River Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the River Ridge Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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% 6% 2 6% 4 4 4 4 5% 7% 45%	125337
	Night	12% 6% 2 5% 4 3 4 3 5% 7% 50%	123910
Transparency	Day	37% 6% 10% 24% 19% 5%	128942
	Night	34% 5% 9% 24% 22% 7%	128381
Seeing	Day	14% 10% 22% 26% 20% 6%	16579
	Night	14% 8% 26% 32% 18% 2	26282

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% 7% 3 6% 3 3 3 2 3 4 49%	4077
	11th to 20th	Day	9% 9% 2 6% 4 3 3 3 4 5% 52%	4080
	21st to end	Day	21% 7% 1 5% 3 2 2 2 3 4 50%	4488
February	1st to 10th	Day	21% 8% 2 5% 4 3 3 3 4 4 42%	1800
	11th to 20th	Day	17% 8% 3 6% 4 4 3 3 5% 5% 42%	1876
	21st to end	Day	20% 8% 3 6% 4 4 3 3 5% 5% 39%	1710
March	1st to 10th	Day	19% 9% 3 6% 4 3 3 3 4 5% 39%	4936
	11th to 20th	Day	10% 5% 2 5% 3 4 4 3 4 6% 53%	4980
	21st to end	Day	14% 8% 3 7% 4 4 4 3 5% 6% 43%	5462
April	1st to 10th	Day	14% 6% 2 5% 4 4 4 3 5% 7% 45%	2391
	11th to 20th	Day	15% 6% 2 7% 4 4 4 3 4 6% 47%	2374
	21st to end	Day	14% 6% 2 6% 5% 4 5% 4 6% 7% 41%	2400
May	1st to 10th	Day	16% 8% 3 8% 4 4 5% 3 5% 7% 37%	5405
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 7% 40%	5834
	21st to end	Day	15% 6% 3 8% 5% 5% 6% 5% 7% 7% 34%	6434
June	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 5% 7% 9% 43%	2725
	11th to 20th	Day	4 4 2 5% 5% 6% 5% 6% 8% 10% 45%	2795
	21st to end	Day	4 3 1 5% 5% 5% 6% 5% 8% 9% 49%	2600
July	1st to 10th	Day	7% 5% 2 6% 6% 6% 7% 6% 9% 11% 36%	5900
	11th to 20th	Day	5% 3 2 4 3 4 5% 5% 7% 10% 53%	5900
	21st to end	Day	8% 7% 2 7% 5% 5% 6% 4 7% 10% 40%	6422
August	1st to 10th	Day	4 2 1 4 3 4 3 4 6% 8% 61%	4234
	11th to 20th	Day	10% 5% 2 6% 4 4 4 5% 8% 10% 41%	3886
	21st to end	Day	5% 4 2 5% 5% 4 5% 5% 6% 8% 51%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 3 5% 4 5% 7% 46%	2400
	11th to 20th	Day	14% 5% 2 5% 3 4 5% 4 5% 7% 47%	2373
	21st to end	Day	10% 5% 2 5% 3 4 5% 4 5% 6% 53%	1981
October	1st to 10th	Day	6% 4 2 5% 3 3 3 3 5% 6% 59%	1900
	11th to 20th	Day	13% 5% 2 4 3 3 2 3 4 5% 58%	1900
	21st to end	Day	18% 4 2 4 3 3 3 2 4 5% 52%	2090
November	1st to 10th	Day	14% 5% 2 4 3 3 3 3 4 6% 55%	1958
	11th to 20th	Day	9% 6% 2 5% 3 3 2 3 5% 6% 56%	1941
	21st to end	Day	17% 8% 2 5% 4 3 3 2 4 6% 46%	1741
December	1st to 10th	Day	17% 8% 2 6% 4 3 3 2 4 4 48%	2610
	11th to 20th	Day	15% 9% 3 8% 4 4 3 3 4 4 43%	3008
	21st to end	Day	18% 7% 2 7% 4 4 4 4 5% 5% 40%	4414
January	1st to 10th	Night	16% 6% 2 6% 3 3 3 3 5% 6% 48%	5888
	11th to 20th	Night	12% 5% 2 3 3 3 3 2 4 4 59%	5900
	21st to end	Night	21% 7% 2 5% 2 3 3 2 3 4 48%	6490
February	1st to 10th	Night	20% 8% 3 6% 3 3 3 3 4 6% 42%	2600
	11th to 20th	Night	18% 8% 3 6% 3 3 4 2 4 5% 44%	2409
	21st to end	Night	17% 7% 2 4 3 3 4 3 4 5% 48%	1935
