Little Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Ranch Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	6% 5% 2 5% 4 4 4 3 6% 8% 54%	135812
	Night	6% 6% 2 6% 4 4 4 4 5% 7% 52%	132660
Transparency	Day	28% 4 12% 27% 22% 6%	130679
	Night	31% 4 12% 26% 21% 6%	128800
Seeing	Day	9% 8% 31% 30% 18% 5%	17267
	Night	9% 8% 38% 36% 9%	27271

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 6% 3 10% 6% 4 4 3 5% 6% 52%	3638
	11th to 20th	Day	3 6% 3 8% 6% 4 4 4 7% 7% 48%	3640
	21st to end	Day	2 4 2 6% 4 4 3 3 4 7% 62%	4159
February	1st to 10th	Day	4 7% 4 8% 6% 4 5% 5% 6% 7% 43%	1867
	11th to 20th	Day	4 7% 3 8% 5% 5% 4 3 5% 7% 48%	1949
	21st to end	Day	3 10% 3 5% 4 4 4 3 4 6% 54%	1650
March	1st to 10th	Day	7% 10% 3 5% 3 3 3 2 5% 6% 52%	4500
	11th to 20th	Day	6% 6% 2 4 3 3 3 3 5% 7% 57%	4654
	21st to end	Day	7% 8% 2 7% 4 4 4 4 6% 9% 46%	5969
April	1st to 10th	Day	9% 7% 2 5% 4 3 4 3 5% 7% 50%	2400
	11th to 20th	Day	12% 7% 2 6% 4 4 4 3 6% 8% 44%	2371
	21st to end	Day	12% 7% 2 7% 4 4 4 4 5% 8% 44%	2503
May	1st to 10th	Day	8% 4 2 6% 4 5% 5% 4 5% 7% 51%	5900
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	6078
	21st to end	Day	14% 6% 2 5% 3 3 4 3 5% 7% 47%	6925
June	1st to 10th	Day	6% 4 1 4 3 4 4 4 7% 8% 55%	2800
	11th to 20th	Day	7% 4 2 4 4 4 4 4 7% 7% 55%	2800
	21st to end	Day	3 3 1 4 2 4 4 3 6% 10% 60%	2800
July	1st to 10th	Day	6% 3 2 5% 3 3 4 4 5% 7% 58%	6339
	11th to 20th	Day	3 3 1 4 3 4 4 4 8% 11% 55%	6340
	21st to end	Day	5% 4 2 4 3 4 5% 4 7% 10% 53%	6903
August	1st to 10th	Day	8% 4 1 4 3 4 4 4 7% 10% 51%	6061
	11th to 20th	Day	4 3 1 4 3 3 4 4 6% 8% 60%	5366
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 7% 8% 50%	5984
September	1st to 10th	Day	6% 4 2 4 3 3 3 3 5% 5% 63%	2400
	11th to 20th	Day	8% 3 1 3 3 3 3 3 4 6% 62%	2284
	21st to end	Day	8% 3 1 3 2 2 2 3 4 7% 64%	2200
October	1st to 10th	Day	6% 3 1 2 2 2 2 1 3 3 74%	3527
	11th to 20th	Day	5% 4 1 5% 4 3 3 2 4 6% 62%	3228
	21st to end	Day	7% 6% 2 5% 3 3 3 3 4 6% 57%	3190
November	1st to 10th	Day	4 5% 1 4 3 2 4 3 6% 8% 59%	1853
	11th to 20th	Day	4 5% 2 4 3 3 2 3 5% 7% 62%	1890
	21st to end	Day	4 6% 2 5% 4 4 3 3 5% 7% 57%	1858
December	1st to 10th	Day	3 4 1 4 3 2 3 3 4 6% 66%	2700
	11th to 20th	Day	2 4 1 4 3 3 3 3 4 8% 65%	3082
	21st to end	Day	4 7% 3 7% 5% 5% 5% 4 5% 7% 48%	4004
January	1st to 10th	Night	3 8% 3 9% 5% 4 4 3 4 6% 50%	6327
	11th to 20th	Night	2 6% 3 7% 4 4 5% 4 6% 8% 51%	6340
	21st to end	Night	2 5% 2 7% 5% 5% 4 3 5% 6% 56%	6864
February	1st to 10th	Night	4 10% 4 8% 5% 5% 4 3 6% 7% 44%	2531
	11th to 20th	Night	4 9% 4 7% 6% 4 4 4 6% 7% 45%	2338
	21st to end	Night	4 8% 3 6% 3 4 4 3 5% 6% 53%	1980
March	1st to 10th	Night	8% 10% 3 6% 3 3 3 2 4 5% 53%	5374
	11th to 20th	Night	6% 8% 2 6% 4 3 3 3 5% 6% 54%	5321
