Charlotte
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charlotte clear sky chart from 2005-11-06 to 2024-12-06.

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 4 4 6% 8% 43%	101480
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	98193
Transparency	Day	38% 6% 12% 21% 19% 5%	105170
	Night	39% 5% 10% 19% 20% 7%	102642
Seeing	Day	16% 6% 22% 24% 21% 11%	15405
	Night	16% 6% 22% 32% 21% 3	25492

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 5% 51%	2836
	11th to 20th	Day	14% 7% 2 5% 3 3 3 3 4 4 52%	2840
	21st to end	Day	23% 7% 2 5% 3 3 4 3 4 4 42%	3124
February	1st to 10th	Day	15% 7% 3 5% 3 4 4 4 6% 7% 42%	1710
	11th to 20th	Day	20% 7% 2 4 3 3 4 3 4 5% 45%	1811
	21st to end	Day	19% 8% 2 6% 4 4 4 3 4 6% 40%	1625
March	1st to 10th	Day	22% 9% 3 6% 3 3 3 2 4 6% 38%	3435
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 53%	3480
	21st to end	Day	20% 7% 2 5% 4 3 3 3 4 6% 43%	3815
April	1st to 10th	Day	11% 4 1 4 3 3 4 4 6% 7% 51%	2092
	11th to 20th	Day	13% 6% 2 4 3 4 4 3 5% 6% 48%	2254
	21st to end	Day	12% 5% 2 5% 4 3 4 4 5% 6% 50%	2413
May	1st to 10th	Day	10% 7% 2 8% 5% 5% 6% 5% 7% 10% 36%	4082
	11th to 20th	Day	16% 7% 3 7% 4 4 4 4 6% 9% 36%	4081
	21st to end	Day	7% 5% 1 5% 4 5% 5% 4 6% 9% 49%	4476
June	1st to 10th	Day	9% 5% 2 7% 4 4 6% 6% 8% 11% 39%	2470
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 8% 11% 44%	2470
	21st to end	Day	6% 4 2 7% 5% 5% 6% 5% 8% 11% 41%	2470
July	1st to 10th	Day	8% 6% 2 6% 6% 5% 5% 6% 8% 11% 37%	4120
	11th to 20th	Day	8% 6% 2 6% 5% 6% 6% 5% 8% 12% 37%	4120
	21st to end	Day	12% 7% 3 8% 6% 6% 6% 6% 9% 11% 27%	4466
August	1st to 10th	Day	20% 7% 3 7% 4 5% 6% 4 8% 11% 26%	4104
	11th to 20th	Day	9% 6% 2 6% 4 5% 6% 5% 8% 11% 37%	4044
	21st to end	Day	6% 3 1 5% 4 3 4 4 7% 10% 51%	4226
September	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 7% 10% 46%	2130
	11th to 20th	Day	13% 6% 2 5% 5% 4 4 4 6% 8% 43%	2090
	21st to end	Day	17% 6% 3 5% 4 5% 5% 3 5% 5% 41%	2090
October	1st to 10th	Day	13% 6% 2 4 2 3 3 3 4 5% 56%	1967
	11th to 20th	Day	13% 5% 1 4 3 2 2 3 3 4 59%	1900
	21st to end	Day	13% 5% 1 5% 2 2 3 2 4 5% 58%	2090
November	1st to 10th	Day	13% 6% 2 5% 3 2 3 2 4 5% 54%	1957
	11th to 20th	Day	13% 6% 1 3 4 3 3 3 4 6% 54%	1860
	21st to end	Day	15% 5% 2 4 4 4 3 3 4 5% 50%	1800
December	1st to 10th	Day	18% 8% 2 6% 3 3 4 4 5% 8% 40%	1755
	11th to 20th	Day	16% 6% 2 4 3 2 2 3 5% 6% 52%	2153
	21st to end	Day	17% 7% 2 5% 3 4 4 4 6% 6% 42%	3124
January	1st to 10th	Night	16% 6% 2 6% 3 4 3 3 3 5% 49%	4109
	11th to 20th	Night	11% 7% 2 6% 4 4 4 4 4 5% 49%	4120
	21st to end	Night	22% 8% 2 5% 3 3 3 2 3 5% 44%	4532
February	1st to 10th	Night	16% 6% 2 6% 4 3 4 3 5% 6% 46%	2470
	11th to 20th	Night	21% 7% 2 5% 4 3 3 2 5% 5% 43%	2252
	21st to end	Night	17% 6% 2 4 4 3 4 4 4 8% 44%	1827
March	1st to 10th	Night	22% 8% 3 7% 4 4 4 3 4 5% 37%	3418
