Cincinnati Observatory Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cincinnati Observatory Center clear sky chart from 2005-11-06 to 2026-10-14.

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% 9% 3 7% 5% 5% 5% 4 6% 8% 36%	149422
	Night	15% 9% 3 8% 5% 4 4 3 5% 7% 36%	142327
Transparency	Day	45% 6% 11% 23% 13% 1	153061
	Night	46% 5% 11% 22% 14% 2	146760
Seeing	Day	19% 14% 27% 22% 13% 5%	17946
	Night	19% 11% 26% 28% 15% 2	27491

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	18% 14% 8% 11% 4 4 3 3 4 6% 25%	4691
	11th to 20th	Day	12% 14% 5% 15% 6% 6% 4 2 4 4 28%	5256
	21st to end	Day	20% 13% 6% 9% 6% 6% 5% 3 5% 6% 21%	5780
February	1st to 10th	Day	19% 13% 4 8% 5% 3 4 4 4 6% 29%	2001
	11th to 20th	Day	17% 11% 5% 10% 5% 4 3 4 4 6% 31%	2048
	21st to end	Day	18% 13% 5% 9% 5% 4 3 3 4 6% 31%	1730
March	1st to 10th	Day	19% 14% 4 8% 4 4 3 3 4 4 31%	4622
	11th to 20th	Day	14% 8% 3 7% 4 4 4 4 5% 8% 39%	5090
	21st to end	Day	18% 9% 3 7% 5% 4 4 4 6% 7% 34%	5586
April	1st to 10th	Day	16% 9% 3 7% 4 4 5% 4 6% 7% 35%	2473
	11th to 20th	Day	16% 9% 3 7% 4 3 4 3 6% 6% 38%	2550
	21st to end	Day	18% 8% 2 6% 5% 5% 4 4 5% 7% 36%	2730
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	7616
	11th to 20th	Day	17% 7% 3 7% 4 4 4 3 5% 7% 37%	7626
	21st to end	Day	17% 8% 3 8% 5% 6% 6% 4 7% 9% 28%	8391
June	1st to 10th	Day	13% 5% 2 7% 5% 4 5% 5% 6% 8% 40%	2730
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	2917
	21st to end	Day	9% 6% 2 7% 6% 5% 6% 5% 6% 9% 39%	2940
July	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 4 6% 10% 40%	8280
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 11% 39%	7928
	21st to end	Day	9% 6% 3 8% 6% 6% 7% 5% 7% 9% 33%	8340
August	1st to 10th	Day	11% 5% 2 6% 4 5% 6% 5% 7% 9% 39%	6014
	11th to 20th	Day	11% 7% 3 8% 5% 5% 6% 5% 6% 10% 35%	5951
	21st to end	Day	5% 3 1 4 3 3 4 3 6% 9% 58%	6126
September	1st to 10th	Day	12% 6% 2 5% 3 4 4 3 5% 7% 50%	2389
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 3 6% 8% 50%	2310
	21st to end	Day	16% 6% 2 6% 4 4 3 3 4 7% 46%	2310
October	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 5% 6% 51%	2310
	11th to 20th	Day	13% 7% 2 5% 4 3 4 3 5% 7% 46%	2062
	21st to end	Day	21% 7% 2 5% 4 3 3 3 4 7% 39%	2052
November	1st to 10th	Day	10% 8% 2 5% 4 4 4 3 4 6% 51%	1852
	11th to 20th	Day	14% 12% 4 8% 4 4 4 3 5% 6% 36%	1890
	21st to end	Day	19% 11% 4 8% 4 4 3 2 4 6% 34%	1890
December	1st to 10th	Day	20% 10% 3 8% 5% 4 3 2 4 5% 37%	3020
	11th to 20th	Day	18% 16% 5% 9% 5% 5% 5% 4 4 5% 26%	3463
	21st to end	Day	23% 19% 5% 9% 5% 5% 4 3 4 5% 18%	4458
January	1st to 10th	Night	15% 15% 6% 13% 6% 5% 5% 4 5% 5% 21%	8217
	11th to 20th	Night	13% 16% 6% 14% 7% 5% 5% 3 4 4 24%	7680
	21st to end	Night	18% 13% 4 8% 6% 4 4 3 4 5% 31%	8401
February	1st to 10th	Night	20% 12% 4 9% 5% 4 4 4 4 5% 29%	2614
