Rock Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rock Hill clear sky chart from 2005-11-06 to 2024-05-14.

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	14% 6% 2 5% 4 4 4 4 5% 7% 44%	83996
	Night	15% 6% 2 5% 4 4 4 4 5% 7% 44%	85533
Transparency	Day	38% 6% 11% 20% 19% 5%	83719
	Night	39% 6% 10% 19% 20% 6%	85329
Seeing	Day	17% 9% 24% 24% 18% 7%	14592
	Night	16% 9% 23% 30% 19% 3	24757

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	17% 5% 2 5% 3 3 3 2 4 6% 51%	2836
	11th to 20th	Day	14% 7% 2 5% 3 3 3 2 4 5% 52%	2840
	21st to end	Day	22% 8% 2 5% 3 3 3 3 4 4 42%	3124
February	1st to 10th	Day	15% 7% 2 6% 4 3 4 4 6% 7% 42%	1710
	11th to 20th	Day	21% 6% 2 5% 3 4 3 3 4 4 46%	1833
	21st to end	Day	19% 8% 2 7% 3 4 4 3 4 5% 40%	1617
March	1st to 10th	Day	24% 7% 3 5% 3 3 3 3 4 5% 39%	3435
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 5% 5% 53%	3480
	21st to end	Day	21% 6% 3 6% 3 3 4 3 4 5% 43%	3815
April	1st to 10th	Day	11% 4 2 5% 3 3 4 5% 6% 8% 50%	2090
	11th to 20th	Day	13% 5% 1 6% 4 5% 5% 3 5% 7% 47%	2241
	21st to end	Day	12% 4 2 5% 4 4 4 3 4 7% 50%	2420
May	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 4 6% 9% 44%	2470
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 5% 6% 7% 42%	2340
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	2531
June	1st to 10th	Day	10% 5% 2 6% 6% 5% 6% 5% 7% 11% 38%	2340
	11th to 20th	Day	8% 5% 2 5% 5% 6% 5% 4 8% 10% 41%	2340
	21st to end	Day	6% 4 2 6% 6% 7% 6% 5% 8% 10% 40%	2340
July	1st to 10th	Day	7% 6% 3 8% 7% 6% 6% 6% 8% 10% 34%	2340
	11th to 20th	Day	8% 5% 2 7% 7% 6% 6% 5% 9% 11% 33%	2340
	21st to end	Day	7% 6% 3 6% 5% 6% 6% 6% 9% 12% 34%	2547
August	1st to 10th	Day	11% 6% 2 6% 6% 6% 7% 6% 8% 9% 32%	2327
	11th to 20th	Day	13% 7% 2 7% 6% 7% 6% 6% 7% 10% 30%	2303
	21st to end	Day	10% 6% 3 7% 6% 6% 5% 5% 7% 10% 36%	2412
September	1st to 10th	Day	8% 5% 2 5% 5% 6% 5% 5% 7% 9% 43%	1994
	11th to 20th	Day	12% 7% 2 7% 4 3 5% 4 6% 8% 41%	1980
	21st to end	Day	17% 6% 2 7% 4 4 4 3 5% 6% 41%	1980
October	1st to 10th	Day	15% 4 2 4 3 3 3 3 4 5% 53%	1873
	11th to 20th	Day	14% 5% 2 4 3 3 3 2 4 5% 56%	1800
	21st to end	Day	13% 4 2 5% 3 3 3 2 4 5% 56%	1980
November	1st to 10th	Day	14% 5% 2 4 3 3 3 2 4 5% 56%	1857
	11th to 20th	Day	14% 5% 2 3 3 3 4 3 4 7% 53%	1764
	21st to end	Day	16% 5% 1 5% 4 3 4 3 4 6% 50%	1710
December	1st to 10th	Day	19% 8% 3 5% 4 4 4 3 5% 7% 39%	1710
	11th to 20th	Day	17% 5% 2 4 3 2 3 2 5% 6% 51%	2153
	21st to end	Day	19% 7% 2 5% 3 3 4 3 4 6% 43%	3124
January	1st to 10th	Night	18% 6% 2 6% 3 3 3 2 4 5% 49%	4109
	11th to 20th	Night	12% 7% 2 5% 4 4 4 4 5% 6% 48%	4120
	21st to end	Night	23% 8% 2 4 3 3 3 2 3 4 45%	4532
February	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 5% 5% 46%	2470
	11th to 20th	Night	21% 6% 2 5% 4 3 3 3 4 4 43%	2228
	21st to end	Night	17% 6% 2 5% 5% 3 4 4 5% 6% 44%	1835
