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 2024-10-25.

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% 9% 57%	101414
	Night	3 4 2 4 3 3 4 3 6% 9% 59%	97643
Transparency	Day	21% 8% 14% 26% 21% 8%	101167
	Night	20% 8% 15% 29% 21% 8%	97480
Seeing	Day	8% 13% 30% 31% 15% 3	15698
	Night	5% 11% 37% 33% 12% 1	25775

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% 3 4 4 4 6% 12% 55%	2538
	11th to 20th	Day	2 1 6% 5% 5% 4 4 8% 11% 55%	2778
	21st to end	Day	2 1 4 3 3 3 3 6% 9% 66%	3146
February	1st to 10th	Day	1 3 2 7% 4 3 4 4 5% 10% 56%	1710
	11th to 20th	Day	4 2 6% 5% 3 4 4 6% 8% 57%	1665
	21st to end	Day	3 3 7% 3 3 5% 4 7% 8% 58%	1460
March	1st to 10th	Day	3 2 5% 3 3 3 5% 8% 11% 57%	3444
	11th to 20th	Day	2 7% 2 5% 4 3 4 2 6% 9% 56%	3490
	21st to end	Day	5% 9% 2 6% 4 4 5% 5% 7% 10% 42%	3825
April	1st to 10th	Day	2 8% 2 6% 3 3 4 4 7% 11% 50%	2253
	11th to 20th	Day	3 7% 3 7% 4 4 5% 4 6% 10% 46%	2278
	21st to end	Day	7% 10% 3 6% 5% 5% 5% 5% 7% 8% 40%	2470
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	8% 8% 2 4 3 3 3 3 4 6% 56%	1900
	11th to 20th	Day	5% 3 1 3 2 2 3 3 4 8% 66%	1900
	21st to end	Day	2 5% 2 4 3 3 3 3 5% 8% 62%	2025
November	1st to 10th	Day	1 3 2 4 3 2 4 3 5% 9% 63%	1629
	11th to 20th	Day	2 1 4 2 3 3 3 6% 11% 65%	1520
	21st to end	Day	1 6% 2 6% 3 3 4 3 5% 7% 61%	1520
December	1st to 10th	Day	3 2 5% 3 2 2 3 6% 10% 64%	1520
	11th to 20th	Day	1 4 2 2 3 3 4 4 6% 10% 60%	1926
	21st to end	Day	1 5% 3 6% 4 3 3 3 6% 7% 60%	2794
January	1st to 10th	Night	2 2 7% 5% 5% 5% 4 6% 10% 54%	4417
	11th to 20th	Night	2 2 5% 5% 5% 4 4 8% 13% 53%	4208
	21st to end	Night	1 4 2 5% 3 3 4 3 6% 9% 60%	4521
February	1st to 10th	Night	1 4 2 7% 4 4 4 4 7% 8% 55%	2470
	11th to 20th	Night	1 4 2 6% 4 3 4 4 6% 7% 58%	2402
	21st to end	Night	4 2 7% 4 4 3 4 6% 8% 59%	1990
March	1st to 10th	Night	1 6% 2 5% 2 3 4 4 5% 8% 59%	3430
	11th to 20th	Night	1 8% 3 5% 3 3 3 4 6% 9% 55%	3490
	21st to end	Night	3 7% 3 8% 5% 4 4 4 6% 10% 46%	3828
April	1st to 10th	Night	3 8% 2 4 3 3 3 4 6% 8% 56%	1925
	11th to 20th	Night	5% 9% 3 6% 4 4 4 3 7% 9% 48%	1847
	21st to end	Night	7% 8% 2 7% 5% 4 4 4 7% 8% 46%	1710
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	8% 7% 2 5% 4 3 3 3 4 6% 56%	2280
	11th to 20th	Night	4 5% 1 4 2 3 3 3 4 6% 65%	2280
	21st to end	Night	2 5% 2 6% 3 3 4 3 5% 9% 59%	2436
November	1st to 10th	Night	2 3 1 4 2 3 3 4 7% 9% 64%	2428
	11th to 20th	Night	1 3 1 3 3 3 3 3 6% 10% 63%	2660
	21st to end	Night	1 5% 2 4 4 4 3 3 6% 9% 59%	2660
December	1st to 10th	Night	3 2 5% 3 3 4 3 6% 10% 61%	2660
	11th to 20th	Night	1 2 1 3 3 3 4 4 7% 11% 61%	3271
	21st to end	Night	1 5% 3 5% 3 3 3 4 6% 9% 59%	4873

