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 2026-07-16.

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% 5% 4 5% 4 6% 8% 37%	138062
	Night	14% 8% 3 7% 4 4 4 4 5% 7% 39%	134604
Transparency	Day	43% 7% 11% 22% 15% 3	141774
	Night	42% 6% 11% 21% 17% 4	138965
Seeing	Day	18% 11% 23% 23% 17% 8%	16991
	Night	17% 9% 23% 28% 18% 3	26826

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	18% 13% 6% 11% 4 4 5% 3 4 5% 28%	5258
	11th to 20th	Day	15% 8% 6% 11% 3 3 3 3 3 5% 40%	5280
	21st to end	Day	21% 10% 4 7% 5% 4 3 3 5% 6% 32%	6115
February	1st to 10th	Day	19% 12% 4 8% 4 3 4 3 4 5% 33%	2100
	11th to 20th	Day	22% 11% 4 8% 5% 4 4 3 4 6% 30%	2048
	21st to end	Day	21% 8% 4 7% 4 4 3 3 4 6% 35%	1730
March	1st to 10th	Day	18% 11% 3 8% 5% 4 4 3 5% 5% 34%	4580
	11th to 20th	Day	12% 8% 3 7% 4 4 3 3 4 5% 46%	5010
	21st to end	Day	13% 8% 3 6% 4 4 4 4 5% 7% 42%	5666
April	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 6% 7% 44%	2520
	11th to 20th	Day	13% 7% 3 5% 5% 4 4 3 5% 7% 44%	2494
	21st to end	Day	13% 7% 2 7% 6% 5% 4 4 6% 6% 40%	2635
May	1st to 10th	Day	18% 8% 3 6% 4 4 5% 4 7% 10% 32%	7616
	11th to 20th	Day	12% 8% 3 9% 6% 5% 5% 4 6% 7% 35%	7626
	21st to end	Day	18% 10% 4 10% 5% 5% 5% 3 5% 6% 29%	8391
June	1st to 10th	Day	10% 7% 2 6% 5% 5% 5% 4 6% 10% 40%	2730
	11th to 20th	Day	6% 5% 2 6% 5% 4 6% 5% 7% 10% 44%	2730
	21st to end	Day	6% 4 2 7% 5% 5% 6% 5% 9% 12% 39%	2839
July	1st to 10th	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 11% 38%	6171
	11th to 20th	Day	8% 6% 2 8% 6% 6% 7% 6% 8% 11% 31%	5965
	21st to end	Day	12% 8% 3 8% 6% 6% 6% 5% 8% 11% 26%	6424
August	1st to 10th	Day	6% 4 2 5% 4 5% 6% 5% 8% 11% 45%	4202
	11th to 20th	Day	6% 5% 2 6% 6% 5% 7% 5% 8% 12% 38%	3849
	21st to end	Day	7% 4 2 5% 5% 5% 5% 5% 6% 8% 50%	4312
September	1st to 10th	Day	12% 7% 3 6% 5% 4 5% 4 7% 7% 40%	2310
	11th to 20th	Day	14% 6% 3 6% 4 4 4 4 5% 7% 44%	2200
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 6% 47%	2200
October	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 5% 6% 53%	2200
	11th to 20th	Day	12% 4 2 5% 3 4 3 2 4 7% 54%	2149
	21st to end	Day	16% 6% 2 5% 3 4 4 3 5% 6% 46%	2032
November	1st to 10th	Day	12% 6% 2 5% 3 3 4 3 5% 6% 53%	1852
	11th to 20th	Day	15% 7% 2 5% 3 3 3 3 5% 6% 47%	1890
	21st to end	Day	16% 10% 3 4 4 4 4 3 5% 5% 43%	1890
December	1st to 10th	Day	16% 10% 3 8% 5% 4 4 3 4 5% 40%	3020
	11th to 20th	Day	21% 13% 5% 9% 4 4 3 3 4 5% 28%	3463
	21st to end	Day	20% 12% 5% 8% 4 4 4 3 5% 8% 27%	4565
January	1st to 10th	Night	17% 12% 3 8% 3 3 3 3 4 6% 38%	7635
	11th to 20th	Night	17% 10% 4 6% 5% 4 3 3 4 4 40%	7680
	21st to end	Night	19% 13% 3 8% 4 4 3 2 4 5% 35%	8062
February	1st to 10th	Night	21% 10% 3 8% 4 4 3 4 5% 7% 31%	2520
	11th to 20th	Night	24% 9% 4 8% 5% 4 2 3 4 5% 32%	2458
	21st to end	Night	23% 11% 3 7% 4 3 4 3 5% 7% 32%	2076
