Cumberland Plateau Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cumberland Plateau Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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% 37%	126643
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 39%	124072
Transparency	Day	43% 7% 11% 21% 15% 3	130354
	Night	42% 6% 11% 21% 16% 3	128429
Seeing	Day	19% 13% 24% 22% 15% 6%	16061
	Night	18% 11% 24% 27% 17% 3	26081

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% 9% 12% 4 4 4 3 5% 5% 26%	4056
	11th to 20th	Day	16% 12% 6% 12% 3 3 3 2 3 4 34%	4060
	21st to end	Day	21% 11% 4 6% 3 3 3 3 5% 6% 35%	4623
February	1st to 10th	Day	18% 12% 4 8% 4 3 4 3 5% 5% 32%	2000
	11th to 20th	Day	21% 12% 5% 9% 5% 4 3 2 3 5% 30%	1948
	21st to end	Day	20% 10% 5% 8% 4 3 3 2 5% 6% 34%	1650
March	1st to 10th	Day	19% 12% 4 7% 4 4 4 3 4 5% 34%	4480
	11th to 20th	Day	13% 9% 3 7% 3 4 4 3 4 5% 45%	4934
	21st to end	Day	14% 8% 3 7% 4 4 4 4 5% 6% 41%	5465
April	1st to 10th	Day	14% 7% 2 7% 5% 5% 4 3 6% 6% 41%	2400
	11th to 20th	Day	14% 8% 2 6% 3 4 4 3 6% 6% 42%	2374
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 4 5% 6% 37%	2545
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 4 6% 8% 26%	5862
	11th to 20th	Day	16% 9% 3 9% 6% 6% 6% 4 5% 7% 28%	5861
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	6433
June	1st to 10th	Day	11% 7% 3 7% 4 5% 6% 5% 6% 8% 38%	2600
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 10% 42%	2600
	21st to end	Day	7% 5% 1 6% 5% 6% 6% 5% 10% 11% 38%	2600
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 39%	5900
	11th to 20th	Day	9% 6% 2 7% 6% 6% 7% 5% 8% 11% 33%	5900
	21st to end	Day	14% 8% 3 8% 6% 6% 6% 5% 8% 11% 24%	6424
August	1st to 10th	Day	7% 5% 2 6% 5% 6% 6% 5% 7% 10% 42%	4234
	11th to 20th	Day	8% 4 2 7% 5% 5% 6% 6% 8% 12% 37%	3894
	21st to end	Day	6% 4 1 4 4 5% 5% 4 6% 9% 50%	4312
September	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 5% 6% 39%	2294
	11th to 20th	Day	13% 6% 2 7% 3 5% 5% 4 6% 7% 43%	2200
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 5% 48%	2200
October	1st to 10th	Day	10% 6% 2 4 3 3 4 2 5% 6% 55%	2200
	11th to 20th	Day	13% 5% 2 5% 3 3 3 2 4 6% 54%	2120
	21st to end	Day	18% 6% 2 4 4 3 3 3 5% 7% 45%	2055
November	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 5% 5% 52%	1852
	11th to 20th	Day	14% 8% 2 6% 3 3 4 3 5% 7% 45%	1890
	21st to end	Day	16% 10% 3 7% 4 4 3 3 5% 5% 41%	1890
December	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 4 5% 39%	2948
	11th to 20th	Day	19% 16% 6% 8% 5% 4 4 3 4 5% 26%	3373
	21st to end	Day	18% 15% 5% 7% 4 4 5% 4 6% 7% 26%	4466
January	1st to 10th	Night	16% 15% 5% 11% 4 3 3 2 4 6% 32%	5889
	11th to 20th	Night	19% 12% 4 7% 5% 5% 3 2 3 3 36%	5900
	21st to end	Night	19% 12% 4 7% 4 3 3 3 4 4 39%	6329
February	1st to 10th	Night	20% 11% 4 8% 4 4 4 3 5% 5% 31%	2400
