Stony Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stony Ridge Observatory clear sky chart from 2005-11-06 to 2025-03-12.

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% 6% 2 6% 4 4 4 4 6% 8% 43%	109354
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 45%	109651
Transparency	Day	38% 6% 11% 19% 19% 6%	113070
	Night	37% 6% 10% 18% 21% 7%	114061
Seeing	Day	16% 10% 25% 24% 18% 7%	15656
	Night	15% 9% 24% 30% 18% 3	25816

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	15% 4 2 4 3 3 3 2 4 6% 54%	4056
	11th to 20th	Day	12% 6% 2 4 3 2 3 2 3 4 59%	4060
	21st to end	Day	17% 8% 3 6% 4 3 3 2 4 5% 45%	4466
February	1st to 10th	Day	14% 7% 3 6% 5% 4 4 3 6% 7% 42%	1850
	11th to 20th	Day	21% 6% 2 5% 3 3 4 3 4 5% 43%	1948
	21st to end	Day	18% 7% 2 6% 4 3 4 3 5% 5% 44%	1676
March	1st to 10th	Day	22% 9% 3 6% 4 3 3 2 4 5% 38%	3545
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 5% 6% 53%	3491
	21st to end	Day	20% 7% 3 5% 4 4 3 3 5% 5% 42%	3815
April	1st to 10th	Day	10% 4 1 5% 4 4 4 4 6% 6% 50%	2090
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 5% 6% 48%	2201
	21st to end	Day	9% 5% 2 4 4 4 4 3 6% 8% 51%	2448
May	1st to 10th	Day	10% 7% 2 7% 5% 4 5% 4 7% 9% 40%	4082
	11th to 20th	Day	17% 7% 3 7% 5% 4 5% 4 5% 7% 37%	4081
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 48%	4476
June	1st to 10th	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 10% 36%	2470
	11th to 20th	Day	7% 5% 2 7% 4 5% 6% 5% 10% 11% 40%	2470
	21st to end	Day	5% 4 2 7% 6% 6% 6% 6% 9% 11% 38%	2470
July	1st to 10th	Day	10% 7% 3 8% 5% 6% 7% 6% 9% 10% 29%	4120
	11th to 20th	Day	5% 5% 2 7% 7% 7% 7% 7% 9% 13% 30%	4120
	21st to end	Day	8% 8% 3 10% 7% 7% 7% 7% 8% 12% 23%	4466
August	1st to 10th	Day	19% 7% 2 8% 5% 6% 6% 6% 7% 10% 24%	4104
	11th to 20th	Day	11% 5% 2 7% 5% 7% 6% 5% 9% 12% 32%	4044
	21st to end	Day	7% 4 1 5% 4 5% 5% 4 7% 10% 48%	4165
September	1st to 10th	Day	8% 5% 2 7% 6% 5% 6% 4 7% 9% 40%	2090
	11th to 20th	Day	13% 7% 3 6% 5% 5% 4 3 6% 8% 38%	2090
	21st to end	Day	16% 7% 2 5% 4 4 4 4 5% 7% 42%	2090
October	1st to 10th	Day	15% 5% 2 5% 3 3 3 2 4 6% 52%	2013
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 4 5% 58%	1900
	21st to end	Day	11% 6% 2 5% 4 2 3 2 3 4 58%	2090
November	1st to 10th	Day	15% 6% 2 5% 3 3 3 3 4 5% 52%	1957
	11th to 20th	Day	14% 5% 2 4 3 3 3 3 4 6% 53%	1841
	21st to end	Day	14% 5% 2 5% 3 3 4 4 4 5% 50%	1800
December	1st to 10th	Day	12% 7% 3 5% 3 3 3 3 4 5% 51%	2930
	11th to 20th	Day	16% 6% 2 6% 3 3 4 3 5% 7% 45%	3373
	21st to end	Day	21% 6% 2 5% 3 2 3 2 5% 6% 46%	4466
January	1st to 10th	Night	12% 4 2 5% 3 3 3 3 3 4 57%	5889
	11th to 20th	Night	11% 6% 2 5% 3 4 3 3 5% 6% 51%	5900
	21st to end	Night	15% 9% 2 7% 3 3 3 2 4 5% 47%	6490
February	1st to 10th	Night	15% 7% 2 6% 3 3 3 4 5% 6% 45%	2545
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 4 5% 43%	2338
