Bremen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bremen clear sky chart from 2005-11-06 to 2024-11-28.

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% 9% 4 8% 5% 5% 4 4 6% 7% 35%	101354
	Night	15% 11% 4 8% 5% 4 4 3 5% 7% 35%	98246
Transparency	Day	46% 6% 11% 22% 13% 1	104953
	Night	48% 5% 11% 22% 14% 1	102788
Seeing	Day	17% 11% 28% 24% 14% 6%	15796
	Night	19% 10% 29% 29% 12% 1	25644

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% 14% 10% 14% 6% 5% 4 3 6% 5% 17%	2527
	11th to 20th	Day	14% 16% 8% 13% 8% 7% 5% 5% 7% 7% 10%	2530
	21st to end	Day	26% 23% 7% 11% 5% 3 2 2 3 4 14%	2783
February	1st to 10th	Day	15% 16% 4 10% 8% 5% 5% 4 5% 5% 23%	1845
	11th to 20th	Day	14% 13% 4 11% 9% 5% 5% 3 5% 6% 25%	1848
	21st to end	Day	16% 14% 6% 11% 5% 4 4 3 6% 6% 25%	1570
March	1st to 10th	Day	19% 14% 6% 8% 5% 5% 4 3 4 5% 27%	3120
	11th to 20th	Day	12% 8% 6% 8% 5% 4 4 4 6% 9% 33%	3351
	21st to end	Day	19% 12% 5% 11% 6% 5% 5% 3 5% 5% 24%	3998
April	1st to 10th	Day	16% 13% 4 8% 5% 4 4 4 5% 6% 31%	2280
	11th to 20th	Day	17% 10% 2 7% 5% 4 4 3 4 7% 35%	2259
	21st to end	Day	19% 8% 3 7% 5% 3 5% 4 6% 7% 33%	2470
May	1st to 10th	Day	18% 8% 3 6% 5% 5% 4 4 6% 8% 32%	4082
	11th to 20th	Day	15% 8% 2 6% 4 4 5% 4 6% 8% 38%	4081
	21st to end	Day	9% 5% 2 6% 5% 4 4 4 7% 9% 45%	4752
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 5% 7% 8% 44%	2660
	11th to 20th	Day	9% 6% 2 5% 5% 5% 5% 3 7% 8% 44%	2660
	21st to end	Day	11% 5% 2 6% 5% 6% 6% 4 7% 9% 39%	2660
July	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 4 7% 10% 37%	4440
	11th to 20th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 47%	4440
	21st to end	Day	8% 6% 3 8% 6% 5% 5% 5% 6% 8% 41%	4796
August	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 4 6% 8% 48%	4104
	11th to 20th	Day	10% 4 1 6% 4 5% 5% 4 6% 9% 46%	3958
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 10% 48%	4180
September	1st to 10th	Day	10% 5% 2 6% 4 5% 4 4 5% 8% 47%	2261
	11th to 20th	Day	11% 5% 1 5% 4 4 4 4 6% 8% 47%	2090
	21st to end	Day	14% 6% 2 6% 5% 4 4 4 5% 7% 42%	2090
October	1st to 10th	Day	13% 6% 3 7% 4 4 4 4 5% 7% 44%	2090
	11th to 20th	Day	17% 9% 3 6% 4 4 4 5% 5% 7% 37%	1887
	21st to end	Day	21% 10% 3 8% 5% 5% 5% 4 6% 6% 27%	1881
November	1st to 10th	Day	12% 10% 3 6% 4 4 4 4 5% 7% 41%	1762
	11th to 20th	Day	17% 14% 3 9% 6% 4 4 3 5% 6% 29%	1800
	21st to end	Day	20% 13% 5% 10% 5% 4 4 4 4 5% 25%	1773
December	1st to 10th	Day	15% 17% 6% 9% 6% 5% 4 3 5% 7% 22%	1625
	11th to 20th	Day	14% 17% 8% 13% 5% 5% 3 2 5% 5% 23%	1918
	21st to end	Day	23% 21% 6% 13% 7% 5% 3 2 4 4 10%	2783
January	1st to 10th	Night	17% 17% 6% 11% 6% 5% 4 4 4 6% 19%	4428
	11th to 20th	Night	16% 19% 8% 15% 6% 4 5% 4 6% 5% 14%	4440
	21st to end	Night	25% 18% 9% 11% 5% 4 3 2 4 4 16%	4884
February	1st to 10th	Night	18% 15% 5% 10% 7% 4 4 3 4 4 26%	2333
