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 2025-02-21.

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	14% 8% 3 7% 4 4 4 4 6% 7% 38%	108498
	Night	15% 9% 3 7% 5% 4 4 3 5% 6% 38%	110193
Transparency	Day	45% 3 11% 24% 15% 2	112155
	Night	46% 3 10% 23% 16% 2	114663
Seeing	Day	17% 11% 26% 24% 16% 6%	15819
	Night	18% 8% 29% 29% 14% 2	25752

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% 14% 7% 10% 4 4 4 4 5% 6% 27%	3617
	11th to 20th	Day	13% 12% 6% 14% 5% 5% 3 3 4 5% 30%	3620
	21st to end	Day	20% 12% 6% 9% 5% 5% 5% 3 3 5% 26%	4324
February	1st to 10th	Day	18% 13% 5% 8% 5% 4 4 3 5% 7% 30%	2000
	11th to 20th	Day	16% 9% 4 9% 5% 4 5% 4 5% 5% 33%	1948
	21st to end	Day	19% 12% 5% 10% 3 3 3 3 4 6% 32%	1570
March	1st to 10th	Day	23% 14% 4 7% 4 3 3 2 4 4 31%	3120
	11th to 20th	Day	14% 8% 3 6% 4 4 4 3 5% 6% 44%	3380
	21st to end	Day	15% 9% 3 8% 6% 4 5% 4 6% 7% 33%	3941
April	1st to 10th	Day	14% 9% 3 8% 5% 4 4 3 5% 8% 36%	2280
	11th to 20th	Day	17% 7% 3 7% 4 4 4 3 5% 6% 39%	2254
	21st to end	Day	18% 8% 3 7% 5% 4 5% 4 4 6% 36%	2441
May	1st to 10th	Day	19% 8% 3 8% 5% 5% 4 4 6% 10% 29%	4082
	11th to 20th	Day	20% 7% 3 6% 4 4 4 3 5% 6% 38%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 4 8% 9% 37%	4476
June	1st to 10th	Day	10% 7% 2 6% 5% 5% 4 4 5% 8% 43%	2646
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 6% 8% 46%	2660
	21st to end	Day	8% 6% 2 7% 5% 6% 5% 5% 7% 9% 42%	2660
July	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 4 7% 11% 38%	4440
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 4 7% 10% 49%	4440
	21st to end	Day	9% 7% 3 7% 5% 7% 7% 6% 8% 9% 33%	4574
August	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 8% 11% 45%	4104
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 12% 41%	3862
	21st to end	Day	5% 4 2 5% 4 3 4 3 5% 9% 56%	4180
September	1st to 10th	Day	13% 5% 2 6% 3 4 4 4 4 6% 48%	2233
	11th to 20th	Day	10% 4 2 7% 4 4 4 4 5% 8% 48%	2090
	21st to end	Day	13% 6% 2 5% 4 3 3 3 5% 7% 49%	2090
October	1st to 10th	Day	11% 5% 2 6% 4 5% 4 4 4 7% 52%	2090
	11th to 20th	Day	12% 5% 1 6% 4 4 4 4 6% 7% 46%	1964
	21st to end	Day	19% 8% 2 6% 5% 4 4 3 5% 6% 38%	1881
November	1st to 10th	Day	8% 6% 2 5% 4 4 4 3 6% 5% 52%	1762
	11th to 20th	Day	16% 9% 3 7% 3 3 3 4 5% 7% 39%	1800
	21st to end	Day	19% 9% 3 7% 4 3 3 3 4 5% 38%	1800
December	1st to 10th	Day	15% 11% 3 6% 4 4 3 3 3 4 44%	2930
	11th to 20th	Day	16% 12% 4 9% 5% 6% 5% 4 5% 5% 28%	3176
	21st to end	Day	25% 16% 6% 8% 5% 4 4 3 4 6% 19%	3982
January	1st to 10th	Night	16% 13% 6% 12% 5% 5% 5% 4 5% 6% 23%	6348
	11th to 20th	Night	13% 16% 6% 14% 6% 6% 5% 3 4 5% 23%	6360
	21st to end	Night	20% 12% 4 7% 5% 4 4 2 4 5% 33%	6631
February	1st to 10th	Night	19% 13% 5% 8% 5% 4 4 4 5% 5% 28%	2400
	11th to 20th	Night	15% 11% 4 9% 5% 5% 4 3 5% 6% 32%	2338
