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 2024-03-18.

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	14% 8% 4 6% 5% 3 4 5% 5% 7% 38%	78644
	Night	15% 9% 4 6% 5% 3 4 4 5% 6% 39%	81187
Transparency	Day	44% 7% 12% 22% 13% 2	78345
	Night	45% 6% 11% 21% 15% 2	81007
Seeing	Day	16% 9% 26% 25% 18% 7%	14665
	Night	17% 9% 29% 30% 14% 1	24705

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	13% 12% 9% 11% 7% 3 5% 5% 5% 7% 24%	2527
	11th to 20th	Day	14% 10% 7% 10% 8% 6% 7% 8% 6% 5% 18%	2530
	21st to end	Day	24% 20% 6% 8% 4 3 3 3 3 5% 20%	3014
February	1st to 10th	Day	16% 11% 6% 9% 6% 4 4 5% 4 6% 29%	1823
	11th to 20th	Day	15% 9% 5% 8% 7% 4 4 4 5% 7% 31%	1848
	21st to end	Day	16% 13% 5% 8% 6% 3 3 3 4 6% 33%	1570
March	1st to 10th	Day	17% 11% 4 7% 5% 3 4 3 4 6% 36%	1900
	11th to 20th	Day	17% 10% 5% 7% 5% 3 4 4 5% 7% 34%	1927
	21st to end	Day	20% 13% 5% 7% 5% 3 5% 4 4 6% 28%	2376
April	1st to 10th	Day	14% 7% 4 6% 5% 3 5% 5% 6% 9% 36%	2160
	11th to 20th	Day	16% 8% 3 7% 5% 3 4 4 5% 6% 40%	2134
	21st to end	Day	20% 7% 3 6% 5% 3 4 4 4 6% 36%	2196
May	1st to 10th	Day	19% 8% 3 6% 5% 3 5% 5% 5% 8% 33%	2340
	11th to 20th	Day	19% 8% 3 5% 6% 3 4 4 5% 7% 37%	2310
	21st to end	Day	9% 5% 3 6% 6% 3 6% 6% 7% 9% 38%	2725
June	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 5% 7% 9% 45%	2520
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 5% 6% 8% 48%	2520
	21st to end	Day	8% 5% 2 6% 6% 3 5% 5% 8% 10% 42%	2520
July	1st to 10th	Day	10% 4 2 5% 5% 3 5% 7% 8% 10% 42%	2520
	11th to 20th	Day	5% 5% 2 5% 6% 3 5% 7% 8% 10% 44%	2520
	21st to end	Day	9% 3 2 5% 5% 4 5% 5% 7% 10% 46%	2743
August	1st to 10th	Day	8% 4 2 4 4 4 5% 6% 5% 10% 47%	2299
	11th to 20th	Day	9% 5% 2 5% 5% 4 6% 5% 7% 12% 41%	2125
	21st to end	Day	7% 3 2 5% 5% 3 4 5% 6% 9% 52%	2376
September	1st to 10th	Day	13% 6% 3 5% 5% 3 4 6% 5% 8% 44%	2160
	11th to 20th	Day	9% 3 2 4 5% 4 5% 5% 6% 8% 48%	2039
	21st to end	Day	10% 5% 2 4 4 3 4 4 5% 8% 51%	1980
October	1st to 10th	Day	12% 5% 2 4 4 2 4 4 5% 8% 51%	1958
	11th to 20th	Day	16% 6% 3 5% 5% 2 4 4 5% 5% 45%	1800
	21st to end	Day	19% 8% 3 6% 4 3 3 3 4 6% 41%	1814
November	1st to 10th	Day	10% 5% 3 4 4 3 3 3 4 6% 54%	1672
	11th to 20th	Day	16% 9% 4 5% 5% 2 3 3 5% 6% 42%	1710
	21st to end	Day	16% 10% 4 6% 5% 3 4 4 4 5% 39%	1710
December	1st to 10th	Day	18% 11% 5% 7% 6% 3 4 4 5% 6% 32%	1577
	11th to 20th	Day	16% 12% 5% 11% 5% 3 3 4 5% 7% 29%	1918
	21st to end	Day	23% 18% 6% 12% 5% 3 5% 3 3 5% 17%	2783
January	1st to 10th	Night	16% 14% 6% 9% 5% 3 4 4 4 5% 29%	4428
	11th to 20th	Night	14% 18% 6% 9% 6% 4 7% 5% 3 3 23%	4440
	21st to end	Night	26% 14% 8% 7% 5% 2 4 3 3 5% 23%	4651
February	1st to 10th	Night	18% 11% 5% 8% 6% 3 4 4 4 6% 31%	2356
	11th to 20th	Night	15% 8% 4 7% 6% 4 4 4 5% 6% 37%	2218
	21st to end	Night	19% 9% 3 7% 5% 3 4 3 4 6% 36%	1884
