Stony Run River Access
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stony Run River Access clear sky chart from 2005-11-06 to 2025-09-04.

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	12% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	125832
	Night	12% 8% 3 8% 5% 4 5% 4 6% 7% 38%	122877
Transparency	Day	42% 6% 11% 24% 14% 3	129435
	Night	42% 6% 12% 24% 14% 2	127343
Seeing	Day	23% 13% 25% 22% 13% 4	15948
	Night	20% 12% 24% 30% 12% 1	25589

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	12% 14% 3 9% 6% 5% 4 3 3 5% 35%	3992
	11th to 20th	Day	10% 13% 5% 10% 7% 5% 4 3 4 5% 35%	4060
	21st to end	Day	13% 9% 4 8% 5% 4 4 4 5% 6% 38%	4466
February	1st to 10th	Day	13% 14% 3 8% 5% 4 5% 4 5% 6% 34%	1800
	11th to 20th	Day	14% 9% 4 9% 5% 5% 5% 3 5% 6% 34%	1753
	21st to end	Day	13% 10% 4 8% 5% 4 4 3 4 7% 38%	1679
March	1st to 10th	Day	15% 10% 4 8% 4 4 3 3 4 5% 40%	4935
	11th to 20th	Day	11% 8% 3 6% 4 3 4 3 5% 8% 46%	4980
	21st to end	Day	14% 10% 3 8% 6% 5% 4 4 5% 6% 36%	5465
April	1st to 10th	Day	12% 11% 3 8% 6% 4 4 4 5% 7% 35%	2355
	11th to 20th	Day	12% 8% 3 7% 5% 5% 3 4 6% 6% 42%	2374
	21st to end	Day	17% 7% 2 7% 5% 4 4 3 6% 7% 37%	2500
May	1st to 10th	Day	17% 7% 3 8% 6% 5% 5% 5% 7% 8% 29%	5862
	11th to 20th	Day	19% 10% 3 8% 5% 5% 5% 4 6% 7% 28%	5861
	21st to end	Day	16% 6% 3 7% 5% 5% 5% 5% 6% 9% 33%	6888
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	2800
	11th to 20th	Day	11% 5% 3 7% 5% 5% 6% 6% 7% 8% 36%	2800
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	2800
July	1st to 10th	Day	5% 5% 2 7% 5% 5% 6% 5% 7% 10% 43%	6230
	11th to 20th	Day	7% 5% 3 7% 7% 6% 6% 6% 7% 11% 33%	5900
	21st to end	Day	9% 7% 2 7% 6% 6% 5% 5% 7% 10% 37%	6424
August	1st to 10th	Day	14% 7% 2 7% 5% 5% 7% 5% 7% 9% 33%	4234
	11th to 20th	Day	8% 6% 2 6% 5% 6% 5% 5% 7% 9% 39%	4158
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 9% 48%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 6% 6% 45%	2316
	11th to 20th	Day	11% 6% 3 7% 4 4 5% 3 6% 8% 44%	2181
	21st to end	Day	19% 8% 2 5% 4 4 5% 4 5% 6% 37%	2037
October	1st to 10th	Day	16% 6% 2 4 3 4 3 3 5% 6% 46%	1900
	11th to 20th	Day	14% 8% 3 7% 4 3 4 4 4 6% 43%	1900
	21st to end	Day	14% 8% 2 5% 3 4 3 4 4 7% 46%	2090
November	1st to 10th	Day	10% 6% 2 6% 3 4 4 3 5% 6% 52%	1957
	11th to 20th	Day	12% 9% 3 7% 5% 4 4 3 5% 7% 40%	1673
	21st to end	Day	14% 10% 3 6% 5% 4 5% 3 4 7% 38%	1600
December	1st to 10th	Day	12% 9% 4 7% 5% 4 4 3 4 5% 43%	2600
	11th to 20th	Day	19% 11% 4 8% 5% 3 3 3 5% 6% 34%	2990
	21st to end	Day	15% 10% 4 9% 5% 5% 5% 5% 7% 8% 28%	3960
January	1st to 10th	Night	9% 13% 6% 14% 6% 4 4 3 4 5% 32%	5935
	11th to 20th	Night	10% 10% 4 13% 5% 4 4 3 4 5% 37%	5900
	21st to end	Night	13% 10% 4 8% 5% 3 4 4 4 5% 41%	6490
February	1st to 10th	Night	12% 10% 4 8% 5% 4 5% 4 6% 6% 37%	2600
	11th to 20th	Night	14% 11% 4 9% 6% 6% 5% 3 5% 5% 33%	2533