	21st to end	Night	20% 11% 4 8% 5% 4 4 3 4 5% 32%	1885
March	1st to 10th	Night	22% 13% 2 6% 4 3 3 3 4 5% 34%	3733
	11th to 20th	Night	12% 7% 3 6% 3 4 4 3 5% 6% 48%	3578
	21st to end	Night	17% 8% 3 7% 5% 4 4 4 5% 5% 40%	3704
April	1st to 10th	Night	13% 8% 3 6% 6% 3 5% 4 6% 7% 39%	1900
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 5% 7% 41%	1875
	21st to end	Night	17% 5% 3 7% 5% 3 4 4 7% 8% 38%	1737
May	1st to 10th	Night	17% 11% 3 8% 6% 5% 5% 4 5% 8% 29%	2813
	11th to 20th	Night	18% 6% 2 6% 4 4 4 3 4 7% 41%	2812
	21st to end	Night	9% 5% 2 7% 4 4 5% 4 7% 10% 43%	3079
June	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 8% 48%	1530
	11th to 20th	Night	9% 4 2 4 4 4 4 4 7% 9% 48%	1520
	21st to end	Night	7% 2 1 4 4 4 5% 4 7% 11% 50%	1520
July	1st to 10th	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 48%	2530
	11th to 20th	Night	6% 4 1 4 3 4 5% 4 6% 9% 55%	2530
	21st to end	Night	9% 6% 2 7% 5% 6% 6% 6% 7% 10% 37%	2979
August	1st to 10th	Night	8% 5% 2 6% 5% 4 3 4 5% 9% 48%	2825
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 49%	2963
	21st to end	Night	4 2 1 4 3 4 4 4 6% 9% 58%	3476
September	1st to 10th	Night	12% 5% 2 4 4 4 4 3 5% 6% 51%	1927
	11th to 20th	Night	8% 3 2 4 3 3 3 4 6% 8% 55%	2090
	21st to end	Night	13% 6% 2 5% 4 3 4 2 5% 5% 50%	2090
October	1st to 10th	Night	9% 4 2 4 4 3 3 2 4 6% 58%	2090
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 5% 5% 48%	2210
	21st to end	Night	17% 7% 2 7% 4 4 4 3 5% 6% 41%	2717
November	1st to 10th	Night	13% 7% 2 6% 3 3 4 3 6% 6% 48%	2536
	11th to 20th	Night	15% 8% 2 7% 4 4 3 4 5% 7% 42%	2600
	21st to end	Night	18% 11% 3 8% 5% 4 4 3 5% 5% 34%	2600
December	1st to 10th	Night	17% 11% 3 7% 4 3 4 3 4 5% 39%	4250
	11th to 20th	Night	19% 11% 4 10% 6% 5% 4 3 5% 5% 29%	5021
	21st to end	Night	25% 17% 6% 10% 5% 4 4 3 4 4 18%	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	58% 3 8% 21% 9% 1	3618
	11th to 20th	Day	58% 3 8% 16% 13% 3	3620
	21st to end	Day	63% 2 7% 18% 7% 3	4324
February	1st to 10th	Day	56% 3 9% 21% 10% 1	2000
	11th to 20th	Day	53% 3 9% 22% 11% 1	1958
	21st to end	Day	55% 2 9% 23% 9% 2	1570
March	1st to 10th	Day	58% 3 6% 19% 10% 4	3120
	11th to 20th	Day	42% 3 9% 29% 15% 2	3380
	21st to end	Day	50% 3 14% 23% 9% 1	3941
April	1st to 10th	Day	47% 4 11% 23% 14% 1	2280
	11th to 20th	Day	46% 3 10% 24% 14% 3	2254
	21st to end	Day	49% 3 9% 23% 13% 3	2441
May	1st to 10th	Day	50% 5% 15% 22% 7%	4120
	11th to 20th	Day	47% 4 12% 25% 12% 1	4085
	21st to end	Day	41% 7% 14% 19% 18% 2	4489
June	1st to 10th	Day	40% 4 11% 25% 17% 3	2646
	11th to 20th	Day	35% 5% 13% 25% 20% 2	2660
	21st to end	Day	38% 6% 16% 20% 17% 3	2660
July	1st to 10th	Day	41% 3 13% 22% 19% 2	4371
	11th to 20th	Day	30% 3 13% 33% 20% 1	4365
	21st to end	Day	46% 4 16% 18% 14% 3	4429
August	1st to 10th	Day	32% 4 15% 33% 14% 1	4091
