Greenville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenville clear sky chart from 2005-11-06 to 2026-01-17.

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% 6% 2 6% 4 4 4 4 5% 7% 44%	126311
	Night	13% 6% 2 5% 4 4 4 3 5% 7% 48%	125537
Transparency	Day	37% 6% 11% 22% 19% 6%	129918
	Night	35% 5% 10% 21% 21% 8%	130007
Seeing	Day	13% 7% 19% 24% 24% 13%	16763
	Night	14% 6% 23% 32% 22% 3	26582

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	16% 10% 4 7% 3 2 2 2 4 4 45%	4167
	11th to 20th	Day	17% 6% 2 4 4 3 3 2 4 5% 50%	4134
	21st to end	Day	21% 9% 2 6% 3 2 2 2 3 4 46%	4488
February	1st to 10th	Day	20% 8% 2 6% 4 3 3 3 5% 5% 41%	1905
	11th to 20th	Day	22% 8% 3 6% 4 3 3 3 4 4 40%	1948
	21st to end	Day	20% 8% 3 7% 4 3 3 3 4 5% 39%	1650
March	1st to 10th	Day	20% 10% 3 9% 5% 4 4 2 4 5% 34%	4819
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 5% 6% 48%	4980
	21st to end	Day	13% 8% 3 9% 5% 5% 4 3 4 5% 40%	5635
April	1st to 10th	Day	13% 7% 2 6% 5% 5% 4 4 6% 6% 43%	2400
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 6% 6% 44%	2374
	21st to end	Day	11% 5% 3 5% 5% 4 4 4 6% 8% 45%	2400
May	1st to 10th	Day	16% 7% 2 7% 5% 5% 4 4 5% 6% 39%	5405
	11th to 20th	Day	11% 6% 3 8% 6% 5% 5% 4 7% 8% 36%	5404
	21st to end	Day	11% 5% 2 7% 5% 6% 6% 4 7% 9% 38%	6465
June	1st to 10th	Day	7% 5% 3 6% 5% 5% 6% 5% 7% 9% 42%	2800
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 7% 9% 46%	2800
	21st to end	Day	6% 4 2 4 5% 5% 5% 5% 7% 10% 48%	2734
July	1st to 10th	Day	5% 6% 3 8% 6% 7% 7% 5% 7% 9% 37%	5900
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 5% 8% 10% 42%	5900
	21st to end	Day	10% 6% 2 6% 5% 4 5% 5% 8% 11% 38%	6422
August	1st to 10th	Day	3 2 1 3 3 4 4 4 5% 7% 65%	3975
	11th to 20th	Day	5% 3 2 5% 4 4 6% 5% 8% 12% 46%	3849
	21st to end	Day	8% 4 2 5% 5% 4 5% 4 6% 8% 48%	4312
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	2400
	11th to 20th	Day	11% 6% 2 6% 3 5% 5% 3 5% 7% 47%	2400
	21st to end	Day	10% 4 1 4 3 4 5% 3 5% 6% 55%	2170
October	1st to 10th	Day	8% 3 1 4 3 4 3 3 5% 7% 62%	2000
	11th to 20th	Day	10% 4 2 5% 2 3 3 3 4 6% 59%	2000
	21st to end	Day	15% 5% 2 4 3 3 3 3 4 5% 54%	2200
November	1st to 10th	Day	13% 5% 2 4 3 3 3 2 4 6% 57%	2058
	11th to 20th	Day	10% 5% 2 4 4 4 4 3 4 5% 55%	1935
	21st to end	Day	17% 7% 3 6% 3 3 3 3 4 7% 45%	1890
December	1st to 10th	Day	18% 8% 3 5% 4 3 3 3 4 5% 44%	2970
	11th to 20th	Day	19% 10% 3 7% 4 3 3 2 4 4 41%	3088
	21st to end	Day	15% 6% 2 6% 4 4 4 3 4 6% 46%	4334
January	1st to 10th	Night	18% 6% 2 5% 3 3 3 2 3 4 49%	6018
	11th to 20th	Night	16% 6% 2 5% 4 3 3 2 3 5% 51%	5979
	21st to end	Night	24% 7% 2 5% 3 3 3 2 3 4 42%	6490
February	1st to 10th	Night	19% 8% 3 6% 4 3 3 3 4 5% 43%	2493
	11th to 20th	Night	21% 8% 3 5% 3 3 3 3 4 5% 43%	2338
	21st to end	Night	20% 8% 3 6% 4 3 4 3 3 5% 44%	1980
