Charleston Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charleston Lake clear sky chart from 2005-11-06 to 2025-02-21.

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	17% 10% 4 8% 5% 4 4 4 5% 7% 32%	108732
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 30%	109827
Transparency	Day	50% 6% 12% 21% 9% 1	112271
	Night	53% 6% 11% 19% 10% 1	114452
Seeing	Day	23% 16% 30% 20% 9% 2	14792
	Night	23% 14% 30% 24% 9% 1	24081

By Month

Percentage Cloud Cover NE (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% 16% 5% 13% 6% 4 4 3 5% 5% 24%	3597
	11th to 20th	Day	13% 18% 9% 16% 6% 5% 4 3 4 4 18%	3570
	21st to end	Day	13% 18% 7% 16% 7% 5% 5% 3 3 4 19%	4254
February	1st to 10th	Day	16% 17% 4 12% 6% 5% 4 3 5% 5% 21%	1800
	11th to 20th	Day	14% 16% 6% 10% 7% 4 4 4 5% 5% 25%	1763
	21st to end	Day	20% 15% 5% 11% 7% 5% 4 3 4 4 23%	1570
March	1st to 10th	Day	22% 12% 4 9% 6% 4 3 3 3 5% 28%	3147
	11th to 20th	Day	13% 16% 5% 10% 6% 4 4 3 5% 5% 29%	3480
	21st to end	Day	15% 9% 3 9% 4 4 4 3 4 6% 40%	4003
April	1st to 10th	Day	21% 13% 3 8% 5% 4 3 2 4 5% 32%	2280
	11th to 20th	Day	23% 9% 3 6% 4 4 4 3 3 5% 37%	2254
	21st to end	Day	21% 11% 4 8% 4 4 4 4 5% 4 32%	2362
May	1st to 10th	Day	21% 9% 3 7% 6% 5% 5% 3 5% 6% 31%	4426
	11th to 20th	Day	17% 9% 4 7% 5% 4 4 3 6% 7% 34%	4398
	21st to end	Day	14% 7% 2 6% 4 4 4 4 6% 9% 40%	4837
June	1st to 10th	Day	20% 8% 3 6% 5% 5% 6% 3 6% 8% 31%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 4 4 6% 8% 38%	2660
	21st to end	Day	17% 8% 3 7% 4 4 5% 5% 6% 7% 34%	2660
July	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 5% 7% 10% 38%	4440
	11th to 20th	Day	13% 6% 2 5% 4 5% 5% 4 6% 10% 40%	4440
	21st to end	Day	11% 5% 2 6% 5% 4 5% 5% 7% 9% 40%	4814
August	1st to 10th	Day	16% 7% 3 8% 4 4 5% 4 5% 7% 37%	4270
	11th to 20th	Day	17% 6% 2 6% 5% 4 5% 4 6% 10% 36%	3983
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 10% 39%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 7% 7% 43%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 47%	2280
	21st to end	Day	17% 7% 3 6% 4 4 5% 4 5% 6% 39%	2024
October	1st to 10th	Day	21% 8% 3 7% 3 4 3 4 4 7% 35%	1900
	11th to 20th	Day	21% 10% 3 8% 5% 5% 4 3 5% 7% 30%	1900
	21st to end	Day	25% 10% 3 7% 5% 4 5% 4 4 5% 27%	1967
November	1st to 10th	Day	15% 10% 3 8% 5% 5% 4 4 6% 7% 32%	1761
	11th to 20th	Day	15% 13% 4 9% 5% 5% 4 3 4 5% 32%	1626