	11th to 20th	Night	23% 10% 5% 9% 4 4 3 2 3 5% 32%	2338
	21st to end	Night	21% 13% 4 7% 4 3 3 4 4 5% 31%	1980
March	1st to 10th	Night	18% 15% 3 6% 4 4 4 3 4 5% 34%	5373
	11th to 20th	Night	13% 6% 2 4 3 3 4 4 5% 7% 48%	5010
	21st to end	Night	14% 9% 3 8% 5% 4 5% 4 5% 6% 37%	5467
April	1st to 10th	Night	13% 7% 2 7% 4 3 5% 4 6% 7% 42%	2015
	11th to 20th	Night	15% 7% 2 4 3 3 3 3 5% 7% 46%	1975
	21st to end	Night	13% 8% 3 6% 4 4 4 4 6% 7% 42%	1855
May	1st to 10th	Night	15% 11% 4 9% 5% 5% 5% 4 7% 7% 29%	4033
	11th to 20th	Night	15% 11% 4 9% 6% 5% 6% 4 6% 8% 26%	4032
	21st to end	Night	13% 7% 3 7% 5% 4 5% 4 7% 9% 36%	4421
June	1st to 10th	Night	7% 6% 2 7% 5% 6% 5% 4 7% 10% 42%	1800
	11th to 20th	Night	5% 4 1 5% 4 4 4 5% 7% 12% 49%	1800
	21st to end	Night	5% 5% 1 5% 5% 5% 6% 5% 8% 11% 42%	1800
July	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 5% 7% 10% 42%	4058
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 5% 8% 12% 38%	4057
	21st to end	Night	10% 8% 3 9% 6% 6% 6% 6% 8% 11% 28%	4427
August	1st to 10th	Night	6% 4 2 6% 4 4 5% 3 6% 9% 51%	2915
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 8% 11% 44%	3151
	21st to end	Night	4 3 1 4 3 3 4 4 6% 9% 60%	3586
September	1st to 10th	Night	11% 6% 2 6% 5% 4 4 3 6% 7% 47%	2085
	11th to 20th	Night	11% 7% 2 7% 4 4 5% 3 5% 7% 46%	2200
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 50%	2200
October	1st to 10th	Night	10% 5% 2 3 2 2 3 3 4 6% 60%	2200
	11th to 20th	Night	16% 4 2 4 3 4 4 3 4 5% 52%	2280
	21st to end	Night	16% 7% 2 6% 3 3 2 2 4 6% 49%	2781
November	1st to 10th	Night	13% 6% 3 6% 3 3 3 3 4 6% 50%	2666
	11th to 20th	Night	14% 8% 2 4 3 3 3 3 4 7% 48%	2730
	21st to end	Night	16% 10% 3 5% 4 3 3 2 4 6% 43%	2730
December	1st to 10th	Night	18% 14% 4 9% 4 3 3 2 3 3 36%	4277
	11th to 20th	Night	23% 13% 4 7% 4 2 3 3 3 5% 33%	4822
	21st to end	Night	14% 14% 5% 10% 6% 6% 5% 4 6% 6% 25%	6490

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	59% 5% 9% 16% 10% 1	4057
	11th to 20th	Day	55% 3 5% 16% 19% 2	4060
	21st to end	Day	49% 4 7% 23% 14% 2	4623
February	1st to 10th	Day	54% 5% 7% 17% 15% 2	2000
	11th to 20th	Day	58% 4 7% 16% 13% 2	1958
	21st to end	Day	51% 4 10% 15% 15% 5%	1650
March	1st to 10th	Day	52% 5% 5% 14% 16% 8%	4480
	11th to 20th	Day	41% 4 8% 21% 19% 7%	4934
	21st to end	Day	42% 6% 9% 27% 15%	5465
April	1st to 10th	Day	41% 6% 11% 23% 16% 3	2400
	11th to 20th	Day	40% 7% 8% 21% 22% 3	2374
	21st to end	Day	45% 7% 10% 25% 12% 1	2545
May	1st to 10th	Day	52% 9% 12% 18% 9% 1	5897
	11th to 20th	Day	53% 8% 14% 18% 8%	5865
	21st to end	Day	46% 9% 10% 19% 14% 2	6447
June	1st to 10th	Day	40% 9% 13% 21% 14% 2	2600
	11th to 20th	Day	34% 10% 17% 21% 16% 2	2600
	21st to end	Day	35% 11% 17% 19% 14% 4	2600
July	1st to 10th	Day	36% 10% 19% 22% 13% 1	5835
	11th to 20th	Day	41% 10% 21% 22% 5% 1	5831
	21st to end	Day	50% 9% 18% 19% 4 1	6240
