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 2024-01-13.

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 4 5% 3 5% 5% 6% 8% 43%	74887
	Night	16% 5% 2 5% 5% 3 4 4 5% 7% 45%	74860
Transparency	Day	38% 9% 12% 19% 17% 5%	74610
	Night	38% 7% 11% 18% 19% 6%	74656
Seeing	Day	18% 10% 23% 24% 17% 8%	13880
	Night	17% 8% 22% 30% 19% 4	23998

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	19% 4 2 4 4 2 3 4 3 6% 49%	1706
	11th to 20th	Day	20% 5% 2 5% 4 2 3 4 3 5% 46%	1638
	21st to end	Day	17% 4 2 4 3 3 3 4 4 5% 51%	1782
February	1st to 10th	Day	17% 5% 3 5% 3 3 4 4 5% 7% 44%	1755
	11th to 20th	Day	22% 5% 2 4 4 2 4 4 5% 6% 44%	1748
	21st to end	Day	22% 5% 2 5% 5% 3 4 3 3 5% 42%	1480
March	1st to 10th	Day	17% 5% 2 3 3 2 4 4 4 6% 50%	1912
	11th to 20th	Day	20% 5% 3 4 3 3 5% 5% 4 6% 41%	1980
	21st to end	Day	19% 5% 2 4 5% 3 5% 5% 5% 7% 40%	2178
April	1st to 10th	Day	13% 3 2 4 3 3 4 5% 7% 8% 47%	1980
	11th to 20th	Day	14% 4 2 4 6% 4 5% 4 4 7% 47%	2138
	21st to end	Day	12% 4 1 4 4 3 4 5% 4 9% 51%	2340
May	1st to 10th	Day	11% 5% 2 5% 5% 3 6% 5% 5% 8% 46%	2340
	11th to 20th	Day	14% 6% 3 4 6% 4 6% 5% 6% 8% 38%	2301
	21st to end	Day	12% 4 2 6% 5% 4 5% 5% 7% 11% 39%	2531
June	1st to 10th	Day	11% 5% 2 5% 6% 3 6% 7% 9% 11% 34%	2340
	11th to 20th	Day	6% 4 2 4 6% 5% 7% 8% 8% 12% 38%	2340
	21st to end	Day	8% 4 1 5% 7% 4 8% 8% 7% 10% 38%	2340
July	1st to 10th	Day	9% 6% 3 7% 7% 5% 8% 8% 8% 11% 29%	2340
	11th to 20th	Day	9% 5% 3 5% 7% 5% 8% 9% 9% 12% 29%	2340
	21st to end	Day	6% 4 3 6% 7% 6% 8% 9% 8% 11% 31%	2547
August	1st to 10th	Day	12% 5% 2 6% 7% 5% 7% 7% 8% 10% 31%	2327
	11th to 20th	Day	11% 5% 2 6% 7% 5% 7% 6% 8% 10% 34%	2303
	21st to end	Day	12% 7% 3 5% 6% 4 6% 8% 8% 10% 33%	2336
September	1st to 10th	Day	10% 5% 2 6% 6% 3 7% 7% 6% 10% 39%	1980
	11th to 20th	Day	16% 5% 2 5% 5% 4 6% 5% 5% 7% 39%	1980
	21st to end	Day	16% 4 2 4 3 3 5% 4 5% 7% 46%	1980
October	1st to 10th	Day	16% 5% 1 2 4 2 3 4 4 5% 55%	1980
	11th to 20th	Day	14% 4 2 4 4 2 2 3 4 5% 57%	1804
	21st to end	Day	15% 4 1 4 3 2 2 3 3 4 58%	1980
November	1st to 10th	Day	13% 4 1 3 4 1 3 2 3 5% 60%	1754
	11th to 20th	Day	16% 4 3 3 3 2 3 3 4 6% 54%	1710
	21st to end	Day	17% 3 2 3 3 2 3 4 5% 7% 50%	1710
December	1st to 10th	Day	23% 5% 3 4 5% 2 4 4 4 6% 40%	1710
	11th to 20th	Day	18% 4 2 4 4 2 3 3 4 6% 50%	2153
	21st to end	Day	24% 4 1 3 3 2 3 3 5% 7% 45%	3124
January	1st to 10th	Night	20% 4 2 4 4 3 3 3 4 5% 49%	2459
	11th to 20th	Night	19% 5% 2 4 4 3 4 4 4 6% 45%	2378
	21st to end	Night	17% 6% 2 5% 4 2 4 3 4 4 50%	2574
February	1st to 10th	Night	16% 4 2 4 4 2 4 5% 4 5% 49%	2200
