Spartanburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spartanburg clear sky chart from 2005-11-06 to 2026-08-15.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 43%	143489
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 43%	138384
Transparency	Day	38% 6% 12% 20% 18% 6%	147174
	Night	39% 5% 11% 19% 20% 7%	142771
Seeing	Day	16% 8% 22% 25% 19% 9%	17535
	Night	17% 7% 23% 30% 20% 3	27558

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	15% 7% 2 4 3 3 3 2 4 5% 52%	5258
	11th to 20th	Day	11% 6% 2 4 3 2 2 2 3 3 63%	5280
	21st to end	Day	21% 8% 2 6% 4 4 4 2 4 5% 41%	5780
February	1st to 10th	Day	15% 6% 2 5% 4 4 5% 3 5% 6% 44%	1951
	11th to 20th	Day	22% 6% 2 5% 3 3 3 3 4 5% 44%	2048
	21st to end	Day	18% 6% 3 6% 4 3 4 4 4 6% 42%	1730
March	1st to 10th	Day	21% 6% 2 7% 4 4 4 3 4 5% 41%	5038
	11th to 20th	Day	9% 5% 2 6% 4 3 3 3 5% 6% 54%	5090
	21st to end	Day	18% 6% 2 5% 3 3 4 3 4 5% 47%	5586
April	1st to 10th	Day	12% 5% 1 5% 4 4 4 4 7% 8% 47%	2310
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 6% 50%	2462
	21st to end	Day	12% 5% 2 4 4 4 4 4 5% 8% 48%	2730
May	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 7% 8% 38%	7616
	11th to 20th	Day	14% 6% 2 7% 5% 4 5% 4 6% 8% 39%	7626
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 7% 8% 33%	8391
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 10% 36%	2730
	11th to 20th	Day	6% 4 2 5% 6% 6% 5% 5% 9% 12% 40%	2730
	21st to end	Day	6% 4 2 7% 5% 5% 6% 5% 8% 10% 41%	2730
July	1st to 10th	Day	5% 5% 2 6% 4 5% 6% 5% 8% 11% 43%	7680
	11th to 20th	Day	8% 5% 2 6% 5% 6% 7% 6% 8% 12% 36%	7680
	21st to end	Day	10% 6% 3 8% 6% 6% 7% 6% 9% 12% 28%	8340
August	1st to 10th	Day	19% 7% 3 7% 5% 5% 6% 5% 7% 10% 28%	4364
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 12% 37%	4226
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 8% 52%	4314
September	1st to 10th	Day	8% 5% 2 6% 5% 5% 4 5% 6% 10% 44%	2200
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 4 6% 8% 43%	2200
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 5% 6% 41%	2200
October	1st to 10th	Day	14% 5% 2 3 2 3 2 3 4 6% 55%	2135
	11th to 20th	Day	12% 5% 1 3 2 3 3 2 3 5% 60%	2000
	21st to end	Day	14% 4 2 4 3 3 3 3 3 5% 58%	2200
November	1st to 10th	Day	13% 6% 2 4 3 3 2 3 3 6% 54%	2036
	11th to 20th	Day	14% 5% 2 4 3 3 4 3 4 6% 53%	1890
	21st to end	Day	15% 4 3 4 3 3 4 3 4 5% 51%	1890
December	1st to 10th	Day	16% 6% 2 5% 3 3 3 2 3 5% 52%	3020
	11th to 20th	Day	20% 7% 2 6% 3 3 4 3 5% 5% 42%	3463
	21st to end	Day	22% 6% 1 4 3 3 2 3 4 6% 46%	4565
January	1st to 10th	Night	15% 5% 2 4 3 3 3 2 3 4 57%	7635
	11th to 20th	Night	12% 6% 2 4 3 3 3 2 4 4 57%	7680
	21st to end	Night	20% 8% 2 5% 3 3 3 2 4 5% 46%	8401
February	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 4 5% 49%	2667
	11th to 20th	Night	21% 7% 2 6% 3 3 3 3 4 4 44%	2458
