John Glenn Astronomy Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the John Glenn Astronomy Park clear sky chart from 2005-11-06 to 2024-01-13.

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% 4 7% 6% 3 5% 5% 5% 7% 34%	74889
	Night	15% 9% 4 6% 5% 3 4 4 5% 7% 37%	74863
Transparency	Day	49% 6% 11% 20% 12% 2	74612
	Night	47% 6% 11% 21% 13% 2	74659
Seeing	Day	22% 13% 27% 21% 12% 5%	13766
	Night	20% 11% 25% 27% 14% 2	23917

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	17% 14% 6% 10% 7% 4 6% 4 5% 5% 22%	1706
	11th to 20th	Day	19% 18% 7% 11% 6% 3 3 3 4 5% 21%	1638
	21st to end	Day	19% 16% 6% 9% 7% 3 4 4 4 5% 22%	1782
February	1st to 10th	Day	22% 15% 5% 7% 7% 3 5% 4 4 6% 24%	1620
	11th to 20th	Day	18% 13% 6% 11% 6% 2 4 4 5% 5% 26%	1721
	21st to end	Day	19% 14% 5% 7% 5% 3 3 3 3 5% 31%	1480
March	1st to 10th	Day	18% 11% 4 5% 5% 3 4 4 5% 7% 34%	1898
	11th to 20th	Day	20% 10% 4 7% 6% 3 5% 4 5% 5% 30%	1980
	21st to end	Day	21% 10% 4 7% 6% 4 4 3 4 6% 31%	2178
April	1st to 10th	Day	14% 11% 4 6% 6% 3 5% 4 4 6% 35%	1986
	11th to 20th	Day	17% 10% 3 6% 5% 3 4 4 4 7% 37%	2279
	21st to end	Day	20% 7% 3 6% 5% 4 5% 5% 5% 6% 33%	2340
May	1st to 10th	Day	19% 8% 4 6% 6% 3 4 5% 4 8% 32%	2340
	11th to 20th	Day	20% 8% 3 6% 5% 4 5% 5% 5% 7% 31%	2301
	21st to end	Day	9% 5% 3 6% 7% 4 5% 7% 7% 10% 37%	2531
June	1st to 10th	Day	13% 6% 2 6% 5% 3 5% 6% 7% 8% 39%	2340
	11th to 20th	Day	10% 6% 3 6% 6% 4 6% 5% 6% 9% 39%	2340
	21st to end	Day	11% 5% 3 5% 7% 5% 6% 6% 7% 9% 36%	2340
July	1st to 10th	Day	12% 6% 3 7% 6% 5% 5% 5% 6% 8% 37%	2340
	11th to 20th	Day	10% 6% 3 6% 6% 3 6% 6% 8% 9% 37%	2340
	21st to end	Day	11% 5% 2 6% 6% 4 6% 7% 7% 9% 37%	2547
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 7% 7% 10% 37%	2327
	11th to 20th	Day	10% 5% 2 6% 6% 5% 6% 6% 7% 11% 35%	2303
	21st to end	Day	9% 5% 2 6% 6% 4 5% 5% 7% 9% 43%	2533
September	1st to 10th	Day	16% 5% 2 4 4 3 4 5% 5% 7% 45%	1980
	11th to 20th	Day	11% 5% 2 4 4 3 5% 5% 4 7% 49%	1980
	21st to end	Day	17% 6% 3 5% 5% 3 3 4 4 6% 44%	1980
October	1st to 10th	Day	13% 6% 2 5% 5% 3 4 4 6% 8% 43%	1918
	11th to 20th	Day	15% 7% 3 5% 5% 3 4 4 5% 6% 43%	1800
	21st to end	Day	22% 8% 3 5% 5% 3 4 4 3 6% 37%	1962
November	1st to 10th	Day	10% 7% 2 5% 5% 3 2 4 4 7% 49%	1672
	11th to 20th	Day	17% 11% 5% 7% 5% 2 3 3 5% 6% 35%	1710
	21st to end	Day	17% 12% 4 7% 4 3 5% 4 5% 6% 33%	1710
December	1st to 10th	Day	23% 14% 7% 8% 6% 3 4 4 4 4 22%	1710
	11th to 20th	Day	17% 17% 7% 9% 6% 3 4 3 5% 6% 24%	2153
	21st to end	Day	20% 22% 6% 10% 6% 3 5% 4 5% 6% 14%	3124
January	1st to 10th	Night	17% 15% 6% 12% 7% 3 5% 5% 4 4 23%	2459
	11th to 20th	Night	19% 15% 6% 11% 6% 4 4 3 4 5% 23%	2378
	21st to end	Night	17% 15% 6% 10% 6% 4 4 3 4 5% 26%	2574
February	1st to 10th	Night	23% 13% 4 8% 5% 3 4 4 3 5% 27%	2340
	11th to 20th	Night	19% 12% 5% 9% 6% 3 4 4 4 6% 27%	2121
