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 2024-12-24.

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% 47%	101665
	Night	13% 5% 2 5% 3 3 3 3 4 6% 52%	98536
Transparency	Day	36% 4 10% 24% 20% 6%	105330
	Night	32% 4 9% 22% 23% 10%	102998
Seeing	Day	14% 6% 21% 27% 24% 8%	15388
	Night	15% 6% 24% 34% 20% 2	25278

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% 6% 2 5% 4 5% 3 2 3 5% 48%	2847
	11th to 20th	Day	13% 6% 1 3 2 3 3 2 3 4 59%	2850
	21st to end	Day	22% 8% 2 6% 3 2 3 2 3 4 44%	3135
February	1st to 10th	Day	21% 9% 3 6% 5% 3 3 2 4 4 41%	1710
	11th to 20th	Day	21% 7% 2 5% 4 4 4 3 4 4 44%	1797
	21st to end	Day	25% 8% 2 5% 2 3 3 2 3 5% 44%	1702
March	1st to 10th	Day	18% 8% 2 6% 4 3 3 3 4 5% 44%	3436
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 39%	3480
	21st to end	Day	18% 9% 3 6% 4 3 4 3 5% 6% 39%	3814
April	1st to 10th	Day	15% 6% 3 6% 4 3 3 3 4 7% 45%	2118
	11th to 20th	Day	17% 7% 2 4 4 3 4 3 5% 7% 44%	2254
	21st to end	Day	16% 7% 2 5% 4 4 4 4 5% 5% 44%	2280
May	1st to 10th	Day	21% 7% 2 6% 5% 4 4 3 5% 6% 36%	4049
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 6% 7% 45%	4082
	21st to end	Day	19% 8% 3 6% 5% 4 4 3 5% 7% 35%	4477
June	1st to 10th	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 45%	2470
	11th to 20th	Day	7% 5% 2 5% 5% 6% 6% 5% 7% 7% 46%	2470
	21st to end	Day	5% 3 2 5% 4 5% 5% 4 7% 9% 52%	2470
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 4 8% 9% 43%	4120
	11th to 20th	Day	4 3 1 5% 4 4 4 4 7% 9% 57%	4120
	21st to end	Day	9% 8% 3 8% 5% 5% 5% 4 6% 10% 36%	4465
August	1st to 10th	Day	3 2 1 3 2 3 4 3 5% 8% 65%	4104
	11th to 20th	Day	5% 3 2 5% 3 4 5% 4 7% 9% 52%	3986
	21st to end	Day	4 4 2 5% 5% 6% 6% 5% 7% 10% 47%	4180
September	1st to 10th	Day	10% 4 3 6% 5% 5% 4 3 5% 6% 50%	2182
	11th to 20th	Day	10% 5% 1 6% 4 4 4 4 6% 8% 47%	2090
	21st to end	Day	8% 5% 1 4 3 4 3 3 5% 7% 56%	2090
October	1st to 10th	Day	7% 4 1 5% 3 3 4 3 5% 6% 60%	1931
	11th to 20th	Day	15% 5% 1 4 2 2 2 2 2 5% 59%	1900
	21st to end	Day	18% 5% 2 4 2 3 3 2 4 4 53%	2090
November	1st to 10th	Day	13% 6% 2 4 4 2 3 3 5% 6% 51%	1958
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 3 6% 57%	1995
	21st to end	Day	17% 7% 2 4 3 2 2 2 3 5% 52%	1800
December	1st to 10th	Day	17% 6% 2 4 4 3 2 3 4 6% 49%	1800
	11th to 20th	Day	16% 9% 3 6% 4 3 4 3 4 6% 42%	2251
	21st to end	Day	19% 8% 2 6% 4 3 3 2 3 5% 45%	3162
January	1st to 10th	Night	15% 9% 2 4 3 3 3 3 4 5% 51%	4108
	11th to 20th	Night	15% 7% 1 3 3 2 2 2 3 4 58%	4120
	21st to end	Night	25% 6% 2 4 2 3 3 3 3 4 46%	4532
February	1st to 10th	Night	19% 6% 2 5% 4 3 3 3 3 4 47%	2470
	11th to 20th	Night	19% 7% 3 5% 3 3 3 3 4 5% 47%	2287
	21st to end	Night	19% 6% 2 5% 3 3 3 3 3 4 49%	1751
March	1st to 10th	Night	20% 8% 3 6% 4 3 3 3 4 6% 40%	3419
