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 2026-06-01.

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	17% 12% 4 10% 5% 5% 4 3 5% 6% 29%	132156
	Night	17% 13% 5% 10% 5% 4 4 3 4 6% 28%	130984
Transparency	Day	54% 6% 11% 19% 10% 1	135759
	Night	56% 5% 10% 17% 10% 1	135452
Seeing	Day	25% 17% 27% 19% 9% 3	16574
	Night	24% 14% 27% 24% 10% 1	26306

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	17% 21% 8% 26% 5% 3 3 2 3 3 9%	5158
	11th to 20th	Day	11% 23% 10% 21% 8% 8% 3 2 2 3 9%	5280
	21st to end	Day	18% 18% 7% 15% 10% 7% 4 3 3 3 13%	5780
February	1st to 10th	Day	17% 19% 6% 14% 8% 5% 3 3 3 4 19%	1890
	11th to 20th	Day	16% 16% 8% 14% 8% 5% 5% 2 4 5% 18%	1843
	21st to end	Day	18% 18% 4 13% 5% 4 4 4 4 6% 21%	1707
March	1st to 10th	Day	18% 12% 6% 11% 5% 3 4 2 4 5% 29%	5045
	11th to 20th	Day	13% 13% 7% 10% 5% 4 4 3 3 5% 33%	5090
	21st to end	Day	21% 13% 5% 9% 5% 4 4 3 4 5% 28%	5586
April	1st to 10th	Day	18% 14% 3 7% 5% 4 4 3 5% 7% 30%	2412
	11th to 20th	Day	19% 13% 3 7% 4 4 4 4 4 6% 32%	2581
	21st to end	Day	21% 11% 3 7% 4 3 3 3 4 6% 34%	2730
May	1st to 10th	Day	22% 10% 3 7% 5% 4 6% 4 6% 6% 28%	5992
	11th to 20th	Day	20% 10% 3 7% 5% 5% 4 4 6% 7% 29%	5991
	21st to end	Day	21% 7% 2 6% 4 4 5% 4 6% 6% 34%	7032
June	1st to 10th	Day	17% 6% 2 7% 5% 4 5% 4 7% 8% 34%	2800
	11th to 20th	Day	14% 8% 3 8% 5% 5% 4 3 6% 8% 35%	2800
	21st to end	Day	14% 5% 2 6% 5% 5% 6% 4 7% 9% 37%	2800
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 10% 41%	6268
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 36%	5900
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	6424
August	1st to 10th	Day	15% 7% 3 8% 6% 6% 6% 4 6% 9% 30%	4234
	11th to 20th	Day	15% 6% 2 7% 4 5% 6% 5% 7% 9% 33%	4174
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 9% 39%	4510
September	1st to 10th	Day	15% 7% 2 7% 4 4 4 3 5% 7% 42%	2389
	11th to 20th	Day	12% 6% 2 5% 5% 5% 5% 4 6% 8% 44%	2200
	21st to end	Day	22% 8% 2 7% 4 4 5% 4 5% 7% 34%	2200
October	1st to 10th	Day	16% 7% 3 7% 4 4 4 3 5% 7% 39%	2010
	11th to 20th	Day	22% 10% 2 7% 5% 4 3 4 5% 6% 32%	2000
	21st to end	Day	26% 12% 3 7% 4 4 4 4 5% 6% 26%	2200
November	1st to 10th	Day	13% 12% 3 7% 5% 4 5% 4 5% 6% 36%	1919
	11th to 20th	Day	19% 16% 4 9% 5% 4 3 3 4 5% 26%	1733
	21st to end	Day	20% 21% 5% 9% 5% 4 4 4 5% 5% 18%	1680
December	1st to 10th	Day	20% 21% 13% 13% 4 4 3 2 3 3 13%	2680
	11th to 20th	Day	23% 22% 7% 10% 6% 3 3 2 4 5% 15%	3070
	21st to end	Day	26% 25% 6% 13% 5% 4 4 2 3 3 10%	4048
January	1st to 10th	Night	16% 21% 9% 24% 5% 3 3 2 3 3 9%	7717
	11th to 20th	Night	13% 20% 10% 21% 9% 6% 4 2 2 3 10%	7680
	21st to end	Night	18% 18% 7% 13% 7% 6% 5% 2 3 4 17%	8401
February	1st to 10th	Night	19% 17% 6% 13% 6% 5% 3 3 4 5% 20%	2730
	11th to 20th	Night	18% 14% 6% 14% 7% 5% 4 4 4 5% 19%	2663
