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 2024-01-12.

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% 7% 3 6% 5% 3 5% 5% 5% 7% 39%	75092
	Night	15% 8% 3 6% 5% 3 4 4 5% 7% 40%	74610
Transparency	Day	44% 6% 11% 22% 14% 2	74805
	Night	43% 6% 11% 22% 15% 3	74417
Seeing	Day	17% 9% 23% 24% 18% 9%	14142
	Night	18% 7% 24% 30% 17% 2	23957

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	17% 8% 5% 9% 5% 4 5% 4 4 6% 33%	1517
	11th to 20th	Day	21% 12% 6% 8% 6% 4 4 4 3 6% 26%	1556
	21st to end	Day	16% 10% 5% 7% 7% 3 4 4 5% 6% 32%	1782
February	1st to 10th	Day	19% 11% 6% 8% 5% 2 4 4 4 6% 31%	1796
	11th to 20th	Day	18% 11% 4 7% 5% 3 5% 4 4 6% 33%	1748
	21st to end	Day	19% 12% 4 7% 4 3 5% 4 5% 6% 30%	1480
March	1st to 10th	Day	19% 8% 3 6% 5% 3 4 4 5% 6% 38%	1800
	11th to 20th	Day	19% 9% 3 7% 6% 4 5% 4 5% 7% 33%	1956
	21st to end	Day	18% 10% 4 7% 6% 3 4 5% 5% 7% 31%	2194
April	1st to 10th	Day	14% 7% 3 5% 5% 3 5% 4 5% 8% 40%	2160
	11th to 20th	Day	18% 8% 2 5% 5% 4 5% 4 4 6% 39%	2134
	21st to end	Day	18% 7% 2 5% 5% 4 4 5% 5% 6% 38%	2328
May	1st to 10th	Day	19% 7% 3 5% 6% 4 5% 4 5% 7% 36%	2340
	11th to 20th	Day	19% 7% 3 5% 5% 3 5% 4 5% 7% 35%	2301
	21st to end	Day	9% 6% 2 6% 7% 4 7% 7% 7% 10% 36%	2531
June	1st to 10th	Day	11% 4 2 7% 6% 3 5% 5% 5% 8% 44%	2348
	11th to 20th	Day	8% 4 2 4 5% 4 6% 6% 7% 9% 44%	2520
	21st to end	Day	8% 5% 2 5% 5% 4 6% 6% 6% 10% 42%	2520
July	1st to 10th	Day	13% 6% 3 5% 5% 4 5% 7% 7% 11% 34%	2520
	11th to 20th	Day	8% 5% 3 6% 6% 4 6% 6% 7% 10% 40%	2453
	21st to end	Day	11% 5% 2 5% 6% 3 5% 6% 7% 9% 40%	2547
August	1st to 10th	Day	8% 6% 2 5% 6% 4 5% 6% 6% 10% 41%	2327
	11th to 20th	Day	9% 6% 3 5% 6% 3 5% 7% 7% 9% 40%	2223
	21st to end	Day	8% 5% 2 5% 6% 4 5% 6% 6% 8% 47%	2376
September	1st to 10th	Day	14% 6% 3 4 5% 3 5% 5% 4 7% 44%	2080
	11th to 20th	Day	12% 4 2 5% 4 3 3 5% 6% 8% 48%	1980
	21st to end	Day	14% 4 2 5% 4 3 4 3 4 7% 50%	1980
October	1st to 10th	Day	11% 4 2 5% 5% 3 5% 4 5% 6% 53%	1980
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 4 5% 7% 46%	1882
	21st to end	Day	18% 7% 2 5% 4 3 3 4 5% 5% 42%	1810
November	1st to 10th	Day	12% 4 3 4 4 2 4 3 4 6% 55%	1672
	11th to 20th	Day	15% 10% 3 6% 4 2 3 3 5% 5% 43%	1710
	21st to end	Day	18% 8% 3 5% 4 2 4 4 5% 6% 40%	1710
December	1st to 10th	Day	22% 12% 3 7% 5% 3 4 4 4 4 32%	1710
	11th to 20th	Day	14% 12% 5% 8% 6% 4 5% 5% 4 5% 32%	2153
	21st to end	Day	19% 16% 6% 7% 5% 3 4 5% 5% 5% 23%	2968
January	1st to 10th	Night	16% 12% 5% 9% 6% 4 4 4 4 6% 31%	2648
	11th to 20th	Night	21% 12% 6% 7% 7% 2 4 5% 4 5% 28%	2437
	21st to end	Night	17% 10% 5% 7% 6% 3 4 4 5% 6% 33%	2574
February	1st to 10th	Night	21% 12% 5% 6% 6% 3 5% 5% 4 6% 27%	2160
	11th to 20th	Night	18% 10% 4 7% 6% 3 5% 4 4 6% 34%	2098
	21st to end	Night	22% 11% 5% 7% 6% 2 4 4 4 5% 29%	1776