March	1st to 10th	Night	17% 7% 3 6% 4 3 3 3 5% 5% 44%	4919
	11th to 20th	Night	11% 5% 2 6% 4 3 3 3 4 6% 52%	4980
	21st to end	Night	12% 6% 3 7% 4 4 4 3 5% 8% 45%	5467
April	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 50%	2007
	11th to 20th	Night	12% 5% 2 4 3 4 4 3 5% 7% 52%	1975
	21st to end	Night	13% 6% 2 6% 4 3 3 4 4 6% 48%	2000
May	1st to 10th	Night	17% 8% 3 6% 5% 4 5% 4 5% 8% 37%	4490
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 6% 7% 37%	4063
	21st to end	Night	17% 7% 2 6% 5% 5% 4 3 5% 6% 39%	4443
June	1st to 10th	Night	5% 5% 1 4 4 4 4 3 7% 10% 54%	1665
	11th to 20th	Night	4 5% 2 4 3 4 4 4 5% 9% 57%	1600
	21st to end	Night	3 3 1 4 3 3 3 4 6% 9% 61%	1789
July	1st to 10th	Night	7% 5% 3 7% 6% 5% 5% 4 7% 9% 42%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 3 7% 10% 57%	4077
	21st to end	Night	5% 5% 2 6% 4 4 5% 4 7% 10% 48%	4449
August	1st to 10th	Night	3 2 1 3 2 3 3 3 5% 8% 68%	2926
	11th to 20th	Night	4 3 1 4 3 4 4 4 6% 10% 56%	3162
	21st to end	Night	4 2 1 4 4 4 5% 4 7% 9% 57%	3586
September	1st to 10th	Night	7% 5% 2 5% 3 4 4 3 5% 6% 57%	2000
	11th to 20th	Night	11% 5% 2 5% 3 4 4 3 5% 7% 52%	1980
	21st to end	Night	8% 4 2 4 3 3 2 3 6% 7% 58%	2177
October	1st to 10th	Night	8% 3 1 4 3 3 3 3 4 6% 62%	2280
	11th to 20th	Night	10% 4 2 4 3 2 3 2 3 5% 62%	2280
	21st to end	Night	17% 5% 1 4 4 3 3 2 3 4 55%	2508
November	1st to 10th	Night	12% 4 2 5% 3 3 3 2 5% 5% 56%	2340
	11th to 20th	Night	11% 4 1 3 3 3 3 3 4 7% 57%	2454
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 5% 52%	2655
December	1st to 10th	Night	16% 6% 2 5% 3 3 3 3 4 5% 50%	4580
	11th to 20th	Night	14% 8% 3 7% 4 5% 3 3 3 4 46%	5199
	21st to end	Night	18% 7% 2 6% 4 4 4 3 4 5% 43%	6559

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	41% 3 8% 27% 19% 3	4078
	11th to 20th	Day	35% 3 8% 22% 27% 4	4080
	21st to end	Day	41% 2 5% 17% 25% 10%	4488
February	1st to 10th	Day	46% 4 9% 21% 16% 4	1800
	11th to 20th	Day	45% 4 7% 20% 19% 5%	1885
	21st to end	Day	48% 4 7% 15% 17% 9%	1710
March	1st to 10th	Day	48% 4 5% 16% 15% 12%	4936
	11th to 20th	Day	33% 4 7% 19% 24% 13%	4980
	21st to end	Day	43% 4 8% 24% 20% 1	5464
April	1st to 10th	Day	38% 6% 9% 22% 20% 5%	2391
	11th to 20th	Day	40% 5% 9% 22% 17% 8%	2374
	21st to end	Day	43% 6% 10% 20% 19% 2	2400
May	1st to 10th	Day	46% 6% 10% 23% 13% 2	5440
	11th to 20th	Day	42% 7% 12% 23% 15% 1	5838
	21st to end	Day	47% 8% 11% 18% 15% 2	6447
June	1st to 10th	Day	35% 8% 13% 24% 17% 2	2725
	11th to 20th	Day	30% 8% 14% 27% 18% 2	2795
	21st to end	Day	28% 8% 11% 29% 20% 4	2600
July	1st to 10th	Day	35% 11% 15% 27% 11% 1	5836
	11th to 20th	Day	25% 7% 14% 35% 17% 2	5831
	21st to end	Day	37% 8% 14% 27% 13% 1	6240
August	1st to 10th	Day	20% 6% 14% 30% 23% 6%	4220
	11th to 20th	Day	36% 7% 13% 32% 11% 1	3922
	21st to end	Day	28% 7% 12% 30% 19% 3	4311
