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 2025-12-18.

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 6% 4 4 4 4 6% 8% 43%	126994
	Night	14% 6% 2 6% 4 4 4 3 6% 7% 44%	124038
Transparency	Day	38% 6% 11% 20% 18% 6%	130731
	Night	38% 5% 10% 19% 21% 7%	128370
Seeing	Day	18% 8% 22% 24% 19% 9%	16508
	Night	17% 9% 21% 30% 20% 4	26558

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	15% 5% 2 4 3 3 3 3 4 5% 53%	4056
	11th to 20th	Day	12% 5% 2 4 3 2 3 2 4 3 60%	4060
	21st to end	Day	21% 6% 2 6% 3 3 3 3 4 6% 44%	4466
February	1st to 10th	Day	15% 6% 3 6% 5% 4 3 4 6% 5% 43%	1960
	11th to 20th	Day	22% 7% 2 5% 3 3 3 2 5% 5% 43%	1948
	21st to end	Day	19% 6% 2 5% 4 4 3 3 4 6% 43%	1650
March	1st to 10th	Day	21% 8% 3 6% 4 3 3 3 4 6% 39%	4792
	11th to 20th	Day	10% 4 2 6% 4 4 3 3 5% 6% 54%	4980
	21st to end	Day	17% 6% 3 6% 5% 4 4 3 4 5% 45%	5465
April	1st to 10th	Day	12% 4 2 5% 4 5% 4 4 6% 7% 47%	2200
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 3 5% 6% 49%	2364
	21st to end	Day	11% 5% 2 4 3 5% 3 3 6% 8% 50%	2600
May	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 6% 9% 37%	5862
	11th to 20th	Day	18% 7% 3 7% 5% 4 5% 5% 7% 9% 30%	5861
	21st to end	Day	13% 6% 2 6% 4 4 4 4 6% 8% 42%	6433
June	1st to 10th	Day	9% 6% 2 7% 6% 5% 6% 6% 8% 11% 34%	2600
	11th to 20th	Day	5% 4 2 6% 5% 6% 7% 5% 9% 12% 40%	2600
	21st to end	Day	6% 3 2 5% 5% 6% 7% 6% 9% 12% 40%	2600
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 6% 6% 8% 11% 37%	5900
	11th to 20th	Day	5% 4 2 6% 5% 6% 7% 5% 9% 13% 37%	5900
	21st to end	Day	9% 6% 3 9% 7% 6% 8% 6% 9% 11% 27%	6424
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 5% 8% 11% 31%	4234
	11th to 20th	Day	9% 5% 2 7% 4 5% 5% 5% 7% 10% 40%	4174
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 8% 51%	4199
September	1st to 10th	Day	8% 5% 2 6% 5% 5% 7% 5% 7% 8% 42%	2200
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 6% 7% 42%	2200
	21st to end	Day	17% 4 2 5% 4 3 3 4 5% 7% 45%	2200
October	1st to 10th	Day	14% 5% 2 5% 2 3 3 3 4 6% 54%	2200
	11th to 20th	Day	12% 5% 1 4 3 3 2 3 3 5% 59%	2005
	21st to end	Day	13% 5% 1 5% 3 3 3 2 3 4 58%	2200
November	1st to 10th	Day	14% 5% 2 4 3 2 2 2 4 5% 56%	1959
	11th to 20th	Day	14% 4 1 4 3 3 4 3 5% 6% 53%	1890
	21st to end	Day	14% 6% 1 5% 3 3 3 3 5% 6% 51%	1890
December	1st to 10th	Day	19% 5% 2 4 3 3 3 3 4 6% 48%	3020
	11th to 20th	Day	17% 5% 2 6% 4 4 4 4 5% 5% 43%	3436
	21st to end	Day	24% 5% 2 4 3 2 3 3 4 7% 44%	4466
January	1st to 10th	Night	15% 4 2 4 3 3 3 2 3 5% 56%	5889
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 5% 52%	5900
	21st to end	Night	19% 6% 2 4 3 3 3 3 4 6% 48%	6490
February	1st to 10th	Night	15% 6% 3 5% 4 4 3 3 5% 6% 48%	2435
	11th to 20th	Night	22% 6% 2 5% 4 3 4 3 4 4 44%	2338
	21st to end	Night	17% 6% 2 5% 4 3 4 4 5% 6% 44%	1980
