Charles Towne Landing State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charles Towne Landing State Historic Site clear sky chart from 2005-11-06 to 2025-12-18.

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 6% 4 5% 5% 4 7% 9% 41%	127082
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	123972
Transparency	Day	36% 9% 15% 19% 16% 5%	130701
	Night	36% 8% 13% 18% 18% 7%	128422
Seeing	Day	12% 7% 23% 28% 22% 8%	17079
	Night	12% 6% 22% 31% 24% 5%	27171

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	11% 5% 2 4 3 3 4 3 4 8% 52%	4056
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 4 7% 49%	4060
	21st to end	Day	14% 9% 2 6% 3 3 3 2 5% 7% 44%	4466
February	1st to 10th	Day	14% 7% 1 6% 4 5% 5% 4 6% 7% 41%	1800
	11th to 20th	Day	18% 7% 2 6% 3 3 3 3 4 5% 45%	1908
	21st to end	Day	12% 7% 3 6% 4 3 4 4 5% 5% 47%	1806
March	1st to 10th	Day	21% 9% 3 7% 4 3 3 3 5% 5% 36%	4935
	11th to 20th	Day	8% 3 1 4 3 4 4 4 6% 7% 55%	4980
	21st to end	Day	12% 5% 2 6% 4 4 4 3 5% 5% 49%	5465
April	1st to 10th	Day	7% 5% 2 4 4 4 4 4 5% 7% 53%	2224
	11th to 20th	Day	9% 4 2 5% 3 4 4 3 6% 8% 52%	2374
	21st to end	Day	5% 4 1 4 3 3 3 4 7% 9% 55%	2400
May	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 11% 39%	5767
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 5% 8% 9% 35%	5861
	21st to end	Day	7% 4 2 6% 4 5% 5% 5% 8% 11% 43%	6433
June	1st to 10th	Day	8% 7% 2 7% 6% 6% 8% 6% 8% 10% 32%	2600
	11th to 20th	Day	7% 5% 2 5% 5% 5% 6% 6% 9% 12% 38%	2600
	21st to end	Day	6% 4 2 6% 5% 6% 7% 6% 10% 12% 34%	2600
July	1st to 10th	Day	11% 6% 3 9% 6% 7% 7% 6% 9% 11% 25%	5900
	11th to 20th	Day	4 4 2 6% 5% 6% 8% 7% 11% 16% 31%	5900
	21st to end	Day	5% 4 2 7% 6% 6% 7% 6% 9% 15% 33%	6424
August	1st to 10th	Day	19% 8% 2 8% 5% 5% 6% 5% 9% 10% 22%	4234
	11th to 20th	Day	6% 6% 2 7% 6% 6% 7% 5% 9% 12% 33%	4047
	21st to end	Day	10% 6% 3 8% 5% 6% 5% 5% 7% 10% 35%	4312
September	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 6% 6% 10% 36%	2289
	11th to 20th	Day	11% 8% 2 8% 5% 5% 6% 5% 8% 8% 35%	2200
	21st to end	Day	14% 7% 3 6% 4 4 4 4 6% 9% 38%	2200
October	1st to 10th	Day	13% 7% 2 6% 4 5% 4 3 5% 5% 46%	2035
	11th to 20th	Day	8% 4 2 4 3 3 3 3 5% 8% 57%	2000
	21st to end	Day	9% 5% 2 5% 4 3 3 2 4 6% 56%	2200
November	1st to 10th	Day	10% 5% 2 4 3 4 3 3 5% 6% 54%	2057
	11th to 20th	Day	11% 7% 2 6% 4 4 3 3 4 6% 51%	2100
	21st to end	Day	12% 6% 1 4 3 3 3 3 5% 7% 52%	1927
December	1st to 10th	Day	9% 5% 2 6% 3 5% 4 4 5% 6% 51%	3020
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 4 6% 49%	3436
	21st to end	Day	18% 8% 3 6% 3 4 4 3 5% 6% 41%	4466
January	1st to 10th	Night	9% 5% 2 5% 3 4 4 3 5% 5% 56%	5889
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 6% 7% 43%	5900
	21st to end	Night	12% 7% 3 7% 4 3 4 4 4 6% 45%	6490
February	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 6% 6% 44%	2600
