Solar Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Solar Hills Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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	3 7% 2 6% 4 4 4 4 6% 7% 54%	117780
	Night	4 8% 3 6% 4 3 4 3 5% 6% 54%	119759
Transparency	Day	26% 8% 11% 21% 23% 11%	117539
	Night	27% 7% 11% 23% 22% 9%	119589
Seeing	Day	7% 10% 26% 31% 20% 5%	15894
	Night	7% 5% 25% 40% 21% 3	26166

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 9% 6% 13% 5% 4 4 4 5% 6% 43%	3942
	11th to 20th	Day	3 11% 3 10% 4 4 4 3 5% 6% 46%	4100
	21st to end	Day	2 8% 3 6% 4 3 4 3 4 6% 57%	4510
February	1st to 10th	Day	5% 11% 3 8% 5% 5% 4 3 6% 7% 44%	1800
	11th to 20th	Day	5% 15% 4 7% 5% 3 4 4 5% 6% 44%	1785
	21st to end	Day	3 12% 4 10% 6% 4 4 3 4 6% 46%	1650
March	1st to 10th	Day	3 10% 3 7% 4 4 4 3 6% 6% 51%	4951
	11th to 20th	Day	3 14% 4 7% 4 4 5% 4 5% 6% 44%	5000
	21st to end	Day	3 11% 4 8% 5% 5% 5% 5% 6% 8% 41%	5501
April	1st to 10th	Day	5% 7% 3 6% 4 3 3 4 5% 8% 51%	2400
	11th to 20th	Day	5% 10% 3 7% 4 5% 5% 4 5% 7% 46%	2371
	21st to end	Day	4 9% 3 4 3 4 5% 4 5% 8% 51%	2341
May	1st to 10th	Day	5% 9% 2 6% 4 5% 5% 4 6% 7% 47%	4066
	11th to 20th	Day	4 4 1 4 4 5% 5% 4 7% 8% 53%	4129
	21st to end	Day	4 5% 1 4 4 4 4 4 5% 7% 57%	4825
June	1st to 10th	Day	3 3 1 4 3 3 3 4 5% 8% 62%	2660
	11th to 20th	Day	4 3 1 3 3 4 3 3 5% 6% 66%	2660
	21st to end	Day	2 3 1 3 3 3 4 4 5% 8% 64%	2660
July	1st to 10th	Day	2 2 1 3 3 3 4 3 4 5% 69%	4430
	11th to 20th	Day	2 2 1 3 3 5% 6% 7% 11% 13% 49%	4112
	21st to end	Day	3 3 1 4 4 4 5% 4 6% 8% 57%	4454
August	1st to 10th	Day	3 3 1 5% 4 5% 7% 7% 10% 14% 40%	4092
	11th to 20th	Day	3 3 2 5% 4 5% 6% 5% 8% 8% 52%	3921
	21st to end	Day	3 3 1 4 5% 5% 6% 5% 8% 9% 51%	4180
September	1st to 10th	Day	5% 3 1 4 3 4 4 4 5% 6% 59%	2280
	11th to 20th	Day	4 3 1 5% 3 4 4 4 5% 7% 61%	2262
	21st to end	Day	4 3 1 4 3 3 3 3 3 6% 67%	2008
October	1st to 10th	Day	4 3 1 2 1 2 2 2 4 4 76%	3170
	11th to 20th	Day	4 4 2 4 4 4 5% 4 7% 7% 54%	3150
	21st to end	Day	5% 5% 1 4 2 3 3 2 4 5% 66%	3438
November	1st to 10th	Day	2 5% 2 3 3 3 3 2 4 6% 67%	1927
	11th to 20th	Day	4 6% 2 5% 3 3 3 2 4 4 63%	1755
	21st to end	Day	4 8% 3 6% 3 3 3 2 4 4 60%	1600
December	1st to 10th	Day	3 8% 2 5% 2 2 2 2 4 4 66%	2620
	11th to 20th	Day	3 8% 3 7% 3 3 2 3 5% 7% 56%	3026
	21st to end	Day	4 10% 4 8% 4 3 4 3 5% 7% 48%	4004
January	1st to 10th	Night	2 11% 6% 13% 5% 4 3 3 4 5% 42%	6051
	11th to 20th	Night	6% 14% 3 8% 3 3 3 2 4 5% 48%	5880
	21st to end	Night	3 12% 4 7% 4 3 3 3 4 5% 52%	6468
February	1st to 10th	Night	5% 12% 4 7% 5% 3 3 2 4 5% 49%	2600
	11th to 20th	Night	6% 10% 4 8% 4 4 3 3 4 6% 47%	2502
	21st to end	Night	4 11% 4 7% 4 4 4 4 4 6% 49%	1980
March	1st to 10th	Night	4 13% 3 7% 4 4 4 3 5% 6% 48%	4940
	11th to 20th	Night	4 11% 4 7% 4 4 4 3 4 6% 48%	5000
