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 2005-11-05 to 2024-10-14.

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 5% 4 6% 8% 42%	100932
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 43%	97559
Transparency	Day	39% 7% 12% 19% 18% 5%	100746
	Night	39% 7% 11% 18% 19% 6%	97420
Seeing	Day	16% 10% 25% 24% 18% 7%	15166
	Night	15% 9% 24% 30% 18% 3	25220

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	17% 4 2 4 4 3 4 3 5% 8% 47%	2836
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 5% 54%	2840
	21st to end	Day	21% 8% 2 6% 3 3 3 2 3 5% 44%	3124
February	1st to 10th	Day	15% 7% 3 6% 5% 4 4 4 6% 7% 41%	1757
	11th to 20th	Day	20% 6% 2 5% 3 3 4 3 4 5% 44%	1848
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 5% 42%	1594
March	1st to 10th	Day	23% 9% 3 6% 4 3 3 2 4 5% 38%	3435
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 5% 6% 53%	3480
	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 5% 5% 57%	1830
	21st to end	Day	11% 6% 2 5% 4 2 2 2 3 4 57%	1980
November	1st to 10th	Day	14% 5% 2 5% 3 3 2 3 4 5% 55%	1857
	11th to 20th	Day	14% 5% 2 4 3 3 3 3 4 6% 53%	1749
	21st to end	Day	15% 5% 2 5% 3 3 4 3 4 5% 49%	1710
December	1st to 10th	Day	17% 9% 4 6% 4 3 3 4 5% 6% 40%	1710
	11th to 20th	Day	17% 4 1 4 3 3 4 3 4 6% 50%	2153
	21st to end	Day	19% 7% 2 5% 3 3 4 2 5% 6% 43%	3124
January	1st to 10th	Night	17% 5% 2 6% 4 3 4 3 4 5% 47%	4109
	11th to 20th	Night	10% 7% 2 5% 4 5% 4 4 6% 6% 45%	4120
	21st to end	Night	19% 9% 2 7% 3 3 3 2 3 4 45%	4532
February	1st to 10th	Night	16% 8% 2 6% 3 3 3 4 5% 6% 44%	2418
	11th to 20th	Night	19% 7% 2 5% 4 4 4 3 4 5% 44%	2218
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 6% 44%	1857
March	1st to 10th	Night	23% 8% 3 6% 4 4 3 3 5% 6% 35%	3418
	11th to 20th	Night	12% 4 2 5% 3 3 4 3 6% 7% 51%	3480
	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% 55%	2203
	21st to end	Night	11% 4 2 5% 4 3 3 2 4 5% 57%	2376
November	1st to 10th	Night	12% 6% 2 5% 3 2 3 3 4 5% 57%	2221
	11th to 20th	Night	13% 6% 3 4 4 3 3 3 4 6% 53%	2427
	21st to end	Night	14% 5% 2 5% 4 3 4 3 5% 7% 48%	2470
December	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 4 5% 43%	2470
	11th to 20th	Night	17% 5% 3 4 3 2 2 3 4 5% 53%	3042
	21st to end	Night	19% 7% 2 6% 4 4 4 3 5% 6% 40%	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	35% 4 8% 23% 22% 7%	2837
	11th to 20th	Day	34% 4 5% 17% 30% 9%	2840
	21st to end	Day	44% 4 4 16% 25% 7%	3124
February	1st to 10th	Day	42% 4 9% 20% 19% 5%	1757
	11th to 20th	Day	42% 5% 5% 18% 24% 6%	1858
	21st to end	Day	43% 5% 10% 16% 19% 8%	1594
March	1st to 10th	Day	49% 5% 7% 16% 14% 10%	3435
	11th to 20th	Day	31% 6% 9% 14% 30% 10%	3480
	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	35% 4 6% 21% 25% 8%	2013
