Edisto Beach State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edisto Beach State Park 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	10% 5% 2 6% 4 4 4 4 6% 9% 45%	127117
	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	123941
Transparency	Day	35% 8% 17% 20% 15% 5%	130749
	Night	36% 7% 14% 19% 18% 7%	128377
Seeing	Day	11% 4 17% 28% 28% 12%	17051
	Night	12% 5% 19% 29% 27% 8%	27134

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	10% 4 2 6% 3 4 3 3 4 6% 55%	4056
	11th to 20th	Day	14% 6% 2 6% 4 3 3 3 4 7% 48%	4060
	21st to end	Day	14% 10% 4 7% 3 3 3 2 4 7% 45%	4466
February	1st to 10th	Day	14% 7% 3 6% 5% 5% 4 4 5% 6% 43%	1800
	11th to 20th	Day	18% 7% 2 5% 3 3 4 3 4 6% 44%	1947
	21st to end	Day	12% 7% 2 6% 5% 4 4 3 5% 6% 47%	1790
March	1st to 10th	Day	18% 9% 3 7% 4 3 4 3 5% 6% 39%	4935
	11th to 20th	Day	7% 4 1 4 3 4 3 3 6% 7% 57%	4980
	21st to end	Day	12% 5% 2 5% 4 5% 4 3 4 5% 50%	5465
April	1st to 10th	Day	7% 5% 2 4 4 3 4 4 6% 9% 53%	2200
	11th to 20th	Day	9% 4 2 4 4 4 3 4 5% 7% 53%	2374
	21st to end	Day	4 3 1 4 4 4 4 3 5% 9% 59%	2400
May	1st to 10th	Day	8% 5% 2 6% 4 4 5% 5% 7% 11% 44%	5814
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 7% 10% 41%	5861
	21st to end	Day	6% 4 2 5% 4 4 5% 4 7% 11% 49%	6433
June	1st to 10th	Day	8% 5% 3 6% 5% 6% 6% 5% 10% 11% 37%	2600
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 5% 8% 11% 44%	2600
	21st to end	Day	5% 5% 2 5% 5% 5% 6% 6% 11% 13% 38%	2600
July	1st to 10th	Day	8% 5% 3 7% 6% 6% 7% 6% 9% 12% 30%	5900
	11th to 20th	Day	4 3 1 5% 5% 5% 6% 6% 10% 15% 40%	5900
	21st to end	Day	4 4 2 5% 5% 5% 5% 5% 8% 14% 43%	6424
August	1st to 10th	Day	19% 7% 3 7% 5% 5% 5% 5% 7% 10% 27%	4234
	11th to 20th	Day	5% 5% 2 6% 4 5% 6% 5% 9% 13% 41%	4075
	21st to end	Day	10% 6% 3 7% 5% 4 5% 5% 7% 9% 40%	4312
September	1st to 10th	Day	11% 6% 2 7% 4 5% 4 4 6% 10% 40%	2242
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 8% 39%	2200
	21st to end	Day	14% 6% 2 6% 3 4 5% 4 6% 8% 41%	2200
October	1st to 10th	Day	13% 6% 2 6% 3 4 5% 4 5% 7% 46%	2055
	11th to 20th	Day	8% 4 1 4 3 3 4 3 4 5% 62%	2000
	21st to end	Day	10% 5% 2 5% 4 3 3 3 4 5% 56%	2200
November	1st to 10th	Day	10% 5% 2 6% 4 4 3 4 4 6% 54%	2057
	11th to 20th	Day	11% 5% 2 6% 3 3 3 3 4 6% 53%	2100
	21st to end	Day	12% 5% 2 5% 4 3 4 2 5% 6% 52%	1915
December	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 6% 6% 54%	3020
	11th to 20th	Day	13% 6% 3 7% 4 3 4 3 5% 7% 47%	3436
	21st to end	Day	16% 9% 3 6% 4 4 3 3 5% 7% 41%	4466
January	1st to 10th	Night	9% 4 1 5% 4 4 4 3 4 5% 57%	5889
	11th to 20th	Night	12% 7% 3 7% 4 4 4 3 6% 7% 42%	5900
	21st to end	Night	12% 7% 3 7% 4 4 4 3 5% 7% 45%	6490
February	1st to 10th	Night	14% 7% 2 7% 4 4 4 3 5% 6% 44%	2598
	11th to 20th	Night	15% 7% 3 6% 4 3 3 3 6% 5% 43%	2338
	21st to end	Night	12% 6% 3 7% 4 4 5% 4 4 7% 44%	1839
