Myrtle Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Myrtle Beach clear sky chart from 2005-11-06 to 2025-08-05.

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	11% 6% 2 6% 5% 4 5% 4 6% 8% 42%	125552
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	122533
Transparency	Day	37% 6% 15% 20% 16% 5%	129155
	Night	37% 5% 13% 19% 18% 7%	126999
Seeing	Day	13% 3 14% 28% 29% 13%	16682
	Night	13% 4 18% 31% 27% 7%	26771

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	12% 5% 2 4 3 3 3 3 5% 7% 54%	4056
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 4 6% 52%	4060
	21st to end	Day	14% 8% 2 7% 4 4 4 3 5% 6% 43%	4466
February	1st to 10th	Day	14% 7% 3 6% 5% 5% 4 4 5% 6% 40%	1800
	11th to 20th	Day	19% 6% 2 6% 3 3 3 3 5% 5% 45%	1847
	21st to end	Day	14% 6% 2 7% 4 4 3 4 5% 6% 44%	1815
March	1st to 10th	Day	20% 9% 3 6% 4 3 3 3 5% 5% 39%	4935
	11th to 20th	Day	9% 4 1 5% 4 4 4 4 6% 7% 54%	4980
	21st to end	Day	11% 5% 2 6% 4 4 4 3 6% 6% 50%	5465
April	1st to 10th	Day	9% 5% 1 4 4 4 5% 4 6% 7% 52%	2300
	11th to 20th	Day	8% 5% 1 4 4 3 3 4 6% 7% 54%	2374
	21st to end	Day	7% 4 1 5% 4 4 5% 4 5% 9% 53%	2400
May	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 5% 8% 10% 40%	5603
	11th to 20th	Day	15% 7% 2 8% 6% 5% 5% 5% 6% 9% 33%	5861
	21st to end	Day	9% 5% 2 6% 4 5% 5% 5% 6% 9% 44%	6433
June	1st to 10th	Day	9% 7% 2 7% 6% 5% 6% 6% 9% 10% 34%	2600
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 5% 8% 11% 40%	2600
	21st to end	Day	6% 5% 2 6% 6% 5% 6% 6% 10% 13% 36%	2600
July	1st to 10th	Day	9% 8% 3 8% 6% 6% 6% 6% 8% 12% 29%	5900
	11th to 20th	Day	5% 5% 2 8% 6% 6% 7% 7% 10% 14% 29%	5900
	21st to end	Day	7% 7% 3 9% 7% 7% 7% 6% 9% 12% 29%	6424
August	1st to 10th	Day	19% 9% 4 9% 5% 5% 6% 5% 8% 10% 21%	4156
	11th to 20th	Day	8% 6% 3 8% 5% 5% 7% 5% 7% 13% 34%	3831
	21st to end	Day	7% 6% 3 7% 4 5% 5% 4 7% 10% 41%	4180
September	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 6% 8% 10% 39%	2280
	11th to 20th	Day	14% 6% 3 7% 5% 4 6% 4 6% 8% 38%	2123
	21st to end	Day	13% 6% 3 8% 5% 4 4 4 6% 8% 39%	2057
October	1st to 10th	Day	13% 6% 2 7% 5% 4 4 3 6% 6% 46%	1900
	11th to 20th	Day	9% 4 1 5% 3 3 4 3 4 6% 58%	1900
	21st to end	Day	9% 5% 2 5% 3 3 3 2 5% 6% 57%	2090
November	1st to 10th	Day	12% 5% 1 4 3 4 3 4 5% 5% 54%	1957
	11th to 20th	Day	12% 6% 3 5% 5% 3 4 3 4 6% 50%	2000
	21st to end	Day	10% 6% 2 6% 3 3 3 3 5% 6% 51%	1890
December	1st to 10th	Day	9% 4 2 6% 4 4 4 4 5% 6% 53%	2930
	11th to 20th	Day	14% 6% 2 7% 5% 4 4 3 4 6% 45%	3373
	21st to end	Day	14% 7% 3 6% 4 4 4 3 4 6% 44%	4466
January	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 4 6% 55%	5889
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 6% 7% 45%	5900
	21st to end	Night	12% 8% 3 7% 5% 4 4 3 4 5% 46%	6490
February	1st to 10th	Night	15% 6% 3 7% 4 4 4 3 6% 7% 44%	2600
	11th to 20th	Night	18% 9% 2 5% 4 3 4 3 4 6% 42%	2433
