West Columbia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Columbia clear sky chart from 2005-11-06 to 2025-08-05.

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% 6% 2 6% 4 4 4 4 6% 8% 43%	125737
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	122334
Transparency	Day	37% 8% 13% 19% 18% 6%	129396
	Night	37% 7% 11% 18% 20% 8%	126744
Seeing	Day	15% 8% 23% 24% 20% 10%	16324
	Night	15% 7% 23% 33% 21% 3	26383

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 2 2 5% 6% 55%	4056
	11th to 20th	Day	12% 5% 2 4 3 3 2 2 3 5% 59%	4060
	21st to end	Day	15% 7% 3 7% 4 4 3 3 4 5% 46%	4466
February	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 5% 7% 42%	1818
	11th to 20th	Day	20% 6% 2 5% 4 3 3 3 4 5% 44%	1948
	21st to end	Day	18% 5% 3 6% 4 4 3 3 5% 6% 45%	1711
March	1st to 10th	Day	21% 9% 3 6% 3 3 4 3 4 5% 40%	4935
	11th to 20th	Day	8% 4 1 5% 4 3 4 3 5% 7% 55%	4980
	21st to end	Day	15% 6% 2 6% 4 4 4 3 4 5% 47%	5465
April	1st to 10th	Day	10% 4 2 5% 4 4 5% 3 6% 7% 52%	2200
	11th to 20th	Day	10% 4 2 5% 4 3 4 3 7% 7% 50%	2344
	21st to end	Day	8% 5% 2 4 4 4 4 4 6% 8% 51%	2520
May	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 10% 40%	5862
	11th to 20th	Day	17% 7% 2 7% 4 5% 5% 5% 7% 9% 32%	5861
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 46%	6433
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 10% 38%	2600
	11th to 20th	Day	7% 5% 1 5% 4 6% 6% 5% 7% 11% 44%	2600
	21st to end	Day	5% 4 2 6% 6% 6% 6% 6% 8% 11% 40%	2600
July	1st to 10th	Day	12% 6% 3 8% 6% 6% 7% 6% 8% 11% 27%	5900
	11th to 20th	Day	5% 5% 2 6% 6% 6% 7% 6% 10% 16% 32%	5900
	21st to end	Day	8% 6% 3 7% 6% 6% 7% 6% 10% 13% 28%	6424
August	1st to 10th	Day	23% 6% 2 7% 5% 5% 6% 5% 8% 10% 24%	4156
	11th to 20th	Day	11% 6% 2 7% 5% 6% 5% 5% 8% 10% 35%	4044
	21st to end	Day	7% 4 2 5% 4 4 5% 5% 7% 11% 46%	4192
September	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 5% 7% 8% 42%	2090
	11th to 20th	Day	14% 6% 3 7% 5% 5% 4 4 5% 8% 40%	2090
	21st to end	Day	17% 6% 2 5% 4 4 4 3 5% 7% 43%	2090
October	1st to 10th	Day	14% 6% 2 5% 4 4 3 3 4 6% 50%	1986
	11th to 20th	Day	10% 4 2 5% 4 3 3 2 3 5% 59%	1900
	21st to end	Day	11% 5% 1 5% 3 3 4 3 3 4 58%	2090
November	1st to 10th	Day	13% 7% 1 4 4 4 3 3 4 5% 53%	1957
	11th to 20th	Day	15% 5% 2 4 3 3 3 2 5% 5% 53%	1890
	21st to end	Day	14% 6% 2 5% 3 4 3 3 4 5% 50%	1800
December	1st to 10th	Day	12% 5% 2 5% 3 4 4 3 5% 6% 51%	2930
	11th to 20th	Day	15% 6% 2 6% 3 4 4 4 4 6% 46%	3373
	21st to end	Day	20% 7% 2 5% 3 3 2 2 5% 6% 46%	4466
January	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 4 5% 57%	5889
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 6% 50%	5900
	21st to end	Night	15% 8% 2 6% 4 3 3 3 4 5% 47%	6490
February	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 5% 6% 46%	2579
	11th to 20th	Night	20% 6% 3 6% 4 3 3 3 4 4 45%	2338
