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 2026-10-29.

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 8% 5% 5% 5% 4 6% 9% 36%	149009
	Night	13% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	143084
Transparency	Day	42% 7% 12% 22% 14% 3	152759
	Night	43% 6% 11% 22% 15% 3	147405
Seeing	Day	17% 10% 21% 24% 19% 9%	17501
	Night	16% 7% 21% 32% 20% 3	27478

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% 10% 4 8% 5% 5% 4 4 6% 6% 31%	5258
	11th to 20th	Day	12% 8% 4 9% 4 4 5% 4 5% 6% 40%	5280
	21st to end	Day	18% 10% 4 9% 5% 4 3 3 5% 7% 33%	5780
February	1st to 10th	Day	17% 10% 3 9% 5% 5% 5% 3 4 6% 34%	2077
	11th to 20th	Day	22% 8% 3 8% 5% 4 4 3 4 6% 33%	2048
	21st to end	Day	18% 9% 3 8% 4 4 4 4 5% 6% 35%	1730
March	1st to 10th	Day	18% 10% 3 7% 5% 4 4 4 5% 6% 34%	4739
	11th to 20th	Day	11% 6% 3 6% 4 4 4 3 5% 7% 47%	5090
	21st to end	Day	15% 7% 2 7% 4 4 4 4 4 7% 43%	5586
April	1st to 10th	Day	11% 5% 3 6% 5% 5% 5% 4 7% 8% 41%	2373
	11th to 20th	Day	12% 7% 2 5% 4 4 5% 4 5% 7% 45%	2520
	21st to end	Day	12% 8% 2 7% 4 4 4 3 6% 8% 41%	2730
May	1st to 10th	Day	14% 9% 3 8% 5% 5% 4 4 6% 8% 33%	7616
	11th to 20th	Day	11% 8% 3 9% 6% 6% 6% 5% 7% 7% 33%	7626
	21st to end	Day	15% 10% 4 10% 6% 5% 5% 4 6% 7% 27%	8391
June	1st to 10th	Day	9% 7% 2 7% 5% 5% 6% 5% 8% 11% 36%	2730
	11th to 20th	Day	5% 4 2 6% 6% 6% 7% 5% 8% 12% 39%	2730
	21st to end	Day	7% 4 2 7% 4 6% 6% 5% 9% 11% 37%	2730
July	1st to 10th	Day	5% 5% 2 6% 5% 6% 6% 6% 9% 13% 38%	7680
	11th to 20th	Day	9% 7% 3 9% 6% 6% 6% 5% 8% 11% 30%	7680
	21st to end	Day	11% 8% 3 9% 6% 6% 7% 6% 8% 11% 24%	8340
August	1st to 10th	Day	7% 6% 3 9% 7% 7% 7% 7% 9% 11% 27%	6014
	11th to 20th	Day	5% 4 2 6% 5% 5% 6% 5% 8% 13% 40%	5843
	21st to end	Day	4 4 2 5% 4 4 5% 4 7% 11% 50%	6080
September	1st to 10th	Day	11% 7% 2 6% 5% 5% 5% 4 5% 8% 42%	2321
	11th to 20th	Day	13% 6% 2 6% 4 6% 4 4 6% 9% 41%	2310
	21st to end	Day	13% 6% 2 5% 4 4 4 4 6% 6% 45%	2310
October	1st to 10th	Day	10% 6% 3 5% 3 4 3 3 5% 6% 51%	2310
	11th to 20th	Day	11% 5% 1 6% 3 3 4 3 5% 7% 52%	2142
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 6% 48%	2265
November	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 5% 6% 52%	1852
	11th to 20th	Day	12% 6% 3 5% 4 3 3 3 4 7% 48%	1890
	21st to end	Day	14% 7% 4 6% 4 3 5% 4 4 7% 42%	1890
December	1st to 10th	Day	14% 8% 3 7% 4 4 4 4 6% 7% 39%	3020
	11th to 20th	Day	17% 13% 4 11% 6% 5% 4 3 4 5% 27%	3463
	21st to end	Day	13% 12% 4 9% 6% 5% 5% 4 6% 8% 28%	4565
January	1st to 10th	Night	16% 9% 3 9% 4 4 4 3 5% 6% 37%	7635
	11th to 20th	Night	17% 8% 3 6% 5% 3 3 3 4 5% 43%	7680
	21st to end	Night	17% 12% 4 7% 4 5% 4 3 5% 5% 36%	8401
February	1st to 10th	Night	16% 9% 3 7% 4 4 4 3 5% 7% 35%	2540
	11th to 20th	Night	21% 10% 3 9% 3 3 4 3 4 5% 33%	2458
	21st to end	Night	21% 10% 3 7% 3 5% 4 3 5% 6% 33%	2076
