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 2024-01-31.

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% 10% 4 8% 6% 3 5% 5% 5% 7% 30%	74754
	Night	16% 11% 4 7% 6% 3 5% 4 5% 7% 32%	75372
Transparency	Day	52% 7% 12% 18% 10% 1	74475
	Night	51% 6% 12% 18% 11% 2	75170
Seeing	Day	20% 13% 27% 21% 13% 5%	13560
	Night	20% 10% 28% 28% 12% 1	23567

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% 16% 8% 11% 8% 4 4 4 4 5% 17%	1706
	11th to 20th	Day	19% 18% 9% 11% 9% 3 4 3 4 5% 15%	1710
	21st to end	Day	18% 20% 8% 12% 8% 3 4 4 4 5% 13%	1872
February	1st to 10th	Day	19% 17% 6% 12% 8% 4 4 3 5% 4 20%	1620
	11th to 20th	Day	16% 13% 7% 12% 9% 3 5% 5% 4 5% 20%	1631
	21st to end	Day	18% 14% 6% 10% 7% 3 4 4 5% 5% 25%	1480
March	1st to 10th	Day	19% 11% 5% 8% 6% 3 4 3 5% 6% 28%	1932
	11th to 20th	Day	16% 13% 6% 9% 5% 4 5% 4 5% 5% 29%	1980
	21st to end	Day	22% 11% 5% 9% 6% 3 3 4 5% 6% 27%	2178
April	1st to 10th	Day	15% 11% 5% 7% 6% 4 4 5% 5% 8% 31%	2011
	11th to 20th	Day	18% 10% 4 8% 5% 3 5% 4 4 6% 33%	2277
	21st to end	Day	19% 11% 3 7% 5% 3 4 4 5% 5% 32%	2340
May	1st to 10th	Day	17% 10% 4 6% 6% 4 5% 5% 6% 7% 29%	2340
	11th to 20th	Day	18% 9% 3 7% 6% 4 6% 5% 6% 6% 31%	2301
	21st to end	Day	10% 5% 2 6% 6% 4 6% 6% 7% 10% 38%	2531
June	1st to 10th	Day	13% 7% 3 6% 6% 4 6% 5% 7% 8% 36%	2510
	11th to 20th	Day	13% 7% 3 7% 6% 3 5% 6% 5% 9% 36%	2520
	21st to end	Day	11% 6% 3 5% 5% 3 5% 6% 7% 10% 38%	2464
July	1st to 10th	Day	11% 6% 3 6% 6% 4 5% 6% 6% 9% 39%	2340
	11th to 20th	Day	11% 5% 2 5% 6% 4 6% 7% 7% 9% 39%	2340
	21st to end	Day	10% 6% 3 6% 6% 4 7% 6% 7% 11% 35%	2547
August	1st to 10th	Day	8% 7% 3 6% 6% 5% 7% 7% 6% 10% 36%	2327
	11th to 20th	Day	10% 8% 3 6% 6% 4 5% 7% 7% 10% 32%	2303
	21st to end	Day	9% 6% 2 7% 6% 4 6% 7% 7% 9% 38%	2531
September	1st to 10th	Day	14% 5% 3 6% 5% 2 4 5% 5% 7% 43%	2060
	11th to 20th	Day	11% 6% 3 5% 5% 3 5% 6% 7% 8% 41%	1980
	21st to end	Day	18% 8% 3 6% 4 3 4 4 5% 7% 39%	1980
October	1st to 10th	Day	15% 6% 3 5% 7% 3 5% 5% 6% 9% 37%	1864
	11th to 20th	Day	18% 11% 3 6% 5% 3 4 4 5% 6% 35%	1800
	21st to end	Day	22% 11% 4 7% 5% 3 5% 4 5% 6% 28%	1980
November	1st to 10th	Day	11% 10% 4 7% 6% 3 4 4 5% 6% 40%	1675
	11th to 20th	Day	18% 12% 5% 6% 6% 2 4 5% 5% 5% 30%	1708
	21st to end	Day	17% 15% 8% 9% 6% 3 5% 4 6% 6% 23%	1520
December	1st to 10th	Day	20% 17% 9% 11% 7% 3 3 4 4 4 18%	1520
	11th to 20th	Day	18% 16% 6% 14% 6% 3 4 4 4 5% 17%	1910
	21st to end	Day	25% 22% 7% 11% 7% 3 3 3 3 4 10%	2966
January	1st to 10th	Night	18% 16% 7% 11% 8% 3 4 4 4 4 20%	2459
	11th to 20th	Night	19% 18% 6% 11% 8% 4 4 4 5% 4 17%	2470
	21st to end	Night	18% 18% 7% 11% 8% 3 5% 4 4 4 19%	2711
February	1st to 10th	Night	22% 13% 6% 10% 7% 4 5% 3 4 5% 20%	2340
	11th to 20th	Night	17% 14% 5% 10% 7% 4 5% 5% 5% 5% 22%	2214
	21st to end	Night	20% 13% 6% 9% 8% 3 4 3 4 4 24%	1776
