Edgewood Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edgewood Skies Observatory clear sky chart from 2005-11-06 to 2026-08-30.

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	2 3 1 3 3 3 4 4 6% 8% 62%	151667
	Night	3 3 1 4 3 3 4 4 6% 8% 62%	148125
Transparency	Day	18% 6% 9% 20% 28% 20%	146684
	Night	19% 5% 9% 20% 29% 19%	144115
Seeing	Day	5% 10% 24% 28% 22% 10%	17498
	Night	4 8% 28% 38% 20% 2	27574

By Month

Percentage Cloud Cover SW (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	1 4 2 4 2 3 3 4 6% 8% 62%	5318
	11th to 20th	Day	1 2 1 3 2 2 3 2 3 4 78%	5340
	21st to end	Day	2 4 2 4 3 3 4 4 5% 7% 63%	5844
February	1st to 10th	Day	1 4 2 4 3 3 3 4 5% 7% 66%	1929
	11th to 20th	Day	2 3 2 5% 2 3 3 3 5% 8% 63%	2049
	21st to end	Day	1 3 2 3 2 2 3 3 4 6% 70%	1730
March	1st to 10th	Day	1 4 1 3 2 2 3 3 5% 7% 68%	4872
	11th to 20th	Day	6% 5% 1 3 2 3 3 3 6% 8% 61%	5110
	21st to end	Day	1 2 1 3 3 3 4 4 7% 9% 64%	5781
April	1st to 10th	Day	2 3 1 2 3 3 3 3 5% 6% 68%	2520
	11th to 20th	Day	2 3 1 3 3 3 3 3 4 7% 66%	2491
	21st to end	Day	2 2 1 2 2 2 3 3 5% 7% 72%	2520
May	1st to 10th	Day	3 3 1 3 3 3 5% 4 6% 8% 60%	7057
	11th to 20th	Day	3 2 1 2 2 3 3 3 4 5% 73%	7162
	21st to end	Day	2 2 1 3 3 3 3 3 5% 7% 69%	9020
June	1st to 10th	Day	1 3 1 3 3 3 4 5% 7% 9% 60%	2940
	11th to 20th	Day	1 2 1 2 2 3 3 4 5% 6% 71%	2940
	21st to end	Day	4 4 1 4 3 3 4 5% 7% 7% 56%	2940
July	1st to 10th	Day	3 2 1 4 4 4 5% 4 6% 9% 57%	7975
	11th to 20th	Day	1 2 1 4 4 6% 8% 6% 10% 12% 45%	7650
	21st to end	Day	3 3 2 5% 5% 6% 8% 7% 9% 12% 40%	8304
August	1st to 10th	Day	1 2 1 3 4 4 6% 5% 8% 12% 54%	5734
	11th to 20th	Day	2 2 1 4 4 5% 6% 5% 8% 10% 52%	5486
	21st to end	Day	2 3 1 5% 5% 6% 6% 6% 8% 11% 46%	6093
September	1st to 10th	Day	5% 4 1 6% 4 4 5% 4 7% 9% 51%	2400
	11th to 20th	Day	5% 4 1 4 3 4 4 4 6% 8% 58%	2400
	21st to end	Day	4 2 1 2 2 2 3 2 5% 7% 69%	2174
October	1st to 10th	Day	4 2 1 2 2 2 3 2 4 5% 74%	3270
	11th to 20th	Day	4 3 1 3 2 2 3 3 5% 7% 67%	3250
	21st to end	Day	2 1 1 1 1 1 2 1 3 6% 81%	3548
November	1st to 10th	Day	2 2 1 1 2 2 2 3 4 8% 74%	2024
	11th to 20th	Day	1 3 1 2 2 2 2 3 5% 6% 73%	1890
