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 2024-11-25.

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 4 4 5% 7% 44%	100674
	Night	13% 6% 2 5% 4 4 4 3 5% 7% 48%	98829
Transparency	Day	37% 6% 10% 21% 19% 6%	104320
	Night	34% 5% 10% 21% 21% 9%	103324
Seeing	Day	13% 7% 19% 24% 24% 13%	15253
	Night	14% 5% 22% 32% 22% 4	25019

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	18% 12% 3 6% 3 2 2 2 4 4 44%	2847
	11th to 20th	Day	23% 7% 3 5% 5% 2 2 2 3 5% 43%	2850
	21st to end	Day	21% 8% 2 6% 4 3 3 2 3 4 44%	3135
February	1st to 10th	Day	19% 8% 2 6% 4 3 3 3 5% 5% 41%	1809
	11th to 20th	Day	22% 8% 3 6% 4 3 3 3 4 4 40%	1848
	21st to end	Day	20% 9% 3 7% 4 3 3 3 4 5% 38%	1570
March	1st to 10th	Day	20% 11% 3 9% 5% 5% 4 2 4 5% 32%	3361
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 3 5% 7% 39%	3480
	21st to end	Day	13% 8% 3 9% 5% 4 4 3 4 5% 43%	3931
April	1st to 10th	Day	13% 7% 2 6% 4 5% 3 4 6% 6% 43%	2280
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 6% 6% 43%	2254
	21st to end	Day	11% 5% 3 5% 5% 4 4 4 5% 8% 46%	2280
May	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 4 6% 7% 42%	3765
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 8% 42%	3764
	21st to end	Day	11% 5% 2 7% 5% 6% 6% 5% 7% 9% 37%	4494
June	1st to 10th	Day	8% 5% 3 6% 5% 5% 6% 5% 7% 9% 42%	2660
	11th to 20th	Day	6% 4 2 5% 5% 5% 6% 5% 6% 9% 47%	2660
	21st to end	Day	6% 4 2 4 5% 5% 5% 5% 7% 10% 48%	2598
July	1st to 10th	Day	6% 6% 3 7% 7% 7% 7% 5% 8% 9% 36%	4120
	11th to 20th	Day	9% 6% 2 6% 5% 6% 6% 5% 9% 10% 35%	4120
	21st to end	Day	14% 9% 3 8% 5% 5% 5% 5% 7% 9% 30%	4465
August	1st to 10th	Day	3 2 1 3 3 4 4 4 5% 7% 65%	3853
	11th to 20th	Day	5% 3 2 5% 4 4 6% 5% 8% 11% 46%	3729
	21st to end	Day	8% 4 2 6% 5% 4 4 4 6% 8% 48%	4180
September	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 7% 45%	2280
	11th to 20th	Day	12% 6% 2 6% 3 5% 4 3 4 7% 46%	2280
	21st to end	Day	10% 4 1 4 4 4 5% 3 5% 6% 55%	2062
October	1st to 10th	Day	8% 3 1 4 3 4 3 3 4 6% 62%	1900
	11th to 20th	Day	11% 4 2 5% 2 3 3 3 4 6% 58%	1900
	21st to end	Day	15% 5% 2 4 3 3 3 3 4 5% 54%	2090
November	1st to 10th	Day	13% 5% 2 4 4 3 3 2 4 6% 56%	1958
	11th to 20th	Day	11% 5% 2 4 4 4 4 3 4 5% 55%	1843
	21st to end	Day	18% 7% 3 5% 3 3 3 2 4 6% 45%	1746
December	1st to 10th	Day	18% 8% 3 6% 5% 4 3 3 4 6% 39%	1687
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 3 4 4 42%	1918
	21st to end	Day	14% 6% 2 7% 5% 4 5% 4 4 7% 42%	2957
January	1st to 10th	Night	18% 8% 2 6% 3 4 3 2 4 5% 45%	4108
	11th to 20th	Night	20% 6% 2 5% 4 3 3 2 3 5% 47%	4120
	21st to end	Night	24% 7% 2 4 3 3 2 2 3 4 46%	4532
February	1st to 10th	Night	19% 8% 3 6% 4 4 3 3 4 5% 42%	2369
