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 2025-01-07.

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 4 4 6% 7% 51%	108715
	Night	2 5% 2 6% 4 4 4 4 6% 7% 54%	109088
Transparency	Day	32% 5% 10% 21% 20% 11%	108480
	Night	29% 5% 12% 24% 20% 10%	108912
Seeing	Day	12% 21% 33% 22% 9% 2	15326
	Night	8% 15% 27% 31% 17% 3	25727

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	1 5% 3 13% 7% 5% 5% 5% 7% 8% 40%	2912
	11th to 20th	Day	1 6% 4 19% 9% 5% 5% 4 5% 6% 37%	2860
	21st to end	Day	1 13% 7% 10% 4 4 2 2 4 5% 48%	3146
February	1st to 10th	Day	2 9% 5% 11% 6% 5% 4 4 6% 7% 41%	1710
	11th to 20th	Day	3 9% 4 12% 5% 4 4 4 7% 8% 40%	1693
	21st to end	Day	1 11% 5% 14% 7% 5% 5% 4 6% 5% 37%	1570
March	1st to 10th	Day	2 10% 7% 13% 6% 4 4 4 6% 7% 37%	3415
	11th to 20th	Day	1 11% 5% 8% 4 4 5% 5% 6% 8% 44%	3490
	21st to end	Day	3 18% 7% 13% 6% 6% 5% 5% 5% 6% 26%	3825
April	1st to 10th	Day	2 10% 3 8% 6% 5% 5% 4 7% 8% 42%	2138
	11th to 20th	Day	3 9% 3 11% 6% 5% 6% 5% 6% 6% 40%	2335
	21st to end	Day	4 8% 3 7% 5% 6% 5% 4 5% 7% 45%	2470
May	1st to 10th	Day	6% 10% 4 9% 5% 5% 6% 4 7% 7% 38%	4110
	11th to 20th	Day	4 6% 2 5% 4 4 4 4 6% 8% 51%	4071
	21st to end	Day	5% 7% 2 6% 5% 5% 5% 5% 6% 8% 46%	4477
June	1st to 10th	Day	4 5% 2 4 4 5% 5% 4 6% 7% 55%	2641
	11th to 20th	Day	4 3 2 5% 3 4 4 3 5% 6% 61%	2660
	21st to end	Day	3 3 1 3 3 5% 4 4 5% 6% 64%	2581
July	1st to 10th	Day	2 3 1 3 2 3 2 2 4 5% 72%	4110
	11th to 20th	Day	3 4 2 5% 5% 5% 6% 5% 8% 9% 48%	4110
	21st to end	Day	4 3 1 5% 4 4 5% 4 6% 7% 57%	4454
August	1st to 10th	Day	3 2 1 5% 4 5% 5% 3 6% 7% 59%	4092
	11th to 20th	Day	2 3 1 4 3 4 5% 4 6% 6% 62%	4028
	21st to end	Day	3 3 1 4 4 4 5% 3 6% 6% 61%	4412
September	1st to 10th	Day	5% 4 1 4 4 4 4 3 5% 6% 62%	2197
	11th to 20th	Day	4 4 1 5% 3 4 4 3 4 6% 61%	2090
	21st to end	Day	4 5% 1 4 3 3 3 2 4 4 66%	2090
October	1st to 10th	Day	5% 5% 1 4 3 2 3 2 4 4 67%	3276
	11th to 20th	Day	6% 7% 2 6% 4 3 3 3 4 6% 56%	3150
	21st to end	Day	2 6% 2 4 3 4 4 3 5% 6% 61%	3438
November	1st to 10th	Day	3 9% 2 6% 4 3 4 3 6% 8% 52%	1816
	11th to 20th	Day	2 6% 2 5% 4 3 4 4 7% 8% 54%	1794
	21st to end	Day	1 7% 4 7% 5% 3 4 4 5% 9% 51%	1600
December	1st to 10th	Day	1 4 2 5% 3 3 4 3 5% 8% 63%	2620
	11th to 20th	Day	1 5% 3 7% 5% 5% 6% 6% 9% 11% 44%	3026
	21st to end	Day	1 7% 4 10% 6% 5% 6% 5% 8% 8% 41%	4308
January	1st to 10th	Night	1 5% 3 13% 9% 5% 5% 4 5% 7% 43%	4175
	11th to 20th	Night	5% 4 17% 10% 7% 5% 4 6% 7% 35%	4110
	21st to end	Night	1 9% 5% 11% 5% 3 3 4 6% 7% 45%	4521
February	1st to 10th	Night	2 7% 3 7% 5% 4 4 5% 9% 7% 48%	2470
	11th to 20th	Night	1 7% 3 7% 5% 4 5% 5% 6% 9% 48%	2369
	21st to end	Night	2 6% 3 8% 5% 6% 6% 3 7% 7% 47%	1884
March	1st to 10th	Night	1 5% 4 9% 5% 5% 5% 4 7% 8% 46%	3448
	11th to 20th	Night	1 7% 4 6% 4 5% 5% 4 6% 9% 49%	3490
