Skyfall Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyfall 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	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	114395
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	114879
Transparency	Day	36% 7% 12% 19% 19% 8%	118225
	Night	35% 6% 10% 18% 20% 10%	119187
Seeing	Day	12% 8% 21% 25% 22% 13%	15719
	Night	13% 6% 23% 32% 23% 4	25798

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	13% 5% 2 5% 3 3 3 3 3 5% 53%	4056
	11th to 20th	Day	14% 5% 2 4 2 2 3 3 4 7% 53%	4060
	21st to end	Day	15% 7% 2 6% 3 3 4 3 5% 7% 44%	4719
February	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 3 6% 6% 41%	2000
	11th to 20th	Day	18% 7% 2 5% 4 4 4 3 5% 6% 44%	1948
	21st to end	Day	15% 7% 2 5% 4 4 3 4 6% 6% 44%	1650
March	1st to 10th	Day	19% 7% 3 6% 4 4 4 4 5% 6% 38%	4728
	11th to 20th	Day	8% 4 2 4 4 4 4 4 6% 7% 54%	4980
	21st to end	Day	15% 6% 3 6% 4 4 4 3 4 7% 46%	5465
April	1st to 10th	Day	11% 6% 2 5% 5% 4 4 3 6% 6% 48%	2200
	11th to 20th	Day	10% 5% 2 5% 4 3 3 3 5% 7% 53%	2333
	21st to end	Day	7% 3 1 4 4 4 4 4 5% 7% 55%	2554
May	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 6% 8% 47%	4212
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 6% 9% 38%	4211
	21st to end	Day	6% 3 2 5% 4 5% 5% 4 7% 9% 50%	4541
June	1st to 10th	Day	11% 5% 2 7% 6% 7% 6% 6% 8% 11% 32%	2470
	11th to 20th	Day	6% 5% 2 5% 5% 5% 5% 6% 8% 11% 44%	2470
	21st to end	Day	5% 5% 2 6% 7% 7% 7% 6% 8% 12% 34%	2470
July	1st to 10th	Day	10% 7% 3 8% 6% 7% 7% 7% 10% 13% 21%	4120
	11th to 20th	Day	5% 4 2 7% 6% 7% 7% 7% 9% 12% 34%	4120
	21st to end	Day	7% 7% 3 9% 7% 7% 8% 7% 10% 13% 23%	4466
August	1st to 10th	Day	11% 5% 2 7% 5% 6% 7% 6% 9% 12% 30%	4104
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 4 7% 10% 47%	3745
	21st to end	Day	7% 5% 2 6% 4 5% 5% 5% 7% 11% 43%	4094
September	1st to 10th	Day	10% 6% 2 8% 6% 5% 5% 6% 7% 9% 38%	2090
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 39%	2090
	21st to end	Day	12% 6% 1 7% 6% 5% 5% 4 5% 6% 44%	2090
October	1st to 10th	Day	11% 6% 2 6% 3 3 3 3 5% 6% 52%	2090
	11th to 20th	Day	11% 3 1 4 3 2 3 3 5% 7% 58%	1978
	21st to end	Day	10% 3 2 4 4 3 4 3 5% 6% 57%	2090
November	1st to 10th	Day	12% 6% 2 4 4 3 4 3 5% 6% 52%	1882
	11th to 20th	Day	12% 5% 2 5% 4 3 3 2 5% 6% 54%	1800
	21st to end	Day	14% 6% 2 5% 4 4 3 2 5% 8% 47%	1800
December	1st to 10th	Day	13% 6% 2 6% 4 3 3 3 4 6% 51%	2930
	11th to 20th	Day	14% 6% 2 6% 3 3 4 3 5% 6% 48%	3373
	21st to end	Day	20% 8% 3 6% 3 2 3 3 4 5% 42%	4466
January	1st to 10th	Night	13% 5% 1 4 3 3 4 3 5% 6% 52%	5889
	11th to 20th	Night	11% 6% 2 7% 5% 4 4 4 5% 6% 46%	5900
	21st to end	Night	16% 7% 3 6% 3 4 4 3 5% 7% 43%	6233
February	1st to 10th	Night	13% 7% 3 6% 4 3 4 4 5% 6% 46%	2400
	11th to 20th	Night	18% 6% 2 5% 4 3 3 3 4 6% 46%	2338