	11th to 20th	Night	20% 8% 3 5% 3 3 3 3 4 5% 45%	2218
	21st to end	Night	21% 8% 3 6% 4 3 3 3 3 4 43%	1884
March	1st to 10th	Night	18% 8% 3 6% 5% 4 4 2 5% 6% 39%	3520
	11th to 20th	Night	16% 6% 2 6% 3 3 4 3 6% 7% 44%	3480
	21st to end	Night	15% 6% 2 7% 4 5% 4 4 5% 7% 42%	3698
April	1st to 10th	Night	12% 5% 2 5% 5% 4 4 3 6% 7% 48%	1900
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 6% 7% 47%	1875
	21st to end	Night	11% 4 2 5% 4 4 5% 3 4 6% 52%	1900
May	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 6% 8% 43%	3130
	11th to 20th	Night	15% 6% 2 5% 4 4 4 3 6% 8% 44%	3129
	21st to end	Night	12% 6% 2 6% 5% 4 5% 5% 8% 8% 40%	3058
June	1st to 10th	Night	5% 4 2 5% 5% 3 6% 5% 7% 11% 48%	1520
	11th to 20th	Night	3 3 1 4 3 4 4 5% 6% 11% 55%	1520
	21st to end	Night	5% 3 1 4 4 3 4 4 8% 10% 53%	1573
July	1st to 10th	Night	5% 5% 2 6% 5% 5% 6% 5% 7% 12% 42%	2850
	11th to 20th	Night	7% 5% 2 5% 4 4 6% 5% 8% 12% 43%	2850
	21st to end	Night	12% 9% 3 7% 4 4 4 4 5% 9% 40%	3098
August	1st to 10th	Night	2 2 1 3 2 3 3 3 4 8% 70%	3075
	11th to 20th	Night	5% 2 1 4 4 4 5% 5% 7% 12% 51%	3100
	21st to end	Night	6% 4 2 7% 5% 4 5% 4 6% 7% 50%	3476
September	1st to 10th	Night	9% 3 1 5% 4 4 4 5% 6% 8% 50%	1900
	11th to 20th	Night	9% 5% 2 6% 5% 4 4 3 5% 6% 51%	1900
	21st to end	Night	9% 4 1 4 3 2 3 3 5% 8% 57%	2095
October	1st to 10th	Night	7% 3 2 3 3 2 3 2 5% 6% 65%	2280
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 5% 59%	2280
	21st to end	Night	14% 5% 2 4 3 3 3 2 4 5% 56%	2508
November	1st to 10th	Night	12% 5% 2 4 3 3 3 2 4 6% 55%	2340
	11th to 20th	Night	12% 4 2 5% 3 3 3 3 4 6% 56%	2554
	21st to end	Night	13% 6% 2 5% 4 4 3 3 4 4 50%	2529
December	1st to 10th	Night	17% 8% 3 5% 4 4 3 2 5% 5% 44%	2489
	11th to 20th	Night	16% 7% 2 5% 4 4 3 3 4 5% 48%	3279
	21st to end	Night	16% 9% 2 5% 4 4 4 4 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	46% 2 5% 18% 26% 3	2848
	11th to 20th	Day	43% 4 11% 18% 21% 2	2850
	21st to end	Day	46% 3 6% 17% 23% 4	3135
February	1st to 10th	Day	45% 5% 6% 19% 17% 7%	1809
	11th to 20th	Day	48% 3 5% 19% 17% 7%	1858
	21st to end	Day	49% 4 7% 14% 18% 8%	1570
March	1st to 10th	Day	54% 5% 7% 11% 16% 6%	3361
	11th to 20th	Day	42% 6% 8% 21% 17% 5%	3480
	21st to end	Day	44% 5% 7% 20% 21% 3	3931
April	1st to 10th	Day	40% 6% 9% 20% 19% 6%	2280
	11th to 20th	Day	40% 5% 10% 17% 22% 6%	2254
	21st to end	Day	36% 6% 10% 21% 24% 3	2280
May	1st to 10th	Day	39% 7% 11% 27% 14% 3	3800
	11th to 20th	Day	37% 8% 13% 23% 17% 2	3768
	21st to end	Day	40% 9% 14% 25% 10% 2	4507
June	1st to 10th	Day	36% 9% 13% 24% 16% 1	2660
	11th to 20th	Day	29% 9% 16% 25% 17% 4	2660
	21st to end	Day	29% 10% 15% 24% 18% 4	2598
