Cheraw State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cheraw State Park clear sky chart from 2005-11-06 to 2024-11-11.

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% 6% 2 6% 4 4 5% 4 6% 8% 42%	101228
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	97894
Transparency	Day	38% 7% 12% 20% 18% 6%	104878
	Night	39% 6% 11% 18% 19% 7%	102370
Seeing	Day	15% 9% 22% 25% 20% 9%	15490
	Night	15% 7% 23% 33% 19% 2	25570

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	16% 5% 2 5% 3 3 3 2 3 7% 50%	2836
	11th to 20th	Day	13% 6% 2 4 4 3 3 3 4 5% 55%	2840
	21st to end	Day	17% 9% 3 7% 3 4 3 2 5% 4 43%	3124
February	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 5% 6% 43%	1710
	11th to 20th	Day	21% 6% 2 5% 3 3 3 2 5% 5% 46%	1757
	21st to end	Day	19% 8% 2 5% 4 4 3 3 4 6% 41%	1693
March	1st to 10th	Day	23% 8% 3 6% 4 3 3 3 4 6% 37%	3435
	11th to 20th	Day	10% 4 2 5% 3 4 4 3 5% 6% 54%	3480
	21st to end	Day	18% 7% 2 7% 4 3 3 3 4 5% 44%	3815
April	1st to 10th	Day	9% 5% 2 4 4 3 4 4 6% 7% 53%	2137
	11th to 20th	Day	11% 6% 1 5% 4 4 4 4 6% 6% 49%	2254
	21st to end	Day	11% 5% 2 5% 4 4 4 3 5% 7% 52%	2304
May	1st to 10th	Day	9% 7% 3 8% 6% 5% 6% 4 7% 10% 37%	4082
	11th to 20th	Day	16% 7% 3 8% 4 4 5% 3 6% 7% 37%	4081
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 7% 10% 47%	4476
June	1st to 10th	Day	9% 5% 2 7% 5% 6% 6% 6% 7% 10% 36%	2470
	11th to 20th	Day	8% 5% 2 5% 5% 5% 6% 5% 8% 11% 41%	2470
	21st to end	Day	8% 4 2 6% 6% 4 6% 6% 9% 11% 39%	2470
July	1st to 10th	Day	8% 6% 3 8% 6% 7% 7% 6% 8% 11% 31%	4120
	11th to 20th	Day	8% 6% 2 8% 6% 6% 7% 6% 9% 12% 30%	4120
	21st to end	Day	10% 7% 3 8% 6% 6% 7% 6% 10% 11% 27%	4466
August	1st to 10th	Day	23% 8% 2 8% 5% 5% 6% 5% 8% 9% 21%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 6% 6% 5% 7% 10% 36%	3982
	21st to end	Day	7% 4 1 5% 4 3 5% 4 7% 11% 49%	4180
September	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 8% 43%	2218
	11th to 20th	Day	14% 5% 2 7% 5% 5% 5% 3 5% 7% 41%	2090
	21st to end	Day	18% 7% 3 6% 4 4 4 4 4 6% 41%	2090
October	1st to 10th	Day	15% 6% 1 4 4 3 4 3 4 6% 50%	1918
	11th to 20th	Day	10% 4 2 5% 3 4 3 3 4 5% 57%	1900
	21st to end	Day	11% 4 2 5% 3 3 3 2 4 6% 57%	2090
November	1st to 10th	Day	13% 6% 1 4 3 3 3 2 4 6% 55%	1957
	11th to 20th	Day	15% 5% 2 4 3 3 3 3 4 5% 53%	1862
	21st to end	Day	14% 5% 2 5% 3 4 3 3 5% 5% 50%	1710
December	1st to 10th	Day	17% 7% 3 6% 4 4 4 3 5% 6% 38%	1710
	11th to 20th	Day	16% 4 1 4 3 2 3 2 4 6% 54%	2153
	21st to end	Day	17% 7% 2 6% 4 3 3 3 5% 5% 45%	3124
January	1st to 10th	Night	15% 6% 2 5% 4 3 3 3 4 5% 50%	4109
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 3 5% 6% 45%	4120
	21st to end	Night	17% 8% 3 6% 4 3 3 3 4 5% 45%	4532
February	1st to 10th	Night	16% 6% 2 6% 4 3 4 3 5% 7% 44%	2470
	11th to 20th	Night	18% 8% 2 6% 4 4 4 3 5% 5% 43%	2305
