Oconee Station State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oconee Station State Historic Site clear sky chart from 2005-11-06 to 2024-11-11.

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	14% 5% 2 5% 4 4 5% 4 6% 8% 43%	101124
	Night	16% 6% 2 6% 4 4 4 4 5% 7% 43%	97999
Transparency	Day	37% 8% 12% 19% 18% 6%	104905
	Night	38% 7% 11% 18% 19% 7%	102357
Seeing	Day	18% 10% 23% 24% 17% 8%	15035
	Night	17% 8% 22% 30% 19% 4	25071

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	18% 4 2 4 3 2 3 3 5% 7% 50%	2836
	11th to 20th	Day	16% 5% 2 5% 4 3 3 2 3 4 54%	2840
	21st to end	Day	27% 3 1 3 2 3 3 2 3 4 47%	3124
February	1st to 10th	Day	16% 7% 2 6% 3 4 4 3 5% 7% 44%	1852
	11th to 20th	Day	21% 6% 2 4 4 3 4 3 5% 6% 44%	1848
	21st to end	Day	21% 6% 2 6% 5% 4 3 3 3 5% 42%	1570
March	1st to 10th	Day	26% 6% 2 4 3 3 3 3 4 5% 41%	3330
	11th to 20th	Day	14% 4 1 4 3 3 4 3 4 5% 54%	3480
	21st to end	Day	20% 5% 2 5% 4 4 4 3 5% 5% 42%	3815
April	1st to 10th	Day	13% 3 1 5% 3 4 5% 4 7% 7% 47%	2090
	11th to 20th	Day	14% 4 1 4 5% 5% 4 4 4 7% 47%	2259
	21st to end	Day	12% 4 1 4 4 4 4 4 4 8% 50%	2470
May	1st to 10th	Day	13% 7% 2 7% 4 5% 5% 4 6% 9% 39%	4082
	11th to 20th	Day	17% 8% 3 6% 4 4 5% 4 6% 7% 36%	4081
	21st to end	Day	9% 4 2 6% 4 4 6% 5% 7% 11% 43%	4476
June	1st to 10th	Day	12% 6% 2 6% 6% 5% 6% 5% 9% 11% 33%	2470
	11th to 20th	Day	6% 5% 2 5% 5% 6% 6% 7% 9% 11% 39%	2470
	21st to end	Day	8% 4 1 6% 6% 6% 7% 6% 7% 10% 39%	2470
July	1st to 10th	Day	7% 6% 2 7% 6% 6% 7% 6% 9% 12% 32%	4120
	11th to 20th	Day	8% 5% 2 6% 5% 7% 7% 6% 8% 12% 34%	4120
	21st to end	Day	10% 7% 4 9% 8% 9% 9% 7% 9% 9% 19%	4466
August	1st to 10th	Day	12% 6% 2 6% 5% 5% 6% 5% 9% 10% 33%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	4044
	21st to end	Day	8% 5% 2 5% 4 4 5% 5% 6% 8% 50%	4098
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 7% 5% 6% 10% 39%	2090
	11th to 20th	Day	17% 5% 2 6% 4 5% 6% 4 6% 7% 38%	2090
	21st to end	Day	17% 5% 2 5% 3 4 4 3 5% 7% 44%	2090
October	1st to 10th	Day	15% 5% 1 3 3 3 3 3 4 6% 56%	2090
	11th to 20th	Day	13% 4 1 4 3 3 3 2 4 5% 58%	1904
	21st to end	Day	15% 4 2 4 2 2 3 3 4 4 58%	2090
November	1st to 10th	Day	14% 5% 1 4 4 2 2 2 3 5% 57%	1848
	11th to 20th	Day	15% 5% 2 3 2 2 3 3 4 6% 54%	1710
	21st to end	Day	17% 4 2 4 3 3 3 3 5% 7% 50%	1710
December	1st to 10th	Day	23% 5% 3 5% 4 4 4 3 4 5% 40%	1710
	11th to 20th	Day	18% 4 2 5% 3 2 3 3 5% 6% 50%	2153
	21st to end	Day	24% 4 1 4 2 3 3 2 5% 7% 45%	3124
January	1st to 10th	Night	19% 4 1 5% 4 4 3 2 4 5% 50%	4109
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 5% 50%	4120
	21st to end	Night	26% 5% 2 5% 3 3 3 2 4 4 44%	4532
February	1st to 10th	Night	16% 6% 2 5% 3 3 3 4 4 6% 49%	2323
	11th to 20th	Night	21% 6% 1 5% 4 3 2 3 5% 5% 44%	2218
	21st to end	Night	20% 5% 2 5% 5% 4 4 3 5% 6% 42%	1884
