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 2026-10-14.

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	6% 6% 1 3 2 2 3 2 4 5% 64%	158181
	Night	8% 8% 2 4 2 2 3 2 4 5% 60%	151058
Transparency	Day	24% 4 7% 19% 26% 21%	153102
	Night	28% 4 8% 20% 24% 16%	147126
Seeing	Day	14% 14% 26% 24% 15% 5%	17543
	Night	13% 6% 17% 38% 23% 2	26729

By Month

Percentage Cloud Cover SW (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% 18% 3 5% 3 3 4 3 5% 6% 38%	4722
	11th to 20th	Day	10% 8% 1 4 3 2 3 2 3 4 59%	4961
	21st to end	Day	10% 10% 3 6% 3 3 4 3 5% 7% 46%	5843
February	1st to 10th	Day	14% 10% 2 4 3 3 4 3 5% 7% 45%	1890
	11th to 20th	Day	8% 15% 3 6% 3 3 3 3 5% 7% 44%	1960
	21st to end	Day	8% 17% 2 5% 3 3 3 2 5% 7% 44%	1730
March	1st to 10th	Day	10% 22% 5% 7% 3 3 3 3 4 5% 36%	4702
	11th to 20th	Day	9% 16% 2 5% 3 3 3 2 4 6% 47%	5110
	21st to end	Day	11% 20% 3 8% 4 3 3 3 4 6% 36%	5864
April	1st to 10th	Day	10% 13% 2 5% 4 3 4 3 6% 7% 43%	2520
	11th to 20th	Day	9% 10% 2 4 4 3 4 3 5% 6% 52%	2489
	21st to end	Day	9% 6% 2 4 3 4 3 4 5% 6% 54%	2520
May	1st to 10th	Day	5% 5% 2 3 2 2 3 2 4 6% 67%	7524
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 5% 74%	8160
	21st to end	Day	6% 4 1 3 2 2 2 2 3 5% 68%	8992
June	1st to 10th	Day	6% 4 2 4 3 3 4 4 5% 7% 59%	2940
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 5% 74%	2940
	21st to end	Day	2 1 1 2 1 1 2 2 3 4 81%	2940
July	1st to 10th	Day	1 1 1 1 1 2 3 89%	8219
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 3 79%	8220
	21st to end	Day	1 1 2 2 2 2 2 3 4 81%	8608
August	1st to 10th	Day	1 1 2 1 1 1 1 2 4 84%	7547
	11th to 20th	Day	1 1 2 2 2 3 5% 85%	7172
	21st to end	Day	3 2 1 3 2 2 2 2 4 4 75%	7750
September	1st to 10th	Day	3 1 1 2 1 1 2 2 2 4 81%	2520
	11th to 20th	Day	3 3 1 2 2 3 2 3 4 5% 74%	2520
	21st to end	Day	4 2 1 2 2 1 2 2 3 6% 74%	2270
October	1st to 10th	Day	4 2 1 3 2 2 2 2 3 5% 74%	3380
	11th to 20th	Day	7% 3 1 3 2 2 2 2 4 6% 67%	3292
	21st to end	Day	7% 5% 2 4 2 3 3 4 5% 6% 60%	3536
November	1st to 10th	Day	11% 7% 1 4 3 3 3 4 6% 7% 53%	1854
	11th to 20th	Day	11% 7% 2 5% 4 3 4 4 6% 8% 46%	1890
	21st to end	Day	8% 8% 2 4 3 4 3 4 4 6% 54%	1696
