Bluewater Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bluewater Lake State Park clear sky chart from 2005-11-06 to 2025-06-10.

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	2 4 2 5% 4 4 5% 4 6% 7% 58%	122885
	Night	2 3 1 4 3 3 4 3 6% 7% 63%	124296
Transparency	Day	23% 5% 9% 18% 27% 19%	122650
	Night	20% 5% 9% 19% 29% 19%	124118
Seeing	Day	7% 15% 25% 27% 18% 7%	15184
	Night	4 11% 27% 35% 21% 3	25849

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	1 2 2 6% 4 4 4 4 5% 6% 62%	4098
	11th to 20th	Day	1 2 1 3 2 3 3 3 5% 6% 71%	4100
	21st to end	Day	1 8% 3 6% 4 3 3 3 5% 6% 59%	4510
February	1st to 10th	Day	1 4 3 5% 3 3 4 4 5% 7% 61%	1800
	11th to 20th	Day	1 4 1 4 5% 4 4 4 6% 10% 57%	1833
	21st to end	Day	1 4 1 5% 4 4 4 3 6% 8% 59%	1730
March	1st to 10th	Day	4 1 4 3 3 4 4 6% 8% 62%	4954
	11th to 20th	Day	1 7% 3 6% 4 5% 5% 5% 7% 8% 49%	5000
	21st to end	Day	1 3 2 5% 4 4 5% 4 7% 9% 56%	5486
April	1st to 10th	Day	1 4 2 5% 3 3 4 3 4 7% 64%	2365
	11th to 20th	Day	2 5% 1 5% 4 4 3 4 5% 6% 62%	2371
	21st to end	Day	2 3 1 4 4 4 4 4 5% 6% 64%	2400
May	1st to 10th	Day	2 3 1 5% 4 5% 5% 4 5% 6% 60%	5568
	11th to 20th	Day	2 2 1 4 3 4 4 4 5% 6% 64%	5841
	21st to end	Day	1 2 1 3 3 3 4 4 5% 6% 68%	6423
June	1st to 10th	Day	2 2 1 4 3 3 4 4 6% 7% 63%	2589
	11th to 20th	Day	2 2 1 2 3 4 3 3 4 6% 71%	2470
	21st to end	Day	3 3 1 6% 4 6% 5% 5% 6% 7% 54%	2470
July	1st to 10th	Day	3 3 2 5% 5% 5% 5% 4 6% 7% 56%	4110
	11th to 20th	Day	2 4 2 7% 7% 8% 9% 6% 9% 10% 36%	4110
	21st to end	Day	4 5% 2 8% 8% 7% 8% 6% 9% 10% 35%	4454
August	1st to 10th	Day	4 4 2 8% 8% 8% 8% 6% 9% 10% 32%	4092
	11th to 20th	Day	3 4 2 7% 6% 6% 8% 6% 8% 9% 42%	3827
	21st to end	Day	5% 4 2 7% 7% 8% 7% 6% 7% 9% 38%	4180
September	1st to 10th	Day	5% 5% 2 8% 5% 7% 5% 5% 6% 7% 46%	2280
	11th to 20th	Day	5% 5% 2 6% 5% 4 4 4 5% 6% 55%	2223
	21st to end	Day	3 3 1 5% 4 3 4 4 5% 5% 63%	2028
October	1st to 10th	Day	3 3 1 5% 3 3 3 3 4 5% 67%	3170
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 6% 65%	3150
	21st to end	Day	1 1 1 2 2 2 2 2 3 5% 79%	3438
November	1st to 10th	Day	1 3 1 2 3 3 2 2 4 6% 73%	1959
	11th to 20th	Day	1 3 1 2 3 2 4 3 4 6% 72%	1995
	21st to end	Day	2 3 1 5% 4 4 4 3 5% 5% 65%	1678
December	1st to 10th	Day	1 3 1 2 1 2 2 2 4 5% 76%	2620
	11th to 20th	Day	1 3 1 3 3 4 4 3 5% 8% 65%	3053
	21st to end	Day	3 1 3 3 4 4 3 5% 7% 66%	4510
January	1st to 10th	Night	4 1 5% 4 4 5% 4 6% 7% 59%	5867
	11th to 20th	Night	1 2 1 2 2 2 3 2 3 6% 77%	5880
	21st to end	Night	1 5% 2 4 3 4 5% 4 6% 7% 59%	6468
February	1st to 10th	Night	1 3 1 4 3 3 3 3 5% 7% 67%	2600
	11th to 20th	Night	1 3 1 4 3 4 5% 3 6% 7% 62%	2452
	21st to end	Night	1 2 1 3 2 3 4 4 6% 7% 69%	1895
March	1st to 10th	Night	3 1 3 2 2 3 3 5% 7% 70%	4940
	11th to 20th	Night	3 7% 3 6% 3 4 4 3 5% 7% 56%	5000
