Tellico Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tellico Skies Observatory clear sky chart from 2005-11-06 to 2025-03-27.

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% 38%	109345
	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 39%	110002
Transparency	Day	40% 8% 12% 22% 15% 3	113140
	Night	40% 8% 11% 21% 17% 4	114345
Seeing	Day	17% 10% 22% 23% 19% 9%	15267
	Night	16% 8% 23% 30% 20% 3	25409

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	15% 11% 3 8% 5% 4 4 4 6% 6% 33%	4056
	11th to 20th	Day	13% 10% 5% 7% 4 4 5% 3 5% 5% 37%	4060
	21st to end	Day	19% 11% 3 7% 4 3 3 3 5% 6% 36%	4494
February	1st to 10th	Day	19% 10% 3 8% 5% 5% 4 3 5% 5% 34%	2000
	11th to 20th	Day	21% 10% 3 8% 5% 4 3 3 4 5% 32%	1948
	21st to end	Day	20% 9% 3 6% 4 4 4 3 5% 6% 36%	1650
March	1st to 10th	Day	21% 11% 3 7% 4 4 4 3 5% 6% 32%	3305
	11th to 20th	Day	13% 6% 3 7% 4 4 4 3 5% 5% 48%	3590
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 5% 6% 39%	3881
April	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 7% 8% 42%	2172
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2254
	21st to end	Day	12% 7% 3 6% 4 5% 4 4 6% 6% 43%	2466
May	1st to 10th	Day	12% 7% 3 8% 6% 5% 5% 4 6% 8% 35%	4082
	11th to 20th	Day	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	4081
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4476
June	1st to 10th	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 37%	2470
	11th to 20th	Day	4 4 2 5% 5% 6% 6% 6% 9% 11% 41%	2470
	21st to end	Day	6% 6% 2 6% 6% 6% 5% 5% 8% 11% 38%	2470
July	1st to 10th	Day	5% 5% 2 6% 6% 7% 7% 6% 10% 13% 34%	4120
	11th to 20th	Day	9% 6% 2 7% 6% 5% 6% 5% 8% 10% 37%	4120
	21st to end	Day	14% 11% 4 11% 7% 7% 7% 6% 6% 8% 19%	4466
August	1st to 10th	Day	6% 5% 2 6% 6% 6% 6% 6% 9% 11% 38%	4104
	11th to 20th	Day	6% 5% 2 7% 5% 6% 7% 5% 8% 11% 38%	3895
	21st to end	Day	6% 4 2 5% 4 5% 5% 4 6% 9% 50%	4180
September	1st to 10th	Day	11% 7% 2 7% 5% 5% 4 4 6% 8% 41%	2115
	11th to 20th	Day	14% 5% 2 6% 5% 4 5% 4 6% 8% 40%	2090
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 4 7% 47%	2090
October	1st to 10th	Day	10% 5% 2 6% 3 3 4 4 4 6% 53%	2090
	11th to 20th	Day	12% 6% 2 4 3 3 3 2 5% 7% 53%	1962
	21st to end	Day	14% 6% 1 5% 3 4 4 3 4 7% 49%	2057
November	1st to 10th	Day	11% 5% 2 5% 3 4 3 3 6% 6% 51%	1762
	11th to 20th	Day	12% 7% 2 5% 5% 3 4 3 5% 7% 47%	1800
	21st to end	Day	13% 8% 2 6% 5% 4 4 4 6% 7% 43%	1800
December	1st to 10th	Day	14% 7% 3 6% 4 4 5% 3 5% 6% 42%	2930
	11th to 20th	Day	18% 13% 3 10% 6% 5% 5% 3 5% 4 28%	3373
	21st to end	Day	14% 11% 3 8% 5% 5% 5% 4 6% 8% 29%	4466
January	1st to 10th	Night	14% 9% 4 10% 5% 4 4 3 5% 6% 36%	5889
	11th to 20th	Night	18% 8% 3 6% 3 3 3 3 5% 6% 41%	5900
	21st to end	Night	15% 10% 3 7% 5% 4 4 3 6% 6% 36%	6444
February	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 4 6% 7% 36%	2400
