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 2024-01-13.

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	13% 7% 3 6% 5% 3 4 4 5% 7% 44%	74629
	Night	12% 7% 3 5% 4 2 4 4 5% 6% 47%	75124
Transparency	Day	40% 6% 13% 25% 15% 2	74351
	Night	37% 5% 11% 25% 17% 3	74922
Seeing	Day	15% 9% 26% 28% 18% 5%	14481
	Night	15% 8% 31% 32% 13% 1	24454

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	13% 7% 4 8% 5% 2 3 5% 5% 7% 42%	1707
	11th to 20th	Day	15% 11% 4 7% 5% 3 4 4 3 6% 38%	1638
	21st to end	Day	13% 10% 4 7% 4 3 4 4 5% 6% 40%	1782
February	1st to 10th	Day	16% 11% 6% 7% 6% 2 4 3 4 6% 36%	1620
	11th to 20th	Day	14% 9% 4 7% 5% 3 4 3 5% 6% 39%	1574
	21st to end	Day	15% 9% 4 7% 6% 3 4 3 5% 6% 39%	1525
March	1st to 10th	Day	12% 10% 4 7% 6% 2 4 4 4 6% 41%	1980
	11th to 20th	Day	21% 10% 4 6% 5% 3 3 4 4 6% 34%	1980
	21st to end	Day	22% 13% 4 6% 5% 2 4 3 4 6% 30%	2178
April	1st to 10th	Day	14% 7% 3 6% 4 3 4 4 4 6% 44%	2122
	11th to 20th	Day	16% 9% 3 5% 4 3 4 4 4 6% 41%	2134
	21st to end	Day	21% 7% 3 7% 6% 3 4 4 4 6% 35%	2204
May	1st to 10th	Day	19% 7% 3 6% 5% 3 4 4 5% 6% 36%	2340
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 5% 4 7% 40%	2302
	21st to end	Day	14% 6% 3 7% 6% 3 6% 5% 5% 9% 35%	2681
June	1st to 10th	Day	7% 4 2 5% 4 3 4 5% 7% 10% 49%	2520
	11th to 20th	Day	8% 4 2 5% 6% 3 6% 6% 5% 9% 48%	2520
	21st to end	Day	7% 3 1 4 4 3 4 6% 7% 10% 52%	2520
July	1st to 10th	Day	10% 5% 2 4 4 3 5% 6% 6% 10% 45%	2441
	11th to 20th	Day	3 4 2 4 4 3 5% 6% 6% 10% 52%	2340
	21st to end	Day	9% 5% 2 5% 4 3 5% 6% 7% 9% 45%	2546
August	1st to 10th	Day	8% 5% 2 4 6% 3 5% 6% 7% 11% 44%	2328
	11th to 20th	Day	9% 5% 2 4 6% 3 5% 5% 6% 8% 48%	2299
	21st to end	Day	7% 3 2 4 5% 3 4 5% 6% 10% 52%	2376
September	1st to 10th	Day	12% 4 2 4 4 2 4 3 5% 8% 52%	2160
	11th to 20th	Day	10% 4 2 4 3 3 5% 4 5% 8% 52%	2073
	21st to end	Day	7% 5% 2 4 4 3 3 4 5% 7% 56%	1925
October	1st to 10th	Day	12% 5% 2 4 4 2 4 3 5% 6% 53%	1800
	11th to 20th	Day	14% 6% 2 5% 4 1 2 3 3 6% 53%	1800
	21st to end	Day	18% 8% 2 6% 4 2 2 2 4 5% 46%	1980
November	1st to 10th	Day	10% 7% 2 4 3 2 3 3 4 7% 54%	1858
	11th to 20th	Day	15% 6% 3 5% 3 2 3 3 4 7% 49%	1633
	21st to end	Day	16% 8% 3 6% 4 2 4 3 3 6% 46%	1520
December	1st to 10th	Day	12% 9% 5% 5% 5% 3 3 3 4 7% 45%	1520
	11th to 20th	Day	13% 10% 4 7% 4 3 4 3 4 5% 42%	1918
	21st to end	Day	17% 15% 7% 10% 6% 2 4 4 4 5% 27%	2785
January	1st to 10th	Night	12% 9% 3 7% 5% 3 3 4 4 5% 47%	2458
	11th to 20th	Night	14% 7% 4 8% 6% 3 4 4 5% 6% 41%	2379
	21st to end	Night	12% 9% 4 7% 5% 3 4 4 5% 5% 41%	2574
February	1st to 10th	Night	14% 10% 4 7% 6% 3 4 4 5% 6% 37%	2340
	11th to 20th	Night	13% 8% 5% 7% 4 2 4 4 5% 6% 42%	2273
	21st to end	Night	14% 9% 4 6% 4 2 4 4 4 5% 44%	1747
March	1st to 10th	Night	13% 7% 3 5% 4 3 3 3 4 6% 48%	1980
