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 2024-03-28.

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% 3 5% 5% 3 5% 5% 6% 8% 42%	79221
	Night	13% 6% 2 4 4 2 4 4 5% 7% 48%	80845
Transparency	Day	39% 7% 11% 18% 16% 8%	78946
	Night	35% 6% 12% 20% 17% 10%	80640
Seeing	Day	13% 6% 19% 26% 25% 12%	13882
	Night	15% 6% 23% 34% 20% 2	23965

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 5% 4 3 4 4 4 5% 43%	2847
	11th to 20th	Day	16% 6% 2 4 3 2 3 2 3 6% 52%	2850
	21st to end	Day	24% 7% 2 6% 4 2 3 4 6% 7% 35%	3173
February	1st to 10th	Day	22% 8% 2 6% 5% 3 2 3 4 6% 40%	1900
	11th to 20th	Day	19% 9% 3 6% 4 3 4 3 4 5% 41%	1849
	21st to end	Day	19% 6% 2 5% 4 2 4 4 4 6% 43%	1654
March	1st to 10th	Day	19% 7% 3 6% 5% 3 5% 5% 5% 6% 36%	2090
	11th to 20th	Day	17% 8% 3 7% 5% 3 4 4 5% 5% 38%	2090
	21st to end	Day	16% 7% 3 5% 5% 2 4 4 5% 6% 42%	2255
April	1st to 10th	Day	16% 6% 4 6% 6% 3 4 4 5% 7% 39%	1980
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 4 4 6% 39%	2003
	21st to end	Day	13% 6% 4 6% 5% 3 4 3 5% 6% 44%	2160
May	1st to 10th	Day	10% 5% 3 6% 6% 3 5% 6% 7% 9% 40%	2328
	11th to 20th	Day	10% 7% 3 5% 5% 4 5% 5% 5% 9% 42%	2302
	21st to end	Day	10% 6% 2 6% 6% 4 7% 7% 8% 10% 34%	2531
June	1st to 10th	Day	5% 3 2 6% 6% 4 6% 6% 7% 9% 46%	2340
	11th to 20th	Day	5% 3 2 4 6% 4 7% 7% 8% 11% 43%	2340
	21st to end	Day	6% 6% 3 6% 8% 6% 8% 8% 7% 10% 32%	2340
July	1st to 10th	Day	11% 4 3 6% 7% 4 5% 6% 8% 10% 35%	2340
	11th to 20th	Day	4 3 2 4 7% 4 7% 7% 10% 12% 40%	2340
	21st to end	Day	4 3 1 5% 7% 4 6% 7% 9% 13% 40%	2546
August	1st to 10th	Day	2 2 2 4 5% 4 6% 7% 7% 11% 49%	2328
	11th to 20th	Day	4 4 1 5% 6% 5% 7% 7% 8% 11% 42%	2275
	21st to end	Day	6% 4 2 5% 7% 4 7% 7% 8% 11% 38%	2178
September	1st to 10th	Day	6% 5% 3 7% 8% 4 6% 7% 7% 9% 39%	1980
	11th to 20th	Day	10% 5% 4 6% 8% 4 6% 6% 6% 7% 38%	1980
	21st to end	Day	7% 5% 2 5% 6% 5% 6% 5% 5% 8% 45%	1980
October	1st to 10th	Day	6% 4 2 4 6% 3 5% 5% 7% 8% 52%	1954
	11th to 20th	Day	13% 6% 2 4 4 3 4 5% 5% 6% 48%	1800
	21st to end	Day	12% 4 2 4 4 3 4 4 4 6% 53%	1980
November	1st to 10th	Day	11% 5% 2 5% 6% 3 4 4 5% 8% 46%	1858
	11th to 20th	Day	11% 6% 2 5% 4 2 4 4 4 6% 51%	1900
	21st to end	Day	17% 7% 3 6% 6% 2 4 4 5% 6% 40%	1744
December	1st to 10th	Day	17% 8% 3 6% 5% 3 4 4 4 7% 41%	1710
	11th to 20th	Day	16% 7% 3 6% 6% 2 5% 3 4 5% 42%	2161
	21st to end	Day	15% 7% 3 5% 4 2 3 3 4 5% 48%	3135
January	1st to 10th	Night	19% 7% 2 4 4 3 3 3 4 6% 45%	4108
	11th to 20th	Night	16% 7% 2 3 3 2 2 2 3 5% 56%	4120
	21st to end	Night	24% 7% 3 5% 4 3 3 2 4 6% 39%	4522
February	1st to 10th	Night	20% 9% 3 4 4 2 3 4 4 6% 40%	2280
	11th to 20th	Night	21% 7% 2 5% 4 2 2 3 4 5% 45%	2218
	21st to end	Night	22% 8% 3 5% 4 2 3 4 4 5% 40%	1799
March	1st to 10th	Night	17% 9% 2 5% 4 2 4 5% 4 7% 40%	2090
	11th to 20th	Night	19% 8% 3 6% 5% 3 4 4 4 6% 39%	2090
	21st to end	Night	15% 6% 2 4 4 2 3 4 5% 6% 47%	2255
April	1st to 10th	Night	13% 7% 3 4 5% 3 4 5% 6% 7% 41%	1980
	11th to 20th	Night	17% 7% 2 6% 4 2 4 3 4 7% 43%	1904