	21st to end	Night	13% 8% 2 5% 3 3 4 3 6% 6% 47%	1980
March	1st to 10th	Night	20% 7% 2 5% 4 3 4 4 5% 6% 40%	5125
	11th to 20th	Night	10% 4 2 4 3 4 4 4 6% 8% 51%	4980
	21st to end	Night	13% 5% 2 6% 4 4 4 4 5% 6% 48%	5467
April	1st to 10th	Night	11% 4 2 5% 4 4 4 3 6% 7% 49%	2200
	11th to 20th	Night	10% 4 2 5% 3 4 4 4 5% 9% 50%	2031
	21st to end	Night	6% 4 1 5% 3 4 4 4 6% 7% 55%	1845
May	1st to 10th	Night	6% 5% 2 7% 5% 4 5% 4 7% 10% 45%	2903
	11th to 20th	Night	14% 5% 2 6% 4 4 4 4 6% 7% 43%	2902
	21st to end	Night	6% 4 2 5% 4 3 4 4 6% 11% 51%	3130
June	1st to 10th	Night	9% 6% 2 8% 6% 5% 7% 6% 8% 10% 33%	1710
	11th to 20th	Night	4 4 2 6% 5% 6% 6% 5% 8% 11% 43%	1710
	21st to end	Night	5% 6% 3 6% 5% 6% 8% 6% 9% 11% 35%	1710
July	1st to 10th	Night	11% 8% 3 9% 7% 7% 7% 6% 9% 11% 23%	2840
	11th to 20th	Night	5% 4 2 6% 6% 6% 7% 7% 10% 13% 33%	2840
	21st to end	Night	8% 8% 3 9% 7% 7% 8% 7% 9% 12% 24%	3087
August	1st to 10th	Night	11% 7% 2 7% 6% 6% 6% 5% 8% 12% 30%	2825
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 5% 8% 12% 43%	3066
	21st to end	Night	6% 4 1 5% 4 4 5% 5% 7% 11% 48%	3528
September	1st to 10th	Night	11% 7% 2 6% 5% 6% 5% 5% 8% 9% 36%	2090
	11th to 20th	Night	11% 7% 3 8% 5% 4 5% 4 5% 7% 40%	2090
	21st to end	Night	9% 6% 3 7% 5% 4 4 5% 6% 7% 44%	2090
October	1st to 10th	Night	10% 6% 2 6% 3 3 4 3 4 6% 53%	2090
	11th to 20th	Night	11% 4 1 4 3 3 3 3 4 5% 60%	2199
	21st to end	Night	10% 5% 1 4 3 3 4 3 3 5% 58%	2508
November	1st to 10th	Night	11% 4 2 5% 4 4 3 3 4 5% 54%	2411
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 4 6% 55%	2600
	21st to end	Night	13% 6% 2 5% 4 3 4 3 4 6% 50%	2600
December	1st to 10th	Night	12% 5% 2 5% 3 3 3 2 4 5% 56%	4250
	11th to 20th	Night	14% 5% 2 5% 4 4 3 3 4 5% 51%	4822
	21st to end	Night	18% 8% 3 6% 4 4 3 3 4 5% 42%	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	34% 4 4 15% 34% 9%	4057
	11th to 20th	Day	32% 3 5% 15% 31% 15%	4060
	21st to end	Day	40% 4 7% 17% 20% 13%	4719
February	1st to 10th	Day	43% 5% 7% 16% 19% 9%	2000
	11th to 20th	Day	42% 4 6% 16% 24% 8%	1958
	21st to end	Day	39% 6% 7% 17% 20% 12%	1650
March	1st to 10th	Day	45% 5% 8% 13% 19% 9%	4728
	11th to 20th	Day	28% 5% 9% 15% 20% 22%	4980
	21st to end	Day	39% 4 8% 19% 18% 11%	5465
April	1st to 10th	Day	36% 6% 8% 21% 18% 11%	2200
	11th to 20th	Day	32% 4 8% 21% 23% 12%	2333
	21st to end	Day	28% 5% 10% 25% 25% 7%	2554
May	1st to 10th	Day	34% 8% 12% 24% 19% 4	4250
	11th to 20th	Day	41% 8% 12% 23% 14% 2	4215
	21st to end	Day	28% 8% 17% 26% 19% 2	4554
June	1st to 10th	Day	42% 11% 16% 18% 12% 2	2470
	11th to 20th	Day	29% 11% 18% 24% 16% 2	2470
	21st to end	Day	38% 13% 18% 17% 11% 2	2470
July	1st to 10th	Day	48% 14% 24% 10% 3 1	4055
	11th to 20th	Day	37% 13% 25% 21% 3 1	4051
	21st to end	Day	47% 15% 20% 13% 4	4324
August	1st to 10th	Day	42% 10% 22% 22% 4	4091
	11th to 20th	Day	30% 8% 16% 31% 14%	3781
