Clarksville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clarksville clear sky chart from 2005-11-06 to 2026-04-17.

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 5% 4 4 4 3 5% 7% 48%	131938
	Night	13% 5% 2 5% 3 3 3 3 4 6% 53%	130517
Transparency	Day	36% 4 10% 24% 20% 6%	135564
	Night	33% 3 9% 22% 23% 10%	134955
Seeing	Day	14% 6% 21% 28% 23% 8%	17091
	Night	15% 6% 24% 34% 19% 2	27051

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% 5% 2 5% 3 4 3 3 4 6% 50%	5289
	11th to 20th	Day	8% 5% 1 4 2 3 3 2 4 6% 62%	5310
	21st to end	Day	22% 8% 2 6% 3 3 3 2 3 4 43%	5812
February	1st to 10th	Day	21% 9% 3 5% 5% 3 3 2 3 4 43%	1890
	11th to 20th	Day	20% 7% 2 5% 4 4 4 3 4 4 43%	1992
	21st to end	Day	22% 8% 2 5% 2 3 3 2 3 5% 47%	1876
March	1st to 10th	Day	21% 7% 2 5% 3 3 3 3 4 5% 45%	5046
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 4 6% 53%	5090
	21st to end	Day	16% 8% 3 6% 3 4 4 3 5% 6% 41%	5583
April	1st to 10th	Day	16% 6% 3 6% 4 3 3 3 5% 7% 44%	2341
	11th to 20th	Day	17% 7% 2 5% 4 3 3 3 5% 7% 44%	2446
	21st to end	Day	16% 7% 3 6% 4 4 5% 3 5% 5% 43%	2400
May	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 38%	5815
	11th to 20th	Day	14% 7% 3 7% 4 4 4 3 5% 7% 41%	5862
	21st to end	Day	16% 8% 3 6% 4 4 4 4 6% 7% 37%	6434
June	1st to 10th	Day	8% 4 2 6% 4 5% 6% 4 7% 9% 45%	2600
	11th to 20th	Day	7% 5% 2 5% 5% 6% 6% 5% 7% 7% 46%	2600
	21st to end	Day	5% 3 2 5% 4 4 5% 4 7% 9% 53%	2600
July	1st to 10th	Day	7% 5% 2 8% 6% 6% 6% 5% 8% 10% 36%	5900
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 9% 60%	5900
	21st to end	Day	6% 6% 2 7% 4 5% 5% 4 6% 9% 45%	6422
August	1st to 10th	Day	3 2 1 3 2 3 4 3 5% 8% 65%	4234
	11th to 20th	Day	5% 3 1 5% 3 4 5% 4 7% 9% 53%	4114
	21st to end	Day	4 4 2 5% 5% 6% 6% 5% 7% 9% 47%	4312
September	1st to 10th	Day	10% 5% 3 6% 5% 4 4 3 5% 6% 50%	2297
	11th to 20th	Day	10% 5% 1 6% 4 4 4 4 6% 8% 47%	2200
	21st to end	Day	8% 5% 1 4 3 4 3 3 5% 7% 56%	2200
October	1st to 10th	Day	7% 3 1 4 3 3 3 3 4 6% 61%	2032
	11th to 20th	Day	15% 5% 1 4 3 2 2 2 2 5% 60%	2000
	21st to end	Day	18% 5% 2 5% 3 3 3 2 4 4 52%	2200
November	1st to 10th	Day	13% 6% 2 4 4 2 3 3 5% 6% 53%	2058
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 3 5% 57%	2095
	21st to end	Day	17% 7% 2 4 3 3 3 2 3 5% 52%	1890
December	1st to 10th	Day	18% 6% 2 4 3 3 2 2 3 5% 52%	3030
	11th to 20th	Day	21% 8% 3 5% 3 2 3 3 4 5% 42%	3481
	21st to end	Day	21% 9% 3 6% 3 3 3 2 3 5% 44%	4587
January	1st to 10th	Night	14% 6% 2 4 3 3 3 3 4 6% 52%	7634
	11th to 20th	Night	8% 4 1 3 2 2 2 2 3 4 70%	7680
	21st to end	Night	25% 7% 2 6% 3 3 3 3 3 4 42%	8402
February	1st to 10th	Night	19% 6% 2 5% 4 3 3 3 3 5% 48%	2730
	11th to 20th	Night	19% 7% 3 5% 3 3 3 3 4 5% 46%	2533
	21st to end	Night	18% 6% 2 4 3 2 3 3 3 4 51%	1929