	11th to 20th	Night	12% 5% 2 4 3 3 3 4 6% 7% 52%	3480
	21st to end	Night	20% 5% 2 5% 4 4 4 3 5% 6% 44%	3817
April	1st to 10th	Night	12% 6% 2 5% 4 4 5% 3 5% 8% 48%	2086
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 6% 51%	1875
	21st to end	Night	12% 4 2 5% 5% 4 5% 4 5% 6% 49%	1781
May	1st to 10th	Night	13% 7% 2 7% 4 4 4 3 5% 9% 41%	2813
	11th to 20th	Night	16% 8% 3 7% 4 5% 4 4 4 7% 38%	2812
	21st to end	Night	8% 5% 2 5% 4 5% 5% 5% 8% 11% 43%	3079
June	1st to 10th	Night	10% 6% 2 7% 7% 5% 6% 4 7% 10% 35%	1710
	11th to 20th	Night	11% 5% 3 5% 5% 5% 6% 5% 8% 11% 36%	1710
	21st to end	Night	6% 5% 2 7% 6% 6% 7% 5% 8% 10% 37%	1710
July	1st to 10th	Night	9% 7% 3 9% 7% 7% 7% 5% 8% 9% 30%	2840
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 6% 10% 13% 33%	2840
	21st to end	Night	15% 9% 4 8% 6% 6% 7% 5% 8% 9% 23%	3087
August	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 5% 7% 9% 23%	2825
	11th to 20th	Night	9% 7% 3 8% 6% 6% 5% 5% 7% 10% 34%	2785
	21st to end	Night	5% 4 2 6% 4 5% 5% 4 7% 9% 50%	3396
September	1st to 10th	Night	8% 6% 2 6% 5% 4 5% 4 7% 10% 43%	2045
	11th to 20th	Night	15% 6% 2 7% 4 4 5% 4 6% 8% 38%	2090
	21st to end	Night	18% 6% 3 6% 5% 4 4 3 6% 6% 39%	2090
October	1st to 10th	Night	13% 6% 2 5% 3 4 3 3 4 6% 51%	2213
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 5% 55%	2280
	21st to end	Night	11% 6% 2 4 3 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 5% 52%	2341
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 52%	2536
	21st to end	Night	13% 4 2 4 4 3 4 4 5% 6% 51%	2600
December	1st to 10th	Night	19% 8% 2 6% 3 4 4 3 5% 5% 42%	2542
	11th to 20th	Night	17% 6% 2 4 3 2 3 3 3 5% 51%	3042
	21st to end	Night	19% 5% 2 5% 3 4 4 4 5% 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	37% 3 5% 26% 23% 6%	2837
	11th to 20th	Day	36% 3 6% 17% 31% 6%	2840
	21st to end	Day	45% 4 4 17% 25% 5%	3124
February	1st to 10th	Day	42% 3 10% 21% 19% 5%	1710
	11th to 20th	Day	42% 4 7% 20% 22% 6%	1821
	21st to end	Day	46% 4 6% 18% 19% 7%	1625
March	1st to 10th	Day	47% 4 7% 17% 16% 9%	3435
	11th to 20th	Day	31% 5% 8% 17% 28% 11%	3480
	21st to end	Day	44% 4 6% 21% 22% 3	3815
April	1st to 10th	Day	30% 5% 10% 22% 26% 6%	2092
	11th to 20th	Day	36% 4 9% 20% 22% 9%	2254
	21st to end	Day	34% 5% 11% 25% 20% 4	2413
May	1st to 10th	Day	41% 8% 16% 20% 13% 2	4120
	11th to 20th	Day	45% 6% 12% 20% 16% 1	4085
	21st to end	Day	30% 6% 16% 22% 21% 4	4489
June	1st to 10th	Day	37% 9% 15% 26% 13% 1	2470
	11th to 20th	Day	33% 8% 19% 24% 15% 1	2470
	21st to end	Day	34% 9% 17% 23% 15% 1	2470
July	1st to 10th	Day	39% 8% 20% 20% 11% 2	4055
	11th to 20th	Day	38% 9% 28% 20% 5% 1	4051
	21st to end	Day	49% 10% 16% 19% 6% 1	4324
August	1st to 10th	Day	51% 6% 19% 18% 5%	4091
	11th to 20th	Day	40% 7% 19% 21% 11% 2	4083
