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 2026-06-16.

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% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	136921
	Night	14% 9% 3 8% 5% 4 4 3 5% 7% 37%	135238
Transparency	Day	46% 3 11% 24% 15% 2	140536
	Night	47% 3 10% 23% 15% 2	139685
Seeing	Day	16% 11% 27% 24% 16% 6%	17641
	Night	18% 8% 29% 29% 14% 2	27467

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	14% 13% 6% 10% 4 4 4 4 6% 8% 27%	4691
	11th to 20th	Day	10% 11% 5% 13% 6% 5% 4 3 5% 5% 32%	4710
	21st to end	Day	17% 13% 6% 10% 7% 6% 5% 4 4 5% 23%	5586
February	1st to 10th	Day	18% 12% 5% 8% 5% 4 3 3 5% 7% 30%	2100
	11th to 20th	Day	16% 10% 4 9% 5% 4 4 4 5% 5% 33%	2048
	21st to end	Day	17% 12% 5% 11% 3 2 3 3 5% 6% 33%	1730
March	1st to 10th	Day	19% 13% 5% 7% 4 4 3 2 4 4 35%	4580
	11th to 20th	Day	12% 8% 3 6% 4 4 4 4 6% 7% 41%	4945
	21st to end	Day	16% 10% 3 8% 6% 5% 5% 4 5% 7% 33%	5770
April	1st to 10th	Day	15% 9% 3 8% 5% 4 4 3 5% 8% 35%	2520
	11th to 20th	Day	17% 8% 3 7% 4 4 4 3 5% 6% 38%	2494
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 5% 7% 37%	2698
May	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 9% 30%	7616
	11th to 20th	Day	18% 6% 3 7% 4 4 4 3 5% 7% 39%	7626
	21st to end	Day	15% 8% 3 8% 6% 6% 6% 5% 8% 9% 27%	8391
June	1st to 10th	Day	10% 7% 2 6% 5% 5% 4 4 6% 8% 44%	2925
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 44%	2871
	21st to end	Day	8% 6% 2 7% 5% 6% 5% 5% 7% 9% 42%	2800
July	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 7% 11% 42%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 11% 39%	6360
	21st to end	Day	10% 7% 3 8% 5% 6% 7% 5% 8% 9% 33%	6588
August	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 8% 11% 45%	4234
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 12% 41%	3986
	21st to end	Day	5% 4 2 5% 4 3 4 4 6% 9% 56%	4312
September	1st to 10th	Day	13% 5% 2 6% 3 4 4 4 5% 7% 49%	2350
	11th to 20th	Day	9% 4 2 6% 4 4 4 4 5% 8% 49%	2200
	21st to end	Day	13% 6% 2 5% 4 3 4 3 5% 7% 49%	2200
October	1st to 10th	Day	11% 5% 2 5% 4 5% 4 4 4 7% 52%	2200
	11th to 20th	Day	12% 5% 1 6% 4 4 4 4 6% 7% 47%	2067
	21st to end	Day	19% 8% 2 6% 5% 4 4 3 5% 5% 38%	1980
November	1st to 10th	Day	8% 7% 2 5% 4 4 4 3 6% 5% 52%	1852
	11th to 20th	Day	16% 9% 3 7% 3 3 3 4 5% 7% 39%	1890
	21st to end	Day	19% 9% 3 8% 4 3 3 3 4 5% 37%	1890
December	1st to 10th	Day	15% 10% 3 7% 4 4 3 3 3 4 43%	3020
	11th to 20th	Day	16% 12% 4 9% 5% 6% 5% 4 5% 5% 28%	3261
	21st to end	Day	24% 16% 6% 8% 5% 4 4 3 4 6% 19%	4070
January	1st to 10th	Night	15% 13% 6% 11% 5% 5% 5% 4 5% 6% 26%	8232
	11th to 20th	Night	11% 14% 6% 14% 6% 6% 5% 3 4 5% 26%	8280
	21st to end	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 32%	8570
February	1st to 10th	Night	18% 12% 5% 8% 5% 4 4 3 5% 5% 29%	2520
	11th to 20th	Night	16% 11% 3 9% 5% 5% 4 3 6% 6% 33%	2458
