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 2024-01-14.

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	12% 5% 2 5% 5% 3 5% 5% 5% 7% 45%	74654
	Night	12% 5% 2 4 4 3 4 4 5% 7% 49%	75093
Transparency	Day	38% 7% 11% 21% 19% 5%	74378
	Night	34% 6% 11% 21% 21% 7%	74890
Seeing	Day	13% 6% 19% 24% 25% 14%	14049
	Night	14% 5% 22% 32% 22% 4	23936

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	20% 7% 4 5% 4 2 3 3 4 5% 44%	1707
	11th to 20th	Day	20% 9% 3 5% 5% 2 3 3 3 5% 42%	1647
	21st to end	Day	17% 8% 2 5% 4 2 3 3 3 5% 48%	1782
February	1st to 10th	Day	18% 8% 2 5% 4 3 4 3 4 5% 42%	1714
	11th to 20th	Day	24% 7% 3 5% 4 2 3 3 4 4 40%	1748
	21st to end	Day	21% 8% 3 7% 5% 2 3 4 4 5% 37%	1480
March	1st to 10th	Day	17% 8% 2 6% 5% 3 4 3 4 6% 41%	1930
	11th to 20th	Day	15% 7% 3 6% 5% 4 5% 4 5% 6% 40%	1980
	21st to end	Day	12% 6% 3 7% 6% 3 5% 5% 5% 6% 43%	2240
April	1st to 10th	Day	12% 6% 3 5% 6% 3 5% 4 6% 7% 43%	2160
	11th to 20th	Day	14% 6% 3 6% 4 3 4 4 6% 6% 44%	2134
	21st to end	Day	11% 5% 3 4 6% 3 4 5% 5% 8% 46%	2160
May	1st to 10th	Day	14% 6% 3 5% 5% 3 5% 4 5% 6% 43%	2160
	11th to 20th	Day	10% 5% 2 6% 6% 4 5% 5% 7% 9% 40%	2124
	21st to end	Day	9% 4 3 5% 7% 4 7% 7% 7% 9% 39%	2535
June	1st to 10th	Day	7% 5% 3 6% 6% 4 6% 6% 6% 9% 42%	2520
	11th to 20th	Day	5% 3 2 5% 5% 4 6% 6% 6% 9% 48%	2520
	21st to end	Day	6% 3 2 4 6% 3 5% 6% 7% 10% 48%	2462
July	1st to 10th	Day	7% 5% 3 5% 8% 5% 7% 8% 8% 11% 35%	2340
	11th to 20th	Day	10% 5% 2 4 5% 4 7% 7% 9% 10% 38%	2340
	21st to end	Day	7% 4 2 5% 6% 4 6% 7% 9% 12% 39%	2546
August	1st to 10th	Day	5% 3 2 4 5% 5% 7% 8% 7% 10% 43%	2189
	11th to 20th	Day	9% 5% 2 6% 6% 3 6% 6% 7% 9% 42%	2125
	21st to end	Day	12% 4 2 4 5% 3 5% 6% 6% 8% 45%	2376
September	1st to 10th	Day	9% 4 2 5% 6% 4 6% 5% 6% 8% 45%	2160
	11th to 20th	Day	11% 6% 2 5% 4 4 5% 4 4 7% 47%	2160
	21st to end	Day	10% 4 2 3 4 3 4 4 5% 6% 56%	1954
October	1st to 10th	Day	8% 3 1 3 4 3 3 4 4 7% 60%	1800
	11th to 20th	Day	11% 4 2 4 3 2 4 3 4 6% 56%	1800
	21st to end	Day	16% 5% 2 3 4 2 3 3 4 5% 53%	1980
November	1st to 10th	Day	12% 4 2 3 4 2 3 2 3 6% 59%	1858
	11th to 20th	Day	11% 4 2 4 4 3 4 4 4 5% 54%	1751
	21st to end	Day	18% 6% 3 5% 4 2 4 3 4 7% 44%	1710
December	1st to 10th	Day	18% 8% 3 5% 5% 2 4 5% 4 6% 39%	1687
	11th to 20th	Day	14% 9% 3 6% 6% 3 4 3 4 5% 43%	1918
	21st to end	Day	14% 6% 2 6% 6% 4 4 5% 4 7% 42%	2957
January	1st to 10th	Night	18% 6% 2 4 3 2 4 3 4 6% 47%	2458
	11th to 20th	Night	19% 8% 2 5% 5% 2 4 4 3 5% 44%	2392
	21st to end	Night	19% 7% 3 4 3 3 3 3 4 4 47%	2574
February	1st to 10th	Night	19% 7% 3 5% 5% 3 3 3 4 6% 42%	2244
	11th to 20th	Night	21% 6% 3 4 3 2 3 4 4 5% 45%	2098
	21st to end	Night	21% 7% 3 5% 5% 2 3 3 3 5% 42%	1776
March	1st to 10th	Night	16% 5% 2 4 5% 2 5% 4 5% 7% 45%	2044