	21st to end	Day	33% 9% 19% 29% 9% 1	4094
September	1st to 10th	Day	40% 10% 18% 15% 15% 3	2090
	11th to 20th	Day	41% 8% 11% 18% 17% 4	2090
	21st to end	Day	41% 7% 9% 18% 19% 7%	2090
October	1st to 10th	Day	34% 3 6% 13% 27% 17%	3480
	11th to 20th	Day	16% 2 5% 17% 25% 34%	3270
	21st to end	Day	19% 4 5% 18% 38% 16%	3428
November	1st to 10th	Day	33% 5% 8% 14% 24% 15%	1882
	11th to 20th	Day	32% 4 6% 16% 26% 16%	1800
	21st to end	Day	37% 5% 7% 17% 23% 11%	1800
December	1st to 10th	Day	36% 4 8% 15% 28% 10%	2930
	11th to 20th	Day	37% 4 7% 23% 23% 7%	3370
	21st to end	Day	45% 4 5% 20% 23% 3	4466
January	1st to 10th	Night	32% 4 6% 16% 33% 10%	5889
	11th to 20th	Night	39% 4 4 17% 26% 10%	5900
	21st to end	Night	42% 4 6% 15% 25% 9%	6233
February	1st to 10th	Night	39% 4 8% 16% 22% 11%	2400
	11th to 20th	Night	40% 4 7% 15% 22% 13%	2339
	21st to end	Night	37% 4 9% 16% 18% 15%	1980
March	1st to 10th	Night	43% 5% 8% 15% 17% 12%	5125
	11th to 20th	Night	30% 5% 9% 14% 23% 19%	4980
	21st to end	Night	37% 4 8% 17% 21% 14%	5467
April	1st to 10th	Night	34% 6% 9% 19% 19% 13%	2200
	11th to 20th	Night	31% 6% 7% 20% 24% 12%	2031
	21st to end	Night	26% 6% 11% 25% 23% 8%	1845
May	1st to 10th	Night	30% 11% 14% 23% 17% 5%	2930
	11th to 20th	Night	37% 9% 15% 24% 13% 2	2903
	21st to end	Night	26% 8% 15% 27% 20% 4	3138
June	1st to 10th	Night	41% 11% 16% 18% 13% 1	1710
	11th to 20th	Night	30% 10% 20% 25% 13% 2	1710
	21st to end	Night	37% 14% 19% 16% 12% 3	1710
July	1st to 10th	Night	50% 15% 21% 8% 4 1	2795
	11th to 20th	Night	38% 14% 26% 17% 4	2786
	21st to end	Night	48% 16% 20% 12% 3 1	2988
August	1st to 10th	Night	45% 10% 22% 21% 2	2814
	11th to 20th	Night	29% 12% 18% 29% 11% 1	3095
	21st to end	Night	28% 9% 22% 31% 9% 1	3528
September	1st to 10th	Night	41% 11% 16% 15% 13% 4	2090
	11th to 20th	Night	41% 9% 13% 15% 17% 4	2090
	21st to end	Night	37% 8% 13% 16% 20% 6%	2090
October	1st to 10th	Night	34% 4 8% 12% 22% 18%	3480
	11th to 20th	Night	17% 3 5% 12% 28% 36%	3646
	21st to end	Night	19% 3 4 19% 33% 21%	4120
November	1st to 10th	Night	33% 4 7% 14% 26% 15%	2411
	11th to 20th	Night	33% 3 6% 15% 28% 16%	2600
	21st to end	Night	36% 5% 7% 19% 22% 12%	2600
December	1st to 10th	Night	32% 3 6% 20% 29% 10%	4250
	11th to 20th	Night	36% 4 9% 18% 24% 8%	4824
	21st to end	Night	44% 4 5% 19% 25% 3	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	13% 19% 47% 16% 4	300
	11th to 20th	Day	14% 19% 36% 20% 9% 2	300
	21st to end	Day	23% 20% 40% 12% 5%	330
February	1st to 10th	Day	15% 19% 36% 23% 6%	300
	11th to 20th	Day	28% 16% 33% 21% 2	300
	21st to end	Day	16% 18% 43% 18% 4	249
March	1st to 10th	Day	16% 18% 30% 26% 9% 1	405
	11th to 20th	Day	14% 12% 35% 28% 9% 1	500
	21st to end	Day	16% 13% 34% 29% 9% 1	550
April	1st to 10th	Day	16% 15% 27% 27% 14% 2	500
	11th to 20th	Day	12% 11% 30% 26% 18% 3	492