	21st to end	Night	15% 5% 2 6% 4 4 4 4 5% 6% 46%	1951
March	1st to 10th	Night	22% 8% 3 6% 4 4 3 3 5% 6% 36%	3528
	11th to 20th	Night	12% 4 2 4 3 3 4 3 6% 7% 51%	3498
	21st to end	Night	19% 5% 2 6% 3 4 4 3 5% 6% 43%	3817
April	1st to 10th	Night	11% 4 1 5% 4 4 4 4 5% 8% 50%	2090
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 4 7% 51%	1927
	21st to end	Night	8% 4 2 6% 4 4 3 3 5% 8% 52%	1746
May	1st to 10th	Night	11% 7% 2 6% 4 3 4 4 7% 10% 42%	2813
	11th to 20th	Night	15% 6% 3 6% 4 4 5% 4 6% 8% 40%	2812
	21st to end	Night	6% 3 1 6% 4 4 5% 4 7% 11% 47%	3079
June	1st to 10th	Night	11% 5% 3 7% 6% 6% 6% 5% 9% 10% 33%	1710
	11th to 20th	Night	8% 6% 2 6% 6% 4 5% 5% 8% 10% 41%	1710
	21st to end	Night	7% 6% 2 6% 5% 5% 6% 6% 9% 12% 34%	1710
July	1st to 10th	Night	12% 9% 3 8% 5% 6% 8% 5% 7% 10% 28%	2840
	11th to 20th	Night	8% 6% 2 9% 6% 5% 6% 6% 10% 12% 30%	2840
	21st to end	Night	11% 9% 4 10% 7% 6% 7% 6% 9% 10% 22%	3087
August	1st to 10th	Night	19% 8% 3 8% 5% 5% 6% 5% 7% 10% 23%	2825
	11th to 20th	Night	11% 7% 2 6% 5% 5% 5% 5% 8% 10% 35%	2785
	21st to end	Night	6% 4 2 5% 4 5% 5% 4 7% 10% 47%	3439
September	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 6% 10% 42%	2090
	11th to 20th	Night	13% 7% 2 7% 6% 5% 5% 4 6% 8% 37%	2090
	21st to end	Night	16% 5% 2 6% 4 4 3 3 5% 7% 44%	2090
October	1st to 10th	Night	13% 6% 2 5% 3 3 2 3 4 5% 52%	2166
	11th to 20th	Night	13% 5% 1 4 3 3 2 2 4 6% 56%	2280
	21st to end	Night	10% 5% 2 5% 4 3 3 2 3 5% 58%	2508
November	1st to 10th	Night	13% 6% 2 5% 3 2 3 3 4 5% 55%	2341
	11th to 20th	Night	13% 6% 3 4 4 3 3 3 4 6% 52%	2555
	21st to end	Night	14% 5% 2 4 4 3 4 3 5% 7% 49%	2600
December	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 4 5% 54%	4250
	11th to 20th	Night	17% 7% 3 5% 3 3 3 3 5% 6% 46%	4822
	21st to end	Night	20% 6% 2 5% 4 3 4 3 5% 6% 43%	6490

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	32% 3 6% 22% 30% 7%	4057
	11th to 20th	Day	31% 3 4 15% 38% 9%	4060
	21st to end	Day	43% 3 4 17% 22% 11%	4466
February	1st to 10th	Day	42% 4 9% 21% 19% 6%	1850
	11th to 20th	Day	44% 4 5% 18% 24% 5%	1958
	21st to end	Day	42% 4 9% 16% 20% 8%	1676
March	1st to 10th	Day	49% 4 7% 16% 14% 10%	3545
	11th to 20th	Day	31% 6% 9% 14% 30% 11%	3491
	21st to end	Day	44% 4 7% 18% 22% 4	3815
April	1st to 10th	Day	32% 5% 11% 19% 27% 6%	2090
	11th to 20th	Day	35% 5% 10% 18% 21% 10%	2201
	21st to end	Day	31% 6% 11% 26% 21% 5%	2448
May	1st to 10th	Day	37% 9% 16% 22% 14% 2	4120
	11th to 20th	Day	45% 7% 12% 19% 16% 1	4085
	21st to end	Day	29% 9% 16% 22% 21% 2	4489
June	1st to 10th	Day	39% 11% 16% 22% 10% 2	2470
	11th to 20th	Day	33% 9% 18% 25% 13% 1	2470
	21st to end	Day	36% 11% 17% 20% 14% 2	2470
July	1st to 10th	Day	45% 10% 18% 18% 7% 2	4055
	11th to 20th	Day	40% 12% 26% 18% 4 1	4051
	21st to end	Day	50% 12% 18% 15% 4 1	4324
August	1st to 10th	Day	54% 7% 17% 17% 5%	4091
