Lake Hartwell State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Hartwell State Park 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	13% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	74888
	Night	14% 5% 2 5% 5% 3 4 4 5% 7% 44%	74864
Transparency	Day	26% 36% 7% 14% 13% 4	74611
	Night	26% 36% 6% 13% 14% 4	74660
Seeing	Day	18% 8% 21% 24% 19% 9%	13899
	Night	17% 8% 21% 30% 20% 4	24016

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	17% 5% 3 5% 5% 2 4 3 4 6% 46%	1706
	11th to 20th	Day	18% 7% 3 4 4 2 4 3 4 5% 44%	1638
	21st to end	Day	18% 6% 2 5% 3 2 3 4 4 6% 48%	1782
February	1st to 10th	Day	16% 5% 2 6% 5% 3 4 4 6% 6% 42%	1764
	11th to 20th	Day	21% 6% 2 5% 4 3 3 3 5% 5% 44%	1748
	21st to end	Day	21% 6% 3 5% 5% 3 3 4 4 6% 41%	1480
March	1st to 10th	Day	16% 5% 2 4 4 2 3 3 5% 6% 51%	1916
	11th to 20th	Day	18% 5% 3 5% 5% 3 4 4 5% 7% 41%	1980
	21st to end	Day	16% 5% 3 5% 5% 3 5% 5% 6% 7% 40%	2178
April	1st to 10th	Day	12% 4 2 4 4 3 5% 4 6% 8% 48%	1980
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 5% 4 7% 48%	2124
	21st to end	Day	10% 4 2 4 3 3 4 5% 5% 8% 52%	2340
May	1st to 10th	Day	10% 4 2 5% 4 3 5% 5% 6% 8% 48%	2340
	11th to 20th	Day	13% 6% 2 5% 6% 3 5% 6% 6% 9% 40%	2301
	21st to end	Day	11% 6% 2 5% 5% 4 4 6% 7% 11% 40%	2531
June	1st to 10th	Day	9% 5% 3 6% 7% 4 6% 7% 8% 12% 34%	2340
	11th to 20th	Day	5% 4 3 5% 6% 4 7% 7% 8% 11% 40%	2340
	21st to end	Day	6% 4 2 4 6% 4 8% 8% 9% 12% 38%	2340
July	1st to 10th	Day	9% 6% 3 6% 8% 5% 6% 8% 8% 11% 29%	2340
	11th to 20th	Day	8% 5% 3 6% 6% 5% 7% 7% 10% 13% 31%	2340
	21st to end	Day	6% 5% 2 6% 7% 4 7% 8% 8% 12% 35%	2547
August	1st to 10th	Day	10% 6% 3 6% 7% 5% 7% 8% 8% 12% 29%	2327
	11th to 20th	Day	11% 6% 3 7% 6% 4 7% 6% 8% 10% 32%	2303
	21st to end	Day	12% 7% 3 6% 7% 4 6% 6% 7% 10% 32%	2322
September	1st to 10th	Day	8% 5% 3 5% 6% 4 6% 7% 7% 8% 41%	1980
	11th to 20th	Day	14% 6% 2 5% 5% 3 5% 6% 5% 7% 43%	1980
	21st to end	Day	17% 4 2 4 4 2 3 5% 5% 7% 47%	1980
October	1st to 10th	Day	15% 4 2 4 3 2 2 3 4 6% 55%	1980
	11th to 20th	Day	13% 5% 2 4 3 2 2 3 3 5% 57%	1805
	21st to end	Day	13% 5% 1 4 3 2 3 3 3 4 58%	1980
November	1st to 10th	Day	13% 5% 2 3 4 2 3 2 4 5% 57%	1769
	11th to 20th	Day	15% 4 2 4 3 2 4 4 5% 6% 52%	1710
	21st to end	Day	15% 5% 2 4 4 3 3 4 5% 6% 50%	1710
December	1st to 10th	Day	23% 6% 3 5% 5% 2 3 4 5% 6% 39%	1710
	11th to 20th	Day	18% 5% 2 4 4 2 4 3 5% 5% 48%	2153
	21st to end	Day	24% 5% 2 4 4 2 3 4 4 7% 42%	3124
January	1st to 10th	Night	19% 5% 2 5% 4 2 4 4 3 4 47%	2459
	11th to 20th	Night	17% 5% 3 5% 4 3 5% 4 5% 6% 43%	2378
	21st to end	Night	17% 5% 3 5% 3 2 3 4 4 6% 49%	2574
February	1st to 10th	Night	16% 5% 3 4 5% 3 4 3 5% 6% 47%	2192
	11th to 20th	Night	21% 6% 2 5% 4 2 4 3 4 5% 45%	2098
	21st to end	Night	20% 6% 2 4 4 3 4 4 5% 7% 41%	1776
