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 2024-11-02.

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	7% 7% 2 4 2 2 3 2 4 5% 62%	101317
	Night	9% 9% 2 4 2 2 3 3 4 5% 57%	97865
Transparency	Day	25% 3 8% 18% 24% 21%	101065
	Night	30% 4 9% 20% 22% 15%	97706
Seeing	Day	15% 15% 27% 24% 15% 5%	15023
	Night	13% 6% 17% 38% 23% 3	24249

By Month

Percentage Cloud Cover SW (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	10% 20% 3 6% 4 3 4 3 5% 6% 37%	2539
	11th to 20th	Day	18% 16% 2 7% 5% 4 4 3 4 4 34%	2649
	21st to end	Day	18% 14% 4 8% 4 4 4 3 4 5% 33%	3146
February	1st to 10th	Day	14% 10% 2 5% 3 3 4 3 5% 7% 45%	1710
	11th to 20th	Day	8% 14% 3 5% 3 3 2 3 5% 8% 46%	1768
	21st to end	Day	8% 19% 2 4 3 3 4 2 5% 7% 43%	1570
March	1st to 10th	Day	13% 28% 6% 7% 3 3 3 2 3 4 29%	3194
	11th to 20th	Day	8% 13% 1 4 2 2 2 2 4 5% 56%	3490
	21st to end	Day	11% 21% 3 7% 4 3 3 3 5% 6% 34%	3999
April	1st to 10th	Day	10% 14% 2 5% 4 3 4 3 6% 7% 43%	2280
	11th to 20th	Day	9% 11% 2 4 4 3 3 3 4 6% 52%	2249
	21st to end	Day	9% 6% 2 3 3 4 3 3 5% 6% 55%	2280
May	1st to 10th	Day	7% 6% 2 3 2 2 2 2 3 5% 66%	4061
	11th to 20th	Day	4 3 1 3 2 2 2 2 3 5% 73%	4377
	21st to end	Day	6% 4 2 4 3 2 2 3 4 5% 66%	4813
June	1st to 10th	Day	6% 4 2 4 3 3 4 4 5% 7% 58%	2660
	11th to 20th	Day	3 2 1 3 2 3 2 2 4 4 73%	2660
	21st to end	Day	3 1 1 2 1 1 2 2 3 4 81%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 3 90%	4420
	11th to 20th	Day	2 1 1 2 1 2 2 1 2 3 83%	4420
	21st to end	Day	1 1 1 1 1 1 1 2 3 86%	4619
August	1st to 10th	Day	2 2 1 3 2 2 2 2 4 5% 75%	4091
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 89%	3817
	21st to end	Day	2 1 1 1 1 1 1 1 2 2 88%	4180
September	1st to 10th	Day	2 1 1 1 1 2 2 2 4 84%	2280
	11th to 20th	Day	3 2 1 3 2 3 2 3 4 5% 73%	2280
	21st to end	Day	4 2 1 2 2 2 2 2 3 6% 75%	2054
October	1st to 10th	Day	6% 3 1 3 2 2 3 2 3 4 70%	1900
	11th to 20th	Day	7% 4 1 3 2 2 2 2 4 5% 67%	1900
	21st to end	Day	8% 4 1 3 2 2 3 3 4 5% 64%	2081
November	1st to 10th	Day	11% 7% 1 4 3 3 3 4 6% 7% 51%	1683
	11th to 20th	Day	10% 6% 2 5% 3 3 4 5% 6% 7% 49%	1710
	21st to end	Day	8% 8% 2 4 3 4 4 4 5% 7% 52%	1535