	11th to 20th	Day	42% 9% 16% 18% 13% 1	4083
	21st to end	Day	30% 8% 15% 29% 16% 3	4165
September	1st to 10th	Day	37% 10% 14% 18% 18% 4	2090
	11th to 20th	Day	43% 7% 11% 18% 19% 3	2090
	21st to end	Day	41% 6% 10% 20% 16% 7%	2090
October	1st to 10th	Day	33% 4 4 18% 30% 10%	3338
	11th to 20th	Day	19% 3 5% 16% 26% 31%	3140
	21st to end	Day	27% 3 4 21% 30% 15%	3428
November	1st to 10th	Day	35% 4 7% 18% 26% 11%	1957
	11th to 20th	Day	32% 4 7% 21% 26% 10%	1841
	21st to end	Day	36% 4 8% 19% 24% 9%	1800
December	1st to 10th	Day	36% 3 6% 17% 28% 10%	2930
	11th to 20th	Day	39% 4 10% 20% 19% 7%	3370
	21st to end	Day	40% 4 7% 22% 24% 2	4466
January	1st to 10th	Night	31% 4 5% 19% 35% 7%	5889
	11th to 20th	Night	34% 4 5% 16% 33% 8%	5900
	21st to end	Night	41% 3 4 15% 28% 9%	6490
February	1st to 10th	Night	39% 4 8% 20% 20% 8%	2545
	11th to 20th	Night	44% 4 7% 17% 21% 8%	2339
	21st to end	Night	37% 6% 9% 16% 22% 10%	1951
March	1st to 10th	Night	47% 6% 11% 13% 17% 7%	3528
	11th to 20th	Night	32% 4 9% 14% 26% 15%	3498
	21st to end	Night	42% 5% 8% 19% 19% 8%	3817
April	1st to 10th	Night	33% 5% 12% 18% 24% 8%	2090
	11th to 20th	Night	32% 4 10% 20% 22% 11%	1927
	21st to end	Night	29% 5% 12% 26% 23% 5%	1746
May	1st to 10th	Night	36% 8% 14% 24% 15% 3	2840
	11th to 20th	Night	39% 9% 16% 20% 16% 1	2813
	21st to end	Night	26% 11% 14% 26% 21% 2	3087
June	1st to 10th	Night	42% 11% 16% 20% 11% 2	1710
	11th to 20th	Night	35% 10% 18% 22% 12% 2	1710
	21st to end	Night	37% 12% 17% 19% 12% 2	1710
July	1st to 10th	Night	48% 10% 19% 14% 7% 2	2795
	11th to 20th	Night	42% 13% 26% 15% 4 1	2786
	21st to end	Night	54% 13% 17% 12% 4 1	2988
August	1st to 10th	Night	55% 9% 18% 14% 4	2814
	11th to 20th	Night	41% 9% 22% 19% 9% 1	2812
	21st to end	Night	29% 8% 15% 27% 17% 3	3439
September	1st to 10th	Night	36% 10% 15% 18% 16% 5%	2090
	11th to 20th	Night	44% 8% 12% 16% 17% 3	2090
	21st to end	Night	39% 7% 12% 19% 18% 5%	2090
October	1st to 10th	Night	32% 4 8% 17% 32% 6%	3608
	11th to 20th	Night	20% 3 5% 16% 26% 30%	3779
	21st to end	Night	26% 3 5% 19% 28% 19%	4120
November	1st to 10th	Night	33% 3 8% 17% 26% 13%	2341
	11th to 20th	Night	34% 3 7% 17% 25% 13%	2555
	21st to end	Night	35% 4 7% 20% 25% 9%	2600
December	1st to 10th	Night	35% 3 6% 17% 30% 9%	4250
	11th to 20th	Night	40% 3 12% 16% 20% 9%	4824
	21st to end	Night	43% 4 7% 25% 19% 3	6490

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	23% 22% 40% 13% 2	300
	11th to 20th	Day	24% 23% 33% 17% 3	300
	21st to end	Day	27% 21% 38% 12% 3	330
February	1st to 10th	Day	19% 22% 39% 15% 5%	300
	11th to 20th	Day	38% 17% 32% 12%	300
	21st to end	Day	25% 21% 35% 16% 3	275
March	1st to 10th	Day	24% 15% 35% 18% 7% 1	500
	11th to 20th	Day	20% 18% 41% 16% 5%	464
	21st to end	Day	22% 18% 37% 15% 7%	506
April	1st to 10th	Day	20% 16% 33% 19% 10% 1	460
	11th to 20th	Day	16% 14% 34% 22% 12% 2	452
	21st to end	Day	14% 11% 31% 25% 15% 3	460
