Green River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green River clear sky chart from 2005-11-06 to 2026-04-02.

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% 8% 58%	140060
	Night	4 5% 2 5% 4 4 4 4 6% 8% 55%	139315
Transparency	Day	24% 4 8% 21% 24% 18%	134868
	Night	27% 4 9% 23% 22% 15%	135512
Seeing	Day	5% 6% 15% 32% 29% 13%	16870
	Night	6% 3 17% 43% 28% 3	27317

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 7% 3 8% 6% 6% 6% 5% 6% 7% 42%	5318
	11th to 20th	Day	2 3 1 5% 4 4 5% 5% 7% 11% 54%	5340
	21st to end	Day	4 7% 2 5% 4 4 4 3 6% 8% 53%	5844
February	1st to 10th	Day	3 6% 2 7% 5% 5% 6% 5% 9% 10% 43%	1890
	11th to 20th	Day	5% 7% 3 7% 6% 4 5% 4 6% 8% 45%	1845
	21st to end	Day	5% 6% 2 6% 5% 4 5% 4 6% 9% 49%	1775
March	1st to 10th	Day	4 7% 2 5% 4 4 4 4 6% 7% 55%	5064
	11th to 20th	Day	5% 9% 4 7% 4 4 4 4 6% 7% 46%	5110
	21st to end	Day	6% 8% 3 7% 4 5% 5% 4 6% 7% 45%	5607
April	1st to 10th	Day	3 4 2 5% 4 4 4 3 6% 7% 58%	2297
	11th to 20th	Day	4 5% 2 5% 4 4 4 4 6% 7% 56%	2371
	21st to end	Day	3 4 1 5% 3 4 4 3 6% 7% 58%	2581
May	1st to 10th	Day	5% 4 2 5% 3 4 5% 3 6% 8% 56%	5880
	11th to 20th	Day	4 3 1 4 3 4 5% 4 6% 7% 57%	5841
	21st to end	Day	3 3 1 3 2 3 3 3 5% 8% 66%	6423
June	1st to 10th	Day	3 3 1 3 2 3 3 3 6% 8% 66%	2775
	11th to 20th	Day	2 3 1 2 2 3 3 3 4 5% 72%	2800
	21st to end	Day	2 2 1 2 2 3 3 3 5% 6% 72%	2698
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 6% 75%	5879
	11th to 20th	Day	1 2 1 3 3 4 5% 5% 8% 11% 57%	5880
	21st to end	Day	2 1 1 3 3 3 3 3 6% 8% 67%	6401
August	1st to 10th	Day	1 2 1 3 3 3 4 4 8% 10% 62%	5779
	11th to 20th	Day	2 2 1 3 2 4 4 4 6% 7% 67%	5798
	21st to end	Day	4 3 1 4 3 4 5% 4 7% 8% 56%	6165
September	1st to 10th	Day	4 2 1 2 3 2 4 3 5% 7% 68%	2375
	11th to 20th	Day	3 3 1 3 3 2 4 3 5% 6% 68%	2200
	21st to end	Day	5% 2 1 3 2 2 2 2 3 5% 73%	2200
October	1st to 10th	Day	4 2 1 2 1 2 2 2 2 4 79%	3313
	11th to 20th	Day	5% 3 2 5% 4 3 4 3 4 8% 59%	3250
	21st to end	Day	3 4 1 3 2 3 4 4 5% 6% 64%	3548
November	1st to 10th	Day	4 4 1 3 3 2 2 2 4 6% 68%	2022
	11th to 20th	Day	3 3 2 3 3 2 3 2 4 7% 67%	1867
	21st to end	Day	5% 4 2 5% 3 3 3 3 4 7% 61%	1680
December	1st to 10th	Day	3 4 1 4 2 4 8% 6% 8% 9% 52%	2700
	11th to 20th	Day	4 5% 2 7% 5% 5% 6% 4 9% 13% 41%	3106
	21st to end	Day	5% 10% 3 7% 5% 5% 5% 5% 9% 8% 38%	4438
January	1st to 10th	Night	5% 8% 3 8% 5% 5% 5% 4 5% 8% 44%	7605
	11th to 20th	Night	2 3 1 4 3 4 5% 4 6% 12% 56%	7650
	21st to end	Night	4 7% 3 7% 4 4 4 3 4 7% 53%	8370
February	1st to 10th	Night	3 5% 2 7% 5% 5% 5% 4 6% 9% 49%	2730
	11th to 20th	Night	5% 7% 3 8% 6% 5% 5% 5% 6% 8% 42%	2662
	21st to end	Night	3 6% 3 6% 5% 5% 5% 4 6% 8% 50%	2024
March	1st to 10th	Night	6% 9% 2 6% 4 4 4 4 5% 7% 49%	5050
