Greeleyville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greeleyville clear sky chart from 2005-11-06 to 2025-04-26.

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% 5% 5% 4 6% 8% 41%	114187
	Night	12% 6% 2 6% 4 4 4 4 6% 7% 45%	114456
Transparency	Day	39% 6% 11% 19% 18% 7%	117851
	Night	37% 6% 11% 18% 20% 8%	118931
Seeing	Day	15% 10% 24% 24% 19% 9%	16112
	Night	14% 8% 23% 33% 19% 3	26286

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	13% 5% 2 5% 3 3 3 3 5% 6% 54%	4056
	11th to 20th	Day	11% 7% 2 5% 3 3 3 2 4 6% 54%	4060
	21st to end	Day	13% 9% 2 7% 4 3 4 3 4 6% 44%	4466
February	1st to 10th	Day	15% 7% 2 5% 5% 4 3 4 6% 7% 43%	1800
	11th to 20th	Day	17% 7% 2 5% 4 3 4 3 4 5% 45%	1888
	21st to end	Day	15% 6% 3 6% 4 4 4 3 5% 6% 45%	1793
March	1st to 10th	Day	21% 9% 2 7% 4 4 3 3 4 5% 39%	4935
	11th to 20th	Day	9% 5% 2 4 3 4 4 3 5% 7% 54%	4980
	21st to end	Day	13% 6% 2 6% 4 4 4 3 5% 5% 48%	5465
April	1st to 10th	Day	9% 4 2 4 5% 4 4 4 6% 7% 51%	2233
	11th to 20th	Day	9% 4 1 5% 4 5% 4 4 6% 7% 51%	2374
	21st to end	Day	8% 5% 2 5% 4 3 4 3 6% 8% 51%	2340
May	1st to 10th	Day	8% 6% 2 7% 5% 5% 7% 5% 6% 10% 38%	4072
	11th to 20th	Day	15% 8% 3 7% 4 4 4 4 5% 7% 37%	4081
	21st to end	Day	6% 4 2 6% 5% 6% 5% 5% 8% 10% 43%	4476
June	1st to 10th	Day	10% 7% 3 7% 7% 6% 6% 5% 7% 9% 32%	2470
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 6% 9% 11% 38%	2470
	21st to end	Day	5% 5% 2 7% 6% 7% 7% 5% 8% 12% 35%	2470
July	1st to 10th	Day	12% 7% 3 9% 7% 7% 7% 6% 9% 9% 24%	4120
	11th to 20th	Day	6% 5% 3 10% 8% 8% 9% 7% 9% 12% 23%	4120
	21st to end	Day	8% 8% 3 9% 7% 7% 8% 6% 9% 11% 23%	4466
August	1st to 10th	Day	21% 7% 3 8% 6% 7% 6% 6% 8% 9% 19%	4104
	11th to 20th	Day	9% 6% 3 8% 5% 7% 7% 5% 7% 12% 32%	3953
	21st to end	Day	7% 5% 2 8% 5% 6% 6% 6% 9% 11% 36%	4180
September	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 4 8% 9% 39%	2190
	11th to 20th	Day	15% 7% 3 7% 4 5% 5% 3 6% 6% 39%	2090
	21st to end	Day	16% 8% 2 6% 4 3 3 4 6% 8% 39%	2090
October	1st to 10th	Day	13% 6% 2 5% 4 4 5% 3 5% 6% 47%	1929
	11th to 20th	Day	9% 4 2 5% 4 4 3 3 4 6% 57%	1900
	21st to end	Day	10% 4 2 6% 3 3 3 3 4 6% 57%	2090
November	1st to 10th	Day	12% 5% 1 5% 4 2 3 3 5% 7% 54%	1957
	11th to 20th	Day	13% 7% 3 5% 3 4 3 3 4 5% 50%	2000
	21st to end	Day	14% 6% 3 5% 4 3 3 3 5% 6% 51%	1800
December	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 5% 6% 52%	2930
	11th to 20th	Day	15% 6% 2 6% 3 3 3 3 5% 7% 47%	3373
	21st to end	Day	18% 8% 3 6% 3 3 4 3 4 5% 43%	4466
January	1st to 10th	Night	11% 5% 2 5% 3 3 3 2 4 5% 56%	5889
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 7% 46%	5900
	21st to end	Night	14% 7% 3 6% 4 4 4 3 4 5% 46%	6490
February	1st to 10th	Night	16% 5% 2 6% 4 4 4 4 5% 6% 44%	2600
	11th to 20th	Night	19% 7% 2 6% 3 3 4 3 4 6% 42%	2395
	21st to end	Night	12% 6% 2 6% 4 4 5% 3 5% 6% 46%	1835