March	1st to 10th	Night	17% 11% 6% 8% 6% 3 4 3 5% 5% 32%	2027
	11th to 20th	Night	17% 10% 3 7% 5% 3 4 4 6% 7% 34%	1980
	21st to end	Night	19% 10% 5% 8% 6% 3 4 5% 5% 5% 31%	2178
April	1st to 10th	Night	15% 11% 5% 6% 6% 4 4 4 5% 7% 33%	1949
	11th to 20th	Night	16% 10% 3 7% 6% 3 4 5% 6% 6% 35%	1647
	21st to end	Night	15% 8% 3 6% 6% 3 5% 5% 5% 7% 37%	1620
May	1st to 10th	Night	16% 9% 4 7% 7% 5% 6% 5% 6% 7% 30%	1620
	11th to 20th	Night	15% 8% 4 5% 5% 3 6% 4 5% 8% 38%	1592
	21st to end	Night	9% 5% 2 6% 5% 3 5% 5% 6% 11% 43%	1744
June	1st to 10th	Night	8% 6% 3 6% 6% 4 6% 4 7% 7% 44%	1445
	11th to 20th	Night	11% 6% 3 5% 5% 3 5% 5% 6% 10% 41%	1440
	21st to end	Night	10% 5% 2 5% 4 3 6% 6% 5% 10% 44%	1488
July	1st to 10th	Night	8% 5% 3 6% 4 3 6% 5% 6% 8% 47%	1620
	11th to 20th	Night	7% 5% 2 4 5% 4 5% 5% 6% 12% 46%	1620
	21st to end	Night	8% 5% 3 6% 6% 4 6% 5% 7% 8% 43%	1771
August	1st to 10th	Night	6% 5% 3 5% 6% 3 4 5% 6% 9% 47%	1611
	11th to 20th	Night	8% 7% 3 5% 6% 3 4 6% 5% 9% 45%	1598
	21st to end	Night	9% 4 2 5% 5% 3 5% 5% 6% 7% 48%	1805
September	1st to 10th	Night	12% 6% 2 5% 5% 3 4 5% 5% 8% 47%	1897
	11th to 20th	Night	9% 4 2 4 4 3 5% 3 6% 8% 52%	1980
	21st to end	Night	14% 7% 3 6% 4 3 5% 4 5% 7% 43%	1980
October	1st to 10th	Night	13% 6% 3 4 5% 3 5% 5% 6% 7% 43%	2096
	11th to 20th	Night	18% 7% 3 7% 6% 4 4 4 5% 6% 35%	2160
	21st to end	Night	22% 10% 4 6% 5% 3 4 4 5% 6% 31%	2376
November	1st to 10th	Night	15% 8% 2 5% 4 3 5% 4 6% 7% 41%	2400
	11th to 20th	Night	17% 13% 5% 7% 5% 3 4 4 5% 7% 30%	2470
	21st to end	Night	19% 14% 6% 7% 6% 3 4 4 5% 7% 25%	2659
December	1st to 10th	Night	21% 17% 7% 8% 6% 3 4 4 4 5% 21%	2660
	11th to 20th	Night	17% 16% 7% 10% 6% 3 4 4 4 6% 22%	3285
	21st to end	Night	25% 20% 8% 9% 6% 3 4 4 3 5% 13%	4684

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	70% 5% 11% 10% 4	1707
	11th to 20th	Day	74% 5% 11% 8% 2	1710
	21st to end	Day	73% 6% 9% 9% 3 1	1872
February	1st to 10th	Day	70% 4 9% 12% 5% 1	1620
	11th to 20th	Day	67% 5% 8% 13% 6%	1640
	21st to end	Day	61% 5% 12% 14% 7% 1	1480
March	1st to 10th	Day	57% 5% 11% 20% 6%	1932
	11th to 20th	Day	57% 5% 10% 16% 10% 1	1980
	21st to end	Day	58% 5% 8% 17% 10% 1	2178
April	1st to 10th	Day	51% 7% 12% 18% 11% 1	2011
	11th to 20th	Day	52% 7% 11% 16% 12% 2	2277
	21st to end	Day	53% 6% 11% 19% 10% 2	2340
May	1st to 10th	Day	53% 7% 12% 17% 9% 1	2340
	11th to 20th	Day	50% 9% 11% 15% 13% 2	2305
	21st to end	Day	40% 9% 15% 23% 12% 1	2531
June	1st to 10th	Day	43% 8% 13% 23% 13% 1	2510
	11th to 20th	Day	43% 9% 13% 21% 13% 1	2520
	21st to end	Day	37% 10% 13% 23% 15% 2	2464
July	1st to 10th	Day	40% 7% 12% 23% 15% 2	2275
	11th to 20th	Day	39% 8% 15% 23% 14% 2	2271
	21st to end	Day	39% 9% 15% 22% 13% 2	2405
August	1st to 10th	Day	41% 10% 14% 24% 11% 1	2314
