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 2025-12-03.

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% 3 8% 5% 5% 5% 4 5% 7% 33%	126991
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 35%	123726
Transparency	Day	48% 5% 10% 22% 13% 2	130664
	Night	48% 5% 10% 21% 13% 2	128122
Seeing	Day	22% 13% 27% 21% 12% 5%	16316
	Night	20% 11% 26% 27% 14% 2	26388

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	15% 22% 7% 13% 7% 4 3 3 4 5% 18%	4056
	11th to 20th	Day	13% 21% 8% 12% 6% 6% 4 3 3 4 21%	4060
	21st to end	Day	21% 15% 6% 9% 7% 5% 5% 3 4 4 20%	4466
February	1st to 10th	Day	21% 15% 4 8% 6% 4 4 3 4 6% 26%	1800
	11th to 20th	Day	18% 14% 5% 12% 5% 3 4 3 5% 4 27%	1918
	21st to end	Day	19% 14% 5% 8% 4 4 3 2 4 5% 32%	1650
March	1st to 10th	Day	18% 15% 5% 8% 5% 4 4 3 4 6% 30%	4746
	11th to 20th	Day	13% 8% 3 7% 4 5% 5% 3 5% 7% 41%	4980
	21st to end	Day	18% 9% 3 8% 5% 5% 4 3 5% 6% 34%	5465
April	1st to 10th	Day	15% 12% 3 8% 5% 4 5% 3 4 6% 33%	2208
	11th to 20th	Day	16% 10% 3 7% 4 4 4 4 5% 7% 37%	2536
	21st to end	Day	19% 8% 2 7% 5% 5% 4 4 6% 7% 34%	2600
May	1st to 10th	Day	19% 10% 3 7% 5% 5% 5% 5% 6% 8% 27%	5862
	11th to 20th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 29%	5861
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 9% 33%	6433
June	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 5% 7% 8% 38%	2600
	11th to 20th	Day	10% 7% 3 7% 5% 6% 5% 4 6% 9% 38%	2600
	21st to end	Day	11% 6% 2 5% 6% 6% 6% 5% 7% 9% 36%	2600
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 6% 8% 43%	5900
	11th to 20th	Day	10% 7% 2 7% 5% 5% 6% 5% 8% 10% 33%	5900
	21st to end	Day	11% 7% 3 8% 5% 6% 6% 5% 7% 8% 33%	6424
August	1st to 10th	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 38%	4234
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 8% 10% 38%	4174
	21st to end	Day	5% 4 2 6% 5% 5% 5% 4 6% 9% 50%	4589
September	1st to 10th	Day	15% 6% 1 4 3 3 4 4 5% 7% 47%	2200
	11th to 20th	Day	10% 5% 2 5% 3 4 5% 4 5% 7% 51%	2200
	21st to end	Day	18% 7% 2 7% 4 4 3 4 4 6% 42%	2200
October	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 6% 8% 46%	2130
	11th to 20th	Day	14% 7% 3 5% 4 4 4 3 4 6% 45%	2000
	21st to end	Day	20% 8% 2 6% 4 5% 3 3 4 6% 38%	2180
November	1st to 10th	Day	11% 8% 2 6% 4 4 3 3 4 7% 49%	1852
	11th to 20th	Day	16% 13% 4 8% 5% 2 4 3 5% 6% 35%	1890
	21st to end	Day	17% 14% 5% 8% 4 4 4 3 4 6% 31%	1890
December	1st to 10th	Day	19% 13% 5% 12% 6% 4 4 3 3 4 26%	2948
	11th to 20th	Day	23% 15% 6% 9% 5% 4 4 2 4 5% 22%	3373
	21st to end	Day	20% 20% 5% 11% 6% 4 5% 3 4 5% 17%	4466
January	1st to 10th	Night	15% 18% 8% 17% 6% 4 3 3 3 4 18%	5889
	11th to 20th	Night	16% 17% 6% 14% 8% 6% 5% 3 4 4 19%	5900
	21st to end	Night	20% 13% 6% 9% 7% 4 3 2 3 4 28%	6490
February	1st to 10th	Night	21% 14% 3 9% 4 4 3 3 4 5% 29%	2600
	11th to 20th	Night	19% 13% 4 11% 5% 4 4 3 4 5% 27%	2364