	21st to end	Night	21% 13% 6% 13% 5% 4 4 3 4 5% 23%	2093
March	1st to 10th	Night	22% 14% 5% 8% 6% 3 3 3 3 5% 28%	5028
	11th to 20th	Night	15% 13% 5% 7% 4 4 3 3 4 6% 36%	5090
	21st to end	Night	20% 13% 5% 8% 4 4 4 3 4 4 32%	5588
April	1st to 10th	Night	20% 15% 4 7% 5% 5% 3 3 5% 6% 28%	2206
	11th to 20th	Night	18% 11% 3 7% 4 5% 5% 3 6% 6% 32%	2005
	21st to end	Night	15% 11% 3 7% 5% 4 5% 4 6% 6% 36%	1890
May	1st to 10th	Night	28% 10% 3 7% 4 4 4 3 4 5% 28%	4123
	11th to 20th	Night	18% 9% 3 7% 4 4 4 3 4 7% 37%	4122
	21st to end	Night	21% 6% 2 4 3 3 4 4 5% 9% 38%	4062
June	1st to 10th	Night	9% 7% 2 7% 5% 5% 5% 5% 6% 8% 41%	1600
	11th to 20th	Night	11% 5% 3 7% 5% 5% 4 4 6% 8% 43%	1600
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 7% 9% 42%	1600
July	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 5% 9% 42%	3684
	11th to 20th	Night	13% 5% 2 6% 4 4 5% 4 6% 9% 41%	4057
	21st to end	Night	10% 5% 2 6% 4 4 5% 3 6% 8% 47%	4427
August	1st to 10th	Night	12% 8% 3 9% 5% 5% 5% 4 6% 6% 39%	2915
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	2875
	21st to end	Night	10% 5% 2 6% 4 5% 6% 5% 6% 8% 44%	3355
September	1st to 10th	Night	13% 5% 2 4 4 4 4 4 5% 7% 48%	2008
	11th to 20th	Night	11% 4 2 5% 3 3 3 3 6% 8% 53%	2200
	21st to end	Night	20% 7% 2 6% 5% 3 4 3 5% 6% 37%	2200
October	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 7% 43%	2390
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 5% 7% 35%	2400
	21st to end	Night	25% 10% 3 6% 5% 3 4 4 5% 5% 31%	2640
November	1st to 10th	Night	14% 11% 3 6% 4 4 4 3 5% 7% 39%	2596
	11th to 20th	Night	18% 18% 5% 7% 5% 4 4 3 5% 6% 26%	2884
	21st to end	Night	22% 18% 4 8% 4 4 4 3 5% 5% 23%	2940
December	1st to 10th	Night	17% 21% 11% 14% 5% 5% 3 3 4 3 15%	4720
	11th to 20th	Night	21% 21% 8% 11% 5% 4 3 2 4 4 17%	5345
	21st to end	Night	25% 21% 7% 12% 4 4 4 3 4 5% 13%	7150

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	82% 3 7% 5% 2	5159
	11th to 20th	Day	83% 3 6% 6% 2	5280
	21st to end	Day	78% 3 7% 9% 3	5780
February	1st to 10th	Day	70% 4 8% 12% 6%	1890
	11th to 20th	Day	70% 4 8% 12% 6%	1852
	21st to end	Day	64% 5% 10% 14% 5% 2	1707
March	1st to 10th	Day	57% 5% 12% 20% 7%	5045
	11th to 20th	Day	53% 5% 15% 20% 6% 1	5090
	21st to end	Day	58% 5% 7% 18% 11% 1	5586
April	1st to 10th	Day	54% 6% 12% 15% 12% 1	2412
	11th to 20th	Day	53% 5% 11% 18% 11% 2	2581
	21st to end	Day	52% 5% 10% 20% 11% 2	2730
May	1st to 10th	Day	55% 7% 8% 19% 8% 4	6027
	11th to 20th	Day	52% 8% 10% 20% 10% 1	5995
	21st to end	Day	48% 8% 12% 19% 12% 3	7047
June	1st to 10th	Day	46% 7% 12% 23% 11% 1	2800
	11th to 20th	Day	46% 7% 13% 20% 13% 1	2800
	21st to end	Day	41% 8% 12% 25% 13% 1	2800
July	1st to 10th	Day	37% 7% 13% 26% 15% 2	6200
	11th to 20th	Day	41% 8% 12% 24% 14% 1	5831
	21st to end	Day	38% 7% 11% 24% 19% 1	6240
August	1st to 10th	Day	47% 9% 14% 21% 9%	4221