	11th to 20th	Day	42% 9% 16% 23% 9% 2	2303
	21st to end	Day	40% 9% 13% 21% 13% 4	2531
September	1st to 10th	Day	40% 7% 14% 20% 15% 4	2060
	11th to 20th	Day	37% 8% 15% 24% 15% 1	1980
	21st to end	Day	44% 7% 11% 22% 15% 1	1980
October	1st to 10th	Day	42% 7% 13% 22% 15% 1	1864
	11th to 20th	Day	50% 6% 12% 20% 11% 1	1800
	21st to end	Day	56% 5% 13% 15% 9% 1	1980
November	1st to 10th	Day	44% 6% 13% 21% 15% 1	1675
	11th to 20th	Day	54% 6% 11% 19% 8% 3	1708
	21st to end	Day	62% 6% 11% 14% 6% 1	1520
December	1st to 10th	Day	70% 5% 9% 12% 4	1520
	11th to 20th	Day	68% 6% 9% 13% 3	1906
	21st to end	Day	78% 5% 9% 6% 2	2966
January	1st to 10th	Night	67% 5% 10% 12% 6%	2459
	11th to 20th	Night	70% 5% 10% 12% 3	2470
	21st to end	Night	69% 4 10% 12% 4 1	2711
February	1st to 10th	Night	67% 5% 10% 13% 5%	2340
	11th to 20th	Night	63% 5% 10% 14% 7%	2216
	21st to end	Night	63% 5% 9% 14% 8% 2	1776
March	1st to 10th	Night	54% 5% 9% 22% 10% 1	2027
	11th to 20th	Night	48% 6% 12% 20% 11% 3	1980
	21st to end	Night	54% 5% 9% 19% 11% 2	2178
April	1st to 10th	Night	50% 6% 11% 18% 14% 1	1949
	11th to 20th	Night	47% 6% 12% 15% 16% 3	1647
	21st to end	Night	46% 6% 13% 18% 15% 2	1620
May	1st to 10th	Night	51% 8% 10% 16% 12% 3	1620
	11th to 20th	Night	44% 8% 12% 17% 15% 4	1593
	21st to end	Night	35% 8% 16% 25% 14% 1	1745
June	1st to 10th	Night	38% 7% 12% 25% 15% 3	1445
	11th to 20th	Night	38% 8% 14% 21% 17% 2	1440
	21st to end	Night	35% 9% 14% 24% 17% 1	1488
July	1st to 10th	Night	35% 8% 13% 22% 18% 4	1575
	11th to 20th	Night	31% 8% 15% 26% 17% 2	1566
	21st to end	Night	36% 7% 16% 23% 16% 3	1672
August	1st to 10th	Night	31% 8% 14% 28% 17% 1	1600
	11th to 20th	Night	35% 8% 15% 27% 12% 2	1598
	21st to end	Night	32% 7% 14% 25% 17% 4	1805
September	1st to 10th	Night	36% 8% 11% 24% 17% 5%	1897
	11th to 20th	Night	31% 6% 14% 25% 23% 2	1980
	21st to end	Night	39% 7% 12% 22% 19% 1	1980
October	1st to 10th	Night	38% 7% 14% 22% 18% 1	2096
	11th to 20th	Night	48% 6% 11% 21% 12% 1	2160
	21st to end	Night	53% 6% 10% 19% 9% 2	2376
November	1st to 10th	Night	42% 6% 12% 22% 15% 3	2400
	11th to 20th	Night	54% 5% 10% 18% 11% 2	2470
	21st to end	Night	59% 6% 12% 17% 6%	2659
December	1st to 10th	Night	67% 6% 11% 11% 5%	2660
	11th to 20th	Night	62% 7% 13% 15% 3	3288
	21st to end	Night	74% 6% 10% 8% 2	4684

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	29% 23% 32% 11% 4 1	270
	11th to 20th	Day	28% 24% 35% 10% 3	270
	21st to end	Day	28% 26% 33% 11% 3	294
February	1st to 10th	Day	33% 21% 36% 10%	240
	11th to 20th	Day	29% 30% 31% 8% 1	240
	21st to end	Day	28% 31% 32% 8% 1	198
March	1st to 10th	Day	24% 21% 33% 18% 5%	372
	11th to 20th	Day	27% 17% 32% 18% 6%	420
	21st to end	Day	32% 16% 27% 20% 4 1	462
April	1st to 10th	Day	21% 21% 30% 18% 9% 1	420
	11th to 20th	Day	26% 18% 26% 17% 9% 5%	412
