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 2024-03-28.

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	17% 9% 4 6% 5% 3 5% 5% 5% 7% 34%	79149
	Night	17% 10% 4 6% 6% 3 4 4 5% 6% 35%	80856
Transparency	Day	50% 3 10% 22% 13% 2	78872
	Night	51% 3 9% 21% 14% 2	80652
Seeing	Day	23% 10% 24% 22% 14% 5%	14164
	Night	23% 8% 21% 30% 16% 2	24362

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	17% 20% 8% 10% 6% 2 3 3 4 6% 20%	2836
	11th to 20th	Day	18% 19% 9% 10% 9% 3 3 3 3 3 20%	2840
	21st to end	Day	23% 19% 5% 8% 5% 3 3 3 3 5% 22%	3124
February	1st to 10th	Day	21% 13% 6% 8% 5% 3 4 3 4 5% 28%	1710
	11th to 20th	Day	23% 11% 5% 8% 5% 3 4 4 4 5% 27%	1787
	21st to end	Day	25% 12% 4 6% 5% 3 3 3 4 5% 31%	1570
March	1st to 10th	Day	18% 10% 4 6% 5% 3 4 6% 5% 5% 35%	2062
	11th to 20th	Day	21% 8% 4 6% 6% 4 5% 4 5% 5% 32%	2090
	21st to end	Day	22% 9% 3 7% 5% 3 4 4 5% 6% 32%	2255
April	1st to 10th	Day	15% 9% 4 6% 6% 3 5% 4 5% 7% 37%	1980
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 3 5% 6% 41%	2224
	21st to end	Day	19% 8% 2 6% 5% 3 5% 4 5% 7% 35%	2340
May	1st to 10th	Day	19% 7% 3 7% 6% 3 5% 5% 6% 6% 32%	2340
	11th to 20th	Day	19% 7% 3 6% 6% 4 5% 4 5% 8% 32%	2301
	21st to end	Day	11% 5% 2 5% 6% 5% 6% 5% 7% 9% 38%	2531
June	1st to 10th	Day	13% 4 3 5% 5% 3 5% 6% 6% 10% 40%	2340
	11th to 20th	Day	10% 5% 3 5% 6% 4 5% 6% 7% 10% 39%	2340
	21st to end	Day	10% 5% 3 6% 5% 4 5% 6% 7% 10% 38%	2340
July	1st to 10th	Day	12% 5% 2 6% 6% 3 6% 6% 7% 9% 38%	2340
	11th to 20th	Day	10% 5% 3 6% 7% 4 7% 5% 7% 10% 36%	2340
	21st to end	Day	13% 5% 3 6% 6% 5% 6% 6% 7% 9% 34%	2547
August	1st to 10th	Day	13% 6% 3 6% 5% 4 6% 7% 8% 10% 32%	2327
	11th to 20th	Day	14% 6% 3 6% 7% 4 6% 7% 6% 10% 33%	2303
	21st to end	Day	11% 5% 2 5% 5% 3 5% 5% 7% 10% 40%	2499
September	1st to 10th	Day	14% 5% 2 4 5% 3 5% 5% 6% 7% 46%	2008
	11th to 20th	Day	11% 5% 2 6% 5% 3 4 4 6% 8% 45%	1980
	21st to end	Day	17% 8% 3 5% 5% 3 3 4 4 6% 42%	1980
October	1st to 10th	Day	16% 6% 2 4 4 3 3 3 5% 9% 44%	1882
	11th to 20th	Day	17% 7% 3 5% 4 3 4 4 5% 6% 44%	1800
	21st to end	Day	22% 7% 2 6% 4 2 3 3 4 6% 40%	1980
November	1st to 10th	Day	12% 5% 3 5% 3 3 3 4 5% 5% 51%	1746
	11th to 20th	Day	16% 9% 4 7% 5% 3 4 4 5% 7% 37%	1710
	21st to end	Day	18% 10% 2 6% 5% 3 4 4 4 7% 37%	1710
December	1st to 10th	Day	25% 14% 5% 8% 5% 3 3 4 3 5% 25%	1710
	11th to 20th	Day	21% 15% 4 9% 4 2 3 4 5% 6% 29%	2153
	21st to end	Day	19% 17% 5% 9% 7% 3 5% 5% 5% 7% 19%	3124
January	1st to 10th	Night	19% 20% 5% 9% 7% 3 4 4 4 4 22%	4109
	11th to 20th	Night	22% 14% 6% 10% 7% 3 4 3 4 4 24%	4120
	21st to end	Night	27% 14% 5% 8% 7% 2 4 3 3 4 22%	4532
February	1st to 10th	Night	19% 13% 5% 7% 7% 3 5% 4 4 5% 28%	2470
	11th to 20th	Night	23% 12% 4 8% 6% 3 4 3 3 5% 27%	2274
	21st to end	Night	23% 13% 4 6% 6% 3 4 4 4 5% 28%	1884
