Greensboro
Clear Sky Chart
History

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

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%	120242
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 46%	118561
Transparency	Day	39% 5% 11% 22% 18% 6%	123890
	Night	38% 5% 10% 20% 21% 6%	123050
Seeing	Day	16% 8% 24% 24% 19% 9%	16275
	Night	16% 7% 25% 31% 18% 2	26381

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% 6% 2 4 3 2 2 2 3 4 57%	4056
	11th to 20th	Day	11% 7% 2 4 3 3 3 2 4 4 58%	4060
	21st to end	Day	15% 8% 2 6% 4 3 4 3 4 4 47%	4466
February	1st to 10th	Day	14% 6% 2 7% 5% 3 3 4 6% 7% 43%	1800
	11th to 20th	Day	21% 7% 2 4 4 4 3 3 4 5% 43%	1808
	21st to end	Day	18% 7% 2 6% 4 4 4 3 6% 6% 41%	1762
March	1st to 10th	Day	19% 7% 2 6% 3 3 3 3 4 7% 42%	4935
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 7% 54%	4980
	21st to end	Day	16% 7% 2 6% 4 4 3 3 4 5% 46%	5465
April	1st to 10th	Day	11% 4 1 4 3 3 4 3 5% 8% 53%	2274
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 5% 7% 49%	2374
	21st to end	Day	13% 6% 2 5% 5% 5% 5% 3 6% 7% 45%	2470
May	1st to 10th	Day	9% 7% 2 7% 5% 6% 6% 5% 8% 11% 34%	5862
	11th to 20th	Day	19% 7% 3 7% 5% 5% 5% 4 7% 8% 29%	5861
	21st to end	Day	12% 5% 2 6% 4 5% 5% 4 6% 10% 41%	6433
June	1st to 10th	Day	9% 6% 2 6% 4 4 5% 5% 8% 11% 41%	2600
	11th to 20th	Day	8% 6% 2 5% 5% 5% 5% 5% 7% 11% 42%	2600
	21st to end	Day	6% 5% 2 5% 5% 5% 5% 5% 8% 11% 42%	2600
July	1st to 10th	Day	7% 5% 2 7% 5% 6% 7% 6% 8% 10% 38%	4185
	11th to 20th	Day	9% 6% 2 7% 6% 5% 5% 5% 9% 12% 34%	4120
	21st to end	Day	12% 8% 3 9% 6% 6% 6% 5% 7% 10% 28%	4466
August	1st to 10th	Day	17% 8% 3 8% 5% 6% 6% 4 8% 11% 26%	4104
	11th to 20th	Day	8% 6% 2 7% 6% 5% 6% 5% 7% 11% 36%	4018
	21st to end	Day	6% 3 2 5% 4 3 4 3 7% 9% 53%	4180
September	1st to 10th	Day	9% 5% 1 7% 5% 5% 4 4 6% 7% 46%	2252
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 8% 42%	2090
	21st to end	Day	21% 7% 2 7% 3 3 4 3 5% 6% 39%	2090
October	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 4 6% 52%	1905
	11th to 20th	Day	12% 5% 2 4 3 4 3 2 4 4 56%	1900
	21st to end	Day	12% 4 2 5% 3 3 3 3 4 5% 57%	2090
November	1st to 10th	Day	12% 6% 3 5% 3 4 3 3 4 5% 54%	1957
	11th to 20th	Day	14% 5% 2 5% 4 2 3 3 5% 6% 52%	1910
	21st to end	Day	12% 5% 2 5% 4 4 3 3 5% 7% 49%	1800
December	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 4 6% 53%	2930
	11th to 20th	Day	17% 6% 2 5% 4 4 4 3 4 5% 45%	3373
	21st to end	Day	19% 6% 2 5% 3 4 4 3 5% 8% 43%	4466
January	1st to 10th	Night	13% 6% 2 4 3 3 3 3 4 5% 56%	5889
	11th to 20th	Night	12% 6% 2 5% 3 2 3 3 3 4 57%	5900
	21st to end	Night	16% 7% 2 5% 3 3 3 3 4 5% 48%	6490
February	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 4 6% 45%	2600
	11th to 20th	Night	20% 7% 1 4 3 3 3 3 4 5% 44%	2473
	21st to end	Night	15% 6% 3 5% 4 4 3 3 5% 6% 46%	1866