	21st to end	Night	15% 7% 2 6% 4 3 3 3 5% 7% 45%	1761
March	1st to 10th	Night	23% 10% 3 8% 5% 3 4 3 4 5% 33%	3418
	11th to 20th	Night	12% 5% 2 5% 4 4 4 4 5% 6% 50%	3480
	21st to end	Night	18% 5% 2 5% 4 3 4 4 5% 7% 45%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 7% 51%	2041
	11th to 20th	Night	10% 5% 2 5% 3 4 5% 2 5% 7% 53%	1875
	21st to end	Night	10% 4 1 4 4 4 4 4 5% 7% 51%	1891
May	1st to 10th	Night	11% 6% 2 7% 4 5% 5% 4 7% 9% 41%	2813
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 3 5% 8% 38%	2812
	21st to end	Night	8% 4 2 6% 5% 4 5% 5% 7% 9% 44%	3079
June	1st to 10th	Night	11% 6% 2 6% 6% 6% 7% 5% 7% 9% 34%	1710
	11th to 20th	Night	10% 6% 2 6% 6% 5% 6% 5% 6% 9% 38%	1710
	21st to end	Night	7% 5% 2 7% 7% 5% 6% 6% 9% 13% 34%	1710
July	1st to 10th	Night	10% 7% 3 8% 7% 6% 6% 5% 8% 10% 30%	2840
	11th to 20th	Night	11% 7% 3 8% 6% 6% 6% 5% 7% 12% 28%	2840
	21st to end	Night	14% 9% 4 9% 7% 6% 6% 5% 7% 10% 23%	3087
August	1st to 10th	Night	24% 7% 2 8% 4 5% 5% 4 7% 9% 24%	2825
	11th to 20th	Night	10% 6% 3 8% 6% 6% 6% 5% 9% 9% 32%	2812
	21st to end	Night	6% 4 2 5% 4 3 5% 4 7% 10% 49%	3476
September	1st to 10th	Night	10% 4 2 6% 6% 6% 4 5% 7% 10% 41%	1957
	11th to 20th	Night	15% 6% 3 8% 5% 4 5% 3 5% 6% 40%	2090
	21st to end	Night	18% 6% 3 7% 4 4 4 4 5% 6% 38%	2090
October	1st to 10th	Night	15% 5% 2 5% 3 3 3 2 5% 6% 51%	2261
	11th to 20th	Night	13% 5% 2 4 3 3 3 2 4 6% 56%	2280
	21st to end	Night	10% 6% 2 5% 3 3 3 3 4 6% 57%	2508
November	1st to 10th	Night	13% 6% 2 4 3 3 3 2 4 4 54%	2341
	11th to 20th	Night	14% 7% 2 4 3 3 3 2 5% 5% 51%	2320
	21st to end	Night	14% 5% 2 5% 3 3 3 4 5% 6% 49%	2470
December	1st to 10th	Night	17% 8% 2 5% 4 4 3 3 5% 6% 42%	2470
	11th to 20th	Night	18% 6% 1 5% 4 2 2 3 4 4 52%	3042
	21st to end	Night	18% 6% 3 6% 4 3 3 3 4 6% 44%	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	36% 3 6% 24% 24% 7%	2837
	11th to 20th	Day	33% 3 6% 18% 30% 9%	2840
	21st to end	Day	45% 4 4 17% 23% 8%	3124
February	1st to 10th	Day	41% 5% 9% 20% 20% 5%	1710
	11th to 20th	Day	41% 4 6% 19% 23% 7%	1766
	21st to end	Day	45% 4 9% 16% 19% 7%	1693
March	1st to 10th	Day	49% 5% 6% 17% 14% 9%	3435
	11th to 20th	Day	31% 5% 8% 16% 28% 12%	3480
	21st to end	Day	42% 5% 6% 20% 21% 5%	3815
April	1st to 10th	Day	29% 6% 12% 20% 27% 6%	2137
	11th to 20th	Day	33% 6% 10% 20% 20% 10%	2254
	21st to end	Day	33% 6% 11% 25% 21% 4	2304
May	1st to 10th	Day	39% 10% 16% 21% 12% 2	4120
	11th to 20th	Day	44% 7% 10% 20% 17% 1	4085
	21st to end	Day	29% 10% 17% 19% 22% 3	4489
June	1st to 10th	Day	38% 10% 16% 22% 11% 2	2470
	11th to 20th	Day	33% 11% 18% 22% 14% 2	2470
	21st to end	Day	35% 11% 16% 22% 15% 1	2470
July	1st to 10th	Day	42% 11% 19% 16% 10% 1	4055
	11th to 20th	Day	42% 13% 25% 16% 4 1	4051
	21st to end	Day	46% 15% 17% 15% 8%	4324
August	1st to 10th	Day	56% 10% 19% 11% 5%	4091
