Clayton Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clayton Lake State Park clear sky chart from 2005-11-06 to 2024-01-17.

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	4 4 2 3 4 2 4 4 5% 8% 60%	74860
	Night	4 4 2 4 4 2 4 4 5% 7% 60%	74975
Transparency	Day	22% 6% 11% 22% 25% 15%	74572
	Night	22% 6% 10% 22% 26% 14%	74786
Seeing	Day	7% 9% 29% 33% 18% 5%	14235
	Night	6% 8% 37% 36% 12% 1	24366

By Month

Percentage Cloud Cover SW (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	2 4 1 4 3 2 3 3 4 7% 66%	1518
	11th to 20th	Day	4 4 2 4 3 1 3 3 5% 5% 67%	1546
	21st to end	Day	2 4 2 4 4 2 4 4 4 6% 66%	1818
February	1st to 10th	Day	2 5% 2 5% 4 2 5% 3 4 8% 59%	1800
	11th to 20th	Day	3 5% 2 6% 4 2 4 4 4 6% 59%	1749
	21st to end	Day	2 4 1 4 3 2 3 4 5% 6% 65%	1480
March	1st to 10th	Day	2 5% 3 4 4 2 5% 4 5% 7% 59%	1800
	11th to 20th	Day	5% 5% 2 4 4 2 3 4 4 6% 62%	1847
	21st to end	Day	5% 5% 2 4 4 2 4 4 6% 7% 58%	2376
April	1st to 10th	Day	4 4 2 3 3 2 4 4 5% 7% 64%	2160
	11th to 20th	Day	6% 5% 2 4 4 2 3 5% 4 7% 58%	2131
	21st to end	Day	6% 4 2 3 4 2 4 4 6% 8% 57%	2160
May	1st to 10th	Day	6% 5% 1 3 4 3 3 4 5% 8% 59%	2287
	11th to 20th	Day	7% 5% 2 3 4 2 3 5% 6% 8% 55%	2302
	21st to end	Day	4 4 1 3 3 2 4 5% 6% 9% 58%	2578
June	1st to 10th	Day	3 3 1 3 3 2 5% 6% 8% 10% 55%	2520
	11th to 20th	Day	3 2 1 2 2 2 4 5% 6% 8% 64%	2520
	21st to end	Day	4 3 2 4 3 3 5% 6% 8% 9% 54%	2520
July	1st to 10th	Day	5% 4 1 3 4 3 6% 5% 7% 9% 51%	2520
	11th to 20th	Day	2 2 1 3 4 4 5% 6% 7% 10% 55%	2520
	21st to end	Day	5% 3 1 3 5% 3 7% 7% 8% 12% 45%	2634
August	1st to 10th	Day	4 3 1 4 5% 3 5% 7% 7% 12% 50%	2149
	11th to 20th	Day	6% 4 2 5% 6% 3 6% 7% 7% 9% 44%	2123
	21st to end	Day	4 3 1 3 4 3 5% 5% 6% 9% 56%	2376
September	1st to 10th	Day	6% 3 2 4 4 2 5% 4 6% 8% 57%	2160
	11th to 20th	Day	6% 3 2 3 3 2 3 3 5% 7% 61%	2048
	21st to end	Day	5% 3 1 2 2 2 3 3 4 6% 68%	1980
October	1st to 10th	Day	7% 4 1 4 3 2 3 3 5% 6% 62%	1980
	11th to 20th	Day	3 3 1 2 2 1 3 2 3 3 76%	1810
	21st to end	Day	5% 5% 1 2 3 1 2 2 3 5% 71%	1878
November	1st to 10th	Day	2 2 1 2 3 1 3 4 4 6% 73%	1673
	11th to 20th	Day	2 3 2 3 2 2 3 3 4 5% 71%	1710
	21st to end	Day	5% 5% 2 3 3 2 3 3 3 5% 65%	1710
December	1st to 10th	Day	2 4 2 4 4 2 3 4 5% 7% 64%	1710
	11th to 20th	Day	4 3 2 4 4 2 4 4 5% 7% 62%	1973
	21st to end	Day	3 5% 2 4 4 2 3 4 5% 6% 63%	2794
January	1st to 10th	Night	3 4 1 4 5% 2 4 4 4 5% 63%	2647
	11th to 20th	Night	4 3 2 4 3 2 3 3 4 6% 65%	2572
	21st to end	Night	2 5% 2 4 4 3 3 3 4 7% 63%	2535
February	1st to 10th	Night	3 5% 2 4 4 2 4 3 4 7% 62%	2160
	11th to 20th	Night	4 6% 2 6% 6% 3 4 4 6% 6% 54%	2098
	21st to end	Night	5% 4 1 3 2 2 2 3 5% 8% 63%	1776
March	1st to 10th	Night	4 4 2 4 4 1 4 4 5% 7% 60%	2160
	11th to 20th	Night	6% 4 2 5% 4 2 4 3 4 6% 61%	2108