	21st to end	Night	17% 7% 2 5% 4 4 4 3 4 6% 44%	2076
March	1st to 10th	Night	18% 6% 2 5% 3 4 4 3 5% 7% 43%	5033
	11th to 20th	Night	9% 4 1 4 3 3 4 3 5% 8% 55%	5090
	21st to end	Night	16% 5% 2 6% 4 4 4 3 5% 6% 47%	5588
April	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 7% 48%	2310
	11th to 20th	Night	11% 5% 3 4 4 3 3 3 6% 7% 53%	2121
	21st to end	Night	11% 5% 2 6% 5% 4 4 3 4 5% 51%	1890
May	1st to 10th	Night	13% 7% 2 8% 5% 4 5% 4 7% 10% 36%	5237
	11th to 20th	Night	16% 6% 3 6% 4 4 5% 4 6% 8% 38%	5234
	21st to end	Night	18% 7% 3 8% 4 5% 5% 4 7% 8% 31%	5761
June	1st to 10th	Night	10% 7% 3 6% 6% 6% 5% 5% 9% 10% 34%	1890
	11th to 20th	Night	10% 6% 3 5% 5% 5% 6% 5% 7% 10% 37%	1890
	21st to end	Night	7% 5% 2 7% 5% 7% 6% 6% 8% 11% 36%	1890
July	1st to 10th	Night	7% 6% 2 8% 6% 6% 7% 6% 9% 11% 31%	5278
	11th to 20th	Night	10% 6% 2 8% 6% 6% 7% 6% 10% 12% 26%	5277
	21st to end	Night	14% 8% 4 10% 6% 6% 6% 5% 8% 11% 22%	5736
August	1st to 10th	Night	18% 9% 3 9% 5% 5% 5% 5% 7% 9% 23%	3005
	11th to 20th	Night	12% 7% 3 9% 7% 7% 7% 5% 7% 10% 28%	2911
	21st to end	Night	6% 5% 3 6% 5% 5% 6% 4 6% 9% 44%	3519
September	1st to 10th	Night	10% 6% 2 6% 5% 5% 4 4 7% 9% 43%	2200
	11th to 20th	Night	16% 7% 2 6% 4 6% 5% 4 6% 8% 36%	2200
	21st to end	Night	16% 7% 2 5% 5% 4 4 3 5% 7% 42%	2200
October	1st to 10th	Night	14% 4 2 5% 4 4 4 3 4 6% 51%	2265
	11th to 20th	Night	13% 4 2 5% 3 2 4 3 4 6% 54%	2400
	21st to end	Night	14% 4 1 4 3 3 3 2 3 4 58%	2640
November	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 4 5% 54%	2477
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 53%	2730
	21st to end	Night	15% 5% 2 4 4 4 4 3 5% 5% 49%	2730
December	1st to 10th	Night	17% 6% 2 4 3 2 3 3 4 5% 53%	4380
	11th to 20th	Night	19% 7% 2 5% 3 3 4 3 4 5% 44%	4952
	21st to end	Night	20% 5% 2 4 3 3 3 3 5% 6% 45%	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	36% 2 9% 23% 24% 6%	5259
	11th to 20th	Day	30% 3 4 12% 39% 14%	5280
	21st to end	Day	47% 2 4 16% 19% 11%	5780
February	1st to 10th	Day	40% 4 9% 22% 21% 5%	1951
	11th to 20th	Day	43% 4 7% 19% 21% 6%	2058
	21st to end	Day	44% 5% 7% 15% 21% 7%	1730
March	1st to 10th	Day	45% 4 6% 15% 18% 12%	5038
	11th to 20th	Day	31% 4 6% 14% 25% 19%	5090
	21st to end	Day	40% 4 7% 22% 22% 5%	5586
April	1st to 10th	Day	33% 6% 10% 20% 25% 5%	2310
	11th to 20th	Day	33% 6% 10% 20% 22% 9%	2462
	21st to end	Day	34% 5% 12% 25% 20% 4	2730
May	1st to 10th	Day	42% 6% 15% 23% 13% 2	7651
	11th to 20th	Day	42% 5% 15% 22% 13% 2	7630
	21st to end	Day	47% 8% 14% 16% 14% 2	8405
June	1st to 10th	Day	38% 11% 16% 23% 10% 2	2730
	11th to 20th	Day	32% 10% 21% 23% 13% 1	2730
	21st to end	Day	34% 12% 18% 21% 14% 2	2730
July	1st to 10th	Day	34% 7% 21% 28% 8% 1	7615
	11th to 20th	Day	39% 8% 29% 19% 4 1	7611
	21st to end	Day	46% 7% 18% 19% 8% 1	8156
August	1st to 10th	Day	51% 7% 17% 20% 5%	4351
	11th to 20th	Day	38% 8% 20% 20% 13% 2	4265
