Great Smokey Mountains National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Smokey Mountains National Park clear sky chart from 2005-11-06 to 2025-04-11.

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% 9% 4 9% 6% 5% 5% 4 6% 7% 33%	113820
	Night	12% 11% 4 9% 5% 4 4 4 5% 6% 35%	114478
Transparency	Day	25% 44% 7% 12% 8% 3	117614
	Night	25% 43% 8% 11% 9% 4	118823
Seeing	Day	19% 16% 26% 21% 13% 5%	15427
	Night	18% 13% 23% 27% 16% 3	25575

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	12% 11% 6% 8% 5% 4 4 4 5% 5% 36%	4056
	11th to 20th	Day	9% 11% 5% 13% 4 3 3 2 4 5% 42%	4060
	21st to end	Day	13% 14% 5% 9% 3 3 3 4 5% 5% 36%	4466
February	1st to 10th	Day	15% 11% 5% 10% 5% 4 5% 4 4 4 32%	1961
	11th to 20th	Day	19% 13% 5% 9% 5% 4 3 3 4 5% 30%	1948
	21st to end	Day	17% 11% 4 9% 4 4 4 3 5% 5% 34%	1650
March	1st to 10th	Day	16% 11% 4 9% 5% 5% 4 3 4 5% 33%	4699
	11th to 20th	Day	11% 9% 3 7% 4 4 3 3 5% 6% 45%	4980
	21st to end	Day	14% 12% 3 7% 5% 4 4 3 4 5% 39%	5465
April	1st to 10th	Day	11% 11% 3 6% 6% 4 4 5% 5% 6% 37%	2216
	11th to 20th	Day	14% 10% 3 6% 5% 4 4 4 5% 6% 38%	2292
	21st to end	Day	16% 9% 3 7% 6% 4 4 4 5% 5% 37%	2470
May	1st to 10th	Day	16% 10% 4 8% 6% 5% 5% 4 5% 6% 30%	4082
	11th to 20th	Day	18% 11% 4 9% 5% 5% 5% 4 5% 6% 26%	4081
	21st to end	Day	12% 7% 3 8% 5% 6% 5% 5% 7% 10% 32%	4476
June	1st to 10th	Day	12% 9% 3 9% 7% 7% 6% 5% 7% 8% 27%	2470
	11th to 20th	Day	8% 7% 3 10% 8% 7% 7% 5% 7% 9% 28%	2470
	21st to end	Day	12% 8% 3 8% 7% 5% 7% 6% 7% 8% 30%	2470
July	1st to 10th	Day	8% 7% 3 9% 7% 8% 9% 7% 10% 10% 23%	4120
	11th to 20th	Day	12% 8% 3 10% 7% 7% 7% 5% 8% 8% 24%	4120
	21st to end	Day	17% 13% 5% 14% 9% 7% 6% 5% 5% 6% 13%	4466
August	1st to 10th	Day	11% 7% 3 9% 7% 8% 7% 6% 8% 9% 25%	4104
	11th to 20th	Day	10% 7% 3 9% 7% 7% 7% 5% 8% 9% 28%	4017
	21st to end	Day	9% 6% 3 9% 6% 6% 7% 6% 8% 10% 30%	4153
September	1st to 10th	Day	13% 8% 4 10% 6% 5% 6% 5% 6% 7% 32%	2090
	11th to 20th	Day	16% 8% 3 8% 6% 5% 5% 4 6% 7% 31%	2090
	21st to end	Day	14% 8% 2 6% 6% 6% 5% 4 6% 6% 37%	2090
October	1st to 10th	Day	12% 7% 2 7% 4 4 4 4 5% 6% 45%	2090
	11th to 20th	Day	12% 9% 2 5% 3 3 3 3 4 6% 50%	1923
	21st to end	Day	13% 7% 2 5% 3 4 4 2 4 6% 49%	2090
November	1st to 10th	Day	10% 9% 2 5% 3 3 3 3 5% 5% 51%	1786
	11th to 20th	Day	10% 9% 3 7% 5% 4 4 4 5% 5% 44%	1800
	21st to end	Day	11% 10% 3 7% 4 4 5% 3 5% 5% 42%	1800
December	1st to 10th	Day	11% 10% 3 8% 5% 4 4 3 5% 5% 41%	2930
	11th to 20th	Day	12% 11% 5% 12% 7% 6% 5% 3 5% 5% 30%	3373
	21st to end	Day	9% 10% 6% 10% 6% 5% 5% 4 5% 7% 34%	4466
January	1st to 10th	Night	10% 15% 5% 10% 5% 4 4 3 4 6% 33%	5889
	11th to 20th	Night	14% 11% 4 10% 5% 5% 3 3 5% 5% 35%	5900
	21st to end	Night	12% 16% 4 8% 4 3 4 3 4 5% 37%	6490
February	1st to 10th	Night	14% 12% 4 10% 5% 4 4 3 5% 5% 33%	2435