	11th to 20th	Night	16% 7% 2 5% 4 4 4 3 4 6% 46%	3480
	21st to end	Night	15% 7% 3 5% 4 4 4 3 5% 6% 46%	3817
April	1st to 10th	Night	12% 5% 1 6% 5% 3 3 3 5% 7% 50%	2061
	11th to 20th	Night	14% 5% 2 4 4 3 4 3 5% 6% 50%	1875
	21st to end	Night	12% 5% 2 5% 4 2 3 3 5% 7% 51%	1900
May	1st to 10th	Night	17% 8% 2 7% 4 3 4 4 5% 7% 38%	2838
	11th to 20th	Night	14% 5% 2 5% 3 3 4 4 5% 7% 47%	2823
	21st to end	Night	14% 6% 2 6% 4 4 4 3 6% 8% 41%	3090
June	1st to 10th	Night	5% 4 1 5% 3 3 4 4 5% 9% 56%	1710
	11th to 20th	Night	5% 3 1 3 2 3 3 3 5% 8% 63%	1710
	21st to end	Night	4 3 1 3 3 4 3 3 6% 10% 59%	1710
July	1st to 10th	Night	7% 4 1 4 3 4 4 4 7% 9% 51%	2850
	11th to 20th	Night	4 2 1 3 2 3 3 3 4 9% 64%	2850
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 4 7% 9% 46%	3098
August	1st to 10th	Night	3 2 2 2 2 2 2 5% 8% 72%	2836
	11th to 20th	Night	3 2 1 3 3 3 4 4 6% 12% 60%	2850
	21st to end	Night	2 3 1 5% 4 4 4 5% 7% 9% 55%	3476
September	1st to 10th	Night	6% 5% 2 5% 3 4 4 3 5% 8% 56%	1993
	11th to 20th	Night	11% 3 1 5% 4 4 5% 3 5% 7% 52%	2090
	21st to end	Night	7% 3 1 4 4 3 3 3 4 6% 63%	2090
October	1st to 10th	Night	7% 3 2 4 3 3 3 3 5% 6% 63%	2228
	11th to 20th	Night	12% 4 1 4 2 2 2 3 4 5% 61%	2280
	21st to end	Night	16% 5% 2 3 2 2 1 2 3 5% 59%	2508
November	1st to 10th	Night	13% 4 1 4 3 3 3 2 4 5% 57%	2340
	11th to 20th	Night	10% 5% 2 4 4 3 3 2 4 5% 59%	2402
	21st to end	Night	16% 6% 2 5% 3 3 3 3 3 5% 52%	2600
December	1st to 10th	Night	16% 6% 2 5% 3 2 3 3 5% 5% 51%	2600
	11th to 20th	Night	15% 8% 2 5% 4 4 3 3 4 4 48%	3166
	21st to end	Night	17% 6% 2 5% 3 2 3 2 4 5% 49%	4578

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	42% 2 6% 23% 25% 3	2848
	11th to 20th	Day	31% 2 9% 28% 26% 4	2850
	21st to end	Day	47% 2 4 17% 21% 8%	3135
February	1st to 10th	Day	49% 2 7% 17% 18% 7%	1710
	11th to 20th	Day	46% 3 5% 21% 19% 7%	1807
	21st to end	Day	46% 2 5% 15% 24% 8%	1702
March	1st to 10th	Day	43% 3 7% 15% 23% 9%	3436
	11th to 20th	Day	45% 4 10% 20% 17% 4	3480
	21st to end	Day	46% 4 9% 21% 17% 3	3814
April	1st to 10th	Day	41% 3 8% 23% 18% 8%	2118
	11th to 20th	Day	40% 4 8% 20% 19% 7%	2254
	21st to end	Day	41% 6% 8% 23% 20% 4	2280
May	1st to 10th	Day	47% 6% 9% 24% 12% 3	4087
	11th to 20th	Day	38% 6% 10% 24% 21% 1	4086
	21st to end	Day	48% 6% 11% 19% 13% 3	4489
June	1st to 10th	Day	34% 6% 14% 28% 15% 3	2470
	11th to 20th	Day	34% 6% 14% 25% 19% 2	2470
	21st to end	Day	27% 7% 11% 33% 20% 2	2470
July	1st to 10th	Day	36% 5% 20% 28% 10% 1	4056
	11th to 20th	Day	23% 4 11% 37% 23% 1	4051
	21st to end	Day	42% 5% 14% 29% 10%	4325
August	1st to 10th	Day	18% 4 13% 30% 27% 9%	4090
	11th to 20th	Day	27% 4 18% 38% 11% 2	4025
	21st to end	Day	31% 6% 17% 30% 14% 2	4179
September	1st to 10th	Day	35% 5% 10% 20% 20% 9%	2182
