Schumann Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Schumann Observatory clear sky chart from 2005-11-06 to 2025-07-21.

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	119955
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	119176
Transparency	Day	22% 42% 8% 14% 11% 3	123587
	Night	24% 40% 7% 15% 12% 3	123682
Seeing	Day	16% 10% 29% 27% 14% 4	16087
	Night	17% 10% 28% 29% 13% 2	25616

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% 3 1 4 3 3 3 3 4 5% 57%	3753
	11th to 20th	Day	11% 7% 2 6% 3 3 3 3 4 5% 51%	4060
	21st to end	Day	12% 7% 3 7% 5% 5% 3 3 5% 6% 44%	4466
February	1st to 10th	Day	12% 9% 2 6% 4 5% 5% 4 6% 7% 40%	1800
	11th to 20th	Day	20% 7% 2 4 3 3 4 3 4 6% 45%	1890
	21st to end	Day	14% 9% 3 5% 5% 6% 4 4 5% 5% 39%	1650
March	1st to 10th	Day	18% 6% 2 7% 4 4 4 4 5% 7% 39%	4752
	11th to 20th	Day	10% 7% 3 5% 3 3 4 3 5% 7% 53%	4980
	21st to end	Day	15% 7% 2 5% 4 4 4 4 5% 6% 44%	5638
April	1st to 10th	Day	12% 6% 2 5% 4 4 3 4 5% 7% 49%	2400
	11th to 20th	Day	10% 6% 2 5% 4 5% 4 4 5% 7% 49%	2374
	21st to end	Day	14% 6% 2 5% 4 4 4 4 5% 7% 45%	2400
May	1st to 10th	Day	16% 7% 2 7% 5% 4 5% 4 6% 10% 34%	5465
	11th to 20th	Day	19% 6% 3 7% 5% 5% 5% 4 6% 9% 33%	6148
	21st to end	Day	14% 5% 2 5% 4 4 4 4 6% 9% 43%	6934
June	1st to 10th	Day	11% 5% 1 4 5% 4 5% 5% 8% 9% 43%	2800
	11th to 20th	Day	11% 4 2 5% 4 4 5% 5% 7% 10% 43%	2800
	21st to end	Day	8% 4 2 5% 5% 4 5% 5% 7% 10% 46%	2800
July	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 5% 8% 12% 42%	4580
	11th to 20th	Day	12% 6% 2 7% 6% 5% 6% 5% 7% 10% 35%	4399
	21st to end	Day	9% 5% 2 8% 6% 6% 6% 6% 8% 11% 34%	4466
August	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 5% 8% 10% 30%	4104
	11th to 20th	Day	10% 5% 3 7% 6% 6% 6% 5% 7% 9% 37%	3735
	21st to end	Day	9% 4 1 4 3 3 4 4 7% 11% 48%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 7% 45%	2280
	11th to 20th	Day	14% 6% 3 6% 4 4 4 3 6% 7% 43%	2280
	21st to end	Day	21% 8% 2 5% 4 3 4 3 5% 6% 38%	2031
October	1st to 10th	Day	16% 5% 2 6% 4 4 3 3 4 7% 45%	1900
	11th to 20th	Day	16% 5% 2 4 2 3 3 3 4 5% 52%	1900
	21st to end	Day	13% 5% 2 4 4 3 4 4 5% 6% 51%	2090
November	1st to 10th	Day	15% 5% 2 5% 3 2 3 3 4 7% 51%	1845
	11th to 20th	Day	14% 6% 2 5% 3 4 4 3 4 7% 49%	1800
	21st to end	Day	15% 4 2 4 3 4 3 3 5% 5% 52%	1705
December	1st to 10th	Day	10% 5% 2 5% 3 3 3 3 4 5% 55%	2600
	11th to 20th	Day	18% 7% 3 6% 3 3 2 2 4 5% 47%	2990
	21st to end	Day	12% 5% 2 5% 3 3 4 3 5% 6% 50%	3960
January	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 4 5% 52%	6188
	11th to 20th	Night	13% 6% 2 6% 3 3 3 2 3 4 55%	5900
	21st to end	Night	15% 7% 3 5% 3 3 3 3 4 5% 49%	6490
February	1st to 10th	Night	16% 8% 3 5% 4 3 4 3 6% 6% 42%	2600
	11th to 20th	Night	21% 6% 2 5% 4 3 3 3 5% 5% 43%	2393
	21st to end	Night	17% 7% 2 5% 3 3 3 3 5% 5% 47%	1980