March	1st to 10th	Night	16% 9% 4 7% 4 3 3 3 4 6% 42%	4918
	11th to 20th	Night	9% 5% 1 5% 3 3 4 4 6% 9% 52%	4980
	21st to end	Night	12% 5% 2 6% 3 3 4 3 5% 8% 50%	5467
April	1st to 10th	Night	8% 5% 2 5% 4 5% 4 4 6% 8% 51%	2200
	11th to 20th	Night	10% 4 2 4 4 3 5% 3 4 7% 54%	1975
	21st to end	Night	6% 4 1 5% 3 4 4 3 6% 9% 54%	2000
May	1st to 10th	Night	5% 6% 2 6% 5% 4 5% 4 7% 10% 47%	4110
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 7% 10% 39%	4032
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 7% 10% 45%	4421
June	1st to 10th	Night	9% 6% 2 6% 4 6% 6% 6% 8% 12% 35%	1800
	11th to 20th	Night	6% 5% 3 6% 6% 6% 5% 7% 8% 13% 36%	1800
	21st to end	Night	5% 4 2 6% 5% 6% 8% 6% 9% 16% 34%	1800
July	1st to 10th	Night	7% 5% 2 7% 7% 6% 8% 6% 10% 13% 28%	4058
	11th to 20th	Night	4 4 2 6% 6% 6% 7% 6% 10% 14% 36%	4057
	21st to end	Night	5% 4 2 8% 6% 6% 7% 6% 9% 13% 33%	4427
August	1st to 10th	Night	17% 7% 3 8% 5% 5% 6% 5% 8% 12% 24%	2915
	11th to 20th	Night	6% 4 2 7% 5% 6% 7% 6% 9% 13% 36%	2938
	21st to end	Night	8% 6% 3 7% 5% 4 6% 4 6% 9% 41%	3586
September	1st to 10th	Night	9% 6% 2 7% 5% 4 5% 5% 8% 10% 38%	2152
	11th to 20th	Night	10% 7% 3 8% 5% 5% 6% 5% 7% 10% 36%	2200
	21st to end	Night	14% 6% 3 6% 5% 5% 5% 4 7% 8% 38%	2200
October	1st to 10th	Night	13% 6% 3 6% 4 4 5% 3 5% 6% 44%	2344
	11th to 20th	Night	9% 4 1 4 3 3 4 3 5% 7% 58%	2400
	21st to end	Night	9% 4 2 5% 3 3 3 4 4 5% 57%	2640
November	1st to 10th	Night	10% 5% 1 5% 3 3 4 3 5% 7% 53%	2461
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 51%	2520
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 6% 48%	2702
December	1st to 10th	Night	9% 6% 2 6% 4 3 3 3 4 6% 55%	4380
	11th to 20th	Night	13% 7% 3 8% 5% 4 3 3 4 5% 44%	4914
	21st to end	Night	15% 7% 2 7% 4 4 4 3 5% 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% 4 7% 18% 31% 8%	4057
	11th to 20th	Day	38% 4 6% 17% 26% 9%	4060
	21st to end	Day	40% 5% 7% 19% 20% 10%	4466
February	1st to 10th	Day	41% 7% 10% 18% 19% 6%	1800
	11th to 20th	Day	41% 5% 8% 15% 23% 7%	1957
	21st to end	Day	38% 5% 10% 19% 18% 11%	1790
March	1st to 10th	Day	46% 5% 8% 15% 18% 8%	4935
	11th to 20th	Day	25% 5% 12% 18% 21% 19%	4980
	21st to end	Day	36% 6% 9% 20% 17% 11%	5465
April	1st to 10th	Day	28% 7% 15% 22% 19% 9%	2200
	11th to 20th	Day	30% 6% 11% 25% 20% 9%	2374
	21st to end	Day	23% 7% 14% 31% 21% 5%	2400
May	1st to 10th	Day	33% 9% 20% 28% 9% 2	5848
	11th to 20th	Day	38% 7% 21% 24% 8% 1	5865
	21st to end	Day	29% 9% 20% 23% 20%	6447
June	1st to 10th	Day	37% 12% 21% 19% 10%	2600
	11th to 20th	Day	31% 11% 23% 26% 8%	2600
	21st to end	Day	32% 15% 26% 20% 7% 1	2600
July	1st to 10th	Day	42% 13% 27% 15% 3	5835
	11th to 20th	Day	29% 16% 41% 11% 2	5831
	21st to end	Day	29% 13% 31% 24% 2	6240
August	1st to 10th	Day	50% 11% 26% 11% 2	4221
	11th to 20th	Day	32% 11% 25% 24% 8%	4114
