Aubright Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aubright 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	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 40%	114408
	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	114877
Transparency	Day	39% 8% 14% 17% 15% 7%	118163
	Night	37% 7% 14% 18% 16% 8%	119261
Seeing	Day	11% 8% 23% 25% 21% 13%	16144
	Night	11% 6% 22% 32% 24% 5%	26260

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	8% 6% 2 4 3 3 3 2 4 6% 58%	4056
	11th to 20th	Day	19% 8% 3 7% 5% 3 3 3 4 6% 38%	4060
	21st to end	Day	10% 7% 2 6% 4 4 4 3 5% 8% 48%	4490
February	1st to 10th	Day	15% 7% 2 5% 5% 3 4 4 4 6% 45%	2000
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 6% 48%	1948
	21st to end	Day	11% 7% 2 6% 4 4 4 3 5% 6% 48%	1715
March	1st to 10th	Day	14% 8% 3 7% 4 4 4 4 5% 7% 40%	4935
	11th to 20th	Day	7% 3 2 4 3 3 4 4 5% 7% 57%	4980
	21st to end	Day	12% 5% 2 5% 3 4 4 4 5% 9% 47%	5465
April	1st to 10th	Day	8% 5% 2 5% 5% 4 4 4 6% 8% 48%	2200
	11th to 20th	Day	9% 6% 3 7% 4 5% 5% 4 6% 7% 45%	2232
	21st to end	Day	5% 4 2 5% 5% 5% 5% 4 6% 8% 51%	2456
May	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 5% 7% 10% 47%	4212
	11th to 20th	Day	9% 6% 3 8% 5% 6% 5% 5% 7% 9% 37%	4211
	21st to end	Day	6% 3 2 5% 4 5% 6% 5% 8% 11% 45%	4541
June	1st to 10th	Day	11% 6% 2 9% 6% 7% 6% 6% 8% 9% 28%	2470
	11th to 20th	Day	6% 5% 3 8% 7% 7% 8% 7% 9% 11% 30%	2470
	21st to end	Day	8% 6% 3 9% 8% 7% 7% 6% 9% 10% 27%	2470
July	1st to 10th	Day	6% 7% 3 10% 9% 8% 9% 8% 10% 10% 20%	4120
	11th to 20th	Day	4 5% 2 7% 7% 8% 8% 6% 10% 15% 27%	4120
	21st to end	Day	4 5% 2 8% 8% 8% 8% 8% 10% 14% 25%	4466
August	1st to 10th	Day	11% 7% 2 9% 8% 7% 8% 6% 8% 11% 24%	4104
	11th to 20th	Day	7% 5% 2 7% 5% 6% 7% 6% 8% 12% 35%	4020
	21st to end	Day	9% 6% 3 9% 7% 8% 8% 6% 9% 11% 25%	3828
September	1st to 10th	Day	11% 8% 4 10% 8% 8% 8% 6% 8% 9% 22%	2090
	11th to 20th	Day	15% 7% 3 9% 7% 8% 8% 5% 7% 9% 22%	2090
	21st to end	Day	12% 7% 3 9% 5% 5% 6% 5% 7% 7% 35%	2090
October	1st to 10th	Day	12% 6% 3 8% 5% 6% 5% 5% 7% 8% 35%	2063
	11th to 20th	Day	7% 5% 2 6% 5% 4 5% 4 4 7% 51%	1900
	21st to end	Day	8% 5% 2 5% 4 4 4 3 6% 8% 50%	2090
November	1st to 10th	Day	10% 6% 2 6% 5% 4 4 4 6% 9% 45%	1957
	11th to 20th	Day	9% 6% 2 6% 6% 4 4 4 7% 8% 44%	1990
	21st to end	Day	12% 6% 3 6% 6% 4 3 3 5% 7% 46%	1800
December	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 7% 55%	2930
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 4 6% 7% 38%	3373
	21st to end	Day	14% 9% 3 7% 4 4 4 3 4 6% 41%	4466
January	1st to 10th	Night	9% 6% 2 4 3 2 3 2 4 6% 58%	5889
	11th to 20th	Night	17% 8% 2 7% 5% 5% 5% 4 6% 7% 35%	5900
	21st to end	Night	13% 7% 3 6% 4 3 4 3 6% 8% 43%	6462
February	1st to 10th	Night	13% 6% 2 7% 5% 4 4 3 5% 6% 46%	2400
	11th to 20th	Night	13% 7% 2 6% 5% 4 3 3 4 6% 48%	2338