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 6% 42%	2373
	21st to end	Night	11% 8% 3 7% 5% 4 4 3 6% 6% 43%	1821
March	1st to 10th	Night	16% 11% 3 7% 4 3 4 3 4 5% 40%	4918
	11th to 20th	Night	9% 5% 2 5% 3 3 3 3 6% 9% 51%	4980
	21st to end	Night	13% 5% 2 5% 3 3 3 3 6% 7% 50%	5467
April	1st to 10th	Night	9% 5% 2 6% 4 4 3 4 6% 7% 51%	2175
	11th to 20th	Night	11% 4 1 5% 3 4 4 3 5% 7% 52%	1975
	21st to end	Night	6% 4 2 4 4 4 4 3 6% 9% 53%	2000
May	1st to 10th	Night	5% 5% 2 6% 4 4 5% 5% 7% 9% 47%	4156
	11th to 20th	Night	13% 6% 2 6% 4 5% 4 4 8% 10% 38%	4032
	21st to end	Night	9% 5% 2 6% 4 4 5% 5% 8% 9% 44%	4421
June	1st to 10th	Night	8% 6% 2 7% 5% 6% 6% 5% 8% 13% 34%	1800
	11th to 20th	Night	6% 5% 2 6% 5% 5% 6% 6% 9% 12% 38%	1800
	21st to end	Night	4 5% 2 6% 6% 6% 6% 6% 9% 12% 37%	1800
July	1st to 10th	Night	9% 5% 3 8% 6% 7% 8% 6% 9% 11% 30%	4058
	11th to 20th	Night	5% 4 2 7% 5% 5% 6% 6% 8% 14% 36%	4057
	21st to end	Night	6% 6% 2 7% 6% 6% 6% 6% 9% 13% 35%	4427
August	1st to 10th	Night	17% 8% 3 8% 4 4 5% 5% 9% 13% 24%	2915
	11th to 20th	Night	7% 5% 2 7% 5% 6% 6% 6% 8% 12% 36%	2967
	21st to end	Night	8% 6% 2 7% 5% 4 4 4 6% 9% 44%	3586
September	1st to 10th	Night	9% 6% 2 8% 6% 6% 5% 5% 7% 10% 37%	2107
	11th to 20th	Night	10% 7% 2 7% 5% 6% 6% 4 6% 8% 38%	2200
	21st to end	Night	14% 6% 3 7% 4 4 4 4 7% 8% 39%	2200
October	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 46%	2365
	11th to 20th	Night	10% 3 2 4 3 2 3 4 5% 6% 57%	2400
	21st to end	Night	10% 5% 2 5% 3 3 3 2 6% 5% 56%	2640
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 6% 55%	2461
	11th to 20th	Night	13% 6% 2 5% 4 3 2 2 5% 7% 51%	2520
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 7% 47%	2688
December	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 4 5% 55%	4380
	11th to 20th	Night	14% 8% 3 8% 5% 3 3 3 4 5% 44%	4914
	21st to end	Night	16% 7% 2 6% 4 4 4 4 4 6% 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	31% 5% 7% 17% 32% 8%	4057
	11th to 20th	Day	36% 4 6% 16% 29% 9%	4060
	21st to end	Day	40% 5% 7% 18% 19% 11%	4466
February	1st to 10th	Day	40% 6% 10% 20% 18% 5%	1800
	11th to 20th	Day	42% 5% 8% 16% 22% 8%	1918
	21st to end	Day	38% 5% 10% 19% 18% 10%	1806
March	1st to 10th	Day	47% 7% 7% 12% 18% 9%	4935
	11th to 20th	Day	27% 7% 11% 15% 23% 18%	4980
	21st to end	Day	36% 7% 10% 19% 19% 10%	5465
April	1st to 10th	Day	29% 7% 14% 22% 20% 9%	2224
	11th to 20th	Day	28% 6% 13% 24% 19% 10%	2374
	21st to end	Day	23% 7% 16% 29% 20% 5%	2400
May	1st to 10th	Day	34% 11% 20% 25% 9% 2	5801
	11th to 20th	Day	40% 9% 21% 22% 8%	5865
	21st to end	Day	31% 11% 18% 21% 19% 1	6447
June	1st to 10th	Day	41% 13% 18% 19% 10%	2600
	11th to 20th	Day	32% 12% 24% 25% 7%	2600
	21st to end	Day	35% 15% 23% 19% 7% 1	2600
July	1st to 10th	Day	47% 13% 23% 14% 3	5835
	11th to 20th	Day	35% 17% 37% 9% 2	5831
	21st to end	Day	35% 14% 25% 23% 2	6240