	21st to end	Night	5% 13% 3 7% 5% 5% 4 4 5% 6% 42%	5472
April	1st to 10th	Night	6% 9% 3 6% 5% 4 4 4 5% 7% 48%	2000
	11th to 20th	Night	7% 10% 3 7% 4 4 5% 4 5% 6% 46%	1977
	21st to end	Night	8% 8% 2 4 3 4 4 4 6% 6% 52%	1955
May	1st to 10th	Night	8% 9% 2 5% 3 3 4 4 6% 7% 49%	2901
	11th to 20th	Night	6% 4 1 4 4 4 4 4 6% 9% 54%	2771
	21st to end	Night	7% 4 1 3 3 3 3 3 4 5% 64%	2762
June	1st to 10th	Night	3 3 1 3 3 3 4 3 6% 7% 64%	1520
	11th to 20th	Night	3 2 1 4 2 3 4 3 5% 5% 69%	1520
	21st to end	Night	3 2 1 2 3 3 4 5% 6% 7% 65%	1520
July	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 5% 71%	2540
	11th to 20th	Night	1 1 1 3 3 4 5% 5% 11% 12% 55%	2853
	21st to end	Night	2 3 1 4 4 5% 5% 5% 7% 10% 55%	3109
August	1st to 10th	Night	3 3 2 5% 5% 5% 7% 6% 10% 12% 42%	2847
	11th to 20th	Night	3 3 1 4 4 5% 6% 5% 6% 10% 54%	2904
	21st to end	Night	3 3 2 5% 5% 5% 5% 5% 7% 9% 52%	3487
September	1st to 10th	Night	4 2 2 4 4 3 4 3 6% 9% 59%	1900
	11th to 20th	Night	4 3 1 4 3 4 4 3 5% 7% 64%	1914
	21st to end	Night	5% 3 1 3 2 3 2 2 3 5% 71%	2171
October	1st to 10th	Night	3 3 1 2 2 2 2 1 3 4 77%	3800
	11th to 20th	Night	3 5% 2 5% 3 4 4 4 5% 8% 58%	3778
	21st to end	Night	6% 7% 2 4 2 3 2 1 3 3 67%	4120
November	1st to 10th	Night	4 6% 2 3 3 2 3 3 5% 5% 65%	2350
	11th to 20th	Night	5% 7% 2 5% 3 2 2 3 3 4 64%	2642
	21st to end	Night	6% 9% 2 5% 4 2 2 3 4 5% 58%	2800
December	1st to 10th	Night	4 7% 2 4 2 2 2 3 4 6% 67%	4570
	11th to 20th	Night	3 8% 3 6% 4 3 4 2 4 7% 54%	5181
	21st to end	Night	5% 13% 5% 9% 4 3 3 3 4 5% 46%	6974

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	36% 10% 17% 23% 14% 1	3943
	11th to 20th	Day	31% 14% 14% 16% 21% 4	4100
	21st to end	Day	27% 8% 10% 28% 21% 6%	4510
February	1st to 10th	Day	40% 7% 16% 19% 13% 5%	1800
	11th to 20th	Day	38% 6% 11% 22% 18% 4	1794
	21st to end	Day	38% 6% 9% 22% 21% 4	1650
March	1st to 10th	Day	24% 10% 11% 22% 24% 8%	4951
	11th to 20th	Day	34% 12% 12% 27% 14% 2	5000
	21st to end	Day	32% 13% 14% 26% 13% 1	5501
April	1st to 10th	Day	30% 7% 12% 24% 20% 7%	2400
	11th to 20th	Day	34% 8% 12% 19% 20% 7%	2374
	21st to end	Day	29% 7% 14% 25% 22% 4	2341
May	1st to 10th	Day	27% 9% 16% 20% 22% 7%	4066
	11th to 20th	Day	22% 11% 13% 24% 23% 7%	4132
	21st to end	Day	20% 7% 14% 18% 33% 8%	4825
June	1st to 10th	Day	19% 5% 9% 20% 29% 18%	2660
	11th to 20th	Day	18% 5% 8% 13% 25% 30%	2660
	21st to end	Day	17% 5% 9% 15% 25% 28%	2660
July	1st to 10th	Day	17% 6% 7% 9% 18% 44%	4361
	11th to 20th	Day	20% 9% 9% 26% 20% 15%	4042
	21st to end	Day	22% 9% 10% 17% 17% 24%	4314
August	1st to 10th	Day	29% 10% 19% 19% 12% 11%	4078
	11th to 20th	Day	28% 8% 13% 15% 24% 13%	3960
	21st to end	Day	26% 8% 12% 17% 23% 13%	4179
September	1st to 10th	Day	26% 8% 8% 13% 26% 20%	2280
	11th to 20th	Day	21% 8% 10% 16% 27% 17%	2262