	11th to 20th	Night	6% 7% 3 7% 4 4 5% 4 5% 8% 48%	5110
	21st to end	Night	6% 7% 3 6% 4 4 4 4 5% 7% 50%	5610
April	1st to 10th	Night	5% 6% 2 5% 3 4 4 4 5% 7% 56%	2124
	11th to 20th	Night	6% 5% 2 6% 4 4 4 4 5% 6% 54%	1977
	21st to end	Night	4 5% 2 5% 2 4 5% 3 6% 8% 56%	1815
May	1st to 10th	Night	7% 6% 3 5% 4 4 5% 3 5% 7% 51%	4100
	11th to 20th	Night	4 5% 2 5% 4 3 4 4 5% 7% 58%	4074
	21st to end	Night	3 3 1 4 3 3 4 4 6% 8% 60%	4474
June	1st to 10th	Night	4 4 1 4 3 4 4 4 6% 7% 59%	1616
	11th to 20th	Night	4 2 1 4 3 3 4 3 5% 7% 64%	1600
	21st to end	Night	2 2 1 2 3 4 4 3 6% 6% 67%	1692
July	1st to 10th	Night	2 2 1 4 3 4 4 3 5% 6% 66%	4100
	11th to 20th	Night	2 3 1 6% 5% 6% 6% 5% 9% 10% 49%	4100
	21st to end	Night	1 2 1 5% 4 4 5% 4 7% 8% 59%	4472
August	1st to 10th	Night	2 3 1 5% 4 6% 5% 5% 7% 10% 52%	4033
	11th to 20th	Night	3 2 2 4 3 4 4 4 6% 7% 61%	4051
	21st to end	Night	3 3 2 6% 4 4 5% 3 6% 7% 55%	4812
September	1st to 10th	Night	3 2 1 4 3 3 4 4 5% 8% 64%	2021
	11th to 20th	Night	3 3 1 4 2 3 3 3 4 6% 68%	2200
	21st to end	Night	3 2 1 3 2 2 3 2 3 5% 72%	2200
October	1st to 10th	Night	4 2 1 3 2 2 2 2 3 5% 74%	3878
	11th to 20th	Night	4 3 2 5% 3 4 4 3 5% 7% 60%	3898
	21st to end	Night	4 5% 2 4 2 2 3 3 4 7% 64%	4252
November	1st to 10th	Night	3 3 2 3 2 3 3 2 4 6% 68%	2494
	11th to 20th	Night	3 3 1 3 3 2 3 3 4 6% 68%	2730
	21st to end	Night	5% 5% 2 4 4 3 4 3 5% 6% 60%	2938
December	1st to 10th	Night	3 3 1 3 3 3 5% 5% 7% 11% 56%	4710
	11th to 20th	Night	4 5% 2 5% 5% 4 4 4 7% 14% 46%	5321
	21st to end	Night	6% 6% 2 7% 5% 5% 5% 5% 7% 11% 41%	6822

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	39% 6% 20% 22% 11% 2	5321
	11th to 20th	Day	24% 6% 15% 33% 16% 6%	5340
	21st to end	Day	30% 4 15% 30% 18% 3	5844
February	1st to 10th	Day	33% 8% 18% 24% 14% 4	1890
	11th to 20th	Day	36% 6% 13% 28% 15% 2	1854
	21st to end	Day	29% 8% 9% 29% 19% 6%	1775
March	1st to 10th	Day	27% 6% 6% 25% 27% 9%	5064
	11th to 20th	Day	37% 4 7% 23% 21% 8%	5110
	21st to end	Day	36% 5% 8% 28% 20% 4	5607
April	1st to 10th	Day	25% 5% 6% 24% 29% 12%	2297
	11th to 20th	Day	25% 5% 6% 23% 27% 13%	2374
	21st to end	Day	23% 4 6% 23% 31% 13%	2581
May	1st to 10th	Day	24% 6% 7% 18% 33% 14%	5880
	11th to 20th	Day	22% 4 5% 19% 30% 19%	5844
	21st to end	Day	16% 4 3 16% 40% 22%	6424
June	1st to 10th	Day	15% 4 5% 16% 32% 28%	2775
	11th to 20th	Day	15% 3 3 10% 23% 47%	2800
	21st to end	Day	13% 3 2 10% 23% 50%	2698
July	1st to 10th	Day	12% 2 3 7% 15% 61%	5816
	11th to 20th	Day	19% 3 3 11% 27% 36%	5811
	21st to end	Day	16% 3 4 14% 25% 39%	6217
August	1st to 10th	Day	21% 3 8% 25% 22% 22%	4208
	11th to 20th	Day	20% 3 9% 19% 23% 26%	4197
	21st to end	Day	21% 3 7% 19% 26% 24%	4444
September	1st to 10th	Day	17% 3 5% 13% 28% 34%	2375
	11th to 20th	Day	18% 3 8% 19% 23% 29%	2200
