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 2026-03-18.

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	13% 6% 2 6% 4 4 4 4 6% 8% 44%	131498
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	130016
Transparency	Day	39% 5% 12% 21% 19% 6%	135144
	Night	39% 4 10% 19% 20% 7%	134440
Seeing	Day	16% 7% 23% 24% 20% 10%	17087
	Night	16% 6% 23% 32% 20% 3	27237

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% 7% 3 5% 3 3 3 2 3 5% 52%	5258
	11th to 20th	Day	11% 6% 2 5% 3 3 3 2 3 3 61%	5280
	21st to end	Day	19% 8% 2 6% 4 4 4 3 4 4 41%	5780
February	1st to 10th	Day	15% 7% 3 6% 3 4 4 4 6% 7% 43%	1890
	11th to 20th	Day	21% 7% 2 4 3 3 4 3 4 5% 45%	2008
	21st to end	Day	19% 8% 2 6% 4 4 4 3 4 6% 41%	1791
March	1st to 10th	Day	20% 8% 3 6% 4 3 4 2 4 6% 40%	5045
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 4 7% 54%	5057
	21st to end	Day	16% 7% 2 6% 4 3 3 3 4 5% 47%	5465
April	1st to 10th	Day	11% 4 1 5% 3 3 4 4 6% 7% 51%	2202
	11th to 20th	Day	12% 6% 2 5% 3 4 4 3 5% 6% 49%	2374
	21st to end	Day	12% 5% 2 5% 5% 4 4 4 5% 6% 49%	2540
May	1st to 10th	Day	10% 6% 2 8% 5% 5% 6% 5% 7% 11% 35%	5862
	11th to 20th	Day	19% 7% 3 7% 5% 5% 5% 4 7% 9% 30%	5861
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 44%	6433
June	1st to 10th	Day	9% 5% 2 7% 4 4 6% 5% 8% 11% 39%	2600
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 8% 11% 43%	2600
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 8% 11% 42%	2600
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 5% 8% 10% 38%	5900
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 9% 13% 36%	5900
	21st to end	Day	10% 6% 2 7% 5% 6% 6% 5% 9% 11% 32%	6424
August	1st to 10th	Day	21% 7% 3 7% 4 5% 6% 4 8% 11% 26%	4234
	11th to 20th	Day	10% 6% 2 6% 4 5% 6% 5% 8% 11% 37%	4174
	21st to end	Day	6% 4 1 5% 4 4 4 4 7% 10% 51%	4360
September	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 7% 10% 46%	2242
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 7% 8% 44%	2200
	21st to end	Day	17% 6% 3 6% 4 5% 5% 3 5% 5% 41%	2200
October	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 4 6% 55%	2070
	11th to 20th	Day	13% 5% 1 5% 3 2 2 3 3 4 59%	2000
	21st to end	Day	14% 5% 1 5% 2 2 3 2 3 5% 57%	2200
November	1st to 10th	Day	13% 6% 2 5% 3 2 3 2 4 5% 55%	2057
	11th to 20th	Day	13% 5% 1 3 4 3 3 3 4 6% 55%	1953
	21st to end	Day	14% 5% 1 4 4 4 3 3 4 6% 50%	1890
December	1st to 10th	Day	16% 6% 2 5% 3 2 3 3 4 6% 51%	3020
	11th to 20th	Day	18% 8% 2 6% 4 3 3 3 5% 6% 42%	3463
	21st to end	Day	20% 7% 2 4 3 3 3 3 5% 6% 44%	4565
January	1st to 10th	Night	13% 6% 2 5% 3 3 2 2 3 5% 55%	7635
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 3 4 57%	7680
	21st to end	Night	19% 9% 2 5% 4 3 3 3 4 5% 44%	8401
February	1st to 10th	Night	16% 6% 2 7% 4 3 4 3 4 6% 46%	2730
	11th to 20th	Night	21% 7% 2 5% 4 4 3 3 5% 5% 42%	2495
