Stargaizer Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargaizer Ridge Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	5% 5% 2 5% 4 4 5% 4 6% 8% 52%	135808
	Night	6% 6% 2 5% 4 3 4 3 5% 7% 54%	132345
Transparency	Day	27% 6% 10% 24% 23% 10%	130756
	Night	28% 6% 11% 25% 23% 8%	128402
Seeing	Day	8% 6% 19% 34% 24% 9%	17099
	Night	8% 4 21% 49% 18% 1	27122

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 7% 4 8% 4 4 3 3 5% 7% 54%	3638
	11th to 20th	Day	2 7% 3 9% 5% 5% 4 3 5% 7% 51%	3665
	21st to end	Day	1 6% 2 5% 3 3 4 4 5% 7% 59%	4510
February	1st to 10th	Day	3 7% 4 7% 3 4 5% 4 5% 7% 51%	1800
	11th to 20th	Day	1 7% 3 5% 4 4 4 4 6% 8% 54%	1919
	21st to end	Day	3 7% 2 6% 3 3 3 4 6% 6% 56%	1650
March	1st to 10th	Day	5% 7% 2 4 2 3 3 3 5% 7% 58%	4500
	11th to 20th	Day	5% 7% 3 6% 4 4 5% 4 5% 8% 50%	4902
	21st to end	Day	5% 8% 2 6% 4 4 5% 4 7% 9% 46%	5836
April	1st to 10th	Day	6% 7% 2 5% 3 4 3 4 6% 8% 52%	2400
	11th to 20th	Day	11% 8% 2 5% 4 4 4 3 6% 8% 45%	2371
	21st to end	Day	11% 8% 2 5% 5% 5% 5% 3 6% 8% 44%	2400
May	1st to 10th	Day	10% 7% 3 6% 4 4 5% 4 5% 6% 45%	5820
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	6298
	21st to end	Day	9% 5% 2 5% 4 5% 6% 4 7% 9% 45%	6925
June	1st to 10th	Day	5% 4 1 4 4 4 5% 5% 7% 10% 50%	2800
	11th to 20th	Day	7% 3 1 4 4 5% 5% 5% 7% 8% 52%	2800
	21st to end	Day	4 3 1 4 4 4 6% 6% 7% 9% 52%	2800
July	1st to 10th	Day	4 3 1 4 3 4 5% 4 7% 9% 56%	6339
	11th to 20th	Day	3 3 1 5% 5% 6% 7% 6% 9% 10% 45%	6340
	21st to end	Day	5% 3 1 6% 5% 5% 6% 5% 8% 8% 48%	6871
August	1st to 10th	Day	8% 3 2 6% 5% 5% 6% 5% 8% 9% 42%	5779
	11th to 20th	Day	3 3 1 3 4 4 5% 5% 7% 10% 55%	5374
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 6% 8% 47%	5984
September	1st to 10th	Day	5% 3 1 4 3 3 4 3 5% 6% 61%	2400
	11th to 20th	Day	5% 2 2 4 4 3 4 4 5% 8% 59%	2370
	21st to end	Day	7% 4 1 3 2 3 3 2 4 5% 65%	2200
October	1st to 10th	Day	5% 4 1 3 2 2 2 2 3 4 72%	3307
	11th to 20th	Day	5% 4 2 5% 3 3 3 3 5% 6% 61%	3250
	21st to end	Day	6% 6% 2 4 3 2 3 3 5% 6% 60%	3387
November	1st to 10th	Day	4 5% 1 3 3 3 3 3 5% 7% 62%	1853
	11th to 20th	Day	3 7% 1 3 4 3 3 3 6% 6% 61%	1890
	21st to end	Day	3 6% 2 5% 4 3 3 3 6% 8% 58%	1764
December	1st to 10th	Day	1 4 1 4 3 3 2 2 4 6% 68%	2636
	11th to 20th	Day	2 5% 2 3 2 2 3 3 4 6% 67%	3026
	21st to end	Day	5% 7% 3 6% 4 4 5% 4 6% 6% 51%	4004
January	1st to 10th	Night	3 10% 3 7% 4 3 3 3 5% 8% 50%	6327
	11th to 20th	Night	1 6% 2 10% 5% 4 3 3 5% 6% 54%	6340
	21st to end	Night	3 7% 3 6% 5% 3 3 3 4 5% 58%	6486
February	1st to 10th	Night	3 9% 4 7% 3 3 3 3 5% 7% 53%	2600
	11th to 20th	Night	3 9% 3 7% 4 5% 4 3 5% 7% 49%	2366
	21st to end	Night	3 9% 3 6% 4 3 3 3 4 5% 57%	1980
March	1st to 10th	Night	5% 10% 3 6% 4 3 3 3 5% 5% 53%	5374
	11th to 20th	Night	8% 8% 2 5% 3 4 4 3 4 5% 54%	5091