March	1st to 10th	Night	17% 7% 2 6% 4 4 3 3 4 5% 45%	4918
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 5% 6% 55%	4980
	21st to end	Night	14% 5% 1 5% 4 3 4 3 5% 7% 48%	5467
April	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 4 7% 49%	2125
	11th to 20th	Night	12% 5% 3 5% 4 3 4 3 6% 7% 49%	1975
	21st to end	Night	13% 4 2 5% 5% 4 4 5% 6% 7% 46%	1946
May	1st to 10th	Night	13% 6% 3 7% 5% 5% 5% 3 6% 9% 38%	4033
	11th to 20th	Night	17% 8% 3 8% 4 4 4 3 5% 9% 36%	4032
	21st to end	Night	15% 5% 2 5% 4 3 4 4 7% 9% 43%	4421
June	1st to 10th	Night	10% 5% 2 6% 5% 5% 6% 6% 8% 10% 38%	1800
	11th to 20th	Night	9% 6% 2 6% 6% 4 5% 3 7% 11% 41%	1800
	21st to end	Night	7% 5% 1 5% 6% 5% 5% 5% 8% 11% 42%	1800
July	1st to 10th	Night	8% 7% 3 7% 6% 6% 6% 5% 8% 10% 34%	2885
	11th to 20th	Night	11% 7% 2 7% 6% 6% 6% 5% 8% 9% 34%	2840
	21st to end	Night	15% 9% 3 8% 6% 5% 5% 6% 7% 8% 29%	3087
August	1st to 10th	Night	21% 7% 2 8% 5% 6% 7% 5% 8% 8% 24%	2825
	11th to 20th	Night	8% 6% 2 6% 4 5% 6% 5% 8% 11% 40%	2785
	21st to end	Night	6% 5% 2 5% 4 5% 5% 4 6% 8% 51%	3467
September	1st to 10th	Night	9% 7% 2 5% 4 4 5% 4 6% 8% 47%	1924
	11th to 20th	Night	13% 7% 2 6% 3 4 5% 4 5% 7% 43%	2090
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 6% 38%	2090
October	1st to 10th	Night	15% 7% 2 5% 4 3 3 3 4 6% 49%	2274
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 5% 55%	2280
	21st to end	Night	12% 5% 1 4 3 3 3 2 4 5% 57%	2508
November	1st to 10th	Night	14% 5% 2 5% 4 3 3 2 4 4 53%	2341
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 4 5% 52%	2488
	21st to end	Night	13% 5% 2 4 3 3 3 4 5% 6% 52%	2600
December	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 4 5% 53%	4250
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 4 5% 40%	4822
	21st to end	Night	19% 5% 1 4 3 3 4 3 5% 7% 46%	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% 3 3 21% 32% 7%	4057
	11th to 20th	Day	32% 3 3 17% 36% 9%	4060
	21st to end	Day	42% 2 4 23% 23% 6%	4466
February	1st to 10th	Day	40% 4 10% 21% 20% 4	1800
	11th to 20th	Day	44% 3 7% 20% 19% 6%	1817
	21st to end	Day	44% 4 10% 16% 20% 6%	1762
March	1st to 10th	Day	43% 3 5% 17% 19% 12%	4935
	11th to 20th	Day	31% 4 6% 19% 23% 17%	4980
	21st to end	Day	42% 3 7% 22% 20% 6%	5465
April	1st to 10th	Day	30% 5% 11% 24% 24% 7%	2274
	11th to 20th	Day	35% 4 11% 22% 20% 8%	2374
	21st to end	Day	39% 5% 11% 25% 16% 4	2470
May	1st to 10th	Day	42% 6% 17% 21% 11% 2	5897
	11th to 20th	Day	51% 6% 12% 20% 9% 1	5865
	21st to end	Day	38% 6% 13% 22% 19% 3	6447
June	1st to 10th	Day	35% 9% 16% 24% 15% 1	2600
	11th to 20th	Day	34% 8% 18% 23% 15% 2	2600
	21st to end	Day	33% 10% 17% 24% 15% 1	2600
July	1st to 10th	Day	41% 8% 18% 19% 12% 3	4120
	11th to 20th	Day	40% 9% 23% 22% 5% 1	4051
	21st to end	Day	50% 9% 14% 18% 9%	4324
August	1st to 10th	Day	52% 6% 17% 20% 5%	4091
	11th to 20th	Day	41% 6% 20% 22% 9% 1	4057
