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 2024-11-02.

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	15% 9% 3 7% 5% 4 4 4 5% 7% 37%	101409
	Night	15% 10% 3 7% 4 4 4 3 5% 7% 38%	97500
Transparency	Day	45% 7% 11% 22% 14% 2	101212
	Night	45% 6% 11% 22% 14% 2	97367
Seeing	Day	19% 13% 27% 22% 13% 5%	15301
	Night	19% 11% 26% 27% 15% 2	24937

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	16% 16% 7% 9% 4 5% 4 3 4 6% 26%	2527
	11th to 20th	Day	17% 14% 6% 13% 7% 8% 6% 3 3 3 21%	2816
	21st to end	Day	29% 17% 8% 8% 4 3 3 2 4 5% 18%	3124
February	1st to 10th	Day	19% 13% 4 9% 5% 3 4 4 4 6% 29%	1809
	11th to 20th	Day	17% 11% 4 10% 5% 4 3 3 4 6% 31%	1848
	21st to end	Day	20% 14% 5% 8% 4 4 4 3 4 6% 30%	1570
March	1st to 10th	Day	23% 16% 4 8% 4 3 3 3 5% 5% 26%	3147
	11th to 20th	Day	14% 8% 2 8% 4 4 4 4 5% 7% 40%	3480
	21st to end	Day	18% 9% 3 6% 5% 4 4 3 6% 6% 35%	3815
April	1st to 10th	Day	16% 10% 3 7% 4 4 5% 5% 5% 6% 35%	2237
	11th to 20th	Day	17% 9% 3 7% 4 3 4 3 6% 6% 39%	2304
	21st to end	Day	19% 8% 3 6% 5% 5% 4 4 5% 7% 35%	2470
May	1st to 10th	Day	22% 9% 3 7% 5% 4 5% 4 5% 7% 29%	4082
	11th to 20th	Day	20% 8% 3 6% 4 4 4 3 5% 7% 36%	4081
	21st to end	Day	10% 7% 3 7% 6% 6% 5% 5% 8% 10% 34%	4476
June	1st to 10th	Day	13% 5% 2 7% 5% 4 5% 5% 6% 8% 40%	2470
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 44%	2639
	21st to end	Day	8% 6% 3 7% 6% 5% 5% 4 6% 9% 40%	2660
July	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 4 7% 10% 38%	4440
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 4 6% 10% 46%	4256
	21st to end	Day	11% 7% 3 8% 6% 6% 7% 6% 7% 10% 30%	4466
August	1st to 10th	Day	9% 5% 2 5% 4 4 6% 4 7% 10% 43%	4104
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	4044
	21st to end	Day	6% 4 1 5% 3 4 4 3 6% 9% 55%	4212
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 48%	2161
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 3 6% 8% 49%	2090
	21st to end	Day	16% 6% 2 6% 4 4 3 3 4 7% 46%	2090
October	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 5% 6% 50%	2090
	11th to 20th	Day	13% 7% 2 6% 5% 3 4 3 5% 7% 45%	1929
	21st to end	Day	21% 8% 2 5% 4 3 3 3 4 7% 39%	1950
November	1st to 10th	Day	9% 8% 2 5% 4 4 4 3 4 6% 53%	1681
	11th to 20th	Day	14% 11% 4 7% 4 4 4 3 5% 6% 37%	1710
	21st to end	Day	18% 10% 3 8% 4 4 3 2 4 7% 36%	1710
December	1st to 10th	Day	22% 13% 4 9% 6% 4 4 3 4 5% 25%	1710
	11th to 20th	Day	16% 16% 5% 10% 5% 4 4 4 5% 5% 29%	2153
	21st to end	Day	22% 20% 5% 9% 6% 4 4 4 4 5% 17%	3058
January	1st to 10th	Night	16% 18% 6% 11% 5% 5% 4 3 5% 5% 22%	4427
	11th to 20th	Night	16% 17% 6% 14% 6% 4 4 3 3 4 23%	4120
	21st to end	Night	26% 18% 5% 7% 5% 3 3 2 3 5% 22%	4532
February	1st to 10th	Night	22% 12% 4 9% 5% 4 4 4 4 4 29%	2366
	11th to 20th	Night	17% 11% 4 9% 5% 4 4 4 5% 6% 31%	2218