	21st to end	Night	21% 15% 6% 7% 4 3 4 3 4 4 29%	1776
March	1st to 10th	Night	16% 10% 5% 6% 5% 3 4 4 5% 6% 37%	2061
	11th to 20th	Night	18% 10% 4 7% 5% 3 3 4 5% 6% 35%	1980
	21st to end	Night	20% 9% 4 7% 5% 2 4 4 4 6% 35%	2178
April	1st to 10th	Night	15% 9% 3 6% 5% 3 4 5% 5% 7% 38%	1980
	11th to 20th	Night	14% 7% 3 5% 5% 3 4 6% 6% 8% 38%	1638
	21st to end	Night	15% 7% 3 6% 6% 3 5% 4 5% 8% 37%	1620
May	1st to 10th	Night	17% 6% 4 6% 5% 3 5% 6% 6% 8% 34%	1620
	11th to 20th	Night	16% 9% 4 5% 6% 3 5% 5% 4 8% 38%	1592
	21st to end	Night	7% 5% 3 5% 5% 3 6% 6% 7% 10% 42%	1744
June	1st to 10th	Night	9% 5% 2 4 5% 3 5% 6% 7% 9% 45%	1620
	11th to 20th	Night	9% 4 2 5% 3 3 5% 6% 7% 10% 45%	1620
	21st to end	Night	11% 4 2 4 5% 3 4 6% 6% 12% 44%	1620
July	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 6% 9% 47%	1620
	11th to 20th	Night	6% 4 3 4 5% 3 6% 4 7% 10% 47%	1620
	21st to end	Night	8% 6% 3 6% 6% 3 6% 5% 7% 9% 43%	1771
August	1st to 10th	Night	6% 5% 3 5% 5% 3 4 6% 7% 11% 45%	1611
	11th to 20th	Night	7% 5% 2 7% 5% 3 5% 6% 7% 9% 44%	1598
	21st to end	Night	8% 4 2 5% 5% 3 3 4 5% 9% 52%	1803
September	1st to 10th	Night	12% 5% 2 4 4 2 4 4 5% 7% 51%	1978
	11th to 20th	Night	9% 4 2 5% 4 2 4 5% 5% 7% 53%	1980
	21st to end	Night	15% 5% 3 5% 4 3 3 4 4 6% 49%	1980
October	1st to 10th	Night	11% 5% 2 4 4 3 4 4 5% 7% 50%	2042
	11th to 20th	Night	15% 7% 2 6% 4 2 3 4 5% 7% 44%	2160
	21st to end	Night	20% 8% 3 4 5% 3 4 4 5% 5% 39%	2389
November	1st to 10th	Night	14% 6% 2 5% 5% 3 3 4 4 5% 49%	2406
	11th to 20th	Night	16% 10% 4 6% 5% 3 4 4 5% 6% 37%	2470
	21st to end	Night	19% 12% 4 6% 6% 3 5% 4 4 7% 33%	2470
December	1st to 10th	Night	22% 14% 6% 7% 5% 3 4 4 4 5% 25%	2470
	11th to 20th	Night	18% 13% 7% 9% 5% 2 4 3 4 7% 28%	3042
	21st to end	Night	20% 18% 6% 9% 8% 4 4 4 4 5% 17%	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	65% 5% 10% 14% 6%	1707
	11th to 20th	Day	68% 4 11% 13% 4	1638
	21st to end	Day	65% 5% 9% 14% 6% 1	1782
February	1st to 10th	Day	62% 5% 12% 15% 6% 1	1620
	11th to 20th	Day	61% 4 10% 17% 8%	1731
	21st to end	Day	58% 4 9% 19% 9% 1	1480
March	1st to 10th	Day	49% 5% 11% 25% 9% 1	1898
	11th to 20th	Day	56% 4 11% 19% 10% 1	1980
	21st to end	Day	56% 5% 10% 19% 10% 1	2178
April	1st to 10th	Day	50% 5% 10% 21% 11% 3	1986
	11th to 20th	Day	47% 6% 10% 19% 15% 4	2279
	21st to end	Day	51% 6% 11% 20% 11% 3	2340
May	1st to 10th	Day	51% 6% 11% 20% 9% 2	2340
	11th to 20th	Day	51% 7% 12% 17% 12% 1	2305
	21st to end	Day	39% 11% 15% 21% 13% 1	2531
June	1st to 10th	Day	40% 8% 12% 23% 16% 2	2340
	11th to 20th	Day	41% 8% 13% 21% 16% 2	2340
	21st to end	Day	41% 10% 13% 21% 14% 2	2340
July	1st to 10th	Day	44% 9% 10% 20% 16% 1	2275
	11th to 20th	Day	40% 10% 12% 22% 15% 2	2271
	21st to end	Day	39% 9% 13% 23% 13% 3	2405
August	1st to 10th	Day	38% 9% 13% 25% 13% 1	2314
