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 2024-04-03.

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	11% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	79297
	Night	11% 6% 3 5% 5% 3 5% 5% 6% 8% 44%	80842
Transparency	Day	25% 36% 9% 14% 12% 3	79019
	Night	26% 35% 8% 13% 13% 4	80639
Seeing	Day	13% 3 14% 28% 29% 13%	14811
	Night	13% 4 18% 31% 27% 7%	25006

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 3 4 3 4 4 6% 8% 47%	2836
	11th to 20th	Day	10% 4 2 5% 5% 3 5% 4 5% 8% 48%	2840
	21st to end	Day	13% 7% 3 6% 6% 3 5% 4 4 5% 44%	3124
February	1st to 10th	Day	14% 6% 3 5% 6% 4 4 5% 5% 7% 40%	1710
	11th to 20th	Day	18% 6% 2 5% 3 2 3 3 5% 5% 47%	1752
	21st to end	Day	15% 6% 2 6% 6% 4 4 4 5% 7% 42%	1727
March	1st to 10th	Day	13% 6% 3 5% 3 2 4 3 5% 6% 50%	2090
	11th to 20th	Day	12% 6% 2 6% 5% 3 4 5% 5% 7% 42%	2090
	21st to end	Day	12% 5% 2 5% 5% 3 5% 5% 6% 7% 44%	2299
April	1st to 10th	Day	9% 4 2 4 4 3 5% 5% 6% 7% 52%	2092
	11th to 20th	Day	9% 4 2 4 5% 2 4 4 7% 7% 53%	2134
	21st to end	Day	7% 4 2 4 5% 3 5% 5% 4 9% 54%	2160
May	1st to 10th	Day	6% 3 2 4 4 3 4 5% 7% 9% 51%	2232
	11th to 20th	Day	10% 6% 2 5% 6% 3 5% 6% 7% 9% 43%	2301
	21st to end	Day	10% 4 2 5% 5% 4 6% 6% 6% 9% 42%	2531
June	1st to 10th	Day	9% 6% 3 6% 7% 4 7% 7% 8% 10% 33%	2340
	11th to 20th	Day	9% 4 2 5% 6% 3 6% 7% 8% 11% 40%	2340
	21st to end	Day	7% 5% 3 5% 7% 4 5% 8% 10% 13% 34%	2340
July	1st to 10th	Day	8% 6% 3 6% 6% 4 7% 8% 8% 12% 33%	2340
	11th to 20th	Day	7% 4 2 6% 7% 4 7% 9% 8% 13% 33%	2340
	21st to end	Day	6% 4 3 6% 7% 4 8% 7% 9% 12% 34%	2547
August	1st to 10th	Day	9% 6% 3 6% 6% 4 7% 8% 10% 13% 30%	2327
	11th to 20th	Day	10% 6% 3 6% 6% 4 7% 6% 8% 13% 30%	2188
	21st to end	Day	11% 6% 3 7% 7% 5% 6% 7% 8% 10% 30%	2376
September	1st to 10th	Day	8% 4 3 5% 5% 4 5% 7% 9% 11% 39%	2160
	11th to 20th	Day	13% 5% 3 6% 6% 3 5% 6% 6% 8% 39%	2012
	21st to end	Day	13% 6% 3 6% 7% 3 4 5% 5% 7% 39%	1949
October	1st to 10th	Day	13% 5% 3 5% 6% 3 3 4 5% 6% 47%	1800
	11th to 20th	Day	10% 3 2 4 4 2 4 4 4 6% 56%	1800
	21st to end	Day	9% 5% 2 4 3 3 3 3 5% 6% 57%	1980
November	1st to 10th	Day	13% 5% 2 3 3 2 3 4 4 5% 55%	1857
	11th to 20th	Day	12% 6% 3 4 6% 3 4 4 3 6% 50%	1900
	21st to end	Day	11% 5% 3 6% 4 2 3 4 5% 7% 51%	1796
December	1st to 10th	Day	14% 5% 4 6% 5% 3 5% 5% 5% 8% 38%	1710
	11th to 20th	Day	14% 4 1 4 3 2 3 3 4 7% 55%	2153
	21st to end	Day	15% 8% 3 5% 5% 3 4 4 4 6% 41%	3124
January	1st to 10th	Night	14% 6% 2 5% 5% 3 4 4 5% 8% 45%	4109