	21st to end	Night	13% 12% 5% 8% 5% 5% 4 4 6% 6% 34%	1946
March	1st to 10th	Night	15% 8% 3 7% 4 3 4 3 4 6% 43%	4918
	11th to 20th	Night	9% 10% 4 6% 4 3 3 3 5% 7% 47%	4980
	21st to end	Night	10% 8% 3 8% 5% 4 4 3 5% 7% 43%	5467
April	1st to 10th	Night	14% 11% 3 8% 6% 4 4 3 6% 6% 36%	2045
	11th to 20th	Night	13% 7% 2 5% 5% 4 5% 5% 5% 8% 41%	1975
	21st to end	Night	15% 6% 2 7% 5% 4 4 4 4 7% 42%	1916
May	1st to 10th	Night	21% 8% 3 7% 4 5% 5% 4 6% 9% 28%	4033
	11th to 20th	Night	21% 10% 3 7% 4 4 5% 4 6% 8% 29%	4032
	21st to end	Night	17% 8% 3 7% 5% 5% 5% 4 7% 9% 32%	3965
June	1st to 10th	Night	10% 5% 2 5% 4 6% 5% 4 6% 9% 45%	1600
	11th to 20th	Night	9% 6% 2 6% 5% 5% 4 5% 6% 10% 42%	1600
	21st to end	Night	8% 4 2 5% 5% 5% 5% 5% 8% 10% 44%	1600
July	1st to 10th	Night	6% 5% 2 6% 5% 4 5% 5% 7% 10% 43%	3723
	11th to 20th	Night	6% 7% 3 10% 6% 7% 7% 6% 8% 9% 31%	4057
	21st to end	Night	7% 6% 2 7% 5% 5% 6% 6% 8% 10% 37%	4427
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 6% 5% 8% 9% 36%	2915
	11th to 20th	Night	11% 5% 2 6% 4 5% 5% 4 5% 9% 43%	2875
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 9% 47%	3567
September	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 5% 7% 48%	1931
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 8% 50%	1995
	21st to end	Night	18% 6% 2 5% 4 4 5% 4 4 7% 41%	2142
October	1st to 10th	Night	16% 6% 2 5% 3 3 4 3 5% 7% 46%	2280
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 5% 7% 49%	2280
	21st to end	Night	16% 6% 2 6% 4 4 3 3 5% 6% 46%	2508
November	1st to 10th	Night	9% 9% 2 6% 4 3 4 3 5% 7% 48%	2341
	11th to 20th	Night	12% 11% 3 6% 5% 3 4 3 5% 7% 40%	2720
	21st to end	Night	12% 8% 3 9% 6% 5% 5% 4 5% 6% 38%	2800
December	1st to 10th	Night	10% 8% 4 9% 4 4 4 4 6% 8% 40%	4580
	11th to 20th	Night	15% 10% 4 9% 6% 5% 5% 4 5% 6% 32%	5205
	21st to end	Night	13% 11% 4 9% 6% 5% 6% 5% 7% 7% 27%	6996

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	48% 6% 7% 22% 13% 3	3993
	11th to 20th	Day	49% 7% 8% 16% 16% 4	4060
	21st to end	Day	44% 4 11% 25% 13% 3	4466
February	1st to 10th	Day	50% 4 11% 22% 12% 1	1800
	11th to 20th	Day	51% 5% 9% 20% 13% 2	1762
	21st to end	Day	48% 3 10% 21% 15% 3	1679
March	1st to 10th	Day	45% 5% 7% 24% 13% 6%	4935
	11th to 20th	Day	36% 5% 9% 28% 17% 5%	4980
	21st to end	Day	48% 5% 9% 19% 15% 3	5465
April	1st to 10th	Day	48% 5% 11% 18% 15% 3	2355
	11th to 20th	Day	42% 4 11% 21% 17% 5%	2374
	21st to end	Day	46% 5% 10% 24% 14% 2	2500
May	1st to 10th	Day	50% 6% 11% 21% 9% 2	5897
	11th to 20th	Day	52% 6% 9% 24% 7% 1	5865
	21st to end	Day	44% 7% 12% 22% 13% 2	6903
June	1st to 10th	Day	39% 7% 13% 25% 16% 1	2800
	11th to 20th	Day	41% 8% 14% 23% 13% 1	2800
	21st to end	Day	37% 7% 15% 25% 14% 2	2800
July	1st to 10th	Day	34% 9% 14% 27% 14% 3	6162
	11th to 20th	Day	39% 11% 17% 24% 8% 1	5831
	21st to end	Day	40% 7% 11% 24% 18% 1	6240
August	1st to 10th	Day	45% 6% 16% 25% 8%	4221