March	1st to 10th	Night	16% 11% 4 6% 6% 3 4 4 4 5% 38%	2280
	11th to 20th	Night	17% 8% 4 6% 5% 2 4 4 5% 7% 39%	2213
	21st to end	Night	21% 8% 3 7% 5% 3 4 4 5% 6% 33%	1980
April	1st to 10th	Night	13% 6% 3 6% 7% 3 4 4 4 7% 44%	1800
	11th to 20th	Night	17% 8% 3 5% 4 3 3 3 4 7% 44%	1775
	21st to end	Night	18% 8% 3 6% 5% 3 6% 5% 5% 5% 36%	1762
May	1st to 10th	Night	16% 6% 3 5% 6% 3 4 5% 5% 9% 38%	1620
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 5% 4 7% 40%	1578
	21st to end	Night	8% 6% 3 5% 5% 4 6% 5% 6% 10% 41%	1551
June	1st to 10th	Night	8% 5% 3 4 4 3 4 5% 5% 7% 50%	1440
	11th to 20th	Night	7% 3 2 5% 5% 3 4 5% 5% 7% 53%	1440
	21st to end	Night	8% 4 2 5% 5% 3 5% 5% 7% 11% 46%	1440
July	1st to 10th	Night	8% 4 2 3 5% 3 5% 6% 6% 10% 49%	1440
	11th to 20th	Night	5% 5% 2 3 4 2 4 4 6% 10% 55%	1440
	21st to end	Night	5% 4 2 5% 4 2 4 5% 6% 10% 54%	1575
August	1st to 10th	Night	7% 3 2 3 4 2 5% 5% 7% 10% 49%	1631
	11th to 20th	Night	6% 4 2 6% 6% 4 4 5% 7% 7% 49%	1776
	21st to end	Night	7% 3 1 3 4 3 3 5% 6% 8% 57%	1980
September	1st to 10th	Night	12% 4 2 4 4 2 3 4 4 8% 52%	1800
	11th to 20th	Night	6% 4 2 4 5% 3 3 4 5% 8% 55%	1903
	21st to end	Night	11% 4 2 4 4 3 4 4 5% 7% 53%	1980
October	1st to 10th	Night	9% 4 2 4 4 3 4 4 5% 6% 56%	1999
	11th to 20th	Night	15% 6% 2 4 4 2 3 3 3 7% 50%	2160
	21st to end	Night	19% 8% 2 5% 4 3 4 4 4 6% 41%	2540
November	1st to 10th	Night	10% 6% 2 5% 4 3 4 4 5% 6% 52%	2406
	11th to 20th	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 45%	2470
	21st to end	Night	19% 9% 4 6% 5% 3 3 3 4 6% 40%	2470
December	1st to 10th	Night	17% 10% 4 7% 6% 3 4 4 5% 7% 33%	2598
	11th to 20th	Night	17% 10% 3 8% 5% 3 4 3 4 5% 37%	3279
	21st to end	Night	24% 18% 6% 8% 6% 3 4 3 3 4 20%	4884

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	57% 8% 9% 19% 7% 1	2528
	11th to 20th	Day	63% 8% 11% 12% 5%	2530
	21st to end	Day	67% 5% 9% 14% 5% 1	3014
February	1st to 10th	Day	54% 5% 12% 17% 10% 1	1823
	11th to 20th	Day	51% 6% 11% 21% 10% 1	1858
	21st to end	Day	53% 5% 8% 22% 9% 2	1570
March	1st to 10th	Day	50% 5% 10% 22% 11% 1	1900
	11th to 20th	Day	49% 6% 12% 22% 10% 1	1927
	21st to end	Day	57% 7% 9% 20% 6% 1	2376
April	1st to 10th	Day	43% 8% 12% 22% 14% 1	2160
	11th to 20th	Day	45% 6% 10% 24% 11% 3	2134
	21st to end	Day	48% 6% 12% 21% 10% 3	2196
May	1st to 10th	Day	48% 8% 14% 21% 9%	2340
	11th to 20th	Day	46% 8% 14% 18% 13% 1	2314
	21st to end	Day	39% 11% 16% 19% 14% 2	2725
June	1st to 10th	Day	33% 8% 14% 26% 16% 3	2520
	11th to 20th	Day	33% 8% 11% 23% 20% 4	2520
	21st to end	Day	35% 9% 16% 21% 15% 4	2520
July	1st to 10th	Day	34% 9% 15% 25% 14% 3	2451
	11th to 20th	Day	31% 9% 16% 26% 16% 2	2445
	21st to end	Day	31% 8% 17% 27% 15% 2	2591
August	1st to 10th	Day	31% 9% 15% 30% 13% 2	2284
	11th to 20th	Day	34% 9% 16% 26% 13% 2	2125
