Hendersonville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hendersonville clear sky chart from 2005-11-06 to 2024-02-25.

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% 7% 3 6% 5% 3 5% 5% 5% 8% 40%	78899
	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 42%	80391
Transparency	Day	42% 8% 11% 21% 15% 3	78612
	Night	40% 7% 11% 21% 17% 4	80198
Seeing	Day	17% 10% 22% 23% 19% 8%	14157
	Night	17% 8% 24% 29% 19% 3	24004

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	14% 13% 6% 8% 7% 3 5% 4 4 5% 29%	2527
	11th to 20th	Day	22% 8% 4 9% 6% 3 5% 4 3 5% 32%	2661
	21st to end	Day	24% 11% 5% 5% 4 3 4 3 4 5% 30%	3387
February	1st to 10th	Day	19% 10% 4 7% 5% 4 4 4 4 6% 35%	1900
	11th to 20th	Day	21% 9% 3 7% 6% 2 4 3 4 6% 34%	1848
	21st to end	Day	21% 9% 3 7% 4 2 4 4 4 5% 37%	1520
March	1st to 10th	Day	15% 10% 2 5% 5% 3 5% 4 5% 6% 39%	1800
	11th to 20th	Day	20% 9% 3 7% 6% 3 4 3 4 6% 35%	1898
	21st to end	Day	16% 8% 3 7% 7% 3 5% 5% 5% 7% 33%	2286
April	1st to 10th	Day	12% 6% 3 5% 5% 2 4 5% 4 7% 47%	2160
	11th to 20th	Day	15% 6% 3 5% 5% 3 4 4 4 7% 43%	2134
	21st to end	Day	13% 6% 3 6% 6% 4 5% 5% 5% 7% 40%	2209
May	1st to 10th	Day	15% 6% 2 5% 5% 2 5% 5% 5% 8% 42%	2340
	11th to 20th	Day	14% 6% 4 7% 6% 3 5% 4 4 7% 41%	2301
	21st to end	Day	8% 6% 3 5% 6% 4 7% 6% 7% 8% 39%	2531
June	1st to 10th	Day	9% 5% 2 5% 5% 4 6% 5% 6% 9% 43%	2340
	11th to 20th	Day	4 4 2 4 5% 4 5% 7% 8% 10% 46%	2520
	21st to end	Day	4 3 2 5% 6% 4 7% 7% 8% 12% 42%	2520
July	1st to 10th	Day	7% 5% 3 8% 8% 5% 7% 6% 7% 11% 33%	2520
	11th to 20th	Day	8% 5% 3 6% 7% 4 7% 7% 8% 10% 37%	2463
	21st to end	Day	8% 5% 2 6% 7% 4 6% 8% 7% 10% 38%	2547
August	1st to 10th	Day	6% 5% 2 5% 7% 4 7% 8% 9% 10% 37%	2239
	11th to 20th	Day	9% 5% 3 6% 6% 5% 7% 7% 7% 9% 36%	2125
	21st to end	Day	10% 5% 1 5% 5% 4 5% 7% 8% 10% 40%	2376
September	1st to 10th	Day	12% 6% 2 5% 5% 4 6% 6% 6% 8% 41%	2129
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 5% 7% 47%	1980
	21st to end	Day	11% 5% 3 4 4 2 4 4 5% 7% 51%	1980
October	1st to 10th	Day	10% 5% 2 4 4 2 3 4 4 7% 54%	1980
	11th to 20th	Day	13% 6% 2 4 4 2 2 4 5% 7% 51%	1949
	21st to end	Day	17% 6% 2 6% 3 4 3 4 4 5% 45%	1783
November	1st to 10th	Day	11% 5% 2 4 3 2 3 3 4 6% 56%	1672
	11th to 20th	Day	15% 6% 3 4 3 2 4 4 5% 6% 49%	1710
	21st to end	Day	15% 8% 2 5% 4 3 4 4 4 6% 45%	1710
December	1st to 10th	Day	24% 8% 3 6% 4 3 4 4 4 6% 35%	1710
	11th to 20th	Day	17% 8% 3 6% 5% 3 5% 4 4 8% 36%	2153
	21st to end	Day	17% 11% 5% 7% 6% 4 5% 5% 6% 7% 28%	2991
January	1st to 10th	Night	18% 10% 3 7% 6% 3 4 4 5% 6% 35%	4428
	11th to 20th	Night	20% 11% 3 7% 6% 3 4 4 4 5% 33%	4283
	21st to end	Night	22% 12% 3 6% 4 3 4 4 4 6% 33%	4267
February	1st to 10th	Night	22% 9% 4 7% 5% 3 5% 4 5% 5% 33%	2280
	11th to 20th	Night	23% 9% 3 5% 6% 3 3 3 5% 4 36%	2218
	21st to end	Night	25% 8% 4 7% 5% 2 3 4 4 5% 32%	1831