	21st to end	Night	13% 6% 3 6% 4 4 4 3 6% 7% 44%	1815
March	1st to 10th	Night	17% 10% 3 7% 4 3 3 2 4 6% 39%	4918
	11th to 20th	Night	11% 5% 1 4 4 3 3 4 6% 8% 50%	4980
	21st to end	Night	12% 5% 2 5% 4 3 3 3 5% 6% 52%	5467
April	1st to 10th	Night	10% 6% 2 6% 5% 4 4 4 4 8% 47%	2098
	11th to 20th	Night	9% 5% 2 6% 4 3 4 4 5% 8% 51%	1975
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 9% 53%	2000
May	1st to 10th	Night	6% 6% 2 7% 4 5% 5% 4 6% 10% 45%	4320
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 7% 10% 37%	4032
	21st to end	Night	10% 6% 2 7% 4 4 5% 5% 6% 10% 42%	4421
June	1st to 10th	Night	9% 6% 3 7% 5% 4 5% 5% 8% 11% 37%	1800
	11th to 20th	Night	9% 5% 2 5% 5% 5% 6% 5% 7% 11% 42%	1800
	21st to end	Night	6% 6% 2 7% 6% 5% 5% 6% 10% 12% 37%	1800
July	1st to 10th	Night	8% 5% 2 8% 7% 6% 7% 6% 9% 11% 31%	4058
	11th to 20th	Night	6% 5% 3 8% 6% 6% 5% 5% 9% 15% 32%	4057
	21st to end	Night	6% 7% 2 7% 7% 6% 7% 6% 9% 12% 30%	4427
August	1st to 10th	Night	17% 9% 3 8% 4 5% 5% 5% 7% 12% 25%	2861
	11th to 20th	Night	5% 5% 2 7% 6% 5% 6% 6% 8% 12% 38%	2966
	21st to end	Night	6% 4 2 7% 4 4 6% 6% 7% 8% 46%	3476
September	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 5% 7% 10% 40%	1900
	11th to 20th	Night	12% 7% 3 8% 6% 6% 5% 5% 6% 6% 38%	2052
	21st to end	Night	16% 7% 3 7% 4 4 4 3 5% 7% 40%	2121
October	1st to 10th	Night	11% 7% 2 6% 4 4 3 3 5% 6% 49%	2280
	11th to 20th	Night	9% 4 2 5% 3 4 3 3 5% 6% 56%	2280
	21st to end	Night	9% 5% 2 4 3 3 3 3 5% 6% 56%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 4 5% 55%	2341
	11th to 20th	Night	13% 7% 2 6% 3 4 3 3 4 6% 49%	2400
	21st to end	Night	10% 5% 3 5% 3 4 4 4 6% 8% 49%	2506
December	1st to 10th	Night	10% 5% 2 6% 3 3 4 3 5% 6% 53%	4250
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 3 4 5% 42%	4822
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 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% 2 6% 18% 36% 6%	4057
	11th to 20th	Day	35% 2 5% 17% 34% 8%	4060
	21st to end	Day	43% 2 7% 18% 20% 10%	4466
February	1st to 10th	Day	43% 4 9% 21% 19% 4	1800
	11th to 20th	Day	42% 3 7% 18% 22% 7%	1856
	21st to end	Day	40% 3 8% 21% 18% 9%	1815
March	1st to 10th	Day	47% 2 9% 14% 20% 8%	4935
	11th to 20th	Day	29% 4 10% 15% 28% 15%	4980
	21st to end	Day	35% 5% 11% 21% 19% 9%	5465
April	1st to 10th	Day	30% 4 14% 22% 24% 6%	2300
	11th to 20th	Day	29% 4 12% 27% 18% 10%	2374
	21st to end	Day	28% 5% 14% 27% 22% 4	2400
May	1st to 10th	Day	37% 6% 21% 26% 8% 1	5635
	11th to 20th	Day	45% 6% 18% 22% 9%	5865
	21st to end	Day	34% 7% 18% 24% 17% 1	6447
June	1st to 10th	Day	40% 9% 18% 23% 10%	2600
	11th to 20th	Day	32% 9% 25% 24% 11%	2600
	21st to end	Day	33% 11% 25% 24% 7% 1	2600
July	1st to 10th	Day	43% 12% 27% 15% 3	5835
	11th to 20th	Day	37% 14% 37% 9% 2	5831
	21st to end	Day	41% 12% 22% 19% 5%	6240
August	1st to 10th	Day	54% 8% 24% 12% 2	4143
