HAS Columbus Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HAS Columbus Site 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	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	126025
	Night	14% 7% 2 5% 4 3 4 3 5% 7% 46%	122982
Transparency	Day	38% 7% 12% 20% 15% 8%	129742
	Night	36% 6% 12% 20% 16% 10%	127328
Seeing	Day	13% 6% 19% 26% 24% 12%	15926
	Night	15% 6% 23% 34% 20% 2	25746

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	19% 12% 4 6% 3 3 3 2 4 4 41%	4077
	11th to 20th	Day	15% 6% 2 6% 4 3 3 2 4 6% 50%	4080
	21st to end	Day	29% 8% 2 5% 3 3 2 2 5% 6% 36%	4554
February	1st to 10th	Day	21% 8% 2 6% 4 3 3 3 4 5% 41%	2000
	11th to 20th	Day	19% 9% 3 8% 4 4 3 3 4 5% 40%	1949
	21st to end	Day	19% 7% 2 5% 4 3 4 3 5% 5% 42%	1739
March	1st to 10th	Day	13% 6% 2 7% 4 5% 4 4 5% 7% 43%	4936
	11th to 20th	Day	14% 7% 3 7% 4 3 3 3 4 5% 47%	4980
	21st to end	Day	18% 8% 2 7% 4 4 4 4 5% 5% 40%	5462
April	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 3 6% 6% 40%	2200
	11th to 20th	Day	15% 7% 3 7% 4 6% 4 4 5% 6% 39%	2229
	21st to end	Day	13% 8% 3 7% 5% 4 5% 3 6% 6% 42%	2400
May	1st to 10th	Day	17% 7% 3 8% 5% 4 5% 4 7% 9% 31%	5850
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 4 6% 8% 44%	5862
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 10% 37%	6434
June	1st to 10th	Day	5% 3 2 6% 5% 5% 6% 5% 7% 9% 47%	2600
	11th to 20th	Day	5% 4 2 5% 5% 5% 6% 6% 8% 11% 43%	2600
	21st to end	Day	6% 6% 3 7% 7% 7% 8% 7% 8% 11% 33%	2600
July	1st to 10th	Day	8% 6% 2 7% 6% 6% 6% 5% 8% 11% 35%	5900
	11th to 20th	Day	5% 5% 3 6% 6% 6% 7% 6% 10% 13% 33%	5900
	21st to end	Day	9% 6% 2 7% 6% 5% 6% 5% 8% 11% 36%	6422
August	1st to 10th	Day	1 1 1 3 3 3 4 4 6% 10% 63%	4234
	11th to 20th	Day	2 3 1 4 3 5% 6% 6% 10% 14% 45%	4101
	21st to end	Day	5% 4 2 6% 5% 6% 7% 5% 8% 11% 40%	3949
September	1st to 10th	Day	5% 6% 3 9% 7% 6% 6% 5% 7% 9% 38%	2123
	11th to 20th	Day	9% 6% 3 7% 6% 5% 6% 4 6% 8% 39%	2090
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 4 6% 8% 46%	2090
October	1st to 10th	Day	5% 4 1 4 5% 4 5% 4 6% 8% 54%	2062
	11th to 20th	Day	12% 6% 2 5% 3 3 4 4 5% 6% 50%	1900
	21st to end	Day	11% 5% 2 5% 3 4 4 3 4 6% 53%	2090
November	1st to 10th	Day	12% 6% 2 6% 5% 4 4 4 5% 8% 45%	1958
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 4 6% 51%	2000
	21st to end	Day	16% 7% 3 7% 4 4 4 3 5% 6% 41%	1835
December	1st to 10th	Day	26% 9% 2 6% 4 3 4 3 4 5% 34%	2940
	11th to 20th	Day	15% 8% 3 7% 4 4 4 3 5% 6% 43%	3391
	21st to end	Day	14% 7% 2 6% 3 3 3 3 4 5% 50%	4488
January	1st to 10th	Night	20% 8% 2 5% 3 3 2 2 4 5% 45%	5888
	11th to 20th	Night	14% 6% 2 4 4 3 3 2 4 6% 53%	5900
	21st to end	Night	31% 7% 2 5% 3 3 3 2 4 5% 36%	6466
February	1st to 10th	Night	20% 10% 3 5% 4 3 3 3 5% 5% 39%	2400
	11th to 20th	Night	22% 8% 2 6% 3 3 2 2 4 5% 44%	2338
