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 2026-08-30.

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	11% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	143673
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	138581
Transparency	Day	40% 6% 13% 19% 17% 6%	147293
	Night	38% 6% 12% 19% 18% 7%	143033
Seeing	Day	15% 10% 24% 25% 19% 9%	17983
	Night	14% 8% 23% 33% 19% 3	28030

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	12% 5% 2 5% 3 3 3 3 5% 7% 52%	5258
	11th to 20th	Day	11% 6% 2 5% 3 3 3 2 4 6% 55%	5280
	21st to end	Day	15% 9% 3 7% 4 4 5% 3 5% 6% 40%	5780
February	1st to 10th	Day	15% 7% 2 5% 5% 4 3 4 6% 7% 43%	1890
	11th to 20th	Day	17% 7% 2 6% 4 3 3 3 4 5% 46%	1985
	21st to end	Day	16% 7% 3 7% 4 4 4 3 4 6% 44%	1880
March	1st to 10th	Day	20% 9% 2 7% 4 4 3 3 5% 5% 39%	5045
	11th to 20th	Day	9% 5% 2 4 3 4 4 3 5% 7% 54%	5090
	21st to end	Day	13% 6% 2 6% 4 4 4 3 5% 5% 48%	5586
April	1st to 10th	Day	9% 4 2 4 5% 4 4 4 6% 7% 51%	2345
	11th to 20th	Day	9% 4 1 5% 4 5% 4 4 5% 8% 52%	2494
	21st to end	Day	8% 5% 2 5% 4 3 4 3 6% 8% 51%	2520
May	1st to 10th	Day	13% 7% 3 8% 5% 5% 6% 4 6% 9% 36%	7592
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 9% 40%	7626
	21st to end	Day	9% 6% 3 8% 6% 7% 6% 5% 8% 9% 34%	8391
June	1st to 10th	Day	9% 7% 3 7% 7% 6% 6% 5% 7% 9% 33%	2730
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 6% 9% 11% 37%	2730
	21st to end	Day	5% 5% 2 7% 6% 6% 7% 5% 8% 12% 37%	2730
July	1st to 10th	Day	8% 6% 3 9% 7% 7% 8% 6% 8% 10% 28%	7680
	11th to 20th	Day	5% 5% 2 9% 7% 8% 8% 7% 11% 13% 25%	7680
	21st to end	Day	7% 7% 3 8% 6% 7% 7% 5% 9% 13% 28%	8340
August	1st to 10th	Day	21% 8% 3 9% 6% 7% 6% 6% 8% 9% 18%	4364
	11th to 20th	Day	8% 5% 3 8% 5% 7% 7% 5% 8% 12% 33%	4207
	21st to end	Day	8% 5% 2 8% 5% 6% 6% 5% 9% 11% 35%	4420
September	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 4 8% 9% 40%	2305
	11th to 20th	Day	15% 6% 3 7% 4 5% 5% 4 7% 6% 39%	2200
	21st to end	Day	16% 8% 3 6% 4 3 3 4 6% 8% 39%	2200
October	1st to 10th	Day	13% 6% 2 5% 4 4 5% 3 5% 7% 46%	2030
	11th to 20th	Day	10% 4 2 5% 4 3 3 3 4 5% 57%	2000
	21st to end	Day	11% 4 2 5% 3 3 3 3 4 6% 57%	2200
November	1st to 10th	Day	12% 5% 1 5% 4 2 3 3 5% 7% 55%	2057
	11th to 20th	Day	13% 7% 3 5% 3 3 3 2 4 5% 52%	2100
	21st to end	Day	13% 6% 2 5% 3 3 3 3 5% 7% 51%	1890
December	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 5% 6% 51%	3020
	11th to 20th	Day	15% 6% 2 6% 3 3 3 3 5% 7% 47%	3463
	21st to end	Day	18% 8% 3 6% 3 3 4 3 4 5% 44%	4565
January	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 4 5% 53%	7635
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 49%	7680
	21st to end	Night	16% 8% 3 7% 4 4 4 3 4 5% 43%	8401
February	1st to 10th	Night	16% 6% 2 6% 4 3 4 3 5% 6% 45%	2730
	11th to 20th	Night	18% 7% 2 6% 3 3 4 3 5% 6% 42%	2518
	21st to end	Night	13% 7% 2 6% 4 4 5% 3 5% 6% 45%	1924
