Congaree National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Congaree National Park clear sky chart from 2005-11-06 to 2025-04-26.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	114204
	Night	12% 6% 2 6% 4 4 4 4 6% 7% 45%	114426
Transparency	Day	37% 7% 11% 19% 19% 6%	117894
	Night	36% 7% 10% 18% 21% 8%	118862
Seeing	Day	14% 9% 23% 24% 20% 10%	15969
	Night	15% 7% 23% 33% 20% 2	26132

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	14% 5% 1 4 3 3 3 3 4 6% 54%	4056
	11th to 20th	Day	11% 5% 2 4 3 3 3 2 4 5% 58%	4060
	21st to end	Day	14% 8% 3 7% 5% 3 4 3 4 5% 45%	4466
February	1st to 10th	Day	14% 7% 2 7% 3 4 4 4 6% 7% 42%	1802
	11th to 20th	Day	19% 7% 3 5% 4 3 3 2 5% 4 44%	1948
	21st to end	Day	16% 6% 2 6% 4 4 5% 3 4 5% 44%	1730
March	1st to 10th	Day	21% 9% 3 6% 4 3 3 3 5% 5% 39%	4935
	11th to 20th	Day	8% 4 2 5% 4 4 4 3 5% 7% 55%	4980
	21st to end	Day	13% 7% 2 6% 4 4 4 3 4 5% 47%	5465
April	1st to 10th	Day	10% 4 1 5% 4 4 4 4 6% 7% 51%	2200
	11th to 20th	Day	10% 4 2 5% 5% 4 4 4 6% 7% 50%	2359
	21st to end	Day	8% 5% 2 6% 4 4 3 4 7% 8% 50%	2424
May	1st to 10th	Day	8% 7% 3 7% 5% 4 5% 4 7% 10% 40%	4082
	11th to 20th	Day	15% 8% 2 7% 4 4 5% 4 5% 8% 38%	4081
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 7% 11% 48%	4476
June	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 5% 9% 10% 35%	2470
	11th to 20th	Day	7% 5% 1 5% 6% 5% 6% 5% 8% 11% 41%	2470
	21st to end	Day	5% 5% 2 6% 6% 6% 6% 7% 9% 10% 38%	2470
July	1st to 10th	Day	13% 7% 3 8% 7% 7% 6% 6% 9% 10% 25%	4120
	11th to 20th	Day	6% 6% 2 7% 6% 8% 7% 7% 10% 13% 28%	4120
	21st to end	Day	9% 7% 3 9% 6% 7% 8% 6% 10% 12% 23%	4466
August	1st to 10th	Day	22% 6% 2 7% 6% 5% 7% 5% 8% 11% 22%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 6% 6% 5% 8% 11% 34%	4044
	21st to end	Day	7% 5% 2 5% 4 4 5% 5% 8% 11% 44%	4186
September	1st to 10th	Day	8% 6% 2 7% 5% 5% 5% 5% 7% 10% 41%	2100
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 4 6% 7% 39%	2090
	21st to end	Day	18% 6% 2 5% 4 4 5% 3 5% 6% 43%	2090
October	1st to 10th	Day	13% 5% 2 6% 4 4 4 3 4 6% 49%	1974
	11th to 20th	Day	10% 4 1 5% 4 3 3 3 4 6% 58%	1900
	21st to end	Day	10% 4 2 5% 3 3 3 3 4 4 57%	2090
November	1st to 10th	Day	12% 5% 2 4 4 3 3 3 5% 5% 53%	1957
	11th to 20th	Day	14% 7% 2 5% 3 2 3 3 5% 6% 51%	1920
	21st to end	Day	14% 5% 2 5% 4 3 4 3 4 7% 49%	1800
December	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 3 5% 5% 52%	2930
	11th to 20th	Day	14% 6% 2 6% 3 4 3 3 5% 7% 46%	3373
	21st to end	Day	19% 8% 2 5% 3 3 3 2 5% 5% 45%	4466
January	1st to 10th	Night	12% 4 2 5% 4 3 3 3 4 5% 56%	5889
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 5% 7% 48%	5900
	21st to end	Night	13% 8% 2 6% 4 3 3 3 4 5% 46%	6490
February	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 6% 44%	2595
	11th to 20th	Night	18% 7% 2 6% 4 3 3 2 5% 5% 44%	2338
	21st to end	Night	13% 6% 2 7% 3 5% 4 3 5% 6% 47%	1898