March	1st to 10th	Night	18% 11% 3 6% 4 3 4 4 4 5% 37%	2117
	11th to 20th	Night	21% 9% 4 7% 5% 3 4 4 6% 7% 33%	2090
	21st to end	Night	18% 9% 3 7% 6% 3 4 4 5% 6% 34%	2256
April	1st to 10th	Night	17% 9% 3 5% 5% 3 4 3 6% 7% 38%	1980
	11th to 20th	Night	15% 6% 3 5% 5% 3 4 5% 6% 8% 39%	1697
	21st to end	Night	17% 6% 3 7% 6% 3 4 5% 5% 5% 39%	1620
May	1st to 10th	Night	20% 7% 3 6% 5% 3 5% 5% 5% 8% 33%	1620
	11th to 20th	Night	17% 7% 3 7% 6% 3 5% 5% 5% 8% 33%	1592
	21st to end	Night	11% 5% 2 5% 5% 2 4 6% 7% 10% 42%	1744
June	1st to 10th	Night	10% 5% 2 6% 4 3 5% 6% 6% 9% 43%	1620
	11th to 20th	Night	8% 5% 3 6% 7% 3 6% 5% 6% 8% 43%	1620
	21st to end	Night	10% 5% 2 5% 5% 4 4 5% 5% 10% 45%	1620
July	1st to 10th	Night	10% 6% 3 7% 6% 3 5% 5% 6% 10% 39%	1620
	11th to 20th	Night	6% 5% 2 5% 6% 4 5% 5% 6% 11% 44%	1620
	21st to end	Night	9% 5% 2 6% 6% 4 5% 5% 7% 10% 41%	1771
August	1st to 10th	Night	10% 5% 3 7% 7% 4 6% 6% 7% 8% 39%	1611
	11th to 20th	Night	11% 6% 3 5% 6% 4 5% 5% 6% 8% 43%	1598
	21st to end	Night	10% 5% 2 4 5% 3 4 6% 6% 9% 47%	1837
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 5% 5% 8% 47%	1948
	11th to 20th	Night	11% 5% 2 4 5% 3 4 4 6% 7% 50%	1980
	21st to end	Night	13% 8% 2 5% 4 4 4 4 6% 7% 43%	1980
October	1st to 10th	Night	13% 4 2 5% 4 3 3 5% 6% 6% 49%	2077
	11th to 20th	Night	16% 7% 4 5% 4 3 4 4 4 6% 44%	2160
	21st to end	Night	22% 6% 2 5% 4 3 4 4 4 6% 40%	2376
November	1st to 10th	Night	13% 6% 2 5% 5% 2 4 4 4 5% 49%	2329
	11th to 20th	Night	19% 9% 3 4 4 3 4 4 6% 7% 39%	2470
	21st to end	Night	17% 10% 3 5% 5% 3 4 4 4 5% 38%	2470
December	1st to 10th	Night	24% 14% 5% 8% 5% 3 4 3 3 5% 27%	2470
	11th to 20th	Night	19% 15% 6% 7% 4 3 3 4 4 5% 28%	3042
	21st to end	Night	17% 17% 6% 8% 7% 4 5% 4 4 5% 22%	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	68% 1 9% 14% 7%	2837
	11th to 20th	Day	73% 1 6% 15% 4 1	2840
	21st to end	Day	68% 1 5% 19% 5% 1	3124
February	1st to 10th	Day	61% 3 7% 19% 10%	1710
	11th to 20th	Day	61% 3 6% 17% 11% 2	1797
	21st to end	Day	58% 2 7% 19% 12% 1	1570
March	1st to 10th	Day	50% 2 9% 25% 11% 2	2062
	11th to 20th	Day	56% 2 7% 19% 13% 2	2090
	21st to end	Day	55% 3 8% 22% 10% 2	2255
April	1st to 10th	Day	48% 2 10% 22% 15% 4	1980
	11th to 20th	Day	45% 3 8% 21% 18% 4	2224
	21st to end	Day	50% 3 10% 22% 11% 3	2340
May	1st to 10th	Day	52% 3 9% 23% 11% 2	2340
	11th to 20th	Day	52% 4 12% 21% 9% 2	2305
	21st to end	Day	41% 6% 15% 26% 12% 1	2531
June	1st to 10th	Day	41% 4 12% 26% 16% 1	2340
	11th to 20th	Day	39% 5% 16% 23% 15% 1	2340
	21st to end	Day	40% 6% 14% 24% 14% 2	2340
July	1st to 10th	Day	42% 6% 13% 21% 16% 2	2275
	11th to 20th	Day	41% 5% 14% 22% 16% 2	2271
	21st to end	Day	45% 5% 12% 23% 13% 2	2405
August	1st to 10th	Day	45% 6% 15% 24% 11% 1	2314
	11th to 20th	Day	46% 5% 11% 24% 12% 1	2303