	21st to end	Night	22% 9% 3 6% 4 3 3 3 4 4 40%	1890
March	1st to 10th	Night	18% 11% 2 6% 3 3 4 3 5% 6% 38%	4919
	11th to 20th	Night	19% 8% 2 6% 3 3 3 2 4 5% 45%	4980
	21st to end	Night	19% 11% 2 6% 3 3 3 2 4 4 41%	5467
April	1st to 10th	Night	14% 8% 3 5% 4 3 4 4 6% 7% 41%	2200
	11th to 20th	Night	17% 7% 2 7% 4 3 3 3 5% 6% 43%	2118
	21st to end	Night	16% 7% 2 7% 4 3 4 3 5% 7% 43%	2000
May	1st to 10th	Night	24% 9% 3 7% 5% 4 4 3 5% 7% 28%	4060
	11th to 20th	Night	10% 7% 2 6% 4 4 4 3 5% 9% 45%	4053
	21st to end	Night	10% 8% 3 9% 5% 6% 5% 5% 7% 9% 32%	4443
June	1st to 10th	Night	5% 3 1 5% 4 3 4 4 6% 10% 55%	1800
	11th to 20th	Night	5% 4 2 4 4 4 3 4 6% 8% 56%	1800
	21st to end	Night	5% 4 2 5% 5% 4 5% 6% 8% 10% 46%	1800
July	1st to 10th	Night	6% 6% 2 6% 5% 4 5% 5% 8% 10% 43%	4078
	11th to 20th	Night	4 4 2 6% 4 5% 5% 5% 7% 10% 49%	4077
	21st to end	Night	6% 6% 3 7% 4 5% 5% 4 7% 11% 43%	4449
August	1st to 10th	Night	1 1 2 2 3 3 5% 9% 74%	2926
	11th to 20th	Night	1 2 1 3 2 3 4 5% 8% 13% 58%	2935
	21st to end	Night	3 2 1 5% 4 4 5% 4 8% 13% 51%	3949
September	1st to 10th	Night	6% 5% 2 6% 3 5% 5% 4 7% 9% 48%	2123
	11th to 20th	Night	8% 6% 2 6% 5% 4 4 3 6% 7% 48%	2090
	21st to end	Night	8% 4 2 4 4 4 3 3 6% 9% 55%	2090
October	1st to 10th	Night	4 4 1 3 2 3 3 3 5% 9% 62%	2099
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 3 6% 59%	2280
	21st to end	Night	10% 5% 2 4 3 2 3 2 3 5% 61%	2508
November	1st to 10th	Night	10% 6% 3 5% 4 3 4 3 5% 6% 51%	2340
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 5% 5% 52%	2400
	21st to end	Night	15% 6% 3 6% 4 3 3 3 5% 7% 46%	2560
December	1st to 10th	Night	24% 11% 4 7% 4 3 3 3 4 4 33%	4250
	11th to 20th	Night	15% 9% 3 6% 3 3 4 3 4 5% 45%	4816
	21st to end	Night	14% 7% 2 5% 3 3 3 2 3 5% 53%	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	49% 4 5% 16% 18% 7%	4078
	11th to 20th	Day	37% 3 6% 19% 21% 14%	4080
	21st to end	Day	51% 3 4 10% 18% 14%	4554
February	1st to 10th	Day	47% 4 6% 12% 17% 14%	2000
	11th to 20th	Day	48% 4 8% 13% 16% 10%	1959
	21st to end	Day	43% 5% 9% 15% 16% 11%	1739
March	1st to 10th	Day	39% 6% 8% 18% 13% 16%	4936
	11th to 20th	Day	40% 5% 6% 9% 17% 23%	4980
	21st to end	Day	44% 5% 7% 19% 18% 7%	5464
April	1st to 10th	Day	44% 6% 8% 16% 14% 11%	2200
	11th to 20th	Day	46% 5% 7% 14% 18% 10%	2229
	21st to end	Day	41% 6% 8% 20% 17% 7%	2400
May	1st to 10th	Day	46% 7% 12% 20% 12% 3	5888
	11th to 20th	Day	37% 6% 12% 20% 19% 5%	5866
	21st to end	Day	37% 9% 12% 30% 11% 1	6447
June	1st to 10th	Day	29% 9% 17% 27% 17% 2	2600
	11th to 20th	Day	31% 10% 13% 24% 18% 3	2600
	21st to end	Day	42% 12% 14% 22% 9% 1	2600
July	1st to 10th	Day	39% 10% 27% 20% 3	5836
	11th to 20th	Day	37% 12% 23% 22% 6%	5831
	21st to end	Day	38% 10% 19% 23% 8% 1	6240
August	1st to 10th	Day	16% 7% 14% 44% 18%	4220
	11th to 20th	Day	24% 11% 29% 28% 5% 1	4140