	11th to 20th	Night	19% 8% 3 6% 4 3 4 4 4 6% 39%	1980
	21st to end	Night	22% 10% 4 6% 5% 2 4 4 4 6% 33%	2178
April	1st to 10th	Night	11% 8% 3 4 3 2 4 4 4 7% 51%	1836
	11th to 20th	Night	15% 8% 3 5% 5% 2 3 3 4 7% 46%	1775
	21st to end	Night	18% 5% 2 6% 5% 3 3 4 5% 7% 42%	1751
May	1st to 10th	Night	15% 5% 3 6% 4 3 4 5% 5% 8% 42%	1620
	11th to 20th	Night	15% 6% 2 5% 5% 3 4 3 5% 8% 46%	1593
	21st to end	Night	12% 5% 2 5% 5% 3 5% 5% 7% 8% 42%	1590
June	1st to 10th	Night	6% 3 1 3 4 3 3 4 6% 10% 56%	1440
	11th to 20th	Night	5% 3 2 4 5% 3 4 6% 7% 11% 49%	1440
	21st to end	Night	4 2 1 3 3 2 4 5% 6% 9% 61%	1440
July	1st to 10th	Night	8% 3 2 4 4 3 5% 4 6% 10% 52%	1514
	11th to 20th	Night	4 2 2 3 4 2 4 5% 6% 8% 60%	1620
	21st to end	Night	8% 3 1 4 4 3 5% 5% 6% 10% 51%	1772
August	1st to 10th	Night	5% 3 1 3 4 3 4 5% 6% 8% 56%	1611
	11th to 20th	Night	7% 4 2 4 3 2 4 5% 5% 7% 59%	1600
	21st to end	Night	6% 3 2 4 4 2 3 4 5% 8% 59%	1980
September	1st to 10th	Night	11% 4 2 3 4 2 4 3 4 7% 56%	1800
	11th to 20th	Night	10% 4 2 4 4 2 3 4 5% 8% 55%	1882
	21st to end	Night	7% 4 1 4 4 2 4 4 4 6% 59%	2016
October	1st to 10th	Night	9% 4 2 4 3 2 4 4 5% 6% 58%	2160
	11th to 20th	Night	15% 4 2 4 3 2 3 3 4 6% 54%	2160
	21st to end	Night	17% 6% 2 5% 4 2 3 3 4 4 51%	2376
November	1st to 10th	Night	11% 4 2 3 4 2 4 3 3 5% 59%	2220
	11th to 20th	Night	11% 6% 2 4 4 3 3 3 4 6% 52%	2541
	21st to end	Night	16% 8% 3 5% 4 2 4 3 3 5% 49%	2660
December	1st to 10th	Night	13% 9% 3 5% 4 3 4 4 4 6% 45%	2660
	11th to 20th	Night	14% 8% 4 6% 4 2 3 3 4 6% 44%	3279
	21st to end	Night	19% 18% 5% 9% 5% 2 3 3 4 4 28%	4879

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	42% 6% 12% 24% 16% 1	1708
	11th to 20th	Day	49% 5% 11% 24% 11% 1	1638
	21st to end	Day	45% 5% 14% 23% 10% 2	1782
February	1st to 10th	Day	51% 4 12% 21% 11% 1	1620
	11th to 20th	Day	46% 6% 12% 20% 14% 2	1583
	21st to end	Day	48% 4 10% 22% 14% 3	1525
March	1st to 10th	Day	45% 5% 11% 22% 14% 3	1980
	11th to 20th	Day	52% 5% 10% 20% 10% 3	1980
	21st to end	Day	57% 5% 12% 18% 7% 1	2178
April	1st to 10th	Day	42% 6% 11% 24% 16% 1	2122
	11th to 20th	Day	44% 5% 13% 23% 14% 1	2134
	21st to end	Day	51% 5% 11% 22% 11%	2204
May	1st to 10th	Day	48% 7% 12% 22% 11% 1	2340
	11th to 20th	Day	44% 8% 13% 23% 13%	2306
	21st to end	Day	46% 9% 13% 20% 10% 1	2681
June	1st to 10th	Day	29% 8% 17% 30% 14% 1	2520
	11th to 20th	Day	32% 9% 14% 26% 16% 2	2520
	21st to end	Day	26% 8% 16% 31% 15% 4	2520
July	1st to 10th	Day	32% 8% 15% 26% 15% 3	2376
	11th to 20th	Day	25% 9% 17% 28% 18% 3	2271
	21st to end	Day	32% 8% 14% 31% 14% 1	2405
August	1st to 10th	Day	32% 9% 19% 25% 14% 1	2314
	11th to 20th	Day	33% 7% 13% 30% 15% 1	2299
	21st to end	Day	27% 7% 14% 26% 20% 6%	2376
September	1st to 10th	Day	31% 7% 13% 27% 17% 6%	2160