	21st to end	Day	39% 4 13% 26% 14% 3	2499
September	1st to 10th	Day	37% 4 11% 24% 19% 5%	2008
	11th to 20th	Day	38% 3 9% 27% 21% 1	1980
	21st to end	Day	45% 3 8% 22% 20% 2	1980
October	1st to 10th	Day	39% 3 10% 24% 21% 3	1882
	11th to 20th	Day	43% 2 8% 27% 19% 1	1800
	21st to end	Day	48% 2 9% 23% 17% 2	1980
November	1st to 10th	Day	37% 2 8% 28% 22% 4	1746
	11th to 20th	Day	49% 2 6% 21% 20% 3	1710
	21st to end	Day	49% 2 10% 22% 16% 1	1710
December	1st to 10th	Day	64% 2 7% 21% 5% 1	1710
	11th to 20th	Day	58% 2 9% 18% 12% 1	2150
	21st to end	Day	67% 2 8% 18% 5%	3124
January	1st to 10th	Night	69% 1 7% 16% 6% 1	4109
	11th to 20th	Night	66% 2 5% 19% 7%	4120
	21st to end	Night	68% 2 5% 18% 6% 1	4532
February	1st to 10th	Night	60% 2 7% 19% 12%	2470
	11th to 20th	Night	62% 2 6% 17% 12% 1	2275
	21st to end	Night	61% 2 8% 16% 10% 4	1884
March	1st to 10th	Night	52% 2 5% 23% 16% 2	2117
	11th to 20th	Night	52% 3 8% 23% 13% 1	2090
	21st to end	Night	52% 2 9% 20% 15% 3	2256
April	1st to 10th	Night	46% 3 8% 22% 18% 3	1980
	11th to 20th	Night	43% 3 10% 22% 16% 7%	1697
	21st to end	Night	47% 4 9% 21% 17% 2	1620
May	1st to 10th	Night	50% 4 11% 19% 14% 3	1620
	11th to 20th	Night	49% 6% 12% 21% 11% 3	1593
	21st to end	Night	37% 5% 16% 26% 14% 1	1745
June	1st to 10th	Night	36% 6% 15% 25% 16% 2	1620
	11th to 20th	Night	40% 5% 16% 18% 19% 2	1620
	21st to end	Night	36% 6% 14% 26% 15% 3	1620
July	1st to 10th	Night	41% 6% 15% 19% 16% 4	1575
	11th to 20th	Night	34% 7% 16% 23% 17% 3	1566
	21st to end	Night	38% 4 15% 27% 15% 1	1672
August	1st to 10th	Night	42% 6% 13% 24% 13% 2	1600
	11th to 20th	Night	39% 5% 14% 26% 16% 1	1598
	21st to end	Night	34% 4 12% 28% 18% 3	1837
September	1st to 10th	Night	36% 5% 12% 23% 18% 7%	1948
	11th to 20th	Night	34% 3 10% 25% 25% 3	1980
	21st to end	Night	40% 3 9% 25% 21% 1	1980
October	1st to 10th	Night	35% 3 11% 26% 21% 4	2077
	11th to 20th	Night	43% 3 7% 23% 21% 3	2160
	21st to end	Night	47% 2 5% 25% 17% 4	2376
November	1st to 10th	Night	39% 2 8% 22% 24% 5%	2329
	11th to 20th	Night	47% 2 7% 20% 20% 4	2470
	21st to end	Night	50% 2 8% 22% 17% 2	2470
December	1st to 10th	Night	63% 2 7% 19% 7% 1	2470
	11th to 20th	Night	60% 2 7% 21% 10% 1	3044
	21st to end	Night	66% 2 7% 17% 8%	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	32% 20% 33% 11% 4 1	270
	11th to 20th	Day	42% 20% 27% 9% 2	270
	21st to end	Day	35% 22% 28% 11% 3	297
February	1st to 10th	Day	36% 19% 29% 13% 4	270
	11th to 20th	Day	47% 21% 23% 6% 2	270
	21st to end	Day	42% 18% 31% 9% 1	225
March	1st to 10th	Day	32% 18% 28% 16% 6%	432
	11th to 20th	Day	29% 21% 31% 14% 5% 1	460
	21st to end	Day	34% 15% 28% 19% 4	490
April	1st to 10th	Day	26% 17% 29% 19% 9%	420
	11th to 20th	Day	25% 15% 30% 16% 10% 4	412
	21st to end	Day	30% 13% 29% 17% 10% 2	420
May	1st to 10th	Day	29% 14% 28% 17% 7% 4	423