	11th to 20th	Night	14% 13% 4 8% 7% 4 6% 3 5% 7% 29%	2218
	21st to end	Night	21% 12% 5% 11% 5% 4 4 3 4 6% 27%	1884
March	1st to 10th	Night	16% 11% 4 8% 5% 5% 4 3 4 6% 35%	3733
	11th to 20th	Night	11% 7% 3 7% 5% 5% 4 3 6% 8% 41%	3608
	21st to end	Night	19% 10% 3 9% 5% 4 4 4 5% 6% 31%	3663
April	1st to 10th	Night	16% 10% 3 5% 4 5% 4 3 6% 7% 37%	1900
	11th to 20th	Night	20% 8% 3 6% 4 5% 3 4 5% 6% 37%	1869
	21st to end	Night	17% 9% 3 6% 5% 5% 4 4 6% 5% 36%	1710
May	1st to 10th	Night	15% 9% 3 7% 5% 5% 5% 4 7% 8% 33%	2813
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 5% 9% 38%	2812
	21st to end	Night	12% 6% 2 6% 4 4 5% 3 5% 8% 45%	2810
June	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 10% 48%	1520
	11th to 20th	Night	8% 6% 2 7% 4 4 4 4 7% 8% 46%	1520
	21st to end	Night	11% 5% 2 6% 5% 4 4 5% 7% 9% 42%	1520
July	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 4 6% 9% 45%	2530
	11th to 20th	Night	7% 3 2 5% 4 3 3 3 6% 8% 55%	2530
	21st to end	Night	7% 5% 2 6% 5% 4 5% 5% 7% 9% 45%	2764
August	1st to 10th	Night	10% 5% 3 5% 4 4 5% 4 7% 9% 45%	2825
	11th to 20th	Night	7% 5% 2 7% 3 4 4 4 6% 8% 50%	2867
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 7% 51%	3476
September	1st to 10th	Night	11% 5% 1 6% 3 4 3 3 5% 7% 52%	1900
	11th to 20th	Night	9% 5% 1 4 3 3 3 3 5% 7% 56%	2090
	21st to end	Night	13% 7% 2 6% 4 3 3 3 5% 7% 46%	2090
October	1st to 10th	Night	12% 7% 2 5% 5% 4 3 3 4 5% 50%	2090
	11th to 20th	Night	17% 8% 3 7% 4 3 4 3 5% 6% 41%	2289
	21st to end	Night	20% 9% 3 7% 4 3 3 3 4 6% 37%	2717
November	1st to 10th	Night	12% 10% 2 7% 5% 4 4 3 5% 6% 41%	2536
	11th to 20th	Night	15% 13% 3 8% 5% 4 5% 4 5% 7% 31%	2600
	21st to end	Night	19% 14% 4 9% 5% 4 4 3 5% 6% 26%	2562
December	1st to 10th	Night	16% 15% 5% 10% 6% 5% 4 3 5% 6% 25%	2552
	11th to 20th	Night	16% 17% 7% 11% 5% 4 4 4 4 5% 22%	3279
	21st to end	Night	25% 20% 7% 10% 5% 4 4 3 4 5% 13%	4884

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	66% 5% 12% 12% 4	2528
	11th to 20th	Day	72% 4 9% 10% 5%	2530
	21st to end	Day	76% 3 6% 11% 3	2783
February	1st to 10th	Day	63% 4 12% 13% 7% 1	1845
	11th to 20th	Day	60% 5% 9% 19% 8% 1	1858
	21st to end	Day	60% 4 12% 16% 7% 1	1570
March	1st to 10th	Day	59% 5% 9% 19% 8%	3120
	11th to 20th	Day	46% 6% 11% 28% 8% 1	3351
	21st to end	Day	61% 7% 12% 17% 3	3998
April	1st to 10th	Day	53% 6% 10% 19% 12%	2280
	11th to 20th	Day	49% 5% 10% 22% 12% 3	2259
	21st to end	Day	49% 6% 12% 19% 12% 3	2470
May	1st to 10th	Day	47% 8% 12% 24% 8% 1	4120
	11th to 20th	Day	43% 8% 14% 25% 10% 1	4085
	21st to end	Day	34% 7% 11% 25% 22% 1	4765
June	1st to 10th	Day	36% 7% 12% 25% 17% 2	2660
	11th to 20th	Day	36% 6% 12% 24% 20% 3	2660
	21st to end	Day	39% 8% 15% 20% 16% 3	2660
July	1st to 10th	Day	43% 6% 13% 21% 16% 3	4371
	11th to 20th	Day	30% 6% 15% 29% 18% 1	4365
	21st to end	Day	38% 8% 13% 17% 20% 3	4645
