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 2024-11-03.

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% 2 6% 5% 4 5% 4 6% 8% 41%	100685
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	98209
Transparency	Day	41% 5% 12% 21% 17% 4	100491
	Night	41% 5% 11% 21% 18% 5%	98073
Seeing	Day	16% 7% 22% 25% 20% 10%	15378
	Night	16% 6% 23% 35% 18% 2	25244

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% 7% 2 6% 4 3 3 2 3 5% 52%	2836
	11th to 20th	Day	13% 6% 2 5% 4 3 4 2 4 5% 52%	2840
	21st to end	Day	15% 10% 3 7% 4 4 4 3 4 6% 42%	3124
February	1st to 10th	Day	14% 7% 2 6% 5% 4 3 3 5% 7% 44%	1710
	11th to 20th	Day	19% 6% 2 6% 4 3 4 2 4 5% 46%	1776
	21st to end	Day	16% 7% 3 6% 4 5% 4 3 6% 6% 40%	1597
March	1st to 10th	Day	23% 9% 2 5% 3 4 3 4 5% 6% 36%	3435
	11th to 20th	Day	11% 5% 2 5% 4 3 3 2 4 6% 55%	3480
	21st to end	Day	18% 6% 2 5% 3 2 4 3 4 5% 47%	3834
April	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 52%	2280
	11th to 20th	Day	9% 5% 2 5% 5% 3 4 3 6% 8% 50%	2254
	21st to end	Day	10% 4 3 6% 5% 4 4 4 6% 6% 48%	2280
May	1st to 10th	Day	8% 6% 2 7% 6% 6% 6% 5% 8% 10% 36%	3794
	11th to 20th	Day	16% 7% 3 8% 5% 5% 5% 5% 6% 8% 33%	4081
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 6% 10% 46%	4602
June	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 6% 7% 10% 37%	2660
	11th to 20th	Day	9% 4 2 5% 5% 5% 6% 5% 7% 10% 43%	2660
	21st to end	Day	8% 5% 2 6% 6% 6% 7% 6% 8% 11% 37%	2633
July	1st to 10th	Day	6% 4 2 7% 6% 6% 7% 7% 9% 12% 33%	4120
	11th to 20th	Day	10% 7% 4 9% 7% 6% 6% 5% 8% 11% 27%	4120
	21st to end	Day	10% 8% 4 9% 7% 6% 6% 6% 8% 10% 27%	4466
August	1st to 10th	Day	20% 11% 4 9% 6% 5% 5% 5% 7% 9% 20%	4104
	11th to 20th	Day	9% 7% 3 8% 6% 5% 6% 5% 7% 9% 35%	3741
	21st to end	Day	6% 5% 2 7% 4 5% 6% 4 7% 11% 43%	4180
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 8% 39%	2280
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 3 6% 7% 40%	2280
	21st to end	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 35%	1991
October	1st to 10th	Day	14% 6% 2 5% 3 4 4 2 5% 7% 47%	1900
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 4 5% 54%	1900
	21st to end	Day	11% 5% 2 6% 4 3 3 2 4 5% 54%	2090
November	1st to 10th	Day	14% 5% 1 5% 4 3 4 3 4 6% 50%	1877
	11th to 20th	Day	15% 6% 1 5% 3 2 3 3 5% 5% 51%	1777
	21st to end	Day	13% 5% 2 4 3 3 3 3 5% 7% 51%	1639
December	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 6% 6% 40%	1520
	11th to 20th	Day	16% 6% 2 5% 3 3 3 2 3 4 53%	1910
	21st to end	Day	14% 7% 3 6% 4 4 4 3 5% 7% 43%	2914
January	1st to 10th	Night	14% 7% 2 5% 4 3 3 4 5% 6% 46%	4109
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 4 5% 5% 42%	4120
	21st to end	Night	15% 7% 2 7% 4 4 4 3 5% 6% 43%	4532
February	1st to 10th	Night	18% 6% 2 5% 4 3 3 3 5% 7% 44%	2470
	11th to 20th	Night	19% 7% 3 6% 3 3 3 4 4 5% 42%	2288
	21st to end	Night	17% 5% 2 5% 3 4 4 3 5% 5% 47%	1855
March	1st to 10th	Night	25% 9% 3 6% 4 3 4 3 4 5% 33%	3418
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 51%	3480
	21st to end	Night	17% 5% 2 4 3 3 3 3 4 6% 50%	3796
April	1st to 10th	Night	12% 6% 2 6% 4 3 4 4 6% 7% 48%	1900
