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 2024-01-17.

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	4 6% 3 6% 6% 3 5% 5% 6% 7% 49%	74650
	Night	3 5% 3 5% 5% 3 5% 5% 6% 8% 53%	75186
Transparency	Day	34% 6% 11% 21% 20% 9%	74375
	Night	30% 5% 13% 24% 19% 9%	74982
Seeing	Day	12% 21% 33% 22% 9% 2	14007
	Night	8% 15% 26% 31% 17% 3	24423

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 8% 3 8% 6% 3 5% 6% 6% 8% 46%	1708
	11th to 20th	Day	1 6% 3 10% 8% 4 4 5% 6% 7% 47%	1674
	21st to end	Day	2 9% 4 11% 6% 3 5% 4 5% 5% 46%	1782
February	1st to 10th	Day	1 8% 5% 9% 7% 4 5% 5% 6% 8% 43%	1620
	11th to 20th	Day	3 8% 5% 11% 6% 3 5% 5% 7% 8% 40%	1602
	21st to end	Day	1 9% 6% 14% 8% 4 5% 5% 5% 6% 36%	1480
March	1st to 10th	Day	3 9% 5% 9% 8% 4 5% 6% 7% 7% 37%	1962
	11th to 20th	Day	2 9% 5% 8% 7% 3 5% 5% 7% 8% 41%	1980
	21st to end	Day	3 11% 5% 10% 8% 4 6% 6% 5% 6% 35%	2178
April	1st to 10th	Day	3 10% 4 7% 6% 3 5% 5% 7% 8% 42%	2025
	11th to 20th	Day	3 9% 4 10% 8% 4 6% 6% 6% 6% 39%	2210
	21st to end	Day	5% 7% 4 7% 6% 4 5% 5% 5% 7% 45%	2340
May	1st to 10th	Day	6% 8% 3 6% 6% 4 6% 5% 6% 7% 41%	2340
	11th to 20th	Day	5% 8% 3 6% 6% 4 6% 5% 6% 8% 42%	2301
	21st to end	Day	7% 9% 3 7% 7% 4 6% 6% 7% 8% 37%	2530
June	1st to 10th	Day	5% 4 2 4 4 3 5% 4 6% 7% 55%	2502
	11th to 20th	Day	4 3 2 4 4 3 4 4 5% 6% 61%	2520
	21st to end	Day	3 3 1 3 3 3 5% 4 5% 6% 63%	2446
July	1st to 10th	Day	4 4 2 5% 4 4 4 5% 7% 8% 53%	2340
	11th to 20th	Day	5% 5% 3 5% 6% 3 5% 5% 6% 7% 51%	2340
	21st to end	Day	6% 4 3 5% 6% 4 6% 6% 7% 8% 46%	2545
August	1st to 10th	Day	5% 3 2 5% 6% 4 6% 5% 7% 7% 50%	2328
	11th to 20th	Day	4 4 1 5% 4 3 4 5% 5% 6% 59%	2299
	21st to end	Day	4 3 2 4 5% 3 6% 5% 6% 7% 55%	2517
September	1st to 10th	Day	5% 3 1 4 4 3 4 4 4 6% 62%	2082
	11th to 20th	Day	4 4 2 5% 4 3 5% 4 4 5% 60%	1980
	21st to end	Day	5% 5% 2 4 3 2 3 3 4 4 66%	1980
October	1st to 10th	Day	9% 8% 2 5% 5% 2 4 3 5% 5% 53%	1864
	11th to 20th	Day	4 6% 2 5% 4 2 3 4 4 6% 61%	1800
	21st to end	Day	2 5% 2 4 4 3 4 4 5% 6% 60%	1980
November	1st to 10th	Day	3 8% 3 5% 5% 2 3 4 5% 8% 53%	1724
	11th to 20th	Day	2 5% 3 5% 5% 2 4 5% 7% 8% 54%	1705
	21st to end	Day	1 6% 4 6% 5% 2 5% 4 5% 9% 51%	1520
December	1st to 10th	Day	1 6% 3 8% 7% 4 6% 5% 6% 8% 46%	1520
	11th to 20th	Day	1 7% 5% 9% 7% 4 6% 6% 7% 8% 39%	1926
	21st to end	Day	2 6% 5% 10% 6% 3 5% 5% 6% 8% 45%	3000
January	1st to 10th	Night	2 7% 4 7% 7% 4 5% 5% 7% 10% 44%	2457
	11th to 20th	Night	1 6% 3 6% 7% 4 5% 4 8% 9% 48%	2430
	21st to end	Night	1 6% 3 8% 6% 3 5% 5% 7% 9% 46%	2574
February	1st to 10th	Night	1 5% 3 6% 5% 3 5% 6% 9% 8% 50%	2340
	11th to 20th	Night	2 6% 4 6% 5% 3 5% 6% 6% 9% 49%	2240
	21st to end	Night	2 5% 4 7% 6% 4 7% 5% 7% 7% 46%	1776
March	1st to 10th	Night	2 6% 4 7% 5% 4 6% 4 8% 11% 44%	1998
