Columbus
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Columbus clear sky chart from 2005-11-06 to 2025-09-04.

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	15% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	126534
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 34%	122205
Transparency	Day	49% 4 11% 22% 13% 1	130182
	Night	49% 4 10% 22% 13% 2	126627
Seeing	Day	18% 10% 25% 23% 16% 8%	16250
	Night	19% 8% 25% 32% 15% 2	25953

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% 20% 7% 16% 7% 4 4 3 4 4 14%	4056
	11th to 20th	Day	15% 21% 6% 13% 6% 7% 6% 2 3 3 17%	4060
	21st to end	Day	21% 17% 7% 10% 9% 7% 5% 3 4 4 14%	4466
February	1st to 10th	Day	21% 15% 5% 11% 5% 5% 3 3 5% 5% 23%	1800
	11th to 20th	Day	17% 12% 5% 13% 6% 5% 4 4 5% 5% 23%	1933
	21st to end	Day	19% 14% 4 10% 4 5% 4 2 4 6% 29%	1650
March	1st to 10th	Day	17% 14% 6% 12% 6% 4 4 3 4 5% 27%	4680
	11th to 20th	Day	13% 8% 3 9% 5% 5% 4 3 4 6% 40%	4980
	21st to end	Day	19% 10% 3 8% 5% 5% 4 3 4 6% 32%	5465
April	1st to 10th	Day	16% 12% 3 7% 5% 4 5% 4 5% 6% 33%	2254
	11th to 20th	Day	17% 9% 3 8% 5% 4 4 4 5% 6% 37%	2519
	21st to end	Day	18% 7% 3 8% 6% 5% 5% 5% 5% 7% 33%	2600
May	1st to 10th	Day	21% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	5862
	11th to 20th	Day	19% 9% 3 7% 4 4 4 4 6% 8% 32%	5861
	21st to end	Day	16% 7% 3 6% 5% 5% 5% 5% 7% 9% 32%	6433
June	1st to 10th	Day	12% 6% 2 8% 6% 6% 5% 4 5% 9% 37%	2600
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 5% 7% 10% 38%	2611
	21st to end	Day	10% 6% 2 6% 5% 6% 6% 5% 8% 11% 37%	2800
July	1st to 10th	Day	9% 7% 2 7% 5% 5% 5% 4 6% 9% 41%	6176
	11th to 20th	Day	9% 7% 3 7% 6% 5% 6% 5% 7% 10% 34%	5900
	21st to end	Day	9% 7% 3 7% 5% 5% 6% 5% 8% 10% 35%	6424
August	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 5% 7% 10% 39%	4234
	11th to 20th	Day	8% 6% 2 6% 4 5% 6% 4 9% 10% 39%	4174
	21st to end	Day	5% 5% 2 5% 4 5% 6% 5% 7% 10% 46%	4582
September	1st to 10th	Day	12% 6% 2 4 3 4 3 4 6% 8% 48%	2133
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 6% 8% 47%	2090
	21st to end	Day	17% 7% 3 6% 5% 3 4 3 4 5% 43%	2090
October	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 6% 7% 44%	2042
	11th to 20th	Day	15% 6% 2 6% 4 5% 5% 4 4 7% 42%	1900
	21st to end	Day	20% 9% 2 8% 4 4 4 3 5% 6% 34%	2028
November	1st to 10th	Day	10% 7% 2 6% 5% 3 4 4 5% 6% 47%	1762
	11th to 20th	Day	16% 12% 3 8% 5% 4 5% 3 5% 6% 33%	1800
	21st to end	Day	19% 13% 4 8% 5% 4 3 4 4 6% 30%	1800
December	1st to 10th	Day	21% 12% 5% 14% 6% 4 4 2 4 5% 25%	2930
	11th to 20th	Day	24% 15% 6% 9% 5% 4 3 3 5% 5% 21%	3373
	21st to end	Day	24% 21% 5% 10% 5% 5% 4 3 4 4 14%	4466
January	1st to 10th	Night	16% 17% 7% 16% 7% 5% 3 3 5% 5% 17%	5889
	11th to 20th	Night	13% 18% 6% 16% 8% 5% 5% 3 4 4 16%	5900
	21st to end	Night	22% 14% 6% 9% 6% 4 4 2 4 5% 24%	6490