March	1st to 10th	Night	19% 13% 3 7% 4 4 4 3 4 7% 33%	5493
	11th to 20th	Night	13% 6% 2 5% 3 4 4 4 6% 7% 48%	5168
	21st to end	Night	15% 7% 3 8% 5% 5% 4 4 4 6% 40%	5547
April	1st to 10th	Night	13% 6% 2 5% 5% 4 5% 4 5% 7% 45%	2100
	11th to 20th	Night	15% 5% 1 5% 3 4 3 3 5% 7% 48%	2075
	21st to end	Night	13% 6% 2 6% 5% 4 4 3 5% 8% 43%	1983
May	1st to 10th	Night	16% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	5237
	11th to 20th	Night	12% 8% 3 8% 6% 5% 5% 4 6% 7% 36%	5234
	21st to end	Night	17% 9% 3 9% 5% 5% 5% 4 6% 8% 29%	5761
June	1st to 10th	Night	7% 6% 2 7% 4 5% 4 4 7% 9% 44%	1890
	11th to 20th	Night	5% 3 2 4 5% 3 5% 5% 7% 12% 50%	1890
	21st to end	Night	6% 4 1 4 5% 5% 6% 4 8% 12% 45%	1756
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 6% 8% 9% 40%	3968
	11th to 20th	Night	8% 6% 3 7% 5% 5% 6% 5% 9% 12% 37%	4102
	21st to end	Night	8% 8% 3 9% 7% 6% 7% 6% 8% 12% 26%	4427
August	1st to 10th	Night	5% 4 2 5% 4 5% 5% 4 7% 9% 51%	2942
	11th to 20th	Night	6% 4 2 6% 4 4 5% 5% 8% 11% 45%	3200
	21st to end	Night	5% 2 1 4 4 4 4 4 7% 10% 56%	3586
September	1st to 10th	Night	10% 6% 3 7% 4 4 4 5% 6% 7% 45%	2068
	11th to 20th	Night	10% 6% 2 7% 5% 4 5% 3 5% 8% 45%	2200
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 50%	2200
October	1st to 10th	Night	10% 5% 1 4 3 3 3 3 4 7% 57%	2200
	11th to 20th	Night	15% 6% 2 4 4 3 3 3 5% 8% 50%	2250
	21st to end	Night	15% 8% 2 5% 3 2 3 3 4 6% 48%	2805
November	1st to 10th	Night	12% 7% 3 5% 3 4 3 3 4 7% 50%	2666
	11th to 20th	Night	14% 8% 2 4 3 3 3 2 5% 7% 49%	2730
	21st to end	Night	17% 9% 3 5% 4 3 3 3 4 7% 42%	2730
December	1st to 10th	Night	19% 11% 3 8% 3 4 4 3 4 5% 35%	4380
	11th to 20th	Night	23% 11% 3 7% 3 3 3 2 3 5% 36%	4952
	21st to end	Night	16% 14% 4 8% 5% 5% 5% 4 5% 7% 28%	6633

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% 10% 18% 10% 1	5259
	11th to 20th	Day	48% 4 3 18% 25% 2	5280
	21st to end	Day	53% 3 7% 22% 11% 4	6115
February	1st to 10th	Day	54% 4 7% 17% 16% 2	2100
	11th to 20th	Day	56% 5% 7% 17% 13% 3	2058
	21st to end	Day	51% 4 8% 15% 17% 5%	1730
March	1st to 10th	Day	51% 4 6% 14% 16% 8%	4580
	11th to 20th	Day	41% 4 7% 20% 19% 8%	5010
	21st to end	Day	41% 5% 10% 28% 15% 1	5668
April	1st to 10th	Day	39% 6% 12% 24% 16% 3	2520
	11th to 20th	Day	39% 5% 8% 22% 23% 3	2494
	21st to end	Day	42% 7% 10% 26% 14% 1	2635
May	1st to 10th	Day	46% 8% 12% 22% 11% 1	7651
	11th to 20th	Day	47% 7% 12% 21% 12%	7630
	21st to end	Day	56% 7% 8% 16% 12% 2	8405
June	1st to 10th	Day	38% 9% 13% 23% 15% 2	2730
	11th to 20th	Day	33% 10% 17% 22% 16% 2	2730
	21st to end	Day	33% 11% 19% 19% 15% 3	2839
July	1st to 10th	Day	36% 11% 17% 24% 11% 1	6106
	11th to 20th	Day	42% 11% 19% 22% 5% 1	5896
	21st to end	Day	50% 10% 17% 19% 4	6240
August	1st to 10th	Day	30% 10% 16% 31% 13% 1	4189
	11th to 20th	Day	35% 9% 15% 25% 15% 1	3885
