Standing Stone Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Standing Stone Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	14% 8% 3 6% 6% 4 5% 5% 6% 7% 35%	74956
	Night	13% 9% 4 6% 6% 3 5% 5% 5% 7% 37%	74853
Transparency	Day	47% 8% 12% 19% 12% 2	74678
	Night	45% 8% 12% 20% 13% 2	74650
Seeing	Day	23% 14% 24% 21% 13% 6%	14073
	Night	20% 13% 21% 28% 17% 2	24227

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	14% 11% 5% 10% 9% 4 4 4 4 7% 29%	1706
	11th to 20th	Day	17% 13% 6% 10% 7% 4 5% 3 3 5% 27%	1665
	21st to end	Day	16% 12% 5% 8% 6% 3 4 4 4 6% 33%	1782
February	1st to 10th	Day	14% 11% 5% 9% 7% 4 4 5% 5% 7% 30%	1620
	11th to 20th	Day	18% 10% 5% 8% 5% 3 5% 4 4 7% 30%	1645
	21st to end	Day	18% 12% 4 9% 5% 3 4 3 5% 6% 31%	1512
March	1st to 10th	Day	15% 8% 4 6% 5% 2 3 4 5% 7% 41%	1980
	11th to 20th	Day	19% 9% 5% 8% 5% 2 4 4 5% 6% 33%	1980
	21st to end	Day	16% 10% 4 7% 6% 4 4 4 5% 7% 33%	2178
April	1st to 10th	Day	12% 9% 3 6% 5% 3 4 4 5% 8% 41%	2020
	11th to 20th	Day	14% 8% 3 6% 6% 3 4 4 4 7% 41%	2134
	21st to end	Day	18% 7% 3 5% 6% 3 6% 4 6% 7% 36%	2340
May	1st to 10th	Day	17% 8% 4 6% 6% 4 5% 5% 7% 7% 33%	2340
	11th to 20th	Day	20% 7% 3 6% 6% 4 5% 5% 6% 8% 29%	2301
	21st to end	Day	12% 7% 3 6% 6% 4 7% 6% 7% 9% 33%	2531
June	1st to 10th	Day	12% 6% 3 6% 6% 4 6% 6% 6% 8% 38%	2340
	11th to 20th	Day	10% 6% 3 6% 7% 4 6% 7% 7% 9% 36%	2340
	21st to end	Day	9% 6% 2 6% 6% 4 6% 6% 8% 9% 37%	2340
July	1st to 10th	Day	11% 7% 3 7% 6% 5% 6% 5% 7% 9% 36%	2340
	11th to 20th	Day	8% 5% 3 5% 6% 5% 7% 7% 8% 10% 36%	2340
	21st to end	Day	11% 6% 3 7% 7% 5% 7% 7% 7% 9% 30%	2547
August	1st to 10th	Day	13% 7% 3 6% 7% 4 7% 7% 8% 10% 28%	2327
	11th to 20th	Day	15% 7% 3 6% 8% 4 6% 7% 7% 9% 30%	2303
	21st to end	Day	10% 6% 3 6% 7% 4 6% 6% 8% 10% 35%	2440
September	1st to 10th	Day	12% 5% 3 5% 5% 4 5% 6% 7% 7% 41%	2082
	11th to 20th	Day	12% 8% 4 7% 6% 4 6% 4 5% 6% 39%	1980
	21st to end	Day	19% 6% 3 5% 6% 4 4 5% 5% 6% 37%	1980
October	1st to 10th	Day	16% 6% 2 5% 5% 2 4 4 6% 7% 44%	1838
	11th to 20th	Day	17% 9% 3 5% 5% 3 3 4 4 6% 43%	1800
	21st to end	Day	16% 10% 3 6% 4 3 4 4 3 6% 42%	1980
November	1st to 10th	Day	11% 7% 3 4 5% 3 4 4 5% 6% 48%	1838
	11th to 20th	Day	12% 9% 4 6% 5% 3 5% 5% 5% 6% 40%	1710
	21st to end	Day	14% 9% 4 6% 4 4 4 4 5% 6% 40%	1710
December	1st to 10th	Day	19% 13% 4 9% 5% 3 5% 5% 5% 6% 27%	1710
	11th to 20th	Day	17% 13% 4 6% 4 2 4 3 4 8% 35%	2153
	21st to end	Day	18% 13% 4 7% 7% 4 6% 5% 6% 7% 23%	3124
January	1st to 10th	Night	14% 12% 5% 10% 8% 4 4 4 6% 5% 28%	2459
	11th to 20th	Night	19% 13% 5% 9% 6% 3 5% 4 5% 5% 27%	2406
	21st to end	Night	14% 13% 7% 7% 7% 3 5% 4 5% 4 32%	2574
February	1st to 10th	Night	15% 10% 5% 8% 6% 4 5% 4 5% 9% 30%	2340
	11th to 20th	Night	19% 9% 5% 9% 7% 4 5% 5% 4 6% 27%	2199
	21st to end	Night	17% 10% 5% 8% 6% 4 5% 4 5% 5% 31%	1742
