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 2024-03-23.

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% 3 5% 5% 3 5% 5% 5% 8% 43%	78807
	Night	13% 6% 3 5% 5% 3 4 4 5% 7% 44%	81055
Transparency	Day	40% 5% 11% 22% 18% 4	78528
	Night	39% 5% 11% 21% 19% 5%	80853
Seeing	Day	16% 7% 22% 25% 20% 10%	14478
	Night	16% 6% 23% 35% 18% 2	24471

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	15% 6% 2 5% 5% 2 3 3 3 5% 52%	2836
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 3 4 5% 52%	2840
	21st to end	Day	15% 10% 3 6% 5% 3 4 4 4 6% 42%	3124
February	1st to 10th	Day	15% 7% 2 6% 5% 3 4 3 5% 7% 44%	1710
	11th to 20th	Day	19% 6% 2 5% 5% 2 3 3 4 5% 46%	1776
	21st to end	Day	16% 6% 3 5% 5% 4 5% 4 5% 6% 40%	1597
March	1st to 10th	Day	14% 6% 2 4 3 3 3 3 4 6% 51%	2090
	11th to 20th	Day	15% 5% 3 5% 5% 3 4 4 5% 7% 44%	2090
	21st to end	Day	16% 7% 3 5% 5% 2 4 5% 5% 6% 42%	2206
April	1st to 10th	Day	12% 4 2 4 3 2 4 4 5% 7% 53%	2160
	11th to 20th	Day	9% 4 2 4 5% 2 4 4 5% 8% 50%	2134
	21st to end	Day	10% 4 3 5% 5% 3 5% 4 6% 7% 48%	2160
May	1st to 10th	Day	9% 5% 2 6% 6% 4 6% 5% 7% 8% 43%	2175
	11th to 20th	Day	13% 7% 3 6% 6% 3 5% 5% 6% 8% 38%	2301
	21st to end	Day	10% 6% 3 6% 6% 3 6% 5% 6% 10% 39%	2602
June	1st to 10th	Day	9% 5% 3 6% 6% 4 6% 7% 7% 10% 37%	2520
	11th to 20th	Day	10% 4 2 5% 6% 3 6% 7% 7% 10% 41%	2520
	21st to end	Day	8% 4 2 5% 6% 3 8% 7% 8% 12% 36%	2495
July	1st to 10th	Day	8% 4 3 6% 7% 4 6% 7% 8% 13% 34%	2340
	11th to 20th	Day	9% 5% 3 6% 7% 4 6% 7% 8% 11% 35%	2340
	21st to end	Day	7% 5% 4 6% 7% 4 6% 7% 8% 11% 35%	2547
August	1st to 10th	Day	12% 6% 3 7% 7% 4 5% 8% 8% 11% 30%	2327
	11th to 20th	Day	11% 6% 2 8% 7% 5% 6% 7% 7% 9% 33%	2137
	21st to end	Day	10% 7% 3 7% 7% 4 6% 6% 8% 10% 32%	2376
September	1st to 10th	Day	11% 5% 3 6% 5% 4 6% 6% 7% 8% 39%	2160
	11th to 20th	Day	12% 7% 3 6% 6% 3 5% 4 6% 7% 41%	2160
	21st to end	Day	18% 7% 4 6% 6% 4 4 4 5% 7% 35%	1887
October	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 4 7% 47%	1800
	11th to 20th	Day	14% 6% 2 4 4 2 4 4 4 5% 52%	1800
	21st to end	Day	12% 5% 2 5% 5% 2 4 3 3 5% 53%	1980
November	1st to 10th	Day	14% 5% 2 5% 5% 3 4 3 4 6% 50%	1857
	11th to 20th	Day	15% 5% 2 5% 4 2 4 3 4 6% 51%	1777
	21st to end	Day	13% 5% 2 3 4 2 3 3 5% 7% 52%	1639
December	1st to 10th	Day	16% 6% 2 5% 6% 4 4 4 6% 6% 40%	1520
	11th to 20th	Day	16% 6% 3 4 4 2 3 2 3 5% 53%	1910
	21st to end	Day	14% 7% 3 6% 5% 3 4 4 5% 7% 44%	2914
January	1st to 10th	Night	14% 7% 2 5% 4 3 3 4 5% 7% 46%	4109
	11th to 20th	Night	16% 7% 3 6% 5% 3 4 5% 5% 5% 42%	4120
	21st to end	Night	15% 7% 2 6% 5% 3 4 4 5% 6% 44%	4532
February	1st to 10th	Night	18% 6% 3 4 4 3 3 4 5% 6% 44%	2470
	11th to 20th	Night	19% 7% 3 6% 4 2 3 5% 4 6% 42%	2288
	21st to end	Night	17% 5% 2 4 4 3 4 4 5% 5% 47%	1855