	11th to 20th	Day	37% 3 12% 33% 15% 1	3901
	21st to end	Day	27% 3 13% 34% 18% 4	4179
September	1st to 10th	Day	37% 4 10% 26% 18% 5%	2233
	11th to 20th	Day	35% 4 10% 27% 20% 4	2090
	21st to end	Day	36% 4 8% 25% 24% 3	2090
October	1st to 10th	Day	24% 2 6% 32% 34% 1	3480
	11th to 20th	Day	32% 2 8% 28% 29% 2	3232
	21st to end	Day	39% 2 8% 25% 25% 2	3081
November	1st to 10th	Day	34% 3 10% 30% 19% 4	1762
	11th to 20th	Day	45% 3 8% 24% 15% 4	1800
	21st to end	Day	50% 2 9% 24% 15% 1	1800
December	1st to 10th	Day	47% 2 8% 27% 15%	2930
	11th to 20th	Day	59% 3 9% 20% 9% 1	3173
	21st to end	Day	68% 2 10% 13% 6%	3982
January	1st to 10th	Night	64% 2 8% 17% 8%	6348
	11th to 20th	Night	67% 1 8% 11% 9% 3	6360
	21st to end	Night	57% 1 7% 22% 11% 1	6631
February	1st to 10th	Night	59% 3 11% 20% 7% 1	2400
	11th to 20th	Night	53% 3 11% 20% 12% 1	2339
	21st to end	Night	56% 3 10% 18% 12% 2	1885
March	1st to 10th	Night	55% 3 6% 23% 12% 1	3733
	11th to 20th	Night	37% 4 13% 24% 21% 1	3578
	21st to end	Night	47% 3 10% 29% 10% 1	3704
April	1st to 10th	Night	43% 4 11% 26% 14% 3	1900
	11th to 20th	Night	44% 3 10% 20% 19% 5%	1875
	21st to end	Night	44% 4 10% 24% 15% 4	1737
May	1st to 10th	Night	55% 5% 13% 20% 6% 2	2840
	11th to 20th	Night	44% 4 14% 27% 10% 1	2813
	21st to end	Night	35% 7% 16% 23% 15% 4	3087
June	1st to 10th	Night	35% 5% 10% 26% 21% 3	1530
	11th to 20th	Night	31% 5% 14% 24% 21% 5%	1520
	21st to end	Night	28% 7% 16% 25% 20% 5%	1520
July	1st to 10th	Night	36% 5% 10% 26% 18% 5%	2490
	11th to 20th	Night	27% 4 13% 34% 21% 2	2482
	21st to end	Night	42% 3 14% 25% 11% 4	2884
August	1st to 10th	Night	34% 4 12% 35% 13% 1	2814
	11th to 20th	Night	34% 3 13% 31% 19% 1	2990
	21st to end	Night	24% 4 15% 31% 23% 4	3476
September	1st to 10th	Night	33% 3 11% 26% 19% 7%	1927
	11th to 20th	Night	27% 5% 10% 26% 28% 4	2090
	21st to end	Night	36% 3 10% 23% 25% 4	2090
October	1st to 10th	Night	22% 2 6% 23% 44% 3	3480
	11th to 20th	Night	28% 2 7% 25% 36% 3	3668
	21st to end	Night	35% 2 7% 24% 26% 5%	4467
November	1st to 10th	Night	37% 3 9% 25% 22% 4	2536
	11th to 20th	Night	44% 2 9% 23% 19% 4	2600
	21st to end	Night	53% 3 9% 22% 13% 1	2600
December	1st to 10th	Night	50% 2 10% 25% 13%	4250
	11th to 20th	Night	58% 2 11% 17% 11% 1	5023
	21st to end	Night	72% 2 9% 12% 5%	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	22% 20% 31% 22% 5%	300
	11th to 20th	Day	26% 22% 34% 15% 3	300
	21st to end	Day	25% 22% 36% 13% 4	330
February	1st to 10th	Day	26% 20% 35% 16% 3	300
	11th to 20th	Day	24% 24% 34% 15% 2	300
	21st to end	Day	29% 15% 44% 10% 1	225
March	1st to 10th	Day	24% 25% 33% 15% 3	270
	11th to 20th	Day	26% 19% 35% 14% 6% 1	399
	21st to end	Day	29% 17% 33% 14% 6% 1	506
April	1st to 10th	Day	20% 21% 29% 22% 7% 1	460
	11th to 20th	Day	21% 18% 26% 22% 11% 2	452
	21st to end	Day	21% 18% 38% 14% 8% 2	460