	21st to end	Day	34% 14% 17% 22% 11% 1	3948
September	1st to 10th	Day	39% 11% 14% 18% 13% 5%	2123
	11th to 20th	Day	41% 8% 14% 16% 16% 4	2090
	21st to end	Day	33% 9% 11% 17% 17% 12%	2090
October	1st to 10th	Day	18% 5% 7% 13% 19% 38%	3426
	11th to 20th	Day	23% 5% 7% 18% 30% 18%	3140
	21st to end	Day	28% 5% 7% 19% 28% 14%	3428
November	1st to 10th	Day	37% 7% 10% 16% 20% 10%	1958
	11th to 20th	Day	34% 6% 11% 15% 20% 15%	2000
	21st to end	Day	44% 6% 8% 14% 16% 12%	1835
December	1st to 10th	Day	53% 4 6% 14% 19% 4	2940
	11th to 20th	Day	41% 6% 9% 12% 21% 11%	3389
	21st to end	Day	36% 5% 5% 19% 21% 14%	4488
January	1st to 10th	Night	43% 4 6% 17% 19% 12%	5888
	11th to 20th	Night	35% 3 4 20% 23% 15%	5900
	21st to end	Night	52% 3 4 11% 18% 13%	6466
February	1st to 10th	Night	46% 4 8% 11% 17% 14%	2400
	11th to 20th	Night	44% 4 8% 15% 17% 12%	2338
	21st to end	Night	49% 4 7% 13% 16% 12%	1890
March	1st to 10th	Night	47% 5% 8% 15% 15% 11%	4919
	11th to 20th	Night	42% 5% 6% 12% 15% 20%	4980
	21st to end	Night	46% 4 8% 14% 18% 10%	5467
April	1st to 10th	Night	41% 6% 11% 17% 14% 10%	2200
	11th to 20th	Night	41% 5% 10% 14% 15% 15%	2118
	21st to end	Night	41% 7% 10% 18% 15% 8%	2000
May	1st to 10th	Night	54% 6% 9% 17% 10% 4	4087
	11th to 20th	Night	35% 7% 12% 23% 17% 6%	4054
	21st to end	Night	45% 9% 16% 23% 7% 1	4452
June	1st to 10th	Night	22% 8% 19% 32% 18% 1	1800
	11th to 20th	Night	24% 8% 16% 31% 17% 4	1800
	21st to end	Night	30% 11% 22% 26% 11% 1	1800
July	1st to 10th	Night	33% 10% 30% 24% 3	4035
	11th to 20th	Night	27% 10% 26% 29% 7%	4026
	21st to end	Night	34% 10% 21% 25% 10% 1	4320
August	1st to 10th	Night	8% 5% 20% 50% 17%	2916
	11th to 20th	Night	16% 9% 35% 35% 5% 1	2962
	21st to end	Night	23% 14% 25% 27% 11% 1	3949
September	1st to 10th	Night	31% 11% 20% 20% 14% 4	2123
	11th to 20th	Night	33% 7% 16% 24% 15% 4	2090
	21st to end	Night	26% 7% 16% 22% 18% 11%	2090
October	1st to 10th	Night	14% 5% 8% 17% 17% 38%	3502
	11th to 20th	Night	16% 3 9% 22% 32% 19%	3779
	21st to end	Night	20% 4 7% 22% 31% 17%	4120
November	1st to 10th	Night	32% 7% 11% 19% 20% 11%	2340
	11th to 20th	Night	34% 5% 10% 17% 19% 14%	2400
	21st to end	Night	39% 5% 10% 16% 18% 12%	2560
December	1st to 10th	Night	55% 4 6% 13% 14% 7%	4250
	11th to 20th	Night	41% 6% 10% 9% 19% 15%	4817
	21st to end	Night	36% 4 5% 16% 28% 12%	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	23% 10% 39% 22% 5% 1	300
	11th to 20th	Day	23% 16% 31% 22% 8% 1	300
	21st to end	Day	24% 13% 32% 21% 10% 1	330
February	1st to 10th	Day	26% 12% 27% 23% 11% 1	300
	11th to 20th	Day	24% 21% 29% 21% 5% 1	300
	21st to end	Day	27% 14% 35% 20% 4	249
March	1st to 10th	Day	20% 14% 37% 23% 6%	300
	11th to 20th	Day	17% 16% 39% 20% 6% 1	300
	21st to end	Day	21% 12% 33% 26% 7% 1	330
April	1st to 10th	Day	19% 17% 32% 23% 8% 1	300