March	1st to 10th	Night	19% 9% 3 7% 4 4 4 3 4 6% 38%	4918
	11th to 20th	Night	11% 4 2 5% 3 3 3 3 5% 8% 53%	4980
	21st to end	Night	12% 4 2 5% 4 3 4 3 5% 6% 51%	5467
April	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 50%	2165
	11th to 20th	Night	10% 5% 2 5% 4 3 3 4 5% 8% 53%	1975
	21st to end	Night	8% 4 2 5% 5% 3 5% 3 6% 6% 53%	1957
May	1st to 10th	Night	6% 5% 2 6% 4 4 5% 4 8% 10% 45%	2850
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 5% 8% 42%	2812
	21st to end	Night	6% 4 2 5% 4 5% 5% 5% 7% 10% 48%	3079
June	1st to 10th	Night	9% 7% 3 6% 4 5% 5% 5% 9% 11% 37%	1710
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 4 8% 11% 41%	1710
	21st to end	Night	6% 4 3 6% 6% 5% 6% 6% 9% 13% 36%	1710
July	1st to 10th	Night	10% 8% 3 10% 6% 6% 6% 5% 8% 10% 30%	2840
	11th to 20th	Night	9% 6% 3 8% 6% 6% 6% 5% 8% 12% 29%	2840
	21st to end	Night	10% 8% 4 9% 7% 6% 6% 6% 8% 9% 26%	3087
August	1st to 10th	Night	19% 7% 3 7% 5% 6% 6% 5% 8% 10% 25%	2825
	11th to 20th	Night	7% 6% 3 9% 5% 6% 6% 5% 7% 10% 35%	2844
	21st to end	Night	7% 4 2 4 4 5% 5% 5% 8% 10% 46%	3476
September	1st to 10th	Night	9% 6% 1 6% 5% 6% 5% 5% 7% 10% 39%	1985
	11th to 20th	Night	10% 9% 3 7% 4 4 5% 3 5% 9% 40%	2090
	21st to end	Night	16% 6% 3 7% 4 4 4 4 5% 7% 39%	2090
October	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 51%	2251
	11th to 20th	Night	10% 4 2 5% 3 3 3 2 4 6% 59%	2280
	21st to end	Night	9% 5% 2 5% 3 3 3 3 5% 5% 56%	2508
November	1st to 10th	Night	12% 6% 1 4 3 4 4 3 4 5% 54%	2341
	11th to 20th	Night	15% 6% 2 5% 3 3 4 2 4 6% 51%	2400
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 7% 49%	2595
December	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 5% 54%	4250
	11th to 20th	Night	15% 8% 3 8% 4 3 3 3 4 6% 43%	4822
	21st to end	Night	17% 7% 2 5% 3 4 4 4 6% 5% 43%	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	32% 3 5% 18% 34% 8%	4057
	11th to 20th	Day	34% 2 5% 17% 33% 9%	4060
	21st to end	Day	43% 3 5% 17% 21% 11%	4466
February	1st to 10th	Day	41% 4 8% 22% 19% 5%	1800
	11th to 20th	Day	42% 4 6% 17% 24% 8%	1898
	21st to end	Day	41% 4 6% 19% 20% 10%	1793
March	1st to 10th	Day	49% 3 7% 11% 20% 9%	4935
	11th to 20th	Day	30% 4 8% 16% 25% 17%	4980
	21st to end	Day	39% 4 8% 17% 22% 11%	5465
April	1st to 10th	Day	31% 5% 12% 20% 24% 8%	2233
	11th to 20th	Day	32% 4 10% 23% 19% 13%	2374
	21st to end	Day	30% 6% 10% 26% 23% 5%	2340
May	1st to 10th	Day	38% 9% 16% 23% 12% 3	4110
	11th to 20th	Day	46% 5% 12% 21% 16% 1	4085
	21st to end	Day	33% 7% 15% 23% 19% 3	4489
June	1st to 10th	Day	44% 9% 15% 20% 10% 1	2470
	11th to 20th	Day	34% 9% 19% 26% 11% 1	2470
	21st to end	Day	38% 12% 19% 21% 9% 1	2470
July	1st to 10th	Day	51% 10% 16% 18% 5% 1	4055
	11th to 20th	Day	47% 14% 24% 11% 3	4051
	21st to end	Day	49% 14% 17% 15% 4 1	4324
August	1st to 10th	Day	58% 9% 19% 11% 2	4091
	11th to 20th	Day	42% 10% 18% 21% 10%	3992