	21st to end	Night	11% 7% 2 6% 4 4 4 3 4 6% 49%	1913
March	1st to 10th	Night	17% 10% 3 6% 4 4 3 3 4 5% 41%	4918
	11th to 20th	Night	5% 5% 2 4 3 3 4 4 6% 10% 54%	4980
	21st to end	Night	9% 6% 2 6% 4 4 4 3 6% 7% 50%	5467
April	1st to 10th	Night	8% 5% 1 4 5% 4 4 4 6% 8% 50%	2200
	11th to 20th	Night	8% 6% 2 5% 3 4 4 3 5% 7% 53%	2115
	21st to end	Night	6% 3 2 4 4 4 4 5% 7% 8% 53%	1958
May	1st to 10th	Night	4 3 2 5% 4 5% 6% 4 7% 9% 52%	2903
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 4 7% 10% 43%	2902
	21st to end	Night	3 3 1 4 3 4 5% 4 7% 10% 56%	3130
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 6% 8% 12% 36%	1710
	11th to 20th	Night	6% 4 2 6% 6% 6% 6% 6% 10% 11% 37%	1710
	21st to end	Night	7% 5% 1 7% 6% 6% 5% 6% 9% 12% 35%	1710
July	1st to 10th	Night	6% 7% 4 10% 7% 6% 7% 6% 9% 12% 28%	2840
	11th to 20th	Night	4 5% 2 7% 7% 6% 7% 6% 11% 16% 30%	2840
	21st to end	Night	5% 6% 3 9% 7% 6% 7% 7% 12% 12% 25%	3087
August	1st to 10th	Night	10% 7% 3 8% 6% 6% 7% 5% 10% 12% 27%	2825
	11th to 20th	Night	4 4 2 7% 6% 6% 6% 6% 9% 11% 40%	2804
	21st to end	Night	7% 6% 2 7% 5% 6% 6% 5% 8% 11% 36%	3794
September	1st to 10th	Night	11% 7% 3 8% 6% 6% 6% 6% 7% 10% 29%	2090
	11th to 20th	Night	12% 7% 3 9% 6% 7% 6% 5% 9% 9% 27%	2090
	21st to end	Night	9% 7% 2 7% 5% 5% 5% 4 6% 10% 41%	2090
October	1st to 10th	Night	11% 6% 2 8% 5% 4 5% 4 6% 7% 42%	2115
	11th to 20th	Night	7% 4 2 5% 4 4 3 3 5% 6% 56%	2280
	21st to end	Night	8% 5% 2 5% 4 4 4 3 5% 8% 51%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 8% 48%	2341
	11th to 20th	Night	10% 6% 3 6% 4 4 4 3 5% 7% 47%	2406
	21st to end	Night	12% 6% 2 5% 5% 4 4 4 5% 7% 47%	2600
December	1st to 10th	Night	10% 5% 1 5% 4 3 4 3 4 6% 55%	4250
	11th to 20th	Night	12% 8% 2 7% 4 4 4 3 5% 6% 45%	4822
	21st to end	Night	13% 9% 3 7% 4 4 4 3 5% 6% 41%	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	30% 2 8% 15% 28% 17%	4057
	11th to 20th	Day	48% 3 5% 13% 18% 14%	4060
	21st to end	Day	35% 5% 8% 24% 17% 11%	4490
February	1st to 10th	Day	41% 5% 9% 14% 21% 10%	2000
	11th to 20th	Day	37% 5% 8% 15% 23% 12%	1958
	21st to end	Day	36% 5% 10% 17% 19% 13%	1715
March	1st to 10th	Day	43% 6% 9% 14% 18% 10%	4935
	11th to 20th	Day	25% 5% 11% 18% 19% 22%	4980
	21st to end	Day	35% 4 9% 21% 19% 11%	5465
April	1st to 10th	Day	33% 7% 10% 20% 19% 12%	2200
	11th to 20th	Day	36% 7% 8% 17% 21% 10%	2232
	21st to end	Day	28% 7% 12% 22% 23% 8%	2456
May	1st to 10th	Day	26% 13% 13% 27% 16% 5%	4250
	11th to 20th	Day	40% 10% 13% 22% 14% 2	4215
	21st to end	Day	28% 9% 16% 29% 17% 1	4554
June	1st to 10th	Day	46% 12% 16% 16% 9% 1	2470
	11th to 20th	Day	40% 15% 18% 21% 6%	2470
	21st to end	Day	47% 14% 20% 12% 6%	2470
July	1st to 10th	Day	52% 12% 24% 11% 1	4055
	11th to 20th	Day	43% 13% 35% 7% 2	4051
	21st to end	Day	44% 15% 30% 10% 1	4324
August	1st to 10th	Day	51% 10% 26% 11% 1	4091