December	1st to 10th	Day	7% 6% 1 3 2 3 3 3 6% 8% 57%	2700
	11th to 20th	Day	19% 14% 2 6% 4 4 5% 4 6% 7% 29%	3108
	21st to end	Day	17% 12% 3 6% 4 4 5% 4 6% 8% 32%	4092
January	1st to 10th	Night	13% 18% 2 5% 3 3 4 3 5% 7% 37%	8172
	11th to 20th	Night	10% 8% 1 3 2 2 3 2 3 6% 60%	8009
	21st to end	Night	10% 11% 2 5% 4 4 5% 3 4 6% 46%	8371
February	1st to 10th	Night	14% 10% 2 4 3 2 3 2 5% 7% 48%	2730
	11th to 20th	Night	10% 13% 2 4 3 3 3 3 5% 7% 45%	2547
	21st to end	Night	9% 15% 3 5% 3 3 3 2 4 5% 47%	2076
March	1st to 10th	Night	9% 24% 4 6% 4 3 3 3 4 6% 36%	5409
	11th to 20th	Night	11% 20% 2 3 2 2 2 2 3 5% 48%	5110
	21st to end	Night	10% 21% 3 7% 4 4 4 3 5% 6% 34%	5352
April	1st to 10th	Night	8% 11% 2 4 4 4 4 3 6% 8% 46%	2100
	11th to 20th	Night	10% 10% 2 4 3 3 3 3 4 7% 51%	2079
	21st to end	Night	8% 8% 1 3 3 2 3 3 5% 7% 57%	2100
May	1st to 10th	Night	6% 7% 1 4 2 3 3 2 4 5% 63%	5425
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 4 74%	4700
	21st to end	Night	5% 4 1 3 2 2 3 2 3 5% 70%	5181
June	1st to 10th	Night	6% 5% 1 4 2 3 3 3 5% 7% 61%	1680
	11th to 20th	Night	3 3 1 2 1 2 2 2 3 5% 74%	1680
	21st to end	Night	3 2 1 2 2 2 1 3 3 3 79%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 3 89%	4740
	11th to 20th	Night	3 3 1 3 1 1 1 1 2 2 81%	4740
	21st to end	Night	1 2 1 2 2 1 2 2 4 5% 79%	5468
August	1st to 10th	Night	1 2 1 1 1 1 1 1 3 3 84%	5275
	11th to 20th	Night	1 1 1 1 1 2 1 3 4 85%	5703
	21st to end	Night	2 2 1 3 2 3 3 3 4 5% 73%	6499
September	1st to 10th	Night	3 1 1 2 1 2 2 2 2 3 81%	2100
	11th to 20th	Night	3 3 1 2 2 2 2 2 3 5% 76%	2100
	21st to end	Night	4 2 1 2 1 2 2 2 3 5% 76%	2347
October	1st to 10th	Night	3 2 1 3 2 2 2 2 2 3 77%	4040
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 4 74%	3933
	21st to end	Night	8% 4 1 2 2 3 3 3 4 6% 64%	4274
November	1st to 10th	Night	11% 8% 2 3 3 2 3 3 6% 6% 52%	2665
	11th to 20th	Night	11% 6% 1 4 3 4 3 4 6% 9% 49%	2730
	21st to end	Night	9% 8% 1 4 3 2 3 3 5% 7% 55%	2921
December	1st to 10th	Night	8% 6% 1 3 2 2 2 2 4 7% 64%	4700
	11th to 20th	Night	17% 16% 2 5% 3 4 5% 4 6% 8% 30%	5316
	21st to end	Night	22% 13% 3 5% 3 3 4 3 5% 6% 33%	7106