March	1st to 10th	Night	17% 7% 3 6% 5% 4 4 3 4 5% 42%	5062
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 7% 49%	4980
	21st to end	Night	15% 6% 3 7% 4 4 4 3 5% 6% 43%	5292
April	1st to 10th	Night	12% 5% 2 5% 5% 4 4 3 6% 7% 48%	2000
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 6% 7% 48%	1975
	21st to end	Night	11% 5% 2 5% 5% 4 5% 3 4 6% 51%	2000
May	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 6% 8% 38%	4490
	11th to 20th	Night	17% 7% 3 8% 5% 5% 5% 4 6% 7% 34%	4489
	21st to end	Night	11% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	4394
June	1st to 10th	Night	5% 4 2 5% 4 3 6% 5% 7% 11% 48%	1600
	11th to 20th	Night	3 3 2 5% 3 4 4 5% 6% 11% 54%	1600
	21st to end	Night	5% 3 1 4 4 4 4 4 8% 11% 52%	1656
July	1st to 10th	Night	4 4 2 6% 5% 5% 7% 6% 8% 12% 42%	4078
	11th to 20th	Night	5% 4 1 4 4 4 5% 4 7% 13% 48%	4077
	21st to end	Night	8% 6% 2 6% 3 4 4 4 7% 11% 44%	4449
August	1st to 10th	Night	2 2 1 3 2 3 3 3 4 8% 70%	3173
	11th to 20th	Night	4 2 1 4 4 4 5% 5% 7% 12% 51%	3200
	21st to end	Night	6% 4 2 7% 5% 4 5% 4 6% 7% 50%	3586
September	1st to 10th	Night	9% 4 2 6% 4 4 4 5% 6% 8% 50%	2000
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 5% 6% 51%	2000
	21st to end	Night	9% 4 1 4 3 2 3 3 6% 8% 57%	2205
October	1st to 10th	Night	7% 3 2 3 2 3 3 2 4 6% 65%	2400
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 5% 60%	2400
	21st to end	Night	14% 5% 2 4 3 3 3 2 4 5% 55%	2640
November	1st to 10th	Night	12% 4 2 4 3 3 3 2 4 6% 56%	2460
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 6% 57%	2682
	21st to end	Night	13% 6% 2 5% 5% 4 3 3 4 5% 50%	2730
December	1st to 10th	Night	19% 7% 2 5% 3 3 3 2 4 5% 46%	4414
	11th to 20th	Night	18% 7% 2 6% 4 4 3 2 4 4 47%	5339
	21st to end	Night	17% 8% 2 5% 4 3 3 3 5% 5% 44%	6868

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	45% 2 5% 26% 19% 2	4168
	11th to 20th	Day	35% 4 8% 22% 26% 5%	4134
	21st to end	Day	45% 3 6% 14% 23% 9%	4488
February	1st to 10th	Day	46% 5% 6% 19% 18% 7%	1905
	11th to 20th	Day	49% 4 5% 19% 16% 7%	1958
	21st to end	Day	48% 4 7% 14% 19% 9%	1650
March	1st to 10th	Day	53% 4 5% 14% 15% 8%	4819
	11th to 20th	Day	36% 4 7% 16% 24% 13%	4980
	21st to end	Day	46% 4 7% 21% 18% 4	5637
April	1st to 10th	Day	41% 6% 9% 20% 18% 6%	2400
	11th to 20th	Day	40% 5% 10% 18% 22% 6%	2374
	21st to end	Day	37% 6% 11% 21% 23% 3	2400
May	1st to 10th	Day	44% 6% 10% 26% 12% 2	5440
	11th to 20th	Day	42% 8% 14% 20% 14% 1	5408
	21st to end	Day	40% 8% 13% 24% 13% 2	6479
June	1st to 10th	Day	35% 9% 14% 24% 17% 1	2800
	11th to 20th	Day	30% 9% 16% 25% 16% 4	2800
	21st to end	Day	28% 10% 16% 25% 17% 4	2734
July	1st to 10th	Day	39% 10% 18% 20% 12% 2	5836
	11th to 20th	Day	33% 9% 22% 31% 6% 1	5831
	21st to end	Day	38% 8% 17% 30% 7%	6240
August	1st to 10th	Day	18% 6% 13% 31% 29% 2	3961
	11th to 20th	Day	29% 8% 19% 30% 11% 2	3885