	11th to 20th	Day	40% 11% 16% 22% 11%	4021
	21st to end	Day	28% 7% 15% 32% 16% 2	4180
September	1st to 10th	Day	35% 10% 15% 17% 18% 4	2218
	11th to 20th	Day	42% 6% 11% 15% 21% 4	2090
	21st to end	Day	43% 6% 9% 20% 17% 6%	2090
October	1st to 10th	Day	34% 4 7% 19% 27% 9%	3178
	11th to 20th	Day	20% 3 5% 18% 27% 28%	3140
	21st to end	Day	25% 3 6% 23% 25% 18%	3428
November	1st to 10th	Day	32% 3 7% 19% 28% 10%	1957
	11th to 20th	Day	34% 4 8% 18% 27% 9%	1862
	21st to end	Day	36% 4 8% 20% 23% 9%	1710
December	1st to 10th	Day	45% 5% 9% 18% 18% 4	1710
	11th to 20th	Day	33% 3 7% 22% 26% 9%	2150
	21st to end	Day	41% 5% 8% 22% 23% 3	3124
January	1st to 10th	Night	36% 4 7% 19% 26% 7%	4109
	11th to 20th	Night	39% 5% 8% 16% 24% 6%	4120
	21st to end	Night	43% 4 5% 15% 26% 7%	4532
February	1st to 10th	Night	41% 4 8% 18% 21% 7%	2470
	11th to 20th	Night	44% 4 6% 15% 23% 8%	2307
	21st to end	Night	39% 5% 8% 18% 20% 9%	1761
March	1st to 10th	Night	53% 6% 7% 13% 15% 6%	3418
	11th to 20th	Night	33% 6% 8% 12% 24% 17%	3480
	21st to end	Night	39% 6% 8% 20% 21% 7%	3817
April	1st to 10th	Night	33% 4 10% 21% 24% 9%	2041
	11th to 20th	Night	32% 5% 11% 22% 20% 10%	1875
	21st to end	Night	31% 7% 13% 24% 22% 4	1891
May	1st to 10th	Night	37% 9% 16% 23% 12% 3	2840
	11th to 20th	Night	42% 9% 12% 20% 16% 1	2813
	21st to end	Night	30% 10% 15% 27% 16% 2	3087
June	1st to 10th	Night	42% 10% 15% 22% 10% 2	1710
	11th to 20th	Night	40% 11% 16% 20% 12% 2	1710
	21st to end	Night	37% 14% 17% 18% 11% 3	1710
July	1st to 10th	Night	45% 11% 19% 16% 7% 1	2795
	11th to 20th	Night	46% 13% 24% 13% 4 1	2786
	21st to end	Night	54% 10% 15% 14% 6% 1	2988
August	1st to 10th	Night	55% 8% 18% 15% 3 1	2814
	11th to 20th	Night	44% 11% 20% 19% 6% 1	2839
	21st to end	Night	28% 7% 14% 29% 17% 4	3476
September	1st to 10th	Night	36% 9% 16% 20% 14% 6%	1957
	11th to 20th	Night	43% 8% 13% 15% 18% 3	2090
	21st to end	Night	46% 6% 12% 17% 14% 5%	2090
October	1st to 10th	Night	36% 5% 8% 20% 24% 7%	3768
	11th to 20th	Night	21% 3 5% 16% 28% 27%	3779
	21st to end	Night	26% 3 6% 20% 27% 18%	4120
November	1st to 10th	Night	34% 3 7% 17% 26% 13%	2341
	11th to 20th	Night	36% 3 7% 16% 26% 12%	2320
	21st to end	Night	35% 4 7% 21% 25% 9%	2470
December	1st to 10th	Night	44% 5% 9% 17% 19% 6%	2470
	11th to 20th	Night	37% 4 6% 19% 25% 9%	3044
	21st to end	Night	41% 4 7% 21% 23% 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	19% 20% 40% 17% 3	270
	11th to 20th	Day	18% 22% 32% 20% 7%	270
	21st to end	Day	22% 18% 40% 16% 4 1	297
February	1st to 10th	Day	19% 21% 30% 24% 6%	270
	11th to 20th	Day	34% 16% 32% 14% 3	270
	21st to end	Day	24% 20% 30% 20% 6%	348
March	1st to 10th	Day	20% 16% 28% 26% 9%	460
	11th to 20th	Day	18% 15% 40% 20% 6% 1	460
	21st to end	Day	20% 15% 33% 22% 8% 2	506
April	1st to 10th	Day	17% 17% 32% 20% 13% 1	460
	11th to 20th	Day	13% 16% 27% 22% 17% 5%	452
