Goat Shed Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goat Shed Observatory clear sky chart from 2005-11-06 to 2025-04-11.

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 4 3 5% 7% 57%	117134
	Night	6% 6% 2 6% 4 4 4 4 5% 7% 52%	119937
Transparency	Day	26% 5% 12% 22% 20% 15%	116878
	Night	31% 6% 13% 22% 17% 11%	119783
Seeing	Day	8% 10% 24% 30% 21% 7%	14964
	Night	9% 5% 22% 42% 21% 2	24507

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	8% 13% 6% 9% 6% 6% 5% 5% 7% 6% 30%	3639
	11th to 20th	Day	6% 10% 3 11% 6% 5% 4 3 5% 6% 41%	3640
	21st to end	Day	8% 8% 3 8% 4 4 4 3 5% 6% 47%	4004
February	1st to 10th	Day	7% 8% 3 7% 6% 5% 4 4 7% 8% 41%	1821
	11th to 20th	Day	7% 8% 2 7% 6% 5% 6% 4 6% 7% 41%	1950
	21st to end	Day	5% 9% 2 7% 4 5% 5% 5% 6% 8% 44%	1650
March	1st to 10th	Day	6% 9% 3 8% 5% 5% 5% 4 6% 8% 40%	4518
	11th to 20th	Day	5% 7% 3 5% 3 3 3 3 6% 7% 54%	4906
	21st to end	Day	5% 6% 3 8% 6% 6% 6% 5% 6% 8% 42%	5590
April	1st to 10th	Day	6% 6% 2 6% 5% 4 4 5% 6% 9% 46%	2400
	11th to 20th	Day	4 6% 2 6% 5% 3 3 4 6% 8% 53%	2325
	21st to end	Day	5% 5% 2 5% 3 4 4 4 6% 9% 54%	2470
May	1st to 10th	Day	6% 6% 2 6% 4 4 4 4 5% 6% 53%	4110
	11th to 20th	Day	3 2 1 3 3 3 3 3 5% 6% 69%	4071
	21st to end	Day	5% 4 1 4 3 3 4 3 6% 8% 59%	4778
June	1st to 10th	Day	6% 3 1 4 4 4 5% 4 7% 9% 52%	2660
	11th to 20th	Day	4 3 1 4 3 3 3 2 4 7% 65%	2660
	21st to end	Day	2 2 1 3 2 2 3 2 4 5% 74%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 4 82%	4420
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 5% 75%	4420
	21st to end	Day	2 2 1 2 2 3 3 3 4 5% 74%	4790
August	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 6% 65%	4096
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 5% 78%	4028
	21st to end	Day	2 3 1 3 2 2 2 1 3 4 77%	4273
September	1st to 10th	Day	1 2 1 2 2 3 2 2 3 5% 76%	2252
	11th to 20th	Day	3 4 1 4 2 3 3 3 4 5% 68%	2090
	21st to end	Day	4 3 1 3 3 2 2 2 4 6% 70%	2090
October	1st to 10th	Day	3 3 1 4 3 3 2 2 4 5% 71%	3490
	11th to 20th	Day	4 4 2 4 3 3 3 3 5% 7% 64%	3102
	21st to end	Day	3 3 1 4 3 3 5% 4 6% 9% 59%	3101
November	1st to 10th	Day	8% 6% 2 6% 5% 4 4 4 5% 9% 47%	1764
	11th to 20th	Day	7% 6% 2 6% 5% 5% 5% 4 6% 8% 46%	1800
	21st to end	Day	8% 7% 2 8% 5% 4 4 5% 6% 8% 43%	1800
December	1st to 10th	Day	6% 5% 2 5% 4 4 3 4 4 7% 56%	2734
	11th to 20th	Day	12% 10% 3 7% 5% 5% 5% 4 7% 8% 32%	3028
	21st to end	Day	11% 10% 4 11% 5% 5% 4 4 6% 6% 34%	4004
January	1st to 10th	Night	10% 12% 5% 12% 5% 5% 5% 4 5% 6% 28%	6306
	11th to 20th	Night	9% 11% 3 9% 7% 5% 5% 4 5% 6% 36%	6320
	21st to end	Night	8% 7% 4 8% 4 4 4 3 5% 6% 47%	6952
February	1st to 10th	Night	11% 8% 3 8% 5% 4 4 5% 6% 7% 38%	2571
	11th to 20th	Night	8% 7% 3 6% 5% 4 4 3 4 7% 48%	2338
	21st to end	Night	7% 8% 2 6% 5% 4 5% 5% 7% 9% 43%	1980