February	1st to 10th	Night	21% 13% 3 9% 6% 4 4 3 5% 4 27%	2600
	11th to 20th	Night	18% 12% 3 10% 6% 5% 4 3 5% 7% 26%	2348
	21st to end	Night	20% 14% 5% 9% 5% 4 4 3 4 4 28%	1980
March	1st to 10th	Night	20% 12% 4 6% 5% 4 4 2 4 6% 34%	5171
	11th to 20th	Night	13% 7% 2 6% 4 4 5% 4 6% 8% 41%	4980
	21st to end	Night	19% 9% 3 7% 4 4 4 4 4 6% 35%	5467
April	1st to 10th	Night	17% 10% 2 7% 4 4 4 3 6% 7% 36%	2163
	11th to 20th	Night	15% 7% 2 7% 5% 5% 5% 4 6% 7% 38%	1828
	21st to end	Night	15% 7% 3 7% 5% 4 4 4 6% 8% 38%	1800
May	1st to 10th	Night	24% 9% 3 7% 5% 4 5% 4 5% 6% 27%	4033
	11th to 20th	Night	16% 8% 2 6% 4 4 4 3 7% 10% 36%	4032
	21st to end	Night	13% 7% 3 6% 5% 5% 5% 4 6% 9% 38%	4421
June	1st to 10th	Night	9% 5% 2 5% 5% 5% 4 4 6% 8% 47%	1800
	11th to 20th	Night	9% 6% 2 5% 4 5% 6% 4 7% 9% 43%	1776
	21st to end	Night	8% 5% 2 5% 4 3 5% 5% 6% 10% 46%	1600
July	1st to 10th	Night	9% 7% 2 7% 4 4 5% 4 6% 8% 43%	3784
	11th to 20th	Night	8% 6% 3 7% 6% 6% 6% 5% 6% 9% 39%	4057
	21st to end	Night	8% 6% 3 8% 5% 5% 5% 5% 6% 9% 41%	4427
August	1st to 10th	Night	9% 6% 3 8% 5% 5% 5% 5% 7% 9% 38%	2915
	11th to 20th	Night	8% 7% 3 8% 5% 5% 5% 3 5% 8% 44%	2875
	21st to end	Night	4 3 2 6% 4 5% 5% 4 7% 10% 49%	3312
September	1st to 10th	Night	12% 5% 2 5% 3 3 4 2 4 7% 53%	2093
	11th to 20th	Night	9% 4 2 4 4 3 3 3 5% 8% 55%	2090
	21st to end	Night	16% 6% 2 5% 4 4 4 3 4 6% 47%	2090
October	1st to 10th	Night	9% 5% 2 6% 4 4 3 3 6% 7% 50%	2137
	11th to 20th	Night	16% 8% 2 5% 3 3 4 3 5% 7% 44%	2280
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 6% 39%	2569
November	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 5% 5% 48%	2536
	11th to 20th	Night	17% 10% 4 7% 5% 4 4 4 5% 6% 36%	2600
	21st to end	Night	19% 12% 4 8% 5% 4 4 4 5% 6% 29%	2600
December	1st to 10th	Night	19% 12% 4 10% 6% 4 4 4 5% 5% 27%	4250
	11th to 20th	Night	19% 17% 6% 11% 5% 4 4 3 4 6% 22%	4822
	21st to end	Night	26% 20% 5% 9% 6% 4 3 3 4 6% 15%	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	74% 3 8% 11% 4	4057
	11th to 20th	Day	72% 3 8% 9% 7%	4060
	21st to end	Day	75% 2 10% 8% 5%	4466
February	1st to 10th	Day	63% 3 9% 16% 8%	1800
	11th to 20th	Day	62% 5% 9% 16% 9%	1943
	21st to end	Day	57% 3 11% 18% 8% 2	1650
March	1st to 10th	Day	60% 2 8% 22% 7% 1	4680
	11th to 20th	Day	45% 3 9% 30% 11% 1	4980
	21st to end	Day	54% 3 9% 22% 10% 2	5465
April	1st to 10th	Day	52% 4 11% 20% 12% 1	2254
	11th to 20th	Day	48% 4 11% 21% 13% 3	2519
	21st to end	Day	50% 4 11% 21% 12% 2	2600
May	1st to 10th	Day	56% 5% 10% 18% 11% 1	5897
	11th to 20th	Day	50% 5% 11% 22% 11%	5865
	21st to end	Day	46% 5% 11% 23% 12% 2	6447
June	1st to 10th	Day	43% 5% 11% 24% 16% 2	2600
	11th to 20th	Day	40% 6% 15% 22% 15% 1	2611
	21st to end	Day	39% 6% 15% 22% 15% 3	2800
July	1st to 10th	Day	39% 5% 10% 27% 16% 2	6111
	11th to 20th	Day	41% 7% 12% 25% 14% 1	5831
	21st to end	Day	41% 7% 12% 21% 17% 3	6240