	21st to end	Night	8% 9% 3 8% 5% 5% 5% 5% 6% 8% 40%	4984
April	1st to 10th	Night	10% 8% 3 6% 5% 3 3 4 6% 7% 46%	2000
	11th to 20th	Night	11% 7% 3 6% 4 4 3 3 5% 6% 48%	1977
	21st to end	Night	14% 8% 3 6% 4 4 5% 3 5% 6% 42%	1895
May	1st to 10th	Night	10% 6% 2 7% 4 4 5% 3 6% 8% 46%	4080
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 51%	3822
	21st to end	Night	17% 8% 2 6% 4 4 4 3 4 6% 42%	3972
June	1st to 10th	Night	8% 4 2 4 4 3 5% 5% 6% 10% 50%	1600
	11th to 20th	Night	8% 4 2 5% 3 5% 4 4 7% 9% 49%	1600
	21st to end	Night	6% 3 2 6% 5% 5% 4 5% 8% 9% 47%	1600
July	1st to 10th	Night	4 3 2 5% 5% 5% 5% 5% 6% 8% 52%	3640
	11th to 20th	Night	5% 4 1 3 3 4 5% 5% 8% 11% 50%	3640
	21st to end	Night	5% 5% 2 6% 6% 5% 5% 5% 6% 9% 46%	3970
August	1st to 10th	Night	10% 5% 2 7% 5% 6% 6% 5% 6% 9% 39%	3751
	11th to 20th	Night	4 5% 2 6% 4 4 5% 5% 7% 8% 50%	4478
	21st to end	Night	7% 7% 2 7% 5% 5% 5% 4 6% 8% 44%	4993
September	1st to 10th	Night	7% 4 1 4 3 4 3 3 5% 8% 59%	2000
	11th to 20th	Night	7% 5% 2 4 3 3 4 2 5% 7% 58%	2115
	21st to end	Night	7% 4 1 4 3 3 4 3 4 6% 60%	2200
October	1st to 10th	Night	7% 3 1 3 2 1 2 2 3 4 74%	3651
	11th to 20th	Night	8% 4 1 3 2 2 3 2 5% 6% 63%	3898
	21st to end	Night	6% 5% 2 5% 4 3 3 3 5% 6% 58%	4600
November	1st to 10th	Night	5% 5% 2 5% 3 4 3 3 6% 7% 58%	2665
	11th to 20th	Night	5% 5% 2 5% 3 4 3 3 5% 8% 58%	2730
	21st to end	Night	5% 7% 2 5% 4 3 4 3 4 6% 57%	2760
December	1st to 10th	Night	3 5% 1 5% 3 3 3 3 4 5% 65%	4710
	11th to 20th	Night	3 4 2 5% 4 4 4 4 6% 8% 57%	5280
	21st to end	Night	5% 8% 4 8% 5% 5% 5% 4 5% 7% 45%	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	34% 3 11% 30% 20% 2	3639
	11th to 20th	Day	33% 4 14% 23% 22% 4	3640
	21st to end	Day	23% 4 15% 28% 24% 5%	4159
February	1st to 10th	Day	37% 5% 14% 23% 16% 4	1867
	11th to 20th	Day	35% 4 11% 26% 19% 4	1959
	21st to end	Day	31% 5% 12% 26% 19% 6%	1650
March	1st to 10th	Day	33% 2 6% 23% 31% 5%	4500
	11th to 20th	Day	27% 3 11% 22% 33% 2	4654
	21st to end	Day	34% 6% 16% 30% 13% 1	5969
April	1st to 10th	Day	34% 4 13% 27% 17% 5%	2400
	11th to 20th	Day	37% 6% 14% 21% 18% 4	2374
	21st to end	Day	37% 5% 11% 27% 18% 2	2503
May	1st to 10th	Day	31% 5% 14% 28% 18% 4	5900
	11th to 20th	Day	30% 6% 13% 28% 22% 1	6082
	21st to end	Day	36% 5% 14% 26% 17% 2	6926
June	1st to 10th	Day	24% 8% 19% 31% 14% 4	2800
	11th to 20th	Day	26% 7% 11% 27% 21% 8%	2800
	21st to end	Day	20% 5% 11% 29% 26% 8%	2800
July	1st to 10th	Day	26% 3 8% 23% 30% 10%	6271
	11th to 20th	Day	23% 3 13% 32% 21% 8%	6265
	21st to end	Day	26% 4 12% 23% 21% 14%	6705
August	1st to 10th	Day	30% 5% 14% 28% 19% 5%	4409
	11th to 20th	Day	26% 6% 13% 23% 25% 8%	3882
	21st to end	Day	23% 3 12% 22% 24% 15%	4311
September	1st to 10th	Day	23% 4 8% 26% 26% 14%	2400
