TwinOaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TwinOaks Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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% 6% 2 6% 4 4 4 4 5% 7% 44%	114617
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	114679
Transparency	Day	37% 6% 11% 20% 20% 6%	118320
	Night	37% 6% 10% 18% 22% 7%	119115
Seeing	Day	17% 10% 25% 24% 18% 7%	15990
	Night	16% 9% 23% 30% 19% 3	26124

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	15% 5% 2 4 3 2 3 2 3 5% 55%	4056
	11th to 20th	Day	12% 6% 2 5% 3 3 2 2 3 3 59%	4060
	21st to end	Day	17% 8% 2 6% 4 3 3 3 4 4 44%	4466
February	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 6% 7% 43%	1800
	11th to 20th	Day	22% 6% 1 4 3 3 3 3 4 4 45%	1938
	21st to end	Day	19% 7% 3 6% 4 4 4 3 4 5% 42%	1698
March	1st to 10th	Day	21% 7% 3 6% 3 3 4 3 4 5% 41%	4935
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 4 6% 54%	4980
	21st to end	Day	17% 6% 2 6% 4 3 3 3 4 5% 47%	5465
April	1st to 10th	Day	12% 4 2 4 3 3 3 4 6% 7% 50%	2200
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 4 6% 49%	2359
	21st to end	Day	12% 5% 2 5% 4 4 4 3 5% 6% 50%	2553
May	1st to 10th	Day	11% 6% 3 7% 4 5% 6% 5% 7% 10% 37%	4212
	11th to 20th	Day	17% 8% 2 6% 5% 4 4 4 5% 8% 37%	4211
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 10% 48%	4541
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 39%	2470
	11th to 20th	Day	8% 5% 2 6% 5% 4 6% 4 7% 10% 43%	2470
	21st to end	Day	7% 4 2 5% 6% 6% 7% 4 8% 11% 40%	2470
July	1st to 10th	Day	9% 6% 2 7% 6% 5% 6% 5% 9% 10% 35%	4120
	11th to 20th	Day	7% 6% 2 7% 6% 6% 6% 5% 8% 13% 35%	4120
	21st to end	Day	11% 9% 3 8% 6% 7% 6% 6% 8% 12% 25%	4466
August	1st to 10th	Day	21% 7% 2 6% 5% 5% 6% 5% 7% 10% 26%	4104
	11th to 20th	Day	12% 5% 2 6% 5% 5% 6% 5% 7% 11% 35%	4044
	21st to end	Day	6% 4 2 4 4 4 4 4 7% 9% 52%	4249
September	1st to 10th	Day	9% 5% 2 5% 5% 5% 5% 4 7% 9% 44%	2100
	11th to 20th	Day	13% 7% 3 6% 4 4 6% 4 5% 8% 40%	2090
	21st to end	Day	18% 7% 3 5% 4 4 3 4 5% 6% 41%	2090
October	1st to 10th	Day	14% 4 2 5% 3 3 3 3 4 5% 54%	1981
	11th to 20th	Day	13% 5% 2 4 3 2 3 2 3 5% 58%	1900
	21st to end	Day	14% 4 2 4 3 2 2 2 4 6% 57%	2090
November	1st to 10th	Day	15% 5% 2 5% 3 3 2 2 4 5% 54%	1957
	11th to 20th	Day	14% 6% 1 3 3 3 3 3 5% 6% 53%	1853
	21st to end	Day	16% 5% 2 4 3 3 4 4 4 6% 51%	1800
December	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 5% 52%	2930
	11th to 20th	Day	18% 7% 3 6% 4 3 3 3 5% 6% 41%	3373
	21st to end	Day	22% 6% 2 4 3 3 3 3 4 6% 45%	4466
January	1st to 10th	Night	14% 5% 1 5% 3 3 3 2 3 4 58%	5889
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	5900
	21st to end	Night	18% 8% 2 5% 3 3 3 2 4 5% 47%	6490
February	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 5% 5% 47%	2600
	11th to 20th	Night	22% 6% 2 5% 4 3 3 3 4 4 43%	2344
