South Lake Norman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Lake Norman clear sky chart from 2005-11-06 to 2025-07-21.

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 6% 4 4 4 4 6% 8% 44%	120456
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	118672
Transparency	Day	37% 6% 11% 21% 18% 6%	124144
	Night	38% 5% 10% 19% 21% 7%	123121
Seeing	Day	16% 7% 22% 24% 20% 11%	16200
	Night	16% 7% 23% 30% 20% 3	26277

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	15% 6% 1 5% 3 2 3 2 3 5% 56%	4056
	11th to 20th	Day	12% 6% 2 4 3 2 2 2 3 4 59%	4060
	21st to end	Day	18% 7% 2 6% 4 4 3 3 4 5% 45%	4466
February	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 6% 7% 43%	1800
	11th to 20th	Day	21% 6% 2 5% 3 3 3 3 4 5% 45%	1913
	21st to end	Day	18% 8% 3 6% 4 3 4 3 3 6% 41%	1697
March	1st to 10th	Day	21% 7% 2 6% 3 3 3 3 4 6% 42%	4935
	11th to 20th	Day	9% 5% 2 6% 3 3 3 3 4 7% 54%	4980
	21st to end	Day	17% 7% 2 6% 4 3 3 2 4 5% 47%	5465
April	1st to 10th	Day	11% 5% 2 4 3 4 4 3 6% 8% 50%	2200
	11th to 20th	Day	14% 4 2 5% 3 3 4 3 5% 7% 50%	2372
	21st to end	Day	13% 6% 2 4 4 3 4 4 5% 6% 48%	2560
May	1st to 10th	Day	10% 7% 2 6% 5% 5% 6% 5% 8% 10% 36%	5862
	11th to 20th	Day	19% 8% 3 7% 5% 4 5% 4 7% 9% 30%	5861
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 43%	6433
June	1st to 10th	Day	9% 6% 2 7% 4 5% 5% 5% 7% 11% 40%	2600
	11th to 20th	Day	8% 5% 2 5% 4 5% 6% 5% 7% 10% 43%	2600
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 11% 42%	2600
July	1st to 10th	Day	8% 6% 3 7% 5% 5% 6% 5% 9% 11% 37%	4250
	11th to 20th	Day	7% 6% 3 6% 6% 6% 6% 5% 8% 11% 36%	4250
	21st to end	Day	12% 9% 4 7% 6% 6% 6% 5% 9% 10% 26%	4466
August	1st to 10th	Day	18% 7% 2 7% 5% 5% 5% 5% 7% 10% 28%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 11% 37%	4044
	21st to end	Day	6% 4 1 4 4 4 4 4 7% 9% 53%	4252
September	1st to 10th	Day	9% 5% 2 5% 5% 5% 6% 5% 8% 9% 44%	2123
	11th to 20th	Day	13% 6% 2 7% 4 3 4 4 6% 9% 43%	2090
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 6% 39%	2090
October	1st to 10th	Day	14% 5% 2 4 3 3 3 2 4 6% 55%	1971
	11th to 20th	Day	13% 5% 2 4 3 2 3 3 3 5% 58%	1900
	21st to end	Day	14% 5% 1 4 3 2 2 3 3 4 57%	2090
November	1st to 10th	Day	14% 6% 2 4 3 3 3 3 4 5% 54%	1957
	11th to 20th	Day	14% 6% 1 4 2 3 3 3 5% 7% 53%	1840
	21st to end	Day	15% 5% 2 4 3 4 4 3 5% 6% 50%	1800
December	1st to 10th	Day	15% 5% 2 4 2 3 3 2 4 4 54%	2930
	11th to 20th	Day	18% 7% 3 7% 4 3 4 3 5% 6% 41%	3373
	21st to end	Day	21% 6% 2 4 3 3 3 3 5% 7% 44%	4466
January	1st to 10th	Night	14% 4 2 4 3 2 3 2 4 4 58%	5889
	11th to 20th	Night	12% 6% 2 4 3 3 3 3 4 4 56%	5900
	21st to end	Night	18% 7% 2 4 3 3 3 3 5% 6% 47%	6490
February	1st to 10th	Night	16% 6% 2 5% 3 4 3 3 5% 6% 46%	2600
	11th to 20th	Night	22% 6% 2 5% 4 4 3 2 4 6% 43%	2368
	21st to end	Night	15% 6% 2 5% 4 3 3 4 6% 6% 46%	1930