	21st to end	Night	2 12% 4 9% 5% 4 5% 4 6% 7% 42%	3828
April	1st to 10th	Night	2 8% 3 6% 4 4 4 4 6% 7% 53%	2040
	11th to 20th	Night	3 6% 2 5% 5% 5% 5% 5% 8% 8% 50%	1789
	21st to end	Night	4 7% 2 5% 3 4 4 4 6% 7% 54%	1710
May	1st to 10th	Night	3 8% 2 9% 5% 5% 6% 5% 7% 7% 42%	2860
	11th to 20th	Night	3 4 2 3 3 4 4 4 6% 7% 60%	2834
	21st to end	Night	4 4 2 4 4 4 5% 3 6% 9% 55%	3110
June	1st to 10th	Night	3 4 2 4 4 4 4 4 6% 9% 56%	1534
	11th to 20th	Night	3 2 1 4 3 4 4 3 4 6% 65%	1520
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 68%	1589
July	1st to 10th	Night	3 3 1 4 3 3 3 3 3 5% 71%	2860
	11th to 20th	Night	2 3 1 4 5% 5% 5% 5% 9% 10% 49%	2860
	21st to end	Night	2 3 2 6% 4 5% 5% 5% 6% 6% 56%	3109
August	1st to 10th	Night	4 2 1 4 3 4 4 4 6% 8% 59%	2847
	11th to 20th	Night	2 3 1 5% 4 4 6% 4 6% 6% 58%	2811
	21st to end	Night	2 3 2 3 3 3 3 3 4 6% 68%	3253
September	1st to 10th	Night	3 2 1 3 2 3 3 3 6% 6% 67%	1980
	11th to 20th	Night	4 2 1 3 3 3 3 3 5% 6% 66%	2090
	21st to end	Night	5% 3 1 4 2 2 2 3 3 5% 69%	2090
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 4 74%	3697
	11th to 20th	Night	3 4 2 5% 3 3 5% 3 6% 6% 60%	3778
	21st to end	Night	1 4 2 5% 2 3 3 3 7% 8% 62%	4120
November	1st to 10th	Night	1 5% 2 6% 4 3 4 3 6% 8% 57%	2480
	11th to 20th	Night	1 4 2 5% 4 3 3 4 7% 8% 59%	2600
	21st to end	Night	2 6% 2 6% 5% 4 4 4 5% 8% 54%	2783
December	1st to 10th	Night	1 4 1 5% 3 2 3 3 4 6% 67%	4570
	11th to 20th	Night	1 6% 2 5% 5% 5% 5% 5% 7% 9% 51%	5181
	21st to end	Night	1 8% 4 8% 6% 4 5% 5% 7% 9% 43%	6698

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	42% 8% 17% 20% 12% 1	2913
	11th to 20th	Day	51% 7% 14% 17% 9% 2	2860
	21st to end	Day	42% 3 20% 22% 12% 2	3146
February	1st to 10th	Day	45% 6% 14% 20% 10% 4	1710
	11th to 20th	Day	43% 5% 13% 23% 14% 2	1702
	21st to end	Day	48% 6% 10% 22% 11% 2	1570
March	1st to 10th	Day	46% 6% 11% 21% 11% 5%	3415
	11th to 20th	Day	38% 7% 17% 28% 9% 2	3490
	21st to end	Day	58% 5% 14% 17% 5% 1	3825
April	1st to 10th	Day	39% 5% 15% 20% 16% 4	2138
	11th to 20th	Day	43% 7% 12% 22% 16% 1	2338
	21st to end	Day	38% 6% 11% 29% 15% 1	2470
May	1st to 10th	Day	41% 7% 10% 20% 18% 3	4110
	11th to 20th	Day	28% 6% 10% 34% 21% 2	4074
	21st to end	Day	33% 5% 10% 25% 24% 2	4477
June	1st to 10th	Day	26% 6% 8% 25% 28% 7%	2641
	11th to 20th	Day	22% 5% 7% 18% 30% 18%	2660
	21st to end	Day	19% 5% 4 14% 29% 29%	2581
July	1st to 10th	Day	16% 3 4 9% 14% 55%	4046
	11th to 20th	Day	27% 5% 7% 16% 23% 22%	4041
	21st to end	Day	21% 6% 7% 14% 21% 30%	4314
August	1st to 10th	Day	23% 5% 8% 23% 22% 19%	4078
	11th to 20th	Day	21% 5% 8% 17% 30% 20%	4067
	21st to end	Day	22% 5% 7% 15% 27% 24%	4411
September	1st to 10th	Day	23% 5% 7% 17% 26% 23%	2197
	11th to 20th	Day	26% 4 7% 18% 27% 18%	2090
