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 2024-01-31.

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% 11% 4 7% 6% 3 5% 5% 5% 7% 30%	74769
	Night	18% 12% 5% 7% 6% 3 4 4 5% 6% 30%	75360
Transparency	Day	54% 6% 12% 18% 9% 1	74487
	Night	55% 6% 11% 17% 10% 1	75162
Seeing	Day	24% 16% 28% 19% 10% 3	13530
	Night	24% 13% 27% 24% 10% 1	23317

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	19% 17% 10% 12% 8% 3 5% 4 3 4 15%	1672
	11th to 20th	Day	19% 22% 7% 12% 7% 4 3 3 3 4 15%	1710
	21st to end	Day	18% 19% 9% 15% 9% 4 4 3 3 4 12%	1872
February	1st to 10th	Day	19% 18% 8% 13% 9% 4 4 2 3 3 17%	1620
	11th to 20th	Day	16% 16% 8% 12% 10% 4 5% 3 4 5% 18%	1573
	21st to end	Day	19% 17% 4 11% 7% 3 4 4 4 5% 21%	1459
March	1st to 10th	Day	19% 12% 6% 9% 6% 3 3 4 6% 6% 25%	1980
	11th to 20th	Day	18% 13% 6% 9% 6% 3 4 4 4 5% 28%	1980
	21st to end	Day	23% 12% 5% 8% 6% 3 4 4 4 5% 28%	2178
April	1st to 10th	Day	17% 13% 5% 6% 6% 3 4 4 5% 7% 31%	2067
	11th to 20th	Day	20% 12% 4 6% 4 3 4 4 4 7% 33%	2208
	21st to end	Day	22% 11% 3 6% 6% 3 3 3 3 6% 34%	2340
May	1st to 10th	Day	18% 11% 3 6% 6% 3 6% 5% 6% 7% 29%	2340
	11th to 20th	Day	22% 8% 3 6% 6% 4 4 5% 5% 7% 31%	2301
	21st to end	Day	14% 6% 2 5% 6% 3 6% 5% 7% 7% 38%	2699
June	1st to 10th	Day	17% 6% 3 6% 6% 4 5% 5% 7% 8% 34%	2520
	11th to 20th	Day	14% 7% 3 6% 6% 4 5% 4 5% 8% 36%	2520
	21st to end	Day	14% 5% 2 5% 6% 3 5% 5% 7% 9% 37%	2520
July	1st to 10th	Day	11% 6% 3 5% 5% 3 5% 5% 5% 9% 42%	2484
	11th to 20th	Day	13% 5% 2 6% 5% 4 5% 6% 7% 9% 39%	2340
	21st to end	Day	12% 6% 2 5% 6% 3 6% 6% 7% 9% 36%	2547
August	1st to 10th	Day	10% 6% 3 6% 6% 4 6% 7% 6% 10% 37%	2327
	11th to 20th	Day	13% 7% 3 7% 6% 4 6% 7% 7% 8% 33%	2303
	21st to end	Day	12% 6% 3 6% 7% 4 5% 6% 7% 9% 36%	2484
September	1st to 10th	Day	16% 7% 3 6% 5% 3 4 4 5% 8% 39%	2151
	11th to 20th	Day	13% 7% 2 5% 6% 4 5% 5% 6% 8% 40%	1980
	21st to end	Day	20% 7% 3 6% 5% 3 5% 5% 4 7% 35%	1980
October	1st to 10th	Day	17% 7% 3 6% 6% 3 4 4 5% 8% 36%	1810
	11th to 20th	Day	23% 10% 3 7% 6% 3 3 4 5% 5% 30%	1800
	21st to end	Day	28% 12% 4 6% 5% 3 4 5% 4 6% 24%	1980
November	1st to 10th	Day	12% 11% 4 7% 5% 3 5% 5% 5% 6% 36%	1733
	11th to 20th	Day	20% 15% 4 7% 6% 4 3 4 4 5% 28%	1569
	21st to end	Day	20% 18% 6% 8% 5% 3 5% 5% 5% 6% 20%	1520
December	1st to 10th	Day	21% 22% 9% 9% 6% 3 4 3 3 3 16%	1520
	11th to 20th	Day	19% 20% 8% 12% 5% 3 4 4 5% 5% 15%	1910
	21st to end	Day	27% 25% 8% 10% 5% 2 3 2 3 3 11%	2772
January	1st to 10th	Night	20% 18% 9% 12% 7% 3 4 4 3 3 16%	2488
	11th to 20th	Night	21% 19% 7% 13% 7% 4 3 3 3 5% 16%	2470
	21st to end	Night	18% 21% 9% 11% 9% 4 4 3 3 3 15%	2711
February	1st to 10th	Night	21% 15% 7% 11% 8% 3 4 3 4 5% 18%	2340
	11th to 20th	Night	19% 14% 7% 12% 7% 3 5% 5% 5% 5% 19%	2273
	21st to end	Night	22% 12% 6% 11% 6% 3 4 3 4 5% 23%	1791
