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 2026-08-15.

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	4 4 2 5% 3 3 4 3 5% 7% 59%	152144
	Night	6% 5% 2 6% 4 4 4 4 5% 7% 53%	147094
Transparency	Day	25% 5% 11% 22% 22% 16%	146938
	Night	30% 5% 13% 22% 18% 12%	143299
Seeing	Day	8% 10% 24% 30% 21% 7%	16751
	Night	8% 5% 22% 42% 21% 2	26078

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% 12% 5% 9% 6% 5% 4 4 7% 7% 32%	4722
	11th to 20th	Day	5% 7% 3 10% 5% 4 4 3 5% 6% 48%	4740
	21st to end	Day	7% 7% 3 8% 5% 5% 6% 4 5% 7% 43%	5187
February	1st to 10th	Day	7% 8% 3 6% 6% 5% 4 4 7% 8% 42%	1913
	11th to 20th	Day	7% 8% 2 8% 6% 5% 6% 4 7% 7% 40%	2050
	21st to end	Day	5% 9% 2 7% 4 5% 5% 5% 6% 8% 44%	1730
March	1st to 10th	Day	6% 9% 3 8% 5% 5% 5% 5% 6% 8% 40%	4618
	11th to 20th	Day	5% 7% 3 5% 3 3 3 3 6% 7% 54%	5014
	21st to end	Day	5% 6% 3 8% 5% 6% 6% 5% 7% 8% 42%	5713
April	1st to 10th	Day	6% 6% 2 6% 5% 4 4 5% 6% 9% 47%	2520
	11th to 20th	Day	4 6% 2 5% 5% 3 4 4 6% 8% 54%	2571
	21st to end	Day	5% 5% 2 5% 3 4 4 4 6% 8% 54%	2730
May	1st to 10th	Day	4 4 1 4 3 3 3 3 5% 7% 63%	7626
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 6% 66%	7596
	21st to end	Day	3 3 1 3 3 3 4 4 6% 8% 62%	8931
June	1st to 10th	Day	6% 3 1 4 4 4 5% 4 7% 9% 53%	2940
	11th to 20th	Day	4 3 1 4 3 3 3 2 4 7% 66%	2940
	21st to end	Day	3 2 1 3 2 2 3 2 4 5% 74%	2940
July	1st to 10th	Day	1 1 1 2 1 2 2 2 4 5% 78%	8219
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 5% 76%	8220
	21st to end	Day	2 2 1 3 2 3 3 3 5% 7% 70%	8922
August	1st to 10th	Day	2 3 1 4 3 3 3 3 5% 6% 68%	5913
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 5% 79%	5851
	21st to end	Day	4 4 2 4 3 3 3 2 4 5% 68%	6116
September	1st to 10th	Day	1 2 1 3 2 3 3 2 4 5% 74%	2370
	11th to 20th	Day	3 4 1 4 2 3 3 3 4 5% 68%	2200
	21st to end	Day	4 3 1 3 3 2 3 2 4 6% 70%	2200
October	1st to 10th	Day	3 3 1 4 3 3 2 2 4 5% 70%	3600
	11th to 20th	Day	4 4 2 5% 3 3 3 3 5% 7% 63%	3200
	21st to end	Day	3 3 1 4 3 3 5% 4 6% 9% 59%	3200
November	1st to 10th	Day	8% 6% 2 6% 5% 4 4 4 6% 9% 47%	1854
	11th to 20th	Day	7% 6% 2 6% 5% 5% 5% 4 6% 8% 46%	1890
	21st to end	Day	8% 7% 2 8% 5% 4 4 5% 6% 8% 43%	1890
December	1st to 10th	Day	6% 5% 2 5% 4 4 3 4 4 7% 55%	2818
	11th to 20th	Day	13% 9% 3 7% 5% 6% 5% 5% 7% 8% 32%	3108
	21st to end	Day	11% 10% 4 11% 5% 5% 4 4 6% 6% 34%	4092
January	1st to 10th	Night	11% 12% 5% 12% 6% 6% 6% 5% 6% 7% 26%	8172
	11th to 20th	Night	7% 8% 3 9% 6% 4 4 3 6% 9% 41%	8220
	21st to end	Night	7% 6% 4 8% 4 4 5% 4 6% 8% 44%	8994
February	1st to 10th	Night	10% 8% 3 8% 5% 4 5% 5% 6% 7% 39%	2699
	11th to 20th	Night	8% 7% 3 6% 5% 4 4 3 4 7% 47%	2458
	21st to end	Night	7% 8% 2 6% 4 4 5% 5% 6% 10% 42%	2076
March	1st to 10th	Night	7% 9% 2 7% 5% 4 4 3 6% 7% 45%	5496