	21st to end	Day	21% 4 4 24% 35% 11%	2090
October	1st to 10th	Day	22% 4 4 16% 38% 15%	3276
	11th to 20th	Day	31% 4 5% 30% 26% 4	3150
	21st to end	Day	25% 4 10% 28% 28% 5%	3438
November	1st to 10th	Day	31% 6% 12% 26% 21% 5%	1816
	11th to 20th	Day	28% 4 16% 28% 21% 2	1794
	21st to end	Day	32% 5% 12% 28% 17% 6%	1600
December	1st to 10th	Day	21% 4 11% 36% 23% 4	2620
	11th to 20th	Day	32% 10% 16% 25% 16% 1	3024
	21st to end	Day	39% 8% 11% 17% 18% 7%	4308
January	1st to 10th	Night	43% 5% 16% 17% 16% 2	4175
	11th to 20th	Night	51% 5% 13% 17% 10% 3	4110
	21st to end	Night	40% 5% 19% 22% 11% 3	4521
February	1st to 10th	Night	36% 6% 19% 24% 12% 3	2470
	11th to 20th	Night	34% 7% 14% 23% 20% 2	2370
	21st to end	Night	37% 5% 14% 25% 14% 5%	1884
March	1st to 10th	Night	35% 5% 14% 28% 15% 3	3448
	11th to 20th	Night	31% 6% 18% 31% 11% 3	3490
	21st to end	Night	41% 6% 15% 22% 14% 2	3828
April	1st to 10th	Night	32% 5% 16% 22% 18% 6%	2040
	11th to 20th	Night	29% 6% 14% 31% 18% 2	1789
	21st to end	Night	29% 5% 14% 32% 19% 1	1710
May	1st to 10th	Night	37% 6% 10% 22% 22% 2	2860
	11th to 20th	Night	20% 6% 10% 33% 25% 5%	2835
	21st to end	Night	25% 5% 11% 31% 26% 3	3110
June	1st to 10th	Night	22% 7% 11% 25% 28% 6%	1534
	11th to 20th	Night	20% 5% 7% 18% 31% 19%	1520
	21st to end	Night	17% 3 5% 16% 26% 34%	1589
July	1st to 10th	Night	17% 3 4 9% 13% 54%	2815
	11th to 20th	Night	25% 5% 8% 15% 24% 24%	2806
	21st to end	Night	25% 6% 9% 16% 18% 26%	3011
August	1st to 10th	Night	23% 4 10% 23% 21% 19%	2838
	11th to 20th	Night	25% 5% 9% 16% 24% 20%	2838
	21st to end	Night	16% 5% 9% 16% 27% 27%	3253
September	1st to 10th	Night	17% 4 7% 19% 28% 24%	1980
	11th to 20th	Night	18% 5% 9% 23% 27% 19%	2090
	21st to end	Night	19% 3 4 19% 39% 15%	2090
October	1st to 10th	Night	16% 3 6% 19% 35% 22%	3697
	11th to 20th	Night	24% 4 6% 32% 27% 7%	3778
	21st to end	Night	21% 4 9% 33% 29% 3	4120
November	1st to 10th	Night	26% 5% 13% 26% 24% 6%	2480
	11th to 20th	Night	24% 5% 15% 33% 20% 3	2600
	21st to end	Night	31% 5% 11% 24% 22% 7%	2783
December	1st to 10th	Night	20% 4 12% 36% 22% 7%	4570
	11th to 20th	Night	30% 7% 17% 31% 14% 1	5182
	21st to end	Night	37% 7% 16% 21% 13% 6%	6698

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	20% 22% 28% 20% 9% 1	288
	11th to 20th	Day	17% 24% 33% 17% 8% 1	270
	21st to end	Day	13% 30% 34% 18% 5% 1	297
February	1st to 10th	Day	21% 34% 34% 8% 3	270
	11th to 20th	Day	17% 37% 26% 14% 5% 1	298
	21st to end	Day	18% 36% 32% 12% 2 1	382
March	1st to 10th	Day	17% 33% 30% 15% 5%	460
	11th to 20th	Day	15% 28% 31% 23% 3 1	460
	21st to end	Day	19% 31% 36% 12% 2	506
April	1st to 10th	Day	21% 24% 31% 18% 4 2	460
	11th to 20th	Day	20% 29% 35% 12% 4 1	452
	21st to end	Day	20% 26% 29% 19% 5% 1	460