	11th to 20th	Night	2 7% 4 5% 5% 3 5% 5% 5% 9% 49%	1980
	21st to end	Night	3 7% 3 6% 6% 3 5% 6% 7% 8% 47%	2178
April	1st to 10th	Night	2 8% 4 5% 5% 3 5% 5% 6% 7% 52%	1933
	11th to 20th	Night	3 5% 2 5% 5% 4 6% 6% 8% 8% 49%	1694
	21st to end	Night	4 6% 2 4 4 3 5% 5% 6% 8% 54%	1620
May	1st to 10th	Night	4 5% 2 6% 5% 4 6% 6% 8% 8% 46%	1620
	11th to 20th	Night	4 5% 2 3 5% 4 5% 6% 6% 9% 53%	1594
	21st to end	Night	5% 4 2 5% 6% 3 6% 5% 7% 10% 46%	1746
June	1st to 10th	Night	3 4 2 4 4 2 5% 5% 6% 9% 57%	1454
	11th to 20th	Night	4 2 1 3 3 3 5% 4 4 5% 65%	1440
	21st to end	Night	2 2 1 3 3 2 4 3 5% 8% 68%	1505
July	1st to 10th	Night	3 3 2 5% 4 4 5% 5% 6% 8% 55%	1620
	11th to 20th	Night	4 4 2 4 6% 3 5% 6% 7% 9% 49%	1620
	21st to end	Night	3 4 2 6% 6% 3 6% 7% 7% 9% 49%	1773
August	1st to 10th	Night	5% 3 1 4 4 4 5% 5% 6% 8% 54%	1611
	11th to 20th	Night	3 3 1 4 4 3 5% 5% 6% 8% 58%	1602
	21st to end	Night	3 2 2 3 4 3 5% 5% 5% 8% 61%	1837
September	1st to 10th	Night	4 2 1 3 3 2 3 3 6% 6% 67%	1875
	11th to 20th	Night	4 2 1 3 3 2 3 4 5% 6% 66%	1980
	21st to end	Night	6% 3 1 3 3 2 2 3 3 5% 69%	1980
October	1st to 10th	Night	6% 5% 2 4 4 2 4 3 5% 5% 60%	2096
	11th to 20th	Night	2 4 1 4 3 3 4 4 5% 6% 64%	2160
	21st to end	Night	2 3 2 4 4 2 4 4 6% 8% 61%	2376
November	1st to 10th	Night	2 5% 2 6% 4 2 4 4 6% 8% 57%	2352
	11th to 20th	Night	1 3 2 5% 4 2 4 5% 7% 8% 59%	2470
	21st to end	Night	2 6% 3 6% 5% 3 4 5% 6% 8% 54%	2643
December	1st to 10th	Night	1 6% 2 8% 5% 3 5% 5% 5% 8% 53%	2660
	11th to 20th	Night	2 7% 3 6% 7% 4 5% 7% 7% 10% 42%	3271
	21st to end	Night	1 6% 4 8% 8% 3 6% 6% 6% 9% 43%	4681

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	37% 7% 18% 24% 12% 1	1709
	11th to 20th	Day	39% 7% 15% 20% 15% 4	1674
	21st to end	Day	42% 5% 16% 24% 9% 4	1782
February	1st to 10th	Day	43% 7% 14% 21% 11% 4	1620
	11th to 20th	Day	43% 5% 13% 22% 14% 3	1611
	21st to end	Day	50% 6% 10% 22% 10% 2	1480
March	1st to 10th	Day	44% 6% 14% 24% 10% 2	1962
	11th to 20th	Day	40% 6% 17% 22% 12% 3	1980
	21st to end	Day	49% 6% 15% 21% 8% 2	2178
April	1st to 10th	Day	40% 5% 15% 20% 16% 4	2025
	11th to 20th	Day	44% 7% 12% 21% 15% 1	2213
	21st to end	Day	39% 5% 11% 29% 15% 1	2340
May	1st to 10th	Day	39% 6% 10% 24% 19% 2	2340
	11th to 20th	Day	38% 6% 9% 28% 16% 3	2304
	21st to end	Day	43% 7% 11% 21% 16% 3	2530
June	1st to 10th	Day	26% 6% 8% 24% 29% 7%	2502
	11th to 20th	Day	23% 5% 7% 18% 29% 18%	2520
	21st to end	Day	20% 5% 3 14% 29% 29%	2446
July	1st to 10th	Day	27% 5% 6% 15% 24% 22%	2276
	11th to 20th	Day	30% 5% 7% 17% 20% 21%	2271
	21st to end	Day	30% 8% 9% 15% 20% 17%	2404
August	1st to 10th	Day	29% 7% 9% 17% 19% 19%	2313
	11th to 20th	Day	25% 5% 7% 14% 29% 21%	2299
	21st to end	Day	26% 6% 7% 19% 29% 14%	2517
September	1st to 10th	Day	23% 5% 7% 16% 25% 24%	2082
