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 2026-08-30.

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 6% 2 5% 4 4 4 4 6% 7% 56%	152620
	Night	4 7% 2 6% 4 3 4 3 5% 7% 55%	147188
Transparency	Day	24% 7% 11% 22% 23% 12%	147506
	Night	26% 7% 11% 23% 23% 10%	143310
Seeing	Day	7% 10% 26% 32% 20% 6%	17808
	Night	6% 5% 26% 39% 20% 2	27886

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	3 9% 5% 12% 5% 5% 4 4 5% 7% 41%	5122
	11th to 20th	Day	3 9% 2 8% 3 3 3 2 4 5% 57%	5340
	21st to end	Day	2 9% 3 7% 4 3 3 2 4 6% 58%	5844
February	1st to 10th	Day	5% 10% 3 8% 4 5% 4 3 6% 7% 45%	1890
	11th to 20th	Day	5% 14% 4 7% 5% 4 4 4 5% 6% 43%	1877
	21st to end	Day	3 11% 4 10% 5% 4 4 3 4 6% 47%	1730
March	1st to 10th	Day	3 10% 3 7% 4 4 4 4 6% 5% 51%	5061
	11th to 20th	Day	3 14% 4 7% 4 4 5% 4 5% 6% 45%	5110
	21st to end	Day	3 11% 4 8% 5% 5% 5% 5% 6% 8% 42%	5622
April	1st to 10th	Day	5% 7% 3 6% 4 3 3 3 5% 8% 52%	2520
	11th to 20th	Day	4 10% 3 7% 4 4 5% 4 5% 7% 47%	2491
	21st to end	Day	4 8% 3 4 3 4 5% 4 5% 8% 50%	2520
May	1st to 10th	Day	4 6% 2 5% 3 4 5% 4 6% 8% 53%	7543
	11th to 20th	Day	3 3 2 5% 4 4 5% 4 7% 8% 56%	7710
	21st to end	Day	3 3 1 4 3 3 4 3 5% 8% 62%	9026
June	1st to 10th	Day	3 3 1 4 3 3 4 4 6% 8% 62%	2940
	11th to 20th	Day	3 3 1 3 2 3 3 3 5% 6% 67%	2940
	21st to end	Day	2 2 1 3 3 3 4 4 5% 7% 66%	2940
July	1st to 10th	Day	2 1 1 2 3 3 3 3 4 5% 73%	8249
	11th to 20th	Day	1 2 1 3 3 4 6% 6% 9% 11% 55%	7652
	21st to end	Day	2 2 1 4 4 5% 6% 6% 9% 11% 51%	8304
August	1st to 10th	Day	3 3 1 4 3 4 6% 6% 9% 13% 50%	5909
	11th to 20th	Day	2 2 1 4 3 4 5% 4 6% 8% 59%	5779
	21st to end	Day	3 3 2 5% 5% 5% 6% 5% 9% 10% 47%	6093
September	1st to 10th	Day	5% 3 1 4 3 4 4 4 6% 6% 59%	2400
	11th to 20th	Day	4 3 1 5% 3 4 4 4 6% 7% 60%	2381
	21st to end	Day	4 3 1 4 3 3 4 3 3 6% 65%	2113
October	1st to 10th	Day	4 3 1 2 2 2 2 2 3 4 76%	3270
	11th to 20th	Day	4 4 2 4 4 4 5% 4 7% 7% 54%	3250
	21st to end	Day	4 5% 1 4 2 3 3 2 4 6% 67%	3548
November	1st to 10th	Day	2 4 2 3 3 3 3 2 4 6% 67%	2025
	11th to 20th	Day	4 6% 2 5% 3 3 3 2 4 5% 63%	1843
	21st to end	Day	4 8% 3 6% 3 3 3 2 4 4 60%	1680
December	1st to 10th	Day	3 9% 2 5% 2 2 2 2 4 4 65%	2700
	11th to 20th	Day	3 8% 3 7% 4 3 2 3 5% 7% 56%	3106
	21st to end	Day	3 10% 3 7% 4 3 4 3 5% 7% 49%	4092
January	1st to 10th	Night	3 13% 6% 13% 5% 5% 4 3 4 5% 40%	7841
	11th to 20th	Night	4 10% 2 7% 3 2 2 2 3 5% 59%	7650
	21st to end	Night	3 12% 3 6% 3 3 3 2 4 5% 56%	8370
February	1st to 10th	Night	5% 11% 4 7% 5% 3 3 2 4 5% 51%	2730
	11th to 20th	Night	6% 11% 4 8% 5% 4 3 3 4 5% 46%	2630
	21st to end	Night	4 11% 4 7% 4 4 4 4 4 6% 50%	2076
March	1st to 10th	Night	4 13% 3 7% 4 4 4 3 5% 5% 48%	5050
	11th to 20th	Night	4 11% 4 7% 4 4 4 3 4 6% 49%	5110
	21st to end	Night	5% 13% 3 7% 5% 5% 4 4 5% 6% 43%	5593