	21st to end	Day	7% 8% 23% 30% 24% 7%	500
May	1st to 10th	Day	7% 9% 26% 30% 21% 7%	503
	11th to 20th	Day	10% 2 18% 34% 22% 14%	527
	21st to end	Day	8% 4 14% 28% 29% 16%	549
June	1st to 10th	Day	12% 1 10% 31% 30% 17%	490
	11th to 20th	Day	8% 2 12% 21% 26% 30%	490
	21st to end	Day	6% 1 11% 25% 33% 24%	490
July	1st to 10th	Day	7% 2 6% 17% 35% 34%	485
	11th to 20th	Day	5% 1 5% 16% 33% 40%	484
	21st to end	Day	5% 2 5% 17% 42% 29%	532
August	1st to 10th	Day	11% 1 8% 20% 31% 29%	486
	11th to 20th	Day	6% 1 5% 18% 35% 35%	479
	21st to end	Day	11% 2 6% 22% 36% 23%	539
September	1st to 10th	Day	11% 3 9% 24% 33% 20%	490
	11th to 20th	Day	14% 2 12% 27% 32% 14%	490
	21st to end	Day	13% 2 13% 27% 30% 16%	490
October	1st to 10th	Day	15% 3 22% 30% 20% 10%	490
	11th to 20th	Day	9% 6% 20% 32% 25% 8%	490
	21st to end	Day	10% 7% 23% 31% 25% 4	539
November	1st to 10th	Day	19% 4 21% 33% 17% 5%	420
	11th to 20th	Day	14% 11% 38% 25% 10% 2	300
	21st to end	Day	11% 15% 30% 28% 14% 2	300
December	1st to 10th	Day	17% 14% 35% 24% 8% 2	300
	11th to 20th	Day	21% 13% 35% 21% 7% 2	300
	21st to end	Day	25% 13% 27% 25% 10% 1	330
January	1st to 10th	Night	17% 13% 38% 26% 6% 1	800
	11th to 20th	Night	15% 11% 32% 32% 10%	800
	21st to end	Night	20% 11% 37% 29% 3	880
February	1st to 10th	Night	16% 10% 34% 32% 8%	800
	11th to 20th	Night	20% 11% 35% 29% 5%	783
	21st to end	Night	17% 9% 38% 32% 3	660
March	1st to 10th	Night	14% 12% 32% 35% 7%	800
	11th to 20th	Night	13% 11% 34% 30% 12% 1	800
	21st to end	Night	11% 12% 33% 33% 10%	880
April	1st to 10th	Night	12% 11% 30% 33% 14%	800
	11th to 20th	Night	12% 7% 29% 33% 17% 1	649
	21st to end	Night	7% 5% 26% 41% 21% 1	600
May	1st to 10th	Night	8% 5% 25% 40% 22% 1	600
	11th to 20th	Night	9% 3 21% 37% 26% 4	591
	21st to end	Night	8% 2 14% 36% 34% 6%	634
June	1st to 10th	Night	10% 3 11% 38% 33% 5%	570
	11th to 20th	Night	5% 1 9% 34% 39% 12%	570
	21st to end	Night	6% 1 9% 32% 43% 8%	570
July	1st to 10th	Night	8% 1 6% 28% 41% 16%	555
	11th to 20th	Night	9% 3 20% 50% 18%	552
	21st to end	Night	7% 1 5% 28% 48% 11%	624
August	1st to 10th	Night	7% 2 8% 25% 44% 15%	567
	11th to 20th	Night	9% 2 5% 22% 52% 11%	564
	21st to end	Night	11% 2 7% 26% 41% 14%	653
September	1st to 10th	Night	11% 1 9% 27% 41% 10%	760
	11th to 20th	Night	14% 1 9% 30% 39% 6%	760
	21st to end	Night	13% 1 12% 33% 39% 3	760
October	1st to 10th	Night	13% 2 19% 35% 27% 5%	760
	11th to 20th	Night	13% 4 19% 34% 26% 3	760
	21st to end	Night	11% 5% 21% 37% 25% 2	836
November	1st to 10th	Night	13% 6% 21% 37% 22% 1	780
	11th to 20th	Night	16% 7% 27% 36% 14% 2	800
	21st to end	Night	16% 9% 30% 29% 16% 1	800
December	1st to 10th	Night	14% 9% 31% 32% 14% 1	800
	11th to 20th	Night	16% 7% 31% 32% 12% 1	800
	21st to end	Night	23% 10% 24% 33% 9% 1	880

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