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 2025-06-10.

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	7% 7% 2 4 2 3 3 2 4 5% 62%	123628
	Night	8% 9% 2 4 2 2 3 3 4 5% 58%	123476
Transparency	Day	25% 4 8% 19% 25% 19%	123377
	Night	29% 5% 9% 20% 23% 14%	123314
Seeing	Day	15% 14% 27% 24% 15% 5%	15742
	Night	13% 6% 17% 38% 23% 2	25058

By Month

Percentage Cloud Cover SW (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	9% 16% 2 5% 4 4 4 3 5% 7% 41%	3639
	11th to 20th	Day	12% 11% 2 5% 3 2 3 2 3 3 54%	3805
	21st to end	Day	13% 12% 3 6% 3 3 3 2 3 4 47%	4510
February	1st to 10th	Day	15% 10% 2 5% 3 3 4 3 5% 7% 44%	1800
	11th to 20th	Day	8% 14% 3 5% 3 3 3 3 5% 8% 45%	1864
	21st to end	Day	8% 18% 2 4 3 3 3 2 4 7% 45%	1650
March	1st to 10th	Day	11% 22% 5% 7% 3 3 3 3 4 5% 34%	4600
	11th to 20th	Day	9% 16% 2 5% 3 3 3 2 4 6% 46%	5000
	21st to end	Day	11% 20% 3 8% 4 3 3 3 4 6% 36%	5738
April	1st to 10th	Day	10% 14% 2 5% 4 3 4 3 6% 7% 43%	2400
	11th to 20th	Day	9% 10% 2 4 3 3 4 3 5% 6% 52%	2369
	21st to end	Day	9% 6% 2 3 3 4 3 3 5% 6% 55%	2400
May	1st to 10th	Day	5% 5% 1 3 2 2 2 2 3 5% 69%	5805
	11th to 20th	Day	4 4 1 4 2 3 2 2 4 5% 69%	6277
	21st to end	Day	4 3 1 3 2 2 2 2 3 5% 74%	6902
June	1st to 10th	Day	6% 4 2 3 3 3 4 4 5% 7% 59%	2789
	11th to 20th	Day	3 2 1 3 2 3 2 2 4 4 73%	2660
	21st to end	Day	3 1 1 2 1 1 2 2 3 4 81%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 3 90%	4420
	11th to 20th	Day	2 1 1 2 1 2 2 1 2 3 83%	4420
	21st to end	Day	1 1 1 1 1 1 1 2 3 86%	4619
August	1st to 10th	Day	2 2 1 3 2 2 2 2 4 5% 75%	4091
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 89%	3817
	21st to end	Day	2 1 1 1 1 1 1 1 2 2 88%	4180
September	1st to 10th	Day	2 1 1 1 1 2 2 2 4 84%	2280
	11th to 20th	Day	3 2 1 3 2 3 2 3 4 5% 73%	2280
	21st to end	Day	4 2 1 2 2 2 2 2 3 6% 75%	2054
October	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 75%	3180
	11th to 20th	Day	7% 3 1 3 2 2 2 2 4 6% 68%	3161
	21st to end	Day	6% 5% 2 4 2 3 3 4 5% 6% 60%	3427
November	1st to 10th	Day	10% 7% 1 4 3 3 3 4 5% 7% 52%	1764
	11th to 20th	Day	10% 6% 2 5% 4 3 4 5% 6% 7% 48%	1800
	21st to end	Day	8% 9% 2 4 3 4 3 4 4 6% 52%	1615