	21st to end	Night	22% 14% 4 7% 4 3 4 3 4 5% 30%	1884
March	1st to 10th	Night	23% 13% 3 5% 4 4 4 3 4 5% 32%	3706
	11th to 20th	Night	14% 7% 3 6% 3 4 4 4 5% 6% 44%	3480
	21st to end	Night	17% 8% 3 7% 4 5% 4 3 5% 5% 39%	3817
April	1st to 10th	Night	14% 10% 3 6% 4 4 4 4 6% 7% 37%	1957
	11th to 20th	Night	15% 8% 2 6% 4 4 4 4 6% 7% 40%	1823
	21st to end	Night	17% 7% 3 6% 4 5% 4 3 6% 8% 37%	1710
May	1st to 10th	Night	21% 12% 3 8% 5% 5% 5% 3 5% 6% 26%	2813
	11th to 20th	Night	19% 6% 2 6% 4 4 4 3 6% 8% 37%	2812
	21st to end	Night	9% 5% 2 5% 4 3 5% 4 6% 10% 45%	3079
June	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 9% 48%	1710
	11th to 20th	Night	8% 4 2 5% 4 4 4 3 7% 11% 48%	1534
	21st to end	Night	6% 4 2 5% 4 5% 5% 4 7% 10% 48%	1520
July	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 5% 8% 50%	2530
	11th to 20th	Night	6% 5% 2 5% 4 4 3 4 6% 10% 51%	2704
	21st to end	Night	11% 6% 2 7% 6% 5% 5% 4 7% 10% 37%	3087
August	1st to 10th	Night	8% 5% 3 6% 5% 4 4 4 6% 9% 45%	2825
	11th to 20th	Night	8% 6% 2 7% 4 3 5% 4 5% 9% 46%	2785
	21st to end	Night	3 3 1 3 3 3 4 3 6% 10% 60%	3440
September	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 5% 7% 52%	2000
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 5% 8% 54%	2090
	21st to end	Night	15% 5% 2 5% 4 3 4 3 4 5% 49%	2090
October	1st to 10th	Night	8% 4 2 5% 4 4 3 3 5% 6% 55%	2090
	11th to 20th	Night	15% 6% 2 6% 4 3 5% 3 5% 6% 45%	2249
	21st to end	Night	18% 9% 3 6% 3 4 3 3 4 6% 42%	2646
November	1st to 10th	Night	13% 7% 3 6% 3 3 4 4 5% 6% 47%	2431
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 5% 7% 39%	2470
	21st to end	Night	20% 11% 3 7% 5% 3 4 3 4 6% 34%	2470
December	1st to 10th	Night	21% 13% 5% 8% 5% 4 4 3 4 5% 29%	2470
	11th to 20th	Night	19% 13% 6% 8% 5% 3 4 3 5% 6% 30%	3042
	21st to end	Night	21% 19% 5% 11% 5% 5% 4 3 4 5% 17%	4573

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	59% 5% 12% 14% 10%	2528
	11th to 20th	Day	63% 8% 10% 13% 6%	2816
	21st to end	Day	70% 4 8% 14% 3 1	3124
February	1st to 10th	Day	57% 5% 10% 17% 10% 2	1809
	11th to 20th	Day	55% 4 10% 19% 10% 1	1858
	21st to end	Day	56% 5% 9% 19% 9% 2	1570
March	1st to 10th	Day	58% 8% 7% 18% 8% 1	3147
	11th to 20th	Day	42% 6% 11% 25% 16% 1	3480
	21st to end	Day	47% 7% 11% 23% 11% 1	3815
April	1st to 10th	Day	47% 7% 10% 22% 13% 1	2237
	11th to 20th	Day	45% 6% 10% 22% 14% 4	2304
	21st to end	Day	48% 6% 11% 22% 12% 2	2470
May	1st to 10th	Day	52% 8% 12% 20% 8% 1	4120
	11th to 20th	Day	46% 8% 12% 22% 12%	4085
	21st to end	Day	40% 11% 14% 19% 15% 2	4489
June	1st to 10th	Day	39% 9% 12% 23% 16% 2	2470
	11th to 20th	Day	35% 8% 14% 23% 18% 2	2639
	21st to end	Day	39% 8% 14% 21% 14% 4	2660
July	1st to 10th	Day	41% 7% 12% 20% 19% 2	4371
	11th to 20th	Day	31% 8% 11% 32% 18% 1	4182
	21st to end	Day	46% 8% 14% 17% 12% 3	4324
August	1st to 10th	Day	33% 8% 16% 31% 11% 1	4091
