Knoxville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Knoxville clear sky chart from 2005-11-06 to 2025-07-06.

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% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	119990
	Night	13% 8% 3 7% 5% 4 4 4 6% 7% 39%	118814
Transparency	Day	42% 6% 11% 22% 15% 3	123782
	Night	42% 6% 10% 22% 16% 3	123158
Seeing	Day	17% 9% 21% 24% 19% 9%	15709
	Night	17% 7% 21% 32% 20% 3	25762

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	16% 11% 4 8% 5% 5% 4 4 6% 6% 31%	4056
	11th to 20th	Day	15% 9% 4 8% 5% 4 5% 4 5% 6% 34%	4060
	21st to end	Day	17% 11% 3 8% 5% 4 3 3 5% 7% 35%	4466
February	1st to 10th	Day	17% 10% 2 9% 5% 4 5% 3 4 6% 34%	1978
	11th to 20th	Day	22% 8% 3 8% 5% 4 4 3 4 6% 32%	1948
	21st to end	Day	19% 9% 3 8% 4 4 4 4 5% 5% 35%	1650
March	1st to 10th	Day	18% 10% 3 7% 5% 4 4 3 5% 6% 34%	4636
	11th to 20th	Day	11% 6% 3 6% 4 4 3 3 5% 7% 48%	4980
	21st to end	Day	15% 8% 3 7% 4 4 4 4 4 6% 42%	5465
April	1st to 10th	Day	11% 5% 3 6% 5% 5% 5% 4 7% 8% 41%	2260
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 5% 7% 44%	2399
	21st to end	Day	12% 8% 2 7% 5% 5% 4 3 6% 8% 41%	2600
May	1st to 10th	Day	14% 10% 4 9% 6% 5% 5% 4 6% 8% 30%	5862
	11th to 20th	Day	13% 9% 4 10% 6% 6% 6% 5% 7% 7% 27%	5861
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 4 7% 8% 35%	6433
June	1st to 10th	Day	9% 7% 2 7% 5% 5% 6% 5% 8% 11% 36%	2600
	11th to 20th	Day	5% 4 2 6% 6% 6% 7% 5% 8% 12% 39%	2600
	21st to end	Day	7% 4 2 6% 4 6% 6% 6% 9% 11% 38%	2600
July	1st to 10th	Day	5% 4 2 6% 5% 6% 7% 6% 9% 14% 35%	4185
	11th to 20th	Day	9% 5% 2 7% 6% 6% 6% 4 7% 10% 39%	4120
	21st to end	Day	15% 11% 5% 11% 7% 6% 7% 5% 7% 8% 18%	4466
August	1st to 10th	Day	6% 5% 3 7% 6% 6% 6% 6% 8% 11% 35%	4104
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 12% 38%	3966
	21st to end	Day	5% 4 2 6% 4 5% 5% 4 6% 10% 48%	4180
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 5% 9% 41%	2100
	11th to 20th	Day	14% 6% 2 6% 4 5% 4 4 6% 8% 40%	2090
	21st to end	Day	14% 7% 2 5% 4 4 3 4 6% 6% 45%	2090
October	1st to 10th	Day	10% 6% 3 5% 3 4 3 4 5% 6% 52%	2090
	11th to 20th	Day	12% 5% 2 6% 3 3 3 3 4 7% 51%	1938
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 6% 48%	2076
November	1st to 10th	Day	11% 5% 2 5% 4 3 3 3 5% 6% 53%	1762
	11th to 20th	Day	12% 6% 3 5% 4 3 3 3 4 7% 48%	1800
	21st to end	Day	13% 8% 4 6% 4 3 5% 4 4 7% 42%	1800
December	1st to 10th	Day	14% 8% 3 7% 4 4 4 4 5% 7% 40%	2930
	11th to 20th	Day	17% 13% 4 11% 6% 5% 5% 3 4 5% 26%	3373
	21st to end	Day	14% 12% 4 9% 6% 5% 5% 4 5% 8% 28%	4466
January	1st to 10th	Night	15% 10% 3 10% 4 4 4 3 5% 6% 36%	5889
	11th to 20th	Night	19% 8% 3 7% 5% 3 3 3 5% 5% 39%	5900
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 5% 38%	6490
February	1st to 10th	Night	17% 9% 3 7% 4 4 4 3 5% 7% 35%	2419
	11th to 20th	Night	22% 10% 4 9% 3 4 4 4 4 5% 33%	2338
