Wild Duck Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wild Duck Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	126801
	Night	14% 9% 3 7% 5% 4 4 3 5% 7% 38%	123626
Transparency	Day	43% 7% 11% 23% 15% 2	130455
	Night	43% 6% 10% 22% 16% 3	128043
Seeing	Day	16% 9% 24% 24% 18% 8%	16690
	Night	18% 8% 25% 31% 17% 2	26359

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% 13% 9% 9% 4 4 4 3 5% 6% 28%	3617
	11th to 20th	Day	14% 12% 5% 14% 4 5% 4 3 4 4 31%	3879
	21st to end	Day	22% 10% 6% 7% 5% 4 3 3 4 6% 30%	4466
February	1st to 10th	Day	18% 12% 5% 8% 4 3 3 3 4 6% 33%	1996
	11th to 20th	Day	18% 11% 4 8% 4 4 5% 3 4 5% 34%	1948
	21st to end	Day	18% 12% 4 7% 4 4 5% 3 5% 6% 32%	1650
March	1st to 10th	Day	19% 12% 4 7% 4 4 3 3 3 5% 36%	4480
	11th to 20th	Day	13% 8% 2 6% 4 4 4 3 6% 8% 42%	4928
	21st to end	Day	15% 8% 3 8% 5% 5% 4 3 5% 8% 36%	5506
April	1st to 10th	Day	15% 8% 3 6% 4 4 4 4 5% 7% 39%	2400
	11th to 20th	Day	17% 8% 2 6% 5% 5% 4 3 5% 6% 39%	2374
	21st to end	Day	17% 7% 2 6% 5% 5% 4 4 5% 6% 38%	2588
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 6% 4 7% 8% 26%	5862
	11th to 20th	Day	18% 8% 3 7% 4 5% 5% 4 6% 7% 33%	5861
	21st to end	Day	13% 7% 2 7% 5% 5% 6% 5% 8% 10% 32%	6433
June	1st to 10th	Day	11% 4 2 7% 5% 5% 5% 4 6% 8% 43%	2610
	11th to 20th	Day	8% 5% 2 5% 5% 5% 6% 5% 8% 9% 43%	2800
	21st to end	Day	8% 5% 2 5% 4 6% 5% 5% 7% 10% 43%	2800
July	1st to 10th	Day	11% 6% 2 6% 4 4 6% 4 7% 10% 39%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 6% 9% 10% 37%	6181
	21st to end	Day	10% 9% 3 9% 6% 7% 6% 5% 8% 9% 28%	6424
August	1st to 10th	Day	7% 5% 2 5% 4 4 5% 5% 7% 10% 47%	4234
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	4019
	21st to end	Day	5% 4 2 4 4 4 4 4 6% 8% 55%	4312
September	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 4 5% 7% 45%	2310
	11th to 20th	Day	11% 4 2 5% 4 4 4 4 7% 8% 49%	2200
	21st to end	Day	15% 5% 2 5% 4 4 4 3 5% 6% 47%	2200
October	1st to 10th	Day	10% 4 1 6% 4 4 4 3 5% 6% 55%	2200
	11th to 20th	Day	12% 5% 2 6% 5% 3 4 3 5% 7% 49%	2090
	21st to end	Day	18% 7% 2 6% 3 4 3 3 5% 5% 43%	2010
November	1st to 10th	Day	13% 5% 2 5% 4 3 3 3 4 6% 52%	1852
	11th to 20th	Day	14% 10% 3 6% 4 3 3 3 5% 6% 42%	1863
	21st to end	Day	18% 10% 3 6% 4 3 4 3 4 6% 38%	1800
December	1st to 10th	Day	18% 10% 2 6% 4 3 3 3 4 5% 41%	2930
	11th to 20th	Day	17% 12% 5% 10% 6% 6% 5% 4 4 5% 28%	3373
	21st to end	Day	21% 17% 5% 9% 4 4 4 3 5% 5% 22%	4245
January	1st to 10th	Night	15% 15% 6% 13% 5% 4 4 3 5% 6% 24%	6348
	11th to 20th	Night	16% 13% 6% 13% 6% 4 4 3 3 4 28%	6068
	21st to end	Night	20% 10% 4 7% 4 4 4 3 4 5% 36%	6490
February	1st to 10th	Night	20% 12% 4 7% 5% 5% 4 4 4 6% 28%	2400
	11th to 20th	Night	19% 10% 4 8% 5% 4 4 3 4 5% 33%	2338
	21st to end	Night	21% 11% 4 8% 5% 3 4 3 4 5% 31%	1980