	21st to end	Day	29% 7% 15% 27% 19% 3	4314
September	1st to 10th	Day	35% 9% 15% 20% 19% 3	2200
	11th to 20th	Day	38% 8% 14% 18% 19% 3	2200
	21st to end	Day	43% 5% 12% 19% 16% 6%	2200
October	1st to 10th	Day	28% 3 7% 20% 32% 10%	3473
	11th to 20th	Day	19% 3 6% 17% 31% 25%	3240
	21st to end	Day	29% 2 4 25% 25% 16%	3538
November	1st to 10th	Day	33% 3 9% 19% 27% 9%	2036
	11th to 20th	Day	32% 4 7% 22% 25% 9%	1890
	21st to end	Day	36% 5% 7% 22% 24% 7%	1890
December	1st to 10th	Day	37% 3 5% 18% 28% 9%	3020
	11th to 20th	Day	45% 4 8% 17% 19% 7%	3460
	21st to end	Day	40% 3 9% 27% 19% 2	4565
January	1st to 10th	Night	33% 2 9% 22% 26% 7%	7636
	11th to 20th	Night	32% 3 4 16% 34% 11%	7680
	21st to end	Night	43% 2 5% 17% 24% 10%	8401
February	1st to 10th	Night	39% 4 8% 21% 21% 7%	2667
	11th to 20th	Night	45% 4 7% 16% 23% 6%	2459
	21st to end	Night	41% 5% 9% 16% 22% 8%	2076
March	1st to 10th	Night	40% 6% 7% 13% 26% 8%	5033
	11th to 20th	Night	27% 4 7% 15% 29% 18%	5090
	21st to end	Night	39% 4 6% 21% 21% 9%	5588
April	1st to 10th	Night	35% 5% 11% 18% 25% 7%	2310
	11th to 20th	Night	30% 5% 9% 23% 24% 9%	2121
	21st to end	Night	35% 4 11% 25% 21% 4	1890
May	1st to 10th	Night	44% 5% 14% 23% 13% 1	5264
	11th to 20th	Night	44% 6% 14% 23% 12% 2	5235
	21st to end	Night	47% 8% 14% 19% 11% 2	5771
June	1st to 10th	Night	41% 10% 16% 19% 12% 2	1890
	11th to 20th	Night	38% 11% 17% 22% 10% 2	1890
	21st to end	Night	37% 12% 18% 16% 13% 4	1890
July	1st to 10th	Night	45% 7% 21% 22% 5% 1	5235
	11th to 20th	Night	47% 9% 25% 15% 3 1	5226
	21st to end	Night	55% 8% 17% 14% 5% 2	5606
August	1st to 10th	Night	55% 8% 18% 14% 4	2994
	11th to 20th	Night	50% 8% 18% 16% 8%	2938
	21st to end	Night	35% 7% 12% 25% 18% 1	3519
September	1st to 10th	Night	37% 9% 14% 19% 17% 4	2200
	11th to 20th	Night	43% 9% 14% 15% 17% 2	2200
	21st to end	Night	41% 6% 13% 18% 17% 5%	2200
October	1st to 10th	Night	32% 4 8% 20% 29% 7%	3707
	11th to 20th	Night	23% 3 5% 18% 27% 25%	3899
	21st to end	Night	30% 2 4 21% 27% 17%	4252
November	1st to 10th	Night	34% 5% 7% 18% 26% 10%	2477
	11th to 20th	Night	33% 3 7% 17% 28% 12%	2730
	21st to end	Night	35% 5% 6% 20% 27% 7%	2730
December	1st to 10th	Night	35% 3 6% 19% 29% 8%	4380
	11th to 20th	Night	44% 4 9% 16% 19% 8%	4954
	21st to end	Night	40% 4 9% 25% 20% 2	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	22% 19% 33% 22% 4	330
	11th to 20th	Day	25% 20% 33% 17% 5%	330
	21st to end	Day	24% 16% 39% 17% 4	363
February	1st to 10th	Day	19% 19% 35% 21% 6%	330
	11th to 20th	Day	37% 16% 30% 14% 3	330
	21st to end	Day	28% 20% 33% 16% 3	273
March	1st to 10th	Day	21% 13% 34% 23% 8% 1	533
	11th to 20th	Day	19% 16% 34% 25% 5% 1	540
	21st to end	Day	19% 14% 36% 22% 7% 1	594
April	1st to 10th	Day	18% 13% 32% 23% 13% 2	540
	11th to 20th	Day	15% 12% 32% 26% 14% 2	532
	21st to end	Day	16% 8% 27% 28% 14% 7%	540