July	1st to 10th	Day	40% 10% 19% 19% 9% 2	4056
	11th to 20th	Day	39% 9% 17% 26% 7% 1	4051
	21st to end	Day	48% 8% 14% 23% 6% 1	4325
August	1st to 10th	Day	18% 6% 13% 31% 29% 2	3839
	11th to 20th	Day	29% 8% 19% 30% 12% 2	3765
	21st to end	Day	32% 7% 12% 22% 23% 3	4179
September	1st to 10th	Day	36% 7% 13% 19% 18% 7%	2280
	11th to 20th	Day	38% 7% 9% 16% 23% 7%	2280
	21st to end	Day	29% 6% 10% 21% 23% 11%	2062
October	1st to 10th	Day	14% 4 5% 15% 24% 38%	3160
	11th to 20th	Day	17% 3 4 16% 36% 25%	3140
	21st to end	Day	25% 3 4 17% 36% 13%	3428
November	1st to 10th	Day	32% 4 9% 18% 28% 9%	1958
	11th to 20th	Day	32% 3 6% 19% 28% 12%	1843
	21st to end	Day	41% 4 7% 18% 23% 8%	1746
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	42% 4 5% 18% 27% 4	4108
	11th to 20th	Night	42% 3 5% 22% 20% 7%	4120
	21st to end	Night	43% 3 7% 19% 22% 6%	4532
February	1st to 10th	Night	45% 4 6% 18% 21% 6%	2369
	11th to 20th	Night	43% 4 6% 18% 20% 9%	2219
	21st to end	Night	46% 4 6% 14% 18% 12%	1884
March	1st to 10th	Night	46% 5% 9% 14% 16% 10%	3520
	11th to 20th	Night	38% 7% 10% 18% 17% 10%	3480
	21st to end	Night	41% 5% 9% 18% 24% 3	3698
April	1st to 10th	Night	35% 5% 11% 20% 20% 9%	1900
	11th to 20th	Night	35% 5% 9% 18% 24% 9%	1875
	21st to end	Night	33% 5% 9% 22% 26% 5%	1900
May	1st to 10th	Night	37% 8% 11% 25% 16% 3	3160
	11th to 20th	Night	38% 6% 11% 29% 15% 1	3130
	21st to end	Night	38% 8% 14% 24% 15% 2	3066
June	1st to 10th	Night	27% 10% 17% 26% 18% 2	1520
	11th to 20th	Night	20% 7% 19% 29% 19% 6%	1520
	21st to end	Night	24% 8% 14% 27% 21% 5%	1573
July	1st to 10th	Night	32% 10% 23% 21% 12% 2	2805
	11th to 20th	Night	28% 9% 23% 29% 9% 2	2796
	21st to end	Night	42% 8% 14% 25% 10% 1	2999
August	1st to 10th	Night	15% 5% 13% 32% 33% 2	3065
	11th to 20th	Night	23% 8% 20% 31% 15% 3	3130
	21st to end	Night	32% 7% 11% 20% 25% 5%	3476
September	1st to 10th	Night	30% 8% 13% 22% 18% 9%	1900
	11th to 20th	Night	34% 7% 8% 18% 24% 8%	1900
	21st to end	Night	26% 5% 9% 24% 25% 12%	2095
October	1st to 10th	Night	14% 3 7% 17% 22% 37%	3800
	11th to 20th	Night	18% 2 4 15% 29% 31%	3779
	21st to end	Night	22% 3 6% 15% 35% 18%	4120
November	1st to 10th	Night	31% 4 8% 18% 27% 12%	2340
	11th to 20th	Night	31% 4 7% 18% 27% 14%	2554
	21st to end	Night	37% 4 7% 17% 24% 11%	2529
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% 15% 33% 19% 6% 2	270
	21st to end	Day	20% 13% 41% 18% 8%	297
February	1st to 10th	Day	26% 11% 34% 18% 9% 2	270
	11th to 20th	Day	30% 19% 28% 19% 5%	270
	21st to end	Day	31% 20% 31% 11% 7%	225
March	1st to 10th	Day	25% 10% 35% 19% 12%	270
	11th to 20th	Day	18% 16% 39% 23% 4	270
	21st to end	Day	13% 20% 34% 22% 10% 2	363
April	1st to 10th	Day	15% 13% 35% 27% 10% 1	460