	11th to 20th	Day	40% 9% 13% 26% 11% 2	2303
	21st to end	Day	35% 8% 14% 22% 16% 5%	2533
September	1st to 10th	Day	37% 7% 10% 21% 20% 4	1980
	11th to 20th	Day	33% 7% 11% 25% 22% 2	1980
	21st to end	Day	42% 4 9% 24% 20% 1	1980
October	1st to 10th	Day	38% 6% 12% 22% 20% 1	1918
	11th to 20th	Day	41% 5% 10% 25% 17% 2	1800
	21st to end	Day	49% 4 10% 22% 13% 2	1962
November	1st to 10th	Day	35% 6% 9% 29% 18% 3	1672
	11th to 20th	Day	50% 4 8% 20% 15% 3	1710
	21st to end	Day	53% 4 10% 21% 12% 1	1710
December	1st to 10th	Day	66% 5% 9% 16% 4	1710
	11th to 20th	Day	62% 3 9% 17% 8%	2150
	21st to end	Day	71% 5% 10% 9% 4	3124
January	1st to 10th	Night	64% 4 9% 15% 8% 1	2459
	11th to 20th	Night	65% 4 12% 14% 4 1	2378
	21st to end	Night	61% 4 10% 17% 6% 2	2574
February	1st to 10th	Night	60% 4 11% 18% 6% 1	2340
	11th to 20th	Night	58% 4 9% 17% 11% 1	2122
	21st to end	Night	60% 4 9% 17% 8% 3	1776
March	1st to 10th	Night	49% 5% 9% 22% 13% 1	2061
	11th to 20th	Night	50% 5% 12% 22% 10% 2	1980
	21st to end	Night	52% 4 9% 21% 12% 2	2178
April	1st to 10th	Night	44% 6% 12% 21% 15% 2	1980
	11th to 20th	Night	41% 6% 11% 18% 19% 5%	1638
	21st to end	Night	45% 6% 10% 23% 14% 2	1620
May	1st to 10th	Night	46% 8% 12% 20% 10% 3	1620
	11th to 20th	Night	46% 7% 11% 20% 13% 3	1593
	21st to end	Night	34% 9% 18% 24% 13% 2	1745
June	1st to 10th	Night	33% 9% 12% 24% 20% 3	1620
	11th to 20th	Night	31% 9% 15% 23% 19% 3	1620
	21st to end	Night	32% 9% 14% 24% 18% 3	1620
July	1st to 10th	Night	35% 7% 13% 22% 20% 3	1575
	11th to 20th	Night	31% 9% 14% 25% 19% 2	1566
	21st to end	Night	36% 8% 13% 25% 16% 2	1672
August	1st to 10th	Night	31% 10% 15% 28% 15% 2	1600
	11th to 20th	Night	34% 9% 14% 24% 19% 1	1598
	21st to end	Night	30% 6% 12% 27% 20% 6%	1803
September	1st to 10th	Night	32% 7% 12% 24% 19% 6%	1978
	11th to 20th	Night	29% 7% 11% 25% 26% 2	1980
	21st to end	Night	37% 5% 9% 22% 26% 1	1980
October	1st to 10th	Night	33% 7% 11% 25% 21% 4	2042
	11th to 20th	Night	39% 7% 9% 25% 18% 2	2160
	21st to end	Night	46% 5% 10% 21% 15% 3	2389
November	1st to 10th	Night	37% 3 11% 24% 20% 4	2406
	11th to 20th	Night	48% 4 8% 20% 16% 3	2470
	21st to end	Night	53% 4 11% 20% 11% 1	2470
December	1st to 10th	Night	61% 5% 9% 18% 6%	2470
	11th to 20th	Night	58% 4 11% 20% 7%	3044
	21st to end	Night	70% 4 9% 14% 4	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	29% 24% 33% 10% 4	270
	11th to 20th	Day	30% 26% 34% 9% 2	246
	21st to end	Day	35% 23% 30% 10% 2	264
February	1st to 10th	Day	40% 25% 23% 11% 2	240
	11th to 20th	Day	39% 28% 30% 3 1	240
	21st to end	Day	37% 26% 30% 6% 1	198
March	1st to 10th	Day	32% 25% 28% 13% 3	338
	11th to 20th	Day	31% 20% 30% 12% 6%	420
	21st to end	Day	35% 17% 30% 13% 4	462
April	1st to 10th	Day	26% 18% 31% 15% 8% 1	420
	11th to 20th	Day	27% 17% 27% 19% 8% 3	412