	21st to end	Day	38% 8% 15% 31% 7% 1	4180
September	1st to 10th	Day	40% 9% 17% 15% 15% 4	2190
	11th to 20th	Day	45% 6% 12% 17% 16% 4	2090
	21st to end	Day	43% 5% 12% 19% 17% 4	2090
October	1st to 10th	Day	38% 4 8% 15% 27% 7%	3202
	11th to 20th	Day	19% 3 5% 15% 30% 29%	3140
	21st to end	Day	25% 3 5% 18% 34% 14%	3428
November	1st to 10th	Day	32% 2 8% 20% 26% 11%	1957
	11th to 20th	Day	37% 3 7% 16% 25% 11%	2000
	21st to end	Day	35% 4 8% 21% 22% 9%	1800
December	1st to 10th	Day	32% 4 9% 17% 24% 13%	2930
	11th to 20th	Day	39% 4 9% 23% 20% 5%	3370
	21st to end	Day	43% 4 6% 22% 22% 3	4466
January	1st to 10th	Night	32% 4 5% 17% 35% 8%	5889
	11th to 20th	Night	38% 3 6% 16% 30% 7%	5900
	21st to end	Night	42% 4 5% 12% 27% 10%	6490
February	1st to 10th	Night	40% 4 8% 21% 20% 8%	2600
	11th to 20th	Night	44% 4 8% 16% 19% 9%	2396
	21st to end	Night	38% 4 11% 16% 19% 13%	1835
March	1st to 10th	Night	48% 3 8% 11% 22% 8%	4918
	11th to 20th	Night	29% 4 8% 13% 28% 18%	4980
	21st to end	Night	34% 3 10% 20% 20% 12%	5467
April	1st to 10th	Night	35% 5% 11% 20% 20% 9%	2165
	11th to 20th	Night	30% 5% 10% 22% 22% 11%	1975
	21st to end	Night	30% 6% 13% 25% 22% 5%	1957
May	1st to 10th	Night	31% 8% 18% 26% 13% 3	2877
	11th to 20th	Night	39% 7% 14% 23% 17% 1	2813
	21st to end	Night	28% 9% 17% 26% 19% 1	3087
June	1st to 10th	Night	38% 10% 19% 21% 11% 1	1710
	11th to 20th	Night	35% 9% 20% 25% 9% 1	1710
	21st to end	Night	34% 13% 23% 22% 6% 1	1710
July	1st to 10th	Night	47% 10% 18% 19% 4 2	2795
	11th to 20th	Night	43% 14% 28% 10% 4	2786
	21st to end	Night	49% 13% 17% 18% 3	2988
August	1st to 10th	Night	51% 10% 24% 12% 2	2814
	11th to 20th	Night	40% 11% 21% 21% 7%	2871
	21st to end	Night	31% 8% 18% 35% 8% 1	3476
September	1st to 10th	Night	37% 10% 18% 17% 13% 6%	1985
	11th to 20th	Night	41% 9% 14% 18% 15% 3	2090
	21st to end	Night	43% 6% 13% 20% 14% 4	2090
October	1st to 10th	Night	36% 4 8% 19% 27% 6%	3758
	11th to 20th	Night	17% 3 5% 14% 26% 35%	3779
	21st to end	Night	24% 3 6% 23% 28% 16%	4120
November	1st to 10th	Night	33% 3 8% 16% 27% 14%	2341
	11th to 20th	Night	37% 4 7% 15% 25% 12%	2400
	21st to end	Night	34% 4 9% 20% 22% 10%	2595
December	1st to 10th	Night	33% 3 8% 13% 30% 12%	4250
	11th to 20th	Night	44% 3 9% 17% 18% 8%	4824
	21st to end	Night	42% 5% 7% 21% 23% 3	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	17% 23% 42% 17% 2	300
	11th to 20th	Day	16% 20% 41% 18% 5% 1	300
	21st to end	Day	25% 23% 36% 13% 2 1	330
February	1st to 10th	Day	20% 20% 36% 21% 3	300
	11th to 20th	Day	32% 20% 35% 11% 1	300
	21st to end	Day	20% 18% 38% 20% 5%	392
March	1st to 10th	Day	22% 17% 28% 23% 8% 1	500
	11th to 20th	Day	17% 16% 41% 19% 7% 1	500
	21st to end	Day	15% 17% 39% 17% 10% 1	550
April	1st to 10th	Day	16% 20% 32% 21% 10% 1	500
	11th to 20th	Day	12% 13% 32% 21% 16% 6%	492
	21st to end	Day	11% 11% 27% 24% 17% 10%	480