	21st to end	Night	17% 7% 2 4 4 2 4 4 4 7% 45%	2013
March	1st to 10th	Night	18% 6% 2 6% 4 4 3 2 4 5% 45%	5028
	11th to 20th	Night	10% 4 2 4 3 3 4 4 6% 7% 54%	5058
	21st to end	Night	16% 5% 1 5% 4 4 4 3 5% 6% 47%	5467
April	1st to 10th	Night	13% 6% 2 4 3 4 5% 3 5% 8% 47%	2196
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 6% 52%	1975
	21st to end	Night	11% 4 2 5% 5% 4 5% 4 5% 6% 48%	1875
May	1st to 10th	Night	13% 7% 3 7% 5% 4 4 3 6% 9% 39%	4033
	11th to 20th	Night	19% 8% 3 7% 4 5% 4 4 5% 9% 32%	4032
	21st to end	Night	14% 5% 2 5% 4 5% 5% 5% 6% 9% 41%	4421
June	1st to 10th	Night	10% 6% 2 7% 7% 5% 6% 4 7% 10% 36%	1800
	11th to 20th	Night	11% 5% 3 5% 5% 5% 6% 5% 8% 12% 35%	1800
	21st to end	Night	6% 5% 2 7% 6% 6% 7% 6% 8% 11% 38%	1800
July	1st to 10th	Night	10% 7% 4 8% 6% 7% 7% 5% 8% 9% 29%	4058
	11th to 20th	Night	9% 6% 2 9% 6% 6% 6% 6% 10% 12% 27%	4057
	21st to end	Night	11% 8% 3 10% 6% 6% 7% 5% 8% 10% 25%	4427
August	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 5% 7% 9% 23%	2915
	11th to 20th	Night	9% 7% 3 8% 5% 6% 5% 5% 7% 10% 34%	2875
	21st to end	Night	5% 4 2 6% 4 5% 5% 4 7% 9% 49%	3503
September	1st to 10th	Night	8% 6% 3 6% 5% 4 5% 4 7% 10% 44%	2153
	11th to 20th	Night	14% 6% 2 7% 4 4 5% 4 6% 8% 39%	2200
	21st to end	Night	18% 6% 3 6% 5% 4 4 3 6% 6% 38%	2200
October	1st to 10th	Night	13% 6% 2 5% 3 4 3 3 5% 6% 50%	2330
	11th to 20th	Night	13% 5% 2 4 3 3 3 2 4 5% 55%	2400
	21st to end	Night	12% 6% 2 4 3 2 3 3 4 5% 57%	2640
November	1st to 10th	Night	14% 6% 2 5% 3 3 2 2 5% 5% 52%	2461
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 5% 6% 53%	2663
	21st to end	Night	13% 5% 2 4 4 4 4 4 5% 6% 50%	2730
December	1st to 10th	Night	16% 7% 2 4 3 3 3 3 5% 4 51%	4380
	11th to 20th	Night	19% 7% 3 6% 4 3 3 3 4 6% 43%	4952
	21st to end	Night	20% 4 2 4 3 3 3 3 5% 6% 46%	6633

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	38% 2 8% 22% 26% 5%	5259
	11th to 20th	Day	31% 2 4 13% 37% 13%	5280
	21st to end	Day	48% 2 3 17% 21% 10%	5780
February	1st to 10th	Day	41% 3 9% 22% 19% 5%	1890
	11th to 20th	Day	43% 3 6% 20% 21% 5%	2018
	21st to end	Day	46% 4 6% 17% 20% 7%	1791
March	1st to 10th	Day	46% 3 5% 15% 19% 12%	5045
	11th to 20th	Day	31% 4 6% 15% 26% 17%	5057
	21st to end	Day	42% 3 5% 23% 22% 5%	5465
April	1st to 10th	Day	31% 5% 10% 23% 26% 6%	2202
	11th to 20th	Day	35% 4 9% 22% 22% 8%	2374
	21st to end	Day	35% 5% 12% 24% 20% 4	2540
May	1st to 10th	Day	41% 6% 18% 22% 12% 1	5897
	11th to 20th	Day	50% 5% 14% 19% 11% 1	5865
	21st to end	Day	38% 5% 13% 21% 19% 4	6447
June	1st to 10th	Day	37% 8% 15% 26% 13% 1	2600
	11th to 20th	Day	33% 8% 20% 23% 15% 1	2600
	21st to end	Day	33% 9% 18% 24% 16% 1	2600
July	1st to 10th	Day	40% 7% 17% 24% 10% 1	5835
	11th to 20th	Day	38% 8% 33% 17% 4	5831
	21st to end	Day	44% 9% 17% 23% 7% 1	6240
August	1st to 10th	Day	52% 6% 19% 18% 5%	4221