	11th to 20th	Day	38% 11% 22% 20% 9%	4059
	21st to end	Day	48% 9% 19% 21% 2	3828
September	1st to 10th	Day	53% 15% 14% 10% 7% 1	2090
	11th to 20th	Day	54% 12% 14% 13% 6%	2090
	21st to end	Day	46% 8% 13% 16% 14% 3	2090
October	1st to 10th	Day	52% 7% 8% 10% 15% 8%	3427
	11th to 20th	Day	27% 4 5% 15% 35% 13%	3140
	21st to end	Day	26% 4 6% 20% 35% 9%	3428
November	1st to 10th	Day	35% 7% 10% 19% 18% 11%	1957
	11th to 20th	Day	37% 6% 9% 16% 21% 11%	1990
	21st to end	Day	38% 5% 10% 17% 22% 8%	1800
December	1st to 10th	Day	29% 5% 11% 24% 20% 11%	2930
	11th to 20th	Day	45% 5% 9% 16% 17% 8%	3370
	21st to end	Day	45% 3 7% 18% 20% 5%	4466
January	1st to 10th	Night	28% 4 8% 11% 35% 14%	5889
	11th to 20th	Night	48% 3 7% 15% 19% 8%	5900
	21st to end	Night	39% 6% 9% 19% 16% 11%	6462
February	1st to 10th	Night	39% 5% 9% 16% 19% 12%	2400
	11th to 20th	Night	38% 5% 9% 18% 18% 12%	2339
	21st to end	Night	36% 5% 9% 19% 18% 12%	1913
March	1st to 10th	Night	45% 5% 8% 16% 16% 11%	4918
	11th to 20th	Night	25% 5% 12% 20% 19% 19%	4980
	21st to end	Night	34% 4 10% 19% 18% 13%	5467
April	1st to 10th	Night	32% 6% 14% 21% 17% 11%	2200
	11th to 20th	Night	31% 6% 9% 23% 21% 10%	2115
	21st to end	Night	25% 7% 16% 26% 20% 6%	1958
May	1st to 10th	Night	23% 13% 17% 28% 14% 4	2930
	11th to 20th	Night	34% 10% 18% 25% 12% 2	2903
	21st to end	Night	21% 8% 16% 33% 20% 1	3138
June	1st to 10th	Night	36% 13% 22% 20% 8%	1710
	11th to 20th	Night	35% 13% 24% 24% 5%	1710
	21st to end	Night	37% 14% 25% 18% 5% 1	1710
July	1st to 10th	Night	46% 11% 29% 13% 1	2795
	11th to 20th	Night	38% 18% 33% 9% 3	2786
	21st to end	Night	44% 13% 29% 12% 1	2988
August	1st to 10th	Night	46% 11% 31% 10% 2	2814
	11th to 20th	Night	35% 11% 24% 20% 10%	2831
	21st to end	Night	39% 11% 26% 20% 3	3794
September	1st to 10th	Night	47% 14% 19% 14% 5% 1	2090
	11th to 20th	Night	48% 14% 16% 15% 7%	2090
	21st to end	Night	38% 9% 16% 20% 14% 3	2090
October	1st to 10th	Night	51% 7% 10% 12% 13% 7%	3531
	11th to 20th	Night	28% 3 5% 18% 35% 10%	3779
	21st to end	Night	24% 4 7% 22% 33% 10%	4120
November	1st to 10th	Night	34% 6% 13% 19% 17% 12%	2341
	11th to 20th	Night	37% 6% 9% 17% 21% 11%	2406
	21st to end	Night	36% 6% 11% 18% 20% 9%	2600
December	1st to 10th	Night	32% 4 10% 21% 18% 15%	4250
	11th to 20th	Night	42% 4 9% 21% 15% 9%	4824
	21st to end	Night	44% 5% 10% 18% 18% 5%	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	10% 20% 48% 17% 4 1	300
	11th to 20th	Day	11% 15% 40% 24% 8% 1	300
	21st to end	Day	14% 22% 47% 15% 2	330
February	1st to 10th	Day	12% 18% 40% 22% 8% 1	300
	11th to 20th	Day	17% 16% 41% 18% 8%	300
	21st to end	Day	12% 16% 37% 26% 8%	314
March	1st to 10th	Day	12% 16% 35% 26% 10%	500
	11th to 20th	Day	13% 12% 35% 24% 13% 3	500
	21st to end	Day	13% 14% 33% 26% 13% 1	550
April	1st to 10th	Day	12% 14% 33% 23% 15% 3	500