	21st to end	Day	29% 17% 29% 15% 6% 2	420
May	1st to 10th	Day	29% 18% 28% 16% 8% 2	423
	11th to 20th	Day	22% 14% 29% 22% 8% 5%	447
	21st to end	Day	15% 8% 25% 28% 18% 6%	485
June	1st to 10th	Day	15% 8% 26% 30% 15% 6%	450
	11th to 20th	Day	15% 9% 26% 31% 15% 5%	450
	21st to end	Day	12% 10% 28% 30% 13% 7%	450
July	1st to 10th	Day	13% 4 19% 27% 19% 18%	445
	11th to 20th	Day	11% 7% 21% 28% 21% 12%	444
	21st to end	Day	12% 2 25% 28% 20% 13%	488
August	1st to 10th	Day	12% 3 20% 29% 24% 11%	446
	11th to 20th	Day	13% 5% 21% 32% 17% 12%	439
	21st to end	Day	11% 4 21% 31% 21% 12%	495
September	1st to 10th	Day	15% 4 20% 23% 26% 12%	450
	11th to 20th	Day	12% 4 15% 28% 30% 12%	450
	21st to end	Day	22% 9% 20% 26% 19% 4	450
October	1st to 10th	Day	14% 8% 29% 26% 18% 5%	450
	11th to 20th	Day	21% 12% 32% 21% 11% 2	450
	21st to end	Day	27% 15% 31% 19% 7%	477
November	1st to 10th	Day	17% 17% 35% 22% 8% 1	270
	11th to 20th	Day	31% 18% 27% 17% 6% 1	270
	21st to end	Day	28% 19% 34% 14% 4	270
December	1st to 10th	Day	30% 21% 34% 12% 3 1	270
	11th to 20th	Day	24% 27% 34% 8% 6%	270
	21st to end	Day	33% 23% 29% 12% 3	297
January	1st to 10th	Night	30% 19% 30% 17% 4	760
	11th to 20th	Night	30% 19% 29% 18% 3	732
	21st to end	Night	26% 20% 32% 21% 2	792
February	1st to 10th	Night	31% 15% 30% 22% 2	720
	11th to 20th	Night	31% 21% 28% 19% 1	703
	21st to end	Night	32% 17% 31% 18% 2	592
March	1st to 10th	Night	25% 18% 30% 23% 4	720
	11th to 20th	Night	26% 18% 28% 21% 7% 1	720
	21st to end	Night	26% 15% 30% 21% 7%	792
April	1st to 10th	Night	21% 16% 33% 23% 6% 1	720
	11th to 20th	Night	17% 13% 33% 25% 11% 1	542
	21st to end	Night	19% 11% 37% 26% 6% 1	540
May	1st to 10th	Night	20% 10% 31% 25% 11% 2	540
	11th to 20th	Night	19% 8% 29% 27% 15% 1	531
	21st to end	Night	10% 5% 23% 32% 27% 3	584
June	1st to 10th	Night	11% 4 23% 40% 21% 1	540
	11th to 20th	Night	11% 4 23% 37% 24% 2	540
	21st to end	Night	11% 4 22% 36% 24% 2	540
July	1st to 10th	Night	12% 2 16% 33% 30% 8%	525
	11th to 20th	Night	7% 2 17% 37% 32% 6%	522
	21st to end	Night	11% 3 17% 31% 34% 4	591
August	1st to 10th	Night	7% 2 14% 41% 34% 3	537
	11th to 20th	Night	8% 2 15% 38% 31% 6%	534
	21st to end	Night	10% 1 17% 32% 33% 7%	594
September	1st to 10th	Night	15% 3 15% 32% 29% 5%	718
	11th to 20th	Night	10% 4 14% 35% 32% 5%	720
	21st to end	Night	16% 7% 22% 32% 19% 3	720
October	1st to 10th	Night	14% 6% 23% 33% 21% 3	720
	11th to 20th	Night	19% 11% 27% 31% 12% 1	720
	21st to end	Night	24% 13% 27% 27% 9% 1	792
November	1st to 10th	Night	19% 10% 24% 28% 17% 1	740
	11th to 20th	Night	23% 17% 26% 24% 9% 1	760
	21st to end	Night	27% 13% 25% 27% 7% 1	760
December	1st to 10th	Night	31% 17% 26% 21% 4 1	760
	11th to 20th	Night	26% 16% 29% 22% 6%	760
	21st to end	Night	30% 18% 27% 24% 3	836

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