	11th to 20th	Night	18% 14% 4 10% 5% 4 4 4 4 3 30%	2338
	21st to end	Night	17% 13% 4 9% 6% 4 5% 4 4 4 31%	1980
March	1st to 10th	Night	15% 14% 7% 10% 5% 4 4 4 4 5% 29%	5153
	11th to 20th	Night	10% 9% 3 7% 5% 4 4 4 5% 6% 44%	4980
	21st to end	Night	11% 9% 4 8% 7% 5% 4 3 5% 5% 38%	5467
April	1st to 10th	Night	13% 12% 4 6% 5% 4 3 3 4 6% 40%	2200
	11th to 20th	Night	12% 12% 4 7% 4 4 3 3 4 6% 41%	1840
	21st to end	Night	14% 9% 3 6% 5% 4 5% 3 4 7% 40%	1710
May	1st to 10th	Night	14% 13% 4 9% 5% 5% 5% 3 5% 7% 30%	2813
	11th to 20th	Night	18% 12% 3 9% 4 3 4 3 5% 7% 30%	2812
	21st to end	Night	11% 7% 3 7% 6% 5% 6% 5% 7% 10% 34%	3079
June	1st to 10th	Night	9% 8% 3 8% 6% 5% 6% 5% 8% 9% 32%	1710
	11th to 20th	Night	6% 5% 2 6% 5% 6% 6% 5% 9% 12% 38%	1710
	21st to end	Night	10% 8% 3 8% 6% 5% 6% 5% 7% 8% 35%	1710
July	1st to 10th	Night	9% 8% 3 9% 7% 7% 7% 6% 8% 9% 28%	2840
	11th to 20th	Night	9% 7% 3 7% 5% 5% 6% 6% 8% 10% 35%	2840
	21st to end	Night	12% 12% 4 12% 8% 6% 7% 5% 7% 8% 19%	3087
August	1st to 10th	Night	10% 6% 3 8% 6% 5% 6% 5% 8% 10% 33%	2825
	11th to 20th	Night	13% 8% 3 7% 5% 6% 6% 6% 7% 8% 32%	2807
	21st to end	Night	7% 5% 2 7% 5% 5% 6% 6% 7% 9% 41%	3476
September	1st to 10th	Night	12% 8% 3 7% 5% 4 5% 4 7% 7% 37%	2084
	11th to 20th	Night	13% 8% 3 8% 5% 5% 5% 3 6% 6% 38%	2090
	21st to end	Night	13% 7% 3 7% 6% 4 4 3 5% 5% 43%	2090
October	1st to 10th	Night	13% 9% 2 5% 3 3 4 3 4 6% 49%	2090
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 4 4 47%	2256
	21st to end	Night	11% 9% 3 5% 4 4 4 3 4 5% 47%	2508
November	1st to 10th	Night	11% 9% 3 6% 5% 4 3 3 5% 5% 46%	2507
	11th to 20th	Night	12% 10% 3 7% 4 3 4 3 5% 5% 43%	2600
	21st to end	Night	12% 11% 3 8% 5% 4 4 3 4 6% 41%	2600
December	1st to 10th	Night	11% 12% 6% 11% 6% 4 4 3 4 4 35%	4250
	11th to 20th	Night	14% 12% 5% 12% 6% 5% 4 3 4 5% 29%	4822
	21st to end	Night	10% 12% 6% 12% 6% 5% 4 4 6% 6% 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	31% 29% 7% 11% 19% 3	4057
	11th to 20th	Day	30% 29% 5% 11% 19% 7%	4060
	21st to end	Day	34% 31% 4 12% 13% 5%	4466
February	1st to 10th	Day	20% 62% 4 7% 6% 1	1961
	11th to 20th	Day	24% 61% 2 6% 6% 1	1958
	21st to end	Day	21% 61% 2 4 8% 3	1650
March	1st to 10th	Day	35% 31% 7% 8% 11% 8%	4699
	11th to 20th	Day	23% 30% 4 14% 15% 15%	4980
	21st to end	Day	28% 32% 6% 22% 8% 3	5465
April	1st to 10th	Day	19% 63% 4 7% 6%	2216
	11th to 20th	Day	19% 66% 3 7% 5% 1	2292
	21st to end	Day	16% 65% 4 9% 5% 1	2470
May	1st to 10th	Day	30% 46% 7% 13% 4	4120
	11th to 20th	Day	31% 45% 6% 15% 2	4085
	21st to end	Day	23% 45% 10% 12% 10% 1	4489
June	1st to 10th	Day	19% 67% 4 6% 4	2470
	11th to 20th	Day	18% 67% 7% 6% 3	2470
	21st to end	Day	18% 66% 7% 6% 3	2470
July	1st to 10th	Day	23% 47% 14% 12% 3	4055
	11th to 20th	Day	28% 44% 14% 12% 1	4051
	21st to end	Day	49% 40% 5% 4 2	4324
August	1st to 10th	Day	27% 44% 12% 14% 3	4091
