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 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	11% 6% 2 6% 5% 4 5% 4 6% 8% 41%	101053
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 43%	97930
Transparency	Day	38% 6% 15% 21% 16% 5%	104700
	Night	38% 5% 13% 20% 17% 6%	102422
Seeing	Day	13% 3 14% 28% 30% 13%	15671
	Night	13% 4 17% 31% 27% 7%	25768

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	14% 5% 2 4 3 4 4 3 6% 8% 46%	2836
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 3 5% 8% 48%	2840
	21st to end	Day	13% 7% 2 7% 5% 5% 4 3 4 5% 44%	3124
February	1st to 10th	Day	14% 7% 3 6% 5% 5% 4 5% 5% 6% 40%	1710
	11th to 20th	Day	18% 7% 2 6% 3 3 3 3 5% 5% 46%	1752
	21st to end	Day	15% 6% 2 7% 5% 4 4 4 5% 6% 42%	1727
March	1st to 10th	Day	20% 10% 4 6% 4 4 3 3 5% 5% 36%	3435
	11th to 20th	Day	8% 4 1 5% 4 4 4 4 5% 7% 53%	3480
	21st to end	Day	15% 6% 2 6% 4 4 3 3 5% 5% 45%	3815
April	1st to 10th	Day	9% 5% 1 4 4 4 5% 4 6% 7% 52%	2185
	11th to 20th	Day	9% 5% 2 4 4 3 4 4 7% 7% 53%	2254
	21st to end	Day	7% 4 1 4 4 4 5% 4 5% 9% 53%	2280
May	1st to 10th	Day	7% 5% 2 6% 5% 6% 5% 4 7% 9% 44%	3907
	11th to 20th	Day	13% 7% 3 8% 5% 4 5% 4 6% 7% 38%	4081
	21st to end	Day	7% 3 2 4 4 5% 5% 5% 7% 10% 47%	4476
June	1st to 10th	Day	9% 7% 2 7% 6% 5% 6% 6% 9% 10% 34%	2470
	11th to 20th	Day	9% 4 2 5% 5% 4 6% 5% 8% 11% 41%	2470
	21st to end	Day	7% 5% 2 6% 6% 5% 6% 6% 10% 12% 34%	2470
July	1st to 10th	Day	10% 7% 3 7% 6% 5% 6% 6% 8% 13% 30%	4120
	11th to 20th	Day	6% 6% 2 9% 7% 7% 7% 7% 9% 12% 27%	4120
	21st to end	Day	7% 7% 3 9% 7% 8% 7% 6% 10% 11% 26%	4466
August	1st to 10th	Day	19% 9% 3 9% 5% 5% 6% 5% 8% 10% 21%	4104
	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 3 4 5% 55%	1887
	11th to 20th	Day	12% 6% 2 5% 5% 3 4 3 4 6% 50%	1900
	21st to end	Day	11% 6% 2 6% 3 3 3 3 5% 6% 51%	1796
December	1st to 10th	Day	14% 6% 3 7% 5% 4 5% 4 5% 8% 38%	1710
	11th to 20th	Day	14% 4 1 4 3 3 3 3 4 6% 55%	2153
	21st to end	Day	14% 9% 3 6% 4 4 4 3 5% 6% 41%	3124
January	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 44%	4109
	11th to 20th	Night	10% 7% 2 6% 4 5% 5% 5% 7% 7% 41%	4120
	21st to end	Night	13% 8% 3 7% 4 4 4 3 4 6% 44%	4532
February	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	2470
	11th to 20th	Night	17% 8% 2 5% 4 3 4 3 4 6% 43%	2309
	21st to end	Night	14% 6% 3 7% 4 5% 4 3 6% 7% 43%	1727
March	1st to 10th	Night	21% 12% 4 7% 5% 4 3 2 3 6% 32%	3418
	11th to 20th	Night	11% 5% 1 5% 5% 4 3 4 6% 7% 48%	3480
	21st to end	Night	16% 5% 2 5% 4 3 3 3 5% 7% 47%	3817
April	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 5% 8% 48%	1993
	11th to 20th	Night	9% 5% 2 6% 4 3 4 4 5% 8% 49%	1875
	21st to end	Night	7% 4 2 5% 4 4 4 4 6% 8% 54%	1900
May	1st to 10th	Night	6% 5% 2 6% 4 5% 5% 4 6% 10% 46%	3016
	11th to 20th	Night	11% 7% 3 7% 4 4 4 4 6% 8% 43%	2812
	21st to end	Night	6% 4 2 5% 3 4 5% 5% 6% 11% 48%	3079
June	1st to 10th	Night	9% 6% 3 7% 5% 4 5% 5% 8% 11% 37%	1710
	11th to 20th	Night	9% 5% 2 5% 5% 4 6% 5% 6% 11% 43%	1710
