Trout Creek Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trout Creek Observing Site clear sky chart from 2005-11-06 to 2026-05-02.

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 6% 3 7% 4 4 5% 4 6% 7% 52%	140497
	Night	2 5% 2 6% 4 4 4 4 6% 7% 56%	139521
Transparency	Day	30% 5% 10% 21% 22% 11%	135257
	Night	27% 5% 11% 24% 22% 11%	135766
Seeing	Day	13% 21% 33% 21% 9% 2	17091
	Night	8% 15% 27% 31% 16% 2	27505

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	2 7% 4 11% 6% 5% 5% 5% 7% 9% 41%	5318
	11th to 20th	Day	3 2 11% 6% 4 3 3 5% 7% 56%	5340
	21st to end	Day	1 7% 4 8% 3 3 2 3 5% 6% 58%	5844
February	1st to 10th	Day	2 9% 4 10% 6% 5% 4 4 6% 7% 43%	1890
	11th to 20th	Day	2 9% 5% 12% 6% 4 5% 4 7% 8% 37%	1877
	21st to end	Day	1 10% 5% 13% 7% 5% 4 4 5% 6% 41%	1730
March	1st to 10th	Day	2 10% 6% 12% 5% 4 4 3 6% 7% 41%	5021
	11th to 20th	Day	1 9% 4 8% 4 5% 5% 5% 6% 8% 43%	5110
	21st to end	Day	2 14% 6% 10% 5% 6% 6% 6% 6% 6% 33%	5607
April	1st to 10th	Day	2 10% 3 8% 5% 5% 4 4 7% 8% 44%	2364
	11th to 20th	Day	2 9% 3 11% 6% 5% 6% 5% 6% 7% 41%	2585
	21st to end	Day	4 8% 3 8% 5% 6% 5% 5% 6% 7% 44%	2730
May	1st to 10th	Day	6% 9% 3 7% 4 5% 5% 4 7% 7% 42%	5894
	11th to 20th	Day	5% 7% 2 5% 5% 5% 5% 5% 7% 8% 46%	5841
	21st to end	Day	4 5% 2 6% 5% 5% 5% 5% 6% 8% 48%	6423
June	1st to 10th	Day	4 4 2 4 4 5% 5% 4 6% 8% 56%	2780
	11th to 20th	Day	4 3 2 5% 3 3 4 3 5% 6% 62%	2800
	21st to end	Day	2 3 1 3 3 4 4 3 5% 6% 64%	2717
July	1st to 10th	Day	2 3 1 4 3 3 3 3 4 5% 69%	5879
	11th to 20th	Day	3 3 1 5% 5% 4 5% 5% 7% 8% 54%	5880
	21st to end	Day	3 3 1 4 3 4 4 5% 6% 7% 60%	6401
August	1st to 10th	Day	2 2 1 3 3 4 4 3 5% 7% 66%	5779
	11th to 20th	Day	2 3 1 4 3 4 4 4 5% 6% 65%	5798
	21st to end	Day	4 4 2 6% 5% 5% 6% 4 7% 7% 51%	6320
September	1st to 10th	Day	4 4 1 4 4 4 4 3 5% 6% 61%	2312
	11th to 20th	Day	4 4 1 5% 3 4 4 3 4 6% 60%	2200
	21st to end	Day	4 5% 1 4 3 3 3 3 4 4 66%	2200
October	1st to 10th	Day	5% 5% 2 4 3 2 3 2 4 4 67%	3379
	11th to 20th	Day	7% 7% 2 5% 4 3 3 3 4 6% 56%	3250
	21st to end	Day	2 6% 2 4 3 4 4 3 5% 6% 61%	3548
November	1st to 10th	Day	3 8% 2 5% 4 3 4 3 6% 8% 54%	1908
	11th to 20th	Day	2 7% 2 6% 4 3 4 4 7% 8% 53%	1883
	21st to end	Day	1 7% 4 6% 4 3 4 4 5% 9% 52%	1680
December	1st to 10th	Day	1 4 2 5% 3 3 4 3 5% 8% 63%	2700
	11th to 20th	Day	1 5% 3 7% 5% 4 6% 6% 9% 11% 44%	3106
	21st to end	Day	1 7% 4 10% 5% 5% 6% 5% 8% 8% 41%	4403
January	1st to 10th	Night	1 7% 4 10% 7% 5% 5% 4 6% 8% 44%	7605
	11th to 20th	Night	3 2 10% 5% 4 3 2 4 6% 59%	7650
	21st to end	Night	1 6% 4 8% 3 3 3 3 5% 7% 59%	8370
February	1st to 10th	Night	1 6% 3 7% 4 4 4 5% 8% 8% 49%	2730
	11th to 20th	Night	1 8% 3 7% 5% 4 5% 5% 6% 9% 47%	2625
	21st to end	Night	2 5% 3 8% 5% 6% 5% 3 7% 7% 50%	2076
March	1st to 10th	Night	1 8% 4 8% 4 5% 5% 4 6% 8% 49%	5082