	11th to 20th	Day	23% 43% 19% 8% 6%	4056
	21st to end	Day	19% 42% 12% 23% 3 1	4153
September	1st to 10th	Day	17% 62% 5% 7% 8% 1	2090
	11th to 20th	Day	18% 62% 5% 9% 6%	2090
	21st to end	Day	17% 62% 8% 9% 5%	2090
October	1st to 10th	Day	17% 39% 4 10% 20% 10%	3480
	11th to 20th	Day	13% 37% 3 12% 17% 18%	3176
	21st to end	Day	12% 39% 4 21% 14% 9%	3428
November	1st to 10th	Day	19% 56% 4 9% 9% 2	1786
	11th to 20th	Day	17% 57% 2 8% 12% 4	1800
	21st to end	Day	18% 58% 4 9% 9% 2	1800
December	1st to 10th	Day	23% 39% 8% 10% 15% 5%	2930
	11th to 20th	Day	34% 36% 8% 10% 10% 3	3370
	21st to end	Day	30% 31% 11% 18% 9% 2	4466
January	1st to 10th	Night	35% 31% 8% 10% 12% 4	5889
	11th to 20th	Night	33% 29% 6% 9% 16% 8%	5900
	21st to end	Night	33% 31% 4 8% 15% 8%	6490
February	1st to 10th	Night	21% 62% 3 7% 6% 1	2435
	11th to 20th	Night	25% 61% 3 5% 5% 1	2339
	21st to end	Night	19% 62% 4 6% 6% 3	1980
March	1st to 10th	Night	36% 33% 7% 9% 10% 4	5153
	11th to 20th	Night	18% 31% 7% 16% 13% 14%	4980
	21st to end	Night	28% 31% 12% 17% 9% 3	5467
April	1st to 10th	Night	19% 62% 5% 7% 5% 1	2200
	11th to 20th	Night	18% 66% 4 6% 4 2	1840
	21st to end	Night	14% 66% 4 10% 5% 1	1710
May	1st to 10th	Night	29% 47% 7% 13% 3 1	2840
	11th to 20th	Night	30% 44% 9% 14% 3	2813
	21st to end	Night	19% 48% 12% 14% 5%	3087
June	1st to 10th	Night	15% 68% 7% 7% 3 1	1710
	11th to 20th	Night	12% 69% 9% 8% 3	1710
	21st to end	Night	15% 66% 7% 8% 3	1710
July	1st to 10th	Night	26% 46% 15% 12% 2	2795
	11th to 20th	Night	21% 43% 21% 13% 2	2786
	21st to end	Night	40% 44% 10% 5% 2	2988
August	1st to 10th	Night	24% 43% 15% 15% 3	2814
	11th to 20th	Night	23% 42% 21% 9% 4	2834
	21st to end	Night	12% 42% 17% 22% 5%	3476
September	1st to 10th	Night	14% 64% 6% 9% 7% 1	2084
	11th to 20th	Night	16% 63% 6% 10% 5%	2090
	21st to end	Night	15% 62% 7% 9% 6%	2090
October	1st to 10th	Night	16% 39% 6% 14% 14% 11%	3480
	11th to 20th	Night	15% 37% 4 11% 13% 20%	3742
	21st to end	Night	11% 37% 4 19% 16% 13%	4120
November	1st to 10th	Night	21% 56% 4 10% 7% 1	2507
	11th to 20th	Night	18% 57% 3 8% 9% 4	2600
	21st to end	Night	20% 58% 3 10% 9% 1	2600
December	1st to 10th	Night	31% 38% 4 7% 15% 4	4250
	11th to 20th	Night	34% 36% 7% 10% 11% 2	4824
	21st to end	Night	34% 31% 10% 13% 11% 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	26% 34% 29% 9% 1	300
	11th to 20th	Day	36% 28% 23% 11% 1	300
	21st to end	Day	26% 34% 30% 9% 2	330
February	1st to 10th	Day	25% 30% 34% 9% 2	300
	11th to 20th	Day	40% 37% 19% 4 1	300
	21st to end	Day	40% 32% 22% 6%	249
March	1st to 10th	Day	29% 25% 30% 12% 3 1	389
	11th to 20th	Day	27% 27% 31% 11% 3 1	500
	21st to end	Day	26% 24% 32% 14% 4	550
April	1st to 10th	Day	25% 25% 26% 17% 7% 1	500
	11th to 20th	Day	23% 22% 26% 19% 9% 2	452
	21st to end	Day	24% 17% 28% 19% 9% 3	460
