Center Hill Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Center Hill Lake clear sky chart from 2005-11-06 to 2025-03-12.

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% 8% 3 7% 4 4 4 4 6% 7% 38%	109378
	Night	14% 8% 3 6% 4 4 4 3 5% 7% 40%	109618
Transparency	Day	42% 7% 10% 22% 16% 3	113132
	Night	41% 6% 10% 22% 17% 4	114002
Seeing	Day	18% 11% 23% 23% 17% 8%	15152
	Night	18% 9% 23% 28% 19% 3	25132

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% 14% 7% 12% 4 4 5% 3 4 5% 27%	4056
	11th to 20th	Day	18% 9% 7% 11% 3 3 3 3 3 5% 34%	4060
	21st to end	Day	21% 11% 4 5% 3 3 3 3 5% 6% 35%	4719
February	1st to 10th	Day	19% 12% 4 8% 4 3 4 3 4 5% 33%	2000
	11th to 20th	Day	22% 11% 4 8% 5% 3 4 3 4 6% 30%	1948
	21st to end	Day	21% 9% 3 6% 4 4 3 3 4 6% 35%	1650
March	1st to 10th	Day	21% 12% 3 8% 4 4 4 3 5% 6% 31%	3220
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 4 5% 47%	3440
	21st to end	Day	15% 8% 2 7% 4 4 4 4 6% 6% 40%	3867
April	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 6% 6% 44%	2280
	11th to 20th	Day	14% 7% 3 5% 4 4 4 3 5% 6% 43%	2254
	21st to end	Day	13% 7% 2 6% 6% 5% 4 4 6% 6% 41%	2384
May	1st to 10th	Day	19% 7% 2 6% 4 4 4 4 7% 8% 35%	4082
	11th to 20th	Day	17% 9% 3 8% 5% 4 5% 3 5% 7% 35%	4081
	21st to end	Day	11% 6% 3 8% 5% 5% 5% 4 6% 8% 40%	4476
June	1st to 10th	Day	10% 7% 2 6% 5% 5% 5% 4 6% 10% 40%	2470
	11th to 20th	Day	5% 5% 2 6% 5% 4 6% 5% 7% 10% 45%	2470
	21st to end	Day	6% 4 2 7% 5% 5% 6% 5% 9% 12% 39%	2568
July	1st to 10th	Day	7% 5% 2 6% 5% 6% 6% 6% 9% 11% 37%	4216
	11th to 20th	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 11% 36%	4120
	21st to end	Day	16% 11% 3 10% 7% 6% 6% 5% 6% 8% 22%	4466
August	1st to 10th	Day	5% 4 2 5% 4 5% 6% 5% 8% 11% 46%	4073
	11th to 20th	Day	6% 5% 2 6% 6% 5% 7% 5% 8% 12% 38%	3729
	21st to end	Day	7% 4 2 5% 5% 5% 5% 5% 6% 8% 50%	4180
September	1st to 10th	Day	12% 7% 3 6% 5% 4 5% 4 7% 8% 40%	2195
	11th to 20th	Day	15% 6% 3 6% 4 4 4 4 5% 7% 43%	2090
	21st to end	Day	12% 6% 2 5% 4 3 4 4 6% 6% 48%	2090
October	1st to 10th	Day	11% 5% 1 5% 4 4 3 3 5% 7% 53%	2090
	11th to 20th	Day	13% 4 2 5% 4 4 3 2 4 7% 52%	2042
	21st to end	Day	16% 6% 2 5% 3 4 4 3 5% 6% 47%	1931
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 5% 6% 53%	1762
	11th to 20th	Day	15% 7% 2 5% 3 3 3 3 5% 6% 47%	1800
	21st to end	Day	16% 10% 3 5% 4 4 4 2 5% 5% 43%	1800
December	1st to 10th	Day	16% 9% 2 8% 5% 4 4 3 4 5% 41%	2930
	11th to 20th	Day	22% 13% 5% 9% 4 4 3 3 5% 5% 27%	3373
	21st to end	Day	20% 12% 5% 8% 4 4 4 3 5% 8% 27%	4466
January	1st to 10th	Night	16% 14% 4 10% 4 3 3 3 4 6% 34%	5889
	11th to 20th	Night	19% 11% 4 6% 5% 4 3 3 4 4 37%	5900
	21st to end	Night	18% 12% 3 7% 4 4 4 2 4 5% 37%	6233
February	1st to 10th	Night	22% 10% 3 8% 4 4 3 3 5% 7% 31%	2400
	11th to 20th	Night	24% 9% 4 8% 4 4 2 3 4 4 32%	2338