December	1st to 10th	Day	13% 10% 2 4 2 3 3 3 6% 8% 46%	1520
	11th to 20th	Day	20% 13% 2 6% 4 4 5% 4 6% 6% 30%	1928
	21st to end	Day	11% 11% 2 5% 4 5% 5% 4 6% 10% 37%	2794
January	1st to 10th	Night	10% 15% 2 6% 4 3 4 3 6% 7% 41%	4406
	11th to 20th	Night	18% 14% 3 6% 4 3 4 3 4 6% 35%	4313
	21st to end	Night	18% 17% 2 6% 4 4 4 3 4 6% 32%	4521
February	1st to 10th	Night	13% 10% 2 4 3 2 4 2 5% 7% 48%	2470
	11th to 20th	Night	10% 13% 2 3 3 3 3 3 5% 7% 47%	2299
	21st to end	Night	8% 16% 3 5% 3 3 3 2 4 5% 47%	1884
March	1st to 10th	Night	12% 31% 5% 5% 3 2 3 2 3 4 31%	3677
	11th to 20th	Night	10% 12% 1 3 2 2 2 2 4 5% 57%	3490
	21st to end	Night	12% 21% 3 6% 4 4 4 4 6% 6% 31%	3653
April	1st to 10th	Night	8% 11% 2 4 4 4 4 3 6% 7% 46%	1900
	11th to 20th	Night	11% 10% 2 4 3 3 3 3 4 7% 52%	1879
	21st to end	Night	8% 8% 1 3 3 2 3 3 5% 7% 58%	1900
May	1st to 10th	Night	7% 10% 1 4 2 2 3 2 4 4 61%	2906
	11th to 20th	Night	5% 3 1 3 2 2 2 2 4 4 72%	2516
	21st to end	Night	6% 4 1 3 2 2 3 3 3 5% 67%	2762
June	1st to 10th	Night	6% 6% 1 4 2 3 3 3 5% 7% 60%	1520
	11th to 20th	Night	3 3 1 2 1 3 3 2 3 5% 73%	1520
	21st to end	Night	3 2 1 2 2 2 2 3 3 3 78%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 2 90%	2540
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 2 84%	2540
	21st to end	Night	1 1 1 2 1 1 1 2 3 4 85%	2936
August	1st to 10th	Night	3 3 1 3 1 2 2 2 5% 5% 72%	2848
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 88%	3027
	21st to end	Night	2 1 1 1 1 1 1 1 1 2 87%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 2 2 3 84%	1900
	11th to 20th	Night	4 2 1 2 2 2 2 2 3 5% 75%	1900
	21st to end	Night	3 2 1 2 1 2 2 2 3 5% 77%	2123
October	1st to 10th	Night	5% 3 1 3 2 3 2 2 2 4 72%	2280
	11th to 20th	Night	6% 3 1 3 2 2 3 2 3 4 71%	2280
	21st to end	Night	8% 4 1 2 1 2 2 3 4 6% 67%	2517
November	1st to 10th	Night	12% 9% 2 3 3 2 3 4 6% 6% 51%	2430
	11th to 20th	Night	10% 6% 1 4 3 4 3 3 6% 10% 51%	2470
	21st to end	Night	8% 8% 1 5% 3 3 3 3 5% 6% 55%	2642
December	1st to 10th	Night	14% 11% 2 3 2 2 2 3 4 8% 49%	2660
	11th to 20th	Night	22% 13% 2 5% 3 3 3 3 5% 7% 34%	3276
	21st to end	Night	15% 13% 4 6% 4 3 4 4 5% 7% 35%	4862