March	1st to 10th	Night	18% 6% 2 5% 4 3 4 3 4 5% 46%	4918
	11th to 20th	Night	10% 3 2 4 3 3 4 3 5% 8% 55%	4980
	21st to end	Night	16% 5% 2 5% 4 4 3 3 5% 6% 48%	5467
April	1st to 10th	Night	13% 6% 2 4 4 4 4 3 5% 7% 48%	2200
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 7% 51%	1975
	21st to end	Night	12% 6% 2 5% 5% 4 4 2 6% 7% 48%	1855
May	1st to 10th	Night	13% 7% 3 8% 5% 4 4 4 6% 8% 38%	4033
	11th to 20th	Night	20% 8% 3 7% 4 4 4 4 6% 8% 33%	4032
	21st to end	Night	15% 5% 2 6% 4 4 4 3 6% 9% 42%	4421
June	1st to 10th	Night	9% 6% 2 6% 5% 6% 6% 6% 8% 10% 36%	1800
	11th to 20th	Night	11% 6% 2 6% 5% 6% 5% 5% 8% 10% 36%	1800
	21st to end	Night	7% 5% 2 6% 6% 6% 6% 5% 8% 11% 38%	1800
July	1st to 10th	Night	9% 8% 3 9% 6% 5% 7% 5% 8% 10% 30%	2930
	11th to 20th	Night	9% 5% 2 6% 5% 5% 6% 5% 9% 13% 33%	2930
	21st to end	Night	14% 9% 4 9% 7% 6% 6% 5% 9% 10% 22%	3087
August	1st to 10th	Night	20% 8% 4 8% 5% 5% 6% 4 7% 9% 24%	2825
	11th to 20th	Night	10% 7% 3 8% 5% 6% 6% 6% 8% 9% 32%	2785
	21st to end	Night	5% 4 2 6% 4 5% 5% 4 7% 10% 49%	3370
September	1st to 10th	Night	9% 6% 2 6% 4 5% 5% 4 6% 8% 44%	2052
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 4 6% 6% 38%	2090
	21st to end	Night	18% 6% 2 6% 5% 4 5% 3 6% 6% 39%	2090
October	1st to 10th	Night	15% 5% 2 5% 3 3 3 3 5% 6% 50%	2209
	11th to 20th	Night	14% 6% 1 3 3 3 3 3 4 5% 54%	2280
	21st to end	Night	12% 5% 1 5% 3 3 3 2 4 3 58%	2508
November	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 4 5% 52%	2341
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 4 5% 52%	2555
	21st to end	Night	14% 4 2 4 2 4 4 3 5% 7% 51%	2600
December	1st to 10th	Night	16% 6% 2 5% 3 2 3 2 4 5% 52%	4250
	11th to 20th	Night	20% 8% 3 6% 3 3 3 3 4 5% 42%	4822
	21st to end	Night	20% 4 2 4 3 3 3 3 5% 6% 47%	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	34% 2 5% 20% 32% 7%	4057
	11th to 20th	Day	31% 3 4 16% 37% 9%	4060
	21st to end	Day	42% 3 5% 20% 23% 8%	4466
February	1st to 10th	Day	39% 5% 10% 22% 19% 5%	1800
	11th to 20th	Day	42% 4 8% 20% 21% 6%	1923
	21st to end	Day	45% 4 6% 16% 21% 7%	1697
March	1st to 10th	Day	45% 3 6% 15% 19% 12%	4935
	11th to 20th	Day	31% 4 7% 16% 25% 18%	4980
	21st to end	Day	41% 4 6% 23% 20% 6%	5465
April	1st to 10th	Day	31% 4 12% 22% 25% 6%	2200
	11th to 20th	Day	35% 4 10% 20% 22% 8%	2372
	21st to end	Day	35% 6% 11% 25% 18% 4	2560
May	1st to 10th	Day	40% 8% 18% 21% 11% 1	5897
	11th to 20th	Day	49% 8% 13% 19% 10% 1	5865
	21st to end	Day	37% 7% 13% 21% 18% 4	6447
June	1st to 10th	Day	37% 8% 16% 25% 13% 1	2600
	11th to 20th	Day	34% 9% 19% 21% 15% 1	2600
	21st to end	Day	33% 10% 18% 22% 14% 2	2600
July	1st to 10th	Day	36% 12% 19% 20% 11% 2	4185
	11th to 20th	Day	38% 11% 26% 19% 5%	4181
	21st to end	Day	49% 11% 15% 18% 6% 1	4324
August	1st to 10th	Day	48% 10% 18% 20% 5%	4091
	11th to 20th	Day	37% 10% 20% 21% 10% 2	4083