	11th to 20th	Day	44% 8% 12% 28% 7% 1	4213
	21st to end	Day	38% 9% 13% 28% 11% 1	4510
September	1st to 10th	Day	41% 7% 11% 23% 15% 2	2389
	11th to 20th	Day	37% 7% 14% 26% 16% 1	2200
	21st to end	Day	50% 6% 12% 21% 10% 1	2200
October	1st to 10th	Day	34% 6% 13% 27% 19% 1	3270
	11th to 20th	Day	44% 7% 13% 19% 12% 4	3240
	21st to end	Day	44% 6% 13% 25% 12% 1	3538
November	1st to 10th	Day	47% 7% 12% 20% 13% 1	1919
	11th to 20th	Day	59% 6% 11% 15% 7% 2	1733
	21st to end	Day	67% 6% 10% 12% 5%	1680
December	1st to 10th	Day	78% 4 9% 7% 2	2680
	11th to 20th	Day	73% 4 8% 12% 2	3066
	21st to end	Day	80% 3 8% 7% 2	4048
January	1st to 10th	Night	81% 4 6% 6% 2	7718
	11th to 20th	Night	82% 3 7% 6% 2	7680
	21st to end	Night	73% 3 8% 11% 4	8401
February	1st to 10th	Night	68% 4 9% 14% 5%	2730
	11th to 20th	Night	68% 5% 9% 13% 5%	2665
	21st to end	Night	65% 5% 8% 14% 7% 1	2093
March	1st to 10th	Night	59% 4 12% 17% 7% 1	5028
	11th to 20th	Night	49% 5% 14% 21% 9% 1	5090
	21st to end	Night	55% 5% 8% 18% 13% 1	5588
April	1st to 10th	Night	57% 5% 9% 16% 11% 1	2206
	11th to 20th	Night	52% 5% 11% 18% 12% 2	2005
	21st to end	Night	47% 6% 12% 21% 11% 3	1890
May	1st to 10th	Night	58% 5% 8% 15% 10% 4	4150
	11th to 20th	Night	47% 6% 10% 23% 12% 1	4123
	21st to end	Night	43% 7% 12% 23% 14% 2	4069
June	1st to 10th	Night	39% 8% 12% 25% 14% 2	1600
	11th to 20th	Night	40% 6% 14% 21% 17% 2	1600
	21st to end	Night	38% 8% 14% 22% 18% 1	1600
July	1st to 10th	Night	39% 6% 10% 24% 18% 1	3645
	11th to 20th	Night	38% 7% 15% 26% 13% 1	4006
	21st to end	Night	34% 7% 11% 19% 28% 1	4297
August	1st to 10th	Night	44% 7% 11% 25% 13% 1	2904
	11th to 20th	Night	42% 7% 11% 31% 9%	2902
	21st to end	Night	35% 8% 14% 28% 13% 2	3355
September	1st to 10th	Night	34% 7% 12% 26% 18% 3	2008
	11th to 20th	Night	30% 6% 15% 27% 20% 2	2200
	21st to end	Night	47% 5% 12% 20% 15% 1	2200
October	1st to 10th	Night	36% 6% 10% 25% 22% 1	3910
	11th to 20th	Night	42% 7% 12% 21% 13% 5%	3899
	21st to end	Night	40% 5% 13% 24% 16% 1	4252
November	1st to 10th	Night	44% 6% 13% 23% 12% 3	2596
	11th to 20th	Night	59% 5% 11% 16% 6% 3	2884
	21st to end	Night	64% 4 12% 16% 3 1	2940
December	1st to 10th	Night	75% 5% 10% 7% 3	4720
	11th to 20th	Night	72% 4 9% 13% 2	5348
	21st to end	Night	74% 5% 9% 10% 1	7150

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	33% 30% 26% 8% 2	311
	11th to 20th	Day	40% 31% 21% 5% 3	330
	21st to end	Day	35% 30% 27% 7% 1	363
February	1st to 10th	Day	31% 29% 30% 8% 1	330
	11th to 20th	Day	38% 28% 27% 7% 1	330
	21st to end	Day	37% 27% 29% 6%	275
March	1st to 10th	Day	31% 24% 29% 13% 2	540
	11th to 20th	Day	32% 22% 31% 11% 3 1	540
	21st to end	Day	35% 24% 24% 14% 2	594
April	1st to 10th	Day	32% 23% 26% 14% 4 1	540
	11th to 20th	Day	33% 21% 22% 16% 7% 2	532
	21st to end	Day	29% 18% 32% 16% 4 1	540
