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 2024-11-03.

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	13% 8% 3 7% 4 4 4 4 6% 8% 38%	101165
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 40%	97881
Transparency	Day	42% 7% 13% 23% 14% 2	100953
	Night	43% 6% 11% 22% 15% 2	97765
Seeing	Day	15% 9% 26% 25% 17% 6%	15635
	Night	17% 9% 29% 30% 14% 1	25442

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% 13% 9% 13% 5% 5% 4 4 5% 7% 24%	2527
	11th to 20th	Day	14% 11% 6% 12% 6% 8% 7% 6% 6% 5% 18%	2530
	21st to end	Day	24% 20% 6% 9% 4 4 3 2 3 5% 20%	3014
February	1st to 10th	Day	15% 12% 5% 10% 5% 5% 3 4 4 6% 29%	1823
	11th to 20th	Day	15% 10% 4 9% 6% 5% 4 3 6% 6% 31%	1848
	21st to end	Day	16% 14% 4 9% 5% 4 3 2 5% 6% 32%	1570
March	1st to 10th	Day	19% 18% 3 7% 4 3 3 2 3 4 33%	3120
	11th to 20th	Day	11% 8% 3 6% 4 3 3 4 5% 7% 45%	3287
	21st to end	Day	14% 12% 4 9% 5% 5% 5% 4 5% 7% 30%	4165
April	1st to 10th	Day	14% 9% 3 7% 5% 4 4 4 6% 9% 35%	2280
	11th to 20th	Day	15% 9% 3 7% 4 4 4 3 5% 6% 40%	2254
	21st to end	Day	19% 8% 3 7% 4 5% 4 3 5% 6% 37%	2318
May	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 7% 11% 29%	4082
	11th to 20th	Day	18% 8% 2 7% 5% 4 4 3 5% 7% 37%	4104
	21st to end	Day	8% 6% 2 6% 5% 4 5% 4 7% 9% 43%	4824
June	1st to 10th	Day	9% 5% 2 5% 4 5% 5% 4 7% 9% 45%	2660
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 4 6% 8% 48%	2660
	21st to end	Day	8% 6% 2 6% 5% 4 5% 4 8% 10% 42%	2660
July	1st to 10th	Day	13% 5% 2 6% 4 4 5% 5% 7% 10% 40%	4440
	11th to 20th	Day	5% 5% 2 6% 5% 5% 5% 5% 7% 11% 44%	4440
	21st to end	Day	9% 5% 3 7% 5% 6% 6% 5% 8% 10% 38%	4813
August	1st to 10th	Day	9% 4 1 4 3 4 4 3 5% 9% 53%	4047
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 7% 10% 41%	3729
	21st to end	Day	5% 3 2 6% 4 4 4 4 6% 10% 51%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 3 5% 4 5% 7% 45%	2280
	11th to 20th	Day	9% 4 2 5% 5% 5% 5% 4 6% 8% 48%	2152
	21st to end	Day	11% 6% 2 5% 3 3 4 3 5% 8% 49%	2090
October	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 52%	2066
	11th to 20th	Day	15% 6% 3 6% 4 3 4 3 4 5% 47%	1900
	21st to end	Day	18% 8% 3 7% 4 3 3 2 4 6% 41%	1914
November	1st to 10th	Day	10% 6% 2 5% 4 4 2 3 5% 6% 54%	1690
	11th to 20th	Day	16% 10% 3 6% 4 3 3 2 5% 6% 42%	1710
	21st to end	Day	16% 11% 4 7% 5% 4 4 3 4 5% 39%	1710
December	1st to 10th	Day	17% 12% 5% 7% 5% 4 4 3 5% 6% 32%	1577
	11th to 20th	Day	15% 13% 5% 11% 4 4 3 3 5% 7% 29%	1918
	21st to end	Day	22% 19% 6% 13% 4 4 4 2 3 5% 17%	2783
January	1st to 10th	Night	16% 14% 6% 10% 4 4 4 3 4 5% 29%	4428
	11th to 20th	Night	14% 18% 5% 10% 5% 6% 7% 4 4 3 23%	4440
	21st to end	Night	25% 15% 7% 8% 4 3 3 3 4 5% 23%	4651
February	1st to 10th	Night	18% 12% 4 8% 5% 4 4 3 4 5% 31%	2356
	11th to 20th	Night	15% 9% 4 8% 5% 5% 3 3 5% 6% 37%	2218
	21st to end	Night	19% 10% 3 8% 4 4 3 3 4 5% 35%	1884
March	1st to 10th	Night	19% 16% 3 6% 4 3 3 3 4 5% 34%	3733
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 4 6% 49%	3701
	21st to end	Night	18% 8% 3 8% 5% 4 5% 3 5% 6% 35%	3466
April	1st to 10th	Night	14% 7% 2 7% 5% 4 4 3 4 6% 43%	1900
	11th to 20th	Night	17% 8% 2 6% 4 3 3 3 4 7% 43%	1875