	21st to end	Day	3 3 1 3 3 3 2 2 4 7% 69%	1890
December	1st to 10th	Day	1 2 1 2 2 1 2 2 3 5% 78%	2802
	11th to 20th	Day	2 2 1 3 3 3 3 2 5% 7% 70%	3106
	21st to end	Day	1 3 1 3 2 3 2 2 4 6% 73%	4108
January	1st to 10th	Night	1 5% 2 5% 3 3 5% 4 6% 7% 59%	7632
	11th to 20th	Night	1 2 1 2 1 1 2 2 4 5% 79%	7650
	21st to end	Night	2 4 2 4 3 3 4 3 5% 8% 62%	8370
February	1st to 10th	Night	1 4 1 3 2 2 2 3 4 7% 70%	2688
	11th to 20th	Night	2 4 1 3 3 3 3 3 6% 8% 62%	2458
	21st to end	Night	1 4 1 3 2 3 3 3 5% 6% 70%	2076
March	1st to 10th	Night	1 3 1 3 2 3 3 3 4 6% 71%	5229
	11th to 20th	Night	8% 6% 1 3 2 2 3 3 4 6% 62%	5110
	21st to end	Night	1 2 1 2 2 3 3 3 5% 7% 73%	5428
April	1st to 10th	Night	2 3 1 3 2 2 3 3 5% 7% 69%	2100
	11th to 20th	Night	2 4 1 3 3 3 3 3 4 7% 67%	2077
	21st to end	Night	2 2 1 3 3 2 3 3 4 5% 71%	2100
May	1st to 10th	Night	5% 5% 2 5% 3 3 4 3 6% 7% 57%	5890
	11th to 20th	Night	3 2 1 2 2 3 3 3 5% 6% 68%	5713
	21st to end	Night	3 2 1 3 3 3 4 3 6% 7% 66%	5185
June	1st to 10th	Night	2 3 1 4 4 4 5% 4 7% 9% 55%	1680
	11th to 20th	Night	2 2 1 4 3 3 4 2 6% 7% 67%	1680
	21st to end	Night	4 4 2 6% 5% 4 5% 4 8% 8% 51%	1680
July	1st to 10th	Night	3 3 2 5% 5% 5% 5% 5% 7% 9% 50%	4995
	11th to 20th	Night	2 3 2 6% 5% 6% 7% 6% 11% 13% 39%	5340
	21st to end	Night	5% 5% 2 7% 6% 6% 8% 7% 11% 12% 32%	5805
August	1st to 10th	Night	2 2 2 6% 6% 7% 7% 6% 9% 12% 42%	4298
	11th to 20th	Night	3 3 1 5% 5% 6% 7% 6% 10% 12% 41%	4583
	21st to end	Night	3 3 2 8% 6% 7% 8% 7% 10% 13% 35%	5083
September	1st to 10th	Night	6% 3 2 5% 5% 4 6% 4 7% 10% 50%	2000
	11th to 20th	Night	6% 3 2 4 3 3 4 3 6% 8% 57%	2000
	21st to end	Night	5% 2 1 3 3 3 3 3 4 6% 66%	2220
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 4 77%	3920
	11th to 20th	Night	5% 2 1 3 2 3 3 3 5% 6% 67%	3898
	21st to end	Night	2 1 1 1 1 2 2 2 3 5% 80%	4252
November	1st to 10th	Night	2 2 1 2 1 2 2 2 4 5% 77%	2471
	11th to 20th	Night	1 2 1 2 2 2 3 3 5% 5% 75%	2730
	21st to end	Night	3 4 1 3 2 3 3 3 5% 6% 67%	2730
December	1st to 10th	Night	1 2 1 3 2 2 2 2 4 6% 75%	4605
	11th to 20th	Night	2 2 1 2 2 2 2 3 5% 8% 71%	5321
	21st to end	Night	2 2 1 3 2 3 3 2 4 6% 72%	7128