	21st to end	Night	16% 6% 2 5% 4 3 4 4 5% 6% 45%	1930
March	1st to 10th	Night	20% 8% 2 6% 3 3 3 3 4 6% 43%	4918
	11th to 20th	Night	10% 4 2 4 3 3 4 3 5% 7% 54%	4980
	21st to end	Night	16% 5% 2 6% 4 3 4 3 5% 6% 47%	5467
April	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 5% 7% 49%	2200
	11th to 20th	Night	11% 5% 2 4 4 3 3 3 5% 7% 53%	1990
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 7% 50%	1863
May	1st to 10th	Night	14% 6% 2 6% 4 5% 4 3 5% 8% 43%	2903
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 4 6% 8% 38%	2902
	21st to end	Night	8% 4 3 6% 4 4 6% 4 6% 12% 43%	3130
June	1st to 10th	Night	10% 6% 2 7% 5% 6% 7% 5% 7% 9% 36%	1710
	11th to 20th	Night	10% 6% 2 6% 5% 6% 6% 5% 8% 9% 38%	1710
	21st to end	Night	7% 6% 2 7% 6% 5% 6% 6% 8% 11% 36%	1710
July	1st to 10th	Night	11% 8% 3 9% 6% 6% 6% 5% 8% 9% 29%	2840
	11th to 20th	Night	9% 6% 2 7% 5% 5% 7% 5% 11% 12% 31%	2840
	21st to end	Night	15% 9% 4 9% 6% 6% 7% 5% 7% 9% 23%	3087
August	1st to 10th	Night	23% 8% 3 6% 5% 4 5% 4 7% 10% 24%	2825
	11th to 20th	Night	11% 7% 3 7% 5% 5% 6% 5% 8% 10% 33%	2785
	21st to end	Night	6% 4 2 5% 4 4 5% 4 7% 9% 49%	3375
September	1st to 10th	Night	10% 4 2 6% 4 5% 4 5% 7% 9% 43%	2076
	11th to 20th	Night	15% 6% 2 7% 6% 4 6% 3 6% 8% 38%	2090
	21st to end	Night	18% 5% 2 6% 5% 4 5% 3 5% 6% 40%	2090
October	1st to 10th	Night	15% 5% 1 5% 3 3 3 3 4 6% 53%	2199
	11th to 20th	Night	13% 5% 2 4 3 3 3 2 4 6% 55%	2280
	21st to end	Night	12% 5% 1 4 3 3 2 3 3 5% 58%	2508
November	1st to 10th	Night	15% 5% 2 4 3 2 3 3 4 5% 54%	2341
	11th to 20th	Night	13% 6% 2 5% 4 4 3 3 4 5% 52%	2545
	21st to end	Night	13% 4 2 4 3 4 4 3 6% 6% 50%	2600
December	1st to 10th	Night	16% 6% 2 5% 3 3 3 3 4 5% 53%	4250
	11th to 20th	Night	18% 7% 2 6% 4 3 4 2 4 6% 44%	4822
	21st to end	Night	21% 5% 1 5% 3 3 3 3 5% 5% 46%	6490

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	33% 3 5% 20% 32% 7%	4057
	11th to 20th	Day	32% 3 5% 15% 37% 10%	4060
	21st to end	Day	43% 4 4 17% 23% 9%	4466
February	1st to 10th	Day	40% 4 10% 21% 19% 5%	1800
	11th to 20th	Day	43% 3 7% 18% 23% 6%	1948
	21st to end	Day	45% 4 7% 16% 21% 8%	1698
March	1st to 10th	Day	45% 4 6% 14% 20% 11%	4935
	11th to 20th	Day	31% 4 7% 14% 25% 19%	4980
	21st to end	Day	41% 4 6% 21% 23% 6%	5465
April	1st to 10th	Day	32% 4 11% 22% 25% 6%	2200
	11th to 20th	Day	36% 5% 9% 20% 22% 9%	2359
	21st to end	Day	34% 6% 12% 22% 21% 4	2553
May	1st to 10th	Day	41% 8% 17% 20% 13% 2	4250
	11th to 20th	Day	46% 6% 12% 20% 15% 1	4215
	21st to end	Day	31% 7% 17% 21% 20% 3	4554
June	1st to 10th	Day	38% 8% 15% 26% 12% 2	2470
	11th to 20th	Day	34% 9% 18% 23% 15% 2	2470
	21st to end	Day	35% 11% 16% 22% 15% 2	2470
July	1st to 10th	Day	39% 11% 20% 19% 9% 2	4055
	11th to 20th	Day	38% 12% 26% 18% 5% 1	4051
	21st to end	Day	49% 12% 16% 17% 5%	4324
August	1st to 10th	Day	51% 9% 18% 17% 5%	4091
	11th to 20th	Day	39% 10% 18% 20% 12% 1	4083
