Astronomy Club of Akron Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astronomy Club of Akron Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	108592
	Night	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	109991
Transparency	Day	52% 6% 11% 19% 11% 1	112280
	Night	53% 5% 11% 19% 11% 1	114442
Seeing	Day	20% 14% 28% 21% 13% 5%	14929
	Night	20% 10% 28% 28% 12% 1	24947

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	14% 21% 7% 22% 5% 4 3 2 3 4 13%	4056
	11th to 20th	Day	12% 23% 9% 16% 7% 5% 5% 2 4 4 14%	4060
	21st to end	Day	22% 20% 8% 12% 7% 5% 5% 3 3 3 12%	4466
February	1st to 10th	Day	18% 18% 5% 13% 6% 5% 3 3 5% 4 21%	1800
	11th to 20th	Day	16% 14% 7% 13% 8% 4 5% 3 5% 5% 21%	1818
	21st to end	Day	18% 15% 5% 11% 5% 4 4 3 5% 5% 25%	1570
March	1st to 10th	Day	22% 14% 5% 9% 5% 4 4 3 5% 5% 25%	3363
	11th to 20th	Day	12% 12% 5% 10% 6% 6% 4 3 4 5% 33%	3480
	21st to end	Day	20% 11% 4 9% 4 4 4 3 5% 6% 29%	3815
April	1st to 10th	Day	14% 13% 4 8% 6% 5% 4 4 5% 8% 30%	2123
	11th to 20th	Day	18% 10% 4 8% 4 5% 4 3 5% 6% 34%	2406
	21st to end	Day	18% 11% 3 8% 5% 4 4 4 5% 6% 32%	2470
May	1st to 10th	Day	20% 10% 4 7% 5% 5% 4 4 5% 7% 29%	4082
	11th to 20th	Day	19% 9% 3 7% 4 5% 5% 4 6% 7% 32%	4081
	21st to end	Day	12% 6% 2 7% 4 5% 5% 5% 7% 9% 39%	4476
June	1st to 10th	Day	12% 7% 2 7% 6% 5% 6% 4 7% 8% 36%	2650
	11th to 20th	Day	12% 7% 3 8% 5% 4 5% 4 6% 8% 37%	2660
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 10% 38%	2600
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 10% 37%	4120
	11th to 20th	Day	9% 4 2 6% 5% 4 6% 5% 7% 10% 41%	4120
	21st to end	Day	10% 7% 2 7% 5% 6% 6% 5% 7% 9% 36%	4466
August	1st to 10th	Day	12% 9% 3 8% 5% 6% 6% 4 6% 9% 33%	4104
	11th to 20th	Day	10% 8% 3 7% 5% 5% 6% 6% 8% 10% 34%	4044
	21st to end	Day	8% 5% 2 8% 5% 5% 6% 5% 7% 9% 39%	4447
September	1st to 10th	Day	13% 6% 2 7% 5% 3 4 4 5% 7% 44%	2174
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 7% 8% 42%	2090
	21st to end	Day	19% 9% 3 6% 4 4 4 3 5% 7% 37%	2090
October	1st to 10th	Day	14% 7% 3 6% 5% 4 4 3 6% 9% 38%	1967
	11th to 20th	Day	17% 11% 3 7% 5% 4 4 3 5% 6% 36%	1900
	21st to end	Day	20% 11% 4 8% 4 4 5% 3 5% 6% 30%	2090
November	1st to 10th	Day	11% 10% 3 7% 5% 4 4 4 5% 6% 40%	1765
	11th to 20th	Day	17% 14% 4 8% 5% 3 5% 4 5% 5% 29%	1797
	21st to end	Day	16% 18% 7% 10% 5% 4 5% 3 5% 6% 21%	1600
December	1st to 10th	Day	19% 14% 7% 16% 6% 4 3 3 4 4 20%	2600
	11th to 20th	Day	23% 18% 7% 13% 4 3 3 3 4 4 18%	2990
	21st to end	Day	25% 22% 6% 13% 6% 5% 4 3 3 4 10%	4252
January	1st to 10th	Night	14% 18% 8% 22% 7% 4 3 3 4 4 13%	5889
	11th to 20th	Night	12% 21% 9% 16% 9% 6% 5% 3 4 4 11%	5900
	21st to end	Night	21% 18% 6% 12% 6% 3 4 2 3 4 18%	6490
February	1st to 10th	Night	20% 15% 5% 11% 6% 6% 4 2 5% 5% 21%	2600
	11th to 20th	Night	17% 15% 4 12% 6% 5% 5% 4 5% 5% 22%	2467