	21st to end	Night	23% 11% 3 6% 4 3 4 3 5% 7% 31%	1980
March	1st to 10th	Night	23% 12% 3 7% 4 3 4 3 4 6% 31%	3853
	11th to 20th	Night	14% 7% 2 5% 3 4 4 3 4 6% 48%	3547
	21st to end	Night	15% 8% 3 8% 5% 5% 5% 4 5% 6% 39%	3791
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 7% 45%	1900
	11th to 20th	Night	16% 6% 2 5% 3 4 3 3 5% 7% 47%	1875
	21st to end	Night	14% 6% 2 6% 5% 4 4 3 5% 8% 43%	1795
May	1st to 10th	Night	15% 7% 2 7% 5% 4 5% 3 6% 8% 38%	2813
	11th to 20th	Night	15% 8% 2 7% 4 4 5% 3 6% 7% 39%	2812
	21st to end	Night	8% 5% 2 7% 5% 4 5% 5% 7% 10% 42%	3079
June	1st to 10th	Night	7% 6% 3 7% 5% 5% 4 4 7% 9% 44%	1710
	11th to 20th	Night	4 3 2 4 4 3 5% 5% 7% 12% 51%	1710
	21st to end	Night	6% 4 1 5% 5% 5% 6% 4 8% 12% 44%	1589
July	1st to 10th	Night	8% 5% 3 7% 5% 6% 6% 6% 9% 10% 37%	2716
	11th to 20th	Night	8% 5% 2 5% 4 5% 5% 4 8% 10% 44%	2840
	21st to end	Night	11% 10% 4 10% 7% 6% 7% 6% 7% 9% 24%	3087
August	1st to 10th	Night	4 4 2 5% 4 5% 4 4 6% 9% 52%	2851
	11th to 20th	Night	6% 4 2 6% 4 4 5% 5% 8% 11% 45%	3100
	21st to end	Night	5% 2 1 4 3 4 4 4 7% 10% 56%	3476
September	1st to 10th	Night	10% 6% 3 7% 4 3 4 5% 6% 8% 45%	1964
	11th to 20th	Night	10% 6% 2 7% 5% 4 5% 3 5% 7% 44%	2090
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 7% 51%	2090
October	1st to 10th	Night	10% 5% 1 4 3 3 3 3 4 7% 58%	2090
	11th to 20th	Night	15% 6% 2 5% 4 3 3 2 5% 7% 48%	2137
	21st to end	Night	15% 8% 2 5% 3 2 3 3 4 6% 48%	2665
November	1st to 10th	Night	12% 7% 2 5% 3 4 3 3 4 7% 50%	2536
	11th to 20th	Night	14% 9% 2 4 3 3 3 2 5% 7% 48%	2600
	21st to end	Night	16% 9% 4 5% 4 3 4 3 4 7% 42%	2600
December	1st to 10th	Night	19% 11% 3 8% 3 4 4 3 4 5% 36%	4250
	11th to 20th	Night	24% 12% 3 7% 3 3 3 2 3 5% 36%	4822
	21st to end	Night	16% 14% 4 8% 5% 5% 5% 4 5% 7% 28%	6490

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	58% 5% 8% 16% 12% 1	4057
	11th to 20th	Day	52% 4 4 17% 21% 1	4060
	21st to end	Day	49% 4 7% 23% 13% 4	4719
February	1st to 10th	Day	54% 4 7% 16% 16% 2	2000
	11th to 20th	Day	56% 5% 7% 16% 13% 3	1958
	21st to end	Day	51% 4 8% 15% 17% 5%	1650
March	1st to 10th	Day	53% 5% 7% 15% 13% 6%	3220
	11th to 20th	Day	39% 5% 9% 24% 16% 6%	3440
	21st to end	Day	43% 6% 10% 26% 13% 1	3867
April	1st to 10th	Day	40% 6% 12% 22% 17% 3	2280
	11th to 20th	Day	41% 5% 7% 20% 23% 4	2254
	21st to end	Day	41% 7% 10% 26% 14% 1	2384
May	1st to 10th	Day	44% 10% 11% 22% 11% 1	4120
	11th to 20th	Day	47% 8% 11% 23% 10%	4085
	21st to end	Day	40% 9% 11% 20% 19% 1	4489
June	1st to 10th	Day	38% 9% 13% 23% 14% 2	2470
	11th to 20th	Day	31% 10% 18% 22% 17% 2	2470
	21st to end	Day	34% 11% 18% 18% 15% 4	2568
July	1st to 10th	Day	36% 11% 19% 23% 8% 2	4151
	11th to 20th	Day	40% 8% 17% 26% 7% 2	4051
	21st to end	Day	59% 9% 11% 15% 5% 1	4324
August	1st to 10th	Day	29% 10% 16% 31% 13% 1	4060
	11th to 20th	Day	35% 8% 15% 25% 15% 1	3765