	21st to end	Day	30% 8% 11% 33% 17% 1	4311
September	1st to 10th	Day	41% 8% 11% 19% 16% 5%	2310
	11th to 20th	Day	39% 7% 11% 23% 18% 2	2200
	21st to end	Day	36% 6% 11% 23% 19% 4	2200
October	1st to 10th	Day	25% 4 6% 18% 36% 10%	3590
	11th to 20th	Day	22% 4 6% 25% 30% 12%	3480
	21st to end	Day	31% 4 7% 25% 25% 9%	3256
November	1st to 10th	Day	33% 4 8% 23% 27% 4	1852
	11th to 20th	Day	38% 4 7% 25% 22% 5%	1890
	21st to end	Day	43% 4 7% 22% 20% 4	1890
December	1st to 10th	Day	47% 4 5% 22% 20% 2	3020
	11th to 20th	Day	58% 4 8% 17% 11% 2	3460
	21st to end	Day	54% 5% 11% 21% 8% 1	4565
January	1st to 10th	Night	48% 3 15% 20% 12% 1	7636
	11th to 20th	Night	47% 4 5% 18% 22% 4	7680
	21st to end	Night	53% 3 7% 16% 15% 5%	8062
February	1st to 10th	Night	53% 4 8% 19% 15% 1	2520
	11th to 20th	Night	56% 4 7% 17% 13% 4	2459
	21st to end	Night	53% 5% 7% 16% 16% 4	2076
March	1st to 10th	Night	51% 5% 7% 15% 17% 4	5493
	11th to 20th	Night	35% 5% 7% 22% 20% 11%	5168
	21st to end	Night	45% 4 9% 27% 13% 2	5547
April	1st to 10th	Night	37% 6% 11% 24% 20% 3	2100
	11th to 20th	Night	35% 5% 10% 23% 22% 6%	2075
	21st to end	Night	39% 5% 12% 27% 16% 1	1983
May	1st to 10th	Night	47% 8% 12% 22% 10% 1	5264
	11th to 20th	Night	46% 8% 14% 17% 15% 1	5235
	21st to end	Night	51% 9% 12% 17% 10% 1	5771
June	1st to 10th	Night	35% 7% 15% 27% 14% 2	1890
	11th to 20th	Night	24% 10% 19% 29% 16% 2	1890
	21st to end	Night	29% 12% 15% 26% 14% 3	1756
July	1st to 10th	Night	36% 10% 19% 22% 12% 1	3925
	11th to 20th	Night	36% 10% 22% 24% 6% 2	4051
	21st to end	Night	47% 11% 19% 18% 5% 1	4297
August	1st to 10th	Night	27% 8% 12% 36% 16% 1	2931
	11th to 20th	Night	30% 8% 21% 27% 13% 1	3230
	21st to end	Night	24% 6% 13% 36% 19% 2	3586
September	1st to 10th	Night	36% 8% 13% 20% 18% 5%	2068
	11th to 20th	Night	36% 8% 11% 20% 23% 1	2200
	21st to end	Night	33% 6% 11% 21% 24% 5%	2200
October	1st to 10th	Night	25% 5% 5% 21% 33% 11%	3590
	11th to 20th	Night	22% 3 6% 24% 30% 15%	3658
	21st to end	Night	26% 3 6% 25% 30% 10%	4531
November	1st to 10th	Night	35% 4 7% 24% 23% 7%	2666
	11th to 20th	Night	36% 3 7% 22% 25% 7%	2730
	21st to end	Night	43% 3 7% 23% 19% 4	2730
December	1st to 10th	Night	51% 4 5% 16% 22% 1	4380
	11th to 20th	Night	51% 5% 6% 20% 17% 2	4954
	21st to end	Night	54% 6% 10% 20% 9%	6633

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	28% 19% 36% 12% 4 1	330
	11th to 20th	Day	32% 25% 25% 13% 4	330
	21st to end	Day	24% 23% 37% 13% 3	363
February	1st to 10th	Day	27% 22% 33% 14% 4	330
	11th to 20th	Day	37% 22% 30% 7% 2 1	330
	21st to end	Day	32% 24% 30% 11% 3	273
March	1st to 10th	Day	26% 21% 35% 14% 5%	330
	11th to 20th	Day	25% 21% 33% 15% 6%	499
	21st to end	Day	26% 17% 33% 17% 7%	594
April	1st to 10th	Day	22% 19% 26% 23% 10% 1	540
	11th to 20th	Day	18% 16% 32% 23% 9% 2	532
	21st to end	Day	18% 16% 29% 23% 11% 2	540