	11th to 20th	Day	34% 7% 12% 32% 15% 1	4083
	21st to end	Day	26% 6% 15% 29% 21% 3	4211
September	1st to 10th	Day	35% 6% 11% 23% 19% 5%	2161
	11th to 20th	Day	32% 7% 11% 26% 21% 3	2090
	21st to end	Day	39% 6% 9% 24% 21% 2	2090
October	1st to 10th	Day	34% 6% 10% 25% 22% 2	2090
	11th to 20th	Day	38% 4 9% 26% 19% 3	1929
	21st to end	Day	46% 4 11% 22% 16% 2	1950
November	1st to 10th	Day	34% 5% 10% 27% 21% 3	1681
	11th to 20th	Day	48% 4 8% 21% 16% 3	1710
	21st to end	Day	50% 4 9% 22% 14% 1	1710
December	1st to 10th	Day	62% 4 10% 17% 6%	1710
	11th to 20th	Day	57% 5% 9% 18% 11%	2150
	21st to end	Day	69% 6% 9% 10% 6% 1	3058
January	1st to 10th	Night	62% 8% 9% 14% 7%	4427
	11th to 20th	Night	65% 5% 9% 14% 6%	4120
	21st to end	Night	66% 4 8% 15% 6% 1	4532
February	1st to 10th	Night	58% 5% 11% 19% 7% 1	2366
	11th to 20th	Night	53% 5% 10% 19% 11% 1	2219
	21st to end	Night	57% 4 10% 16% 10% 2	1884
March	1st to 10th	Night	53% 5% 7% 23% 10% 1	3706
	11th to 20th	Night	38% 7% 13% 26% 15% 1	3480
	21st to end	Night	46% 6% 9% 27% 11% 1	3817
April	1st to 10th	Night	44% 7% 11% 24% 12% 2	1957
	11th to 20th	Night	40% 6% 10% 19% 19% 5%	1823
	21st to end	Night	45% 6% 12% 20% 13% 3	1710
May	1st to 10th	Night	55% 8% 9% 18% 7% 2	2840
	11th to 20th	Night	42% 9% 14% 25% 9% 1	2813
	21st to end	Night	30% 10% 15% 26% 14% 5%	3087
June	1st to 10th	Night	32% 8% 11% 26% 20% 3	1710
	11th to 20th	Night	29% 9% 14% 23% 21% 4	1534
	21st to end	Night	30% 9% 17% 22% 17% 5%	1520
July	1st to 10th	Night	33% 7% 11% 24% 19% 6%	2490
	11th to 20th	Night	28% 7% 13% 31% 20% 2	2655
	21st to end	Night	41% 7% 13% 22% 13% 4	2988
August	1st to 10th	Night	33% 8% 14% 32% 12% 1	2814
	11th to 20th	Night	34% 7% 11% 28% 18% 1	2812
	21st to end	Night	20% 6% 16% 32% 23% 3	3440
September	1st to 10th	Night	31% 6% 12% 25% 20% 7%	2000
	11th to 20th	Night	28% 8% 10% 24% 27% 3	2090
	21st to end	Night	37% 5% 9% 22% 24% 2	2090
October	1st to 10th	Night	29% 6% 10% 27% 24% 3	2090
	11th to 20th	Night	37% 6% 8% 24% 22% 2	2249
	21st to end	Night	44% 4 10% 21% 18% 3	2646
November	1st to 10th	Night	37% 4 11% 21% 23% 4	2431
	11th to 20th	Night	45% 4 9% 20% 19% 3	2470
	21st to end	Night	52% 5% 10% 20% 12% 1	2470
December	1st to 10th	Night	56% 5% 11% 18% 9% 1	2470
	11th to 20th	Night	55% 5% 10% 20% 9% 1	3044
	21st to end	Night	68% 6% 9% 12% 5%	4573

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% 13% 4	270
	11th to 20th	Day	31% 26% 33% 8% 1	270
	21st to end	Day	33% 24% 29% 11% 2	297
February	1st to 10th	Day	30% 26% 30% 13% 1	270
	11th to 20th	Day	32% 29% 30% 7% 1	270
	21st to end	Day	32% 26% 36% 5%	225
March	1st to 10th	Day	26% 32% 29% 12% 1	284
	11th to 20th	Day	26% 23% 31% 15% 4	460
	21st to end	Day	33% 17% 30% 14% 5%	506
April	1st to 10th	Day	23% 21% 30% 18% 8% 1	460
	11th to 20th	Day	24% 21% 26% 17% 9% 3	452