March	1st to 10th	Night	25% 7% 2 5% 4 3 3 3 4 5% 38%	3523
	11th to 20th	Night	10% 4 2 4 3 4 4 3 5% 7% 53%	3480
	21st to end	Night	21% 5% 2 6% 4 4 4 3 4 6% 42%	3817
April	1st to 10th	Night	14% 5% 2 4 3 3 4 3 4 6% 51%	2090
	11th to 20th	Night	13% 5% 2 5% 4 4 3 3 5% 6% 51%	1882
	21st to end	Night	11% 5% 2 5% 4 3 4 3 5% 6% 51%	1710
May	1st to 10th	Night	14% 7% 3 6% 4 4 5% 4 6% 8% 39%	2813
	11th to 20th	Night	20% 6% 2 6% 4 4 4 4 5% 7% 39%	2812
	21st to end	Night	9% 4 2 6% 4 5% 5% 4 7% 10% 43%	3079
June	1st to 10th	Night	10% 7% 3 7% 6% 5% 6% 6% 8% 9% 36%	1710
	11th to 20th	Night	8% 5% 2 4 6% 4 6% 5% 6% 11% 41%	1710
	21st to end	Night	8% 4 2 6% 5% 5% 6% 5% 9% 11% 40%	1710
July	1st to 10th	Night	13% 7% 3 9% 7% 6% 6% 5% 7% 9% 27%	2840
	11th to 20th	Night	9% 6% 2 6% 7% 6% 6% 7% 9% 12% 31%	2840
	21st to end	Night	13% 9% 3 10% 6% 6% 6% 4 8% 10% 23%	3087
August	1st to 10th	Night	13% 7% 3 7% 5% 6% 5% 5% 8% 11% 32%	2825
	11th to 20th	Night	14% 9% 4 9% 5% 5% 6% 4 6% 9% 29%	2785
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 4 6% 9% 43%	3520
September	1st to 10th	Night	11% 7% 3 6% 5% 6% 6% 4 7% 7% 38%	2090
	11th to 20th	Night	18% 6% 2 7% 5% 4 5% 4 5% 7% 37%	2090
	21st to end	Night	17% 4 2 7% 4 4 3 3 5% 6% 45%	2090
October	1st to 10th	Night	14% 5% 2 4 3 3 4 3 4 6% 52%	2090
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 4 55%	2275
	21st to end	Night	14% 4 1 3 3 2 3 2 4 5% 58%	2508
November	1st to 10th	Night	15% 5% 2 4 3 2 2 3 3 4 55%	2446
	11th to 20th	Night	16% 5% 2 4 3 3 2 3 3 5% 53%	2477
	21st to end	Night	18% 4 1 4 3 3 4 4 5% 6% 48%	2470
December	1st to 10th	Night	22% 6% 2 5% 4 4 3 2 4 5% 42%	2470
	11th to 20th	Night	17% 5% 2 4 3 2 3 2 4 4 54%	3042
	21st to end	Night	24% 6% 1 5% 3 4 4 3 5% 6% 38%	4532

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% 5% 7% 22% 23% 9%	2837
	11th to 20th	Day	36% 4 6% 15% 31% 8%	2840
	21st to end	Day	40% 3 6% 19% 23% 9%	3124
February	1st to 10th	Day	41% 5% 8% 20% 20% 7%	1852
	11th to 20th	Day	41% 5% 8% 17% 22% 7%	1858
	21st to end	Day	44% 6% 8% 14% 19% 9%	1570
March	1st to 10th	Day	45% 5% 9% 16% 15% 10%	3330
	11th to 20th	Day	32% 6% 8% 14% 27% 13%	3480
	21st to end	Day	42% 6% 8% 20% 20% 3	3815
April	1st to 10th	Day	33% 6% 11% 20% 23% 6%	2090
	11th to 20th	Day	36% 7% 8% 18% 21% 9%	2259
	21st to end	Day	31% 6% 12% 27% 20% 4	2470
May	1st to 10th	Day	39% 11% 13% 19% 14% 4	4120
	11th to 20th	Day	44% 10% 12% 20% 13% 1	4085
	21st to end	Day	31% 11% 16% 21% 19% 2	4489
June	1st to 10th	Day	39% 12% 17% 21% 7% 3	2470
	11th to 20th	Day	33% 13% 18% 22% 12% 2	2470
	21st to end	Day	35% 13% 17% 19% 13% 3	2470
July	1st to 10th	Day	39% 15% 21% 19% 6% 1	4055
	11th to 20th	Day	37% 13% 26% 19% 3 2	4051
	21st to end	Day	54% 15% 16% 11% 4	4324
August	1st to 10th	Day	41% 10% 15% 27% 6%	4091
	11th to 20th	Day	34% 10% 23% 18% 13% 2	4083