	11th to 20th	Night	11% 6% 2 5% 4 5% 3 4 5% 8% 49%	1875
	21st to end	Night	11% 5% 2 5% 3 3 3 4 6% 8% 51%	1900
May	1st to 10th	Night	9% 8% 2 8% 6% 6% 6% 4 5% 8% 39%	3116
	11th to 20th	Night	18% 7% 3 7% 5% 5% 4 4 5% 6% 35%	2812
	21st to end	Night	8% 5% 2 6% 5% 4 5% 3 7% 10% 45%	2934
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 9% 10% 41%	1520
	11th to 20th	Night	9% 7% 2 7% 5% 6% 6% 5% 7% 10% 38%	1520
	21st to end	Night	7% 6% 2 7% 6% 6% 4 7% 7% 11% 38%	1540
July	1st to 10th	Night	7% 5% 3 7% 5% 5% 5% 5% 9% 14% 36%	2840
	11th to 20th	Night	11% 7% 3 8% 5% 5% 6% 4 9% 12% 30%	2840
	21st to end	Night	15% 9% 4 10% 5% 5% 6% 5% 6% 7% 29%	3087
August	1st to 10th	Night	18% 9% 4 9% 5% 5% 6% 4 7% 9% 25%	2825
	11th to 20th	Night	9% 7% 4 9% 6% 5% 6% 5% 8% 10% 32%	3054
	21st to end	Night	6% 5% 2 6% 5% 6% 6% 5% 8% 10% 41%	3476
September	1st to 10th	Night	9% 5% 2 7% 6% 5% 4 4 6% 9% 43%	1900
	11th to 20th	Night	14% 7% 3 7% 5% 3 4 4 4 8% 41%	1900
	21st to end	Night	18% 7% 4 9% 5% 4 5% 4 5% 6% 34%	2184
October	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 49%	2280
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	2280
	21st to end	Night	10% 5% 2 5% 4 3 3 3 4 6% 56%	2508
November	1st to 10th	Night	14% 7% 2 4 4 3 4 3 4 5% 51%	2246
	11th to 20th	Night	15% 7% 2 5% 4 3 3 3 5% 5% 49%	2399
	21st to end	Night	13% 5% 2 5% 3 3 3 3 4 7% 51%	2536
December	1st to 10th	Night	16% 7% 3 7% 4 4 4 3 6% 6% 41%	2660
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 6% 47%	3285
	21st to end	Night	15% 6% 2 5% 4 3 3 3 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	50% 3 9% 17% 14% 7%	3435
	11th to 20th	Day	33% 3 7% 19% 25% 13%	3480
	21st to end	Day	41% 3 9% 24% 19% 5%	3834
April	1st to 10th	Day	31% 4 9% 23% 25% 7%	2280
	11th to 20th	Day	32% 4 11% 23% 23% 7%	2254
	21st to end	Day	35% 4 13% 25% 20% 4	2280
May	1st to 10th	Day	43% 5% 18% 20% 11% 2	3829
	11th to 20th	Day	49% 5% 11% 23% 12% 1	4085
	21st to end	Day	33% 6% 14% 28% 17% 3	4616
June	1st to 10th	Day	40% 7% 14% 21% 16% 2	2660
	11th to 20th	Day	35% 7% 16% 25% 15% 2	2660
	21st to end	Day	37% 9% 17% 22% 13% 2	2633
July	1st to 10th	Day	39% 10% 18% 21% 11% 1	4055
	11th to 20th	Day	49% 10% 20% 16% 5% 1	4051
	21st to end	Day	49% 9% 14% 18% 10%	4324
August	1st to 10th	Day	59% 6% 18% 12% 5%	4091
	11th to 20th	Day	42% 7% 14% 25% 11% 1	3777
	21st to end	Day	35% 5% 15% 29% 14% 2	4180
September	1st to 10th	Day	40% 9% 14% 17% 17% 3	2280
	11th to 20th	Day	42% 6% 11% 19% 20% 3	2280
	21st to end	Day	48% 4 9% 21% 14% 3	1991
October	1st to 10th	Day	37% 4 9% 24% 22% 3	1900
	11th to 20th	Day	34% 3 6% 25% 24% 8%	1900
	21st to end	Day	35% 2 6% 20% 29% 7%	2090
November	1st to 10th	Day	37% 3 7% 21% 27% 6%	1877
	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	55% 3 8% 15% 14% 4	3418
	11th to 20th	Night	34% 5% 9% 13% 24% 16%	3480
	21st to end	Night	37% 4 9% 26% 19% 6%	3796
April	1st to 10th	Night	36% 5% 10% 18% 24% 7%	1900
	11th to 20th	Night	34% 4 10% 24% 21% 6%	1875
	21st to end	Night	32% 4 13% 29% 17% 5%	1900
May	1st to 10th	Night	43% 6% 17% 22% 10% 2	3146