	11th to 20th	Day	26% 5% 7% 18% 25% 19%	1980
	21st to end	Day	22% 4 5% 24% 35% 10%	1980
October	1st to 10th	Day	34% 5% 7% 22% 23% 9%	1864
	11th to 20th	Day	27% 4 6% 32% 25% 7%	1800
	21st to end	Day	27% 4 14% 29% 23% 4	1980
November	1st to 10th	Day	31% 7% 12% 26% 21% 4	1724
	11th to 20th	Day	29% 4 16% 28% 21% 2	1705
	21st to end	Day	32% 5% 13% 27% 16% 6%	1520
December	1st to 10th	Day	36% 7% 19% 22% 10% 5%	1520
	11th to 20th	Day	42% 6% 14% 22% 15% 1	1924
	21st to end	Day	40% 6% 12% 13% 20% 10%	3000
January	1st to 10th	Night	38% 6% 18% 23% 13% 3	2457
	11th to 20th	Night	35% 5% 17% 23% 15% 5%	2430
	21st to end	Night	36% 5% 18% 25% 10% 5%	2574
February	1st to 10th	Night	34% 6% 19% 25% 13% 3	2340
	11th to 20th	Night	34% 6% 13% 23% 20% 2	2241
	21st to end	Night	38% 5% 14% 25% 13% 5%	1776
March	1st to 10th	Night	36% 5% 18% 26% 15% 1	1998
	11th to 20th	Night	33% 5% 16% 29% 13% 4	1980
	21st to end	Night	35% 6% 19% 26% 11% 3	2178
April	1st to 10th	Night	33% 5% 16% 20% 19% 6%	1933
	11th to 20th	Night	30% 6% 14% 30% 18% 2	1694
	21st to end	Night	28% 5% 14% 32% 19% 1	1620
May	1st to 10th	Night	33% 6% 13% 28% 18% 2	1620
	11th to 20th	Night	26% 7% 13% 30% 19% 4	1595
	21st to end	Night	32% 6% 16% 28% 16% 3	1746
June	1st to 10th	Night	23% 7% 10% 26% 28% 7%	1454
	11th to 20th	Night	20% 5% 7% 18% 30% 19%	1440
	21st to end	Night	16% 3 4 16% 27% 34%	1505
July	1st to 10th	Night	26% 5% 8% 16% 23% 23%	1575
	11th to 20th	Night	28% 5% 11% 16% 19% 21%	1566
	21st to end	Night	29% 8% 13% 17% 17% 17%	1674
August	1st to 10th	Night	27% 5% 14% 18% 19% 18%	1602
	11th to 20th	Night	24% 4 9% 18% 26% 20%	1602
	21st to end	Night	21% 6% 10% 19% 28% 17%	1837
September	1st to 10th	Night	17% 5% 7% 19% 27% 25%	1875
	11th to 20th	Night	18% 5% 9% 23% 26% 19%	1980
	21st to end	Night	21% 3 4 19% 39% 14%	1980
October	1st to 10th	Night	27% 4 10% 25% 25% 10%	2096
	11th to 20th	Night	22% 4 7% 30% 30% 8%	2160
	21st to end	Night	22% 4 14% 30% 24% 5%	2376
November	1st to 10th	Night	26% 5% 14% 27% 23% 6%	2352
	11th to 20th	Night	25% 5% 15% 32% 20% 3	2470
	21st to end	Night	31% 5% 12% 24% 21% 7%	2643
December	1st to 10th	Night	32% 5% 19% 25% 14% 5%	2660
	11th to 20th	Night	38% 7% 15% 25% 13% 2	3272
	21st to end	Night	39% 6% 16% 18% 12% 9%	4681

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% 21% 27% 21% 9% 1	270
	11th to 20th	Day	16% 25% 33% 17% 8% 1	258
	21st to end	Day	13% 30% 36% 16% 4 1	264
February	1st to 10th	Day	20% 37% 32% 8% 3	240
	11th to 20th	Day	15% 39% 25% 15% 5% 1	267
	21st to end	Day	18% 36% 32% 11% 3 1	346
March	1st to 10th	Day	16% 34% 30% 15% 5%	420
	11th to 20th	Day	15% 28% 32% 23% 2 1	420
	21st to end	Day	18% 32% 36% 12% 2	462
April	1st to 10th	Day	21% 25% 29% 18% 4 2	420
	11th to 20th	Day	21% 29% 34% 11% 4 1	412
	21st to end	Day	20% 28% 26% 19% 5% 1	420
