Corydon Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Corydon Ridge Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	14% 8% 3 7% 5% 4 5% 4 6% 7% 38%	126148
	Night	15% 9% 3 7% 4 4 4 3 5% 7% 39%	123361
Transparency	Day	43% 4 11% 24% 16% 2	129791
	Night	44% 4 10% 23% 17% 2	127790
Seeing	Day	19% 11% 26% 24% 14% 6%	16637
	Night	19% 10% 26% 28% 16% 2	26346

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% 13% 7% 9% 3 4 4 3 5% 6% 29%	3617
	11th to 20th	Day	15% 11% 4 14% 5% 4 3 3 3 5% 34%	3620
	21st to end	Day	21% 10% 5% 7% 5% 4 4 3 5% 6% 31%	4553
February	1st to 10th	Day	18% 12% 4 9% 4 3 2 2 4 7% 34%	2000
	11th to 20th	Day	17% 9% 5% 7% 5% 4 5% 3 5% 7% 35%	1948
	21st to end	Day	17% 12% 5% 7% 4 4 5% 3 5% 7% 31%	1650
March	1st to 10th	Day	19% 13% 4 6% 4 3 3 2 3 5% 37%	4480
	11th to 20th	Day	12% 9% 2 6% 4 4 4 3 5% 7% 43%	4839
	21st to end	Day	16% 8% 2 7% 5% 5% 4 4 5% 7% 36%	5641
April	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 3 5% 7% 39%	2400
	11th to 20th	Day	16% 9% 3 6% 5% 4 4 3 5% 6% 38%	2374
	21st to end	Day	17% 6% 2 7% 5% 5% 4 4 5% 6% 38%	2547
May	1st to 10th	Day	21% 8% 2 7% 5% 5% 6% 5% 7% 8% 26%	5862
	11th to 20th	Day	20% 8% 3 7% 4 5% 5% 4 5% 6% 34%	5861
	21st to end	Day	14% 6% 3 7% 6% 6% 6% 4 7% 9% 33%	6433
June	1st to 10th	Day	12% 5% 2 6% 5% 4 4 4 6% 8% 45%	2710
	11th to 20th	Day	8% 5% 2 6% 6% 5% 5% 4 7% 9% 44%	2800
	21st to end	Day	8% 4 2 5% 5% 5% 6% 5% 7% 10% 43%	2800
July	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	6360
	21st to end	Day	10% 7% 3 9% 6% 6% 7% 5% 8% 10% 30%	6452
August	1st to 10th	Day	8% 4 1 6% 4 4 4 4 7% 10% 48%	4234
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 6% 7% 10% 40%	3921
	21st to end	Day	5% 3 1 4 4 4 4 4 5% 10% 56%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 5% 4 5% 6% 48%	2345
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 48%	2200
	21st to end	Day	13% 5% 2 6% 4 4 4 3 5% 5% 49%	2200
October	1st to 10th	Day	11% 4 2 4 3 3 4 3 4 6% 55%	2123
	11th to 20th	Day	13% 5% 3 6% 4 4 4 3 4 7% 48%	2000
	21st to end	Day	17% 7% 3 6% 4 4 4 3 6% 5% 42%	1881
November	1st to 10th	Day	12% 4 2 5% 4 3 4 3 5% 6% 52%	1762
	11th to 20th	Day	16% 10% 3 5% 4 3 3 3 5% 6% 42%	1800
	21st to end	Day	20% 9% 3 6% 3 4 3 3 5% 6% 39%	1800
December	1st to 10th	Day	18% 11% 3 5% 4 2 3 2 3 5% 44%	2930
	11th to 20th	Day	17% 12% 5% 9% 5% 6% 4 3 4 6% 29%	3351
	21st to end	Day	22% 17% 5% 8% 5% 4 4 3 4 5% 22%	3982
January	1st to 10th	Night	16% 14% 6% 11% 4 4 4 4 5% 6% 27%	6348
	11th to 20th	Night	16% 13% 6% 11% 6% 5% 4 3 4 4 29%	6360
	21st to end	Night	20% 10% 4 6% 4 3 4 3 4 6% 37%	6398
February	1st to 10th	Night	22% 11% 4 9% 5% 4 4 3 5% 5% 29%	2400
	11th to 20th	Night	19% 9% 4 9% 5% 4 4 3 4 5% 35%	2338
	21st to end	Night	21% 10% 3 8% 4 4 3 3 4 6% 33%	1980