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	20% 4 6% 32% 32% 6%	5321
	11th to 20th	Day	11% 3 6% 24% 37% 19%	5340
	21st to end	Day	21% 4 6% 16% 40% 14%	5844
February	1st to 10th	Day	18% 5% 6% 24% 31% 17%	1929
	11th to 20th	Day	20% 4 5% 25% 31% 16%	2059
	21st to end	Day	16% 2 3 19% 34% 26%	1730
March	1st to 10th	Day	14% 4 3 12% 35% 31%	4872
	11th to 20th	Day	19% 6% 5% 19% 29% 22%	5110
	21st to end	Day	16% 4 5% 20% 42% 13%	5781
April	1st to 10th	Day	15% 4 5% 18% 37% 21%	2520
	11th to 20th	Day	18% 4 4 17% 31% 26%	2494
	21st to end	Day	13% 3 5% 20% 39% 20%	2520
May	1st to 10th	Day	18% 7% 9% 18% 30% 19%	7057
	11th to 20th	Day	13% 4 4 14% 30% 35%	7165
	21st to end	Day	14% 5% 7% 14% 17% 42%	9021
June	1st to 10th	Day	16% 6% 9% 21% 25% 23%	2940
	11th to 20th	Day	12% 5% 4 13% 23% 42%	2940
	21st to end	Day	23% 6% 7% 19% 20% 24%	2940
July	1st to 10th	Day	20% 8% 10% 14% 20% 29%	7911
	11th to 20th	Day	21% 12% 21% 26% 13% 6%	7581
	21st to end	Day	28% 12% 20% 27% 11% 3	8120
August	1st to 10th	Day	22% 10% 19% 25% 16% 8%	4207
	11th to 20th	Day	20% 8% 12% 25% 24% 11%	4002
	21st to end	Day	27% 11% 17% 25% 17% 3	4420
September	1st to 10th	Day	27% 7% 11% 22% 24% 11%	2400
	11th to 20th	Day	22% 6% 9% 18% 26% 17%	2400
	21st to end	Day	16% 3 7% 23% 32% 19%	2174
October	1st to 10th	Day	14% 4 5% 13% 31% 34%	3270
	11th to 20th	Day	17% 4 7% 16% 29% 27%	3250
	21st to end	Day	8% 2 3 16% 44% 27%	3548
November	1st to 10th	Day	11% 3 3 21% 42% 20%	2024
	11th to 20th	Day	13% 3 6% 23% 39% 16%	1890
	21st to end	Day	17% 3 6% 23% 35% 18%	1890
December	1st to 10th	Day	11% 3 5% 28% 37% 16%	2802
	11th to 20th	Day	16% 2 7% 26% 37% 12%	3104
	21st to end	Day	13% 3 7% 26% 36% 15%	4108
January	1st to 10th	Night	23% 4 7% 26% 32% 8%	7632
	11th to 20th	Night	10% 2 6% 24% 41% 17%	7650
	21st to end	Night	20% 4 6% 16% 37% 17%	8370
February	1st to 10th	Night	15% 4 7% 24% 31% 19%	2688
	11th to 20th	Night	19% 5% 6% 22% 31% 16%	2458
	21st to end	Night	15% 3 4 18% 34% 25%	2076
March	1st to 10th	Night	14% 4 3 12% 38% 29%	5229
	11th to 20th	Night	23% 4 5% 16% 33% 19%	5110
	21st to end	Night	11% 4 5% 24% 40% 16%	5428
April	1st to 10th	Night	15% 4 5% 20% 34% 23%	2100
	11th to 20th	Night	17% 4 5% 16% 30% 28%	2077
	21st to end	Night	15% 4 5% 20% 36% 20%	2100
May	1st to 10th	Night	23% 7% 9% 19% 25% 18%	5888
	11th to 20th	Night	15% 6% 6% 15% 27% 31%	5714
	21st to end	Night	15% 6% 9% 12% 15% 43%	5186
June	1st to 10th	Night	23% 7% 12% 16% 20% 24%	1680
	11th to 20th	Night	15% 4 6% 15% 21% 39%	1680
	21st to end	Night	28% 6% 11% 15% 15% 23%	1680
July	1st to 10th	Night	26% 8% 11% 18% 15% 22%	4951
	11th to 20th	Night	27% 12% 26% 23% 9% 4	5286
	21st to end	Night	35% 12% 21% 22% 9% 1	5677
August	1st to 10th	Night	32% 12% 18% 18% 13% 7%	3149
	11th to 20th	Night	26% 10% 14% 23% 18% 9%	3343
	21st to end	Night	33% 12% 19% 22% 10% 4	3687
September	1st to 10th	Night	27% 8% 14% 21% 21% 9%	2000
	11th to 20th	Night	23% 6% 11% 19% 22% 20%	2000
	21st to end	Night	20% 4 7% 19% 30% 21%	2220
October	1st to 10th	Night	14% 3 5% 14% 30% 34%	3920
	11th to 20th	Night	17% 5% 7% 16% 26% 29%	3898
	21st to end	Night	9% 2 4 17% 41% 27%	4252
November	1st to 10th	Night	11% 3 4 22% 41% 20%	2471
	11th to 20th	Night	11% 4 6% 21% 39% 19%	2730
	21st to end	Night	19% 4 5% 19% 32% 20%	2730
December	1st to 10th	Night	12% 3 6% 31% 30% 18%	4605
	11th to 20th	Night	13% 3 6% 22% 41% 15%	5322
	21st to end	Night	14% 3 7% 24% 38% 13%	7128