December	1st to 10th	Day	8% 6% 1 3 2 3 3 3 6% 7% 57%	2620
	11th to 20th	Day	19% 14% 2 6% 4 4 5% 4 6% 7% 28%	3028
	21st to end	Day	17% 11% 3 6% 4 4 5% 4 6% 8% 32%	4004
January	1st to 10th	Night	9% 13% 2 5% 3 4 5% 3 6% 8% 41%	6306
	11th to 20th	Night	13% 10% 2 5% 3 2 3 2 3 5% 53%	6161
	21st to end	Night	13% 12% 2 5% 3 3 4 3 3 5% 48%	6468
February	1st to 10th	Night	15% 11% 2 4 3 2 3 2 5% 7% 47%	2600
	11th to 20th	Night	10% 13% 2 3 3 3 3 3 6% 8% 47%	2423
	21st to end	Night	8% 16% 3 5% 3 3 3 3 4 5% 48%	1980
March	1st to 10th	Night	9% 24% 4 6% 4 3 3 3 4 6% 35%	5291
	11th to 20th	Night	12% 20% 2 3 2 2 2 2 3 5% 47%	5000
	21st to end	Night	10% 21% 3 7% 4 4 4 3 5% 6% 33%	5236
April	1st to 10th	Night	8% 11% 2 4 4 4 4 3 6% 7% 46%	2000
	11th to 20th	Night	10% 10% 2 3 3 3 3 3 4 7% 53%	1979
	21st to end	Night	8% 8% 1 3 3 2 3 3 5% 7% 57%	2000
May	1st to 10th	Night	5% 7% 1 4 2 2 2 2 3 5% 67%	4174
	11th to 20th	Night	4 3 1 3 3 3 3 2 4 4 70%	3616
	21st to end	Night	4 3 1 3 2 2 2 2 3 4 74%	3972
June	1st to 10th	Night	6% 6% 1 3 2 3 3 3 5% 7% 61%	1595
	11th to 20th	Night	3 3 1 2 1 3 3 2 3 5% 73%	1520
	21st to end	Night	3 2 1 2 2 2 2 3 3 3 78%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 2 90%	2540
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 2 84%	2540
	21st to end	Night	1 1 1 2 1 1 1 2 3 4 85%	2936
August	1st to 10th	Night	3 3 1 3 1 2 2 2 5% 5% 72%	2848
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 88%	3027
	21st to end	Night	2 1 1 1 1 1 1 1 1 2 87%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 2 2 3 84%	1900
	11th to 20th	Night	4 2 1 2 2 2 2 2 3 5% 75%	1900
	21st to end	Night	3 2 1 2 1 2 2 2 3 5% 77%	2123
October	1st to 10th	Night	3 2 1 3 2 3 2 2 2 3 78%	3800
	11th to 20th	Night	4 3 1 3 2 2 2 2 3 4 74%	3777
	21st to end	Night	8% 4 1 2 2 3 3 3 4 6% 64%	4141
November	1st to 10th	Night	11% 9% 2 4 3 2 3 4 6% 6% 51%	2535
	11th to 20th	Night	10% 6% 1 4 3 4 3 4 6% 10% 50%	2600
	21st to end	Night	9% 8% 1 5% 3 3 3 3 5% 6% 54%	2782
December	1st to 10th	Night	8% 6% 1 3 2 2 2 2 4 6% 63%	4560
	11th to 20th	Night	17% 17% 2 5% 3 4 5% 4 6% 8% 29%	5176
	21st to end	Night	21% 13% 3 5% 3 3 4 3 5% 6% 33%	6952