	21st to end	Day	26% 8% 15% 35% 14% 2	4252
September	1st to 10th	Day	33% 10% 14% 21% 19% 4	2123
	11th to 20th	Day	37% 8% 13% 18% 20% 3	2090
	21st to end	Day	45% 6% 9% 19% 17% 4	2090
October	1st to 10th	Day	29% 5% 6% 21% 29% 11%	3270
	11th to 20th	Day	20% 3 5% 19% 27% 25%	3140
	21st to end	Day	26% 3 5% 26% 23% 16%	3428
November	1st to 10th	Day	34% 4 6% 20% 28% 8%	1957
	11th to 20th	Day	32% 3 8% 24% 27% 7%	1840
	21st to end	Day	35% 4 8% 22% 24% 6%	1800
December	1st to 10th	Day	35% 3 6% 20% 28% 8%	2930
	11th to 20th	Day	44% 5% 9% 16% 21% 6%	3370
	21st to end	Day	40% 3 9% 28% 17% 2	4466
January	1st to 10th	Night	31% 2 6% 17% 35% 9%	5889
	11th to 20th	Night	33% 3 5% 15% 36% 8%	5900
	21st to end	Night	40% 2 5% 19% 25% 9%	6490
February	1st to 10th	Night	39% 4 10% 21% 21% 5%	2600
	11th to 20th	Night	44% 4 7% 16% 22% 7%	2369
	21st to end	Night	38% 4 10% 18% 23% 7%	1930
March	1st to 10th	Night	41% 3 7% 12% 27% 9%	4918
	11th to 20th	Night	29% 4 7% 15% 27% 18%	4980
	21st to end	Night	38% 4 6% 24% 20% 7%	5467
April	1st to 10th	Night	36% 4 10% 21% 24% 6%	2200
	11th to 20th	Night	33% 5% 9% 22% 23% 9%	1975
	21st to end	Night	37% 5% 12% 21% 21% 4	1855
May	1st to 10th	Night	43% 6% 15% 21% 13% 1	4060
	11th to 20th	Night	48% 8% 13% 19% 11% 1	4033
	21st to end	Night	37% 7% 14% 25% 15% 2	4429
June	1st to 10th	Night	39% 10% 16% 21% 12% 2	1800
	11th to 20th	Night	40% 10% 17% 21% 11% 2	1800
	21st to end	Night	36% 11% 17% 19% 13% 4	1800
July	1st to 10th	Night	46% 10% 18% 15% 10% 2	2885
	11th to 20th	Night	37% 13% 26% 19% 4 1	2876
	21st to end	Night	53% 13% 14% 15% 5%	2988
August	1st to 10th	Night	54% 9% 18% 14% 4	2814
	11th to 20th	Night	43% 10% 22% 16% 9% 1	2812
	21st to end	Night	29% 8% 13% 29% 19% 2	3370
September	1st to 10th	Night	36% 9% 14% 19% 17% 5%	2052
	11th to 20th	Night	44% 8% 10% 16% 20% 2	2090
	21st to end	Night	45% 6% 12% 16% 16% 4	2090
October	1st to 10th	Night	36% 4 10% 18% 25% 7%	3690
	11th to 20th	Night	23% 2 6% 21% 27% 21%	3779
	21st to end	Night	28% 3 5% 21% 27% 16%	4120
November	1st to 10th	Night	35% 4 7% 20% 24% 11%	2341
	11th to 20th	Night	35% 4 6% 19% 25% 11%	2555
	21st to end	Night	33% 4 7% 22% 27% 7%	2600
December	1st to 10th	Night	36% 3 6% 20% 27% 7%	4250
	11th to 20th	Night	46% 4 8% 15% 18% 8%	4824
	21st to end	Night	39% 3 12% 22% 22% 2	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	21% 17% 35% 23% 5%	300
	11th to 20th	Day	24% 21% 28% 22% 5% 1	300
	21st to end	Day	22% 15% 40% 18% 5%	330
February	1st to 10th	Day	21% 17% 35% 20% 6% 1	300
	11th to 20th	Day	35% 11% 39% 11% 3	300
	21st to end	Day	24% 13% 37% 21% 5%	296
March	1st to 10th	Day	22% 11% 33% 24% 8% 1	500
	11th to 20th	Day	20% 13% 39% 22% 6%	500
	21st to end	Day	20% 16% 34% 22% 7% 1	550
April	1st to 10th	Day	18% 15% 32% 23% 10% 3	500
	11th to 20th	Day	15% 11% 31% 23% 16% 4	492
	21st to end	Day	16% 8% 27% 26% 18% 5%	500