May	1st to 10th	Day	21% 14% 32% 22% 8% 3	463
	11th to 20th	Day	23% 9% 26% 23% 13% 6%	487
	21st to end	Day	13% 7% 27% 27% 17% 9%	529
June	1st to 10th	Day	12% 6% 26% 29% 20% 6%	666
	11th to 20th	Day	10% 5% 24% 32% 21% 8%	680
	21st to end	Day	11% 5% 27% 29% 20% 8%	680
July	1st to 10th	Day	12% 4 16% 28% 25% 16%	671
	11th to 20th	Day	7% 3 20% 34% 26% 10%	668
	21st to end	Day	11% 3 14% 32% 29% 11%	601
August	1st to 10th	Day	8% 4 15% 29% 28% 15%	486
	11th to 20th	Day	14% 4 16% 32% 25% 10%	479
	21st to end	Day	9% 4 14% 24% 33% 16%	539
September	1st to 10th	Day	11% 5% 17% 26% 32% 10%	490
	11th to 20th	Day	10% 2 14% 28% 30% 16%	490
	21st to end	Day	16% 8% 21% 24% 21% 9%	490
October	1st to 10th	Day	10% 6% 23% 32% 22% 7%	490
	11th to 20th	Day	11% 15% 34% 24% 12% 4	448
	21st to end	Day	26% 15% 34% 18% 5% 1	330
November	1st to 10th	Day	12% 15% 34% 27% 8% 3	300
	11th to 20th	Day	20% 23% 27% 20% 9% 1	300
	21st to end	Day	23% 15% 34% 23% 5%	300
December	1st to 10th	Day	18% 22% 38% 15% 5% 1	300
	11th to 20th	Day	20% 16% 42% 17% 4 1	300
	21st to end	Day	29% 20% 32% 13% 4 1	330
January	1st to 10th	Night	23% 15% 35% 23% 4	1000
	11th to 20th	Night	25% 14% 37% 21% 3	1000
	21st to end	Night	23% 13% 37% 24% 3	953
February	1st to 10th	Night	26% 12% 37% 22% 3	800
	11th to 20th	Night	24% 15% 39% 21% 2	783
	21st to end	Night	27% 13% 38% 20% 2	629
March	1st to 10th	Night	22% 15% 35% 23% 4	760
	11th to 20th	Night	22% 12% 38% 22% 5% 1	760
	21st to end	Night	26% 10% 33% 26% 5% 1	774
April	1st to 10th	Night	17% 10% 39% 27% 7%	570
	11th to 20th	Night	20% 10% 33% 27% 10% 1	563
	21st to end	Night	19% 6% 42% 25% 7%	570
May	1st to 10th	Night	20% 8% 33% 28% 11% 1	570
	11th to 20th	Night	16% 7% 25% 31% 18% 3	561
	21st to end	Night	10% 4 24% 35% 24% 3	617
June	1st to 10th	Night	11% 3 23% 41% 23%	570
	11th to 20th	Night	10% 2 18% 45% 24% 1	570
	21st to end	Night	8% 2 22% 39% 27% 2	570
July	1st to 10th	Night	10% 2 11% 35% 33% 9%	555
	11th to 20th	Night	8% 2 13% 40% 33% 5%	552
	21st to end	Night	10% 1 15% 39% 32% 4	624
August	1st to 10th	Night	10% 2 12% 34% 38% 4	567
	11th to 20th	Night	8% 2 11% 39% 35% 5%	564
	21st to end	Night	6% 13% 33% 42% 6%	627
September	1st to 10th	Night	14% 2 13% 35% 31% 5%	597
	11th to 20th	Night	9% 2 16% 32% 37% 4	760
	21st to end	Night	15% 5% 22% 32% 24% 3	760
October	1st to 10th	Night	11% 5% 23% 33% 24% 4	760
	11th to 20th	Night	17% 9% 28% 29% 14% 2	760
	21st to end	Night	20% 9% 35% 28% 8% 1	836
November	1st to 10th	Night	16% 7% 33% 29% 12% 1	780
	11th to 20th	Night	18% 14% 33% 25% 9% 1	800
	21st to end	Night	24% 12% 28% 30% 6% 1	800
December	1st to 10th	Night	22% 11% 39% 22% 5%	800
	11th to 20th	Night	26% 9% 35% 24% 6% 1	890
	21st to end	Night	30% 14% 31% 20% 4	1100

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

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