	11th to 20th	Night	16% 6% 3 6% 4 2 4 4 5% 7% 43%	1980
	21st to end	Night	15% 5% 3 4 4 2 3 3 4 7% 47%	2114
April	1st to 10th	Night	11% 4 2 5% 5% 3 4 4 5% 7% 49%	1800
	11th to 20th	Night	13% 6% 2 4 4 2 3 4 6% 7% 48%	1775
	21st to end	Night	11% 4 2 5% 5% 3 4 4 4 6% 53%	1800
May	1st to 10th	Night	10% 4 2 4 4 2 3 4 6% 9% 52%	1800
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 7% 9% 45%	1769
	21st to end	Night	7% 4 2 4 5% 3 5% 5% 8% 10% 48%	1729
June	1st to 10th	Night	4 4 2 4 5% 2 6% 6% 7% 11% 48%	1440
	11th to 20th	Night	3 2 1 3 4 2 5% 5% 5% 12% 57%	1440
	21st to end	Night	5% 2 2 4 5% 2 3 5% 7% 11% 53%	1490
July	1st to 10th	Night	5% 3 2 4 5% 4 6% 5% 8% 13% 44%	1620
	11th to 20th	Night	6% 2 2 3 4 3 6% 5% 7% 12% 50%	1620
	21st to end	Night	4 3 2 3 4 3 4 6% 6% 12% 53%	1772
August	1st to 10th	Night	3 3 1 3 4 3 4 6% 7% 12% 53%	1746
	11th to 20th	Night	7% 3 2 4 5% 3 5% 6% 6% 12% 47%	1776
	21st to end	Night	9% 4 2 5% 5% 2 4 5% 6% 9% 49%	1980
September	1st to 10th	Night	9% 3 2 4 5% 3 4 6% 6% 8% 50%	1800
	11th to 20th	Night	8% 5% 2 6% 5% 3 4 4 5% 6% 52%	1800
	21st to end	Night	10% 3 2 3 4 2 3 3 5% 8% 57%	1984
October	1st to 10th	Night	7% 3 2 3 3 2 3 3 4 7% 64%	2160
	11th to 20th	Night	10% 5% 2 4 4 2 4 3 4 5% 57%	2160
	21st to end	Night	15% 5% 2 4 3 2 3 3 4 5% 55%	2376
November	1st to 10th	Night	11% 4 2 3 4 2 3 3 4 6% 58%	2220
	11th to 20th	Night	12% 4 2 4 4 3 3 3 4 6% 56%	2426
	21st to end	Night	13% 5% 2 5% 5% 3 4 4 4 5% 49%	2470
December	1st to 10th	Night	17% 7% 3 4 4 2 4 3 5% 6% 44%	2489
	11th to 20th	Night	16% 6% 2 5% 5% 3 3 3 4 5% 48%	3279
	21st to end	Night	16% 9% 2 5% 5% 3 4 5% 6% 6% 40%	4692

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% 3 6% 21% 20% 5%	1708
	11th to 20th	Day	47% 4 7% 17% 22% 4	1647
	21st to end	Day	41% 3 5% 21% 25% 4	1782
February	1st to 10th	Day	45% 5% 7% 19% 18% 7%	1714
	11th to 20th	Day	49% 4 5% 19% 17% 6%	1758
	21st to end	Day	50% 5% 6% 13% 19% 8%	1480
March	1st to 10th	Day	45% 5% 8% 15% 18% 10%	1930
	11th to 20th	Day	44% 5% 9% 19% 18% 4	1980
	21st to end	Day	40% 6% 10% 21% 20% 2	2240
April	1st to 10th	Day	40% 6% 10% 21% 19% 5%	2160
	11th to 20th	Day	40% 5% 10% 18% 22% 5%	2134
	21st to end	Day	36% 6% 10% 21% 24% 2	2160
May	1st to 10th	Day	41% 7% 9% 19% 19% 4	2160
	11th to 20th	Day	38% 9% 14% 23% 15% 2	2128
	21st to end	Day	37% 9% 14% 25% 14% 1	2535
June	1st to 10th	Day	36% 9% 14% 24% 15% 1	2520
	11th to 20th	Day	29% 9% 16% 26% 16% 3	2520
	21st to end	Day	30% 10% 15% 24% 18% 4	2462
July	1st to 10th	Day	38% 12% 21% 18% 8% 3	2276
	11th to 20th	Day	34% 11% 20% 22% 10% 3	2271
	21st to end	Day	33% 11% 19% 27% 9% 1	2405
August	1st to 10th	Day	31% 10% 20% 29% 10%	2175
	11th to 20th	Day	36% 10% 18% 21% 13% 3	2125
	21st to end	Day	34% 9% 17% 23% 13% 4	2376
September	1st to 10th	Day	36% 7% 13% 20% 18% 6%	2160
