Duck Creek Conservation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Duck Creek Conservation Area clear sky chart from 2005-11-06 to 2025-07-06.

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	12% 6% 2 6% 4 4 4 4 6% 7% 45%	119688
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 46%	119311
Transparency	Day	37% 6% 11% 25% 18% 4	123338
	Night	36% 5% 10% 24% 20% 5%	123792
Seeing	Day	15% 9% 23% 26% 19% 8%	16380
	Night	16% 7% 26% 32% 17% 2	26199

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	16% 7% 2 6% 4 4 3 3 5% 6% 43%	3617
	11th to 20th	Day	11% 6% 2 6% 4 4 3 3 5% 6% 51%	4052
	21st to end	Day	20% 6% 2 5% 3 3 3 2 5% 5% 44%	4488
February	1st to 10th	Day	18% 9% 3 6% 4 4 3 4 4 6% 40%	1855
	11th to 20th	Day	18% 7% 3 6% 5% 4 3 3 5% 6% 42%	1948
	21st to end	Day	15% 9% 3 7% 4 4 4 4 5% 5% 39%	1650
March	1st to 10th	Day	18% 8% 4 7% 4 4 3 3 4 5% 41%	4521
	11th to 20th	Day	11% 6% 2 4 3 3 3 3 5% 6% 54%	4980
	21st to end	Day	14% 6% 2 6% 5% 5% 4 4 5% 7% 43%	5783
April	1st to 10th	Day	13% 6% 2 4 4 4 4 3 6% 7% 47%	2400
	11th to 20th	Day	15% 6% 3 6% 5% 4 4 3 5% 6% 42%	2374
	21st to end	Day	16% 8% 3 5% 4 4 5% 3 5% 8% 39%	2400
May	1st to 10th	Day	12% 7% 3 8% 6% 6% 6% 5% 7% 9% 29%	5446
	11th to 20th	Day	14% 7% 3 8% 6% 5% 5% 4 7% 8% 33%	5989
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 6% 7% 39%	6935
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 4 4 6% 9% 45%	2800
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 5% 7% 10% 49%	2800
	21st to end	Day	4 3 2 5% 5% 5% 5% 5% 9% 11% 48%	2800
July	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 5% 7% 10% 42%	4511
	11th to 20th	Day	5% 3 1 4 4 5% 5% 4 7% 10% 52%	4440
	21st to end	Day	9% 6% 3 8% 5% 6% 7% 5% 8% 9% 35%	4469
August	1st to 10th	Day	3 2 1 3 3 4 5% 4 6% 11% 57%	3954
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 46%	3729
	21st to end	Day	5% 4 1 4 3 4 4 3 5% 9% 58%	4180
September	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	2280
	11th to 20th	Day	10% 6% 2 6% 4 4 3 3 5% 7% 48%	2236
	21st to end	Day	11% 5% 2 5% 4 3 4 3 5% 7% 52%	2090
October	1st to 10th	Day	8% 4 1 4 4 3 3 2 5% 6% 59%	1937
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 4 6% 53%	1900
	21st to end	Day	17% 6% 2 5% 3 3 3 2 5% 6% 48%	2090
November	1st to 10th	Day	12% 5% 2 4 4 3 3 2 5% 6% 54%	1767
	11th to 20th	Day	13% 8% 2 5% 4 3 3 3 5% 5% 50%	1800
	21st to end	Day	19% 7% 2 5% 4 3 2 3 5% 4 46%	1800
December	1st to 10th	Day	11% 6% 2 6% 4 4 4 3 4 5% 51%	2677
	11th to 20th	Day	16% 7% 2 7% 4 3 4 3 4 5% 44%	3008
	21st to end	Day	24% 12% 4 8% 5% 4 3 3 4 5% 29%	3982
January	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 7% 39%	6348
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 5% 6% 47%	5923
	21st to end	Night	19% 6% 3 6% 4 3 4 3 4 5% 44%	6490
February	1st to 10th	Night	18% 10% 4 6% 4 3 3 3 4 6% 40%	2542
