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 2026-07-16.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	138032
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	134647
Transparency	Day	39% 6% 12% 19% 18% 6%	141704
	Night	38% 5% 11% 18% 20% 7%	139034
Seeing	Day	16% 10% 26% 25% 18% 6%	17513
	Night	15% 9% 24% 31% 18% 2	27569

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% 4 2 6% 4 3 4 3 5% 7% 49%	5258
	11th to 20th	Day	12% 6% 2 4 3 2 2 2 3 4 61%	5280
	21st to end	Day	19% 9% 3 7% 4 3 3 3 4 5% 40%	5780
February	1st to 10th	Day	14% 7% 3 5% 5% 4 4 4 6% 6% 42%	1943
	11th to 20th	Day	21% 6% 2 5% 3 3 4 3 4 5% 43%	2048
	21st to end	Day	19% 7% 2 6% 4 3 3 3 5% 5% 43%	1757
March	1st to 10th	Day	20% 8% 3 7% 4 3 3 2 4 5% 39%	5045
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 4 6% 54%	5090
	21st to end	Day	16% 7% 3 6% 4 4 3 3 4 4 46%	5586
April	1st to 10th	Day	10% 4 2 5% 4 4 4 5% 6% 7% 49%	2310
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 6% 50%	2435
	21st to end	Day	9% 6% 2 4 4 5% 4 3 6% 8% 50%	2706
May	1st to 10th	Day	13% 7% 2 7% 4 4 5% 4 6% 9% 39%	7616
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 38%	7626
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 35%	8391
June	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 36%	2730
	11th to 20th	Day	7% 5% 2 7% 4 5% 5% 5% 10% 12% 39%	2730
	21st to end	Day	5% 4 2 7% 6% 6% 6% 6% 9% 11% 39%	2730
July	1st to 10th	Day	9% 7% 3 8% 6% 7% 7% 6% 9% 10% 29%	6030
	11th to 20th	Day	4 5% 2 7% 6% 7% 7% 7% 10% 14% 31%	5965
	21st to end	Day	7% 6% 3 9% 7% 7% 8% 7% 9% 13% 26%	6424
August	1st to 10th	Day	20% 7% 2 8% 5% 6% 6% 6% 7% 10% 24%	4234
	11th to 20th	Day	11% 5% 2 6% 5% 7% 6% 6% 9% 12% 32%	4174
	21st to end	Day	7% 4 1 5% 4 5% 5% 4 7% 10% 48%	4297
September	1st to 10th	Day	8% 5% 2 7% 6% 5% 6% 4 7% 9% 42%	2200
	11th to 20th	Day	12% 7% 3 6% 5% 5% 5% 3 6% 9% 39%	2200
	21st to end	Day	16% 7% 2 5% 5% 4 4 4 5% 7% 41%	2200
October	1st to 10th	Day	14% 5% 2 5% 4 3 3 3 4 6% 51%	2119
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 4 5% 59%	2000
	21st to end	Day	12% 6% 2 4 3 2 3 2 3 4 58%	2200
November	1st to 10th	Day	14% 5% 2 5% 3 3 3 3 4 5% 53%	2057
	11th to 20th	Day	14% 5% 2 4 3 3 3 3 4 6% 54%	1933
	21st to end	Day	13% 5% 2 6% 3 3 4 4 4 6% 50%	1890
December	1st to 10th	Day	13% 7% 3 5% 3 3 3 3 4 5% 50%	3020
	11th to 20th	Day	16% 6% 2 6% 3 3 4 3 5% 7% 46%	3463
	21st to end	Day	20% 6% 2 5% 3 2 3 2 5% 6% 46%	4565
January	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 3 5% 53%	7635
	11th to 20th	Night	11% 6% 2 5% 3 4 3 3 5% 5% 53%	7680
	21st to end	Night	18% 9% 2 6% 3 3 3 2 3 5% 45%	8401
February	1st to 10th	Night	14% 8% 2 6% 3 3 3 4 5% 6% 46%	2672
	11th to 20th	Night	19% 7% 2 5% 4 4 4 3 4 5% 43%	2458
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 6% 45%	2046