March	1st to 10th	Night	15% 6% 2 4 4 2 3 4 5% 6% 50%	2044
	11th to 20th	Night	16% 5% 3 4 5% 3 5% 5% 5% 6% 43%	1980
	21st to end	Night	15% 6% 3 5% 4 2 4 5% 6% 6% 44%	2178
April	1st to 10th	Night	13% 3 2 4 4 3 4 5% 5% 7% 51%	1980
	11th to 20th	Night	11% 5% 2 5% 5% 2 3 3 4 8% 51%	1798
	21st to end	Night	11% 5% 2 4 5% 3 4 4 5% 7% 52%	1620
May	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 5% 8% 48%	1620
	11th to 20th	Night	12% 5% 3 5% 6% 4 5% 5% 7% 8% 39%	1592
	21st to end	Night	10% 6% 3 6% 6% 3 6% 5% 7% 8% 40%	1744
June	1st to 10th	Night	10% 4 3 6% 7% 3 6% 7% 9% 11% 34%	1620
	11th to 20th	Night	7% 4 2 6% 5% 3 7% 5% 7% 12% 41%	1620
	21st to end	Night	8% 5% 2 5% 5% 3 6% 7% 9% 11% 39%	1620
July	1st to 10th	Night	9% 5% 3 7% 6% 4 6% 8% 9% 12% 29%	1620
	11th to 20th	Night	8% 4 3 6% 6% 5% 7% 7% 10% 14% 31%	1620
	21st to end	Night	6% 5% 3 7% 8% 4 7% 7% 9% 12% 32%	1771
August	1st to 10th	Night	11% 7% 3 6% 7% 5% 6% 7% 10% 11% 28%	1611
	11th to 20th	Night	11% 5% 3 6% 8% 5% 6% 6% 6% 11% 33%	1598
	21st to end	Night	12% 8% 3 7% 6% 4 6% 6% 7% 9% 31%	2011
September	1st to 10th	Night	9% 5% 3 6% 6% 3 6% 6% 7% 9% 40%	1980
	11th to 20th	Night	15% 6% 3 5% 4 4 4 5% 6% 8% 39%	1980
	21st to end	Night	14% 5% 3 5% 4 2 4 4 5% 7% 47%	1980
October	1st to 10th	Night	14% 4 2 4 4 2 3 4 5% 6% 53%	1980
	11th to 20th	Night	14% 4 2 4 5% 2 4 4 4 5% 54%	2154
	21st to end	Night	13% 3 2 3 3 2 3 3 5% 5% 58%	2376
November	1st to 10th	Night	13% 5% 2 3 3 2 3 2 3 5% 57%	2306
	11th to 20th	Night	16% 5% 2 4 3 2 3 3 3 6% 53%	2470
	21st to end	Night	16% 4 2 4 4 3 5% 3 5% 6% 48%	2470
December	1st to 10th	Night	19% 7% 2 5% 5% 3 4 3 5% 5% 42%	2470
	11th to 20th	Night	18% 5% 2 3 3 2 3 3 4 5% 53%	3042
	21st to end	Night	20% 6% 3 5% 6% 3 5% 4 5% 7% 37%	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	24% 39% 4 14% 15% 3	1707
	11th to 20th	Day	27% 40% 4 11% 15% 3	1638
	21st to end	Day	28% 36% 3 14% 15% 5%	1782
February	1st to 10th	Day	29% 35% 5% 12% 14% 4	1764
	11th to 20th	Day	28% 36% 3 14% 15% 5%	1758
	21st to end	Day	29% 35% 6% 11% 14% 5%	1480
March	1st to 10th	Day	22% 35% 5% 15% 17% 6%	1916
	11th to 20th	Day	29% 36% 7% 11% 11% 5%	1980
	21st to end	Day	30% 36% 6% 15% 12% 1	2178
April	1st to 10th	Day	22% 35% 7% 15% 17% 5%	1980
	11th to 20th	Day	23% 34% 3 15% 17% 8%	2124
	21st to end	Day	20% 36% 6% 21% 14% 3	2340
May	1st to 10th	Day	25% 36% 10% 13% 11% 4	2340
	11th to 20th	Day	28% 38% 11% 13% 11% 1	2305
	21st to end	Day	23% 37% 9% 18% 12% 1	2531
June	1st to 10th	Day	26% 38% 12% 16% 7% 1	2340
	11th to 20th	Day	23% 38% 12% 17% 9% 1	2340
	21st to end	Day	22% 39% 10% 14% 10% 4	2340
July	1st to 10th	Day	31% 39% 10% 10% 7% 2	2275
	11th to 20th	Day	26% 41% 12% 10% 7% 4	2271
	21st to end	Day	26% 40% 16% 11% 7%	2405
August	1st to 10th	Day	27% 39% 12% 16% 6%	2314
	11th to 20th	Day	31% 37% 11% 14% 6% 1	2303
	21st to end	Day	34% 37% 9% 12% 6% 2	2322