	11th to 20th	Day	30% 5% 11% 26% 26% 3	2073
	21st to end	Day	28% 5% 11% 30% 22% 4	1925
October	1st to 10th	Day	32% 5% 11% 26% 23% 3	1800
	11th to 20th	Day	34% 4 8% 27% 22% 4	1800
	21st to end	Day	43% 4 8% 22% 18% 5%	1980
November	1st to 10th	Day	31% 5% 13% 26% 20% 5%	1858
	11th to 20th	Day	37% 4 10% 24% 22% 3	1633
	21st to end	Day	43% 3 9% 27% 17% 1	1520
December	1st to 10th	Day	41% 4 11% 30% 12% 1	1520
	11th to 20th	Day	45% 5% 12% 26% 10% 2	1915
	21st to end	Day	60% 5% 11% 16% 8% 1	2785
January	1st to 10th	Night	41% 5% 12% 24% 17% 1	2458
	11th to 20th	Night	45% 5% 12% 25% 13% 1	2379
	21st to end	Night	44% 5% 14% 23% 13% 2	2574
February	1st to 10th	Night	49% 5% 12% 20% 13% 2	2340
	11th to 20th	Night	44% 4 12% 21% 17% 3	2274
	21st to end	Night	43% 5% 10% 22% 16% 5%	1747
March	1st to 10th	Night	39% 4 10% 24% 19% 4	1980
	11th to 20th	Night	47% 5% 9% 21% 15% 3	1980
	21st to end	Night	53% 6% 11% 19% 9% 1	2178
April	1st to 10th	Night	34% 6% 10% 25% 21% 4	1836
	11th to 20th	Night	39% 5% 9% 26% 17% 4	1775
	21st to end	Night	42% 6% 9% 26% 16% 1	1751
May	1st to 10th	Night	40% 8% 13% 24% 14% 1	1620
	11th to 20th	Night	38% 7% 14% 24% 16% 1	1594
	21st to end	Night	37% 8% 16% 25% 12% 2	1591
June	1st to 10th	Night	23% 7% 17% 33% 17% 3	1440
	11th to 20th	Night	26% 9% 14% 29% 20% 3	1440
	21st to end	Night	18% 6% 17% 33% 20% 5%	1440
July	1st to 10th	Night	27% 7% 16% 31% 16% 4	1470
	11th to 20th	Night	21% 6% 15% 33% 23% 4	1566
	21st to end	Night	26% 7% 15% 33% 17% 1	1673
August	1st to 10th	Night	24% 8% 18% 32% 15% 2	1601
	11th to 20th	Night	25% 6% 10% 34% 24% 1	1600
	21st to end	Night	23% 5% 13% 26% 25% 7%	1980
September	1st to 10th	Night	28% 5% 11% 26% 22% 7%	1800
	11th to 20th	Night	29% 5% 11% 26% 25% 5%	1882
	21st to end	Night	26% 5% 9% 27% 28% 5%	2016
October	1st to 10th	Night	28% 5% 9% 27% 25% 6%	2160
	11th to 20th	Night	33% 4 8% 27% 21% 7%	2160
	21st to end	Night	37% 5% 8% 22% 23% 4	2376
November	1st to 10th	Night	29% 4 12% 27% 22% 5%	2220
	11th to 20th	Night	35% 4 8% 26% 24% 5%	2541
	21st to end	Night	41% 4 9% 27% 17% 3	2660
December	1st to 10th	Night	41% 5% 12% 26% 15% 1	2660
	11th to 20th	Night	42% 4 11% 29% 14% 1	3281
	21st to end	Night	61% 4 8% 17% 8% 2	4879

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	20% 14% 36% 24% 6%	270
	11th to 20th	Day	34% 12% 35% 17% 2	246
	21st to end	Day	16% 18% 45% 18% 4	264
February	1st to 10th	Day	26% 15% 39% 15% 5%	240
	11th to 20th	Day	20% 22% 38% 14% 5% 1	240
	21st to end	Day	24% 22% 36% 15% 3 1	198
March	1st to 10th	Day	18% 18% 46% 15% 3	240
	11th to 20th	Day	30% 13% 32% 21% 4	240
	21st to end	Day	36% 17% 31% 11% 5%	264
April	1st to 10th	Day	18% 16% 35% 24% 7% 1	382
	11th to 20th	Day	22% 13% 34% 24% 7%	412
	21st to end	Day	24% 11% 32% 23% 9%	464