	11th to 20th	Night	21% 10% 3 7% 4 4 4 3 5% 4 35%	2338
	21st to end	Night	20% 9% 2 7% 4 5% 4 4 4 6% 34%	1980
March	1st to 10th	Night	21% 9% 3 6% 6% 5% 5% 3 6% 6% 29%	3766
	11th to 20th	Night	11% 7% 2 5% 3 4 3 3 5% 8% 49%	3590
	21st to end	Night	14% 8% 3 8% 4 5% 4 3 4 6% 40%	3890
April	1st to 10th	Night	12% 5% 1 6% 4 4 4 3 5% 8% 47%	2023
	11th to 20th	Night	13% 7% 3 5% 4 3 3 4 4 6% 48%	1875
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 4 6% 6% 43%	1711
May	1st to 10th	Night	10% 8% 3 9% 5% 6% 5% 4 6% 8% 36%	2813
	11th to 20th	Night	16% 8% 3 7% 4 4 3 4 6% 8% 37%	2812
	21st to end	Night	6% 5% 3 8% 6% 4 6% 4 8% 10% 40%	3079
June	1st to 10th	Night	6% 6% 3 7% 6% 6% 6% 5% 8% 10% 38%	1710
	11th to 20th	Night	3 3 2 5% 4 4 4 5% 9% 13% 47%	1710
	21st to end	Night	5% 5% 2 7% 6% 5% 6% 5% 7% 10% 41%	1710
July	1st to 10th	Night	7% 6% 2 8% 6% 7% 7% 6% 8% 10% 32%	2840
	11th to 20th	Night	8% 5% 2 5% 5% 5% 6% 5% 8% 10% 41%	2840
	21st to end	Night	12% 11% 4 10% 7% 7% 6% 6% 8% 9% 22%	3087
August	1st to 10th	Night	6% 5% 2 7% 6% 6% 4 5% 8% 12% 39%	2825
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 5% 7% 9% 44%	2930
	21st to end	Night	5% 4 2 5% 4 5% 5% 4 7% 10% 48%	3476
September	1st to 10th	Night	9% 7% 2 6% 6% 5% 5% 4 7% 7% 41%	2044
	11th to 20th	Night	12% 8% 2 8% 5% 4 5% 3 6% 8% 40%	2090
	21st to end	Night	11% 5% 2 5% 5% 5% 5% 4 5% 7% 46%	2090
October	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 4 7% 54%	2090
	11th to 20th	Night	14% 4 2 4 4 4 4 3 4 5% 52%	2216
	21st to end	Night	13% 6% 2 5% 4 3 3 3 4 5% 52%	2536
November	1st to 10th	Night	13% 6% 2 6% 4 4 4 2 5% 6% 50%	2536
	11th to 20th	Night	13% 6% 3 6% 4 4 3 3 5% 7% 48%	2600
	21st to end	Night	14% 7% 3 5% 4 4 5% 3 6% 7% 43%	2600
December	1st to 10th	Night	14% 7% 3 7% 5% 5% 4 3 6% 7% 38%	4250
	11th to 20th	Night	20% 9% 4 7% 5% 5% 4 4 5% 6% 30%	4822
	21st to end	Night	15% 9% 4 8% 5% 5% 5% 5% 6% 8% 30%	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	46% 7% 7% 24% 15% 1	4057
	11th to 20th	Day	45% 8% 7% 17% 22% 1	4060
	21st to end	Day	48% 5% 8% 24% 14% 2	4494
February	1st to 10th	Day	51% 5% 10% 18% 14% 2	2000
	11th to 20th	Day	53% 5% 9% 18% 13% 2	1958
	21st to end	Day	48% 5% 9% 15% 17% 5%	1650
March	1st to 10th	Day	50% 7% 9% 16% 12% 6%	3305
	11th to 20th	Day	37% 6% 8% 21% 22% 6%	3590
	21st to end	Day	44% 6% 9% 27% 12% 2	3881
April	1st to 10th	Day	37% 9% 11% 23% 17% 3	2172
	11th to 20th	Day	38% 6% 9% 17% 24% 5%	2254
	21st to end	Day	40% 7% 11% 26% 14% 3	2466
May	1st to 10th	Day	43% 11% 11% 22% 12% 1	4120
	11th to 20th	Day	46% 10% 11% 22% 9% 1	4085
	21st to end	Day	37% 10% 13% 21% 16% 2	4489
June	1st to 10th	Day	38% 12% 15% 20% 13% 2	2470
	11th to 20th	Day	31% 12% 20% 21% 14% 2	2470
	21st to end	Day	36% 12% 17% 19% 13% 3	2470
July	1st to 10th	Day	35% 13% 22% 20% 10% 1	4055
	11th to 20th	Day	39% 10% 20% 21% 7% 2	4051
	21st to end	Day	60% 10% 12% 13% 4	4324