March	1st to 10th	Night	24% 9% 3 6% 4 3 3 3 4 6% 35%	3418
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 7% 51%	3480
	21st to end	Night	19% 5% 2 5% 4 3 4 4 5% 5% 44%	3817
April	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 49%	2090
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 5% 7% 51%	1886
	21st to end	Night	11% 5% 1 6% 3 4 4 3 5% 7% 51%	1775
May	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 5% 8% 48%	1710
	11th to 20th	Night	11% 6% 3 7% 5% 6% 5% 4 7% 8% 37%	1625
	21st to end	Night	11% 6% 3 6% 4 5% 5% 4 6% 10% 40%	1744
June	1st to 10th	Night	10% 6% 3 7% 5% 6% 7% 5% 8% 10% 34%	1620
	11th to 20th	Night	11% 5% 2 6% 5% 6% 6% 5% 7% 11% 36%	1620
	21st to end	Night	7% 7% 2 7% 6% 5% 6% 6% 8% 12% 35%	1620
July	1st to 10th	Night	8% 8% 2 7% 6% 6% 7% 6% 8% 12% 30%	1620
	11th to 20th	Night	8% 6% 2 7% 4 5% 7% 5% 9% 12% 35%	1620
	21st to end	Night	7% 6% 2 7% 8% 6% 6% 6% 9% 11% 33%	1771
August	1st to 10th	Night	11% 6% 3 7% 6% 5% 5% 5% 9% 12% 32%	1611
	11th to 20th	Night	10% 8% 3 7% 5% 6% 5% 5% 7% 9% 34%	1598
	21st to end	Night	10% 6% 3 7% 6% 6% 6% 7% 7% 12% 31%	1923
September	1st to 10th	Night	9% 4 2 6% 5% 4 5% 5% 7% 10% 43%	1962
	11th to 20th	Night	13% 6% 2 7% 5% 4 5% 4 5% 8% 41%	1980
	21st to end	Night	17% 7% 2 6% 5% 4 4 4 5% 7% 39%	1980
October	1st to 10th	Night	15% 5% 2 4 3 4 3 3 4 5% 53%	2085
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 53%	2160
	21st to end	Night	13% 5% 1 5% 3 3 3 2 3 5% 56%	2376
November	1st to 10th	Night	14% 5% 2 5% 3 2 2 3 3 5% 55%	2221
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 3 5% 52%	2413
	21st to end	Night	14% 5% 2 4 3 4 4 4 5% 7% 49%	2470
December	1st to 10th	Night	19% 7% 2 6% 4 3 4 3 4 5% 42%	2470
	11th to 20th	Night	17% 6% 2 5% 3 2 3 2 3 5% 52%	3042
	21st to end	Night	20% 5% 2 5% 3 4 4 3 5% 6% 43%	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% 4 6% 25% 23% 7%	2837
	11th to 20th	Day	36% 3 7% 16% 31% 6%	2840
	21st to end	Day	45% 4 4 17% 25% 5%	3124
February	1st to 10th	Day	41% 4 10% 20% 19% 5%	1710
	11th to 20th	Day	42% 4 7% 18% 23% 6%	1843
	21st to end	Day	46% 4 7% 17% 19% 7%	1617
March	1st to 10th	Day	46% 5% 8% 16% 16% 9%	3435
	11th to 20th	Day	32% 5% 9% 15% 28% 12%	3480
	21st to end	Day	44% 4 7% 20% 23% 3	3815
April	1st to 10th	Day	31% 4 11% 22% 26% 6%	2090
	11th to 20th	Day	37% 4 9% 18% 22% 9%	2241
	21st to end	Day	33% 6% 11% 23% 22% 4	2420
May	1st to 10th	Day	35% 8% 14% 22% 19% 3	2470
	11th to 20th	Day	40% 6% 16% 20% 16% 2	2344
	21st to end	Day	40% 7% 14% 23% 14% 2	2531
June	1st to 10th	Day	38% 8% 14% 26% 12% 2	2340
	11th to 20th	Day	35% 9% 18% 22% 14% 2	2340
	21st to end	Day	35% 11% 17% 21% 15% 2	2340
July	1st to 10th	Day	40% 10% 20% 17% 10% 3	2275
	11th to 20th	Day	39% 11% 21% 19% 8% 1	2271
	21st to end	Day	37% 11% 20% 22% 9% 1	2405
August	1st to 10th	Day	43% 10% 18% 20% 8% 1	2314