	21st to end	Night	15% 5% 2 6% 5% 4 4 3 5% 6% 46%	1917
March	1st to 10th	Night	20% 8% 3 6% 4 3 4 3 4 6% 40%	4918
	11th to 20th	Night	11% 3 1 4 3 3 4 3 6% 7% 55%	4980
	21st to end	Night	14% 4 2 5% 4 3 4 3 5% 7% 48%	5467
April	1st to 10th	Night	11% 5% 2 5% 3 4 4 3 5% 7% 52%	2200
	11th to 20th	Night	11% 4 2 5% 3 3 3 4 5% 5% 54%	2004
	21st to end	Night	9% 4 2 5% 4 3 4 3 5% 7% 53%	1895
May	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 3 7% 10% 41%	4033
	11th to 20th	Night	18% 5% 2 6% 4 5% 5% 4 6% 10% 35%	4032
	21st to end	Night	11% 5% 2 5% 4 5% 4 5% 6% 9% 44%	4421
June	1st to 10th	Night	12% 5% 2 6% 5% 4 6% 5% 9% 10% 35%	1800
	11th to 20th	Night	8% 5% 2 6% 6% 6% 6% 5% 7% 11% 39%	1800
	21st to end	Night	6% 4 3 6% 6% 5% 6% 7% 10% 13% 34%	1800
July	1st to 10th	Night	13% 8% 3 9% 6% 6% 6% 6% 8% 10% 26%	4058
	11th to 20th	Night	7% 6% 2 8% 5% 6% 6% 7% 10% 15% 26%	4057
	21st to end	Night	11% 8% 4 10% 7% 6% 7% 5% 8% 10% 23%	4427
August	1st to 10th	Night	22% 7% 3 7% 5% 5% 6% 6% 7% 9% 23%	2861
	11th to 20th	Night	11% 7% 3 7% 5% 6% 6% 6% 6% 9% 35%	2785
	21st to end	Night	6% 4 1 6% 3 3 3 4 7% 12% 51%	3425
September	1st to 10th	Night	9% 5% 2 7% 5% 5% 5% 4 9% 9% 41%	2090
	11th to 20th	Night	12% 6% 2 9% 5% 5% 5% 3 5% 6% 41%	2090
	21st to end	Night	16% 6% 3 6% 4 4 5% 4 5% 6% 42%	2090
October	1st to 10th	Night	13% 6% 1 6% 3 3 3 2 4 6% 53%	2192
	11th to 20th	Night	13% 5% 2 3 3 3 3 3 4 5% 56%	2280
	21st to end	Night	10% 5% 1 4 3 2 3 4 5% 5% 57%	2508
November	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	2341
	11th to 20th	Night	14% 6% 2 4 4 3 3 3 4 5% 53%	2505
	21st to end	Night	14% 5% 2 5% 3 4 4 3 6% 6% 49%	2600
December	1st to 10th	Night	13% 5% 2 5% 3 3 3 3 4 5% 55%	4250
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 4 6% 45%	4822
	21st to end	Night	19% 7% 2 5% 4 3 4 3 4 6% 42%	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	30% 4 7% 21% 31% 7%	4057
	11th to 20th	Day	30% 4 5% 15% 37% 9%	4060
	21st to end	Day	42% 3 5% 17% 22% 11%	4466
February	1st to 10th	Day	41% 5% 10% 20% 19% 6%	1818
	11th to 20th	Day	43% 5% 5% 17% 24% 6%	1958
	21st to end	Day	42% 5% 8% 15% 21% 9%	1711
March	1st to 10th	Day	47% 5% 6% 12% 20% 10%	4935
	11th to 20th	Day	28% 6% 8% 14% 26% 18%	4980
	21st to end	Day	40% 5% 7% 18% 22% 9%	5465
April	1st to 10th	Day	31% 6% 11% 20% 25% 7%	2200
	11th to 20th	Day	31% 7% 11% 20% 21% 10%	2344
	21st to end	Day	29% 8% 12% 26% 22% 4	2520
May	1st to 10th	Day	37% 9% 17% 24% 12% 1	5897
	11th to 20th	Day	47% 8% 17% 17% 11% 1	5865
	21st to end	Day	35% 8% 14% 19% 21% 3	6447
June	1st to 10th	Day	38% 11% 17% 22% 11% 2	2600
	11th to 20th	Day	31% 10% 20% 25% 13% 1	2600
	21st to end	Day	33% 12% 20% 21% 12% 2	2600
July	1st to 10th	Day	46% 12% 18% 17% 5% 1	5835
	11th to 20th	Day	34% 17% 32% 13% 2 1	5831
	21st to end	Day	42% 13% 19% 20% 6%	6240
August	1st to 10th	Day	52% 11% 20% 13% 4	4143
	11th to 20th	Day	40% 11% 16% 19% 13%	4083