	21st to end	Night	15% 6% 2 5% 4 2 4 4 5% 7% 45%	1800
May	1st to 10th	Night	13% 6% 3 6% 5% 3 5% 5% 6% 8% 41%	1627
	11th to 20th	Night	10% 7% 2 4 5% 3 4 4 5% 10% 47%	1593
	21st to end	Night	7% 6% 3 5% 5% 4 6% 5% 7% 11% 42%	1745
June	1st to 10th	Night	5% 3 2 4 4 2 4 4 6% 10% 56%	1620
	11th to 20th	Night	5% 3 2 4 4 3 4 4 6% 8% 57%	1620
	21st to end	Night	6% 4 2 5% 5% 3 6% 7% 8% 9% 46%	1620
July	1st to 10th	Night	6% 4 2 5% 5% 3 5% 5% 6% 11% 48%	1620
	11th to 20th	Night	2 3 1 3 3 2 4 5% 6% 11% 60%	1620
	21st to end	Night	3 2 2 3 4 3 5% 5% 7% 13% 54%	1772
August	1st to 10th	Night	1 1 2 3 1 3 4 6% 11% 69%	1611
	11th to 20th	Night	2 3 2 4 3 2 5% 5% 9% 12% 54%	1619
	21st to end	Night	5% 2 1 4 5% 3 5% 6% 8% 13% 47%	2178
September	1st to 10th	Night	6% 4 2 4 4 3 6% 5% 7% 10% 49%	1980
	11th to 20th	Night	9% 5% 3 5% 6% 3 4 5% 6% 7% 47%	1980
	21st to end	Night	8% 4 2 4 4 2 4 4 5% 9% 54%	1980
October	1st to 10th	Night	5% 4 2 3 2 2 3 4 5% 9% 61%	1988
	11th to 20th	Night	10% 4 2 4 4 2 3 3 4 6% 58%	2160
	21st to end	Night	11% 5% 2 4 3 2 3 2 3 5% 60%	2376
November	1st to 10th	Night	9% 5% 3 5% 4 3 4 4 5% 6% 53%	2220
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 5% 5% 51%	2280
	21st to end	Night	15% 6% 3 5% 4 2 4 4 4 7% 45%	2432
December	1st to 10th	Night	18% 7% 2 5% 4 3 4 4 4 6% 44%	2470
	11th to 20th	Night	17% 9% 2 6% 5% 3 4 4 4 5% 41%	3036
	21st to end	Night	16% 8% 2 4 4 2 3 3 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% 6% 10% 13% 16% 8%	2090
	11th to 20th	Day	48% 5% 7% 10% 19% 10%	2090
	21st to end	Day	42% 5% 8% 16% 19% 9%	2255
April	1st to 10th	Day	45% 6% 8% 17% 14% 9%	1980
	11th to 20th	Day	46% 5% 7% 14% 18% 10%	2003
	21st to end	Day	41% 5% 7% 20% 18% 8%	2160
May	1st to 10th	Day	39% 8% 11% 19% 15% 8%	2328
	11th to 20th	Day	39% 7% 13% 20% 17% 4	2306
	21st to end	Day	42% 10% 13% 19% 15% 1	2531
June	1st to 10th	Day	30% 9% 17% 25% 17% 2	2340
	11th to 20th	Day	31% 10% 14% 25% 17% 3	2340
	21st to end	Day	44% 12% 13% 22% 9% 1	2340
July	1st to 10th	Day	41% 10% 18% 22% 8% 1	2276
	11th to 20th	Day	33% 12% 20% 21% 13%	2271
	21st to end	Day	29% 12% 24% 28% 6% 1	2405
August	1st to 10th	Day	26% 11% 20% 31% 12% 1	2314
	11th to 20th	Day	33% 12% 20% 24% 9% 2	2275
	21st to end	Day	38% 12% 17% 21% 9% 2	2178
September	1st to 10th	Day	38% 11% 14% 19% 13% 5%	1980
	11th to 20th	Day	42% 8% 15% 16% 15% 4	1980
	21st to end	Day	34% 10% 12% 17% 17% 11%	1980
October	1st to 10th	Day	28% 7% 11% 21% 21% 12%	1954
	11th to 20th	Day	35% 6% 8% 17% 18% 16%	1800
	21st to end	Day	33% 4 6% 16% 22% 19%	1980
November	1st to 10th	Day	36% 7% 10% 17% 20% 10%	1858
	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	44% 6% 11% 16% 16% 8%	2090
	11th to 20th	Night	47% 6% 8% 12% 16% 10%	2090
	21st to end	Night	38% 5% 11% 15% 19% 12%	2255
April	1st to 10th	Night	41% 7% 11% 17% 15% 9%	1980
	11th to 20th	Night	42% 4 11% 14% 14% 14%	1904
	21st to end	Night	40% 6% 10% 18% 16% 9%	1800
May	1st to 10th	Night	40% 7% 11% 19% 14% 9%	1627
	11th to 20th	Night	35% 7% 11% 24% 18% 4	1594