May	1st to 10th	Day	10% 9% 32% 27% 17% 5%	503
	11th to 20th	Day	19% 6% 17% 25% 22% 12%	527
	21st to end	Day	17% 5% 13% 22% 27% 17%	573
June	1st to 10th	Day	12% 3 14% 28% 29% 13%	530
	11th to 20th	Day	10% 2 17% 27% 22% 22%	530
	21st to end	Day	9% 2 10% 27% 35% 17%	530
July	1st to 10th	Day	11% 2 8% 20% 33% 26%	525
	11th to 20th	Day	6% 2 6% 26% 33% 27%	524
	21st to end	Day	8% 2 8% 27% 35% 21%	532
August	1st to 10th	Day	14% 2 10% 23% 31% 19%	486
	11th to 20th	Day	11% 3 8% 24% 32% 22%	479
	21st to end	Day	12% 2 6% 24% 29% 27%	539
September	1st to 10th	Day	13% 2 9% 22% 33% 22%	490
	11th to 20th	Day	17% 3 12% 19% 28% 20%	490
	21st to end	Day	24% 3 17% 24% 25% 8%	490
October	1st to 10th	Day	16% 4 19% 23% 26% 12%	490
	11th to 20th	Day	12% 5% 23% 29% 22% 8%	490
	21st to end	Day	17% 7% 19% 29% 21% 7%	539
November	1st to 10th	Day	21% 7% 24% 27% 17% 4	495
	11th to 20th	Day	16% 9% 34% 27% 12% 2	340
	21st to end	Day	13% 8% 31% 29% 15% 3	300
December	1st to 10th	Day	25% 11% 33% 24% 6% 1	300
	11th to 20th	Day	21% 11% 30% 24% 12% 2	300
	21st to end	Day	25% 11% 31% 22% 11% 1	330
January	1st to 10th	Night	21% 13% 34% 26% 6%	800
	11th to 20th	Night	21% 11% 35% 29% 5%	800
	21st to end	Night	18% 11% 38% 30% 3	880
February	1st to 10th	Night	18% 11% 36% 32% 3	800
	11th to 20th	Night	24% 13% 38% 22% 2	783
	21st to end	Night	18% 13% 38% 27% 4	660
March	1st to 10th	Night	17% 11% 34% 33% 5%	800
	11th to 20th	Night	18% 12% 35% 27% 8% 1	800
	21st to end	Night	21% 9% 35% 28% 6%	880
April	1st to 10th	Night	16% 12% 33% 29% 10%	800
	11th to 20th	Night	14% 12% 29% 30% 15% 1	791
	21st to end	Night	13% 7% 28% 35% 16%	655
May	1st to 10th	Night	12% 8% 27% 34% 18% 1	600
	11th to 20th	Night	17% 4 21% 32% 23% 2	591
	21st to end	Night	17% 2 11% 31% 35% 4	650
June	1st to 10th	Night	11% 3 13% 38% 30% 5%	600
	11th to 20th	Night	11% 3 14% 28% 35% 10%	600
	21st to end	Night	9% 1 10% 33% 41% 6%	600
July	1st to 10th	Night	10% 2 7% 28% 43% 9%	585
	11th to 20th	Night	9% 2 5% 29% 46% 10%	582
	21st to end	Night	8% 1 8% 32% 43% 8%	624
August	1st to 10th	Night	14% 2 7% 27% 42% 8%	567
	11th to 20th	Night	14% 2 6% 28% 42% 8%	564
	21st to end	Night	11% 2 7% 25% 46% 9%	769
September	1st to 10th	Night	12% 3 6% 29% 40% 9%	760
	11th to 20th	Night	17% 4 12% 23% 38% 7%	760
	21st to end	Night	20% 3 16% 30% 27% 4	760
October	1st to 10th	Night	16% 4 16% 30% 28% 6%	760
	11th to 20th	Night	16% 5% 21% 33% 22% 3	760
	21st to end	Night	14% 6% 22% 34% 22% 2	836
November	1st to 10th	Night	17% 5% 24% 34% 18% 3	780
	11th to 20th	Night	16% 7% 31% 33% 13% 1	800
	21st to end	Night	16% 7% 30% 34% 14% 1	800
December	1st to 10th	Night	23% 9% 27% 33% 8%	800
	11th to 20th	Night	20% 6% 29% 35% 9% 1	800
	21st to end	Night	25% 9% 25% 32% 9%	880

Page generated at 2025-07-18 01:10:05. Version ac07

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