	21st to end	Night	6% 6% 2 7% 6% 5% 5% 6% 10% 12% 34%	1710
July	1st to 10th	Night	8% 6% 3 8% 7% 7% 6% 6% 8% 11% 31%	2840
	11th to 20th	Night	7% 6% 3 9% 6% 6% 5% 5% 8% 12% 31%	2840
	21st to end	Night	6% 7% 2 7% 6% 7% 7% 7% 11% 13% 28%	3087
August	1st to 10th	Night	18% 9% 3 8% 4 4 5% 5% 8% 12% 25%	2825
	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 3 3 4 5% 56%	2264
	11th to 20th	Night	13% 7% 2 6% 3 4 3 3 4 6% 49%	2280
	21st to end	Night	11% 5% 3 5% 3 4 4 4 6% 8% 48%	2380
December	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 7% 40%	2470
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 4 4 50%	3042
	21st to end	Night	16% 7% 2 6% 4 4 4 4 6% 7% 42%	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	35% 3 8% 22% 26% 6%	2837
	11th to 20th	Day	36% 3 6% 20% 26% 9%	2840
	21st to end	Day	43% 3 6% 21% 18% 8%	3124
February	1st to 10th	Day	43% 4 9% 21% 19% 4	1710
	11th to 20th	Day	41% 3 7% 19% 22% 7%	1761
	21st to end	Day	42% 3 9% 19% 17% 9%	1727
March	1st to 10th	Day	50% 3 10% 16% 15% 6%	3435
	11th to 20th	Day	30% 4 11% 18% 27% 10%	3480
	21st to end	Day	40% 4 10% 20% 20% 6%	3815
April	1st to 10th	Day	31% 4 14% 21% 25% 6%	2185
	11th to 20th	Day	30% 4 13% 25% 18% 11%	2254
	21st to end	Day	28% 5% 13% 27% 22% 4	2280
May	1st to 10th	Day	34% 6% 21% 26% 11% 2	3942
	11th to 20th	Day	43% 4 15% 25% 13% 1	4085
	21st to end	Day	28% 6% 22% 28% 16% 1	4489
June	1st to 10th	Day	40% 9% 18% 23% 10%	2470
	11th to 20th	Day	32% 8% 23% 25% 11%	2470
	21st to end	Day	35% 11% 23% 23% 8% 1	2470
July	1st to 10th	Day	42% 11% 22% 20% 4 1	4055
	11th to 20th	Day	42% 13% 30% 11% 3	4051
	21st to end	Day	44% 13% 22% 15% 5%	4324
August	1st to 10th	Day	53% 8% 24% 12% 2	4091
	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% 3 9% 18% 27% 11%	1887
	11th to 20th	Day	38% 3 8% 18% 24% 9%	1900
	21st to end	Day	35% 3 9% 22% 24% 8%	1796
December	1st to 10th	Day	43% 5% 14% 18% 14% 6%	1710
	11th to 20th	Day	32% 3 7% 26% 25% 7%	2150
	21st to end	Day	44% 3 9% 19% 22% 3	3124
January	1st to 10th	Night	39% 3 7% 20% 22% 8%	4109
	11th to 20th	Night	40% 4 8% 19% 25% 5%	4120
	21st to end	Night	43% 2 7% 14% 27% 6%	4532
February	1st to 10th	Night	40% 3 9% 20% 20% 8%	2470
	11th to 20th	Night	44% 4 8% 17% 19% 9%	2311
	21st to end	Night	41% 3 10% 19% 16% 10%	1727
March	1st to 10th	Night	55% 2 11% 14% 12% 6%	3418
	11th to 20th	Night	34% 5% 9% 16% 23% 13%	3480
	21st to end	Night	39% 3 10% 23% 18% 6%	3817
April	1st to 10th	Night	35% 4 12% 19% 21% 9%	1993
	11th to 20th	Night	33% 4 12% 22% 19% 10%	1875
	21st to end	Night	28% 5% 15% 26% 21% 5%	1900
May	1st to 10th	Night	33% 5% 20% 27% 13% 3	3046
	11th to 20th	Night	40% 5% 15% 24% 16% 1	2813
	21st to end	Night	30% 6% 18% 28% 17% 1	3087
June	1st to 10th	Night	39% 8% 20% 23% 9% 1	1710
	11th to 20th	Night	34% 8% 22% 26% 10%	1710
	21st to end	Night	35% 12% 24% 22% 6% 1	1710
July	1st to 10th	Night	43% 10% 20% 21% 5% 1	2795
	11th to 20th	Night	42% 13% 32% 9% 3	2786
	21st to end	Night	41% 16% 19% 19% 4	2988
