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 2024-08-30.

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 8% 5% 4 4 3 5% 7% 30%	95480
	Night	18% 13% 5% 9% 5% 4 4 3 5% 6% 30%	93509
Transparency	Day	54% 6% 11% 18% 9% 1	95250
	Night	55% 6% 11% 17% 10% 1	93344
Seeing	Day	24% 16% 28% 19% 10% 3	14350
	Night	24% 13% 27% 25% 10% 1	23985

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	20% 24% 9% 13% 4 3 3 2 3 4 14%	2776
	11th to 20th	Day	13% 25% 8% 15% 7% 6% 3 2 2 4 14%	2840
	21st to end	Day	26% 22% 9% 16% 6% 4 3 2 3 2 8%	3124
February	1st to 10th	Day	18% 20% 6% 14% 8% 4 3 3 3 3 18%	1710
	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	11% 6% 3 7% 5% 6% 6% 5% 7% 10% 36%	2457
	11th to 20th	Day	13% 7% 3 8% 4 5% 6% 5% 7% 8% 33%	2433
	21st to end	Day	12% 6% 2 7% 6% 5% 5% 5% 7% 9% 37%	2600
September	1st to 10th	Day	16% 7% 3 7% 4 4 4 3 5% 8% 39%	2151
	11th to 20th	Day	13% 7% 2 5% 5% 5% 5% 4 6% 8% 40%	1980
	21st to end	Day	20% 7% 2 7% 4 4 5% 4 4 7% 35%	1980
October	1st to 10th	Day	17% 8% 3 8% 5% 4 4 3 5% 7% 36%	1810
	11th to 20th	Day	23% 11% 3 8% 5% 4 3 4 5% 6% 30%	1800
	21st to end	Day	27% 13% 3 7% 4 4 4 4 5% 6% 24%	1980
November	1st to 10th	Day	12% 12% 4 8% 5% 4 5% 3 5% 6% 36%	1733
	11th to 20th	Day	19% 16% 4 8% 5% 4 4 3 4 5% 27%	1569
	21st to end	Day	20% 19% 5% 9% 5% 4 4 4 5% 5% 19%	1520
December	1st to 10th	Day	20% 25% 6% 10% 5% 5% 4 3 3 3 16%	1520
	11th to 20th	Day	19% 21% 8% 13% 4 3 4 3 5% 5% 15%	1910
	21st to end	Day	27% 26% 7% 11% 4 3 3 2 3 3 11%	2772
January	1st to 10th	Night	18% 24% 11% 15% 5% 3 3 2 3 4 11%	4164
	11th to 20th	Night	17% 21% 9% 18% 5% 5% 5% 3 3 4 11%	4120
	21st to end	Night	27% 20% 9% 13% 6% 4 3 2 2 3 12%	4532
February	1st to 10th	Night	20% 17% 6% 12% 6% 5% 3 3 4 5% 19%	2470
	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	9% 5% 2 7% 4 5% 5% 4 6% 7% 46%	1701
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 7% 9% 41%	1688
	21st to end	Night	11% 5% 2 5% 4 4 5% 4 6% 8% 46%	1947
September	1st to 10th	Night	14% 6% 2 4 4 4 4 4 5% 7% 46%	1806
	11th to 20th	Night	13% 4 2 5% 3 3 3 3 6% 8% 51%	1980
	21st to end	Night	18% 7% 2 6% 5% 4 5% 3 5% 6% 39%	1980
October	1st to 10th	Night	17% 6% 2 6% 4 4 4 4 5% 7% 41%	2150
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 5% 8% 33%	2160
	21st to end	Night	26% 11% 3 6% 5% 3 4 4 5% 5% 29%	2376
November	1st to 10th	Night	15% 11% 3 6% 4 4 4 3 5% 7% 38%	2342
	11th to 20th	Night	18% 17% 5% 7% 5% 4 4 3 5% 6% 27%	2608
	21st to end	Night	21% 18% 4 8% 5% 4 4 3 5% 6% 23%	2660
December	1st to 10th	Night	22% 22% 7% 10% 5% 4 4 3 4 3 17%	2660
	11th to 20th	Night	19% 20% 6% 12% 6% 4 3 3 4 5% 18%	3285
	21st to end	Night	27% 22% 8% 11% 4 4 4 3 4 4 10%	4884