	21st to end	Night	9% 9% 2 7% 4 4 3 4 5% 7% 46%	5122
April	1st to 10th	Night	6% 8% 2 6% 4 4 4 4 5% 6% 54%	2000
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 5% 6% 46%	1977
	21st to end	Night	14% 9% 2 6% 4 4 3 3 5% 7% 44%	2000
May	1st to 10th	Night	12% 7% 3 6% 4 4 4 3 6% 7% 44%	4144
	11th to 20th	Night	10% 6% 2 7% 4 4 4 4 6% 8% 44%	3617
	21st to end	Night	12% 6% 2 4 3 4 4 3 5% 6% 50%	3972
June	1st to 10th	Night	7% 3 1 4 3 4 3 4 5% 10% 56%	1600
	11th to 20th	Night	6% 3 1 4 3 4 4 3 6% 8% 60%	1600
	21st to end	Night	5% 3 1 5% 3 4 5% 4 7% 7% 57%	1600
July	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 8% 59%	3640
	11th to 20th	Night	4 3 2 4 4 4 5% 5% 8% 11% 51%	3640
	21st to end	Night	4 4 1 5% 4 4 6% 5% 7% 9% 50%	3985
August	1st to 10th	Night	9% 3 2 6% 4 4 5% 4 8% 9% 46%	4033
	11th to 20th	Night	3 3 1 4 3 4 5% 5% 8% 10% 53%	4474
	21st to end	Night	7% 5% 3 6% 4 4 4 4 7% 9% 45%	4993
September	1st to 10th	Night	5% 3 1 5% 3 4 4 4 5% 7% 59%	2000
	11th to 20th	Night	7% 2 1 4 3 3 4 3 5% 7% 62%	2030
	21st to end	Night	8% 3 1 3 2 3 3 3 5% 5% 63%	2200
October	1st to 10th	Night	6% 3 1 4 2 2 2 2 4 4 70%	3877
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 5% 6% 58%	3898
	21st to end	Night	7% 6% 2 4 3 2 3 2 3 7% 63%	4379
November	1st to 10th	Night	4 4 2 4 3 3 3 3 4 7% 63%	2665
	11th to 20th	Night	4 5% 2 4 2 2 4 3 4 6% 62%	2730
	21st to end	Night	4 7% 2 4 3 3 3 3 5% 6% 59%	2851
December	1st to 10th	Night	2 5% 2 3 3 3 3 3 4 5% 69%	4599
	11th to 20th	Night	2 5% 2 4 3 3 3 3 6% 9% 62%	5181
	21st to end	Night	5% 10% 3 6% 4 3 4 3 5% 6% 50%	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	29% 4 8% 33% 19% 6%	3639
	11th to 20th	Day	30% 6% 11% 22% 24% 7%	3665
	21st to end	Day	23% 5% 10% 26% 26% 10%	4510
February	1st to 10th	Day	31% 5% 12% 27% 19% 6%	1800
	11th to 20th	Day	27% 6% 9% 29% 24% 5%	1929
	21st to end	Day	27% 4 9% 24% 25% 10%	1650
March	1st to 10th	Day	25% 3 8% 19% 33% 12%	4500
	11th to 20th	Day	29% 7% 12% 23% 24% 5%	4902
	21st to end	Day	29% 8% 13% 34% 14% 2	5836
April	1st to 10th	Day	28% 6% 12% 25% 21% 8%	2400
	11th to 20th	Day	36% 5% 9% 22% 20% 8%	2374
	21st to end	Day	37% 6% 10% 25% 20% 2	2400
May	1st to 10th	Day	35% 7% 12% 25% 17% 4	5820
	11th to 20th	Day	31% 9% 11% 21% 20% 9%	6302
	21st to end	Day	31% 9% 14% 24% 18% 4	6926
June	1st to 10th	Day	26% 8% 17% 24% 18% 7%	2800
	11th to 20th	Day	26% 8% 11% 18% 24% 14%	2800
	21st to end	Day	23% 7% 10% 23% 24% 13%	2800
July	1st to 10th	Day	20% 7% 8% 18% 30% 16%	6271
	11th to 20th	Day	25% 9% 13% 24% 18% 11%	6265
	21st to end	Day	28% 8% 10% 18% 19% 17%	6673
August	1st to 10th	Day	35% 8% 15% 18% 16% 9%	4208
	11th to 20th	Day	24% 9% 12% 19% 22% 13%	3890
	21st to end	Day	24% 6% 10% 19% 25% 16%	4311
September	1st to 10th	Day	22% 4 7% 22% 27% 18%	2400
