Asheville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Asheville clear sky chart from 2005-11-06 to 2025-05-11.

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	10% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	114319
	Night	10% 7% 3 7% 5% 5% 5% 4 6% 8% 41%	114643
Transparency	Day	38% 9% 12% 19% 16% 5%	118074
	Night	36% 9% 13% 20% 17% 5%	119027
Seeing	Day	18% 15% 24% 22% 14% 7%	15684
	Night	16% 13% 22% 28% 18% 3	25817

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	9% 5% 2 7% 4 4 3 3 5% 8% 50%	4056
	11th to 20th	Day	8% 5% 2 5% 4 4 4 3 6% 6% 53%	4060
	21st to end	Day	12% 9% 4 8% 3 4 4 3 4 6% 43%	4466
February	1st to 10th	Day	11% 8% 2 6% 5% 5% 4 4 6% 7% 41%	1885
	11th to 20th	Day	12% 10% 4 7% 5% 4 4 3 5% 6% 38%	1948
	21st to end	Day	11% 9% 3 7% 5% 5% 5% 4 5% 6% 40%	1650
March	1st to 10th	Day	14% 8% 3 8% 5% 4 4 3 5% 6% 39%	4835
	11th to 20th	Day	9% 8% 3 6% 4 3 3 3 5% 6% 50%	4980
	21st to end	Day	13% 7% 3 6% 4 3 4 3 5% 6% 44%	5465
April	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 4 7% 8% 43%	2200
	11th to 20th	Day	12% 8% 2 6% 5% 3 4 4 5% 8% 43%	2396
	21st to end	Day	11% 6% 2 6% 4 5% 5% 5% 5% 7% 44%	2600
May	1st to 10th	Day	9% 8% 3 9% 6% 5% 6% 5% 7% 8% 33%	4212
	11th to 20th	Day	14% 8% 3 8% 5% 6% 6% 5% 6% 7% 30%	4081
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 10% 39%	4476
June	1st to 10th	Day	9% 7% 2 8% 6% 7% 7% 5% 8% 10% 31%	2470
	11th to 20th	Day	6% 6% 3 7% 6% 6% 6% 6% 9% 9% 35%	2470
	21st to end	Day	7% 6% 2 7% 7% 6% 7% 6% 8% 9% 34%	2470
July	1st to 10th	Day	5% 6% 3 8% 7% 7% 7% 6% 8% 10% 32%	4120
	11th to 20th	Day	8% 6% 3 8% 6% 7% 7% 6% 8% 8% 31%	4120
	21st to end	Day	11% 8% 4 12% 9% 8% 9% 6% 7% 7% 17%	4466
August	1st to 10th	Day	10% 8% 3 9% 7% 7% 7% 6% 9% 11% 24%	4104
	11th to 20th	Day	7% 5% 3 7% 6% 7% 7% 5% 9% 12% 32%	4044
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 6% 8% 47%	4195
September	1st to 10th	Day	9% 7% 3 8% 6% 6% 6% 5% 7% 7% 36%	2090
	11th to 20th	Day	15% 6% 3 8% 6% 6% 5% 4 7% 8% 32%	2090
	21st to end	Day	12% 6% 3 7% 5% 5% 6% 5% 6% 6% 38%	2090
October	1st to 10th	Day	11% 6% 2 7% 4 4 4 4 5% 5% 48%	2057
	11th to 20th	Day	8% 5% 3 6% 4 3 5% 3 4 5% 54%	1900
	21st to end	Day	11% 7% 2 6% 4 3 3 3 4 6% 53%	2090
November	1st to 10th	Day	8% 7% 2 6% 4 3 4 2 3 6% 54%	1864
	11th to 20th	Day	9% 7% 2 5% 5% 3 5% 3 5% 7% 50%	1800
	21st to end	Day	11% 7% 3 6% 3 3 4 4 6% 7% 47%	1800
December	1st to 10th	Day	9% 5% 2 7% 4 4 5% 3 5% 7% 48%	2930
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 6% 9% 38%	3373
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 4 8% 39%	4466
January	1st to 10th	Night	9% 6% 2 10% 5% 5% 5% 4 5% 7% 40%	5889
	11th to 20th	Night	9% 7% 2 6% 4 5% 4 3 5% 7% 47%	5900
	21st to end	Night	11% 9% 3 7% 4 4 3 3 5% 6% 45%	6490
February	1st to 10th	Night	10% 8% 2 7% 5% 5% 5% 4 6% 8% 41%	2510
	11th to 20th	Night	14% 9% 3 7% 4 4 4 3 5% 7% 38%	2338