	11th to 20th	Day	37% 7% 9% 16% 23% 8%	2160
	21st to end	Day	29% 6% 10% 21% 23% 11%	1954
October	1st to 10th	Day	25% 6% 8% 26% 24% 12%	1800
	11th to 20th	Day	30% 4 6% 19% 29% 11%	1800
	21st to end	Day	34% 5% 5% 18% 27% 11%	1980
November	1st to 10th	Day	29% 4 9% 19% 30% 10%	1858
	11th to 20th	Day	33% 3 6% 19% 27% 11%	1751
	21st to end	Day	42% 4 7% 17% 22% 8%	1710
December	1st to 10th	Day	47% 4 8% 17% 18% 6%	1687
	11th to 20th	Day	45% 3 7% 15% 24% 5%	1915
	21st to end	Day	41% 5% 9% 19% 22% 4	2957
January	1st to 10th	Night	39% 4 6% 21% 25% 5%	2458
	11th to 20th	Night	45% 3 6% 19% 20% 7%	2392
	21st to end	Night	42% 3 5% 18% 25% 7%	2574
February	1st to 10th	Night	45% 4 6% 18% 21% 6%	2244
	11th to 20th	Night	43% 4 7% 19% 19% 8%	2099
	21st to end	Night	47% 4 6% 14% 18% 11%	1776
March	1st to 10th	Night	38% 4 8% 18% 20% 12%	2044
	11th to 20th	Night	40% 7% 11% 18% 17% 7%	1980
	21st to end	Night	38% 4 8% 21% 23% 6%	2114
April	1st to 10th	Night	35% 5% 11% 21% 20% 9%	1800
	11th to 20th	Night	35% 5% 9% 19% 25% 8%	1775
	21st to end	Night	32% 5% 9% 23% 26% 5%	1800
May	1st to 10th	Night	29% 6% 12% 25% 22% 6%	1800
	11th to 20th	Night	35% 6% 14% 26% 17% 2	1770
	21st to end	Night	28% 8% 16% 28% 19% 2	1730
June	1st to 10th	Night	27% 10% 16% 27% 17% 2	1440
	11th to 20th	Night	19% 7% 19% 30% 19% 5%	1440
	21st to end	Night	24% 8% 14% 27% 22% 5%	1490
July	1st to 10th	Night	28% 11% 23% 24% 11% 3	1575
	11th to 20th	Night	22% 11% 26% 26% 12% 4	1566
	21st to end	Night	23% 10% 21% 30% 15% 1	1673
August	1st to 10th	Night	22% 9% 22% 31% 14% 1	1736
	11th to 20th	Night	27% 10% 20% 23% 15% 5%	1776
	21st to end	Night	31% 8% 16% 23% 17% 5%	1980
September	1st to 10th	Night	29% 8% 13% 23% 19% 8%	1800
	11th to 20th	Night	33% 7% 8% 18% 24% 9%	1800
	21st to end	Night	26% 5% 9% 23% 25% 12%	1984
October	1st to 10th	Night	21% 4 10% 23% 26% 15%	2160
	11th to 20th	Night	30% 4 6% 18% 28% 15%	2160
	21st to end	Night	33% 3 6% 17% 27% 13%	2376
November	1st to 10th	Night	29% 4 8% 19% 28% 13%	2220
	11th to 20th	Night	31% 4 7% 19% 27% 13%	2426
	21st to end	Night	38% 4 7% 17% 24% 10%	2470
December	1st to 10th	Night	42% 5% 8% 19% 20% 7%	2489
	11th to 20th	Night	40% 3 6% 16% 27% 8%	3281
	21st to end	Night	43% 5% 8% 19% 21% 4	4692

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% 15% 39% 16% 8% 1	270
	11th to 20th	Day	26% 13% 33% 19% 6% 2	249
	21st to end	Day	20% 13% 42% 18% 8%	264
February	1st to 10th	Day	25% 11% 35% 18% 9% 2	240
	11th to 20th	Day	32% 18% 29% 18% 4	240
	21st to end	Day	31% 18% 31% 13% 8%	198
March	1st to 10th	Day	25% 10% 35% 18% 11%	240
	11th to 20th	Day	20% 15% 38% 22% 5%	240
	21st to end	Day	12% 21% 32% 22% 11% 2	326
April	1st to 10th	Day	14% 10% 35% 28% 11% 1	420
	11th to 20th	Day	19% 8% 30% 28% 12% 3	412