	11th to 20th	Day	22% 6% 8% 20% 27% 17%	2370
	21st to end	Day	22% 3 6% 21% 36% 12%	2200
October	1st to 10th	Day	17% 3 5% 17% 34% 24%	3307
	11th to 20th	Day	24% 4 10% 26% 28% 9%	3250
	21st to end	Day	23% 4 6% 26% 31% 10%	3387
November	1st to 10th	Day	22% 4 9% 27% 27% 11%	1853
	11th to 20th	Day	22% 5% 7% 25% 33% 8%	1890
	21st to end	Day	25% 3 9% 25% 29% 9%	1764
December	1st to 10th	Day	18% 4 7% 34% 27% 9%	2636
	11th to 20th	Day	18% 4 7% 33% 32% 5%	3024
	21st to end	Day	32% 5% 10% 25% 20% 8%	4004
January	1st to 10th	Night	30% 5% 11% 28% 19% 6%	6327
	11th to 20th	Night	29% 6% 12% 22% 23% 9%	6340
	21st to end	Night	28% 5% 10% 24% 25% 8%	6486
February	1st to 10th	Night	31% 5% 12% 26% 22% 5%	2600
	11th to 20th	Night	34% 5% 10% 26% 21% 5%	2366
	21st to end	Night	29% 3 6% 25% 25% 12%	1980
March	1st to 10th	Night	32% 3 7% 16% 34% 7%	5374
	11th to 20th	Night	31% 5% 10% 16% 27% 10%	5091
	21st to end	Night	35% 7% 13% 29% 14% 2	5122
April	1st to 10th	Night	31% 5% 11% 25% 21% 8%	2000
	11th to 20th	Night	37% 5% 12% 23% 18% 6%	1977
	21st to end	Night	39% 6% 9% 26% 18% 3	2000
May	1st to 10th	Night	37% 8% 12% 26% 12% 5%	4142
	11th to 20th	Night	33% 9% 14% 21% 15% 7%	3618
	21st to end	Night	32% 8% 17% 25% 13% 4	3972
June	1st to 10th	Night	24% 6% 20% 30% 13% 6%	1600
	11th to 20th	Night	23% 6% 13% 21% 22% 14%	1600
	21st to end	Night	23% 6% 11% 25% 27% 8%	1600
July	1st to 10th	Night	21% 7% 10% 24% 30% 9%	3600
	11th to 20th	Night	22% 8% 20% 25% 19% 6%	3592
	21st to end	Night	25% 9% 15% 21% 19% 10%	3871
August	1st to 10th	Night	34% 9% 15% 21% 15% 4	2928
	11th to 20th	Night	26% 9% 17% 22% 16% 10%	3234
	21st to end	Night	24% 7% 14% 22% 24% 9%	3597
September	1st to 10th	Night	23% 6% 10% 22% 22% 17%	2000
	11th to 20th	Night	21% 5% 10% 24% 23% 16%	2030
	21st to end	Night	22% 4 9% 21% 32% 12%	2200
October	1st to 10th	Night	18% 4 7% 18% 30% 22%	3877
	11th to 20th	Night	25% 5% 10% 25% 27% 8%	3898
	21st to end	Night	23% 3 6% 26% 31% 10%	4379
November	1st to 10th	Night	21% 4 9% 26% 27% 12%	2665
	11th to 20th	Night	22% 4 7% 29% 31% 8%	2730
	21st to end	Night	26% 4 10% 24% 29% 7%	2851
December	1st to 10th	Night	18% 4 9% 37% 27% 6%	4599
	11th to 20th	Night	20% 3 7% 37% 29% 4	5182
	21st to end	Night	33% 5% 9% 24% 25% 4	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	5% 6% 14% 43% 26% 6%	300
	11th to 20th	Day	7% 7% 19% 45% 20% 2	300
	21st to end	Day	5% 4 22% 47% 17% 4	330
February	1st to 10th	Day	6% 7% 28% 45% 12% 3	300
	11th to 20th	Day	2 3 34% 47% 10% 3	300
	21st to end	Day	6% 8% 26% 45% 12% 3	249
March	1st to 10th	Day	7% 8% 22% 41% 17% 6%	300
	11th to 20th	Day	12% 9% 26% 33% 14% 5%	454
	21st to end	Day	12% 11% 29% 32% 14% 3	550
April	1st to 10th	Day	12% 11% 25% 32% 18% 3	500
	11th to 20th	Day	15% 16% 29% 27% 10% 4	492
	21st to end	Day	16% 11% 26% 28% 15% 3	500
