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 2026-08-30.

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% 42%	143710
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	138517
Transparency	Day	38% 7% 13% 19% 17% 6%	147356
	Night	38% 7% 11% 18% 19% 7%	142930
Seeing	Day	14% 9% 23% 24% 20% 9%	17833
	Night	15% 7% 23% 33% 20% 2	27860

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 5% 3 3 3 3 5% 7% 52%	5258
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 3 4 59%	5280
	21st to end	Day	16% 8% 3 7% 5% 4 4 3 4 5% 41%	5780
February	1st to 10th	Day	14% 7% 2 6% 3 4 4 4 5% 7% 43%	1892
	11th to 20th	Day	19% 7% 3 6% 4 3 3 2 5% 4 44%	2048
	21st to end	Day	16% 7% 2 7% 4 4 5% 3 4 5% 44%	1814
March	1st to 10th	Day	21% 9% 3 6% 4 3 3 3 5% 6% 39%	5045
	11th to 20th	Day	8% 4 2 5% 4 4 4 3 5% 7% 55%	5090
	21st to end	Day	13% 7% 2 6% 4 4 4 3 4 5% 48%	5586
April	1st to 10th	Day	9% 4 1 5% 4 4 4 4 6% 8% 50%	2310
	11th to 20th	Day	9% 4 2 5% 4 4 4 4 6% 7% 51%	2478
	21st to end	Day	8% 5% 2 6% 4 4 3 4 7% 7% 50%	2613
May	1st to 10th	Day	12% 7% 3 7% 4 4 5% 4 6% 9% 38%	7616
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 40%	7626
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 4 7% 9% 36%	8391
June	1st to 10th	Day	9% 5% 2 7% 6% 5% 6% 5% 9% 10% 36%	2730
	11th to 20th	Day	7% 4 2 5% 6% 5% 6% 5% 8% 11% 40%	2730
	21st to end	Day	5% 4 2 6% 5% 6% 6% 6% 9% 11% 39%	2730
July	1st to 10th	Day	9% 5% 2 8% 6% 7% 6% 6% 9% 11% 31%	7680
	11th to 20th	Day	6% 5% 2 7% 6% 7% 8% 7% 10% 14% 29%	7680
	21st to end	Day	7% 6% 3 8% 6% 6% 7% 6% 10% 13% 28%	8340
August	1st to 10th	Day	22% 6% 2 7% 6% 5% 6% 5% 8% 10% 21%	4364
	11th to 20th	Day	10% 6% 2 6% 5% 6% 6% 5% 8% 11% 35%	4304
	21st to end	Day	7% 5% 2 5% 4 4 5% 5% 8% 11% 43%	4426
September	1st to 10th	Day	7% 6% 2 6% 5% 4 5% 5% 7% 10% 43%	2210
	11th to 20th	Day	13% 7% 2 6% 4 5% 5% 4 6% 7% 40%	2200
	21st to end	Day	18% 6% 2 6% 4 4 5% 3 5% 6% 43%	2200
October	1st to 10th	Day	13% 5% 2 6% 5% 4 4 3 4 6% 48%	2078
	11th to 20th	Day	10% 4 1 4 4 3 3 3 4 6% 58%	2000
	21st to end	Day	11% 4 2 4 3 3 3 3 4 4 57%	2200
November	1st to 10th	Day	12% 5% 2 4 4 3 3 3 5% 5% 54%	2057
	11th to 20th	Day	13% 7% 2 5% 2 2 3 3 5% 6% 53%	2016
	21st to end	Day	13% 6% 2 5% 4 3 4 3 4 7% 49%	1890
December	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 3 5% 5% 50%	3020
	11th to 20th	Day	14% 6% 2 6% 3 4 3 3 5% 6% 47%	3463
	21st to end	Day	19% 7% 2 5% 3 3 3 2 5% 5% 45%	4565
January	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 4 5% 54%	7635
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 5% 6% 51%	7680
	21st to end	Night	16% 9% 2 7% 4 4 3 3 4 5% 44%	8401
February	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 6% 45%	2725
	11th to 20th	Night	18% 7% 2 6% 4 3 4 2 4 5% 44%	2458
	21st to end	Night	14% 7% 2 7% 3 5% 4 3 5% 6% 46%	1990