March	1st to 10th	Night	18% 9% 3 7% 4 4 4 3 4 6% 38%	5028
	11th to 20th	Night	11% 4 2 5% 3 3 3 3 5% 8% 53%	5090
	21st to end	Night	12% 4 2 5% 4 3 4 3 5% 6% 51%	5588
April	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 50%	2273
	11th to 20th	Night	10% 4 1 5% 4 3 3 4 5% 8% 54%	2075
	21st to end	Night	7% 4 2 5% 5% 3 5% 4 6% 6% 53%	2100
May	1st to 10th	Night	9% 7% 3 7% 4 4 5% 4 7% 10% 40%	5302
	11th to 20th	Night	12% 5% 2 5% 4 4 4 4 6% 9% 44%	5234
	21st to end	Night	9% 7% 3 8% 5% 6% 6% 5% 7% 9% 35%	5761
June	1st to 10th	Night	9% 7% 2 6% 5% 5% 5% 5% 9% 10% 36%	1890
	11th to 20th	Night	9% 5% 2 6% 5% 5% 6% 4 8% 11% 39%	1890
	21st to end	Night	5% 4 3 6% 6% 5% 6% 6% 9% 13% 37%	1890
July	1st to 10th	Night	7% 6% 2 8% 6% 6% 6% 6% 9% 11% 31%	5278
	11th to 20th	Night	8% 6% 3 8% 6% 6% 7% 5% 9% 13% 29%	5277
	21st to end	Night	9% 8% 3 9% 7% 6% 6% 6% 8% 12% 27%	5736
August	1st to 10th	Night	19% 8% 3 7% 5% 6% 6% 5% 7% 10% 24%	3005
	11th to 20th	Night	7% 6% 3 9% 5% 6% 7% 5% 8% 10% 35%	3028
	21st to end	Night	7% 5% 2 5% 4 5% 5% 5% 8% 10% 45%	3677
September	1st to 10th	Night	8% 6% 1 6% 5% 6% 5% 5% 7% 10% 40%	2090
	11th to 20th	Night	10% 9% 3 7% 5% 5% 5% 4 6% 9% 40%	2200
	21st to end	Night	17% 6% 3 7% 4 4 4 4 5% 7% 39%	2200
October	1st to 10th	Night	13% 6% 2 5% 4 4 3 3 5% 6% 50%	2370
	11th to 20th	Night	11% 3 2 4 3 3 3 2 4 6% 59%	2400
	21st to end	Night	10% 5% 2 5% 3 3 3 3 5% 5% 56%	2640
November	1st to 10th	Night	11% 6% 1 4 3 4 3 3 4 5% 55%	2461
	11th to 20th	Night	14% 6% 2 5% 3 2 4 2 4 6% 52%	2520
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 7% 50%	2725
December	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 5% 53%	4380
	11th to 20th	Night	15% 8% 3 7% 4 3 3 3 4 6% 44%	4952
	21st to end	Night	17% 6% 2 5% 3 4 4 4 6% 6% 43%	6633

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	33% 3 8% 23% 27% 6%	5259
	11th to 20th	Day	33% 2 5% 16% 32% 13%	5280
	21st to end	Day	46% 3 5% 17% 18% 11%	5780
February	1st to 10th	Day	41% 4 8% 22% 20% 5%	1890
	11th to 20th	Day	42% 4 5% 18% 24% 7%	1995
	21st to end	Day	42% 4 6% 19% 19% 10%	1880
March	1st to 10th	Day	48% 3 8% 12% 20% 9%	5045
	11th to 20th	Day	30% 4 9% 16% 25% 17%	5090
	21st to end	Day	38% 4 8% 17% 22% 11%	5586
April	1st to 10th	Day	31% 5% 12% 20% 24% 8%	2345
	11th to 20th	Day	31% 4 9% 24% 20% 13%	2494
	21st to end	Day	31% 5% 10% 26% 23% 4	2520
May	1st to 10th	Day	43% 7% 14% 24% 10% 2	7627
	11th to 20th	Day	40% 6% 16% 23% 14% 2	7630
	21st to end	Day	44% 8% 14% 16% 15% 2	8405
June	1st to 10th	Day	44% 8% 15% 20% 11% 1	2730
	11th to 20th	Day	35% 9% 20% 25% 10% 1	2730
	21st to end	Day	36% 11% 20% 23% 8% 1	2730
July	1st to 10th	Day	46% 10% 20% 19% 4 1	7615
	11th to 20th	Day	43% 15% 28% 11% 2	7611
	21st to end	Day	44% 11% 19% 17% 7% 1	8156
August	1st to 10th	Day	59% 10% 19% 10% 2	4351
	11th to 20th	Day	41% 10% 19% 21% 9%	4246