	11th to 20th	Day	34% 5% 11% 22% 20% 7%	2090
	21st to end	Day	27% 4 9% 22% 25% 12%	2090
October	1st to 10th	Day	16% 3 7% 12% 32% 32%	3204
	11th to 20th	Day	21% 2 2 18% 34% 22%	3140
	21st to end	Day	28% 2 5% 31% 26% 8%	3428
November	1st to 10th	Day	34% 4 7% 22% 24% 8%	1958
	11th to 20th	Day	31% 2 7% 20% 29% 11%	1995
	21st to end	Day	38% 2 6% 19% 29% 8%	1800
December	1st to 10th	Day	37% 3 9% 24% 21% 6%	1800
	11th to 20th	Day	44% 3 5% 18% 22% 8%	2249
	21st to end	Day	44% 3 4 20% 23% 6%	3162
January	1st to 10th	Night	38% 3 5% 18% 31% 6%	4108
	11th to 20th	Night	33% 2 10% 20% 28% 7%	4120
	21st to end	Night	45% 3 6% 15% 23% 9%	4532
February	1st to 10th	Night	41% 3 7% 19% 21% 8%	2470
	11th to 20th	Night	42% 3 7% 18% 22% 8%	2287
	21st to end	Night	40% 3 5% 16% 23% 12%	1751
March	1st to 10th	Night	47% 3 6% 15% 17% 12%	3419
	11th to 20th	Night	40% 4 8% 22% 16% 10%	3480
	21st to end	Night	40% 4 9% 20% 25% 3	3817
April	1st to 10th	Night	35% 4 9% 20% 19% 13%	2061
	11th to 20th	Night	36% 4 7% 21% 21% 11%	1875
	21st to end	Night	33% 4 11% 24% 24% 5%	1900
May	1st to 10th	Night	44% 7% 9% 21% 13% 6%	2865
	11th to 20th	Night	36% 5% 13% 24% 20% 2	2824
	21st to end	Night	39% 8% 13% 21% 12% 6%	3099
June	1st to 10th	Night	25% 6% 15% 29% 22% 4	1710
	11th to 20th	Night	20% 5% 11% 36% 22% 5%	1710
	21st to end	Night	20% 6% 12% 29% 29% 4	1710
July	1st to 10th	Night	27% 5% 19% 31% 16% 1	2805
	11th to 20th	Night	19% 4 11% 40% 24% 4	2796
	21st to end	Night	33% 5% 16% 29% 16% 1	2999
August	1st to 10th	Night	12% 3 14% 28% 37% 7%	2826
	11th to 20th	Night	18% 4 16% 38% 20% 4	2877
	21st to end	Night	24% 5% 15% 29% 24% 2	3476
September	1st to 10th	Night	27% 5% 10% 23% 24% 11%	1993
	11th to 20th	Night	32% 5% 9% 23% 21% 10%	2090
	21st to end	Night	23% 3 10% 21% 28% 15%	2090
October	1st to 10th	Night	14% 2 6% 14% 24% 40%	3722
	11th to 20th	Night	18% 2 4 15% 36% 25%	3779
	21st to end	Night	26% 2 4 26% 27% 15%	4120
November	1st to 10th	Night	31% 4 8% 19% 26% 13%	2340
	11th to 20th	Night	29% 3 6% 20% 27% 14%	2402
	21st to end	Night	36% 2 7% 19% 27% 9%	2600
December	1st to 10th	Night	36% 3 9% 20% 22% 9%	2600
	11th to 20th	Night	41% 2 5% 17% 24% 11%	3167
	21st to end	Night	38% 3 6% 21% 25% 7%	4578

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	23% 10% 34% 26% 6%	270
	11th to 20th	Day	19% 20% 33% 24% 4 1	270
	21st to end	Day	21% 14% 37% 17% 11%	297
February	1st to 10th	Day	29% 10% 34% 19% 7% 1	270
	11th to 20th	Day	26% 17% 35% 19% 4	270
	21st to end	Day	35% 16% 36% 9% 4	225
March	1st to 10th	Day	21% 14% 37% 23% 6%	270
	11th to 20th	Day	23% 18% 34% 16% 7% 1	270
	21st to end	Day	19% 16% 39% 22% 3	297
April	1st to 10th	Day	21% 15% 34% 23% 6% 1	298
	11th to 20th	Day	25% 14% 28% 25% 8%	452
	21st to end	Day	19% 10% 32% 27% 10% 2	460