March	1st to 10th	Night	19% 8% 2 6% 4 4 3 3 4 6% 40%	5028
	11th to 20th	Night	11% 4 1 4 3 3 3 3 5% 7% 55%	5090
	21st to end	Night	12% 5% 2 5% 4 4 4 4 6% 7% 49%	5588
April	1st to 10th	Night	10% 5% 1 5% 4 4 4 4 7% 7% 50%	2310
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 8% 53%	2091
	21st to end	Night	9% 4 2 5% 4 4 4 4 6% 7% 53%	2023
May	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 4 7% 9% 37%	5237
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 4 7% 9% 42%	5234
	21st to end	Night	11% 8% 3 8% 5% 5% 5% 4 7% 8% 35%	5761
June	1st to 10th	Night	11% 6% 2 6% 5% 5% 6% 6% 8% 11% 34%	1890
	11th to 20th	Night	8% 6% 2 6% 5% 5% 6% 4 8% 10% 40%	1890
	21st to end	Night	6% 5% 2 7% 5% 6% 6% 6% 11% 12% 35%	1890
July	1st to 10th	Night	10% 6% 3 8% 6% 6% 7% 6% 9% 11% 30%	5278
	11th to 20th	Night	8% 6% 3 8% 6% 6% 7% 6% 10% 13% 26%	5277
	21st to end	Night	10% 8% 3 9% 7% 7% 7% 6% 9% 11% 23%	5736
August	1st to 10th	Night	22% 7% 3 8% 5% 6% 6% 5% 8% 9% 21%	3005
	11th to 20th	Night	8% 7% 3 8% 5% 5% 6% 4 8% 11% 35%	2965
	21st to end	Night	6% 3 2 5% 4 3 5% 4 7% 13% 48%	3634
September	1st to 10th	Night	8% 6% 2 7% 5% 6% 5% 4 6% 9% 41%	2184
	11th to 20th	Night	12% 7% 3 7% 4 6% 5% 4 5% 7% 41%	2200
	21st to end	Night	16% 7% 2 6% 4 4 5% 3 6% 6% 41%	2200
October	1st to 10th	Night	13% 6% 2 4 3 4 3 3 4 5% 52%	2320
	11th to 20th	Night	13% 4 1 4 3 3 3 3 5% 6% 56%	2400
	21st to end	Night	10% 5% 2 5% 3 2 3 3 5% 6% 56%	2640
November	1st to 10th	Night	13% 5% 2 5% 2 3 3 3 4 5% 55%	2461
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 6% 52%	2601
	21st to end	Night	13% 5% 2 5% 3 4 4 3 5% 8% 49%	2730
December	1st to 10th	Night	13% 6% 2 6% 3 3 3 2 4 5% 53%	4380
	11th to 20th	Night	16% 7% 3 6% 4 3 3 3 4 5% 46%	4952
	21st to end	Night	17% 7% 3 5% 3 3 4 3 4 6% 43%	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	32% 4 9% 25% 25% 6%	5259
	11th to 20th	Day	31% 3 4 15% 36% 12%	5280
	21st to end	Day	46% 3 5% 16% 20% 11%	5780
February	1st to 10th	Day	40% 5% 9% 21% 19% 6%	1892
	11th to 20th	Day	44% 4 5% 19% 23% 6%	2058
	21st to end	Day	43% 5% 7% 15% 21% 9%	1814
March	1st to 10th	Day	47% 4 7% 13% 20% 9%	5045
	11th to 20th	Day	29% 5% 8% 16% 25% 17%	5090
	21st to end	Day	39% 5% 7% 18% 21% 9%	5586
April	1st to 10th	Day	31% 7% 11% 21% 24% 7%	2310
	11th to 20th	Day	32% 5% 11% 21% 22% 10%	2478
	21st to end	Day	30% 7% 11% 26% 22% 4	2613
May	1st to 10th	Day	41% 8% 14% 24% 12% 2	7651
	11th to 20th	Day	40% 7% 15% 22% 14% 2	7630
	21st to end	Day	42% 9% 15% 15% 16% 2	8405
June	1st to 10th	Day	38% 10% 17% 22% 11% 2	2730
	11th to 20th	Day	33% 10% 19% 24% 12% 1	2730
	21st to end	Day	33% 13% 19% 23% 11% 1	2730
July	1st to 10th	Day	41% 11% 21% 21% 5% 1	7615
	11th to 20th	Day	37% 17% 29% 15% 2	7611
	21st to end	Day	41% 12% 19% 18% 8% 1	8156
August	1st to 10th	Day	54% 10% 20% 12% 4	4351
	11th to 20th	Day	38% 11% 17% 21% 12%	4343