	21st to end	Day	27% 7% 15% 33% 15% 2	4226
September	1st to 10th	Day	33% 8% 14% 21% 19% 4	2130
	11th to 20th	Day	39% 8% 11% 18% 21% 3	2090
	21st to end	Day	44% 5% 9% 21% 17% 4	2090
October	1st to 10th	Day	30% 3 5% 23% 29% 10%	3266
	11th to 20th	Day	21% 2 4 20% 27% 26%	3140
	21st to end	Day	26% 2 4 27% 24% 17%	3428
November	1st to 10th	Day	33% 3 7% 20% 28% 8%	1957
	11th to 20th	Day	32% 3 7% 23% 28% 7%	1860
	21st to end	Day	36% 4 8% 22% 24% 7%	1800
December	1st to 10th	Day	44% 4 8% 22% 18% 4	1755
	11th to 20th	Day	34% 2 7% 21% 28% 8%	2150
	21st to end	Day	41% 5% 7% 23% 20% 3	3124
January	1st to 10th	Night	39% 3 6% 18% 27% 7%	4109
	11th to 20th	Night	37% 5% 6% 16% 29% 7%	4120
	21st to end	Night	45% 2 4 16% 26% 6%	4532
February	1st to 10th	Night	41% 4 8% 20% 21% 6%	2470
	11th to 20th	Night	45% 2 7% 16% 23% 7%	2253
	21st to end	Night	40% 3 10% 19% 21% 7%	1827
March	1st to 10th	Night	49% 5% 8% 14% 17% 7%	3418
	11th to 20th	Night	32% 5% 7% 16% 25% 16%	3480
	21st to end	Night	42% 3 8% 20% 20% 7%	3817
April	1st to 10th	Night	35% 4 9% 20% 25% 7%	2086
	11th to 20th	Night	33% 4 9% 22% 23% 9%	1875
	21st to end	Night	34% 4 12% 24% 21% 5%	1781
May	1st to 10th	Night	40% 6% 15% 23% 14% 2	2840
	11th to 20th	Night	45% 6% 11% 21% 15% 1	2813
	21st to end	Night	31% 8% 15% 29% 15% 2	3087
June	1st to 10th	Night	41% 9% 14% 23% 11% 2	1710
	11th to 20th	Night	39% 8% 18% 23% 11% 2	1710
	21st to end	Night	38% 11% 16% 19% 12% 4	1710
July	1st to 10th	Night	47% 9% 18% 14% 11% 2	2795
	11th to 20th	Night	39% 11% 27% 18% 4 1	2786
	21st to end	Night	55% 9% 16% 15% 5% 1	2988
August	1st to 10th	Night	55% 7% 19% 15% 4	2814
	11th to 20th	Night	44% 7% 23% 17% 8% 1	2812
	21st to end	Night	30% 6% 13% 28% 20% 3	3396
September	1st to 10th	Night	36% 8% 14% 20% 17% 5%	2045
	11th to 20th	Night	43% 8% 12% 15% 20% 2	2090
	21st to end	Night	44% 7% 11% 17% 17% 5%	2090
October	1st to 10th	Night	36% 4 7% 21% 26% 6%	3694
	11th to 20th	Night	23% 2 5% 20% 27% 23%	3779
	21st to end	Night	29% 2 5% 22% 25% 17%	4120
November	1st to 10th	Night	35% 3 7% 20% 25% 12%	2341
	11th to 20th	Night	34% 4 6% 18% 26% 12%	2536
	21st to end	Night	34% 4 6% 22% 27% 8%	2600
December	1st to 10th	Night	44% 4 8% 18% 20% 6%	2542
	11th to 20th	Night	38% 3 7% 18% 24% 10%	3044
	21st to end	Night	41% 4 8% 22% 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	23% 11% 41% 20% 6%	270
	11th to 20th	Day	21% 20% 30% 21% 7% 1	270
	21st to end	Day	21% 17% 38% 16% 7% 1	297
February	1st to 10th	Day	21% 14% 37% 19% 8% 1	270
	11th to 20th	Day	35% 11% 38% 14% 2	270
	21st to end	Day	28% 16% 34% 18% 4 1	280
March	1st to 10th	Day	20% 11% 35% 24% 9% 2	460
	11th to 20th	Day	20% 9% 41% 22% 8%	460
	21st to end	Day	22% 10% 36% 24% 7% 1	506
April	1st to 10th	Day	18% 12% 31% 24% 12% 3	460
	11th to 20th	Day	14% 11% 31% 24% 16% 4	452
	21st to end	Day	15% 9% 24% 29% 17% 6%	460