	11th to 20th	Night	49% 5% 9% 22% 13% 1	2813
	21st to end	Night	33% 7% 18% 26% 14% 1	2941
June	1st to 10th	Night	35% 8% 18% 22% 14% 2	1520
	11th to 20th	Night	38% 8% 16% 23% 13% 2	1520
	21st to end	Night	38% 9% 18% 22% 12% 1	1540
July	1st to 10th	Night	37% 12% 21% 19% 10% 2	2795
	11th to 20th	Night	44% 11% 25% 15% 4 1	2786
	21st to end	Night	53% 7% 13% 16% 10% 1	2988
August	1st to 10th	Night	55% 7% 20% 15% 4	2814
	11th to 20th	Night	44% 9% 19% 19% 8% 1	3084
	21st to end	Night	35% 7% 15% 29% 14% 2	3476
September	1st to 10th	Night	38% 7% 17% 17% 17% 4	1900
	11th to 20th	Night	41% 7% 11% 21% 17% 3	1900
	21st to end	Night	50% 5% 10% 17% 15% 2	2184
October	1st to 10th	Night	36% 5% 9% 23% 24% 4	2280
	11th to 20th	Night	33% 4 7% 22% 24% 10%	2280
	21st to end	Night	31% 2 8% 24% 26% 9%	2508
November	1st to 10th	Night	37% 3 6% 21% 28% 6%	2246
	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% 33% 25% 8% 2	506
April	1st to 10th	Day	18% 17% 29% 23% 10% 3	460
	11th to 20th	Day	12% 12% 30% 28% 13% 6%	452
	21st to end	Day	13% 9% 29% 25% 20% 4	460
May	1st to 10th	Day	13% 11% 32% 22% 15% 6%	463
	11th to 20th	Day	17% 3 19% 29% 22% 9%	487
	21st to end	Day	15% 2 16% 27% 23% 16%	529
June	1st to 10th	Day	12% 2 15% 33% 26% 12%	490
	11th to 20th	Day	13% 3 15% 23% 27% 19%	490
	21st to end	Day	10% 2 14% 27% 31% 16%	490
July	1st to 10th	Day	10% 1 6% 24% 37% 22%	485
	11th to 20th	Day	11% 2 5% 27% 35% 20%	484
	21st to end	Day	10% 2 9% 29% 37% 14%	532
August	1st to 10th	Day	16% 4 10% 23% 27% 19%	486
	11th to 20th	Day	13% 2 8% 23% 32% 21%	479
	21st to end	Day	10% 3 7% 27% 27% 26%	539
September	1st to 10th	Day	13% 3 11% 26% 25% 23%	490
	11th to 20th	Day	17% 3 10% 27% 28% 14%	490
	21st to end	Day	23% 2 17% 24% 24% 10%	490
October	1st to 10th	Day	18% 2 17% 25% 25% 13%	490
	11th to 20th	Day	14% 7% 22% 30% 21% 6%	490
	21st to end	Day	14% 5% 24% 27% 22% 8%	539
November	1st to 10th	Day	21% 5% 23% 30% 16% 4	463
	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% 8% 36% 31% 7%	836
April	1st to 10th	Night	16% 10% 35% 34% 6%	760
	11th to 20th	Night	14% 9% 33% 32% 11% 1	751
	21st to end	Night	13% 5% 32% 40% 9% 1	760
May	1st to 10th	Night	13% 8% 31% 37% 11% 1	759
	11th to 20th	Night	16% 4 20% 42% 17% 1	561
	21st to end	Night	10% 1 13% 42% 32% 1	536
June	1st to 10th	Night	10% 2 17% 49% 21% 2	380
	11th to 20th	Night	11% 3 13% 47% 24% 3	380
	21st to end	Night	8% 3 13% 47% 28% 2	400
July	1st to 10th	Night	9% 2 6% 39% 39% 5%	555
	11th to 20th	Night	11% 1 4 36% 42% 5%	552
	21st to end	Night	8% 2 10% 42% 33% 5%	624
August	1st to 10th	Night	14% 2 5% 40% 35% 4	567
	11th to 20th	Night	13% 2 5% 36% 37% 6%	719
	21st to end	Night	13% 2 7% 31% 41% 6%	836
September	1st to 10th	Night	12% 2 10% 33% 37% 7%	760
	11th to 20th	Night	17% 3 10% 35% 32% 4	760
	21st to end	Night	22% 3 11% 34% 27% 2	760
October	1st to 10th	Night	17% 3 15% 33% 27% 5%	760
	11th to 20th	Night	15% 5% 21% 37% 19% 2	760
	21st to end	Night	13% 4 23% 35% 21% 3	836
November	1st to 10th	Night	17% 4 21% 38% 17% 3	749
	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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