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 2024-11-03.

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	12% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	101007
	Night	13% 8% 3 7% 5% 4 4 4 6% 7% 39%	97938
Transparency	Day	43% 6% 12% 23% 14% 3	100819
	Night	43% 6% 11% 22% 15% 3	97795
Seeing	Day	17% 9% 21% 24% 19% 9%	14854
	Night	17% 7% 21% 32% 20% 3	24871

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% 10% 4 8% 5% 5% 5% 5% 7% 6% 29%	2836
	11th to 20th	Day	17% 9% 3 9% 6% 5% 5% 4 5% 5% 29%	2840
	21st to end	Day	19% 13% 4 8% 5% 4 3 3 5% 6% 31%	3124
February	1st to 10th	Day	18% 11% 2 9% 5% 4 4 3 4 6% 34%	1879
	11th to 20th	Day	22% 8% 3 8% 5% 4 4 3 4 6% 34%	1848
	21st to end	Day	20% 10% 3 8% 5% 4 4 4 5% 5% 34%	1570
March	1st to 10th	Day	22% 11% 3 8% 5% 4 4 3 4 5% 32%	3234
	11th to 20th	Day	12% 6% 3 7% 4 4 3 3 4 6% 47%	3480
	21st to end	Day	15% 9% 3 8% 4 4 4 4 5% 6% 38%	3815
April	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 4 7% 7% 41%	2147
	11th to 20th	Day	13% 8% 2 6% 4 4 4 4 5% 6% 44%	2278
	21st to end	Day	12% 8% 2 7% 4 5% 4 3 6% 7% 41%	2470
May	1st to 10th	Day	14% 8% 3 8% 6% 5% 5% 4 6% 7% 34%	4082
	11th to 20th	Day	14% 8% 4 8% 5% 5% 6% 4 6% 7% 32%	4081
	21st to end	Day	9% 7% 3 7% 5% 5% 5% 5% 7% 9% 39%	4476
June	1st to 10th	Day	9% 7% 2 7% 5% 5% 6% 5% 8% 11% 36%	2470
	11th to 20th	Day	5% 4 2 6% 6% 6% 6% 5% 9% 12% 40%	2470
	21st to end	Day	7% 5% 2 7% 5% 7% 6% 6% 9% 10% 37%	2470
July	1st to 10th	Day	5% 4 2 6% 5% 6% 7% 6% 9% 14% 35%	4120
	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% 7% 48%	2076
November	1st to 10th	Day	12% 5% 2 5% 4 3 3 2 5% 6% 53%	1690
	11th to 20th	Day	13% 6% 3 5% 4 3 3 3 4 7% 49%	1710
	21st to end	Day	14% 7% 4 6% 4 3 5% 4 4 7% 43%	1710
December	1st to 10th	Day	19% 9% 3 8% 4 4 4 4 6% 7% 32%	1710
	11th to 20th	Day	14% 11% 2 9% 5% 5% 5% 4 5% 6% 34%	2153
	21st to end	Day	16% 13% 4 8% 6% 5% 5% 4 4 7% 29%	3124
January	1st to 10th	Night	17% 11% 4 9% 4 4 4 4 5% 6% 32%	4109
	11th to 20th	Night	19% 10% 3 7% 6% 3 3 3 4 5% 37%	4120
	21st to end	Night	20% 13% 4 7% 5% 5% 4 3 5% 4 31%	4532
February	1st to 10th	Night	16% 9% 3 7% 4 4 4 4 5% 7% 35%	2299
	11th to 20th	Night	21% 10% 4 8% 3 4 4 4 4 5% 34%	2218
	21st to end	Night	22% 10% 3 7% 4 5% 4 3 5% 6% 32%	1884
March	1st to 10th	Night	20% 10% 3 9% 5% 4 4 4 5% 6% 28%	3619
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 6% 7% 48%	3480
	21st to end	Night	14% 6% 3 8% 5% 4 5% 4 5% 5% 41%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 7% 7% 46%	2047
	11th to 20th	Night	12% 8% 2 6% 4 4 4 3 5% 6% 45%	1851
	21st to end	Night	13% 5% 2 7% 5% 4 5% 4 5% 7% 43%	1710
May	1st to 10th	Night	13% 9% 3 9% 5% 5% 5% 4 6% 8% 32%	2813
	11th to 20th	Night	16% 9% 3 8% 4 4 4 4 6% 7% 35%	2812
	21st to end	Night	6% 6% 3 8% 6% 5% 5% 4 8% 9% 41%	3079
June	1st to 10th	Night	7% 7% 2 8% 5% 4 6% 5% 8% 12% 36%	1710
	11th to 20th	Night	3 5% 2 5% 4 4 5% 5% 9% 13% 46%	1710
	21st to end	Night	6% 6% 2 7% 6% 5% 6% 4 8% 11% 39%	1710
July	1st to 10th	Night	8% 6% 2 8% 5% 7% 7% 6% 10% 11% 31%	2840
	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% 2 5% 4 3 3 3 3 6% 51%	2433
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 5% 6% 47%	2470
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	2470
December	1st to 10th	Night	19% 10% 3 7% 6% 4 4 3 5% 5% 33%	2470
	11th to 20th	Night	16% 10% 3 8% 4 3 4 3 4 7% 37%	3042
	21st to end	Night	16% 12% 3 8% 6% 6% 6% 5% 6% 7% 25%	4532

