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 2024-11-04.

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% 5% 5% 4 6% 8% 41%	100998
	Night	13% 6% 2 5% 4 3 4 3 5% 7% 47%	98113
Transparency	Day	38% 7% 12% 20% 16% 8%	104754
	Night	35% 6% 13% 20% 17% 9%	102484
Seeing	Day	12% 6% 19% 26% 25% 12%	14779
	Night	15% 6% 22% 34% 20% 2	24656

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% 10% 3 6% 3 4 4 3 4 5% 43%	2847
	11th to 20th	Day	15% 6% 2 4 3 3 3 1 3 6% 52%	2850
	21st to end	Day	24% 7% 2 6% 3 3 3 3 6% 7% 35%	3173
February	1st to 10th	Day	22% 8% 2 6% 4 3 3 2 4 5% 40%	1900
	11th to 20th	Day	19% 9% 3 7% 4 4 3 3 4 5% 41%	1849
	21st to end	Day	19% 7% 2 5% 4 3 4 3 5% 5% 43%	1654
March	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 7% 34%	3436
	11th to 20th	Day	19% 10% 4 10% 6% 5% 4 3 6% 5% 29%	3480
	21st to end	Day	16% 7% 2 6% 4 3 4 4 5% 6% 43%	3814
April	1st to 10th	Day	16% 7% 3 7% 5% 4 5% 3 6% 6% 39%	2090
	11th to 20th	Day	16% 7% 3 7% 4 6% 4 4 5% 5% 39%	2116
	21st to end	Day	13% 8% 3 7% 5% 4 4 3 5% 5% 43%	2280
May	1st to 10th	Day	17% 7% 3 8% 5% 4 5% 4 7% 8% 32%	4070
	11th to 20th	Day	13% 7% 2 7% 4 5% 5% 3 5% 7% 41%	4082
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 10% 39%	4477
June	1st to 10th	Day	5% 3 2 6% 5% 5% 6% 5% 7% 9% 46%	2470
	11th to 20th	Day	5% 4 1 5% 5% 5% 6% 6% 8% 11% 43%	2470
	21st to end	Day	6% 6% 3 7% 7% 7% 8% 6% 7% 10% 33%	2470
July	1st to 10th	Day	9% 4 2 5% 5% 5% 5% 5% 7% 11% 43%	4120
	11th to 20th	Day	5% 6% 3 7% 6% 6% 8% 6% 10% 12% 32%	4120
	21st to end	Day	11% 8% 2 8% 6% 6% 6% 5% 8% 10% 29%	4465
August	1st to 10th	Day	1 1 1 3 3 3 4 4 6% 10% 63%	4104
	11th to 20th	Day	2 3 1 4 4 5% 6% 6% 10% 14% 45%	3973
	21st to end	Day	5% 4 2 6% 5% 6% 7% 5% 8% 11% 40%	3828
September	1st to 10th	Day	6% 6% 3 9% 7% 6% 6% 5% 7% 9% 38%	2090
	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	11% 6% 2 6% 5% 4 4 4 5% 8% 46%	1888
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 4 6% 51%	1900
	21st to end	Day	16% 7% 3 7% 4 3 4 3 6% 6% 40%	1744
December	1st to 10th	Day	17% 9% 2 7% 4 3 4 3 4 6% 41%	1710
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 3 4 5% 42%	2161
	21st to end	Day	15% 7% 3 6% 3 3 3 3 4 5% 48%	3135
January	1st to 10th	Night	19% 8% 2 5% 3 3 3 3 4 6% 45%	4108
	11th to 20th	Night	16% 7% 2 4 3 2 2 2 3 5% 56%	4120
	21st to end	Night	24% 7% 2 6% 3 3 3 2 4 6% 39%	4522
February	1st to 10th	Night	20% 10% 3 5% 4 3 3 3 5% 6% 39%	2280
	11th to 20th	Night	21% 8% 2 6% 3 3 2 2 4 5% 45%	2218
