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 2025-02-06.

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 5% 4 4 4 3 5% 7% 50%	109115
	Night	12% 5% 2 4 3 3 3 3 4 6% 55%	109347
Transparency	Day	33% 6% 10% 24% 21% 6%	112832
	Night	30% 5% 9% 22% 24% 10%	113757
Seeing	Day	12% 7% 22% 28% 23% 7%	15464
	Night	13% 7% 27% 34% 17% 2	25467

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	14% 7% 2 6% 3 3 2 2 4 5% 51%	4077
	11th to 20th	Day	9% 5% 1 3 2 3 2 2 4 6% 63%	4080
	21st to end	Day	22% 9% 3 6% 2 2 2 2 3 3 46%	4488
February	1st to 10th	Day	19% 7% 2 6% 4 4 3 3 4 4 44%	1802
	11th to 20th	Day	19% 7% 2 5% 4 3 3 2 4 5% 44%	1849
	21st to end	Day	22% 7% 2 4 3 2 2 2 3 4 49%	1638
March	1st to 10th	Day	16% 7% 2 5% 3 3 3 3 4 7% 47%	3436
	11th to 20th	Day	18% 6% 2 6% 5% 4 4 3 4 6% 40%	3480
	21st to end	Day	16% 8% 3 5% 4 4 4 4 5% 7% 40%	3814
April	1st to 10th	Day	13% 6% 3 7% 4 3 4 3 5% 6% 45%	2090
	11th to 20th	Day	14% 7% 2 6% 4 3 4 4 5% 6% 44%	2212
	21st to end	Day	14% 4 2 5% 5% 4 5% 4 6% 7% 46%	2348
May	1st to 10th	Day	19% 7% 2 7% 4 4 4 4 4 5% 38%	4082
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 47%	4082
	21st to end	Day	17% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4477
June	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 4 6% 8% 48%	2470
	11th to 20th	Day	5% 5% 1 5% 5% 4 5% 5% 6% 10% 49%	2470
	21st to end	Day	5% 3 1 4 4 4 5% 4 6% 8% 54%	2470
July	1st to 10th	Day	7% 4 2 6% 4 4 5% 4 6% 8% 49%	4120
	11th to 20th	Day	3 2 1 3 3 3 4 4 6% 9% 60%	4120
	21st to end	Day	7% 6% 2 8% 5% 5% 5% 5% 8% 10% 40%	4465
August	1st to 10th	Day	1 1 1 3 2 3 4 3 5% 8% 69%	4104
	11th to 20th	Day	4 2 1 3 3 3 4 4 8% 9% 58%	4041
	21st to end	Day	3 3 1 4 4 4 5% 5% 7% 11% 53%	4143
September	1st to 10th	Day	9% 5% 1 6% 3 4 4 3 5% 6% 53%	2090
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 5% 7% 48%	2090
	21st to end	Day	7% 4 1 4 3 3 3 4 6% 6% 59%	2090
October	1st to 10th	Day	6% 3 1 5% 3 3 3 3 5% 6% 62%	1995
	11th to 20th	Day	13% 4 1 3 3 3 2 3 4 6% 59%	1900
	21st to end	Day	15% 5% 2 3 2 3 2 2 3 4 57%	2090
November	1st to 10th	Day	13% 6% 2 3 3 3 4 3 3 6% 55%	1958
	11th to 20th	Day	9% 4 2 5% 4 3 3 3 3 6% 59%	1925
	21st to end	Day	14% 7% 2 4 3 3 3 2 3 5% 54%	1800
December	1st to 10th	Day	18% 5% 1 5% 3 2 3 3 3 6% 51%	2940
	11th to 20th	Day	19% 9% 2 6% 4 3 3 2 3 4 45%	3391
	21st to end	Day	19% 8% 3 5% 3 2 3 2 4 5% 46%	4488
January	1st to 10th	Night	15% 5% 2 4 3 3 3 2 4 5% 55%	5888
	11th to 20th	Night	8% 4 1 3 2 1 2 2 3 5% 69%	5900
	21st to end	Night	23% 8% 2 5% 3 2 2 2 3 4 46%	6490
February	1st to 10th	Night	15% 6% 2 6% 3 3 3 2 4 4 51%	2505
	11th to 20th	Night	16% 7% 2 5% 4 3 3 2 4 5% 48%	2218
	21st to end	Night	19% 5% 2 4 2 3 2 2 4 5% 51%	1813
March	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 5% 6% 43%	3419