	21st to end	Day	30% 8% 11% 33% 17% 1	4179
September	1st to 10th	Day	41% 8% 12% 18% 16% 5%	2195
	11th to 20th	Day	40% 7% 11% 22% 17% 2	2090
	21st to end	Day	36% 6% 11% 24% 19% 5%	2090
October	1st to 10th	Day	25% 4 6% 18% 36% 11%	3480
	11th to 20th	Day	23% 4 6% 24% 30% 12%	3373
	21st to end	Day	30% 4 8% 25% 25% 9%	3155
November	1st to 10th	Day	32% 4 8% 24% 27% 5%	1762
	11th to 20th	Day	38% 4 6% 24% 22% 5%	1800
	21st to end	Day	43% 4 7% 22% 20% 4	1800
December	1st to 10th	Day	46% 4 5% 23% 21% 2	2930
	11th to 20th	Day	59% 4 7% 18% 10% 2	3370
	21st to end	Day	54% 5% 11% 21% 8% 1	4466
January	1st to 10th	Night	51% 4 10% 19% 15% 1	5889
	11th to 20th	Night	51% 4 5% 17% 19% 5%	5900
	21st to end	Night	50% 4 6% 19% 17% 5%	6233
February	1st to 10th	Night	53% 4 8% 18% 15% 1	2400
	11th to 20th	Night	56% 4 7% 16% 13% 4	2339
	21st to end	Night	52% 5% 7% 16% 16% 4	1980
March	1st to 10th	Night	54% 6% 8% 12% 15% 4	3853
	11th to 20th	Night	37% 6% 8% 25% 14% 11%	3547
	21st to end	Night	46% 5% 9% 24% 16% 1	3791
April	1st to 10th	Night	37% 6% 10% 24% 20% 3	1900
	11th to 20th	Night	36% 5% 9% 20% 22% 7%	1875
	21st to end	Night	39% 5% 11% 28% 16% 1	1795
May	1st to 10th	Night	40% 10% 13% 23% 12% 1	2840
	11th to 20th	Night	42% 9% 14% 20% 14% 1	2813
	21st to end	Night	32% 12% 14% 23% 17% 2	3087
June	1st to 10th	Night	36% 7% 14% 27% 14% 2	1710
	11th to 20th	Night	22% 10% 19% 30% 16% 3	1710
	21st to end	Night	29% 12% 16% 26% 13% 4	1589
July	1st to 10th	Night	37% 11% 20% 23% 8% 1	2671
	11th to 20th	Night	32% 8% 18% 31% 8% 3	2786
	21st to end	Night	54% 11% 12% 15% 7% 1	2988
August	1st to 10th	Night	27% 8% 12% 36% 17% 1	2840
	11th to 20th	Night	30% 8% 21% 26% 13% 1	3130
	21st to end	Night	23% 6% 13% 37% 18% 2	3476
September	1st to 10th	Night	36% 8% 13% 21% 17% 5%	1964
	11th to 20th	Night	37% 8% 11% 20% 23% 2	2090
	21st to end	Night	32% 5% 11% 22% 24% 5%	2090
October	1st to 10th	Night	25% 5% 5% 21% 33% 11%	3480
	11th to 20th	Night	23% 3 6% 23% 30% 16%	3545
	21st to end	Night	25% 3 7% 25% 30% 10%	4391
November	1st to 10th	Night	35% 4 6% 23% 24% 7%	2536
	11th to 20th	Night	37% 3 7% 21% 25% 7%	2600
	21st to end	Night	43% 3 7% 23% 20% 4	2600
December	1st to 10th	Night	51% 4 5% 15% 22% 1	4250
	11th to 20th	Night	52% 5% 6% 20% 16% 2	4824
	21st to end	Night	54% 6% 10% 20% 9%	6490

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	27% 21% 37% 11% 4 1	300
	11th to 20th	Day	34% 25% 25% 12% 4	300
	21st to end	Day	23% 23% 39% 12% 3	330
February	1st to 10th	Day	28% 23% 31% 14% 4	300
	11th to 20th	Day	38% 22% 31% 6% 2 1	300
	21st to end	Day	33% 24% 30% 10% 2	249
March	1st to 10th	Day	27% 21% 33% 14% 5%	300
	11th to 20th	Day	24% 20% 33% 15% 7%	426
	21st to end	Day	27% 16% 31% 18% 8%	506
April	1st to 10th	Day	23% 20% 25% 22% 10% 1	460
	11th to 20th	Day	20% 14% 32% 22% 10% 2	452
	21st to end	Day	19% 16% 30% 22% 11% 2	460