	11th to 20th	Night	18% 11% 4 9% 5% 4 4 4 5% 6% 30%	2458
	21st to end	Night	21% 14% 4 8% 4 3 3 3 4 6% 31%	2076
March	1st to 10th	Night	20% 13% 2 6% 4 3 3 3 4 5% 36%	5451
	11th to 20th	Night	13% 7% 3 6% 4 4 5% 4 5% 7% 43%	5090
	21st to end	Night	18% 9% 3 8% 4 5% 4 3 5% 5% 34%	5588
April	1st to 10th	Night	15% 9% 3 6% 4 4 4 4 6% 7% 36%	2163
	11th to 20th	Night	14% 8% 2 6% 4 4 4 4 6% 7% 40%	2017
	21st to end	Night	17% 7% 3 6% 4 5% 4 3 6% 9% 37%	1890
May	1st to 10th	Night	20% 9% 3 7% 5% 5% 5% 4 6% 7% 31%	5237
	11th to 20th	Night	16% 6% 2 7% 5% 5% 5% 4 7% 8% 36%	5234
	21st to end	Night	16% 8% 3 8% 5% 5% 5% 4 6% 9% 32%	5761
June	1st to 10th	Night	8% 6% 2 6% 4 4 4 4 6% 8% 48%	1890
	11th to 20th	Night	9% 4 3 5% 4 4 3 4 6% 11% 47%	1696
	21st to end	Night	7% 4 2 5% 4 5% 5% 4 7% 10% 47%	1680
July	1st to 10th	Night	9% 6% 2 7% 4 4 5% 3 6% 8% 47%	4708
	11th to 20th	Night	9% 6% 2 7% 5% 5% 4 4 7% 9% 42%	5024
	21st to end	Night	9% 6% 2 6% 6% 5% 5% 5% 7% 10% 39%	5736
August	1st to 10th	Night	11% 7% 3 7% 5% 5% 4 4 6% 9% 41%	4135
	11th to 20th	Night	12% 6% 3 8% 4 5% 5% 4 6% 9% 40%	4095
	21st to end	Night	3 3 1 4 3 3 4 3 6% 10% 60%	4996
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 5% 7% 53%	2210
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 5% 8% 53%	2310
	21st to end	Night	16% 5% 2 5% 4 3 3 3 4 5% 49%	2310
October	1st to 10th	Night	8% 4 2 5% 4 4 3 3 5% 6% 56%	2310
	11th to 20th	Night	15% 5% 2 6% 4 3 5% 3 5% 6% 46%	2403
	21st to end	Night	18% 8% 3 6% 3 4 3 3 4 6% 41%	2785
November	1st to 10th	Night	13% 7% 3 6% 3 3 4 4 5% 6% 47%	2666
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 5% 7% 40%	2730
	21st to end	Night	20% 12% 3 7% 5% 3 4 3 3 6% 33%	2730
December	1st to 10th	Night	18% 12% 4 8% 4 3 3 2 4 5% 37%	4380
	11th to 20th	Night	20% 14% 6% 8% 5% 4 4 3 5% 5% 27%	4952
	21st to end	Night	23% 18% 6% 11% 5% 4 4 3 4 5% 17%	6704

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	61% 4 13% 16% 5%	4692
	11th to 20th	Day	59% 5% 9% 15% 11% 1	5256
	21st to end	Day	64% 4 9% 16% 6% 1	5780
February	1st to 10th	Day	57% 4 10% 19% 9% 1	2001
	11th to 20th	Day	56% 4 10% 19% 10% 1	2058
	21st to end	Day	55% 5% 10% 20% 9% 2	1730
March	1st to 10th	Day	54% 6% 6% 19% 12% 2	4622
	11th to 20th	Day	43% 5% 9% 27% 15% 1	5090
	21st to end	Day	48% 6% 12% 21% 12% 2	5586
April	1st to 10th	Day	47% 7% 11% 21% 13% 1	2473
	11th to 20th	Day	45% 6% 10% 22% 14% 3	2550
	21st to end	Day	47% 6% 11% 23% 11% 2	2730
May	1st to 10th	Day	50% 7% 12% 20% 10% 1	7651
	11th to 20th	Day	45% 6% 11% 24% 13%	7630
	21st to end	Day	49% 8% 11% 19% 11% 2	8405
June	1st to 10th	Day	39% 8% 12% 22% 17% 2	2730
	11th to 20th	Day	37% 7% 14% 23% 18% 2	2917
	21st to end	Day	39% 8% 14% 21% 14% 4	2940
July	1st to 10th	Day	38% 6% 13% 25% 16% 1	8211
	11th to 20th	Day	38% 7% 13% 29% 12%	7854
	21st to end	Day	44% 7% 13% 21% 14% 2	8156
August	1st to 10th	Day	38% 8% 16% 26% 11% 2	6001