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% 6% 11% 26% 10%	4723
	11th to 20th	Day	30% 4 6% 19% 25% 16%	4961
	21st to end	Day	38% 4 10% 16% 23% 9%	5843
February	1st to 10th	Day	39% 4 11% 23% 17% 5%	1890
	11th to 20th	Day	41% 5% 9% 24% 17% 3	1969
	21st to end	Day	41% 4 11% 25% 15% 5%	1730
March	1st to 10th	Day	51% 5% 7% 17% 16% 4	4702
	11th to 20th	Day	38% 5% 10% 28% 16% 2	5110
	21st to end	Day	48% 6% 12% 22% 10% 1	5864
April	1st to 10th	Day	40% 5% 14% 23% 17% 2	2520
	11th to 20th	Day	33% 5% 12% 24% 20% 6%	2492
	21st to end	Day	30% 5% 14% 26% 21% 3	2520
May	1st to 10th	Day	20% 4 7% 22% 39% 8%	7524
	11th to 20th	Day	14% 3 8% 19% 43% 13%	8163
	21st to end	Day	19% 3 6% 27% 38% 6%	8994
June	1st to 10th	Day	23% 5% 10% 23% 30% 9%	2940
	11th to 20th	Day	14% 3 7% 20% 36% 21%	2940
	21st to end	Day	9% 2 4 15% 37% 34%	2940
July	1st to 10th	Day	4 1 2 9% 22% 62%	8151
	11th to 20th	Day	12% 2 2 5% 15% 64%	8145
	21st to end	Day	8% 3 4 11% 25% 49%	8416
August	1st to 10th	Day	9% 1 2 6% 23% 58%	5976
	11th to 20th	Day	6% 1 2 15% 39% 35%	5654
	21st to end	Day	12% 2 3 16% 40% 27%	6077
September	1st to 10th	Day	9% 2 3 11% 30% 46%	2520
	11th to 20th	Day	14% 2 6% 19% 33% 24%	2520
	21st to end	Day	14% 2 5% 20% 33% 24%	2270
October	1st to 10th	Day	15% 2 4 14% 31% 33%	3380
	11th to 20th	Day	20% 3 6% 21% 39% 11%	3292
	21st to end	Day	24% 5% 8% 29% 24% 10%	3536
November	1st to 10th	Day	30% 6% 12% 22% 22% 8%	1854
	11th to 20th	Day	35% 5% 13% 24% 19% 3	1890
	21st to end	Day	31% 4 11% 24% 23% 7%	1696
December	1st to 10th	Day	26% 4 8% 28% 28% 6%	2700
	11th to 20th	Day	52% 7% 10% 18% 12% 1	3108
	21st to end	Day	47% 8% 16% 22% 7% 1	4092
January	1st to 10th	Night	46% 7% 13% 23% 11% 1	8172
	11th to 20th	Night	27% 5% 8% 16% 29% 15%	8009
	21st to end	Night	41% 4 8% 13% 26% 8%	8371
February	1st to 10th	Night	38% 5% 8% 25% 18% 6%	2730
	11th to 20th	Night	39% 5% 11% 25% 18% 2	2549
	21st to end	Night	39% 5% 12% 22% 16% 6%	2076
March	1st to 10th	Night	49% 6% 8% 21% 12% 5%	5409
	11th to 20th	Night	40% 5% 10% 22% 21% 2	5110
	21st to end	Night	49% 8% 14% 21% 8% 1	5352
April	1st to 10th	Night	37% 6% 15% 23% 16% 4	2100
	11th to 20th	Night	34% 6% 14% 23% 18% 6%	2079
	21st to end	Night	27% 6% 15% 33% 17% 3	2100
May	1st to 10th	Night	24% 5% 9% 22% 34% 6%	5423
	11th to 20th	Night	16% 3 7% 24% 39% 11%	4700
	21st to end	Night	18% 4 9% 34% 31% 4	5182
June	1st to 10th	Night	22% 7% 13% 25% 26% 6%	1680
	11th to 20th	Night	14% 2 10% 21% 36% 16%	1680
	21st to end	Night	12% 3 5% 17% 34% 29%	1680
July	1st to 10th	Night	4 1 2 10% 25% 57%	4700
	11th to 20th	Night	13% 2 2 6% 17% 60%	4692
	21st to end	Night	9% 3 4 14% 24% 46%	5349
August	1st to 10th	Night	9% 1 2 7% 25% 55%	4169
	11th to 20th	Night	7% 2 2 17% 41% 31%	4490
	21st to end	Night	13% 2 3 19% 39% 24%	5092
September	1st to 10th	Night	11% 2 2 10% 32% 42%	2100
	11th to 20th	Night	14% 3 7% 18% 36% 23%	2100
	21st to end	Night	13% 2 6% 21% 34% 24%	2347
October	1st to 10th	Night	16% 2 5% 12% 31% 34%	4040
	11th to 20th	Night	16% 3 6% 27% 37% 11%	3933
	21st to end	Night	22% 4 8% 29% 26% 11%	4274
November	1st to 10th	Night	33% 5% 11% 22% 20% 9%	2665
	11th to 20th	Night	32% 6% 13% 25% 20% 4	2730
	21st to end	Night	30% 4 11% 26% 22% 8%	2921
December	1st to 10th	Night	23% 5% 9% 28% 25% 10%	4700
	11th to 20th	Night	52% 6% 8% 20% 12% 2	5316
	21st to end	Night	51% 6% 14% 18% 10% 1	7106