May	1st to 10th	Day	18% 15% 31% 22% 9% 4	543
	11th to 20th	Day	15% 11% 26% 26% 16% 8%	567
	21st to end	Day	16% 8% 21% 26% 16% 12%	617
June	1st to 10th	Day	12% 6% 20% 27% 24% 12%	570
	11th to 20th	Day	6% 5% 18% 29% 27% 15%	570
	21st to end	Day	9% 3 17% 29% 26% 16%	679
July	1st to 10th	Day	11% 3 11% 26% 28% 21%	628
	11th to 20th	Day	11% 3 9% 25% 28% 23%	544
	21st to end	Day	12% 4 9% 24% 30% 22%	576
August	1st to 10th	Day	10% 4 12% 26% 29% 19%	526
	11th to 20th	Day	10% 3 13% 30% 32% 12%	519
	21st to end	Day	11% 2 9% 24% 32% 21%	583
September	1st to 10th	Day	12% 3 11% 24% 34% 15%	530
	11th to 20th	Day	14% 5% 10% 23% 32% 16%	530
	21st to end	Day	16% 5% 18% 26% 26% 9%	530
October	1st to 10th	Day	12% 4 20% 29% 25% 10%	530
	11th to 20th	Day	13% 9% 28% 27% 18% 4	530
	21st to end	Day	20% 12% 26% 27% 11% 3	415
November	1st to 10th	Day	20% 11% 28% 28% 10% 3	330
	11th to 20th	Day	15% 15% 38% 26% 6%	330
	21st to end	Day	21% 18% 32% 20% 8% 2	330
December	1st to 10th	Day	25% 22% 31% 17% 3 1	330
	11th to 20th	Day	26% 18% 28% 19% 8%	330
	21st to end	Day	30% 20% 30% 15% 6% 1	363
January	1st to 10th	Night	25% 17% 32% 22% 4	840
	11th to 20th	Night	27% 19% 31% 20% 4	840
	21st to end	Night	22% 16% 38% 22% 2	924
February	1st to 10th	Night	25% 16% 32% 24% 3	840
	11th to 20th	Night	29% 18% 34% 18% 1	823
	21st to end	Night	30% 17% 33% 19% 1	692
March	1st to 10th	Night	22% 14% 34% 26% 3	840
	11th to 20th	Night	23% 14% 33% 23% 6% 1	840
	21st to end	Night	20% 14% 32% 26% 8%	908
April	1st to 10th	Night	17% 10% 32% 30% 10%	630
	11th to 20th	Night	17% 8% 34% 30% 10%	623
	21st to end	Night	17% 8% 29% 33% 13% 1	630
May	1st to 10th	Night	15% 7% 30% 32% 16% 1	630
	11th to 20th	Night	13% 6% 22% 36% 20% 3	621
	21st to end	Night	11% 4 16% 36% 28% 5%	683
June	1st to 10th	Night	8% 4 13% 38% 33% 4	630
	11th to 20th	Night	6% 3 12% 36% 36% 7%	630
	21st to end	Night	6% 2 12% 36% 36% 8%	630
July	1st to 10th	Night	10% 2 7% 28% 41% 11%	615
	11th to 20th	Night	8% 3 9% 26% 43% 11%	597
	21st to end	Night	9% 1 7% 32% 41% 11%	657
August	1st to 10th	Night	8% 2 7% 29% 47% 8%	597
	11th to 20th	Night	8% 1 8% 34% 41% 7%	594
	21st to end	Night	9% 1 7% 31% 43% 9%	660
September	1st to 10th	Night	10% 3 10% 30% 39% 7%	668
	11th to 20th	Night	13% 3 11% 31% 36% 6%	800
	21st to end	Night	14% 2 16% 32% 31% 5%	800
October	1st to 10th	Night	12% 5% 17% 32% 29% 6%	800
	11th to 20th	Night	17% 8% 22% 34% 19% 2	800
	21st to end	Night	19% 8% 26% 30% 15% 2	880
November	1st to 10th	Night	15% 9% 23% 34% 17% 1	820
	11th to 20th	Night	18% 13% 30% 28% 10% 1	840
	21st to end	Night	22% 13% 27% 28% 10% 1	840
December	1st to 10th	Night	27% 14% 27% 26% 6%	840
	11th to 20th	Night	25% 11% 28% 28% 7%	840
	21st to end	Night	26% 16% 28% 24% 5%	924

Page generated at 2026-07-13 02:14:52. Version ac07

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