	11th to 20th	Day	19% 16% 29% 25% 10% 1	347
	21st to end	Day	19% 8% 34% 27% 11% 1	500
May	1st to 10th	Day	13% 13% 40% 24% 10% 1	691
	11th to 20th	Day	14% 7% 30% 32% 16% 2	725
	21st to end	Day	12% 5% 25% 35% 20% 3	789
June	1st to 10th	Day	6% 1 13% 35% 34% 10%	730
	11th to 20th	Day	8% 1 10% 41% 30% 10%	730
	21st to end	Day	8% 1 9% 29% 34% 18%	730
July	1st to 10th	Day	8% 3 7% 26% 35% 22%	721
	11th to 20th	Day	4 1 4 22% 44% 24%	718
	21st to end	Day	5% 1 5% 23% 42% 24%	794
August	1st to 10th	Day	3 3 20% 44% 29%	726
	11th to 20th	Day	5% 4 19% 44% 28%	684
	21st to end	Day	9% 1 4 17% 29% 40%	363
September	1st to 10th	Day	6% 1 5% 21% 35% 32%	309
	11th to 20th	Day	7% 2 5% 19% 37% 29%	300
	21st to end	Day	8% 1 5% 26% 38% 22%	300
October	1st to 10th	Day	6% 2 9% 28% 42% 13%	300
	11th to 20th	Day	10% 3 13% 33% 28% 13%	300
	21st to end	Day	18% 8% 20% 22% 23% 8%	330
November	1st to 10th	Day	16% 5% 19% 31% 22% 7%	300
	11th to 20th	Day	18% 7% 18% 33% 21% 3	300
	21st to end	Day	19% 15% 29% 21% 12% 4	300
December	1st to 10th	Day	21% 7% 31% 27% 11% 4	300
	11th to 20th	Day	19% 14% 32% 25% 9% 2	300
	21st to end	Day	18% 8% 35% 26% 10% 2	330
January	1st to 10th	Night	23% 9% 29% 30% 9%	1000
	11th to 20th	Night	22% 11% 28% 31% 8%	1000
	21st to end	Night	25% 9% 29% 32% 6%	1089
February	1st to 10th	Night	27% 11% 26% 31% 5%	800
	11th to 20th	Night	27% 11% 30% 27% 5%	784
	21st to end	Night	26% 12% 36% 23% 2	570
March	1st to 10th	Night	23% 11% 35% 29% 4	600
	11th to 20th	Night	21% 12% 32% 31% 4	600
	21st to end	Night	19% 7% 40% 28% 5% 1	660
April	1st to 10th	Night	17% 9% 38% 32% 4	600
	11th to 20th	Night	21% 9% 34% 28% 7%	593
	21st to end	Night	21% 8% 36% 28% 8% 1	600
May	1st to 10th	Night	18% 8% 38% 30% 7%	600
	11th to 20th	Night	14% 5% 30% 40% 11%	591
	21st to end	Night	8% 4 31% 42% 14% 1	650
June	1st to 10th	Night	6% 2 14% 50% 28% 1	600
	11th to 20th	Night	5% 2 17% 55% 21% 1	600
	21st to end	Night	6% 2 11% 38% 36% 7%	600
July	1st to 10th	Night	6% 2 7% 38% 42% 6%	585
	11th to 20th	Night	3 1 6% 36% 49% 5%	582
	21st to end	Night	3 2 5% 38% 47% 5%	657
August	1st to 10th	Night	1 3 42% 49% 6%	597
	11th to 20th	Night	2 4 38% 49% 7%	594
	21st to end	Night	5% 5% 26% 56% 7%	660
September	1st to 10th	Night	7% 6% 29% 49% 9%	579
	11th to 20th	Night	10% 1 4 34% 45% 6%	570
	21st to end	Night	9% 1 9% 29% 46% 5%	570
October	1st to 10th	Night	5% 2 9% 39% 41% 4	579
	11th to 20th	Night	10% 3 21% 42% 22% 3	760
	21st to end	Night	12% 6% 22% 38% 20% 2	836
November	1st to 10th	Night	12% 4 21% 43% 18% 1	780
	11th to 20th	Night	16% 6% 22% 39% 17% 1	800
	21st to end	Night	19% 7% 26% 34% 14% 1	960
December	1st to 10th	Night	22% 7% 26% 30% 14% 1	1000
	11th to 20th	Night	25% 10% 27% 30% 8%	1000
	21st to end	Night	22% 8% 27% 33% 9% 1	1100

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