March	1st to 10th	Night	18% 6% 3 6% 4 3 3 2 5% 6% 45%	5098
	11th to 20th	Night	13% 7% 3 5% 3 4 3 3 4 5% 50%	4980
	21st to end	Night	14% 7% 3 6% 4 4 4 3 4 6% 46%	5293
April	1st to 10th	Night	14% 7% 3 5% 4 4 3 4 6% 6% 42%	2000
	11th to 20th	Night	12% 6% 2 6% 3 3 4 3 5% 7% 49%	1975
	21st to end	Night	16% 6% 2 5% 4 4 3 3 5% 7% 45%	2000
May	1st to 10th	Night	16% 6% 2 8% 5% 5% 5% 4 7% 8% 32%	4472
	11th to 20th	Night	23% 8% 3 7% 4 4 4 3 5% 7% 32%	3741
	21st to end	Night	17% 6% 2 6% 4 4 4 4 6% 8% 39%	3920
June	1st to 10th	Night	12% 5% 2 6% 4 5% 6% 4 7% 8% 41%	1600
	11th to 20th	Night	11% 5% 1 5% 5% 5% 5% 4 8% 10% 41%	1600
	21st to end	Night	8% 4 2 5% 6% 5% 5% 5% 8% 10% 43%	1600
July	1st to 10th	Night	9% 4 2 7% 6% 6% 5% 4 7% 11% 39%	2600
	11th to 20th	Night	9% 6% 2 6% 5% 5% 6% 5% 8% 12% 37%	2762
	21st to end	Night	12% 8% 3 8% 6% 5% 6% 5% 6% 9% 31%	3087
August	1st to 10th	Night	16% 8% 3 8% 6% 5% 4 5% 7% 9% 30%	2825
	11th to 20th	Night	8% 6% 3 7% 5% 5% 4 5% 7% 10% 40%	3062
	21st to end	Night	10% 4 2 6% 4 3 4 4 6% 8% 50%	3476
September	1st to 10th	Night	13% 5% 2 4 4 3 4 4 6% 8% 47%	1900
	11th to 20th	Night	12% 5% 3 6% 4 4 4 4 5% 7% 45%	1900
	21st to end	Night	22% 7% 3 6% 3 3 5% 3 5% 6% 36%	2144
October	1st to 10th	Night	16% 5% 2 6% 4 4 4 3 5% 7% 44%	2280
	11th to 20th	Night	16% 5% 2 5% 3 4 3 3 4 6% 50%	2280
	21st to end	Night	15% 5% 2 5% 4 2 3 3 4 7% 51%	2508
November	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 4 6% 49%	2451
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 4 5% 48%	2600
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 6% 51%	2690
December	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 5% 6% 54%	4580
	11th to 20th	Night	18% 7% 2 7% 4 4 4 3 5% 6% 39%	5205
	21st to end	Night	12% 7% 3 7% 4 3 4 3 5% 8% 46%	6996

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	21% 26% 4 19% 20% 9%	3754
	11th to 20th	Day	25% 27% 4 16% 22% 7%	4060
	21st to end	Day	31% 30% 6% 22% 9% 1	4466
February	1st to 10th	Day	16% 62% 5% 11% 4 1	1800
	11th to 20th	Day	18% 62% 4 7% 7% 2	1899
	21st to end	Day	17% 62% 5% 7% 6% 2	1650
March	1st to 10th	Day	33% 32% 7% 11% 13% 5%	4752
	11th to 20th	Day	21% 30% 7% 16% 19% 7%	4980
	21st to end	Day	27% 32% 8% 12% 15% 5%	5638
April	1st to 10th	Day	15% 63% 4 9% 7% 1	2400
	11th to 20th	Day	13% 63% 5% 10% 7% 2	2374
	21st to end	Day	15% 63% 5% 9% 6% 2	2400
May	1st to 10th	Day	32% 35% 12% 14% 6% 1	5497
	11th to 20th	Day	33% 34% 12% 15% 5%	6152
	21st to end	Day	26% 33% 11% 17% 11% 2	6949
June	1st to 10th	Day	14% 65% 6% 9% 6% 1	2800
	11th to 20th	Day	11% 64% 7% 10% 7%	2800
	21st to end	Day	10% 62% 8% 12% 7%	2800
July	1st to 10th	Day	19% 42% 19% 11% 7% 2	4510
	11th to 20th	Day	30% 39% 16% 12% 2	4325
	21st to end	Day	28% 40% 10% 11% 10% 1	4324
August	1st to 10th	Day	32% 40% 12% 13% 2	4091
	11th to 20th	Day	23% 42% 8% 18% 8%	3771