September	1st to 10th	Day	27% 38% 8% 12% 12% 3	1980
	11th to 20th	Day	29% 37% 6% 13% 15% 2	1980
	21st to end	Day	24% 36% 5% 14% 15% 6%	1980
October	1st to 10th	Day	20% 35% 4 13% 23% 5%	1980
	11th to 20th	Day	24% 34% 4 14% 16% 7%	1805
	21st to end	Day	20% 36% 3 13% 22% 7%	1980
November	1st to 10th	Day	14% 39% 5% 11% 22% 9%	1769
	11th to 20th	Day	22% 39% 3 14% 18% 5%	1710
	21st to end	Day	24% 38% 3 13% 16% 5%	1710
December	1st to 10th	Day	28% 39% 4 12% 13% 5%	1710
	11th to 20th	Day	28% 31% 4 14% 15% 7%	2150
	21st to end	Day	31% 23% 4 18% 21% 2	3124
January	1st to 10th	Night	24% 39% 5% 13% 17% 3	2459
	11th to 20th	Night	27% 40% 3 13% 13% 3	2378
	21st to end	Night	28% 36% 3 12% 16% 5%	2574
February	1st to 10th	Night	27% 34% 5% 13% 15% 5%	2192
	11th to 20th	Night	28% 35% 3 12% 16% 6%	2099
	21st to end	Night	28% 35% 5% 11% 14% 6%	1776
March	1st to 10th	Night	23% 35% 4 13% 18% 7%	2044
	11th to 20th	Night	27% 37% 8% 10% 15% 4	1980
	21st to end	Night	27% 36% 6% 14% 14% 2	2178
April	1st to 10th	Night	21% 35% 7% 15% 17% 4	1980
	11th to 20th	Night	20% 34% 3 15% 21% 8%	1798
	21st to end	Night	22% 36% 6% 17% 15% 4	1620
May	1st to 10th	Night	26% 36% 10% 13% 14% 2	1620
	11th to 20th	Night	31% 38% 10% 12% 9% 1	1593
	21st to end	Night	26% 37% 9% 18% 8% 2	1745
June	1st to 10th	Night	26% 38% 12% 14% 9% 1	1620
	11th to 20th	Night	24% 37% 11% 17% 10% 1	1620
	21st to end	Night	23% 39% 12% 12% 10% 4	1620
July	1st to 10th	Night	33% 40% 12% 7% 7% 1	1575
	11th to 20th	Night	28% 42% 13% 9% 6% 2	1566
	21st to end	Night	27% 41% 16% 11% 4 1	1672
August	1st to 10th	Night	27% 38% 14% 15% 5%	1600
	11th to 20th	Night	31% 36% 10% 14% 8% 1	1598
	21st to end	Night	37% 38% 10% 9% 5% 1	2011
September	1st to 10th	Night	28% 38% 9% 13% 9% 3	1980
	11th to 20th	Night	30% 37% 7% 12% 13% 2	1980
	21st to end	Night	24% 36% 6% 13% 16% 6%	1980
October	1st to 10th	Night	22% 35% 5% 11% 23% 5%	1980
	11th to 20th	Night	25% 35% 4 14% 16% 6%	2154
	21st to end	Night	20% 36% 4 15% 19% 7%	2376
November	1st to 10th	Night	15% 39% 4 12% 20% 10%	2306
	11th to 20th	Night	23% 38% 3 12% 18% 7%	2470
	21st to end	Night	25% 38% 2 13% 16% 6%	2470
December	1st to 10th	Night	25% 39% 4 13% 14% 5%	2470
	11th to 20th	Night	25% 31% 6% 12% 22% 4	3044
	21st to end	Night	35% 24% 4 19% 16% 3	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	23% 16% 37% 20% 4	270
	11th to 20th	Day	28% 18% 26% 22% 6%	246
	21st to end	Day	26% 22% 31% 16% 3 1	264
February	1st to 10th	Day	23% 18% 40% 16% 3	240
	11th to 20th	Day	37% 18% 29% 15% 2	240
	21st to end	Day	37% 15% 36% 10% 2	198
March	1st to 10th	Day	22% 12% 31% 26% 8%	356
	11th to 20th	Day	22% 15% 37% 15% 10%	420
	21st to end	Day	24% 15% 32% 19% 10% 1	462
April	1st to 10th	Day	21% 15% 26% 24% 13% 1	420
	11th to 20th	Day	15% 12% 34% 22% 13% 3	412
	21st to end	Day	17% 8% 28% 22% 18% 7%	420