August	1st to 10th	Day	34% 12% 18% 27% 9% 1	4091
	11th to 20th	Day	34% 10% 18% 23% 12% 1	3934
	21st to end	Day	30% 9% 13% 33% 13% 2	4179
September	1st to 10th	Day	38% 8% 14% 18% 17% 6%	2115
	11th to 20th	Day	40% 9% 11% 20% 18% 3	2090
	21st to end	Day	36% 7% 11% 22% 18% 6%	2090
October	1st to 10th	Day	26% 5% 7% 20% 31% 12%	3480
	11th to 20th	Day	22% 4 7% 24% 31% 12%	3241
	21st to end	Day	27% 4 10% 27% 23% 9%	3371
November	1st to 10th	Day	33% 4 10% 22% 26% 5%	1762
	11th to 20th	Day	36% 5% 7% 24% 24% 4	1800
	21st to end	Day	39% 6% 9% 24% 19% 3	1800
December	1st to 10th	Day	42% 6% 7% 22% 22% 2	2930
	11th to 20th	Day	57% 6% 7% 16% 12% 1	3370
	21st to end	Day	49% 7% 14% 23% 8% 1	4466
January	1st to 10th	Night	45% 6% 10% 22% 16% 1	5889
	11th to 20th	Night	43% 7% 6% 19% 21% 5%	5900
	21st to end	Night	46% 6% 7% 20% 17% 4	6444
February	1st to 10th	Night	48% 6% 9% 19% 17% 2	2400
	11th to 20th	Night	52% 6% 7% 17% 14% 4	2339
	21st to end	Night	49% 7% 9% 16% 16% 4	1980
March	1st to 10th	Night	48% 10% 11% 14% 14% 3	3766
	11th to 20th	Night	33% 6% 9% 23% 19% 10%	3590
	21st to end	Night	42% 7% 9% 23% 16% 2	3890
April	1st to 10th	Night	35% 7% 12% 22% 20% 3	2023
	11th to 20th	Night	36% 6% 9% 21% 22% 6%	1875
	21st to end	Night	38% 7% 11% 27% 15% 1	1711
May	1st to 10th	Night	42% 11% 14% 21% 11% 1	2840
	11th to 20th	Night	42% 9% 15% 21% 12% 1	2813
	21st to end	Night	33% 13% 15% 24% 15% 1	3087
June	1st to 10th	Night	37% 11% 16% 21% 13% 2	1710
	11th to 20th	Night	24% 12% 23% 26% 13% 2	1710
	21st to end	Night	35% 11% 15% 22% 12% 4	1710
July	1st to 10th	Night	42% 13% 18% 19% 8% 1	2795
	11th to 20th	Night	34% 9% 23% 24% 7% 3	2786
	21st to end	Night	55% 12% 14% 13% 5% 1	2988
August	1st to 10th	Night	34% 10% 17% 28% 10% 1	2814
	11th to 20th	Night	33% 11% 19% 24% 12% 1	2957
	21st to end	Night	26% 10% 15% 35% 13% 1	3476
September	1st to 10th	Night	37% 10% 15% 17% 15% 5%	2044
	11th to 20th	Night	40% 9% 13% 17% 20% 1	2090
	21st to end	Night	35% 7% 12% 20% 19% 6%	2090
October	1st to 10th	Night	29% 5% 8% 18% 27% 13%	3480
	11th to 20th	Night	22% 4 5% 23% 30% 15%	3676
	21st to end	Night	24% 4 5% 28% 27% 11%	4172
November	1st to 10th	Night	35% 5% 8% 20% 24% 8%	2536
	11th to 20th	Night	37% 6% 6% 21% 23% 7%	2600
	21st to end	Night	40% 5% 8% 23% 21% 3	2600
December	1st to 10th	Night	45% 7% 7% 19% 21% 2	4250
	11th to 20th	Night	52% 6% 8% 18% 15% 1	4824
	21st to end	Night	48% 7% 15% 19% 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	28% 20% 30% 19% 3	300
	11th to 20th	Day	28% 23% 28% 14% 6% 1	300
	21st to end	Day	20% 23% 38% 13% 5%	330
February	1st to 10th	Day	26% 20% 29% 16% 8% 1	300
	11th to 20th	Day	34% 24% 31% 9% 2	300
	21st to end	Day	37% 19% 29% 13% 1	249
March	1st to 10th	Day	25% 17% 32% 18% 6% 1	346
	11th to 20th	Day	20% 20% 36% 17% 7%	500
	21st to end	Day	24% 17% 32% 19% 8% 1	530
April	1st to 10th	Day	20% 18% 23% 26% 11% 2	460