August	1st to 10th	Day	32% 10% 16% 27% 14% 1	4221
	11th to 20th	Day	34% 10% 17% 25% 13% 1	3931
	21st to end	Day	28% 9% 12% 36% 14% 1	4311
September	1st to 10th	Day	42% 8% 12% 17% 17% 3	2294
	11th to 20th	Day	40% 7% 12% 23% 18% 2	2200
	21st to end	Day	36% 7% 12% 22% 20% 3	2200
October	1st to 10th	Day	24% 4 7% 21% 38% 7%	3590
	11th to 20th	Day	23% 4 9% 23% 31% 10%	3438
	21st to end	Day	31% 4 8% 27% 22% 9%	3292
November	1st to 10th	Day	34% 5% 9% 22% 26% 4	1852
	11th to 20th	Day	39% 5% 8% 23% 21% 5%	1890
	21st to end	Day	44% 5% 7% 21% 19% 4	1890
December	1st to 10th	Day	47% 4 6% 20% 21% 1	2948
	11th to 20th	Day	61% 4 7% 16% 10% 2	3370
	21st to end	Day	56% 6% 10% 19% 8% 2	4466
January	1st to 10th	Night	54% 4 9% 18% 13% 1	5889
	11th to 20th	Night	53% 4 5% 15% 17% 5%	5900
	21st to end	Night	50% 4 6% 17% 19% 4	6329
February	1st to 10th	Night	55% 5% 9% 17% 14% 1	2400
	11th to 20th	Night	56% 4 7% 17% 13% 4	2339
	21st to end	Night	55% 5% 6% 14% 16% 3	1980
March	1st to 10th	Night	52% 5% 7% 16% 16% 5%	5373
	11th to 20th	Night	35% 5% 8% 22% 20% 10%	5010
	21st to end	Night	46% 6% 9% 25% 13% 1	5467
April	1st to 10th	Night	40% 7% 10% 22% 18% 3	2015
	11th to 20th	Night	38% 5% 9% 21% 22% 5%	1975
	21st to end	Night	40% 7% 11% 27% 14% 1	1855
May	1st to 10th	Night	51% 8% 13% 19% 8% 1	4060
	11th to 20th	Night	53% 9% 13% 15% 9%	4033
	21st to end	Night	41% 10% 15% 21% 12% 1	4429
June	1st to 10th	Night	34% 9% 13% 28% 14% 2	1800
	11th to 20th	Night	27% 9% 20% 26% 17% 2	1800
	21st to end	Night	31% 12% 16% 24% 14% 4	1800
July	1st to 10th	Night	33% 11% 18% 22% 14% 1	4015
	11th to 20th	Night	35% 10% 22% 24% 7% 2	4006
	21st to end	Night	47% 11% 19% 17% 5%	4297
August	1st to 10th	Night	28% 8% 14% 33% 16% 1	2904
	11th to 20th	Night	30% 10% 20% 28% 11% 1	3180
	21st to end	Night	20% 7% 12% 39% 20% 2	3586
September	1st to 10th	Night	35% 9% 12% 20% 19% 5%	2085
	11th to 20th	Night	36% 7% 11% 22% 22% 1	2200
	21st to end	Night	33% 6% 11% 21% 23% 5%	2200
October	1st to 10th	Night	22% 5% 7% 24% 33% 9%	3590
	11th to 20th	Night	23% 3 6% 25% 28% 15%	3701
	21st to end	Night	26% 3 8% 23% 28% 11%	4494
November	1st to 10th	Night	36% 4 7% 24% 23% 6%	2666
	11th to 20th	Night	37% 5% 8% 21% 23% 6%	2730
	21st to end	Night	44% 3 7% 24% 18% 4	2730
December	1st to 10th	Night	54% 4 5% 15% 21% 1	4277
	11th to 20th	Night	54% 5% 7% 19% 14% 2	4824
	21st to end	Night	56% 8% 11% 17% 8%	6490

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% 23% 35% 11% 2 1	300
	11th to 20th	Day	36% 30% 22% 8% 3	300
	21st to end	Day	28% 27% 35% 7% 3	330
February	1st to 10th	Day	29% 27% 28% 14% 1	300
	11th to 20th	Day	40% 27% 26% 4 2 1	300
	21st to end	Day	39% 24% 31% 5% 1	249
March	1st to 10th	Day	32% 22% 32% 10% 3	300
	11th to 20th	Day	30% 22% 29% 15% 4 1	480
	21st to end	Day	29% 21% 30% 14% 6%	550
April	1st to 10th	Day	28% 18% 27% 19% 8%	500
	11th to 20th	Day	21% 19% 32% 19% 8% 1	492
