Goat Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goat 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	12% 7% 3 6% 4 4 4 3 5% 7% 45%	126917
	Night	12% 7% 3 6% 4 4 3 3 5% 6% 47%	124360
Transparency	Day	38% 5% 12% 26% 17% 3	130528
	Night	37% 4 11% 25% 18% 4	128825
Seeing	Day	15% 10% 27% 27% 16% 4	17157
	Night	15% 9% 31% 31% 12% 1	27012

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	16% 10% 4 9% 5% 4 4 3 5% 5% 35%	4077
	11th to 20th	Day	8% 10% 4 9% 5% 7% 5% 3 4 5% 40%	4080
	21st to end	Day	15% 14% 3 7% 3 4 4 3 4 4 40%	4488
February	1st to 10th	Day	16% 12% 5% 7% 6% 3 3 3 4 6% 35%	1800
	11th to 20th	Day	14% 11% 3 8% 5% 4 3 3 5% 6% 39%	1754
	21st to end	Day	14% 8% 4 7% 4 4 4 3 5% 6% 42%	1700
March	1st to 10th	Day	14% 10% 3 5% 3 2 3 2 3 5% 51%	4936
	11th to 20th	Day	10% 6% 2 4 3 3 3 3 5% 6% 54%	4980
	21st to end	Day	15% 12% 3 7% 4 4 4 4 6% 7% 34%	5462
April	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 4 6% 43%	2358
	11th to 20th	Day	16% 9% 3 5% 4 3 4 3 5% 6% 41%	2374
	21st to end	Day	20% 8% 3 8% 6% 4 4 3 5% 6% 34%	2450
May	1st to 10th	Day	15% 7% 2 7% 5% 4 4 3 6% 7% 39%	5862
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 7% 43%	5862
	21st to end	Day	20% 6% 2 5% 4 4 4 3 5% 7% 41%	6835
June	1st to 10th	Day	8% 4 2 6% 4 4 4 4 7% 9% 48%	2800
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 5% 5% 9% 47%	2800
	21st to end	Day	7% 4 1 4 5% 4 4 5% 7% 9% 51%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 9% 47%	6141
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 4 6% 11% 45%	5900
	21st to end	Day	7% 4 2 6% 4 5% 5% 6% 8% 11% 42%	6422
August	1st to 10th	Day	5% 4 2 4 4 4 4 4 6% 10% 53%	4234
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 48%	4155
	21st to end	Day	6% 3 1 4 4 4 4 4 7% 9% 55%	4312
September	1st to 10th	Day	11% 4 2 5% 3 3 3 3 5% 8% 53%	2400
	11th to 20th	Day	9% 5% 2 5% 3 4 5% 4 5% 8% 50%	2303
	21st to end	Day	8% 6% 2 5% 3 3 4 3 5% 7% 54%	2138
October	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 55%	2000
	11th to 20th	Day	13% 6% 2 5% 3 2 2 2 4 6% 54%	2000
	21st to end	Day	17% 9% 2 7% 3 3 2 2 4 5% 46%	2200
November	1st to 10th	Day	10% 6% 2 4 3 3 3 3 4 6% 54%	2058
	11th to 20th	Day	14% 7% 3 6% 3 3 3 3 4 7% 49%	1804
	21st to end	Day	17% 9% 3 7% 3 3 3 2 4 5% 44%	1680
December	1st to 10th	Day	7% 7% 3 7% 4 3 3 3 4 7% 53%	2690
	11th to 20th	Day	11% 7% 4 7% 4 4 3 2 4 5% 48%	3064
	21st to end	Day	19% 20% 7% 11% 4 3 3 2 3 4 24%	3998
January	1st to 10th	Night	14% 10% 4 15% 6% 5% 3 2 3 4 35%	5888
	11th to 20th	Night	12% 8% 3 12% 5% 6% 4 3 3 4 41%	5900
	21st to end	Night	16% 11% 3 8% 3 3 4 3 4 4 41%	6490
February	1st to 10th	Night	14% 11% 4 7% 5% 4 4 3 5% 6% 37%	2600
	11th to 20th	Night	13% 10% 4 8% 4 4 4 3 4 6% 41%	2533
	21st to end	Night	13% 9% 3 6% 4 3 4 3 4 5% 46%	1947