	21st to end	Day	39% 8% 15% 30% 7% 1	4420
September	1st to 10th	Day	38% 9% 16% 17% 15% 4	2305
	11th to 20th	Day	44% 6% 12% 18% 16% 4	2200
	21st to end	Day	43% 5% 13% 20% 16% 4	2200
October	1st to 10th	Day	39% 4 9% 15% 26% 7%	3303
	11th to 20th	Day	20% 3 5% 15% 30% 28%	3240
	21st to end	Day	26% 3 5% 18% 34% 14%	3538
November	1st to 10th	Day	31% 2 9% 20% 26% 12%	2057
	11th to 20th	Day	36% 3 7% 17% 26% 11%	2100
	21st to end	Day	34% 4 9% 21% 23% 9%	1890
December	1st to 10th	Day	33% 4 9% 17% 24% 13%	3020
	11th to 20th	Day	38% 4 9% 22% 21% 6%	3460
	21st to end	Day	43% 4 7% 22% 22% 3	4565
January	1st to 10th	Night	34% 4 7% 22% 27% 6%	7636
	11th to 20th	Night	35% 3 6% 15% 30% 11%	7680
	21st to end	Night	45% 3 5% 13% 24% 9%	8401
February	1st to 10th	Night	40% 4 8% 21% 20% 8%	2730
	11th to 20th	Night	44% 4 8% 17% 19% 9%	2519
	21st to end	Night	40% 4 10% 15% 18% 13%	1924
March	1st to 10th	Night	48% 3 8% 11% 21% 8%	5028
	11th to 20th	Night	29% 4 8% 13% 28% 18%	5090
	21st to end	Night	34% 3 11% 20% 20% 12%	5588
April	1st to 10th	Night	34% 5% 12% 21% 19% 9%	2273
	11th to 20th	Night	29% 5% 9% 23% 23% 11%	2075
	21st to end	Night	30% 5% 12% 26% 22% 5%	2100
May	1st to 10th	Night	38% 7% 18% 25% 11% 2	5329
	11th to 20th	Night	36% 7% 18% 23% 14% 2	5235
	21st to end	Night	42% 10% 15% 18% 14% 1	5771
June	1st to 10th	Night	39% 9% 18% 21% 11% 2	1890
	11th to 20th	Night	36% 9% 21% 24% 9% 1	1890
	21st to end	Night	33% 13% 23% 24% 6% 1	1890
July	1st to 10th	Night	42% 10% 25% 18% 4 1	5235
	11th to 20th	Night	42% 13% 32% 10% 2	5226
	21st to end	Night	46% 10% 19% 18% 5% 1	5606
August	1st to 10th	Night	52% 10% 24% 12% 2	2994
	11th to 20th	Night	40% 11% 22% 20% 7%	3055
	21st to end	Night	32% 8% 17% 35% 7%	3677
September	1st to 10th	Night	37% 9% 17% 19% 12% 5%	2090
	11th to 20th	Night	40% 9% 14% 20% 15% 3	2200
	21st to end	Night	44% 6% 14% 20% 13% 4	2200
October	1st to 10th	Night	36% 4 8% 20% 27% 6%	3877
	11th to 20th	Night	18% 2 5% 14% 26% 35%	3899
	21st to end	Night	24% 3 6% 23% 28% 16%	4252
November	1st to 10th	Night	32% 3 8% 16% 27% 14%	2461
	11th to 20th	Night	35% 4 7% 16% 26% 12%	2520
	21st to end	Night	33% 5% 9% 21% 22% 11%	2725
December	1st to 10th	Night	35% 3 8% 13% 29% 12%	4380
	11th to 20th	Night	44% 3 10% 17% 18% 8%	4954
	21st to end	Night	41% 5% 7% 22% 23% 3	6633

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	16% 22% 43% 17% 2	330
	11th to 20th	Day	16% 21% 40% 17% 5% 1	330
	21st to end	Day	25% 23% 38% 12% 2 1	363
February	1st to 10th	Day	20% 20% 38% 19% 3	330
	11th to 20th	Day	32% 21% 35% 10% 2	330
	21st to end	Day	22% 17% 37% 18% 4	423
March	1st to 10th	Day	21% 16% 28% 24% 9% 1	540
	11th to 20th	Day	17% 16% 41% 19% 7% 1	540
	21st to end	Day	14% 16% 39% 19% 10% 1	594
April	1st to 10th	Day	15% 20% 30% 22% 11% 1	540
	11th to 20th	Day	11% 12% 32% 22% 17% 6%	532
	21st to end	Day	10% 12% 26% 25% 18% 9%	540