	21st to end	Day	23% 15% 33% 17% 9% 2	500
May	1st to 10th	Day	20% 18% 33% 18% 7% 4	503
	11th to 20th	Day	17% 13% 29% 24% 10% 7%	527
	21st to end	Day	15% 9% 26% 24% 16% 9%	573
June	1st to 10th	Day	12% 7% 24% 28% 18% 10%	530
	11th to 20th	Day	7% 5% 20% 32% 27% 10%	530
	21st to end	Day	8% 5% 24% 28% 22% 13%	530
July	1st to 10th	Day	11% 2 16% 28% 26% 16%	525
	11th to 20th	Day	8% 7% 15% 26% 28% 15%	524
	21st to end	Day	12% 5% 13% 27% 29% 14%	576
August	1st to 10th	Day	12% 3 15% 28% 31% 12%	526
	11th to 20th	Day	12% 5% 14% 33% 27% 9%	519
	21st to end	Day	11% 4 11% 28% 31% 15%	583
September	1st to 10th	Day	13% 5% 16% 26% 30% 11%	530
	11th to 20th	Day	14% 4 13% 28% 28% 13%	530
	21st to end	Day	16% 7% 19% 29% 21% 8%	530
October	1st to 10th	Day	12% 6% 21% 31% 24% 6%	530
	11th to 20th	Day	14% 13% 27% 27% 16% 4	530
	21st to end	Day	24% 13% 28% 24% 8% 2	438
November	1st to 10th	Day	19% 14% 32% 24% 9% 2	330
	11th to 20th	Day	21% 18% 37% 20% 4	330
	21st to end	Day	24% 18% 32% 18% 6% 2	330
December	1st to 10th	Day	31% 23% 29% 14% 3	306
	11th to 20th	Day	32% 22% 24% 15% 7%	300
	21st to end	Day	30% 24% 28% 15% 3	330
January	1st to 10th	Night	26% 21% 29% 21% 3	800
	11th to 20th	Night	30% 24% 25% 18% 3	800
	21st to end	Night	24% 18% 36% 20% 2	880
February	1st to 10th	Night	27% 16% 34% 21% 3	800
	11th to 20th	Night	31% 20% 32% 15% 1	783
	21st to end	Night	32% 21% 29% 17% 1	660
March	1st to 10th	Night	24% 17% 33% 23% 3	800
	11th to 20th	Night	24% 18% 31% 21% 6% 1	800
	21st to end	Night	23% 17% 32% 22% 6%	880
April	1st to 10th	Night	17% 17% 32% 27% 8%	615
	11th to 20th	Night	20% 12% 34% 23% 11%	593
	21st to end	Night	17% 11% 32% 30% 9% 1	600
May	1st to 10th	Night	17% 9% 31% 29% 13% 1	600
	11th to 20th	Night	14% 7% 26% 34% 17% 3	591
	21st to end	Night	9% 3 22% 34% 27% 4	650
June	1st to 10th	Night	8% 5% 16% 38% 28% 5%	600
	11th to 20th	Night	5% 2 16% 38% 32% 7%	600
	21st to end	Night	5% 2 15% 38% 34% 7%	600
July	1st to 10th	Night	10% 3 11% 27% 42% 8%	585
	11th to 20th	Night	8% 3 11% 26% 44% 8%	582
	21st to end	Night	9% 3 6% 32% 43% 7%	657
August	1st to 10th	Night	11% 3 7% 29% 43% 7%	597
	11th to 20th	Night	8% 1 9% 40% 35% 6%	594
	21st to end	Night	8% 2 7% 34% 41% 8%	660
September	1st to 10th	Night	11% 4 11% 31% 38% 6%	685
	11th to 20th	Night	12% 3 12% 30% 36% 6%	800
	21st to end	Night	13% 4 17% 32% 29% 5%	800
October	1st to 10th	Night	11% 5% 18% 32% 29% 5%	800
	11th to 20th	Night	19% 8% 20% 35% 17% 2	800
	21st to end	Night	19% 10% 28% 28% 14% 2	880
November	1st to 10th	Night	15% 10% 24% 35% 14% 2	820
	11th to 20th	Night	17% 16% 29% 28% 10% 1	840
	21st to end	Night	23% 14% 27% 27% 9%	840
December	1st to 10th	Night	29% 15% 27% 24% 4	809
	11th to 20th	Night	25% 15% 30% 24% 6% 1	800
	21st to end	Night	26% 20% 26% 24% 4	880

Page generated at 2025-11-30 00:00:56. Version ac07

Copyright © 2025 Attilla Danko.