March	1st to 10th	Night	21% 14% 3 5% 3 4 4 3 4 5% 36%	5373
	11th to 20th	Night	13% 8% 2 6% 3 3 4 3 5% 5% 48%	5119
	21st to end	Night	16% 8% 2 8% 5% 5% 4 4 5% 6% 35%	5330
April	1st to 10th	Night	14% 7% 2 6% 4 4 5% 4 5% 8% 41%	2000
	11th to 20th	Night	15% 8% 3 6% 4 4 4 2 5% 7% 42%	1975
	21st to end	Night	16% 7% 3 6% 5% 4 3 4 5% 7% 38%	1851
May	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 4 5% 9% 28%	4033
	11th to 20th	Night	17% 7% 3 8% 5% 5% 4 4 6% 8% 34%	4032
	21st to end	Night	12% 7% 3 7% 5% 6% 5% 4 7% 9% 36%	4421
June	1st to 10th	Night	9% 5% 2 6% 5% 3 4 3 7% 10% 47%	1685
	11th to 20th	Night	7% 4 2 5% 4 3 4 5% 6% 9% 49%	1600
	21st to end	Night	5% 3 1 4 3 4 5% 5% 8% 12% 51%	1600
July	1st to 10th	Night	9% 5% 2 7% 4 4 5% 4 6% 8% 47%	3618
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 7% 10% 46%	3617
	21st to end	Night	9% 6% 2 8% 6% 6% 6% 6% 9% 10% 34%	4383
August	1st to 10th	Night	6% 4 2 5% 3 3 4 4 6% 9% 55%	2915
	11th to 20th	Night	7% 5% 2 5% 4 5% 5% 5% 6% 9% 48%	3125
	21st to end	Night	4 3 1 3 2 2 3 3 5% 10% 64%	3586
September	1st to 10th	Night	12% 3 2 5% 4 4 3 3 5% 7% 51%	2034
	11th to 20th	Night	10% 5% 1 5% 4 3 3 3 6% 9% 52%	2200
	21st to end	Night	13% 5% 2 6% 3 3 3 2 4 7% 52%	2200
October	1st to 10th	Night	8% 5% 1 5% 3 3 3 3 5% 6% 59%	2124
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 5% 6% 49%	2177
	21st to end	Night	17% 7% 1 6% 3 3 3 2 4 6% 46%	2717
November	1st to 10th	Night	13% 6% 2 5% 4 4 3 3 4 5% 50%	2536
	11th to 20th	Night	15% 8% 2 5% 4 4 3 3 4 6% 45%	2600
	21st to end	Night	18% 10% 3 6% 4 4 4 3 4 6% 39%	2600
December	1st to 10th	Night	17% 11% 3 6% 4 3 3 3 3 5% 41%	4250
	11th to 20th	Night	20% 11% 4 7% 4 3 3 3 5% 6% 35%	4840
	21st to end	Night	24% 16% 5% 9% 5% 5% 4 3 3 4 20%	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	56% 3 10% 22% 8% 1	3618
	11th to 20th	Day	55% 2 7% 19% 14% 3	3620
	21st to end	Day	55% 3 9% 20% 9% 4	4553
February	1st to 10th	Day	53% 2 9% 23% 12% 2	2000
	11th to 20th	Day	51% 3 9% 22% 13% 2	1958
	21st to end	Day	52% 3 9% 21% 12% 3	1650
March	1st to 10th	Day	52% 2 5% 19% 17% 5%	4480
	11th to 20th	Day	41% 4 8% 27% 18% 2	4839
	21st to end	Day	47% 4 12% 23% 13% 1	5643
April	1st to 10th	Day	44% 3 12% 23% 17% 1	2400
	11th to 20th	Day	47% 3 8% 23% 16% 3	2374
	21st to end	Day	46% 4 10% 25% 12% 3	2547
May	1st to 10th	Day	54% 5% 13% 17% 11%	5897
	11th to 20th	Day	50% 4 12% 23% 12%	5865
	21st to end	Day	45% 6% 14% 18% 16% 1	6447
June	1st to 10th	Day	38% 4 10% 26% 19% 3	2710
	11th to 20th	Day	36% 5% 13% 25% 19% 2	2800
	21st to end	Day	35% 6% 14% 22% 20% 4	2800
July	1st to 10th	Day	38% 5% 11% 25% 20% 2	6291
	11th to 20th	Day	36% 7% 15% 29% 11% 1	6285
	21st to end	Day	48% 7% 16% 20% 9% 1	6268
August	1st to 10th	Day	29% 5% 14% 36% 14% 1	4221
	11th to 20th	Day	36% 5% 12% 30% 16% 1	3959
	21st to end	Day	25% 5% 12% 38% 17% 3	4311