	11th to 20th	Night	17% 9% 3 7% 3 3 3 3 4 5% 44%	2338
	21st to end	Night	18% 7% 3 5% 4 3 3 3 5% 6% 43%	1980
March	1st to 10th	Night	17% 8% 3 7% 5% 4 4 3 4 4 41%	5373
	11th to 20th	Night	12% 6% 3 7% 4 4 4 3 4 6% 48%	4982
	21st to end	Night	13% 6% 2 7% 5% 5% 4 4 5% 8% 42%	5146
April	1st to 10th	Night	12% 5% 2 6% 3 3 3 3 5% 8% 49%	2000
	11th to 20th	Night	13% 5% 2 6% 4 4 4 4 5% 8% 45%	1975
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 7% 40%	2000
May	1st to 10th	Night	17% 7% 3 6% 5% 4 5% 4 6% 7% 36%	4448
	11th to 20th	Night	15% 8% 3 8% 5% 5% 4 4 5% 7% 38%	3906
	21st to end	Night	16% 7% 3 7% 5% 4 5% 4 5% 6% 38%	3942
June	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 7% 9% 46%	1600
	11th to 20th	Night	5% 4 1 3 3 3 4 4 6% 11% 56%	1600
	21st to end	Night	3 3 1 3 4 4 4 4 9% 10% 56%	1600
July	1st to 10th	Night	9% 4 1 5% 4 4 5% 3 7% 10% 48%	2570
	11th to 20th	Night	4 3 1 5% 3 4 4 3 6% 9% 58%	2530
	21st to end	Night	8% 7% 3 7% 5% 5% 5% 4 7% 9% 39%	3089
August	1st to 10th	Night	3 2 1 4 2 3 3 4 6% 9% 63%	2978
	11th to 20th	Night	7% 4 2 5% 4 5% 5% 3 6% 9% 51%	3100
	21st to end	Night	4 3 1 4 3 3 4 4 6% 10% 58%	3476
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 5% 7% 56%	1900
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 3 5% 7% 51%	1924
	21st to end	Night	9% 5% 1 5% 3 3 3 3 5% 5% 56%	2090
October	1st to 10th	Night	6% 4 1 4 3 3 4 3 4 6% 62%	2239
	11th to 20th	Night	12% 5% 1 4 3 3 3 3 4 5% 57%	2280
	21st to end	Night	18% 6% 2 5% 3 3 3 3 4 4 50%	2508
November	1st to 10th	Night	13% 5% 1 4 3 2 2 2 4 6% 57%	2531
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 8% 52%	2600
	21st to end	Night	18% 6% 2 5% 4 3 3 2 4 6% 49%	2600
December	1st to 10th	Night	15% 6% 2 4 3 4 4 3 5% 5% 48%	4508
	11th to 20th	Night	17% 7% 2 6% 4 4 3 2 4 5% 45%	5199
	21st to end	Night	24% 8% 3 7% 4 4 3 3 4 5% 34%	6996

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	42% 3 11% 27% 14% 2	3618
	11th to 20th	Day	35% 5% 7% 28% 20% 5%	4052
	21st to end	Day	42% 4 9% 18% 18% 9%	4488
February	1st to 10th	Day	47% 4 12% 22% 13% 1	1855
	11th to 20th	Day	45% 4 11% 22% 14% 5%	1958
	21st to end	Day	45% 6% 9% 20% 14% 6%	1650
March	1st to 10th	Day	46% 5% 5% 21% 17% 7%	4521
	11th to 20th	Day	31% 4 9% 27% 22% 7%	4980
	21st to end	Day	40% 5% 12% 28% 14% 1	5785
April	1st to 10th	Day	36% 5% 11% 25% 20% 2	2400
	11th to 20th	Day	41% 6% 10% 21% 16% 5%	2374
	21st to end	Day	43% 6% 11% 23% 16% 1	2400
May	1st to 10th	Day	46% 9% 14% 19% 11% 1	5481
	11th to 20th	Day	46% 9% 12% 21% 11% 1	5993
	21st to end	Day	42% 6% 11% 21% 18% 3	6949
June	1st to 10th	Day	33% 8% 14% 25% 19% 1	2800
	11th to 20th	Day	28% 8% 13% 29% 19% 4	2800
	21st to end	Day	26% 9% 17% 25% 18% 5%	2800
July	1st to 10th	Day	34% 8% 14% 25% 16% 3	4442
	11th to 20th	Day	24% 7% 13% 35% 19% 2	4365
	21st to end	Day	42% 9% 15% 26% 8% 1	4328
August	1st to 10th	Day	20% 7% 16% 32% 24% 1	3940