May	1st to 10th	Day	16% 8% 33% 32% 11% 1	633
	11th to 20th	Day	16% 5% 28% 33% 16% 3	675
	21st to end	Day	13% 7% 21% 36% 17% 6%	734
June	1st to 10th	Day	8% 3 13% 33% 34% 10%	680
	11th to 20th	Day	7% 2 15% 36% 33% 8%	680
	21st to end	Day	5% 1 14% 30% 36% 14%	680
July	1st to 10th	Day	7% 2 9% 30% 37% 14%	671
	11th to 20th	Day	3 6% 31% 42% 17%	668
	21st to end	Day	6% 1 6% 28% 41% 17%	739
August	1st to 10th	Day	5% 1 4 29% 46% 15%	676
	11th to 20th	Day	10% 1 6% 28% 44% 12%	636
	21st to end	Day	8% 1 4 19% 44% 24%	539
September	1st to 10th	Day	9% 1 6% 23% 41% 20%	392
	11th to 20th	Day	5% 3 8% 26% 35% 23%	300
	21st to end	Day	12% 3 10% 30% 25% 20%	300
October	1st to 10th	Day	4 2 15% 35% 34% 11%	300
	11th to 20th	Day	14% 6% 26% 29% 17% 8%	300
	21st to end	Day	22% 8% 22% 27% 18% 3	330
November	1st to 10th	Day	17% 8% 30% 26% 14% 4	300
	11th to 20th	Day	17% 6% 31% 31% 12% 2	300
	21st to end	Day	20% 14% 26% 25% 12% 3	300
December	1st to 10th	Day	20% 10% 32% 26% 10% 2	300
	11th to 20th	Day	25% 10% 37% 21% 7% 1	300
	21st to end	Day	22% 12% 40% 19% 7% 1	306
January	1st to 10th	Night	20% 8% 32% 33% 7%	950
	11th to 20th	Night	21% 10% 34% 27% 7%	950
	21st to end	Night	20% 8% 36% 30% 6%	1045
February	1st to 10th	Night	22% 10% 33% 29% 6%	950
	11th to 20th	Night	24% 9% 36% 27% 3	812
	21st to end	Night	25% 13% 36% 24% 2	495
March	1st to 10th	Night	21% 9% 33% 30% 6%	570
	11th to 20th	Night	18% 10% 34% 32% 6%	570
	21st to end	Night	17% 9% 38% 30% 6%	627
April	1st to 10th	Night	14% 9% 40% 30% 7%	570
	11th to 20th	Night	16% 9% 37% 27% 11%	563
	21st to end	Night	14% 8% 39% 28% 10% 1	570
May	1st to 10th	Night	11% 6% 34% 39% 10% 1	570
	11th to 20th	Night	12% 5% 27% 35% 18% 2	561
	21st to end	Night	10% 3 23% 38% 23% 3	617
June	1st to 10th	Night	6% 3 11% 42% 35% 3	570
	11th to 20th	Night	6% 14% 48% 30% 2	570
	21st to end	Night	4 9% 39% 43% 6%	570
July	1st to 10th	Night	5% 1 5% 37% 48% 4	555
	11th to 20th	Night	3 1 4 35% 50% 7%	552
	21st to end	Night	4 1 4 36% 47% 8%	624
August	1st to 10th	Night	2 1 5% 36% 51% 5%	567
	11th to 20th	Night	7% 1 6% 33% 49% 5%	564
	21st to end	Night	5% 1 3 35% 50% 6%	627
September	1st to 10th	Night	8% 2 5% 34% 46% 6%	570
	11th to 20th	Night	13% 1 8% 35% 40% 4	570
	21st to end	Night	7% 2 11% 40% 36% 5%	570
October	1st to 10th	Night	8% 2 13% 43% 31% 3	708
	11th to 20th	Night	14% 5% 22% 40% 18% 2	760
	21st to end	Night	18% 6% 25% 31% 18% 2	836
November	1st to 10th	Night	14% 4 24% 41% 16% 1	780
	11th to 20th	Night	12% 8% 29% 39% 11% 1	802
	21st to end	Night	18% 9% 29% 31% 13% 1	1000
December	1st to 10th	Night	20% 7% 30% 37% 7%	1000
	11th to 20th	Night	24% 7% 28% 34% 7%	1000
	21st to end	Night	21% 8% 31% 31% 8%	1063

Page generated at 2024-12-21 03:13:47. Version ac07

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