March	1st to 10th	Night	16% 10% 3 9% 5% 4 4 4 5% 6% 33%	5334
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 6% 8% 50%	5090
	21st to end	Night	12% 6% 3 8% 5% 5% 5% 4 6% 6% 41%	5588
April	1st to 10th	Night	11% 5% 2 5% 4 4 5% 3 7% 8% 46%	2263
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 5% 6% 47%	2048
	21st to end	Night	12% 5% 2 7% 5% 4 5% 4 6% 7% 43%	1890
May	1st to 10th	Night	14% 9% 3 9% 4 5% 5% 4 7% 9% 30%	5237
	11th to 20th	Night	12% 9% 4 9% 5% 5% 5% 4 6% 7% 35%	5234
	21st to end	Night	15% 10% 4 10% 6% 5% 5% 4 6% 7% 29%	5761
June	1st to 10th	Night	7% 7% 2 8% 6% 4 6% 5% 8% 11% 36%	1890
	11th to 20th	Night	3 5% 2 5% 4 4 6% 5% 8% 13% 44%	1890
	21st to end	Night	6% 6% 2 6% 6% 5% 6% 5% 8% 11% 39%	1890
July	1st to 10th	Night	7% 6% 2 8% 5% 6% 7% 6% 10% 12% 32%	5278
	11th to 20th	Night	9% 7% 3 8% 6% 6% 7% 5% 8% 11% 29%	5277
	21st to end	Night	11% 9% 4 10% 7% 6% 7% 5% 8% 11% 22%	5736
August	1st to 10th	Night	7% 7% 3 10% 7% 8% 7% 6% 7% 10% 28%	4135
	11th to 20th	Night	6% 5% 3 6% 4 4 4 4 6% 11% 47%	4185
	21st to end	Night	5% 4 2 6% 4 4 5% 4 8% 11% 47%	5046
September	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 5% 6% 7% 43%	2277
	11th to 20th	Night	9% 7% 3 8% 5% 6% 5% 3 5% 8% 40%	2310
	21st to end	Night	11% 7% 3 6% 4 5% 4 4 4 7% 46%	2310
October	1st to 10th	Night	11% 6% 3 6% 3 4 3 4 4 6% 50%	2310
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	2475
	21st to end	Night	13% 6% 2 6% 4 3 3 3 4 5% 52%	2749
November	1st to 10th	Night	13% 6% 3 6% 4 3 3 3 3 7% 49%	2666
	11th to 20th	Night	14% 6% 2 6% 5% 3 4 3 5% 6% 47%	2730
	21st to end	Night	14% 8% 3 6% 4 4 4 3 5% 6% 44%	2730
December	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 3 5% 6% 37%	4380
	11th to 20th	Night	19% 11% 4 8% 5% 4 4 3 5% 6% 32%	4952
	21st to end	Night	15% 11% 3 8% 5% 5% 5% 4 6% 8% 29%	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	50% 5% 9% 25% 9% 1	5259
	11th to 20th	Day	44% 4 5% 21% 23% 3	5280
	21st to end	Day	52% 4 7% 24% 12% 1	5780
February	1st to 10th	Day	51% 5% 8% 20% 15% 2	2077
	11th to 20th	Day	53% 4 9% 20% 13% 2	2058
	21st to end	Day	50% 4 7% 18% 16% 5%	1730
March	1st to 10th	Day	50% 5% 6% 15% 16% 8%	4739
	11th to 20th	Day	37% 3 6% 20% 27% 8%	5090
	21st to end	Day	42% 4 7% 31% 14% 1	5586
April	1st to 10th	Day	38% 6% 11% 25% 17% 3	2373
	11th to 20th	Day	39% 4 9% 20% 23% 5%	2520
	21st to end	Day	42% 4 10% 28% 14% 2	2730
May	1st to 10th	Day	47% 6% 12% 23% 12% 1	7651
	11th to 20th	Day	46% 7% 14% 21% 10% 2	7630
	21st to end	Day	53% 8% 10% 16% 11% 2	8405
June	1st to 10th	Day	40% 8% 15% 23% 13% 2	2730
	11th to 20th	Day	35% 8% 19% 22% 13% 2	2730
	21st to end	Day	36% 10% 17% 21% 12% 4	2730
July	1st to 10th	Day	33% 11% 23% 22% 11% 1	7615
	11th to 20th	Day	44% 10% 21% 19% 4 2	7611
	21st to end	Day	49% 10% 16% 17% 7% 1	8156
August	1st to 10th	Day	45% 11% 17% 19% 6%	6001
	11th to 20th	Day	31% 9% 24% 25% 9% 1	5882