	11th to 20th	Day	35% 6% 14% 24% 17% 3	3765
	21st to end	Day	24% 5% 13% 37% 18% 3	4179
September	1st to 10th	Day	32% 6% 12% 27% 20% 4	2280
	11th to 20th	Day	35% 6% 9% 23% 26% 2	2236
	21st to end	Day	32% 6% 7% 25% 26% 4	2090
October	1st to 10th	Day	16% 3 5% 19% 43% 14%	3210
	11th to 20th	Day	23% 3 5% 20% 38% 11%	3140
	21st to end	Day	30% 4 5% 28% 28% 5%	3428
November	1st to 10th	Day	32% 5% 10% 25% 22% 7%	1767
	11th to 20th	Day	37% 3 7% 24% 23% 6%	1800
	21st to end	Day	41% 4 8% 25% 20% 2	1800
December	1st to 10th	Day	36% 4 8% 34% 17% 1	2677
	11th to 20th	Day	42% 4 9% 27% 15% 2	3005
	21st to end	Day	57% 5% 11% 16% 9% 2	3982
January	1st to 10th	Night	44% 5% 10% 26% 15% 1	6348
	11th to 20th	Night	37% 5% 7% 26% 21% 3	5923
	21st to end	Night	43% 3 8% 25% 16% 5%	6490
February	1st to 10th	Night	47% 4 10% 22% 16% 2	2542
	11th to 20th	Night	44% 3 11% 20% 18% 4	2339
	21st to end	Night	42% 4 8% 22% 18% 5%	1980
March	1st to 10th	Night	46% 4 6% 19% 18% 8%	5373
	11th to 20th	Night	36% 4 8% 22% 17% 11%	4982
	21st to end	Night	40% 5% 9% 30% 15% 2	5146
April	1st to 10th	Night	33% 5% 12% 26% 20% 4	2000
	11th to 20th	Night	37% 5% 10% 22% 21% 6%	1975
	21st to end	Night	43% 6% 9% 23% 17% 3	2000
May	1st to 10th	Night	44% 8% 16% 22% 9% 1	4478
	11th to 20th	Night	45% 7% 13% 19% 13% 2	3907
	21st to end	Night	43% 8% 10% 21% 15% 4	3950
June	1st to 10th	Night	33% 7% 14% 23% 22% 2	1600
	11th to 20th	Night	22% 7% 12% 30% 23% 7%	1600
	21st to end	Night	20% 8% 16% 29% 19% 8%	1600
July	1st to 10th	Night	31% 7% 14% 27% 17% 4	2530
	11th to 20th	Night	23% 6% 13% 35% 19% 5%	2482
	21st to end	Night	39% 8% 16% 24% 12% 1	2991
August	1st to 10th	Night	17% 6% 18% 35% 23% 1	2968
	11th to 20th	Night	30% 7% 16% 26% 16% 5%	3130
	21st to end	Night	20% 5% 11% 38% 22% 4	3476
September	1st to 10th	Night	28% 6% 8% 29% 22% 7%	1900
	11th to 20th	Night	32% 6% 9% 24% 25% 4	1924
	21st to end	Night	29% 7% 8% 21% 30% 5%	2090
October	1st to 10th	Night	14% 2 6% 17% 42% 19%	3733
	11th to 20th	Night	22% 3 4 17% 41% 13%	3779
	21st to end	Night	29% 4 6% 24% 30% 8%	4120
November	1st to 10th	Night	30% 4 8% 27% 25% 6%	2531
	11th to 20th	Night	32% 3 7% 25% 24% 8%	2600
	21st to end	Night	38% 3 8% 25% 22% 3	2600
December	1st to 10th	Night	37% 4 8% 30% 18% 2	4508
	11th to 20th	Night	42% 3 10% 22% 21% 2	5201
	21st to end	Night	52% 5% 10% 20% 11% 2	6996

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	26% 13% 37% 18% 5%	300
	11th to 20th	Day	25% 16% 43% 14% 3	300
	21st to end	Day	19% 15% 43% 20% 2	330
February	1st to 10th	Day	25% 16% 39% 15% 5%	300
	11th to 20th	Day	28% 20% 34% 15% 2	300
	21st to end	Day	26% 17% 35% 18% 3	249
March	1st to 10th	Day	22% 14% 42% 17% 5% 1	300
	11th to 20th	Day	25% 18% 36% 16% 4	300
	21st to end	Day	23% 16% 34% 19% 8%	470
April	1st to 10th	Day	19% 14% 31% 25% 9% 1	500
	11th to 20th	Day	20% 17% 28% 21% 13% 1	492