August	1st to 10th	Day	34% 7% 14% 28% 16% 1	4091
	11th to 20th	Day	33% 8% 12% 28% 18% 1	3997
	21st to end	Day	32% 6% 13% 26% 20% 4	4179
September	1st to 10th	Day	35% 7% 14% 22% 19% 3	2261
	11th to 20th	Day	33% 6% 11% 26% 22% 2	2090
	21st to end	Day	40% 6% 9% 24% 19% 2	2090
October	1st to 10th	Day	29% 4 9% 34% 23% 1	3480
	11th to 20th	Day	37% 5% 10% 21% 26%	3103
	21st to end	Day	47% 5% 10% 25% 12% 2	3081
November	1st to 10th	Day	42% 5% 13% 25% 15% 1	1762
	11th to 20th	Day	56% 4 11% 19% 10% 1	1800
	21st to end	Day	60% 5% 12% 18% 6%	1773
December	1st to 10th	Day	62% 5% 11% 16% 6%	1625
	11th to 20th	Day	64% 4 10% 18% 3	1915
	21st to end	Day	79% 4 7% 7% 3	2783
January	1st to 10th	Night	64% 6% 10% 15% 5%	4428
	11th to 20th	Night	73% 3 9% 11% 3	4440
	21st to end	Night	72% 4 7% 13% 4	4884
February	1st to 10th	Night	61% 4 10% 15% 8% 1	2333
	11th to 20th	Night	54% 5% 10% 21% 10% 1	2219
	21st to end	Night	59% 3 10% 17% 9% 2	1884
March	1st to 10th	Night	51% 5% 10% 25% 8% 1	3733
	11th to 20th	Night	40% 6% 10% 27% 14% 2	3608
	21st to end	Night	53% 6% 13% 21% 7% 1	3663
April	1st to 10th	Night	45% 6% 12% 21% 14% 1	1900
	11th to 20th	Night	47% 5% 7% 21% 17% 3	1869
	21st to end	Night	47% 6% 10% 20% 14% 3	1710
May	1st to 10th	Night	47% 8% 10% 23% 11% 1	2840
	11th to 20th	Night	43% 6% 12% 27% 11% 1	2813
	21st to end	Night	37% 7% 11% 20% 22% 3	2818
June	1st to 10th	Night	32% 6% 11% 29% 19% 3	1520
	11th to 20th	Night	35% 6% 12% 25% 20% 2	1520
	21st to end	Night	36% 8% 16% 22% 16% 3	1520
July	1st to 10th	Night	35% 6% 13% 25% 15% 6%	2490
	11th to 20th	Night	27% 6% 13% 26% 25% 2	2482
	21st to end	Night	34% 7% 14% 19% 23% 3	2676
August	1st to 10th	Night	34% 7% 13% 30% 15% 1	2814
	11th to 20th	Night	31% 7% 12% 29% 19% 1	2894
	21st to end	Night	32% 6% 10% 28% 21% 3	3476
September	1st to 10th	Night	32% 4 13% 24% 20% 5%	1900
	11th to 20th	Night	27% 4 8% 30% 26% 3	2090
	21st to end	Night	38% 5% 10% 26% 19% 2	2090
October	1st to 10th	Night	24% 4 8% 33% 30% 1	3480
	11th to 20th	Night	38% 3 8% 23% 27% 1	3812
	21st to end	Night	38% 3 9% 29% 19% 1	4467
November	1st to 10th	Night	42% 5% 10% 25% 16% 2	2536
	11th to 20th	Night	52% 4 12% 21% 10% 2	2600
	21st to end	Night	59% 3 12% 19% 7%	2562
December	1st to 10th	Night	60% 5% 11% 16% 7%	2552
	11th to 20th	Night	63% 5% 11% 15% 5%	3281
	21st to end	Night	74% 5% 10% 8% 4	4884

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	20% 19% 35% 20% 5% 1	270
	11th to 20th	Day	23% 14% 40% 17% 4 1	270
	21st to end	Day	30% 15% 30% 20% 4 1	297
February	1st to 10th	Day	24% 17% 36% 18% 4 1	270
	11th to 20th	Day	24% 20% 33% 19% 4	270
	21st to end	Day	25% 23% 40% 8% 4	225
March	1st to 10th	Day	23% 19% 41% 16% 2	270
	11th to 20th	Day	21% 17% 33% 21% 7% 1	383
	21st to end	Day	29% 16% 29% 18% 6% 1	506
April	1st to 10th	Day	24% 14% 33% 22% 6% 2	460