May	1st to 10th	Day	30% 22% 27% 15% 5% 2	543
	11th to 20th	Day	25% 15% 29% 22% 7% 3	567
	21st to end	Day	22% 11% 27% 25% 11% 5%	617
June	1st to 10th	Day	17% 15% 33% 25% 8% 2	530
	11th to 20th	Day	19% 13% 28% 25% 14% 2	530
	21st to end	Day	17% 11% 33% 25% 11% 3	530
July	1st to 10th	Day	12% 7% 24% 29% 21% 7%	525
	11th to 20th	Day	14% 8% 28% 31% 13% 7%	524
	21st to end	Day	13% 6% 29% 30% 17% 6%	576
August	1st to 10th	Day	12% 7% 27% 28% 18% 8%	526
	11th to 20th	Day	17% 8% 24% 26% 15% 10%	519
	21st to end	Day	11% 8% 24% 31% 19% 8%	583
September	1st to 10th	Day	15% 11% 23% 25% 19% 7%	530
	11th to 20th	Day	10% 6% 22% 27% 25% 10%	530
	21st to end	Day	24% 12% 26% 19% 14% 4	530
October	1st to 10th	Day	16% 13% 26% 25% 17% 3	530
	11th to 20th	Day	25% 17% 34% 15% 6% 2	530
	21st to end	Day	36% 17% 29% 14% 4	583
November	1st to 10th	Day	23% 23% 32% 14% 8% 1	397
	11th to 20th	Day	37% 23% 25% 13% 2 1	247
	21st to end	Day	33% 21% 36% 10%	220
December	1st to 10th	Day	35% 30% 26% 5% 2 1	220
	11th to 20th	Day	39% 20% 30% 9% 1	220
	21st to end	Day	38% 23% 30% 9%	242
January	1st to 10th	Night	32% 23% 31% 11% 3	840
	11th to 20th	Night	34% 23% 28% 13% 2	840
	21st to end	Night	28% 23% 33% 14% 2	924
February	1st to 10th	Night	31% 20% 28% 19% 2	840
	11th to 20th	Night	30% 21% 33% 15% 1	823
	21st to end	Night	31% 20% 34% 14% 2	692
March	1st to 10th	Night	28% 17% 35% 17% 3	840
	11th to 20th	Night	30% 20% 26% 20% 4	840
	21st to end	Night	26% 19% 32% 19% 4	924
April	1st to 10th	Night	28% 17% 30% 20% 5%	840
	11th to 20th	Night	25% 15% 32% 20% 7% 1	761
	21st to end	Night	22% 10% 35% 29% 4 1	630
May	1st to 10th	Night	24% 10% 25% 32% 9%	630
	11th to 20th	Night	20% 9% 29% 33% 8% 1	621
	21st to end	Night	14% 5% 31% 31% 17% 2	484
June	1st to 10th	Night	10% 6% 30% 41% 14% 1	400
	11th to 20th	Night	13% 7% 26% 42% 13%	400
	21st to end	Night	10% 7% 29% 34% 20%	400
July	1st to 10th	Night	9% 4 17% 43% 22% 5%	423
	11th to 20th	Night	11% 3 20% 36% 26% 4	582
	21st to end	Night	11% 4 15% 45% 25% 2	657
August	1st to 10th	Night	10% 3 17% 43% 24% 3	597
	11th to 20th	Night	14% 3 14% 39% 27% 4	594
	21st to end	Night	13% 5% 19% 33% 26% 4	740
September	1st to 10th	Night	15% 6% 20% 32% 24% 3	800
	11th to 20th	Night	13% 4 17% 36% 28% 3	800
	21st to end	Night	23% 9% 21% 27% 18% 3	800
October	1st to 10th	Night	18% 7% 27% 28% 19% 2	800
	11th to 20th	Night	24% 12% 30% 25% 8% 1	800
	21st to end	Night	31% 12% 29% 24% 4	880
November	1st to 10th	Night	22% 12% 31% 25% 8% 1	820
	11th to 20th	Night	30% 18% 28% 18% 5% 1	840
	21st to end	Night	34% 16% 31% 16% 3	840
December	1st to 10th	Night	34% 20% 28% 14% 4	840
	11th to 20th	Night	31% 24% 27% 14% 3	840
	21st to end	Night	33% 20% 31% 15% 2	924

Page generated at 2026-05-29 01:53:25. Version ac07

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