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	47% 5% 12% 26% 8% 1	2539
	11th to 20th	Day	53% 6% 12% 17% 8% 4	2649
	21st to end	Day	52% 4 12% 18% 11% 2	3146
February	1st to 10th	Day	40% 4 12% 24% 16% 5%	1710
	11th to 20th	Day	39% 4 9% 25% 18% 3	1777
	21st to end	Day	42% 4 10% 25% 14% 4	1570
March	1st to 10th	Day	60% 5% 8% 14% 12% 2	3194
	11th to 20th	Day	32% 3 9% 31% 22% 3	3490
	21st to end	Day	50% 6% 13% 21% 8% 2	3999
April	1st to 10th	Day	41% 5% 14% 22% 16% 2	2280
	11th to 20th	Day	34% 5% 12% 25% 19% 6%	2252
	21st to end	Day	29% 5% 15% 26% 22% 3	2280
May	1st to 10th	Day	23% 3 10% 26% 31% 8%	4061
	11th to 20th	Day	16% 2 7% 19% 43% 13%	4380
	21st to end	Day	22% 3 9% 31% 31% 3	4814
June	1st to 10th	Day	25% 5% 10% 23% 28% 9%	2660
	11th to 20th	Day	15% 3 7% 21% 36% 18%	2660
	21st to end	Day	10% 2 4 14% 36% 35%	2660
July	1st to 10th	Day	4 1 2 6% 15% 72%	4351
	11th to 20th	Day	8% 2 2 8% 17% 63%	4345
	21st to end	Day	6% 1 2 6% 28% 56%	4473
August	1st to 10th	Day	12% 2 3 8% 24% 51%	4076
	11th to 20th	Day	5% 1 2 7% 39% 47%	3855
	21st to end	Day	6% 1 2 13% 40% 37%	4179
September	1st to 10th	Day	7% 1 2 9% 30% 50%	2280
	11th to 20th	Day	14% 2 7% 20% 32% 24%	2280
	21st to end	Day	13% 2 5% 21% 33% 26%	2054
October	1st to 10th	Day	21% 3 6% 20% 29% 22%	1900
	11th to 20th	Day	21% 3 8% 20% 33% 16%	1900
	21st to end	Day	22% 4 9% 25% 25% 15%	2081
November	1st to 10th	Day	32% 6% 11% 20% 22% 9%	1683
	11th to 20th	Day	34% 5% 12% 25% 20% 3	1710
	21st to end	Day	32% 4 11% 23% 23% 7%	1535
December	1st to 10th	Day	38% 5% 9% 24% 21% 3	1520
	11th to 20th	Day	53% 6% 9% 18% 13% 1	1928
	21st to end	Day	39% 8% 18% 24% 10% 2	2794
January	1st to 10th	Night	41% 7% 17% 24% 9% 1	4406
	11th to 20th	Night	48% 9% 13% 15% 11% 4	4313
	21st to end	Night	55% 5% 10% 16% 12% 2	4521
February	1st to 10th	Night	37% 5% 9% 26% 17% 6%	2470
	11th to 20th	Night	38% 5% 11% 26% 19% 2	2301
	21st to end	Night	40% 5% 12% 23% 16% 5%	1884
March	1st to 10th	Night	57% 6% 9% 15% 10% 2	3677
	11th to 20th	Night	31% 5% 8% 29% 25% 2	3490
	21st to end	Night	50% 9% 14% 19% 7% 1	3653
April	1st to 10th	Night	38% 6% 15% 23% 15% 3	1900
	11th to 20th	Night	34% 5% 15% 24% 16% 5%	1879
	21st to end	Night	27% 6% 15% 32% 17% 3	1900
May	1st to 10th	Night	27% 5% 10% 26% 27% 6%	2906
	11th to 20th	Night	17% 4 9% 20% 36% 14%	2516
	21st to end	Night	19% 5% 12% 36% 23% 4	2762
June	1st to 10th	Night	23% 8% 14% 25% 24% 6%	1520
	11th to 20th	Night	15% 2 11% 22% 35% 14%	1520
	21st to end	Night	12% 3 5% 17% 33% 30%	1520
July	1st to 10th	Night	5% 1 2 6% 18% 69%	2500
	11th to 20th	Night	9% 2 2 8% 16% 63%	2492
	21st to end	Night	7% 2 2 7% 31% 52%	2844
August	1st to 10th	Night	13% 2 3 9% 25% 47%	2839
	11th to 20th	Night	5% 1 2 10% 42% 40%	3055
	21st to end	Night	8% 2 3 14% 41% 33%	3498
September	1st to 10th	Night	9% 2 2 9% 31% 47%	1900
	11th to 20th	Night	14% 3 7% 19% 34% 23%	1900
	21st to end	Night	12% 2 6% 22% 33% 25%	2123
October	1st to 10th	Night	20% 3 7% 19% 29% 23%	2280
	11th to 20th	Night	18% 3 7% 23% 31% 19%	2280
	21st to end	Night	20% 3 10% 25% 28% 14%	2517
November	1st to 10th	Night	34% 5% 10% 21% 20% 10%	2430
	11th to 20th	Night	30% 6% 12% 26% 21% 4	2470
	21st to end	Night	30% 4 11% 25% 22% 8%	2642
December	1st to 10th	Night	36% 6% 10% 21% 22% 5%	2660
	11th to 20th	Night	52% 4 7% 18% 17% 1	3276
	21st to end	Night	47% 6% 14% 19% 12% 2	4862