	21st to end	Day	32% 7% 12% 22% 23% 3	4311
September	1st to 10th	Day	35% 7% 13% 20% 18% 7%	2400
	11th to 20th	Day	37% 7% 9% 18% 22% 7%	2400
	21st to end	Day	29% 6% 10% 21% 23% 11%	2170
October	1st to 10th	Day	15% 4 5% 16% 24% 37%	3260
	11th to 20th	Day	17% 2 3 16% 37% 24%	3240
	21st to end	Day	26% 3 4 18% 36% 13%	3538
November	1st to 10th	Day	31% 4 9% 18% 29% 9%	2058
	11th to 20th	Day	32% 4 7% 20% 27% 11%	1935
	21st to end	Day	41% 4 7% 18% 23% 7%	1890
December	1st to 10th	Day	43% 3 6% 21% 23% 3	2970
	11th to 20th	Day	48% 3 5% 18% 20% 7%	3085
	21st to end	Day	39% 4 9% 24% 22% 3	4334
January	1st to 10th	Night	39% 3 6% 27% 22% 3	6018
	11th to 20th	Night	37% 3 4 21% 26% 8%	5979
	21st to end	Night	46% 3 6% 17% 21% 7%	6490
February	1st to 10th	Night	45% 4 6% 18% 21% 6%	2493
	11th to 20th	Night	44% 4 6% 18% 19% 8%	2339
	21st to end	Night	44% 4 6% 15% 18% 12%	1980
March	1st to 10th	Night	44% 4 7% 14% 19% 12%	5062
	11th to 20th	Night	34% 5% 8% 16% 18% 18%	4980
	21st to end	Night	41% 4 8% 20% 21% 6%	5292
April	1st to 10th	Night	36% 5% 11% 20% 20% 9%	2000
	11th to 20th	Night	34% 5% 9% 19% 24% 9%	1975
	21st to end	Night	34% 6% 9% 22% 24% 5%	2000
May	1st to 10th	Night	42% 7% 12% 21% 15% 2	4520
	11th to 20th	Night	48% 6% 12% 23% 11% 1	4490
	21st to end	Night	39% 8% 13% 21% 15% 4	4402
June	1st to 10th	Night	27% 10% 17% 26% 18% 2	1600
	11th to 20th	Night	22% 7% 20% 28% 18% 5%	1600
	21st to end	Night	24% 9% 15% 28% 20% 4	1656
July	1st to 10th	Night	31% 10% 21% 24% 13% 1	4035
	11th to 20th	Night	24% 9% 27% 31% 8% 1	4026
	21st to end	Night	33% 8% 18% 31% 9%	4320
August	1st to 10th	Night	14% 6% 13% 33% 32% 2	3163
	11th to 20th	Night	23% 8% 21% 31% 14% 3	3230
	21st to end	Night	32% 7% 11% 20% 25% 5%	3586
September	1st to 10th	Night	30% 8% 13% 22% 18% 9%	2000
	11th to 20th	Night	33% 7% 9% 19% 23% 8%	2000
	21st to end	Night	26% 5% 10% 23% 25% 12%	2205
October	1st to 10th	Night	14% 3 7% 17% 22% 37%	3920
	11th to 20th	Night	18% 2 4 16% 30% 31%	3899
	21st to end	Night	23% 3 6% 15% 35% 18%	4252
November	1st to 10th	Night	31% 4 8% 18% 27% 12%	2460
	11th to 20th	Night	30% 4 7% 20% 26% 13%	2682
	21st to end	Night	37% 4 7% 18% 23% 10%	2730
December	1st to 10th	Night	41% 3 6% 22% 23% 4	4414
	11th to 20th	Night	42% 3 8% 17% 23% 7%	5341
	21st to end	Night	41% 4 9% 22% 21% 3	6868

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	21% 16% 38% 17% 7% 1	330
	11th to 20th	Day	24% 15% 34% 20% 6% 2	318
	21st to end	Day	20% 13% 41% 18% 7%	330
February	1st to 10th	Day	26% 11% 35% 17% 9% 2	300
	11th to 20th	Day	30% 20% 29% 17% 4	300
	21st to end	Day	29% 19% 32% 12% 8%	249
March	1st to 10th	Day	26% 10% 35% 18% 11%	300
	11th to 20th	Day	18% 16% 40% 22% 4	300
	21st to end	Day	14% 19% 33% 23% 10% 2	400
April	1st to 10th	Day	16% 13% 34% 26% 10% 1	500
	11th to 20th	Day	19% 10% 31% 26% 11% 3	492