	11th to 20th	Day	22% 5% 8% 24% 29% 12%	2284
	21st to end	Day	22% 4 7% 25% 33% 9%	2200
October	1st to 10th	Day	17% 2 6% 20% 33% 22%	3527
	11th to 20th	Day	25% 2 9% 35% 22% 7%	3228
	21st to end	Day	29% 2 11% 28% 24% 6%	3190
November	1st to 10th	Day	22% 4 14% 28% 23% 9%	1853
	11th to 20th	Day	22% 3 11% 31% 28% 5%	1890
	21st to end	Day	27% 3 11% 30% 23% 6%	1858
December	1st to 10th	Day	20% 3 11% 34% 28% 5%	2700
	11th to 20th	Day	20% 3 12% 40% 21% 3	3080
	21st to end	Day	34% 5% 8% 35% 15% 2	4004
January	1st to 10th	Night	35% 4 12% 28% 16% 4	6327
	11th to 20th	Night	31% 3 14% 24% 24% 4	6340
	21st to end	Night	28% 5% 12% 28% 22% 5%	6864
February	1st to 10th	Night	38% 5% 14% 23% 16% 3	2531
	11th to 20th	Night	37% 5% 13% 26% 15% 4	2338
	21st to end	Night	30% 4 11% 26% 23% 7%	1980
March	1st to 10th	Night	33% 4 6% 21% 29% 7%	5374
	11th to 20th	Night	32% 3 9% 20% 31% 5%	5321
	21st to end	Night	40% 6% 19% 22% 12% 1	4984
April	1st to 10th	Night	36% 7% 13% 21% 18% 5%	2000
	11th to 20th	Night	37% 5% 13% 25% 16% 4	1977
	21st to end	Night	41% 8% 9% 26% 16% 1	1895
May	1st to 10th	Night	35% 6% 16% 26% 14% 3	4080
	11th to 20th	Night	29% 7% 15% 31% 15% 3	3823
	21st to end	Night	42% 6% 14% 24% 12% 2	3972
June	1st to 10th	Night	29% 8% 24% 26% 12% 2	1600
	11th to 20th	Night	29% 8% 16% 25% 15% 7%	1600
	21st to end	Night	30% 8% 14% 24% 20% 5%	1600
July	1st to 10th	Night	29% 4 11% 25% 27% 4	3600
	11th to 20th	Night	28% 4 21% 25% 16% 6%	3592
	21st to end	Night	35% 4 14% 20% 17% 9%	3856
August	1st to 10th	Night	40% 5% 17% 21% 15% 2	2727
	11th to 20th	Night	35% 5% 14% 23% 18% 5%	3238
	21st to end	Night	29% 4 16% 20% 20% 11%	3597
September	1st to 10th	Night	25% 4 10% 24% 26% 11%	2000
	11th to 20th	Night	26% 5% 10% 26% 22% 12%	2115
	21st to end	Night	26% 4 7% 27% 26% 11%	2200
October	1st to 10th	Night	17% 2 6% 20% 30% 25%	3651
	11th to 20th	Night	24% 3 9% 31% 26% 7%	3898
	21st to end	Night	27% 3 10% 29% 23% 8%	4600
November	1st to 10th	Night	25% 4 14% 26% 24% 8%	2665
	11th to 20th	Night	26% 4 11% 28% 24% 8%	2730
	21st to end	Night	28% 4 10% 28% 24% 6%	2760
December	1st to 10th	Night	22% 2 12% 34% 26% 4	4710
	11th to 20th	Night	24% 3 11% 39% 19% 3	5281
	21st to end	Night	38% 4 9% 31% 17% 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% 10% 38% 29% 14% 2	300
	11th to 20th	Day	8% 13% 41% 31% 7%	300
	21st to end	Day	8% 11% 51% 21% 7% 2	330
February	1st to 10th	Day	8% 12% 56% 21% 3	300
	11th to 20th	Day	9% 11% 48% 24% 7% 1	300
	21st to end	Day	9% 19% 43% 23% 5% 1	249
March	1st to 10th	Day	8% 14% 37% 27% 12% 2	300
	11th to 20th	Day	10% 9% 33% 30% 15% 3	309
	21st to end	Day	13% 12% 40% 25% 8% 2	550
April	1st to 10th	Day	13% 17% 38% 24% 7% 1	500
	11th to 20th	Day	17% 15% 35% 23% 8% 2	492
	21st to end	Day	15% 13% 31% 27% 13% 2	603