	21st to end	Day	28% 6% 15% 35% 15% 2	4180
September	1st to 10th	Day	35% 8% 12% 21% 19% 4	2252
	11th to 20th	Day	40% 6% 10% 19% 21% 3	2090
	21st to end	Day	46% 5% 8% 20% 18% 3	2090
October	1st to 10th	Day	34% 3 6% 19% 27% 10%	3165
	11th to 20th	Day	21% 2 5% 22% 25% 26%	3140
	21st to end	Day	25% 2 7% 26% 23% 16%	3428
November	1st to 10th	Day	34% 3 7% 22% 26% 8%	1957
	11th to 20th	Day	33% 4 7% 23% 26% 7%	1910
	21st to end	Day	36% 4 7% 22% 27% 4	1800
December	1st to 10th	Day	34% 3 6% 22% 28% 8%	2930
	11th to 20th	Day	43% 3 9% 17% 23% 5%	3370
	21st to end	Day	41% 4 9% 27% 18% 2	4466
January	1st to 10th	Night	31% 4 4 17% 32% 11%	5889
	11th to 20th	Night	33% 3 4 18% 35% 8%	5900
	21st to end	Night	39% 3 5% 21% 27% 5%	6490
February	1st to 10th	Night	41% 4 9% 22% 20% 5%	2600
	11th to 20th	Night	43% 3 8% 17% 21% 7%	2475
	21st to end	Night	39% 4 9% 19% 22% 7%	1866
March	1st to 10th	Night	43% 4 4 15% 24% 10%	4918
	11th to 20th	Night	31% 3 5% 16% 26% 18%	4980
	21st to end	Night	38% 3 6% 25% 23% 5%	5467
April	1st to 10th	Night	36% 4 10% 19% 25% 6%	2125
	11th to 20th	Night	35% 3 9% 22% 23% 8%	1975
	21st to end	Night	36% 5% 12% 25% 18% 4	1946
May	1st to 10th	Night	44% 5% 16% 20% 14% 1	4060
	11th to 20th	Night	47% 6% 13% 19% 14% 1	4033
	21st to end	Night	37% 6% 13% 27% 14% 3	4429
June	1st to 10th	Night	37% 10% 15% 22% 14% 1	1800
	11th to 20th	Night	38% 7% 17% 22% 15% 2	1800
	21st to end	Night	34% 10% 17% 23% 13% 3	1800
July	1st to 10th	Night	43% 11% 15% 16% 14% 2	2840
	11th to 20th	Night	45% 9% 22% 17% 6% 2	2786
	21st to end	Night	50% 9% 15% 18% 8%	2988
August	1st to 10th	Night	56% 6% 17% 15% 5% 1	2814
	11th to 20th	Night	35% 7% 22% 25% 9% 1	2812
	21st to end	Night	31% 6% 12% 31% 18% 2	3467
September	1st to 10th	Night	35% 9% 13% 21% 17% 6%	1924
	11th to 20th	Night	40% 7% 11% 18% 22% 2	2090
	21st to end	Night	46% 7% 10% 16% 17% 4	2090
October	1st to 10th	Night	41% 2 6% 18% 25% 7%	3794
	11th to 20th	Night	24% 2 6% 23% 28% 18%	3779
	21st to end	Night	25% 2 5% 27% 24% 17%	4120
November	1st to 10th	Night	36% 3 7% 20% 25% 10%	2341
	11th to 20th	Night	36% 3 7% 18% 26% 11%	2488
	21st to end	Night	33% 3 7% 24% 26% 6%	2600
December	1st to 10th	Night	35% 3 6% 21% 30% 5%	4250
	11th to 20th	Night	48% 3 7% 17% 16% 8%	4824
	21st to end	Night	38% 3 12% 23% 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	24% 16% 37% 18% 5%	300
	11th to 20th	Day	22% 19% 37% 16% 6%	300
	21st to end	Day	18% 18% 41% 20% 4	330
February	1st to 10th	Day	16% 15% 44% 18% 7% 1	300
	11th to 20th	Day	34% 15% 37% 9% 5%	300
	21st to end	Day	25% 16% 35% 19% 4	361
March	1st to 10th	Day	23% 11% 34% 24% 8% 1	500
	11th to 20th	Day	17% 13% 42% 22% 5% 1	500
	21st to end	Day	20% 14% 37% 21% 6% 1	550
April	1st to 10th	Day	19% 15% 33% 22% 11% 1	500
	11th to 20th	Day	13% 14% 29% 26% 14% 4	492
	21st to end	Day	17% 9% 27% 29% 17% 2	500