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	37% 9% 20% 22% 11% 1	180
	11th to 20th	Day	29% 11% 21% 24% 13% 2	250
	21st to end	Day	23% 15% 23% 25% 12% 2	407
February	1st to 10th	Day	28% 12% 24% 24% 11% 1	370
	11th to 20th	Day	26% 19% 28% 20% 8% 1	414
	21st to end	Day	20% 19% 29% 24% 7%	382
March	1st to 10th	Day	35% 22% 22% 13% 5% 2	460
	11th to 20th	Day	30% 15% 25% 19% 11% 1	460
	21st to end	Day	26% 23% 29% 14% 7%	506
April	1st to 10th	Day	25% 20% 28% 19% 7% 1	460
	11th to 20th	Day	25% 21% 23% 20% 9% 2	452
	21st to end	Day	18% 18% 28% 20% 13% 3	460
May	1st to 10th	Day	17% 25% 26% 21% 9% 2	463
	11th to 20th	Day	18% 16% 28% 21% 11% 6%	488
	21st to end	Day	14% 15% 26% 25% 13% 6%	529
June	1st to 10th	Day	11% 16% 29% 21% 14% 8%	490
	11th to 20th	Day	9% 19% 32% 22% 13% 4	490
	21st to end	Day	3 15% 28% 29% 16% 8%	490
July	1st to 10th	Day	3 7% 38% 27% 15% 10%	486
	11th to 20th	Day	1 9% 35% 29% 17% 10%	484
	21st to end	Day	2 9% 34% 26% 18% 11%	531
August	1st to 10th	Day	4 10% 32% 25% 18% 11%	487
	11th to 20th	Day	3 10% 29% 29% 19% 10%	477
	21st to end	Day	4 11% 29% 31% 19% 6%	539
September	1st to 10th	Day	4 11% 29% 32% 20% 5%	490
	11th to 20th	Day	7% 15% 25% 28% 21% 4	490
	21st to end	Day	6% 14% 27% 33% 16% 4	490
October	1st to 10th	Day	6% 16% 27% 24% 22% 6%	490
	11th to 20th	Day	12% 12% 22% 27% 23% 5%	490
	21st to end	Day	16% 12% 23% 27% 17% 4	530
November	1st to 10th	Day	18% 10% 17% 29% 21% 5%	273
	11th to 20th	Day	11% 7% 26% 27% 22% 7%	270
	21st to end	Day	14% 13% 20% 28% 20% 4	187
December	1st to 10th	Day	24% 9% 21% 23% 16% 7%	180
	11th to 20th	Day	21% 12% 23% 21% 19% 4	180
	21st to end	Day	24% 12% 19% 25% 17% 2	198
January	1st to 10th	Night	19% 8% 23% 36% 12% 1	760
	11th to 20th	Night	17% 7% 25% 40% 10% 1	760
	21st to end	Night	21% 6% 25% 32% 14% 2	836
February	1st to 10th	Night	21% 6% 22% 39% 12% 1	760
	11th to 20th	Night	19% 8% 22% 36% 14% 1	744
	21st to end	Night	21% 9% 20% 40% 9% 1	628
March	1st to 10th	Night	25% 13% 20% 30% 10% 2	760
	11th to 20th	Night	21% 8% 20% 30% 20% 1	760
	21st to end	Night	22% 13% 21% 29% 14% 1	836
April	1st to 10th	Night	16% 9% 23% 38% 14% 1	760
	11th to 20th	Night	18% 10% 22% 32% 16% 3	751
	21st to end	Night	13% 9% 19% 36% 21% 3	760
May	1st to 10th	Night	12% 12% 22% 33% 19% 1	603
	11th to 20th	Night	11% 4 14% 41% 27% 3	374
	21st to end	Night	13% 4 15% 30% 35% 4	411
June	1st to 10th	Night	8% 4 15% 34% 36% 3	380
	11th to 20th	Night	4 4 16% 42% 31% 2	380
	21st to end	Night	4 2 10% 44% 38% 2	380
July	1st to 10th	Night	2 1 4 44% 46% 3	370
	11th to 20th	Night	1 2 6% 47% 43% 1	368
	21st to end	Night	1 1 2 37% 55% 4	516
August	1st to 10th	Night	2 1 3 42% 48% 5%	567
	11th to 20th	Night	2 3 9% 42% 40% 5%	689
	21st to end	Night	1 1 9% 46% 39% 3	836
September	1st to 10th	Night	2 2 10% 46% 35% 4	760
	11th to 20th	Night	4 4 10% 37% 38% 7%	760
	21st to end	Night	4 4 12% 44% 28% 8%	760
October	1st to 10th	Night	7% 6% 15% 39% 28% 4	760
	11th to 20th	Night	8% 5% 13% 39% 31% 4	760
	21st to end	Night	11% 5% 17% 36% 26% 5%	836
November	1st to 10th	Night	16% 6% 17% 35% 23% 3	748
	11th to 20th	Night	14% 5% 20% 44% 16% 1	760
	21st to end	Night	14% 6% 22% 38% 19% 1	760
December	1st to 10th	Night	22% 7% 18% 38% 14% 1	760
	11th to 20th	Night	25% 6% 19% 35% 14% 1	760
	21st to end	Night	24% 9% 25% 34% 9%	836

Page generated at 2024-10-30 10:19:23. Version ac07

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