March	1st to 10th	Night	20% 6% 2 6% 4 3 4 3 6% 7% 40%	5061
	11th to 20th	Night	9% 3 2 4 3 3 4 4 6% 8% 55%	4980
	21st to end	Night	16% 5% 2 5% 4 4 4 3 5% 6% 46%	5467
April	1st to 10th	Night	13% 3 2 5% 4 4 4 4 5% 6% 50%	2200
	11th to 20th	Night	11% 5% 2 6% 4 3 3 2 5% 8% 51%	1999
	21st to end	Night	10% 5% 1 6% 5% 4 3 4 5% 7% 50%	1800
May	1st to 10th	Night	11% 7% 3 8% 5% 5% 5% 4 6% 9% 36%	4033
	11th to 20th	Night	21% 6% 3 6% 5% 5% 4 4 6% 9% 31%	4032
	21st to end	Night	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	4421
June	1st to 10th	Night	9% 5% 3 7% 6% 6% 6% 5% 9% 11% 34%	1800
	11th to 20th	Night	8% 5% 2 6% 5% 4 7% 4 8% 12% 41%	1800
	21st to end	Night	7% 5% 2 6% 4 6% 5% 6% 9% 11% 40%	1800
July	1st to 10th	Night	10% 6% 3 9% 6% 6% 7% 6% 8% 9% 29%	4058
	11th to 20th	Night	7% 5% 3 8% 6% 7% 7% 6% 10% 12% 29%	4057
	21st to end	Night	12% 9% 3 9% 6% 6% 6% 4 7% 10% 27%	4427
August	1st to 10th	Night	13% 7% 3 7% 5% 5% 6% 5% 8% 11% 30%	2915
	11th to 20th	Night	13% 7% 3 8% 7% 6% 7% 4 7% 9% 29%	2875
	21st to end	Night	8% 6% 2 8% 5% 5% 5% 4 6% 8% 43%	3647
September	1st to 10th	Night	9% 6% 3 7% 5% 5% 6% 5% 7% 9% 39%	2200
	11th to 20th	Night	16% 7% 3 6% 4 5% 5% 4 6% 8% 37%	2200
	21st to end	Night	15% 5% 3 6% 4 3 4 3 5% 7% 45%	2200
October	1st to 10th	Night	13% 4 2 4 3 3 3 4 5% 6% 53%	2200
	11th to 20th	Night	12% 4 2 5% 4 3 4 3 4 5% 56%	2394
	21st to end	Night	13% 3 1 4 3 2 3 2 4 5% 58%	2640
November	1st to 10th	Night	14% 5% 2 4 3 3 3 2 3 5% 56%	2556
	11th to 20th	Night	15% 6% 2 4 3 3 2 2 4 6% 53%	2730
	21st to end	Night	15% 5% 2 4 4 4 4 3 5% 6% 49%	2730
December	1st to 10th	Night	17% 5% 2 4 3 3 3 2 5% 4 51%	4380
	11th to 20th	Night	19% 6% 2 5% 3 3 3 3 4 4 46%	4914
	21st to end	Night	21% 5% 2 5% 4 3 4 3 4 5% 44%	6490

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	35% 3 5% 21% 28% 9%	4057
	11th to 20th	Day	30% 3 5% 18% 33% 11%	4060
	21st to end	Day	45% 2 3 18% 21% 11%	4466
February	1st to 10th	Day	42% 3 7% 22% 20% 6%	1960
	11th to 20th	Day	44% 3 5% 19% 22% 7%	1958
	21st to end	Day	44% 3 7% 15% 22% 9%	1650
March	1st to 10th	Day	47% 3 6% 14% 20% 10%	4792
	11th to 20th	Day	31% 4 6% 14% 24% 21%	4980
	21st to end	Day	43% 3 5% 22% 21% 6%	5465
April	1st to 10th	Day	35% 3 10% 21% 24% 6%	2200
	11th to 20th	Day	36% 4 7% 21% 22% 10%	2364
	21st to end	Day	32% 5% 10% 28% 20% 4	2600
May	1st to 10th	Day	42% 6% 15% 21% 13% 3	5897
	11th to 20th	Day	49% 7% 15% 18% 10% 1	5865
	21st to end	Day	39% 6% 12% 21% 19% 2	6447
June	1st to 10th	Day	40% 8% 17% 23% 10% 2	2600
	11th to 20th	Day	32% 9% 19% 25% 12% 2	2600
	21st to end	Day	34% 9% 18% 21% 14% 4	2600
July	1st to 10th	Day	36% 12% 18% 25% 7% 1	5835
	11th to 20th	Day	33% 14% 30% 18% 4 1	5831
	21st to end	Day	45% 13% 19% 17% 6%	6240
August	1st to 10th	Day	43% 8% 17% 26% 5%	4221
	11th to 20th	Day	36% 8% 21% 19% 14% 2	4213
	21st to end	Day	31% 7% 16% 23% 21% 3	4199