March	1st to 10th	Night	17% 6% 2 5% 5% 3 5% 5% 5% 6% 41%	2160
	11th to 20th	Night	18% 9% 3 6% 6% 3 4 4 4 6% 37%	2062
	21st to end	Night	15% 8% 3 7% 5% 3 4 5% 5% 7% 38%	2084
April	1st to 10th	Night	11% 5% 2 5% 4 3 5% 5% 5% 7% 49%	1800
	11th to 20th	Night	16% 6% 2 3 4 2 4 4 5% 7% 47%	1775
	21st to end	Night	14% 5% 3 5% 5% 3 4 4 6% 9% 42%	1750
May	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 5% 5% 6% 46%	1620
	11th to 20th	Night	10% 5% 3 5% 6% 3 4 3 6% 9% 46%	1592
	21st to end	Night	5% 4 3 5% 6% 4 6% 7% 8% 10% 43%	1744
June	1st to 10th	Night	8% 5% 2 6% 5% 3 4 5% 6% 8% 47%	1614
	11th to 20th	Night	3 3 1 3 5% 3 5% 5% 8% 11% 54%	1440
	21st to end	Night	3 3 2 5% 4 3 6% 7% 7% 11% 48%	1440
July	1st to 10th	Night	8% 4 3 5% 6% 3 6% 6% 7% 11% 41%	1440
	11th to 20th	Night	6% 5% 2 4 5% 4 5% 5% 6% 12% 45%	1494
	21st to end	Night	7% 3 2 5% 6% 4 6% 7% 6% 13% 42%	1771
August	1st to 10th	Night	6% 4 2 5% 5% 4 4 5% 7% 10% 46%	1695
	11th to 20th	Night	7% 5% 2 5% 5% 3 5% 5% 7% 11% 45%	1776
	21st to end	Night	8% 4 2 5% 4 3 6% 6% 7% 9% 46%	1980
September	1st to 10th	Night	10% 5% 2 6% 5% 3 4 5% 5% 7% 49%	1813
	11th to 20th	Night	9% 5% 3 6% 5% 3 4 4 5% 7% 48%	1980
	21st to end	Night	10% 4 2 4 4 2 4 4 6% 6% 54%	1980
October	1st to 10th	Night	9% 4 2 3 3 2 3 3 3 7% 59%	1980
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 4 7% 49%	2006
	21st to end	Night	15% 7% 2 4 4 2 4 3 4 6% 49%	2570
November	1st to 10th	Night	11% 5% 2 5% 4 2 4 4 5% 5% 54%	2406
	11th to 20th	Night	13% 6% 2 5% 4 2 3 4 5% 7% 50%	2470
	21st to end	Night	17% 6% 3 4 4 2 4 3 5% 6% 45%	2470
December	1st to 10th	Night	21% 10% 3 6% 5% 3 4 4 5% 5% 34%	2470
	11th to 20th	Night	18% 8% 3 5% 4 2 4 4 3 6% 43%	3042
	21st to end	Night	18% 11% 4 8% 6% 5% 5% 4 5% 6% 28%	4660

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	53% 7% 9% 18% 10% 2	2528
	11th to 20th	Day	54% 6% 9% 20% 11% 1	2661
	21st to end	Day	55% 5% 9% 22% 9% 1	3387
February	1st to 10th	Day	52% 4 9% 20% 12% 2	1900
	11th to 20th	Day	53% 4 7% 18% 14% 3	1858
	21st to end	Day	50% 4 10% 17% 14% 7%	1520
March	1st to 10th	Day	45% 5% 9% 19% 17% 5%	1800
	11th to 20th	Day	52% 6% 9% 19% 13% 2	1898
	21st to end	Day	49% 8% 11% 19% 12% 1	2286
April	1st to 10th	Day	37% 7% 10% 24% 20% 3	2160
	11th to 20th	Day	40% 7% 7% 21% 21% 5%	2134
	21st to end	Day	42% 8% 9% 24% 15% 2	2209
May	1st to 10th	Day	40% 7% 12% 24% 15% 2	2340
	11th to 20th	Day	43% 8% 11% 22% 14% 1	2305
	21st to end	Day	38% 12% 14% 22% 12% 2	2531
June	1st to 10th	Day	36% 9% 12% 23% 17% 2	2340
	11th to 20th	Day	28% 11% 17% 23% 17% 3	2520
	21st to end	Day	31% 11% 17% 22% 14% 5%	2520
July	1st to 10th	Day	39% 13% 16% 16% 11% 4	2451
	11th to 20th	Day	39% 11% 17% 19% 11% 3	2388
	21st to end	Day	36% 11% 17% 23% 10% 2	2405
August	1st to 10th	Day	36% 13% 18% 22% 11% 1	2226
	11th to 20th	Day	40% 11% 13% 20% 15% 2	2125