	21st to end	Night	21% 8% 3 6% 4 3 3 3 4 4 40%	1799
March	1st to 10th	Night	21% 13% 3 7% 4 3 4 3 5% 7% 32%	3419
	11th to 20th	Night	26% 10% 3 7% 5% 4 4 3 4 6% 29%	3480
	21st to end	Night	15% 7% 2 6% 4 4 3 3 5% 5% 46%	3817
April	1st to 10th	Night	14% 8% 3 5% 5% 3 4 4 7% 7% 41%	2090
	11th to 20th	Night	17% 7% 2 6% 4 4 3 3 5% 6% 42%	2011
	21st to end	Night	16% 7% 2 6% 4 3 4 3 5% 7% 44%	1900
May	1st to 10th	Night	24% 9% 3 7% 4 3 4 3 5% 6% 30%	2830
	11th to 20th	Night	13% 8% 2 5% 4 4 4 3 5% 7% 45%	2823
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 5% 8% 10% 37%	3090
June	1st to 10th	Night	5% 3 1 5% 3 3 4 4 6% 10% 56%	1710
	11th to 20th	Night	5% 4 2 4 4 4 3 4 6% 8% 56%	1710
	21st to end	Night	5% 4 2 5% 5% 4 5% 6% 7% 9% 46%	1710
July	1st to 10th	Night	5% 4 1 4 4 3 5% 4 7% 10% 53%	2850
	11th to 20th	Night	4 5% 2 7% 4 5% 5% 5% 7% 11% 47%	2850
	21st to end	Night	7% 7% 3 8% 5% 5% 5% 4 7% 11% 38%	3098
August	1st to 10th	Night	1 1 2 2 3 3 5% 9% 74%	2836
	11th to 20th	Night	1 2 1 3 2 3 4 5% 8% 13% 58%	2844
	21st to end	Night	3 2 1 5% 4 4 5% 4 8% 13% 51%	3828
September	1st to 10th	Night	6% 5% 2 6% 3 5% 5% 4 7% 9% 48%	2090
	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	9% 6% 3 6% 4 3 4 3 5% 6% 52%	2263
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 5% 51%	2280
	21st to end	Night	15% 7% 3 6% 4 3 4 3 5% 7% 45%	2432
December	1st to 10th	Night	18% 7% 2 5% 4 4 3 3 4 6% 44%	2470
	11th to 20th	Night	17% 9% 2 6% 4 3 4 3 4 5% 41%	3036
	21st to end	Night	16% 8% 2 5% 3 3 4 2 4 5% 48%	4532

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	44% 5% 7% 14% 21% 10%	2848
	11th to 20th	Day	34% 4 7% 21% 23% 12%	2850
	21st to end	Day	47% 4 5% 12% 21% 10%	3173
February	1st to 10th	Day	48% 4 6% 13% 17% 13%	1900
	11th to 20th	Day	47% 4 8% 13% 17% 11%	1859
	21st to end	Day	43% 6% 9% 15% 16% 11%	1654
March	1st to 10th	Day	47% 7% 10% 16% 14% 6%	3436
	11th to 20th	Day	56% 6% 8% 8% 16% 7%	3480
	21st to end	Day	41% 5% 9% 19% 19% 8%	3814
April	1st to 10th	Day	44% 6% 8% 17% 14% 11%	2090
	11th to 20th	Day	46% 6% 8% 14% 18% 10%	2116
	21st to end	Day	41% 6% 8% 20% 17% 8%	2280
May	1st to 10th	Day	47% 7% 12% 18% 10% 5%	4108
	11th to 20th	Day	42% 7% 10% 17% 20% 5%	4086
	21st to end	Day	35% 10% 12% 32% 10% 1	4489
June	1st to 10th	Day	29% 9% 17% 25% 18% 2	2470
	11th to 20th	Day	31% 10% 13% 24% 18% 3	2470
	21st to end	Day	42% 11% 13% 23% 9% 1	2470
July	1st to 10th	Day	33% 9% 28% 26% 4	4056
	11th to 20th	Day	40% 12% 20% 19% 9%	4051