March	1st to 10th	Night	7% 9% 2 7% 5% 4 4 3 6% 7% 45%	5376
	11th to 20th	Night	8% 7% 2 6% 4 4 5% 4 5% 6% 49%	5093
	21st to end	Night	5% 6% 2 7% 5% 6% 6% 4 6% 9% 45%	5368
April	1st to 10th	Night	6% 6% 3 5% 5% 5% 5% 5% 6% 7% 47%	2000
	11th to 20th	Night	5% 6% 2 6% 5% 4 5% 4 5% 7% 50%	1809
	21st to end	Night	4 5% 2 5% 4 4 4 4 6% 7% 55%	1710
May	1st to 10th	Night	8% 6% 2 5% 3 3 4 3 6% 7% 53%	2860
	11th to 20th	Night	4 2 1 3 2 3 3 3 4 7% 68%	2834
	21st to end	Night	4 4 2 5% 3 4 4 4 5% 6% 59%	2795
June	1st to 10th	Night	5% 4 2 5% 4 4 5% 5% 7% 8% 51%	1520
	11th to 20th	Night	4 3 1 3 3 3 3 3 4 8% 65%	1520
	21st to end	Night	1 1 1 3 3 2 4 2 4 5% 75%	1520
July	1st to 10th	Night	1 1 2 2 2 2 2 3 4 81%	2540
	11th to 20th	Night	1 1 2 2 2 3 3 4 5% 77%	2540
	21st to end	Night	2 2 1 3 3 3 4 3 4 6% 68%	2761
August	1st to 10th	Night	3 3 1 4 3 3 4 3 6% 7% 63%	2842
	11th to 20th	Night	2 1 1 2 2 3 3 4 5% 77%	2811
	21st to end	Night	2 3 1 3 2 2 3 2 3 4 76%	3398
September	1st to 10th	Night	2 2 1 3 2 2 3 2 4 4 76%	1927
	11th to 20th	Night	4 3 1 3 2 3 4 3 5% 6% 66%	2090
	21st to end	Night	5% 3 1 3 2 3 3 2 3 5% 71%	2090
October	1st to 10th	Night	4 2 1 3 2 2 2 2 3 5% 73%	3490
	11th to 20th	Night	5% 4 2 5% 4 3 3 3 4 6% 62%	3824
	21st to end	Night	5% 4 1 6% 4 4 5% 4 5% 7% 55%	4457
November	1st to 10th	Night	9% 6% 2 6% 4 4 5% 3 5% 7% 50%	2535
	11th to 20th	Night	9% 5% 3 7% 5% 4 5% 4 6% 7% 45%	2600
	21st to end	Night	7% 6% 2 7% 4 4 5% 4 6% 7% 47%	2600
December	1st to 10th	Night	6% 5% 2 6% 4 3 4 3 4 8% 55%	4432
	11th to 20th	Night	12% 11% 4 10% 6% 5% 5% 5% 7% 8% 28%	5176
	21st to end	Night	11% 8% 3 9% 6% 6% 6% 5% 6% 7% 33%	6952

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	49% 11% 20% 17% 3	3639
	11th to 20th	Day	42% 10% 20% 21% 5% 1	3640
	21st to end	Day	37% 8% 20% 26% 8% 1	4004
February	1st to 10th	Day	38% 10% 22% 22% 6% 1	1821
	11th to 20th	Day	39% 9% 20% 22% 9% 1	1960
	21st to end	Day	37% 7% 18% 27% 10% 1	1650
March	1st to 10th	Day	39% 8% 14% 28% 10% 2	4518
	11th to 20th	Day	28% 5% 12% 36% 17% 1	4906
	21st to end	Day	36% 8% 20% 25% 10% 1	5590
April	1st to 10th	Day	33% 7% 15% 24% 17% 4	2400
	11th to 20th	Day	27% 6% 14% 29% 20% 5%	2328
	21st to end	Day	27% 5% 13% 28% 24% 3	2470
May	1st to 10th	Day	28% 6% 9% 26% 24% 7%	4110
	11th to 20th	Day	16% 5% 7% 26% 33% 14%	4074
	21st to end	Day	21% 6% 13% 28% 27% 5%	4778
June	1st to 10th	Day	27% 7% 12% 25% 26% 4	2660
	11th to 20th	Day	20% 4 7% 21% 33% 15%	2660
	21st to end	Day	13% 3 5% 16% 33% 30%	2660
July	1st to 10th	Day	8% 2 3 9% 18% 61%	4351
	11th to 20th	Day	13% 2 2 6% 19% 58%	4345
	21st to end	Day	13% 3 3 7% 27% 47%	4639
August	1st to 10th	Day	20% 3 4 11% 26% 36%	4081
	11th to 20th	Day	11% 2 3 13% 35% 36%	4067
	21st to end	Day	13% 2 3 13% 36% 34%	4272
September	1st to 10th	Day	12% 3 5% 14% 32% 35%	2252