	21st to end	Night	20% 14% 5% 11% 7% 5% 4 3 4 4 24%	1885
March	1st to 10th	Night	23% 14% 4 7% 3 4 3 2 4 5% 33%	3489
	11th to 20th	Night	16% 10% 4 8% 4 4 5% 4 6% 6% 34%	3480
	21st to end	Night	17% 11% 4 8% 5% 3 4 3 5% 6% 34%	3817
April	1st to 10th	Night	15% 13% 4 7% 6% 4 4 3 5% 6% 33%	2057
	11th to 20th	Night	16% 11% 3 8% 5% 4 4 4 6% 6% 35%	1739
	21st to end	Night	15% 9% 2 7% 5% 4 4 4 6% 6% 37%	1710
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 3 5% 6% 27%	2813
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 4 8% 38%	2812
	21st to end	Night	10% 5% 2 6% 3 4 5% 3 7% 11% 45%	3079
June	1st to 10th	Night	8% 7% 2 7% 5% 5% 5% 3 6% 7% 43%	1525
	11th to 20th	Night	10% 6% 3 6% 5% 4 5% 4 6% 10% 41%	1520
	21st to end	Night	10% 6% 2 5% 4 4 6% 5% 6% 10% 43%	1571
July	1st to 10th	Night	11% 6% 2 7% 3 4 4 3 6% 9% 45%	2840
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 3 6% 10% 47%	2840
	21st to end	Night	7% 6% 3 7% 5% 5% 5% 4 7% 8% 44%	3087
August	1st to 10th	Night	10% 8% 3 8% 5% 4 4 4 6% 8% 39%	2825
	11th to 20th	Night	11% 9% 3 7% 4 4 4 4 5% 7% 43%	2785
	21st to end	Night	7% 4 2 7% 5% 6% 6% 5% 7% 7% 44%	3175
September	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 5% 8% 48%	2003
	11th to 20th	Night	9% 4 1 5% 4 4 4 3 6% 8% 52%	2090
	21st to end	Night	16% 8% 2 6% 4 4 5% 3 5% 6% 42%	2090
October	1st to 10th	Night	13% 6% 3 5% 4 4 5% 3 5% 8% 44%	2213
	11th to 20th	Night	17% 8% 3 8% 5% 5% 4 3 5% 6% 36%	2280
	21st to end	Night	20% 10% 3 7% 4 4 4 4 5% 6% 32%	2508
November	1st to 10th	Night	14% 9% 2 5% 4 5% 4 3 6% 7% 41%	2530
	11th to 20th	Night	17% 14% 4 9% 5% 4 3 3 5% 7% 30%	2600
	21st to end	Night	19% 15% 5% 8% 5% 5% 4 3 5% 6% 25%	2799
December	1st to 10th	Night	17% 15% 7% 11% 6% 5% 4 3 4 5% 22%	4580
	11th to 20th	Night	20% 18% 7% 12% 5% 4 4 3 4 5% 19%	5205
	21st to end	Night	24% 20% 6% 11% 5% 4 4 3 4 5% 13%	6698

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	75% 4 8% 8% 4	4057
	11th to 20th	Day	76% 3 8% 7% 5%	4060
	21st to end	Day	78% 3 7% 8% 3	4466
February	1st to 10th	Day	68% 4 9% 13% 6% 1	1800
	11th to 20th	Day	66% 5% 8% 14% 7%	1827
	21st to end	Day	60% 5% 12% 14% 7% 2	1570
March	1st to 10th	Day	60% 5% 9% 20% 5%	3363
	11th to 20th	Day	51% 6% 12% 22% 7% 1	3480
	21st to end	Day	54% 7% 10% 17% 12% 1	3815
April	1st to 10th	Day	52% 7% 11% 17% 11% 1	2123
	11th to 20th	Day	51% 7% 11% 17% 12% 2	2406
	21st to end	Day	51% 7% 11% 19% 10% 2	2470
May	1st to 10th	Day	53% 7% 11% 20% 8% 1	4120
	11th to 20th	Day	48% 8% 12% 21% 9% 1	4085
	21st to end	Day	38% 9% 14% 20% 14% 4	4489
June	1st to 10th	Day	43% 8% 13% 23% 12% 1	2650
	11th to 20th	Day	42% 8% 13% 21% 14% 1	2660
	21st to end	Day	38% 9% 13% 23% 15% 2	2600
July	1st to 10th	Day	42% 5% 12% 23% 16% 2	4055
	11th to 20th	Day	36% 5% 13% 26% 19% 1	4051
	21st to end	Day	42% 6% 15% 17% 19% 2	4324