	21st to end	Day	27% 8% 17% 31% 16% 2	4249
September	1st to 10th	Day	34% 8% 15% 20% 19% 4	2100
	11th to 20th	Day	41% 8% 11% 17% 21% 3	2090
	21st to end	Day	44% 6% 9% 20% 16% 5%	2090
October	1st to 10th	Day	29% 4 7% 20% 29% 10%	3293
	11th to 20th	Day	20% 2 6% 18% 28% 26%	3140
	21st to end	Day	26% 3 5% 25% 26% 16%	3428
November	1st to 10th	Day	34% 3 8% 18% 28% 9%	1957
	11th to 20th	Day	32% 3 8% 21% 28% 8%	1853
	21st to end	Day	35% 4 8% 21% 24% 7%	1800
December	1st to 10th	Day	36% 3 6% 19% 28% 9%	2930
	11th to 20th	Day	45% 4 7% 18% 21% 6%	3370
	21st to end	Day	40% 5% 8% 25% 20% 3	4466
January	1st to 10th	Night	31% 3 5% 17% 36% 8%	5889
	11th to 20th	Night	32% 4 6% 15% 35% 8%	5900
	21st to end	Night	41% 3 4 17% 28% 8%	6490
February	1st to 10th	Night	40% 4 9% 21% 21% 6%	2600
	11th to 20th	Night	45% 2 7% 17% 22% 7%	2345
	21st to end	Night	39% 3 10% 17% 23% 8%	1930
March	1st to 10th	Night	43% 5% 7% 12% 26% 7%	4918
	11th to 20th	Night	29% 4 7% 14% 28% 18%	4980
	21st to end	Night	38% 4 7% 21% 21% 8%	5467
April	1st to 10th	Night	35% 4 10% 19% 24% 7%	2200
	11th to 20th	Night	31% 4 9% 23% 23% 9%	1990
	21st to end	Night	33% 5% 11% 27% 20% 4	1863
May	1st to 10th	Night	40% 6% 15% 22% 15% 2	2930
	11th to 20th	Night	43% 9% 12% 20% 15% 1	2903
	21st to end	Night	30% 10% 15% 28% 15% 2	3138
June	1st to 10th	Night	41% 10% 15% 20% 12% 2	1710
	11th to 20th	Night	39% 10% 15% 21% 12% 2	1710
	21st to end	Night	38% 12% 17% 18% 11% 3	1710
July	1st to 10th	Night	46% 12% 18% 14% 9% 2	2795
	11th to 20th	Night	39% 14% 26% 16% 4 1	2786
	21st to end	Night	55% 11% 15% 13% 5% 1	2988
August	1st to 10th	Night	53% 8% 19% 15% 4	2814
	11th to 20th	Night	41% 12% 23% 16% 8% 1	2812
	21st to end	Night	30% 8% 13% 26% 20% 3	3375
September	1st to 10th	Night	35% 9% 14% 20% 16% 5%	2076
	11th to 20th	Night	42% 8% 13% 15% 20% 2	2090
	21st to end	Night	43% 7% 11% 18% 16% 5%	2090
October	1st to 10th	Night	33% 5% 10% 19% 27% 6%	3667
	11th to 20th	Night	22% 3 6% 18% 27% 24%	3779
	21st to end	Night	27% 3 6% 21% 26% 17%	4120
November	1st to 10th	Night	34% 3 8% 18% 26% 11%	2341
	11th to 20th	Night	35% 4 6% 18% 26% 12%	2545
	21st to end	Night	34% 4 6% 22% 27% 7%	2600
December	1st to 10th	Night	35% 3 6% 19% 29% 8%	4250
	11th to 20th	Night	44% 4 10% 15% 18% 9%	4824
	21st to end	Night	40% 3 10% 23% 22% 2	6490

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	21% 22% 39% 17% 2	300
	11th to 20th	Day	26% 21% 32% 16% 4	300
	21st to end	Day	22% 23% 39% 12% 3	330
February	1st to 10th	Day	21% 20% 40% 13% 5%	300
	11th to 20th	Day	37% 20% 33% 8% 1	300
	21st to end	Day	26% 21% 35% 16% 3	297
March	1st to 10th	Day	24% 17% 32% 19% 7% 1	500
	11th to 20th	Day	22% 15% 39% 18% 5% 1	500
	21st to end	Day	23% 18% 35% 18% 5% 1	550
April	1st to 10th	Day	19% 18% 34% 19% 9% 1	500
	11th to 20th	Day	16% 15% 34% 21% 11% 3	492
	21st to end	Day	17% 8% 30% 27% 15% 4	500