	21st to end	Day	14% 39% 11% 22% 14% 1	4180
September	1st to 10th	Day	15% 63% 7% 9% 5% 1	2280
	11th to 20th	Day	16% 61% 7% 8% 6% 2	2280
	21st to end	Day	23% 59% 4 10% 3 1	2031
October	1st to 10th	Day	17% 39% 7% 18% 16% 2	3160
	11th to 20th	Day	12% 37% 3 13% 28% 7%	3140
	21st to end	Day	9% 37% 6% 21% 19% 10%	3428
November	1st to 10th	Day	17% 56% 4 13% 8% 2	1845
	11th to 20th	Day	16% 57% 4 8% 11% 3	1800
	21st to end	Day	16% 56% 4 13% 10% 1	1705
December	1st to 10th	Day	21% 36% 5% 21% 14% 4	2600
	11th to 20th	Day	29% 32% 9% 14% 12% 4	2986
	21st to end	Day	23% 29% 11% 23% 12% 1	3960
January	1st to 10th	Night	25% 27% 5% 15% 22% 6%	6188
	11th to 20th	Night	23% 27% 3 19% 23% 5%	5900
	21st to end	Night	28% 29% 5% 23% 13% 2	6490
February	1st to 10th	Night	17% 63% 6% 10% 4 1	2600
	11th to 20th	Night	19% 60% 4 8% 7% 2	2395
	21st to end	Night	15% 62% 4 10% 7% 3	1980
March	1st to 10th	Night	31% 31% 5% 14% 12% 7%	5098
	11th to 20th	Night	24% 30% 6% 15% 18% 7%	4980
	21st to end	Night	28% 30% 5% 18% 14% 5%	5293
April	1st to 10th	Night	18% 63% 4 6% 8% 1	2000
	11th to 20th	Night	14% 63% 4 10% 7% 1	1975
	21st to end	Night	16% 63% 5% 8% 7% 1	2000
May	1st to 10th	Night	35% 34% 12% 14% 5%	4502
	11th to 20th	Night	36% 33% 9% 16% 5%	3742
	21st to end	Night	31% 33% 10% 17% 9%	3927
June	1st to 10th	Night	17% 64% 5% 7% 7% 1	1600
	11th to 20th	Night	14% 64% 7% 8% 7% 1	1600
	21st to end	Night	11% 62% 6% 12% 7% 2	1600
July	1st to 10th	Night	25% 43% 11% 13% 7% 1	2560
	11th to 20th	Night	27% 39% 18% 15% 2	2714
	21st to end	Night	35% 40% 7% 10% 8%	2988
August	1st to 10th	Night	35% 40% 10% 12% 2	2814
	11th to 20th	Night	22% 41% 12% 19% 7%	3092
	21st to end	Night	17% 38% 5% 20% 20%	3476
September	1st to 10th	Night	13% 64% 8% 8% 4 2	1900
	11th to 20th	Night	16% 61% 4 9% 8% 2	1900
	21st to end	Night	25% 60% 4 8% 3	2144
October	1st to 10th	Night	23% 39% 8% 13% 15% 2	3800
	11th to 20th	Night	12% 38% 4 15% 23% 8%	3779
	21st to end	Night	8% 36% 4 25% 17% 10%	4120
November	1st to 10th	Night	20% 56% 5% 10% 8% 2	2451
	11th to 20th	Night	17% 57% 4 9% 9% 5%	2600
	21st to end	Night	13% 57% 4 13% 11% 2	2690
December	1st to 10th	Night	19% 36% 6% 19% 18% 3	4580
	11th to 20th	Night	34% 33% 9% 13% 8% 4	5208
	21st to end	Night	26% 29% 11% 22% 11%	6996

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	21% 19% 39% 16% 4	233
	11th to 20th	Day	20% 24% 39% 14% 3	300
	21st to end	Day	17% 17% 43% 22% 2	330
February	1st to 10th	Day	18% 18% 45% 15% 4	300
	11th to 20th	Day	28% 19% 38% 13% 2	438
	21st to end	Day	22% 17% 39% 17% 5%	414
March	1st to 10th	Day	18% 19% 41% 18% 4	500
	11th to 20th	Day	20% 19% 35% 18% 6% 1	500
	21st to end	Day	18% 15% 45% 17% 4 1	550
April	1st to 10th	Day	16% 20% 41% 18% 5% 1	500
	11th to 20th	Day	12% 14% 41% 25% 7% 2	492
	21st to end	Day	17% 13% 37% 25% 8% 1	500