August	1st to 10th	Day	37% 7% 14% 28% 12% 1	4221
	11th to 20th	Day	36% 6% 11% 31% 16% 1	4213
	21st to end	Day	31% 7% 14% 31% 15% 3	4581
September	1st to 10th	Day	33% 5% 10% 25% 23% 4	2133
	11th to 20th	Day	34% 6% 9% 27% 21% 3	2090
	21st to end	Day	43% 4 8% 22% 21% 1	2090
October	1st to 10th	Day	26% 3 9% 34% 26% 1	3393
	11th to 20th	Day	34% 4 10% 27% 23% 2	3140
	21st to end	Day	39% 3 11% 26% 18% 2	3317
November	1st to 10th	Day	37% 5% 10% 28% 18% 3	1762
	11th to 20th	Day	52% 4 9% 21% 12% 2	1800
	21st to end	Day	56% 3 11% 20% 10% 1	1800
December	1st to 10th	Day	64% 2 13% 18% 4	2930
	11th to 20th	Day	67% 3 10% 15% 5%	3370
	21st to end	Day	73% 3 9% 10% 4	4466
January	1st to 10th	Night	69% 2 9% 15% 4	5889
	11th to 20th	Night	71% 2 8% 11% 6% 1	5900
	21st to end	Night	63% 3 11% 14% 6% 2	6490
February	1st to 10th	Night	60% 3 10% 18% 8% 1	2600
	11th to 20th	Night	59% 3 10% 18% 10% 1	2349
	21st to end	Night	59% 3 10% 17% 9% 2	1980
March	1st to 10th	Night	52% 2 7% 27% 10% 2	5171
	11th to 20th	Night	40% 4 10% 33% 12% 1	4980
	21st to end	Night	51% 4 7% 24% 13% 2	5467
April	1st to 10th	Night	47% 4 12% 21% 14% 2	2163
	11th to 20th	Night	44% 4 11% 18% 18% 4	1828
	21st to end	Night	45% 4 11% 23% 15% 2	1800
May	1st to 10th	Night	56% 5% 10% 17% 8% 3	4060
	11th to 20th	Night	44% 5% 11% 25% 13% 1	4033
	21st to end	Night	42% 5% 12% 28% 10% 2	4429
June	1st to 10th	Night	35% 5% 13% 24% 20% 3	1800
	11th to 20th	Night	34% 6% 14% 25% 17% 3	1776
	21st to end	Night	32% 8% 16% 24% 18% 3	1600
July	1st to 10th	Night	38% 5% 11% 24% 18% 4	3743
	11th to 20th	Night	38% 8% 13% 26% 14% 1	4006
	21st to end	Night	38% 7% 13% 20% 17% 4	4297
August	1st to 10th	Night	40% 6% 15% 26% 13% 1	2904
	11th to 20th	Night	38% 5% 9% 27% 20%	2902
	21st to end	Night	29% 6% 15% 29% 19% 3	3312
September	1st to 10th	Night	33% 4 12% 24% 21% 6%	2093
	11th to 20th	Night	28% 4 10% 27% 27% 4	2090
	21st to end	Night	39% 3 9% 21% 25% 1	2090
October	1st to 10th	Night	26% 4 6% 30% 32% 2	3566
	11th to 20th	Night	30% 3 10% 29% 25% 3	3779
	21st to end	Night	34% 3 7% 25% 26% 4	4230
November	1st to 10th	Night	38% 3 11% 25% 20% 3	2536
	11th to 20th	Night	49% 4 8% 23% 15% 2	2600
	21st to end	Night	56% 2 12% 21% 9% 1	2600
December	1st to 10th	Night	59% 3 13% 19% 6%	4250
	11th to 20th	Night	64% 4 12% 15% 5%	4824
	21st to end	Night	72% 3 9% 13% 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	26% 16% 33% 18% 5% 2	300
	11th to 20th	Day	26% 21% 38% 11% 5%	300
	21st to end	Day	29% 16% 35% 15% 5%	330
February	1st to 10th	Day	30% 19% 32% 14% 5%	300
	11th to 20th	Day	28% 17% 36% 15% 3 1	300
	21st to end	Day	24% 21% 38% 15% 2	249
March	1st to 10th	Day	22% 16% 34% 21% 6%	383
	11th to 20th	Day	24% 15% 33% 20% 7% 2	500
	21st to end	Day	28% 14% 31% 21% 5%	550
April	1st to 10th	Day	22% 13% 33% 20% 10% 2	500
	11th to 20th	Day	22% 15% 27% 22% 10% 5%	492