March	1st to 10th	Night	20% 7% 2 5% 4 3 3 2 4 5% 44%	5029
	11th to 20th	Night	12% 5% 2 4 3 4 4 3 4 7% 53%	5090
	21st to end	Night	15% 6% 2 4 3 4 4 3 5% 6% 48%	5588
April	1st to 10th	Night	13% 5% 2 6% 4 4 3 3 5% 7% 49%	2277
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 50%	2035
	21st to end	Night	12% 5% 2 5% 4 2 3 3 5% 8% 51%	2000
May	1st to 10th	Night	18% 7% 2 6% 4 4 4 4 5% 7% 38%	4081
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	4053
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 8% 44%	4443
June	1st to 10th	Night	6% 4 2 5% 3 3 4 4 5% 9% 56%	1800
	11th to 20th	Night	5% 3 1 4 2 3 3 3 5% 8% 62%	1800
	21st to end	Night	4 3 1 3 3 4 4 3 6% 10% 60%	1800
July	1st to 10th	Night	6% 4 2 6% 5% 5% 5% 5% 8% 11% 43%	4078
	11th to 20th	Night	4 2 1 3 2 3 3 3 5% 9% 65%	4077
	21st to end	Night	4 4 2 5% 4 4 5% 4 7% 9% 53%	4449
August	1st to 10th	Night	3 2 2 2 2 2 2 5% 8% 72%	2926
	11th to 20th	Night	3 2 1 3 3 3 4 4 6% 12% 60%	2942
	21st to end	Night	3 3 2 5% 4 4 5% 5% 7% 9% 54%	3586
September	1st to 10th	Night	6% 5% 2 5% 3 4 4 3 5% 8% 57%	2098
	11th to 20th	Night	10% 3 1 5% 4 4 5% 3 6% 7% 52%	2200
	21st to end	Night	6% 3 1 4 4 3 3 3 4 6% 63%	2200
October	1st to 10th	Night	6% 3 2 4 3 3 2 3 5% 6% 64%	2346
	11th to 20th	Night	12% 4 1 4 2 2 2 3 3 5% 62%	2400
	21st to end	Night	16% 5% 2 3 2 2 2 2 3 5% 59%	2640
November	1st to 10th	Night	13% 4 1 4 3 3 3 2 4 5% 58%	2460
	11th to 20th	Night	10% 5% 2 4 3 3 3 2 4 5% 59%	2522
	21st to end	Night	16% 6% 2 5% 3 3 3 3 3 5% 52%	2730
December	1st to 10th	Night	15% 7% 2 5% 3 2 3 3 4 4 53%	4380
	11th to 20th	Night	17% 8% 3 5% 4 4 3 2 3 3 48%	4946
	21st to end	Night	18% 8% 3 6% 3 2 3 2 3 5% 47%	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	38% 1 8% 29% 22% 2	5290
	11th to 20th	Day	26% 2 7% 26% 36% 4	5310
	21st to end	Day	47% 2 3 17% 21% 10%	5812
February	1st to 10th	Day	48% 2 6% 18% 19% 7%	1890
	11th to 20th	Day	46% 2 6% 21% 18% 6%	2002
	21st to end	Day	43% 2 5% 16% 25% 9%	1876
March	1st to 10th	Day	42% 3 5% 15% 20% 14%	5046
	11th to 20th	Day	34% 3 7% 17% 20% 19%	5090
	21st to end	Day	44% 3 9% 23% 17% 3	5585
April	1st to 10th	Day	42% 3 8% 22% 17% 8%	2341
	11th to 20th	Day	41% 4 9% 20% 20% 7%	2446
	21st to end	Day	42% 5% 8% 22% 19% 4	2400
May	1st to 10th	Day	47% 4 10% 25% 12% 2	5853
	11th to 20th	Day	43% 4 11% 20% 19% 2	5866
	21st to end	Day	45% 5% 12% 21% 14% 3	6447
June	1st to 10th	Day	34% 6% 14% 28% 15% 3	2600
	11th to 20th	Day	34% 6% 14% 25% 18% 2	2600
	21st to end	Day	26% 6% 13% 33% 19% 2	2600
July	1st to 10th	Day	41% 5% 19% 27% 8%	5836
	11th to 20th	Day	22% 4 14% 39% 21% 1	5831
	21st to end	Day	34% 4 14% 34% 12% 1	6240
August	1st to 10th	Day	18% 4 12% 31% 26% 8%	4220
	11th to 20th	Day	27% 4 18% 39% 11% 2	4153
	21st to end	Day	31% 6% 17% 30% 14% 2	4311