May	1st to 10th	Day	11% 9% 33% 25% 17% 6%	463
	11th to 20th	Day	17% 6% 16% 27% 23% 11%	487
	21st to end	Day	13% 1 16% 23% 28% 19%	529
June	1st to 10th	Day	10% 3 11% 32% 31% 13%	490
	11th to 20th	Day	11% 4 14% 25% 26% 20%	490
	21st to end	Day	8% 1 12% 31% 30% 18%	490
July	1st to 10th	Day	9% 1 7% 19% 36% 28%	485
	11th to 20th	Day	8% 2 6% 25% 34% 24%	484
	21st to end	Day	7% 2 7% 23% 39% 22%	532
August	1st to 10th	Day	14% 4 10% 23% 27% 22%	486
	11th to 20th	Day	12% 4 8% 22% 30% 24%	479
	21st to end	Day	12% 1 7% 24% 29% 26%	539
September	1st to 10th	Day	12% 1 9% 26% 32% 20%	490
	11th to 20th	Day	17% 3 11% 20% 30% 19%	490
	21st to end	Day	19% 4 17% 25% 26% 9%	490
October	1st to 10th	Day	16% 3 19% 25% 23% 14%	490
	11th to 20th	Day	12% 5% 21% 29% 23% 9%	490
	21st to end	Day	15% 5% 20% 30% 23% 7%	539
November	1st to 10th	Day	19% 5% 23% 30% 19% 4	495
	11th to 20th	Day	17% 8% 33% 28% 10% 3	360
	21st to end	Day	14% 8% 32% 30% 13% 3	300
December	1st to 10th	Day	24% 13% 33% 22% 8%	285
	11th to 20th	Day	20% 7% 34% 27% 10% 3	270
	21st to end	Day	23% 11% 34% 21% 8% 2	297
January	1st to 10th	Night	21% 9% 34% 28% 7%	760
	11th to 20th	Night	20% 8% 34% 32% 6%	760
	21st to end	Night	20% 7% 37% 33% 4	836
February	1st to 10th	Night	18% 7% 36% 35% 4	760
	11th to 20th	Night	25% 8% 39% 25% 2	743
	21st to end	Night	21% 11% 37% 27% 4	628
March	1st to 10th	Night	18% 9% 32% 36% 6%	760
	11th to 20th	Night	17% 11% 34% 29% 9% 1	760
	21st to end	Night	20% 9% 31% 32% 8%	836
April	1st to 10th	Night	16% 11% 33% 30% 10% 1	760
	11th to 20th	Night	15% 9% 27% 33% 16% 1	751
	21st to end	Night	14% 5% 25% 39% 17%	641
May	1st to 10th	Night	12% 7% 25% 40% 16%	570
	11th to 20th	Night	14% 4 20% 37% 24% 1	561
	21st to end	Night	14% 2 9% 35% 37% 3	617
June	1st to 10th	Night	13% 3 10% 39% 30% 5%	570
	11th to 20th	Night	14% 2 12% 27% 37% 7%	570
	21st to end	Night	9% 2 11% 33% 40% 5%	570
July	1st to 10th	Night	10% 3 6% 29% 43% 10%	555
	11th to 20th	Night	10% 2 4 28% 48% 8%	552
	21st to end	Night	8% 2 5% 33% 44% 8%	624
August	1st to 10th	Night	14% 1 6% 28% 44% 7%	567
	11th to 20th	Night	13% 2 6% 30% 42% 8%	564
	21st to end	Night	10% 2 6% 28% 47% 8%	782
September	1st to 10th	Night	11% 2 7% 28% 45% 7%	760
	11th to 20th	Night	18% 2 8% 25% 39% 7%	760
	21st to end	Night	21% 2 14% 33% 27% 3	760
October	1st to 10th	Night	15% 4 15% 31% 29% 7%	760
	11th to 20th	Night	16% 5% 21% 34% 22% 3	760
	21st to end	Night	13% 5% 22% 34% 22% 3	836
November	1st to 10th	Night	16% 4 24% 34% 19% 3	780
	11th to 20th	Night	14% 7% 30% 35% 13% 1	800
	21st to end	Night	15% 6% 28% 36% 14% 1	800
December	1st to 10th	Night	21% 7% 29% 35% 8%	783
	11th to 20th	Night	20% 5% 26% 37% 11%	760
	21st to end	Night	24% 8% 24% 35% 9%	836

Page generated at 2024-12-03 06:45:11. Version ac07

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