	21st to end	Day	16% 3 3 15% 36% 27%	2200
October	1st to 10th	Day	13% 2 4 15% 32% 35%	3313
	11th to 20th	Day	26% 2 3 25% 33% 10%	3250
	21st to end	Day	22% 2 9% 30% 30% 6%	3548
November	1st to 10th	Day	19% 3 10% 31% 30% 6%	2022
	11th to 20th	Day	19% 3 12% 39% 25% 2	1867
	21st to end	Day	26% 4 14% 34% 19% 3	1680
December	1st to 10th	Day	27% 5% 21% 32% 11% 3	2700
	11th to 20th	Day	34% 6% 24% 31% 5%	3104
	21st to end	Day	40% 6% 17% 20% 16% 1	4438
January	1st to 10th	Night	38% 5% 16% 26% 11% 3	7605
	11th to 20th	Night	20% 6% 13% 35% 24% 3	7650
	21st to end	Night	33% 4 13% 26% 19% 5%	8370
February	1st to 10th	Night	30% 6% 17% 28% 14% 4	2730
	11th to 20th	Night	39% 6% 8% 25% 19% 3	2663
	21st to end	Night	29% 6% 10% 28% 21% 6%	2024
March	1st to 10th	Night	34% 5% 4 20% 25% 12%	5050
	11th to 20th	Night	34% 5% 5% 25% 22% 8%	5110
	21st to end	Night	33% 5% 5% 29% 24% 4	5610
April	1st to 10th	Night	28% 5% 5% 19% 26% 16%	2124
	11th to 20th	Night	31% 5% 5% 18% 27% 15%	1977
	21st to end	Night	25% 5% 5% 22% 30% 13%	1815
May	1st to 10th	Night	32% 5% 5% 13% 31% 15%	4097
	11th to 20th	Night	23% 6% 3 18% 35% 14%	4075
	21st to end	Night	20% 4 3 18% 37% 17%	4474
June	1st to 10th	Night	22% 5% 4 12% 30% 28%	1616
	11th to 20th	Night	20% 3 4 9% 18% 45%	1600
	21st to end	Night	16% 5% 3 8% 18% 50%	1692
July	1st to 10th	Night	19% 3 3 7% 10% 58%	4055
	11th to 20th	Night	28% 4 3 10% 24% 32%	4046
	21st to end	Night	21% 3 5% 11% 20% 40%	4344
August	1st to 10th	Night	29% 4 7% 24% 15% 21%	2928
	11th to 20th	Night	26% 3 8% 15% 19% 28%	2928
	21st to end	Night	22% 4 8% 17% 20% 30%	3464
September	1st to 10th	Night	18% 4 5% 14% 18% 40%	2021
	11th to 20th	Night	19% 4 5% 19% 22% 31%	2200
	21st to end	Night	17% 3 4 12% 29% 36%	2200
October	1st to 10th	Night	15% 2 3 12% 27% 41%	3878
	11th to 20th	Night	25% 2 5% 20% 35% 14%	3898
	21st to end	Night	22% 2 5% 31% 32% 8%	4252
November	1st to 10th	Night	20% 3 5% 26% 35% 12%	2494
	11th to 20th	Night	19% 3 8% 35% 31% 4	2730
	21st to end	Night	26% 3 8% 30% 28% 5%	2938
December	1st to 10th	Night	23% 4 16% 39% 16% 2	4710
	11th to 20th	Night	27% 5% 24% 36% 7%	5322
	21st to end	Night	37% 5% 17% 25% 14% 1	6822

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	10% 3 10% 42% 26% 10%	330
	11th to 20th	Day	7% 1 13% 41% 28% 11%	330
	21st to end	Day	3 3 8% 44% 33% 9%	363
February	1st to 10th	Day	6% 2 11% 51% 22% 8%	330
	11th to 20th	Day	8% 3 13% 45% 27% 4	330
	21st to end	Day	6% 9% 14% 41% 26% 5%	441
March	1st to 10th	Day	8% 9% 16% 34% 24% 8%	540
	11th to 20th	Day	7% 9% 17% 37% 22% 7%	540
	21st to end	Day	7% 12% 23% 35% 19% 4	594
April	1st to 10th	Day	6% 12% 21% 30% 24% 8%	505
	11th to 20th	Day	8% 15% 20% 34% 18% 5%	492
	21st to end	Day	6% 12% 24% 28% 23% 7%	500
May	1st to 10th	Day	6% 11% 22% 32% 21% 8%	503