May	1st to 10th	Day	15% 10% 31% 25% 15% 4	703
	11th to 20th	Day	17% 7% 26% 31% 15% 4	725
	21st to end	Day	13% 8% 28% 29% 18% 4	789
June	1st to 10th	Day	8% 5% 23% 31% 25% 8%	730
	11th to 20th	Day	7% 6% 33% 31% 19% 4	730
	21st to end	Day	5% 4 28% 34% 23% 6%	730
July	1st to 10th	Day	8% 2 19% 37% 28% 7%	721
	11th to 20th	Day	4 2 16% 39% 32% 7%	718
	21st to end	Day	6% 2 16% 36% 33% 8%	794
August	1st to 10th	Day	7% 2 17% 37% 32% 5%	726
	11th to 20th	Day	4 3 21% 36% 26% 10%	517
	21st to end	Day	6% 2 21% 35% 27% 9%	583
September	1st to 10th	Day	7% 2 21% 36% 25% 9%	530
	11th to 20th	Day	6% 2 20% 35% 28% 10%	414
	21st to end	Day	10% 3 24% 27% 23% 13%	330
October	1st to 10th	Day	11% 6% 25% 26% 22% 10%	330
	11th to 20th	Day	8% 11% 35% 28% 12% 5%	330
	21st to end	Day	10% 12% 38% 25% 12% 3	363
November	1st to 10th	Day	8% 8% 43% 27% 11% 4	330
	11th to 20th	Day	6% 12% 43% 25% 13% 1	330
	21st to end	Day	9% 8% 38% 31% 12% 1	330
December	1st to 10th	Day	6% 12% 47% 24% 10%	330
	11th to 20th	Day	7% 13% 47% 26% 6%	321
	21st to end	Day	11% 15% 47% 20% 7% 1	330
January	1st to 10th	Night	6% 12% 42% 31% 8% 1	1000
	11th to 20th	Night	6% 15% 45% 29% 5%	1000
	21st to end	Night	7% 11% 48% 29% 5%	1055
February	1st to 10th	Night	9% 11% 51% 25% 4	800
	11th to 20th	Night	7% 11% 51% 25% 6%	784
	21st to end	Night	8% 10% 53% 26% 3	660
March	1st to 10th	Night	10% 10% 43% 32% 5%	800
	11th to 20th	Night	11% 7% 42% 32% 8%	767
	21st to end	Night	12% 10% 40% 32% 5%	660
April	1st to 10th	Night	12% 13% 41% 31% 4	600
	11th to 20th	Night	15% 11% 40% 31% 3	593
	21st to end	Night	18% 13% 30% 34% 6%	600
May	1st to 10th	Night	15% 10% 33% 34% 8% 1	600
	11th to 20th	Night	18% 5% 30% 37% 10%	591
	21st to end	Night	16% 10% 34% 30% 10%	650
June	1st to 10th	Night	9% 5% 32% 39% 15% 1	600
	11th to 20th	Night	10% 5% 39% 40% 7%	600
	21st to end	Night	6% 5% 29% 49% 11% 1	600
July	1st to 10th	Night	8% 2 26% 46% 16% 1	585
	11th to 20th	Night	6% 1 24% 54% 15%	582
	21st to end	Night	5% 2 23% 51% 20%	657
August	1st to 10th	Night	8% 2 19% 54% 17% 1	597
	11th to 20th	Night	7% 2 27% 51% 13%	594
	21st to end	Night	6% 2 24% 54% 14%	660
September	1st to 10th	Night	9% 3 28% 46% 14% 1	600
	11th to 20th	Night	9% 3 29% 43% 16% 2	600
	21st to end	Night	11% 4 29% 44% 13%	600
October	1st to 10th	Night	14% 6% 29% 36% 14% 1	635
	11th to 20th	Night	9% 8% 37% 35% 10%	800
	21st to end	Night	10% 8% 37% 35% 9% 1	1090
November	1st to 10th	Night	8% 6% 42% 36% 7% 1	1025
	11th to 20th	Night	8% 12% 42% 33% 6% 1	1050
	21st to end	Night	8% 9% 39% 35% 7% 1	1050
December	1st to 10th	Night	8% 11% 48% 28% 5% 1	1050
	11th to 20th	Night	6% 9% 49% 30% 6%	1036
	21st to end	Night	9% 13% 43% 30% 4	1100

Page generated at 2025-12-14 23:13:51. Version ac07

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