	21st to end	Night	18% 8% 3 7% 5% 5% 5% 4 6% 5% 36%	1859
May	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 5% 8% 33%	2813
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 5% 7% 40%	2785
	21st to end	Night	9% 7% 3 6% 5% 5% 5% 3 6% 9% 43%	2743
June	1st to 10th	Night	8% 6% 3 5% 4 4 4 4 5% 7% 50%	1520
	11th to 20th	Night	7% 4 2 6% 5% 4 4 4 5% 7% 53%	1520
	21st to end	Night	7% 5% 2 6% 4 4 4 4 7% 10% 46%	1520
July	1st to 10th	Night	11% 5% 2 5% 4 3 5% 3 5% 10% 47%	2530
	11th to 20th	Night	4 4 1 4 3 3 4 4 7% 10% 56%	2530
	21st to end	Night	8% 6% 3 8% 5% 4 4 4 8% 11% 40%	2750
August	1st to 10th	Night	7% 4 2 4 3 4 4 4 6% 9% 54%	2877
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 6% 8% 50%	3100
	21st to end	Night	5% 3 1 4 3 4 4 4 5% 9% 57%	3476
September	1st to 10th	Night	11% 5% 2 4 3 3 4 3 5% 7% 54%	1900
	11th to 20th	Night	6% 5% 2 5% 4 4 3 3 6% 8% 55%	2009
	21st to end	Night	11% 5% 2 4 4 3 5% 3 6% 7% 51%	2090
October	1st to 10th	Night	9% 4 2 5% 4 3 3 3 5% 6% 57%	2111
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 3 6% 52%	2280
	21st to end	Night	18% 8% 2 5% 4 4 4 3 5% 6% 42%	2682
November	1st to 10th	Night	10% 6% 2 5% 3 4 3 4 5% 5% 53%	2433
	11th to 20th	Night	13% 8% 3 6% 4 3 3 3 5% 6% 45%	2470
	21st to end	Night	19% 9% 3 7% 4 3 3 2 4 6% 39%	2470
December	1st to 10th	Night	17% 11% 3 8% 5% 4 4 4 5% 6% 33%	2598
	11th to 20th	Night	17% 11% 3 9% 5% 4 3 3 4 5% 37%	3279
	21st to end	Night	24% 18% 6% 9% 5% 4 4 3 3 4 19%	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	55% 5% 7% 17% 13% 2	3120
	11th to 20th	Day	36% 7% 13% 25% 17% 1	3287
	21st to end	Day	48% 11% 13% 22% 5% 1	4165
April	1st to 10th	Day	43% 8% 12% 21% 14% 1	2280
	11th to 20th	Day	44% 6% 10% 24% 11% 3	2254
	21st to end	Day	48% 6% 12% 21% 10% 3	2318
May	1st to 10th	Day	44% 11% 16% 22% 7%	4120
	11th to 20th	Day	44% 8% 13% 25% 9%	4108
	21st to end	Day	32% 11% 14% 20% 21% 3	4837
June	1st to 10th	Day	33% 8% 14% 25% 15% 4	2660
	11th to 20th	Day	32% 8% 11% 23% 22% 4	2660
	21st to end	Day	35% 9% 16% 21% 16% 4	2660
July	1st to 10th	Day	39% 6% 11% 27% 14% 2	4371
	11th to 20th	Day	31% 7% 15% 28% 17% 1	4365
	21st to end	Day	38% 7% 19% 21% 14% 1	4662
August	1st to 10th	Day	27% 6% 15% 35% 15% 1	4032
	11th to 20th	Day	36% 7% 15% 25% 16% 1	3765
	21st to end	Day	28% 5% 17% 31% 14% 4	4179
September	1st to 10th	Day	36% 7% 11% 23% 19% 4	2280
	11th to 20th	Day	32% 6% 12% 22% 23% 4	2152
	21st to end	Day	33% 6% 10% 25% 24% 3	2090
October	1st to 10th	Day	31% 6% 13% 26% 21% 3	2066
	11th to 20th	Day	38% 5% 9% 23% 23% 2	1900
	21st to end	Day	45% 4 9% 24% 16% 1	1914
November	1st to 10th	Day	33% 4 14% 26% 18% 5%	1690
	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	52% 6% 9% 21% 11% 1	3733
	11th to 20th	Night	34% 8% 10% 25% 21% 2	3701
	21st to end	Night	47% 9% 12% 24% 7% 1	3466
April	1st to 10th	Night	41% 6% 11% 24% 16% 2	1900
	11th to 20th	Night	41% 6% 10% 23% 17% 4	1875
	21st to end	Night	47% 8% 11% 19% 12% 3	1859
May	1st to 10th	Night	45% 11% 15% 21% 8% 1	2840
	11th to 20th	Night	41% 8% 14% 26% 11% 1	2786
	21st to end	Night	35% 10% 13% 20% 18% 4	2751