	21st to end	Day	24% 21% 32% 13% 8% 2	460
May	1st to 10th	Day	25% 19% 30% 16% 6% 4	463
	11th to 20th	Day	22% 11% 32% 21% 9% 5%	487
	21st to end	Day	13% 9% 29% 27% 14% 8%	529
June	1st to 10th	Day	15% 9% 24% 29% 16% 7%	490
	11th to 20th	Day	12% 7% 26% 32% 18% 5%	659
	21st to end	Day	10% 7% 30% 29% 17% 7%	680
July	1st to 10th	Day	14% 5% 18% 26% 22% 15%	671
	11th to 20th	Day	8% 6% 24% 30% 22% 9%	563
	21st to end	Day	12% 4 21% 30% 22% 11%	532
August	1st to 10th	Day	11% 4 18% 30% 22% 15%	486
	11th to 20th	Day	12% 4 22% 32% 20% 10%	479
	21st to end	Day	9% 4 17% 28% 28% 14%	539
September	1st to 10th	Day	13% 5% 18% 29% 26% 9%	490
	11th to 20th	Day	11% 3 18% 25% 31% 12%	490
	21st to end	Day	20% 8% 22% 24% 19% 7%	490
October	1st to 10th	Day	11% 7% 26% 31% 19% 6%	490
	11th to 20th	Day	16% 16% 30% 22% 12% 4	490
	21st to end	Day	24% 14% 37% 20% 6%	399
November	1st to 10th	Day	15% 18% 33% 22% 9% 3	273
	11th to 20th	Day	21% 24% 27% 19% 6% 1	270
	21st to end	Day	26% 18% 37% 15% 3	270
December	1st to 10th	Day	25% 23% 33% 13% 6%	270
	11th to 20th	Day	22% 23% 39% 11% 4	270
	21st to end	Day	33% 22% 32% 10% 2 1	297
January	1st to 10th	Night	24% 20% 31% 21% 4	949
	11th to 20th	Night	30% 18% 32% 17% 3	760
	21st to end	Night	26% 18% 33% 20% 3	836
February	1st to 10th	Night	29% 13% 32% 23% 2	760
	11th to 20th	Night	25% 20% 32% 21% 2	743
	21st to end	Night	29% 18% 33% 19% 1	628
March	1st to 10th	Night	23% 18% 32% 22% 5%	760
	11th to 20th	Night	24% 16% 32% 22% 6% 1	760
	21st to end	Night	24% 13% 32% 25% 6%	836
April	1st to 10th	Night	19% 15% 34% 24% 8%	627
	11th to 20th	Night	20% 11% 34% 24% 11% 1	563
	21st to end	Night	20% 11% 38% 23% 8% 1	570
May	1st to 10th	Night	22% 11% 30% 25% 11% 1	570
	11th to 20th	Night	18% 6% 25% 32% 17% 2	561
	21st to end	Night	10% 3 24% 34% 25% 4	617
June	1st to 10th	Night	10% 4 21% 41% 22% 2	570
	11th to 20th	Night	10% 3 17% 42% 25% 3	570
	21st to end	Night	7% 2 26% 38% 24% 3	570
July	1st to 10th	Night	12% 2 15% 31% 32% 8%	555
	11th to 20th	Night	7% 2 18% 35% 34% 3	552
	21st to end	Night	11% 2 13% 38% 32% 4	624
August	1st to 10th	Night	9% 2 14% 37% 35% 4	567
	11th to 20th	Night	9% 3 14% 39% 29% 6%	564
	21st to end	Night	6% 1 14% 33% 39% 7%	627
September	1st to 10th	Night	14% 3 17% 31% 32% 4	670
	11th to 20th	Night	9% 3 16% 32% 34% 5%	760
	21st to end	Night	17% 6% 22% 31% 23% 2	760
October	1st to 10th	Night	10% 6% 22% 35% 23% 4	760
	11th to 20th	Night	18% 10% 26% 30% 14% 2	760
	21st to end	Night	22% 12% 31% 23% 11%	836
November	1st to 10th	Night	17% 11% 29% 27% 15% 1	748
	11th to 20th	Night	21% 17% 28% 24% 10% 1	760
	21st to end	Night	26% 12% 27% 28% 6% 1	760
December	1st to 10th	Night	26% 15% 31% 23% 5%	760
	11th to 20th	Night	26% 13% 32% 23% 6% 1	760
	21st to end	Night	31% 16% 30% 20% 3	864

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