	21st to end	Day	30% 8% 15% 25% 20% 2	4098
September	1st to 10th	Day	37% 12% 15% 16% 17% 3	2090
	11th to 20th	Day	41% 10% 12% 17% 18% 2	2090
	21st to end	Day	37% 7% 13% 21% 17% 6%	2090
October	1st to 10th	Day	25% 5% 7% 19% 35% 10%	3480
	11th to 20th	Day	20% 3 6% 15% 29% 26%	3144
	21st to end	Day	29% 4 5% 22% 25% 15%	3428
November	1st to 10th	Day	32% 4 8% 18% 27% 11%	1848
	11th to 20th	Day	33% 4 7% 20% 27% 9%	1710
	21st to end	Day	35% 5% 8% 20% 26% 7%	1710
December	1st to 10th	Day	46% 5% 7% 18% 18% 7%	1710
	11th to 20th	Day	35% 6% 7% 19% 21% 12%	2150
	21st to end	Day	39% 5% 8% 21% 22% 4	3124
January	1st to 10th	Night	35% 5% 8% 17% 26% 8%	4109
	11th to 20th	Night	36% 5% 8% 16% 27% 9%	4120
	21st to end	Night	44% 4 7% 15% 24% 8%	4532
February	1st to 10th	Night	37% 6% 8% 20% 22% 7%	2323
	11th to 20th	Night	43% 4 5% 17% 23% 7%	2219
	21st to end	Night	43% 5% 9% 15% 20% 8%	1884
March	1st to 10th	Night	45% 6% 11% 14% 15% 8%	3523
	11th to 20th	Night	29% 6% 9% 16% 25% 15%	3480
	21st to end	Night	43% 5% 7% 17% 18% 9%	3817
April	1st to 10th	Night	34% 5% 9% 20% 25% 6%	2090
	11th to 20th	Night	33% 5% 8% 21% 23% 9%	1882
	21st to end	Night	33% 6% 11% 25% 21% 3	1710
May	1st to 10th	Night	39% 11% 13% 20% 15% 2	2840
	11th to 20th	Night	42% 9% 14% 19% 15% 1	2813
	21st to end	Night	30% 11% 16% 26% 15% 2	3087
June	1st to 10th	Night	41% 12% 15% 19% 10% 2	1710
	11th to 20th	Night	34% 10% 19% 23% 12% 1	1710
	21st to end	Night	33% 14% 17% 18% 14% 4	1710
July	1st to 10th	Night	49% 13% 17% 15% 5% 1	2795
	11th to 20th	Night	40% 15% 24% 17% 4 1	2786
	21st to end	Night	53% 15% 16% 11% 4 1	2988
August	1st to 10th	Night	44% 10% 21% 20% 5%	2814
	11th to 20th	Night	49% 11% 15% 14% 9% 1	2812
	21st to end	Night	35% 9% 15% 24% 15% 2	3520
September	1st to 10th	Night	41% 9% 14% 19% 13% 3	2090
	11th to 20th	Night	44% 10% 13% 16% 15% 2	2090
	21st to end	Night	40% 6% 11% 19% 17% 6%	2090
October	1st to 10th	Night	28% 7% 12% 13% 32% 8%	3480
	11th to 20th	Night	20% 3 6% 17% 30% 24%	3774
	21st to end	Night	29% 4 5% 19% 26% 17%	4120
November	1st to 10th	Night	33% 4 8% 18% 25% 11%	2446
	11th to 20th	Night	35% 4 5% 16% 28% 12%	2477
	21st to end	Night	36% 6% 7% 19% 25% 7%	2470
December	1st to 10th	Night	45% 4 8% 17% 19% 7%	2470
	11th to 20th	Night	35% 4 8% 17% 27% 10%	3044
	21st to end	Night	44% 6% 8% 20% 17% 5%	4532

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	26% 19% 37% 15% 3	270
	11th to 20th	Day	30% 20% 30% 17% 4	270
	21st to end	Day	25% 26% 35% 11% 3	297
February	1st to 10th	Day	23% 20% 39% 16% 3	270
	11th to 20th	Day	36% 19% 35% 9%	270
	21st to end	Day	34% 22% 36% 7% 1	225
March	1st to 10th	Day	23% 17% 32% 21% 7%	389
	11th to 20th	Day	22% 19% 33% 19% 5% 1	460
	21st to end	Day	23% 20% 29% 21% 6% 1	506
April	1st to 10th	Day	23% 14% 29% 23% 10% 2	460
	11th to 20th	Day	16% 16% 34% 22% 11% 2	452