March	1st to 10th	Night	17% 12% 7% 9% 7% 3 4 4 4 5% 28%	1980
	11th to 20th	Night	20% 12% 5% 6% 6% 3 3 4 4 6% 31%	1980
	21st to end	Night	19% 13% 6% 8% 5% 3 4 4 4 4 30%	2178
April	1st to 10th	Night	18% 13% 5% 7% 5% 4 4 3 5% 6% 31%	1891
	11th to 20th	Night	18% 10% 3 6% 5% 4 5% 3 5% 6% 34%	1716
	21st to end	Night	15% 10% 3 6% 6% 3 5% 4 5% 7% 35%	1620
May	1st to 10th	Night	20% 7% 3 6% 7% 4 5% 5% 5% 6% 33%	1620
	11th to 20th	Night	16% 9% 3 6% 5% 3 4 4 4 7% 38%	1592
	21st to end	Night	11% 5% 2 5% 5% 3 5% 5% 5% 11% 44%	1575
June	1st to 10th	Night	9% 6% 3 5% 5% 5% 5% 6% 6% 9% 41%	1440
	11th to 20th	Night	11% 5% 3 5% 6% 3 5% 4 5% 8% 44%	1440
	21st to end	Night	12% 5% 2 4 5% 3 5% 5% 7% 10% 43%	1440
July	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 4 6% 8% 48%	1470
	11th to 20th	Night	10% 4 2 4 5% 3 5% 4 6% 9% 48%	1620
	21st to end	Night	10% 5% 2 5% 5% 4 6% 5% 7% 10% 42%	1771
August	1st to 10th	Night	8% 5% 2 6% 5% 3 5% 5% 6% 7% 47%	1611
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 5% 7% 9% 42%	1598
	21st to end	Night	12% 4 2 4 5% 3 4 5% 6% 8% 46%	1854
September	1st to 10th	Night	15% 5% 2 4 4 3 5% 5% 5% 7% 46%	1806
	11th to 20th	Night	13% 4 2 4 4 2 4 3 6% 8% 51%	1980
	21st to end	Night	19% 6% 3 6% 5% 3 4 4 5% 7% 39%	1980
October	1st to 10th	Night	17% 6% 3 6% 4 3 4 5% 5% 7% 41%	2150
	11th to 20th	Night	19% 8% 3 6% 5% 3 5% 5% 5% 8% 33%	2160
	21st to end	Night	26% 10% 3 5% 5% 2 4 5% 5% 5% 29%	2376
November	1st to 10th	Night	15% 10% 3 6% 5% 3 4 4 5% 7% 38%	2342
	11th to 20th	Night	18% 15% 6% 6% 5% 3 4 4 5% 6% 27%	2608
	21st to end	Night	22% 17% 4 7% 6% 2 5% 4 5% 6% 23%	2660
December	1st to 10th	Night	22% 20% 8% 9% 6% 3 4 3 4 4 17%	2660
	11th to 20th	Night	19% 19% 7% 11% 7% 3 4 3 4 5% 18%	3285
	21st to end	Night	27% 21% 8% 10% 6% 3 4 4 4 4 10%	4884

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	74% 4 10% 9% 3	1673
	11th to 20th	Day	75% 4 10% 9% 2	1710
	21st to end	Day	78% 4 7% 8% 2 1	1872
February	1st to 10th	Day	74% 3 8% 10% 4	1620
	11th to 20th	Day	71% 4 8% 12% 6%	1582
	21st to end	Day	65% 5% 10% 14% 5% 2	1459
March	1st to 10th	Day	58% 5% 13% 18% 5%	1980
	11th to 20th	Day	58% 6% 10% 16% 9% 2	1980
	21st to end	Day	60% 3 7% 18% 10% 1	2178
April	1st to 10th	Day	52% 6% 12% 17% 12% 1	2067
	11th to 20th	Day	53% 4 11% 17% 12% 3	2208
	21st to end	Day	54% 4 10% 20% 10% 2	2340
May	1st to 10th	Day	53% 7% 11% 18% 9% 1	2340
	11th to 20th	Day	52% 7% 10% 16% 12% 2	2305
	21st to end	Day	43% 8% 15% 22% 11% 2	2699
June	1st to 10th	Day	46% 7% 12% 23% 11% 1	2520
	11th to 20th	Day	46% 7% 13% 20% 13% 1	2520
	21st to end	Day	41% 7% 12% 26% 12% 1	2520
July	1st to 10th	Day	38% 8% 13% 23% 15% 3	2416
	11th to 20th	Day	40% 8% 14% 24% 14% 1	2271
	21st to end	Day	41% 9% 14% 20% 14% 1	2405
August	1st to 10th	Day	40% 9% 15% 25% 10%	2314