March	1st to 10th	Night	13% 10% 4 6% 4 3 5% 4 5% 6% 40%	1980
	11th to 20th	Night	18% 8% 4 7% 6% 2 5% 5% 6% 7% 32%	1980
	21st to end	Night	15% 9% 3 6% 6% 3 6% 5% 5% 6% 36%	2178
April	1st to 10th	Night	11% 9% 4 6% 5% 4 4 4 5% 8% 40%	1940
	11th to 20th	Night	13% 6% 3 5% 5% 4 5% 4 6% 8% 41%	1775
	21st to end	Night	15% 6% 3 6% 5% 3 5% 5% 5% 8% 40%	1634
May	1st to 10th	Night	16% 7% 4 5% 5% 3 5% 5% 6% 6% 38%	1620
	11th to 20th	Night	13% 7% 4 7% 6% 3 5% 5% 5% 9% 35%	1592
	21st to end	Night	10% 6% 2 6% 5% 4 5% 6% 7% 10% 39%	1744
June	1st to 10th	Night	7% 6% 3 5% 5% 3 5% 5% 7% 10% 44%	1620
	11th to 20th	Night	10% 6% 2 5% 5% 3 5% 5% 6% 10% 44%	1620
	21st to end	Night	9% 5% 2 4 5% 3 4 7% 7% 11% 44%	1620
July	1st to 10th	Night	9% 5% 3 7% 6% 4 5% 6% 8% 8% 40%	1620
	11th to 20th	Night	7% 3 2 4 5% 3 6% 5% 8% 10% 48%	1620
	21st to end	Night	7% 4 2 5% 5% 4 6% 6% 8% 11% 41%	1771
August	1st to 10th	Night	10% 6% 3 7% 6% 4 7% 5% 5% 9% 39%	1611
	11th to 20th	Night	12% 6% 3 6% 5% 3 5% 4 6% 8% 42%	1598
	21st to end	Night	9% 5% 2 5% 6% 3 5% 5% 7% 8% 45%	1898
September	1st to 10th	Night	10% 6% 2 5% 5% 3 4 5% 6% 6% 47%	1875
	11th to 20th	Night	11% 5% 3 5% 6% 2 5% 5% 5% 8% 45%	1980
	21st to end	Night	13% 7% 3 6% 4 4 5% 5% 5% 7% 40%	1980
October	1st to 10th	Night	14% 6% 3 4 5% 3 5% 4 5% 7% 46%	2120
	11th to 20th	Night	13% 8% 3 6% 5% 3 5% 4 4 6% 44%	2160
	21st to end	Night	14% 9% 3 5% 6% 2 4 4 5% 5% 43%	2376
November	1st to 10th	Night	12% 7% 3 5% 4 3 4 4 4 6% 48%	2237
	11th to 20th	Night	12% 9% 4 6% 5% 3 4 5% 5% 6% 41%	2470
	21st to end	Night	13% 9% 3 7% 6% 3 5% 5% 5% 6% 40%	2470
December	1st to 10th	Night	18% 12% 5% 8% 6% 3 5% 4 5% 6% 28%	2470
	11th to 20th	Night	15% 10% 6% 8% 6% 3 5% 4 5% 6% 31%	3042
	21st to end	Night	17% 15% 6% 8% 6% 3 5% 4 5% 6% 24%	4532

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	57% 5% 8% 18% 10% 1	1707
	11th to 20th	Day	60% 5% 9% 15% 9% 1	1665
	21st to end	Day	54% 5% 9% 18% 12% 2	1782
February	1st to 10th	Day	54% 6% 8% 20% 10% 2	1620
	11th to 20th	Day	55% 5% 10% 17% 11% 2	1654
	21st to end	Day	55% 5% 9% 15% 13% 3	1512
March	1st to 10th	Day	43% 5% 11% 25% 14% 3	1980
	11th to 20th	Day	53% 6% 10% 16% 12% 3	1980
	21st to end	Day	51% 7% 9% 20% 10% 2	2178
April	1st to 10th	Day	43% 7% 11% 20% 15% 4	2020
	11th to 20th	Day	44% 6% 11% 22% 15% 3	2134
	21st to end	Day	47% 8% 12% 20% 11% 2	2340
May	1st to 10th	Day	49% 10% 12% 17% 11% 1	2340
	11th to 20th	Day	52% 10% 13% 19% 5% 2	2305
	21st to end	Day	45% 12% 16% 18% 9%	2531
June	1st to 10th	Day	42% 10% 14% 21% 13%	2340
	11th to 20th	Day	42% 11% 16% 17% 14% 1	2340
	21st to end	Day	41% 11% 14% 21% 12% 1	2340
July	1st to 10th	Day	44% 12% 13% 18% 11% 2	2275
	11th to 20th	Day	39% 13% 16% 17% 14% 1	2271
	21st to end	Day	46% 11% 14% 19% 9% 1	2405
August	1st to 10th	Day	46% 12% 17% 18% 7%	2314
	11th to 20th	Day	48% 13% 13% 18% 8%	2303