September	1st to 10th	Day	37% 4 11% 25% 20% 5%	2345
	11th to 20th	Day	34% 5% 11% 26% 22% 3	2200
	21st to end	Day	38% 4 7% 24% 24% 3	2200
October	1st to 10th	Day	20% 2 5% 30% 40% 3	3513
	11th to 20th	Day	27% 3 10% 27% 31% 3	3294
	21st to end	Day	33% 2 9% 27% 23% 6%	3081
November	1st to 10th	Day	35% 2 8% 30% 20% 5%	1762
	11th to 20th	Day	44% 2 8% 24% 18% 5%	1800
	21st to end	Day	47% 2 8% 24% 18% 1	1800
December	1st to 10th	Day	45% 2 10% 26% 17% 1	2930
	11th to 20th	Day	58% 2 8% 20% 10% 2	3348
	21st to end	Day	65% 3 10% 15% 6%	3982
January	1st to 10th	Night	58% 3 8% 20% 10% 1	6348
	11th to 20th	Night	59% 4 6% 17% 11% 2	6360
	21st to end	Night	50% 2 7% 23% 16% 2	6398
February	1st to 10th	Night	57% 3 9% 21% 8% 1	2400
	11th to 20th	Night	54% 2 7% 22% 14% 2	2339
	21st to end	Night	54% 3 10% 18% 12% 3	1980
March	1st to 10th	Night	53% 2 5% 22% 13% 4	5373
	11th to 20th	Night	39% 2 10% 26% 21% 3	5119
	21st to end	Night	49% 3 9% 25% 14% 1	5330
April	1st to 10th	Night	41% 4 11% 24% 17% 3	2000
	11th to 20th	Night	43% 2 9% 23% 18% 5%	1975
	21st to end	Night	45% 3 11% 24% 15% 3	1851
May	1st to 10th	Night	54% 4 12% 20% 8% 1	4060
	11th to 20th	Night	49% 5% 12% 24% 10% 1	4033
	21st to end	Night	42% 5% 15% 22% 14% 2	4429
June	1st to 10th	Night	33% 4 11% 28% 20% 4	1685
	11th to 20th	Night	30% 4 16% 23% 21% 5%	1600
	21st to end	Night	25% 6% 18% 25% 19% 7%	1600
July	1st to 10th	Night	35% 6% 10% 27% 20% 2	3580
	11th to 20th	Night	33% 7% 16% 29% 12% 2	3572
	21st to end	Night	42% 8% 16% 22% 12% 1	4254
August	1st to 10th	Night	26% 5% 14% 39% 15% 1	2904
	11th to 20th	Night	30% 6% 14% 32% 17% 1	3153
	21st to end	Night	17% 4 15% 37% 24% 4	3586
September	1st to 10th	Night	33% 4 10% 25% 23% 6%	2034
	11th to 20th	Night	31% 3 8% 28% 25% 5%	2200
	21st to end	Night	35% 3 8% 25% 26% 5%	2200
October	1st to 10th	Night	20% 3 6% 19% 49% 4	3514
	11th to 20th	Night	25% 2 5% 25% 38% 4	3622
	21st to end	Night	31% 2 7% 23% 30% 7%	4467
November	1st to 10th	Night	37% 3 8% 24% 24% 4	2536
	11th to 20th	Night	41% 3 7% 23% 21% 6%	2600
	21st to end	Night	48% 2 8% 23% 17% 1	2600
December	1st to 10th	Night	48% 2 10% 24% 16%	4250
	11th to 20th	Night	51% 3 12% 20% 13% 1	4842
	21st to end	Night	68% 3 8% 15% 6% 1	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	29% 18% 32% 17% 4	300
	11th to 20th	Day	29% 26% 30% 12% 3	300
	21st to end	Day	30% 27% 28% 12% 2	330
February	1st to 10th	Day	27% 23% 37% 11% 2	300
	11th to 20th	Day	32% 27% 31% 8% 2	300
	21st to end	Day	33% 22% 34% 9% 2	249
March	1st to 10th	Day	29% 21% 34% 13% 2	300
	11th to 20th	Day	28% 19% 34% 11% 5% 1	437
	21st to end	Day	31% 16% 34% 15% 4 1	550
April	1st to 10th	Day	26% 17% 29% 20% 7% 1	500
	11th to 20th	Day	26% 17% 27% 22% 7% 2	492
	21st to end	Day	23% 15% 34% 16% 9% 1	500