	11th to 20th	Day	45% 10% 15% 20% 9% 2	2303
	21st to end	Day	41% 9% 13% 22% 12% 2	2484
September	1st to 10th	Day	43% 7% 12% 21% 14% 2	2151
	11th to 20th	Day	40% 7% 14% 24% 15% 1	1980
	21st to end	Day	48% 6% 12% 23% 11%	1980
October	1st to 10th	Day	47% 7% 13% 19% 13% 1	1810
	11th to 20th	Day	55% 6% 13% 19% 7% 1	1800
	21st to end	Day	60% 6% 12% 13% 8% 1	1980
November	1st to 10th	Day	47% 7% 12% 18% 14% 2	1733
	11th to 20th	Day	59% 6% 11% 15% 7% 3	1569
	21st to end	Day	65% 6% 11% 13% 5%	1520
December	1st to 10th	Day	74% 4 9% 10% 3	1520
	11th to 20th	Day	72% 5% 10% 11% 2	1906
	21st to end	Day	81% 3 8% 7% 1	2772
January	1st to 10th	Night	74% 4 8% 10% 4	2488
	11th to 20th	Night	73% 4 10% 10% 2	2470
	21st to end	Night	74% 4 8% 11% 3 1	2711
February	1st to 10th	Night	70% 4 10% 12% 4	2340
	11th to 20th	Night	68% 5% 9% 13% 5%	2275
	21st to end	Night	65% 5% 8% 14% 7% 1	1791
March	1st to 10th	Night	59% 5% 9% 19% 9%	1980
	11th to 20th	Night	54% 5% 12% 17% 11% 1	1980
	21st to end	Night	57% 4 6% 17% 13% 2	2178
April	1st to 10th	Night	54% 6% 10% 18% 11% 1	1891
	11th to 20th	Night	50% 5% 11% 18% 13% 3	1716
	21st to end	Night	48% 6% 11% 20% 11% 3	1620
May	1st to 10th	Night	51% 6% 10% 18% 12% 3	1620
	11th to 20th	Night	46% 7% 11% 18% 15% 3	1593
	21st to end	Night	35% 7% 16% 25% 14% 2	1576
June	1st to 10th	Night	39% 8% 12% 25% 14% 2	1440
	11th to 20th	Night	39% 6% 14% 21% 18% 2	1440
	21st to end	Night	37% 8% 14% 23% 17% 1	1440
July	1st to 10th	Night	35% 8% 10% 24% 19% 3	1429
	11th to 20th	Night	33% 7% 13% 25% 19% 3	1566
	21st to end	Night	36% 10% 14% 21% 18% 2	1672
August	1st to 10th	Night	34% 8% 13% 30% 15% 1	1600
	11th to 20th	Night	37% 8% 15% 26% 13% 1	1598
	21st to end	Night	34% 8% 13% 25% 16% 3	1854
September	1st to 10th	Night	36% 7% 13% 24% 17% 3	1806
	11th to 20th	Night	31% 7% 15% 25% 20% 2	1980
	21st to end	Night	45% 5% 13% 21% 16% 1	1980
October	1st to 10th	Night	41% 8% 13% 21% 16% 1	2150
	11th to 20th	Night	48% 7% 14% 20% 10% 1	2160
	21st to end	Night	56% 7% 11% 17% 9% 2	2376
November	1st to 10th	Night	44% 6% 14% 22% 11% 3	2342
	11th to 20th	Night	58% 5% 11% 16% 7% 3	2608
	21st to end	Night	63% 4 12% 16% 4 1	2660
December	1st to 10th	Night	72% 5% 10% 9% 4	2660
	11th to 20th	Night	70% 5% 12% 12% 2	3288
	21st to end	Night	78% 5% 9% 6% 1	4884

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% 29% 25% 9% 3	254
	11th to 20th	Day	37% 30% 23% 6% 3	270
	21st to end	Day	34% 29% 30% 7% 1	294
February	1st to 10th	Day	35% 28% 31% 6%	240
	11th to 20th	Day	39% 28% 27% 6%	240
	21st to end	Day	40% 29% 26% 6%	199
March	1st to 10th	Day	32% 23% 30% 13% 2	420
	11th to 20th	Day	29% 21% 33% 12% 3 1	420
	21st to end	Day	36% 22% 23% 15% 3	462
April	1st to 10th	Day	28% 24% 26% 15% 5% 1	420
	11th to 20th	Day	30% 20% 22% 17% 9% 2	412