August	1st to 10th	Night	50% 9% 25% 14% 2	2814
	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	32% 3 9% 17% 26% 12%	2264
	11th to 20th	Night	37% 3 9% 16% 23% 11%	2280
	21st to end	Night	34% 3 10% 22% 22% 8%	2380
December	1st to 10th	Night	43% 5% 13% 17% 17% 6%	2470
	11th to 20th	Night	38% 3 8% 19% 26% 7%	3044
	21st to end	Night	42% 3 8% 21% 22% 4	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	13% 4 27% 43% 12%	270
	11th to 20th	Day	9% 4 24% 45% 16% 2	270
	21st to end	Day	20% 3 30% 36% 10% 1	297
February	1st to 10th	Day	16% 5% 27% 37% 14% 1	270
	11th to 20th	Day	25% 3 27% 32% 12% 1	321
	21st to end	Day	14% 5% 31% 37% 12% 1	382
March	1st to 10th	Day	16% 3 28% 31% 20% 2	460
	11th to 20th	Day	14% 4 27% 37% 16% 2	460
	21st to end	Day	13% 3 26% 37% 18% 2	506
April	1st to 10th	Day	12% 5% 24% 37% 20% 3	460
	11th to 20th	Day	10% 2 19% 30% 32% 7%	452
	21st to end	Day	8% 3 16% 35% 27% 11%	460
May	1st to 10th	Day	6% 2 19% 36% 26% 11%	463
	11th to 20th	Day	12% 1 10% 29% 35% 13%	487
	21st to end	Day	13% 1 6% 23% 36% 21%	529
June	1st to 10th	Day	10% 2 3 29% 40% 16%	490
	11th to 20th	Day	11% 1 7% 20% 38% 23%	490
	21st to end	Day	9% 2 2 22% 44% 21%	490
July	1st to 10th	Day	9% 2 2 12% 47% 28%	485
	11th to 20th	Day	9% 2 2 13% 43% 31%	484
	21st to end	Day	6% 3 3 18% 50% 21%	532
August	1st to 10th	Day	17% 2 2 17% 39% 22%	486
	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%	467
	11th to 20th	Day	15% 3 21% 38% 18% 4	460
	21st to end	Day	13% 4 19% 36% 24% 5%	356
December	1st to 10th	Day	20% 2 17% 38% 20% 3	270
	11th to 20th	Day	18% 3 23% 33% 20% 4	270
	21st to end	Day	19% 5% 22% 35% 15% 5%	297
January	1st to 10th	Night	15% 9% 31% 34% 10% 1	760
	11th to 20th	Night	13% 7% 30% 34% 14% 1	760
	21st to end	Night	17% 7% 35% 35% 6%	836
February	1st to 10th	Night	18% 5% 30% 38% 10%	760
	11th to 20th	Night	21% 7% 29% 37% 5%	743
	21st to end	Night	17% 4 28% 38% 13%	628
March	1st to 10th	Night	15% 5% 29% 36% 15%	760
	11th to 20th	Night	15% 4 24% 41% 14% 2	760
	21st to end	Night	15% 4 26% 38% 16% 1	836
April	1st to 10th	Night	12% 5% 25% 38% 18% 2	760
	11th to 20th	Night	11% 4 21% 31% 28% 5%	751
	21st to end	Night	8% 3 20% 38% 25% 6%	760
May	1st to 10th	Night	8% 3 18% 39% 26% 5%	698
	11th to 20th	Night	13% 3 11% 35% 32% 6%	561
	21st to end	Night	9% 1 5% 25% 42% 18%	617
June	1st to 10th	Night	10% 4 5% 31% 41% 9%	570
	11th to 20th	Night	10% 2 3 22% 46% 16%	570
	21st to end	Night	8% 1 5% 27% 44% 14%	570
July	1st to 10th	Night	9% 3 4 18% 49% 17%	555
	11th to 20th	Night	9% 1 1 17% 54% 17%	552
	21st to end	Night	6% 2 3 24% 51% 14%	624
August	1st to 10th	Night	10% 1 3 20% 48% 17%	567
	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 20% 33% 25% 5%	755
	11th to 20th	Night	15% 5% 24% 34% 18% 3	760
	21st to end	Night	12% 6% 25% 34% 19% 4	760
December	1st to 10th	Night	18% 5% 24% 36% 16% 2	760
	11th to 20th	Night	18% 6% 25% 34% 16% 2	760
	21st to end	Night	20% 6% 26% 32% 15% 1	836

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