March	1st to 10th	Night	15% 5% 3 4 4 2 3 4 4 6% 51%	2090
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 6% 8% 42%	2090
	21st to end	Night	15% 5% 2 5% 5% 3 4 5% 5% 7% 45%	2193
April	1st to 10th	Night	13% 5% 2 4 4 2 4 4 6% 7% 48%	1800
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 5% 8% 48%	1775
	21st to end	Night	11% 4 2 5% 3 3 4 5% 6% 8% 50%	1800
May	1st to 10th	Night	10% 7% 2 6% 6% 4 5% 4 5% 8% 45%	1800
	11th to 20th	Night	12% 6% 3 5% 5% 4 6% 6% 6% 8% 40%	1592
	21st to end	Night	9% 5% 2 5% 5% 3 5% 4 7% 9% 45%	1668
June	1st to 10th	Night	9% 4 3 5% 5% 4 5% 6% 9% 10% 41%	1440
	11th to 20th	Night	10% 5% 3 6% 5% 4 6% 7% 6% 11% 37%	1440
	21st to end	Night	7% 5% 3 6% 7% 4 5% 7% 8% 11% 37%	1458
July	1st to 10th	Night	8% 5% 3 6% 6% 4 6% 6% 7% 12% 37%	1620
	11th to 20th	Night	8% 3 2 5% 5% 4 5% 7% 9% 12% 39%	1620
	21st to end	Night	6% 5% 2 7% 5% 4 7% 7% 8% 11% 38%	1771
August	1st to 10th	Night	10% 6% 3 7% 6% 4 5% 6% 7% 11% 35%	1611
	11th to 20th	Night	10% 6% 3 6% 6% 3 6% 7% 8% 11% 33%	1744
	21st to end	Night	11% 6% 3 7% 6% 4 7% 5% 7% 9% 36%	1980
September	1st to 10th	Night	9% 4 2 6% 7% 4 5% 5% 6% 9% 43%	1800
	11th to 20th	Night	13% 6% 3 6% 5% 3 4 5% 4 8% 43%	1800
	21st to end	Night	18% 6% 4 7% 6% 3 5% 5% 4 6% 34%	2068
October	1st to 10th	Night	13% 5% 2 4 4 3 4 4 5% 6% 50%	2160
	11th to 20th	Night	13% 6% 2 4 4 2 3 3 4 6% 52%	2160
	21st to end	Night	11% 5% 2 4 5% 3 3 3 4 6% 55%	2376
November	1st to 10th	Night	14% 6% 2 4 4 2 4 3 4 6% 52%	2221
	11th to 20th	Night	15% 6% 2 5% 4 2 3 4 5% 5% 49%	2399
	21st to end	Night	13% 5% 2 4 4 2 3 4 4 7% 52%	2536
December	1st to 10th	Night	16% 7% 3 6% 5% 3 4 3 6% 6% 41%	2660
	11th to 20th	Night	17% 5% 3 5% 3 2 3 4 4 6% 48%	3285
	21st to end	Night	15% 6% 2 4 4 3 3 4 5% 6% 47%	4724

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	38% 2 6% 25% 24% 5%	2837
	11th to 20th	Day	37% 3 5% 17% 31% 7%	2840
	21st to end	Day	46% 3 7% 16% 19% 9%	3124
February	1st to 10th	Day	42% 3 9% 22% 20% 4	1710
	11th to 20th	Day	44% 3 6% 19% 23% 6%	1785
	21st to end	Day	45% 4 9% 19% 18% 6%	1597
March	1st to 10th	Day	37% 3 9% 22% 22% 7%	2090
	11th to 20th	Day	41% 3 9% 21% 19% 7%	2090
	21st to end	Day	44% 4 10% 19% 18% 5%	2206
April	1st to 10th	Day	31% 4 9% 24% 25% 7%	2160
	11th to 20th	Day	33% 4 11% 23% 22% 7%	2134
	21st to end	Day	35% 4 13% 24% 20% 4	2160
May	1st to 10th	Day	38% 5% 14% 22% 17% 3	2175
	11th to 20th	Day	44% 5% 14% 22% 13% 1	2305
	21st to end	Day	40% 6% 15% 25% 13% 1	2602
June	1st to 10th	Day	41% 7% 14% 21% 16% 2	2520
	11th to 20th	Day	37% 8% 17% 23% 14% 2	2520
	21st to end	Day	37% 9% 18% 21% 13% 2	2495
July	1st to 10th	Day	39% 9% 17% 21% 11% 2	2275
	11th to 20th	Day	40% 8% 18% 23% 8% 2	2271
	21st to end	Day	38% 8% 19% 25% 9% 1	2405
August	1st to 10th	Day	45% 7% 21% 19% 8%	2314
	11th to 20th	Day	45% 8% 16% 20% 10% 1	2137