	11th to 20th	Night	15% 6% 2 6% 4 4 3 3 5% 5% 45%	3480
	21st to end	Night	15% 6% 2 5% 4 3 4 3 4 6% 47%	3817
April	1st to 10th	Night	11% 5% 1 5% 4 3 3 3 5% 8% 52%	2090
	11th to 20th	Night	14% 5% 2 5% 3 3 4 4 5% 5% 50%	1915
	21st to end	Night	12% 5% 2 4 4 2 3 3 5% 7% 53%	1827
May	1st to 10th	Night	18% 9% 2 6% 4 3 4 3 5% 7% 38%	2823
	11th to 20th	Night	12% 6% 2 5% 4 4 3 3 4 7% 50%	2823
	21st to end	Night	11% 6% 2 5% 5% 4 5% 4 6% 8% 45%	3090
June	1st to 10th	Night	5% 3 2 4 4 3 4 3 7% 8% 57%	1710
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 8% 62%	1710
	21st to end	Night	3 2 1 4 3 3 4 4 6% 11% 59%	1710
July	1st to 10th	Night	4 4 1 4 3 3 4 4 7% 12% 54%	2850
	11th to 20th	Night	3 2 1 3 2 2 3 3 5% 9% 66%	2850
	21st to end	Night	4 4 1 5% 5% 5% 5% 5% 7% 9% 51%	3098
August	1st to 10th	Night	1 1 1 2 1 2 2 3 4 10% 74%	2836
	11th to 20th	Night	4 2 1 2 2 2 3 3 5% 10% 66%	2798
	21st to end	Night	2 3 1 3 3 3 4 5% 7% 9% 60%	3495
September	1st to 10th	Night	8% 4 2 4 3 3 3 4 5% 8% 56%	2090
	11th to 20th	Night	11% 4 1 4 3 3 4 3 5% 6% 55%	2090
	21st to end	Night	6% 2 1 4 3 3 3 3 5% 6% 63%	2090
October	1st to 10th	Night	6% 3 1 3 3 2 2 3 5% 6% 65%	2166
	11th to 20th	Night	12% 4 1 3 2 2 2 3 4 6% 62%	2280
	21st to end	Night	16% 4 2 3 2 2 2 2 2 4 61%	2508
November	1st to 10th	Night	12% 5% 2 4 2 3 3 3 3 4 59%	2340
	11th to 20th	Night	8% 5% 1 4 3 3 3 3 4 6% 59%	2472
	21st to end	Night	15% 6% 1 5% 3 3 2 3 3 5% 55%	2600
December	1st to 10th	Night	16% 7% 2 5% 2 3 3 2 4 4 54%	4250
	11th to 20th	Night	17% 7% 2 6% 4 3 2 2 3 4 50%	4816
	21st to end	Night	15% 8% 2 5% 3 3 3 2 3 5% 51%	6490

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	36% 4 7% 28% 23% 3	4078
	11th to 20th	Day	25% 3 7% 23% 35% 6%	4080
	21st to end	Day	46% 3 4 14% 22% 12%	4488
February	1st to 10th	Day	44% 4 6% 18% 20% 8%	1802
	11th to 20th	Day	43% 4 6% 21% 18% 8%	1859
	21st to end	Day	41% 3 5% 15% 26% 10%	1638
March	1st to 10th	Day	36% 6% 9% 17% 24% 9%	3436
	11th to 20th	Day	43% 7% 9% 21% 16% 3	3480
	21st to end	Day	43% 7% 9% 19% 18% 3	3814
April	1st to 10th	Day	38% 5% 10% 20% 18% 9%	2090
	11th to 20th	Day	40% 6% 9% 17% 20% 8%	2212
	21st to end	Day	37% 7% 9% 21% 23% 4	2348
May	1st to 10th	Day	45% 8% 8% 22% 12% 3	4120
	11th to 20th	Day	38% 6% 9% 25% 21% 1	4086
	21st to end	Day	46% 9% 12% 18% 11% 4	4489
June	1st to 10th	Day	30% 9% 15% 26% 17% 2	2470
	11th to 20th	Day	28% 8% 15% 26% 19% 4	2470
	21st to end	Day	25% 7% 14% 29% 22% 3	2470
July	1st to 10th	Day	30% 8% 18% 33% 10%	4056
	11th to 20th	Day	18% 6% 13% 40% 22% 1	4051
	21st to end	Day	35% 7% 15% 31% 11%	4325
August	1st to 10th	Day	13% 5% 13% 30% 32% 6%	4090
	11th to 20th	Day	19% 6% 18% 39% 16% 2	4080
	21st to end	Day	22% 10% 20% 34% 12% 2	4142
September	1st to 10th	Day	30% 7% 10% 22% 19% 11%	2090