March	1st to 10th	Night	18% 9% 3 5% 6% 2 4 3 4 5% 41%	2160
	11th to 20th	Night	20% 8% 3 7% 5% 3 4 4 4 7% 35%	2003
	21st to end	Night	18% 9% 4 7% 6% 3 4 4 5% 7% 35%	2177
April	1st to 10th	Night	14% 5% 3 5% 5% 3 5% 5% 5% 7% 43%	1800
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 4 4 6% 42%	1775
	21st to end	Night	18% 6% 3 6% 6% 3 5% 4 5% 6% 39%	1630
May	1st to 10th	Night	17% 6% 3 6% 7% 4 5% 5% 5% 8% 35%	1620
	11th to 20th	Night	15% 4 2 6% 6% 4 5% 5% 5% 8% 39%	1592
	21st to end	Night	8% 4 2 6% 6% 3 6% 7% 7% 12% 40%	1744
June	1st to 10th	Night	8% 4 2 5% 4 3 5% 3 6% 10% 50%	1605
	11th to 20th	Night	7% 4 2 5% 5% 3 4 5% 7% 9% 50%	1440
	21st to end	Night	6% 3 2 4 5% 4 4 5% 8% 12% 47%	1440
July	1st to 10th	Night	10% 4 2 6% 6% 4 4 4 6% 9% 44%	1440
	11th to 20th	Night	7% 4 2 5% 4 2 5% 4 6% 10% 50%	1502
	21st to end	Night	8% 5% 2 5% 5% 3 4 4 5% 10% 49%	1771
August	1st to 10th	Night	8% 4 2 5% 4 3 4 5% 7% 11% 49%	1611
	11th to 20th	Night	6% 5% 2 5% 5% 4 6% 5% 6% 10% 45%	1674
	21st to end	Night	6% 4 1 4 3 3 4 5% 7% 9% 53%	1980
September	1st to 10th	Night	11% 5% 2 4 4 3 4 4 6% 8% 49%	1862
	11th to 20th	Night	10% 5% 2 4 4 3 3 5% 6% 6% 52%	1980
	21st to end	Night	11% 5% 2 5% 4 2 4 4 4 6% 54%	1980
October	1st to 10th	Night	8% 5% 2 4 4 2 3 3 4 6% 57%	1980
	11th to 20th	Night	14% 5% 3 6% 4 4 5% 4 4 7% 46%	2077
	21st to end	Night	18% 6% 3 5% 5% 3 4 4 4 6% 44%	2544
November	1st to 10th	Night	13% 5% 3 4 4 3 3 4 4 6% 51%	2406
	11th to 20th	Night	15% 7% 3 5% 6% 2 4 4 4 7% 44%	2470
	21st to end	Night	18% 9% 3 6% 4 3 4 4 4 7% 39%	2470
December	1st to 10th	Night	21% 9% 5% 6% 5% 3 4 5% 4 5% 33%	2470
	11th to 20th	Night	19% 10% 4 7% 6% 3 3 4 4 6% 34%	3042
	21st to end	Night	19% 16% 5% 9% 7% 4 6% 4 5% 5% 21%	4672

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	52% 5% 8% 21% 11% 2	1518
	11th to 20th	Day	61% 4 9% 17% 8% 1	1556
	21st to end	Day	52% 6% 10% 23% 7% 1	1782
February	1st to 10th	Day	55% 4 8% 22% 8% 2	1796
	11th to 20th	Day	53% 5% 8% 21% 10% 3	1758
	21st to end	Day	56% 5% 9% 19% 10% 3	1480
March	1st to 10th	Day	47% 4 10% 23% 15% 1	1800
	11th to 20th	Day	51% 6% 10% 19% 11% 3	1956
	21st to end	Day	53% 6% 10% 20% 9% 1	2194
April	1st to 10th	Day	41% 7% 12% 24% 14% 2	2160
	11th to 20th	Day	46% 5% 9% 21% 16% 4	2134
	21st to end	Day	47% 6% 10% 24% 11% 3	2328
May	1st to 10th	Day	47% 7% 13% 22% 11% 1	2340
	11th to 20th	Day	48% 8% 11% 19% 12% 1	2305
	21st to end	Day	41% 9% 16% 19% 13% 1	2531
June	1st to 10th	Day	37% 8% 11% 26% 17% 3	2348
	11th to 20th	Day	34% 9% 13% 24% 18% 2	2520
	21st to end	Day	35% 9% 14% 21% 17% 4	2520
July	1st to 10th	Day	41% 10% 13% 19% 14% 3	2451
	11th to 20th	Day	37% 9% 14% 22% 14% 3	2378
	21st to end	Day	37% 9% 15% 23% 14% 2	2405
August	1st to 10th	Day	36% 9% 14% 24% 15% 2	2314
	11th to 20th	Day	37% 8% 14% 24% 16% 1	2223