	11th to 20th	Day	43% 7% 12% 27% 11%	5990
	21st to end	Day	23% 6% 17% 34% 18% 2	6125
September	1st to 10th	Day	33% 6% 11% 26% 19% 5%	2389
	11th to 20th	Day	31% 7% 12% 26% 22% 3	2310
	21st to end	Day	40% 5% 8% 23% 22% 2	2310
October	1st to 10th	Day	23% 4 8% 32% 31% 2	3700
	11th to 20th	Day	29% 4 9% 30% 25% 2	3315
	21st to end	Day	36% 3 10% 26% 23% 2	3289
November	1st to 10th	Day	36% 5% 10% 28% 20% 3	1852
	11th to 20th	Day	49% 4 8% 21% 15% 3	1890
	21st to end	Day	51% 4 9% 21% 13% 1	1890
December	1st to 10th	Day	52% 3 10% 26% 9%	3020
	11th to 20th	Day	61% 5% 8% 18% 7%	3460
	21st to end	Day	68% 5% 10% 11% 5%	4458
January	1st to 10th	Night	63% 6% 10% 15% 6%	8218
	11th to 20th	Night	63% 5% 7% 13% 10% 2	7680
	21st to end	Night	56% 3 10% 20% 9% 1	8401
February	1st to 10th	Night	57% 4 11% 19% 7% 1	2614
	11th to 20th	Night	54% 4 10% 19% 11% 1	2459
	21st to end	Night	56% 4 11% 18% 10% 2	2076
March	1st to 10th	Night	51% 4 6% 27% 11% 2	5451
	11th to 20th	Night	39% 6% 11% 27% 16% 1	5090
	21st to end	Night	51% 5% 8% 24% 11% 1	5588
April	1st to 10th	Night	45% 6% 11% 24% 12% 2	2163
	11th to 20th	Night	41% 6% 11% 20% 17% 5%	2017
	21st to end	Night	44% 5% 12% 22% 14% 3	1890
May	1st to 10th	Night	50% 7% 10% 22% 9% 2	5264
	11th to 20th	Night	43% 7% 14% 23% 13% 1	5235
	21st to end	Night	46% 7% 14% 18% 10% 4	5771
June	1st to 10th	Night	32% 8% 11% 25% 22% 2	1890
	11th to 20th	Night	31% 8% 13% 23% 20% 4	1696
	21st to end	Night	31% 9% 17% 22% 17% 5%	1680
July	1st to 10th	Night	35% 7% 13% 25% 17% 3	4670
	11th to 20th	Night	37% 7% 13% 28% 14% 1	4978
	21st to end	Night	38% 6% 14% 24% 16% 3	5606
August	1st to 10th	Night	39% 7% 13% 26% 13% 2	4124
	11th to 20th	Night	41% 7% 14% 24% 13%	4122
	21st to end	Night	20% 5% 18% 34% 21% 2	4996
September	1st to 10th	Night	30% 6% 12% 25% 21% 6%	2210
	11th to 20th	Night	28% 8% 10% 24% 27% 3	2310
	21st to end	Night	37% 5% 8% 22% 25% 3	2310
October	1st to 10th	Night	22% 4 7% 27% 38% 3	3700
	11th to 20th	Night	27% 4 9% 25% 32% 2	3889
	21st to end	Night	33% 3 8% 23% 28% 4	4498
November	1st to 10th	Night	38% 4 11% 22% 22% 3	2666
	11th to 20th	Night	44% 4 9% 22% 18% 3	2730
	21st to end	Night	53% 5% 10% 20% 11% 1	2730
December	1st to 10th	Night	51% 3 11% 23% 11%	4380
	11th to 20th	Night	59% 4 12% 18% 7% 1	4954
	21st to end	Night	69% 5% 9% 13% 4	6704

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	26% 26% 32% 12% 4	330
	11th to 20th	Day	30% 28% 33% 8% 2	330
	21st to end	Day	31% 25% 31% 12% 2	363
February	1st to 10th	Day	29% 23% 32% 13% 2 1	330
	11th to 20th	Day	32% 29% 30% 8% 1	330
	21st to end	Day	29% 26% 38% 6% 1	273
March	1st to 10th	Day	28% 30% 30% 12% 1	346
	11th to 20th	Day	28% 23% 30% 15% 4	540
	21st to end	Day	33% 19% 30% 14% 5%	594
April	1st to 10th	Day	24% 21% 31% 17% 7% 1	540
	11th to 20th	Day	24% 22% 27% 16% 8% 2	532
	21st to end	Day	24% 19% 32% 14% 8% 2	540