	11th to 20th	Day	46% 11% 16% 17% 10% 1	2303
	21st to end	Day	41% 9% 18% 19% 9% 3	2412
September	1st to 10th	Day	35% 8% 15% 20% 18% 4	1994
	11th to 20th	Day	39% 8% 11% 17% 21% 4	1980
	21st to end	Day	44% 6% 7% 21% 17% 5%	1980
October	1st to 10th	Day	33% 5% 8% 21% 28% 5%	1873
	11th to 20th	Day	31% 3 9% 24% 24% 8%	1800
	21st to end	Day	31% 3 6% 22% 28% 9%	1980
November	1st to 10th	Day	32% 3 8% 18% 30% 9%	1857
	11th to 20th	Day	32% 3 8% 21% 28% 8%	1764
	21st to end	Day	36% 5% 8% 20% 23% 8%	1710
December	1st to 10th	Day	45% 4 8% 21% 18% 4	1710
	11th to 20th	Day	36% 2 7% 21% 26% 9%	2150
	21st to end	Day	41% 6% 8% 21% 21% 3	3124
January	1st to 10th	Night	37% 4 7% 19% 26% 7%	4109
	11th to 20th	Night	36% 5% 8% 16% 28% 7%	4120
	21st to end	Night	45% 3 4 17% 26% 6%	4532
February	1st to 10th	Night	40% 4 8% 20% 22% 6%	2470
	11th to 20th	Night	45% 2 6% 16% 23% 7%	2229
	21st to end	Night	41% 3 11% 17% 21% 7%	1835
March	1st to 10th	Night	50% 6% 9% 13% 15% 7%	3418
	11th to 20th	Night	31% 5% 7% 16% 26% 15%	3480
	21st to end	Night	43% 4 8% 18% 20% 7%	3817
April	1st to 10th	Night	35% 4 10% 19% 25% 7%	2090
	11th to 20th	Night	32% 4 9% 22% 23% 9%	1886
	21st to end	Night	33% 5% 11% 26% 21% 4	1775
May	1st to 10th	Night	33% 7% 16% 22% 18% 4	1710
	11th to 20th	Night	43% 9% 12% 19% 16% 1	1626
	21st to end	Night	38% 9% 13% 24% 14% 2	1745
June	1st to 10th	Night	41% 10% 15% 20% 12% 2	1620
	11th to 20th	Night	40% 10% 16% 21% 11% 2	1620
	21st to end	Night	38% 12% 17% 18% 11% 3	1620
July	1st to 10th	Night	42% 11% 21% 15% 8% 3	1575
	11th to 20th	Night	36% 11% 25% 18% 7% 2	1566
	21st to end	Night	39% 13% 20% 19% 9% 1	1672
August	1st to 10th	Night	41% 11% 22% 19% 7% 1	1600
	11th to 20th	Night	43% 11% 20% 15% 11% 1	1598
	21st to end	Night	42% 10% 17% 20% 8% 2	1923
September	1st to 10th	Night	34% 10% 15% 20% 16% 5%	1962
	11th to 20th	Night	40% 8% 14% 16% 20% 2	1980
	21st to end	Night	43% 7% 10% 18% 17% 5%	1980
October	1st to 10th	Night	33% 5% 10% 20% 27% 5%	2085
	11th to 20th	Night	33% 4 8% 23% 22% 10%	2160
	21st to end	Night	31% 3 6% 21% 27% 12%	2376
November	1st to 10th	Night	33% 3 7% 18% 27% 12%	2221
	11th to 20th	Night	35% 4 6% 17% 25% 12%	2413
	21st to end	Night	35% 4 6% 21% 26% 7%	2470
December	1st to 10th	Night	45% 4 8% 17% 20% 6%	2470
	11th to 20th	Night	37% 3 7% 18% 25% 10%	3044
	21st to end	Night	41% 4 9% 21% 23% 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	21% 20% 39% 17% 2	270
	11th to 20th	Day	27% 20% 31% 17% 4	270
	21st to end	Day	22% 22% 40% 11% 4	297
February	1st to 10th	Day	23% 21% 37% 13% 6%	270
	11th to 20th	Day	35% 19% 35% 9% 1	270
	21st to end	Day	28% 21% 33% 15% 3	272
March	1st to 10th	Day	23% 16% 32% 20% 7% 1	460
	11th to 20th	Day	22% 15% 40% 17% 5% 1	460
	21st to end	Day	24% 17% 35% 18% 6% 1	506
April	1st to 10th	Day	19% 18% 34% 18% 9% 1	460
	11th to 20th	Day	17% 16% 32% 21% 12% 3	452