	11th to 20th	Day	19% 3 7% 26% 25% 20%	2090
	21st to end	Day	17% 3 7% 22% 36% 15%	2090
October	1st to 10th	Day	19% 3 7% 19% 36% 16%	3490
	11th to 20th	Day	22% 3 10% 31% 27% 8%	3102
	21st to end	Day	22% 5% 13% 33% 25% 3	3101
November	1st to 10th	Day	35% 6% 14% 28% 15% 2	1764
	11th to 20th	Day	34% 8% 21% 29% 7% 1	1800
	21st to end	Day	38% 7% 21% 28% 7%	1800
December	1st to 10th	Day	28% 7% 25% 33% 6%	2734
	11th to 20th	Day	47% 9% 25% 18% 1	3028
	21st to end	Day	49% 7% 17% 22% 5%	4004
January	1st to 10th	Night	54% 8% 21% 15% 3	6306
	11th to 20th	Night	44% 9% 18% 21% 6% 1	6320
	21st to end	Night	37% 8% 17% 28% 11%	6952
February	1st to 10th	Night	43% 10% 21% 21% 5% 1	2571
	11th to 20th	Night	35% 7% 22% 25% 10% 1	2339
	21st to end	Night	35% 7% 19% 28% 10% 1	1980
March	1st to 10th	Night	35% 8% 13% 31% 12% 1	5376
	11th to 20th	Night	34% 5% 10% 31% 18% 2	5093
	21st to end	Night	33% 7% 19% 28% 11% 1	5368
April	1st to 10th	Night	34% 5% 14% 24% 17% 5%	2000
	11th to 20th	Night	32% 6% 10% 26% 22% 4	1809
	21st to end	Night	27% 5% 14% 27% 24% 4	1710
May	1st to 10th	Night	27% 6% 10% 26% 23% 9%	2860
	11th to 20th	Night	16% 4 8% 22% 37% 13%	2835
	21st to end	Night	24% 5% 11% 23% 32% 4	2795
June	1st to 10th	Night	28% 8% 11% 23% 25% 4	1520
	11th to 20th	Night	19% 4 8% 19% 36% 14%	1520
	21st to end	Night	12% 3 6% 15% 30% 33%	1520
July	1st to 10th	Night	9% 2 3 7% 17% 62%	2500
	11th to 20th	Night	11% 2 3 5% 17% 62%	2492
	21st to end	Night	17% 3 3 7% 28% 42%	2674
August	1st to 10th	Night	20% 3 3 9% 22% 42%	2834
	11th to 20th	Night	10% 3 3 11% 30% 42%	2838
	21st to end	Night	15% 2 3 12% 31% 38%	3398
September	1st to 10th	Night	13% 3 4 12% 30% 39%	1927
	11th to 20th	Night	19% 4 6% 20% 26% 25%	2090
	21st to end	Night	19% 3 5% 19% 33% 22%	2090
October	1st to 10th	Night	16% 2 5% 17% 31% 29%	3490
	11th to 20th	Night	25% 3 6% 27% 30% 8%	3824
	21st to end	Night	27% 5% 11% 32% 23% 3	4457
November	1st to 10th	Night	33% 7% 13% 26% 19% 2	2535
	11th to 20th	Night	35% 8% 15% 30% 11% 1	2600
	21st to end	Night	34% 6% 20% 31% 9%	2600
December	1st to 10th	Night	28% 7% 27% 31% 7%	4432
	11th to 20th	Night	51% 8% 21% 19% 1	5176
	21st to end	Night	46% 8% 20% 20% 6%	6952

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	17% 13% 25% 30% 13% 4	200
	11th to 20th	Day	8% 11% 31% 31% 16% 4	200
	21st to end	Day	10% 7% 27% 32% 19% 5%	220
February	1st to 10th	Day	14% 13% 31% 28% 13% 1	323
	11th to 20th	Day	13% 14% 30% 28% 13% 2	495
	21st to end	Day	9% 15% 32% 35% 9%	414
March	1st to 10th	Day	8% 12% 38% 31% 10% 1	500
	11th to 20th	Day	9% 15% 29% 29% 15% 3	500
	21st to end	Day	10% 17% 33% 25% 13% 1	550
April	1st to 10th	Day	13% 16% 27% 23% 15% 6%	500
	11th to 20th	Day	10% 20% 32% 24% 11% 4	453
	21st to end	Day	8% 21% 29% 25% 15% 2	460
May	1st to 10th	Day	6% 16% 33% 27% 14% 4	463