August	1st to 10th	Day	47% 6% 13% 23% 12%	4091
	11th to 20th	Day	42% 5% 11% 29% 11% 1	4083
	21st to end	Day	40% 6% 13% 30% 10% 2	4447
September	1st to 10th	Day	38% 7% 13% 21% 17% 4	2174
	11th to 20th	Day	37% 7% 14% 24% 16% 2	2090
	21st to end	Day	47% 6% 10% 21% 15% 1	2090
October	1st to 10th	Day	32% 4 13% 30% 19% 1	3266
	11th to 20th	Day	47% 4 10% 20% 15% 4	3140
	21st to end	Day	42% 3 12% 25% 16% 1	3428
November	1st to 10th	Day	44% 6% 12% 22% 15% 1	1765
	11th to 20th	Day	55% 5% 10% 18% 8% 2	1797
	21st to end	Day	64% 6% 11% 13% 6% 1	1600
December	1st to 10th	Day	70% 3 11% 13% 3	2600
	11th to 20th	Day	71% 4 10% 12% 4	2986
	21st to end	Day	79% 4 7% 8% 2	4252
January	1st to 10th	Night	76% 4 7% 9% 4	5889
	11th to 20th	Night	78% 4 8% 7% 3	5900
	21st to end	Night	72% 3 9% 10% 6% 1	6490
February	1st to 10th	Night	66% 5% 10% 14% 5%	2600
	11th to 20th	Night	63% 6% 10% 15% 6%	2469
	21st to end	Night	63% 5% 9% 13% 8% 2	1885
March	1st to 10th	Night	55% 4 10% 21% 9%	3489
	11th to 20th	Night	46% 9% 16% 20% 8% 1	3480
	21st to end	Night	48% 7% 10% 24% 10% 1	3817
April	1st to 10th	Night	50% 6% 11% 18% 13% 2	2057
	11th to 20th	Night	48% 6% 12% 16% 15% 3	1739
	21st to end	Night	45% 6% 12% 19% 15% 2	1710
May	1st to 10th	Night	55% 7% 9% 19% 8% 2	2840
	11th to 20th	Night	43% 8% 12% 23% 12% 2	2813
	21st to end	Night	31% 8% 16% 26% 15% 3	3087
June	1st to 10th	Night	39% 7% 12% 24% 16% 3	1525
	11th to 20th	Night	37% 7% 15% 21% 17% 3	1520
	21st to end	Night	36% 8% 14% 24% 16% 1	1571
July	1st to 10th	Night	37% 5% 12% 23% 18% 5%	2795
	11th to 20th	Night	33% 5% 13% 31% 17% 1	2786
	21st to end	Night	37% 5% 14% 18% 24% 2	2988
August	1st to 10th	Night	43% 5% 12% 24% 14% 1	2814
	11th to 20th	Night	41% 5% 10% 28% 15% 1	2812
	21st to end	Night	37% 5% 13% 29% 13% 2	3175
September	1st to 10th	Night	35% 7% 11% 25% 18% 4	2003
	11th to 20th	Night	31% 6% 13% 25% 23% 2	2090
	21st to end	Night	42% 7% 11% 21% 18% 1	2090
October	1st to 10th	Night	32% 4 9% 30% 25% 1	3694
	11th to 20th	Night	44% 4 11% 21% 17% 3	3779
	21st to end	Night	39% 4 10% 29% 16% 2	4120
November	1st to 10th	Night	42% 6% 12% 22% 15% 3	2530
	11th to 20th	Night	55% 5% 10% 17% 11% 3	2600
	21st to end	Night	60% 5% 12% 16% 6%	2799
December	1st to 10th	Night	65% 4 11% 17% 4	4580
	11th to 20th	Night	68% 4 11% 14% 2	5208
	21st to end	Night	74% 5% 10% 10% 2	6698

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	28% 23% 34% 11% 4 1	300
	11th to 20th	Day	27% 26% 35% 9% 3	300
	21st to end	Day	28% 26% 32% 11% 2	330
February	1st to 10th	Day	29% 23% 36% 11% 1	300
	11th to 20th	Day	29% 29% 31% 10% 1	300
	21st to end	Day	28% 31% 32% 8%	225
March	1st to 10th	Day	25% 20% 31% 18% 5%	410
	11th to 20th	Day	27% 17% 33% 17% 6%	460
	21st to end	Day	31% 16% 28% 20% 4 1	506
April	1st to 10th	Day	20% 22% 32% 17% 8% 1	460
	11th to 20th	Day	26% 19% 25% 17% 8% 4	452