	21st to end	Night	1 2 1 2 2 3 3 3 6% 8% 70%	5489
April	1st to 10th	Night	1 4 1 4 3 3 4 3 5% 7% 66%	2035
	11th to 20th	Night	2 3 1 4 3 3 3 3 5% 6% 66%	1977
	21st to end	Night	1 3 1 3 3 3 3 3 5% 7% 69%	2000
May	1st to 10th	Night	3 3 1 4 3 3 4 3 5% 7% 63%	4395
	11th to 20th	Night	1 3 1 4 4 3 3 3 4 5% 69%	4074
	21st to end	Night	1 2 1 4 2 3 3 2 5% 5% 72%	4474
June	1st to 10th	Night	2 2 1 4 3 4 4 3 5% 7% 65%	1795
	11th to 20th	Night	3 2 1 3 1 3 3 2 5% 5% 72%	1710
	21st to end	Night	3 3 2 5% 5% 5% 5% 5% 7% 7% 53%	1710
July	1st to 10th	Night	2 3 2 5% 4 4 5% 4 5% 6% 59%	2860
	11th to 20th	Night	3 4 2 7% 6% 7% 8% 7% 10% 11% 36%	2860
	21st to end	Night	4 4 2 8% 5% 6% 8% 6% 10% 11% 35%	3109
August	1st to 10th	Night	3 4 2 9% 7% 9% 8% 7% 10% 11% 30%	2847
	11th to 20th	Night	3 4 2 7% 6% 7% 6% 6% 9% 11% 39%	3012
	21st to end	Night	3 3 2 7% 5% 6% 7% 6% 11% 12% 37%	3487
September	1st to 10th	Night	5% 4 2 6% 4 5% 5% 4 7% 9% 47%	1900
	11th to 20th	Night	3 3 1 4 3 3 5% 4 5% 6% 62%	1952
	21st to end	Night	3 3 1 4 2 2 3 3 4 7% 68%	2152
October	1st to 10th	Night	2 3 1 3 3 3 3 3 4 6% 69%	3800
	11th to 20th	Night	5% 4 2 4 3 3 4 3 4 6% 61%	3778
	21st to end	Night	1 1 1 2 2 2 3 2 3 5% 77%	4120
November	1st to 10th	Night	1 3 1 3 2 3 3 2 5% 6% 73%	2340
	11th to 20th	Night	1 2 2 2 2 3 4 6% 75%	2400
	21st to end	Night	2 4 2 3 3 3 3 3 4 6% 66%	2699
December	1st to 10th	Night	1 1 1 2 2 2 2 2 4 7% 76%	4570
	11th to 20th	Night	1 2 1 3 3 3 3 3 6% 9% 66%	5181
	21st to end	Night	1 3 1 3 3 3 4 3 4 7% 69%	6468

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	23% 4 8% 26% 33% 6%	4099
	11th to 20th	Day	14% 4 9% 25% 25% 23%	4100
	21st to end	Day	26% 5% 5% 15% 25% 24%	4510
February	1st to 10th	Day	22% 4 11% 21% 26% 16%	1800
	11th to 20th	Day	23% 6% 7% 24% 26% 14%	1842
	21st to end	Day	23% 5% 7% 18% 27% 21%	1730
March	1st to 10th	Day	17% 4 7% 14% 36% 22%	4954
	11th to 20th	Day	27% 6% 9% 16% 29% 14%	5000
	21st to end	Day	22% 5% 8% 29% 29% 7%	5486
April	1st to 10th	Day	20% 4 7% 18% 35% 17%	2365
	11th to 20th	Day	22% 3 6% 17% 32% 20%	2374
	21st to end	Day	20% 4 8% 18% 35% 16%	2400
May	1st to 10th	Day	21% 5% 7% 18% 31% 18%	5568
	11th to 20th	Day	18% 5% 8% 9% 34% 26%	5844
	21st to end	Day	15% 3 6% 10% 25% 42%	6424
June	1st to 10th	Day	18% 5% 7% 13% 29% 27%	2589
	11th to 20th	Day	15% 4 5% 9% 23% 45%	2470
	21st to end	Day	26% 6% 8% 13% 23% 24%	2470
July	1st to 10th	Day	25% 7% 8% 10% 11% 39%	4046
	11th to 20th	Day	35% 11% 11% 24% 13% 5%	4041
	21st to end	Day	37% 11% 14% 22% 12% 3	4314
August	1st to 10th	Day	39% 11% 19% 15% 11% 5%	4078
	11th to 20th	Day	32% 9% 14% 21% 15% 9%	3865
	21st to end	Day	37% 9% 15% 18% 16% 5%	4179
September	1st to 10th	Day	36% 7% 10% 14% 19% 14%	2280
	11th to 20th	Day	28% 5% 8% 14% 25% 19%	2223