May	1st to 10th	Day	17% 15% 29% 24% 10% 5%	463
	11th to 20th	Day	15% 10% 24% 26% 16% 9%	487
	21st to end	Day	13% 6% 21% 28% 18% 14%	529
June	1st to 10th	Day	12% 5% 21% 26% 24% 12%	490
	11th to 20th	Day	5% 4 17% 29% 28% 17%	490
	21st to end	Day	9% 2 18% 31% 24% 14%	588
July	1st to 10th	Day	11% 3 12% 27% 28% 20%	542
	11th to 20th	Day	12% 3 10% 25% 28% 22%	484
	21st to end	Day	13% 4 10% 26% 28% 20%	532
August	1st to 10th	Day	10% 4 12% 26% 30% 19%	486
	11th to 20th	Day	10% 3 14% 31% 32% 11%	479
	21st to end	Day	12% 2 8% 23% 33% 21%	539
September	1st to 10th	Day	12% 3 11% 24% 35% 15%	490
	11th to 20th	Day	14% 5% 11% 24% 31% 16%	490
	21st to end	Day	16% 5% 18% 26% 27% 9%	490
October	1st to 10th	Day	12% 4 21% 29% 24% 10%	490
	11th to 20th	Day	13% 10% 30% 26% 17% 4	490
	21st to end	Day	20% 11% 26% 28% 12% 3	380
November	1st to 10th	Day	20% 10% 29% 28% 10% 4	300
	11th to 20th	Day	16% 14% 37% 27% 5%	300
	21st to end	Day	21% 17% 32% 20% 9% 2	300
December	1st to 10th	Day	26% 21% 31% 16% 4 1	300
	11th to 20th	Day	28% 18% 27% 18% 9%	300
	21st to end	Day	29% 19% 31% 15% 6% 1	330
January	1st to 10th	Night	25% 18% 31% 21% 5%	800
	11th to 20th	Night	27% 19% 30% 19% 4	800
	21st to end	Night	22% 16% 39% 21% 3	880
February	1st to 10th	Night	26% 16% 32% 23% 4	800
	11th to 20th	Night	29% 18% 34% 18% 2	783
	21st to end	Night	30% 16% 34% 19% 1	660
March	1st to 10th	Night	23% 14% 34% 26% 4	800
	11th to 20th	Night	23% 15% 33% 22% 7% 1	767
	21st to end	Night	21% 14% 31% 25% 9%	822
April	1st to 10th	Night	16% 11% 34% 29% 11%	570
	11th to 20th	Night	18% 9% 34% 28% 11%	563
	21st to end	Night	17% 8% 30% 32% 12% 1	570
May	1st to 10th	Night	14% 7% 29% 31% 18% 1	570
	11th to 20th	Night	14% 5% 21% 37% 20% 4	561
	21st to end	Night	8% 3 16% 36% 30% 6%	617
June	1st to 10th	Night	8% 4 14% 36% 33% 4	570
	11th to 20th	Night	5% 2 13% 35% 38% 8%	570
	21st to end	Night	6% 1 12% 38% 36% 7%	570
July	1st to 10th	Night	10% 1 8% 30% 40% 10%	555
	11th to 20th	Night	8% 2 10% 27% 42% 12%	552
	21st to end	Night	9% 1 7% 33% 40% 10%	624
August	1st to 10th	Night	8% 2 7% 29% 47% 8%	567
	11th to 20th	Night	8% 1 9% 35% 41% 5%	564
	21st to end	Night	9% 1 7% 30% 44% 9%	627
September	1st to 10th	Night	10% 3 10% 29% 39% 8%	634
	11th to 20th	Night	14% 3 11% 31% 34% 6%	760
	21st to end	Night	14% 2 16% 32% 31% 5%	760
October	1st to 10th	Night	12% 5% 17% 31% 29% 6%	760
	11th to 20th	Night	17% 8% 22% 33% 18% 2	760
	21st to end	Night	18% 8% 25% 30% 16% 2	836
November	1st to 10th	Night	15% 9% 23% 34% 18% 1	780
	11th to 20th	Night	18% 13% 30% 27% 11% 1	800
	21st to end	Night	22% 12% 27% 28% 11% 1	800
December	1st to 10th	Night	27% 14% 27% 26% 6%	800
	11th to 20th	Night	26% 11% 28% 28% 7%	800
	21st to end	Night	26% 17% 28% 24% 5%	880

Page generated at 2025-03-09 07:08:47. Version ac07

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