	21st to end	Day	28% 8% 15% 26% 17% 7%	2376
September	1st to 10th	Day	37% 8% 11% 23% 17% 4	2160
	11th to 20th	Day	32% 7% 12% 23% 23% 3	2039
	21st to end	Day	31% 6% 10% 25% 24% 3	1980
October	1st to 10th	Day	32% 6% 13% 26% 20% 3	1958
	11th to 20th	Day	39% 6% 9% 23% 22% 2	1800
	21st to end	Day	46% 5% 9% 24% 15% 1	1814
November	1st to 10th	Day	33% 4 14% 26% 18% 5%	1672
	11th to 20th	Day	44% 4 9% 23% 16% 4	1710
	21st to end	Day	49% 4 10% 22% 14% 1	1710
December	1st to 10th	Day	53% 6% 12% 18% 10% 1	1577
	11th to 20th	Day	54% 5% 9% 25% 6% 1	1915
	21st to end	Day	70% 6% 10% 10% 4	2783
January	1st to 10th	Night	55% 6% 12% 18% 8%	4428
	11th to 20th	Night	65% 5% 9% 14% 7%	4440
	21st to end	Night	63% 4 8% 16% 7%	4651
February	1st to 10th	Night	55% 5% 12% 17% 10% 2	2356
	11th to 20th	Night	47% 5% 12% 21% 13% 2	2219
	21st to end	Night	50% 5% 10% 21% 12% 2	1884
March	1st to 10th	Night	49% 6% 9% 22% 14% 1	2280
	11th to 20th	Night	44% 7% 12% 22% 13% 2	2213
	21st to end	Night	51% 6% 12% 20% 9% 2	1980
April	1st to 10th	Night	41% 6% 11% 25% 16% 2	1800
	11th to 20th	Night	41% 5% 10% 22% 18% 4	1775
	21st to end	Night	48% 7% 11% 19% 12% 3	1762
May	1st to 10th	Night	43% 8% 12% 24% 11% 1	1620
	11th to 20th	Night	42% 8% 13% 21% 15% 1	1579
	21st to end	Night	37% 9% 15% 19% 15% 5%	1552
June	1st to 10th	Night	33% 6% 11% 25% 20% 5%	1440
	11th to 20th	Night	30% 7% 12% 25% 23% 5%	1440
	21st to end	Night	30% 8% 16% 22% 18% 5%	1440
July	1st to 10th	Night	29% 9% 15% 25% 15% 5%	1400
	11th to 20th	Night	23% 7% 15% 31% 21% 3	1392
	21st to end	Night	25% 6% 17% 28% 21% 3	1487
August	1st to 10th	Night	26% 10% 15% 28% 19% 2	1622
	11th to 20th	Night	32% 7% 13% 26% 19% 2	1776
	21st to end	Night	23% 8% 14% 27% 21% 7%	1980
September	1st to 10th	Night	31% 5% 11% 27% 19% 7%	1800
	11th to 20th	Night	27% 6% 10% 27% 25% 5%	1903
	21st to end	Night	29% 8% 10% 24% 26% 4	1980
October	1st to 10th	Night	29% 6% 11% 26% 24% 4	1999
	11th to 20th	Night	35% 5% 8% 26% 23% 4	2160
	21st to end	Night	44% 6% 9% 21% 17% 3	2540
November	1st to 10th	Night	33% 5% 10% 24% 21% 6%	2406
	11th to 20th	Night	38% 5% 10% 24% 20% 2	2470
	21st to end	Night	47% 5% 10% 23% 15% 1	2470
December	1st to 10th	Night	51% 5% 12% 19% 12% 1	2598
	11th to 20th	Night	50% 5% 11% 21% 13%	3281
	21st to end	Night	69% 5% 8% 11% 6% 1	4884

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	21% 18% 32% 20% 8% 1	270
	11th to 20th	Day	26% 17% 37% 17% 3	270
	21st to end	Day	23% 16% 37% 18% 6%	297
February	1st to 10th	Day	24% 17% 34% 20% 4	270
	11th to 20th	Day	24% 19% 34% 18% 4 2	270
	21st to end	Day	28% 12% 40% 17% 4	225
March	1st to 10th	Day	23% 19% 35% 20% 3	270
	11th to 20th	Day	27% 19% 33% 18% 4	280
	21st to end	Day	31% 14% 33% 14% 6% 1	462
April	1st to 10th	Day	19% 13% 34% 25% 8% 1	420
	11th to 20th	Day	20% 16% 28% 21% 14% 2	412
	21st to end	Day	26% 12% 35% 17% 8% 2	420