	21st to end	Night	19% 11% 4 8% 5% 3 4 3 4 6% 33%	2076
March	1st to 10th	Night	20% 13% 3 6% 4 3 3 2 4 5% 37%	5493
	11th to 20th	Night	12% 6% 3 7% 4 4 4 3 5% 7% 47%	5233
	21st to end	Night	16% 9% 3 8% 5% 5% 5% 4 5% 6% 34%	5430
April	1st to 10th	Night	14% 8% 3 6% 6% 3 5% 4 6% 7% 38%	2100
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 7% 40%	2075
	21st to end	Night	16% 5% 3 7% 5% 3 4 4 7% 8% 38%	1919
May	1st to 10th	Night	18% 9% 3 8% 5% 4 5% 4 5% 8% 32%	5237
	11th to 20th	Night	15% 7% 3 7% 4 4 4 4 6% 8% 39%	5234
	21st to end	Night	15% 8% 3 9% 5% 5% 5% 4 6% 8% 32%	5761
June	1st to 10th	Night	10% 5% 2 7% 4 4 4 4 6% 8% 47%	1690
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 7% 9% 47%	1640
	21st to end	Night	7% 3 1 4 4 4 5% 4 7% 11% 50%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 6% 8% 47%	3618
	11th to 20th	Night	7% 5% 2 6% 4 5% 6% 4 7% 10% 44%	3617
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	4267
August	1st to 10th	Night	8% 5% 2 6% 5% 4 3 3 5% 9% 49%	2915
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 49%	3059
	21st to end	Night	3 2 1 4 3 4 4 4 5% 9% 59%	3586
September	1st to 10th	Night	11% 5% 2 4 4 4 4 3 5% 6% 52%	2029
	11th to 20th	Night	7% 3 2 5% 3 3 3 3 6% 8% 55%	2200
	21st to end	Night	13% 6% 2 6% 4 3 4 2 5% 5% 50%	2200
October	1st to 10th	Night	9% 4 2 4 4 3 3 2 5% 6% 58%	2200
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 5% 5% 48%	2327
	21st to end	Night	17% 7% 2 7% 4 4 4 3 5% 6% 40%	2860
November	1st to 10th	Night	12% 7% 2 6% 3 3 4 3 6% 6% 48%	2666
	11th to 20th	Night	14% 8% 2 7% 4 4 3 4 5% 7% 42%	2730
	21st to end	Night	18% 11% 3 8% 5% 4 4 3 5% 5% 34%	2730
December	1st to 10th	Night	17% 11% 3 8% 4 3 4 3 4 5% 38%	4380
	11th to 20th	Night	18% 11% 4 10% 6% 5% 4 3 5% 5% 29%	5156
	21st to end	Night	25% 17% 6% 10% 5% 4 4 3 4 4 18%	7150

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	56% 2 12% 22% 8% 1	4692
	11th to 20th	Day	55% 2 8% 18% 14% 3	4710
	21st to end	Day	66% 2 7% 16% 6% 4	5586
February	1st to 10th	Day	56% 2 9% 22% 10% 1	2100
	11th to 20th	Day	54% 3 9% 22% 12% 1	2058
	21st to end	Day	53% 2 9% 24% 10% 2	1730
March	1st to 10th	Day	54% 2 5% 18% 16% 5%	4580
	11th to 20th	Day	43% 2 8% 30% 14% 2	4945
	21st to end	Day	52% 2 13% 21% 11% 2	5772
April	1st to 10th	Day	47% 4 12% 22% 14% 1	2520
	11th to 20th	Day	47% 3 11% 23% 14% 3	2494
	21st to end	Day	48% 3 9% 24% 13% 2	2698
May	1st to 10th	Day	51% 3 14% 21% 11%	7651
	11th to 20th	Day	46% 2 12% 24% 15%	7630
	21st to end	Day	52% 4 11% 19% 12% 2	8405
June	1st to 10th	Day	39% 4 11% 24% 18% 3	2925
	11th to 20th	Day	37% 4 13% 24% 20% 2	2871
	21st to end	Day	38% 5% 16% 20% 18% 3	2800
July	1st to 10th	Day	38% 3 11% 26% 21% 2	6291
	11th to 20th	Day	40% 4 14% 28% 15% 1	6285
	21st to end	Day	47% 3 15% 21% 12% 2	6401
August	1st to 10th	Day	32% 4 15% 34% 14% 1	4221
