Von Braun Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Von Braun Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	14% 6% 3 5% 5% 3 5% 5% 6% 8% 40%	74871
	Night	14% 6% 2 5% 5% 3 4 5% 5% 7% 44%	74828
Transparency	Day	42% 6% 11% 20% 17% 4	74594
	Night	39% 6% 10% 21% 19% 5%	74624
Seeing	Day	18% 12% 23% 22% 17% 8%	13453
	Night	17% 9% 21% 28% 21% 4	23512

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	21% 9% 2 5% 3 2 4 4 4 6% 40%	1706
	11th to 20th	Day	23% 9% 3 7% 4 2 3 4 4 5% 37%	1669
	21st to end	Day	18% 7% 3 5% 4 2 4 4 4 6% 44%	1980
February	1st to 10th	Day	20% 10% 3 5% 4 2 4 4 4 7% 37%	1800
	11th to 20th	Day	23% 8% 3 6% 4 3 4 3 4 5% 36%	1748
	21st to end	Day	24% 7% 3 5% 4 3 5% 4 4 5% 36%	1480
March	1st to 10th	Day	16% 7% 4 5% 5% 3 4 5% 5% 5% 41%	1800
	11th to 20th	Day	20% 8% 3 6% 5% 3 5% 4 4 6% 36%	1908
	21st to end	Day	16% 6% 4 5% 5% 4 5% 6% 6% 7% 36%	2268
April	1st to 10th	Day	14% 6% 2 4 5% 3 5% 3 6% 7% 44%	2160
	11th to 20th	Day	15% 6% 3 5% 5% 3 3 4 4 7% 45%	2134
	21st to end	Day	11% 6% 2 5% 6% 3 4 5% 6% 9% 44%	2176
May	1st to 10th	Day	15% 5% 2 4 5% 3 4 5% 6% 7% 45%	2340
	11th to 20th	Day	12% 7% 3 5% 6% 4 6% 5% 5% 7% 41%	2301
	21st to end	Day	9% 5% 3 6% 6% 4 5% 5% 6% 9% 42%	2531
June	1st to 10th	Day	10% 5% 3 5% 6% 4 6% 8% 8% 10% 36%	2340
	11th to 20th	Day	6% 3 2 4 4 4 7% 6% 8% 10% 44%	2340
	21st to end	Day	7% 5% 2 6% 6% 4 6% 6% 7% 11% 40%	2353
July	1st to 10th	Day	9% 5% 3 6% 8% 5% 6% 8% 8% 11% 30%	2341
	11th to 20th	Day	9% 5% 2 5% 7% 5% 8% 8% 9% 11% 32%	2340
	21st to end	Day	8% 5% 3 6% 7% 5% 8% 7% 8% 11% 33%	2547
August	1st to 10th	Day	7% 4 2 7% 7% 6% 8% 7% 9% 9% 32%	2179
	11th to 20th	Day	8% 6% 3 6% 8% 5% 8% 7% 7% 9% 34%	2125
	21st to end	Day	12% 6% 3 6% 7% 3 7% 7% 7% 8% 34%	2376
September	1st to 10th	Day	12% 5% 2 4 6% 3 5% 6% 6% 9% 41%	2111
	11th to 20th	Day	11% 5% 2 5% 6% 4 6% 5% 6% 7% 43%	1980
	21st to end	Day	10% 4 2 5% 4 3 4 4 5% 6% 51%	1980
October	1st to 10th	Day	9% 5% 2 5% 5% 4 4 4 4 4 55%	1980
	11th to 20th	Day	11% 5% 2 4 4 3 4 4 5% 7% 53%	1980
	21st to end	Day	15% 5% 2 4 4 3 4 3 4 6% 50%	1819
November	1st to 10th	Day	12% 5% 2 3 3 3 4 3 4 5% 56%	1672
	11th to 20th	Day	13% 5% 3 5% 5% 3 3 3 5% 7% 49%	1710
	21st to end	Day	16% 6% 2 5% 4 3 4 4 4 7% 44%	1710
December	1st to 10th	Day	22% 7% 3 6% 5% 3 4 4 6% 5% 35%	1710
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 5% 4 6% 39%	2153
	21st to end	Day	19% 11% 5% 6% 6% 3 5% 4 5% 7% 30%	3124
January	1st to 10th	Night	20% 8% 2 5% 4 3 4 3 4 6% 42%	2459
	11th to 20th	Night	21% 9% 4 6% 5% 3 4 4 5% 5% 34%	2397
	21st to end	Night	16% 8% 2 5% 4 2 4 3 4 5% 44%	2376
February	1st to 10th	Night	20% 9% 2 5% 4 2 3 4 4 7% 40%	2160
	11th to 20th	Night	22% 8% 3 5% 5% 2 4 3 5% 4 40%	2098
	21st to end	Night	25% 7% 3 5% 5% 3 4 4 4 5% 35%	1776