March	1st to 10th	Night	19% 7% 2 5% 4 3 4 3 5% 7% 40%	5028
	11th to 20th	Night	11% 4 1 4 3 3 3 3 6% 7% 55%	5090
	21st to end	Night	15% 5% 2 5% 3 4 4 3 5% 6% 48%	5588
April	1st to 10th	Night	11% 4 1 5% 4 4 4 4 6% 8% 49%	2310
	11th to 20th	Night	10% 4 2 4 3 3 4 4 4 8% 53%	2133
	21st to end	Night	8% 5% 2 6% 4 4 3 3 6% 8% 51%	1930
May	1st to 10th	Night	12% 8% 3 8% 4 4 4 4 7% 9% 37%	5237
	11th to 20th	Night	15% 5% 2 6% 4 4 5% 4 6% 8% 40%	5234
	21st to end	Night	15% 7% 3 7% 4 5% 5% 4 7% 9% 35%	5761
June	1st to 10th	Night	11% 6% 3 7% 6% 6% 6% 5% 8% 9% 34%	1890
	11th to 20th	Night	9% 6% 2 6% 5% 5% 5% 5% 8% 10% 40%	1890
	21st to end	Night	7% 6% 2 6% 5% 6% 6% 6% 9% 12% 35%	1890
July	1st to 10th	Night	11% 8% 3 8% 6% 6% 7% 5% 8% 11% 27%	4148
	11th to 20th	Night	6% 5% 2 8% 6% 5% 7% 7% 11% 15% 28%	4102
	21st to end	Night	10% 9% 4 10% 7% 6% 7% 5% 8% 10% 23%	4427
August	1st to 10th	Night	20% 9% 3 9% 5% 5% 6% 5% 7% 10% 22%	2915
	11th to 20th	Night	11% 7% 2 6% 5% 5% 5% 5% 8% 10% 35%	2875
	21st to end	Night	6% 4 2 5% 4 5% 5% 4 7% 10% 47%	3548
September	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 7% 10% 42%	2200
	11th to 20th	Night	12% 6% 2 7% 6% 5% 5% 4 6% 8% 38%	2200
	21st to end	Night	16% 5% 2 6% 4 4 3 3 5% 7% 44%	2200
October	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 6% 53%	2280
	11th to 20th	Night	13% 6% 1 4 2 3 2 2 4 6% 56%	2400
	21st to end	Night	11% 5% 2 5% 4 3 3 2 3 5% 58%	2640
November	1st to 10th	Night	13% 5% 2 4 3 2 3 3 4 5% 56%	2461
	11th to 20th	Night	13% 6% 3 4 3 3 3 3 4 6% 54%	2683
	21st to end	Night	13% 5% 2 5% 4 3 4 3 5% 7% 49%	2730
December	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 4 5% 53%	4380
	11th to 20th	Night	17% 7% 3 5% 3 3 3 3 5% 6% 46%	4952
	21st to end	Night	20% 6% 2 5% 3 3 4 3 5% 6% 44%	6633

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% 3 10% 24% 23% 5%	5259
	11th to 20th	Day	30% 2 3 13% 38% 12%	5280
	21st to end	Day	48% 3 4 16% 19% 11%	5780
February	1st to 10th	Day	42% 4 8% 21% 19% 6%	1943
	11th to 20th	Day	43% 4 5% 19% 23% 5%	2058
	21st to end	Day	43% 4 9% 16% 20% 8%	1757
March	1st to 10th	Day	48% 3 5% 14% 19% 10%	5045
	11th to 20th	Day	30% 4 7% 14% 26% 18%	5090
	21st to end	Day	42% 3 6% 19% 23% 7%	5586
April	1st to 10th	Day	32% 5% 11% 19% 26% 6%	2310
	11th to 20th	Day	33% 5% 9% 21% 22% 10%	2435
	21st to end	Day	32% 6% 11% 26% 21% 4	2706
May	1st to 10th	Day	42% 6% 15% 23% 12% 2	7651
	11th to 20th	Day	42% 6% 16% 20% 15% 2	7630
	21st to end	Day	45% 8% 13% 16% 15% 2	8405
June	1st to 10th	Day	39% 10% 15% 23% 10% 2	2730
	11th to 20th	Day	33% 9% 19% 25% 13% 1	2730
	21st to end	Day	34% 11% 18% 21% 14% 2	2730
July	1st to 10th	Day	45% 9% 18% 21% 6% 1	5965
	11th to 20th	Day	39% 11% 30% 16% 3 1	5896
	21st to end	Day	46% 11% 17% 20% 5% 1	6240
August	1st to 10th	Day	55% 7% 17% 16% 5%	4221
	11th to 20th	Day	42% 9% 17% 18% 13% 1	4213