	21st to end	Day	21% 12% 29% 26% 10% 2	500
May	1st to 10th	Day	16% 13% 29% 30% 10% 3	503
	11th to 20th	Day	17% 8% 24% 26% 18% 8%	577
	21st to end	Day	11% 7% 24% 31% 18% 8%	789
June	1st to 10th	Day	13% 3 17% 27% 27% 12%	730
	11th to 20th	Day	6% 3 13% 40% 27% 10%	730
	21st to end	Day	5% 3 20% 36% 25% 11%	730
July	1st to 10th	Day	9% 2 12% 26% 29% 22%	697
	11th to 20th	Day	6% 1 11% 34% 33% 15%	668
	21st to end	Day	8% 2 11% 30% 34% 15%	739
August	1st to 10th	Day	7% 2 7% 34% 35% 15%	591
	11th to 20th	Day	14% 2 12% 29% 29% 13%	479
	21st to end	Day	9% 2 7% 25% 37% 19%	539
September	1st to 10th	Day	8% 3 9% 29% 36% 15%	490
	11th to 20th	Day	9% 2 11% 28% 31% 18%	490
	21st to end	Day	15% 5% 19% 24% 28% 9%	490
October	1st to 10th	Day	7% 6% 20% 35% 24% 8%	337
	11th to 20th	Day	16% 11% 27% 28% 11% 7%	300
	21st to end	Day	21% 15% 31% 21% 11% 1	330
November	1st to 10th	Day	19% 8% 32% 27% 12% 3	300
	11th to 20th	Day	13% 16% 33% 22% 14% 2	300
	21st to end	Day	22% 13% 34% 21% 9% 1	300
December	1st to 10th	Day	15% 14% 36% 25% 9% 2	300
	11th to 20th	Day	24% 16% 30% 20% 10%	300
	21st to end	Day	25% 19% 35% 17% 4	330
January	1st to 10th	Night	22% 8% 37% 27% 5%	1000
	11th to 20th	Night	22% 12% 39% 23% 4	1000
	21st to end	Night	19% 9% 40% 29% 2	1100
February	1st to 10th	Night	23% 10% 38% 25% 4	942
	11th to 20th	Night	23% 11% 40% 24% 2	783
	21st to end	Night	22% 13% 40% 23% 2	660
March	1st to 10th	Night	21% 11% 37% 28% 3	800
	11th to 20th	Night	21% 10% 33% 30% 6%	602
	21st to end	Night	21% 10% 33% 29% 7%	660
April	1st to 10th	Night	14% 10% 42% 29% 6%	600
	11th to 20th	Night	15% 11% 31% 30% 11% 1	593
	21st to end	Night	19% 6% 33% 31% 10%	600
May	1st to 10th	Night	17% 5% 28% 35% 13% 1	600
	11th to 20th	Night	16% 4 26% 33% 18% 2	591
	21st to end	Night	11% 4 19% 39% 24% 3	650
June	1st to 10th	Night	10% 3 14% 38% 32% 4	600
	11th to 20th	Night	5% 2 11% 51% 29% 2	600
	21st to end	Night	4 2 14% 45% 32% 4	600
July	1st to 10th	Night	7% 1 7% 33% 42% 9%	570
	11th to 20th	Night	5% 1 7% 42% 36% 9%	552
	21st to end	Night	8% 2 8% 35% 42% 6%	624
August	1st to 10th	Night	6% 1 6% 38% 43% 6%	567
	11th to 20th	Night	8% 2 9% 34% 42% 4	564
	21st to end	Night	6% 2 5% 35% 45% 7%	627
September	1st to 10th	Night	12% 1 8% 33% 40% 6%	570
	11th to 20th	Night	11% 2 9% 33% 36% 8%	594
	21st to end	Night	11% 4 18% 33% 30% 4	760
October	1st to 10th	Night	8% 3 17% 41% 26% 4	760
	11th to 20th	Night	15% 4 31% 33% 17% 2	760
	21st to end	Night	21% 6% 28% 33% 11% 1	836
November	1st to 10th	Night	14% 6% 30% 36% 13% 1	780
	11th to 20th	Night	17% 7% 32% 34% 10% 1	800
	21st to end	Night	20% 8% 30% 32% 10% 1	800
December	1st to 10th	Night	22% 8% 32% 32% 6% 1	954
	11th to 20th	Night	23% 7% 32% 31% 7%	1000
	21st to end	Night	26% 12% 31% 27% 5%	1100

Page generated at 2025-07-03 00:30:11. Version ac07

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