	21st to end	Day	29% 9% 15% 31% 15% 2	4192
September	1st to 10th	Day	36% 11% 14% 17% 17% 5%	2090
	11th to 20th	Day	42% 8% 11% 16% 19% 3	2090
	21st to end	Day	41% 7% 9% 20% 17% 7%	2090
October	1st to 10th	Day	33% 4 7% 19% 27% 9%	3298
	11th to 20th	Day	17% 3 5% 17% 28% 29%	3140
	21st to end	Day	25% 4 5% 20% 31% 15%	3428
November	1st to 10th	Day	34% 4 7% 17% 25% 12%	1957
	11th to 20th	Day	34% 4 7% 20% 24% 11%	1890
	21st to end	Day	36% 5% 8% 19% 23% 9%	1800
December	1st to 10th	Day	34% 5% 7% 18% 27% 9%	2930
	11th to 20th	Day	38% 5% 10% 21% 19% 6%	3370
	21st to end	Day	40% 4 8% 22% 23% 2	4466
January	1st to 10th	Night	30% 4 6% 18% 35% 7%	5889
	11th to 20th	Night	34% 5% 6% 16% 31% 8%	5900
	21st to end	Night	40% 5% 4 14% 28% 9%	6490
February	1st to 10th	Night	39% 5% 8% 20% 19% 8%	2579
	11th to 20th	Night	43% 5% 7% 17% 21% 8%	2339
	21st to end	Night	38% 5% 8% 17% 19% 12%	1917
March	1st to 10th	Night	44% 6% 7% 11% 23% 8%	4918
	11th to 20th	Night	27% 5% 7% 12% 29% 19%	4980
	21st to end	Night	35% 5% 8% 20% 21% 12%	5467
April	1st to 10th	Night	32% 6% 12% 18% 22% 9%	2200
	11th to 20th	Night	30% 6% 10% 21% 21% 12%	2004
	21st to end	Night	29% 7% 12% 25% 22% 5%	1895
May	1st to 10th	Night	36% 9% 16% 24% 13% 2	4060
	11th to 20th	Night	43% 9% 20% 16% 11%	4033
	21st to end	Night	34% 10% 13% 23% 19% 2	4429
June	1st to 10th	Night	39% 12% 18% 19% 12% 1	1800
	11th to 20th	Night	36% 11% 19% 23% 10% 2	1800
	21st to end	Night	34% 15% 20% 19% 11% 2	1800
July	1st to 10th	Night	50% 12% 19% 13% 5% 1	4015
	11th to 20th	Night	41% 17% 29% 10% 3 1	4006
	21st to end	Night	54% 12% 16% 13% 4	4297
August	1st to 10th	Night	54% 12% 18% 12% 3 1	2850
	11th to 20th	Night	41% 11% 21% 20% 7% 1	2812
	21st to end	Night	25% 9% 17% 31% 16% 2	3425
September	1st to 10th	Night	37% 10% 17% 18% 13% 5%	2090
	11th to 20th	Night	43% 9% 10% 16% 18% 3	2090
	21st to end	Night	41% 8% 12% 17% 16% 5%	2090
October	1st to 10th	Night	33% 5% 9% 17% 29% 7%	3660
	11th to 20th	Night	19% 3 6% 15% 25% 32%	3779
	21st to end	Night	24% 5% 6% 19% 28% 19%	4120
November	1st to 10th	Night	32% 5% 8% 15% 25% 14%	2341
	11th to 20th	Night	34% 5% 7% 16% 25% 13%	2505
	21st to end	Night	34% 5% 9% 18% 24% 10%	2600
December	1st to 10th	Night	34% 5% 6% 16% 31% 9%	4250
	11th to 20th	Night	41% 4 10% 17% 19% 9%	4824
	21st to end	Night	43% 5% 7% 23% 20% 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	18% 16% 44% 18% 3	300
	11th to 20th	Day	20% 17% 37% 19% 6%	300
	21st to end	Day	22% 22% 37% 16% 3	330
February	1st to 10th	Day	17% 19% 37% 21% 6%	300
	11th to 20th	Day	31% 16% 36% 15% 2	300
	21st to end	Day	21% 14% 39% 19% 6%	310
March	1st to 10th	Day	21% 16% 27% 25% 11%	500
	11th to 20th	Day	17% 14% 40% 22% 6% 1	500
	21st to end	Day	18% 15% 33% 24% 10% 1	550
April	1st to 10th	Day	15% 16% 32% 25% 11% 1	500
	11th to 20th	Day	11% 14% 29% 26% 16% 4	492