	21st to end	Day	33% 8% 14% 24% 16% 5%	2376
September	1st to 10th	Day	39% 5% 12% 22% 17% 5%	2080
	11th to 20th	Day	34% 6% 12% 23% 22% 3	1980
	21st to end	Day	35% 5% 9% 24% 25% 3	1980
October	1st to 10th	Day	32% 6% 8% 25% 24% 4	1980
	11th to 20th	Day	36% 5% 9% 25% 21% 4	1882
	21st to end	Day	43% 5% 9% 24% 15% 3	1810
November	1st to 10th	Day	32% 4 9% 29% 22% 5%	1672
	11th to 20th	Day	43% 4 8% 23% 18% 5%	1710
	21st to end	Day	45% 5% 8% 23% 17% 1	1710
December	1st to 10th	Day	55% 4 10% 20% 9% 1	1710
	11th to 20th	Day	54% 6% 8% 19% 13% 1	2150
	21st to end	Day	61% 6% 10% 15% 7% 1	2968
January	1st to 10th	Night	55% 5% 9% 18% 11% 2	2648
	11th to 20th	Night	59% 5% 9% 17% 9% 1	2437
	21st to end	Night	53% 5% 10% 22% 9% 2	2574
February	1st to 10th	Night	58% 5% 11% 19% 6% 1	2160
	11th to 20th	Night	52% 4 9% 21% 12% 1	2099
	21st to end	Night	58% 5% 10% 13% 11% 3	1776
March	1st to 10th	Night	46% 4 7% 21% 19% 3	2160
	11th to 20th	Night	50% 4 12% 20% 12% 3	2003
	21st to end	Night	49% 6% 12% 23% 8% 2	2177
April	1st to 10th	Night	39% 6% 11% 25% 17% 3	1800
	11th to 20th	Night	43% 4 9% 18% 20% 6%	1775
	21st to end	Night	45% 6% 11% 22% 13% 3	1630
May	1st to 10th	Night	47% 8% 10% 22% 11% 3	1620
	11th to 20th	Night	42% 8% 14% 20% 13% 2	1593
	21st to end	Night	35% 11% 15% 22% 14% 4	1745
June	1st to 10th	Night	31% 5% 12% 28% 19% 4	1605
	11th to 20th	Night	29% 7% 15% 24% 21% 5%	1440
	21st to end	Night	28% 8% 18% 22% 17% 7%	1440
July	1st to 10th	Night	37% 8% 14% 23% 15% 4	1400
	11th to 20th	Night	28% 7% 16% 26% 18% 4	1454
	21st to end	Night	31% 9% 15% 28% 16% 2	1672
August	1st to 10th	Night	29% 9% 18% 26% 17% 3	1600
	11th to 20th	Night	32% 9% 14% 25% 17% 2	1674
	21st to end	Night	24% 7% 18% 27% 19% 5%	1980
September	1st to 10th	Night	32% 7% 12% 23% 19% 6%	1862
	11th to 20th	Night	31% 6% 9% 26% 23% 4	1980
	21st to end	Night	32% 5% 8% 24% 26% 5%	1980
October	1st to 10th	Night	29% 5% 9% 26% 26% 4	1980
	11th to 20th	Night	38% 5% 8% 23% 22% 4	2077
	21st to end	Night	43% 4 8% 23% 19% 4	2544
November	1st to 10th	Night	35% 4 9% 24% 23% 5%	2406
	11th to 20th	Night	41% 4 8% 20% 22% 5%	2470
	21st to end	Night	47% 4 9% 23% 16% 1	2470
December	1st to 10th	Night	53% 5% 11% 19% 12% 1	2470
	11th to 20th	Night	52% 4 9% 21% 12% 2	3044
	21st to end	Night	64% 6% 10% 13% 7% 1	4672

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	20% 17% 35% 18% 9% 1	270
	11th to 20th	Day	27% 18% 33% 15% 7%	245
	21st to end	Day	23% 19% 39% 17% 2	264
February	1st to 10th	Day	24% 20% 39% 13% 4	240
	11th to 20th	Day	28% 22% 39% 9% 3	240
	21st to end	Day	32% 16% 33% 15% 5%	198
March	1st to 10th	Day	20% 18% 41% 18% 3	240
	11th to 20th	Day	23% 14% 34% 19% 8% 1	396
	21st to end	Day	25% 15% 31% 21% 7%	462
April	1st to 10th	Day	18% 15% 28% 24% 14% 1	420
	11th to 20th	Day	24% 12% 24% 22% 12% 6%	412