	21st to end	Day	45% 7% 16% 20% 9% 3	2376
September	1st to 10th	Day	40% 9% 15% 18% 16% 3	2160
	11th to 20th	Day	40% 6% 11% 20% 20% 3	2160
	21st to end	Day	48% 4 9% 21% 15% 3	1887
October	1st to 10th	Day	38% 4 9% 24% 22% 3	1800
	11th to 20th	Day	36% 3 6% 26% 24% 5%	1800
	21st to end	Day	36% 3 6% 20% 29% 7%	1980
November	1st to 10th	Day	36% 3 7% 21% 27% 6%	1857
	11th to 20th	Day	36% 3 8% 21% 24% 8%	1777
	21st to end	Day	34% 3 7% 26% 24% 6%	1639
December	1st to 10th	Day	45% 3 11% 22% 15% 4	1520
	11th to 20th	Day	37% 3 6% 27% 20% 9%	1906
	21st to end	Day	41% 3 8% 23% 23% 2	2914
January	1st to 10th	Night	39% 3 6% 23% 24% 5%	4109
	11th to 20th	Night	44% 4 6% 18% 22% 6%	4120
	21st to end	Night	43% 3 7% 18% 21% 7%	4532
February	1st to 10th	Night	42% 3 7% 22% 20% 6%	2470
	11th to 20th	Night	45% 4 8% 16% 20% 7%	2290
	21st to end	Night	39% 3 9% 21% 20% 8%	1855
March	1st to 10th	Night	37% 3 9% 22% 21% 7%	2090
	11th to 20th	Night	40% 5% 10% 19% 19% 7%	2090
	21st to end	Night	40% 4 10% 22% 18% 5%	2193
April	1st to 10th	Night	36% 5% 10% 18% 24% 7%	1800
	11th to 20th	Night	35% 4 10% 23% 21% 6%	1775
	21st to end	Night	33% 4 13% 28% 18% 5%	1800
May	1st to 10th	Night	38% 4 16% 23% 17% 3	1800
	11th to 20th	Night	42% 6% 13% 22% 15% 1	1593
	21st to end	Night	35% 7% 18% 24% 13% 2	1669
June	1st to 10th	Night	35% 8% 18% 23% 14% 2	1440
	11th to 20th	Night	39% 9% 17% 21% 12% 2	1440
	21st to end	Night	39% 10% 18% 20% 13% 1	1458
July	1st to 10th	Night	38% 10% 18% 21% 10% 2	1575
	11th to 20th	Night	33% 11% 24% 23% 8% 1	1566
	21st to end	Night	36% 8% 22% 24% 8% 1	1672
August	1st to 10th	Night	42% 7% 23% 21% 6%	1600
	11th to 20th	Night	42% 9% 21% 18% 9% 1	1744
	21st to end	Night	43% 8% 17% 20% 8% 3	1980
September	1st to 10th	Night	38% 7% 18% 17% 16% 4	1800
	11th to 20th	Night	40% 6% 12% 22% 17% 3	1800
	21st to end	Night	50% 5% 10% 18% 15% 3	2068
October	1st to 10th	Night	36% 5% 8% 24% 24% 4	2160
	11th to 20th	Night	35% 4 8% 23% 24% 7%	2160
	21st to end	Night	32% 3 8% 23% 27% 8%	2376
November	1st to 10th	Night	36% 3 6% 21% 28% 6%	2221
	11th to 20th	Night	38% 3 8% 16% 25% 9%	2399
	21st to end	Night	34% 3 8% 24% 25% 7%	2536
December	1st to 10th	Night	44% 4 12% 18% 18% 4	2660
	11th to 20th	Night	39% 3 7% 20% 24% 7%	3288
	21st to end	Night	39% 3 7% 24% 24% 3	4724

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% 17% 39% 16% 7%	270
	11th to 20th	Day	19% 21% 34% 20% 7%	270
	21st to end	Day	21% 16% 38% 19% 5% 1	297
February	1st to 10th	Day	17% 12% 44% 21% 5%	270
	11th to 20th	Day	28% 12% 38% 17% 4	384
	21st to end	Day	22% 12% 36% 22% 6% 1	382
March	1st to 10th	Day	20% 13% 35% 26% 6% 1	460
	11th to 20th	Day	19% 17% 35% 21% 7% 1	460
	21st to end	Day	19% 11% 32% 26% 9% 3	470
April	1st to 10th	Day	18% 16% 28% 24% 11% 3	420
	11th to 20th	Day	11% 12% 30% 28% 13% 6%	412