April	1st to 10th	Night	7% 9% 3 6% 5% 3 4 3 5% 7% 48%	2100
	11th to 20th	Night	6% 10% 3 7% 4 4 5% 4 5% 6% 46%	2077
	21st to end	Night	8% 7% 3 4 3 4 4 4 6% 6% 52%	2100
May	1st to 10th	Night	6% 7% 2 5% 4 4 4 4 6% 8% 50%	5388
	11th to 20th	Night	5% 5% 2 5% 4 4 4 3 5% 8% 54%	5177
	21st to end	Night	5% 3 1 3 2 3 3 3 4 6% 66%	5181
June	1st to 10th	Night	3 3 1 3 3 3 4 3 6% 7% 65%	1680
	11th to 20th	Night	3 2 1 3 2 3 3 3 4 5% 70%	1680
	21st to end	Night	3 2 1 2 3 3 4 5% 6% 6% 66%	1680
July	1st to 10th	Night	1 1 1 3 3 3 4 3 5% 6% 70%	4740
	11th to 20th	Night	1 2 1 4 4 5% 5% 5% 10% 12% 51%	5333
	21st to end	Night	2 3 1 4 4 5% 5% 5% 8% 13% 50%	5805
August	1st to 10th	Night	3 2 1 4 4 4 6% 5% 8% 10% 52%	4123
	11th to 20th	Night	2 2 1 3 3 4 5% 4 6% 10% 60%	4276
	21st to end	Night	3 4 2 6% 5% 5% 6% 6% 8% 9% 46%	5083
September	1st to 10th	Night	4 3 1 4 3 3 4 3 6% 9% 60%	2000
	11th to 20th	Night	4 3 1 4 3 4 4 3 5% 7% 64%	2015
	21st to end	Night	5% 3 1 3 2 3 2 2 4 5% 70%	2286
October	1st to 10th	Night	3 3 1 2 2 2 2 1 3 4 77%	3920
	11th to 20th	Night	3 5% 2 5% 3 4 4 3 5% 7% 58%	3898
	21st to end	Night	6% 7% 2 4 2 3 2 1 3 3 67%	4252
November	1st to 10th	Night	4 6% 2 3 3 2 3 3 5% 5% 66%	2471
	11th to 20th	Night	5% 7% 1 5% 3 2 2 3 3 5% 64%	2774
	21st to end	Night	6% 9% 2 5% 3 2 3 3 4 5% 58%	2940
December	1st to 10th	Night	4 7% 2 4 2 2 2 3 4 5% 66%	4710
	11th to 20th	Night	3 8% 3 6% 4 3 4 2 4 7% 55%	5321
	21st to end	Night	5% 13% 5% 9% 4 3 3 3 4 5% 46%	7128

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% 18% 26% 11%	5125
	11th to 20th	Day	24% 11% 14% 24% 23% 4	5340
	21st to end	Day	28% 6% 10% 28% 23% 6%	5844
February	1st to 10th	Day	39% 7% 16% 21% 14% 5%	1890
	11th to 20th	Day	39% 7% 11% 21% 18% 4	1886
	21st to end	Day	37% 6% 9% 23% 22% 4	1730
March	1st to 10th	Day	24% 10% 11% 22% 25% 8%	5061
	11th to 20th	Day	33% 11% 11% 27% 14% 3	5110
	21st to end	Day	32% 13% 14% 26% 14% 2	5622
April	1st to 10th	Day	30% 6% 11% 24% 21% 7%	2520
	11th to 20th	Day	33% 8% 12% 20% 21% 7%	2494
	21st to end	Day	28% 7% 13% 25% 23% 4	2520
May	1st to 10th	Day	23% 7% 13% 29% 24% 4	7543
	11th to 20th	Day	20% 9% 8% 24% 30% 8%	7713
	21st to end	Day	17% 6% 9% 26% 35% 7%	9027
June	1st to 10th	Day	19% 5% 9% 19% 31% 17%	2940
	11th to 20th	Day	17% 5% 7% 13% 25% 33%	2940
	21st to end	Day	16% 5% 8% 15% 24% 31%	2940
July	1st to 10th	Day	14% 5% 4 7% 17% 53%	8181
	11th to 20th	Day	19% 7% 10% 27% 21% 16%	7582
	21st to end	Day	23% 8% 18% 17% 18% 16%	8120
August	1st to 10th	Day	28% 9% 18% 19% 13% 12%	4338
	11th to 20th	Day	27% 8% 13% 16% 24% 13%	4214
	21st to end	Day	26% 8% 13% 18% 22% 13%	4420
September	1st to 10th	Day	25% 7% 9% 14% 26% 19%	2400
	11th to 20th	Day	22% 8% 10% 16% 27% 16%	2381
	21st to end	Day	20% 6% 7% 17% 36% 14%	2113