	11th to 20th	Night	1 7% 4 7% 5% 5% 6% 5% 7% 10% 44%	5110
	21st to end	Night	1 8% 3 7% 4 3 4 4 7% 8% 50%	5610
April	1st to 10th	Night	1 8% 3 5% 4 4 4 4 5% 7% 54%	2254
	11th to 20th	Night	3 6% 2 5% 5% 5% 5% 4 7% 8% 51%	1979
	21st to end	Night	4 7% 2 4 3 4 4 5% 6% 8% 53%	1890
May	1st to 10th	Night	3 7% 2 8% 4 5% 5% 4 7% 7% 48%	4109
	11th to 20th	Night	2 4 1 3 3 4 4 4 6% 8% 61%	4074
	21st to end	Night	3 3 1 3 3 4 4 3 6% 9% 59%	4474
June	1st to 10th	Night	3 4 2 4 4 3 4 4 6% 9% 57%	1615
	11th to 20th	Night	3 2 1 4 3 4 4 3 4 6% 66%	1600
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 69%	1673
July	1st to 10th	Night	2 2 1 4 3 3 3 3 4 5% 70%	4100
	11th to 20th	Night	2 3 1 5% 4 4 4 5% 8% 9% 55%	4100
	21st to end	Night	2 2 1 4 4 4 4 4 6% 7% 62%	4472
August	1st to 10th	Night	3 2 1 3 3 3 3 3 5% 8% 66%	4033
	11th to 20th	Night	2 3 1 5% 3 4 5% 4 6% 6% 62%	4051
	21st to end	Night	2 3 2 5% 4 5% 5% 4 5% 7% 57%	4655
September	1st to 10th	Night	4 2 1 3 2 3 3 2 6% 7% 67%	2084
	11th to 20th	Night	4 2 1 3 3 3 3 3 5% 6% 66%	2200
	21st to end	Night	5% 3 1 4 2 2 2 3 4 6% 69%	2200
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 4 74%	3814
	11th to 20th	Night	4 4 2 5% 3 3 5% 3 6% 6% 60%	3898
	21st to end	Night	1 4 2 5% 2 3 3 3 6% 8% 62%	4252
November	1st to 10th	Night	1 5% 2 6% 4 3 4 3 6% 8% 59%	2607
	11th to 20th	Night	1 4 2 5% 3 3 3 4 7% 8% 58%	2730
	21st to end	Night	2 6% 2 6% 4 4 4 4 5% 8% 55%	2922
December	1st to 10th	Night	1 4 1 5% 3 3 3 3 4 6% 67%	4710
	11th to 20th	Night	1 6% 2 5% 5% 5% 5% 5% 7% 9% 51%	5321
	21st to end	Night	1 7% 4 8% 6% 4 5% 5% 7% 9% 44%	6846

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% 9% 17% 22% 11% 2	5321
	11th to 20th	Day	30% 5% 11% 23% 23% 8%	5340
	21st to end	Day	28% 3 15% 22% 23% 9%	5844
February	1st to 10th	Day	43% 6% 14% 21% 11% 5%	1890
	11th to 20th	Day	45% 6% 12% 22% 13% 2	1886
	21st to end	Day	45% 5% 10% 25% 12% 4	1730
March	1st to 10th	Day	42% 5% 10% 19% 16% 8%	5021
	11th to 20th	Day	37% 6% 15% 28% 13% 2	5110
	21st to end	Day	50% 6% 17% 19% 7% 1	5607
April	1st to 10th	Day	38% 5% 14% 22% 17% 3	2364
	11th to 20th	Day	41% 6% 11% 23% 17% 1	2588
	21st to end	Day	39% 6% 10% 28% 16% 1	2730
May	1st to 10th	Day	36% 7% 11% 22% 20% 3	5894
	11th to 20th	Day	31% 7% 9% 29% 22% 1	5844
	21st to end	Day	31% 6% 9% 24% 28% 2	6424
June	1st to 10th	Day	25% 6% 8% 25% 29% 7%	2780
	11th to 20th	Day	21% 5% 6% 18% 30% 19%	2800
	21st to end	Day	19% 4 3 14% 31% 29%	2717
July	1st to 10th	Day	18% 3 4 8% 17% 51%	5816
	11th to 20th	Day	23% 4 6% 14% 27% 25%	5811
	21st to end	Day	19% 5% 7% 13% 27% 30%	6217
August	1st to 10th	Day	23% 5% 8% 23% 22% 19%	4208
	11th to 20th	Day	21% 5% 8% 17% 30% 20%	4197
	21st to end	Day	23% 5% 7% 15% 27% 23%	4551
September	1st to 10th	Day	23% 5% 7% 18% 26% 22%	2312
	11th to 20th	Day	26% 5% 7% 18% 27% 17%	2200