	21st to end	Night	19% 15% 5% 8% 4 4 4 3 4 4 30%	1980
March	1st to 10th	Night	18% 14% 4 6% 4 4 4 3 4 6% 35%	5106
	11th to 20th	Night	12% 9% 3 6% 4 4 4 3 6% 7% 43%	4980
	21st to end	Night	17% 10% 3 8% 5% 4 5% 4 4 5% 34%	5467
April	1st to 10th	Night	17% 10% 3 6% 5% 4 4 4 5% 7% 36%	2200
	11th to 20th	Night	13% 8% 3 6% 5% 4 4 5% 6% 8% 38%	1821
	21st to end	Night	14% 8% 3 8% 5% 4 4 3 6% 8% 38%	1800
May	1st to 10th	Night	24% 9% 3 7% 5% 4 4 4 6% 7% 27%	4033
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 6% 10% 36%	4032
	21st to end	Night	14% 7% 2 6% 5% 5% 5% 4 7% 9% 36%	4421
June	1st to 10th	Night	10% 6% 2 5% 4 4 5% 5% 7% 8% 45%	1800
	11th to 20th	Night	9% 5% 2 5% 4 5% 4 4 7% 10% 44%	1800
	21st to end	Night	10% 4 2 5% 5% 4 5% 5% 7% 11% 43%	1800
July	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 5% 8% 46%	4058
	11th to 20th	Night	9% 6% 2 7% 5% 6% 6% 4 7% 10% 37%	4057
	21st to end	Night	7% 7% 3 8% 5% 5% 5% 4 7% 9% 39%	4427
August	1st to 10th	Night	6% 7% 3 8% 5% 5% 5% 4 7% 10% 40%	2915
	11th to 20th	Night	9% 8% 3 8% 5% 4 4 4 5% 7% 44%	2875
	21st to end	Night	5% 3 2 5% 5% 4 4 4 7% 10% 51%	3273
September	1st to 10th	Night	11% 5% 1 4 4 4 4 4 5% 6% 52%	2198
	11th to 20th	Night	8% 5% 2 5% 3 3 5% 3 5% 7% 54%	2200
	21st to end	Night	16% 6% 3 6% 4 4 3 3 4 5% 46%	2200
October	1st to 10th	Night	11% 5% 2 4 3 3 4 3 5% 7% 52%	2270
	11th to 20th	Night	14% 7% 2 6% 3 3 4 3 5% 7% 46%	2400
	21st to end	Night	19% 8% 2 5% 4 4 4 3 5% 5% 40%	2655
November	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 4 6% 49%	2666
	11th to 20th	Night	15% 11% 3 7% 5% 4 4 3 5% 5% 37%	2730
	21st to end	Night	19% 13% 4 7% 5% 4 4 3 4 6% 31%	2730
December	1st to 10th	Night	18% 13% 5% 10% 5% 4 4 3 4 6% 29%	4277
	11th to 20th	Night	19% 17% 7% 11% 4 3 4 3 4 5% 24%	4822
	21st to end	Night	21% 18% 6% 11% 6% 5% 4 3 4 6% 17%	6490

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% 3 10% 12% 4	4057
	11th to 20th	Day	68% 3 9% 11% 9% 1	4060
	21st to end	Day	68% 3 8% 13% 6% 1	4466
February	1st to 10th	Day	59% 4 12% 16% 8% 1	1800
	11th to 20th	Day	60% 4 9% 16% 10%	1928
	21st to end	Day	56% 4 10% 20% 9% 1	1650
March	1st to 10th	Day	56% 4 6% 22% 10% 2	4746
	11th to 20th	Day	43% 4 10% 28% 14% 2	4980
	21st to end	Day	51% 4 9% 21% 12% 2	5465
April	1st to 10th	Day	51% 5% 10% 20% 11% 3	2208
	11th to 20th	Day	46% 6% 10% 21% 14% 4	2536
	21st to end	Day	49% 5% 11% 20% 12% 2	2600
May	1st to 10th	Day	53% 6% 10% 18% 11% 2	5897
	11th to 20th	Day	51% 7% 10% 21% 11% 1	5865
	21st to end	Day	44% 9% 12% 19% 13% 3	6447
June	1st to 10th	Day	40% 8% 12% 22% 17% 2	2600
	11th to 20th	Day	41% 8% 13% 20% 16% 1	2600
	21st to end	Day	40% 10% 13% 21% 15% 2	2600
July	1st to 10th	Day	39% 6% 10% 27% 16% 2	5835
	11th to 20th	Day	42% 8% 12% 26% 11% 1	5831
	21st to end	Day	45% 7% 11% 18% 16% 2	6240
August	1st to 10th	Day	38% 8% 14% 29% 11% 1	4221