May	1st to 10th	Day	18% 12% 35% 24% 10% 1	603
	11th to 20th	Day	19% 9% 29% 27% 13% 3	625
	21st to end	Day	17% 9% 26% 24% 19% 6%	679
June	1st to 10th	Day	6% 3 19% 33% 29% 9%	630
	11th to 20th	Day	9% 3 22% 36% 24% 5%	630
	21st to end	Day	6% 5% 28% 38% 19% 4	630
July	1st to 10th	Day	12% 3 12% 28% 31% 14%	621
	11th to 20th	Day	5% 3 16% 35% 31% 10%	618
	21st to end	Day	10% 2 13% 35% 32% 9%	684
August	1st to 10th	Day	7% 3 14% 41% 30% 5%	626
	11th to 20th	Day	8% 3 17% 34% 31% 7%	613
	21st to end	Day	10% 1 10% 30% 36% 13%	495
September	1st to 10th	Day	12% 4 14% 36% 27% 8%	450
	11th to 20th	Day	7% 2 13% 41% 28% 9%	363
	21st to end	Day	10% 6% 23% 33% 22% 7%	270
October	1st to 10th	Day	17% 7% 28% 26% 15% 7%	270
	11th to 20th	Day	14% 14% 42% 23% 7%	270
	21st to end	Day	26% 17% 31% 20% 6% 1	297
November	1st to 10th	Day	15% 10% 33% 28% 9% 4	270
	11th to 20th	Day	16% 17% 30% 26% 9% 2	270
	21st to end	Day	25% 10% 31% 26% 7%	270
December	1st to 10th	Day	14% 14% 40% 22% 9% 1	270
	11th to 20th	Day	22% 15% 34% 23% 5% 1	270
	21st to end	Day	23% 21% 38% 18%	297
January	1st to 10th	Night	16% 12% 39% 26% 7%	950
	11th to 20th	Night	17% 14% 40% 24% 4 1	915
	21st to end	Night	15% 13% 41% 28% 3	990
February	1st to 10th	Night	18% 12% 43% 23% 3	900
	11th to 20th	Night	17% 15% 39% 26% 4	879
	21st to end	Night	22% 15% 41% 19% 3	563
March	1st to 10th	Night	16% 14% 42% 23% 4	540
	11th to 20th	Night	21% 11% 32% 30% 6% 1	540
	21st to end	Night	26% 12% 34% 24% 4	594
April	1st to 10th	Night	14% 11% 38% 31% 4	540
	11th to 20th	Night	19% 11% 31% 30% 8%	533
	21st to end	Night	20% 8% 36% 29% 7%	540
May	1st to 10th	Night	17% 6% 33% 37% 7%	540
	11th to 20th	Night	17% 5% 26% 35% 15% 1	531
	21st to end	Night	12% 5% 29% 32% 20% 2	584
June	1st to 10th	Night	7% 2 15% 46% 28% 2	540
	11th to 20th	Night	6% 2 24% 44% 21% 2	540
	21st to end	Night	4 2 26% 48% 20% 1	540
July	1st to 10th	Night	8% 2 10% 44% 32% 4	525
	11th to 20th	Night	4 1 14% 46% 33% 2	522
	21st to end	Night	9% 1 13% 41% 35% 2	591
August	1st to 10th	Night	6% 3 10% 47% 33% 1	537
	11th to 20th	Night	6% 2 14% 43% 33% 3	534
	21st to end	Night	6% 1 12% 38% 40% 3	594
September	1st to 10th	Night	12% 2 14% 43% 25% 3	540
	11th to 20th	Night	9% 3 18% 37% 26% 6%	540
	21st to end	Night	6% 4 22% 41% 22% 4	576
October	1st to 10th	Night	11% 4 28% 34% 20% 3	720
	11th to 20th	Night	16% 7% 38% 29% 9% 1	720
	21st to end	Night	19% 9% 34% 27% 10%	792
November	1st to 10th	Night	13% 8% 37% 32% 10%	740
	11th to 20th	Night	15% 13% 35% 28% 9%	869
	21st to end	Night	19% 11% 36% 27% 6%	950
December	1st to 10th	Night	18% 10% 39% 27% 6% 1	950
	11th to 20th	Night	21% 10% 35% 29% 4	950
	21st to end	Night	20% 15% 37% 25% 2	1045

Page generated at 2024-01-10 09:16:11. Version ac07

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