	21st to end	Night	21% 10% 3 6% 3 5% 4 3 5% 6% 34%	1980
March	1st to 10th	Night	16% 10% 3 9% 5% 4 4 4 5% 6% 34%	5217
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 6% 8% 50%	4980
	21st to end	Night	12% 7% 3 8% 5% 5% 5% 4 6% 6% 41%	5467
April	1st to 10th	Night	11% 5% 2 5% 4 4 5% 3 7% 8% 46%	2155
	11th to 20th	Night	12% 7% 2 7% 4 4 4 3 5% 6% 46%	1949
	21st to end	Night	13% 5% 2 7% 5% 5% 5% 4 6% 7% 42%	1800
May	1st to 10th	Night	14% 9% 3 9% 5% 5% 5% 4 7% 9% 28%	4033
	11th to 20th	Night	15% 11% 4 10% 5% 5% 5% 4 6% 7% 28%	4032
	21st to end	Night	12% 8% 3 8% 6% 4 4 4 6% 8% 36%	4421
June	1st to 10th	Night	7% 7% 2 8% 5% 4 6% 5% 8% 11% 36%	1800
	11th to 20th	Night	3 5% 2 5% 4 5% 5% 5% 8% 12% 45%	1800
	21st to end	Night	6% 6% 2 7% 6% 5% 6% 5% 8% 11% 40%	1800
July	1st to 10th	Night	8% 6% 2 8% 5% 7% 7% 6% 10% 11% 31%	2885
	11th to 20th	Night	8% 5% 2 5% 4 5% 5% 5% 8% 10% 42%	2840
	21st to end	Night	11% 10% 4 10% 8% 7% 7% 5% 7% 9% 22%	3087
August	1st to 10th	Night	5% 5% 2 8% 6% 7% 6% 5% 7% 10% 37%	2825
	11th to 20th	Night	8% 6% 3 7% 4 4 4 4 6% 9% 44%	2845
	21st to end	Night	5% 4 2 5% 4 4 5% 4 8% 11% 49%	3476
September	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 5% 6% 7% 43%	2060
	11th to 20th	Night	10% 8% 4 8% 5% 5% 5% 3 5% 8% 39%	2090
	21st to end	Night	11% 6% 2 6% 4 5% 4 4 4 6% 47%	2090
October	1st to 10th	Night	11% 6% 2 6% 3 4 3 4 4 6% 52%	2090
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 6% 50%	2239
	21st to end	Night	13% 6% 2 6% 4 3 4 3 4 5% 51%	2519
November	1st to 10th	Night	13% 6% 3 5% 4 3 3 3 4 7% 50%	2536
	11th to 20th	Night	14% 6% 2 6% 5% 3 4 3 5% 6% 46%	2600
	21st to end	Night	14% 8% 2 6% 4 4 4 3 5% 7% 44%	2600
December	1st to 10th	Night	16% 9% 3 7% 5% 4 4 3 5% 6% 38%	4250
	11th to 20th	Night	19% 11% 4 8% 5% 4 4 3 5% 6% 31%	4822
	21st to end	Night	15% 11% 4 8% 5% 5% 5% 4 6% 8% 29%	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	50% 5% 6% 26% 11% 1	4057
	11th to 20th	Day	48% 5% 6% 20% 21% 1	4060
	21st to end	Day	49% 4 8% 25% 14% 1	4466
February	1st to 10th	Day	51% 5% 9% 20% 15% 2	1978
	11th to 20th	Day	53% 4 9% 19% 13% 2	1958
	21st to end	Day	50% 4 7% 17% 16% 5%	1650
March	1st to 10th	Day	50% 5% 6% 16% 16% 8%	4636
	11th to 20th	Day	37% 3 6% 19% 27% 8%	4980
	21st to end	Day	42% 4 7% 31% 14% 1	5465
April	1st to 10th	Day	39% 6% 10% 25% 17% 3	2260
	11th to 20th	Day	40% 4 8% 19% 23% 5%	2399
	21st to end	Day	42% 4 10% 27% 14% 2	2600
May	1st to 10th	Day	50% 6% 12% 21% 9% 1	5897
	11th to 20th	Day	52% 8% 14% 18% 7% 1	5865
	21st to end	Day	44% 7% 11% 20% 15% 3	6447
June	1st to 10th	Day	40% 8% 15% 22% 12% 2	2600
	11th to 20th	Day	35% 8% 20% 22% 13% 2	2600
	21st to end	Day	36% 11% 17% 21% 13% 4	2600
July	1st to 10th	Day	34% 11% 22% 21% 11% 1	4120
	11th to 20th	Day	38% 7% 20% 24% 7% 3	4051
	21st to end	Day	60% 9% 12% 13% 5% 1	4324
August	1st to 10th	Day	39% 9% 17% 26% 9% 1	4091