	21st to end	Night	12% 7% 3 8% 5% 5% 5% 5% 5% 6% 38%	1980
March	1st to 10th	Night	15% 10% 4 8% 5% 4 4 4 5% 6% 35%	5016
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 8% 49%	4980
	21st to end	Night	13% 8% 2 6% 5% 4 4 3 5% 7% 43%	5467
April	1st to 10th	Night	10% 7% 3 6% 5% 4 4 4 6% 8% 44%	2200
	11th to 20th	Night	8% 7% 3 6% 4 4 4 4 6% 8% 46%	1969
	21st to end	Night	9% 6% 2 7% 5% 4 4 3 5% 8% 47%	1800
May	1st to 10th	Night	9% 8% 4 9% 5% 5% 4 4 7% 9% 36%	2903
	11th to 20th	Night	12% 8% 4 9% 6% 5% 5% 5% 6% 8% 33%	2818
	21st to end	Night	7% 4 2 7% 5% 5% 5% 5% 8% 12% 39%	3079
June	1st to 10th	Night	6% 7% 3 7% 5% 6% 7% 5% 8% 13% 34%	1710
	11th to 20th	Night	5% 7% 2 5% 5% 4 4 5% 9% 12% 41%	1710
	21st to end	Night	6% 6% 2 5% 6% 5% 6% 5% 8% 11% 42%	1710
July	1st to 10th	Night	5% 7% 3 9% 7% 6% 8% 5% 7% 11% 32%	2840
	11th to 20th	Night	7% 5% 2 7% 6% 6% 6% 6% 9% 11% 35%	2840
	21st to end	Night	10% 10% 5% 13% 8% 7% 7% 5% 7% 8% 21%	3087
August	1st to 10th	Night	7% 7% 3 8% 7% 6% 7% 6% 8% 10% 31%	2825
	11th to 20th	Night	7% 7% 3 9% 7% 7% 7% 5% 8% 9% 31%	2785
	21st to end	Night	6% 5% 2 5% 3 4 6% 4 7% 9% 48%	3423
September	1st to 10th	Night	9% 5% 2 7% 6% 6% 5% 5% 6% 8% 40%	2090
	11th to 20th	Night	13% 7% 3 10% 5% 6% 5% 3 5% 7% 35%	2090
	21st to end	Night	10% 6% 3 7% 4 5% 5% 4 5% 6% 45%	2090
October	1st to 10th	Night	12% 6% 2 7% 4 4 4 3 5% 6% 48%	2123
	11th to 20th	Night	10% 6% 2 6% 4 5% 4 4 6% 6% 48%	2280
	21st to end	Night	10% 7% 2 5% 3 3 4 3 5% 5% 53%	2508
November	1st to 10th	Night	10% 6% 3 6% 3 4 4 4 5% 6% 48%	2431
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 3 5% 7% 48%	2600
	21st to end	Night	11% 7% 3 6% 4 5% 5% 4 6% 7% 45%	2600
December	1st to 10th	Night	10% 5% 3 6% 4 4 5% 4 6% 7% 46%	4250
	11th to 20th	Night	13% 9% 4 10% 5% 5% 5% 4 5% 7% 34%	4822
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 4 6% 6% 38%	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	30% 4 8% 24% 30% 3	4057
	11th to 20th	Day	27% 6% 8% 16% 34% 9%	4060
	21st to end	Day	37% 7% 8% 20% 22% 7%	4466
February	1st to 10th	Day	40% 6% 12% 21% 17% 4	1885
	11th to 20th	Day	44% 6% 10% 18% 17% 5%	1958
	21st to end	Day	43% 7% 10% 15% 19% 6%	1650
March	1st to 10th	Day	41% 7% 8% 14% 20% 10%	4835
	11th to 20th	Day	33% 6% 7% 15% 22% 18%	4980
	21st to end	Day	38% 7% 9% 25% 15% 4	5465
April	1st to 10th	Day	34% 9% 14% 21% 18% 4	2200
	11th to 20th	Day	38% 7% 10% 19% 20% 6%	2396
	21st to end	Day	36% 9% 13% 25% 14% 2	2600
May	1st to 10th	Day	44% 11% 15% 19% 11% 1	4250
	11th to 20th	Day	45% 14% 13% 17% 10% 1	4085
	21st to end	Day	34% 13% 18% 19% 16% 1	4489
June	1st to 10th	Day	43% 15% 18% 16% 7% 1	2470
	11th to 20th	Day	40% 13% 18% 17% 10% 1	2470
	21st to end	Day	42% 13% 16% 15% 11% 2	2470
July	1st to 10th	Day	41% 16% 18% 18% 7%	4055
	11th to 20th	Day	44% 15% 20% 16% 5% 1	4051
	21st to end	Day	60% 15% 13% 9% 4	4324
August	1st to 10th	Day	48% 14% 17% 17% 3	4091