March	1st to 10th	Night	17% 6% 3 5% 4 3 4 4 5% 7% 41%	2160
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 5% 5% 6% 38%	2052
	21st to end	Night	16% 7% 3 5% 4 3 4 5% 4 6% 43%	2102
April	1st to 10th	Night	13% 4 2 5% 5% 2 4 4 5% 9% 47%	1800
	11th to 20th	Night	15% 4 2 4 4 2 3 3 5% 8% 50%	1775
	21st to end	Night	12% 5% 2 4 4 3 3 5% 5% 7% 50%	1782
May	1st to 10th	Night	11% 3 2 4 4 2 4 4 6% 8% 51%	1620
	11th to 20th	Night	11% 5% 3 4 5% 3 6% 7% 5% 10% 43%	1592
	21st to end	Night	7% 4 2 4 5% 3 6% 6% 7% 10% 46%	1744
June	1st to 10th	Night	7% 5% 3 7% 6% 3 5% 5% 7% 10% 42%	1620
	11th to 20th	Night	5% 2 1 3 4 4 5% 6% 6% 11% 53%	1620
	21st to end	Night	7% 3 2 4 5% 3 5% 5% 6% 12% 47%	1547
July	1st to 10th	Night	9% 5% 4 6% 6% 5% 6% 7% 6% 9% 39%	1574
	11th to 20th	Night	7% 4 2 4 5% 4 7% 7% 8% 11% 43%	1620
	21st to end	Night	7% 5% 2 5% 7% 3 6% 6% 9% 13% 38%	1771
August	1st to 10th	Night	5% 3 2 5% 4 4 6% 7% 9% 12% 44%	1755
	11th to 20th	Night	9% 5% 2 5% 5% 4 5% 5% 9% 10% 41%	1776
	21st to end	Night	10% 5% 3 6% 5% 4 5% 5% 6% 8% 43%	1980
September	1st to 10th	Night	9% 4 2 6% 4 3 5% 4 5% 9% 49%	1829
	11th to 20th	Night	9% 5% 3 6% 5% 3 4 6% 5% 9% 45%	1980
	21st to end	Night	8% 4 2 5% 4 3 4 4 5% 7% 54%	1980
October	1st to 10th	Night	10% 4 2 4 3 2 3 4 3 5% 60%	1980
	11th to 20th	Night	13% 6% 2 5% 5% 2 3 4 4 4 52%	1980
	21st to end	Night	16% 6% 2 3 3 2 3 4 4 6% 52%	2533
November	1st to 10th	Night	12% 5% 2 3 3 2 4 5% 4 6% 54%	2406
	11th to 20th	Night	12% 6% 2 3 4 2 3 4 4 6% 52%	2470
	21st to end	Night	17% 7% 2 5% 4 2 4 3 5% 5% 46%	2470
December	1st to 10th	Night	20% 7% 3 5% 5% 3 3 4 5% 6% 38%	2470
	11th to 20th	Night	18% 7% 3 4 4 3 3 3 4 6% 46%	3042
	21st to end	Night	19% 10% 4 6% 6% 3 4 5% 6% 7% 30%	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	46% 3 8% 19% 19% 4	1707
	11th to 20th	Day	52% 3 7% 18% 17% 3	1669
	21st to end	Day	42% 4 7% 23% 21% 3	1980
February	1st to 10th	Day	49% 4 6% 20% 18% 3	1800
	11th to 20th	Day	52% 4 6% 19% 15% 4	1758
	21st to end	Day	52% 4 7% 13% 18% 6%	1480
March	1st to 10th	Day	45% 4 8% 16% 21% 7%	1800
	11th to 20th	Day	50% 5% 9% 15% 16% 4	1908
	21st to end	Day	46% 5% 11% 22% 13% 1	2268
April	1st to 10th	Day	39% 5% 10% 24% 16% 5%	2160
	11th to 20th	Day	40% 4 7% 21% 23% 5%	2134
	21st to end	Day	38% 5% 10% 28% 17% 2	2176
May	1st to 10th	Day	39% 6% 11% 25% 15% 4	2340
	11th to 20th	Day	43% 7% 12% 23% 14%	2305
	21st to end	Day	38% 8% 13% 25% 15% 2	2531
June	1st to 10th	Day	41% 9% 13% 20% 15% 1	2340
	11th to 20th	Day	31% 8% 18% 25% 16% 2	2340
	21st to end	Day	37% 9% 17% 20% 13% 4	2353
July	1st to 10th	Day	44% 10% 15% 20% 9% 2	2276
	11th to 20th	Day	40% 12% 18% 18% 9% 3	2271
	21st to end	Day	41% 10% 18% 22% 9% 1	2405
August	1st to 10th	Day	41% 13% 17% 20% 9% 1	2166
	11th to 20th	Day	43% 10% 14% 19% 13% 1	2125
	21st to end	Day	45% 9% 13% 19% 11% 3	2376
