Trout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trout Observatory clear sky chart from 2005-11-06 to 2024-09-14.

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	14% 10% 3 8% 5% 5% 5% 4 6% 7% 33%	100578
	Night	15% 11% 4 8% 5% 4 4 4 5% 7% 34%	97267
Transparency	Day	48% 7% 12% 20% 11% 1	100380
	Night	49% 7% 12% 20% 12% 1	97135
Seeing	Day	16% 7% 24% 29% 18% 6%	15182
	Night	19% 8% 27% 29% 15% 2	25070

By Month

Percentage Cloud Cover SE (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	18% 18% 7% 12% 7% 5% 4 3 5% 5% 16%	2527
	11th to 20th	Day	15% 21% 6% 13% 7% 6% 9% 3 4 3 12%	2682
	21st to end	Day	28% 19% 10% 12% 5% 4 3 2 3 3 11%	3124
February	1st to 10th	Day	16% 16% 5% 12% 7% 5% 5% 3 5% 5% 21%	1710
	11th to 20th	Day	15% 12% 5% 12% 8% 6% 6% 3 5% 5% 24%	1803
	21st to end	Day	17% 14% 4 10% 6% 4 4 4 5% 7% 25%	1570
March	1st to 10th	Day	20% 14% 5% 10% 5% 4 4 3 4 6% 26%	3233
	11th to 20th	Day	12% 12% 4 8% 5% 5% 4 4 5% 6% 34%	3480
	21st to end	Day	19% 12% 5% 10% 5% 4 4 3 5% 6% 26%	3815
April	1st to 10th	Day	13% 12% 4 9% 7% 4 4 5% 6% 6% 30%	2175
	11th to 20th	Day	16% 8% 3 7% 5% 5% 4 3 6% 7% 34%	2406
	21st to end	Day	18% 10% 3 6% 4 4 4 4 5% 8% 35%	2470
May	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 5% 6% 33%	4082
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 6% 7% 42%	4476
June	1st to 10th	Day	11% 6% 2 7% 4 5% 5% 5% 8% 8% 39%	2532
	11th to 20th	Day	9% 5% 2 6% 6% 4 5% 4 6% 8% 44%	2660
	21st to end	Day	10% 6% 3 6% 5% 5% 5% 5% 6% 9% 39%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 10% 38%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 5% 7% 10% 45%	4349
	21st to end	Day	7% 6% 2 7% 6% 6% 6% 5% 7% 9% 41%	4466
August	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 9% 43%	4104
	11th to 20th	Day	8% 6% 2 6% 5% 5% 7% 6% 8% 11% 37%	4044
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 7% 10% 41%	4478
September	1st to 10th	Day	13% 5% 2 6% 5% 4 4 3 6% 7% 45%	2124
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 5% 9% 45%	2014
	21st to end	Day	16% 7% 2 6% 4 4 4 3 6% 7% 42%	1980
October	1st to 10th	Day	12% 7% 3 6% 5% 5% 5% 3 6% 6% 41%	1927
	11th to 20th	Day	17% 8% 2 7% 5% 4 4 3 5% 8% 36%	1800
	21st to end	Day	18% 10% 2 9% 5% 5% 4 4 6% 7% 30%	1872
November	1st to 10th	Day	10% 10% 3 7% 4 4 5% 4 6% 7% 41%	1672
	11th to 20th	Day	16% 11% 3 8% 5% 5% 4 3 5% 6% 34%	1710