	11th to 20th	Day	30% 4 8% 24% 24% 10%	1831
	21st to end	Day	31% 4 6% 18% 30% 11%	1980
November	1st to 10th	Day	33% 4 6% 18% 27% 11%	1857
	11th to 20th	Day	32% 4 7% 21% 25% 10%	1749
	21st to end	Day	37% 4 8% 19% 23% 9%	1710
December	1st to 10th	Day	45% 5% 8% 19% 16% 6%	1710
	11th to 20th	Day	35% 5% 7% 20% 22% 11%	2150
	21st to end	Day	41% 5% 7% 20% 23% 3	3124
January	1st to 10th	Night	37% 5% 6% 19% 25% 7%	4109
	11th to 20th	Night	36% 6% 7% 18% 25% 8%	4120
	21st to end	Night	44% 4 4 15% 25% 7%	4532
February	1st to 10th	Night	40% 4 8% 19% 21% 8%	2418
	11th to 20th	Night	43% 4 7% 17% 21% 8%	2219
	21st to end	Night	39% 6% 9% 17% 21% 9%	1857
March	1st to 10th	Night	48% 6% 11% 13% 15% 7%	3418
	11th to 20th	Night	32% 4 9% 14% 26% 14%	3480
	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	34% 5% 9% 17% 29% 6%	2166
	11th to 20th	Night	31% 4 9% 22% 22% 12%	2207
	21st to end	Night	31% 3 6% 19% 27% 13%	2376
November	1st to 10th	Night	32% 3 8% 17% 27% 14%	2221
	11th to 20th	Night	34% 4 7% 18% 24% 14%	2427
	21st to end	Night	36% 4 7% 20% 24% 9%	2470
December	1st to 10th	Night	43% 5% 8% 19% 19% 7%	2470
	11th to 20th	Night	36% 3 8% 17% 26% 10%	3044
	21st to end	Night	44% 5% 8% 20% 20% 4	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	23% 22% 39% 14% 2	270
	11th to 20th	Day	24% 23% 32% 18% 3	270
	21st to end	Day	27% 21% 37% 12% 3	297
February	1st to 10th	Day	20% 23% 38% 14% 5%	270
	11th to 20th	Day	35% 17% 34% 13%	270
	21st to end	Day	27% 22% 35% 13% 3	249
March	1st to 10th	Day	22% 15% 36% 18% 8% 1	460
	11th to 20th	Day	20% 18% 42% 15% 5%	460
	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	13% 9% 24% 28% 21% 5%	462
	21st to end	Day	16% 7% 26% 29% 17% 5%	495
November	1st to 10th	Day	19% 7% 27% 25% 16% 6%	455
	11th to 20th	Day	19% 11% 38% 26% 6% 1	309
	21st to end	Day	13% 14% 37% 24% 10% 2	270
December	1st to 10th	Day	29% 13% 37% 15% 5% 1	270
	11th to 20th	Day	24% 13% 36% 20% 5% 2	270
	21st to end	Day	29% 16% 32% 15% 5% 3	297
January	1st to 10th	Night	22% 19% 28% 26% 6%	760
	11th to 20th	Night	19% 16% 33% 26% 7%	760
	21st to end	Night	21% 19% 33% 24% 3	836
February	1st to 10th	Night	21% 15% 28% 31% 4	760
	11th to 20th	Night	23% 15% 37% 22% 2	743
	21st to end	Night	18% 17% 35% 27% 3	628
March	1st to 10th	Night	19% 13% 35% 28% 6%	760
	11th to 20th	Night	18% 14% 37% 24% 7% 1	760
	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	735
	21st to end	Night	13% 8% 24% 32% 22% 2	792
November	1st to 10th	Night	15% 8% 23% 33% 18% 3	740
	11th to 20th	Night	15% 11% 31% 31% 11% 1	760
	21st to end	Night	15% 10% 27% 33% 14% 1	760
December	1st to 10th	Night	20% 13% 26% 31% 9% 1	760
	11th to 20th	Night	20% 10% 26% 33% 10% 1	760
	21st to end	Night	25% 14% 25% 27% 8%	836

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