	11th to 20th	Day	37% 10% 23% 21% 9%	3870
	21st to end	Day	36% 7% 19% 33% 5%	4180
September	1st to 10th	Day	35% 10% 20% 18% 14% 3	2280
	11th to 20th	Day	43% 7% 15% 17% 15% 4	2123
	21st to end	Day	41% 5% 14% 22% 15% 3	2057
October	1st to 10th	Day	40% 4 9% 18% 25% 5%	3160
	11th to 20th	Day	19% 2 6% 16% 30% 26%	3140
	21st to end	Day	27% 3 7% 21% 34% 8%	3428
November	1st to 10th	Day	32% 4 9% 18% 27% 10%	1957
	11th to 20th	Day	38% 3 8% 18% 24% 9%	2000
	21st to end	Day	35% 3 9% 21% 25% 8%	1890
December	1st to 10th	Day	32% 4 9% 17% 24% 14%	2930
	11th to 20th	Day	41% 4 8% 22% 20% 4	3370
	21st to end	Day	42% 3 11% 23% 19% 3	4466
January	1st to 10th	Night	31% 3 6% 17% 36% 8%	5889
	11th to 20th	Night	38% 3 6% 16% 31% 6%	5900
	21st to end	Night	42% 2 6% 14% 28% 8%	6490
February	1st to 10th	Night	41% 3 9% 21% 19% 7%	2600
	11th to 20th	Night	45% 3 8% 17% 19% 8%	2435
	21st to end	Night	40% 3 10% 18% 18% 10%	1815
March	1st to 10th	Night	48% 2 8% 13% 22% 7%	4918
	11th to 20th	Night	31% 4 9% 14% 25% 17%	4980
	21st to end	Night	35% 3 10% 23% 19% 10%	5467
April	1st to 10th	Night	36% 3 12% 20% 20% 9%	2098
	11th to 20th	Night	32% 4 12% 23% 19% 10%	1975
	21st to end	Night	28% 5% 15% 27% 21% 4	2000
May	1st to 10th	Night	34% 5% 21% 28% 10% 2	4350
	11th to 20th	Night	42% 6% 21% 20% 11%	4033
	21st to end	Night	37% 6% 16% 23% 17% 1	4429
June	1st to 10th	Night	39% 8% 20% 23% 10% 1	1800
	11th to 20th	Night	34% 9% 22% 25% 9%	1800
	21st to end	Night	34% 11% 25% 24% 6% 1	1800
July	1st to 10th	Night	43% 11% 26% 16% 4	4015
	11th to 20th	Night	39% 13% 38% 8% 2	4006
	21st to end	Night	41% 14% 18% 23% 3	4297
August	1st to 10th	Night	51% 9% 25% 13% 2	2850
	11th to 20th	Night	35% 10% 25% 25% 6%	2993
	21st to end	Night	32% 8% 19% 35% 6%	3476
September	1st to 10th	Night	38% 10% 18% 17% 13% 3	1900
	11th to 20th	Night	45% 8% 13% 17% 15% 2	2052
	21st to end	Night	44% 4 13% 22% 13% 3	2121
October	1st to 10th	Night	36% 4 10% 20% 25% 5%	3800
	11th to 20th	Night	19% 2 5% 15% 24% 34%	3779
	21st to end	Night	25% 4 7% 23% 29% 14%	4120
November	1st to 10th	Night	33% 3 9% 18% 26% 12%	2341
	11th to 20th	Night	37% 3 9% 16% 24% 11%	2400
	21st to end	Night	34% 3 10% 22% 23% 8%	2506
December	1st to 10th	Night	33% 3 9% 14% 28% 13%	4250
	11th to 20th	Night	45% 3 10% 17% 19% 7%	4824
	21st to end	Night	40% 4 9% 24% 20% 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	13% 5% 29% 42% 11%	300
	11th to 20th	Day	10% 5% 25% 43% 15% 2	300
	21st to end	Day	20% 4 31% 35% 9% 1	330
February	1st to 10th	Day	16% 4 25% 40% 14% 1	300
	11th to 20th	Day	27% 3 28% 31% 10% 1	354
	21st to end	Day	13% 5% 30% 37% 13% 1	414
March	1st to 10th	Day	16% 4 28% 31% 18% 2	500
	11th to 20th	Day	13% 4 27% 38% 15% 2	500
	21st to end	Day	13% 3 27% 38% 18% 2	550
April	1st to 10th	Day	11% 5% 24% 38% 19% 3	500
	11th to 20th	Day	9% 3 19% 32% 31% 7%	492