	21st to end	Day	31% 10% 14% 31% 13% 1	4426
September	1st to 10th	Day	34% 11% 15% 18% 17% 5%	2210
	11th to 20th	Day	42% 8% 10% 18% 19% 3	2200
	21st to end	Day	42% 6% 10% 21% 16% 6%	2200
October	1st to 10th	Day	36% 4 8% 16% 27% 8%	3377
	11th to 20th	Day	18% 3 6% 17% 29% 28%	3240
	21st to end	Day	25% 3 5% 20% 31% 15%	3538
November	1st to 10th	Day	32% 5% 7% 18% 26% 12%	2057
	11th to 20th	Day	33% 4 8% 19% 26% 10%	2016
	21st to end	Day	35% 4 9% 20% 22% 9%	1890
December	1st to 10th	Day	36% 4 7% 17% 26% 10%	3020
	11th to 20th	Day	38% 4 10% 22% 20% 6%	3460
	21st to end	Day	41% 4 7% 23% 23% 2	4565
January	1st to 10th	Night	33% 4 7% 23% 27% 5%	7636
	11th to 20th	Night	33% 4 6% 15% 31% 11%	7680
	21st to end	Night	45% 4 4 14% 25% 9%	8401
February	1st to 10th	Night	39% 5% 8% 19% 20% 8%	2725
	11th to 20th	Night	43% 4 7% 18% 20% 8%	2459
	21st to end	Night	39% 6% 7% 16% 19% 13%	1990
March	1st to 10th	Night	45% 5% 8% 12% 22% 9%	5028
	11th to 20th	Night	28% 5% 7% 13% 29% 19%	5090
	21st to end	Night	34% 5% 8% 21% 20% 12%	5588
April	1st to 10th	Night	32% 6% 13% 19% 22% 9%	2310
	11th to 20th	Night	30% 5% 10% 21% 23% 11%	2091
	21st to end	Night	29% 7% 12% 25% 22% 5%	2023
May	1st to 10th	Night	40% 9% 15% 23% 12% 1	5264
	11th to 20th	Night	36% 8% 18% 22% 14% 1	5235
	21st to end	Night	43% 10% 13% 18% 14% 2	5771
June	1st to 10th	Night	39% 12% 16% 19% 11% 2	1890
	11th to 20th	Night	36% 10% 20% 23% 10% 2	1890
	21st to end	Night	34% 14% 22% 20% 9% 1	1890
July	1st to 10th	Night	43% 12% 21% 19% 4 1	5235
	11th to 20th	Night	44% 15% 28% 11% 2	5226
	21st to end	Night	50% 13% 18% 13% 6% 1	5606
August	1st to 10th	Night	55% 12% 19% 11% 3 1	2994
	11th to 20th	Night	40% 12% 22% 20% 7% 1	2992
	21st to end	Night	27% 8% 16% 34% 14% 1	3634
September	1st to 10th	Night	38% 10% 15% 20% 13% 5%	2184
	11th to 20th	Night	42% 9% 11% 18% 17% 4	2200
	21st to end	Night	42% 7% 14% 18% 14% 5%	2200
October	1st to 10th	Night	34% 4 9% 18% 28% 7%	3788
	11th to 20th	Night	20% 3 5% 15% 25% 32%	3899
	21st to end	Night	24% 4 6% 19% 28% 18%	4252
November	1st to 10th	Night	32% 5% 8% 15% 26% 14%	2461
	11th to 20th	Night	34% 4 7% 16% 26% 13%	2601
	21st to end	Night	34% 5% 8% 19% 23% 10%	2730
December	1st to 10th	Night	34% 5% 6% 16% 30% 9%	4380
	11th to 20th	Night	41% 4 9% 18% 18% 9%	4954
	21st to end	Night	42% 5% 6% 22% 21% 3	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	18% 18% 44% 15% 5% 1	330
	11th to 20th	Day	18% 20% 35% 20% 5% 1	330
	21st to end	Day	21% 24% 37% 16% 2	363
February	1st to 10th	Day	17% 20% 40% 18% 5%	330
	11th to 20th	Day	31% 20% 35% 11% 3	330
	21st to end	Day	22% 20% 36% 17% 5% 1	357
March	1st to 10th	Day	19% 16% 29% 26% 11%	540
	11th to 20th	Day	16% 15% 39% 21% 8% 1	540
	21st to end	Day	16% 15% 36% 22% 9% 1	594
April	1st to 10th	Day	15% 15% 32% 24% 12% 1	540
	11th to 20th	Day	10% 13% 28% 27% 17% 4	532