March	1st to 10th	Night	19% 8% 2 7% 4 4 3 3 4 6% 39%	4918
	11th to 20th	Night	11% 4 1 4 3 3 3 3 5% 8% 54%	4980
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 7% 49%	5467
April	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 6% 50%	2200
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 4 8% 52%	1990
	21st to end	Night	9% 4 2 5% 4 4 4 4 5% 7% 53%	1888
May	1st to 10th	Night	9% 6% 2 6% 5% 5% 4 4 7% 9% 43%	2813
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 6% 9% 40%	2812
	21st to end	Night	6% 5% 2 5% 5% 4 5% 5% 7% 10% 47%	3079
June	1st to 10th	Night	10% 6% 2 7% 5% 5% 6% 6% 8% 11% 34%	1710
	11th to 20th	Night	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	1710
	21st to end	Night	6% 6% 2 7% 5% 6% 6% 6% 11% 11% 33%	1710
July	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 5% 8% 10% 29%	2840
	11th to 20th	Night	8% 6% 3 7% 6% 6% 7% 6% 10% 13% 28%	2840
	21st to end	Night	12% 8% 3 9% 7% 6% 7% 6% 9% 10% 23%	3087
August	1st to 10th	Night	21% 7% 3 8% 5% 6% 6% 6% 8% 9% 22%	2825
	11th to 20th	Night	8% 7% 3 8% 5% 5% 6% 4 8% 11% 35%	2785
	21st to end	Night	6% 3 2 5% 4 3 5% 4 7% 13% 49%	3435
September	1st to 10th	Night	8% 6% 2 7% 6% 6% 5% 4 6% 9% 40%	2075
	11th to 20th	Night	13% 8% 3 7% 4 6% 5% 3 5% 7% 40%	2090
	21st to end	Night	16% 7% 2 6% 4 4 5% 3 5% 6% 41%	2090
October	1st to 10th	Night	14% 6% 2 4 3 4 3 3 4 6% 52%	2204
	11th to 20th	Night	12% 4 1 4 3 3 3 3 5% 5% 56%	2280
	21st to end	Night	9% 5% 2 5% 3 2 3 3 5% 6% 56%	2508
November	1st to 10th	Night	14% 5% 2 5% 2 3 3 3 4 5% 54%	2341
	11th to 20th	Night	14% 7% 2 4 3 3 3 3 4 6% 51%	2477
	21st to end	Night	13% 5% 2 5% 3 4 4 3 5% 7% 48%	2600
December	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	4250
	11th to 20th	Night	16% 7% 3 6% 4 3 3 3 4 5% 45%	4822
	21st to end	Night	18% 7% 3 6% 3 4 4 3 4 6% 42%	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% 4 6% 21% 31% 7%	4057
	11th to 20th	Day	31% 3 4 16% 36% 9%	4060
	21st to end	Day	42% 3 5% 16% 22% 11%	4466
February	1st to 10th	Day	40% 5% 10% 20% 19% 6%	1802
	11th to 20th	Day	44% 4 5% 18% 24% 6%	1958
	21st to end	Day	42% 5% 8% 15% 21% 9%	1730
March	1st to 10th	Day	48% 4 7% 12% 21% 9%	4935
	11th to 20th	Day	30% 5% 7% 15% 25% 17%	4980
	21st to end	Day	40% 5% 7% 18% 22% 9%	5465
April	1st to 10th	Day	31% 7% 11% 21% 24% 7%	2200
	11th to 20th	Day	33% 5% 11% 20% 21% 10%	2359
	21st to end	Day	30% 7% 11% 26% 22% 4	2424
May	1st to 10th	Day	35% 10% 16% 23% 13% 2	4120
	11th to 20th	Day	43% 7% 11% 22% 15% 1	4085
	21st to end	Day	27% 10% 18% 21% 22% 2	4489
June	1st to 10th	Day	39% 11% 17% 22% 10% 1	2470
	11th to 20th	Day	32% 10% 19% 24% 13% 1	2470
	21st to end	Day	34% 13% 17% 22% 12% 1	2470
July	1st to 10th	Day	46% 13% 17% 16% 6% 2	4055
	11th to 20th	Day	40% 16% 26% 14% 4 1	4051
	21st to end	Day	47% 15% 18% 16% 4	4324
August	1st to 10th	Day	53% 10% 19% 13% 4	4091