	21st to end	Day	21% 4 5% 24% 34% 12%	2200
October	1st to 10th	Day	22% 4 4 16% 38% 16%	3379
	11th to 20th	Day	30% 4 5% 31% 26% 4	3250
	21st to end	Day	25% 4 10% 27% 29% 4	3548
November	1st to 10th	Day	29% 6% 12% 27% 21% 5%	1908
	11th to 20th	Day	30% 4 16% 28% 20% 2	1883
	21st to end	Day	30% 5% 13% 30% 17% 6%	1680
December	1st to 10th	Day	21% 4 12% 36% 22% 4	2700
	11th to 20th	Day	32% 10% 15% 25% 16% 2	3104
	21st to end	Day	39% 8% 11% 17% 18% 7%	4403
January	1st to 10th	Night	40% 7% 15% 19% 17% 3	7605
	11th to 20th	Night	29% 4 10% 24% 25% 9%	7650
	21st to end	Night	27% 4 14% 21% 25% 9%	8370
February	1st to 10th	Night	34% 6% 17% 26% 13% 4	2730
	11th to 20th	Night	35% 7% 13% 24% 19% 3	2626
	21st to end	Night	34% 5% 13% 26% 14% 7%	2076
March	1st to 10th	Night	34% 4 12% 25% 19% 6%	5082
	11th to 20th	Night	33% 7% 15% 29% 14% 3	5110
	21st to end	Night	31% 7% 19% 27% 15% 1	5610
April	1st to 10th	Night	31% 5% 15% 23% 21% 6%	2254
	11th to 20th	Night	28% 6% 13% 30% 20% 3	1979
	21st to end	Night	28% 6% 13% 32% 19% 1	1890
May	1st to 10th	Night	33% 6% 10% 23% 25% 3	4106
	11th to 20th	Night	20% 6% 9% 34% 27% 4	4075
	21st to end	Night	22% 4 9% 33% 31% 2	4474
June	1st to 10th	Night	22% 7% 10% 25% 29% 7%	1615
	11th to 20th	Night	20% 5% 7% 17% 31% 20%	1600
	21st to end	Night	16% 3 4 15% 28% 33%	1673
July	1st to 10th	Night	18% 3 4 8% 14% 54%	4055
	11th to 20th	Night	23% 4 6% 13% 24% 30%	4046
	21st to end	Night	20% 4 8% 13% 26% 29%	4344
August	1st to 10th	Night	22% 4 9% 23% 21% 21%	2928
	11th to 20th	Night	25% 4 9% 16% 25% 20%	2928
	21st to end	Night	17% 5% 9% 16% 26% 26%	3355
September	1st to 10th	Night	17% 5% 7% 20% 28% 23%	2084
	11th to 20th	Night	18% 5% 8% 23% 28% 18%	2200
	21st to end	Night	19% 4 5% 19% 38% 15%	2200
October	1st to 10th	Night	16% 3 6% 19% 34% 22%	3814
	11th to 20th	Night	24% 4 6% 32% 27% 7%	3898
	21st to end	Night	21% 4 9% 33% 30% 3	4252
November	1st to 10th	Night	25% 5% 13% 27% 24% 6%	2607
	11th to 20th	Night	25% 5% 14% 33% 19% 3	2730
	21st to end	Night	30% 5% 12% 26% 21% 7%	2922
December	1st to 10th	Night	20% 4 12% 36% 22% 6%	4710
	11th to 20th	Night	29% 7% 17% 31% 14% 2	5322
	21st to end	Night	37% 7% 16% 21% 13% 6%	6846

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	22% 22% 29% 18% 8% 1	330
	11th to 20th	Day	19% 24% 31% 16% 8% 2	330
	21st to end	Day	15% 29% 34% 17% 4 1	363
February	1st to 10th	Day	24% 31% 33% 8% 4 1	330
	11th to 20th	Day	17% 37% 27% 14% 4 1	362
	21st to end	Day	20% 34% 30% 12% 3	446
March	1st to 10th	Day	19% 31% 30% 15% 5% 1	540
	11th to 20th	Day	19% 28% 29% 20% 3 1	540
	21st to end	Day	18% 32% 36% 12% 3	594
April	1st to 10th	Day	20% 24% 31% 19% 5% 2	540
	11th to 20th	Day	20% 28% 34% 12% 5% 1	532
	21st to end	Day	21% 27% 29% 17% 5% 1	540
May	1st to 10th	Day	19% 24% 33% 17% 6% 1	508
