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 2024-11-04.

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	15% 9% 3 7% 5% 4 4 4 6% 7% 35%	101216
	Night	16% 10% 3 7% 5% 4 4 3 5% 6% 35%	97754
Transparency	Day	48% 3 10% 23% 14% 2	104919
	Night	49% 3 8% 22% 15% 3	102190
Seeing	Day	23% 10% 24% 23% 14% 5%	15048
	Night	22% 8% 21% 30% 16% 2	25114

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% 21% 7% 11% 5% 3 3 2 4 6% 20%	2836
	11th to 20th	Day	18% 20% 9% 12% 7% 4 3 2 3 3 20%	2840
	21st to end	Day	23% 20% 5% 9% 5% 4 3 2 3 5% 22%	3124
February	1st to 10th	Day	21% 14% 5% 8% 5% 4 3 3 4 5% 28%	1710
	11th to 20th	Day	23% 13% 4 9% 4 4 4 3 4 5% 27%	1787
	21st to end	Day	24% 14% 3 6% 4 4 3 2 4 5% 30%	1570
March	1st to 10th	Day	21% 13% 4 7% 4 4 5% 4 5% 5% 28%	3396
	11th to 20th	Day	16% 7% 3 6% 4 4 4 3 5% 6% 41%	3480
	21st to end	Day	20% 9% 3 7% 5% 4 5% 4 6% 7% 32%	3815
April	1st to 10th	Day	15% 10% 3 7% 5% 4 5% 3 5% 7% 36%	2090
	11th to 20th	Day	16% 7% 3 6% 5% 4 4 3 5% 6% 41%	2350
	21st to end	Day	18% 8% 2 7% 4 5% 4 4 5% 7% 35%	2470
May	1st to 10th	Day	20% 10% 4 9% 5% 5% 5% 4 6% 6% 27%	4082
	11th to 20th	Day	18% 9% 3 7% 4 4 5% 4 6% 7% 32%	4081
	21st to end	Day	10% 6% 2 6% 5% 6% 6% 4 8% 10% 37%	4476
June	1st to 10th	Day	12% 5% 3 6% 5% 4 5% 5% 7% 9% 39%	2470
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 5% 7% 11% 39%	2470
	21st to end	Day	10% 5% 3 6% 5% 5% 5% 5% 7% 10% 39%	2470
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	4120
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 41%	4120
	21st to end	Day	17% 9% 3 9% 6% 6% 5% 4 6% 7% 28%	4466
August	1st to 10th	Day	11% 7% 3 7% 5% 6% 6% 5% 7% 10% 34%	4104
	11th to 20th	Day	12% 6% 2 8% 5% 5% 6% 5% 7% 9% 35%	4044
	21st to end	Day	6% 3 2 4 4 4 4 4 7% 9% 52%	4387
September	1st to 10th	Day	13% 5% 2 5% 4 4 5% 3 5% 7% 47%	2119
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 45%	2090
	21st to end	Day	18% 8% 3 6% 4 4 3 3 4 6% 41%	2090
October	1st to 10th	Day	16% 5% 2 5% 4 4 4 2 6% 9% 45%	1986
	11th to 20th	Day	16% 7% 2 5% 3 4 3 3 5% 6% 45%	1900
	21st to end	Day	21% 6% 2 7% 3 3 3 3 4 6% 41%	2090
November	1st to 10th	Day	12% 6% 2 6% 3 4 3 3 5% 5% 51%	1776
	11th to 20th	Day	15% 11% 3 7% 4 3 4 3 5% 7% 37%	1710
	21st to end	Day	17% 11% 2 7% 4 4 3 4 4 7% 37%	1710
December	1st to 10th	Day	25% 15% 4 8% 4 3 3 3 4 5% 25%	1710
	11th to 20th	Day	20% 15% 4 10% 3 3 3 3 5% 5% 29%	2153
	21st to end	Day	18% 18% 4 10% 5% 5% 5% 3 5% 6% 19%	3124
January	1st to 10th	Night	18% 20% 5% 11% 5% 4 4 3 4 4 22%	4109
	11th to 20th	Night	21% 14% 5% 11% 6% 4 3 3 4 4 24%	4120
	21st to end	Night	27% 15% 4 9% 6% 4 3 3 3 4 22%	4532
February	1st to 10th	Night	19% 14% 4 8% 6% 4 4 3 4 5% 28%	2470
	11th to 20th	Night	23% 13% 4 8% 5% 4 4 3 3 5% 27%	2274
	21st to end	Night	22% 14% 3 7% 4 4 4 3 4 5% 28%	1884
March	1st to 10th	Night	22% 13% 3 7% 4 4 4 3 4 6% 31%	3456
	11th to 20th	Night	16% 11% 3 7% 4 3 4 3 5% 7% 38%	3480
	21st to end	Night	15% 9% 2 7% 5% 4 4 3 5% 7% 39%	3817
April	1st to 10th	Night	16% 10% 2 6% 4 4 4 3 6% 7% 37%	2090