March	1st to 10th	Night	19% 13% 2 6% 4 4 3 3 4 5% 36%	5373
	11th to 20th	Night	13% 6% 2 7% 4 4 5% 3 5% 6% 46%	5031
	21st to end	Night	16% 9% 3 9% 6% 5% 5% 3 6% 6% 34%	5453
April	1st to 10th	Night	15% 6% 3 6% 5% 4 5% 4 5% 7% 40%	2000
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 4 6% 42%	1975
	21st to end	Night	17% 6% 2 7% 5% 5% 4 4 6% 7% 38%	1810
May	1st to 10th	Night	19% 10% 3 9% 6% 5% 4 4 5% 8% 26%	4033
	11th to 20th	Night	16% 7% 2 7% 6% 5% 5% 5% 7% 7% 33%	4032
	21st to end	Night	11% 6% 3 8% 5% 4 6% 5% 7% 10% 36%	4421
June	1st to 10th	Night	9% 5% 2 5% 4 4 5% 3 6% 9% 49%	1783
	11th to 20th	Night	7% 4 2 6% 5% 3 5% 4 7% 8% 49%	1600
	21st to end	Night	5% 4 1 5% 5% 4 4 5% 8% 12% 47%	1600
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 4 3 6% 8% 48%	3618
	11th to 20th	Night	7% 5% 2 6% 5% 5% 6% 4 7% 10% 43%	3783
	21st to end	Night	8% 8% 3 9% 6% 6% 6% 4 8% 10% 33%	4427
August	1st to 10th	Night	6% 4 2 5% 3 3 4 3 7% 10% 52%	2915
	11th to 20th	Night	5% 5% 2 7% 5% 5% 5% 4 6% 10% 44%	3025
	21st to end	Night	3 3 1 4 2 3 3 3 6% 10% 61%	3586
September	1st to 10th	Night	10% 6% 2 4 4 4 4 3 6% 8% 50%	2070
	11th to 20th	Night	9% 5% 2 5% 3 3 4 4 6% 6% 53%	2200
	21st to end	Night	13% 6% 2 5% 3 3 4 3 4 6% 51%	2200
October	1st to 10th	Night	8% 5% 2 5% 3 3 3 2 4 6% 58%	2200
	11th to 20th	Night	12% 5% 2 6% 3 5% 4 3 4 7% 49%	2309
	21st to end	Night	18% 7% 2 5% 4 4 3 3 4 6% 45%	2828
November	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 49%	2666
	11th to 20th	Night	14% 8% 3 6% 5% 3 4 3 4 7% 44%	2692
	21st to end	Night	17% 10% 3 7% 4 4 3 3 4 7% 38%	2600
December	1st to 10th	Night	19% 11% 4 7% 4 3 3 3 4 4 39%	4250
	11th to 20th	Night	20% 11% 4 8% 4 4 3 3 4 6% 34%	4822
	21st to end	Night	22% 15% 5% 11% 6% 5% 5% 3 4 4 20%	6700

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	56% 4 9% 21% 9% 1	3618
	11th to 20th	Day	57% 4 6% 18% 12% 2	3879
	21st to end	Day	56% 4 9% 20% 8% 3	4466
February	1st to 10th	Day	52% 4 9% 22% 10% 2	1996
	11th to 20th	Day	53% 5% 8% 20% 12% 2	1958
	21st to end	Day	53% 5% 9% 21% 11% 2	1650
March	1st to 10th	Day	51% 4 6% 18% 15% 6%	4480
	11th to 20th	Day	40% 5% 10% 26% 18% 2	4928
	21st to end	Day	45% 6% 13% 23% 12% 1	5508
April	1st to 10th	Day	43% 7% 12% 22% 14% 2	2400
	11th to 20th	Day	45% 5% 9% 22% 15% 3	2374
	21st to end	Day	46% 6% 10% 24% 11% 2	2588
May	1st to 10th	Day	52% 9% 13% 17% 10%	5897
	11th to 20th	Day	48% 8% 12% 22% 10%	5865
	21st to end	Day	42% 9% 16% 17% 14% 1	6447
June	1st to 10th	Day	37% 8% 11% 25% 17% 3	2610
	11th to 20th	Day	35% 9% 13% 24% 18% 2	2800
	21st to end	Day	34% 9% 14% 21% 19% 4	2800
July	1st to 10th	Day	37% 8% 12% 22% 19% 1	6291
	11th to 20th	Day	36% 11% 15% 26% 11% 1	6106
	21st to end	Day	47% 10% 14% 17% 10% 1	6240
August	1st to 10th	Day	29% 9% 15% 34% 13% 1	4221
	11th to 20th	Day	34% 8% 13% 28% 15% 2	4058
	21st to end	Day	24% 7% 13% 34% 17% 4	4311
