3548
November	1st to 10th	Day	1 3 2 4 3 2 4 4 6% 9% 63%	1803
	11th to 20th	Day	2 1 4 2 3 4 3 6% 10% 64%	1680
	21st to end	Day	5% 2 5% 3 3 3 3 5% 8% 62%	1680
December	1st to 10th	Day	2 1 3 2 1 2 2 4 7% 75%	2700
	11th to 20th	Day	2 1 3 3 3 4 4 7% 10% 61%	3106
	21st to end	Day	1 5% 2 6% 4 4 4 4 7% 9% 54%	4092
January	1st to 10th	Night	3 2 6% 4 4 4 4 6% 10% 55%	8201
	11th to 20th	Night	2 2 6% 4 5% 4 3 6% 10% 57%	7832
	21st to end	Night	3 2 6% 3 3 4 3 5% 8% 63%	8370
February	1st to 10th	Night	1 4 2 6% 4 4 4 4 7% 9% 56%	2730
	11th to 20th	Night	1 4 2 6% 4 3 4 5% 6% 7% 58%	2662
	21st to end	Night	4 2 6% 3 3 3 4 5% 8% 61%	2192
March	1st to 10th	Night	2 10% 2 5% 3 3 4 3 5% 7% 56%	5050
	11th to 20th	Night	2 8% 3 5% 3 3 3 3 5% 8% 58%	5110
	21st to end	Night	3 7% 3 7% 4 3 4 3 5% 10% 50%	5610
April	1st to 10th	Night	2 7% 2 4 3 3 3 4 6% 8% 57%	2127
	11th to 20th	Night	4 8% 3 6% 3 3 4 3 6% 9% 50%	2043
	21st to end	Night	6% 10% 2 7% 5% 4 4 4 7% 8% 44%	1890
May	1st to 10th	Night	8% 9% 3 6% 3 3 4 3 5% 6% 50%	5321
	11th to 20th	Night	6% 7% 2 6% 3 3 4 3 5% 5% 55%	4742
	21st to end	Night	7% 5% 2 4 3 4 4 4 8% 12% 48%	5181
June	1st to 10th	Night	4 3 2 4 3 3 4 4 7% 9% 59%	1680
	11th to 20th	Night	5% 4 1 3 3 3 4 3 5% 8% 62%	1680
	21st to end	Night	3 2 1 3 3 3 3 3 5% 7% 69%	1680
July	1st to 10th	Night	3 2 1 3 3 3 4 4 7% 8% 63%	4740
	11th to 20th	Night	1 1 1 3 3 3 3 3 6% 10% 67%	4740
	21st to end	Night	2 2 1 3 2 3 3 3 7% 9% 64%	5738
August	1st to 10th	Night	4 3 1 3 2 2 3 3 5% 7% 66%	4123
	11th to 20th	Night	2 2 1 3 2 4 5% 4 7% 8% 63%	4141
	21st to end	Night	3 4 2 4 3 3 4 3 5% 8% 62%	4845
September	1st to 10th	Night	3 2 1 2 2 2 3 3 5% 7% 70%	2000
	11th to 20th	Night	4 3 1 4 3 3 4 2 4 7% 64%	2100
	21st to end	Night	6% 3 1 3 2 2 2 2 4 6% 69%	2233
October	1st to 10th	Night	5% 4 1 3 2 2 2 2 3 4 72%	3920
	11th to 20th	Night	5% 5% 1 5% 3 3 3 3 4 6% 61%	3898
	21st to end	Night	4 6% 2 5% 3 3 4 3 5% 7% 59%	4252
November	1st to 10th	Night	1 3 1 3 2 3 4 4 7% 9% 64%	2690
	11th to 20th	Night	1 3 1 4 3 3 3 3 6% 10% 63%	2940
	21st to end	Night	1 4 2 4 4 4 3 3 6% 10% 60%	2940
December	1st to 10th	Night	2 1 3 2 2 3 2 5% 8% 72%	4710
	11th to 20th	Night	1 2 1 3 3 3 4 4 6% 11% 64%	5321
	21st to end	Night	1 4 2 5% 3 3 4 4 7% 10% 58%	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	21% 7% 20% 33% 18% 1	4723
	11th to 20th	Day	16% 9% 20% 29% 21% 6%	5202
	21st to end	Day	14% 7% 18% 34% 22% 6%	5844
February	1st to 10th	Day	22% 7% 22% 30% 17% 3	1890
	11th to 20th	Day	23% 8% 19% 31% 15% 4	1854
	21st to end	Day	19% 9% 17% 30% 21% 5%	1609
March	1st to 10th	Day	21% 8% 13% 34% 17% 8%	5064
	11th to 20th	Day	20% 9% 15% 30% 24% 1	5110
	21st to end	Day	28% 9% 22% 33% 8% 1	5607
April	1st to 10th	Day	26% 9% 20% 29% 14% 3	2491
	11th to 20th	Day	29% 8% 19% 30% 14% 1	2524
	21st to end	Day	40% 9% 14% 27% 10%	2730
May	1st to 10th	Day	28% 9% 15% 33% 13% 3	7626
	11th to 20th	Day	26% 8% 12% 29% 20% 7%	8154
	21st to end	Day	26% 11% 17% 31% 13% 2	9027
June	1st to 10th	Day	22% 11% 20% 25% 17% 5%	2940