March	1st to 10th	Night	16% 10% 3 5% 4 3 3 2 4 4 46%	4919
	11th to 20th	Night	10% 7% 2 4 3 3 3 3 5% 6% 55%	4980
	21st to end	Night	15% 10% 4 7% 5% 4 4 3 5% 6% 37%	5467
April	1st to 10th	Night	11% 8% 2 4 3 4 3 3 5% 6% 50%	2040
	11th to 20th	Night	15% 8% 3 5% 3 2 3 3 4 7% 47%	1975
	21st to end	Night	18% 6% 2 6% 4 3 3 3 5% 7% 41%	1945
May	1st to 10th	Night	17% 7% 2 6% 4 3 3 3 5% 7% 42%	4053
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 8% 46%	4053
	21st to end	Night	16% 6% 2 5% 4 4 3 3 5% 6% 47%	4037
June	1st to 10th	Night	7% 3 1 5% 3 4 3 4 7% 9% 54%	1600
	11th to 20th	Night	6% 4 1 4 4 4 4 4 7% 12% 50%	1600
	21st to end	Night	4 3 1 2 3 4 4 4 7% 9% 59%	1600
July	1st to 10th	Night	10% 5% 2 5% 3 4 4 3 6% 9% 49%	3818
	11th to 20th	Night	6% 4 2 6% 4 4 4 4 6% 9% 51%	4077
	21st to end	Night	6% 3 2 5% 4 4 4 4 8% 13% 45%	4449
August	1st to 10th	Night	3 2 1 3 3 3 4 3 6% 8% 64%	2926
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 4 7% 53%	2901
	21st to end	Night	4 3 2 4 4 3 4 3 5% 8% 59%	3586
September	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 7% 56%	2000
	11th to 20th	Night	9% 4 2 5% 3 3 3 3 6% 8% 54%	2092
	21st to end	Night	8% 4 1 4 4 3 4 3 4 6% 58%	2240
October	1st to 10th	Night	8% 4 2 4 3 3 3 3 4 6% 60%	2400
	11th to 20th	Night	14% 4 2 5% 3 2 3 2 5% 6% 55%	2400
	21st to end	Night	17% 6% 2 5% 3 3 3 3 3 4 51%	2640
November	1st to 10th	Night	11% 5% 2 4 3 2 4 2 4 5% 58%	2460
	11th to 20th	Night	11% 7% 1 5% 4 3 3 3 4 6% 52%	2809
	21st to end	Night	15% 9% 3 6% 3 3 3 2 3 5% 48%	2940
December	1st to 10th	Night	8% 7% 3 5% 4 3 3 3 5% 6% 53%	4720
	11th to 20th	Night	13% 9% 3 7% 3 3 3 2 4 6% 45%	5298
	21st to end	Night	21% 17% 5% 9% 4 4 3 2 3 4 27%	6977

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	50% 5% 10% 23% 11% 1	4078
	11th to 20th	Day	47% 4 8% 22% 14% 4	4080
	21st to end	Day	49% 3 10% 17% 18% 4	4488
February	1st to 10th	Day	51% 4 12% 21% 11% 1	1800
	11th to 20th	Day	47% 5% 11% 19% 15% 2	1763
	21st to end	Day	44% 4 10% 23% 16% 4	1700
March	1st to 10th	Day	39% 3 7% 24% 22% 5%	4936
	11th to 20th	Day	32% 4 9% 22% 26% 7%	4980
	21st to end	Day	48% 6% 16% 24% 5%	5464
April	1st to 10th	Day	42% 5% 10% 24% 16% 2	2358
	11th to 20th	Day	43% 5% 13% 23% 15% 1	2374
	21st to end	Day	51% 5% 11% 22% 11% 1	2450
May	1st to 10th	Day	43% 7% 13% 24% 13% 1	5900
	11th to 20th	Day	39% 7% 13% 24% 14% 2	5866
	21st to end	Day	42% 6% 10% 28% 12% 1	6849
June	1st to 10th	Day	29% 9% 17% 29% 15% 1	2800
	11th to 20th	Day	32% 8% 14% 27% 16% 2	2800
	21st to end	Day	27% 8% 17% 30% 15% 4	2800
July	1st to 10th	Day	35% 5% 12% 27% 19% 2	6076
	11th to 20th	Day	34% 6% 15% 31% 14% 1	5831
	21st to end	Day	33% 6% 19% 33% 9%	6240
August	1st to 10th	Day	26% 6% 17% 29% 21% 1	4220
	11th to 20th	Day	35% 5% 16% 28% 15% 1	4194