	21st to end	Day	26% 15% 32% 17% 8% 2	420
May	1st to 10th	Day	25% 16% 29% 19% 9% 3	423
	11th to 20th	Day	19% 12% 33% 21% 11% 5%	447
	21st to end	Day	15% 6% 25% 28% 20% 6%	485
June	1st to 10th	Day	13% 8% 30% 32% 14% 3	450
	11th to 20th	Day	17% 8% 23% 31% 16% 5%	450
	21st to end	Day	14% 8% 28% 30% 15% 6%	450
July	1st to 10th	Day	12% 3 19% 29% 23% 14%	445
	11th to 20th	Day	10% 7% 20% 30% 22% 10%	444
	21st to end	Day	11% 5% 23% 25% 25% 10%	488
August	1st to 10th	Day	12% 5% 19% 26% 27% 11%	446
	11th to 20th	Day	15% 6% 20% 26% 21% 12%	439
	21st to end	Day	9% 5% 19% 29% 23% 14%	495
September	1st to 10th	Day	16% 6% 20% 24% 22% 12%	450
	11th to 20th	Day	10% 4 17% 26% 28% 14%	450
	21st to end	Day	22% 10% 21% 22% 18% 7%	450
October	1st to 10th	Day	12% 10% 26% 26% 21% 5%	450
	11th to 20th	Day	20% 15% 36% 20% 8% 1	450
	21st to end	Day	28% 17% 29% 19% 5% 1	495
November	1st to 10th	Day	16% 21% 34% 16% 11% 2	273
	11th to 20th	Day	28% 21% 29% 16% 6% 1	268
	21st to end	Day	24% 21% 39% 13% 2	180
December	1st to 10th	Day	27% 23% 32% 13% 4 2	180
	11th to 20th	Day	23% 24% 38% 12% 2	180
	21st to end	Day	31% 23% 32% 11% 3	254
January	1st to 10th	Night	24% 21% 34% 17% 4	760
	11th to 20th	Night	30% 17% 33% 17% 4	760
	21st to end	Night	27% 18% 30% 22% 3	835
February	1st to 10th	Night	28% 16% 32% 21% 3	720
	11th to 20th	Night	26% 15% 35% 21% 2	703
	21st to end	Night	29% 15% 37% 17% 2	592
March	1st to 10th	Night	23% 15% 35% 22% 5%	720
	11th to 20th	Night	23% 13% 33% 25% 6% 1	720
	21st to end	Night	24% 10% 32% 25% 7% 1	792
April	1st to 10th	Night	22% 12% 35% 25% 6% 1	720
	11th to 20th	Night	20% 12% 34% 22% 11% 1	583
	21st to end	Night	18% 9% 36% 30% 7% 1	540
May	1st to 10th	Night	21% 7% 30% 31% 10% 1	540
	11th to 20th	Night	20% 5% 25% 37% 11% 2	531
	21st to end	Night	12% 2 19% 41% 23% 3	584
June	1st to 10th	Night	8% 3 27% 43% 18% 1	365
	11th to 20th	Night	12% 4 23% 44% 16% 1	360
	21st to end	Night	12% 4 22% 42% 20%	408
July	1st to 10th	Night	9% 2 13% 42% 30% 4	525
	11th to 20th	Night	9% 2 19% 40% 27% 4	522
	21st to end	Night	9% 2 16% 43% 28% 2	591
August	1st to 10th	Night	8% 2 15% 42% 30% 3	537
	11th to 20th	Night	11% 2 13% 41% 29% 4	534
	21st to end	Night	10% 3 16% 34% 32% 4	617
September	1st to 10th	Night	13% 4 17% 34% 26% 5%	720
	11th to 20th	Night	10% 3 15% 36% 32% 5%	720
	21st to end	Night	16% 6% 22% 32% 20% 4	720
October	1st to 10th	Night	16% 6% 23% 33% 18% 3	720
	11th to 20th	Night	23% 10% 29% 28% 9% 1	720
	21st to end	Night	27% 13% 27% 28% 6%	792
November	1st to 10th	Night	20% 10% 28% 29% 12% 1	740
	11th to 20th	Night	22% 16% 32% 22% 6% 1	760
	21st to end	Night	27% 14% 33% 19% 7%	760
December	1st to 10th	Night	30% 14% 32% 19% 4	760
	11th to 20th	Night	25% 17% 33% 21% 3	760
	21st to end	Night	28% 16% 34% 20% 2	836

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