	11th to 20th	Day	34% 9% 11% 18% 22% 6%	2090
	21st to end	Day	24% 7% 10% 21% 28% 11%	2090
October	1st to 10th	Day	14% 3 7% 13% 33% 31%	3320
	11th to 20th	Day	19% 2 4 20% 33% 21%	3140
	21st to end	Day	24% 4 6% 30% 26% 9%	3428
November	1st to 10th	Day	33% 4 7% 23% 24% 9%	1958
	11th to 20th	Day	28% 4 9% 19% 28% 12%	1925
	21st to end	Day	35% 3 6% 20% 27% 9%	1800
December	1st to 10th	Day	36% 4 5% 28% 23% 4	2940
	11th to 20th	Day	43% 4 4 14% 25% 9%	3389
	21st to end	Day	41% 4 6% 22% 21% 6%	4488
January	1st to 10th	Night	33% 4 6% 26% 26% 5%	5888
	11th to 20th	Night	20% 3 7% 19% 35% 15%	5900
	21st to end	Night	44% 3 4 13% 22% 13%	6490
February	1st to 10th	Night	37% 4 8% 18% 22% 11%	2505
	11th to 20th	Night	39% 4 7% 17% 24% 9%	2218
	21st to end	Night	37% 5% 7% 15% 22% 15%	1813
March	1st to 10th	Night	42% 7% 7% 14% 19% 11%	3419
	11th to 20th	Night	38% 6% 9% 19% 20% 7%	3480
	21st to end	Night	38% 5% 9% 18% 26% 4	3817
April	1st to 10th	Night	31% 5% 12% 20% 18% 13%	2090
	11th to 20th	Night	34% 6% 9% 20% 18% 13%	1915
	21st to end	Night	30% 5% 11% 21% 26% 5%	1827
May	1st to 10th	Night	43% 9% 10% 19% 13% 6%	2850
	11th to 20th	Night	33% 7% 14% 21% 23% 1	2824
	21st to end	Night	33% 10% 15% 23% 12% 6%	3099
June	1st to 10th	Night	22% 8% 17% 30% 20% 4	1710
	11th to 20th	Night	20% 6% 13% 34% 21% 7%	1710
	21st to end	Night	20% 7% 13% 30% 25% 5%	1710
July	1st to 10th	Night	21% 8% 20% 36% 14% 1	2805
	11th to 20th	Night	15% 4 12% 43% 24% 3	2796
	21st to end	Night	27% 7% 17% 34% 14% 1	2999
August	1st to 10th	Night	8% 4 12% 30% 39% 7%	2826
	11th to 20th	Night	15% 4 14% 41% 21% 5%	2825
	21st to end	Night	18% 8% 20% 32% 20% 2	3495
September	1st to 10th	Night	26% 6% 12% 23% 23% 11%	2090
	11th to 20th	Night	29% 5% 11% 22% 22% 10%	2090
	21st to end	Night	21% 4 9% 21% 28% 16%	2090
October	1st to 10th	Night	12% 2 6% 15% 28% 37%	3608
	11th to 20th	Night	17% 2 4 16% 34% 26%	3779
	21st to end	Night	24% 3 4 27% 26% 16%	4120
November	1st to 10th	Night	29% 5% 7% 20% 25% 14%	2340
	11th to 20th	Night	27% 4 7% 19% 27% 16%	2472
	21st to end	Night	34% 4 8% 17% 27% 11%	2600
December	1st to 10th	Night	36% 3 6% 21% 26% 8%	4250
	11th to 20th	Night	41% 3 5% 14% 24% 14%	4817
	21st to end	Night	38% 3 6% 19% 26% 8%	6490

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	22% 12% 37% 23% 7%	300
	11th to 20th	Day	18% 18% 38% 20% 5% 2	300
	21st to end	Day	21% 14% 36% 22% 7% 1	330
February	1st to 10th	Day	22% 15% 35% 19% 7% 1	285
	11th to 20th	Day	23% 16% 40% 16% 5%	270
	21st to end	Day	30% 16% 40% 12% 2	225
March	1st to 10th	Day	20% 14% 36% 24% 4	270
	11th to 20th	Day	20% 19% 37% 18% 4 1	270
	21st to end	Day	19% 13% 41% 20% 6%	297
April	1st to 10th	Day	14% 19% 39% 23% 4 1	270
	11th to 20th	Day	19% 15% 32% 24% 10%	410
	21st to end	Day	15% 14% 36% 24% 9% 2	528