	21st to end	Day	25% 5% 15% 36% 14% 4	4311
September	1st to 10th	Day	31% 6% 13% 25% 19% 6%	2400
	11th to 20th	Day	32% 4 11% 26% 24% 2	2303
	21st to end	Day	30% 5% 10% 29% 23% 4	2138
October	1st to 10th	Day	19% 3 6% 21% 40% 11%	3260
	11th to 20th	Day	22% 2 5% 23% 39% 8%	3240
	21st to end	Day	37% 3 7% 25% 25% 3	3538
November	1st to 10th	Day	31% 5% 12% 27% 20% 4	2058
	11th to 20th	Day	37% 4 10% 24% 22% 4	1804
	21st to end	Day	44% 3 9% 28% 16% 1	1680
December	1st to 10th	Day	33% 3 12% 35% 16% 1	2690
	11th to 20th	Day	39% 4 12% 30% 13% 1	3061
	21st to end	Day	65% 3 11% 14% 6% 1	3998
January	1st to 10th	Night	55% 4 10% 21% 10% 1	5888
	11th to 20th	Night	48% 4 8% 22% 13% 4	5900
	21st to end	Night	47% 3 11% 18% 17% 4	6490
February	1st to 10th	Night	48% 5% 12% 20% 13% 3	2600
	11th to 20th	Night	44% 4 12% 20% 17% 3	2534
	21st to end	Night	40% 5% 9% 22% 18% 5%	1947
March	1st to 10th	Night	42% 4 7% 20% 23% 4	4919
	11th to 20th	Night	31% 4 6% 23% 29% 7%	4980
	21st to end	Night	46% 6% 14% 24% 9% 2	5467
April	1st to 10th	Night	35% 6% 10% 24% 21% 4	2040
	11th to 20th	Night	38% 5% 9% 26% 18% 5%	1975
	21st to end	Night	43% 5% 10% 26% 15% 1	1945
May	1st to 10th	Night	41% 7% 15% 22% 14% 1	4080
	11th to 20th	Night	36% 6% 13% 22% 17% 5%	4054
	21st to end	Night	37% 6% 10% 24% 22% 1	4045
June	1st to 10th	Night	25% 6% 17% 32% 17% 4	1600
	11th to 20th	Night	25% 8% 14% 29% 21% 3	1600
	21st to end	Night	20% 6% 17% 32% 20% 5%	1600
July	1st to 10th	Night	32% 4 13% 26% 22% 2	3776
	11th to 20th	Night	28% 4 15% 35% 16% 2	4026
	21st to end	Night	28% 5% 18% 38% 10% 1	4320
August	1st to 10th	Night	17% 5% 22% 30% 23% 3	2916
	11th to 20th	Night	32% 5% 10% 31% 20% 1	2928
	21st to end	Night	24% 4 13% 37% 17% 4	3586
September	1st to 10th	Night	29% 5% 11% 25% 22% 8%	2000
	11th to 20th	Night	29% 5% 12% 27% 23% 5%	2092
	21st to end	Night	27% 5% 9% 26% 29% 4	2240
October	1st to 10th	Night	16% 3 5% 23% 42% 11%	3920
	11th to 20th	Night	22% 3 7% 24% 29% 16%	3899
	21st to end	Night	34% 3 7% 29% 24% 3	4252
November	1st to 10th	Night	30% 4 11% 28% 22% 5%	2460
	11th to 20th	Night	34% 3 9% 25% 23% 5%	2809
	21st to end	Night	42% 3 9% 27% 16% 3	2940
December	1st to 10th	Night	34% 3 12% 35% 15% 1	4720
	11th to 20th	Night	42% 3 12% 26% 16% 1	5300
	21st to end	Night	62% 3 10% 17% 6% 1	6977

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	21% 14% 37% 22% 6%	300
	11th to 20th	Day	30% 17% 36% 15% 1	300
	21st to end	Day	18% 18% 43% 18% 3	330
February	1st to 10th	Day	28% 16% 37% 14% 5%	300
	11th to 20th	Day	22% 22% 37% 14% 4 1	300
	21st to end	Day	20% 24% 40% 13% 2	249
March	1st to 10th	Day	19% 18% 43% 18% 3	300
	11th to 20th	Day	28% 14% 34% 20% 4	300
	21st to end	Day	32% 20% 31% 12% 5% 1	330
April	1st to 10th	Day	21% 16% 34% 22% 6% 1	458
	11th to 20th	Day	23% 16% 34% 21% 6%	492