	21st to end	Day	25% 16% 32% 17% 8% 2	460
May	1st to 10th	Day	24% 17% 29% 18% 9% 3	463
	11th to 20th	Day	19% 12% 32% 20% 12% 5%	487
	21st to end	Day	15% 6% 26% 27% 20% 6%	529
June	1st to 10th	Day	13% 8% 29% 32% 14% 3	490
	11th to 20th	Day	17% 8% 23% 32% 16% 5%	490
	21st to end	Day	15% 8% 29% 28% 14% 6%	490
July	1st to 10th	Day	12% 4 20% 29% 22% 13%	485
	11th to 20th	Day	10% 8% 22% 29% 22% 10%	484
	21st to end	Day	11% 5% 23% 26% 25% 10%	532
August	1st to 10th	Day	12% 5% 21% 26% 26% 10%	486
	11th to 20th	Day	15% 6% 21% 26% 20% 11%	479
	21st to end	Day	9% 5% 19% 30% 24% 13%	539
September	1st to 10th	Day	15% 7% 20% 25% 22% 12%	490
	11th to 20th	Day	10% 4 16% 28% 29% 14%	490
	21st to end	Day	25% 10% 21% 21% 16% 7%	490
October	1st to 10th	Day	11% 10% 26% 26% 21% 5%	490
	11th to 20th	Day	20% 15% 34% 19% 9% 2	490
	21st to end	Day	27% 17% 29% 20% 6% 1	539
November	1st to 10th	Day	17% 20% 35% 16% 10% 2	303
	11th to 20th	Day	29% 21% 30% 15% 5% 1	297
	21st to end	Day	25% 22% 39% 14% 2	200
December	1st to 10th	Day	27% 21% 34% 13% 4 2	200
	11th to 20th	Day	25% 23% 37% 13% 4	200
	21st to end	Day	31% 22% 32% 12% 2	283
January	1st to 10th	Night	24% 20% 35% 17% 4	800
	11th to 20th	Night	29% 18% 33% 16% 3	800
	21st to end	Night	27% 18% 31% 21% 3	880
February	1st to 10th	Night	28% 17% 32% 21% 3	800
	11th to 20th	Night	26% 16% 35% 21% 3	783
	21st to end	Night	28% 16% 36% 17% 2	629
March	1st to 10th	Night	23% 15% 34% 23% 5%	760
	11th to 20th	Night	22% 14% 33% 24% 6% 1	760
	21st to end	Night	24% 11% 33% 25% 7% 1	836
April	1st to 10th	Night	22% 12% 35% 25% 5% 1	760
	11th to 20th	Night	21% 12% 34% 22% 10% 1	615
	21st to end	Night	18% 9% 35% 31% 6% 1	570
May	1st to 10th	Night	21% 7% 29% 32% 9% 1	570
	11th to 20th	Night	19% 6% 24% 38% 11% 2	561
	21st to end	Night	12% 2 19% 42% 23% 3	617
June	1st to 10th	Night	9% 4 27% 42% 18% 1	385
	11th to 20th	Night	11% 4 24% 45% 16% 1	380
	21st to end	Night	12% 4 23% 41% 20%	431
July	1st to 10th	Night	10% 2 13% 43% 29% 4	555
	11th to 20th	Night	9% 2 19% 40% 26% 3	552
	21st to end	Night	9% 1 15% 44% 28% 2	624
August	1st to 10th	Night	9% 2 16% 41% 29% 3	567
	11th to 20th	Night	12% 2 13% 41% 28% 4	564
	21st to end	Night	9% 3 15% 36% 32% 4	652
September	1st to 10th	Night	13% 4 17% 35% 25% 5%	760
	11th to 20th	Night	10% 2 15% 36% 32% 4	760
	21st to end	Night	18% 6% 22% 31% 19% 4	760
October	1st to 10th	Night	16% 6% 23% 33% 19% 3	760
	11th to 20th	Night	23% 10% 28% 28% 10% 2	760
	21st to end	Night	25% 12% 27% 29% 7%	836
November	1st to 10th	Night	20% 10% 28% 30% 12% 1	780
	11th to 20th	Night	23% 16% 32% 22% 6% 1	800
	21st to end	Night	28% 13% 33% 19% 6%	800
December	1st to 10th	Night	30% 14% 33% 19% 5%	800
	11th to 20th	Night	26% 17% 33% 21% 3	800
	21st to end	Night	28% 15% 34% 21% 2	880

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