September	1st to 10th	Day	38% 9% 14% 18% 17% 4	2111
	11th to 20th	Day	39% 7% 11% 17% 22% 4	1980
	21st to end	Day	34% 6% 9% 22% 21% 7%	1980
October	1st to 10th	Day	33% 5% 7% 21% 27% 7%	1980
	11th to 20th	Day	32% 5% 8% 22% 24% 9%	1980
	21st to end	Day	38% 3 5% 18% 29% 8%	1819
November	1st to 10th	Day	32% 3 8% 19% 30% 7%	1672
	11th to 20th	Day	37% 4 5% 21% 25% 8%	1710
	21st to end	Day	43% 4 5% 20% 24% 5%	1710
December	1st to 10th	Day	51% 4 6% 17% 18% 3	1710
	11th to 20th	Day	48% 4 6% 20% 19% 4	2150
	21st to end	Day	53% 4 9% 20% 11% 3	3124
January	1st to 10th	Night	45% 4 9% 20% 19% 4	2459
	11th to 20th	Night	53% 4 7% 18% 15% 3	2397
	21st to end	Night	44% 3 6% 22% 21% 4	2376
February	1st to 10th	Night	46% 3 9% 19% 20% 4	2160
	11th to 20th	Night	49% 3 7% 17% 16% 6%	2099
	21st to end	Night	52% 5% 6% 17% 15% 7%	1776
March	1st to 10th	Night	42% 4 9% 16% 20% 9%	2160
	11th to 20th	Night	46% 5% 10% 18% 17% 4	2052
	21st to end	Night	43% 4 10% 23% 18% 2	2102
April	1st to 10th	Night	35% 5% 12% 22% 21% 5%	1800
	11th to 20th	Night	35% 4 7% 21% 22% 11%	1775
	21st to end	Night	34% 5% 10% 28% 19% 3	1782
May	1st to 10th	Night	31% 7% 11% 23% 25% 3	1620
	11th to 20th	Night	37% 8% 16% 22% 17% 1	1593
	21st to end	Night	32% 8% 16% 25% 17% 2	1745
June	1st to 10th	Night	37% 8% 14% 22% 17% 2	1620
	11th to 20th	Night	24% 8% 18% 30% 18% 3	1620
	21st to end	Night	30% 7% 17% 24% 17% 4	1547
July	1st to 10th	Night	39% 10% 16% 20% 11% 4	1529
	11th to 20th	Night	30% 13% 20% 21% 12% 4	1566
	21st to end	Night	35% 11% 19% 23% 11% 1	1672
August	1st to 10th	Night	28% 13% 21% 24% 13%	1744
	11th to 20th	Night	35% 10% 19% 19% 13% 3	1776
	21st to end	Night	38% 9% 14% 23% 11% 4	1980
September	1st to 10th	Night	32% 7% 17% 21% 17% 5%	1829
	11th to 20th	Night	35% 8% 14% 16% 24% 3	1980
	21st to end	Night	30% 6% 8% 23% 24% 10%	1980
October	1st to 10th	Night	28% 4 7% 24% 28% 9%	1980
	11th to 20th	Night	36% 4 6% 21% 22% 11%	1980
	21st to end	Night	36% 3 5% 19% 29% 9%	2533
November	1st to 10th	Night	33% 4 8% 20% 25% 11%	2406
	11th to 20th	Night	35% 4 6% 18% 28% 10%	2470
	21st to end	Night	42% 3 5% 20% 24% 6%	2470
December	1st to 10th	Night	47% 5% 7% 19% 18% 3	2470
	11th to 20th	Night	42% 3 6% 19% 26% 5%	3044
	21st to end	Night	53% 4 8% 20% 14% 2	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	30% 27% 27% 13% 3	270
	11th to 20th	Day	30% 29% 27% 9% 5% 1	255
	21st to end	Day	22% 32% 32% 11% 2	264
February	1st to 10th	Day	29% 28% 30% 11% 2	240
	11th to 20th	Day	40% 25% 26% 8%	240
	21st to end	Day	39% 25% 29% 7% 1	198
March	1st to 10th	Day	26% 25% 35% 10% 2	240
	11th to 20th	Day	26% 23% 28% 16% 6% 1	348
	21st to end	Day	26% 21% 28% 17% 6% 1	462
April	1st to 10th	Day	21% 16% 27% 23% 12% 1	420
	11th to 20th	Day	21% 17% 27% 23% 9% 2	412
	21st to end	Day	20% 15% 28% 26% 10% 1	420