	11th to 20th	Day	11% 12% 31% 26% 14% 6%	492
	21st to end	Day	5% 7% 31% 28% 19% 10%	500
May	1st to 10th	Day	4 8% 28% 30% 20% 9%	503
	11th to 20th	Day	9% 3 26% 29% 21% 12%	527
	21st to end	Day	9% 3 14% 27% 29% 17%	549
June	1st to 10th	Day	12% 2 12% 31% 25% 17%	490
	11th to 20th	Day	7% 2 17% 22% 27% 25%	490
	21st to end	Day	5% 2 10% 23% 33% 26%	490
July	1st to 10th	Day	7% 2 5% 20% 32% 34%	485
	11th to 20th	Day	5% 1 5% 15% 37% 38%	484
	21st to end	Day	7% 2 7% 20% 37% 27%	532
August	1st to 10th	Day	11% 2 10% 17% 33% 28%	486
	11th to 20th	Day	7% 1 6% 18% 33% 34%	479
	21st to end	Day	10% 3 7% 23% 32% 25%	539
September	1st to 10th	Day	13% 4 8% 19% 29% 26%	490
	11th to 20th	Day	15% 2 13% 26% 25% 18%	490
	21st to end	Day	12% 3 11% 24% 32% 17%	490
October	1st to 10th	Day	16% 4 23% 32% 19% 6%	490
	11th to 20th	Day	8% 8% 21% 30% 27% 7%	490
	21st to end	Day	9% 6% 24% 37% 20% 5%	539
November	1st to 10th	Day	14% 8% 27% 28% 18% 4	495
	11th to 20th	Day	13% 11% 33% 25% 15% 3	490
	21st to end	Day	12% 13% 38% 24% 11% 1	300
December	1st to 10th	Day	8% 17% 34% 25% 14% 2	300
	11th to 20th	Day	17% 15% 34% 29% 5%	300
	21st to end	Day	16% 11% 35% 28% 8% 2	330
January	1st to 10th	Night	14% 13% 34% 30% 8% 1	800
	11th to 20th	Night	14% 13% 28% 34% 11% 1	800
	21st to end	Night	17% 12% 36% 29% 6%	880
February	1st to 10th	Night	16% 9% 29% 36% 10%	800
	11th to 20th	Night	16% 11% 32% 33% 7%	783
	21st to end	Night	15% 10% 34% 36% 5%	660
March	1st to 10th	Night	12% 11% 33% 36% 8%	800
	11th to 20th	Night	10% 11% 35% 33% 11% 1	800
	21st to end	Night	10% 10% 34% 35% 11%	880
April	1st to 10th	Night	10% 10% 33% 37% 11%	800
	11th to 20th	Night	10% 10% 31% 33% 15%	791
	21st to end	Night	7% 5% 28% 43% 17% 1	758
May	1st to 10th	Night	5% 4 21% 47% 21% 2	600
	11th to 20th	Night	7% 3 20% 37% 30% 3	591
	21st to end	Night	7% 1 11% 37% 37% 6%	634
June	1st to 10th	Night	12% 2 11% 35% 35% 6%	570
	11th to 20th	Night	6% 1 9% 30% 40% 14%	570
	21st to end	Night	7% 2 9% 25% 41% 16%	570
July	1st to 10th	Night	6% 1 7% 24% 44% 17%	555
	11th to 20th	Night	5% 4 19% 51% 20%	552
	21st to end	Night	5% 6% 23% 53% 13%	624
August	1st to 10th	Night	8% 1 6% 23% 47% 15%	567
	11th to 20th	Night	6% 1 4 19% 51% 19%	564
	21st to end	Night	12% 2 10% 22% 39% 16%	815
September	1st to 10th	Night	14% 2 7% 22% 43% 12%	760
	11th to 20th	Night	14% 2 11% 29% 38% 8%	760
	21st to end	Night	11% 3 12% 30% 36% 8%	760
October	1st to 10th	Night	15% 2 20% 31% 29% 3	760
	11th to 20th	Night	8% 5% 19% 37% 29% 3	760
	21st to end	Night	9% 4 22% 37% 26% 2	836
November	1st to 10th	Night	12% 5% 25% 34% 22% 1	780
	11th to 20th	Night	14% 7% 26% 33% 19% 2	800
	21st to end	Night	14% 8% 28% 32% 18% 1	800
December	1st to 10th	Night	14% 8% 28% 31% 19% 1	800
	11th to 20th	Night	15% 8% 26% 35% 15% 2	800
	21st to end	Night	16% 9% 28% 34% 13%	880

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