May	1st to 10th	Day	15% 9% 32% 34% 8% 1	653
	11th to 20th	Day	16% 6% 27% 33% 16% 3	675
	21st to end	Day	13% 8% 26% 31% 18% 4	734
June	1st to 10th	Day	6% 2 13% 40% 30% 9%	680
	11th to 20th	Day	7% 2 15% 41% 27% 8%	680
	21st to end	Day	5% 1 12% 36% 33% 12%	680
July	1st to 10th	Day	5% 2 11% 32% 37% 14%	671
	11th to 20th	Day	2 1 6% 33% 45% 13%	668
	21st to end	Day	5% 1 4 27% 47% 15%	739
August	1st to 10th	Day	3 5% 29% 49% 13%	676
	11th to 20th	Day	9% 2 6% 30% 42% 12%	665
	21st to end	Day	5% 2 6% 25% 38% 25%	528
September	1st to 10th	Day	9% 1 3 20% 42% 26%	300
	11th to 20th	Day	4 1 9% 25% 38% 23%	300
	21st to end	Day	11% 2 10% 26% 35% 16%	300
October	1st to 10th	Day	2 1 18% 32% 36% 11%	300
	11th to 20th	Day	11% 4 26% 35% 20% 3	300
	21st to end	Day	22% 10% 23% 25% 19% 2	330
November	1st to 10th	Day	18% 8% 31% 25% 14% 4	300
	11th to 20th	Day	12% 9% 30% 33% 13% 2	300
	21st to end	Day	17% 13% 34% 25% 10% 1	300
December	1st to 10th	Day	19% 11% 34% 24% 11% 1	300
	11th to 20th	Day	21% 13% 36% 23% 6%	300
	21st to end	Day	20% 13% 39% 22% 5% 1	330
January	1st to 10th	Night	16% 11% 35% 31% 7%	1000
	11th to 20th	Night	17% 15% 34% 29% 5% 1	1000
	21st to end	Night	17% 10% 38% 30% 5%	1100
February	1st to 10th	Night	17% 12% 39% 27% 5%	945
	11th to 20th	Night	22% 12% 38% 26% 3	744
	21st to end	Night	24% 15% 37% 21% 3	557
March	1st to 10th	Night	18% 11% 36% 28% 6%	570
	11th to 20th	Night	17% 11% 37% 29% 5%	570
	21st to end	Night	14% 13% 36% 31% 5%	627
April	1st to 10th	Night	12% 9% 44% 28% 6%	570
	11th to 20th	Night	17% 11% 38% 26% 8%	563
	21st to end	Night	13% 8% 40% 29% 9% 1	570
May	1st to 10th	Night	10% 8% 40% 32% 9% 1	570
	11th to 20th	Night	12% 3 32% 35% 17% 1	561
	21st to end	Night	8% 4 28% 41% 17% 2	617
June	1st to 10th	Night	5% 3 16% 42% 32% 2	570
	11th to 20th	Night	5% 1 19% 52% 22% 1	570
	21st to end	Night	4 1 14% 40% 37% 5%	570
July	1st to 10th	Night	3 1 11% 40% 40% 5%	555
	11th to 20th	Night	3 7% 39% 47% 4	552
	21st to end	Night	3 1 5% 41% 46% 4	624
August	1st to 10th	Night	2 4 43% 47% 4	567
	11th to 20th	Night	7% 1 5% 37% 44% 5%	564
	21st to end	Night	4 1 4 38% 46% 7%	627
September	1st to 10th	Night	9% 1 7% 36% 41% 6%	570
	11th to 20th	Night	12% 1 8% 35% 40% 3	570
	21st to end	Night	6% 1 14% 39% 34% 5%	570
October	1st to 10th	Night	8% 1 20% 41% 28% 3	646
	11th to 20th	Night	14% 2 26% 40% 16% 2	760
	21st to end	Night	17% 8% 29% 29% 16% 1	836
November	1st to 10th	Night	13% 4 28% 39% 16% 1	780
	11th to 20th	Night	11% 10% 31% 37% 11% 1	872
	21st to end	Night	18% 11% 32% 30% 10%	1000
December	1st to 10th	Night	16% 10% 35% 32% 7%	1000
	11th to 20th	Night	21% 9% 34% 31% 6%	1000
	21st to end	Night	19% 9% 36% 29% 7%	1100

Page generated at 2025-02-03 02:05:56. Version ac07

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