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	42% 7% 13% 25% 13% 1	3639
	11th to 20th	Day	37% 4 8% 23% 20% 9%	3805
	21st to end	Day	41% 3 8% 14% 24% 9%	4510
February	1st to 10th	Day	41% 4 11% 23% 16% 5%	1800
	11th to 20th	Day	40% 5% 9% 25% 18% 3	1873
	21st to end	Day	41% 4 10% 25% 15% 5%	1650
March	1st to 10th	Day	52% 5% 7% 16% 16% 4	4600
	11th to 20th	Day	39% 5% 10% 28% 16% 2	5000
	21st to end	Day	48% 6% 12% 22% 10% 1	5738
April	1st to 10th	Day	40% 5% 14% 23% 16% 2	2400
	11th to 20th	Day	33% 5% 12% 25% 20% 6%	2372
	21st to end	Day	30% 5% 15% 26% 22% 3	2400
May	1st to 10th	Day	19% 3 7% 22% 38% 9%	5805
	11th to 20th	Day	18% 4 10% 21% 37% 10%	6280
	21st to end	Day	15% 3 7% 27% 41% 8%	6904
June	1st to 10th	Day	24% 5% 10% 22% 30% 9%	2789
	11th to 20th	Day	15% 3 7% 21% 36% 18%	2660
	21st to end	Day	10% 2 4 14% 36% 35%	2660
July	1st to 10th	Day	4 1 2 6% 15% 72%	4351
	11th to 20th	Day	8% 2 2 8% 17% 63%	4345
	21st to end	Day	6% 1 2 6% 28% 56%	4473
August	1st to 10th	Day	12% 2 3 8% 24% 51%	4076
	11th to 20th	Day	5% 1 2 7% 39% 47%	3855
	21st to end	Day	6% 1 2 13% 40% 37%	4179
September	1st to 10th	Day	7% 1 2 9% 30% 50%	2280
	11th to 20th	Day	14% 2 7% 20% 32% 24%	2280
	21st to end	Day	13% 2 5% 21% 33% 26%	2054
October	1st to 10th	Day	15% 2 4 14% 31% 33%	3180
	11th to 20th	Day	20% 3 6% 21% 39% 11%	3161
	21st to end	Day	24% 4 8% 29% 25% 10%	3427
November	1st to 10th	Day	31% 6% 11% 21% 22% 9%	1764
	11th to 20th	Day	35% 5% 13% 25% 20% 3	1800
	21st to end	Day	33% 4 11% 22% 23% 7%	1615
December	1st to 10th	Day	26% 4 7% 27% 29% 6%	2620
	11th to 20th	Day	52% 7% 10% 18% 12%	3028
	21st to end	Day	47% 8% 16% 22% 7% 1	4004
January	1st to 10th	Night	39% 8% 15% 24% 13% 1	6306
	11th to 20th	Night	34% 6% 9% 20% 24% 7%	6161
	21st to end	Night	41% 4 8% 13% 27% 8%	6468
February	1st to 10th	Night	39% 5% 9% 25% 17% 6%	2600
	11th to 20th	Night	38% 5% 11% 26% 19% 2	2425
	21st to end	Night	39% 5% 11% 22% 16% 6%	1980
March	1st to 10th	Night	49% 6% 8% 20% 11% 5%	5291
	11th to 20th	Night	41% 5% 10% 22% 21% 2	5000
	21st to end	Night	50% 8% 14% 20% 7% 1	5236
April	1st to 10th	Night	38% 6% 15% 23% 15% 3	2000
	11th to 20th	Night	33% 5% 14% 24% 18% 6%	1979
	21st to end	Night	27% 6% 14% 33% 17% 3	2000
May	1st to 10th	Night	22% 4 8% 25% 33% 7%	4171
	11th to 20th	Night	20% 4 9% 25% 33% 10%	3616
	21st to end	Night	15% 4 8% 32% 35% 5%	3972
June	1st to 10th	Night	23% 7% 13% 26% 25% 6%	1595
	11th to 20th	Night	15% 2 11% 22% 35% 14%	1520
	21st to end	Night	12% 3 5% 17% 33% 30%	1520
July	1st to 10th	Night	5% 1 2 6% 18% 69%	2500
	11th to 20th	Night	9% 2 2 8% 16% 63%	2492
	21st to end	Night	7% 2 2 7% 31% 52%	2844
August	1st to 10th	Night	13% 2 3 9% 25% 47%	2839
	11th to 20th	Night	5% 1 2 10% 42% 40%	3055
	21st to end	Night	8% 2 3 14% 41% 33%	3498
September	1st to 10th	Night	9% 2 2 9% 31% 47%	1900
	11th to 20th	Night	14% 3 7% 19% 34% 23%	1900
	21st to end	Night	12% 2 6% 22% 33% 25%	2123
October	1st to 10th	Night	15% 2 5% 12% 31% 35%	3800
	11th to 20th	Night	15% 3 6% 27% 37% 11%	3777
	21st to end	Night	22% 4 9% 29% 26% 12%	4141
November	1st to 10th	Night	33% 5% 11% 21% 20% 9%	2535
	11th to 20th	Night	31% 6% 13% 26% 21% 4	2600
	21st to end	Night	31% 4 11% 24% 22% 8%	2782
December	1st to 10th	Night	24% 5% 8% 27% 26% 10%	4560
	11th to 20th	Night	53% 6% 8% 21% 12% 1	5176
	21st to end	Night	50% 6% 15% 18% 10% 1	6952