	21st to end	Day	17% 13% 5% 8% 5% 4 5% 3 6% 6% 27%	1706
December	1st to 10th	Day	16% 17% 6% 13% 7% 5% 5% 3 5% 4 20%	1520
	11th to 20th	Day	14% 15% 5% 11% 7% 5% 5% 3 6% 6% 22%	2045
	21st to end	Day	23% 22% 7% 12% 6% 5% 4 3 3 4 12%	2841
January	1st to 10th	Night	16% 18% 5% 11% 6% 5% 5% 3 5% 5% 21%	4428
	11th to 20th	Night	15% 19% 8% 14% 6% 5% 6% 5% 4 5% 13%	4278
	21st to end	Night	26% 18% 8% 11% 5% 4 3 2 3 4 15%	4532
February	1st to 10th	Night	17% 16% 5% 10% 7% 5% 4 4 5% 5% 24%	2470
	11th to 20th	Night	14% 14% 4 10% 6% 5% 5% 4 5% 5% 27%	2261
	21st to end	Night	20% 12% 4 9% 7% 5% 4 3 4 6% 27%	1884
March	1st to 10th	Night	20% 13% 3 7% 4 3 3 2 4 5% 35%	3619
	11th to 20th	Night	11% 8% 2 6% 5% 4 5% 4 6% 7% 42%	3480
	21st to end	Night	16% 11% 4 7% 5% 5% 4 3 5% 7% 35%	3817
April	1st to 10th	Night	15% 11% 3 8% 5% 4 4 4 5% 6% 35%	2019
	11th to 20th	Night	16% 7% 3 7% 5% 5% 4 4 5% 7% 37%	1721
	21st to end	Night	16% 10% 2 7% 5% 4 4 4 6% 7% 36%	1710
May	1st to 10th	Night	18% 9% 3 7% 6% 4 5% 4 6% 7% 30%	2813
	11th to 20th	Night	17% 7% 3 7% 4 4 4 4 5% 7% 38%	2812
	21st to end	Night	9% 5% 2 6% 5% 4 4 4 5% 9% 47%	3079
June	1st to 10th	Night	12% 5% 3 5% 5% 4 5% 4 5% 8% 45%	1644
	11th to 20th	Night	8% 6% 3 7% 4 4 3 5% 7% 8% 44%	1520
	21st to end	Night	9% 5% 2 4 5% 4 5% 4 7% 10% 44%	1520
July	1st to 10th	Night	9% 4 2 5% 3 4 4 4 6% 9% 48%	2530
	11th to 20th	Night	7% 4 1 4 4 4 5% 5% 8% 9% 48%	2613
	21st to end	Night	5% 5% 3 6% 5% 4 5% 5% 8% 9% 45%	3087
August	1st to 10th	Night	12% 6% 3 6% 4 4 4 4 5% 10% 42%	2825
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	2785
	21st to end	Night	6% 5% 3 6% 5% 5% 6% 4 6% 8% 46%	3174
September	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 5% 7% 49%	2035
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 4 8% 51%	2024
	21st to end	Night	12% 7% 2 7% 5% 4 4 3 5% 6% 44%	1980
October	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 5% 7% 45%	2031
	11th to 20th	Night	18% 9% 3 7% 4 4 3 4 5% 6% 38%	2160
	21st to end	Night	21% 8% 3 8% 5% 4 4 3 5% 6% 33%	2479
November	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 5% 7% 41%	2406
	11th to 20th	Night	15% 11% 4 8% 5% 4 5% 3 6% 7% 32%	2470
	21st to end	Night	20% 12% 4 8% 6% 5% 5% 4 5% 6% 27%	2470
December	1st to 10th	Night	16% 16% 5% 10% 6% 6% 5% 4 6% 5% 23%	2655
	11th to 20th	Night	17% 15% 5% 9% 5% 5% 4 3 4 7% 26%	3134
	21st to end	Night	26% 20% 6% 11% 5% 4 4 3 4 5% 12%	4802