	11th to 20th	Night	10% 6% 3 5% 5% 3 5% 6% 6% 8% 42%	4120
	21st to end	Night	13% 7% 3 7% 5% 3 4 4 4 6% 44%	4532
February	1st to 10th	Night	15% 6% 2 6% 4 2 4 4 5% 6% 44%	2470
	11th to 20th	Night	18% 8% 3 5% 4 2 3 4 4 7% 43%	2309
	21st to end	Night	14% 6% 3 6% 5% 3 4 5% 6% 7% 43%	1727
March	1st to 10th	Night	13% 6% 2 5% 5% 2 4 3 4 7% 48%	2090
	11th to 20th	Night	12% 5% 2 5% 6% 4 4 5% 7% 7% 43%	2090
	21st to end	Night	12% 5% 2 4 5% 3 3 4 6% 8% 47%	2299
April	1st to 10th	Night	10% 5% 2 6% 5% 3 4 4 4 8% 49%	1912
	11th to 20th	Night	10% 5% 2 5% 5% 2 4 5% 5% 8% 49%	1775
	21st to end	Night	7% 4 2 4 4 3 3 5% 5% 9% 54%	1800
May	1st to 10th	Night	7% 4 2 5% 4 2 5% 5% 6% 9% 50%	1742
	11th to 20th	Night	11% 5% 3 4 5% 2 5% 4 6% 10% 45%	1592
	21st to end	Night	8% 5% 2 4 4 3 5% 6% 6% 11% 46%	1744
June	1st to 10th	Night	10% 5% 4 6% 5% 3 5% 6% 8% 11% 37%	1620
	11th to 20th	Night	9% 4 2 4 5% 3 6% 6% 6% 11% 42%	1620
	21st to end	Night	6% 5% 2 5% 7% 4 6% 8% 10% 13% 34%	1620
July	1st to 10th	Night	7% 5% 3 5% 7% 4 7% 8% 8% 10% 37%	1620
	11th to 20th	Night	7% 5% 4 7% 6% 3 6% 5% 8% 13% 36%	1620
	21st to end	Night	5% 6% 2 5% 6% 4 7% 6% 8% 11% 40%	1771
August	1st to 10th	Night	7% 5% 2 7% 5% 4 6% 7% 9% 14% 34%	1611
	11th to 20th	Night	7% 5% 3 7% 7% 4 8% 7% 8% 12% 31%	1695
	21st to end	Night	10% 5% 3 6% 7% 4 6% 8% 9% 10% 32%	1980
September	1st to 10th	Night	8% 4 3 6% 6% 4 6% 6% 7% 11% 41%	1800
	11th to 20th	Night	11% 6% 3 6% 7% 4 5% 6% 6% 6% 39%	1944
	21st to end	Night	16% 7% 3 6% 6% 3 4 4 5% 7% 39%	2009
October	1st to 10th	Night	11% 7% 2 5% 4 3 4 4 5% 6% 49%	2160
	11th to 20th	Night	10% 4 2 4 4 3 4 4 5% 6% 54%	2160
	21st to end	Night	9% 5% 2 4 4 2 3 4 5% 6% 55%	2376
November	1st to 10th	Night	12% 4 2 4 4 2 4 3 4 5% 56%	2221
	11th to 20th	Night	13% 6% 3 5% 4 3 3 4 5% 6% 49%	2280
	21st to end	Night	11% 5% 3 4 4 3 4 5% 6% 8% 48%	2380
December	1st to 10th	Night	15% 7% 2 5% 5% 3 5% 5% 5% 8% 41%	2470
	11th to 20th	Night	16% 6% 2 4 4 2 3 4 4 5% 50%	3042
	21st to end	Night	16% 6% 2 5% 5% 3 4 5% 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	25% 25% 7% 18% 22% 5%	2837
	11th to 20th	Day	26% 25% 4 17% 21% 7%	2840
	21st to end	Day	36% 23% 5% 16% 13% 7%	3124
February	1st to 10th	Day	29% 35% 6% 13% 14% 3	1710
	11th to 20th	Day	27% 35% 5% 11% 15% 7%	1761
	21st to end	Day	27% 34% 7% 15% 12% 6%	1727
March	1st to 10th	Day	24% 33% 7% 13% 18% 5%	2090
	11th to 20th	Day	27% 36% 9% 13% 11% 4	2090
	21st to end	Day	27% 36% 10% 13% 12% 3	2299
April	1st to 10th	Day	19% 37% 8% 14% 17% 4	2092