	21st to end	Day	21% 12% 32% 23% 9% 4	420
May	1st to 10th	Day	20% 11% 28% 24% 12% 5%	423
	11th to 20th	Day	19% 6% 23% 27% 17% 7%	447
	21st to end	Day	15% 4 18% 26% 23% 14%	485
June	1st to 10th	Day	13% 4 15% 26% 27% 14%	458
	11th to 20th	Day	8% 5% 17% 34% 24% 12%	630
	21st to end	Day	10% 4 21% 28% 25% 12%	630
July	1st to 10th	Day	15% 2 13% 23% 24% 23%	621
	11th to 20th	Day	9% 3 16% 25% 31% 15%	551
	21st to end	Day	12% 3 14% 26% 27% 18%	488
August	1st to 10th	Day	11% 1 13% 28% 28% 19%	446
	11th to 20th	Day	12% 3 13% 30% 28% 13%	439
	21st to end	Day	10% 2 9% 29% 29% 21%	495
September	1st to 10th	Day	17% 1 13% 26% 30% 13%	450
	11th to 20th	Day	10% 3 11% 26% 34% 16%	450
	21st to end	Day	16% 5% 17% 24% 27% 11%	450
October	1st to 10th	Day	11% 4 17% 36% 25% 8%	450
	11th to 20th	Day	13% 11% 31% 29% 13% 4	450
	21st to end	Day	21% 12% 36% 19% 12% 1	325
November	1st to 10th	Day	16% 9% 27% 31% 12% 5%	270
	11th to 20th	Day	19% 17% 29% 25% 9% 2	270
	21st to end	Day	23% 8% 32% 29% 8%	270
December	1st to 10th	Day	21% 21% 28% 21% 8% 1	270
	11th to 20th	Day	23% 10% 39% 18% 10%	270
	21st to end	Day	29% 18% 30% 19% 4	297
January	1st to 10th	Night	22% 15% 31% 26% 5%	950
	11th to 20th	Night	28% 13% 35% 22% 4	800
	21st to end	Night	24% 12% 37% 24% 2	792
February	1st to 10th	Night	27% 11% 33% 26% 3	720
	11th to 20th	Night	25% 12% 38% 24% 1	703
	21st to end	Night	28% 12% 38% 20% 1	592
March	1st to 10th	Night	22% 13% 33% 26% 6%	720
	11th to 20th	Night	24% 11% 34% 23% 7% 1	720
	21st to end	Night	22% 10% 29% 31% 7% 1	791
April	1st to 10th	Night	16% 9% 32% 34% 9%	540
	11th to 20th	Night	19% 9% 27% 32% 12% 2	533
	21st to end	Night	19% 6% 32% 32% 10% 1	540
May	1st to 10th	Night	20% 6% 29% 29% 15% 1	540
	11th to 20th	Night	16% 6% 16% 39% 20% 3	531
	21st to end	Night	9% 2 17% 36% 29% 6%	584
June	1st to 10th	Night	11% 2 15% 41% 27% 4	540
	11th to 20th	Night	7% 4 11% 43% 31% 4	540
	21st to end	Night	7% 1 15% 42% 31% 4	540
July	1st to 10th	Night	12% 2 8% 29% 39% 10%	525
	11th to 20th	Night	9% 2 9% 34% 42% 5%	522
	21st to end	Night	12% 1 9% 37% 34% 7%	591
August	1st to 10th	Night	9% 2 6% 33% 45% 5%	537
	11th to 20th	Night	7% 1 9% 39% 37% 7%	534
	21st to end	Night	8% 7% 36% 43% 7%	594
September	1st to 10th	Night	13% 1 9% 35% 37% 5%	602
	11th to 20th	Night	12% 3 12% 28% 40% 5%	720
	21st to end	Night	13% 3 18% 32% 30% 3	720
October	1st to 10th	Night	10% 4 18% 36% 26% 5%	720
	11th to 20th	Night	15% 7% 26% 35% 16% 1	720
	21st to end	Night	21% 7% 30% 30% 12% 1	792
November	1st to 10th	Night	14% 7% 27% 32% 17% 2	740
	11th to 20th	Night	17% 10% 33% 29% 11%	760
	21st to end	Night	22% 10% 27% 30% 11% 1	760
December	1st to 10th	Night	26% 10% 30% 28% 6%	760
	11th to 20th	Night	26% 9% 34% 24% 7% 1	760
	21st to end	Night	29% 12% 31% 24% 4	924

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