	21st to end	Day	18% 8% 30% 26% 14% 4	460
May	1st to 10th	Day	11% 14% 34% 22% 14% 4	463
	11th to 20th	Day	17% 4 22% 26% 22% 8%	459
	21st to end	Day	15% 4 18% 25% 27% 12%	485
June	1st to 10th	Day	11% 3 16% 32% 27% 10%	450
	11th to 20th	Day	10% 4 19% 25% 28% 13%	450
	21st to end	Day	9% 2 16% 35% 28% 10%	450
July	1st to 10th	Day	9% 2 9% 30% 29% 21%	445
	11th to 20th	Day	9% 3 8% 30% 33% 17%	444
	21st to end	Day	6% 2 11% 31% 37% 13%	488
August	1st to 10th	Day	14% 2 13% 30% 22% 18%	446
	11th to 20th	Day	15% 3 10% 25% 27% 19%	439
	21st to end	Day	13% 3 11% 29% 26% 18%	495
September	1st to 10th	Day	10% 3 11% 30% 32% 15%	450
	11th to 20th	Day	16% 4 14% 25% 28% 14%	450
	21st to end	Day	19% 7% 15% 27% 26% 6%	450
October	1st to 10th	Day	17% 4 23% 24% 23% 9%	450
	11th to 20th	Day	12% 10% 24% 26% 24% 5%	450
	21st to end	Day	17% 9% 24% 27% 19% 4	495
November	1st to 10th	Day	20% 7% 25% 27% 16% 4	455
	11th to 20th	Day	18% 13% 35% 25% 7% 2	324
	21st to end	Day	16% 10% 36% 24% 11% 2	270
December	1st to 10th	Day	29% 12% 39% 15% 6%	270
	11th to 20th	Day	22% 12% 33% 22% 9% 1	270
	21st to end	Day	27% 14% 36% 14% 6% 3	297
January	1st to 10th	Night	21% 18% 28% 26% 6%	760
	11th to 20th	Night	20% 15% 30% 30% 5%	760
	21st to end	Night	20% 14% 35% 27% 4	836
February	1st to 10th	Night	19% 12% 36% 30% 4	760
	11th to 20th	Night	27% 14% 37% 21% 1	743
	21st to end	Night	21% 18% 35% 22% 4	628
March	1st to 10th	Night	19% 12% 33% 30% 6%	760
	11th to 20th	Night	19% 15% 32% 25% 8% 1	760
	21st to end	Night	20% 14% 33% 27% 7%	836
April	1st to 10th	Night	17% 16% 32% 25% 9%	760
	11th to 20th	Night	14% 13% 27% 30% 14% 1	751
	21st to end	Night	14% 8% 29% 35% 15%	635
May	1st to 10th	Night	11% 9% 29% 35% 15%	570
	11th to 20th	Night	13% 6% 23% 36% 21% 1	542
	21st to end	Night	14% 3 12% 37% 32% 2	584
June	1st to 10th	Night	11% 4 16% 39% 26% 5%	540
	11th to 20th	Night	14% 2 15% 29% 31% 9%	540
	21st to end	Night	10% 3 11% 38% 33% 6%	540
July	1st to 10th	Night	11% 2 10% 32% 36% 9%	525
	11th to 20th	Night	10% 2 6% 32% 41% 8%	522
	21st to end	Night	7% 3 10% 31% 42% 7%	591
August	1st to 10th	Night	14% 1 7% 31% 36% 10%	537
	11th to 20th	Night	13% 3 8% 29% 40% 7%	534
	21st to end	Night	12% 2 9% 27% 43% 7%	735
September	1st to 10th	Night	10% 3 9% 32% 41% 6%	720
	11th to 20th	Night	14% 3 12% 27% 38% 6%	720
	21st to end	Night	19% 5% 15% 31% 27% 3	720
October	1st to 10th	Night	16% 5% 17% 30% 26% 6%	720
	11th to 20th	Night	17% 6% 22% 31% 22% 3	720
	21st to end	Night	15% 9% 22% 31% 20% 3	792
November	1st to 10th	Night	16% 7% 24% 31% 19% 3	740
	11th to 20th	Night	15% 11% 29% 33% 11% 1	760
	21st to end	Night	15% 10% 26% 34% 14% 1	760
December	1st to 10th	Night	22% 11% 27% 33% 7% 1	760
	11th to 20th	Night	20% 10% 25% 33% 12% 1	760
	21st to end	Night	25% 13% 22% 31% 9%	836

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