September	1st to 10th	Day	38% 7% 14% 17% 19% 4	2200
	11th to 20th	Day	41% 7% 10% 20% 21% 2	2200
	21st to end	Day	38% 5% 11% 21% 19% 6%	2200
October	1st to 10th	Day	27% 3 7% 17% 35% 11%	3590
	11th to 20th	Day	22% 2 5% 15% 29% 27%	3245
	21st to end	Day	27% 4 4 21% 30% 14%	3538
November	1st to 10th	Day	32% 3 8% 18% 28% 12%	1959
	11th to 20th	Day	31% 4 6% 24% 26% 9%	1890
	21st to end	Day	35% 3 7% 22% 27% 7%	1890
December	1st to 10th	Day	39% 3 5% 17% 26% 10%	3020
	11th to 20th	Day	42% 5% 7% 18% 19% 10%	3433
	21st to end	Day	41% 3 7% 27% 20% 2	4466
January	1st to 10th	Night	33% 3 5% 20% 30% 10%	5889
	11th to 20th	Night	35% 3 4 18% 30% 11%	5900
	21st to end	Night	40% 2 4 17% 29% 8%	6490
February	1st to 10th	Night	39% 3 7% 22% 23% 7%	2435
	11th to 20th	Night	45% 2 5% 17% 22% 8%	2339
	21st to end	Night	41% 3 6% 19% 21% 10%	1980
March	1st to 10th	Night	43% 3 7% 14% 25% 7%	5061
	11th to 20th	Night	27% 4 7% 13% 30% 18%	4980
	21st to end	Night	40% 3 5% 20% 22% 10%	5467
April	1st to 10th	Night	34% 4 10% 21% 24% 8%	2200
	11th to 20th	Night	33% 2 6% 23% 24% 11%	1999
	21st to end	Night	34% 5% 10% 27% 20% 5%	1800
May	1st to 10th	Night	42% 6% 15% 22% 13% 2	4060
	11th to 20th	Night	49% 7% 15% 17% 11% 1	4033
	21st to end	Night	37% 7% 13% 25% 18% 2	4429
June	1st to 10th	Night	39% 9% 17% 21% 12% 2	1800
	11th to 20th	Night	34% 8% 18% 24% 15% 1	1800
	21st to end	Night	33% 10% 20% 20% 14% 4	1800
July	1st to 10th	Night	45% 12% 19% 18% 5% 1	4015
	11th to 20th	Night	40% 16% 25% 15% 3 1	4006
	21st to end	Night	50% 10% 18% 17% 5% 1	4297
August	1st to 10th	Night	43% 9% 23% 20% 5%	2904
	11th to 20th	Night	45% 12% 17% 17% 9% 1	2902
	21st to end	Night	36% 9% 13% 20% 20% 2	3647
September	1st to 10th	Night	38% 8% 15% 19% 16% 4	2200
	11th to 20th	Night	42% 8% 12% 19% 17% 2	2200
	21st to end	Night	38% 4 13% 20% 20% 6%	2200
October	1st to 10th	Night	26% 5% 10% 17% 35% 8%	3590
	11th to 20th	Night	20% 2 5% 17% 31% 25%	3893
	21st to end	Night	25% 3 5% 21% 28% 18%	4252
November	1st to 10th	Night	33% 3 7% 18% 27% 12%	2556
	11th to 20th	Night	33% 3 5% 18% 29% 12%	2730
	21st to end	Night	37% 3 5% 21% 25% 8%	2730
December	1st to 10th	Night	37% 3 6% 17% 30% 7%	4380
	11th to 20th	Night	42% 4 8% 16% 21% 8%	4916
	21st to end	Night	43% 3 6% 27% 18% 3	6490

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% 3	300
	11th to 20th	Day	28% 21% 27% 19% 5%	300
	21st to end	Day	26% 22% 33% 15% 3 1	330
February	1st to 10th	Day	21% 16% 41% 18% 4	300
	11th to 20th	Day	39% 17% 28% 16% 1	300
	21st to end	Day	34% 16% 37% 11% 3	249
March	1st to 10th	Day	25% 13% 28% 25% 9%	430
	11th to 20th	Day	21% 17% 37% 16% 9%	500
	21st to end	Day	24% 15% 32% 20% 8% 1	550
April	1st to 10th	Day	22% 16% 28% 22% 11% 1	500
	11th to 20th	Day	14% 12% 37% 23% 12% 3	492
	21st to end	Day	16% 8% 29% 23% 17% 6%	500