	11th to 20th	Day	5% 7% 23% 28% 25% 13%	528
	21st to end	Day	4 9% 19% 29% 26% 13%	573
June	1st to 10th	Day	4 6% 14% 30% 33% 13%	705
	11th to 20th	Day	3 7% 18% 32% 31% 9%	730
	21st to end	Day	4 4 18% 33% 32% 9%	628
July	1st to 10th	Day	2 2 12% 29% 37% 18%	526
	11th to 20th	Day	2 13% 22% 39% 24%	524
	21st to end	Day	2 2 9% 22% 39% 26%	575
August	1st to 10th	Day	3 3 10% 28% 36% 20%	527
	11th to 20th	Day	4 1 8% 30% 33% 24%	517
	21st to end	Day	5% 2 10% 22% 42% 20%	583
September	1st to 10th	Day	3 3 12% 18% 36% 28%	530
	11th to 20th	Day	2 6% 17% 23% 34% 18%	530
	21st to end	Day	6% 6% 12% 21% 33% 22%	530
October	1st to 10th	Day	6% 5% 13% 23% 27% 27%	360
	11th to 20th	Day	6% 5% 11% 30% 32% 17%	330
	21st to end	Day	4 5% 10% 34% 34% 11%	363
November	1st to 10th	Day	5% 5% 13% 33% 27% 16%	330
	11th to 20th	Day	2 2 11% 44% 28% 14%	330
	21st to end	Day	8% 3 10% 35% 30% 13%	330
December	1st to 10th	Day	7% 2 12% 43% 24% 12%	330
	11th to 20th	Day	5% 2 10% 40% 35% 9%	330
	21st to end	Day	11% 5% 14% 43% 20% 7%	363
January	1st to 10th	Night	8% 3 12% 47% 25% 5%	840
	11th to 20th	Night	7% 2 14% 45% 29% 4	840
	21st to end	Night	8% 1 15% 50% 23% 4	924
February	1st to 10th	Night	5% 1 19% 52% 20% 3	840
	11th to 20th	Night	7% 3 20% 50% 18% 2	824
	21st to end	Night	5% 3 22% 52% 16% 1	692
March	1st to 10th	Night	7% 3 23% 44% 22% 1	840
	11th to 20th	Night	5% 5% 19% 45% 24% 1	840
	21st to end	Night	6% 5% 26% 46% 17% 1	924
April	1st to 10th	Night	7% 7% 26% 40% 18% 1	717
	11th to 20th	Night	8% 7% 30% 39% 16% 1	593
	21st to end	Night	5% 7% 28% 35% 21% 3	600
May	1st to 10th	Night	6% 7% 26% 42% 17% 2	600
	11th to 20th	Night	5% 3 20% 42% 26% 3	591
	21st to end	Night	5% 7% 23% 39% 25% 2	650
June	1st to 10th	Night	4 4 17% 44% 29% 1	600
	11th to 20th	Night	4 4 24% 46% 22% 1	600
	21st to end	Night	2 3 17% 47% 31% 1	600
July	1st to 10th	Night	4 1 13% 38% 42% 3	585
	11th to 20th	Night	2 1 6% 38% 48% 5%	582
	21st to end	Night	2 1 4 35% 54% 4	657
August	1st to 10th	Night	4 2 9% 39% 43% 4	597
	11th to 20th	Night	3 1 11% 41% 41% 3	594
	21st to end	Night	3 1 9% 38% 44% 5%	660
September	1st to 10th	Night	5% 11% 37% 42% 5%	621
	11th to 20th	Night	4 1 13% 40% 38% 4	800
	21st to end	Night	4 2 16% 31% 38% 8%	800
October	1st to 10th	Night	8% 2 16% 42% 28% 5%	800
	11th to 20th	Night	5% 2 16% 42% 31% 4	800
	21st to end	Night	7% 3 17% 36% 33% 4	880
November	1st to 10th	Night	4 3 14% 45% 31% 3	820
	11th to 20th	Night	4 2 15% 48% 25% 5%	840
	21st to end	Night	7% 4 15% 41% 29% 4	1048
December	1st to 10th	Night	5% 2 14% 52% 24% 4	1050
	11th to 20th	Night	7% 2 16% 48% 25% 2	1050
	21st to end	Night	11% 3 15% 48% 20% 2	1018

Page generated at 2026-03-30 00:18:46. Version ac07

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