	21st to end	Day	20% 12% 30% 25% 10% 2	500
May	1st to 10th	Day	25% 13% 25% 22% 12% 4	503
	11th to 20th	Day	21% 8% 23% 25% 16% 7%	527
	21st to end	Day	14% 7% 23% 24% 21% 10%	573
June	1st to 10th	Day	13% 5% 24% 29% 20% 9%	530
	11th to 20th	Day	14% 6% 19% 27% 25% 9%	541
	21st to end	Day	12% 5% 25% 29% 21% 8%	730
July	1st to 10th	Day	12% 4 16% 23% 25% 20%	645
	11th to 20th	Day	10% 4 17% 25% 27% 17%	524
	21st to end	Day	10% 3 13% 28% 28% 17%	576
August	1st to 10th	Day	9% 4 13% 25% 31% 18%	526
	11th to 20th	Day	10% 4 21% 28% 22% 15%	519
	21st to end	Day	7% 4 12% 30% 29% 19%	583
September	1st to 10th	Day	12% 3 15% 25% 27% 18%	502
	11th to 20th	Day	10% 2 13% 22% 35% 19%	490
	21st to end	Day	20% 10% 15% 26% 19% 11%	490
October	1st to 10th	Day	11% 6% 22% 31% 21% 10%	490
	11th to 20th	Day	13% 11% 31% 26% 16% 3	490
	21st to end	Day	21% 12% 30% 26% 9% 1	477
November	1st to 10th	Day	15% 10% 33% 26% 13% 4	300
	11th to 20th	Day	21% 17% 27% 21% 12% 2	300
	21st to end	Day	26% 12% 36% 20% 5% 1	300
December	1st to 10th	Day	25% 17% 33% 18% 6% 2	300
	11th to 20th	Day	25% 13% 40% 17% 5%	300
	21st to end	Day	32% 16% 28% 18% 5%	330
January	1st to 10th	Night	22% 15% 35% 23% 5%	800
	11th to 20th	Night	28% 13% 33% 23% 4	800
	21st to end	Night	25% 11% 33% 27% 4	880
February	1st to 10th	Night	27% 11% 30% 29% 2	800
	11th to 20th	Night	25% 13% 35% 25% 2	783
	21st to end	Night	26% 11% 36% 25% 2	660
March	1st to 10th	Night	23% 10% 33% 28% 7%	800
	11th to 20th	Night	20% 13% 34% 27% 7%	800
	21st to end	Night	24% 10% 31% 25% 8%	880
April	1st to 10th	Night	21% 11% 34% 27% 6% 1	763
	11th to 20th	Night	17% 8% 34% 29% 11% 1	593
	21st to end	Night	17% 6% 38% 31% 8% 1	600
May	1st to 10th	Night	19% 9% 31% 30% 12%	600
	11th to 20th	Night	20% 5% 24% 35% 16% 1	591
	21st to end	Night	9% 4 19% 39% 27% 2	650
June	1st to 10th	Night	9% 4 22% 43% 21% 1	600
	11th to 20th	Night	11% 5% 15% 43% 25% 2	600
	21st to end	Night	9% 3 19% 42% 25% 2	600
July	1st to 10th	Night	10% 3 12% 40% 28% 8%	585
	11th to 20th	Night	7% 2 12% 38% 37% 4	582
	21st to end	Night	10% 2 10% 39% 36% 3	657
August	1st to 10th	Night	7% 3 11% 42% 35% 4	597
	11th to 20th	Night	9% 3 11% 39% 35% 4	594
	21st to end	Night	7% 2 10% 37% 37% 7%	660
September	1st to 10th	Night	14% 2 14% 32% 32% 5%	742
	11th to 20th	Night	10% 2 11% 36% 35% 6%	760
	21st to end	Night	18% 5% 18% 32% 24% 2	760
October	1st to 10th	Night	12% 4 23% 36% 22% 4	760
	11th to 20th	Night	19% 6% 27% 33% 13% 1	760
	21st to end	Night	22% 9% 28% 31% 10% 1	836
November	1st to 10th	Night	18% 7% 26% 33% 16% 1	780
	11th to 20th	Night	20% 12% 31% 28% 10%	800
	21st to end	Night	25% 10% 27% 31% 7%	800
December	1st to 10th	Night	28% 10% 30% 27% 5%	800
	11th to 20th	Night	25% 9% 31% 29% 5% 1	800
	21st to end	Night	30% 13% 27% 26% 4	880

Page generated at 2025-09-01 01:51:06. Version ac07

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