	21st to end	Day	19% 10% 27% 26% 14% 5%	460
May	1st to 10th	Day	12% 14% 30% 26% 10% 7%	463
	11th to 20th	Day	20% 7% 20% 25% 20% 8%	487
	21st to end	Day	15% 7% 20% 27% 19% 12%	529
June	1st to 10th	Day	15% 5% 17% 31% 20% 12%	490
	11th to 20th	Day	8% 6% 16% 29% 23% 18%	490
	21st to end	Day	10% 3 20% 31% 22% 14%	490
July	1st to 10th	Day	9% 4 11% 25% 30% 20%	485
	11th to 20th	Day	7% 3 12% 25% 31% 22%	484
	21st to end	Day	6% 2 11% 31% 30% 20%	532
August	1st to 10th	Day	17% 4 15% 22% 25% 18%	486
	11th to 20th	Day	10% 4 12% 28% 30% 16%	479
	21st to end	Day	14% 3 10% 25% 32% 15%	539
September	1st to 10th	Day	9% 3 17% 28% 31% 12%	490
	11th to 20th	Day	18% 4 14% 21% 32% 10%	490
	21st to end	Day	20% 6% 14% 30% 23% 7%	490
October	1st to 10th	Day	19% 5% 18% 31% 19% 8%	490
	11th to 20th	Day	14% 7% 24% 33% 18% 3	490
	21st to end	Day	18% 8% 25% 29% 17% 4	539
November	1st to 10th	Day	22% 8% 29% 25% 13% 3	386
	11th to 20th	Day	18% 19% 31% 27% 5%	270
	21st to end	Day	14% 11% 38% 24% 10% 1	270
December	1st to 10th	Day	28% 17% 32% 19% 4	270
	11th to 20th	Day	24% 14% 36% 21% 5% 1	270
	21st to end	Day	31% 15% 32% 15% 4 2	297
January	1st to 10th	Night	21% 14% 33% 26% 6%	760
	11th to 20th	Night	21% 13% 32% 28% 6%	760
	21st to end	Night	22% 14% 36% 26% 3	836
February	1st to 10th	Night	17% 13% 31% 34% 5%	760
	11th to 20th	Night	23% 16% 33% 25% 3	743
	21st to end	Night	22% 15% 34% 25% 4	628
March	1st to 10th	Night	18% 12% 31% 33% 5%	760
	11th to 20th	Night	17% 12% 34% 28% 8% 1	760
	21st to end	Night	21% 12% 29% 29% 9%	836
April	1st to 10th	Night	16% 13% 29% 32% 10%	760
	11th to 20th	Night	16% 12% 24% 33% 14% 1	625
	21st to end	Night	13% 7% 22% 36% 20% 2	570
May	1st to 10th	Night	13% 7% 24% 33% 22% 1	570
	11th to 20th	Night	17% 5% 19% 31% 23% 5%	561
	21st to end	Night	15% 2 11% 31% 32% 8%	617
June	1st to 10th	Night	12% 3 12% 33% 33% 7%	570
	11th to 20th	Night	9% 2 14% 29% 32% 14%	570
	21st to end	Night	9% 1 11% 33% 38% 8%	570
July	1st to 10th	Night	12% 3 8% 24% 42% 12%	555
	11th to 20th	Night	11% 2 7% 23% 41% 15%	552
	21st to end	Night	8% 2 8% 28% 43% 12%	624
August	1st to 10th	Night	16% 1 7% 25% 38% 12%	567
	11th to 20th	Night	14% 4 9% 28% 35% 10%	564
	21st to end	Night	13% 3 7% 25% 40% 12%	658
September	1st to 10th	Night	13% 3 11% 28% 36% 9%	760
	11th to 20th	Night	20% 3 13% 26% 32% 6%	760
	21st to end	Night	18% 3 14% 34% 27% 4	760
October	1st to 10th	Night	16% 5% 18% 29% 26% 7%	760
	11th to 20th	Night	15% 5% 23% 34% 20% 3	760
	21st to end	Night	16% 7% 20% 37% 18% 3	836
November	1st to 10th	Night	17% 7% 20% 35% 18% 3	780
	11th to 20th	Night	18% 9% 25% 33% 13% 1	763
	21st to end	Night	19% 8% 25% 33% 13% 1	760
December	1st to 10th	Night	24% 11% 25% 32% 8% 1	760
	11th to 20th	Night	20% 8% 29% 33% 9% 1	760
	21st to end	Night	28% 10% 26% 31% 5%	836

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