May	1st to 10th	Day	11% 13% 33% 26% 12% 3	463
	11th to 20th	Day	16% 7% 21% 31% 17% 8%	487
	21st to end	Day	12% 6% 20% 24% 25% 12%	529
June	1st to 10th	Day	11% 5% 19% 32% 25% 7%	490
	11th to 20th	Day	9% 4 20% 28% 26% 13%	490
	21st to end	Day	7% 2 18% 35% 27% 10%	490
July	1st to 10th	Day	7% 4 11% 25% 31% 22%	485
	11th to 20th	Day	7% 4 11% 29% 33% 15%	484
	21st to end	Day	6% 2 11% 36% 34% 11%	532
August	1st to 10th	Day	14% 4 13% 28% 28% 13%	486
	11th to 20th	Day	13% 4 10% 29% 31% 14%	479
	21st to end	Day	13% 2 12% 29% 29% 15%	539
September	1st to 10th	Day	9% 3 15% 29% 35% 10%	490
	11th to 20th	Day	17% 5% 16% 24% 28% 10%	490
	21st to end	Day	18% 5% 19% 28% 24% 7%	490
October	1st to 10th	Day	17% 4 26% 26% 20% 7%	490
	11th to 20th	Day	12% 9% 25% 28% 20% 5%	490
	21st to end	Day	15% 7% 26% 28% 19% 5%	539
November	1st to 10th	Day	20% 7% 26% 25% 15% 5%	495
	11th to 20th	Day	19% 11% 37% 25% 6% 1	341
	21st to end	Day	14% 13% 38% 23% 10% 2	300
December	1st to 10th	Day	27% 16% 37% 15% 4 1	300
	11th to 20th	Day	24% 12% 37% 20% 6% 2	300
	21st to end	Day	30% 15% 31% 16% 5% 3	330
January	1st to 10th	Night	21% 19% 29% 26% 6%	800
	11th to 20th	Night	19% 16% 33% 25% 7%	800
	21st to end	Night	21% 20% 33% 23% 3	880
February	1st to 10th	Night	20% 16% 28% 31% 4	800
	11th to 20th	Night	24% 16% 36% 22% 2	783
	21st to end	Night	18% 17% 35% 28% 3	660
March	1st to 10th	Night	19% 13% 35% 28% 6%	800
	11th to 20th	Night	18% 14% 37% 24% 7% 1	767
	21st to end	Night	17% 15% 37% 25% 6%	836
April	1st to 10th	Night	15% 16% 31% 28% 9%	760
	11th to 20th	Night	14% 12% 28% 32% 13%	751
	21st to end	Night	10% 10% 31% 35% 14%	606
May	1st to 10th	Night	11% 8% 32% 34% 14% 1	570
	11th to 20th	Night	12% 4 28% 33% 20% 3	561
	21st to end	Night	11% 2 15% 37% 31% 4	617
June	1st to 10th	Night	12% 4 18% 38% 25% 4	570
	11th to 20th	Night	10% 3 15% 33% 29% 9%	570
	21st to end	Night	9% 3 14% 38% 30% 6%	570
July	1st to 10th	Night	9% 2 10% 34% 37% 9%	555
	11th to 20th	Night	9% 2 7% 34% 38% 9%	552
	21st to end	Night	8% 3 11% 34% 36% 7%	624
August	1st to 10th	Night	12% 2 11% 30% 38% 6%	567
	11th to 20th	Night	13% 1 10% 34% 35% 7%	564
	21st to end	Night	11% 3 11% 31% 37% 6%	757
September	1st to 10th	Night	9% 2 13% 33% 37% 6%	760
	11th to 20th	Night	15% 3 14% 27% 35% 6%	760
	21st to end	Night	18% 4 15% 32% 28% 4	760
October	1st to 10th	Night	14% 6% 18% 30% 28% 4	760
	11th to 20th	Night	16% 6% 23% 30% 22% 3	760
	21st to end	Night	13% 8% 23% 32% 23% 2	836
November	1st to 10th	Night	16% 7% 23% 33% 18% 3	780
	11th to 20th	Night	15% 12% 30% 31% 11% 1	800
	21st to end	Night	15% 10% 28% 33% 13% 1	800
December	1st to 10th	Night	20% 14% 27% 31% 9% 1	800
	11th to 20th	Night	20% 10% 26% 33% 10% 1	800
	21st to end	Night	25% 14% 25% 28% 8%	880

Page generated at 2025-03-09 08:08:47. Version ac07

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