	11th to 20th	Day	18% 35% 9% 16% 14% 8%	2134
	21st to end	Day	20% 38% 9% 15% 15% 3	2160
May	1st to 10th	Day	19% 39% 13% 19% 9% 2	2232
	11th to 20th	Day	24% 38% 15% 13% 9%	2305
	21st to end	Day	24% 39% 13% 15% 8%	2531
June	1st to 10th	Day	28% 40% 10% 15% 6%	2340
	11th to 20th	Day	25% 39% 15% 15% 6%	2340
	21st to end	Day	24% 41% 13% 14% 6%	2340
July	1st to 10th	Day	27% 42% 12% 12% 5% 1	2275
	11th to 20th	Day	23% 43% 17% 10% 5% 1	2271
	21st to end	Day	25% 43% 19% 12% 2	2405
August	1st to 10th	Day	23% 40% 18% 16% 2	2314
	11th to 20th	Day	29% 40% 14% 12% 4	2188
	21st to end	Day	34% 40% 13% 9% 4	2376
September	1st to 10th	Day	24% 41% 11% 12% 10% 2	2160
	11th to 20th	Day	25% 40% 10% 11% 10% 4	2012
	21st to end	Day	28% 37% 6% 14% 11% 3	1949
October	1st to 10th	Day	26% 37% 5% 11% 20% 3	1800
	11th to 20th	Day	21% 36% 5% 16% 16% 6%	1800
	21st to end	Day	21% 37% 4 13% 19% 6%	1980
November	1st to 10th	Day	16% 40% 5% 12% 19% 9%	1857
	11th to 20th	Day	24% 39% 5% 12% 15% 6%	1900
	21st to end	Day	24% 39% 5% 12% 14% 6%	1796
December	1st to 10th	Day	24% 41% 8% 12% 9% 5%	1710
	11th to 20th	Day	22% 31% 6% 18% 18% 4	2150
	21st to end	Day	32% 25% 6% 14% 20% 3	3124
January	1st to 10th	Night	29% 25% 6% 16% 18% 6%	4109
	11th to 20th	Night	32% 26% 5% 14% 20% 3	4120
	21st to end	Night	36% 23% 5% 10% 22% 4	4532
February	1st to 10th	Night	28% 34% 5% 12% 14% 6%	2470
	11th to 20th	Night	30% 34% 5% 10% 13% 7%	2311
	21st to end	Night	25% 35% 8% 15% 10% 7%	1727
March	1st to 10th	Night	25% 34% 6% 12% 15% 8%	2090
	11th to 20th	Night	26% 36% 10% 12% 13% 4	2090
	21st to end	Night	25% 35% 10% 16% 10% 4	2299
April	1st to 10th	Night	23% 35% 8% 13% 15% 6%	1912
	11th to 20th	Night	21% 36% 7% 13% 15% 8%	1775
	21st to end	Night	18% 37% 11% 15% 15% 3	1800
May	1st to 10th	Night	20% 38% 12% 16% 11% 2	1742
	11th to 20th	Night	25% 39% 12% 13% 10%	1593
	21st to end	Night	21% 40% 13% 18% 7%	1745
June	1st to 10th	Night	28% 39% 11% 16% 6%	1620
	11th to 20th	Night	27% 39% 12% 17% 5%	1620
	21st to end	Night	24% 42% 14% 15% 5%	1620
July	1st to 10th	Night	27% 42% 11% 11% 8% 1	1575
	11th to 20th	Night	25% 42% 19% 9% 4	1566
	21st to end	Night	23% 43% 18% 14% 2	1672
August	1st to 10th	Night	23% 40% 18% 16% 3	1600
	11th to 20th	Night	31% 40% 12% 14% 3	1695
	21st to end	Night	32% 40% 12% 11% 4 1	1980
September	1st to 10th	Night	26% 40% 10% 11% 11% 2	1800
	11th to 20th	Night	25% 41% 10% 11% 11% 1	1944
	21st to end	Night	31% 36% 5% 14% 11% 3	2009
October	1st to 10th	Night	24% 37% 6% 11% 19% 4	2160