	11th to 20th	Day	37% 7% 10% 30% 15% 1	4213
	21st to end	Day	30% 6% 14% 30% 18% 3	4589
September	1st to 10th	Day	35% 7% 10% 22% 22% 5%	2200
	11th to 20th	Day	32% 7% 11% 25% 24% 2	2200
	21st to end	Day	44% 4 9% 22% 19% 1	2200
October	1st to 10th	Day	25% 4 9% 30% 31% 2	3468
	11th to 20th	Day	33% 4 10% 29% 22% 3	3240
	21st to end	Day	36% 3 11% 27% 20% 2	3506
November	1st to 10th	Day	36% 6% 9% 29% 18% 3	1852
	11th to 20th	Day	50% 4 9% 21% 14% 2	1890
	21st to end	Day	55% 4 10% 20% 11% 1	1890
December	1st to 10th	Day	62% 4 10% 20% 5%	2948
	11th to 20th	Day	65% 3 9% 17% 6%	3370
	21st to end	Day	69% 4 10% 12% 5%	4466
January	1st to 10th	Night	71% 3 8% 13% 4	5889
	11th to 20th	Night	70% 3 9% 11% 6% 2	5900
	21st to end	Night	62% 3 9% 18% 7% 2	6490
February	1st to 10th	Night	58% 4 11% 18% 8% 1	2600
	11th to 20th	Night	59% 4 9% 16% 12% 1	2365
	21st to end	Night	59% 4 9% 17% 9% 2	1980
March	1st to 10th	Night	51% 4 7% 26% 11% 2	5106
	11th to 20th	Night	39% 4 10% 30% 15% 1	4980
	21st to end	Night	52% 4 7% 23% 13% 2	5467
April	1st to 10th	Night	47% 5% 11% 20% 14% 2	2200
	11th to 20th	Night	41% 6% 11% 19% 18% 5%	1821
	21st to end	Night	45% 6% 10% 23% 15% 2	1800
May	1st to 10th	Night	54% 7% 10% 16% 8% 4	4060
	11th to 20th	Night	44% 8% 12% 23% 12% 1	4033
	21st to end	Night	42% 8% 14% 24% 9% 3	4429
June	1st to 10th	Night	34% 8% 11% 23% 21% 3	1800
	11th to 20th	Night	33% 9% 15% 22% 19% 2	1800
	21st to end	Night	32% 10% 14% 23% 19% 3	1800
July	1st to 10th	Night	36% 5% 10% 25% 20% 4	4015
	11th to 20th	Night	40% 8% 15% 25% 11% 1	4006
	21st to end	Night	40% 7% 13% 21% 15% 4	4297
August	1st to 10th	Night	38% 8% 15% 27% 11% 1	2904
	11th to 20th	Night	39% 7% 9% 24% 21% 1	2902
	21st to end	Night	28% 6% 14% 29% 20% 3	3273
September	1st to 10th	Night	31% 7% 12% 23% 22% 6%	2198
	11th to 20th	Night	29% 6% 10% 25% 27% 3	2200
	21st to end	Night	40% 5% 9% 21% 25% 1	2200
October	1st to 10th	Night	27% 4 7% 27% 32% 3	3712
	11th to 20th	Night	30% 4 9% 26% 24% 7%	3899
	21st to end	Night	33% 4 8% 24% 26% 5%	4279
November	1st to 10th	Night	37% 3 11% 25% 20% 3	2666
	11th to 20th	Night	48% 4 8% 21% 16% 3	2730
	21st to end	Night	55% 4 10% 20% 10% 1	2730
December	1st to 10th	Night	57% 4 12% 22% 5%	4277
	11th to 20th	Night	63% 3 11% 17% 5%	4824
	21st to end	Night	69% 4 9% 14% 4	6490

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	31% 22% 33% 10% 3	300
	11th to 20th	Day	33% 28% 31% 7% 1	300
	21st to end	Day	35% 24% 31% 9% 2	330
February	1st to 10th	Day	36% 24% 26% 12% 2	300
	11th to 20th	Day	40% 26% 29% 3 2	300
	21st to end	Day	36% 25% 33% 5% 1	249
March	1st to 10th	Day	32% 25% 27% 13% 4	410
	11th to 20th	Day	31% 21% 31% 11% 6%	500
	21st to end	Day	35% 18% 31% 13% 3	550
April	1st to 10th	Day	28% 20% 30% 14% 7% 1	500
	11th to 20th	Day	27% 18% 28% 18% 7% 2	492
	21st to end	Day	28% 17% 30% 17% 6% 2	500