May	1st to 10th	Day	18% 12% 30% 23% 12% 5%	423
	11th to 20th	Day	13% 9% 27% 27% 16% 9%	447
	21st to end	Day	14% 4 19% 31% 17% 15%	485
June	1st to 10th	Day	13% 6% 18% 25% 24% 14%	450
	11th to 20th	Day	7% 5% 15% 26% 27% 20%	450
	21st to end	Day	12% 5% 16% 27% 24% 16%	463
July	1st to 10th	Day	10% 3 13% 23% 29% 22%	446
	11th to 20th	Day	11% 2 13% 21% 29% 24%	444
	21st to end	Day	9% 2 11% 25% 31% 22%	488
August	1st to 10th	Day	12% 2 13% 22% 32% 19%	446
	11th to 20th	Day	12% 2 14% 28% 33% 11%	439
	21st to end	Day	16% 2 12% 22% 34% 14%	495
September	1st to 10th	Day	13% 3 10% 29% 31% 14%	450
	11th to 20th	Day	11% 4 18% 22% 30% 14%	450
	21st to end	Day	14% 5% 15% 31% 28% 8%	450
October	1st to 10th	Day	11% 7% 27% 26% 20% 9%	450
	11th to 20th	Day	14% 11% 32% 26% 15% 3	450
	21st to end	Day	23% 13% 27% 23% 11% 2	311
November	1st to 10th	Day	20% 13% 30% 24% 11% 2	270
	11th to 20th	Day	15% 21% 39% 20% 4	270
	21st to end	Day	20% 21% 31% 16% 10% 1	270
December	1st to 10th	Day	31% 21% 27% 15% 6%	270
	11th to 20th	Day	24% 24% 33% 11% 8%	270
	21st to end	Day	27% 24% 33% 13% 3	297
January	1st to 10th	Night	26% 18% 29% 21% 5% 1	760
	11th to 20th	Night	27% 18% 27% 21% 7%	741
	21st to end	Night	20% 16% 32% 27% 4	792
February	1st to 10th	Night	25% 15% 28% 28% 5%	720
	11th to 20th	Night	28% 17% 27% 25% 2	703
	21st to end	Night	30% 18% 26% 23% 3	592
March	1st to 10th	Night	20% 17% 26% 31% 5%	720
	11th to 20th	Night	21% 16% 28% 26% 8% 1	720
	21st to end	Night	20% 14% 29% 26% 11%	716
April	1st to 10th	Night	15% 11% 30% 30% 13% 1	540
	11th to 20th	Night	16% 11% 32% 25% 15% 1	533
	21st to end	Night	15% 8% 25% 35% 15% 1	540
May	1st to 10th	Night	14% 6% 24% 33% 20% 3	540
	11th to 20th	Night	13% 5% 20% 32% 27% 4	531
	21st to end	Night	6% 3 13% 38% 35% 7%	584
June	1st to 10th	Night	9% 2 14% 32% 36% 7%	540
	11th to 20th	Night	5% 2 9% 30% 42% 11%	540
	21st to end	Night	8% 1 9% 30% 42% 10%	540
July	1st to 10th	Night	11% 1 8% 26% 39% 15%	525
	11th to 20th	Night	8% 1 6% 24% 43% 18%	522
	21st to end	Night	8% 1 8% 23% 46% 13%	591
August	1st to 10th	Night	6% 1 5% 24% 53% 12%	537
	11th to 20th	Night	11% 1 7% 28% 44% 8%	534
	21st to end	Night	11% 1 9% 26% 43% 10%	594
September	1st to 10th	Night	11% 2 11% 24% 44% 9%	569
	11th to 20th	Night	10% 3 17% 28% 36% 7%	720
	21st to end	Night	11% 3 14% 31% 38% 3	720
October	1st to 10th	Night	12% 5% 20% 28% 29% 7%	720
	11th to 20th	Night	16% 8% 24% 30% 21% 2	720
	21st to end	Night	18% 10% 19% 32% 18% 2	792
November	1st to 10th	Night	15% 9% 21% 33% 19% 3	740
	11th to 20th	Night	14% 14% 26% 31% 13% 1	760
	21st to end	Night	22% 12% 24% 29% 13% 1	760
December	1st to 10th	Night	25% 16% 23% 28% 8%	760
	11th to 20th	Night	24% 14% 24% 29% 9%	760
	21st to end	Night	27% 14% 26% 28% 5%	836

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