	11th to 20th	Night	23% 36% 5% 13% 17% 6%	2160
	21st to end	Night	21% 37% 5% 12% 18% 7%	2376
November	1st to 10th	Night	16% 40% 5% 12% 19% 9%	2221
	11th to 20th	Night	25% 39% 6% 10% 14% 7%	2280
	21st to end	Night	23% 40% 6% 13% 14% 5%	2380
December	1st to 10th	Night	24% 41% 7% 11% 11% 5%	2470
	11th to 20th	Night	27% 32% 6% 12% 20% 3	3044
	21st to end	Night	29% 25% 5% 18% 20% 3	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% 25% 34% 21% 4	428
	11th to 20th	Day	10% 2 19% 30% 32% 7%	412
	21st to end	Day	8% 3 16% 35% 26% 11%	420
May	1st to 10th	Day	6% 2 20% 37% 26% 9%	423
	11th to 20th	Day	12% 1 10% 27% 36% 14%	447
	21st to end	Day	14% 1 6% 21% 37% 21%	485
June	1st to 10th	Day	10% 2 3 31% 39% 15%	450
	11th to 20th	Day	12% 1 6% 18% 38% 24%	450
	21st to end	Day	10% 2 2 22% 44% 21%	450
July	1st to 10th	Day	9% 2 2 13% 45% 29%	445
	11th to 20th	Day	8% 2 2 13% 44% 32%	444
	21st to end	Day	5% 3 2 18% 51% 21%	488
August	1st to 10th	Day	15% 2 2 16% 40% 24%	446
	11th to 20th	Day	13% 2 13% 40% 32%	439
	21st to end	Day	13% 3 3 14% 38% 29%	495
September	1st to 10th	Day	10% 2 3 17% 41% 27%	450
	11th to 20th	Day	16% 2 8% 20% 35% 18%	450
	21st to end	Day	17% 1 6% 22% 38% 17%	450
October	1st to 10th	Day	18% 2 8% 30% 26% 17%	450
	11th to 20th	Day	11% 1 14% 26% 30% 16%	450
	21st to end	Day	11% 1 16% 29% 29% 13%	495
November	1st to 10th	Day	16% 4 15% 27% 27% 11%	455
	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% 37% 18% 2	729
	11th to 20th	Night	11% 4 21% 31% 28% 5%	711
	21st to end	Night	8% 3 21% 38% 25% 5%	720
May	1st to 10th	Night	9% 3 19% 40% 24% 5%	662
	11th to 20th	Night	13% 3 11% 34% 32% 7%	531
	21st to end	Night	9% 1 5% 25% 42% 18%	584
June	1st to 10th	Night	11% 4 6% 31% 40% 9%	540
	11th to 20th	Night	11% 2 3 22% 46% 17%	540
	21st to end	Night	8% 1 4 27% 45% 14%	540
July	1st to 10th	Night	9% 3 3 19% 50% 15%	525
	11th to 20th	Night	9% 1 1 18% 54% 16%	522
	21st to end	Night	6% 2 3 24% 52% 15%	591
August	1st to 10th	Night	9% 1 2 21% 49% 18%	537
	11th to 20th	Night	10% 2 1 20% 49% 18%	631
	21st to end	Night	11% 2 3 17% 47% 20%	792
September	1st to 10th	Night	9% 3 3 22% 49% 14%	720
	11th to 20th	Night	15% 3 5% 28% 38% 12%	720
	21st to end	Night	21% 2 5% 25% 36% 11%	720
October	1st to 10th	Night	14% 3 13% 32% 29% 8%	720
	11th to 20th	Night	12% 3 18% 33% 28% 7%	720
	21st to end	Night	12% 5% 17% 31% 29% 6%	792
November	1st to 10th	Night	14% 4 20% 33% 24% 5%	740
	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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