	21st to end	Day	40% 12% 17% 18% 11% 2	2440
September	1st to 10th	Day	39% 9% 14% 19% 15% 3	2082
	11th to 20th	Day	44% 7% 10% 21% 17% 1	1980
	21st to end	Day	48% 7% 11% 18% 15% 1	1980
October	1st to 10th	Day	39% 7% 13% 22% 15% 4	1838
	11th to 20th	Day	42% 6% 11% 21% 17% 2	1800
	21st to end	Day	45% 5% 8% 24% 15% 3	1980
November	1st to 10th	Day	36% 5% 10% 23% 23% 3	1838
	11th to 20th	Day	44% 5% 8% 20% 19% 3	1710
	21st to end	Day	44% 5% 11% 21% 16% 2	1710
December	1st to 10th	Day	57% 6% 9% 16% 9% 2	1710
	11th to 20th	Day	49% 4 9% 19% 17% 1	2150
	21st to end	Day	57% 9% 10% 17% 7%	3124
January	1st to 10th	Night	57% 6% 9% 14% 12% 2	2459
	11th to 20th	Night	59% 5% 8% 14% 11% 2	2406
	21st to end	Night	55% 5% 9% 19% 11% 1	2574
February	1st to 10th	Night	53% 6% 11% 18% 11% 1	2340
	11th to 20th	Night	58% 6% 7% 15% 11% 3	2201
	21st to end	Night	55% 5% 10% 16% 9% 4	1742
March	1st to 10th	Night	46% 5% 10% 20% 16% 3	1980
	11th to 20th	Night	51% 7% 11% 21% 10% 1	1980
	21st to end	Night	47% 8% 12% 17% 14% 3	2178
April	1st to 10th	Night	44% 8% 12% 20% 14% 3	1940
	11th to 20th	Night	39% 6% 14% 20% 17% 4	1775
	21st to end	Night	42% 8% 14% 24% 11% 1	1634
May	1st to 10th	Night	45% 9% 14% 18% 12% 2	1620
	11th to 20th	Night	46% 10% 17% 19% 7% 1	1593
	21st to end	Night	40% 12% 17% 24% 7% 1	1745
June	1st to 10th	Night	35% 11% 17% 23% 13% 1	1620
	11th to 20th	Night	34% 11% 19% 21% 13% 1	1620
	21st to end	Night	32% 12% 19% 23% 13% 2	1620
July	1st to 10th	Night	38% 13% 16% 17% 13% 3	1575
	11th to 20th	Night	30% 12% 20% 22% 13% 3	1566
	21st to end	Night	32% 13% 18% 25% 12%	1672
August	1st to 10th	Night	40% 11% 17% 23% 9%	1600
	11th to 20th	Night	39% 9% 16% 23% 11% 1	1598
	21st to end	Night	33% 11% 16% 26% 11% 2	1898
September	1st to 10th	Night	36% 10% 15% 20% 15% 4	1875
	11th to 20th	Night	35% 8% 12% 25% 18% 2	1980
	21st to end	Night	42% 8% 13% 23% 14% 1	1980
October	1st to 10th	Night	37% 8% 12% 24% 17% 3	2120
	11th to 20th	Night	41% 5% 10% 24% 17% 2	2160
	21st to end	Night	42% 5% 8% 24% 15% 5%	2376
November	1st to 10th	Night	37% 6% 10% 21% 22% 4	2237
	11th to 20th	Night	43% 5% 9% 19% 19% 4	2470
	21st to end	Night	45% 6% 9% 21% 16% 3	2470
December	1st to 10th	Night	57% 6% 9% 18% 8% 2	2470
	11th to 20th	Night	53% 6% 9% 17% 14% 1	3044
	21st to end	Night	58% 8% 10% 14% 9%	4532

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	39% 26% 21% 9% 4 1	270
	11th to 20th	Day	39% 25% 28% 7% 1	255
	21st to end	Day	41% 25% 23% 9% 3	264
February	1st to 10th	Day	35% 26% 27% 10% 1	240
	11th to 20th	Day	52% 22% 18% 7% 1	240
	21st to end	Day	44% 22% 24% 7% 2	230
March	1st to 10th	Day	33% 22% 23% 18% 4	420
	11th to 20th	Day	32% 25% 23% 13% 5% 1	420
	21st to end	Day	29% 23% 26% 15% 7%	462
April	1st to 10th	Day	25% 25% 25% 15% 9% 1	420
	11th to 20th	Day	25% 17% 27% 17% 11% 3	412