	21st to end	Day	45% 11% 20% 21% 4	4325
August	1st to 10th	Day	16% 7% 14% 43% 19%	4090
	11th to 20th	Day	25% 11% 29% 28% 6% 1	4012
	21st to end	Day	35% 14% 17% 23% 11% 1	3827
September	1st to 10th	Day	39% 11% 13% 18% 14% 5%	2090
	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% 17% 20% 9%	1888
	11th to 20th	Day	35% 6% 11% 15% 19% 13%	1900
	21st to end	Day	45% 6% 7% 14% 16% 12%	1744
December	1st to 10th	Day	45% 5% 7% 19% 18% 6%	1710
	11th to 20th	Day	43% 5% 7% 11% 22% 12%	2159
	21st to end	Day	40% 4 5% 17% 21% 12%	3135
January	1st to 10th	Night	42% 4 7% 14% 16% 16%	4108
	11th to 20th	Night	34% 3 6% 17% 25% 15%	4120
	21st to end	Night	47% 3 5% 13% 22% 10%	4522
February	1st to 10th	Night	46% 4 8% 11% 17% 14%	2280
	11th to 20th	Night	43% 4 8% 15% 17% 13%	2218
	21st to end	Night	48% 4 7% 13% 16% 13%	1799
March	1st to 10th	Night	53% 6% 10% 14% 13% 5%	3419
	11th to 20th	Night	56% 7% 8% 13% 10% 6%	3480
	21st to end	Night	39% 5% 11% 14% 21% 10%	3817
April	1st to 10th	Night	41% 7% 11% 17% 14% 10%	2090
	11th to 20th	Night	42% 5% 11% 14% 14% 14%	2011
	21st to end	Night	41% 6% 10% 19% 16% 9%	1900
May	1st to 10th	Night	53% 6% 10% 17% 9% 5%	2857
	11th to 20th	Night	38% 7% 12% 19% 17% 8%	2824
	21st to end	Night	39% 10% 17% 27% 8% 1	3099
June	1st to 10th	Night	21% 8% 19% 32% 19% 1	1710
	11th to 20th	Night	24% 8% 16% 31% 17% 4	1710
	21st to end	Night	31% 10% 21% 26% 11% 1	1710
July	1st to 10th	Night	24% 9% 31% 32% 4	2805
	11th to 20th	Night	29% 11% 23% 27% 10%	2796
	21st to end	Night	39% 11% 23% 23% 4	2999
August	1st to 10th	Night	7% 5% 20% 50% 17%	2826
	11th to 20th	Night	16% 9% 34% 35% 5% 1	2871
	21st to end	Night	23% 14% 25% 26% 11% 1	3828
September	1st to 10th	Night	30% 11% 19% 20% 15% 4	2090
	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%	2263
	11th to 20th	Night	35% 6% 11% 18% 18% 13%	2280
	21st to end	Night	40% 5% 9% 16% 18% 12%	2432
December	1st to 10th	Night	41% 5% 10% 20% 15% 9%	2470
	11th to 20th	Night	44% 6% 6% 11% 17% 15%	3037
	21st to end	Night	40% 4 5% 14% 25% 11%	4532

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% 8% 39% 24% 6% 1	270
	11th to 20th	Day	23% 14% 30% 23% 9% 1	270
	21st to end	Day	22% 13% 31% 22% 11% 1	297
February	1st to 10th	Day	27% 13% 28% 21% 9% 1	270
	11th to 20th	Day	22% 20% 30% 22% 5% 1	270
	21st to end	Day	25% 14% 37% 20% 3	225
March	1st to 10th	Day	21% 13% 37% 22% 7%	270
	11th to 20th	Day	19% 15% 39% 20% 7% 1	270
	21st to end	Day	20% 13% 34% 26% 7% 1	297