	21st to end	Night	34% 10% 17% 25% 13% 1	1746
June	1st to 10th	Night	22% 8% 19% 31% 19% 1	1620
	11th to 20th	Night	23% 8% 17% 32% 16% 4	1620
	21st to end	Night	32% 10% 20% 25% 11% 1	1620
July	1st to 10th	Night	29% 11% 24% 29% 7%	1575
	11th to 20th	Night	16% 11% 28% 34% 11%	1566
	21st to end	Night	19% 11% 30% 32% 7%	1673
August	1st to 10th	Night	10% 6% 30% 41% 13%	1601
	11th to 20th	Night	21% 12% 28% 31% 7% 1	1619
	21st to end	Night	26% 13% 25% 26% 8% 2	2178
September	1st to 10th	Night	29% 11% 20% 21% 14% 4	1980
	11th to 20th	Night	34% 8% 17% 23% 14% 4	1980
	21st to end	Night	27% 7% 16% 22% 18% 10%	1980
October	1st to 10th	Night	21% 6% 13% 27% 20% 12%	1988
	11th to 20th	Night	28% 5% 10% 21% 21% 16%	2160
	21st to end	Night	28% 4 8% 17% 22% 21%	2376
November	1st to 10th	Night	31% 7% 11% 20% 20% 11%	2220
	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	19% 14% 33% 26% 6% 1	285
April	1st to 10th	Day	21% 12% 35% 24% 8%	240
	11th to 20th	Day	20% 17% 25% 25% 11% 1	281
	21st to end	Day	19% 7% 34% 27% 12% 1	420
May	1st to 10th	Day	12% 12% 39% 25% 11% 1	591
	11th to 20th	Day	13% 6% 29% 32% 17% 3	625
	21st to end	Day	12% 5% 23% 35% 22% 3	679
June	1st to 10th	Day	7% 1 13% 33% 35% 11%	630
	11th to 20th	Day	7% 10% 41% 31% 10%	630
	21st to end	Day	9% 1 11% 28% 34% 17%	630
July	1st to 10th	Day	7% 2 7% 27% 35% 22%	621
	11th to 20th	Day	2 1 5% 22% 44% 26%	618
	21st to end	Day	3 1 4 23% 44% 24%	684
August	1st to 10th	Day	3 4 22% 44% 27%	626
	11th to 20th	Day	5% 4 20% 44% 26%	589
	21st to end	Day	10% 1 4 18% 25% 42%	297
September	1st to 10th	Day	7% 4 18% 37% 35%	270
	11th to 20th	Day	8% 2 4 19% 37% 30%	270
	21st to end	Day	9% 1 4 26% 37% 23%	270
October	1st to 10th	Day	7% 2 9% 27% 41% 14%	270
	11th to 20th	Day	11% 4 13% 33% 26% 14%	270
	21st to end	Day	19% 9% 20% 22% 23% 6%	297
November	1st to 10th	Day	15% 4 16% 31% 25% 8%	270
	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% 40% 28% 6% 1	615
April	1st to 10th	Night	16% 8% 39% 32% 5%	540
	11th to 20th	Night	21% 9% 34% 28% 8%	533
	21st to end	Night	19% 8% 37% 28% 8% 1	540
May	1st to 10th	Night	15% 7% 38% 32% 7%	540
	11th to 20th	Night	14% 4 28% 42% 12%	531
	21st to end	Night	8% 3 29% 43% 16% 1	584
June	1st to 10th	Night	6% 1 13% 51% 29% 1	540
	11th to 20th	Night	5% 2 17% 55% 21% 1	540
	21st to end	Night	6% 1 12% 38% 36% 7%	540
July	1st to 10th	Night	6% 2 7% 38% 40% 6%	525
	11th to 20th	Night	3 1 5% 37% 49% 6%	522
	21st to end	Night	2 1 5% 39% 48% 5%	591
August	1st to 10th	Night	1 3 42% 48% 6%	537
	11th to 20th	Night	3 4 39% 47% 7%	534
	21st to end	Night	5% 5% 27% 56% 7%	594
September	1st to 10th	Night	6% 5% 29% 51% 9%	540
	11th to 20th	Night	11% 1 4 33% 46% 6%	540
	21st to end	Night	9% 1 10% 29% 46% 6%	540
October	1st to 10th	Night	5% 2 10% 38% 41% 4	548
	11th to 20th	Night	11% 3 21% 40% 22% 3	720
	21st to end	Night	13% 6% 22% 37% 20% 2	792
November	1st to 10th	Night	11% 4 21% 43% 19% 1	740
	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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