May	1st to 10th	Day	18% 25% 35% 15% 6% 1	423
	11th to 20th	Day	17% 20% 36% 17% 8% 2	448
	21st to end	Day	16% 20% 31% 21% 12% 2	485
June	1st to 10th	Day	8% 17% 34% 23% 15% 3	612
	11th to 20th	Day	10% 19% 35% 23% 12% 1	630
	21st to end	Day	6% 13% 42% 26% 11% 2	556
July	1st to 10th	Day	4 9% 37% 36% 11% 2	446
	11th to 20th	Day	5% 10% 43% 28% 10% 3	444
	21st to end	Day	6% 5% 35% 33% 17% 4	487
August	1st to 10th	Day	6% 11% 40% 28% 12% 3	447
	11th to 20th	Day	5% 10% 33% 35% 12% 5%	437
	21st to end	Day	4 11% 33% 34% 12% 6%	495
September	1st to 10th	Day	6% 15% 29% 28% 14% 8%	450
	11th to 20th	Day	8% 18% 33% 24% 12% 4	450
	21st to end	Day	10% 17% 28% 27% 15% 4	450
October	1st to 10th	Day	14% 18% 27% 22% 15% 4	334
	11th to 20th	Day	11% 23% 26% 21% 16% 3	270
	21st to end	Day	13% 25% 33% 21% 8%	297
November	1st to 10th	Day	16% 26% 27% 16% 12% 2	270
	11th to 20th	Day	10% 22% 36% 21% 7% 4	270
	21st to end	Day	12% 21% 29% 23% 12% 3	270
December	1st to 10th	Day	12% 23% 33% 19% 9% 3	270
	11th to 20th	Day	9% 29% 33% 24% 4 1	270
	21st to end	Day	18% 26% 30% 21% 5% 1	297
January	1st to 10th	Night	10% 19% 28% 28% 12% 3	760
	11th to 20th	Night	10% 19% 30% 30% 8% 3	748
	21st to end	Night	7% 21% 33% 27% 9% 2	792
February	1st to 10th	Night	9% 25% 34% 22% 8% 2	720
	11th to 20th	Night	8% 25% 32% 26% 9% 1	704
	21st to end	Night	11% 20% 35% 27% 6% 1	592
March	1st to 10th	Night	8% 20% 32% 29% 9% 2	720
	11th to 20th	Night	7% 16% 30% 32% 14% 2	720
	21st to end	Night	11% 22% 30% 27% 8% 2	792
April	1st to 10th	Night	10% 20% 31% 27% 10% 1	673
	11th to 20th	Night	10% 20% 32% 28% 9%	533
	21st to end	Night	11% 22% 26% 24% 14% 2	540
May	1st to 10th	Night	8% 17% 30% 31% 14% 1	540
	11th to 20th	Night	9% 7% 24% 36% 21% 2	531
	21st to end	Night	9% 14% 24% 31% 20% 2	584
June	1st to 10th	Night	6% 13% 23% 35% 21% 2	540
	11th to 20th	Night	6% 16% 27% 35% 14% 1	540
	21st to end	Night	2 5% 28% 39% 24% 3	540
July	1st to 10th	Night	4 4 14% 39% 35% 3	525
	11th to 20th	Night	7% 3 14% 41% 32% 3	522
	21st to end	Night	4 2 8% 40% 41% 4	591
August	1st to 10th	Night	7% 3 13% 45% 30% 2	537
	11th to 20th	Night	4 3 14% 42% 33% 4	534
	21st to end	Night	4 4 15% 39% 35% 4	594
September	1st to 10th	Night	5% 5% 18% 36% 30% 6%	615
	11th to 20th	Night	6% 4 19% 33% 31% 8%	720
	21st to end	Night	8% 9% 17% 30% 28% 8%	720
October	1st to 10th	Night	7% 12% 28% 28% 22% 4	720
	11th to 20th	Night	6% 16% 24% 31% 19% 4	720
	21st to end	Night	7% 18% 24% 30% 18% 3	792
November	1st to 10th	Night	7% 14% 29% 30% 17% 2	740
	11th to 20th	Night	7% 21% 28% 30% 11% 3	760
	21st to end	Night	9% 20% 25% 32% 11% 3	933
December	1st to 10th	Night	9% 20% 34% 27% 10% 1	950
	11th to 20th	Night	9% 20% 33% 28% 9% 1	950
	21st to end	Night	12% 21% 36% 22% 7% 1	931

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