April	1st to 10th	Day	20% 15% 34% 24% 7%	270
	11th to 20th	Day	19% 16% 30% 24% 10% 1	314
	21st to end	Day	18% 7% 35% 27% 12% 1	460
May	1st to 10th	Day	13% 12% 39% 24% 11% 1	641
	11th to 20th	Day	15% 6% 28% 32% 17% 3	675
	21st to end	Day	12% 5% 25% 35% 20% 3	734
June	1st to 10th	Day	6% 1 13% 34% 35% 10%	680
	11th to 20th	Day	8% 10% 41% 31% 10%	680
	21st to end	Day	9% 1 10% 28% 34% 18%	680
July	1st to 10th	Day	7% 2 7% 26% 36% 22%	671
	11th to 20th	Day	4 1 5% 22% 43% 25%	668
	21st to end	Day	5% 1 5% 24% 42% 23%	739
August	1st to 10th	Day	3 3 21% 44% 28%	676
	11th to 20th	Day	5% 4 19% 45% 27%	636
	21st to end	Day	10% 1 4 17% 28% 40%	330
September	1st to 10th	Day	7% 1 5% 21% 34% 32%	300
	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% 17% 30% 24% 8%	279
	11th to 20th	Day	19% 7% 17% 35% 20% 2	270
	21st to end	Day	21% 15% 29% 22% 10% 3	270
December	1st to 10th	Day	19% 6% 30% 28% 12% 4	270
	11th to 20th	Day	20% 14% 33% 25% 7% 1	270
	21st to end	Day	19% 8% 37% 24% 10% 2	297
January	1st to 10th	Night	22% 9% 30% 30% 10%	950
	11th to 20th	Night	22% 11% 27% 31% 9%	950
	21st to end	Night	23% 9% 29% 33% 6%	1035
February	1st to 10th	Night	26% 11% 27% 31% 5%	760
	11th to 20th	Night	27% 10% 30% 28% 5%	744
	21st to end	Night	25% 13% 37% 23% 2	543
March	1st to 10th	Night	23% 10% 34% 29% 4	570
	11th to 20th	Night	21% 11% 32% 32% 5%	570
	21st to end	Night	18% 7% 41% 28% 5% 1	627
April	1st to 10th	Night	17% 8% 39% 31% 5%	570
	11th to 20th	Night	21% 9% 34% 28% 7%	563
	21st to end	Night	20% 8% 36% 28% 8% 1	570
May	1st to 10th	Night	17% 8% 38% 31% 7%	570
	11th to 20th	Night	14% 4 28% 42% 11%	561
	21st to end	Night	8% 4 30% 42% 15% 1	617
June	1st to 10th	Night	6% 2 13% 50% 28% 1	570
	11th to 20th	Night	5% 2 17% 55% 21% 1	570
	21st to end	Night	6% 2 12% 38% 35% 7%	570
July	1st to 10th	Night	6% 2 7% 38% 41% 6%	555
	11th to 20th	Night	3 1 5% 36% 49% 5%	552
	21st to end	Night	3 2 4 39% 47% 5%	624
August	1st to 10th	Night	1 3 41% 49% 6%	567
	11th to 20th	Night	2 4 39% 48% 7%	564
	21st to end	Night	5% 5% 27% 56% 7%	627
September	1st to 10th	Night	7% 6% 30% 49% 9%	570
	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% 5% 21% 43% 19% 1	755
	11th to 20th	Night	16% 6% 22% 38% 16% 1	760
	21st to end	Night	19% 7% 26% 33% 13% 1	912
December	1st to 10th	Night	21% 7% 26% 31% 14% 1	950
	11th to 20th	Night	25% 10% 27% 29% 8%	950
	21st to end	Night	22% 8% 28% 32% 9% 1	1045

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