	21st to end	Day	38% 9% 19% 31% 3	4312
September	1st to 10th	Day	39% 11% 19% 17% 12% 3	2242
	11th to 20th	Day	40% 10% 17% 20% 11% 2	2200
	21st to end	Day	40% 9% 16% 20% 13% 3	2200
October	1st to 10th	Day	42% 5% 8% 13% 24% 8%	3341
	11th to 20th	Day	17% 4 7% 14% 32% 27%	3240
	21st to end	Day	23% 5% 8% 19% 37% 8%	3538
November	1st to 10th	Day	32% 6% 11% 17% 23% 11%	2057
	11th to 20th	Day	33% 5% 10% 18% 24% 10%	2100
	21st to end	Day	33% 5% 10% 22% 22% 7%	1915
December	1st to 10th	Day	31% 5% 10% 19% 22% 13%	3020
	11th to 20th	Day	37% 4 10% 22% 21% 5%	3433
	21st to end	Day	43% 5% 7% 22% 19% 3	4466
January	1st to 10th	Night	29% 4 7% 15% 35% 9%	5889
	11th to 20th	Night	40% 5% 6% 17% 26% 6%	5900
	21st to end	Night	39% 5% 8% 14% 24% 11%	6490
February	1st to 10th	Night	40% 5% 8% 20% 19% 7%	2598
	11th to 20th	Night	42% 6% 9% 14% 20% 9%	2339
	21st to end	Night	39% 7% 9% 17% 15% 12%	1839
March	1st to 10th	Night	44% 5% 9% 14% 17% 11%	4918
	11th to 20th	Night	29% 5% 10% 15% 24% 17%	4980
	21st to end	Night	34% 4 12% 18% 20% 11%	5467
April	1st to 10th	Night	31% 6% 13% 22% 19% 9%	2200
	11th to 20th	Night	31% 5% 9% 23% 21% 11%	1975
	21st to end	Night	27% 6% 14% 26% 23% 5%	2000
May	1st to 10th	Night	31% 8% 20% 29% 10% 2	4137
	11th to 20th	Night	38% 9% 22% 21% 10% 1	4033
	21st to end	Night	32% 8% 16% 28% 15% 1	4429
June	1st to 10th	Night	38% 11% 21% 20% 10%	1800
	11th to 20th	Night	35% 13% 21% 24% 6%	1800
	21st to end	Night	34% 15% 24% 21% 5%	1800
July	1st to 10th	Night	42% 12% 28% 15% 2 1	4015
	11th to 20th	Night	35% 13% 40% 9% 2	4006
	21st to end	Night	38% 12% 24% 23% 2	4297
August	1st to 10th	Night	49% 13% 25% 11% 2	2904
	11th to 20th	Night	34% 13% 24% 22% 6%	2965
	21st to end	Night	38% 10% 17% 32% 3	3586
September	1st to 10th	Night	39% 12% 19% 17% 12% 1	2152
	11th to 20th	Night	41% 11% 16% 19% 11% 1	2200
	21st to end	Night	43% 8% 15% 20% 12% 2	2200
October	1st to 10th	Night	39% 5% 10% 15% 23% 8%	3838
	11th to 20th	Night	18% 4 6% 14% 29% 30%	3899
	21st to end	Night	23% 5% 7% 18% 33% 14%	4252
November	1st to 10th	Night	31% 5% 11% 18% 23% 12%	2461
	11th to 20th	Night	35% 4 7% 19% 24% 10%	2520
	21st to end	Night	36% 5% 9% 18% 22% 9%	2702
December	1st to 10th	Night	32% 4 8% 18% 26% 11%	4380
	11th to 20th	Night	43% 4 11% 15% 21% 7%	4916
	21st to end	Night	42% 5% 8% 21% 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	11% 7% 33% 42% 7% 1	300
	11th to 20th	Day	10% 7% 27% 38% 14% 4	300
	21st to end	Day	19% 9% 33% 32% 6%	330
February	1st to 10th	Day	15% 9% 26% 36% 14% 1	300
	11th to 20th	Day	24% 7% 26% 33% 10%	300
	21st to end	Day	11% 8% 35% 36% 9% 1	389
March	1st to 10th	Day	14% 6% 30% 32% 18% 1	500
	11th to 20th	Day	12% 6% 29% 38% 13% 2	500
	21st to end	Day	12% 7% 30% 34% 15% 2	550
April	1st to 10th	Day	11% 9% 26% 36% 16% 2	500
	11th to 20th	Day	8% 4 25% 34% 22% 8%	492