September	1st to 10th	Day	35% 5% 10% 20% 21% 9%	2297
	11th to 20th	Day	34% 5% 12% 24% 19% 7%	2200
	21st to end	Day	28% 4 9% 22% 25% 12%	2200
October	1st to 10th	Day	15% 3 7% 12% 33% 31%	3305
	11th to 20th	Day	21% 2 3 19% 34% 22%	3240
	21st to end	Day	29% 2 5% 30% 26% 8%	3538
November	1st to 10th	Day	33% 4 7% 22% 25% 8%	2058
	11th to 20th	Day	31% 2 8% 21% 28% 10%	2095
	21st to end	Day	38% 2 6% 20% 28% 7%	1890
December	1st to 10th	Day	37% 2 7% 30% 21% 4	3030
	11th to 20th	Day	46% 3 4 19% 23% 7%	3479
	21st to end	Day	46% 2 4 21% 23% 4	4587
January	1st to 10th	Night	35% 2 8% 27% 26% 3	7635
	11th to 20th	Night	21% 2 6% 20% 37% 14%	7680
	21st to end	Night	48% 2 4 14% 20% 10%	8402
February	1st to 10th	Night	41% 3 6% 20% 21% 9%	2730
	11th to 20th	Night	43% 2 7% 19% 21% 7%	2533
	21st to end	Night	38% 3 5% 16% 24% 13%	1929
March	1st to 10th	Night	44% 2 5% 13% 20% 15%	5029
	11th to 20th	Night	32% 3 6% 18% 17% 23%	5090
	21st to end	Night	38% 3 9% 20% 25% 5%	5588
April	1st to 10th	Night	36% 4 9% 21% 19% 12%	2277
	11th to 20th	Night	36% 4 7% 21% 21% 11%	2035
	21st to end	Night	33% 4 11% 24% 23% 5%	2000
May	1st to 10th	Night	46% 5% 11% 22% 12% 4	4108
	11th to 20th	Night	39% 4 13% 20% 20% 2	4054
	21st to end	Night	38% 6% 14% 21% 13% 8%	4452
June	1st to 10th	Night	26% 6% 15% 28% 22% 4	1800
	11th to 20th	Night	21% 5% 12% 36% 22% 5%	1800
	21st to end	Night	20% 6% 12% 29% 29% 4	1800
July	1st to 10th	Night	33% 5% 20% 29% 13% 1	4035
	11th to 20th	Night	18% 3 14% 39% 23% 2	4026
	21st to end	Night	27% 5% 16% 33% 17% 3	4320
August	1st to 10th	Night	12% 3 14% 28% 37% 7%	2916
	11th to 20th	Night	19% 4 16% 38% 19% 4	2969
	21st to end	Night	25% 5% 15% 29% 24% 3	3586
September	1st to 10th	Night	28% 5% 10% 22% 25% 11%	2098
	11th to 20th	Night	31% 5% 9% 25% 20% 10%	2200
	21st to end	Night	23% 3 10% 21% 28% 15%	2200
October	1st to 10th	Night	14% 2 6% 14% 24% 40%	3840
	11th to 20th	Night	18% 2 4 16% 36% 25%	3899
	21st to end	Night	26% 2 4 26% 27% 15%	4252
November	1st to 10th	Night	29% 4 8% 19% 27% 13%	2460
	11th to 20th	Night	29% 3 7% 20% 27% 14%	2522
	21st to end	Night	37% 2 7% 19% 27% 9%	2730
December	1st to 10th	Night	37% 2 6% 25% 25% 5%	4380
	11th to 20th	Night	44% 2 5% 15% 23% 11%	4947
	21st to end	Night	42% 3 6% 19% 24% 6%	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% 10% 35% 26% 7%	330
	11th to 20th	Day	16% 18% 33% 27% 5% 1	330
	21st to end	Day	21% 13% 38% 18% 9%	363
February	1st to 10th	Day	28% 10% 37% 18% 7% 1	330
	11th to 20th	Day	25% 15% 38% 18% 4	330
	21st to end	Day	29% 14% 40% 12% 5%	273
March	1st to 10th	Day	23% 13% 36% 21% 6%	330
	11th to 20th	Day	22% 18% 38% 15% 5% 1	330
	21st to end	Day	17% 14% 39% 25% 5%	363
April	1st to 10th	Day	22% 13% 33% 23% 7% 1	361
	11th to 20th	Day	25% 15% 28% 24% 7%	516
	21st to end	Day	19% 9% 31% 27% 11% 2	500