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	69% 6% 11% 10% 3	2528
	11th to 20th	Day	76% 5% 9% 6% 3	2682
	21st to end	Day	80% 4 7% 6% 3	3124
February	1st to 10th	Day	64% 6% 11% 13% 6%	1710
	11th to 20th	Day	61% 6% 10% 16% 7% 1	1813
	21st to end	Day	57% 7% 14% 14% 6% 2	1570
March	1st to 10th	Day	61% 5% 11% 18% 5%	3233
	11th to 20th	Day	48% 7% 15% 21% 8% 1	3480
	21st to end	Day	56% 8% 13% 15% 7%	3815
April	1st to 10th	Day	51% 7% 13% 16% 12% 1	2175
	11th to 20th	Day	48% 6% 12% 18% 13% 2	2406
	21st to end	Day	47% 5% 14% 21% 11% 2	2470
May	1st to 10th	Day	49% 8% 11% 22% 9% 1	4120
	11th to 20th	Day	45% 9% 14% 22% 9% 1	4085
	21st to end	Day	36% 9% 11% 19% 18% 5%	4489
June	1st to 10th	Day	39% 9% 11% 26% 12% 3	2532
	11th to 20th	Day	37% 7% 15% 22% 17% 3	2660
	21st to end	Day	39% 8% 14% 20% 16% 4	2660
July	1st to 10th	Day	41% 6% 11% 23% 16% 3	4371
	11th to 20th	Day	31% 7% 13% 30% 18% 1	4274
	21st to end	Day	37% 8% 14% 18% 21% 3	4324
August	1st to 10th	Day	35% 8% 15% 26% 15% 1	4091
	11th to 20th	Day	36% 8% 14% 30% 11% 1	4083
	21st to end	Day	36% 7% 13% 30% 12% 2	4477
September	1st to 10th	Day	38% 6% 14% 22% 17% 3	2124
	11th to 20th	Day	34% 7% 11% 28% 18% 1	2014
	21st to end	Day	40% 7% 13% 23% 17%	1980
October	1st to 10th	Day	42% 7% 11% 25% 14% 2	1927
	11th to 20th	Day	46% 6% 12% 22% 14% 1	1800
	21st to end	Day	52% 7% 13% 17% 10% 1	1872
November	1st to 10th	Day	42% 6% 12% 23% 16% 1	1672
	11th to 20th	Day	51% 5% 12% 19% 11% 1	1710
	21st to end	Day	55% 7% 13% 17% 8%	1706
December	1st to 10th	Day	67% 6% 10% 13% 4	1520
	11th to 20th	Day	60% 6% 13% 15% 5%	2042
	21st to end	Day	77% 5% 8% 7% 3	2841
January	1st to 10th	Night	63% 7% 10% 15% 5%	4428
	11th to 20th	Night	72% 6% 10% 9% 3	4278
	21st to end	Night	74% 5% 9% 9% 3	4532
February	1st to 10th	Night	61% 6% 11% 15% 5% 1	2470
	11th to 20th	Night	57% 6% 10% 18% 8% 1	2262
	21st to end	Night	58% 6% 10% 17% 8% 1	1884
March	1st to 10th	Night	52% 4 12% 23% 8% 1	3619
	11th to 20th	Night	38% 7% 17% 21% 15% 1	3480
	21st to end	Night	47% 7% 12% 24% 9% 1	3817
April	1st to 10th	Night	49% 6% 12% 18% 14% 2	2019
	11th to 20th	Night	46% 6% 11% 18% 17% 2	1721
	21st to end	Night	45% 7% 11% 20% 15% 3	1710
May	1st to 10th	Night	51% 7% 11% 18% 12% 2	2840
	11th to 20th	Night	43% 9% 11% 23% 12% 1	2813
	21st to end	Night	32% 8% 12% 26% 20% 3	3087
June	1st to 10th	Night	37% 7% 11% 26% 16% 3	1644
	11th to 20th	Night	35% 8% 13% 25% 16% 3	1520
	21st to end	Night	32% 8% 14% 26% 18% 2	1520
July	1st to 10th	Night	32% 6% 11% 27% 18% 6%	2490
	11th to 20th	Night	28% 7% 16% 30% 16% 2	2565
	21st to end	Night	32% 8% 17% 21% 18% 4	2988
August	1st to 10th	Night	38% 8% 12% 25% 15% 2	2814
	11th to 20th	Night	33% 7% 12% 29% 17% 1	2812
	21st to end	Night	34% 7% 13% 28% 17% 2	3174
September	1st to 10th	Night	34% 7% 12% 25% 18% 4	2035
	11th to 20th	Night	31% 7% 11% 26% 24% 1	2024
	21st to end	Night	38% 7% 12% 23% 19% 2	1980
October	1st to 10th	Night	39% 6% 12% 22% 19% 2	2031
	11th to 20th	Night	46% 5% 11% 22% 15% 1	2160
	21st to end	Night	51% 6% 11% 21% 10% 1	2479
November	1st to 10th	Night	42% 6% 11% 23% 16% 2	2406
	11th to 20th	Night	49% 7% 12% 21% 11% 1	2470
	21st to end	Night	58% 6% 12% 18% 6%	2470
December	1st to 10th	Night	61% 6% 11% 14% 7%	2655
	11th to 20th	Night	56% 8% 15% 15% 5%	3136
	21st to end	Night	73% 7% 10% 7% 2	4802

