Charleston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charleston clear sky chart from 2005-11-06 to 2024-03-23.

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% 5% 2 5% 5% 3 5% 5% 6% 9% 43%	79152
	Night	11% 6% 2 5% 5% 3 5% 5% 6% 8% 44%	80740
Transparency	Day	35% 9% 15% 20% 15% 5%	78875
	Night	37% 8% 13% 19% 17% 6%	80536
Seeing	Day	11% 5% 20% 28% 27% 10%	14668
	Night	12% 6% 20% 29% 26% 7%	24855

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% 6% 2 5% 4 3 4 5% 6% 10% 43%	2836
	11th to 20th	Day	12% 5% 2 5% 5% 3 4 4 5% 9% 46%	2840
	21st to end	Day	15% 8% 3 5% 4 2 4 3 4 6% 45%	3124
February	1st to 10th	Day	14% 6% 2 6% 4 3 5% 5% 6% 7% 41%	1710
	11th to 20th	Day	17% 7% 2 5% 4 2 3 4 4 6% 46%	1806
	21st to end	Day	13% 6% 4 5% 5% 2 4 4 4 5% 46%	1723
March	1st to 10th	Day	13% 5% 2 5% 4 2 3 3 5% 7% 49%	2090
	11th to 20th	Day	11% 5% 2 4 5% 3 5% 4 6% 8% 46%	2090
	21st to end	Day	11% 5% 2 5% 5% 3 5% 5% 5% 7% 46%	2200
April	1st to 10th	Day	8% 4 2 4 4 3 4 5% 5% 6% 54%	2002
	11th to 20th	Day	10% 3 2 5% 3 2 4 5% 6% 8% 51%	2134
	21st to end	Day	6% 3 2 3 3 2 4 5% 5% 10% 58%	2160
May	1st to 10th	Day	7% 3 2 4 5% 3 5% 6% 6% 8% 51%	2294
	11th to 20th	Day	10% 5% 3 4 5% 2 5% 6% 7% 9% 45%	2301
	21st to end	Day	9% 4 2 5% 6% 4 5% 7% 8% 11% 39%	2531
June	1st to 10th	Day	8% 5% 3 6% 6% 4 7% 8% 8% 11% 32%	2340
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 7% 10% 12% 38%	2340
	21st to end	Day	6% 4 2 6% 5% 4 8% 8% 9% 13% 34%	2340
July	1st to 10th	Day	8% 5% 2 5% 5% 4 7% 8% 8% 13% 33%	2340
	11th to 20th	Day	8% 5% 3 6% 7% 5% 7% 7% 8% 12% 33%	2340
	21st to end	Day	6% 5% 3 6% 6% 5% 7% 8% 8% 12% 34%	2547
August	1st to 10th	Day	9% 4 3 6% 7% 4 6% 8% 10% 15% 28%	2327
	11th to 20th	Day	7% 5% 3 7% 8% 5% 7% 7% 9% 11% 31%	2231
	21st to end	Day	13% 6% 3 7% 7% 5% 8% 7% 7% 10% 27%	2376
September	1st to 10th	Day	12% 5% 2 5% 6% 4 6% 7% 7% 10% 37%	2066
	11th to 20th	Day	12% 7% 3 6% 6% 4 6% 6% 7% 9% 35%	1980
	21st to end	Day	14% 7% 3 6% 5% 2 4 5% 6% 9% 38%	1980
October	1st to 10th	Day	12% 6% 2 6% 4 3 4 4 5% 6% 49%	1828
	11th to 20th	Day	9% 3 2 3 5% 2 3 4 5% 7% 57%	1800
	21st to end	Day	9% 5% 2 5% 4 3 4 3 4 6% 56%	1980
November	1st to 10th	Day	10% 5% 2 3 4 2 4 4 5% 6% 55%	1857
	11th to 20th	Day	12% 6% 2 6% 4 3 4 3 5% 6% 48%	1900
	21st to end	Day	13% 4 3 4 4 2 4 3 6% 6% 52%	1752
December	1st to 10th	Day	13% 7% 2 6% 5% 3 5% 5% 5% 7% 43%	1710
	11th to 20th	Day	15% 5% 2 4 3 2 3 3 4 6% 54%	2153
	21st to end	Day	16% 9% 3 5% 4 3 3 4 4 6% 43%	3124
January	1st to 10th	Night	13% 6% 2 5% 5% 3 5% 5% 6% 7% 43%	4109
	11th to 20th	Night	11% 7% 3 5% 6% 3 5% 5% 5% 8% 42%	4120
	21st to end	Night	13% 8% 3 6% 5% 2 4 4 4 6% 44%	4532
February	1st to 10th	Night	14% 6% 3 6% 5% 3 4 5% 5% 6% 44%	2470
	11th to 20th	Night	16% 7% 3 5% 5% 3 4 4 5% 6% 43%	2256
	21st to end	Night	12% 8% 3 6% 6% 3 4 4 5% 6% 43%	1728