May	1st to 10th	Day	26% 11% 32% 22% 6% 4	503
	11th to 20th	Day	22% 12% 28% 24% 10% 5%	527
	21st to end	Day	15% 8% 27% 25% 16% 9%	573
June	1st to 10th	Day	15% 5% 28% 28% 16% 8%	640
	11th to 20th	Day	9% 6% 25% 34% 19% 7%	730
	21st to end	Day	10% 5% 27% 29% 20% 9%	730
July	1st to 10th	Day	15% 3 16% 26% 24% 16%	721
	11th to 20th	Day	10% 3 21% 34% 22% 10%	718
	21st to end	Day	11% 2 15% 36% 25% 11%	591
August	1st to 10th	Day	12% 3 18% 28% 24% 16%	526
	11th to 20th	Day	14% 3 20% 32% 21% 10%	519
	21st to end	Day	9% 2 15% 33% 25% 15%	583
September	1st to 10th	Day	14% 4 18% 30% 25% 9%	530
	11th to 20th	Day	10% 3 15% 31% 29% 12%	530
	21st to end	Day	17% 8% 19% 27% 21% 9%	530
October	1st to 10th	Day	12% 5% 22% 36% 19% 6%	502
	11th to 20th	Day	17% 14% 31% 23% 11% 4	466
	21st to end	Day	26% 12% 38% 18% 5% 1	330
November	1st to 10th	Day	17% 14% 34% 22% 9% 3	300
	11th to 20th	Day	29% 15% 31% 19% 4 1	300
	21st to end	Day	28% 14% 35% 17% 6%	300
December	1st to 10th	Day	28% 20% 30% 15% 5% 1	300
	11th to 20th	Day	26% 16% 38% 14% 5% 1	300
	21st to end	Day	37% 17% 32% 12% 3	330
January	1st to 10th	Night	23% 18% 33% 23% 4	1000
	11th to 20th	Night	28% 17% 33% 19% 3	1000
	21st to end	Night	24% 18% 35% 21% 2	886
February	1st to 10th	Night	29% 14% 33% 22% 2	800
	11th to 20th	Night	26% 18% 34% 19% 2	783
	21st to end	Night	30% 15% 34% 19% 2	660
March	1st to 10th	Night	25% 16% 30% 24% 4	800
	11th to 20th	Night	25% 15% 33% 22% 6%	800
	21st to end	Night	25% 13% 31% 27% 5% 1	820
April	1st to 10th	Night	18% 12% 34% 27% 9%	600
	11th to 20th	Night	20% 11% 31% 26% 10% 1	593
	21st to end	Night	19% 9% 33% 29% 8% 1	600
May	1st to 10th	Night	20% 8% 33% 27% 13% 1	600
	11th to 20th	Night	17% 6% 21% 35% 18% 4	591
	21st to end	Night	10% 3 23% 33% 24% 6%	650
June	1st to 10th	Night	12% 2 22% 35% 26% 3	600
	11th to 20th	Night	8% 4 17% 42% 26% 3	600
	21st to end	Night	5% 2 20% 40% 29% 4	600
July	1st to 10th	Night	12% 2 11% 30% 36% 9%	585
	11th to 20th	Night	8% 2 10% 37% 36% 7%	582
	21st to end	Night	10% 1 13% 35% 34% 7%	657
August	1st to 10th	Night	10% 1 11% 34% 39% 6%	597
	11th to 20th	Night	7% 2 12% 39% 34% 6%	594
	21st to end	Night	7% 1 11% 34% 41% 7%	660
September	1st to 10th	Night	12% 2 12% 34% 35% 5%	634
	11th to 20th	Night	11% 3 14% 31% 35% 5%	800
	21st to end	Night	14% 6% 19% 30% 28% 4	800
October	1st to 10th	Night	10% 5% 20% 33% 27% 5%	773
	11th to 20th	Night	16% 10% 27% 28% 17% 3	760
	21st to end	Night	22% 9% 33% 24% 11%	836
November	1st to 10th	Night	17% 11% 29% 26% 16% 1	780
	11th to 20th	Night	19% 15% 31% 25% 10% 1	800
	21st to end	Night	25% 14% 23% 27% 11%	800
December	1st to 10th	Night	25% 14% 31% 25% 6%	800
	11th to 20th	Night	25% 14% 29% 25% 7% 1	805
	21st to end	Night	32% 13% 28% 23% 4	1100

Page generated at 2025-10-01 01:39:07. Version ac07

Copyright © 2025 Attilla Danko.