	21st to end	Day	21% 5% 8% 16% 28% 21%	2028
October	1st to 10th	Day	20% 3 6% 13% 23% 35%	3170
	11th to 20th	Day	20% 3 6% 14% 37% 19%	3150
	21st to end	Day	9% 3 4 16% 39% 29%	3438
November	1st to 10th	Day	15% 3 6% 22% 36% 18%	1959
	11th to 20th	Day	15% 3 6% 20% 38% 18%	1995
	21st to end	Day	22% 4 7% 16% 33% 18%	1678
December	1st to 10th	Day	13% 3 6% 26% 35% 17%	2620
	11th to 20th	Day	19% 5% 7% 23% 38% 7%	3051
	21st to end	Day	17% 4 9% 26% 30% 14%	4510
January	1st to 10th	Night	22% 6% 9% 23% 31% 9%	5867
	11th to 20th	Night	11% 4 8% 24% 31% 22%	5880
	21st to end	Night	24% 6% 6% 16% 25% 24%	6468
February	1st to 10th	Night	18% 5% 11% 22% 28% 17%	2600
	11th to 20th	Night	21% 5% 8% 25% 25% 16%	2453
	21st to end	Night	14% 7% 7% 18% 35% 18%	1895
March	1st to 10th	Night	14% 4 5% 17% 40% 20%	4940
	11th to 20th	Night	27% 5% 6% 18% 31% 13%	5000
	21st to end	Night	12% 5% 8% 28% 41% 6%	5489
April	1st to 10th	Night	17% 4 6% 23% 34% 17%	2035
	11th to 20th	Night	18% 4 6% 18% 32% 23%	1977
	21st to end	Night	16% 4 8% 18% 37% 18%	2000
May	1st to 10th	Night	20% 5% 9% 18% 32% 16%	4392
	11th to 20th	Night	17% 5% 7% 12% 36% 24%	4075
	21st to end	Night	14% 2 6% 9% 26% 43%	4474
June	1st to 10th	Night	18% 5% 7% 14% 26% 30%	1795
	11th to 20th	Night	15% 2 5% 9% 22% 47%	1710
	21st to end	Night	27% 5% 11% 13% 17% 26%	1710
July	1st to 10th	Night	24% 6% 9% 10% 11% 38%	2815
	11th to 20th	Night	33% 11% 14% 25% 11% 6%	2806
	21st to end	Night	35% 12% 21% 21% 9% 1	3011
August	1st to 10th	Night	40% 13% 18% 13% 10% 7%	2838
	11th to 20th	Night	33% 9% 19% 15% 12% 12%	3040
	21st to end	Night	33% 12% 20% 18% 11% 6%	3487
September	1st to 10th	Night	31% 7% 12% 17% 18% 15%	1900
	11th to 20th	Night	21% 6% 10% 17% 24% 22%	1952
	21st to end	Night	17% 5% 8% 15% 30% 25%	2152
October	1st to 10th	Night	16% 4 7% 13% 27% 33%	3800
	11th to 20th	Night	23% 4 5% 17% 30% 22%	3778
	21st to end	Night	11% 2 5% 15% 43% 24%	4120
November	1st to 10th	Night	13% 3 6% 23% 37% 17%	2340
	11th to 20th	Night	11% 4 7% 21% 38% 20%	2400
	21st to end	Night	20% 4 8% 17% 34% 18%	2699
December	1st to 10th	Night	11% 3 6% 29% 29% 22%	4570
	11th to 20th	Night	16% 4 8% 17% 39% 15%	5182
	21st to end	Night	17% 5% 8% 24% 32% 15%	6468

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	5% 26% 29% 26% 13% 1	300
	11th to 20th	Day	9% 27% 24% 23% 15% 2	300
	21st to end	Day	5% 16% 35% 26% 13% 4	330
February	1st to 10th	Day	7% 24% 29% 26% 12% 2	300
	11th to 20th	Day	10% 21% 35% 24% 9%	300
	21st to end	Day	11% 31% 27% 21% 9% 1	329
March	1st to 10th	Day	12% 27% 27% 23% 9% 1	500
	11th to 20th	Day	12% 26% 30% 20% 10% 2	500
	21st to end	Day	12% 30% 33% 17% 6% 1	550
April	1st to 10th	Day	9% 22% 34% 23% 9% 3	500
	11th to 20th	Day	11% 27% 34% 19% 7% 2	492
	21st to end	Day	10% 23% 34% 21% 11% 1	500
May	1st to 10th	Day	6% 17% 39% 28% 7% 2	503