	11th to 20th	Day	37% 3 12% 33% 15% 1	4025
	21st to end	Day	27% 3 13% 34% 18% 4	4311
September	1st to 10th	Day	36% 4 10% 27% 18% 5%	2350
	11th to 20th	Day	34% 3 10% 28% 21% 4	2200
	21st to end	Day	36% 4 8% 24% 25% 3	2200
October	1st to 10th	Day	24% 2 6% 32% 34% 1	3590
	11th to 20th	Day	32% 2 8% 28% 28% 2	3335
	21st to end	Day	40% 1 8% 24% 25% 2	3180
November	1st to 10th	Day	35% 3 10% 30% 18% 4	1852
	11th to 20th	Day	46% 2 9% 24% 15% 4	1890
	21st to end	Day	51% 2 9% 23% 14% 1	1890
December	1st to 10th	Day	48% 2 9% 27% 15%	3020
	11th to 20th	Day	59% 2 9% 20% 9% 1	3258
	21st to end	Day	68% 2 10% 13% 6%	4070
January	1st to 10th	Night	61% 2 10% 19% 8%	8233
	11th to 20th	Night	63% 1 8% 13% 13% 3	8280
	21st to end	Night	56% 1 9% 23% 10% 1	8570
February	1st to 10th	Night	58% 3 11% 21% 7% 1	2520
	11th to 20th	Night	53% 3 11% 21% 12% 1	2459
	21st to end	Night	55% 2 10% 19% 12% 2	2076
March	1st to 10th	Night	52% 2 5% 26% 12% 3	5493
	11th to 20th	Night	39% 2 10% 26% 21% 1	5233
	21st to end	Night	52% 2 8% 27% 10% 1	5430
April	1st to 10th	Night	44% 3 12% 26% 13% 2	2100
	11th to 20th	Night	44% 3 11% 19% 18% 5%	2075
	21st to end	Night	44% 4 10% 26% 14% 3	1919
May	1st to 10th	Night	52% 3 12% 24% 8% 2	5264
	11th to 20th	Night	45% 3 12% 25% 15%	5235
	21st to end	Night	50% 4 14% 19% 10% 3	5771
June	1st to 10th	Night	36% 4 11% 24% 23% 3	1690
	11th to 20th	Night	33% 5% 13% 24% 21% 5%	1640
	21st to end	Night	28% 6% 16% 25% 21% 5%	1600
July	1st to 10th	Night	36% 4 10% 27% 19% 5%	3580
	11th to 20th	Night	36% 4 15% 29% 14% 2	3572
	21st to end	Night	40% 3 15% 27% 12% 3	4141
August	1st to 10th	Night	34% 3 12% 36% 13% 1	2904
	11th to 20th	Night	34% 3 13% 31% 19% 1	3086
	21st to end	Night	24% 4 14% 32% 23% 4	3586
September	1st to 10th	Night	33% 3 10% 27% 20% 7%	2029
	11th to 20th	Night	27% 5% 9% 26% 29% 4	2200
	21st to end	Night	36% 3 10% 22% 25% 4	2200
October	1st to 10th	Night	22% 2 6% 23% 44% 3	3590
	11th to 20th	Night	28% 2 7% 24% 36% 3	3785
	21st to end	Night	36% 2 7% 24% 26% 5%	4610
November	1st to 10th	Night	37% 3 9% 25% 22% 3	2666
	11th to 20th	Night	43% 2 9% 23% 19% 4	2730
	21st to end	Night	53% 3 9% 22% 13% 1	2730
December	1st to 10th	Night	51% 2 11% 24% 12%	4380
	11th to 20th	Night	58% 2 10% 18% 11% 1	5158
	21st to end	Night	72% 2 8% 12% 5%	7150

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	22% 20% 32% 20% 5%	330
	11th to 20th	Day	25% 23% 35% 15% 2	330
	21st to end	Day	25% 22% 35% 14% 4	363
February	1st to 10th	Day	26% 18% 35% 18% 3	330
	11th to 20th	Day	25% 25% 33% 16% 2	330
	21st to end	Day	26% 15% 45% 12% 2	273
March	1st to 10th	Day	24% 23% 35% 15% 3	330
	11th to 20th	Day	24% 19% 37% 13% 6% 1	473
	21st to end	Day	28% 17% 34% 15% 5% 1	594
April	1st to 10th	Day	20% 21% 30% 22% 6% 1	540
	11th to 20th	Day	20% 19% 27% 22% 10% 2	532
	21st to end	Day	20% 17% 36% 16% 9% 2	540