September	1st to 10th	Day	36% 8% 10% 21% 19% 7%	2400
	11th to 20th	Day	37% 5% 11% 19% 23% 5%	2373
	21st to end	Day	32% 5% 7% 21% 26% 8%	1981
October	1st to 10th	Day	16% 3 5% 13% 37% 26%	3160
	11th to 20th	Day	19% 2 3 20% 38% 18%	3140
	21st to end	Day	31% 4 5% 28% 26% 6%	3428
November	1st to 10th	Day	32% 4 8% 26% 22% 8%	1958
	11th to 20th	Day	29% 4 8% 21% 28% 10%	1941
	21st to end	Day	42% 3 6% 18% 24% 6%	1741
December	1st to 10th	Day	43% 2 6% 26% 19% 3	2610
	11th to 20th	Day	46% 3 5% 22% 21% 4	3005
	21st to end	Day	45% 4 7% 25% 15% 4	4414
January	1st to 10th	Night	37% 3 8% 27% 23% 2	5888
	11th to 20th	Night	29% 4 8% 20% 31% 7%	5900
	21st to end	Night	42% 3 7% 17% 25% 6%	6490
February	1st to 10th	Night	46% 3 7% 20% 18% 5%	2600
	11th to 20th	Night	44% 3 6% 21% 20% 6%	2410
	21st to end	Night	40% 3 8% 18% 22% 9%	1935
March	1st to 10th	Night	42% 5% 6% 15% 20% 13%	4919
	11th to 20th	Night	33% 4 7% 23% 18% 14%	4980
	21st to end	Night	39% 4 8% 26% 21% 3	5467
April	1st to 10th	Night	35% 4 11% 23% 19% 9%	2007
	11th to 20th	Night	32% 5% 8% 24% 22% 9%	1975
	21st to end	Night	36% 4 10% 24% 21% 3	2000
May	1st to 10th	Night	46% 7% 11% 21% 12% 2	4520
	11th to 20th	Night	46% 6% 12% 23% 12% 1	4064
	21st to end	Night	44% 6% 12% 20% 13% 5%	4452
June	1st to 10th	Night	24% 7% 15% 30% 21% 2	1665
	11th to 20th	Night	25% 5% 12% 30% 26% 3	1600
	21st to end	Night	19% 7% 13% 30% 24% 7%	1789
July	1st to 10th	Night	35% 8% 14% 28% 14% 1	4035
	11th to 20th	Night	20% 7% 15% 37% 18% 2	4026
	21st to end	Night	30% 8% 15% 29% 18% 1	4320
August	1st to 10th	Night	15% 5% 15% 34% 26% 5%	2916
	11th to 20th	Night	22% 6% 18% 37% 15% 2	3192
	21st to end	Night	22% 6% 13% 30% 26% 3	3586
September	1st to 10th	Night	28% 6% 10% 26% 21% 9%	2000
	11th to 20th	Night	31% 6% 9% 22% 25% 6%	1980
	21st to end	Night	25% 4 11% 21% 29% 9%	2177
October	1st to 10th	Night	16% 3 7% 15% 29% 31%	3800
	11th to 20th	Night	16% 2 4 15% 38% 24%	3779
	21st to end	Night	28% 3 5% 22% 29% 13%	4120
November	1st to 10th	Night	31% 3 7% 23% 25% 10%	2340
	11th to 20th	Night	28% 4 5% 24% 28% 11%	2454
	21st to end	Night	35% 4 7% 20% 29% 6%	2655
December	1st to 10th	Night	37% 3 7% 31% 18% 4	4580
	11th to 20th	Night	45% 3 4 21% 21% 7%	5201
	21st to end	Night	43% 4 9% 24% 16% 3	6559

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	27% 15% 36% 18% 4 1	300
	11th to 20th	Day	23% 21% 38% 16% 2	300
	21st to end	Day	19% 25% 34% 17% 5%	330
February	1st to 10th	Day	28% 18% 32% 17% 4	300
	11th to 20th	Day	28% 27% 29% 13% 3	300
	21st to end	Day	31% 22% 32% 11% 3	249
March	1st to 10th	Day	24% 21% 31% 18% 5%	300
	11th to 20th	Day	25% 27% 34% 13% 1	300
	21st to end	Day	24% 23% 36% 13% 3	330
April	1st to 10th	Day	22% 17% 34% 19% 7% 1	491
	11th to 20th	Day	21% 21% 31% 21% 7%	492
	21st to end	Day	19% 15% 33% 23% 10% 1	500