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	51% 6% 6% 24% 12% 1	2837
	11th to 20th	Day	54% 5% 8% 19% 14% 1	2840
	21st to end	Day	53% 5% 7% 22% 13%	3124
February	1st to 10th	Day	52% 4 8% 20% 15% 1	1879
	11th to 20th	Day	52% 4 8% 20% 14% 2	1858
	21st to end	Day	51% 4 8% 16% 15% 5%	1570
March	1st to 10th	Day	52% 6% 7% 18% 12% 5%	3234
	11th to 20th	Day	39% 4 7% 24% 23% 3	3480
	21st to end	Day	45% 5% 7% 28% 13% 2	3815
April	1st to 10th	Day	39% 6% 10% 24% 18% 3	2147
	11th to 20th	Day	40% 4 8% 19% 23% 5%	2278
	21st to end	Day	42% 4 10% 28% 15% 2	2470
May	1st to 10th	Day	47% 6% 12% 22% 11% 1	4120
	11th to 20th	Day	49% 7% 11% 23% 10% 1	4085
	21st to end	Day	38% 8% 13% 21% 17% 3	4489
June	1st to 10th	Day	40% 8% 15% 22% 12% 2	2470
	11th to 20th	Day	34% 7% 20% 22% 14% 3	2470
	21st to end	Day	37% 10% 16% 20% 13% 4	2470
July	1st to 10th	Day	34% 11% 23% 21% 11% 1	4055
	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	32% 5% 8% 24% 25% 6%	2090
	11th to 20th	Day	33% 4 8% 24% 24% 6%	1938
	21st to end	Day	36% 4 6% 26% 22% 5%	2076
November	1st to 10th	Day	32% 5% 7% 24% 27% 5%	1690
	11th to 20th	Day	36% 3 8% 25% 24% 5%	1710
	21st to end	Day	41% 4 6% 25% 20% 3	1710
December	1st to 10th	Day	51% 4 9% 23% 11% 2	1710
	11th to 20th	Day	49% 4 10% 20% 15% 2	2150
	21st to end	Day	53% 6% 8% 25% 8% 1	3124
January	1st to 10th	Night	51% 5% 8% 20% 14% 1	4109
	11th to 20th	Night	50% 4 7% 17% 19% 3	4120
	21st to end	Night	54% 5% 6% 19% 14% 1	4532
February	1st to 10th	Night	48% 4 9% 21% 16% 2	2299
	11th to 20th	Night	53% 4 7% 18% 15% 4	2219
	21st to end	Night	54% 3 8% 16% 15% 4	1884
March	1st to 10th	Night	52% 8% 9% 14% 14% 3	3619
	11th to 20th	Night	36% 4 9% 24% 18% 9%	3480
	21st to end	Night	43% 5% 8% 27% 15% 2	3817
April	1st to 10th	Night	36% 4 12% 25% 19% 3	2047
	11th to 20th	Night	39% 4 9% 20% 22% 7%	1851
	21st to end	Night	39% 5% 11% 28% 15% 2	1710
May	1st to 10th	Night	47% 7% 13% 22% 10% 1	2840
	11th to 20th	Night	46% 6% 14% 22% 11% 1	2813
	21st to end	Night	36% 8% 14% 26% 15% 1	3087
June	1st to 10th	Night	38% 9% 16% 21% 14% 2	1710
	11th to 20th	Night	26% 9% 22% 26% 14% 2	1710
	21st to end	Night	36% 9% 16% 22% 13% 5%	1710
July	1st to 10th	Night	41% 11% 20% 18% 9% 1	2795
	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	33% 4 9% 20% 25% 8%	2090
	11th to 20th	Night	35% 5% 7% 24% 24% 7%	2239
	21st to end	Night	34% 5% 4 24% 26% 7%	2519
November	1st to 10th	Night	36% 3 7% 22% 25% 7%	2433
	11th to 20th	Night	38% 4 6% 22% 23% 7%	2470
	21st to end	Night	40% 3 7% 27% 20% 3	2470
December	1st to 10th	Night	52% 4 9% 20% 12% 2	2470
	11th to 20th	Night	47% 3 8% 22% 17% 2	3044
	21st to end	Night	52% 8% 8% 19% 11% 1	4532