	21st to end	Day	22% 14% 4 9% 6% 4 5% 3 5% 6% 22%	1600
December	1st to 10th	Day	21% 17% 5% 11% 6% 5% 5% 3 5% 6% 17%	2600
	11th to 20th	Day	19% 19% 6% 11% 4 4 4 2 4 4 22%	2986
	21st to end	Day	22% 17% 5% 11% 5% 4 4 3 3 4 23%	3960
January	1st to 10th	Night	16% 17% 6% 14% 6% 5% 4 3 4 4 22%	6349
	11th to 20th	Night	12% 18% 8% 15% 8% 6% 5% 3 4 4 17%	6315
	21st to end	Night	17% 16% 8% 12% 7% 6% 5% 3 4 4 18%	6702
February	1st to 10th	Night	18% 15% 5% 11% 7% 5% 5% 4 5% 4 21%	2600
	11th to 20th	Night	14% 14% 5% 11% 7% 5% 4 3 5% 5% 27%	2523
	21st to end	Night	18% 14% 5% 9% 6% 5% 4 3 4 5% 27%	1885
March	1st to 10th	Night	20% 12% 3 9% 5% 4 3 3 4 5% 32%	3678
	11th to 20th	Night	19% 18% 5% 8% 5% 3 3 3 5% 6% 26%	3479
	21st to end	Night	17% 12% 3 8% 5% 4 3 3 4 5% 39%	3628
April	1st to 10th	Night	21% 11% 3 7% 4 3 4 3 4 6% 33%	1900
	11th to 20th	Night	21% 8% 4 6% 4 4 4 3 4 6% 36%	1875
	21st to end	Night	22% 9% 3 7% 5% 4 3 3 4 6% 33%	1831
May	1st to 10th	Night	23% 9% 3 7% 4 4 4 4 5% 6% 29%	2514
	11th to 20th	Night	19% 9% 3 7% 4 5% 4 3 4 6% 35%	2495
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 9% 41%	2738
June	1st to 10th	Night	16% 8% 2 7% 6% 5% 4 4 6% 8% 33%	1520
	11th to 20th	Night	14% 5% 2 6% 4 5% 4 4 6% 8% 42%	1520
	21st to end	Night	18% 7% 3 6% 4 5% 5% 4 5% 8% 35%	1520
July	1st to 10th	Night	13% 7% 2 7% 5% 5% 5% 5% 5% 8% 38%	2520
	11th to 20th	Night	14% 5% 2 5% 5% 3 4 3 6% 8% 44%	2520
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 7% 44%	2739
August	1st to 10th	Night	12% 8% 3 7% 4 4 4 4 6% 8% 40%	2655
	11th to 20th	Night	14% 7% 2 7% 4 4 3 4 6% 8% 41%	2812
	21st to end	Night	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 39%	3476
September	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 7% 46%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 3 4 6% 7% 49%	1900
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 7% 41%	2151
October	1st to 10th	Night	19% 8% 3 6% 4 4 4 4 6% 7% 35%	2280
	11th to 20th	Night	20% 8% 3 8% 5% 5% 5% 3 5% 6% 33%	2280
	21st to end	Night	25% 9% 3 8% 5% 4 4 4 4 5% 29%	2631
November	1st to 10th	Night	19% 11% 3 7% 4 4 4 3 5% 6% 36%	2537
	11th to 20th	Night	17% 10% 4 8% 4 5% 4 4 5% 6% 33%	2770
	21st to end	Night	21% 14% 3 9% 5% 5% 5% 4 4 6% 23%	2800
December	1st to 10th	Night	19% 17% 5% 12% 6% 5% 5% 4 5% 6% 16%	4580
	11th to 20th	Night	23% 15% 5% 9% 4 3 3 3 4 4 27%	5208
	21st to end	Night	28% 14% 4 12% 4 4 4 3 5% 4 19%	6996