	11th to 20th	Day	39% 11% 16% 20% 13%	4083
	21st to end	Day	30% 10% 14% 32% 13% 1	4186
September	1st to 10th	Day	36% 11% 16% 16% 17% 5%	2100
	11th to 20th	Day	43% 8% 10% 16% 20% 3	2090
	21st to end	Day	41% 6% 10% 20% 17% 6%	2090
October	1st to 10th	Day	36% 4 8% 16% 27% 9%	3273
	11th to 20th	Day	17% 3 6% 17% 29% 28%	3140
	21st to end	Day	25% 4 5% 20% 31% 15%	3428
November	1st to 10th	Day	33% 5% 7% 18% 25% 12%	1957
	11th to 20th	Day	35% 4 7% 19% 25% 10%	1920
	21st to end	Day	35% 4 9% 20% 22% 9%	1800
December	1st to 10th	Day	35% 4 7% 18% 26% 10%	2930
	11th to 20th	Day	38% 5% 10% 22% 20% 6%	3370
	21st to end	Day	41% 4 7% 23% 23% 2	4466
January	1st to 10th	Night	30% 4 5% 18% 35% 7%	5889
	11th to 20th	Night	34% 5% 6% 16% 31% 7%	5900
	21st to end	Night	40% 5% 5% 13% 28% 9%	6490
February	1st to 10th	Night	40% 5% 8% 19% 20% 8%	2595
	11th to 20th	Night	43% 4 7% 18% 20% 8%	2339
	21st to end	Night	38% 6% 8% 17% 19% 13%	1898
March	1st to 10th	Night	45% 5% 8% 11% 22% 9%	4918
	11th to 20th	Night	28% 5% 7% 12% 29% 20%	4980
	21st to end	Night	34% 5% 8% 20% 21% 12%	5467
April	1st to 10th	Night	32% 6% 12% 19% 22% 9%	2200
	11th to 20th	Night	31% 5% 10% 21% 22% 11%	1990
	21st to end	Night	29% 7% 12% 24% 22% 5%	1888
May	1st to 10th	Night	34% 11% 16% 24% 13% 2	2840
	11th to 20th	Night	38% 9% 15% 21% 16%	2813
	21st to end	Night	27% 12% 13% 26% 19% 2	3087
June	1st to 10th	Night	39% 12% 17% 20% 11% 1	1710
	11th to 20th	Night	35% 10% 19% 23% 10% 2	1710
	21st to end	Night	35% 15% 21% 19% 9% 2	1710
July	1st to 10th	Night	46% 12% 18% 16% 5% 2	2795
	11th to 20th	Night	42% 15% 25% 13% 4 1	2786
	21st to end	Night	50% 16% 17% 12% 4	2988
August	1st to 10th	Night	54% 12% 19% 12% 3 1	2814
	11th to 20th	Night	41% 12% 21% 20% 7%	2812
	21st to end	Night	26% 8% 16% 35% 14% 1	3435
September	1st to 10th	Night	38% 11% 15% 18% 12% 5%	2075
	11th to 20th	Night	43% 9% 11% 16% 17% 4	2090
	21st to end	Night	42% 7% 13% 18% 15% 5%	2090
October	1st to 10th	Night	34% 4 9% 17% 28% 7%	3672
	11th to 20th	Night	19% 3 5% 15% 24% 33%	3779
	21st to end	Night	24% 4 6% 20% 28% 19%	4120
November	1st to 10th	Night	33% 5% 8% 15% 25% 14%	2341
	11th to 20th	Night	35% 4 6% 16% 25% 13%	2477
	21st to end	Night	34% 5% 8% 19% 23% 10%	2600
December	1st to 10th	Night	33% 5% 6% 16% 31% 10%	4250
	11th to 20th	Night	42% 4 9% 18% 18% 9%	4824
	21st to end	Night	43% 5% 6% 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	19% 18% 44% 15% 4 1	300
	11th to 20th	Day	16% 20% 36% 21% 6% 1	300
	21st to end	Day	21% 23% 37% 16% 2	330
February	1st to 10th	Day	17% 19% 40% 19% 5%	300
	11th to 20th	Day	31% 20% 35% 12% 3	300
	21st to end	Day	19% 19% 37% 19% 5% 1	329
March	1st to 10th	Day	19% 16% 28% 26% 10%	500
	11th to 20th	Day	16% 15% 40% 21% 7% 1	500
	21st to end	Day	17% 15% 35% 22% 9% 1	550
April	1st to 10th	Day	15% 16% 33% 23% 12% 1	500
	11th to 20th	Day	11% 14% 29% 26% 17% 4	492
