Greenville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenville clear sky chart from 2005-11-06 to 2025-02-06.

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	17% 12% 4 9% 5% 4 4 3 5% 6% 29%	108575
	Night	18% 13% 5% 10% 5% 4 4 3 4 6% 28%	109683
Transparency	Day	54% 6% 11% 19% 9% 1	112222
	Night	56% 6% 11% 17% 9% 1	114176
Seeing	Day	24% 16% 28% 19% 10% 3	14845
	Night	24% 13% 27% 24% 10% 1	24622

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% 22% 9% 25% 4 3 3 2 2 3 11%	3982
	11th to 20th	Day	12% 25% 9% 20% 7% 8% 2 2 2 3 10%	4060
	21st to end	Day	21% 20% 8% 14% 7% 5% 4 2 3 3 12%	4466
February	1st to 10th	Day	18% 20% 6% 14% 8% 4 3 3 3 3 19%	1755
	11th to 20th	Day	15% 17% 7% 14% 9% 5% 5% 2 4 5% 19%	1663
	21st to end	Day	19% 18% 3 13% 5% 4 3 4 4 5% 22%	1549
March	1st to 10th	Day	22% 12% 6% 9% 5% 4 4 3 5% 5% 26%	3435
	11th to 20th	Day	12% 16% 6% 11% 5% 4 4 3 4 5% 30%	3480
	21st to end	Day	22% 12% 4 9% 4 4 4 3 4 6% 29%	3815
April	1st to 10th	Day	17% 15% 3 7% 5% 4 4 3 5% 7% 30%	2182
	11th to 20th	Day	19% 12% 3 7% 4 4 4 4 4 6% 33%	2333
	21st to end	Day	22% 12% 3 7% 4 4 3 3 3 6% 33%	2470
May	1st to 10th	Day	21% 10% 3 7% 5% 4 5% 4 5% 6% 29%	4082
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 4 6% 7% 30%	4081
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 7% 7% 40%	4783
June	1st to 10th	Day	17% 7% 2 7% 5% 5% 5% 4 7% 8% 33%	2660
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 3 6% 8% 36%	2660
	21st to end	Day	14% 5% 2 6% 5% 5% 6% 4 7% 9% 36%	2660
July	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 5% 6% 10% 39%	4376
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	4120
	21st to end	Day	11% 6% 2 7% 6% 5% 5% 5% 6% 8% 38%	4466
August	1st to 10th	Day	16% 7% 3 8% 6% 6% 6% 4 6% 9% 29%	4104
	11th to 20th	Day	15% 6% 2 7% 4 5% 6% 5% 7% 9% 33%	4044
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 4 7% 9% 39%	4372
September	1st to 10th	Day	16% 7% 3 6% 4 4 4 3 5% 7% 41%	2270
	11th to 20th	Day	12% 7% 2 5% 5% 5% 5% 4 6% 8% 42%	2090
	21st to end	Day	22% 8% 2 7% 4 4 4 4 4 7% 34%	2090
October	1st to 10th	Day	16% 7% 3 8% 5% 4 4 3 5% 7% 37%	1910
	11th to 20th	Day	23% 10% 2 8% 5% 4 3 4 5% 5% 31%	1900
	21st to end	Day	26% 12% 3 7% 4 4 4 4 5% 6% 25%	2090
November	1st to 10th	Day	12% 12% 3 7% 5% 4 5% 3 5% 6% 36%	1826
	11th to 20th	Day	19% 16% 4 8% 5% 4 4 3 4 5% 27%	1651
	21st to end	Day	20% 20% 5% 9% 5% 4 4 4 5% 5% 19%	1600
December	1st to 10th	Day	20% 21% 13% 13% 4 4 3 2 3 3 13%	2600
	11th to 20th	Day	24% 22% 7% 10% 5% 3 3 2 4 4 15%	2990
	21st to end	Day	26% 25% 6% 12% 5% 4 4 2 3 3 10%	3960
January	1st to 10th	Night	16% 20% 10% 25% 5% 3 3 2 3 3 11%	5958
	11th to 20th	Night	13% 21% 11% 19% 8% 5% 5% 3 3 3 10%	5900
	21st to end	Night	22% 19% 8% 14% 6% 4 5% 2 3 3 14%	6490
February	1st to 10th	Night	21% 17% 6% 12% 6% 4 3 3 4 5% 19%	2536