	11th to 20th	Day	20% 10% 31% 26% 11% 3	452
	21st to end	Day	12% 10% 28% 27% 19% 3	460
May	1st to 10th	Day	12% 13% 24% 32% 17% 3	463
	11th to 20th	Day	10% 3 26% 27% 23% 10%	487
	21st to end	Day	8% 3 18% 33% 25% 13%	670
June	1st to 10th	Day	9% 4 11% 28% 33% 16%	680
	11th to 20th	Day	6% 3 10% 30% 36% 16%	680
	21st to end	Day	7% 2 11% 29% 30% 21%	680
July	1st to 10th	Day	5% 3 6% 24% 38% 24%	671
	11th to 20th	Day	6% 2 6% 21% 36% 30%	668
	21st to end	Day	6% 1 6% 22% 38% 27%	739
August	1st to 10th	Day	6% 1 5% 21% 40% 28%	529
	11th to 20th	Day	8% 1 5% 19% 41% 25%	479
	21st to end	Day	14% 1 4 15% 32% 35%	539
September	1st to 10th	Day	9% 2 7% 24% 37% 22%	490
	11th to 20th	Day	10% 2 8% 22% 33% 25%	490
	21st to end	Day	11% 3 9% 26% 35% 16%	462
October	1st to 10th	Day	8% 1 17% 32% 27% 15%	300
	11th to 20th	Day	9% 5% 24% 29% 26% 7%	300
	21st to end	Day	17% 8% 21% 30% 17% 6%	330
November	1st to 10th	Day	20% 6% 24% 23% 23% 4	300
	11th to 20th	Day	11% 8% 31% 34% 12% 3	300
	21st to end	Day	20% 13% 24% 26% 13% 4	282
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	21% 10% 34% 27% 7%	950
	21st to end	Night	22% 8% 35% 32% 3	1045
February	1st to 10th	Night	22% 10% 33% 29% 5%	849
	11th to 20th	Night	22% 10% 35% 28% 4	743
	21st to end	Night	25% 13% 33% 26% 3	628
March	1st to 10th	Night	18% 9% 31% 35% 7%	637
	11th to 20th	Night	17% 9% 32% 35% 6% 1	570
	21st to end	Night	16% 8% 32% 31% 12%	627
April	1st to 10th	Night	14% 8% 36% 33% 9% 1	570
	11th to 20th	Night	14% 9% 31% 33% 12% 1	563
	21st to end	Night	11% 8% 31% 35% 14% 1	570
May	1st to 10th	Night	11% 5% 22% 45% 15% 1	570
	11th to 20th	Night	12% 3 23% 40% 20% 2	561
	21st to end	Night	7% 2 16% 35% 32% 7%	617
June	1st to 10th	Night	6% 2 8% 38% 40% 6%	570
	11th to 20th	Night	4 1 8% 32% 48% 7%	570
	21st to end	Night	5% 1 8% 33% 42% 11%	570
July	1st to 10th	Night	4 1 6% 28% 52% 9%	555
	11th to 20th	Night	5% 1 6% 26% 50% 13%	552
	21st to end	Night	4 1 4 29% 48% 14%	624
August	1st to 10th	Night	4 1 4 25% 52% 14%	567
	11th to 20th	Night	7% 1 3 28% 51% 10%	564
	21st to end	Night	10% 1 5% 22% 48% 14%	627
September	1st to 10th	Night	9% 1 8% 32% 44% 6%	570
	11th to 20th	Night	10% 1 8% 30% 44% 7%	570
	21st to end	Night	10% 1 11% 34% 38% 6%	741
October	1st to 10th	Night	8% 2 13% 36% 36% 6%	760
	11th to 20th	Night	12% 4 20% 39% 23% 2	760
	21st to end	Night	15% 6% 21% 35% 21% 2	836
November	1st to 10th	Night	13% 3 23% 36% 22% 2	780
	11th to 20th	Night	13% 5% 29% 39% 14% 1	800
	21st to end	Night	15% 7% 29% 33% 14% 2	779
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

Page generated at 2024-11-22 07:02:26. Version ac07

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