September	1st to 10th	Day	37% 5% 12% 21% 19% 5%	2310
	11th to 20th	Day	32% 6% 12% 24% 23% 3	2200
	21st to end	Day	38% 5% 8% 22% 25% 3	2200
October	1st to 10th	Day	20% 4 5% 28% 39% 3	3590
	11th to 20th	Day	25% 4 10% 28% 31% 3	3382
	21st to end	Day	32% 4 8% 28% 21% 7%	3222
November	1st to 10th	Day	34% 4 9% 28% 21% 4	1852
	11th to 20th	Day	43% 4 8% 23% 18% 5%	1863
	21st to end	Day	47% 5% 8% 23% 17% 1	1800
December	1st to 10th	Day	46% 4 9% 25% 16% 1	2930
	11th to 20th	Day	58% 5% 8% 18% 10% 1	3370
	21st to end	Day	63% 6% 11% 14% 6% 1	4245
January	1st to 10th	Night	60% 5% 9% 16% 9% 1	6348
	11th to 20th	Night	60% 5% 7% 15% 10% 3	6068
	21st to end	Night	50% 4 8% 22% 14% 2	6490
February	1st to 10th	Night	57% 5% 10% 18% 8% 1	2400
	11th to 20th	Night	53% 4 8% 21% 13% 1	2339
	21st to end	Night	55% 5% 10% 15% 12% 3	1980
March	1st to 10th	Night	51% 4 6% 22% 13% 4	5373
	11th to 20th	Night	38% 5% 10% 25% 20% 2	5031
	21st to end	Night	48% 6% 9% 23% 12% 1	5453
April	1st to 10th	Night	41% 6% 11% 23% 16% 3	2000
	11th to 20th	Night	43% 5% 9% 19% 19% 5%	1975
	21st to end	Night	45% 6% 11% 22% 13% 3	1810
May	1st to 10th	Night	53% 9% 10% 18% 8% 1	4060
	11th to 20th	Night	47% 8% 13% 22% 9% 1	4033
	21st to end	Night	39% 10% 16% 22% 12% 2	4429
June	1st to 10th	Night	31% 6% 12% 28% 19% 4	1783
	11th to 20th	Night	30% 8% 14% 23% 21% 5%	1600
	21st to end	Night	28% 9% 18% 22% 18% 6%	1600
July	1st to 10th	Night	34% 7% 12% 25% 20% 2	3580
	11th to 20th	Night	33% 11% 16% 27% 12% 2	3738
	21st to end	Night	41% 11% 15% 19% 13% 1	4297
August	1st to 10th	Night	25% 8% 15% 36% 14% 2	2904
	11th to 20th	Night	31% 9% 13% 29% 16% 1	3052
	21st to end	Night	17% 6% 15% 34% 23% 4	3586
September	1st to 10th	Night	31% 7% 12% 23% 21% 6%	2070
	11th to 20th	Night	30% 6% 10% 26% 24% 5%	2200
	21st to end	Night	34% 5% 9% 22% 25% 5%	2200
October	1st to 10th	Night	20% 4 6% 20% 47% 3	3590
	11th to 20th	Night	25% 3 7% 25% 34% 6%	3756
	21st to end	Night	32% 3 7% 21% 29% 7%	4566
November	1st to 10th	Night	36% 4 9% 24% 23% 4	2666
	11th to 20th	Night	40% 4 8% 22% 21% 5%	2692
	21st to end	Night	48% 4 9% 23% 16% 1	2600
December	1st to 10th	Night	49% 4 10% 22% 14%	4250
	11th to 20th	Night	51% 4 11% 20% 12% 1	4824
	21st to end	Night	66% 5% 8% 14% 6%	6700

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% 18% 34% 18% 8% 1	300
	11th to 20th	Day	25% 20% 36% 14% 6%	300
	21st to end	Day	24% 18% 39% 17% 2	330
February	1st to 10th	Day	22% 18% 41% 15% 4	300
	11th to 20th	Day	26% 23% 39% 9% 4	300
	21st to end	Day	28% 18% 35% 15% 5%	249
March	1st to 10th	Day	21% 20% 36% 18% 4	300
	11th to 20th	Day	23% 15% 35% 19% 7% 1	474
	21st to end	Day	24% 17% 33% 20% 6%	550
April	1st to 10th	Day	21% 15% 29% 22% 12% 1	500
	11th to 20th	Day	22% 14% 27% 21% 11% 5%	492
	21st to end	Day	19% 12% 31% 25% 9% 3	500