	11th to 20th	Night	18% 15% 6% 13% 7% 5% 4 4 4 4 20%	2403
	21st to end	Night	22% 13% 6% 12% 6% 4 4 3 4 5% 23%	1899
March	1st to 10th	Night	24% 14% 4 7% 5% 4 3 3 3 5% 29%	3418
	11th to 20th	Night	19% 15% 7% 7% 5% 3 3 3 4 6% 29%	3480
	21st to end	Night	18% 12% 5% 8% 4 4 3 3 4 5% 35%	3817
April	1st to 10th	Night	19% 15% 4 7% 5% 4 3 3 5% 6% 30%	1996
	11th to 20th	Night	18% 10% 3 7% 4 5% 5% 3 6% 6% 33%	1812
	21st to end	Night	15% 11% 3 7% 5% 4 5% 4 6% 7% 35%	1710
May	1st to 10th	Night	27% 9% 3 6% 4 4 4 3 4 6% 30%	2813
	11th to 20th	Night	17% 10% 3 7% 4 4 4 3 5% 7% 36%	2812
	21st to end	Night	13% 5% 2 4 3 3 5% 4 6% 11% 45%	2771
June	1st to 10th	Night	9% 7% 2 7% 5% 5% 5% 5% 6% 9% 40%	1520
	11th to 20th	Night	10% 5% 3 6% 5% 5% 4 4 6% 8% 44%	1520
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 7% 9% 42%	1520
July	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 5% 9% 42%	2578
	11th to 20th	Night	12% 5% 2 5% 4 4 4 4 6% 8% 46%	2840
	21st to end	Night	10% 5% 2 7% 5% 4 5% 3 6% 8% 43%	3087
August	1st to 10th	Night	12% 8% 3 9% 5% 5% 5% 4 5% 6% 38%	2825
	11th to 20th	Night	17% 7% 2 6% 4 4 4 3 5% 7% 40%	2785
	21st to end	Night	10% 5% 2 6% 4 5% 6% 5% 6% 8% 44%	3252
September	1st to 10th	Night	14% 5% 2 4 4 4 4 4 5% 7% 47%	1907
	11th to 20th	Night	12% 4 2 5% 3 3 3 3 6% 8% 51%	2090
	21st to end	Night	20% 7% 2 7% 5% 3 4 3 5% 6% 37%	2090
October	1st to 10th	Night	16% 6% 2 6% 3 4 4 3 5% 7% 42%	2270
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 5% 8% 34%	2280
	21st to end	Night	25% 10% 3 6% 5% 3 4 4 5% 6% 30%	2508
November	1st to 10th	Night	14% 11% 3 6% 4 4 4 3 5% 7% 39%	2469
	11th to 20th	Night	18% 17% 5% 7% 5% 4 4 3 5% 6% 26%	2746
	21st to end	Night	22% 18% 4 8% 5% 4 4 3 5% 5% 23%	2800
December	1st to 10th	Night	17% 21% 11% 14% 5% 5% 3 3 4 3 14%	4580
	11th to 20th	Night	21% 22% 8% 11% 5% 4 3 2 4 4 17%	5205
	21st to end	Night	25% 21% 7% 11% 4 4 4 3 4 5% 13%	6996

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	80% 3 7% 6% 3	3983
	11th to 20th	Day	82% 3 6% 7% 2	4060
	21st to end	Day	79% 3 7% 8% 3	4466
February	1st to 10th	Day	71% 3 8% 12% 5%	1755
	11th to 20th	Day	69% 4 8% 13% 6%	1672
	21st to end	Day	64% 5% 10% 14% 5% 2	1549
March	1st to 10th	Day	59% 6% 10% 21% 4	3435
	11th to 20th	Day	55% 6% 15% 17% 5% 1	3480
	21st to end	Day	56% 5% 9% 18% 11% 1	3815
April	1st to 10th	Day	53% 6% 12% 16% 12% 1	2182
	11th to 20th	Day	52% 5% 11% 18% 12% 2	2333
	21st to end	Day	53% 5% 10% 20% 10% 2	2470
May	1st to 10th	Day	54% 7% 9% 22% 8% 1	4120
	11th to 20th	Day	51% 8% 11% 20% 9% 1	4085
	21st to end	Day	40% 8% 13% 21% 14% 4	4797
June	1st to 10th	Day	46% 7% 12% 23% 11% 1	2660
	11th to 20th	Day	45% 7% 13% 21% 14% 1	2660
	21st to end	Day	42% 7% 12% 26% 12% 1	2660
July	1st to 10th	Day	39% 8% 13% 23% 15% 3	4308
	11th to 20th	Day	37% 7% 12% 26% 17% 1	4051
	21st to end	Day	40% 8% 13% 21% 16% 1	4324