	21st to end	Day	8% 3 15% 34% 29% 11%	500
May	1st to 10th	Day	7% 2 19% 37% 26% 10%	503
	11th to 20th	Day	13% 1 10% 30% 34% 12%	527
	21st to end	Day	13% 2 8% 25% 34% 19%	573
June	1st to 10th	Day	10% 2 4 31% 39% 15%	530
	11th to 20th	Day	11% 1 6% 20% 39% 22%	530
	21st to end	Day	8% 2 2 22% 46% 21%	530
July	1st to 10th	Day	9% 3 3 13% 46% 27%	525
	11th to 20th	Day	9% 2 2 12% 44% 33%	524
	21st to end	Day	6% 3 3 17% 48% 23%	576
August	1st to 10th	Day	17% 3 3 16% 39% 22%	502
	11th to 20th	Day	13% 2 1 16% 38% 30%	479
	21st to end	Day	12% 3 4 14% 38% 28%	539
September	1st to 10th	Day	11% 2 4 19% 39% 25%	490
	11th to 20th	Day	19% 2 8% 20% 34% 18%	490
	21st to end	Day	17% 2 5% 23% 37% 17%	490
October	1st to 10th	Day	18% 2 8% 30% 27% 16%	490
	11th to 20th	Day	11% 1 15% 28% 30% 15%	490
	21st to end	Day	11% 1 16% 29% 31% 13%	539
November	1st to 10th	Day	16% 4 15% 27% 28% 11%	495
	11th to 20th	Day	15% 4 21% 38% 18% 4	500
	21st to end	Day	12% 5% 21% 35% 23% 5%	390
December	1st to 10th	Day	18% 3 19% 38% 19% 3	300
	11th to 20th	Day	18% 3 21% 34% 21% 4	300
	21st to end	Day	18% 5% 22% 36% 15% 4	330
January	1st to 10th	Night	15% 9% 32% 34% 10% 1	800
	11th to 20th	Night	13% 7% 31% 34% 14% 1	800
	21st to end	Night	17% 6% 35% 35% 6%	880
February	1st to 10th	Night	17% 5% 29% 38% 10%	800
	11th to 20th	Night	22% 8% 30% 36% 5%	783
	21st to end	Night	16% 5% 28% 39% 13%	660
March	1st to 10th	Night	15% 5% 30% 36% 14% 1	800
	11th to 20th	Night	15% 4 24% 42% 14% 2	800
	21st to end	Night	14% 4 26% 38% 16% 1	880
April	1st to 10th	Night	13% 5% 25% 38% 18% 2	800
	11th to 20th	Night	10% 4 21% 33% 27% 4	791
	21st to end	Night	8% 2 19% 38% 26% 6%	800
May	1st to 10th	Night	8% 3 18% 40% 26% 5%	734
	11th to 20th	Night	13% 3 12% 36% 31% 6%	591
	21st to end	Night	9% 2 6% 26% 41% 17%	650
June	1st to 10th	Night	11% 4 6% 31% 40% 9%	600
	11th to 20th	Night	10% 2 3 23% 47% 15%	600
	21st to end	Night	8% 1 5% 26% 45% 15%	600
July	1st to 10th	Night	9% 3 4 19% 49% 17%	585
	11th to 20th	Night	9% 1 1 16% 54% 18%	582
	21st to end	Night	6% 2 3 23% 51% 16%	657
August	1st to 10th	Night	10% 2 3 20% 47% 17%	579
	11th to 20th	Night	10% 2 1 21% 48% 18%	667
	21st to end	Night	11% 2 3 18% 46% 20%	836
September	1st to 10th	Night	9% 3 3 22% 48% 14%	760
	11th to 20th	Night	17% 3 5% 27% 36% 12%	760
	21st to end	Night	20% 3 5% 26% 36% 11%	760
October	1st to 10th	Night	14% 3 12% 33% 29% 8%	760
	11th to 20th	Night	11% 3 19% 34% 27% 6%	760
	21st to end	Night	12% 5% 16% 31% 30% 7%	836
November	1st to 10th	Night	13% 3 19% 34% 25% 6%	780
	11th to 20th	Night	15% 6% 24% 34% 18% 3	800
	21st to end	Night	12% 6% 26% 34% 19% 4	800
December	1st to 10th	Night	17% 5% 24% 37% 15% 2	800
	11th to 20th	Night	18% 6% 25% 34% 16% 2	800
	21st to end	Night	20% 5% 26% 33% 14% 1	880

Page generated at 2025-08-02 01:32:24. Version ac07

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