	21st to end	Day	11% 9% 27% 28% 18% 7%	500
May	1st to 10th	Day	8% 11% 31% 25% 20% 5%	503
	11th to 20th	Day	17% 6% 19% 26% 21% 12%	527
	21st to end	Day	13% 5% 15% 26% 24% 17%	573
June	1st to 10th	Day	9% 4 15% 28% 30% 13%	530
	11th to 20th	Day	9% 3 14% 28% 28% 18%	530
	21st to end	Day	7% 2 11% 29% 32% 19%	530
July	1st to 10th	Day	8% 3 8% 21% 31% 29%	525
	11th to 20th	Day	9% 2 6% 22% 37% 24%	524
	21st to end	Day	6% 2 9% 28% 35% 21%	576
August	1st to 10th	Day	16% 3 11% 23% 29% 18%	502
	11th to 20th	Day	13% 3 11% 20% 31% 21%	479
	21st to end	Day	12% 2 10% 21% 32% 22%	539
September	1st to 10th	Day	9% 3 10% 26% 32% 19%	490
	11th to 20th	Day	18% 3 12% 23% 30% 14%	490
	21st to end	Day	19% 2 15% 25% 27% 12%	490
October	1st to 10th	Day	16% 3 18% 32% 21% 9%	490
	11th to 20th	Day	10% 5% 22% 30% 23% 10%	490
	21st to end	Day	13% 6% 24% 29% 22% 7%	539
November	1st to 10th	Day	15% 7% 27% 27% 19% 5%	495
	11th to 20th	Day	20% 9% 32% 26% 10% 2	390
	21st to end	Day	13% 12% 32% 27% 14% 2	300
December	1st to 10th	Day	23% 16% 36% 20% 5% 1	300
	11th to 20th	Day	21% 10% 38% 20% 10% 1	300
	21st to end	Day	25% 14% 32% 20% 7% 2	330
January	1st to 10th	Night	20% 12% 32% 29% 7%	800
	11th to 20th	Night	18% 11% 34% 30% 7%	800
	21st to end	Night	18% 11% 36% 32% 3	880
February	1st to 10th	Night	18% 11% 31% 35% 5%	800
	11th to 20th	Night	23% 12% 34% 30% 2	783
	21st to end	Night	17% 14% 33% 30% 6%	660
March	1st to 10th	Night	17% 11% 32% 34% 6%	800
	11th to 20th	Night	16% 9% 38% 29% 8%	800
	21st to end	Night	15% 10% 37% 29% 9%	880
April	1st to 10th	Night	13% 14% 32% 31% 10%	800
	11th to 20th	Night	13% 10% 29% 33% 15%	791
	21st to end	Night	11% 6% 26% 41% 15%	695
May	1st to 10th	Night	9% 7% 28% 39% 17% 1	600
	11th to 20th	Night	12% 4 24% 38% 19% 3	591
	21st to end	Night	11% 2 14% 38% 32% 3	650
June	1st to 10th	Night	13% 3 13% 40% 27% 4	600
	11th to 20th	Night	10% 1 14% 34% 31% 10%	600
	21st to end	Night	8% 2 11% 37% 36% 6%	600
July	1st to 10th	Night	10% 2 8% 32% 40% 7%	585
	11th to 20th	Night	9% 1 6% 28% 48% 8%	582
	21st to end	Night	7% 2 9% 33% 44% 6%	657
August	1st to 10th	Night	12% 1 8% 27% 44% 7%	579
	11th to 20th	Night	13% 3 6% 31% 41% 7%	564
	21st to end	Night	12% 1 10% 27% 43% 7%	790
September	1st to 10th	Night	10% 2 10% 29% 43% 6%	760
	11th to 20th	Night	14% 2 12% 29% 38% 4	760
	21st to end	Night	19% 2 13% 31% 31% 3	760
October	1st to 10th	Night	14% 3 17% 32% 29% 5%	760
	11th to 20th	Night	14% 5% 20% 34% 24% 3	760
	21st to end	Night	12% 5% 23% 33% 26% 2	836
November	1st to 10th	Night	15% 6% 23% 34% 19% 3	780
	11th to 20th	Night	16% 9% 27% 33% 14% 1	800
	21st to end	Night	14% 8% 26% 35% 17% 1	800
December	1st to 10th	Night	18% 9% 28% 34% 10% 1	800
	11th to 20th	Night	19% 7% 26% 35% 12% 1	800
	21st to end	Night	23% 11% 25% 31% 9%	880

Page generated at 2025-08-02 01:32:26. Version ac07

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