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	4 21% 31% 31% 13% 1	330
	11th to 20th	Day	7% 17% 32% 26% 14% 3	330
	21st to end	Day	2 12% 36% 31% 16% 4	363
February	1st to 10th	Day	4 18% 36% 28% 12% 2	330
	11th to 20th	Day	8% 16% 43% 25% 7% 1	330
	21st to end	Day	7% 25% 36% 23% 8% 1	273
March	1st to 10th	Day	6% 19% 39% 24% 13% 1	446
	11th to 20th	Day	11% 20% 32% 22% 13% 1	540
	21st to end	Day	7% 23% 37% 22% 9% 2	594
April	1st to 10th	Day	9% 17% 35% 23% 11% 4	540
	11th to 20th	Day	7% 23% 40% 20% 8% 2	532
	21st to end	Day	7% 20% 39% 24% 10% 1	540
May	1st to 10th	Day	5% 16% 37% 30% 10% 3	543
	11th to 20th	Day	7% 13% 31% 27% 16% 7%	568
	21st to end	Day	3 10% 28% 38% 18% 4	838
June	1st to 10th	Day	2 6% 20% 35% 29% 8%	780
	11th to 20th	Day	2 4 22% 35% 30% 7%	780
	21st to end	Day	6% 4 16% 33% 28% 12%	780
July	1st to 10th	Day	4 2 8% 32% 35% 20%	683
	11th to 20th	Day	4 5% 22% 37% 33%	564
	21st to end	Day	5% 2 5% 20% 35% 34%	619
August	1st to 10th	Day	2 2 5% 27% 34% 30%	567
	11th to 20th	Day	4 2 9% 27% 34% 25%	557
	21st to end	Day	4 2 8% 30% 33% 23%	620
September	1st to 10th	Day	5% 2 11% 30% 35% 18%	530
	11th to 20th	Day	4 2 18% 34% 30% 13%	530
	21st to end	Day	6% 5% 18% 32% 27% 14%	355
October	1st to 10th	Day	7% 8% 24% 22% 25% 14%	330
	11th to 20th	Day	9% 8% 24% 28% 21% 10%	330
	21st to end	Day	8% 10% 25% 27% 24% 6%	363
November	1st to 10th	Day	6% 14% 31% 25% 21% 3	330
	11th to 20th	Day	4 10% 27% 30% 22% 6%	330
	21st to end	Day	6% 12% 37% 27% 15% 3	330
December	1st to 10th	Day	4 16% 29% 32% 14% 4	330
	11th to 20th	Day	5% 16% 32% 29% 16% 2	330
	21st to end	Day	7% 20% 34% 26% 12% 1	363
January	1st to 10th	Night	4 12% 31% 37% 14% 2	854
	11th to 20th	Night	4 9% 37% 37% 12% 1	840
	21st to end	Night	4 9% 35% 36% 14% 2	924
February	1st to 10th	Night	3 12% 35% 39% 10% 1	840
	11th to 20th	Night	5% 11% 43% 33% 7%	824
	21st to end	Night	3 12% 50% 30% 5%	692
March	1st to 10th	Night	4 12% 40% 34% 10%	840
	11th to 20th	Night	7% 11% 33% 37% 12%	840
	21st to end	Night	3 13% 39% 37% 9%	845
April	1st to 10th	Night	4 13% 43% 32% 7%	630
	11th to 20th	Night	4 14% 44% 32% 6%	623
	21st to end	Night	3 12% 42% 36% 7% 1	630
May	1st to 10th	Night	4 9% 35% 41% 10%	630
	11th to 20th	Night	6% 6% 29% 40% 18% 1	621
	21st to end	Night	5% 5% 32% 44% 13%	683
June	1st to 10th	Night	3 4 24% 47% 22% 1	630
	11th to 20th	Night	2 3 27% 49% 19% 1	630
	21st to end	Night	5% 3 16% 46% 29% 2	630
July	1st to 10th	Night	3 3 7% 44% 38% 4	615
	11th to 20th	Night	3 1 4 35% 50% 7%	612
	21st to end	Night	5% 4 4 28% 52% 8%	690
August	1st to 10th	Night	4 2 6% 30% 49% 9%	627
	11th to 20th	Night	6% 2 5% 35% 48% 5%	624
	21st to end	Night	2 2 5% 36% 51% 5%	687
September	1st to 10th	Night	6% 3 8% 40% 40% 4	600
	11th to 20th	Night	8% 2 10% 43% 35% 3	600
	21st to end	Night	5% 3 18% 42% 30% 2	647
October	1st to 10th	Night	7% 5% 20% 41% 25% 3	800
	11th to 20th	Night	5% 5% 22% 44% 21% 2	800
	21st to end	Night	5% 6% 24% 38% 24% 3	880
November	1st to 10th	Night	3 5% 26% 43% 22% 2	831
	11th to 20th	Night	2 8% 28% 41% 19% 2	1050
	21st to end	Night	6% 9% 30% 35% 18% 2	1050
December	1st to 10th	Night	4 10% 33% 39% 14% 1	1050
	11th to 20th	Night	4 11% 36% 36% 12%	1050
	21st to end	Night	3 13% 37% 38% 8% 1	1155

Page generated at 2026-08-27 02:07:13. Version ac07

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