May	1st to 10th	Day	20% 15% 33% 21% 8% 3	543
	11th to 20th	Day	22% 9% 28% 23% 13% 6%	567
	21st to end	Day	14% 7% 26% 27% 17% 9%	617
June	1st to 10th	Day	12% 6% 26% 30% 20% 6%	765
	11th to 20th	Day	10% 5% 24% 33% 21% 7%	756
	21st to end	Day	11% 5% 25% 29% 21% 9%	730
July	1st to 10th	Day	11% 4 15% 27% 27% 16%	721
	11th to 20th	Day	7% 3 19% 34% 26% 11%	718
	21st to end	Day	11% 3 13% 31% 29% 13%	649
August	1st to 10th	Day	7% 4 16% 28% 29% 16%	526
	11th to 20th	Day	14% 4 15% 30% 25% 12%	519
	21st to end	Day	8% 4 14% 25% 34% 15%	583
September	1st to 10th	Day	10% 5% 17% 25% 32% 12%	530
	11th to 20th	Day	10% 2 13% 27% 30% 18%	530
	21st to end	Day	17% 8% 19% 24% 22% 10%	530
October	1st to 10th	Day	11% 6% 21% 31% 24% 7%	530
	11th to 20th	Day	10% 14% 33% 25% 14% 4	486
	21st to end	Day	26% 16% 34% 18% 5% 1	363
November	1st to 10th	Day	13% 15% 35% 27% 8% 3	330
	11th to 20th	Day	22% 22% 27% 19% 9% 1	330
	21st to end	Day	23% 16% 33% 22% 6%	330
December	1st to 10th	Day	17% 22% 38% 16% 5% 1	330
	11th to 20th	Day	20% 16% 43% 16% 4 1	330
	21st to end	Day	29% 19% 33% 15% 4 1	363
January	1st to 10th	Night	23% 14% 35% 24% 4	1050
	11th to 20th	Night	25% 14% 38% 20% 3	1050
	21st to end	Night	23% 13% 39% 23% 3	1000
February	1st to 10th	Night	25% 12% 36% 24% 3	840
	11th to 20th	Night	24% 15% 39% 21% 2	823
	21st to end	Night	26% 12% 39% 21% 2	692
March	1st to 10th	Night	23% 15% 35% 24% 4	840
	11th to 20th	Night	21% 13% 37% 23% 5%	840
	21st to end	Night	25% 10% 33% 27% 5% 1	856
April	1st to 10th	Night	18% 10% 38% 28% 7%	630
	11th to 20th	Night	19% 10% 34% 27% 9% 1	623
	21st to end	Night	18% 7% 40% 26% 8%	630
May	1st to 10th	Night	20% 8% 34% 28% 10% 1	630
	11th to 20th	Night	16% 7% 25% 33% 17% 3	621
	21st to end	Night	12% 3 24% 35% 23% 2	683
June	1st to 10th	Night	11% 3 23% 40% 23%	630
	11th to 20th	Night	10% 3 18% 44% 24% 1	615
	21st to end	Night	8% 2 21% 39% 28% 3	600
July	1st to 10th	Night	10% 2 10% 34% 35% 9%	585
	11th to 20th	Night	8% 2 12% 39% 33% 5%	582
	21st to end	Night	9% 1 14% 39% 33% 4	657
August	1st to 10th	Night	9% 2 12% 34% 39% 4	597
	11th to 20th	Night	7% 2 10% 39% 37% 5%	594
	21st to end	Night	6% 1 13% 35% 40% 5%	660
September	1st to 10th	Night	13% 2 13% 36% 32% 5%	629
	11th to 20th	Night	9% 2 15% 32% 38% 5%	800
	21st to end	Night	15% 5% 21% 32% 25% 3	800
October	1st to 10th	Night	10% 6% 22% 33% 25% 4	800
	11th to 20th	Night	17% 9% 28% 30% 15% 2	800
	21st to end	Night	20% 9% 35% 27% 7% 1	880
November	1st to 10th	Night	16% 7% 34% 30% 12% 1	820
	11th to 20th	Night	18% 14% 34% 26% 9% 1	840
	21st to end	Night	24% 12% 28% 30% 6%	840
December	1st to 10th	Night	23% 11% 38% 23% 5%	840
	11th to 20th	Night	25% 9% 35% 24% 6% 1	935
	21st to end	Night	30% 14% 32% 20% 3	1155

Page generated at 2026-06-13 02:31:38. Version ac07

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