	21st to end	Night	4 5% 1 3 3 2 4 5% 5% 7% 60%	1980
April	1st to 10th	Night	4 3 1 2 3 2 4 4 4 7% 65%	1800
	11th to 20th	Night	6% 5% 2 4 4 2 4 4 5% 8% 56%	1777
	21st to end	Night	7% 4 2 3 3 2 3 4 6% 7% 59%	1800
May	1st to 10th	Night	6% 3 2 3 2 2 4 5% 4 6% 62%	1670
	11th to 20th	Night	8% 5% 2 5% 4 3 5% 5% 4 8% 51%	1593
	21st to end	Night	6% 3 1 3 3 3 4 4 5% 9% 58%	1693
June	1st to 10th	Night	4 2 1 4 3 3 4 6% 8% 10% 55%	1440
	11th to 20th	Night	2 2 1 3 3 2 4 5% 5% 9% 64%	1440
	21st to end	Night	4 3 2 5% 4 2 5% 5% 8% 11% 51%	1440
July	1st to 10th	Night	4 4 2 3 4 3 5% 5% 6% 12% 52%	1440
	11th to 20th	Night	3 2 1 4 4 2 7% 5% 7% 13% 52%	1440
	21st to end	Night	8% 4 2 5% 5% 3 6% 7% 9% 14% 38%	1677
August	1st to 10th	Night	4 3 2 4 6% 5% 7% 7% 7% 13% 42%	1790
	11th to 20th	Night	7% 5% 2 5% 4 3 7% 7% 7% 10% 43%	1778
	21st to end	Night	4 3 1 3 4 3 5% 6% 6% 10% 55%	1980
September	1st to 10th	Night	5% 4 2 3 4 2 5% 4 5% 9% 57%	1800
	11th to 20th	Night	7% 4 2 3 3 2 3 4 5% 8% 59%	1911
	21st to end	Night	5% 3 1 3 3 2 3 3 4 6% 65%	1980
October	1st to 10th	Night	9% 3 2 3 4 2 4 4 4 6% 59%	1980
	11th to 20th	Night	3 2 1 2 2 1 2 2 3 5% 75%	2146
	21st to end	Night	6% 4 1 2 3 2 3 3 3 5% 68%	2457
November	1st to 10th	Night	2 3 1 2 2 1 3 3 4 6% 73%	2405
	11th to 20th	Night	1 3 1 3 3 2 3 3 3 5% 73%	2470
	21st to end	Night	4 4 2 3 3 2 3 4 5% 6% 64%	2470
December	1st to 10th	Night	2 4 2 4 4 3 3 3 4 7% 62%	2470
	11th to 20th	Night	3 4 2 3 4 2 4 4 5% 7% 63%	3219
	21st to end	Night	2 5% 2 4 4 3 5% 4 5% 6% 59%	4873

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	19% 5% 7% 25% 34% 11%	1519
	11th to 20th	Day	20% 3 8% 24% 33% 12%	1546
	21st to end	Day	21% 3 7% 25% 31% 13%	1818
February	1st to 10th	Day	24% 5% 10% 23% 24% 14%	1800
	11th to 20th	Day	25% 4 9% 23% 24% 15%	1759
	21st to end	Day	19% 3 6% 20% 29% 22%	1480
March	1st to 10th	Day	24% 5% 8% 18% 27% 19%	1800
	11th to 20th	Day	24% 5% 7% 21% 29% 14%	1847
	21st to end	Day	24% 5% 8% 23% 27% 12%	2376
April	1st to 10th	Day	19% 5% 9% 21% 29% 18%	2160
	11th to 20th	Day	26% 5% 8% 21% 23% 17%	2134
	21st to end	Day	24% 6% 11% 24% 26% 10%	2160
May	1st to 10th	Day	24% 6% 10% 23% 22% 15%	2287
	11th to 20th	Day	26% 6% 13% 24% 22% 9%	2306
	21st to end	Day	21% 7% 14% 21% 21% 17%	2578
June	1st to 10th	Day	19% 9% 17% 22% 20% 13%	2520
	11th to 20th	Day	15% 6% 11% 19% 26% 24%	2520
	21st to end	Day	23% 7% 12% 23% 20% 16%	2520
July	1st to 10th	Day	26% 9% 14% 19% 22% 10%	2451
	11th to 20th	Day	18% 10% 15% 25% 25% 8%	2445
	21st to end	Day	26% 12% 19% 25% 15% 2	2487
August	1st to 10th	Day	24% 10% 19% 26% 13% 8%	2136
	11th to 20th	Day	31% 11% 13% 19% 18% 8%	2123
	21st to end	Day	21% 8% 13% 26% 24% 8%	2376
September	1st to 10th	Day	25% 6% 12% 22% 21% 14%	2160