	11th to 20th	Night	15% 7% 3 6% 5% 4 4 4 6% 8% 39%	1792
	21st to end	Night	16% 7% 3 8% 5% 4 4 4 5% 5% 39%	1710
May	1st to 10th	Night	24% 10% 3 8% 5% 5% 4 4 5% 7% 24%	2813
	11th to 20th	Night	20% 9% 3 7% 4 3 5% 3 4 7% 34%	2812
	21st to end	Night	13% 7% 3 7% 5% 4 5% 4 6% 9% 37%	3079
June	1st to 10th	Night	10% 6% 2 6% 4 4 5% 5% 6% 9% 42%	1710
	11th to 20th	Night	8% 5% 2 8% 6% 5% 5% 5% 6% 8% 42%	1710
	21st to end	Night	10% 6% 2 5% 5% 5% 4 4 6% 10% 44%	1710
July	1st to 10th	Night	8% 6% 2 7% 5% 4 5% 5% 7% 11% 39%	2840
	11th to 20th	Night	9% 6% 2 6% 5% 5% 4 4 6% 9% 44%	2840
	21st to end	Night	13% 9% 3 8% 5% 5% 5% 3 6% 8% 33%	3087
August	1st to 10th	Night	12% 7% 3 8% 6% 5% 5% 5% 7% 8% 34%	2825
	11th to 20th	Night	14% 6% 3 7% 5% 4 5% 4 5% 7% 41%	2785
	21st to end	Night	6% 4 2 4 4 4 5% 4 6% 9% 55%	3235
September	1st to 10th	Night	11% 6% 2 6% 4 5% 5% 3 5% 8% 47%	2057
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 7% 50%	2090
	21st to end	Night	14% 8% 2 6% 4 5% 3 4 6% 7% 42%	2090
October	1st to 10th	Night	13% 4 2 5% 4 3 4 4 6% 6% 50%	2193
	11th to 20th	Night	15% 7% 3 6% 3 4 4 3 4 6% 45%	2280
	21st to end	Night	21% 7% 2 6% 4 4 4 3 4 5% 42%	2508
November	1st to 10th	Night	13% 6% 2 6% 4 3 4 3 4 5% 49%	2372
	11th to 20th	Night	18% 9% 2 5% 4 4 4 3 6% 7% 38%	2470
	21st to end	Night	17% 11% 3 6% 4 5% 4 3 4 5% 38%	2470
December	1st to 10th	Night	23% 15% 4 9% 4 4 3 2 4 5% 27%	2470
	11th to 20th	Night	19% 16% 6% 8% 4 4 3 3 4 5% 28%	3042
	21st to end	Night	17% 18% 5% 9% 6% 5% 5% 3 5% 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	59% 2 7% 21% 9% 1	3396
	11th to 20th	Day	46% 1 8% 27% 17% 1	3480
	21st to end	Day	53% 2 7% 24% 13% 2	3815
April	1st to 10th	Day	49% 2 9% 21% 14% 4	2090
	11th to 20th	Day	45% 3 8% 23% 18% 4	2350
	21st to end	Day	50% 3 10% 23% 11% 3	2470
May	1st to 10th	Day	58% 2 9% 20% 10% 1	4120
	11th to 20th	Day	52% 3 10% 22% 12% 1	4085
	21st to end	Day	41% 4 14% 23% 14% 4	4489
June	1st to 10th	Day	41% 4 12% 25% 16% 1	2470
	11th to 20th	Day	38% 5% 15% 24% 16% 1	2470
	21st to end	Day	39% 6% 14% 24% 14% 3	2470
July	1st to 10th	Day	39% 5% 14% 27% 13% 3	4055
	11th to 20th	Day	39% 3 11% 33% 13% 1	4051
	21st to end	Day	56% 4 10% 16% 14% 1	4324
August	1st to 10th	Day	45% 4 14% 27% 10%	4091
	11th to 20th	Day	45% 3 8% 28% 15% 1	4083
	21st to end	Day	29% 3 14% 33% 20% 2	4387
September	1st to 10th	Day	37% 4 10% 23% 21% 5%	2119
	11th to 20th	Day	38% 3 9% 26% 22% 2	2090
	21st to end	Day	46% 3 9% 21% 19% 2	2090
October	1st to 10th	Day	32% 2 6% 24% 33% 3	3298
	11th to 20th	Day	32% 1 10% 27% 23% 6%	3140
	21st to end	Day	32% 1 9% 31% 21% 6%	3428
November	1st to 10th	Day	36% 2 7% 28% 22% 4	1776
	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	57% 1 4 23% 13% 1	3456
	11th to 20th	Night	47% 2 6% 27% 16% 1	3480
	21st to end	Night	47% 2 7% 25% 18% 2	3817
April	1st to 10th	Night	47% 3 8% 22% 18% 3	2090
	11th to 20th	Night	44% 3 9% 22% 16% 6%	1792
	21st to end	Night	47% 3 9% 21% 18% 2	1710
May	1st to 10th	Night	60% 4 9% 16% 10% 1	2840
	11th to 20th	Night	51% 4 10% 23% 10% 2	2813
	21st to end	Night	44% 4 11% 23% 13% 4	3087