	21st to end	Day	35% 11% 15% 21% 14% 3	2376
September	1st to 10th	Day	38% 10% 12% 19% 17% 3	2129
	11th to 20th	Day	37% 6% 11% 23% 20% 2	1980
	21st to end	Day	32% 6% 11% 24% 22% 5%	1980
October	1st to 10th	Day	30% 6% 10% 23% 26% 5%	1980
	11th to 20th	Day	33% 5% 8% 21% 25% 8%	1949
	21st to end	Day	40% 6% 7% 20% 22% 4	1783
November	1st to 10th	Day	30% 4 9% 25% 26% 6%	1672
	11th to 20th	Day	36% 5% 8% 23% 23% 6%	1710
	21st to end	Day	41% 5% 7% 24% 19% 5%	1710
December	1st to 10th	Day	51% 4 9% 20% 14% 2	1710
	11th to 20th	Day	46% 7% 11% 21% 14% 1	2150
	21st to end	Day	51% 8% 13% 19% 8% 1	2991
January	1st to 10th	Night	46% 7% 10% 21% 14% 1	4428
	11th to 20th	Night	52% 7% 6% 16% 15% 4	4283
	21st to end	Night	52% 5% 9% 21% 12% 1	4267
February	1st to 10th	Night	53% 5% 9% 18% 14% 1	2280
	11th to 20th	Night	52% 4 7% 19% 15% 4	2219
	21st to end	Night	55% 5% 7% 13% 15% 5%	1831
March	1st to 10th	Night	43% 7% 9% 15% 19% 6%	2160
	11th to 20th	Night	47% 6% 10% 19% 15% 2	2062
	21st to end	Night	45% 7% 12% 22% 13% 2	2084
April	1st to 10th	Night	34% 6% 12% 24% 21% 3	1800
	11th to 20th	Night	36% 5% 9% 19% 23% 8%	1775
	21st to end	Night	38% 7% 10% 26% 17% 2	1750
May	1st to 10th	Night	37% 8% 11% 24% 18% 3	1620
	11th to 20th	Night	35% 9% 17% 22% 16% 1	1593
	21st to end	Night	32% 12% 16% 23% 15% 2	1745
June	1st to 10th	Night	34% 8% 13% 26% 16% 4	1614
	11th to 20th	Night	22% 7% 19% 31% 18% 3	1440
	21st to end	Night	27% 11% 18% 27% 14% 4	1440
July	1st to 10th	Night	33% 11% 19% 20% 14% 3	1400
	11th to 20th	Night	29% 10% 20% 23% 14% 5%	1446
	21st to end	Night	31% 11% 17% 27% 12% 2	1672
August	1st to 10th	Night	31% 10% 15% 28% 15% 1	1684
	11th to 20th	Night	30% 10% 20% 23% 15% 2	1776
	21st to end	Night	31% 9% 15% 25% 15% 4	1980
September	1st to 10th	Night	34% 8% 12% 23% 19% 4	1813
	11th to 20th	Night	34% 6% 10% 22% 23% 3	1980
	21st to end	Night	29% 6% 11% 22% 24% 7%	1980
October	1st to 10th	Night	26% 4 9% 23% 29% 8%	1980
	11th to 20th	Night	36% 5% 9% 21% 22% 7%	2006
	21st to end	Night	36% 4 7% 23% 24% 5%	2570
November	1st to 10th	Night	32% 4 7% 23% 25% 8%	2406
	11th to 20th	Night	33% 5% 7% 21% 26% 7%	2470
	21st to end	Night	40% 4 8% 24% 19% 4	2470
December	1st to 10th	Night	51% 6% 8% 19% 14% 2	2470
	11th to 20th	Night	42% 6% 8% 21% 20% 3	3044
	21st to end	Night	53% 8% 10% 17% 11% 1	4660

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	24% 23% 32% 15% 5% 1	270
	11th to 20th	Day	31% 26% 26% 13% 3 1	270
	21st to end	Day	23% 23% 40% 12% 2	297
February	1st to 10th	Day	27% 21% 32% 16% 3 1	270
	11th to 20th	Day	36% 24% 28% 8% 3	270
	21st to end	Day	33% 23% 34% 9% 1	210
March	1st to 10th	Day	27% 22% 33% 14% 4	240
	11th to 20th	Day	27% 20% 30% 15% 7% 1	338
	21st to end	Day	28% 16% 29% 18% 9%	462
April	1st to 10th	Day	20% 15% 29% 26% 9% 1	420
	11th to 20th	Day	22% 11% 29% 23% 12% 2	412