	21st to end	Day	11% 8% 27% 28% 19% 6%	540
May	1st to 10th	Day	10% 13% 29% 26% 15% 6%	543
	11th to 20th	Day	14% 9% 19% 21% 25% 11%	567
	21st to end	Day	14% 5% 16% 25% 24% 16%	617
June	1st to 10th	Day	11% 4 15% 30% 28% 13%	570
	11th to 20th	Day	9% 3 15% 28% 28% 16%	570
	21st to end	Day	5% 2 12% 34% 29% 17%	570
July	1st to 10th	Day	7% 2 10% 23% 32% 26%	565
	11th to 20th	Day	8% 3 5% 24% 36% 24%	564
	21st to end	Day	7% 3 9% 27% 36% 17%	620
August	1st to 10th	Day	17% 4 11% 26% 24% 19%	566
	11th to 20th	Day	12% 2 8% 22% 34% 21%	559
	21st to end	Day	14% 1 11% 23% 31% 20%	619
September	1st to 10th	Day	9% 3 14% 26% 33% 15%	530
	11th to 20th	Day	17% 4 12% 23% 33% 11%	530
	21st to end	Day	19% 2 16% 27% 25% 12%	530
October	1st to 10th	Day	14% 5% 21% 30% 21% 8%	530
	11th to 20th	Day	11% 5% 23% 31% 22% 9%	530
	21st to end	Day	13% 7% 25% 28% 21% 7%	583
November	1st to 10th	Day	15% 6% 28% 28% 18% 5%	535
	11th to 20th	Day	18% 12% 33% 25% 10% 2	456
	21st to end	Day	11% 15% 35% 25% 12% 3	330
December	1st to 10th	Day	23% 16% 35% 20% 5% 1	330
	11th to 20th	Day	19% 12% 35% 23% 10% 2	330
	21st to end	Day	23% 15% 35% 17% 8% 2	363
January	1st to 10th	Night	19% 15% 33% 27% 7%	840
	11th to 20th	Night	19% 11% 33% 31% 6%	840
	21st to end	Night	18% 12% 37% 30% 3	924
February	1st to 10th	Night	20% 11% 31% 33% 5%	840
	11th to 20th	Night	22% 13% 34% 30% 2	823
	21st to end	Night	17% 15% 35% 29% 4	692
March	1st to 10th	Night	17% 10% 33% 32% 7%	840
	11th to 20th	Night	15% 11% 37% 28% 8%	840
	21st to end	Night	14% 11% 38% 28% 8%	924
April	1st to 10th	Night	13% 15% 32% 32% 9%	840
	11th to 20th	Night	11% 12% 28% 35% 14% 1	831
	21st to end	Night	10% 7% 27% 44% 12%	763
May	1st to 10th	Night	10% 8% 28% 40% 14%	630
	11th to 20th	Night	11% 5% 25% 38% 18% 2	621
	21st to end	Night	11% 3 15% 35% 33% 3	683
June	1st to 10th	Night	13% 2 13% 41% 26% 4	630
	11th to 20th	Night	10% 2 15% 35% 31% 8%	630
	21st to end	Night	8% 2 10% 39% 37% 5%	630
July	1st to 10th	Night	12% 2 7% 34% 39% 7%	615
	11th to 20th	Night	9% 2 5% 33% 44% 7%	612
	21st to end	Night	9% 3 10% 34% 39% 5%	690
August	1st to 10th	Night	14% 2 7% 28% 41% 7%	627
	11th to 20th	Night	10% 3 8% 31% 40% 8%	624
	21st to end	Night	14% 2 10% 29% 39% 6%	887
September	1st to 10th	Night	9% 3 12% 30% 41% 5%	800
	11th to 20th	Night	15% 3 11% 30% 37% 5%	800
	21st to end	Night	19% 3 12% 32% 30% 4	800
October	1st to 10th	Night	15% 3 18% 34% 26% 4	800
	11th to 20th	Night	15% 4 21% 32% 25% 2	800
	21st to end	Night	12% 8% 22% 34% 23% 2	880
November	1st to 10th	Night	15% 7% 22% 36% 18% 3	820
	11th to 20th	Night	16% 9% 27% 34% 13% 1	840
	21st to end	Night	14% 9% 28% 32% 15% 1	840
December	1st to 10th	Night	20% 10% 27% 33% 10%	840
	11th to 20th	Night	19% 7% 24% 38% 10% 1	840
	21st to end	Night	23% 11% 24% 32% 8%	924

Page generated at 2026-08-27 04:07:12. Version ac07

Copyright © 2026 Attilla Danko.