March	1st to 10th	Night	11% 6% 3 6% 4 2 4 4 4 7% 48%	2090
	11th to 20th	Night	11% 6% 2 6% 6% 3 3 5% 6% 7% 46%	2090
	21st to end	Night	10% 6% 2 5% 5% 3 4 5% 6% 9% 46%	2201
April	1st to 10th	Night	10% 5% 2 4 5% 2 4 4 6% 7% 52%	1955
	11th to 20th	Night	12% 3 1 5% 4 3 5% 4 4 8% 51%	1775
	21st to end	Night	7% 4 3 4 4 2 4 4 5% 9% 54%	1800
May	1st to 10th	Night	6% 4 1 4 4 4 5% 5% 6% 9% 53%	1680
	11th to 20th	Night	8% 4 2 4 5% 3 5% 5% 6% 10% 48%	1592
	21st to end	Night	8% 4 2 5% 5% 3 6% 5% 8% 11% 43%	1744
June	1st to 10th	Night	9% 6% 3 6% 6% 4 6% 7% 8% 12% 35%	1620
	11th to 20th	Night	6% 4 3 4 6% 4 5% 7% 8% 12% 40%	1620
	21st to end	Night	5% 5% 3 5% 6% 4 6% 8% 10% 14% 34%	1620
July	1st to 10th	Night	7% 4 2 6% 5% 4 6% 7% 10% 13% 37%	1620
	11th to 20th	Night	7% 5% 2 6% 7% 3 7% 7% 9% 12% 34%	1620
	21st to end	Night	6% 4 2 5% 6% 4 6% 6% 9% 13% 39%	1771
August	1st to 10th	Night	8% 5% 2 5% 6% 3 7% 8% 11% 14% 32%	1611
	11th to 20th	Night	7% 5% 3 7% 7% 5% 8% 7% 8% 13% 30%	1650
	21st to end	Night	11% 7% 3 6% 7% 5% 6% 7% 7% 12% 30%	1980
September	1st to 10th	Night	10% 5% 2 6% 8% 4 6% 6% 8% 10% 36%	1890
	11th to 20th	Night	10% 6% 3 6% 6% 4 5% 6% 7% 9% 38%	1980
	21st to end	Night	14% 6% 3 7% 5% 3 4 5% 7% 9% 38%	1980
October	1st to 10th	Night	12% 6% 2 4 5% 3 4 5% 5% 8% 47%	2130
	11th to 20th	Night	9% 4 2 3 3 2 4 5% 6% 7% 55%	2160
	21st to end	Night	9% 5% 3 4 3 2 4 3 5% 6% 56%	2376
November	1st to 10th	Night	10% 5% 1 5% 3 2 4 4 4 6% 56%	2221
	11th to 20th	Night	14% 6% 2 4 4 2 3 3 5% 6% 51%	2280
	21st to end	Night	11% 5% 3 5% 5% 3 4 5% 6% 8% 46%	2425
December	1st to 10th	Night	14% 6% 3 5% 5% 3 5% 4 6% 7% 41%	2470
	11th to 20th	Night	16% 6% 2 5% 3 2 3 4 4 6% 49%	3042
	21st to end	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 40%	4532

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% 6% 10% 20% 21% 7%	2837
	11th to 20th	Day	36% 6% 8% 18% 22% 10%	2840
	21st to end	Day	40% 7% 8% 17% 21% 7%	3124
February	1st to 10th	Day	41% 7% 10% 19% 18% 5%	1710
	11th to 20th	Day	40% 5% 9% 15% 22% 8%	1816
	21st to end	Day	40% 6% 9% 20% 15% 10%	1723
March	1st to 10th	Day	35% 5% 11% 20% 18% 11%	2090
	11th to 20th	Day	35% 8% 15% 19% 15% 8%	2090
	21st to end	Day	36% 7% 13% 21% 18% 5%	2200
April	1st to 10th	Day	28% 7% 15% 21% 21% 8%	2002
	11th to 20th	Day	29% 7% 12% 24% 18% 9%	2134
	21st to end	Day	21% 8% 15% 31% 20% 5%	2160
May	1st to 10th	Day	28% 8% 14% 27% 18% 5%	2294
	11th to 20th	Day	32% 9% 19% 25% 13% 1	2305
	21st to end	Day	33% 13% 18% 24% 13%	2531
June	1st to 10th	Day	38% 15% 19% 17% 10%	2340
	11th to 20th	Day	31% 12% 23% 26% 8%	2340
	21st to end	Day	33% 17% 23% 20% 7%	2340
July	1st to 10th	Day	33% 16% 24% 20% 6% 1	2275
	11th to 20th	Day	37% 14% 26% 16% 6%	2271
	21st to end	Day	33% 15% 27% 22% 2 1	2405
August	1st to 10th	Day	36% 17% 25% 19% 3	2314
	11th to 20th	Day	39% 17% 23% 18% 3	2231
	21st to end	Day	45% 15% 19% 17% 4	2376