	11th to 20th	Day	22% 10% 26% 25% 13% 4	447
	21st to end	Day	14% 6% 23% 27% 20% 9%	485
June	1st to 10th	Day	17% 5% 24% 26% 19% 8%	450
	11th to 20th	Day	14% 7% 22% 30% 20% 8%	450
	21st to end	Day	14% 6% 29% 26% 18% 8%	450
July	1st to 10th	Day	16% 3 14% 28% 21% 18%	445
	11th to 20th	Day	9% 2 20% 35% 22% 11%	444
	21st to end	Day	15% 2 17% 30% 24% 12%	488
August	1st to 10th	Day	16% 3 15% 30% 24% 12%	446
	11th to 20th	Day	17% 3 13% 28% 28% 11%	439
	21st to end	Day	14% 2 16% 31% 26% 12%	495
September	1st to 10th	Day	15% 4 15% 28% 27% 12%	450
	11th to 20th	Day	13% 1 14% 30% 30% 12%	450
	21st to end	Day	22% 6% 23% 26% 17% 6%	450
October	1st to 10th	Day	19% 5% 23% 26% 23% 5%	450
	11th to 20th	Day	20% 10% 27% 25% 14% 3	450
	21st to end	Day	28% 12% 27% 21% 9% 2	495
November	1st to 10th	Day	19% 12% 28% 27% 12% 2	344
	11th to 20th	Day	30% 17% 24% 21% 7% 1	270
	21st to end	Day	25% 16% 34% 22% 3	270
December	1st to 10th	Day	35% 16% 28% 15% 4 2	270
	11th to 20th	Day	30% 16% 32% 17% 4 1	270
	21st to end	Day	34% 15% 31% 13% 6%	297
January	1st to 10th	Night	32% 14% 27% 21% 5%	760
	11th to 20th	Night	36% 15% 24% 21% 4	760
	21st to end	Night	30% 16% 28% 23% 4	836
February	1st to 10th	Night	28% 12% 30% 28% 3	760
	11th to 20th	Night	34% 17% 27% 19% 2	743
	21st to end	Night	34% 14% 29% 21% 2	628
March	1st to 10th	Night	28% 15% 25% 27% 4	760
	11th to 20th	Night	28% 16% 28% 21% 7%	760
	21st to end	Night	25% 12% 28% 28% 7%	821
April	1st to 10th	Night	24% 15% 28% 26% 7%	720
	11th to 20th	Night	20% 10% 28% 28% 13% 1	633
	21st to end	Night	21% 7% 31% 33% 8% 1	540
May	1st to 10th	Night	23% 7% 27% 30% 12% 1	540
	11th to 20th	Night	20% 5% 23% 34% 17% 1	531
	21st to end	Night	15% 2 18% 34% 27% 3	584
June	1st to 10th	Night	12% 2 18% 38% 27% 3	540
	11th to 20th	Night	11% 2 15% 38% 30% 4	540
	21st to end	Night	12% 4 14% 41% 28% 2	540
July	1st to 10th	Night	14% 2 10% 34% 32% 7%	525
	11th to 20th	Night	9% 1 10% 36% 38% 6%	522
	21st to end	Night	13% 2 8% 35% 37% 5%	591
August	1st to 10th	Night	14% 8% 37% 37% 4	537
	11th to 20th	Night	14% 2 5% 36% 37% 6%	534
	21st to end	Night	12% 1 9% 35% 35% 7%	649
September	1st to 10th	Night	14% 1 11% 32% 35% 6%	720
	11th to 20th	Night	13% 3 14% 31% 34% 5%	720
	21st to end	Night	18% 3 17% 32% 26% 3	720
October	1st to 10th	Night	16% 4 19% 33% 25% 3	720
	11th to 20th	Night	22% 7% 22% 32% 16% 1	720
	21st to end	Night	27% 7% 21% 32% 13% 1	792
November	1st to 10th	Night	17% 8% 23% 34% 17% 1	740
	11th to 20th	Night	25% 13% 23% 28% 11% 1	760
	21st to end	Night	26% 10% 22% 32% 9% 1	760
December	1st to 10th	Night	33% 11% 25% 25% 5%	760
	11th to 20th	Night	27% 14% 26% 28% 6%	760
	21st to end	Night	31% 12% 23% 29% 4	836

Page generated at 2024-03-24 23:36:59. Version ac07

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