	21st to end	Day	13% 10% 27% 27% 19% 3	500
May	1st to 10th	Day	13% 13% 24% 31% 16% 2	503
	11th to 20th	Day	12% 5% 27% 25% 21% 10%	527
	21st to end	Day	8% 3 18% 33% 25% 12%	722
June	1st to 10th	Day	8% 5% 12% 28% 32% 15%	730
	11th to 20th	Day	6% 3 10% 31% 35% 15%	730
	21st to end	Day	6% 2 11% 27% 32% 23%	730
July	1st to 10th	Day	5% 2 6% 23% 40% 24%	721
	11th to 20th	Day	6% 2 6% 20% 36% 30%	718
	21st to end	Day	6% 1 5% 21% 39% 28%	794
August	1st to 10th	Day	5% 1 5% 22% 40% 27%	571
	11th to 20th	Day	8% 1 5% 19% 41% 27%	519
	21st to end	Day	14% 1 5% 16% 31% 33%	583
September	1st to 10th	Day	9% 2 8% 25% 36% 21%	530
	11th to 20th	Day	10% 2 8% 21% 35% 25%	530
	21st to end	Day	11% 3 9% 27% 34% 16%	500
October	1st to 10th	Day	8% 1 16% 34% 26% 14%	330
	11th to 20th	Day	8% 5% 24% 29% 26% 7%	330
	21st to end	Day	19% 8% 21% 29% 17% 6%	363
November	1st to 10th	Day	19% 7% 24% 23% 23% 4	330
	11th to 20th	Day	10% 8% 33% 34% 13% 3	330
	21st to end	Day	17% 13% 28% 26% 12% 4	330
December	1st to 10th	Day	19% 13% 34% 22% 10% 2	330
	11th to 20th	Day	20% 11% 34% 22% 12% 2	330
	21st to end	Day	18% 16% 35% 21% 9% 1	363
January	1st to 10th	Night	21% 8% 34% 31% 6%	1050
	11th to 20th	Night	20% 10% 35% 28% 7%	1031
	21st to end	Night	23% 8% 35% 31% 3	1100
February	1st to 10th	Night	23% 10% 33% 29% 5%	893
	11th to 20th	Night	23% 10% 35% 27% 4	783
	21st to end	Night	24% 13% 33% 27% 3	660
March	1st to 10th	Night	18% 10% 32% 33% 7%	670
	11th to 20th	Night	16% 10% 33% 34% 6% 1	600
	21st to end	Night	16% 8% 32% 31% 11%	660
April	1st to 10th	Night	13% 9% 36% 32% 9% 1	600
	11th to 20th	Night	14% 8% 32% 33% 12% 1	593
	21st to end	Night	12% 7% 31% 36% 14% 1	600
May	1st to 10th	Night	12% 5% 23% 45% 15% 1	600
	11th to 20th	Night	12% 4 24% 38% 19% 2	591
	21st to end	Night	8% 2 16% 37% 31% 6%	650
June	1st to 10th	Night	6% 2 9% 39% 39% 6%	600
	11th to 20th	Night	4 1 8% 33% 47% 6%	600
	21st to end	Night	5% 1 8% 32% 44% 11%	600
July	1st to 10th	Night	4 1 6% 28% 52% 9%	585
	11th to 20th	Night	5% 1 6% 26% 50% 13%	582
	21st to end	Night	4 1 4 29% 49% 14%	657
August	1st to 10th	Night	4 1 4 26% 52% 14%	597
	11th to 20th	Night	7% 1 3 27% 52% 10%	594
	21st to end	Night	10% 1 5% 23% 47% 14%	660
September	1st to 10th	Night	9% 2 9% 33% 42% 6%	600
	11th to 20th	Night	10% 1 7% 30% 46% 7%	600
	21st to end	Night	10% 2 11% 35% 37% 5%	780
October	1st to 10th	Night	7% 2 13% 36% 36% 5%	800
	11th to 20th	Night	12% 4 19% 39% 25% 2	800
	21st to end	Night	15% 6% 22% 35% 20% 2	880
November	1st to 10th	Night	13% 4 23% 36% 22% 2	820
	11th to 20th	Night	13% 5% 29% 39% 14% 1	840
	21st to end	Night	16% 7% 29% 33% 13% 2	840
December	1st to 10th	Night	20% 7% 31% 33% 9%	861
	11th to 20th	Night	21% 8% 29% 34% 8%	1050
	21st to end	Night	22% 9% 30% 31% 7%	1155

Page generated at 2026-01-14 00:14:31. Version ac07

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