	11th to 20th	Day	8% 16% 33% 25% 14% 5%	528
	21st to end	Day	6% 17% 32% 29% 11% 4	573
June	1st to 10th	Day	5% 9% 28% 34% 20% 4	527
	11th to 20th	Day	3 9% 28% 34% 18% 8%	490
	21st to end	Day	5% 7% 27% 36% 18% 7%	490
July	1st to 10th	Day	5% 1 17% 38% 28% 11%	486
	11th to 20th	Day	6% 2 6% 27% 36% 23%	484
	21st to end	Day	5% 1 7% 27% 37% 23%	531
August	1st to 10th	Day	8% 1 11% 29% 33% 18%	487
	11th to 20th	Day	8% 2 13% 30% 28% 18%	477
	21st to end	Day	7% 2 15% 29% 33% 15%	539
September	1st to 10th	Day	7% 4 13% 33% 28% 14%	490
	11th to 20th	Day	7% 4 23% 32% 27% 6%	490
	21st to end	Day	6% 8% 25% 29% 21% 11%	428
October	1st to 10th	Day	5% 12% 23% 23% 25% 12%	300
	11th to 20th	Day	9% 11% 23% 24% 23% 10%	300
	21st to end	Day	6% 13% 21% 28% 27% 6%	330
November	1st to 10th	Day	4 16% 29% 30% 17% 4	300
	11th to 20th	Day	6% 11% 23% 31% 22% 7%	300
	21st to end	Day	7% 19% 28% 25% 17% 4	300
December	1st to 10th	Day	7% 17% 22% 33% 18% 3	300
	11th to 20th	Day	4 23% 26% 27% 17% 3	300
	21st to end	Day	9% 26% 32% 22% 10% 2	330
January	1st to 10th	Night	2 16% 27% 35% 17% 3	800
	11th to 20th	Night	5% 16% 30% 32% 15% 3	800
	21st to end	Night	4 14% 31% 32% 17% 3	880
February	1st to 10th	Night	4 17% 31% 33% 13% 2	800
	11th to 20th	Night	4 18% 37% 30% 10% 1	784
	21st to end	Night	2 22% 37% 33% 6%	660
March	1st to 10th	Night	3 21% 31% 33% 12% 1	800
	11th to 20th	Night	6% 15% 30% 34% 15% 1	800
	21st to end	Night	3 17% 38% 31% 11%	880
April	1st to 10th	Night	3 19% 34% 34% 9%	635
	11th to 20th	Night	5% 21% 37% 29% 9%	593
	21st to end	Night	3 17% 40% 31% 9% 1	600
May	1st to 10th	Night	5% 10% 39% 37% 9% 1	600
	11th to 20th	Night	4 8% 34% 37% 15% 2	591
	21st to end	Night	2 9% 36% 36% 15% 1	650
June	1st to 10th	Night	3 5% 31% 43% 18% 1	599
	11th to 20th	Night	3 7% 32% 41% 17% 1	570
	21st to end	Night	4 3 23% 41% 27% 2	570
July	1st to 10th	Night	5% 2 14% 40% 37% 2	555
	11th to 20th	Night	4 1 8% 33% 44% 9%	552
	21st to end	Night	6% 2 7% 25% 50% 11%	624
August	1st to 10th	Night	5% 1 8% 29% 46% 11%	567
	11th to 20th	Night	6% 2 6% 39% 41% 7%	564
	21st to end	Night	4 1 9% 33% 46% 6%	627
September	1st to 10th	Night	7% 2 9% 42% 35% 5%	570
	11th to 20th	Night	4 2 16% 43% 31% 5%	622
	21st to end	Night	4 4 19% 37% 31% 6%	760
October	1st to 10th	Night	5% 6% 26% 38% 22% 3	760
	11th to 20th	Night	3 6% 23% 43% 21% 3	760
	21st to end	Night	3 9% 24% 35% 23% 5%	836
November	1st to 10th	Night	2 8% 26% 37% 23% 3	780
	11th to 20th	Night	1 9% 26% 37% 22% 5%	800
	21st to end	Night	6% 15% 25% 30% 21% 3	980
December	1st to 10th	Night	5% 13% 25% 39% 16% 2	1000
	11th to 20th	Night	4 17% 33% 29% 16% 1	1000
	21st to end	Night	5% 17% 34% 31% 11% 2	880

Page generated at 2025-06-07 08:28:20. Version ac07

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