	21st to end	Day	30% 8% 15% 28% 16% 3	4297
September	1st to 10th	Day	35% 9% 14% 19% 18% 4	2200
	11th to 20th	Day	42% 7% 12% 18% 19% 3	2200
	21st to end	Day	41% 6% 11% 20% 15% 7%	2200
October	1st to 10th	Day	34% 4 5% 18% 29% 10%	3444
	11th to 20th	Day	19% 3 5% 16% 27% 30%	3240
	21st to end	Day	27% 3 4 21% 31% 15%	3538
November	1st to 10th	Day	34% 4 7% 19% 26% 11%	2057
	11th to 20th	Day	31% 4 7% 22% 26% 10%	1933
	21st to end	Day	36% 4 8% 20% 24% 8%	1890
December	1st to 10th	Day	37% 3 6% 17% 27% 9%	3020
	11th to 20th	Day	39% 4 10% 20% 19% 8%	3460
	21st to end	Day	40% 4 7% 23% 24% 2	4565
January	1st to 10th	Night	35% 3 7% 23% 27% 5%	7636
	11th to 20th	Night	33% 4 5% 15% 33% 11%	7680
	21st to end	Night	45% 2 4 16% 24% 9%	8401
February	1st to 10th	Night	39% 4 8% 21% 21% 8%	2672
	11th to 20th	Night	44% 4 7% 17% 21% 7%	2459
	21st to end	Night	39% 5% 8% 16% 21% 10%	2046
March	1st to 10th	Night	43% 4 8% 12% 25% 7%	5028
	11th to 20th	Night	28% 3 8% 13% 29% 19%	5090
	21st to end	Night	37% 4 7% 20% 21% 11%	5588
April	1st to 10th	Night	33% 5% 12% 18% 23% 7%	2310
	11th to 20th	Night	30% 4 10% 23% 23% 11%	2133
	21st to end	Night	31% 5% 11% 26% 23% 4	1930
May	1st to 10th	Night	43% 6% 13% 24% 13% 2	5264
	11th to 20th	Night	40% 6% 17% 21% 14% 1	5235
	21st to end	Night	44% 8% 12% 18% 15% 2	5771
June	1st to 10th	Night	42% 10% 16% 19% 12% 2	1890
	11th to 20th	Night	36% 9% 19% 23% 11% 2	1890
	21st to end	Night	36% 11% 17% 21% 12% 2	1890
July	1st to 10th	Night	49% 9% 19% 16% 6% 1	4105
	11th to 20th	Night	40% 14% 30% 12% 3 1	4051
	21st to end	Night	54% 10% 17% 14% 4	4297
August	1st to 10th	Night	56% 9% 18% 14% 4	2904
	11th to 20th	Night	41% 9% 22% 19% 9% 1	2902
	21st to end	Night	30% 8% 15% 27% 17% 3	3548
September	1st to 10th	Night	36% 10% 15% 19% 16% 5%	2200
	11th to 20th	Night	42% 8% 12% 17% 18% 3	2200
	21st to end	Night	39% 7% 12% 19% 17% 5%	2200
October	1st to 10th	Night	32% 4 8% 18% 32% 6%	3722
	11th to 20th	Night	20% 3 5% 16% 26% 29%	3899
	21st to end	Night	27% 3 5% 19% 28% 18%	4252
November	1st to 10th	Night	33% 3 8% 17% 26% 13%	2461
	11th to 20th	Night	33% 3 7% 17% 26% 13%	2683
	21st to end	Night	35% 4 7% 20% 25% 9%	2730
December	1st to 10th	Night	36% 3 6% 17% 29% 8%	4380
	11th to 20th	Night	40% 3 12% 16% 20% 9%	4954
	21st to end	Night	42% 4 7% 25% 19% 3	6633

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	22% 21% 41% 13% 2	330
	11th to 20th	Day	25% 24% 33% 15% 2	330
	21st to end	Day	28% 21% 38% 11% 2	363
February	1st to 10th	Day	20% 22% 39% 14% 4	330
	11th to 20th	Day	37% 18% 33% 12%	330
	21st to end	Day	28% 20% 34% 14% 3	300
March	1st to 10th	Day	24% 14% 35% 20% 7% 1	540
	11th to 20th	Day	21% 18% 40% 17% 5%	540
	21st to end	Day	21% 18% 38% 17% 7%	594
April	1st to 10th	Day	19% 15% 33% 21% 10% 1	540
	11th to 20th	Day	14% 14% 34% 23% 12% 3	532
	21st to end	Day	13% 11% 31% 27% 15% 3	540