	21st to end	Day	4 4 17% 36% 29% 10%	500
May	1st to 10th	Day	7% 3 24% 32% 25% 8%	503
	11th to 20th	Day	10% 2 15% 33% 29% 10%	527
	21st to end	Day	10% 2 10% 27% 36% 15%	573
June	1st to 10th	Day	9% 1 10% 29% 38% 12%	530
	11th to 20th	Day	8% 2 8% 24% 36% 23%	530
	21st to end	Day	6% 2 4 23% 42% 23%	530
July	1st to 10th	Day	7% 1 5% 16% 42% 28%	525
	11th to 20th	Day	7% 5% 11% 44% 32%	524
	21st to end	Day	6% 1 6% 18% 46% 23%	576
August	1st to 10th	Day	13% 1 6% 17% 40% 23%	526
	11th to 20th	Day	8% 1 4 12% 45% 30%	519
	21st to end	Day	16% 1 6% 18% 36% 23%	583
September	1st to 10th	Day	13% 2 8% 18% 39% 20%	530
	11th to 20th	Day	13% 2 9% 22% 41% 13%	530
	21st to end	Day	14% 1 8% 24% 34% 18%	530
October	1st to 10th	Day	16% 3 13% 32% 25% 12%	530
	11th to 20th	Day	9% 3 15% 31% 31% 12%	530
	21st to end	Day	12% 4 15% 27% 33% 8%	583
November	1st to 10th	Day	14% 5% 17% 30% 27% 8%	535
	11th to 20th	Day	14% 6% 24% 35% 18% 3	540
	21st to end	Day	11% 5% 21% 36% 24% 4	355
December	1st to 10th	Day	20% 3 23% 33% 19% 2	330
	11th to 20th	Day	15% 4 25% 35% 17% 4	321
	21st to end	Day	22% 6% 21% 33% 16% 2	330
January	1st to 10th	Night	13% 11% 33% 33% 9% 1	800
	11th to 20th	Night	13% 9% 31% 31% 15% 1	800
	21st to end	Night	17% 10% 34% 31% 7%	880
February	1st to 10th	Night	17% 7% 27% 35% 14%	800
	11th to 20th	Night	17% 10% 29% 35% 9%	783
	21st to end	Night	15% 6% 28% 40% 10% 1	660
March	1st to 10th	Night	12% 5% 31% 38% 14% 1	800
	11th to 20th	Night	12% 8% 25% 38% 15% 2	800
	21st to end	Night	10% 7% 27% 34% 19% 2	880
April	1st to 10th	Night	9% 8% 26% 34% 20% 3	800
	11th to 20th	Night	11% 6% 20% 34% 24% 5%	791
	21st to end	Night	8% 4 18% 34% 30% 6%	800
May	1st to 10th	Night	6% 3 21% 36% 26% 9%	638
	11th to 20th	Night	9% 2 17% 33% 27% 12%	591
	21st to end	Night	8% 2 9% 24% 39% 18%	650
June	1st to 10th	Night	12% 1 7% 30% 38% 13%	600
	11th to 20th	Night	8% 1 7% 23% 41% 21%	600
	21st to end	Night	6% 1 6% 25% 43% 19%	600
July	1st to 10th	Night	8% 1 6% 19% 45% 20%	585
	11th to 20th	Night	9% 1 4 11% 52% 23%	582
	21st to end	Night	6% 1 4 21% 52% 16%	657
August	1st to 10th	Night	11% 1 7% 17% 47% 16%	597
	11th to 20th	Night	8% 1 6% 18% 47% 21%	631
	21st to end	Night	13% 1 7% 18% 39% 22%	880
September	1st to 10th	Night	11% 2 7% 21% 43% 16%	800
	11th to 20th	Night	12% 2 9% 21% 44% 12%	800
	21st to end	Night	16% 1 11% 20% 40% 12%	800
October	1st to 10th	Night	15% 2 16% 28% 30% 9%	800
	11th to 20th	Night	10% 3 17% 31% 29% 9%	800
	21st to end	Night	11% 5% 19% 29% 31% 6%	880
November	1st to 10th	Night	12% 5% 18% 33% 28% 5%	820
	11th to 20th	Night	15% 8% 23% 32% 21% 2	840
	21st to end	Night	13% 8% 22% 32% 21% 3	840
December	1st to 10th	Night	15% 6% 29% 33% 14% 2	840
	11th to 20th	Night	17% 7% 26% 30% 17% 3	829
	21st to end	Night	19% 8% 27% 32% 14% 1	880

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