	11th to 20th	Day	23% 5% 9% 20% 25% 18%	2048
	21st to end	Day	18% 4 9% 20% 35% 15%	1980
October	1st to 10th	Day	24% 6% 8% 20% 27% 15%	1980
	11th to 20th	Day	15% 3 6% 14% 34% 28%	1810
	21st to end	Day	19% 2 6% 21% 32% 20%	1878
November	1st to 10th	Day	13% 4 7% 21% 31% 24%	1673
	11th to 20th	Day	16% 3 6% 25% 33% 17%	1710
	21st to end	Day	22% 3 7% 14% 29% 24%	1710
December	1st to 10th	Day	20% 4 11% 27% 25% 13%	1710
	11th to 20th	Day	22% 5% 7% 20% 31% 16%	1971
	21st to end	Day	20% 6% 10% 23% 24% 18%	2794
January	1st to 10th	Night	22% 4 9% 25% 29% 11%	2647
	11th to 20th	Night	21% 3 8% 24% 30% 15%	2572
	21st to end	Night	22% 3 7% 23% 34% 12%	2535
February	1st to 10th	Night	23% 4 9% 22% 29% 13%	2160
	11th to 20th	Night	30% 5% 8% 21% 23% 12%	2098
	21st to end	Night	20% 2 5% 20% 33% 20%	1776
March	1st to 10th	Night	23% 3 8% 21% 29% 16%	2160
	11th to 20th	Night	25% 4 9% 22% 26% 14%	2108
	21st to end	Night	23% 6% 11% 21% 24% 15%	1980
April	1st to 10th	Night	19% 4 9% 24% 26% 18%	1800
	11th to 20th	Night	25% 6% 11% 22% 22% 14%	1777
	21st to end	Night	24% 7% 14% 24% 18% 13%	1800
May	1st to 10th	Night	23% 7% 8% 24% 23% 16%	1670
	11th to 20th	Night	30% 9% 13% 23% 16% 10%	1594
	21st to end	Night	24% 8% 15% 18% 17% 18%	1694
June	1st to 10th	Night	23% 9% 17% 26% 13% 13%	1440
	11th to 20th	Night	18% 6% 13% 20% 20% 22%	1440
	21st to end	Night	24% 9% 13% 24% 17% 13%	1440
July	1st to 10th	Night	25% 9% 17% 23% 19% 8%	1400
	11th to 20th	Night	20% 11% 17% 24% 22% 6%	1392
	21st to end	Night	32% 12% 22% 22% 11% 1	1584
August	1st to 10th	Night	28% 13% 20% 22% 13% 5%	1779
	11th to 20th	Night	31% 10% 16% 24% 13% 6%	1778
	21st to end	Night	23% 10% 14% 25% 21% 7%	1980
September	1st to 10th	Night	24% 7% 16% 21% 21% 11%	1800
	11th to 20th	Night	24% 5% 12% 21% 22% 16%	1911
	21st to end	Night	21% 4 8% 20% 33% 13%	1980
October	1st to 10th	Night	26% 6% 10% 19% 24% 16%	1980
	11th to 20th	Night	14% 3 6% 16% 34% 26%	2146
	21st to end	Night	20% 3 5% 22% 30% 19%	2457
November	1st to 10th	Night	13% 4 8% 20% 31% 24%	2405
	11th to 20th	Night	15% 3 5% 24% 37% 16%	2470
	21st to end	Night	21% 4 6% 18% 29% 23%	2470
December	1st to 10th	Night	22% 4 9% 26% 28% 11%	2470
	11th to 20th	Night	21% 5% 7% 20% 35% 13%	3220
	21st to end	Night	22% 7% 10% 21% 27% 13%	4873

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	7% 10% 33% 37% 11% 3	270
	11th to 20th	Day	9% 13% 36% 27% 13% 2	258
	21st to end	Day	4 13% 38% 31% 12% 2	264
February	1st to 10th	Day	5% 11% 45% 26% 11% 2	240
	11th to 20th	Day	8% 13% 49% 23% 6% 2	240
	21st to end	Day	9% 16% 45% 25% 5%	198
March	1st to 10th	Day	4 14% 46% 28% 8%	240
	11th to 20th	Day	12% 18% 33% 26% 11% 1	273
	21st to end	Day	14% 23% 37% 18% 7% 1	462
April	1st to 10th	Day	6% 22% 40% 24% 7% 1	420
	11th to 20th	Day	13% 21% 37% 22% 5% 1	412