June	1st to 10th	Night	33% 6% 11% 25% 20% 5%	1520
	11th to 20th	Night	30% 7% 11% 24% 23% 5%	1520
	21st to end	Night	31% 8% 16% 22% 18% 5%	1520
July	1st to 10th	Night	34% 6% 11% 26% 18% 4	2490
	11th to 20th	Night	22% 6% 13% 32% 24% 2	2482
	21st to end	Night	36% 5% 19% 20% 17% 3	2662
August	1st to 10th	Night	25% 7% 15% 36% 16% 1	2868
	11th to 20th	Night	32% 5% 14% 28% 20% 1	3130
	21st to end	Night	24% 6% 14% 32% 19% 4	3476
September	1st to 10th	Night	30% 5% 11% 27% 21% 7%	1900
	11th to 20th	Night	27% 5% 10% 27% 26% 5%	2009
	21st to end	Night	31% 7% 10% 23% 25% 4	2090
October	1st to 10th	Night	28% 5% 10% 27% 26% 4	2111
	11th to 20th	Night	34% 4 8% 27% 24% 4	2280
	21st to end	Night	43% 6% 9% 22% 18% 3	2682
November	1st to 10th	Night	33% 5% 10% 24% 22% 6%	2433
	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% 18% 34% 17% 4	291
	21st to end	Day	30% 14% 35% 15% 6% 1	506
April	1st to 10th	Day	19% 14% 34% 24% 7% 1	460
	11th to 20th	Day	19% 16% 29% 20% 13% 2	452
	21st to end	Day	25% 12% 36% 17% 8% 2	460
May	1st to 10th	Day	20% 12% 31% 24% 11% 2	463
	11th to 20th	Day	20% 6% 27% 26% 16% 4	497
	21st to end	Day	10% 5% 31% 28% 18% 8%	734
June	1st to 10th	Day	10% 5% 26% 29% 22% 8%	680
	11th to 20th	Day	9% 5% 24% 35% 20% 6%	680
	21st to end	Day	9% 6% 30% 28% 19% 7%	680
July	1st to 10th	Day	11% 2 15% 27% 24% 20%	671
	11th to 20th	Day	7% 3 18% 34% 26% 13%	668
	21st to end	Day	10% 2 15% 33% 31% 9%	739
August	1st to 10th	Day	8% 3 14% 31% 32% 12%	545
	11th to 20th	Day	13% 2 19% 27% 25% 14%	479
	21st to end	Day	6% 2 12% 32% 33% 15%	539
September	1st to 10th	Day	11% 4 17% 28% 31% 9%	490
	11th to 20th	Day	8% 2 13% 29% 33% 14%	490
	21st to end	Day	13% 7% 23% 24% 22% 11%	490
October	1st to 10th	Day	11% 5% 26% 29% 21% 8%	466
	11th to 20th	Day	14% 16% 34% 22% 13% 1	300
	21st to end	Day	27% 18% 30% 19% 5%	330
November	1st to 10th	Day	10% 12% 31% 26% 16% 4	276
	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% 37% 25% 6% 1	736
	21st to end	Night	23% 11% 32% 28% 6%	627
April	1st to 10th	Night	18% 12% 36% 28% 6%	570
	11th to 20th	Night	20% 12% 30% 27% 10%	563
	21st to end	Night	22% 8% 36% 26% 7% 1	570
May	1st to 10th	Night	17% 6% 35% 32% 8% 1	570
	11th to 20th	Night	17% 5% 27% 34% 17% 1	561
	21st to end	Night	11% 4 23% 36% 23% 2	617
June	1st to 10th	Night	11% 3 23% 42% 22%	570
	11th to 20th	Night	9% 2 24% 45% 20% 1	570
	21st to end	Night	10% 2 24% 37% 26% 1	570
July	1st to 10th	Night	10% 1 12% 32% 38% 7%	555
	11th to 20th	Night	5% 3 15% 43% 30% 5%	552
	21st to end	Night	8% 2 13% 43% 31% 3	624
August	1st to 10th	Night	7% 2 11% 42% 33% 4	567
	11th to 20th	Night	6% 3 14% 39% 33% 4	564
	21st to end	Night	6% 2 14% 34% 41% 4	627
September	1st to 10th	Night	13% 3 13% 36% 31% 4	570
	11th to 20th	Night	7% 3 14% 40% 33% 4	679
	21st to end	Night	14% 5% 21% 30% 26% 4	760
October	1st to 10th	Night	10% 5% 23% 38% 20% 5%	760
	11th to 20th	Night	18% 11% 28% 28% 14% 1	760
	21st to end	Night	22% 12% 34% 26% 6%	836
November	1st to 10th	Night	12% 10% 36% 30% 11% 1	749
	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 2024-10-31 02:39:20. Version ac07

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