May	1st to 10th	Day	24% 20% 32% 15% 6% 3	543
	11th to 20th	Day	22% 12% 32% 22% 8% 4	567
	21st to end	Day	16% 10% 29% 24% 14% 7%	617
June	1st to 10th	Day	15% 8% 26% 28% 16% 7%	570
	11th to 20th	Day	12% 8% 27% 31% 17% 5%	757
	21st to end	Day	10% 7% 28% 30% 18% 7%	780
July	1st to 10th	Day	13% 4 17% 26% 25% 15%	771
	11th to 20th	Day	9% 6% 22% 31% 23% 10%	651
	21st to end	Day	11% 4 20% 31% 22% 11%	620
August	1st to 10th	Day	10% 4 19% 29% 23% 14%	566
	11th to 20th	Day	12% 4 21% 32% 21% 10%	559
	21st to end	Day	9% 4 17% 28% 29% 13%	627
September	1st to 10th	Day	12% 6% 18% 29% 26% 9%	570
	11th to 20th	Day	10% 3 16% 26% 31% 14%	570
	21st to end	Day	21% 7% 22% 24% 19% 7%	570
October	1st to 10th	Day	11% 7% 25% 31% 20% 6%	570
	11th to 20th	Day	16% 15% 29% 23% 13% 4	542
	21st to end	Day	25% 14% 37% 19% 5%	435
November	1st to 10th	Day	16% 18% 35% 20% 8% 2	330
	11th to 20th	Day	23% 25% 28% 18% 5% 1	330
	21st to end	Day	28% 18% 38% 14% 2	330
December	1st to 10th	Day	23% 22% 37% 12% 5%	330
	11th to 20th	Day	24% 22% 39% 11% 4	330
	21st to end	Day	34% 21% 32% 10% 2 1	363
January	1st to 10th	Night	24% 20% 31% 21% 4	1048
	11th to 20th	Night	29% 18% 33% 17% 3	840
	21st to end	Night	25% 18% 34% 20% 3	924
February	1st to 10th	Night	27% 13% 33% 24% 2	840
	11th to 20th	Night	26% 19% 32% 21% 1	823
	21st to end	Night	27% 18% 34% 20% 1	692
March	1st to 10th	Night	24% 17% 31% 23% 4	840
	11th to 20th	Night	25% 16% 32% 22% 6%	840
	21st to end	Night	24% 14% 32% 25% 6%	924
April	1st to 10th	Night	20% 15% 33% 25% 7%	693
	11th to 20th	Night	19% 11% 35% 24% 10% 1	623
	21st to end	Night	19% 11% 37% 24% 9% 1	630
May	1st to 10th	Night	22% 11% 31% 25% 11% 1	630
	11th to 20th	Night	17% 8% 25% 32% 16% 2	621
	21st to end	Night	12% 3 24% 35% 23% 3	683
June	1st to 10th	Night	10% 4 21% 41% 22% 2	630
	11th to 20th	Night	11% 4 18% 41% 24% 3	630
	21st to end	Night	8% 2 24% 37% 26% 3	630
July	1st to 10th	Night	12% 3 14% 30% 35% 8%	615
	11th to 20th	Night	7% 2 18% 34% 34% 4	612
	21st to end	Night	11% 2 13% 38% 33% 4	690
August	1st to 10th	Night	9% 2 15% 37% 34% 3	627
	11th to 20th	Night	9% 3 14% 39% 30% 5%	624
	21st to end	Night	6% 1 14% 35% 37% 6%	693
September	1st to 10th	Night	13% 2 17% 32% 33% 3	740
	11th to 20th	Night	9% 3 16% 32% 35% 5%	840
	21st to end	Night	18% 6% 20% 31% 22% 3	840
October	1st to 10th	Night	10% 5% 21% 37% 23% 3	840
	11th to 20th	Night	17% 10% 25% 32% 14% 1	813
	21st to end	Night	23% 12% 31% 23% 11%	880
November	1st to 10th	Night	17% 11% 29% 27% 15% 1	820
	11th to 20th	Night	21% 17% 28% 25% 9% 1	840
	21st to end	Night	26% 13% 27% 26% 7% 1	840
December	1st to 10th	Night	27% 15% 31% 23% 5%	840
	11th to 20th	Night	26% 13% 32% 23% 5% 1	840
	21st to end	Night	32% 16% 29% 20% 3	956

Page generated at 2026-10-11 05:06:30. Version ac07

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