May	1st to 10th	Day	20% 11% 28% 23% 12% 5%	503
	11th to 20th	Day	19% 7% 24% 26% 17% 7%	527
	21st to end	Day	15% 6% 20% 27% 20% 12%	573
June	1st to 10th	Day	13% 5% 19% 26% 25% 13%	540
	11th to 20th	Day	8% 4 17% 34% 25% 11%	730
	21st to end	Day	10% 3 20% 28% 25% 13%	730
July	1st to 10th	Day	15% 2 14% 24% 25% 21%	721
	11th to 20th	Day	9% 4 16% 27% 30% 14%	643
	21st to end	Day	11% 3 13% 26% 29% 18%	576
August	1st to 10th	Day	9% 2 13% 28% 28% 20%	526
	11th to 20th	Day	11% 3 13% 29% 30% 14%	519
	21st to end	Day	9% 2 9% 30% 30% 20%	583
September	1st to 10th	Day	15% 2 14% 27% 29% 13%	530
	11th to 20th	Day	10% 3 9% 25% 36% 17%	530
	21st to end	Day	17% 5% 17% 25% 26% 10%	530
October	1st to 10th	Day	10% 3 16% 34% 28% 9%	530
	11th to 20th	Day	12% 10% 30% 28% 15% 6%	530
	21st to end	Day	20% 13% 35% 20% 11% 1	393
November	1st to 10th	Day	18% 11% 28% 29% 11% 4	330
	11th to 20th	Day	19% 17% 31% 23% 9% 2	321
	21st to end	Day	23% 9% 32% 27% 7%	300
December	1st to 10th	Day	21% 20% 30% 21% 7% 1	300
	11th to 20th	Day	24% 10% 39% 18% 9%	300
	21st to end	Day	31% 16% 29% 19% 4	330
January	1st to 10th	Night	22% 15% 32% 26% 5%	1000
	11th to 20th	Night	27% 14% 35% 21% 3	877
	21st to end	Night	24% 11% 39% 24% 2	880
February	1st to 10th	Night	26% 12% 34% 26% 3	800
	11th to 20th	Night	26% 12% 38% 22% 2	783
	21st to end	Night	27% 12% 39% 21% 1	660
March	1st to 10th	Night	23% 13% 32% 27% 5%	800
	11th to 20th	Night	23% 11% 34% 24% 7% 1	800
	21st to end	Night	22% 10% 31% 29% 7%	878
April	1st to 10th	Night	17% 11% 34% 31% 8%	600
	11th to 20th	Night	18% 10% 28% 32% 10% 2	593
	21st to end	Night	18% 6% 32% 34% 10% 1	600
May	1st to 10th	Night	20% 7% 29% 29% 15% 1	600
	11th to 20th	Night	16% 6% 16% 38% 20% 3	591
	21st to end	Night	10% 2 19% 36% 27% 5%	650
June	1st to 10th	Night	11% 3 16% 41% 25% 4	600
	11th to 20th	Night	8% 4 11% 43% 31% 4	600
	21st to end	Night	6% 1 15% 42% 31% 5%	600
July	1st to 10th	Night	12% 2 8% 30% 40% 9%	585
	11th to 20th	Night	9% 2 9% 36% 40% 5%	582
	21st to end	Night	12% 2 9% 36% 35% 7%	657
August	1st to 10th	Night	9% 2 7% 33% 44% 5%	597
	11th to 20th	Night	7% 1 9% 39% 37% 7%	594
	21st to end	Night	7% 7% 36% 43% 7%	660
September	1st to 10th	Night	12% 2 10% 36% 36% 5%	670
	11th to 20th	Night	11% 3 11% 30% 40% 5%	800
	21st to end	Night	15% 4 17% 33% 29% 3	800
October	1st to 10th	Night	10% 4 17% 37% 28% 5%	800
	11th to 20th	Night	14% 7% 25% 36% 17% 1	800
	21st to end	Night	20% 7% 30% 30% 13%	880
November	1st to 10th	Night	14% 8% 29% 32% 15% 2	820
	11th to 20th	Night	17% 10% 33% 29% 11%	829
	21st to end	Night	22% 10% 27% 29% 11% 1	800
December	1st to 10th	Night	26% 10% 31% 28% 5%	800
	11th to 20th	Night	26% 9% 34% 23% 7% 1	800
	21st to end	Night	29% 13% 30% 24% 4	973

Page generated at 2025-11-15 00:55:57. Version ac07

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