September	1st to 10th	Day	37% 13% 20% 16% 11% 3	2066
	11th to 20th	Day	41% 11% 15% 19% 11% 2	1980
	21st to end	Day	41% 9% 15% 20% 13% 3	1980
October	1st to 10th	Day	36% 6% 11% 20% 21% 6%	1828
	11th to 20th	Day	27% 5% 12% 24% 24% 8%	1800
	21st to end	Day	29% 6% 8% 20% 27% 10%	1980
November	1st to 10th	Day	31% 5% 11% 19% 24% 10%	1857
	11th to 20th	Day	37% 6% 9% 19% 20% 9%	1900
	21st to end	Day	32% 5% 11% 23% 22% 7%	1752
December	1st to 10th	Day	39% 7% 12% 21% 14% 6%	1710
	11th to 20th	Day	33% 4 9% 23% 24% 6%	2150
	21st to end	Day	42% 6% 9% 19% 21% 4	3124
January	1st to 10th	Night	37% 7% 8% 15% 22% 10%	4109
	11th to 20th	Night	39% 5% 9% 18% 25% 5%	4120
	21st to end	Night	41% 6% 7% 13% 23% 9%	4532
February	1st to 10th	Night	40% 5% 8% 21% 18% 8%	2470
	11th to 20th	Night	41% 6% 10% 14% 20% 10%	2257
	21st to end	Night	41% 5% 11% 18% 14% 11%	1728
March	1st to 10th	Night	34% 6% 12% 19% 18% 11%	2090
	11th to 20th	Night	36% 8% 14% 19% 15% 8%	2090
	21st to end	Night	35% 7% 14% 20% 16% 7%	2201
April	1st to 10th	Night	32% 7% 12% 19% 21% 8%	1955
	11th to 20th	Night	32% 6% 10% 22% 19% 10%	1775
	21st to end	Night	26% 7% 13% 27% 22% 4	1800
May	1st to 10th	Night	28% 6% 15% 26% 20% 5%	1680
	11th to 20th	Night	30% 11% 19% 23% 15% 1	1593
	21st to end	Night	33% 12% 16% 26% 12% 1	1745
June	1st to 10th	Night	38% 13% 20% 20% 9%	1620
	11th to 20th	Night	32% 13% 22% 25% 7%	1620
	21st to end	Night	35% 15% 25% 20% 5%	1620
July	1st to 10th	Night	33% 14% 24% 21% 7% 1	1575
	11th to 20th	Night	38% 15% 26% 15% 6%	1566
	21st to end	Night	31% 15% 26% 26% 2	1672
August	1st to 10th	Night	36% 17% 25% 19% 3	1600
	11th to 20th	Night	41% 17% 20% 19% 3	1650
	21st to end	Night	45% 13% 20% 18% 3	1980
September	1st to 10th	Night	41% 14% 16% 17% 11% 2	1890
	11th to 20th	Night	41% 11% 17% 19% 11% 1	1980
	21st to end	Night	42% 9% 15% 19% 13% 2	1980
October	1st to 10th	Night	37% 6% 11% 20% 20% 5%	2130
	11th to 20th	Night	27% 7% 11% 22% 24% 8%	2160
	21st to end	Night	30% 5% 8% 19% 24% 13%	2376
November	1st to 10th	Night	30% 6% 10% 19% 24% 11%	2221
	11th to 20th	Night	36% 5% 9% 17% 21% 11%	2280
	21st to end	Night	35% 6% 11% 18% 21% 9%	2425
December	1st to 10th	Night	41% 7% 14% 16% 16% 6%	2470
	11th to 20th	Night	38% 5% 8% 17% 26% 5%	3044
	21st to end	Night	43% 6% 8% 21% 18% 4	4532

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	10% 7% 43% 34% 6%	270
	11th to 20th	Day	8% 9% 36% 31% 14% 2	270
	21st to end	Day	19% 10% 39% 27% 4 1	297
February	1st to 10th	Day	16% 9% 34% 30% 11%	270
	11th to 20th	Day	24% 9% 33% 27% 6%	270
	21st to end	Day	11% 10% 40% 31% 7% 2	378
March	1st to 10th	Day	13% 9% 34% 28% 16%	460
	11th to 20th	Day	13% 8% 34% 33% 10% 2	460
	21st to end	Day	11% 7% 35% 29% 14% 3	470
April	1st to 10th	Day	12% 8% 31% 31% 16% 2	420
	11th to 20th	Day	8% 8% 29% 26% 21% 8%	412
	21st to end	Day	6% 4 25% 30% 27% 8%	420