	11th to 20th	Day	40% 7% 19% 21% 11% 2	4213
	21st to end	Day	28% 6% 15% 33% 15% 2	4360
September	1st to 10th	Day	33% 8% 15% 21% 19% 4	2242
	11th to 20th	Day	38% 7% 12% 20% 21% 3	2200
	21st to end	Day	44% 5% 10% 21% 16% 4	2200
October	1st to 10th	Day	30% 3 6% 23% 29% 10%	3369
	11th to 20th	Day	21% 2 4 20% 28% 25%	3240
	21st to end	Day	27% 2 4 26% 25% 16%	3538
November	1st to 10th	Day	32% 3 8% 20% 28% 9%	2057
	11th to 20th	Day	31% 3 7% 23% 28% 7%	1953
	21st to end	Day	36% 4 7% 23% 24% 7%	1890
December	1st to 10th	Day	37% 2 6% 19% 28% 8%	3020
	11th to 20th	Day	44% 3 8% 18% 22% 5%	3460
	21st to end	Day	41% 4 8% 27% 18% 2	4565
January	1st to 10th	Night	35% 2 8% 21% 28% 7%	7636
	11th to 20th	Night	32% 3 4 15% 36% 11%	7680
	21st to end	Night	45% 2 3 18% 23% 9%	8401
February	1st to 10th	Night	41% 4 8% 20% 21% 6%	2730
	11th to 20th	Night	46% 2 7% 16% 22% 7%	2496
	21st to end	Night	40% 3 9% 18% 23% 7%	2013
March	1st to 10th	Night	42% 4 6% 12% 27% 8%	5028
	11th to 20th	Night	30% 4 6% 15% 27% 18%	5058
	21st to end	Night	38% 3 7% 23% 21% 7%	5467
April	1st to 10th	Night	36% 4 9% 20% 24% 7%	2196
	11th to 20th	Night	32% 4 9% 23% 23% 9%	1975
	21st to end	Night	35% 4 12% 23% 21% 4	1875
May	1st to 10th	Night	41% 4 17% 22% 14% 1	4060
	11th to 20th	Night	49% 6% 14% 19% 11% 1	4033
	21st to end	Night	38% 6% 13% 26% 15% 2	4429
June	1st to 10th	Night	41% 9% 14% 22% 12% 2	1800
	11th to 20th	Night	39% 8% 18% 22% 11% 2	1800
	21st to end	Night	37% 11% 17% 19% 13% 3	1800
July	1st to 10th	Night	49% 7% 18% 16% 9% 1	4015
	11th to 20th	Night	46% 12% 26% 13% 3 1	4006
	21st to end	Night	53% 7% 17% 18% 5%	4297
August	1st to 10th	Night	55% 7% 18% 15% 4	2904
	11th to 20th	Night	44% 7% 23% 17% 8% 1	2902
	21st to end	Night	31% 6% 13% 27% 20% 3	3503
September	1st to 10th	Night	36% 7% 14% 21% 17% 5%	2153
	11th to 20th	Night	42% 8% 12% 16% 21% 2	2200
	21st to end	Night	45% 6% 11% 17% 16% 5%	2200
October	1st to 10th	Night	36% 4 7% 21% 26% 6%	3811
	11th to 20th	Night	24% 2 5% 20% 27% 22%	3899
	21st to end	Night	29% 2 5% 22% 26% 17%	4252
November	1st to 10th	Night	35% 3 6% 20% 25% 11%	2461
	11th to 20th	Night	33% 4 7% 18% 26% 12%	2663
	21st to end	Night	35% 3 5% 22% 27% 8%	2730
December	1st to 10th	Night	37% 3 6% 19% 27% 8%	4380
	11th to 20th	Night	45% 3 9% 16% 18% 9%	4954
	21st to end	Night	40% 3 10% 23% 22% 2	6633

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	22% 14% 41% 18% 5%	330
	11th to 20th	Day	22% 20% 32% 20% 6% 1	330
	21st to end	Day	22% 18% 38% 16% 6% 1	363
February	1st to 10th	Day	19% 14% 39% 19% 7% 1	330
	11th to 20th	Day	37% 11% 38% 12% 2	330
	21st to end	Day	28% 16% 33% 18% 4 1	334
March	1st to 10th	Day	21% 11% 34% 25% 8% 1	540
	11th to 20th	Day	20% 12% 39% 22% 7%	528
	21st to end	Day	21% 12% 36% 23% 7% 1	550
April	1st to 10th	Day	18% 13% 31% 24% 11% 3	500
	11th to 20th	Day	14% 11% 33% 24% 15% 3	492