	11th to 20th	Day	21% 19% 30% 19% 8% 3	452
	21st to end	Day	27% 14% 30% 19% 9% 2	460
May	1st to 10th	Day	24% 14% 29% 20% 9% 3	463
	11th to 20th	Day	20% 9% 29% 22% 15% 4	487
	21st to end	Day	12% 7% 29% 26% 18% 7%	688
June	1st to 10th	Day	11% 8% 29% 29% 19% 5%	680
	11th to 20th	Day	12% 6% 30% 28% 18% 6%	680
	21st to end	Day	14% 6% 29% 28% 16% 6%	680
July	1st to 10th	Day	11% 4 20% 29% 22% 14%	671
	11th to 20th	Day	9% 3 26% 30% 19% 13%	668
	21st to end	Day	8% 4 22% 34% 23% 9%	734
August	1st to 10th	Day	8% 3 16% 29% 27% 16%	486
	11th to 20th	Day	10% 5% 19% 31% 26% 9%	479
	21st to end	Day	9% 3 15% 32% 29% 12%	539
September	1st to 10th	Day	13% 7% 18% 30% 24% 9%	490
	11th to 20th	Day	8% 6% 15% 26% 31% 14%	490
	21st to end	Day	15% 13% 21% 24% 21% 6%	490
October	1st to 10th	Day	13% 7% 28% 29% 17% 6%	490
	11th to 20th	Day	21% 18% 26% 27% 7% 1	390
	21st to end	Day	28% 15% 33% 19% 4 1	330
November	1st to 10th	Day	14% 15% 37% 23% 9% 2	300
	11th to 20th	Day	26% 18% 30% 18% 8%	300
	21st to end	Day	30% 14% 35% 18% 3	291
December	1st to 10th	Day	19% 21% 37% 16% 7%	270
	11th to 20th	Day	19% 21% 38% 16% 6% 1	270
	21st to end	Day	25% 24% 36% 14% 1	297
January	1st to 10th	Night	23% 16% 35% 21% 5%	950
	11th to 20th	Night	25% 15% 36% 20% 4 1	950
	21st to end	Night	22% 14% 36% 24% 4	1045
February	1st to 10th	Night	28% 10% 34% 25% 3	760
	11th to 20th	Night	20% 15% 38% 24% 3	743
	21st to end	Night	26% 15% 37% 18% 3	628
March	1st to 10th	Night	21% 12% 36% 25% 6% 1	760
	11th to 20th	Night	18% 11% 37% 28% 6%	760
	21st to end	Night	25% 11% 31% 28% 5%	746
April	1st to 10th	Night	18% 15% 35% 25% 6% 1	570
	11th to 20th	Night	22% 11% 35% 24% 7% 1	563
	21st to end	Night	21% 11% 32% 26% 10% 1	570
May	1st to 10th	Night	21% 8% 32% 32% 8%	570
	11th to 20th	Night	19% 6% 27% 32% 15%	561
	21st to end	Night	12% 5% 23% 42% 17% 1	617
June	1st to 10th	Night	10% 4 25% 45% 16%	570
	11th to 20th	Night	11% 4 27% 40% 18% 1	570
	21st to end	Night	11% 5% 24% 35% 23% 1	570
July	1st to 10th	Night	7% 1 17% 43% 27% 5%	555
	11th to 20th	Night	9% 3 19% 38% 28% 3	552
	21st to end	Night	6% 2 15% 42% 33% 2	624
August	1st to 10th	Night	8% 2 10% 48% 29% 4	567
	11th to 20th	Night	8% 1 15% 44% 28% 4	564
	21st to end	Night	10% 2 14% 38% 33% 3	627
September	1st to 10th	Night	13% 4 16% 38% 26% 3	570
	11th to 20th	Night	11% 4 15% 36% 31% 4	760
	21st to end	Night	16% 5% 25% 31% 20% 3	760
October	1st to 10th	Night	14% 6% 26% 33% 19% 2	760
	11th to 20th	Night	21% 13% 30% 26% 9% 1	760
	21st to end	Night	26% 12% 32% 24% 6%	836
November	1st to 10th	Night	17% 12% 35% 26% 10% 1	780
	11th to 20th	Night	23% 15% 35% 22% 5% 1	800
	21st to end	Night	26% 12% 32% 25% 5%	789
December	1st to 10th	Night	24% 16% 35% 20% 5%	842
	11th to 20th	Night	24% 12% 37% 22% 4	950
	21st to end	Night	30% 15% 34% 18% 3	1045

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