May	1st to 10th	Day	4 6% 31% 31% 21% 8%	423
	11th to 20th	Day	10% 2 17% 30% 30% 12%	447
	21st to end	Day	11% 2 9% 29% 32% 17%	485
June	1st to 10th	Day	10% 2 12% 32% 32% 12%	450
	11th to 20th	Day	8% 2 12% 26% 31% 22%	450
	21st to end	Day	6% 2 9% 29% 37% 17%	450
July	1st to 10th	Day	8% 1 4 20% 49% 19%	445
	11th to 20th	Day	7% 1 5% 18% 49% 21%	444
	21st to end	Day	6% 1 5% 29% 44% 15%	488
August	1st to 10th	Day	9% 2 7% 22% 43% 18%	446
	11th to 20th	Day	5% 2 5% 20% 45% 23%	439
	21st to end	Day	13% 2 7% 19% 40% 19%	495
September	1st to 10th	Day	9% 4 5% 22% 43% 17%	450
	11th to 20th	Day	15% 3 10% 26% 35% 11%	450
	21st to end	Day	14% 2 8% 25% 36% 14%	450
October	1st to 10th	Day	16% 3 18% 31% 21% 11%	450
	11th to 20th	Day	9% 4 17% 31% 28% 12%	450
	21st to end	Day	10% 5% 18% 31% 31% 5%	495
November	1st to 10th	Day	15% 4 24% 29% 22% 7%	455
	11th to 20th	Day	17% 5% 27% 32% 17% 2	460
	21st to end	Day	13% 8% 23% 34% 21% 2	312
December	1st to 10th	Day	16% 7% 26% 36% 15%	270
	11th to 20th	Day	15% 7% 33% 29% 13% 3	270
	21st to end	Day	21% 8% 25% 29% 15% 2	297
January	1st to 10th	Night	13% 11% 34% 33% 9% 1	760
	11th to 20th	Night	14% 11% 30% 31% 13% 1	760
	21st to end	Night	16% 10% 37% 31% 5%	836
February	1st to 10th	Night	16% 9% 30% 33% 11%	760
	11th to 20th	Night	17% 12% 30% 34% 8%	743
	21st to end	Night	15% 8% 31% 35% 10% 1	628
March	1st to 10th	Night	11% 7% 31% 36% 14%	760
	11th to 20th	Night	12% 8% 28% 37% 13% 2	760
	21st to end	Night	11% 6% 31% 32% 18% 2	801
April	1st to 10th	Night	10% 10% 27% 31% 20% 2	720
	11th to 20th	Night	12% 6% 24% 30% 23% 5%	711
	21st to end	Night	8% 5% 23% 34% 27% 4	720
May	1st to 10th	Night	7% 5% 22% 36% 24% 7%	600
	11th to 20th	Night	9% 3 18% 29% 31% 10%	531
	21st to end	Night	9% 1 10% 25% 38% 18%	584
June	1st to 10th	Night	9% 4 10% 31% 38% 9%	540
	11th to 20th	Night	7% 2 8% 21% 41% 21%	540
	21st to end	Night	6% 2 8% 28% 41% 15%	540
July	1st to 10th	Night	9% 1 6% 19% 50% 15%	525
	11th to 20th	Night	10% 1 2 18% 49% 19%	522
	21st to end	Night	6% 2 4 26% 50% 13%	591
August	1st to 10th	Night	9% 2 4 23% 47% 16%	537
	11th to 20th	Night	9% 2 6% 21% 45% 18%	586
	21st to end	Night	13% 1 6% 20% 41% 19%	792
September	1st to 10th	Night	10% 2 8% 22% 44% 14%	720
	11th to 20th	Night	13% 2 7% 26% 41% 11%	720
	21st to end	Night	16% 2 10% 23% 38% 11%	720
October	1st to 10th	Night	14% 3 16% 32% 26% 10%	720
	11th to 20th	Night	9% 4 21% 29% 29% 7%	720
	21st to end	Night	10% 6% 20% 31% 27% 6%	792
November	1st to 10th	Night	11% 6% 23% 33% 24% 4	740
	11th to 20th	Night	16% 8% 24% 32% 18% 3	760
	21st to end	Night	13% 9% 23% 35% 17% 4	760
December	1st to 10th	Night	16% 8% 26% 33% 15% 2	760
	11th to 20th	Night	18% 7% 27% 28% 17% 2	760
	21st to end	Night	19% 8% 29% 30% 13% 1	836

Page generated at 2024-03-19 23:31:03. Version ac07

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