August	1st to 10th	Day	52% 12% 23% 10% 2	4221
	11th to 20th	Day	38% 14% 20% 21% 7%	4086
	21st to end	Day	40% 10% 16% 30% 3	4312
September	1st to 10th	Day	40% 12% 17% 15% 13% 2	2289
	11th to 20th	Day	42% 11% 14% 19% 11% 3	2200
	21st to end	Day	42% 8% 15% 19% 13% 3	2200
October	1st to 10th	Day	42% 5% 8% 14% 27% 5%	3308
	11th to 20th	Day	17% 4 6% 14% 32% 26%	3240
	21st to end	Day	24% 5% 7% 18% 37% 8%	3538
November	1st to 10th	Day	30% 5% 11% 16% 25% 11%	2057
	11th to 20th	Day	35% 5% 8% 19% 23% 11%	2100
	21st to end	Day	32% 5% 11% 21% 23% 7%	1927
December	1st to 10th	Day	32% 6% 9% 18% 19% 16%	3020
	11th to 20th	Day	37% 4 10% 21% 23% 4	3433
	21st to end	Day	44% 5% 7% 22% 20% 3	4466
January	1st to 10th	Night	28% 6% 6% 14% 36% 9%	5889
	11th to 20th	Night	40% 5% 6% 17% 26% 7%	5900
	21st to end	Night	39% 5% 7% 13% 24% 11%	6490
February	1st to 10th	Night	40% 5% 9% 20% 19% 8%	2600
	11th to 20th	Night	43% 6% 9% 14% 19% 10%	2374
	21st to end	Night	41% 5% 10% 17% 15% 12%	1821
March	1st to 10th	Night	46% 6% 8% 13% 19% 9%	4918
	11th to 20th	Night	29% 5% 10% 14% 25% 16%	4980
	21st to end	Night	33% 6% 10% 20% 19% 11%	5467
April	1st to 10th	Night	32% 7% 13% 20% 19% 9%	2175
	11th to 20th	Night	31% 6% 9% 23% 20% 11%	1975
	21st to end	Night	26% 8% 14% 26% 22% 4	2000
May	1st to 10th	Night	30% 10% 20% 29% 9% 2	4184
	11th to 20th	Night	38% 10% 20% 20% 10% 1	4033
	21st to end	Night	33% 9% 16% 25% 16% 1	4429
June	1st to 10th	Night	37% 13% 20% 20% 10%	1800
	11th to 20th	Night	33% 13% 22% 24% 7% 1	1800
	21st to end	Night	33% 13% 27% 21% 4 1	1800
July	1st to 10th	Night	43% 13% 25% 16% 2	4015
	11th to 20th	Night	36% 15% 38% 8% 2	4006
	21st to end	Night	36% 15% 24% 23% 2	4297
August	1st to 10th	Night	47% 15% 24% 11% 2	2904
	11th to 20th	Night	36% 13% 23% 22% 6%	2994
	21st to end	Night	35% 10% 17% 34% 3	3586
September	1st to 10th	Night	40% 12% 17% 18% 11% 2	2107
	11th to 20th	Night	40% 11% 16% 19% 12% 2	2200
	21st to end	Night	41% 8% 15% 21% 12% 2	2200
October	1st to 10th	Night	36% 6% 10% 17% 25% 6%	3872
	11th to 20th	Night	16% 5% 6% 14% 27% 32%	3899
	21st to end	Night	25% 5% 6% 19% 30% 15%	4252
November	1st to 10th	Night	31% 5% 9% 18% 24% 12%	2461
	11th to 20th	Night	34% 4 8% 18% 24% 12%	2520
	21st to end	Night	35% 5% 10% 17% 22% 10%	2688
December	1st to 10th	Night	32% 5% 8% 15% 28% 12%	4380
	11th to 20th	Night	44% 5% 10% 15% 20% 7%	4916
	21st to end	Night	40% 6% 8% 22% 21% 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	13% 10% 47% 26% 4	300
	11th to 20th	Day	10% 12% 40% 24% 12% 2	300
	21st to end	Day	20% 16% 40% 20% 3 1	330
February	1st to 10th	Day	15% 14% 38% 25% 8%	300
	11th to 20th	Day	27% 11% 37% 21% 3	300
	21st to end	Day	10% 12% 43% 27% 7% 1	405
March	1st to 10th	Day	14% 15% 33% 27% 11%	500
	11th to 20th	Day	13% 10% 38% 30% 7% 2	500
	21st to end	Day	12% 11% 41% 25% 10% 2	550
April	1st to 10th	Day	12% 13% 36% 27% 11% 1	500