	21st to end	Day	13% 10% 27% 27% 21% 2	420
May	1st to 10th	Day	13% 12% 22% 32% 18% 3	423
	11th to 20th	Day	11% 3 25% 25% 25% 11%	447
	21st to end	Day	8% 3 15% 34% 26% 15%	618
June	1st to 10th	Day	9% 3 11% 27% 33% 17%	630
	11th to 20th	Day	5% 3 9% 30% 36% 16%	630
	21st to end	Day	7% 2 12% 29% 29% 21%	630
July	1st to 10th	Day	5% 2 5% 24% 38% 24%	621
	11th to 20th	Day	6% 2 6% 20% 36% 31%	618
	21st to end	Day	5% 1 5% 22% 39% 29%	684
August	1st to 10th	Day	6% 1 5% 18% 40% 30%	487
	11th to 20th	Day	9% 1 4 19% 42% 26%	439
	21st to end	Day	15% 1 4 14% 32% 35%	495
September	1st to 10th	Day	8% 1 6% 22% 39% 24%	450
	11th to 20th	Day	10% 2 8% 21% 32% 26%	450
	21st to end	Day	11% 2 6% 27% 36% 18%	424
October	1st to 10th	Day	9% 1 17% 29% 27% 16%	270
	11th to 20th	Day	10% 6% 23% 31% 24% 6%	270
	21st to end	Day	19% 9% 23% 30% 15% 5%	297
November	1st to 10th	Day	18% 5% 23% 25% 25% 4	270
	11th to 20th	Day	11% 7% 33% 33% 12% 3	270
	21st to end	Day	20% 13% 24% 26% 13% 4	270
December	1st to 10th	Day	18% 13% 31% 24% 11% 2	270
	11th to 20th	Day	20% 12% 32% 23% 12% 1	270
	21st to end	Day	18% 16% 36% 21% 8% 1	297
January	1st to 10th	Night	21% 7% 35% 30% 6%	950
	11th to 20th	Night	22% 9% 34% 28% 8%	920
	21st to end	Night	22% 8% 35% 32% 3	990
February	1st to 10th	Night	22% 10% 34% 29% 5%	804
	11th to 20th	Night	22% 10% 35% 29% 4	703
	21st to end	Night	25% 13% 32% 27% 3	592
March	1st to 10th	Night	19% 9% 31% 35% 7%	604
	11th to 20th	Night	17% 9% 32% 35% 7% 1	540
	21st to end	Night	17% 8% 31% 31% 12% 1	594
April	1st to 10th	Night	12% 7% 36% 34% 10% 1	540
	11th to 20th	Night	14% 8% 29% 34% 13% 2	533
	21st to end	Night	11% 7% 31% 35% 14% 1	540
May	1st to 10th	Night	11% 4 22% 47% 15% 1	540
	11th to 20th	Night	11% 2 23% 40% 21% 2	531
	21st to end	Night	8% 1 15% 35% 34% 7%	584
June	1st to 10th	Night	6% 2 8% 38% 41% 6%	540
	11th to 20th	Night	3 1 8% 32% 49% 7%	540
	21st to end	Night	5% 1 9% 33% 41% 11%	540
July	1st to 10th	Night	4 1 6% 28% 52% 10%	525
	11th to 20th	Night	4 1 6% 25% 51% 13%	522
	21st to end	Night	4 1 4 29% 49% 14%	591
August	1st to 10th	Night	4 1 4 24% 52% 15%	537
	11th to 20th	Night	7% 1 3 27% 51% 10%	534
	21st to end	Night	11% 1 5% 21% 49% 14%	594
September	1st to 10th	Night	9% 1 7% 31% 45% 7%	540
	11th to 20th	Night	9% 1 8% 30% 45% 7%	540
	21st to end	Night	11% 1 10% 34% 38% 6%	702
October	1st to 10th	Night	8% 2 13% 34% 37% 6%	720
	11th to 20th	Night	13% 4 20% 38% 23% 2	720
	21st to end	Night	15% 6% 22% 33% 21% 2	792
November	1st to 10th	Night	12% 3 22% 38% 23% 2	740
	11th to 20th	Night	13% 5% 29% 38% 13% 1	760
	21st to end	Night	16% 7% 28% 33% 14% 2	760
December	1st to 10th	Night	19% 7% 30% 33% 10%	779
	11th to 20th	Night	21% 8% 29% 34% 8%	950
	21st to end	Night	23% 9% 31% 31% 7%	1045

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