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% 14% 34% 23% 5% 2	270
	11th to 20th	Day	23% 10% 44% 16% 7%	270
	21st to end	Day	27% 12% 28% 26% 6%	297
February	1st to 10th	Day	23% 13% 38% 20% 6%	270
	11th to 20th	Day	20% 18% 37% 23% 2	270
	21st to end	Day	21% 16% 44% 14% 4	225
March	1st to 10th	Day	20% 13% 34% 25% 8%	331
	11th to 20th	Day	20% 10% 34% 27% 7% 1	460
	21st to end	Day	25% 11% 31% 26% 6% 1	506
April	1st to 10th	Day	17% 10% 33% 27% 12% 1	460
	11th to 20th	Day	19% 11% 33% 24% 9% 4	452
	21st to end	Day	22% 9% 31% 27% 10% 2	460
May	1st to 10th	Day	21% 6% 28% 27% 15% 3	463
	11th to 20th	Day	17% 5% 26% 29% 18% 5%	487
	21st to end	Day	13% 3 20% 29% 26% 9%	529
June	1st to 10th	Day	11% 4 22% 37% 23% 3	552
	11th to 20th	Day	11% 4 18% 37% 25% 4	680
	21st to end	Day	12% 4 18% 39% 22% 5%	680
July	1st to 10th	Day	8% 3 14% 34% 29% 12%	671
	11th to 20th	Day	9% 3 15% 33% 29% 11%	616
	21st to end	Day	8% 2 13% 33% 33% 11%	532
August	1st to 10th	Day	10% 2 11% 33% 30% 13%	486
	11th to 20th	Day	11% 3 11% 34% 31% 10%	479
	21st to end	Day	10% 3 13% 28% 33% 12%	539
September	1st to 10th	Day	14% 2 16% 27% 29% 13%	490
	11th to 20th	Day	12% 2 12% 29% 30% 16%	463
	21st to end	Day	17% 5% 24% 24% 20% 10%	450
October	1st to 10th	Day	12% 6% 22% 30% 19% 11%	450
	11th to 20th	Day	19% 14% 28% 27% 11% 2	450
	21st to end	Day	23% 13% 32% 25% 6% 1	387
November	1st to 10th	Day	13% 13% 27% 29% 14% 4	270
	11th to 20th	Day	21% 19% 26% 23% 9% 1	270
	21st to end	Day	24% 10% 37% 27% 3	268
December	1st to 10th	Day	19% 16% 36% 22% 7% 1	180
	11th to 20th	Day	19% 15% 41% 20% 5%	222
	21st to end	Day	24% 13% 36% 24% 3	297
January	1st to 10th	Night	24% 11% 36% 21% 7%	950
	11th to 20th	Night	27% 12% 35% 21% 5%	853
	21st to end	Night	24% 10% 34% 28% 4 1	836
February	1st to 10th	Night	24% 9% 36% 26% 5%	760
	11th to 20th	Night	23% 10% 35% 29% 4	743
	21st to end	Night	25% 12% 37% 23% 4	628
March	1st to 10th	Night	19% 9% 34% 29% 9%	760
	11th to 20th	Night	19% 11% 32% 28% 8% 1	760
	21st to end	Night	23% 8% 28% 31% 9% 1	836
April	1st to 10th	Night	20% 9% 33% 32% 7%	689
	11th to 20th	Night	20% 6% 33% 28% 10% 2	563
	21st to end	Night	21% 6% 30% 30% 11% 1	570
May	1st to 10th	Night	21% 4 28% 32% 12% 3	570
	11th to 20th	Night	21% 4 24% 32% 18% 2	561
	21st to end	Night	11% 2 20% 35% 25% 5%	617
June	1st to 10th	Night	13% 4 20% 39% 22% 2	570
	11th to 20th	Night	11% 3 19% 40% 25% 2	570
	21st to end	Night	11% 2 20% 39% 25% 3	570
July	1st to 10th	Night	10% 2 10% 37% 36% 5%	555
	11th to 20th	Night	9% 3 13% 41% 27% 6%	552
	21st to end	Night	8% 1 12% 42% 33% 4	624
August	1st to 10th	Night	9% 3 10% 41% 31% 6%	567
	11th to 20th	Night	10% 1 14% 35% 34% 7%	564
	21st to end	Night	10% 2 13% 33% 36% 6%	627
September	1st to 10th	Night	13% 3 16% 30% 31% 7%	705
	11th to 20th	Night	11% 4 13% 31% 35% 6%	736
	21st to end	Night	16% 6% 19% 32% 22% 6%	720
October	1st to 10th	Night	18% 6% 20% 31% 19% 5%	720
	11th to 20th	Night	23% 12% 27% 25% 11% 2	720
	21st to end	Night	27% 10% 30% 27% 6% 1	792
November	1st to 10th	Night	19% 11% 29% 26% 13% 2	740
	11th to 20th	Night	22% 13% 35% 21% 8% 1	760
	21st to end	Night	28% 11% 32% 23% 6%	760
December	1st to 10th	Night	26% 13% 34% 21% 6%	760
	11th to 20th	Night	25% 12% 37% 22% 4	760
	21st to end	Night	30% 11% 32% 24% 4	1002

Page generated at 2024-09-11 10:00:04. Version ac07

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