	11th to 20th	Night	22% 5% 2 4 4 3 3 3 4 5% 44%	2098
	21st to end	Night	21% 5% 2 4 6% 3 4 4 4 7% 41%	1776
March	1st to 10th	Night	14% 6% 2 4 4 2 4 4 4 6% 49%	2048
	11th to 20th	Night	17% 5% 2 4 4 3 4 4 5% 6% 44%	1980
	21st to end	Night	18% 5% 3 5% 4 2 4 4 5% 6% 43%	2178
April	1st to 10th	Night	13% 5% 2 4 3 3 4 4 4 6% 52%	1980
	11th to 20th	Night	14% 5% 2 4 4 2 4 3 5% 6% 52%	1782
	21st to end	Night	11% 4 2 5% 4 2 4 4 5% 7% 52%	1620
May	1st to 10th	Night	12% 4 2 4 5% 3 5% 5% 6% 6% 48%	1620
	11th to 20th	Night	14% 6% 3 5% 5% 4 5% 5% 6% 8% 38%	1592
	21st to end	Night	13% 6% 2 6% 5% 4 5% 5% 6% 9% 40%	1744
June	1st to 10th	Night	10% 6% 3 6% 7% 3 6% 7% 7% 9% 36%	1620
	11th to 20th	Night	8% 4 3 4 7% 3 5% 6% 6% 12% 42%	1620
	21st to end	Night	8% 4 2 5% 5% 4 5% 6% 9% 12% 39%	1620
July	1st to 10th	Night	11% 6% 3 7% 8% 4 6% 7% 7% 12% 29%	1620
	11th to 20th	Night	10% 5% 2 5% 8% 5% 6% 8% 9% 12% 30%	1620
	21st to end	Night	6% 5% 3 8% 6% 4 7% 7% 9% 11% 34%	1771
August	1st to 10th	Night	13% 6% 2 6% 5% 4 6% 6% 8% 11% 32%	1611
	11th to 20th	Night	14% 6% 3 6% 6% 5% 6% 6% 6% 10% 32%	1598
	21st to end	Night	12% 6% 3 6% 7% 5% 5% 7% 7% 10% 34%	1996
September	1st to 10th	Night	11% 6% 3 5% 6% 4 6% 6% 7% 7% 38%	1980
	11th to 20th	Night	17% 6% 2 6% 5% 3 4 6% 4 8% 38%	1980
	21st to end	Night	16% 4 2 5% 5% 3 4 4 5% 6% 46%	1980
October	1st to 10th	Night	15% 5% 2 4 3 3 3 4 4 6% 52%	1980
	11th to 20th	Night	14% 5% 2 5% 4 2 3 4 4 4 53%	2155
	21st to end	Night	14% 3 1 3 3 2 3 3 4 5% 58%	2376
November	1st to 10th	Night	14% 4 2 4 3 2 3 3 3 5% 58%	2320
	11th to 20th	Night	16% 4 2 4 3 2 3 3 3 5% 53%	2470
	21st to end	Night	18% 3 1 4 3 2 4 5% 5% 6% 48%	2470
December	1st to 10th	Night	22% 5% 3 4 5% 3 3 3 4 6% 42%	2470
	11th to 20th	Night	17% 5% 2 3 3 2 3 3 4 5% 54%	3042
	21st to end	Night	24% 5% 2 4 4 2 4 4 5% 7% 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	37% 5% 7% 21% 22% 7%	1707
	11th to 20th	Day	43% 5% 7% 18% 21% 6%	1638
	21st to end	Day	36% 3 7% 22% 24% 8%	1782
February	1st to 10th	Day	41% 5% 9% 20% 18% 7%	1755
	11th to 20th	Day	41% 6% 9% 17% 22% 6%	1758
	21st to end	Day	45% 6% 8% 14% 18% 10%	1480
March	1st to 10th	Day	36% 5% 8% 19% 23% 10%	1912
	11th to 20th	Day	43% 6% 10% 16% 17% 8%	1980
	21st to end	Day	42% 7% 11% 20% 18% 3	2178
April	1st to 10th	Day	33% 6% 11% 21% 23% 6%	1980
	11th to 20th	Day	37% 7% 8% 19% 21% 9%	2138
	21st to end	Day	31% 6% 12% 27% 20% 4	2340
May	1st to 10th	Day	34% 9% 14% 20% 18% 5%	2340
	11th to 20th	Day	41% 11% 14% 19% 13% 2	2305
	21st to end	Day	37% 11% 15% 21% 14% 1	2531
June	1st to 10th	Day	39% 12% 17% 21% 8% 2	2340