	11th to 20th	Night	7% 7% 2 6% 4 4 5% 4 5% 6% 49%	5205
	21st to end	Night	5% 6% 2 7% 5% 5% 6% 4 6% 9% 45%	5487
April	1st to 10th	Night	6% 6% 2 5% 4 5% 5% 5% 6% 7% 48%	2100
	11th to 20th	Night	5% 5% 2 6% 5% 4 5% 4 6% 7% 50%	1997
	21st to end	Night	4 5% 2 6% 4 4 4 4 6% 7% 55%	1890
May	1st to 10th	Night	5% 3 1 4 3 2 3 3 6% 7% 62%	5321
	11th to 20th	Night	4 4 2 5% 3 4 3 3 5% 7% 62%	5296
	21st to end	Night	3 3 2 4 3 4 4 4 5% 7% 62%	5242
June	1st to 10th	Night	5% 4 2 5% 4 4 5% 4 7% 7% 53%	1680
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 8% 65%	1680
	21st to end	Night	1 2 1 3 2 2 4 2 4 5% 73%	1680
July	1st to 10th	Night	2 1 3 2 2 2 3 4 5% 76%	4740
	11th to 20th	Night	1 2 1 3 2 2 3 3 4 5% 75%	4740
	21st to end	Night	2 3 1 3 3 3 4 4 6% 9% 62%	5153
August	1st to 10th	Night	2 3 1 4 3 3 3 3 5% 6% 68%	4118
	11th to 20th	Night	1 1 1 2 2 3 3 4 6% 78%	4087
	21st to end	Night	4 3 1 4 3 3 3 3 4 5% 68%	4873
September	1st to 10th	Night	2 2 1 3 2 2 3 3 4 5% 74%	2029
	11th to 20th	Night	4 3 1 3 2 3 4 3 6% 6% 66%	2200
	21st to end	Night	5% 2 1 3 2 3 3 2 3 5% 70%	2200
October	1st to 10th	Night	4 2 1 3 2 2 3 2 3 5% 73%	3600
	11th to 20th	Night	5% 4 2 5% 4 3 3 3 4 6% 61%	3946
	21st to end	Night	5% 4 1 6% 4 4 4 4 5% 7% 56%	4600
November	1st to 10th	Night	9% 6% 2 6% 4 4 5% 3 5% 7% 49%	2665
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 4 6% 7% 44%	2730
	21st to end	Night	7% 6% 2 7% 5% 4 6% 4 6% 7% 46%	2730
December	1st to 10th	Night	6% 5% 2 6% 4 3 4 3 4 8% 54%	4568
	11th to 20th	Night	11% 11% 4 10% 5% 5% 6% 5% 7% 8% 28%	5316
	21st to end	Night	11% 8% 3 9% 6% 6% 6% 5% 6% 7% 34%	7106

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	47% 10% 23% 17% 3	4723
	11th to 20th	Day	36% 8% 21% 28% 6%	4740
	21st to end	Day	40% 8% 20% 26% 7%	5187
February	1st to 10th	Day	38% 10% 23% 22% 6% 1	1913
	11th to 20th	Day	39% 9% 20% 22% 9% 1	2060
	21st to end	Day	37% 7% 18% 27% 10% 1	1730
March	1st to 10th	Day	39% 8% 14% 28% 9% 2	4618
	11th to 20th	Day	28% 5% 13% 36% 18% 1	5014
	21st to end	Day	36% 8% 20% 25% 10% 1	5713
April	1st to 10th	Day	32% 6% 14% 25% 18% 4	2520
	11th to 20th	Day	27% 6% 13% 28% 21% 5%	2574
	21st to end	Day	28% 5% 12% 28% 24% 3	2730
May	1st to 10th	Day	21% 4 6% 24% 36% 9%	7626
	11th to 20th	Day	19% 3 5% 26% 34% 12%	7599
	21st to end	Day	19% 4 9% 28% 31% 10%	8932
June	1st to 10th	Day	26% 6% 11% 24% 27% 6%	2940
	11th to 20th	Day	19% 4 6% 21% 34% 16%	2940
	21st to end	Day	13% 3 5% 17% 33% 29%	2940
July	1st to 10th	Day	10% 2 2 11% 24% 51%	8151
	11th to 20th	Day	13% 2 2 9% 22% 53%	8145
	21st to end	Day	14% 3 2 12% 30% 38%	8723
August	1st to 10th	Day	19% 3 4 12% 26% 36%	4341
	11th to 20th	Day	11% 2 3 13% 35% 36%	4250
	21st to end	Day	14% 2 3 13% 35% 33%	4407
September	1st to 10th	Day	13% 3 5% 14% 31% 33%	2370