	21st to end	Day	30% 20% 22% 15% 10% 2	420
May	1st to 10th	Day	26% 19% 28% 14% 10% 4	423
	11th to 20th	Day	22% 12% 28% 20% 12% 5%	447
	21st to end	Day	15% 9% 25% 23% 18% 9%	485
June	1st to 10th	Day	13% 12% 25% 24% 17% 8%	450
	11th to 20th	Day	11% 11% 28% 24% 17% 8%	450
	21st to end	Day	12% 12% 26% 27% 16% 8%	450
July	1st to 10th	Day	12% 6% 21% 27% 21% 13%	445
	11th to 20th	Day	5% 5% 20% 36% 20% 14%	444
	21st to end	Day	13% 5% 22% 28% 20% 13%	488
August	1st to 10th	Day	16% 6% 21% 22% 22% 13%	446
	11th to 20th	Day	15% 5% 20% 22% 23% 14%	439
	21st to end	Day	11% 5% 19% 27% 23% 15%	495
September	1st to 10th	Day	13% 6% 20% 25% 23% 13%	450
	11th to 20th	Day	13% 4 17% 28% 26% 11%	450
	21st to end	Day	22% 11% 20% 28% 16% 3	450
October	1st to 10th	Day	18% 9% 24% 26% 18% 6%	450
	11th to 20th	Day	20% 15% 22% 25% 16% 2	450
	21st to end	Day	25% 15% 25% 21% 12% 2	495
November	1st to 10th	Day	21% 13% 28% 24% 11% 3	436
	11th to 20th	Day	31% 17% 25% 19% 7%	270
	21st to end	Day	27% 19% 30% 19% 5% 1	270
December	1st to 10th	Day	36% 24% 25% 10% 4 1	270
	11th to 20th	Day	33% 20% 26% 15% 6% 1	270
	21st to end	Day	33% 21% 24% 14% 7% 1	297
January	1st to 10th	Night	30% 23% 25% 18% 3	760
	11th to 20th	Night	34% 19% 25% 20% 3	741
	21st to end	Night	30% 22% 28% 18% 2	792
February	1st to 10th	Night	28% 18% 29% 23% 2	720
	11th to 20th	Night	34% 26% 24% 17%	703
	21st to end	Night	26% 26% 28% 18% 1	592
March	1st to 10th	Night	26% 19% 29% 23% 3	720
	11th to 20th	Night	28% 21% 23% 20% 8%	720
	21st to end	Night	23% 17% 28% 24% 7%	792
April	1st to 10th	Night	20% 21% 27% 25% 7%	720
	11th to 20th	Night	19% 15% 26% 27% 12%	711
	21st to end	Night	17% 15% 25% 35% 8%	554
May	1st to 10th	Night	19% 14% 23% 30% 14% 1	540
	11th to 20th	Night	15% 10% 22% 34% 17% 1	531
	21st to end	Night	11% 5% 16% 34% 28% 5%	584
June	1st to 10th	Night	8% 5% 18% 39% 28% 3	540
	11th to 20th	Night	11% 4 13% 34% 35% 2	540
	21st to end	Night	9% 4 15% 40% 29% 3	540
July	1st to 10th	Night	10% 2 11% 39% 33% 6%	525
	11th to 20th	Night	6% 3 9% 33% 45% 5%	522
	21st to end	Night	8% 3 10% 36% 39% 5%	591
August	1st to 10th	Night	12% 2 11% 35% 37% 3	537
	11th to 20th	Night	14% 2 11% 30% 37% 5%	534
	21st to end	Night	10% 2 9% 33% 39% 6%	710
September	1st to 10th	Night	12% 5% 11% 32% 35% 6%	720
	11th to 20th	Night	12% 4 13% 32% 35% 4	720
	21st to end	Night	15% 7% 18% 30% 28% 2	720
October	1st to 10th	Night	14% 9% 19% 29% 26% 3	720
	11th to 20th	Night	17% 15% 20% 29% 18% 1	720
	21st to end	Night	21% 13% 21% 32% 12% 2	792
November	1st to 10th	Night	17% 9% 23% 34% 15% 1	740
	11th to 20th	Night	24% 15% 20% 30% 10% 1	760
	21st to end	Night	20% 17% 21% 32% 8% 1	760
December	1st to 10th	Night	31% 20% 25% 19% 6%	760
	11th to 20th	Night	25% 19% 26% 25% 5%	760
	21st to end	Night	27% 17% 26% 27% 3	836

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