May	1st to 10th	Day	14% 13% 30% 24% 14% 5%	503
	11th to 20th	Day	17% 5% 24% 24% 22% 9%	527
	21st to end	Day	17% 5% 17% 25% 22% 14%	573
June	1st to 10th	Day	12% 2 18% 31% 26% 12%	530
	11th to 20th	Day	9% 3 17% 27% 25% 18%	530
	21st to end	Day	7% 1 14% 29% 36% 12%	530
July	1st to 10th	Day	11% 1 8% 24% 37% 20%	505
	11th to 20th	Day	6% 1 10% 25% 36% 23%	484
	21st to end	Day	9% 1 8% 26% 36% 19%	532
August	1st to 10th	Day	14% 1 13% 25% 27% 19%	486
	11th to 20th	Day	10% 2 11% 25% 30% 22%	479
	21st to end	Day	9% 1 10% 23% 31% 26%	539
September	1st to 10th	Day	13% 2 11% 21% 31% 22%	490
	11th to 20th	Day	18% 3 11% 23% 26% 20%	490
	21st to end	Day	25% 4 18% 28% 21% 6%	490
October	1st to 10th	Day	18% 5% 18% 28% 22% 10%	490
	11th to 20th	Day	13% 7% 21% 29% 24% 6%	490
	21st to end	Day	14% 7% 23% 31% 20% 5%	539
November	1st to 10th	Day	19% 5% 28% 27% 16% 5%	495
	11th to 20th	Day	16% 11% 34% 23% 14% 2	410
	21st to end	Day	10% 17% 30% 25% 15% 3	300
December	1st to 10th	Day	20% 15% 37% 22% 5% 1	300
	11th to 20th	Day	16% 12% 34% 27% 10% 2	300
	21st to end	Day	24% 13% 29% 22% 10% 2	330
January	1st to 10th	Night	20% 14% 36% 25% 5%	800
	11th to 20th	Night	19% 11% 38% 27% 4	800
	21st to end	Night	18% 10% 42% 28% 2	880
February	1st to 10th	Night	20% 10% 38% 29% 3	800
	11th to 20th	Night	25% 15% 38% 20% 1	783
	21st to end	Night	18% 14% 37% 27% 4	660
March	1st to 10th	Night	18% 13% 34% 30% 5% 1	800
	11th to 20th	Night	18% 13% 36% 25% 7%	800
	21st to end	Night	18% 11% 36% 29% 6%	880
April	1st to 10th	Night	16% 14% 33% 30% 7%	800
	11th to 20th	Night	14% 9% 34% 30% 13% 1	791
	21st to end	Night	14% 7% 29% 39% 11% 1	746
May	1st to 10th	Night	13% 8% 30% 34% 15%	600
	11th to 20th	Night	15% 5% 22% 37% 20% 2	591
	21st to end	Night	15% 2 13% 34% 31% 4	650
June	1st to 10th	Night	11% 2 16% 40% 29% 2	600
	11th to 20th	Night	12% 3 13% 33% 34% 6%	600
	21st to end	Night	9% 1 12% 36% 39% 3	600
July	1st to 10th	Night	10% 1 10% 30% 42% 6%	570
	11th to 20th	Night	7% 1 6% 30% 48% 8%	552
	21st to end	Night	9% 1 8% 36% 39% 6%	624
August	1st to 10th	Night	15% 1 7% 34% 38% 5%	567
	11th to 20th	Night	11% 1 10% 31% 40% 7%	564
	21st to end	Night	11% 1 8% 31% 40% 8%	827
September	1st to 10th	Night	11% 1 11% 33% 37% 7%	760
	11th to 20th	Night	18% 3 13% 28% 34% 6%	760
	21st to end	Night	22% 3 18% 31% 26% 1	760
October	1st to 10th	Night	18% 3 17% 30% 27% 6%	760
	11th to 20th	Night	17% 5% 25% 32% 19% 3	760
	21st to end	Night	14% 7% 25% 34% 18% 2	836
November	1st to 10th	Night	16% 7% 23% 35% 17% 2	780
	11th to 20th	Night	15% 9% 30% 34% 12%	800
	21st to end	Night	15% 8% 31% 33% 13% 1	800
December	1st to 10th	Night	20% 9% 33% 31% 7%	800
	11th to 20th	Night	18% 7% 35% 32% 8%	800
	21st to end	Night	23% 10% 27% 33% 7%	880

Page generated at 2025-07-03 01:30:12. Version ac07

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