	11th to 20th	Day	19% 3 7% 26% 26% 19%	2200
	21st to end	Day	18% 3 7% 21% 36% 15%	2200
October	1st to 10th	Day	18% 3 7% 19% 36% 16%	3600
	11th to 20th	Day	22% 3 10% 31% 26% 8%	3200
	21st to end	Day	22% 5% 12% 33% 25% 4	3200
November	1st to 10th	Day	35% 6% 14% 29% 15% 2	1854
	11th to 20th	Day	34% 8% 22% 29% 6% 1	1890
	21st to end	Day	37% 7% 21% 28% 7%	1890
December	1st to 10th	Day	28% 7% 25% 33% 6%	2818
	11th to 20th	Day	46% 9% 24% 18% 2	3108
	21st to end	Day	49% 7% 17% 22% 5%	4092
January	1st to 10th	Night	55% 8% 22% 13% 2	8172
	11th to 20th	Night	36% 9% 21% 27% 6% 1	8220
	21st to end	Night	35% 8% 19% 29% 9%	8994
February	1st to 10th	Night	42% 10% 21% 22% 5% 1	2699
	11th to 20th	Night	37% 6% 21% 25% 10% 1	2459
	21st to end	Night	34% 7% 18% 29% 10% 1	2076
March	1st to 10th	Night	34% 8% 13% 31% 12% 1	5496
	11th to 20th	Night	34% 5% 10% 31% 19% 2	5205
	21st to end	Night	33% 7% 19% 28% 11% 2	5487
April	1st to 10th	Night	34% 6% 14% 25% 17% 4	2100
	11th to 20th	Night	31% 6% 10% 25% 24% 4	1997
	21st to end	Night	27% 5% 14% 26% 24% 4	1890
May	1st to 10th	Night	20% 4 8% 23% 35% 11%	5319
	11th to 20th	Night	23% 3 6% 20% 37% 12%	5297
	21st to end	Night	22% 4 8% 21% 37% 8%	5243
June	1st to 10th	Night	27% 7% 10% 22% 27% 7%	1680
	11th to 20th	Night	19% 4 7% 19% 35% 16%	1680
	21st to end	Night	13% 3 5% 15% 31% 32%	1680
July	1st to 10th	Night	12% 2 2 10% 20% 53%	4700
	11th to 20th	Night	13% 2 2 6% 21% 55%	4692
	21st to end	Night	18% 3 2 12% 31% 34%	5040
August	1st to 10th	Night	19% 3 3 9% 22% 43%	3014
	11th to 20th	Night	11% 2 3 12% 30% 42%	2964
	21st to end	Night	15% 2 3 12% 31% 37%	3505
September	1st to 10th	Night	14% 3 4 12% 30% 37%	2029
	11th to 20th	Night	19% 4 6% 20% 27% 24%	2200
	21st to end	Night	19% 3 5% 19% 33% 22%	2200
October	1st to 10th	Night	16% 2 5% 17% 31% 28%	3600
	11th to 20th	Night	25% 3 6% 28% 30% 8%	3946
	21st to end	Night	27% 5% 11% 32% 23% 3	4600
November	1st to 10th	Night	34% 6% 13% 26% 19% 2	2665
	11th to 20th	Night	36% 8% 15% 30% 11% 1	2730
	21st to end	Night	34% 6% 20% 31% 8%	2730
December	1st to 10th	Night	28% 7% 27% 30% 7%	4568
	11th to 20th	Night	51% 8% 20% 20% 1	5316
	21st to end	Night	46% 8% 20% 20% 6%	7106

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	16% 12% 25% 29% 14% 4	220
	11th to 20th	Day	7% 10% 29% 32% 19% 4	220
	21st to end	Day	10% 7% 26% 34% 18% 4	242
February	1st to 10th	Day	12% 14% 30% 28% 15% 1	355
	11th to 20th	Day	13% 14% 30% 29% 12% 2	535
	21st to end	Day	10% 15% 33% 34% 8%	446
March	1st to 10th	Day	9% 13% 37% 29% 11% 1	540
	11th to 20th	Day	9% 15% 29% 29% 15% 3	540
	21st to end	Day	10% 17% 33% 26% 13% 1	594
April	1st to 10th	Day	13% 15% 28% 23% 15% 7%	540
	11th to 20th	Day	11% 18% 31% 24% 12% 4	532
	21st to end	Day	8% 20% 30% 24% 15% 3	540
May	1st to 10th	Day	6% 14% 32% 28% 16% 5%	543