August	1st to 10th	Day	48% 9% 13% 21% 9%	4091
	11th to 20th	Day	44% 8% 12% 28% 7% 1	4083
	21st to end	Day	38% 9% 13% 28% 12% 1	4372
September	1st to 10th	Day	42% 7% 11% 22% 15% 2	2270
	11th to 20th	Day	39% 7% 14% 23% 16% 1	2090
	21st to end	Day	50% 6% 12% 22% 10%	2090
October	1st to 10th	Day	35% 6% 14% 26% 18% 1	3170
	11th to 20th	Day	45% 7% 13% 19% 12% 4	3140
	21st to end	Day	44% 6% 13% 25% 12%	3428
November	1st to 10th	Day	47% 7% 12% 19% 14% 1	1826
	11th to 20th	Day	59% 6% 11% 15% 8% 3	1651
	21st to end	Day	67% 6% 10% 12% 5%	1600
December	1st to 10th	Day	78% 4 9% 7% 2	2600
	11th to 20th	Day	73% 4 8% 12% 2	2986
	21st to end	Day	80% 3 8% 7% 2	3960
January	1st to 10th	Night	80% 4 6% 7% 3	5958
	11th to 20th	Night	81% 3 7% 7% 2	5900
	21st to end	Night	77% 3 7% 8% 4 1	6490
February	1st to 10th	Night	69% 5% 9% 13% 4	2536
	11th to 20th	Night	67% 5% 9% 14% 5%	2405
	21st to end	Night	65% 5% 9% 14% 7% 1	1899
March	1st to 10th	Night	58% 4 10% 19% 7%	3418
	11th to 20th	Night	56% 5% 15% 16% 7% 1	3480
	21st to end	Night	50% 6% 8% 22% 12% 1	3817
April	1st to 10th	Night	55% 6% 9% 17% 11% 1	1996
	11th to 20th	Night	51% 5% 11% 18% 13% 2	1812
	21st to end	Night	47% 7% 12% 20% 11% 3	1710
May	1st to 10th	Night	55% 5% 9% 19% 10% 2	2840
	11th to 20th	Night	46% 7% 11% 23% 11% 2	2813
	21st to end	Night	32% 8% 15% 26% 16% 3	2778
June	1st to 10th	Night	39% 8% 12% 25% 14% 2	1520
	11th to 20th	Night	38% 6% 14% 22% 17% 2	1520
	21st to end	Night	38% 8% 14% 22% 17% 1	1520
July	1st to 10th	Night	41% 7% 11% 21% 18% 2	2537
	11th to 20th	Night	34% 7% 13% 28% 16% 2	2786
	21st to end	Night	37% 8% 12% 16% 25% 1	2988
August	1st to 10th	Night	45% 7% 11% 25% 12% 1	2814
	11th to 20th	Night	42% 7% 11% 31% 8%	2812
	21st to end	Night	35% 8% 14% 28% 13% 2	3252
September	1st to 10th	Night	35% 7% 12% 25% 18% 3	1907
	11th to 20th	Night	31% 6% 14% 25% 21% 2	2090
	21st to end	Night	47% 5% 12% 20% 15% 1	2090
October	1st to 10th	Night	36% 6% 10% 25% 21% 1	3790
	11th to 20th	Night	43% 7% 11% 21% 13% 6%	3779
	21st to end	Night	40% 5% 14% 25% 15% 1	4120
November	1st to 10th	Night	44% 6% 14% 22% 12% 3	2469
	11th to 20th	Night	59% 5% 10% 16% 7% 3	2746
	21st to end	Night	64% 4 12% 16% 3 1	2800
December	1st to 10th	Night	76% 5% 10% 7% 2	4580
	11th to 20th	Night	72% 4 10% 12% 2	5208
	21st to end	Night	74% 5% 10% 10% 1	6996

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	33% 31% 24% 9% 2	283
	11th to 20th	Day	38% 30% 22% 6% 3	300
	21st to end	Day	34% 30% 29% 7% 1	330
February	1st to 10th	Day	34% 28% 31% 7% 1	285
	11th to 20th	Day	37% 29% 27% 7% 1	270
	21st to end	Day	40% 29% 25% 7%	227
March	1st to 10th	Day	32% 23% 29% 14% 3	460
	11th to 20th	Day	30% 21% 32% 12% 3 1	460
	21st to end	Day	36% 23% 23% 15% 3	506
April	1st to 10th	Day	30% 23% 26% 15% 5% 1	460
	11th to 20th	Day	31% 21% 22% 16% 8% 2	452