October	1st to 10th	Day	14% 4 6% 14% 37% 25%	3270
	11th to 20th	Day	25% 5% 7% 28% 29% 6%	3250
	21st to end	Day	19% 5% 7% 26% 37% 6%	3548
November	1st to 10th	Day	17% 7% 12% 26% 33% 5%	2025
	11th to 20th	Day	24% 5% 10% 34% 23% 5%	1843
	21st to end	Day	28% 5% 11% 28% 23% 5%	1680
December	1st to 10th	Day	24% 5% 10% 38% 21% 3	2700
	11th to 20th	Day	28% 5% 12% 28% 25% 1	3104
	21st to end	Day	33% 7% 13% 23% 20% 4	4092
January	1st to 10th	Night	43% 8% 14% 23% 11% 1	7842
	11th to 20th	Night	22% 10% 13% 26% 24% 4	7650
	21st to end	Night	29% 6% 10% 24% 26% 4	8370
February	1st to 10th	Night	36% 5% 14% 25% 17% 3	2730
	11th to 20th	Night	37% 7% 13% 23% 17% 3	2631
	21st to end	Night	32% 5% 12% 24% 21% 5%	2076
March	1st to 10th	Night	30% 10% 9% 20% 25% 6%	5050
	11th to 20th	Night	30% 10% 12% 24% 20% 4	5110
	21st to end	Night	32% 12% 13% 29% 11% 2	5593
April	1st to 10th	Night	33% 6% 12% 22% 20% 7%	2100
	11th to 20th	Night	34% 8% 10% 19% 20% 8%	2077
	21st to end	Night	28% 8% 13% 22% 25% 4	2100
May	1st to 10th	Night	26% 6% 13% 29% 22% 4	5386
	11th to 20th	Night	24% 7% 10% 25% 27% 7%	5178
	21st to end	Night	17% 5% 8% 23% 35% 12%	5182
June	1st to 10th	Night	15% 7% 10% 21% 29% 19%	1680
	11th to 20th	Night	16% 5% 7% 13% 21% 38%	1680
	21st to end	Night	15% 5% 7% 15% 24% 33%	1680
July	1st to 10th	Night	15% 4 6% 8% 12% 54%	4700
	11th to 20th	Night	21% 6% 13% 29% 14% 17%	5280
	21st to end	Night	22% 7% 21% 17% 17% 15%	5677
August	1st to 10th	Night	29% 8% 20% 16% 13% 13%	3018
	11th to 20th	Night	25% 6% 19% 15% 18% 18%	3117
	21st to end	Night	27% 7% 12% 19% 22% 13%	3687
September	1st to 10th	Night	20% 6% 11% 18% 23% 22%	2000
	11th to 20th	Night	18% 7% 12% 17% 27% 19%	2015
	21st to end	Night	17% 4 7% 19% 38% 15%	2286
October	1st to 10th	Night	13% 3 6% 14% 38% 26%	3920
	11th to 20th	Night	24% 5% 8% 26% 30% 7%	3898
	21st to end	Night	24% 3 5% 27% 34% 7%	4252
November	1st to 10th	Night	19% 5% 11% 27% 31% 7%	2471
	11th to 20th	Night	24% 4 10% 31% 27% 4	2774
	21st to end	Night	28% 5% 10% 25% 26% 5%	2940
December	1st to 10th	Night	20% 5% 10% 40% 23% 2	4710
	11th to 20th	Night	27% 7% 10% 33% 22% 1	5322
	21st to end	Night	38% 6% 11% 22% 21% 2	7128

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% 26% 35% 15% 6%	330
	11th to 20th	Day	6% 11% 27% 38% 16% 2	330
	21st to end	Day	6% 5% 28% 43% 14% 4	363
February	1st to 10th	Day	11% 11% 34% 33% 8% 3	330
	11th to 20th	Day	14% 16% 35% 26% 8% 1	330
	21st to end	Day	10% 13% 34% 33% 8% 2	273
March	1st to 10th	Day	12% 17% 32% 28% 9% 2	537
	11th to 20th	Day	9% 15% 34% 27% 13% 2	540
	21st to end	Day	13% 22% 31% 24% 9% 1	594
April	1st to 10th	Day	11% 17% 31% 28% 11% 3	540
	11th to 20th	Day	13% 25% 32% 19% 9% 2	532
	21st to end	Day	9% 21% 35% 22% 11% 2	540
May	1st to 10th	Day	11% 18% 33% 25% 10% 2	543