June	1st to 10th	Night	37% 5% 14% 25% 16% 2	1710
	11th to 20th	Night	40% 5% 15% 19% 19% 2	1710
	21st to end	Night	37% 5% 14% 26% 16% 3	1710
July	1st to 10th	Night	40% 4 15% 22% 15% 3	2795
	11th to 20th	Night	37% 4 11% 32% 14% 2	2786
	21st to end	Night	49% 3 11% 20% 14% 2	2988
August	1st to 10th	Night	47% 4 14% 25% 10% 1	2814
	11th to 20th	Night	44% 3 9% 25% 19%	2812
	21st to end	Night	28% 3 11% 35% 22% 2	3235
September	1st to 10th	Night	36% 4 11% 22% 19% 8%	2057
	11th to 20th	Night	34% 3 10% 24% 25% 4	2090
	21st to end	Night	42% 3 9% 25% 20% 1	2090
October	1st to 10th	Night	31% 2 7% 26% 29% 5%	3661
	11th to 20th	Night	34% 2 6% 26% 23% 10%	3779
	21st to end	Night	32% 1 6% 28% 24% 8%	4120
November	1st to 10th	Night	39% 2 8% 22% 24% 5%	2372
	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% 18% 4	506
April	1st to 10th	Day	28% 17% 28% 18% 8%	460
	11th to 20th	Day	26% 15% 30% 15% 9% 4	452
	21st to end	Day	29% 13% 29% 17% 10% 2	460
May	1st to 10th	Day	29% 13% 29% 17% 7% 4	463
	11th to 20th	Day	23% 9% 25% 25% 14% 4	487
	21st to end	Day	14% 7% 24% 27% 20% 8%	529
June	1st to 10th	Day	17% 6% 24% 27% 18% 8%	490
	11th to 20th	Day	13% 6% 22% 31% 21% 7%	490
	21st to end	Day	12% 6% 29% 27% 17% 8%	490
July	1st to 10th	Day	16% 3 15% 29% 20% 17%	485
	11th to 20th	Day	10% 2 21% 35% 21% 11%	484
	21st to end	Day	17% 2 18% 29% 23% 11%	532
August	1st to 10th	Day	17% 3 15% 29% 24% 12%	486
	11th to 20th	Day	17% 3 15% 28% 27% 10%	479
	21st to end	Day	12% 2 15% 31% 27% 12%	539
September	1st to 10th	Day	14% 4 14% 29% 27% 12%	490
	11th to 20th	Day	14% 1 14% 30% 30% 11%	490
	21st to end	Day	24% 6% 23% 25% 17% 6%	490
October	1st to 10th	Day	19% 5% 23% 25% 23% 5%	490
	11th to 20th	Day	20% 10% 26% 25% 14% 4	490
	21st to end	Day	26% 11% 27% 23% 10% 3	539
November	1st to 10th	Day	18% 12% 29% 28% 12% 2	356
	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%	836
April	1st to 10th	Night	24% 15% 28% 26% 7%	760
	11th to 20th	Night	20% 10% 28% 28% 12% 1	668
	21st to end	Night	21% 7% 32% 33% 7% 1	570
May	1st to 10th	Night	22% 7% 26% 31% 12% 1	570
	11th to 20th	Night	20% 5% 22% 34% 17% 1	561
	21st to end	Night	15% 2 18% 34% 27% 3	617
June	1st to 10th	Night	12% 2 19% 39% 26% 3	570
	11th to 20th	Night	10% 2 15% 39% 30% 4	570
	21st to end	Night	12% 4 15% 40% 28% 2	570
July	1st to 10th	Night	15% 2 11% 34% 32% 6%	555
	11th to 20th	Night	10% 1 10% 36% 38% 5%	552
	21st to end	Night	14% 2 8% 36% 35% 5%	624
August	1st to 10th	Night	14% 9% 37% 37% 4	567
	11th to 20th	Night	15% 2 6% 36% 35% 5%	564
	21st to end	Night	12% 1 9% 36% 36% 7%	686
September	1st to 10th	Night	14% 2 11% 33% 34% 6%	760
	11th to 20th	Night	14% 2 14% 31% 34% 5%	760
	21st to end	Night	19% 3 18% 32% 25% 3	760
October	1st to 10th	Night	16% 4 19% 33% 25% 3	760
	11th to 20th	Night	21% 7% 22% 32% 17% 1	760
	21st to end	Night	25% 7% 20% 33% 13% 1	836
November	1st to 10th	Night	17% 8% 23% 34% 17% 1	755
	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 2024-11-01 22:47:49. Version ac07

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