	21st to end	Day	14% 9% 28% 25% 20% 4	420
May	1st to 10th	Day	13% 11% 33% 22% 15% 6%	423
	11th to 20th	Day	17% 4 18% 29% 23% 10%	447
	21st to end	Day	16% 2 14% 27% 23% 18%	485
June	1st to 10th	Day	12% 2 15% 31% 28% 12%	450
	11th to 20th	Day	14% 4 14% 21% 27% 20%	450
	21st to end	Day	11% 1 14% 26% 32% 16%	450
July	1st to 10th	Day	10% 2 5% 24% 36% 22%	445
	11th to 20th	Day	11% 2 4 25% 37% 22%	444
	21st to end	Day	10% 1 8% 28% 38% 15%	488
August	1st to 10th	Day	14% 4 9% 24% 29% 21%	446
	11th to 20th	Day	14% 2 6% 21% 34% 23%	439
	21st to end	Day	11% 3 7% 25% 27% 27%	495
September	1st to 10th	Day	13% 2 8% 26% 26% 24%	450
	11th to 20th	Day	15% 3 9% 28% 29% 16%	450
	21st to end	Day	22% 2 17% 25% 23% 10%	450
October	1st to 10th	Day	18% 2 17% 24% 25% 14%	450
	11th to 20th	Day	15% 6% 22% 28% 22% 7%	450
	21st to end	Day	15% 6% 25% 28% 20% 6%	495
November	1st to 10th	Day	22% 5% 23% 29% 16% 4	455
	11th to 20th	Day	18% 8% 30% 31% 12% 2	402
	21st to end	Day	17% 8% 25% 27% 20% 2	299
December	1st to 10th	Day	21% 10% 39% 21% 8% 1	180
	11th to 20th	Day	18% 8% 38% 23% 11% 3	180
	21st to end	Day	20% 10% 34% 21% 12% 3	240
January	1st to 10th	Night	19% 11% 35% 28% 6% 1	760
	11th to 20th	Night	18% 11% 30% 35% 7%	760
	21st to end	Night	19% 8% 38% 31% 4	836
February	1st to 10th	Night	21% 8% 35% 31% 5%	760
	11th to 20th	Night	23% 13% 38% 24% 2	743
	21st to end	Night	20% 12% 34% 30% 4	628
March	1st to 10th	Night	18% 9% 35% 32% 6%	760
	11th to 20th	Night	20% 9% 37% 26% 7% 1	760
	21st to end	Night	18% 9% 35% 31% 7%	801
April	1st to 10th	Night	16% 10% 33% 35% 6%	720
	11th to 20th	Night	14% 8% 32% 33% 12% 1	711
	21st to end	Night	14% 5% 32% 40% 9% 1	720
May	1st to 10th	Night	13% 8% 31% 37% 11% 1	720
	11th to 20th	Night	15% 4 21% 42% 17% 1	531
	21st to end	Night	11% 1 13% 42% 32% 1	508
June	1st to 10th	Night	10% 2 18% 48% 21% 2	360
	11th to 20th	Night	11% 3 12% 46% 25% 4	360
	21st to end	Night	8% 3 12% 47% 28% 2	378
July	1st to 10th	Night	8% 2 6% 39% 39% 6%	525
	11th to 20th	Night	11% 1 4 35% 43% 6%	522
	21st to end	Night	7% 2 10% 43% 34% 5%	591
August	1st to 10th	Night	13% 1 4 40% 37% 4	537
	11th to 20th	Night	13% 2 5% 35% 38% 7%	680
	21st to end	Night	13% 3 7% 30% 41% 7%	792
September	1st to 10th	Night	12% 2 8% 33% 39% 7%	720
	11th to 20th	Night	16% 2 9% 36% 32% 4	720
	21st to end	Night	23% 3 10% 35% 27% 3	720
October	1st to 10th	Night	17% 3 15% 33% 27% 5%	720
	11th to 20th	Night	16% 6% 20% 36% 20% 3	720
	21st to end	Night	14% 4 24% 35% 20% 3	792
November	1st to 10th	Night	17% 4 20% 38% 17% 3	740
	11th to 20th	Night	19% 8% 23% 36% 13% 1	760
	21st to end	Night	15% 6% 27% 36% 15% 1	760
December	1st to 10th	Night	19% 8% 28% 37% 8%	760
	11th to 20th	Night	18% 6% 28% 39% 9%	760
	21st to end	Night	17% 8% 30% 35% 9%	836

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