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% 17% 34% 20% 5% 1	270
	11th to 20th	Day	29% 20% 30% 14% 6% 1	270
	21st to end	Day	20% 21% 36% 15% 7%	297
February	1st to 10th	Day	30% 16% 26% 19% 9% 1	270
	11th to 20th	Day	34% 20% 26% 17% 3	270
	21st to end	Day	37% 17% 33% 11% 3	225
March	1st to 10th	Day	24% 18% 29% 19% 9% 2	332
	11th to 20th	Day	22% 17% 34% 21% 7%	460
	21st to end	Day	23% 14% 29% 25% 8% 1	506
April	1st to 10th	Day	20% 17% 25% 24% 12% 3	460
	11th to 20th	Day	19% 12% 28% 23% 14% 4	452
	21st to end	Day	20% 11% 27% 26% 14% 3	460
May	1st to 10th	Day	16% 10% 31% 24% 13% 5%	463
	11th to 20th	Day	15% 7% 26% 23% 21% 9%	487
	21st to end	Day	15% 7% 18% 24% 20% 17%	529
June	1st to 10th	Day	13% 6% 17% 30% 22% 13%	490
	11th to 20th	Day	6% 5% 14% 28% 31% 16%	490
	21st to end	Day	11% 3 17% 28% 25% 16%	490
July	1st to 10th	Day	9% 3 13% 23% 29% 24%	485
	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	19% 7% 24% 30% 16% 4	276
	11th to 20th	Day	14% 11% 33% 31% 9% 1	270
	21st to end	Day	13% 10% 33% 29% 14% 1	270
December	1st to 10th	Day	26% 17% 29% 21% 6%	270
	11th to 20th	Day	23% 14% 29% 24% 9% 1	270
	21st to end	Day	26% 15% 28% 21% 9% 1	297
January	1st to 10th	Night	21% 13% 26% 34% 5%	760
	11th to 20th	Night	26% 12% 30% 27% 6%	760
	21st to end	Night	21% 13% 33% 31% 3	836
February	1st to 10th	Night	21% 11% 31% 34% 4	760
	11th to 20th	Night	27% 12% 36% 23% 3	743
	21st to end	Night	28% 12% 32% 25% 3	628
March	1st to 10th	Night	21% 12% 28% 34% 4	760
	11th to 20th	Night	22% 11% 32% 27% 7% 1	760
	21st to end	Night	20% 10% 30% 31% 9%	836
April	1st to 10th	Night	15% 10% 30% 34% 10%	717
	11th to 20th	Night	15% 10% 32% 27% 15% 1	563
	21st to end	Night	15% 6% 27% 38% 13% 1	570
May	1st to 10th	Night	14% 6% 23% 36% 19% 2	570
	11th to 20th	Night	16% 5% 18% 31% 26% 4	561
	21st to end	Night	9% 4 18% 28% 38% 5%	617
June	1st to 10th	Night	9% 2 14% 38% 34% 4	570
	11th to 20th	Night	5% 3 13% 34% 36% 9%	570
	21st to end	Night	8% 3 12% 34% 37% 7%	570
July	1st to 10th	Night	11% 3 8% 27% 40% 12%	555
	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	17% 5% 18% 37% 21% 3	749
	11th to 20th	Night	16% 9% 25% 37% 12% 1	760
	21st to end	Night	18% 8% 24% 37% 14%	760
December	1st to 10th	Night	24% 10% 25% 33% 8%	760
	11th to 20th	Night	21% 11% 24% 35% 9%	760
	21st to end	Night	24% 13% 22% 34% 7%	836

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