	11th to 20th	Day	20% 14% 29% 21% 14% 2	452
	21st to end	Day	20% 10% 30% 24% 13% 3	460
May	1st to 10th	Day	14% 13% 32% 22% 14% 5%	463
	11th to 20th	Day	13% 7% 24% 27% 20% 9%	487
	21st to end	Day	13% 6% 19% 26% 19% 15%	529
June	1st to 10th	Day	12% 6% 20% 27% 24% 11%	490
	11th to 20th	Day	7% 4 12% 27% 31% 19%	490
	21st to end	Day	9% 3 17% 28% 26% 17%	490
July	1st to 10th	Day	11% 2 14% 21% 30% 23%	485
	11th to 20th	Day	12% 1 11% 26% 29% 21%	484
	21st to end	Day	11% 2 9% 24% 33% 20%	532
August	1st to 10th	Day	12% 3 13% 24% 30% 18%	486
	11th to 20th	Day	10% 3 12% 32% 30% 13%	479
	21st to end	Day	10% 2 12% 20% 32% 23%	539
September	1st to 10th	Day	9% 4 12% 25% 34% 16%	490
	11th to 20th	Day	15% 3 9% 23% 31% 18%	490
	21st to end	Day	16% 6% 14% 24% 31% 10%	490
October	1st to 10th	Day	11% 7% 19% 27% 26% 11%	490
	11th to 20th	Day	12% 11% 22% 30% 21% 4	490
	21st to end	Day	19% 7% 21% 29% 19% 4	506
November	1st to 10th	Day	16% 8% 30% 28% 15% 3	300
	11th to 20th	Day	15% 13% 30% 32% 8% 1	300
	21st to end	Day	13% 13% 33% 29% 11% 1	300
December	1st to 10th	Day	27% 17% 32% 18% 6% 1	300
	11th to 20th	Day	23% 18% 25% 22% 10% 1	300
	21st to end	Day	25% 18% 28% 18% 10% 1	330
January	1st to 10th	Night	24% 15% 32% 25% 4	800
	11th to 20th	Night	25% 16% 30% 25% 5%	800
	21st to end	Night	21% 13% 37% 27% 2	880
February	1st to 10th	Night	20% 12% 33% 31% 4	800
	11th to 20th	Night	27% 17% 33% 21% 2	783
	21st to end	Night	27% 15% 33% 22% 3	660
March	1st to 10th	Night	22% 14% 29% 31% 4	800
	11th to 20th	Night	24% 11% 32% 26% 7% 1	800
	21st to end	Night	21% 13% 30% 27% 8%	863
April	1st to 10th	Night	15% 13% 31% 32% 9% 1	693
	11th to 20th	Night	15% 10% 32% 28% 14%	563
	21st to end	Night	15% 8% 29% 36% 12% 1	570
May	1st to 10th	Night	11% 7% 24% 37% 18% 3	570
	11th to 20th	Night	14% 6% 19% 32% 25% 4	561
	21st to end	Night	8% 3 13% 33% 38% 4	617
June	1st to 10th	Night	8% 3 15% 36% 33% 5%	570
	11th to 20th	Night	3 2 13% 35% 36% 11%	570
	21st to end	Night	7% 3 12% 32% 38% 8%	570
July	1st to 10th	Night	10% 2 7% 26% 46% 10%	555
	11th to 20th	Night	10% 3 6% 27% 43% 11%	552
	21st to end	Night	8% 2 9% 29% 40% 12%	624
August	1st to 10th	Night	9% 2 8% 26% 45% 11%	567
	11th to 20th	Night	8% 2 10% 31% 43% 5%	564
	21st to end	Night	10% 1 9% 23% 46% 11%	627
September	1st to 10th	Night	10% 3 11% 29% 39% 9%	714
	11th to 20th	Night	15% 3 9% 30% 37% 5%	760
	21st to end	Night	14% 3 18% 31% 33% 3	760
October	1st to 10th	Night	11% 6% 19% 25% 31% 7%	760
	11th to 20th	Night	16% 5% 23% 33% 21% 2	760
	21st to end	Night	15% 6% 20% 38% 19% 2	836
November	1st to 10th	Night	15% 6% 21% 34% 22% 3	780
	11th to 20th	Night	14% 11% 29% 34% 11% 1	800
	21st to end	Night	18% 10% 27% 33% 13%	800
December	1st to 10th	Night	24% 12% 28% 30% 7%	800
	11th to 20th	Night	23% 10% 27% 32% 9%	800
	21st to end	Night	25% 14% 24% 31% 6%	880

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