	21st to end	Day	29% 18% 32% 15% 4 1	460
May	1st to 10th	Day	29% 20% 27% 16% 6% 2	463
	11th to 20th	Day	24% 14% 28% 23% 8% 3	487
	21st to end	Day	17% 10% 28% 26% 12% 5%	529
June	1st to 10th	Day	16% 14% 32% 26% 9% 2	490
	11th to 20th	Day	18% 12% 28% 26% 15% 2	490
	21st to end	Day	18% 11% 33% 24% 11% 3	490
July	1st to 10th	Day	12% 7% 24% 29% 21% 8%	485
	11th to 20th	Day	13% 7% 28% 30% 13% 7%	484
	21st to end	Day	13% 6% 30% 29% 17% 5%	532
August	1st to 10th	Day	13% 7% 26% 27% 18% 9%	486
	11th to 20th	Day	18% 8% 25% 25% 15% 10%	479
	21st to end	Day	11% 8% 23% 31% 19% 8%	539
September	1st to 10th	Day	16% 10% 24% 26% 18% 7%	490
	11th to 20th	Day	11% 7% 22% 28% 23% 9%	490
	21st to end	Day	24% 12% 27% 18% 13% 4	490
October	1st to 10th	Day	17% 14% 27% 24% 16% 3	490
	11th to 20th	Day	26% 17% 33% 16% 7% 2	490
	21st to end	Day	36% 16% 29% 15% 5%	539
November	1st to 10th	Day	22% 21% 33% 14% 9% 1	364
	11th to 20th	Day	34% 24% 27% 12% 2 1	225
	21st to end	Day	32% 21% 37% 10% 1	200
December	1st to 10th	Day	35% 30% 26% 6% 3 2	200
	11th to 20th	Day	39% 20% 32% 9% 1	200
	21st to end	Day	36% 23% 31% 9%	220
January	1st to 10th	Night	31% 23% 32% 11% 3	800
	11th to 20th	Night	35% 22% 29% 13% 2	800
	21st to end	Night	28% 22% 33% 15% 2	880
February	1st to 10th	Night	32% 20% 28% 19% 1	781
	11th to 20th	Night	30% 20% 34% 14% 2	743
	21st to end	Night	32% 20% 32% 14% 2	628
March	1st to 10th	Night	27% 18% 35% 18% 3	760
	11th to 20th	Night	29% 20% 26% 20% 5%	760
	21st to end	Night	25% 18% 31% 19% 5%	836
April	1st to 10th	Night	26% 17% 31% 21% 5%	760
	11th to 20th	Night	25% 13% 32% 21% 7% 1	688
	21st to end	Night	22% 9% 36% 28% 4 1	570
May	1st to 10th	Night	23% 10% 25% 32% 10%	570
	11th to 20th	Night	20% 8% 28% 33% 9% 1	561
	21st to end	Night	11% 5% 31% 33% 18% 2	438
June	1st to 10th	Night	10% 5% 31% 40% 14% 1	380
	11th to 20th	Night	13% 6% 24% 44% 13%	380
	21st to end	Night	11% 7% 30% 35% 18%	380
July	1st to 10th	Night	9% 4 17% 43% 22% 5%	401
	11th to 20th	Night	11% 3 20% 36% 26% 4	552
	21st to end	Night	11% 3 15% 46% 24% 1	624
August	1st to 10th	Night	10% 3 17% 42% 25% 3	567
	11th to 20th	Night	14% 3 14% 39% 26% 4	564
	21st to end	Night	13% 5% 19% 33% 26% 4	703
September	1st to 10th	Night	16% 6% 20% 31% 24% 3	760
	11th to 20th	Night	13% 4 17% 35% 27% 3	760
	21st to end	Night	23% 9% 21% 26% 18% 3	760
October	1st to 10th	Night	19% 7% 28% 26% 18% 2	760
	11th to 20th	Night	24% 13% 29% 25% 8% 1	760
	21st to end	Night	31% 13% 29% 23% 4	836
November	1st to 10th	Night	21% 12% 31% 26% 9% 1	780
	11th to 20th	Night	30% 18% 28% 18% 6% 1	800
	21st to end	Night	33% 16% 31% 16% 4	800
December	1st to 10th	Night	35% 20% 28% 13% 4	800
	11th to 20th	Night	31% 24% 27% 15% 4	800
	21st to end	Night	33% 19% 31% 16% 2	880

Page generated at 2025-02-03 03:05:55. Version ac07

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