May	1st to 10th	Day	13% 13% 34% 26% 11% 3	543
	11th to 20th	Day	16% 8% 22% 31% 16% 7%	567
	21st to end	Day	14% 7% 20% 25% 23% 11%	617
June	1st to 10th	Day	11% 6% 20% 32% 24% 7%	570
	11th to 20th	Day	9% 4 22% 29% 25% 12%	570
	21st to end	Day	6% 2 17% 36% 29% 10%	570
July	1st to 10th	Day	7% 4 12% 26% 32% 20%	565
	11th to 20th	Day	7% 4 10% 29% 33% 16%	544
	21st to end	Day	6% 2 10% 35% 34% 12%	576
August	1st to 10th	Day	16% 4 13% 28% 26% 13%	526
	11th to 20th	Day	13% 4 10% 28% 31% 14%	519
	21st to end	Day	13% 2 13% 29% 28% 14%	583
September	1st to 10th	Day	8% 3 16% 30% 34% 9%	530
	11th to 20th	Day	16% 5% 16% 25% 29% 10%	530
	21st to end	Day	18% 5% 19% 28% 23% 6%	530
October	1st to 10th	Day	17% 4 26% 26% 20% 7%	530
	11th to 20th	Day	13% 9% 25% 29% 20% 5%	530
	21st to end	Day	17% 7% 27% 27% 17% 4	583
November	1st to 10th	Day	20% 8% 27% 25% 15% 5%	535
	11th to 20th	Day	18% 12% 38% 24% 6% 1	373
	21st to end	Day	13% 15% 39% 23% 9% 2	330
December	1st to 10th	Day	29% 15% 37% 14% 4 1	330
	11th to 20th	Day	24% 12% 36% 21% 5% 2	330
	21st to end	Day	28% 16% 32% 17% 5% 2	363
January	1st to 10th	Night	22% 19% 28% 26% 5%	840
	11th to 20th	Night	19% 17% 34% 25% 6%	840
	21st to end	Night	21% 20% 34% 23% 3	924
February	1st to 10th	Night	20% 16% 29% 31% 4	840
	11th to 20th	Night	24% 16% 36% 22% 2	823
	21st to end	Night	18% 17% 34% 27% 3	692
March	1st to 10th	Night	18% 13% 35% 29% 6%	840
	11th to 20th	Night	17% 14% 37% 25% 7% 1	840
	21st to end	Night	16% 15% 38% 25% 6%	924
April	1st to 10th	Night	15% 15% 32% 29% 9%	840
	11th to 20th	Night	13% 12% 29% 32% 13%	831
	21st to end	Night	11% 10% 30% 36% 14%	670
May	1st to 10th	Night	12% 8% 32% 34% 13% 1	630
	11th to 20th	Night	12% 5% 29% 33% 19% 2	621
	21st to end	Night	13% 4 14% 37% 29% 4	683
June	1st to 10th	Night	12% 4 18% 37% 24% 4	630
	11th to 20th	Night	11% 3 16% 34% 28% 8%	630
	21st to end	Night	9% 3 13% 39% 30% 5%	630
July	1st to 10th	Night	9% 2 9% 34% 37% 8%	615
	11th to 20th	Night	10% 2 7% 35% 37% 9%	597
	21st to end	Night	8% 3 11% 33% 37% 8%	657
August	1st to 10th	Night	14% 2 12% 29% 36% 6%	597
	11th to 20th	Night	13% 2 10% 33% 35% 8%	594
	21st to end	Night	11% 3 11% 33% 36% 6%	797
September	1st to 10th	Night	9% 2 14% 34% 35% 6%	800
	11th to 20th	Night	14% 3 13% 28% 35% 6%	800
	21st to end	Night	18% 4 15% 32% 27% 4	800
October	1st to 10th	Night	13% 6% 19% 31% 28% 4	800
	11th to 20th	Night	16% 7% 23% 30% 22% 2	800
	21st to end	Night	14% 8% 24% 31% 22% 2	880
November	1st to 10th	Night	16% 8% 23% 34% 17% 3	820
	11th to 20th	Night	14% 12% 30% 31% 11% 1	840
	21st to end	Night	14% 10% 29% 33% 13% 1	840
December	1st to 10th	Night	20% 13% 27% 30% 8% 1	840
	11th to 20th	Night	20% 10% 26% 33% 10% 1	840
	21st to end	Night	24% 14% 25% 29% 8%	924

Page generated at 2026-07-13 03:14:50. Version ac07

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