	21st to end	Day	15% 19% 38% 21% 5% 1	420
May	1st to 10th	Day	7% 14% 37% 29% 11% 2	550
	11th to 20th	Day	9% 10% 36% 28% 13% 4	625
	21st to end	Day	8% 10% 39% 31% 10% 1	679
June	1st to 10th	Day	5% 6% 26% 35% 23% 5%	630
	11th to 20th	Day	5% 4 32% 38% 18% 3	630
	21st to end	Day	7% 4 24% 39% 21% 5%	630
July	1st to 10th	Day	7% 2 15% 37% 30% 8%	621
	11th to 20th	Day	3 1 11% 41% 33% 11%	618
	21st to end	Day	5% 1 7% 39% 35% 12%	634
August	1st to 10th	Day	5% 2 13% 35% 33% 11%	447
	11th to 20th	Day	5% 3 18% 43% 25% 6%	437
	21st to end	Day	4 2 13% 46% 26% 9%	495
September	1st to 10th	Day	7% 1 20% 40% 25% 7%	450
	11th to 20th	Day	6% 1 22% 39% 23% 9%	338
	21st to end	Day	9% 4 25% 29% 26% 8%	270
October	1st to 10th	Day	11% 7% 26% 32% 19% 5%	270
	11th to 20th	Day	5% 7% 30% 31% 19% 7%	270
	21st to end	Day	12% 7% 29% 32% 15% 5%	297
November	1st to 10th	Day	6% 11% 31% 33% 15% 4	270
	11th to 20th	Day	7% 10% 27% 35% 17% 4	270
	21st to end	Day	10% 15% 33% 24% 13% 5%	270
December	1st to 10th	Day	4 11% 41% 30% 12% 2	270
	11th to 20th	Day	9% 11% 36% 31% 13%	270
	21st to end	Day	11% 13% 41% 28% 7%	297
January	1st to 10th	Night	4 9% 40% 36% 9% 1	950
	11th to 20th	Night	6% 9% 40% 34% 9% 2	890
	21st to end	Night	4 7% 47% 32% 9% 1	792
February	1st to 10th	Night	5% 10% 46% 31% 9%	720
	11th to 20th	Night	7% 11% 53% 22% 6% 1	704
	21st to end	Night	9% 11% 52% 25% 3	592
March	1st to 10th	Night	6% 12% 46% 30% 5% 1	720
	11th to 20th	Night	8% 13% 37% 33% 8% 1	704
	21st to end	Night	6% 14% 55% 20% 5%	594
April	1st to 10th	Night	6% 11% 53% 26% 4	540
	11th to 20th	Night	8% 13% 50% 26% 2	533
	21st to end	Night	9% 12% 42% 31% 6%	540
May	1st to 10th	Night	8% 11% 40% 34% 7%	540
	11th to 20th	Night	9% 8% 38% 33% 11% 1	531
	21st to end	Night	7% 9% 46% 30% 7% 1	584
June	1st to 10th	Night	5% 6% 33% 41% 14% 1	540
	11th to 20th	Night	3 4 45% 39% 9%	540
	21st to end	Night	5% 3 32% 44% 16%	540
July	1st to 10th	Night	6% 2 17% 52% 22% 2	525
	11th to 20th	Night	3 2 14% 51% 28% 2	522
	21st to end	Night	8% 1 12% 48% 28% 3	591
August	1st to 10th	Night	5% 1 15% 41% 34% 3	537
	11th to 20th	Night	8% 1 13% 53% 24% 1	534
	21st to end	Night	5% 1 16% 50% 24% 3	594
September	1st to 10th	Night	7% 2 19% 52% 19% 1	540
	11th to 20th	Night	10% 1 32% 40% 16% 1	540
	21st to end	Night	7% 6% 30% 38% 17% 2	540
October	1st to 10th	Night	10% 5% 32% 41% 11% 1	540
	11th to 20th	Night	4 6% 40% 34% 13% 3	706
	21st to end	Night	8% 8% 34% 33% 14% 4	873
November	1st to 10th	Night	4 6% 34% 42% 11% 2	925
	11th to 20th	Night	4 8% 40% 35% 11% 1	950
	21st to end	Night	6% 10% 34% 35% 13% 1	950
December	1st to 10th	Night	4 9% 40% 34% 12% 1	950
	11th to 20th	Night	6% 10% 38% 37% 8% 1	950
	21st to end	Night	7% 14% 40% 31% 8% 1	1045

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