	11th to 20th	Day	9% 12% 30% 26% 18% 5%	604
	21st to end	Day	4 14% 26% 31% 19% 5%	844
June	1st to 10th	Day	3 8% 26% 33% 24% 6%	780
	11th to 20th	Day	5% 8% 30% 33% 20% 4	780
	21st to end	Day	2 8% 27% 35% 23% 5%	780
July	1st to 10th	Day	1 2 16% 39% 34% 8%	771
	11th to 20th	Day	2 2 12% 37% 34% 13%	565
	21st to end	Day	4 2 14% 32% 36% 13%	619
August	1st to 10th	Day	4 3 18% 34% 31% 10%	567
	11th to 20th	Day	3 3 17% 34% 33% 10%	557
	21st to end	Day	4 1 15% 40% 29% 11%	620
September	1st to 10th	Day	6% 4 19% 31% 30% 10%	530
	11th to 20th	Day	5% 6% 29% 34% 21% 5%	530
	21st to end	Day	5% 10% 22% 26% 28% 8%	443
October	1st to 10th	Day	5% 12% 20% 28% 23% 13%	330
	11th to 20th	Day	4 10% 25% 33% 22% 6%	330
	21st to end	Day	7% 7% 26% 29% 26% 5%	363
November	1st to 10th	Day	5% 12% 29% 29% 20% 6%	330
	11th to 20th	Day	4 8% 27% 37% 17% 7%	330
	21st to end	Day	6% 9% 28% 34% 18% 6%	330
December	1st to 10th	Day	8% 8% 31% 33% 16% 4	330
	11th to 20th	Day	7% 7% 26% 33% 23% 4	330
	21st to end	Day	12% 9% 30% 34% 12% 3	363
January	1st to 10th	Night	7% 6% 25% 40% 18% 3	924
	11th to 20th	Night	7% 6% 28% 40% 17% 3	840
	21st to end	Night	9% 4 28% 42% 14% 3	924
February	1st to 10th	Night	8% 6% 35% 38% 11% 1	840
	11th to 20th	Night	8% 8% 36% 35% 11% 1	824
	21st to end	Night	9% 7% 38% 38% 7%	692
March	1st to 10th	Night	7% 8% 36% 37% 11% 1	840
	11th to 20th	Night	6% 5% 31% 39% 18% 1	840
	21st to end	Night	7% 11% 34% 36% 11% 1	919
April	1st to 10th	Night	9% 9% 35% 37% 9%	630
	11th to 20th	Night	9% 13% 33% 35% 10% 1	623
	21st to end	Night	9% 7% 35% 33% 14% 2	630
May	1st to 10th	Night	8% 6% 32% 41% 12% 1	630
	11th to 20th	Night	7% 5% 24% 42% 19% 3	621
	21st to end	Night	6% 9% 26% 39% 18% 2	683
June	1st to 10th	Night	3 3 23% 43% 25% 3	630
	11th to 20th	Night	3 3 29% 42% 20% 3	630
	21st to end	Night	3 3 21% 41% 29% 3	630
July	1st to 10th	Night	4 1 16% 38% 38% 3	615
	11th to 20th	Night	2 1 8% 42% 42% 4	612
	21st to end	Night	3 2 10% 36% 45% 4	690
August	1st to 10th	Night	4 1 15% 37% 39% 4	627
	11th to 20th	Night	4 1 11% 44% 36% 4	624
	21st to end	Night	3 2 13% 44% 33% 5%	687
September	1st to 10th	Night	4 2 13% 49% 31% 3	600
	11th to 20th	Night	3 2 20% 41% 29% 4	615
	21st to end	Night	5% 3 20% 39% 28% 6%	800
October	1st to 10th	Night	5% 5% 25% 42% 22% 2	800
	11th to 20th	Night	4 5% 27% 40% 21% 4	800
	21st to end	Night	8% 5% 25% 37% 20% 4	880
November	1st to 10th	Night	5% 5% 29% 38% 21% 3	831
	11th to 20th	Night	6% 7% 27% 39% 18% 3	1050
	21st to end	Night	7% 6% 29% 37% 18% 3	1050
December	1st to 10th	Night	8% 6% 28% 42% 15% 2	1050
	11th to 20th	Night	10% 8% 26% 37% 18% 2	1050
	21st to end	Night	11% 8% 30% 40% 10% 1	1155

Page generated at 2026-08-27 02:07:16. Version ac07

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