May	1st to 10th	Day	20% 20% 33% 16% 8% 4	463
	11th to 20th	Day	15% 13% 29% 26% 10% 7%	487
	21st to end	Day	16% 9% 25% 27% 12% 11%	529
June	1st to 10th	Day	11% 10% 27% 28% 18% 7%	490
	11th to 20th	Day	7% 8% 24% 28% 23% 10%	490
	21st to end	Day	14% 6% 26% 30% 14% 10%	490
July	1st to 10th	Day	11% 6% 20% 25% 25% 12%	485
	11th to 20th	Day	11% 5% 19% 30% 19% 15%	484
	21st to end	Day	12% 6% 18% 28% 24% 13%	532
August	1st to 10th	Day	16% 8% 18% 25% 21% 13%	486
	11th to 20th	Day	11% 10% 17% 29% 24% 9%	479
	21st to end	Day	15% 2 15% 27% 30% 12%	539
September	1st to 10th	Day	10% 6% 20% 26% 29% 9%	490
	11th to 20th	Day	18% 6% 17% 28% 24% 8%	490
	21st to end	Day	16% 9% 18% 33% 19% 5%	490
October	1st to 10th	Day	16% 9% 25% 27% 17% 6%	490
	11th to 20th	Day	16% 14% 30% 25% 11% 3	490
	21st to end	Day	19% 13% 29% 26% 10% 2	539
November	1st to 10th	Day	17% 20% 31% 22% 8% 1	324
	11th to 20th	Day	19% 25% 34% 18% 4	300
	21st to end	Day	19% 25% 32% 19% 4	300
December	1st to 10th	Day	29% 27% 30% 13% 1	300
	11th to 20th	Day	21% 24% 33% 18% 3	300
	21st to end	Day	24% 24% 37% 12% 4	330
January	1st to 10th	Night	23% 23% 29% 22% 4	800
	11th to 20th	Night	26% 25% 28% 16% 4	800
	21st to end	Night	21% 24% 33% 21% 2	880
February	1st to 10th	Night	23% 18% 32% 25% 2	800
	11th to 20th	Night	27% 24% 32% 15% 1	783
	21st to end	Night	27% 25% 29% 17% 2	660
March	1st to 10th	Night	23% 20% 30% 23% 4	800
	11th to 20th	Night	23% 21% 28% 22% 6% 1	800
	21st to end	Night	21% 20% 30% 20% 7%	880
April	1st to 10th	Night	21% 21% 29% 20% 8% 1	800
	11th to 20th	Night	21% 14% 29% 24% 12% 1	565
	21st to end	Night	18% 11% 31% 29% 10% 1	570
May	1st to 10th	Night	18% 11% 28% 27% 13% 3	570
	11th to 20th	Night	15% 9% 23% 32% 18% 2	561
	21st to end	Night	12% 3 17% 34% 29% 5%	617
June	1st to 10th	Night	9% 5% 18% 36% 27% 4	570
	11th to 20th	Night	5% 4 17% 35% 30% 9%	570
	21st to end	Night	9% 4 16% 33% 31% 7%	570
July	1st to 10th	Night	12% 2 11% 29% 40% 6%	555
	11th to 20th	Night	10% 3 10% 30% 37% 10%	552
	21st to end	Night	8% 4 11% 29% 39% 9%	624
August	1st to 10th	Night	8% 5% 8% 33% 38% 8%	567
	11th to 20th	Night	12% 4 11% 34% 35% 5%	564
	21st to end	Night	12% 3 9% 31% 37% 9%	627
September	1st to 10th	Night	12% 5% 10% 30% 36% 7%	754
	11th to 20th	Night	16% 4 13% 31% 29% 7%	760
	21st to end	Night	16% 5% 17% 32% 27% 2	760
October	1st to 10th	Night	17% 6% 19% 23% 27% 8%	760
	11th to 20th	Night	18% 10% 25% 29% 15% 2	760
	21st to end	Night	17% 12% 25% 31% 13% 3	836
November	1st to 10th	Night	18% 10% 21% 33% 16% 3	780
	11th to 20th	Night	17% 16% 26% 28% 11% 2	800
	21st to end	Night	20% 15% 27% 27% 11% 1	800
December	1st to 10th	Night	22% 22% 27% 23% 6%	800
	11th to 20th	Night	20% 20% 29% 25% 6% 1	800
	21st to end	Night	21% 19% 30% 25% 4	880

Page generated at 2025-04-08 09:17:30. Version ac07

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