	11th to 20th	Day	35% 8% 19% 24% 12% 2	4005
	21st to end	Day	30% 7% 14% 35% 13% 2	4179
September	1st to 10th	Day	39% 8% 11% 19% 17% 6%	2100
	11th to 20th	Day	40% 7% 11% 22% 18% 3	2090
	21st to end	Day	37% 6% 10% 22% 19% 6%	2090
October	1st to 10th	Day	27% 4 6% 22% 31% 11%	3480
	11th to 20th	Day	24% 4 6% 25% 30% 10%	3204
	21st to end	Day	28% 5% 9% 28% 22% 9%	3402
November	1st to 10th	Day	32% 5% 7% 24% 27% 5%	1762
	11th to 20th	Day	36% 3 7% 25% 24% 5%	1800
	21st to end	Day	42% 4 7% 25% 20% 3	1800
December	1st to 10th	Day	42% 4 7% 23% 21% 1	2930
	11th to 20th	Day	59% 5% 8% 18% 10% 1	3370
	21st to end	Day	52% 6% 12% 22% 8% 1	4466
January	1st to 10th	Night	48% 4 9% 23% 15% 1	5889
	11th to 20th	Night	47% 4 5% 20% 20% 4	5900
	21st to end	Night	47% 4 6% 23% 19% 3	6490
February	1st to 10th	Night	48% 4 9% 21% 16% 2	2419
	11th to 20th	Night	54% 4 8% 17% 14% 3	2339
	21st to end	Night	51% 3 8% 18% 16% 4	1980
March	1st to 10th	Night	49% 5% 7% 18% 16% 5%	5217
	11th to 20th	Night	32% 3 8% 22% 25% 10%	4980
	21st to end	Night	42% 5% 9% 28% 14% 2	5467
April	1st to 10th	Night	36% 4 13% 25% 19% 3	2155
	11th to 20th	Night	39% 4 8% 20% 22% 6%	1949
	21st to end	Night	40% 5% 11% 27% 14% 2	1800
May	1st to 10th	Night	49% 7% 15% 20% 9% 1	4060
	11th to 20th	Night	55% 6% 14% 17% 8%	4033
	21st to end	Night	44% 7% 12% 23% 13% 1	4429
June	1st to 10th	Night	38% 9% 16% 22% 14% 2	1800
	11th to 20th	Night	28% 10% 22% 25% 14% 2	1800
	21st to end	Night	35% 9% 16% 22% 13% 5%	1800
July	1st to 10th	Night	41% 11% 20% 18% 9% 1	2840
	11th to 20th	Night	34% 9% 21% 26% 8% 3	2786
	21st to end	Night	54% 11% 15% 14% 6%	2988
August	1st to 10th	Night	38% 8% 18% 26% 9%	2814
	11th to 20th	Night	36% 7% 16% 28% 13% 1	2872
	21st to end	Night	28% 6% 15% 37% 12% 2	3476
September	1st to 10th	Night	38% 8% 13% 19% 17% 6%	2060
	11th to 20th	Night	42% 8% 11% 17% 20% 1	2090
	21st to end	Night	37% 6% 10% 21% 21% 5%	2090
October	1st to 10th	Night	32% 4 6% 20% 27% 11%	3480
	11th to 20th	Night	24% 3 5% 25% 32% 12%	3712
	21st to end	Night	26% 4 4 28% 29% 9%	4143
November	1st to 10th	Night	36% 3 7% 22% 24% 7%	2536
	11th to 20th	Night	39% 4 6% 22% 23% 6%	2600
	21st to end	Night	40% 4 7% 26% 20% 3	2600
December	1st to 10th	Night	47% 4 7% 21% 19% 2	4250
	11th to 20th	Night	54% 4 8% 20% 13% 2	4824
	21st to end	Night	49% 8% 12% 20% 10% 1	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	25% 16% 33% 21% 5% 1	300
	11th to 20th	Day	28% 20% 31% 14% 7% 1	300
	21st to end	Day	21% 21% 36% 16% 6%	330
February	1st to 10th	Day	28% 17% 27% 18% 9% 1	300
	11th to 20th	Day	35% 20% 27% 16% 3	300
	21st to end	Day	34% 16% 34% 13% 3	249
March	1st to 10th	Day	25% 18% 28% 19% 8% 1	365
	11th to 20th	Day	23% 16% 33% 21% 6%	500
	21st to end	Day	23% 15% 30% 25% 7% 1	550
April	1st to 10th	Day	20% 17% 26% 24% 11% 2	500
	11th to 20th	Day	18% 13% 28% 24% 14% 3	492