	21st to end	Day	26% 7% 15% 36% 15% 1	6079
September	1st to 10th	Day	38% 8% 11% 21% 17% 6%	2321
	11th to 20th	Day	38% 7% 13% 23% 17% 3	2310
	21st to end	Day	37% 6% 11% 22% 19% 5%	2310
October	1st to 10th	Day	27% 4 6% 22% 31% 10%	3700
	11th to 20th	Day	24% 4 6% 25% 30% 10%	3408
	21st to end	Day	29% 4 8% 28% 21% 9%	3591
November	1st to 10th	Day	33% 5% 8% 24% 26% 5%	1852
	11th to 20th	Day	36% 3 8% 26% 23% 4	1890
	21st to end	Day	42% 4 7% 25% 19% 2	1890
December	1st to 10th	Day	43% 5% 8% 23% 21% 1	3020
	11th to 20th	Day	58% 4 8% 18% 10% 2	3460
	21st to end	Day	51% 6% 12% 22% 8% 1	4565
January	1st to 10th	Night	47% 4 13% 23% 12% 1	7636
	11th to 20th	Night	44% 3 5% 21% 25% 3	7680
	21st to end	Night	50% 4 6% 20% 16% 4	8401
February	1st to 10th	Night	48% 4 9% 22% 16% 2	2540
	11th to 20th	Night	54% 4 7% 18% 14% 3	2459
	21st to end	Night	52% 3 7% 18% 15% 4	2076
March	1st to 10th	Night	49% 5% 7% 18% 16% 5%	5334
	11th to 20th	Night	33% 3 7% 22% 25% 10%	5090
	21st to end	Night	42% 5% 9% 28% 14% 2	5588
April	1st to 10th	Night	35% 4 13% 26% 19% 3	2263
	11th to 20th	Night	38% 4 8% 22% 22% 6%	2048
	21st to end	Night	40% 5% 11% 27% 15% 2	1890
May	1st to 10th	Night	48% 6% 13% 22% 10% 1	5264
	11th to 20th	Night	48% 5% 14% 20% 13%	5235
	21st to end	Night	52% 7% 11% 20% 10% 1	5771
June	1st to 10th	Night	39% 9% 15% 21% 14% 2	1890
	11th to 20th	Night	28% 10% 22% 26% 14% 2	1890
	21st to end	Night	35% 9% 16% 22% 13% 5%	1890
July	1st to 10th	Night	39% 12% 20% 21% 7% 1	5235
	11th to 20th	Night	45% 12% 20% 17% 4 1	5226
	21st to end	Night	51% 11% 17% 13% 6% 1	5606
August	1st to 10th	Night	47% 11% 16% 19% 6%	4124
	11th to 20th	Night	30% 8% 23% 28% 11%	4212
	21st to end	Night	29% 6% 16% 35% 12% 1	5046
September	1st to 10th	Night	37% 8% 13% 19% 18% 5%	2277
	11th to 20th	Night	41% 8% 12% 19% 19% 1	2310
	21st to end	Night	38% 6% 10% 21% 20% 5%	2310
October	1st to 10th	Night	33% 4 6% 20% 26% 11%	3700
	11th to 20th	Night	24% 3 5% 24% 32% 12%	3948
	21st to end	Night	26% 4 4 28% 29% 10%	4373
November	1st to 10th	Night	36% 4 7% 23% 24% 7%	2666
	11th to 20th	Night	38% 4 6% 23% 23% 6%	2730
	21st to end	Night	41% 4 7% 26% 19% 3	2730
December	1st to 10th	Night	47% 5% 7% 21% 19% 2	4380
	11th to 20th	Night	53% 4 8% 20% 13% 2	4954
	21st to end	Night	49% 8% 12% 20% 10% 1	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	25% 16% 32% 21% 5% 1	330
	11th to 20th	Day	26% 21% 31% 15% 6% 1	330
	21st to end	Day	21% 21% 36% 16% 6%	363
February	1st to 10th	Day	27% 17% 29% 19% 8% 1	330
	11th to 20th	Day	34% 20% 28% 16% 2	330
	21st to end	Day	32% 17% 33% 14% 3	273
March	1st to 10th	Day	25% 19% 29% 18% 8% 2	398
	11th to 20th	Day	23% 17% 32% 22% 6%	540
	21st to end	Day	22% 15% 31% 25% 7% 1	594
April	1st to 10th	Day	19% 16% 25% 25% 11% 3	540
	11th to 20th	Day	17% 13% 28% 24% 14% 3	532
	21st to end	Day	19% 11% 27% 26% 14% 4	540