May	1st to 10th	Day	9% 16% 28% 24% 15% 8%	463
	11th to 20th	Day	12% 6% 22% 29% 22% 9%	487
	21st to end	Day	11% 4 16% 30% 25% 15%	529
June	1st to 10th	Day	11% 5% 14% 32% 27% 11%	490
	11th to 20th	Day	11% 4 17% 27% 23% 19%	490
	21st to end	Day	8% 2 13% 34% 27% 16%	490
July	1st to 10th	Day	9% 2 8% 25% 36% 20%	485
	11th to 20th	Day	9% 2 8% 26% 36% 20%	484
	21st to end	Day	8% 2 10% 29% 35% 16%	532
August	1st to 10th	Day	14% 4 9% 26% 27% 20%	486
	11th to 20th	Day	10% 2 8% 27% 32% 22%	479
	21st to end	Day	13% 3 11% 24% 28% 21%	539
September	1st to 10th	Day	11% 4 12% 26% 28% 19%	490
	11th to 20th	Day	20% 4 12% 28% 28% 9%	490
	21st to end	Day	21% 2 17% 25% 25% 11%	490
October	1st to 10th	Day	18% 4 21% 28% 20% 9%	490
	11th to 20th	Day	12% 6% 25% 27% 23% 8%	490
	21st to end	Day	13% 8% 24% 29% 22% 5%	539
November	1st to 10th	Day	16% 7% 29% 24% 17% 6%	495
	11th to 20th	Day	19% 12% 32% 26% 10% 2	500
	21st to end	Day	12% 13% 35% 29% 9% 2	300
December	1st to 10th	Day	18% 20% 34% 21% 6% 1	300
	11th to 20th	Day	19% 14% 38% 19% 8% 2	300
	21st to end	Day	22% 16% 36% 16% 7% 2	330
January	1st to 10th	Night	18% 13% 34% 28% 7% 1	800
	11th to 20th	Night	17% 14% 32% 29% 8%	800
	21st to end	Night	19% 15% 35% 28% 3	880
February	1st to 10th	Night	19% 13% 33% 30% 6%	800
	11th to 20th	Night	23% 14% 34% 26% 2	783
	21st to end	Night	16% 14% 37% 27% 5%	660
March	1st to 10th	Night	17% 11% 34% 31% 7%	800
	11th to 20th	Night	15% 12% 36% 28% 8%	800
	21st to end	Night	14% 13% 37% 28% 8%	880
April	1st to 10th	Night	13% 15% 34% 29% 9% 1	800
	11th to 20th	Night	13% 11% 32% 31% 13% 1	791
	21st to end	Night	9% 9% 31% 37% 13%	783
May	1st to 10th	Night	6% 7% 30% 37% 18% 1	594
	11th to 20th	Night	12% 4 22% 41% 19% 2	561
	21st to end	Night	9% 1 13% 39% 33% 4	617
June	1st to 10th	Night	11% 3 11% 44% 27% 4	570
	11th to 20th	Night	11% 2 11% 36% 31% 8%	570
	21st to end	Night	7% 2 11% 36% 38% 7%	570
July	1st to 10th	Night	8% 2 6% 40% 39% 6%	555
	11th to 20th	Night	11% 1 4 35% 39% 9%	552
	21st to end	Night	7% 2 6% 38% 42% 6%	624
August	1st to 10th	Night	10% 2 5% 33% 43% 8%	567
	11th to 20th	Night	11% 2 4 34% 42% 6%	597
	21st to end	Night	15% 2 7% 30% 37% 9%	836
September	1st to 10th	Night	10% 3 10% 31% 41% 5%	760
	11th to 20th	Night	13% 3 9% 37% 31% 6%	760
	21st to end	Night	19% 4 12% 32% 29% 4	760
October	1st to 10th	Night	15% 4 16% 36% 26% 4	760
	11th to 20th	Night	11% 5% 23% 33% 24% 4	760
	21st to end	Night	10% 6% 25% 35% 22% 3	836
November	1st to 10th	Night	15% 7% 22% 34% 18% 3	780
	11th to 20th	Night	18% 9% 27% 31% 14% 1	800
	21st to end	Night	13% 9% 29% 32% 15% 2	800
December	1st to 10th	Night	18% 10% 27% 33% 11% 1	800
	11th to 20th	Night	19% 11% 25% 34% 10% 1	800
	21st to end	Night	22% 12% 27% 30% 9%	880

Page generated at 2025-04-23 09:25:04. Version ac07

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