May	1st to 10th	Day	15% 7% 25% 33% 17% 4	658
	11th to 20th	Day	18% 5% 16% 30% 25% 6%	725
	21st to end	Day	11% 6% 20% 30% 25% 8%	789
June	1st to 10th	Day	6% 5% 14% 32% 29% 15%	730
	11th to 20th	Day	7% 5% 20% 35% 26% 8%	730
	21st to end	Day	5% 4 17% 36% 28% 10%	730
July	1st to 10th	Day	6% 2 14% 27% 35% 15%	721
	11th to 20th	Day	4 2 11% 32% 36% 15%	718
	21st to end	Day	6% 3 12% 25% 39% 16%	787
August	1st to 10th	Day	6% 3 17% 30% 29% 15%	527
	11th to 20th	Day	3 3 16% 34% 30% 15%	517
	21st to end	Day	5% 3 19% 28% 31% 14%	583
September	1st to 10th	Day	7% 3 13% 30% 32% 15%	530
	11th to 20th	Day	5% 3 16% 32% 32% 12%	500
	21st to end	Day	8% 2 14% 26% 32% 19%	330
October	1st to 10th	Day	11% 6% 12% 24% 29% 18%	330
	11th to 20th	Day	3 6% 19% 37% 25% 11%	330
	21st to end	Day	9% 6% 20% 34% 24% 7%	363
November	1st to 10th	Day	6% 6% 19% 40% 20% 9%	330
	11th to 20th	Day	5% 6% 15% 44% 23% 6%	330
	21st to end	Day	5% 4 18% 46% 22% 5%	330
December	1st to 10th	Day	4 7% 17% 45% 19% 8%	306
	11th to 20th	Day	4 7% 18% 50% 19% 2	300
	21st to end	Day	7% 6% 26% 43% 14% 4	330
January	1st to 10th	Night	5% 4 25% 51% 13% 3	1000
	11th to 20th	Night	4 6% 28% 51% 11% 1	1000
	21st to end	Night	6% 2 24% 55% 11% 1	885
February	1st to 10th	Night	7% 4 33% 47% 8% 1	800
	11th to 20th	Night	6% 4 30% 51% 9%	784
	21st to end	Night	7% 4 34% 50% 5%	660
March	1st to 10th	Night	6% 4 29% 52% 9%	800
	11th to 20th	Night	10% 4 22% 50% 14% 1	800
	21st to end	Night	10% 5% 27% 49% 10%	720
April	1st to 10th	Night	9% 8% 29% 48% 6%	600
	11th to 20th	Night	15% 6% 30% 40% 9% 1	593
	21st to end	Night	17% 7% 23% 39% 15%	600
May	1st to 10th	Night	13% 7% 22% 41% 16% 1	600
	11th to 20th	Night	18% 3 15% 42% 20% 2	591
	21st to end	Night	10% 4 21% 42% 22% 1	650
June	1st to 10th	Night	7% 3 15% 48% 26% 2	600
	11th to 20th	Night	6% 3 19% 54% 18%	600
	21st to end	Night	5% 3 15% 50% 27% 1	600
July	1st to 10th	Night	7% 2 11% 41% 35% 3	585
	11th to 20th	Night	3 1 8% 49% 36% 2	582
	21st to end	Night	5% 2 7% 40% 42% 3	657
August	1st to 10th	Night	7% 2 11% 40% 38% 2	597
	11th to 20th	Night	4 2 8% 48% 36% 2	594
	21st to end	Night	4 2 10% 44% 37% 3	660
September	1st to 10th	Night	6% 2 10% 48% 28% 5%	600
	11th to 20th	Night	8% 1 11% 49% 27% 3	600
	21st to end	Night	8% 2 15% 50% 25% 2	600
October	1st to 10th	Night	11% 2 16% 46% 23% 2	770
	11th to 20th	Night	7% 3 20% 50% 19% 1	800
	21st to end	Night	10% 4 19% 50% 15% 2	958
November	1st to 10th	Night	6% 3 23% 53% 15% 1	1025
	11th to 20th	Night	6% 4 26% 53% 10% 1	1050
	21st to end	Night	8% 4 22% 51% 14% 1	1050
December	1st to 10th	Night	6% 3 26% 53% 11%	1011
	11th to 20th	Night	7% 4 27% 52% 9% 1	1000
	21st to end	Night	8% 3 29% 50% 9% 1	1100

Page generated at 2025-11-29 23:00:50. Version ac07

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