Myrtle Beach State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Myrtle Beach State Park clear sky chart from 2005-11-06 to 2025-12-18.

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	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	126971
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	124087
Transparency	Day	37% 6% 15% 20% 17% 5%	130574
	Night	37% 5% 13% 19% 18% 7%	128553
Seeing	Day	13% 3 14% 28% 29% 13%	17199
	Night	13% 4 18% 32% 27% 7%	27303

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	11% 5% 2 4 3 3 3 3 5% 6% 55%	4056
	11th to 20th	Day	11% 5% 2 5% 4 4 3 3 4 7% 51%	4060
	21st to end	Day	13% 8% 3 7% 4 4 3 3 4 7% 44%	4466
February	1st to 10th	Day	14% 6% 3 6% 5% 5% 4 4 6% 5% 41%	1800
	11th to 20th	Day	18% 6% 3 6% 3 3 3 3 5% 5% 46%	1851
	21st to end	Day	14% 5% 2 8% 4 4 3 3 5% 7% 45%	1815
March	1st to 10th	Day	19% 8% 3 6% 4 3 4 3 5% 5% 40%	4935
	11th to 20th	Day	8% 4 2 4 4 4 4 3 6% 7% 54%	4980
	21st to end	Day	11% 5% 2 6% 4 4 4 3 6% 5% 50%	5465
April	1st to 10th	Day	9% 5% 1 4 3 5% 5% 3 6% 7% 53%	2300
	11th to 20th	Day	8% 4 2 4 3 4 4 3 6% 7% 54%	2374
	21st to end	Day	7% 4 2 5% 4 4 4 4 5% 8% 55%	2400
May	1st to 10th	Day	7% 6% 2 7% 5% 4 5% 4 7% 11% 41%	5589
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 9% 35%	5861
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 7% 10% 45%	6433
June	1st to 10th	Day	9% 6% 3 8% 5% 5% 6% 5% 8% 11% 36%	2600
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 5% 8% 12% 43%	2600
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 6% 10% 12% 38%	2600
July	1st to 10th	Day	9% 7% 3 8% 5% 5% 6% 5% 8% 11% 32%	5900
	11th to 20th	Day	5% 4 2 7% 5% 6% 7% 6% 9% 13% 35%	5900
	21st to end	Day	7% 5% 3 7% 6% 5% 7% 6% 9% 11% 34%	6424
August	1st to 10th	Day	19% 8% 4 7% 5% 5% 6% 5% 7% 11% 23%	4234
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 5% 7% 10% 40%	3954
	21st to end	Day	9% 6% 3 6% 4 5% 4 4 7% 9% 43%	4312
September	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 5% 7% 9% 42%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 40%	2233
	21st to end	Day	14% 6% 3 8% 4 4 4 3 6% 8% 41%	2166
October	1st to 10th	Day	13% 5% 3 7% 4 4 4 3 5% 6% 46%	2000
	11th to 20th	Day	9% 4 2 5% 4 3 3 3 3 5% 60%	2000
	21st to end	Day	10% 4 2 5% 3 3 3 2 4 7% 58%	2200
November	1st to 10th	Day	12% 5% 2 4 3 3 4 3 4 5% 56%	2057
	11th to 20th	Day	11% 6% 2 6% 4 4 3 3 4 5% 52%	2100
	21st to end	Day	10% 5% 2 7% 4 3 3 3 5% 6% 52%	1984
December	1st to 10th	Day	9% 5% 2 6% 4 4 4 3 5% 6% 52%	3020
	11th to 20th	Day	13% 7% 3 8% 4 4 3 3 4 6% 46%	3436
	21st to end	Day	14% 8% 2 6% 4 4 4 3 5% 7% 43%	4466
January	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 6% 55%	5889
	11th to 20th	Night	12% 6% 3 6% 4 4 4 4 6% 8% 44%	5900
	21st to end	Night	11% 7% 3 8% 4 4 4 3 4 6% 46%	6490
February	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 5% 6% 43%	2600
	11th to 20th	Night	18% 8% 3 6% 4 4 3 3 4 6% 42%	2432
	21st to end	Night	13% 6% 2 7% 4 4 4 3 5% 7% 43%	1815
March	1st to 10th	Night	16% 11% 3 7% 4 4 3 3 4 5% 40%	4918
	11th to 20th	Night	11% 4 1 5% 3 3 3 4 6% 8% 51%	4980
	21st to end	Night	12% 4 2 6% 4 3 3 3 5% 6% 52%	5467
April	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 4 5% 7% 48%	2100
	11th to 20th	Night	8% 5% 2 6% 4 3 5% 3 6% 7% 51%	1975
	21st to end	Night	6% 4 2 5% 5% 3 3 4 7% 8% 53%	2000
May	1st to 10th	Night	6% 5% 2 7% 5% 4 5% 4 7% 10% 45%	4334
	11th to 20th	Night	14% 7% 2 6% 4 4 5% 4 7% 10% 37%	4032
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 10% 41%	4421
June	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 5% 7% 10% 38%	1800
	11th to 20th	Night	8% 5% 1 6% 4 5% 5% 5% 7% 11% 42%	1800
	21st to end	Night	5% 6% 2 7% 6% 4 5% 6% 10% 12% 38%	1800
July	1st to 10th	Night	9% 5% 2 7% 7% 6% 7% 6% 8% 13% 31%	4058
	11th to 20th	Night	6% 6% 3 8% 5% 5% 6% 6% 9% 14% 33%	4057
	21st to end	Night	6% 6% 3 7% 6% 6% 7% 6% 9% 13% 31%	4427
August	1st to 10th	Night	17% 9% 3 8% 4 5% 5% 5% 8% 12% 25%	2915
	11th to 20th	Night	6% 5% 3 6% 4 6% 6% 5% 8% 13% 39%	3062