May	1st to 10th	Day	12% 11% 34% 23% 15% 5%	543
	11th to 20th	Day	16% 7% 18% 26% 24% 9%	567
	21st to end	Day	16% 4 19% 25% 22% 13%	617
June	1st to 10th	Day	12% 3 17% 28% 27% 12%	570
	11th to 20th	Day	9% 4 14% 28% 26% 18%	570
	21st to end	Day	8% 4 14% 28% 29% 18%	570
July	1st to 10th	Day	8% 2 8% 22% 33% 26%	565
	11th to 20th	Day	7% 2 5% 27% 35% 23%	564
	21st to end	Day	9% 2 9% 30% 33% 17%	620
August	1st to 10th	Day	19% 4 11% 22% 27% 16%	566
	11th to 20th	Day	11% 3 8% 29% 29% 21%	535
	21st to end	Day	13% 1 10% 21% 30% 25%	583
September	1st to 10th	Day	9% 2 12% 28% 31% 18%	530
	11th to 20th	Day	17% 3 13% 20% 29% 18%	530
	21st to end	Day	21% 3 20% 25% 23% 8%	530
October	1st to 10th	Day	18% 4 18% 27% 23% 10%	530
	11th to 20th	Day	13% 6% 24% 28% 24% 6%	530
	21st to end	Day	19% 9% 19% 30% 18% 6%	583
November	1st to 10th	Day	20% 7% 24% 28% 17% 4	514
	11th to 20th	Day	17% 13% 35% 23% 10% 2	330
	21st to end	Day	14% 12% 31% 28% 12% 2	330
December	1st to 10th	Day	29% 11% 33% 22% 6%	330
	11th to 20th	Day	24% 11% 33% 23% 8% 1	330
	21st to end	Day	26% 11% 31% 21% 8% 2	363
January	1st to 10th	Night	21% 15% 33% 27% 5%	840
	11th to 20th	Night	21% 15% 32% 29% 4	840
	21st to end	Night	20% 13% 38% 27% 2	924
February	1st to 10th	Night	19% 12% 33% 32% 3	840
	11th to 20th	Night	26% 13% 37% 23% 2	823
	21st to end	Night	21% 13% 39% 25% 2	692
March	1st to 10th	Night	18% 12% 31% 33% 6%	840
	11th to 20th	Night	19% 12% 35% 26% 7% 1	840
	21st to end	Night	18% 12% 34% 29% 8%	924
April	1st to 10th	Night	16% 12% 32% 29% 10%	840
	11th to 20th	Night	13% 12% 30% 31% 14%	807
	21st to end	Night	13% 5% 28% 35% 18% 1	630
May	1st to 10th	Night	12% 8% 28% 34% 17%	630
	11th to 20th	Night	16% 5% 20% 34% 23% 2	621
	21st to end	Night	17% 2 14% 28% 33% 5%	683
June	1st to 10th	Night	13% 2 14% 35% 31% 5%	630
	11th to 20th	Night	12% 3 14% 30% 32% 9%	630
	21st to end	Night	8% 2 11% 32% 41% 7%	630
July	1st to 10th	Night	10% 2 7% 27% 44% 10%	615
	11th to 20th	Night	11% 3 7% 25% 44% 11%	612
	21st to end	Night	10% 2 9% 31% 40% 9%	690
August	1st to 10th	Night	16% 3 8% 26% 37% 10%	627
	11th to 20th	Night	15% 2 6% 29% 40% 9%	606
	21st to end	Night	12% 2 10% 24% 45% 8%	760
September	1st to 10th	Night	12% 3 11% 29% 40% 7%	800
	11th to 20th	Night	20% 2 12% 25% 36% 6%	800
	21st to end	Night	17% 3 17% 31% 29% 2	800
October	1st to 10th	Night	15% 3 18% 30% 29% 5%	800
	11th to 20th	Night	16% 5% 24% 32% 21% 2	800
	21st to end	Night	16% 6% 23% 33% 20% 2	880
November	1st to 10th	Night	17% 5% 23% 36% 18% 3	820
	11th to 20th	Night	15% 10% 30% 32% 12% 1	840
	21st to end	Night	16% 9% 29% 33% 12% 1	840
December	1st to 10th	Night	23% 10% 25% 33% 7%	840
	11th to 20th	Night	20% 9% 28% 33% 10%	840
	21st to end	Night	26% 9% 26% 32% 8%	924

Page generated at 2026-08-12 03:37:20. Version ac07

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