	21st to end	Day	15% 8% 24% 30% 18% 5%	500
May	1st to 10th	Day	11% 9% 34% 25% 16% 5%	503
	11th to 20th	Day	18% 6% 17% 27% 21% 11%	527
	21st to end	Day	15% 3 17% 22% 26% 17%	573
June	1st to 10th	Day	11% 4 13% 31% 29% 12%	530
	11th to 20th	Day	11% 4 14% 27% 25% 19%	530
	21st to end	Day	8% 1 11% 30% 32% 18%	530
July	1st to 10th	Day	9% 1 8% 19% 36% 26%	525
	11th to 20th	Day	8% 2 5% 24% 35% 25%	524
	21st to end	Day	7% 1 7% 22% 41% 22%	576
August	1st to 10th	Day	17% 4 10% 24% 25% 21%	526
	11th to 20th	Day	12% 4 8% 22% 30% 24%	519
	21st to end	Day	12% 2 8% 24% 30% 25%	583
September	1st to 10th	Day	11% 1 10% 28% 30% 19%	530
	11th to 20th	Day	16% 2 11% 22% 30% 20%	530
	21st to end	Day	20% 4 19% 24% 25% 9%	530
October	1st to 10th	Day	15% 3 19% 25% 24% 13%	530
	11th to 20th	Day	13% 5% 23% 30% 21% 8%	530
	21st to end	Day	16% 5% 22% 28% 21% 7%	583
November	1st to 10th	Day	18% 6% 24% 30% 18% 4	535
	11th to 20th	Day	16% 9% 34% 28% 10% 3	393
	21st to end	Day	15% 10% 32% 29% 12% 2	330
December	1st to 10th	Day	26% 12% 34% 21% 7%	330
	11th to 20th	Day	20% 8% 34% 26% 9% 3	330
	21st to end	Day	23% 12% 34% 22% 7% 2	363
January	1st to 10th	Night	21% 10% 34% 28% 6%	840
	11th to 20th	Night	20% 10% 35% 31% 5%	840
	21st to end	Night	19% 8% 39% 31% 3	924
February	1st to 10th	Night	18% 8% 36% 34% 4	840
	11th to 20th	Night	25% 9% 39% 24% 2	823
	21st to end	Night	21% 11% 37% 27% 5%	692
March	1st to 10th	Night	18% 9% 32% 36% 6%	840
	11th to 20th	Night	17% 12% 35% 28% 8% 1	829
	21st to end	Night	20% 9% 33% 31% 7%	880
April	1st to 10th	Night	17% 11% 33% 30% 9% 1	800
	11th to 20th	Night	14% 9% 29% 32% 15% 1	791
	21st to end	Night	13% 5% 25% 39% 17%	675
May	1st to 10th	Night	12% 7% 27% 40% 15%	600
	11th to 20th	Night	15% 4 20% 37% 23% 1	591
	21st to end	Night	16% 3 10% 34% 35% 3	650
June	1st to 10th	Night	13% 3 11% 39% 30% 5%	600
	11th to 20th	Night	14% 2 13% 28% 36% 7%	600
	21st to end	Night	9% 2 10% 34% 40% 5%	600
July	1st to 10th	Night	10% 2 6% 29% 43% 9%	585
	11th to 20th	Night	10% 2 4 29% 47% 9%	582
	21st to end	Night	8% 2 5% 32% 44% 8%	657
August	1st to 10th	Night	16% 1 6% 28% 42% 7%	597
	11th to 20th	Night	13% 2 6% 29% 42% 8%	594
	21st to end	Night	10% 3 6% 28% 46% 8%	823
September	1st to 10th	Night	11% 2 8% 29% 44% 7%	800
	11th to 20th	Night	17% 2 8% 27% 39% 7%	800
	21st to end	Night	22% 2 14% 33% 27% 3	800
October	1st to 10th	Night	14% 4 15% 32% 29% 6%	800
	11th to 20th	Night	16% 5% 21% 34% 21% 3	800
	21st to end	Night	14% 5% 23% 33% 21% 3	880
November	1st to 10th	Night	16% 5% 23% 35% 18% 3	820
	11th to 20th	Night	14% 8% 30% 35% 12% 1	840
	21st to end	Night	15% 6% 29% 36% 14% 1	840
December	1st to 10th	Night	22% 8% 29% 34% 7%	840
	11th to 20th	Night	21% 6% 27% 36% 10%	840
	21st to end	Night	23% 8% 24% 35% 9%	924

Page generated at 2026-03-15 02:23:51. Version ac07

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