May	1st to 10th	Day	22% 12% 31% 23% 10% 2	423
	11th to 20th	Day	21% 6% 26% 27% 16% 4	456
	21st to end	Day	10% 4 30% 28% 19% 9%	679
June	1st to 10th	Day	10% 5% 24% 30% 23% 8%	630
	11th to 20th	Day	9% 4 23% 36% 21% 7%	630
	21st to end	Day	9% 6% 28% 29% 20% 7%	630
July	1st to 10th	Day	10% 1 14% 27% 26% 22%	621
	11th to 20th	Day	7% 2 16% 35% 26% 14%	618
	21st to end	Day	10% 2 14% 32% 32% 10%	684
August	1st to 10th	Day	7% 2 12% 31% 34% 13%	502
	11th to 20th	Day	13% 2 15% 28% 27% 15%	439
	21st to end	Day	6% 2 12% 30% 34% 16%	495
September	1st to 10th	Day	12% 4 16% 26% 32% 10%	450
	11th to 20th	Day	8% 2 14% 28% 34% 14%	450
	21st to end	Day	11% 6% 22% 25% 23% 12%	450
October	1st to 10th	Day	12% 5% 27% 28% 21% 7%	428
	11th to 20th	Day	15% 16% 36% 22% 11%	270
	21st to end	Day	28% 18% 30% 19% 5%	297
November	1st to 10th	Day	10% 13% 32% 25% 16% 4	270
	11th to 20th	Day	17% 17% 33% 22% 9% 1	270
	21st to end	Day	23% 13% 31% 27% 6% 1	270
December	1st to 10th	Day	16% 17% 39% 19% 6% 3	270
	11th to 20th	Day	21% 15% 36% 20% 9%	270
	21st to end	Day	28% 19% 32% 15% 6%	297
January	1st to 10th	Night	20% 15% 38% 23% 4	950
	11th to 20th	Night	23% 15% 35% 22% 4	950
	21st to end	Night	22% 14% 36% 25% 2	1045
February	1st to 10th	Night	25% 13% 35% 24% 2	836
	11th to 20th	Night	19% 16% 38% 24% 3	743
	21st to end	Night	26% 14% 36% 23% 1	628
March	1st to 10th	Night	21% 14% 36% 26% 4	760
	11th to 20th	Night	20% 12% 36% 25% 6% 1	730
	21st to end	Night	24% 11% 31% 28% 6%	594
April	1st to 10th	Night	18% 11% 36% 29% 6%	540
	11th to 20th	Night	20% 11% 29% 28% 11%	533
	21st to end	Night	23% 8% 34% 26% 8% 1	540
May	1st to 10th	Night	17% 6% 35% 32% 8% 1	540
	11th to 20th	Night	17% 5% 27% 33% 16% 1	531
	21st to end	Night	11% 4 23% 35% 24% 2	584
June	1st to 10th	Night	10% 3 22% 42% 23%	540
	11th to 20th	Night	9% 1 22% 46% 21% 1	540
	21st to end	Night	10% 2 22% 38% 27% 1	540
July	1st to 10th	Night	10% 1 10% 31% 40% 7%	525
	11th to 20th	Night	5% 2 15% 43% 31% 5%	522
	21st to end	Night	7% 2 13% 43% 32% 3	591
August	1st to 10th	Night	7% 2 10% 42% 34% 4	537
	11th to 20th	Night	7% 3 12% 40% 34% 4	534
	21st to end	Night	6% 2 14% 33% 41% 4	594
September	1st to 10th	Night	14% 3 12% 36% 32% 4	540
	11th to 20th	Night	7% 3 14% 39% 33% 4	643
	21st to end	Night	13% 5% 20% 30% 27% 5%	720
October	1st to 10th	Night	10% 5% 23% 38% 20% 4	720
	11th to 20th	Night	18% 11% 29% 28% 13%	720
	21st to end	Night	22% 12% 34% 25% 6% 1	792
November	1st to 10th	Night	12% 10% 36% 30% 11% 1	740
	11th to 20th	Night	17% 12% 33% 29% 8% 1	760
	21st to end	Night	24% 12% 31% 26% 7%	760
December	1st to 10th	Night	22% 11% 38% 24% 5% 1	888
	11th to 20th	Night	24% 8% 35% 27% 6%	950
	21st to end	Night	29% 16% 32% 20% 3	1045

Page generated at 2024-03-15 13:01:40. Version ac07

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