May	1st to 10th	Day	11% 15% 34% 22% 13% 4	503
	11th to 20th	Day	19% 5% 23% 27% 20% 7%	527
	21st to end	Day	13% 5% 20% 25% 25% 11%	549
June	1st to 10th	Day	10% 3 17% 34% 26% 10%	490
	11th to 20th	Day	9% 4 19% 26% 28% 13%	490
	21st to end	Day	9% 2 16% 36% 28% 10%	490
July	1st to 10th	Day	9% 2 9% 29% 29% 22%	485
	11th to 20th	Day	8% 3 7% 31% 33% 17%	484
	21st to end	Day	7% 3 12% 30% 35% 13%	532
August	1st to 10th	Day	16% 3 12% 31% 22% 17%	486
	11th to 20th	Day	15% 3 11% 27% 26% 18%	479
	21st to end	Day	12% 2 10% 30% 27% 18%	539
September	1st to 10th	Day	10% 3 11% 32% 30% 14%	490
	11th to 20th	Day	18% 4 15% 24% 26% 13%	490
	21st to end	Day	20% 7% 16% 28% 25% 5%	490
October	1st to 10th	Day	16% 4 24% 24% 24% 9%	490
	11th to 20th	Day	11% 9% 24% 27% 24% 5%	490
	21st to end	Day	16% 8% 23% 27% 20% 5%	539
November	1st to 10th	Day	20% 7% 27% 28% 15% 3	495
	11th to 20th	Day	19% 14% 34% 24% 7% 2	353
	21st to end	Day	17% 11% 35% 24% 11% 2	300
December	1st to 10th	Day	27% 15% 38% 15% 5%	300
	11th to 20th	Day	22% 12% 35% 22% 9% 1	300
	21st to end	Day	27% 14% 35% 15% 7% 2	330
January	1st to 10th	Night	21% 19% 29% 25% 6%	800
	11th to 20th	Night	20% 15% 31% 30% 5%	800
	21st to end	Night	20% 15% 35% 27% 4	880
February	1st to 10th	Night	19% 12% 36% 29% 4	800
	11th to 20th	Night	27% 14% 37% 21% 1	783
	21st to end	Night	20% 17% 35% 23% 4	660
March	1st to 10th	Night	19% 13% 33% 29% 6%	800
	11th to 20th	Night	19% 15% 33% 25% 7% 1	800
	21st to end	Night	20% 13% 34% 26% 7%	880
April	1st to 10th	Night	18% 16% 32% 25% 9%	800
	11th to 20th	Night	14% 14% 28% 30% 13% 1	791
	21st to end	Night	13% 7% 29% 35% 15%	663
May	1st to 10th	Night	11% 9% 29% 36% 14%	600
	11th to 20th	Night	14% 7% 23% 36% 20% 1	591
	21st to end	Night	13% 3 14% 37% 31% 2	634
June	1st to 10th	Night	11% 4 16% 39% 25% 5%	570
	11th to 20th	Night	13% 2 15% 30% 31% 9%	570
	21st to end	Night	9% 3 11% 38% 33% 6%	570
July	1st to 10th	Night	11% 2 11% 32% 36% 9%	555
	11th to 20th	Night	10% 2 6% 33% 41% 8%	552
	21st to end	Night	8% 3 10% 31% 41% 7%	624
August	1st to 10th	Night	15% 2 8% 31% 35% 9%	567
	11th to 20th	Night	13% 3 8% 30% 39% 7%	564
	21st to end	Night	11% 2 9% 28% 43% 7%	774
September	1st to 10th	Night	10% 3 10% 31% 39% 6%	760
	11th to 20th	Night	16% 3 12% 27% 37% 6%	760
	21st to end	Night	19% 5% 16% 31% 26% 3	760
October	1st to 10th	Night	16% 5% 17% 31% 26% 6%	760
	11th to 20th	Night	16% 6% 22% 31% 21% 2	760
	21st to end	Night	14% 9% 22% 31% 21% 3	836
November	1st to 10th	Night	16% 7% 25% 32% 18% 3	780
	11th to 20th	Night	15% 11% 29% 33% 11% 1	800
	21st to end	Night	15% 11% 27% 33% 14% 1	800
December	1st to 10th	Night	21% 12% 26% 34% 7% 1	800
	11th to 20th	Night	20% 11% 25% 33% 11% 1	800
	21st to end	Night	25% 13% 22% 31% 9%	880

Page generated at 2025-05-23 09:21:00. Version ac07

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