	21st to end	Day	15% 9% 29% 24% 18% 5%	460
May	1st to 10th	Day	10% 14% 30% 23% 17% 6%	463
	11th to 20th	Day	15% 5% 22% 25% 24% 9%	487
	21st to end	Day	14% 4 17% 24% 25% 16%	529
June	1st to 10th	Day	10% 3 19% 30% 26% 11%	490
	11th to 20th	Day	11% 4 14% 29% 26% 17%	490
	21st to end	Day	9% 2 13% 32% 29% 14%	490
July	1st to 10th	Day	8% 2 7% 24% 35% 24%	485
	11th to 20th	Day	11% 2 7% 25% 36% 19%	484
	21st to end	Day	8% 2 11% 29% 38% 12%	532
August	1st to 10th	Day	14% 4 10% 27% 26% 19%	486
	11th to 20th	Day	13% 2 8% 25% 33% 19%	479
	21st to end	Day	12% 1 9% 26% 30% 22%	539
September	1st to 10th	Day	9% 2 12% 28% 28% 20%	490
	11th to 20th	Day	17% 4 12% 24% 29% 13%	490
	21st to end	Day	21% 4 15% 28% 24% 8%	490
October	1st to 10th	Day	15% 5% 20% 26% 23% 11%	490
	11th to 20th	Day	10% 9% 24% 25% 24% 8%	490
	21st to end	Day	12% 6% 24% 29% 23% 6%	539
November	1st to 10th	Day	18% 6% 26% 29% 16% 5%	495
	11th to 20th	Day	19% 10% 31% 27% 10% 2	422
	21st to end	Day	13% 13% 35% 23% 13% 3	270
December	1st to 10th	Day	20% 13% 39% 20% 7%	270
	11th to 20th	Day	21% 13% 32% 21% 11% 1	270
	21st to end	Day	25% 12% 34% 18% 8% 3	297
January	1st to 10th	Night	21% 11% 32% 28% 7%	760
	11th to 20th	Night	16% 12% 32% 32% 7%	760
	21st to end	Night	19% 9% 35% 34% 3	836
February	1st to 10th	Night	19% 11% 32% 33% 5%	760
	11th to 20th	Night	22% 13% 38% 25% 2	743
	21st to end	Night	18% 13% 36% 28% 5%	628
March	1st to 10th	Night	19% 8% 33% 33% 6%	760
	11th to 20th	Night	17% 10% 36% 28% 8% 1	760
	21st to end	Night	17% 9% 36% 31% 7%	836
April	1st to 10th	Night	14% 14% 34% 29% 8% 1	760
	11th to 20th	Night	13% 12% 28% 33% 13% 1	751
	21st to end	Night	12% 6% 31% 39% 11%	751
May	1st to 10th	Night	11% 6% 28% 41% 14%	570
	11th to 20th	Night	14% 4 21% 39% 21% 1	561
	21st to end	Night	11% 3 11% 39% 33% 2	617
June	1st to 10th	Night	13% 3 16% 37% 27% 4	570
	11th to 20th	Night	11% 3 13% 34% 32% 6%	570
	21st to end	Night	8% 2 13% 40% 31% 6%	570
July	1st to 10th	Night	8% 2 10% 34% 40% 6%	555
	11th to 20th	Night	10% 1 6% 33% 43% 6%	552
	21st to end	Night	8% 4 6% 38% 39% 5%	624
August	1st to 10th	Night	15% 2 7% 28% 41% 7%	567
	11th to 20th	Night	14% 2 6% 34% 38% 6%	578
	21st to end	Night	13% 2 8% 31% 40% 6%	836
September	1st to 10th	Night	10% 3 9% 30% 41% 6%	760
	11th to 20th	Night	16% 4 10% 31% 33% 5%	760
	21st to end	Night	20% 4 12% 33% 28% 3	760
October	1st to 10th	Night	16% 3 18% 29% 28% 5%	760
	11th to 20th	Night	14% 6% 23% 32% 24% 2	760
	21st to end	Night	13% 7% 22% 33% 23% 3	836
November	1st to 10th	Night	16% 7% 23% 34% 17% 3	780
	11th to 20th	Night	16% 9% 27% 34% 13% 1	763
	21st to end	Night	15% 8% 27% 33% 16% 1	760
December	1st to 10th	Night	22% 8% 25% 37% 8% 1	760
	11th to 20th	Night	19% 8% 25% 36% 11%	760
	21st to end	Night	23% 10% 26% 31% 9% 1	836

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