	21st to end	Day	30% 18% 32% 15% 4 1	420
May	1st to 10th	Day	29% 21% 26% 16% 6% 2	423
	11th to 20th	Day	25% 13% 29% 23% 8% 2	447
	21st to end	Day	17% 10% 28% 25% 13% 6%	485
June	1st to 10th	Day	16% 13% 33% 26% 9% 3	450
	11th to 20th	Day	20% 13% 26% 25% 15% 2	450
	21st to end	Day	17% 10% 33% 26% 11% 3	450
July	1st to 10th	Day	12% 6% 22% 29% 22% 8%	445
	11th to 20th	Day	14% 6% 28% 31% 14% 7%	444
	21st to end	Day	13% 7% 31% 28% 16% 6%	488
August	1st to 10th	Day	11% 6% 26% 28% 19% 10%	446
	11th to 20th	Day	18% 8% 24% 25% 15% 10%	439
	21st to end	Day	11% 9% 24% 31% 17% 8%	495
September	1st to 10th	Day	17% 9% 24% 27% 17% 7%	450
	11th to 20th	Day	11% 7% 23% 27% 23% 9%	450
	21st to end	Day	22% 12% 28% 19% 15% 4	450
October	1st to 10th	Day	17% 13% 28% 24% 16% 3	450
	11th to 20th	Day	27% 17% 34% 15% 6% 1	450
	21st to end	Day	39% 15% 29% 13% 4	495
November	1st to 10th	Day	22% 21% 32% 15% 9% 1	331
	11th to 20th	Day	36% 24% 24% 13% 2 1	203
	21st to end	Day	28% 22% 38% 11% 1	180
December	1st to 10th	Day	36% 29% 26% 6% 3 2	180
	11th to 20th	Day	37% 21% 33% 9% 1	180
	21st to end	Day	36% 24% 30% 9% 1	198
January	1st to 10th	Night	31% 23% 32% 11% 3	760
	11th to 20th	Night	36% 20% 29% 14% 2	760
	21st to end	Night	28% 21% 33% 15% 2	835
February	1st to 10th	Night	33% 20% 28% 18% 2	720
	11th to 20th	Night	31% 20% 34% 14% 2	703
	21st to end	Night	32% 20% 32% 14% 1	592
March	1st to 10th	Night	27% 18% 35% 17% 3	720
	11th to 20th	Night	29% 19% 27% 20% 5%	720
	21st to end	Night	26% 18% 31% 20% 5% 1	792
April	1st to 10th	Night	25% 17% 31% 21% 6%	720
	11th to 20th	Night	25% 13% 32% 22% 8% 1	652
	21st to end	Night	22% 9% 37% 27% 4 1	540
May	1st to 10th	Night	22% 10% 26% 32% 10%	540
	11th to 20th	Night	21% 8% 29% 33% 8% 1	531
	21st to end	Night	11% 5% 32% 31% 20% 2	415
June	1st to 10th	Night	9% 5% 30% 41% 14% 1	360
	11th to 20th	Night	13% 6% 24% 43% 13%	360
	21st to end	Night	10% 6% 30% 36% 18%	360
July	1st to 10th	Night	8% 4 17% 42% 23% 5%	379
	11th to 20th	Night	10% 3 21% 35% 26% 4	522
	21st to end	Night	11% 3 15% 45% 25% 1	591
August	1st to 10th	Night	10% 3 17% 42% 25% 3	537
	11th to 20th	Night	13% 3 14% 39% 28% 4	534
	21st to end	Night	13% 5% 20% 32% 26% 5%	666
September	1st to 10th	Night	16% 6% 19% 31% 24% 3	720
	11th to 20th	Night	14% 5% 18% 35% 25% 3	720
	21st to end	Night	20% 9% 22% 27% 19% 3	720
October	1st to 10th	Night	19% 7% 28% 26% 18% 2	720
	11th to 20th	Night	25% 13% 29% 26% 7% 1	720
	21st to end	Night	33% 13% 28% 22% 3	792
November	1st to 10th	Night	22% 12% 30% 26% 9% 1	740
	11th to 20th	Night	29% 18% 29% 18% 6% 1	760
	21st to end	Night	32% 16% 31% 17% 4	760
December	1st to 10th	Night	35% 19% 28% 14% 4	760
	11th to 20th	Night	30% 24% 27% 15% 4	760
	21st to end	Night	33% 19% 31% 15% 1	836

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