	21st to end	Day	19% 11% 27% 26% 15% 3	500
May	1st to 10th	Day	16% 12% 32% 23% 12% 5%	503
	11th to 20th	Day	15% 8% 26% 23% 20% 9%	527
	21st to end	Day	16% 8% 18% 24% 18% 15%	573
June	1st to 10th	Day	12% 7% 18% 29% 22% 12%	530
	11th to 20th	Day	7% 5% 15% 28% 31% 15%	530
	21st to end	Day	10% 3 16% 27% 27% 18%	530
July	1st to 10th	Day	9% 3 12% 23% 30% 23%	505
	11th to 20th	Day	12% 4 8% 27% 29% 19%	484
	21st to end	Day	11% 4 9% 29% 31% 17%	532
August	1st to 10th	Day	14% 3 10% 24% 30% 18%	486
	11th to 20th	Day	11% 3 10% 33% 28% 14%	479
	21st to end	Day	12% 2 6% 23% 29% 27%	539
September	1st to 10th	Day	11% 2 10% 24% 34% 19%	490
	11th to 20th	Day	15% 4 8% 23% 31% 18%	490
	21st to end	Day	18% 5% 12% 27% 29% 10%	490
October	1st to 10th	Day	14% 6% 19% 24% 26% 11%	490
	11th to 20th	Day	14% 10% 21% 28% 22% 5%	490
	21st to end	Day	20% 6% 20% 27% 23% 3	525
November	1st to 10th	Day	18% 7% 25% 30% 15% 4	300
	11th to 20th	Day	14% 12% 32% 31% 10% 1	300
	21st to end	Day	13% 12% 32% 28% 14% 1	300
December	1st to 10th	Day	24% 19% 30% 20% 6%	300
	11th to 20th	Day	23% 15% 28% 26% 8% 1	300
	21st to end	Day	25% 15% 27% 22% 10% 2	330
January	1st to 10th	Night	21% 13% 27% 34% 5%	800
	11th to 20th	Night	26% 11% 30% 27% 6%	800
	21st to end	Night	20% 12% 34% 32% 2	880
February	1st to 10th	Night	22% 11% 31% 33% 4	800
	11th to 20th	Night	27% 12% 36% 23% 2	783
	21st to end	Night	27% 11% 33% 26% 3	660
March	1st to 10th	Night	20% 13% 28% 34% 4	800
	11th to 20th	Night	21% 11% 32% 28% 7% 1	800
	21st to end	Night	20% 10% 30% 32% 8%	880
April	1st to 10th	Night	15% 10% 31% 34% 9%	755
	11th to 20th	Night	15% 10% 32% 28% 15% 1	593
	21st to end	Night	15% 6% 27% 38% 13% 1	600
May	1st to 10th	Night	14% 7% 23% 37% 18% 2	600
	11th to 20th	Night	16% 6% 18% 31% 25% 4	591
	21st to end	Night	10% 4 18% 27% 36% 5%	650
June	1st to 10th	Night	10% 3 13% 38% 33% 4	600
	11th to 20th	Night	6% 3 13% 34% 36% 8%	600
	21st to end	Night	7% 3 12% 32% 39% 8%	600
July	1st to 10th	Night	11% 3 8% 26% 41% 12%	570
	11th to 20th	Night	7% 2 5% 30% 46% 10%	552
	21st to end	Night	9% 3 8% 31% 40% 10%	624
August	1st to 10th	Night	9% 3 6% 27% 44% 10%	567
	11th to 20th	Night	12% 2 6% 32% 42% 6%	564
	21st to end	Night	11% 2 6% 25% 46% 10%	627
September	1st to 10th	Night	11% 3 7% 30% 41% 7%	730
	11th to 20th	Night	14% 4 9% 29% 37% 6%	760
	21st to end	Night	14% 4 15% 34% 31% 3	760
October	1st to 10th	Night	14% 6% 14% 28% 31% 7%	760
	11th to 20th	Night	17% 6% 21% 36% 19% 2	760
	21st to end	Night	15% 5% 22% 36% 20% 1	836
November	1st to 10th	Night	16% 4 18% 39% 20% 2	780
	11th to 20th	Night	17% 9% 25% 38% 12% 1	800
	21st to end	Night	18% 8% 24% 37% 14%	800
December	1st to 10th	Night	24% 10% 26% 33% 8%	800
	11th to 20th	Night	22% 10% 25% 35% 9%	800
	21st to end	Night	24% 12% 22% 35% 7%	880

Page generated at 2025-07-03 01:30:13. Version ac07

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