	11th to 20th	Day	11% 13% 24% 28% 19% 5%	488
	21st to end	Day	7% 9% 22% 27% 22% 12%	529
June	1st to 10th	Day	5% 10% 26% 28% 22% 9%	490
	11th to 20th	Day	8% 16% 29% 25% 17% 5%	490
	21st to end	Day	3 7% 26% 34% 21% 8%	490
July	1st to 10th	Day	2 5% 23% 34% 28% 9%	486
	11th to 20th	Day	3 4 20% 37% 29% 7%	484
	21st to end	Day	2 3 17% 34% 36% 9%	531
August	1st to 10th	Day	5% 3 18% 38% 26% 9%	487
	11th to 20th	Day	2 5% 15% 31% 33% 14%	477
	21st to end	Day	2 6% 19% 29% 29% 15%	539
September	1st to 10th	Day	2 5% 16% 26% 36% 14%	490
	11th to 20th	Day	5% 5% 17% 29% 32% 12%	490
	21st to end	Day	6% 9% 19% 28% 28% 9%	490
October	1st to 10th	Day	8% 8% 18% 26% 28% 12%	490
	11th to 20th	Day	6% 11% 22% 24% 26% 12%	348
	21st to end	Day	8% 9% 20% 42% 17% 4	330
November	1st to 10th	Day	15% 10% 21% 29% 23% 1	300
	11th to 20th	Day	10% 10% 24% 33% 20% 3	300
	21st to end	Day	15% 8% 19% 35% 19% 5%	300
December	1st to 10th	Day	16% 9% 20% 27% 18% 9%	237
	11th to 20th	Day	13% 11% 28% 33% 15% 2	200
	21st to end	Day	16% 12% 23% 32% 10% 6%	220
January	1st to 10th	Night	12% 6% 23% 39% 17% 2	800
	11th to 20th	Night	13% 5% 23% 37% 20% 1	800
	21st to end	Night	9% 4 23% 40% 21% 2	880
February	1st to 10th	Night	15% 7% 27% 39% 12%	800
	11th to 20th	Night	10% 7% 27% 39% 17% 1	784
	21st to end	Night	9% 8% 28% 41% 14%	660
March	1st to 10th	Night	8% 8% 27% 44% 13% 1	800
	11th to 20th	Night	9% 6% 26% 40% 16% 2	800
	21st to end	Night	11% 8% 30% 37% 13% 1	880
April	1st to 10th	Night	9% 8% 26% 40% 15% 2	800
	11th to 20th	Night	6% 11% 31% 39% 13% 1	679
	21st to end	Night	5% 8% 30% 40% 15% 2	570
May	1st to 10th	Night	8% 9% 30% 36% 15% 2	570
	11th to 20th	Night	7% 7% 17% 44% 21% 3	561
	21st to end	Night	8% 5% 19% 38% 27% 4	432
June	1st to 10th	Night	8% 7% 16% 42% 24% 3	380
	11th to 20th	Night	5% 7% 20% 47% 20% 1	380
	21st to end	Night	1 3 19% 52% 23% 1	380
July	1st to 10th	Night	1 1 13% 55% 28% 1	370
	11th to 20th	Night	1 1 16% 55% 26% 1	368
	21st to end	Night	2 1 8% 54% 33% 1	416
August	1st to 10th	Night	4 2 13% 52% 28% 1	562
	11th to 20th	Night	2 2 12% 52% 30% 1	564
	21st to end	Night	3 2 15% 45% 31% 3	775
September	1st to 10th	Night	3 2 11% 46% 33% 4	760
	11th to 20th	Night	6% 2 13% 39% 34% 5%	760
	21st to end	Night	6% 5% 14% 38% 30% 8%	760
October	1st to 10th	Night	7% 4 18% 41% 28% 3	760
	11th to 20th	Night	8% 5% 17% 40% 27% 4	760
	21st to end	Night	7% 5% 24% 39% 22% 4	836
November	1st to 10th	Night	12% 5% 19% 42% 21% 1	780
	11th to 20th	Night	11% 6% 26% 41% 16% 1	800
	21st to end	Night	10% 4 24% 38% 22% 2	800
December	1st to 10th	Night	13% 5% 23% 39% 19% 2	800
	11th to 20th	Night	17% 6% 20% 40% 16% 2	800
	21st to end	Night	18% 7% 29% 35% 10% 1	880

Page generated at 2025-04-08 07:17:28. Version ac07

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