	21st to end	Day	21% 15% 29% 21% 12% 2	420
May	1st to 10th	Day	20% 13% 28% 22% 12% 4	423
	11th to 20th	Day	15% 8% 27% 25% 17% 7%	447
	21st to end	Day	12% 5% 18% 27% 24% 15%	485
June	1st to 10th	Day	12% 4 17% 23% 26% 17%	450
	11th to 20th	Day	5% 4 18% 29% 30% 14%	630
	21st to end	Day	5% 3 21% 34% 22% 15%	630
July	1st to 10th	Day	9% 3 12% 28% 31% 18%	621
	11th to 20th	Day	8% 3 10% 26% 35% 18%	561
	21st to end	Day	7% 3 11% 28% 31% 20%	488
August	1st to 10th	Day	10% 4 10% 27% 31% 18%	446
	11th to 20th	Day	10% 3 13% 32% 30% 12%	439
	21st to end	Day	13% 2 11% 20% 36% 18%	495
September	1st to 10th	Day	11% 3 11% 27% 32% 16%	450
	11th to 20th	Day	13% 3 10% 28% 29% 17%	450
	21st to end	Day	16% 7% 18% 25% 27% 8%	450
October	1st to 10th	Day	12% 4 22% 28% 27% 8%	450
	11th to 20th	Day	16% 14% 30% 26% 12% 2	419
	21st to end	Day	24% 14% 27% 26% 7% 1	297
November	1st to 10th	Day	17% 11% 29% 27% 14% 2	270
	11th to 20th	Day	14% 21% 36% 22% 7%	270
	21st to end	Day	21% 15% 32% 23% 7% 2	270
December	1st to 10th	Day	29% 18% 26% 21% 6%	270
	11th to 20th	Day	22% 20% 33% 16% 9%	270
	21st to end	Day	27% 19% 33% 18% 3	297
January	1st to 10th	Night	24% 16% 29% 26% 5%	950
	11th to 20th	Night	29% 15% 29% 22% 5%	858
	21st to end	Night	21% 14% 37% 24% 3	836
February	1st to 10th	Night	26% 14% 32% 24% 4	760
	11th to 20th	Night	28% 15% 34% 21% 3	743
	21st to end	Night	29% 16% 33% 21% 1	611
March	1st to 10th	Night	22% 14% 31% 28% 5%	720
	11th to 20th	Night	22% 13% 32% 26% 7% 1	720
	21st to end	Night	21% 11% 31% 29% 8%	698
April	1st to 10th	Night	13% 11% 33% 32% 10%	540
	11th to 20th	Night	20% 9% 32% 27% 12%	533
	21st to end	Night	17% 7% 31% 31% 11% 2	540
May	1st to 10th	Night	12% 6% 33% 30% 17% 1	540
	11th to 20th	Night	11% 5% 25% 35% 20% 5%	531
	21st to end	Night	6% 2 16% 38% 32% 6%	584
June	1st to 10th	Night	11% 3 15% 37% 30% 4	540
	11th to 20th	Night	4 1 11% 39% 37% 7%	540
	21st to end	Night	5% 2 14% 36% 37% 6%	540
July	1st to 10th	Night	9% 3 6% 30% 40% 11%	525
	11th to 20th	Night	7% 2 6% 30% 44% 11%	522
	21st to end	Night	8% 2 8% 30% 44% 8%	591
August	1st to 10th	Night	7% 1 5% 31% 47% 8%	537
	11th to 20th	Night	6% 2 8% 38% 38% 7%	534
	21st to end	Night	8% 2 8% 29% 44% 9%	594
September	1st to 10th	Night	10% 1 11% 32% 39% 6%	553
	11th to 20th	Night	11% 3 14% 29% 37% 6%	720
	21st to end	Night	12% 3 17% 28% 36% 4	720
October	1st to 10th	Night	11% 5% 20% 30% 29% 6%	720
	11th to 20th	Night	19% 7% 23% 34% 16% 2	720
	21st to end	Night	18% 10% 27% 28% 16% 2	792
November	1st to 10th	Night	15% 7% 22% 35% 19% 2	740
	11th to 20th	Night	16% 10% 33% 31% 10% 1	760
	21st to end	Night	21% 10% 26% 32% 10% 1	760
December	1st to 10th	Night	28% 11% 28% 26% 7%	760
	11th to 20th	Night	24% 9% 31% 29% 7% 1	760
	21st to end	Night	28% 13% 28% 25% 5%	912

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