May	1st to 10th	Day	13% 14% 30% 22% 15% 6%	503
	11th to 20th	Day	18% 8% 19% 28% 17% 11%	527
	21st to end	Day	18% 6% 18% 24% 22% 12%	573
June	1st to 10th	Day	13% 4 16% 33% 22% 12%	530
	11th to 20th	Day	8% 4 15% 29% 26% 18%	530
	21st to end	Day	9% 2 15% 30% 27% 17%	530
July	1st to 10th	Day	10% 2 10% 22% 31% 26%	525
	11th to 20th	Day	10% 1 8% 25% 36% 20%	524
	21st to end	Day	7% 2 7% 30% 34% 19%	576
August	1st to 10th	Day	18% 5% 11% 24% 24% 18%	526
	11th to 20th	Day	13% 4 6% 29% 30% 18%	519
	21st to end	Day	15% 2 8% 26% 30% 19%	583
September	1st to 10th	Day	11% 2 12% 31% 29% 15%	530
	11th to 20th	Day	18% 3 9% 22% 34% 14%	530
	21st to end	Day	19% 5% 18% 24% 24% 10%	530
October	1st to 10th	Day	18% 4 17% 32% 19% 9%	530
	11th to 20th	Day	13% 7% 22% 30% 24% 5%	530
	21st to end	Day	19% 8% 22% 28% 20% 3	583
November	1st to 10th	Day	23% 7% 24% 26% 16% 4	437
	11th to 20th	Day	18% 14% 35% 25% 7% 1	330
	21st to end	Day	17% 13% 35% 22% 12% 2	330
December	1st to 10th	Day	32% 12% 32% 20% 5%	330
	11th to 20th	Day	25% 12% 35% 21% 6% 1	321
	21st to end	Day	33% 14% 27% 17% 8% 2	330
January	1st to 10th	Night	23% 18% 27% 27% 5%	800
	11th to 20th	Night	21% 17% 29% 27% 7%	800
	21st to end	Night	21% 17% 32% 28% 2	880
February	1st to 10th	Night	18% 14% 30% 34% 5%	800
	11th to 20th	Night	26% 14% 32% 25% 4	783
	21st to end	Night	21% 15% 33% 28% 3	660
March	1st to 10th	Night	20% 12% 30% 32% 6%	800
	11th to 20th	Night	17% 13% 36% 24% 10% 1	800
	21st to end	Night	18% 13% 31% 29% 9% 1	880
April	1st to 10th	Night	15% 15% 30% 29% 11%	800
	11th to 20th	Night	14% 11% 27% 33% 15% 1	670
	21st to end	Night	14% 6% 25% 33% 21% 1	600
May	1st to 10th	Night	11% 8% 25% 34% 21% 1	600
	11th to 20th	Night	16% 5% 20% 33% 21% 5%	591
	21st to end	Night	14% 3 12% 35% 31% 5%	650
June	1st to 10th	Night	12% 3 12% 35% 33% 7%	600
	11th to 20th	Night	10% 2 13% 29% 35% 12%	600
	21st to end	Night	9% 2 11% 32% 37% 10%	600
July	1st to 10th	Night	11% 2 7% 29% 38% 13%	585
	11th to 20th	Night	9% 3 5% 27% 44% 13%	582
	21st to end	Night	7% 3 6% 30% 44% 9%	657
August	1st to 10th	Night	16% 2 8% 28% 36% 12%	597
	11th to 20th	Night	13% 2 8% 29% 38% 10%	594
	21st to end	Night	15% 3 6% 25% 40% 11%	700
September	1st to 10th	Night	11% 3 11% 29% 37% 10%	800
	11th to 20th	Night	19% 3 10% 27% 36% 5%	800
	21st to end	Night	17% 4 13% 32% 31% 3	800
October	1st to 10th	Night	14% 5% 18% 30% 27% 7%	800
	11th to 20th	Night	14% 6% 22% 33% 22% 3	800
	21st to end	Night	15% 7% 23% 33% 21% 2	880
November	1st to 10th	Night	16% 7% 21% 34% 19% 3	820
	11th to 20th	Night	17% 11% 28% 31% 12% 1	840
	21st to end	Night	17% 10% 26% 32% 14% 1	840
December	1st to 10th	Night	22% 13% 25% 30% 9%	840
	11th to 20th	Night	21% 12% 25% 30% 10% 1	829
	21st to end	Night	26% 12% 24% 30% 7%	880

Page generated at 2025-12-15 01:13:53. Version ac07

Copyright © 2025 Attilla Danko.