May	1st to 10th	Day	21% 25% 34% 14% 5% 1	463
	11th to 20th	Day	16% 20% 36% 17% 8% 2	488
	21st to end	Day	16% 19% 31% 20% 11% 2	529
June	1st to 10th	Day	7% 16% 35% 23% 15% 3	661
	11th to 20th	Day	10% 19% 35% 22% 12% 1	680
	21st to end	Day	6% 14% 43% 25% 10% 2	601
July	1st to 10th	Day	5% 11% 37% 34% 11% 2	486
	11th to 20th	Day	5% 10% 42% 29% 11% 3	484
	21st to end	Day	6% 7% 35% 31% 17% 4	531
August	1st to 10th	Day	6% 11% 39% 29% 12% 3	487
	11th to 20th	Day	5% 11% 35% 34% 11% 4	477
	21st to end	Day	4 13% 33% 32% 12% 6%	539
September	1st to 10th	Day	6% 14% 29% 29% 13% 8%	490
	11th to 20th	Day	9% 18% 33% 23% 12% 4	490
	21st to end	Day	9% 17% 28% 28% 14% 3	490
October	1st to 10th	Day	13% 16% 28% 22% 15% 5%	367
	11th to 20th	Day	12% 21% 28% 20% 16% 3	300
	21st to end	Day	14% 24% 32% 20% 8%	330
November	1st to 10th	Day	15% 26% 28% 17% 11% 2	300
	11th to 20th	Day	11% 21% 37% 21% 6% 3	300
	21st to end	Day	12% 22% 30% 22% 11% 2	300
December	1st to 10th	Day	12% 23% 31% 21% 10% 3	300
	11th to 20th	Day	11% 27% 33% 24% 4 1	300
	21st to end	Day	20% 26% 28% 21% 4 1	330
January	1st to 10th	Night	10% 19% 28% 28% 12% 2	784
	11th to 20th	Night	10% 19% 30% 30% 8% 3	760
	21st to end	Night	7% 20% 32% 28% 10% 2	836
February	1st to 10th	Night	10% 26% 33% 22% 8% 2	760
	11th to 20th	Night	8% 26% 33% 25% 8% 1	744
	21st to end	Night	12% 20% 35% 26% 6% 1	628
March	1st to 10th	Night	8% 20% 32% 29% 9% 2	760
	11th to 20th	Night	7% 15% 30% 32% 14% 2	760
	21st to end	Night	12% 22% 30% 27% 8% 1	836
April	1st to 10th	Night	11% 20% 32% 27% 10% 1	710
	11th to 20th	Night	10% 20% 32% 29% 8%	563
	21st to end	Night	12% 21% 27% 24% 14% 2	570
May	1st to 10th	Night	9% 18% 29% 30% 13% 1	570
	11th to 20th	Night	8% 7% 26% 37% 20% 2	561
	21st to end	Night	10% 14% 25% 30% 19% 2	617
June	1st to 10th	Night	6% 12% 23% 36% 21% 2	570
	11th to 20th	Night	6% 15% 29% 35% 14% 1	570
	21st to end	Night	2 5% 28% 40% 22% 3	570
July	1st to 10th	Night	4 5% 16% 38% 33% 3	555
	11th to 20th	Night	7% 3 13% 42% 33% 3	552
	21st to end	Night	4 2 9% 42% 39% 4	624
August	1st to 10th	Night	7% 3 13% 46% 30% 2	567
	11th to 20th	Night	5% 3 17% 40% 31% 4	564
	21st to end	Night	4 4 16% 39% 34% 3	627
September	1st to 10th	Night	4 4 18% 36% 31% 6%	650
	11th to 20th	Night	6% 4 20% 32% 30% 7%	760
	21st to end	Night	7% 9% 17% 32% 27% 8%	760
October	1st to 10th	Night	7% 11% 26% 29% 22% 4	760
	11th to 20th	Night	6% 15% 24% 32% 19% 4	760
	21st to end	Night	7% 17% 25% 31% 17% 3	836
November	1st to 10th	Night	7% 15% 29% 30% 17% 2	780
	11th to 20th	Night	7% 21% 29% 29% 11% 3	800
	21st to end	Night	9% 20% 25% 32% 11% 3	983
December	1st to 10th	Night	9% 20% 33% 27% 11% 1	1000
	11th to 20th	Night	9% 20% 34% 28% 8% 1	1000
	21st to end	Night	13% 21% 37% 21% 7% 1	980

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