May	1st to 10th	Day	17% 16% 30% 28% 9% 1	503
	11th to 20th	Day	15% 9% 27% 30% 18% 3	710
	21st to end	Day	10% 8% 25% 33% 20% 5%	789
June	1st to 10th	Day	10% 4 20% 31% 27% 8%	730
	11th to 20th	Day	5% 3 17% 37% 30% 8%	730
	21st to end	Day	4 3 16% 36% 30% 10%	730
July	1st to 10th	Day	5% 4 11% 31% 37% 13%	721
	11th to 20th	Day	4 2 11% 32% 34% 16%	718
	21st to end	Day	7% 3 8% 31% 35% 16%	794
August	1st to 10th	Day	6% 1 10% 36% 37% 9%	726
	11th to 20th	Day	13% 3 8% 28% 35% 14%	544
	21st to end	Day	10% 2 7% 25% 38% 18%	583
September	1st to 10th	Day	10% 3 9% 27% 37% 13%	530
	11th to 20th	Day	11% 2 13% 23% 37% 14%	519
	21st to end	Day	12% 6% 19% 35% 21% 7%	300
October	1st to 10th	Day	7% 4 25% 35% 24% 5%	300
	11th to 20th	Day	13% 11% 32% 26% 15% 2	300
	21st to end	Day	25% 14% 29% 22% 9% 1	330
November	1st to 10th	Day	20% 12% 31% 21% 14% 2	300
	11th to 20th	Day	12% 17% 34% 27% 8% 1	300
	21st to end	Day	23% 18% 27% 22% 9% 1	300
December	1st to 10th	Day	22% 20% 32% 17% 8% 1	300
	11th to 20th	Day	25% 19% 32% 17% 8%	300
	21st to end	Day	21% 23% 36% 17% 4	330
January	1st to 10th	Night	21% 13% 34% 28% 4	1000
	11th to 20th	Night	19% 15% 36% 25% 4	1000
	21st to end	Night	20% 12% 38% 26% 3	1100
February	1st to 10th	Night	24% 14% 33% 26% 4	1000
	11th to 20th	Night	22% 14% 40% 23% 1	854
	21st to end	Night	22% 15% 38% 22% 2	615
March	1st to 10th	Night	19% 11% 37% 30% 4	600
	11th to 20th	Night	21% 13% 34% 28% 5%	600
	21st to end	Night	15% 12% 38% 28% 6%	660
April	1st to 10th	Night	17% 11% 36% 29% 6%	600
	11th to 20th	Night	14% 12% 38% 27% 9% 1	593
	21st to end	Night	13% 10% 37% 29% 10%	600
May	1st to 10th	Night	15% 6% 27% 43% 9%	600
	11th to 20th	Night	16% 7% 28% 31% 17% 2	591
	21st to end	Night	10% 4 23% 37% 23% 4	650
June	1st to 10th	Night	5% 2 14% 41% 34% 4	600
	11th to 20th	Night	5% 2 11% 46% 35% 3	600
	21st to end	Night	4 1 11% 40% 40% 5%	600
July	1st to 10th	Night	4 1 8% 39% 41% 6%	585
	11th to 20th	Night	4 1 8% 35% 45% 7%	582
	21st to end	Night	4 1 8% 36% 43% 9%	657
August	1st to 10th	Night	4 1 5% 40% 43% 6%	597
	11th to 20th	Night	7% 1 7% 37% 41% 7%	594
	21st to end	Night	7% 1 9% 32% 46% 5%	660
September	1st to 10th	Night	7% 2 8% 38% 41% 4	600
	11th to 20th	Night	12% 1 10% 34% 40% 4	594
	21st to end	Night	9% 3 15% 34% 35% 4	659
October	1st to 10th	Night	9% 2 17% 36% 32% 3	760
	11th to 20th	Night	12% 6% 27% 38% 17% 1	760
	21st to end	Night	18% 8% 27% 32% 15% 1	836
November	1st to 10th	Night	13% 7% 26% 40% 14% 1	780
	11th to 20th	Night	13% 11% 30% 36% 11%	800
	21st to end	Night	15% 13% 30% 30% 11%	855
December	1st to 10th	Night	21% 9% 34% 31% 6%	1000
	11th to 20th	Night	23% 11% 27% 33% 6%	1000
	21st to end	Night	21% 14% 31% 29% 5%	1100

Page generated at 2025-09-16 00:49:17. Version ac07

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