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	36% 10% 21% 21% 11% 1	220
	11th to 20th	Day	24% 11% 20% 26% 17% 3	298
	21st to end	Day	21% 15% 22% 25% 15% 3	473
February	1st to 10th	Day	29% 12% 22% 24% 12% 1	430
	11th to 20th	Day	26% 18% 27% 21% 7% 1	486
	21st to end	Day	20% 19% 28% 26% 7%	446
March	1st to 10th	Day	31% 24% 23% 14% 7% 1	540
	11th to 20th	Day	29% 15% 24% 19% 11% 1	540
	21st to end	Day	25% 22% 28% 15% 8% 1	594
April	1st to 10th	Day	24% 19% 27% 19% 9% 2	540
	11th to 20th	Day	23% 21% 24% 20% 9% 3	532
	21st to end	Day	18% 18% 28% 19% 13% 4	540
May	1st to 10th	Day	15% 23% 27% 21% 10% 3	543
	11th to 20th	Day	18% 16% 30% 20% 10% 6%	568
	21st to end	Day	13% 15% 26% 25% 14% 7%	617
June	1st to 10th	Day	10% 15% 28% 23% 15% 8%	570
	11th to 20th	Day	9% 18% 32% 22% 14% 5%	570
	21st to end	Day	4 14% 28% 28% 16% 9%	570
July	1st to 10th	Day	3 8% 37% 27% 15% 10%	566
	11th to 20th	Day	2 9% 33% 29% 17% 10%	564
	21st to end	Day	2 9% 33% 25% 19% 12%	619
August	1st to 10th	Day	4 9% 31% 26% 19% 12%	567
	11th to 20th	Day	3 10% 29% 28% 19% 11%	557
	21st to end	Day	4 11% 29% 30% 19% 7%	627
September	1st to 10th	Day	6% 12% 28% 31% 19% 5%	570
	11th to 20th	Day	7% 15% 24% 28% 22% 5%	570
	21st to end	Day	7% 14% 25% 32% 16% 5%	570
October	1st to 10th	Day	6% 15% 26% 24% 22% 6%	570
	11th to 20th	Day	12% 13% 22% 26% 23% 5%	543
	21st to end	Day	16% 12% 22% 27% 19% 4	573
November	1st to 10th	Day	18% 10% 16% 28% 23% 5%	330
	11th to 20th	Day	15% 7% 25% 28% 19% 6%	330
	21st to end	Day	16% 12% 18% 27% 21% 5%	228
December	1st to 10th	Day	20% 9% 19% 26% 18% 9%	220
	11th to 20th	Day	21% 13% 20% 22% 18% 6%	220
	21st to end	Day	29% 11% 19% 24% 16% 2	242
January	1st to 10th	Night	20% 9% 23% 35% 11% 1	840
	11th to 20th	Night	15% 7% 24% 41% 11% 1	840
	21st to end	Night	19% 6% 25% 34% 15% 1	924
February	1st to 10th	Night	22% 6% 22% 39% 11% 1	840
	11th to 20th	Night	19% 8% 23% 36% 13% 1	824
	21st to end	Night	20% 9% 21% 41% 8% 1	692
March	1st to 10th	Night	23% 12% 22% 31% 10% 2	840
	11th to 20th	Night	22% 8% 19% 31% 20% 1	840
	21st to end	Night	22% 12% 20% 31% 13% 1	924
April	1st to 10th	Night	16% 9% 22% 38% 15% 1	840
	11th to 20th	Night	17% 10% 23% 32% 16% 2	831
	21st to end	Night	13% 9% 18% 36% 21% 3	840
May	1st to 10th	Night	12% 12% 22% 33% 20% 1	667
	11th to 20th	Night	11% 5% 15% 42% 24% 3	414
	21st to end	Night	13% 4 15% 32% 34% 4	455
June	1st to 10th	Night	8% 4 14% 36% 35% 2	420
	11th to 20th	Night	4 4 16% 44% 31% 1	420
	21st to end	Night	5% 2 10% 43% 38% 2	420
July	1st to 10th	Night	1 1 5% 46% 44% 3	410
	11th to 20th	Night	1 2 6% 48% 42% 1	408
	21st to end	Night	1 1 2 38% 54% 4	570
August	1st to 10th	Night	2 1 3 40% 50% 4	627
	11th to 20th	Night	2 2 9% 43% 39% 5%	763
	21st to end	Night	1 1 10% 46% 38% 3	924
September	1st to 10th	Night	3 3 11% 46% 33% 4	840
	11th to 20th	Night	4 4 10% 39% 36% 6%	840
	21st to end	Night	4 4 13% 43% 28% 7%	840
October	1st to 10th	Night	7% 7% 16% 39% 28% 4	840
	11th to 20th	Night	8% 5% 14% 39% 30% 3	812
	21st to end	Night	12% 5% 16% 37% 26% 5%	880
November	1st to 10th	Night	15% 7% 17% 35% 23% 3	820
	11th to 20th	Night	15% 6% 20% 43% 15% 1	840
	21st to end	Night	14% 6% 21% 39% 18% 1	840
December	1st to 10th	Night	20% 6% 19% 39% 15% 1	840
	11th to 20th	Night	25% 6% 18% 35% 14% 1	840
	21st to end	Night	27% 9% 25% 32% 8%	924

Page generated at 2026-10-11 02:06:33. Version ac07

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