	11th to 20th	Day	34% 13% 19% 21% 11% 2	2340
	21st to end	Day	36% 13% 17% 19% 11% 3	2340
July	1st to 10th	Day	43% 14% 16% 16% 9% 2	2275
	11th to 20th	Day	40% 17% 21% 14% 6% 3	2271
	21st to end	Day	38% 16% 20% 18% 7%	2405
August	1st to 10th	Day	43% 14% 16% 20% 7%	2314
	11th to 20th	Day	41% 13% 19% 18% 7% 1	2303
	21st to end	Day	42% 12% 17% 18% 9% 2	2336
September	1st to 10th	Day	37% 12% 15% 16% 16% 4	1980
	11th to 20th	Day	40% 10% 12% 17% 19% 2	1980
	21st to end	Day	37% 7% 11% 22% 17% 7%	1980
October	1st to 10th	Day	31% 6% 9% 20% 27% 7%	1980
	11th to 20th	Day	30% 4 10% 22% 23% 10%	1804
	21st to end	Day	31% 4 6% 20% 28% 12%	1980
November	1st to 10th	Day	29% 5% 8% 18% 29% 11%	1754
	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	39% 4 8% 17% 24% 7%	2459
	11th to 20th	Night	41% 5% 9% 17% 23% 5%	2378
	21st to end	Night	39% 3 6% 19% 25% 8%	2574
February	1st to 10th	Night	38% 6% 9% 20% 21% 7%	2200
	11th to 20th	Night	43% 4 5% 18% 23% 6%	2099
	21st to end	Night	44% 5% 9% 15% 19% 8%	1776
March	1st to 10th	Night	36% 4 8% 17% 22% 12%	2048
	11th to 20th	Night	40% 7% 11% 15% 20% 7%	1980
	21st to end	Night	41% 6% 10% 20% 19% 4	2178
April	1st to 10th	Night	33% 5% 9% 20% 25% 6%	1980
	11th to 20th	Night	34% 5% 8% 22% 23% 10%	1782
	21st to end	Night	33% 6% 11% 25% 22% 3	1620
May	1st to 10th	Night	34% 9% 13% 21% 20% 3	1620
	11th to 20th	Night	41% 10% 15% 19% 14% 1	1593
	21st to end	Night	39% 11% 13% 24% 12% 2	1745
June	1st to 10th	Night	41% 12% 16% 20% 10% 2	1620
	11th to 20th	Night	34% 11% 20% 23% 11% 1	1620
	21st to end	Night	33% 15% 17% 18% 12% 4	1620
July	1st to 10th	Night	44% 15% 18% 13% 8% 1	1575
	11th to 20th	Night	39% 18% 22% 14% 6% 2	1566
	21st to end	Night	37% 17% 21% 18% 6% 1	1672
August	1st to 10th	Night	44% 12% 19% 18% 7%	1600
	11th to 20th	Night	44% 14% 16% 15% 10% 2	1598
	21st to end	Night	43% 12% 17% 19% 7% 3	1996
September	1st to 10th	Night	41% 10% 14% 19% 13% 4	1980
	11th to 20th	Night	43% 10% 13% 16% 16% 2	1980
	21st to end	Night	38% 6% 11% 20% 18% 6%	1980
October	1st to 10th	Night	33% 7% 12% 15% 27% 6%	1980
	11th to 20th	Night	33% 5% 10% 21% 21% 10%	2155
	21st to end	Night	29% 4 6% 20% 28% 12%	2376
November	1st to 10th	Night	32% 4 8% 18% 26% 12%	2320
	11th to 20th	Night	35% 4 5% 16% 28% 12%	2470
	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% 18% 30% 18% 4	246
	21st to end	Day	23% 27% 35% 11% 3	264
February	1st to 10th	Day	23% 20% 39% 15% 3	240
	11th to 20th	Day	38% 18% 37% 8%	240
	21st to end	Day	34% 21% 36% 8% 2	198
March	1st to 10th	Day	21% 17% 34% 21% 7%	352
	11th to 20th	Day	23% 20% 32% 19% 6% 1	420
	21st to end	Day	24% 19% 28% 22% 6% 1	462