	11th to 20th	Day	37% 14% 22% 15% 9% 3	4083
	21st to end	Day	32% 11% 13% 31% 12% 2	4195
September	1st to 10th	Day	42% 10% 14% 16% 14% 3	2090
	11th to 20th	Day	46% 11% 11% 17% 13% 2	2090
	21st to end	Day	43% 9% 13% 17% 14% 5%	2090
October	1st to 10th	Day	27% 6% 9% 19% 27% 11%	3421
	11th to 20th	Day	21% 4 7% 21% 24% 22%	3140
	21st to end	Day	27% 4 8% 25% 23% 14%	3428
November	1st to 10th	Day	32% 5% 8% 21% 26% 8%	1864
	11th to 20th	Day	32% 6% 7% 22% 25% 7%	1800
	21st to end	Day	33% 6% 9% 24% 22% 5%	1800
December	1st to 10th	Day	34% 7% 7% 19% 28% 6%	2930
	11th to 20th	Day	37% 7% 12% 21% 19% 5%	3370
	21st to end	Day	38% 7% 13% 25% 14% 3	4466
January	1st to 10th	Night	32% 6% 11% 25% 22% 4	5889
	11th to 20th	Night	28% 6% 9% 21% 28% 8%	5900
	21st to end	Night	38% 6% 7% 19% 22% 8%	6490
February	1st to 10th	Night	38% 7% 13% 21% 18% 4	2510
	11th to 20th	Night	43% 6% 11% 19% 16% 5%	2339
	21st to end	Night	42% 8% 11% 17% 17% 6%	1980
March	1st to 10th	Night	40% 11% 9% 13% 21% 6%	5016
	11th to 20th	Night	28% 8% 8% 19% 23% 14%	4980
	21st to end	Night	40% 8% 10% 25% 12% 5%	5467
April	1st to 10th	Night	34% 8% 15% 22% 18% 3	2200
	11th to 20th	Night	33% 7% 12% 23% 20% 4	1969
	21st to end	Night	34% 9% 16% 24% 16% 2	1800
May	1st to 10th	Night	40% 12% 16% 23% 9% 1	2930
	11th to 20th	Night	41% 13% 17% 20% 8%	2819
	21st to end	Night	28% 14% 23% 25% 10% 1	3087
June	1st to 10th	Night	37% 16% 20% 19% 7% 1	1710
	11th to 20th	Night	32% 13% 25% 21% 8% 1	1710
	21st to end	Night	32% 15% 19% 19% 12% 2	1710
July	1st to 10th	Night	42% 16% 19% 16% 6%	2795
	11th to 20th	Night	36% 19% 25% 16% 4 1	2786
	21st to end	Night	54% 16% 14% 11% 4	2988
August	1st to 10th	Night	40% 18% 24% 14% 4	2814
	11th to 20th	Night	39% 18% 21% 14% 8%	2812
	21st to end	Night	30% 12% 16% 33% 9% 1	3423
September	1st to 10th	Night	39% 13% 14% 19% 12% 3	2090
	11th to 20th	Night	45% 11% 13% 15% 15% 1	2090
	21st to end	Night	38% 8% 13% 21% 17% 3	2090
October	1st to 10th	Night	29% 8% 11% 17% 25% 10%	3539
	11th to 20th	Night	22% 7% 7% 20% 24% 20%	3779
	21st to end	Night	28% 5% 8% 23% 23% 13%	4120
November	1st to 10th	Night	34% 9% 9% 19% 21% 8%	2431
	11th to 20th	Night	34% 5% 9% 20% 23% 8%	2600
	21st to end	Night	35% 7% 8% 23% 21% 6%	2600
December	1st to 10th	Night	33% 6% 10% 22% 24% 4	4250
	11th to 20th	Night	41% 9% 11% 18% 16% 4	4824
	21st to end	Night	40% 7% 14% 20% 17% 2	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	35% 25% 31% 7% 1	300
	11th to 20th	Day	37% 21% 25% 14% 3	300
	21st to end	Day	27% 33% 28% 10% 2	330
February	1st to 10th	Day	27% 30% 30% 13% 1	300
	11th to 20th	Day	41% 30% 23% 6% 1	300
	21st to end	Day	36% 33% 23% 8% 1	249
March	1st to 10th	Day	27% 24% 28% 16% 5%	448
	11th to 20th	Day	28% 23% 29% 15% 4 1	500
	21st to end	Day	27% 24% 29% 16% 5%	550
April	1st to 10th	Day	24% 24% 26% 17% 8% 1	500
	11th to 20th	Day	19% 23% 26% 21% 10% 2	492