May	1st to 10th	Day	12% 13% 31% 23% 14% 7%	423
	11th to 20th	Day	16% 6% 17% 29% 20% 13%	447
	21st to end	Day	18% 4 15% 24% 25% 14%	485
June	1st to 10th	Day	13% 4 13% 34% 23% 14%	450
	11th to 20th	Day	9% 4 13% 29% 24% 20%	450
	21st to end	Day	10% 2 17% 31% 23% 17%	450
July	1st to 10th	Day	11% 2 9% 22% 30% 26%	445
	11th to 20th	Day	11% 2 7% 25% 37% 18%	444
	21st to end	Day	7% 2 7% 29% 36% 20%	488
August	1st to 10th	Day	16% 4 10% 25% 26% 20%	446
	11th to 20th	Day	14% 3 5% 29% 30% 18%	439
	21st to end	Day	16% 2 8% 26% 29% 19%	495
September	1st to 10th	Day	11% 1 11% 28% 32% 17%	450
	11th to 20th	Day	19% 2 9% 22% 35% 13%	450
	21st to end	Day	20% 3 16% 25% 25% 10%	450
October	1st to 10th	Day	20% 4 16% 31% 19% 10%	450
	11th to 20th	Day	14% 7% 22% 30% 22% 6%	450
	21st to end	Day	20% 7% 22% 28% 20% 3	495
November	1st to 10th	Day	22% 7% 23% 27% 17% 5%	367
	11th to 20th	Day	20% 13% 34% 26% 6% 1	270
	21st to end	Day	16% 10% 36% 24% 13% 2	270
December	1st to 10th	Day	32% 10% 30% 22% 5%	270
	11th to 20th	Day	26% 11% 37% 19% 6% 1	270
	21st to end	Day	34% 13% 27% 16% 7% 2	297
January	1st to 10th	Night	23% 16% 28% 27% 6%	760
	11th to 20th	Night	21% 15% 28% 28% 8%	732
	21st to end	Night	21% 17% 32% 27% 3	792
February	1st to 10th	Night	19% 14% 29% 32% 5%	720
	11th to 20th	Night	25% 14% 32% 25% 4	703
	21st to end	Night	23% 14% 32% 27% 4	592
March	1st to 10th	Night	19% 12% 31% 33% 5%	720
	11th to 20th	Night	18% 12% 34% 25% 11% 1	720
	21st to end	Night	18% 13% 29% 30% 9% 1	792
April	1st to 10th	Night	15% 14% 28% 30% 12%	720
	11th to 20th	Night	14% 10% 27% 32% 16% 1	603
	21st to end	Night	14% 7% 25% 32% 22% 1	540
May	1st to 10th	Night	11% 8% 25% 34% 21% 1	540
	11th to 20th	Night	16% 4 19% 34% 23% 5%	531
	21st to end	Night	14% 3 10% 36% 33% 5%	584
June	1st to 10th	Night	12% 3 11% 34% 34% 7%	540
	11th to 20th	Night	10% 2 13% 28% 34% 13%	540
	21st to end	Night	9% 2 11% 33% 35% 10%	540
July	1st to 10th	Night	12% 2 7% 29% 37% 13%	525
	11th to 20th	Night	10% 2 4 27% 44% 13%	522
	21st to end	Night	7% 2 5% 31% 45% 10%	591
August	1st to 10th	Night	14% 1 6% 28% 38% 13%	537
	11th to 20th	Night	13% 1 7% 30% 40% 10%	534
	21st to end	Night	15% 3 6% 24% 41% 10%	630
September	1st to 10th	Night	11% 2 9% 28% 40% 11%	720
	11th to 20th	Night	18% 2 10% 27% 37% 6%	720
	21st to end	Night	16% 3 13% 32% 31% 4	720
October	1st to 10th	Night	15% 4 19% 27% 27% 7%	720
	11th to 20th	Night	15% 5% 22% 33% 21% 4	720
	21st to end	Night	15% 7% 22% 33% 21% 2	792
November	1st to 10th	Night	16% 7% 21% 34% 20% 3	740
	11th to 20th	Night	18% 11% 27% 31% 12% 1	760
	21st to end	Night	18% 9% 25% 32% 15% 1	760
December	1st to 10th	Night	22% 12% 25% 31% 10%	760
	11th to 20th	Night	22% 12% 25% 30% 11% 1	760
	21st to end	Night	27% 12% 25% 30% 7%	836

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