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	19% 8% 19% 31% 22% 2	2539
	11th to 20th	Day	18% 13% 22% 28% 18% 2	2778
	21st to end	Day	14% 8% 26% 33% 15% 5%	3146
February	1st to 10th	Day	23% 7% 23% 30% 15% 2	1710
	11th to 20th	Day	23% 8% 20% 31% 14% 4	1674
	21st to end	Day	20% 10% 18% 31% 18% 3	1460
March	1st to 10th	Day	14% 11% 15% 36% 20% 4	3444
	11th to 20th	Day	20% 12% 20% 34% 14% 1	3490
	21st to end	Day	32% 10% 20% 32% 5% 1	3825
April	1st to 10th	Day	27% 9% 20% 28% 12% 3	2253
	11th to 20th	Day	31% 8% 19% 30% 11% 1	2281
	21st to end	Day	39% 9% 14% 28% 9%	2470
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	30% 6% 11% 25% 21% 8%	1900
	11th to 20th	Day	17% 6% 15% 35% 21% 6%	1900
	21st to end	Day	20% 6% 17% 31% 23% 3	2025
November	1st to 10th	Day	17% 10% 17% 27% 23% 6%	1629
	11th to 20th	Day	14% 7% 22% 30% 22% 5%	1520
	21st to end	Day	22% 7% 17% 28% 21% 5%	1520
December	1st to 10th	Day	16% 8% 23% 30% 17% 7%	1520
	11th to 20th	Day	16% 10% 27% 30% 15% 1	1924
	21st to end	Day	23% 8% 11% 30% 21% 7%	2794
January	1st to 10th	Night	20% 11% 18% 29% 21% 1	4417
	11th to 20th	Night	18% 10% 27% 23% 18% 4	4208
	21st to end	Night	19% 7% 22% 36% 13% 2	4521
February	1st to 10th	Night	23% 8% 19% 34% 14% 2	2470
	11th to 20th	Night	21% 9% 18% 30% 18% 3	2403
	21st to end	Night	21% 8% 17% 30% 21% 4	1990
March	1st to 10th	Night	18% 10% 12% 33% 20% 7%	3430
	11th to 20th	Night	21% 10% 21% 34% 13% 1	3490
	21st to end	Night	29% 11% 19% 34% 6% 1	3828
April	1st to 10th	Night	23% 10% 21% 27% 15% 4	1925
	11th to 20th	Night	30% 9% 19% 26% 14% 2	1847
	21st to end	Night	32% 10% 15% 31% 12%	1710
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	30% 6% 10% 28% 20% 7%	2280
	11th to 20th	Night	21% 5% 13% 35% 21% 6%	2280
	21st to end	Night	20% 9% 17% 32% 18% 4	2436
November	1st to 10th	Night	15% 11% 18% 29% 23% 5%	2428
	11th to 20th	Night	15% 7% 20% 34% 19% 3	2660
	21st to end	Night	19% 9% 16% 30% 20% 5%	2660
December	1st to 10th	Night	17% 8% 22% 31% 17% 5%	2660
	11th to 20th	Night	15% 9% 25% 34% 16% 1	3272
	21st to end	Night	20% 8% 13% 31% 19% 9%	4873

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	6% 18% 28% 31% 14% 3	270
	11th to 20th	Day	7% 17% 35% 24% 14% 3	270
	21st to end	Day	6% 15% 41% 23% 11% 3	297
February	1st to 10th	Day	10% 27% 41% 16% 5% 1	270
	11th to 20th	Day	7% 20% 42% 22% 7% 1	270
	21st to end	Day	8% 19% 38% 26% 9%	234
March	1st to 10th	Day	6% 22% 38% 28% 5% 1	460
	11th to 20th	Day	7% 20% 35% 28% 10% 1	460
	21st to end	Day	11% 20% 32% 27% 8% 1	506
April	1st to 10th	Day	11% 24% 32% 25% 7% 1	460
	11th to 20th	Day	12% 21% 34% 26% 7%	452
	21st to end	Day	14% 18% 26% 27% 13% 2	460
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	6% 17% 41% 25% 9% 1	311
November	1st to 10th	Day	7% 17% 41% 26% 6% 2	270
	11th to 20th	Day	9% 17% 34% 30% 9% 1	270
	21st to end	Day	6% 22% 34% 25% 11% 2	270
December	1st to 10th	Day	8% 17% 41% 23% 9% 1	270
	11th to 20th	Day	3 24% 41% 21% 10% 1	270
	21st to end	Day	7% 17% 39% 23% 11% 3	297
January	1st to 10th	Night	4 19% 40% 27% 8% 1	950
	11th to 20th	Night	3 20% 48% 17% 10% 2	819
	21st to end	Night	2 17% 47% 25% 7% 2	836
February	1st to 10th	Night	3 22% 44% 22% 8%	760
	11th to 20th	Night	3 17% 47% 23% 8% 2	744
	21st to end	Night	3 16% 52% 21% 7% 1	628
March	1st to 10th	Night	3 13% 46% 30% 7% 1	760
	11th to 20th	Night	3 12% 42% 33% 9% 1	760
	21st to end	Night	6% 10% 41% 35% 7%	836
April	1st to 10th	Night	7% 13% 43% 30% 7%	595
	11th to 20th	Night	7% 12% 42% 32% 6%	563
	21st to end	Night	9% 12% 31% 36% 10% 1	570
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	4 13% 45% 27% 8% 2	812
November	1st to 10th	Night	3 15% 49% 26% 6% 1	835
	11th to 20th	Night	3 15% 51% 25% 5% 1	950
	21st to end	Night	3 14% 48% 26% 7% 1	950
December	1st to 10th	Night	4 17% 47% 25% 6% 1	950
	11th to 20th	Night	3 16% 49% 24% 7%	950
	21st to end	Night	3 18% 45% 25% 7% 2	1045

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