	11th to 20th	Day	10% 14% 27% 26% 18% 4	568
	21st to end	Day	7% 11% 21% 28% 22% 12%	617
June	1st to 10th	Day	6% 11% 26% 26% 21% 10%	570
	11th to 20th	Day	7% 14% 29% 25% 18% 7%	570
	21st to end	Day	4 7% 25% 34% 22% 8%	570
July	1st to 10th	Day	2 5% 21% 34% 28% 10%	566
	11th to 20th	Day	3 4 21% 35% 29% 8%	564
	21st to end	Day	2 3 16% 33% 35% 11%	619
August	1st to 10th	Day	4 4 19% 37% 26% 10%	567
	11th to 20th	Day	2 5% 15% 33% 32% 14%	534
	21st to end	Day	4 5% 18% 29% 29% 15%	583
September	1st to 10th	Day	2 5% 15% 27% 35% 15%	530
	11th to 20th	Day	5% 5% 17% 30% 32% 11%	530
	21st to end	Day	5% 9% 19% 28% 29% 9%	530
October	1st to 10th	Day	8% 8% 19% 25% 29% 11%	530
	11th to 20th	Day	7% 11% 22% 25% 24% 11%	380
	21st to end	Day	8% 9% 20% 41% 18% 4	363
November	1st to 10th	Day	15% 10% 22% 29% 23% 1	330
	11th to 20th	Day	10% 9% 23% 34% 19% 5%	330
	21st to end	Day	14% 8% 20% 35% 19% 5%	330
December	1st to 10th	Day	15% 9% 22% 29% 17% 8%	261
	11th to 20th	Day	14% 10% 26% 33% 14% 3	220
	21st to end	Day	17% 12% 24% 32% 10% 5%	242
January	1st to 10th	Night	12% 6% 23% 40% 16% 2	840
	11th to 20th	Night	12% 5% 22% 38% 22% 1	840
	21st to end	Night	9% 4 23% 41% 21% 2	924
February	1st to 10th	Night	15% 6% 26% 40% 13%	840
	11th to 20th	Night	11% 6% 27% 39% 17% 1	824
	21st to end	Night	9% 8% 28% 41% 13%	692
March	1st to 10th	Night	8% 8% 27% 43% 13% 1	840
	11th to 20th	Night	9% 7% 26% 41% 15% 2	840
	21st to end	Night	11% 8% 30% 38% 12% 1	924
April	1st to 10th	Night	9% 8% 25% 41% 16% 2	840
	11th to 20th	Night	6% 10% 30% 41% 12% 1	749
	21st to end	Night	5% 8% 29% 41% 15% 2	630
May	1st to 10th	Night	7% 8% 29% 37% 17% 2	630
	11th to 20th	Night	8% 7% 19% 44% 19% 3	621
	21st to end	Night	7% 5% 18% 39% 27% 4	478
June	1st to 10th	Night	8% 7% 16% 43% 24% 3	420
	11th to 20th	Night	5% 7% 20% 48% 19% 1	420
	21st to end	Night	2 4 18% 53% 22% 1	420
July	1st to 10th	Night	2 1 13% 55% 28% 1	410
	11th to 20th	Night	1 1 15% 56% 26%	408
	21st to end	Night	3 1 8% 53% 33% 2	460
August	1st to 10th	Night	4 2 14% 52% 27% 1	622
	11th to 20th	Night	2 2 12% 53% 30% 1	606
	21st to end	Night	3 2 15% 45% 31% 3	816
September	1st to 10th	Night	3 2 11% 47% 34% 4	800
	11th to 20th	Night	6% 2 13% 39% 35% 5%	800
	21st to end	Night	6% 5% 14% 38% 30% 7%	800
October	1st to 10th	Night	7% 4 18% 41% 27% 3	800
	11th to 20th	Night	8% 5% 19% 39% 26% 4	800
	21st to end	Night	7% 4 24% 38% 23% 3	880
November	1st to 10th	Night	11% 4 20% 42% 21% 1	820
	11th to 20th	Night	10% 6% 25% 42% 16% 1	840
	21st to end	Night	10% 4 24% 38% 22% 2	840
December	1st to 10th	Night	13% 5% 23% 40% 18% 2	840
	11th to 20th	Night	16% 6% 20% 40% 15% 2	840
	21st to end	Night	18% 7% 30% 34% 10% 1	924

Page generated at 2026-08-12 01:37:14. Version ac07

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