May	1st to 10th	Day	10% 15% 29% 24% 14% 7%	543
	11th to 20th	Day	12% 6% 23% 29% 21% 9%	567
	21st to end	Day	12% 6% 16% 30% 22% 13%	617
June	1st to 10th	Day	10% 6% 15% 32% 27% 10%	570
	11th to 20th	Day	11% 5% 17% 28% 23% 16%	570
	21st to end	Day	7% 2 12% 34% 28% 16%	570
July	1st to 10th	Day	8% 2 9% 27% 36% 18%	565
	11th to 20th	Day	8% 1 8% 27% 36% 20%	564
	21st to end	Day	8% 2 10% 30% 35% 15%	620
August	1st to 10th	Day	15% 4 10% 26% 27% 18%	566
	11th to 20th	Day	9% 2 7% 26% 34% 22%	559
	21st to end	Day	14% 3 12% 26% 27% 19%	619
September	1st to 10th	Day	10% 4 15% 27% 26% 18%	530
	11th to 20th	Day	18% 5% 13% 28% 27% 9%	530
	21st to end	Day	21% 2 18% 26% 25% 10%	530
October	1st to 10th	Day	19% 4 22% 27% 19% 9%	530
	11th to 20th	Day	13% 6% 25% 26% 23% 7%	530
	21st to end	Day	14% 8% 25% 28% 20% 5%	583
November	1st to 10th	Day	16% 8% 30% 24% 16% 6%	535
	11th to 20th	Day	18% 12% 32% 26% 10% 2	540
	21st to end	Day	12% 14% 37% 28% 8% 2	330
December	1st to 10th	Day	21% 18% 35% 20% 5% 1	330
	11th to 20th	Day	19% 14% 37% 21% 7% 2	330
	21st to end	Day	21% 16% 38% 17% 7% 2	363
January	1st to 10th	Night	17% 13% 35% 28% 7%	840
	11th to 20th	Night	17% 14% 32% 29% 8%	840
	21st to end	Night	20% 15% 35% 27% 3	924
February	1st to 10th	Night	19% 13% 33% 30% 5%	840
	11th to 20th	Night	23% 15% 35% 25% 2	823
	21st to end	Night	17% 15% 37% 26% 5%	692
March	1st to 10th	Night	17% 11% 33% 32% 7%	840
	11th to 20th	Night	15% 13% 36% 28% 7%	840
	21st to end	Night	13% 13% 37% 28% 8%	924
April	1st to 10th	Night	12% 15% 33% 30% 9%	840
	11th to 20th	Night	12% 11% 32% 31% 13% 1	831
	21st to end	Night	9% 10% 31% 38% 13%	840
May	1st to 10th	Night	8% 7% 30% 37% 17% 1	656
	11th to 20th	Night	12% 5% 23% 41% 18% 2	621
	21st to end	Night	10% 3 14% 39% 31% 4	683
June	1st to 10th	Night	11% 3 13% 44% 25% 3	630
	11th to 20th	Night	11% 2 12% 38% 30% 7%	630
	21st to end	Night	7% 2 10% 37% 38% 6%	630
July	1st to 10th	Night	8% 2 7% 40% 39% 5%	615
	11th to 20th	Night	10% 2 4 36% 39% 9%	612
	21st to end	Night	7% 2 7% 37% 41% 6%	690
August	1st to 10th	Night	11% 2 5% 32% 42% 8%	627
	11th to 20th	Night	10% 2 4 32% 42% 9%	661
	21st to end	Night	15% 2 8% 31% 35% 8%	917
September	1st to 10th	Night	10% 3 12% 32% 39% 5%	800
	11th to 20th	Night	13% 3 9% 38% 31% 6%	800
	21st to end	Night	19% 4 12% 32% 29% 4	800
October	1st to 10th	Night	15% 4 17% 36% 25% 4	800
	11th to 20th	Night	12% 5% 23% 34% 23% 3	800
	21st to end	Night	11% 7% 25% 34% 21% 2	880
November	1st to 10th	Night	15% 7% 23% 35% 17% 3	820
	11th to 20th	Night	17% 10% 27% 32% 14% 1	840
	21st to end	Night	13% 9% 30% 31% 15% 2	840
December	1st to 10th	Night	19% 11% 27% 32% 10% 1	840
	11th to 20th	Night	19% 11% 25% 34% 10% 1	840
	21st to end	Night	21% 12% 27% 30% 9%	924

Page generated at 2026-08-27 04:07:15. Version ac07

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