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	61% 8% 9% 16% 5% 1	3598
	11th to 20th	Day	68% 6% 10% 9% 7%	3600
	21st to end	Day	68% 6% 8% 8% 9% 1	4254
February	1st to 10th	Day	65% 4 9% 16% 6% 1	1800
	11th to 20th	Day	61% 5% 10% 16% 8% 1	1772
	21st to end	Day	66% 4 8% 12% 9% 1	1570
March	1st to 10th	Day	58% 5% 10% 18% 8% 1	3150
	11th to 20th	Day	55% 7% 14% 13% 10% 1	3480
	21st to end	Day	44% 6% 8% 24% 15% 3	4003
April	1st to 10th	Day	55% 4 8% 18% 13% 3	2280
	11th to 20th	Day	51% 5% 7% 20% 16% 2	2254
	21st to end	Day	54% 5% 9% 16% 13% 4	2362
May	1st to 10th	Day	51% 7% 10% 20% 10% 1	4440
	11th to 20th	Day	48% 8% 12% 22% 9% 1	4402
	21st to end	Day	39% 8% 13% 25% 13% 2	4837
June	1st to 10th	Day	50% 7% 10% 20% 11% 1	2660
	11th to 20th	Day	42% 6% 12% 26% 12% 2	2660
	21st to end	Day	47% 7% 14% 20% 11% 1	2660
July	1st to 10th	Day	38% 7% 14% 28% 12%	4370
	11th to 20th	Day	37% 8% 16% 31% 8%	4365
	21st to end	Day	37% 9% 16% 29% 10%	4661
August	1st to 10th	Day	45% 6% 15% 23% 10% 1	4256
	11th to 20th	Day	42% 7% 15% 26% 9%	4022
	21st to end	Day	39% 6% 16% 27% 11%	4180
September	1st to 10th	Day	38% 7% 16% 26% 12% 1	2280
	11th to 20th	Day	35% 6% 13% 31% 15%	2280
	21st to end	Day	44% 7% 13% 25% 10%	2024
October	1st to 10th	Day	44% 6% 13% 28% 8%	3160
	11th to 20th	Day	47% 6% 15% 24% 7%	3140
	21st to end	Day	48% 6% 14% 24% 7%	3218
November	1st to 10th	Day	48% 8% 13% 22% 8% 1	1761
	11th to 20th	Day	54% 7% 11% 18% 9% 1	1626
	21st to end	Day	62% 8% 13% 11% 7%	1600
December	1st to 10th	Day	68% 6% 14% 10% 2	2600
	11th to 20th	Day	66% 6% 10% 13% 5%	2986
	21st to end	Day	65% 5% 8% 16% 5%	3960
January	1st to 10th	Night	66% 6% 12% 12% 5%	6349
	11th to 20th	Night	68% 8% 9% 10% 5%	6360
	21st to end	Night	68% 6% 8% 8% 9% 1	6702
February	1st to 10th	Night	65% 5% 9% 14% 6% 1	2600
	11th to 20th	Night	58% 5% 11% 18% 8% 1	2525
	21st to end	Night	60% 5% 9% 16% 9% 1	1885
March	1st to 10th	Night	54% 5% 10% 22% 9% 1	3688
	11th to 20th	Night	58% 7% 12% 13% 9% 1	3480
	21st to end	Night	47% 4 8% 22% 16% 3	3628
April	1st to 10th	Night	52% 5% 8% 19% 14% 1	1900
	11th to 20th	Night	49% 6% 9% 18% 16% 1	1875
	21st to end	Night	52% 4 10% 16% 14% 3	1831
May	1st to 10th	Night	51% 9% 12% 16% 9% 3	2520
	11th to 20th	Night	48% 8% 13% 20% 9% 2	2496
	21st to end	Night	38% 8% 13% 21% 18% 2	2739
June	1st to 10th	Night	47% 7% 14% 20% 11% 1	1520
	11th to 20th	Night	39% 7% 13% 22% 17% 2	1520
	21st to end	Night	45% 8% 12% 20% 13% 1	1520
July	1st to 10th	Night	42% 7% 12% 23% 15% 2	2480
	11th to 20th	Night	36% 6% 14% 35% 8%	2472
	21st to end	Night	37% 9% 15% 25% 13% 1	2651
August	1st to 10th	Night	40% 8% 14% 25% 12%	2645
	11th to 20th	Night	40% 7% 14% 30% 8% 1	2839
	21st to end	Night	36% 9% 17% 27% 11% 1	3476
September	1st to 10th	Night	37% 7% 13% 28% 14% 1	1900
	11th to 20th	Night	33% 7% 14% 31% 14% 1	1900
	21st to end	Night	41% 6% 12% 28% 12% 1	2151
October	1st to 10th	Night	41% 7% 13% 27% 12% 1	3800
	11th to 20th	Night	43% 6% 15% 26% 9%	3779
	21st to end	Night	49% 6% 15% 23% 8%	4330
November	1st to 10th	Night	48% 6% 13% 22% 9% 1	2537
	11th to 20th	Night	50% 6% 13% 19% 10% 2	2770
	21st to end	Night	61% 7% 11% 15% 5%	2800
December	1st to 10th	Night	69% 7% 11% 11% 2	4580
	11th to 20th	Night	62% 6% 9% 14% 9%	5208
	21st to end	Night	67% 5% 7% 11% 9%	6996