	21st to end	Day	12% 8% 27% 28% 19% 8%	480
May	1st to 10th	Day	8% 13% 29% 26% 17% 8%	463
	11th to 20th	Day	14% 8% 18% 22% 26% 13%	487
	21st to end	Day	12% 4 14% 25% 27% 18%	529
June	1st to 10th	Day	10% 3 14% 30% 29% 14%	490
	11th to 20th	Day	9% 3 14% 26% 29% 19%	490
	21st to end	Day	6% 2 13% 33% 29% 17%	490
July	1st to 10th	Day	8% 1 10% 22% 30% 28%	485
	11th to 20th	Day	9% 3 5% 24% 36% 24%	484
	21st to end	Day	7% 3 8% 26% 38% 18%	532
August	1st to 10th	Day	15% 3 11% 25% 26% 20%	486
	11th to 20th	Day	13% 2 9% 23% 31% 22%	479
	21st to end	Day	14% 1 10% 22% 31% 22%	539
September	1st to 10th	Day	10% 3 11% 26% 34% 17%	490
	11th to 20th	Day	18% 4 11% 22% 33% 11%	490
	21st to end	Day	19% 2 16% 26% 26% 12%	490
October	1st to 10th	Day	15% 5% 20% 31% 21% 9%	490
	11th to 20th	Day	10% 5% 24% 30% 22% 9%	490
	21st to end	Day	12% 6% 23% 29% 22% 7%	539
November	1st to 10th	Day	16% 6% 27% 28% 18% 6%	495
	11th to 20th	Day	19% 10% 33% 25% 10% 2	420
	21st to end	Day	12% 14% 33% 26% 13% 3	300
December	1st to 10th	Day	21% 16% 35% 21% 6% 1	300
	11th to 20th	Day	18% 12% 35% 22% 11% 2	300
	21st to end	Day	24% 15% 35% 16% 8% 2	330
January	1st to 10th	Night	19% 14% 33% 27% 7%	800
	11th to 20th	Night	19% 11% 33% 32% 6%	800
	21st to end	Night	17% 11% 38% 31% 3	880
February	1st to 10th	Night	20% 11% 31% 33% 5%	800
	11th to 20th	Night	23% 11% 34% 30% 2	783
	21st to end	Night	16% 14% 36% 30% 5%	660
March	1st to 10th	Night	18% 10% 33% 31% 7%	800
	11th to 20th	Night	15% 11% 37% 28% 8%	800
	21st to end	Night	15% 11% 37% 29% 9%	880
April	1st to 10th	Night	13% 15% 33% 31% 9%	800
	11th to 20th	Night	12% 12% 27% 35% 14% 1	791
	21st to end	Night	10% 7% 28% 42% 12% 1	714
May	1st to 10th	Night	9% 7% 27% 40% 15% 1	570
	11th to 20th	Night	11% 4 25% 38% 19% 2	561
	21st to end	Night	9% 2 14% 37% 36% 3	617
June	1st to 10th	Night	13% 2 12% 41% 27% 4	570
	11th to 20th	Night	9% 1 14% 35% 32% 8%	570
	21st to end	Night	9% 2 9% 39% 36% 5%	570
July	1st to 10th	Night	12% 2 7% 33% 39% 7%	555
	11th to 20th	Night	9% 2 5% 33% 46% 7%	552
	21st to end	Night	8% 3 9% 35% 39% 6%	624
August	1st to 10th	Night	12% 2 7% 28% 43% 8%	567
	11th to 20th	Night	10% 3 8% 33% 40% 7%	564
	21st to end	Night	14% 2 9% 28% 40% 7%	808
September	1st to 10th	Night	9% 3 10% 29% 43% 6%	760
	11th to 20th	Night	16% 3 11% 29% 37% 5%	760
	21st to end	Night	19% 3 12% 31% 31% 3	760
October	1st to 10th	Night	15% 3 17% 34% 27% 4	760
	11th to 20th	Night	14% 4 22% 32% 25% 2	760
	21st to end	Night	11% 7% 21% 35% 24% 2	836
November	1st to 10th	Night	15% 6% 22% 36% 18% 3	780
	11th to 20th	Night	16% 9% 27% 34% 13% 1	800
	21st to end	Night	15% 8% 27% 33% 16% 1	800
December	1st to 10th	Night	19% 9% 28% 33% 11%	800
	11th to 20th	Night	20% 7% 25% 37% 11% 1	800
	21st to end	Night	24% 11% 24% 31% 9%	880

Page generated at 2025-04-23 09:25:05. Version ac07

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