	11th to 20th	Day	19% 8% 15% 23% 24% 11%	2940
	21st to end	Day	14% 8% 10% 27% 28% 14%	2940
July	1st to 10th	Day	15% 6% 7% 22% 28% 22%	8181
	11th to 20th	Day	13% 7% 10% 22% 25% 22%	8175
	21st to end	Day	21% 9% 11% 20% 26% 13%	8181
August	1st to 10th	Day	22% 7% 9% 22% 22% 17%	4338
	11th to 20th	Day	21% 7% 8% 21% 31% 13%	4327
	21st to end	Day	14% 5% 7% 18% 40% 16%	4597
September	1st to 10th	Day	20% 6% 9% 19% 31% 16%	2400
	11th to 20th	Day	20% 4 9% 26% 30% 11%	2296
	21st to end	Day	21% 5% 9% 26% 32% 7%	2166
October	1st to 10th	Day	19% 4 7% 21% 28% 20%	3270
	11th to 20th	Day	17% 5% 11% 35% 23% 8%	3250
	21st to end	Day	19% 5% 11% 36% 26% 4	3548
November	1st to 10th	Day	16% 9% 17% 29% 23% 5%	1803
	11th to 20th	Day	14% 7% 21% 32% 21% 5%	1680
	21st to end	Day	21% 7% 18% 28% 22% 4	1680
December	1st to 10th	Day	10% 5% 16% 38% 26% 5%	2700
	11th to 20th	Day	14% 9% 30% 29% 16% 2	3104
	21st to end	Day	23% 8% 12% 31% 21% 5%	4092
January	1st to 10th	Night	20% 8% 19% 30% 21% 1	8202
	11th to 20th	Night	19% 8% 20% 30% 18% 5%	7832
	21st to end	Night	17% 6% 17% 34% 23% 3	8370
February	1st to 10th	Night	22% 8% 19% 33% 15% 3	2730
	11th to 20th	Night	22% 8% 18% 30% 19% 3	2663
	21st to end	Night	20% 7% 16% 30% 22% 5%	2192
March	1st to 10th	Night	25% 8% 10% 29% 20% 9%	5050
	11th to 20th	Night	22% 7% 16% 32% 21% 1	5110
	21st to end	Night	27% 9% 19% 35% 9% 1	5610
April	1st to 10th	Night	22% 10% 20% 29% 15% 4	2127
	11th to 20th	Night	29% 9% 18% 27% 16% 2	2043
	21st to end	Night	33% 9% 15% 30% 12% 1	1890
May	1st to 10th	Night	32% 8% 10% 34% 15% 2	5319
	11th to 20th	Night	27% 8% 10% 27% 18% 10%	4743
	21st to end	Night	24% 9% 17% 35% 13% 2	5182
June	1st to 10th	Night	21% 9% 21% 25% 20% 4	1680
	11th to 20th	Night	19% 7% 12% 22% 26% 14%	1680
	21st to end	Night	14% 6% 9% 24% 29% 18%	1680
July	1st to 10th	Night	15% 6% 8% 21% 33% 18%	4700
	11th to 20th	Night	12% 5% 8% 21% 31% 24%	4692
	21st to end	Night	14% 5% 10% 27% 25% 19%	5612
August	1st to 10th	Night	19% 5% 8% 23% 29% 17%	3018
	11th to 20th	Night	18% 7% 8% 25% 28% 14%	3018
	21st to end	Night	11% 5% 8% 22% 29% 24%	3509
September	1st to 10th	Night	13% 6% 8% 20% 35% 17%	2000
	11th to 20th	Night	19% 6% 8% 27% 29% 10%	2100
	21st to end	Night	19% 5% 8% 30% 31% 7%	2233
October	1st to 10th	Night	18% 4 6% 25% 32% 15%	3920
	11th to 20th	Night	24% 5% 10% 30% 26% 6%	3898
	21st to end	Night	22% 7% 12% 31% 20% 8%	4252
November	1st to 10th	Night	14% 10% 17% 31% 23% 5%	2690
	11th to 20th	Night	16% 7% 19% 35% 19% 3	2940
	21st to end	Night	18% 8% 16% 32% 20% 5%	2940
December	1st to 10th	Night	11% 5% 18% 36% 26% 3	4710
	11th to 20th	Night	14% 7% 24% 37% 16% 1	5322
	21st to end	Night	19% 8% 14% 32% 20% 7%	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	8% 19% 28% 30% 12% 2	330
	11th to 20th	Day	10% 18% 34% 23% 12% 2	330
	21st to end	Day	9% 17% 39% 22% 10% 3	363
February	1st to 10th	Day	11% 26% 41% 16% 5% 1	330
	11th to 20th	Day	7% 19% 43% 23% 7% 1	330
	21st to end	Day	11% 20% 36% 24% 8%	283
March	1st to 10th	Day	7% 23% 35% 28% 6% 1	540