	11th to 20th	Day	19% 20% 35% 17% 7% 2	528
	21st to end	Day	15% 19% 31% 21% 11% 2	573
June	1st to 10th	Day	7% 16% 35% 24% 15% 3	710
	11th to 20th	Day	10% 19% 37% 22% 11% 1	730
	21st to end	Day	8% 14% 41% 25% 10% 2	647
July	1st to 10th	Day	5% 11% 38% 33% 10% 2	526
	11th to 20th	Day	5% 10% 44% 28% 10% 3	524
	21st to end	Day	6% 8% 37% 30% 16% 4	575
August	1st to 10th	Day	6% 14% 39% 27% 11% 3	527
	11th to 20th	Day	5% 10% 35% 34% 12% 4	517
	21st to end	Day	5% 13% 33% 32% 12% 6%	583
September	1st to 10th	Day	6% 13% 30% 30% 13% 8%	530
	11th to 20th	Day	9% 19% 33% 24% 12% 4	530
	21st to end	Day	9% 15% 29% 29% 14% 3	530
October	1st to 10th	Day	13% 17% 29% 23% 14% 5%	400
	11th to 20th	Day	14% 22% 28% 19% 14% 3	330
	21st to end	Day	15% 23% 33% 20% 9%	363
November	1st to 10th	Day	15% 26% 29% 17% 11% 2	330
	11th to 20th	Day	12% 21% 36% 21% 6% 3	330
	21st to end	Day	13% 22% 31% 21% 11% 2	330
December	1st to 10th	Day	14% 25% 29% 19% 9% 3	330
	11th to 20th	Day	12% 27% 33% 23% 4 1	330
	21st to end	Day	21% 26% 27% 20% 5% 1	363
January	1st to 10th	Night	10% 20% 28% 27% 11% 2	840
	11th to 20th	Night	10% 19% 32% 28% 8% 3	840
	21st to end	Night	7% 21% 35% 27% 9% 2	924
February	1st to 10th	Night	11% 25% 34% 21% 8% 2	840
	11th to 20th	Night	9% 25% 34% 23% 7% 1	824
	21st to end	Night	12% 21% 35% 26% 6% 1	692
March	1st to 10th	Night	10% 20% 33% 28% 8% 2	840
	11th to 20th	Night	10% 16% 29% 31% 13% 2	840
	21st to end	Night	11% 22% 31% 27% 7% 1	924
April	1st to 10th	Night	11% 19% 31% 28% 10% 1	784
	11th to 20th	Night	11% 20% 33% 28% 7%	623
	21st to end	Night	12% 22% 28% 24% 13% 1	630
May	1st to 10th	Night	8% 17% 30% 30% 14% 1	603
	11th to 20th	Night	8% 10% 25% 36% 19% 2	591
	21st to end	Night	9% 14% 25% 30% 19% 2	650
June	1st to 10th	Night	6% 12% 24% 36% 21% 2	600
	11th to 20th	Night	6% 15% 29% 36% 13% 1	600
	21st to end	Night	3 6% 27% 39% 22% 3	600
July	1st to 10th	Night	4 5% 16% 40% 32% 3	585
	11th to 20th	Night	6% 3 14% 42% 31% 3	582
	21st to end	Night	4 2 9% 44% 38% 4	657
August	1st to 10th	Night	6% 3 16% 45% 28% 2	597
	11th to 20th	Night	5% 3 16% 42% 30% 4	594
	21st to end	Night	3 5% 16% 39% 33% 3	660
September	1st to 10th	Night	5% 4 18% 38% 30% 6%	684
	11th to 20th	Night	6% 4 21% 34% 29% 7%	800
	21st to end	Night	7% 9% 18% 32% 27% 8%	800
October	1st to 10th	Night	7% 11% 28% 30% 21% 3	800
	11th to 20th	Night	8% 15% 24% 31% 18% 4	800
	21st to end	Night	7% 17% 26% 31% 16% 3	880
November	1st to 10th	Night	7% 15% 29% 31% 16% 2	820
	11th to 20th	Night	7% 21% 30% 29% 10% 3	840
	21st to end	Night	10% 19% 26% 32% 11% 3	1032
December	1st to 10th	Night	10% 20% 33% 26% 10% 1	1050
	11th to 20th	Night	10% 20% 34% 27% 8% 1	1050
	21st to end	Night	13% 21% 37% 21% 7% 1	1029

Page generated at 2026-04-29 00:21:47. Version ac07

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