	11th to 20th	Day	7% 11% 31% 27% 17% 6%	492
	21st to end	Day	5% 7% 27% 33% 20% 8%	500
May	1st to 10th	Day	5% 9% 33% 30% 17% 6%	503
	11th to 20th	Day	12% 4 23% 30% 23% 9%	527
	21st to end	Day	10% 4 16% 33% 25% 12%	573
June	1st to 10th	Day	8% 3 18% 35% 25% 12%	530
	11th to 20th	Day	8% 3 14% 28% 28% 18%	530
	21st to end	Day	6% 2 12% 32% 33% 15%	530
July	1st to 10th	Day	7% 3 6% 26% 41% 18%	525
	11th to 20th	Day	7% 2 5% 23% 43% 21%	524
	21st to end	Day	5% 3 6% 33% 39% 14%	576
August	1st to 10th	Day	13% 2 10% 26% 34% 15%	526
	11th to 20th	Day	6% 3 6% 24% 41% 21%	519
	21st to end	Day	14% 2 10% 23% 33% 17%	583
September	1st to 10th	Day	11% 5% 8% 26% 35% 15%	530
	11th to 20th	Day	14% 3 13% 31% 29% 10%	530
	21st to end	Day	16% 2 12% 29% 28% 12%	530
October	1st to 10th	Day	18% 5% 21% 30% 18% 8%	530
	11th to 20th	Day	10% 4 21% 32% 24% 9%	530
	21st to end	Day	11% 5% 24% 31% 25% 4	583
November	1st to 10th	Day	14% 6% 27% 28% 21% 5%	535
	11th to 20th	Day	15% 6% 35% 28% 15% 2	540
	21st to end	Day	12% 10% 31% 31% 14% 2	367
December	1st to 10th	Day	18% 10% 31% 30% 10% 1	330
	11th to 20th	Day	17% 10% 35% 24% 12% 2	321
	21st to end	Day	22% 10% 31% 26% 10% 1	330
January	1st to 10th	Night	13% 11% 36% 34% 6%	800
	11th to 20th	Night	14% 10% 32% 32% 12%	800
	21st to end	Night	16% 10% 39% 30% 4	880
February	1st to 10th	Night	16% 9% 32% 33% 10%	800
	11th to 20th	Night	19% 11% 33% 31% 5%	783
	21st to end	Night	15% 9% 34% 34% 7% 1	660
March	1st to 10th	Night	12% 9% 34% 35% 11%	800
	11th to 20th	Night	13% 9% 30% 36% 11% 1	800
	21st to end	Night	12% 7% 35% 32% 14% 1	880
April	1st to 10th	Night	10% 10% 30% 34% 15% 1	800
	11th to 20th	Night	12% 9% 25% 32% 21% 3	791
	21st to end	Night	9% 5% 24% 37% 24% 1	800
May	1st to 10th	Night	8% 5% 23% 37% 23% 4	659
	11th to 20th	Night	10% 3 21% 31% 28% 6%	591
	21st to end	Night	9% 2 12% 27% 38% 11%	650
June	1st to 10th	Night	10% 3 13% 36% 32% 7%	600
	11th to 20th	Night	6% 2 9% 28% 41% 15%	600
	21st to end	Night	6% 2 9% 31% 42% 12%	600
July	1st to 10th	Night	8% 2 6% 24% 47% 12%	585
	11th to 20th	Night	9% 1 4 21% 48% 17%	582
	21st to end	Night	5% 3 4 30% 48% 11%	657
August	1st to 10th	Night	12% 3 4 24% 44% 13%	597
	11th to 20th	Night	8% 2 6% 24% 44% 15%	647
	21st to end	Night	11% 2 8% 24% 38% 16%	880
September	1st to 10th	Night	10% 3 10% 27% 41% 10%	800
	11th to 20th	Night	10% 3 9% 32% 36% 10%	800
	21st to end	Night	16% 2 10% 28% 34% 9%	800
October	1st to 10th	Night	15% 3 17% 31% 27% 7%	800
	11th to 20th	Night	11% 4 21% 33% 26% 5%	800
	21st to end	Night	12% 5% 22% 31% 26% 4	880
November	1st to 10th	Night	12% 5% 22% 36% 22% 3	820
	11th to 20th	Night	15% 7% 25% 35% 16% 2	840
	21st to end	Night	11% 9% 26% 34% 18% 2	840
December	1st to 10th	Night	16% 7% 31% 32% 13% 1	840
	11th to 20th	Night	17% 8% 28% 29% 17% 1	829
	21st to end	Night	20% 10% 29% 30% 11% 1	880

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