	21st to end	Day	20% 6% 6% 17% 36% 14%	2008
October	1st to 10th	Day	13% 4 6% 14% 36% 25%	3170
	11th to 20th	Day	25% 5% 7% 29% 29% 6%	3150
	21st to end	Day	19% 5% 7% 26% 37% 6%	3438
November	1st to 10th	Day	18% 7% 12% 24% 34% 6%	1927
	11th to 20th	Day	24% 5% 10% 32% 24% 5%	1755
	21st to end	Day	28% 5% 9% 28% 24% 5%	1600
December	1st to 10th	Day	23% 5% 9% 38% 22% 3	2620
	11th to 20th	Day	28% 5% 12% 28% 25% 1	3024
	21st to end	Day	33% 7% 13% 23% 20% 4	4004
January	1st to 10th	Night	39% 9% 13% 23% 15% 1	6051
	11th to 20th	Night	29% 13% 13% 18% 22% 4	5880
	21st to end	Night	31% 8% 11% 23% 23% 4	6468
February	1st to 10th	Night	37% 6% 15% 23% 16% 3	2600
	11th to 20th	Night	36% 7% 13% 23% 17% 4	2503
	21st to end	Night	33% 6% 12% 23% 22% 5%	1980
March	1st to 10th	Night	30% 10% 9% 20% 25% 6%	4940
	11th to 20th	Night	30% 11% 12% 24% 20% 4	5000
	21st to end	Night	33% 13% 13% 29% 11% 1	5472
April	1st to 10th	Night	33% 6% 12% 22% 20% 7%	2000
	11th to 20th	Night	34% 8% 11% 19% 20% 8%	1977
	21st to end	Night	28% 7% 14% 22% 24% 4	1955
May	1st to 10th	Night	25% 8% 14% 22% 26% 5%	2901
	11th to 20th	Night	20% 8% 16% 29% 20% 7%	2772
	21st to end	Night	18% 6% 10% 18% 31% 17%	2762
June	1st to 10th	Night	15% 7% 9% 20% 29% 19%	1520
	11th to 20th	Night	16% 5% 8% 14% 21% 36%	1520
	21st to end	Night	16% 5% 8% 16% 25% 30%	1520
July	1st to 10th	Night	16% 5% 8% 10% 15% 46%	2500
	11th to 20th	Night	16% 7% 11% 34% 15% 18%	2800
	21st to end	Night	21% 9% 14% 18% 17% 21%	3011
August	1st to 10th	Night	30% 9% 21% 16% 12% 12%	2838
	11th to 20th	Night	26% 6% 20% 14% 16% 18%	2931
	21st to end	Night	27% 7% 11% 18% 23% 14%	3487
September	1st to 10th	Night	20% 6% 11% 17% 23% 23%	1900
	11th to 20th	Night	18% 7% 13% 16% 26% 20%	1914
	21st to end	Night	17% 4 6% 18% 39% 15%	2171
October	1st to 10th	Night	13% 3 6% 14% 37% 27%	3800
	11th to 20th	Night	24% 5% 8% 26% 29% 7%	3778
	21st to end	Night	24% 3 5% 27% 34% 7%	4120
November	1st to 10th	Night	20% 6% 11% 26% 30% 7%	2350
	11th to 20th	Night	24% 4 9% 31% 28% 4	2642
	21st to end	Night	29% 5% 9% 25% 28% 6%	2800
December	1st to 10th	Night	20% 5% 9% 41% 24% 2	4570
	11th to 20th	Night	28% 7% 10% 33% 22% 1	5182
	21st to end	Night	39% 6% 10% 22% 21% 2	6974

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	8% 9% 24% 37% 15% 7%	300
	11th to 20th	Day	7% 12% 27% 37% 15% 3	300
	21st to end	Day	5% 5% 28% 42% 15% 5%	330
February	1st to 10th	Day	11% 12% 35% 32% 7% 2	300
	11th to 20th	Day	14% 15% 35% 27% 9% 1	300
	21st to end	Day	10% 14% 34% 33% 8% 2	249
March	1st to 10th	Day	12% 18% 31% 28% 9% 2	497
	11th to 20th	Day	9% 16% 34% 27% 12% 2	500
	21st to end	Day	13% 23% 31% 23% 9%	550
April	1st to 10th	Day	11% 17% 32% 28% 10% 3	500
	11th to 20th	Day	13% 25% 32% 20% 8% 2	492
	21st to end	Day	10% 21% 35% 22% 11% 2	481