	11th to 20th	Day	38% 6% 13% 30% 13%	4197
	21st to end	Day	32% 7% 15% 29% 16% 1	4312
September	1st to 10th	Day	38% 6% 12% 21% 20% 3	2316
	11th to 20th	Day	38% 4 9% 27% 19% 3	2181
	21st to end	Day	47% 4 10% 21% 17% 1	2037
October	1st to 10th	Day	31% 4 9% 26% 26% 5%	3160
	11th to 20th	Day	33% 5% 10% 24% 18% 11%	3140
	21st to end	Day	27% 3 10% 31% 25% 4	3428
November	1st to 10th	Day	35% 3 10% 26% 22% 4	1957
	11th to 20th	Day	43% 5% 11% 18% 20% 3	1673
	21st to end	Day	44% 5% 11% 24% 15% 1	1600
December	1st to 10th	Day	41% 6% 12% 27% 10% 3	2600
	11th to 20th	Day	50% 5% 13% 20% 10% 2	2986
	21st to end	Day	51% 6% 14% 17% 12%	3960
January	1st to 10th	Night	48% 9% 7% 21% 15% 1	5935
	11th to 20th	Night	45% 8% 9% 19% 14% 6%	5900
	21st to end	Night	44% 6% 10% 27% 13% 1	6490
February	1st to 10th	Night	47% 4 13% 23% 12% 1	2600
	11th to 20th	Night	52% 5% 9% 19% 13% 2	2535
	21st to end	Night	50% 5% 10% 19% 11% 4	1946
March	1st to 10th	Night	41% 4 8% 29% 13% 6%	4918
	11th to 20th	Night	36% 6% 10% 31% 13% 4	4980
	21st to end	Night	41% 5% 11% 23% 17% 3	5467
April	1st to 10th	Night	49% 5% 10% 20% 15% 3	2045
	11th to 20th	Night	41% 7% 11% 22% 15% 5%	1975
	21st to end	Night	42% 5% 10% 26% 14% 3	1916
May	1st to 10th	Night	53% 6% 13% 17% 9% 2	4060
	11th to 20th	Night	52% 5% 10% 24% 8% 1	4033
	21st to end	Night	47% 7% 14% 22% 7% 3	3972
June	1st to 10th	Night	35% 7% 12% 28% 16% 2	1600
	11th to 20th	Night	38% 7% 14% 28% 12% 1	1600
	21st to end	Night	32% 7% 17% 25% 17% 2	1600
July	1st to 10th	Night	35% 10% 19% 22% 11% 3	3683
	11th to 20th	Night	43% 11% 17% 20% 8% 1	4006
	21st to end	Night	36% 9% 15% 25% 15%	4297
August	1st to 10th	Night	43% 7% 17% 25% 8%	2904
	11th to 20th	Night	37% 6% 14% 25% 17% 1	2902
	21st to end	Night	34% 6% 14% 32% 13% 1	3567
September	1st to 10th	Night	36% 6% 14% 21% 19% 4	1931
	11th to 20th	Night	33% 4 10% 31% 20% 2	1995
	21st to end	Night	42% 6% 11% 22% 17% 1	2142
October	1st to 10th	Night	36% 4 10% 27% 22% 2	3800
	11th to 20th	Night	28% 5% 10% 24% 26% 8%	3779
	21st to end	Night	28% 4 10% 30% 24% 5%	4120
November	1st to 10th	Night	36% 3 12% 24% 20% 5%	2341
	11th to 20th	Night	43% 5% 7% 24% 17% 4	2720
	21st to end	Night	46% 5% 11% 21% 15% 2	2800
December	1st to 10th	Night	39% 8% 13% 29% 11% 1	4580
	11th to 20th	Night	49% 7% 13% 19% 12% 1	5208
	21st to end	Night	52% 7% 14% 16% 11%	6996

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	40% 22% 22% 13% 3 1	287
	11th to 20th	Day	43% 18% 27% 9% 3	300
	21st to end	Day	35% 22% 30% 10% 3	330
February	1st to 10th	Day	37% 22% 26% 12% 2	300
	11th to 20th	Day	51% 17% 26% 5%	300
	21st to end	Day	35% 21% 29% 13% 2	366
March	1st to 10th	Day	34% 20% 22% 21% 3	500
	11th to 20th	Day	34% 20% 25% 15% 5% 1	500
	21st to end	Day	29% 19% 30% 16% 5% 1	550
April	1st to 10th	Day	29% 22% 25% 18% 4 1	500
	11th to 20th	Day	25% 17% 28% 18% 9% 3	492