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	36% 10% 21% 23% 11% 1	200
	11th to 20th	Day	26% 12% 21% 25% 14% 2	274
	21st to end	Day	23% 15% 23% 24% 13% 3	440
February	1st to 10th	Day	31% 12% 23% 23% 10% 1	400
	11th to 20th	Day	26% 17% 28% 20% 7% 1	450
	21st to end	Day	20% 18% 28% 26% 8%	414
March	1st to 10th	Day	33% 23% 23% 14% 6% 2	500
	11th to 20th	Day	31% 15% 24% 18% 10% 1	500
	21st to end	Day	27% 22% 28% 14% 8% 1	550
April	1st to 10th	Day	24% 20% 27% 20% 8% 1	500
	11th to 20th	Day	24% 21% 24% 20% 9% 2	492
	21st to end	Day	18% 18% 28% 19% 13% 4	500
May	1st to 10th	Day	16% 24% 27% 21% 9% 3	503
	11th to 20th	Day	18% 16% 29% 21% 10% 6%	528
	21st to end	Day	13% 15% 26% 26% 14% 6%	573
June	1st to 10th	Day	11% 15% 28% 22% 16% 8%	527
	11th to 20th	Day	9% 19% 32% 22% 13% 4	490
	21st to end	Day	3 15% 28% 29% 16% 8%	490
July	1st to 10th	Day	3 7% 38% 27% 15% 10%	486
	11th to 20th	Day	1 9% 35% 29% 17% 10%	484
	21st to end	Day	2 9% 34% 26% 18% 11%	531
August	1st to 10th	Day	4 10% 32% 25% 18% 11%	487
	11th to 20th	Day	3 10% 29% 29% 19% 10%	477
	21st to end	Day	4 11% 29% 31% 19% 6%	539
September	1st to 10th	Day	4 11% 29% 32% 20% 5%	490
	11th to 20th	Day	7% 15% 25% 28% 21% 4	490
	21st to end	Day	6% 14% 27% 33% 16% 4	490
October	1st to 10th	Day	6% 16% 27% 24% 22% 6%	490
	11th to 20th	Day	12% 12% 22% 27% 23% 5%	490
	21st to end	Day	16% 12% 23% 27% 17% 4	530
November	1st to 10th	Day	18% 11% 17% 29% 21% 5%	300
	11th to 20th	Day	13% 8% 26% 28% 20% 6%	300
	21st to end	Day	18% 13% 18% 26% 20% 5%	207
December	1st to 10th	Day	22% 9% 19% 25% 17% 9%	200
	11th to 20th	Day	21% 13% 22% 24% 17% 5%	200
	21st to end	Day	27% 11% 20% 25% 15% 2	220
January	1st to 10th	Night	19% 8% 24% 36% 12% 1	800
	11th to 20th	Night	16% 7% 25% 40% 10% 1	800
	21st to end	Night	20% 6% 25% 33% 15% 1	880
February	1st to 10th	Night	22% 6% 22% 38% 11% 1	800
	11th to 20th	Night	18% 8% 23% 37% 13% 1	784
	21st to end	Night	20% 9% 20% 41% 9% 1	660
March	1st to 10th	Night	24% 13% 20% 31% 10% 2	800
	11th to 20th	Night	23% 8% 20% 29% 20% 1	800
	21st to end	Night	23% 13% 20% 29% 14% 1	880
April	1st to 10th	Night	16% 9% 22% 38% 14% 1	800
	11th to 20th	Night	17% 10% 22% 33% 16% 3	791
	21st to end	Night	13% 9% 19% 37% 21% 3	800
May	1st to 10th	Night	12% 12% 22% 33% 20% 1	635
	11th to 20th	Night	11% 5% 15% 41% 25% 3	394
	21st to end	Night	12% 4 15% 31% 34% 4	433
June	1st to 10th	Night	8% 4 15% 35% 36% 3	399
	11th to 20th	Night	4 4 16% 42% 31% 2	380
	21st to end	Night	4 2 10% 44% 38% 2	380
July	1st to 10th	Night	2 1 4 44% 46% 3	370
	11th to 20th	Night	1 2 6% 47% 43% 1	368
	21st to end	Night	1 1 2 37% 55% 4	516
August	1st to 10th	Night	2 1 3 42% 48% 5%	567
	11th to 20th	Night	2 3 9% 42% 40% 5%	689
	21st to end	Night	1 1 9% 46% 39% 3	836
September	1st to 10th	Night	2 2 10% 46% 35% 4	760
	11th to 20th	Night	4 4 10% 37% 38% 7%	760
	21st to end	Night	4 4 12% 44% 28% 8%	760
October	1st to 10th	Night	7% 6% 15% 39% 28% 4	760
	11th to 20th	Night	8% 5% 13% 39% 31% 4	760
	21st to end	Night	11% 5% 17% 36% 26% 5%	836
November	1st to 10th	Night	15% 6% 18% 35% 23% 3	780
	11th to 20th	Night	14% 6% 21% 43% 15% 1	800
	21st to end	Night	15% 6% 22% 38% 19% 1	800
December	1st to 10th	Night	21% 6% 18% 38% 16% 1	800
	11th to 20th	Night	25% 6% 19% 36% 14% 1	800
	21st to end	Night	25% 9% 25% 33% 8%	880

Page generated at 2025-06-07 07:28:17. Version ac07

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