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	76% 4 9% 8% 3	2777
	11th to 20th	Day	76% 4 8% 10% 2	2840
	21st to end	Day	84% 3 6% 5% 1	3124
February	1st to 10th	Day	72% 4 8% 12% 5%	1710
	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	41% 9% 14% 25% 10%	2444
	11th to 20th	Day	45% 9% 14% 21% 9% 2	2433
	21st to end	Day	40% 9% 13% 23% 12% 2	2600
September	1st to 10th	Day	43% 7% 12% 21% 14% 2	2151
	11th to 20th	Day	40% 7% 14% 24% 15% 1	1980
	21st to end	Day	48% 6% 12% 23% 11%	1980
October	1st to 10th	Day	47% 7% 13% 19% 13% 1	1810
	11th to 20th	Day	55% 6% 13% 19% 7% 1	1800
	21st to end	Day	60% 6% 12% 13% 8% 1	1980
November	1st to 10th	Day	47% 7% 12% 18% 14% 2	1733
	11th to 20th	Day	59% 6% 11% 15% 7% 3	1569
	21st to end	Day	65% 6% 11% 13% 5%	1520
December	1st to 10th	Day	74% 4 9% 10% 3	1520
	11th to 20th	Day	72% 5% 10% 11% 2	1906
	21st to end	Day	81% 3 8% 7% 1	2772
January	1st to 10th	Night	78% 4 8% 8% 2	4164
	11th to 20th	Night	79% 4 8% 8% 2	4120
	21st to end	Night	80% 3 6% 8% 2	4532
February	1st to 10th	Night	68% 5% 9% 13% 5%	2470
	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	35% 8% 13% 29% 15% 1	1690
	11th to 20th	Night	38% 8% 15% 26% 13% 1	1688
	21st to end	Night	34% 8% 13% 26% 15% 3	1947
September	1st to 10th	Night	36% 7% 13% 24% 17% 3	1806
	11th to 20th	Night	31% 7% 15% 25% 20% 2	1980
	21st to end	Night	45% 5% 13% 21% 16% 1	1980
October	1st to 10th	Night	41% 8% 13% 21% 16% 1	2150
	11th to 20th	Night	48% 7% 14% 20% 10% 1	2160
	21st to end	Night	56% 7% 11% 17% 9% 2	2376
November	1st to 10th	Night	44% 6% 14% 22% 11% 3	2342
	11th to 20th	Night	58% 5% 11% 16% 7% 3	2608
	21st to end	Night	63% 4 12% 16% 4 1	2660
December	1st to 10th	Night	72% 5% 10% 9% 4	2660
	11th to 20th	Night	70% 5% 12% 12% 2	3288
	21st to end	Night	78% 5% 9% 6% 1	4884

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% 29% 25% 9% 3	254
	11th to 20th	Day	37% 30% 23% 6% 3	270
	21st to end	Day	33% 29% 29% 7% 1	297
February	1st to 10th	Day	33% 27% 31% 8% 1	270
	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% 18% 8%	532
September	1st to 10th	Day	17% 9% 24% 27% 17% 7%	450
	11th to 20th	Day	11% 7% 23% 27% 23% 9%	450
	21st to end	Day	22% 12% 28% 19% 15% 4	450
October	1st to 10th	Day	17% 13% 28% 24% 16% 3	450
	11th to 20th	Day	27% 17% 34% 15% 6% 1	450
	21st to end	Day	39% 15% 29% 13% 4	495
November	1st to 10th	Day	22% 21% 32% 15% 9% 1	331
	11th to 20th	Day	36% 24% 24% 13% 2 1	203
	21st to end	Day	28% 22% 38% 11% 1	180
December	1st to 10th	Day	36% 29% 26% 6% 3 2	180
	11th to 20th	Day	37% 21% 33% 9% 1	180
	21st to end	Day	36% 24% 30% 9% 1	198
January	1st to 10th	Night	31% 23% 32% 11% 3	760
	11th to 20th	Night	36% 20% 29% 14% 2	760
	21st to end	Night	28% 21% 33% 15% 2	836
February	1st to 10th	Night	31% 20% 28% 19% 1	760
	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% 32% 26% 4	699
September	1st to 10th	Night	16% 6% 19% 31% 24% 3	720
	11th to 20th	Night	14% 5% 18% 35% 25% 3	720
	21st to end	Night	20% 9% 22% 27% 19% 3	720
October	1st to 10th	Night	19% 7% 28% 26% 18% 2	720
	11th to 20th	Night	25% 13% 29% 26% 7% 1	720
	21st to end	Night	33% 13% 28% 22% 3	792
November	1st to 10th	Night	22% 12% 30% 26% 9% 1	740
	11th to 20th	Night	29% 18% 29% 18% 6% 1	760
	21st to end	Night	32% 16% 31% 17% 4	760
December	1st to 10th	Night	35% 19% 28% 14% 4	760
	11th to 20th	Night	30% 24% 27% 15% 4	760
	21st to end	Night	33% 19% 31% 15% 1	836

Page generated at 2024-08-27 09:49:39. Version ac07

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