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	24% 22% 38% 10% 6% 1	200
	11th to 20th	Day	31% 21% 32% 15% 2 1	200
	21st to end	Day	23% 23% 35% 14% 4	283
February	1st to 10th	Day	31% 26% 33% 10% 1	300
	11th to 20th	Day	32% 25% 35% 8% 1	310
	21st to end	Day	34% 19% 34% 12% 2	382
March	1st to 10th	Day	25% 21% 31% 19% 4	460
	11th to 20th	Day	27% 21% 33% 15% 4	460
	21st to end	Day	33% 21% 25% 13% 7% 1	506
April	1st to 10th	Day	32% 17% 30% 16% 5%	460
	11th to 20th	Day	31% 21% 26% 13% 7% 3	452
	21st to end	Day	29% 18% 32% 12% 7% 2	460
May	1st to 10th	Day	22% 18% 30% 23% 6% 1	463
	11th to 20th	Day	18% 15% 36% 21% 9% 2	487
	21st to end	Day	17% 16% 31% 23% 11% 2	529
June	1st to 10th	Day	23% 15% 31% 21% 9% 2	490
	11th to 20th	Day	16% 12% 35% 24% 10% 2	490
	21st to end	Day	19% 15% 31% 22% 10% 3	490
July	1st to 10th	Day	14% 9% 27% 31% 16% 2	485
	11th to 20th	Day	14% 12% 29% 26% 15% 3	484
	21st to end	Day	13% 9% 32% 32% 11% 3	532
August	1st to 10th	Day	15% 8% 29% 28% 15% 4	486
	11th to 20th	Day	14% 6% 26% 30% 17% 6%	479
	21st to end	Day	14% 10% 34% 23% 13% 6%	539
September	1st to 10th	Day	15% 11% 32% 25% 11% 7%	490
	11th to 20th	Day	12% 8% 25% 24% 19% 12%	490
	21st to end	Day	19% 11% 28% 23% 15% 3	490
October	1st to 10th	Day	26% 14% 25% 17% 11% 5%	490
	11th to 20th	Day	26% 20% 27% 19% 6% 2	490
	21st to end	Day	33% 17% 27% 18% 5%	474
November	1st to 10th	Day	27% 19% 30% 17% 7%	395
	11th to 20th	Day	25% 18% 38% 13% 6% 1	226
	21st to end	Day	33% 20% 33% 13% 3	200
December	1st to 10th	Day	34% 24% 23% 15% 5%	200
	11th to 20th	Day	32% 25% 33% 7% 4	200
	21st to end	Day	35% 20% 27% 15% 4	220
January	1st to 10th	Night	30% 18% 31% 18% 3	800
	11th to 20th	Night	28% 18% 31% 19% 4	800
	21st to end	Night	21% 16% 34% 23% 5%	880
February	1st to 10th	Night	27% 20% 33% 18% 2	800
	11th to 20th	Night	23% 19% 36% 18% 3	783
	21st to end	Night	26% 19% 31% 20% 4	629
March	1st to 10th	Night	26% 14% 34% 22% 4	760
	11th to 20th	Night	27% 16% 31% 21% 4 1	760
	21st to end	Night	25% 15% 32% 21% 7%	836
April	1st to 10th	Night	26% 16% 34% 21% 3	760
	11th to 20th	Night	24% 19% 32% 18% 7% 1	751
	21st to end	Night	26% 11% 30% 23% 9% 1	691
May	1st to 10th	Night	25% 9% 28% 27% 9% 1	380
	11th to 20th	Night	14% 9% 37% 31% 8%	374
	21st to end	Night	12% 9% 37% 30% 12% 1	411
June	1st to 10th	Night	18% 9% 30% 33% 9% 1	380
	11th to 20th	Night	14% 11% 28% 34% 12% 1	380
	21st to end	Night	19% 7% 25% 35% 13%	380
July	1st to 10th	Night	11% 5% 30% 39% 16%	370
	11th to 20th	Night	13% 4 26% 36% 19% 1	368
	21st to end	Night	11% 5% 29% 42% 12% 1	416
August	1st to 10th	Night	13% 4 25% 37% 21%	462
	11th to 20th	Night	13% 6% 20% 35% 24% 3	578
	21st to end	Night	12% 7% 28% 36% 16% 2	836
September	1st to 10th	Night	15% 8% 29% 31% 16% 2	760
	11th to 20th	Night	15% 7% 21% 28% 23% 6%	760
	21st to end	Night	19% 10% 24% 26% 19% 2	760
October	1st to 10th	Night	23% 12% 27% 20% 17% 1	760
	11th to 20th	Night	24% 14% 28% 25% 8% 1	760
	21st to end	Night	30% 14% 27% 24% 5%	836
November	1st to 10th	Night	27% 15% 29% 22% 7%	780
	11th to 20th	Night	25% 18% 31% 18% 9%	800
	21st to end	Night	33% 17% 27% 17% 6%	800
December	1st to 10th	Night	32% 18% 29% 17% 4	800
	11th to 20th	Night	28% 20% 32% 17% 3 1	800
	21st to end	Night	34% 16% 31% 18% 2	880

Page generated at 2025-02-18 03:26:27. Version ac07

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