May	1st to 10th	Day	17% 12% 32% 23% 12% 4	543
	11th to 20th	Day	14% 8% 26% 25% 20% 8%	567
	21st to end	Day	16% 8% 18% 25% 19% 14%	617
June	1st to 10th	Day	12% 6% 17% 29% 22% 13%	570
	11th to 20th	Day	6% 5% 16% 29% 30% 14%	570
	21st to end	Day	10% 3 16% 26% 27% 17%	570
July	1st to 10th	Day	9% 3 12% 23% 28% 24%	565
	11th to 20th	Day	13% 4 8% 27% 29% 20%	564
	21st to end	Day	12% 4 9% 28% 29% 17%	620
August	1st to 10th	Day	15% 3 10% 24% 29% 19%	566
	11th to 20th	Day	10% 3 11% 30% 29% 17%	559
	21st to end	Day	11% 2 7% 25% 29% 26%	627
September	1st to 10th	Day	11% 2 10% 24% 33% 21%	570
	11th to 20th	Day	13% 4 8% 22% 32% 22%	570
	21st to end	Day	17% 4 12% 27% 29% 10%	570
October	1st to 10th	Day	14% 6% 18% 24% 27% 11%	570
	11th to 20th	Day	13% 10% 20% 30% 23% 5%	570
	21st to end	Day	20% 7% 19% 27% 23% 4	600
November	1st to 10th	Day	18% 9% 25% 30% 15% 4	330
	11th to 20th	Day	13% 14% 32% 30% 10% 1	330
	21st to end	Day	14% 12% 32% 28% 14% 1	330
December	1st to 10th	Day	25% 18% 30% 20% 6%	330
	11th to 20th	Day	22% 15% 28% 26% 8% 1	330
	21st to end	Day	24% 16% 27% 21% 10% 1	363
January	1st to 10th	Night	21% 12% 28% 34% 5%	840
	11th to 20th	Night	25% 12% 31% 27% 5%	840
	21st to end	Night	20% 13% 33% 32% 2	924
February	1st to 10th	Night	22% 10% 31% 33% 4	840
	11th to 20th	Night	27% 13% 36% 22% 2	823
	21st to end	Night	27% 11% 32% 26% 3	692
March	1st to 10th	Night	20% 12% 28% 35% 4	840
	11th to 20th	Night	21% 11% 32% 28% 7% 1	840
	21st to end	Night	19% 10% 31% 31% 8%	924
April	1st to 10th	Night	15% 10% 31% 34% 10%	793
	11th to 20th	Night	15% 9% 31% 29% 15% 1	623
	21st to end	Night	15% 6% 27% 38% 14% 1	630
May	1st to 10th	Night	14% 7% 23% 37% 17% 2	630
	11th to 20th	Night	15% 6% 18% 33% 24% 4	621
	21st to end	Night	11% 4 18% 28% 35% 5%	683
June	1st to 10th	Night	9% 3 13% 38% 33% 3	630
	11th to 20th	Night	6% 3 13% 34% 35% 8%	630
	21st to end	Night	8% 3 11% 33% 38% 7%	630
July	1st to 10th	Night	11% 3 7% 26% 41% 13%	615
	11th to 20th	Night	8% 2 6% 28% 46% 11%	612
	21st to end	Night	10% 4 7% 29% 39% 10%	690
August	1st to 10th	Night	10% 3 6% 26% 44% 10%	627
	11th to 20th	Night	12% 2 6% 31% 42% 8%	624
	21st to end	Night	10% 2 6% 27% 45% 9%	693
September	1st to 10th	Night	11% 3 7% 30% 41% 8%	807
	11th to 20th	Night	13% 4 8% 28% 39% 7%	840
	21st to end	Night	14% 4 14% 35% 31% 3	840
October	1st to 10th	Night	14% 5% 14% 28% 31% 7%	840
	11th to 20th	Night	16% 5% 20% 37% 19% 2	840
	21st to end	Night	15% 5% 22% 36% 20% 1	913
November	1st to 10th	Night	16% 5% 18% 39% 19% 2	820
	11th to 20th	Night	16% 10% 24% 38% 11% 1	840
	21st to end	Night	18% 8% 24% 36% 13%	840
December	1st to 10th	Night	24% 10% 26% 33% 8%	840
	11th to 20th	Night	22% 10% 25% 35% 8%	840
	21st to end	Night	24% 12% 22% 35% 7%	924

Page generated at 2026-10-26 04:37:49. Version ac07

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