May	1st to 10th	Day	17% 13% 37% 24% 9% 1	503
	11th to 20th	Day	20% 7% 31% 29% 10% 2	527
	21st to end	Day	21% 4 28% 27% 17% 4	573
June	1st to 10th	Day	14% 5% 22% 34% 20% 4	530
	11th to 20th	Day	12% 5% 20% 36% 22% 6%	530
	21st to end	Day	9% 3 21% 37% 24% 6%	530
July	1st to 10th	Day	10% 3 14% 35% 31% 7%	525
	11th to 20th	Day	7% 1 11% 40% 31% 9%	524
	21st to end	Day	11% 2 18% 38% 24% 7%	532
August	1st to 10th	Day	13% 3 17% 37% 22% 8%	486
	11th to 20th	Day	14% 2 12% 37% 27% 7%	479
	21st to end	Day	10% 3 17% 31% 28% 11%	539
September	1st to 10th	Day	15% 4 18% 32% 21% 11%	490
	11th to 20th	Day	15% 4 19% 34% 20% 8%	490
	21st to end	Day	29% 6% 22% 28% 12% 3	490
October	1st to 10th	Day	20% 4 23% 28% 18% 7%	490
	11th to 20th	Day	16% 10% 28% 28% 15% 4	490
	21st to end	Day	13% 10% 33% 27% 12% 4	539
November	1st to 10th	Day	17% 11% 29% 26% 13% 4	438
	11th to 20th	Day	17% 16% 32% 26% 9% 1	400
	21st to end	Day	17% 14% 31% 25% 11% 1	305
December	1st to 10th	Day	22% 13% 39% 21% 6% 1	200
	11th to 20th	Day	22% 14% 33% 27% 6%	200
	21st to end	Day	20% 14% 33% 24% 9%	220
January	1st to 10th	Night	18% 21% 36% 22% 4	800
	11th to 20th	Night	20% 17% 34% 24% 6%	800
	21st to end	Night	20% 16% 37% 25% 2	880
February	1st to 10th	Night	20% 12% 41% 24% 3	800
	11th to 20th	Night	24% 22% 36% 16% 2	783
	21st to end	Night	20% 17% 37% 23% 3	660
March	1st to 10th	Night	17% 15% 38% 24% 6%	800
	11th to 20th	Night	22% 15% 33% 24% 6% 1	800
	21st to end	Night	19% 14% 41% 22% 4	880
April	1st to 10th	Night	18% 16% 41% 20% 5%	800
	11th to 20th	Night	14% 12% 39% 26% 8%	791
	21st to end	Night	18% 9% 34% 31% 8% 1	800
May	1st to 10th	Night	18% 10% 34% 31% 7% 1	795
	11th to 20th	Night	18% 7% 28% 36% 11% 1	469
	21st to end	Night	16% 4 17% 37% 23% 2	433
June	1st to 10th	Night	14% 3 19% 44% 20% 2	400
	11th to 20th	Night	11% 4 21% 39% 21% 5%	400
	21st to end	Night	8% 2 20% 42% 24% 4	400
July	1st to 10th	Night	13% 2 12% 42% 28% 3	390
	11th to 20th	Night	6% 1 10% 44% 33% 6%	485
	21st to end	Night	8% 3 14% 44% 27% 3	624
August	1st to 10th	Night	11% 2 13% 43% 27% 5%	567
	11th to 20th	Night	12% 4 13% 38% 31% 3	727
	21st to end	Night	12% 3 14% 34% 31% 7%	836
September	1st to 10th	Night	16% 2 14% 35% 28% 5%	760
	11th to 20th	Night	14% 3 15% 34% 28% 6%	760
	21st to end	Night	24% 5% 20% 29% 19% 3	760
October	1st to 10th	Night	18% 6% 21% 30% 22% 5%	760
	11th to 20th	Night	18% 9% 25% 30% 15% 2	760
	21st to end	Night	18% 11% 26% 28% 15% 3	836
November	1st to 10th	Night	17% 9% 27% 28% 15% 3	780
	11th to 20th	Night	18% 14% 30% 27% 10% 1	800
	21st to end	Night	14% 18% 28% 30% 9% 2	800
December	1st to 10th	Night	19% 14% 34% 22% 9% 2	800
	11th to 20th	Night	18% 13% 38% 25% 6%	800
	21st to end	Night	18% 14% 29% 32% 7%	880

Page generated at 2025-07-18 01:10:03. Version ac07

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