	21st to end	Day	23% 13% 33% 22% 8%	550
May	1st to 10th	Day	17% 12% 37% 24% 9% 1	703
	11th to 20th	Day	19% 10% 27% 27% 14% 3	725
	21st to end	Day	17% 10% 26% 25% 17% 5%	789
June	1st to 10th	Day	7% 4 20% 34% 26% 8%	730
	11th to 20th	Day	9% 3 25% 36% 22% 5%	730
	21st to end	Day	6% 5% 31% 37% 18% 4	730
July	1st to 10th	Day	12% 3 15% 29% 29% 13%	721
	11th to 20th	Day	6% 3 19% 34% 29% 9%	718
	21st to end	Day	9% 2 14% 34% 31% 9%	794
August	1st to 10th	Day	7% 3 18% 41% 27% 5%	726
	11th to 20th	Day	8% 3 18% 34% 29% 7%	712
	21st to end	Day	9% 2 13% 31% 33% 11%	583
September	1st to 10th	Day	11% 4 15% 37% 26% 7%	530
	11th to 20th	Day	6% 3 15% 41% 26% 8%	433
	21st to end	Day	12% 5% 23% 31% 20% 8%	330
October	1st to 10th	Day	15% 6% 29% 29% 15% 6%	330
	11th to 20th	Day	15% 14% 39% 24% 8%	330
	21st to end	Day	26% 19% 31% 19% 5% 1	363
November	1st to 10th	Day	16% 14% 34% 25% 8% 3	330
	11th to 20th	Day	16% 20% 31% 23% 8% 2	330
	21st to end	Day	28% 11% 32% 23% 6%	330
December	1st to 10th	Day	16% 17% 39% 20% 7% 1	330
	11th to 20th	Day	21% 18% 35% 20% 5% 1	321
	21st to end	Day	26% 20% 37% 17%	330
January	1st to 10th	Night	16% 13% 39% 25% 6%	1000
	11th to 20th	Night	18% 16% 39% 23% 4 1	1000
	21st to end	Night	16% 13% 41% 27% 3	1100
February	1st to 10th	Night	19% 14% 42% 23% 4	1000
	11th to 20th	Night	18% 16% 38% 25% 3	979
	21st to end	Night	20% 14% 44% 18% 3	627
March	1st to 10th	Night	17% 15% 41% 23% 4	600
	11th to 20th	Night	21% 12% 34% 28% 5% 1	600
	21st to end	Night	25% 13% 35% 22% 3	660
April	1st to 10th	Night	15% 13% 39% 30% 4	600
	11th to 20th	Night	19% 12% 32% 29% 8%	593
	21st to end	Night	21% 8% 36% 28% 6%	600
May	1st to 10th	Night	17% 6% 34% 36% 7%	600
	11th to 20th	Night	17% 6% 25% 35% 16% 1	591
	21st to end	Night	12% 5% 30% 32% 18% 2	650
June	1st to 10th	Night	8% 3 16% 45% 26% 2	600
	11th to 20th	Night	7% 2 25% 44% 21% 2	600
	21st to end	Night	5% 2 28% 47% 18% 1	600
July	1st to 10th	Night	9% 3 11% 44% 30% 4	585
	11th to 20th	Night	4 1 16% 45% 31% 2	582
	21st to end	Night	9% 1 14% 41% 34% 2	657
August	1st to 10th	Night	6% 3 13% 47% 31% 1	597
	11th to 20th	Night	6% 2 16% 42% 32% 2	594
	21st to end	Night	6% 1 13% 39% 38% 3	660
September	1st to 10th	Night	12% 2 15% 42% 25% 3	600
	11th to 20th	Night	9% 3 19% 38% 26% 6%	600
	21st to end	Night	7% 4 21% 42% 22% 4	640
October	1st to 10th	Night	10% 4 29% 35% 20% 3	800
	11th to 20th	Night	16% 7% 38% 30% 9% 1	800
	21st to end	Night	20% 10% 34% 26% 9%	880
November	1st to 10th	Night	14% 9% 37% 31% 9%	820
	11th to 20th	Night	15% 14% 36% 27% 8%	961
	21st to end	Night	21% 12% 35% 26% 6%	1050
December	1st to 10th	Night	18% 12% 38% 26% 5% 1	1050
	11th to 20th	Night	21% 11% 36% 28% 4	1036
	21st to end	Night	21% 15% 36% 25% 2	1100

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