May	1st to 10th	Day	16% 7% 34% 32% 11% 1	682
	11th to 20th	Day	16% 7% 28% 32% 15% 3	725
	21st to end	Day	13% 6% 21% 37% 17% 6%	789
June	1st to 10th	Day	8% 3 14% 33% 33% 9%	730
	11th to 20th	Day	7% 2 15% 36% 32% 8%	730
	21st to end	Day	5% 1 13% 30% 38% 13%	730
July	1st to 10th	Day	7% 2 9% 30% 38% 14%	721
	11th to 20th	Day	3 6% 32% 41% 17%	718
	21st to end	Day	6% 1 5% 28% 41% 18%	794
August	1st to 10th	Day	5% 1 4 29% 46% 15%	726
	11th to 20th	Day	10% 1 5% 27% 44% 13%	684
	21st to end	Day	9% 1 4 20% 43% 23%	583
September	1st to 10th	Day	9% 1 7% 24% 40% 19%	427
	11th to 20th	Day	4 2 8% 25% 36% 25%	330
	21st to end	Day	12% 3 11% 30% 23% 20%	330
October	1st to 10th	Day	4 2 14% 36% 34% 11%	330
	11th to 20th	Day	13% 5% 26% 30% 18% 8%	330
	21st to end	Day	23% 8% 23% 26% 18% 3	363
November	1st to 10th	Day	16% 8% 30% 26% 16% 4	330
	11th to 20th	Day	16% 6% 31% 33% 12% 2	330
	21st to end	Day	20% 13% 27% 26% 12% 2	330
December	1st to 10th	Day	21% 9% 33% 26% 10% 2	330
	11th to 20th	Day	25% 10% 35% 21% 8% 1	330
	21st to end	Day	21% 12% 39% 21% 6%	363
January	1st to 10th	Night	20% 8% 32% 33% 7%	1050
	11th to 20th	Night	19% 10% 36% 28% 7%	1050
	21st to end	Night	21% 8% 36% 30% 6%	1155
February	1st to 10th	Night	22% 9% 33% 29% 6%	1050
	11th to 20th	Night	24% 10% 36% 26% 3	898
	21st to end	Night	23% 12% 36% 26% 3	545
March	1st to 10th	Night	22% 9% 33% 30% 6%	630
	11th to 20th	Night	17% 11% 34% 32% 6%	630
	21st to end	Night	16% 9% 37% 32% 6%	693
April	1st to 10th	Night	15% 9% 39% 31% 7%	630
	11th to 20th	Night	16% 10% 37% 26% 10%	611
	21st to end	Night	13% 8% 38% 29% 11% 1	600
May	1st to 10th	Night	12% 5% 33% 39% 10% 1	600
	11th to 20th	Night	13% 6% 28% 34% 18% 2	591
	21st to end	Night	10% 3 23% 39% 22% 3	650
June	1st to 10th	Night	7% 3 11% 42% 34% 3	600
	11th to 20th	Night	6% 1 14% 48% 30% 2	600
	21st to end	Night	4 8% 38% 44% 5%	600
July	1st to 10th	Night	5% 1 5% 36% 49% 4	585
	11th to 20th	Night	4 1 4 35% 50% 7%	582
	21st to end	Night	4 1 4 36% 47% 9%	657
August	1st to 10th	Night	3 1 5% 35% 51% 6%	597
	11th to 20th	Night	7% 1 5% 32% 49% 6%	594
	21st to end	Night	6% 1 3 35% 49% 6%	660
September	1st to 10th	Night	8% 2 5% 34% 45% 6%	600
	11th to 20th	Night	12% 1 7% 34% 41% 5%	600
	21st to end	Night	7% 2 11% 41% 35% 5%	600
October	1st to 10th	Night	7% 1 13% 44% 32% 3	746
	11th to 20th	Night	13% 5% 22% 40% 19% 2	800
	21st to end	Night	18% 6% 25% 31% 17% 2	880
November	1st to 10th	Night	14% 4 24% 42% 16% 1	820
	11th to 20th	Night	12% 7% 29% 39% 11% 1	842
	21st to end	Night	19% 9% 29% 31% 12% 1	1050
December	1st to 10th	Night	19% 7% 31% 36% 7%	1050
	11th to 20th	Night	24% 6% 28% 34% 7%	1050
	21st to end	Night	21% 8% 31% 32% 8%	1155

Page generated at 2026-04-14 01:44:30. Version ac07

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