May	1st to 10th	Day	29% 18% 28% 16% 8% 2	503
	11th to 20th	Day	22% 15% 27% 22% 9% 5%	527
	21st to end	Day	17% 9% 27% 25% 17% 5%	573
June	1st to 10th	Day	15% 10% 27% 29% 15% 5%	530
	11th to 20th	Day	16% 8% 25% 32% 14% 5%	530
	21st to end	Day	11% 10% 27% 30% 15% 7%	530
July	1st to 10th	Day	13% 4 21% 27% 19% 16%	525
	11th to 20th	Day	11% 6% 23% 28% 21% 11%	524
	21st to end	Day	12% 3 25% 28% 21% 11%	576
August	1st to 10th	Day	11% 3 22% 30% 23% 10%	526
	11th to 20th	Day	12% 5% 22% 32% 18% 11%	519
	21st to end	Day	10% 4 21% 31% 23% 11%	583
September	1st to 10th	Day	14% 5% 19% 24% 25% 12%	530
	11th to 20th	Day	10% 3 14% 29% 31% 13%	530
	21st to end	Day	23% 9% 21% 25% 17% 4	530
October	1st to 10th	Day	12% 7% 28% 27% 20% 6%	530
	11th to 20th	Day	20% 12% 32% 21% 12% 3	530
	21st to end	Day	25% 15% 33% 19% 7%	563
November	1st to 10th	Day	19% 16% 36% 21% 6% 1	330
	11th to 20th	Day	33% 17% 29% 15% 5% 1	330
	21st to end	Day	32% 20% 32% 12% 4	330
December	1st to 10th	Day	30% 20% 35% 11% 2 1	306
	11th to 20th	Day	27% 25% 34% 8% 5%	300
	21st to end	Day	32% 22% 29% 13% 3	330
January	1st to 10th	Night	30% 19% 30% 16% 4	800
	11th to 20th	Night	31% 20% 29% 17% 3	800
	21st to end	Night	27% 20% 32% 20% 2	880
February	1st to 10th	Night	30% 16% 30% 22% 1	800
	11th to 20th	Night	31% 22% 28% 17% 1	783
	21st to end	Night	30% 17% 31% 19% 2	660
March	1st to 10th	Night	25% 18% 30% 23% 4	800
	11th to 20th	Night	26% 18% 28% 21% 6% 1	800
	21st to end	Night	26% 16% 31% 20% 7%	880
April	1st to 10th	Night	23% 16% 33% 21% 6% 1	800
	11th to 20th	Night	17% 13% 35% 24% 10% 1	602
	21st to end	Night	19% 11% 37% 26% 6% 1	600
May	1st to 10th	Night	20% 11% 30% 26% 11% 2	600
	11th to 20th	Night	19% 8% 29% 27% 16% 1	591
	21st to end	Night	12% 6% 24% 32% 25% 2	650
June	1st to 10th	Night	12% 4 23% 40% 21% 1	600
	11th to 20th	Night	11% 4 21% 38% 24% 2	600
	21st to end	Night	11% 4 22% 36% 25% 3	600
July	1st to 10th	Night	11% 3 16% 34% 29% 7%	585
	11th to 20th	Night	7% 2 18% 36% 32% 5%	582
	21st to end	Night	11% 3 16% 32% 34% 4	657
August	1st to 10th	Night	7% 3 15% 40% 33% 3	597
	11th to 20th	Night	8% 3 15% 38% 31% 5%	594
	21st to end	Night	9% 2 17% 32% 33% 7%	660
September	1st to 10th	Night	14% 4 16% 33% 28% 5%	798
	11th to 20th	Night	9% 4 14% 36% 33% 5%	800
	21st to end	Night	18% 7% 22% 32% 19% 3	800
October	1st to 10th	Night	14% 6% 22% 33% 22% 4	800
	11th to 20th	Night	18% 10% 27% 31% 13% 1	800
	21st to end	Night	22% 13% 28% 27% 10% 1	880
November	1st to 10th	Night	20% 10% 26% 28% 16%	820
	11th to 20th	Night	25% 16% 27% 24% 8% 1	840
	21st to end	Night	28% 14% 25% 27% 6% 1	840
December	1st to 10th	Night	31% 17% 27% 20% 4	809
	11th to 20th	Night	27% 16% 30% 21% 5%	800
	21st to end	Night	30% 17% 26% 24% 3	880

Page generated at 2025-11-30 01:00:52. Version ac07

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