	21st to end	Night	6% 4 2 7% 5% 5% 5% 6% 7% 8% 45%	3586
September	1st to 10th	Night	9% 5% 3 7% 5% 4 6% 5% 7% 9% 41%	2000
	11th to 20th	Night	13% 7% 2 7% 5% 5% 6% 4 7% 7% 36%	2162
	21st to end	Night	17% 8% 2 7% 4 4 3 3 5% 6% 40%	2232
October	1st to 10th	Night	12% 7% 2 6% 3 4 4 3 5% 7% 46%	2400
	11th to 20th	Night	11% 4 2 5% 3 4 3 2 5% 6% 55%	2400
	21st to end	Night	9% 5% 2 5% 3 3 4 3 4 5% 57%	2640
November	1st to 10th	Night	11% 5% 1 5% 4 4 4 3 3 6% 55%	2461
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 5% 6% 49%	2520
	21st to end	Night	9% 5% 2 4 4 4 4 4 6% 9% 48%	2630
December	1st to 10th	Night	11% 6% 2 6% 3 4 3 3 4 6% 53%	4380
	11th to 20th	Night	15% 7% 3 9% 5% 4 3 3 4 5% 43%	4914
	21st to end	Night	13% 7% 2 6% 4 4 4 4 6% 7% 44%	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%	1860
	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	5621
	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% 23% 12% 2	4221
	11th to 20th	Day	38% 10% 23% 21% 9%	3993
	21st to end	Day	36% 7% 18% 33% 5%	4312
September	1st to 10th	Day	35% 10% 19% 19% 14% 3	2400
	11th to 20th	Day	42% 7% 14% 19% 14% 4	2233
	21st to end	Day	42% 5% 15% 21% 14% 3	2166
October	1st to 10th	Day	40% 4 9% 18% 25% 4	3260
	11th to 20th	Day	20% 2 6% 17% 30% 26%	3240
	21st to end	Day	27% 3 7% 20% 34% 9%	3538
November	1st to 10th	Day	31% 4 10% 18% 27% 10%	2057
	11th to 20th	Day	37% 3 8% 19% 25% 9%	2100
	21st to end	Day	34% 3 10% 21% 25% 7%	1984
December	1st to 10th	Day	33% 4 9% 16% 23% 14%	3020
	11th to 20th	Day	40% 4 8% 22% 20% 5%	3433
	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%	2434
	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% 4 12% 20% 20% 9%	2100
	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	4364
	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% 24% 13% 2	2904
	11th to 20th	Night	35% 10% 25% 24% 6%	3089
	21st to end	Night	33% 8% 19% 34% 6%	3586
September	1st to 10th	Night	38% 9% 18% 19% 13% 3	2000
	11th to 20th	Night	45% 8% 13% 19% 14% 2	2162
	21st to end	Night	45% 4 13% 22% 12% 3	2232
October	1st to 10th	Night	37% 4 10% 20% 25% 5%	3920
	11th to 20th	Night	20% 2 5% 15% 25% 34%	3899
	21st to end	Night	25% 4 7% 23% 29% 13%	4252
November	1st to 10th	Night	32% 4 9% 18% 26% 12%	2461
	11th to 20th	Night	36% 3 9% 16% 25% 11%	2520
	21st to end	Night	33% 3 11% 22% 22% 8%	2630
December	1st to 10th	Night	34% 3 9% 14% 27% 13%	4380
	11th to 20th	Night	44% 3 10% 17% 19% 7%	4916
	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	18% 3 3 16% 39% 21%	526
	11th to 20th	Day	13% 2 1 17% 37% 31%	519
	21st to end	Day	13% 3 4 16% 37% 26%	583
September	1st to 10th	Day	11% 2 4 22% 38% 24%	530
	11th to 20th	Day	18% 2 8% 21% 34% 17%	530
	21st to end	Day	18% 2 5% 23% 36% 16%	530
October	1st to 10th	Day	18% 2 8% 30% 27% 15%	530
	11th to 20th	Day	12% 1 15% 28% 30% 15%	530
	21st to end	Day	12% 1 17% 30% 29% 12%	583
November	1st to 10th	Day	15% 4 16% 28% 27% 10%	535
	11th to 20th	Day	14% 4 21% 39% 18% 4	540
	21st to end	Day	12% 4 21% 36% 22% 4	424
December	1st to 10th	Day	20% 3 19% 38% 18% 3	330
	11th to 20th	Day	17% 3 21% 34% 21% 3	321
	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%	735
	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	11% 2 4 20% 48% 16%	597
	11th to 20th	Night	10% 2 1 20% 47% 19%	703
	21st to end	Night	11% 2 3 19% 45% 19%	880
September	1st to 10th	Night	10% 3 4 24% 47% 13%	800
	11th to 20th	Night	16% 3 5% 28% 36% 12%	800
	21st to end	Night	21% 3 5% 25% 37% 10%	800
October	1st to 10th	Night	15% 3 12% 33% 29% 8%	800
	11th to 20th	Night	12% 2 18% 34% 27% 6%	800
	21st to end	Night	13% 5% 17% 30% 29% 6%	880
November	1st to 10th	Night	13% 4 20% 34% 24% 5%	820
	11th to 20th	Night	15% 6% 23% 35% 18% 3	840
	21st to end	Night	11% 6% 26% 35% 18% 4	840
December	1st to 10th	Night	18% 5% 24% 37% 14% 1	840
	11th to 20th	Night	17% 6% 24% 34% 16% 2	829
	21st to end	Night	20% 5% 26% 33% 14% 1	880

Page generated at 2025-12-15 01:13:54. Version ac07

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