	21st to end	Day	19% 17% 28% 20% 12% 4	500
May	1st to 10th	Day	17% 21% 27% 21% 9% 5%	503
	11th to 20th	Day	16% 13% 24% 26% 13% 8%	487
	21st to end	Day	12% 10% 24% 24% 18% 12%	529
June	1st to 10th	Day	13% 6% 27% 27% 16% 11%	490
	11th to 20th	Day	8% 7% 24% 24% 23% 13%	490
	21st to end	Day	9% 7% 28% 25% 18% 12%	490
July	1st to 10th	Day	8% 4 14% 28% 29% 15%	485
	11th to 20th	Day	7% 4 14% 28% 26% 20%	484
	21st to end	Day	9% 2 14% 27% 31% 16%	532
August	1st to 10th	Day	17% 5% 19% 23% 19% 17%	486
	11th to 20th	Day	8% 4 20% 30% 22% 15%	479
	21st to end	Day	10% 3 16% 27% 29% 15%	539
September	1st to 10th	Day	9% 5% 17% 30% 27% 13%	490
	11th to 20th	Day	16% 7% 18% 23% 27% 10%	490
	21st to end	Day	16% 10% 18% 30% 22% 5%	490
October	1st to 10th	Day	17% 10% 19% 29% 18% 7%	490
	11th to 20th	Day	13% 17% 23% 28% 15% 3	490
	21st to end	Day	18% 14% 24% 28% 12% 3	539
November	1st to 10th	Day	17% 15% 30% 25% 10% 2	402
	11th to 20th	Day	23% 22% 33% 17% 5%	300
	21st to end	Day	21% 23% 31% 17% 7% 1	300
December	1st to 10th	Day	27% 28% 30% 14% 1	300
	11th to 20th	Day	23% 22% 33% 16% 5% 1	300
	21st to end	Day	25% 22% 35% 12% 5% 1	330
January	1st to 10th	Night	27% 22% 26% 21% 5%	800
	11th to 20th	Night	21% 22% 30% 23% 4	800
	21st to end	Night	20% 21% 34% 22% 3	880
February	1st to 10th	Night	18% 19% 32% 28% 4	800
	11th to 20th	Night	26% 26% 28% 19% 1	783
	21st to end	Night	22% 25% 30% 21% 2	660
March	1st to 10th	Night	20% 22% 30% 25% 4	800
	11th to 20th	Night	22% 18% 31% 22% 7% 1	800
	21st to end	Night	21% 18% 33% 21% 7%	880
April	1st to 10th	Night	18% 22% 27% 25% 7%	800
	11th to 20th	Night	17% 18% 27% 27% 10% 1	690
	21st to end	Night	13% 13% 23% 35% 16% 1	600
May	1st to 10th	Night	13% 12% 25% 33% 17% 1	600
	11th to 20th	Night	14% 9% 20% 32% 22% 2	563
	21st to end	Night	11% 5% 16% 29% 33% 7%	617
June	1st to 10th	Night	8% 4 16% 37% 30% 6%	570
	11th to 20th	Night	7% 2 16% 29% 35% 10%	570
	21st to end	Night	6% 3 12% 35% 37% 6%	570
July	1st to 10th	Night	10% 3 8% 25% 46% 7%	555
	11th to 20th	Night	8% 4 7% 24% 45% 12%	552
	21st to end	Night	8% 2 7% 29% 43% 12%	624
August	1st to 10th	Night	10% 2 11% 26% 41% 10%	567
	11th to 20th	Night	12% 3 11% 28% 38% 9%	564
	21st to end	Night	9% 2 9% 28% 43% 9%	676
September	1st to 10th	Night	10% 3 15% 29% 37% 6%	760
	11th to 20th	Night	15% 6% 16% 27% 32% 5%	760
	21st to end	Night	15% 7% 17% 31% 27% 3	760
October	1st to 10th	Night	15% 10% 18% 26% 25% 6%	760
	11th to 20th	Night	15% 11% 25% 29% 18% 2	760
	21st to end	Night	15% 14% 19% 35% 15% 3	836
November	1st to 10th	Night	16% 10% 22% 33% 16% 3	780
	11th to 20th	Night	18% 14% 23% 33% 11% 1	800
	21st to end	Night	19% 16% 23% 30% 12% 1	800
December	1st to 10th	Night	22% 18% 25% 28% 6%	800
	11th to 20th	Night	18% 16% 29% 30% 7% 1	800
	21st to end	Night	23% 17% 26% 28% 5%	880

Page generated at 2025-05-08 09:33:58. Version ac07

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