	21st to end	Day	30% 14% 28% 19% 8% 1	500
May	1st to 10th	Day	27% 17% 27% 18% 8% 3	503
	11th to 20th	Day	23% 15% 28% 19% 12% 2	527
	21st to end	Day	19% 11% 25% 22% 17% 6%	573
June	1st to 10th	Day	18% 9% 30% 22% 17% 5%	530
	11th to 20th	Day	18% 10% 27% 24% 16% 5%	530
	21st to end	Day	11% 10% 28% 30% 17% 4	530
July	1st to 10th	Day	10% 6% 23% 28% 23% 10%	525
	11th to 20th	Day	8% 6% 23% 29% 23% 9%	524
	21st to end	Day	14% 5% 21% 32% 22% 6%	576
August	1st to 10th	Day	13% 7% 21% 28% 21% 10%	526
	11th to 20th	Day	12% 6% 22% 28% 22% 10%	519
	21st to end	Day	12% 6% 20% 29% 24% 9%	583
September	1st to 10th	Day	18% 7% 18% 25% 25% 8%	502
	11th to 20th	Day	15% 5% 20% 28% 23% 10%	490
	21st to end	Day	27% 8% 24% 22% 15% 4	490
October	1st to 10th	Day	22% 7% 22% 27% 17% 5%	490
	11th to 20th	Day	21% 15% 23% 24% 14% 2	490
	21st to end	Day	19% 17% 28% 24% 9% 3	539
November	1st to 10th	Day	18% 14% 28% 24% 13% 2	495
	11th to 20th	Day	28% 14% 30% 20% 8% 1	261
	21st to end	Day	33% 15% 33% 16% 4 1	200
December	1st to 10th	Day	31% 22% 29% 13% 5% 1	200
	11th to 20th	Day	34% 20% 21% 22% 5%	200
	21st to end	Day	28% 17% 29% 20% 6%	220
January	1st to 10th	Night	26% 22% 28% 21% 3	800
	11th to 20th	Night	26% 20% 28% 24% 3	800
	21st to end	Night	25% 21% 33% 20% 2	880
February	1st to 10th	Night	24% 20% 26% 28% 2	800
	11th to 20th	Night	30% 26% 27% 17% 1	783
	21st to end	Night	29% 20% 32% 18% 2	660
March	1st to 10th	Night	25% 18% 32% 23% 3	800
	11th to 20th	Night	28% 19% 26% 22% 4 1	800
	21st to end	Night	25% 17% 31% 22% 5% 1	880
April	1st to 10th	Night	26% 18% 29% 22% 5%	800
	11th to 20th	Night	20% 15% 29% 28% 8%	791
	21st to end	Night	23% 11% 27% 30% 9%	716
May	1st to 10th	Night	22% 9% 22% 31% 15% 1	600
	11th to 20th	Night	20% 6% 24% 34% 14% 1	591
	21st to end	Night	13% 4 23% 38% 19% 3	453
June	1st to 10th	Night	11% 4 25% 40% 17% 3	400
	11th to 20th	Night	13% 4 19% 44% 18% 3	400
	21st to end	Night	7% 5% 24% 44% 19% 1	400
July	1st to 10th	Night	10% 3 13% 46% 23% 5%	435
	11th to 20th	Night	7% 2 11% 40% 36% 3	582
	21st to end	Night	9% 3 16% 39% 31% 3	657
August	1st to 10th	Night	10% 2 9% 46% 30% 3	597
	11th to 20th	Night	11% 2 11% 45% 29% 3	594
	21st to end	Night	11% 3 16% 39% 29% 2	861
September	1st to 10th	Night	15% 3 14% 38% 25% 5%	773
	11th to 20th	Night	14% 5% 12% 33% 33% 4	760
	21st to end	Night	21% 6% 20% 31% 21% 2	760
October	1st to 10th	Night	21% 7% 17% 31% 21% 3	760
	11th to 20th	Night	18% 13% 24% 32% 12% 1	760
	21st to end	Night	20% 12% 27% 29% 11% 1	836
November	1st to 10th	Night	16% 12% 25% 35% 11% 1	780
	11th to 20th	Night	23% 17% 24% 27% 8% 1	800
	21st to end	Night	22% 18% 26% 29% 6%	800
December	1st to 10th	Night	26% 16% 29% 24% 5%	800
	11th to 20th	Night	21% 19% 27% 30% 3	800
	21st to end	Night	23% 15% 28% 32% 2	880

Page generated at 2025-09-01 01:51:05. Version ac07

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