	11th to 20th	Day	9% 22% 33% 26% 8% 1	540
	21st to end	Day	11% 21% 33% 26% 8% 1	594
April	1st to 10th	Day	10% 24% 31% 26% 8% 1	540
	11th to 20th	Day	11% 21% 34% 26% 8%	532
	21st to end	Day	13% 19% 26% 26% 14% 2	540
May	1st to 10th	Day	11% 19% 27% 26% 14% 3	543
	11th to 20th	Day	14% 11% 24% 33% 14% 4	759
	21st to end	Day	13% 8% 23% 33% 19% 5%	844
June	1st to 10th	Day	5% 11% 27% 32% 20% 5%	780
	11th to 20th	Day	6% 14% 33% 33% 12% 2	780
	21st to end	Day	4 9% 30% 36% 17% 4	780
July	1st to 10th	Day	3 5% 21% 40% 24% 6%	771
	11th to 20th	Day	1 6% 26% 40% 23% 4	768
	21st to end	Day	5% 6% 25% 36% 25% 4	643
August	1st to 10th	Day	5% 4 29% 37% 20% 4	567
	11th to 20th	Day	4 4 31% 37% 19% 6%	557
	21st to end	Day	3 7% 26% 38% 19% 6%	620
September	1st to 10th	Day	5% 5% 27% 39% 18% 6%	530
	11th to 20th	Day	6% 10% 29% 33% 17% 5%	530
	21st to end	Day	7% 11% 25% 33% 19% 5%	496
October	1st to 10th	Day	11% 9% 21% 37% 16% 5%	330
	11th to 20th	Day	12% 17% 25% 26% 14% 6%	330
	21st to end	Day	7% 17% 40% 26% 9% 2	363
November	1st to 10th	Day	6% 19% 40% 28% 5% 2	330
	11th to 20th	Day	9% 17% 34% 29% 10% 1	330
	21st to end	Day	6% 22% 34% 26% 10% 2	330
December	1st to 10th	Day	11% 21% 36% 22% 8% 2	330
	11th to 20th	Day	5% 26% 41% 19% 8% 1	330
	21st to end	Day	6% 18% 42% 23% 10% 2	363
January	1st to 10th	Night	4 19% 41% 27% 8% 1	1050
	11th to 20th	Night	4 21% 46% 18% 9% 2	905
	21st to end	Night	3 18% 46% 25% 6% 2	924
February	1st to 10th	Night	3 22% 45% 22% 8%	840
	11th to 20th	Night	3 16% 48% 24% 8% 2	824
	21st to end	Night	4 18% 50% 20% 7% 1	692
March	1st to 10th	Night	4 14% 46% 29% 7%	840
	11th to 20th	Night	4 13% 41% 33% 8% 1	840
	21st to end	Night	6% 11% 42% 34% 6% 1	924
April	1st to 10th	Night	6% 14% 41% 32% 7%	657
	11th to 20th	Night	6% 13% 42% 33% 6%	623
	21st to end	Night	9% 13% 31% 36% 10% 1	630
May	1st to 10th	Night	15% 9% 24% 36% 14% 1	630
	11th to 20th	Night	14% 7% 25% 37% 16% 1	621
	21st to end	Night	13% 7% 24% 37% 19% 1	683
June	1st to 10th	Night	5% 8% 28% 38% 21% 2	630
	11th to 20th	Night	6% 9% 36% 39% 10%	630
	21st to end	Night	3 4 28% 46% 19% 1	630
July	1st to 10th	Night	2 2 18% 51% 26% 2	615
	11th to 20th	Night	1 2 22% 56% 18% 1	612
	21st to end	Night	2 2 18% 55% 21% 2	690
August	1st to 10th	Night	4 2 17% 52% 24% 1	627
	11th to 20th	Night	3 2 17% 53% 24% 1	624
	21st to end	Night	3 2 22% 51% 21% 1	687
September	1st to 10th	Night	4 3 21% 49% 22% 1	600
	11th to 20th	Night	5% 5% 26% 44% 16% 3	700
	21st to end	Night	9% 4 29% 36% 18% 4	800
October	1st to 10th	Night	11% 7% 29% 35% 15% 2	800
	11th to 20th	Night	9% 12% 34% 31% 12% 2	800
	21st to end	Night	4 12% 46% 27% 8% 2	880
November	1st to 10th	Night	3 14% 49% 27% 6% 1	925
	11th to 20th	Night	4 15% 51% 25% 5%	1050
	21st to end	Night	3 15% 48% 27% 7% 1	1050
December	1st to 10th	Night	4 19% 46% 25% 6% 1	1050
	11th to 20th	Night	4 18% 48% 22% 7%	1050
	21st to end	Night	3 18% 47% 24% 6% 2	1155

Page generated at 2026-08-27 02:07:16. Version ac07

Copyright © 2026 Attilla Danko.