April	1st to 10th	Day	21% 14% 28% 24% 10% 2	420
	11th to 20th	Day	15% 16% 33% 22% 12% 2	412
	21st to end	Day	19% 10% 25% 26% 15% 5%	420
May	1st to 10th	Day	12% 14% 31% 26% 9% 7%	423
	11th to 20th	Day	19% 6% 20% 25% 21% 9%	447
	21st to end	Day	16% 6% 17% 27% 20% 13%	485
June	1st to 10th	Day	15% 4 16% 31% 20% 13%	450
	11th to 20th	Day	8% 6% 15% 28% 24% 19%	450
	21st to end	Day	10% 3 20% 31% 21% 14%	450
July	1st to 10th	Day	10% 4 11% 26% 30% 20%	445
	11th to 20th	Day	8% 2 12% 26% 31% 22%	444
	21st to end	Day	5% 1 10% 30% 32% 21%	488
August	1st to 10th	Day	17% 3 14% 21% 25% 19%	446
	11th to 20th	Day	10% 3 10% 28% 31% 17%	439
	21st to end	Day	16% 3 11% 24% 31% 15%	495
September	1st to 10th	Day	10% 2 16% 27% 33% 13%	450
	11th to 20th	Day	16% 4 14% 22% 34% 11%	450
	21st to end	Day	18% 6% 14% 31% 24% 7%	450
October	1st to 10th	Day	21% 5% 18% 29% 19% 9%	450
	11th to 20th	Day	16% 8% 24% 32% 18% 3	450
	21st to end	Day	18% 8% 26% 29% 15% 4	495
November	1st to 10th	Day	21% 7% 28% 26% 14% 3	352
	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	22% 12% 32% 29% 6%	732
	21st to end	Night	21% 14% 36% 26% 3	792
February	1st to 10th	Night	18% 13% 32% 33% 5%	720
	11th to 20th	Night	23% 16% 33% 25% 3	703
	21st to end	Night	22% 15% 33% 26% 4	592
March	1st to 10th	Night	17% 12% 33% 34% 4	720
	11th to 20th	Night	17% 12% 33% 28% 9% 1	720
	21st to end	Night	20% 12% 29% 29% 10%	792
April	1st to 10th	Night	15% 13% 28% 33% 10%	720
	11th to 20th	Night	16% 11% 24% 32% 15% 2	592
	21st to end	Night	13% 7% 21% 37% 21% 2	540
May	1st to 10th	Night	13% 7% 23% 33% 22% 1	540
	11th to 20th	Night	17% 5% 19% 31% 24% 5%	531
	21st to end	Night	16% 2 10% 29% 34% 9%	584
June	1st to 10th	Night	13% 2 12% 33% 34% 7%	540
	11th to 20th	Night	9% 2 14% 29% 32% 15%	540
	21st to end	Night	9% 1 11% 33% 38% 8%	540
July	1st to 10th	Night	12% 2 8% 24% 42% 13%	525
	11th to 20th	Night	11% 2 7% 23% 41% 16%	522
	21st to end	Night	7% 1 8% 28% 44% 12%	591
August	1st to 10th	Night	17% 1 7% 24% 39% 12%	537
	11th to 20th	Night	15% 3 9% 27% 36% 10%	534
	21st to end	Night	14% 3 7% 26% 39% 12%	623
September	1st to 10th	Night	13% 3 11% 28% 37% 10%	720
	11th to 20th	Night	19% 2 13% 26% 34% 6%	720
	21st to end	Night	17% 2 14% 35% 28% 4	720
October	1st to 10th	Night	17% 5% 18% 27% 26% 7%	720
	11th to 20th	Night	15% 6% 22% 33% 20% 3	720
	21st to end	Night	16% 7% 20% 37% 18% 3	792
November	1st to 10th	Night	16% 6% 20% 35% 19% 3	740
	11th to 20th	Night	18% 9% 25% 34% 13% 1	760
	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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