May	1st to 10th	Day	12% 20% 33% 24% 9% 2	463
	11th to 20th	Day	9% 12% 28% 27% 19% 5%	520
	21st to end	Day	5% 15% 25% 31% 20% 4	734
June	1st to 10th	Day	3 8% 26% 33% 24% 6%	680
	11th to 20th	Day	5% 8% 30% 33% 21% 4	680
	21st to end	Day	1 7% 25% 37% 24% 5%	680
July	1st to 10th	Day	1 2 14% 39% 35% 8%	671
	11th to 20th	Day	2 2 12% 37% 34% 13%	485
	21st to end	Day	5% 2 14% 33% 35% 12%	531
August	1st to 10th	Day	5% 3 17% 33% 32% 10%	487
	11th to 20th	Day	3 3 19% 35% 31% 9%	477
	21st to end	Day	4 1 16% 41% 28% 10%	539
September	1st to 10th	Day	6% 4 19% 30% 30% 10%	490
	11th to 20th	Day	5% 7% 29% 34% 20% 5%	490
	21st to end	Day	5% 11% 23% 25% 29% 8%	408
October	1st to 10th	Day	5% 12% 18% 28% 23% 14%	300
	11th to 20th	Day	4 9% 22% 33% 24% 7%	300
	21st to end	Day	8% 7% 27% 29% 25% 4	330
November	1st to 10th	Day	6% 13% 29% 28% 19% 5%	300
	11th to 20th	Day	4 8% 29% 36% 16% 7%	300
	21st to end	Day	5% 10% 28% 34% 17% 6%	300
December	1st to 10th	Day	8% 8% 31% 32% 17% 4	300
	11th to 20th	Day	7% 7% 26% 33% 23% 4	300
	21st to end	Day	13% 9% 29% 33% 12% 4	330
January	1st to 10th	Night	7% 6% 24% 40% 19% 3	880
	11th to 20th	Night	7% 6% 27% 39% 18% 3	800
	21st to end	Night	9% 4 26% 43% 15% 3	880
February	1st to 10th	Night	9% 6% 35% 38% 11% 2	800
	11th to 20th	Night	9% 7% 36% 36% 12% 1	784
	21st to end	Night	9% 7% 37% 39% 8%	660
March	1st to 10th	Night	8% 8% 35% 37% 11% 1	800
	11th to 20th	Night	6% 4 29% 40% 19% 1	800
	21st to end	Night	8% 11% 32% 37% 11% 1	875
April	1st to 10th	Night	9% 9% 35% 38% 9% 1	600
	11th to 20th	Night	9% 12% 32% 35% 11% 1	593
	21st to end	Night	9% 7% 33% 34% 15% 2	587
May	1st to 10th	Night	8% 6% 29% 42% 14% 1	570
	11th to 20th	Night	7% 5% 20% 43% 22% 3	561
	21st to end	Night	6% 9% 24% 38% 20% 3	617
June	1st to 10th	Night	4 3 19% 43% 28% 3	570
	11th to 20th	Night	3 3 26% 43% 22% 3	570
	21st to end	Night	3 2 16% 44% 32% 3	570
July	1st to 10th	Night	4 1 11% 39% 41% 4	555
	11th to 20th	Night	3 1 7% 41% 45% 5%	552
	21st to end	Night	4 1 8% 34% 49% 4	624
August	1st to 10th	Night	5% 1 12% 36% 43% 4	567
	11th to 20th	Night	4 2 9% 42% 39% 5%	564
	21st to end	Night	3 2 12% 43% 35% 5%	627
September	1st to 10th	Night	3 2 11% 49% 32% 3	570
	11th to 20th	Night	3 3 18% 41% 30% 4	584
	21st to end	Night	5% 3 19% 38% 29% 6%	760
October	1st to 10th	Night	5% 5% 23% 43% 23% 2	760
	11th to 20th	Night	4 4 25% 41% 22% 4	760
	21st to end	Night	8% 6% 24% 37% 21% 4	836
November	1st to 10th	Night	5% 4 28% 38% 22% 3	790
	11th to 20th	Night	6% 7% 26% 39% 18% 3	1000
	21st to end	Night	7% 6% 28% 37% 19% 3	1000
December	1st to 10th	Night	8% 6% 26% 43% 16% 2	1000
	11th to 20th	Night	10% 8% 26% 36% 18% 2	1000
	21st to end	Night	11% 8% 28% 41% 10% 1	1100

Page generated at 2025-04-23 07:25:05. Version ac07

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