Potsdam
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Potsdam clear sky chart from 2005-11-06 to 2026-04-02.

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	18% 12% 4 9% 5% 5% 4 3 5% 6% 29%	131539
	Night	18% 14% 5% 10% 5% 4 4 3 4 5% 26%	130285
Transparency	Day	55% 7% 11% 19% 8% 1	134991
	Night	59% 6% 10% 16% 8% 1	134920
Seeing	Day	27% 18% 29% 18% 7% 2	16259
	Night	27% 16% 29% 21% 7%	25462

By Month

Percentage Cloud Cover NE (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% 23% 7% 17% 7% 6% 4 3 3 4 13%	4661
	11th to 20th	Day	11% 21% 9% 21% 8% 6% 3 3 3 4 12%	4650
	21st to end	Day	11% 18% 8% 14% 9% 11% 5% 3 3 3 14%	5300
February	1st to 10th	Day	16% 17% 5% 15% 8% 5% 4 3 4 5% 19%	1890
	11th to 20th	Day	15% 16% 8% 13% 7% 5% 4 2 4 4 21%	1906
	21st to end	Day	18% 19% 6% 11% 7% 5% 3 3 4 4 19%	1730
March	1st to 10th	Day	20% 16% 6% 11% 4 4 5% 3 4 4 23%	4576
	11th to 20th	Day	12% 17% 4 9% 6% 5% 5% 4 5% 5% 27%	4986
	21st to end	Day	20% 12% 4 9% 5% 5% 3 2 3 4 32%	5977
April	1st to 10th	Day	22% 14% 4 7% 4 4 4 3 4 5% 30%	2412
	11th to 20th	Day	22% 11% 3 7% 4 4 3 3 4 4 35%	2374
	21st to end	Day	24% 11% 3 6% 4 4 4 3 5% 5% 31%	2487
May	1st to 10th	Day	27% 12% 4 8% 5% 5% 4 3 4 5% 23%	6346
	11th to 20th	Day	20% 9% 3 9% 6% 5% 5% 3 5% 6% 29%	6318
	21st to end	Day	23% 9% 2 7% 5% 4 4 3 6% 6% 31%	6949
June	1st to 10th	Day	24% 7% 2 7% 5% 4 4 4 6% 7% 30%	2800
	11th to 20th	Day	18% 5% 2 6% 5% 4 5% 6% 5% 9% 35%	2800
	21st to end	Day	22% 7% 3 7% 4 5% 4 5% 5% 7% 32%	2800
July	1st to 10th	Day	14% 6% 3 7% 4 5% 5% 5% 7% 9% 35%	6360
	11th to 20th	Day	12% 5% 2 7% 5% 5% 5% 4 6% 8% 40%	6360
	21st to end	Day	13% 6% 2 5% 4 4 4 4 6% 10% 42%	6926
August	1st to 10th	Day	17% 7% 3 7% 4 5% 4 4 6% 8% 35%	4538
	11th to 20th	Day	17% 6% 3 7% 4 4 4 4 6% 7% 37%	4024
	21st to end	Day	17% 6% 2 6% 3 4 4 4 6% 8% 38%	4312
September	1st to 10th	Day	16% 6% 2 6% 3 4 4 4 5% 8% 42%	2400
	11th to 20th	Day	15% 5% 2 5% 4 3 4 4 5% 7% 46%	2365
	21st to end	Day	19% 6% 2 6% 4 5% 5% 3 6% 6% 38%	2190
October	1st to 10th	Day	21% 9% 3 8% 4 4 4 3 5% 6% 34%	2000
	11th to 20th	Day	20% 13% 3 8% 6% 4 5% 3 4 6% 28%	2000
	21st to end	Day	27% 13% 3 7% 5% 3 4 3 4 5% 26%	2011
November	1st to 10th	Day	17% 13% 4 9% 6% 4 4 4 5% 6% 28%	1851
	11th to 20th	Day	17% 16% 5% 8% 5% 5% 6% 3 4 4 27%	1766
	21st to end	Day	21% 20% 6% 10% 5% 4 4 3 4 4 19%	1680
December	1st to 10th	Day	21% 22% 6% 16% 7% 4 4 3 4 4 11%	2680
	11th to 20th	Day	19% 20% 7% 11% 5% 4 3 3 3 4 20%	3066
	21st to end	Day	21% 19% 4 13% 5% 4 4 3 3 4 20%	4048
January	1st to 10th	Night	14% 24% 9% 16% 6% 4 3 3 3 3 15%	8234
	11th to 20th	Night	14% 22% 9% 18% 7% 5% 4 3 3 3 10%	8235
	21st to end	Night	14% 16% 7% 15% 9% 8% 5% 3 4 4 15%	8877
February	1st to 10th	Night	17% 19% 6% 14% 8% 5% 3 3 4 4 17%	2730
	11th to 20th	Night	15% 17% 6% 13% 6% 5% 4 3 4 5% 23%	2599
	21st to end	Night	16% 18% 5% 12% 7% 3 3 3 4 4 24%	2076
March	1st to 10th	Night	20% 16% 4 10% 6% 4 3 2 3 4 28%	5484
	11th to 20th	Night	16% 17% 4 7% 4 4 4 4 5% 7% 29%	5188
	21st to end	Night	20% 16% 4 10% 5% 4 3 2 3 4 29%	5196
April	1st to 10th	Night	22% 13% 4 9% 5% 3 3 3 4 5% 29%	2011
	11th to 20th	Night	23% 11% 3 7% 5% 4 4 2 3 6% 33%	1975
	21st to end	Night	23% 12% 2 6% 4 4 4 2 4 5% 33%	1921
May	1st to 10th	Night	29% 12% 3 7% 4 4 4 3 5% 6% 22%	3602
	11th to 20th	Night	20% 10% 3 8% 4 4 4 3 5% 8% 31%	3575
	21st to end	Night	21% 9% 3 7% 5% 4 4 3 5% 7% 30%	3926
June	1st to 10th	Night	22% 6% 3 6% 6% 5% 5% 4 6% 7% 30%	1600
	11th to 20th	Night	18% 7% 2 7% 4 4 4 5% 5% 9% 38%	1600
	21st to end	Night	20% 7% 3 6% 5% 5% 6% 5% 4 7% 31%	1600
July	1st to 10th	Night	16% 6% 3 6% 5% 5% 5% 4 6% 8% 37%	3600
	11th to 20th	Night	16% 7% 3 6% 4 4 3 3 6% 7% 42%	3600
	21st to end	Night	12% 6% 2 7% 4 4 5% 4 6% 7% 43%	3926
August	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 5% 7% 38%	2609
	11th to 20th	Night	17% 8% 3 8% 5% 4 4 3 5% 7% 37%	2992
	21st to end	Night	14% 6% 3 7% 5% 4 5% 3 6% 8% 40%	3586
September	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 4 6% 44%	2000
	11th to 20th	Night	15% 5% 2 5% 3 4 3 3 4 7% 50%	2034
	21st to end	Night	17% 8% 2 6% 4 4 4 4 5% 7% 38%	2206
October	1st to 10th	Night	22% 8% 2 6% 4 4 3 4 4 7% 35%	2400
	11th to 20th	Night	20% 9% 3 7% 5% 4 5% 3 5% 6% 32%	2400
	21st to end	Night	27% 12% 3 7% 5% 5% 4 3 4 6% 26%	2827
November	1st to 10th	Night	21% 14% 3 7% 4 3 4 4 4 6% 31%	2667
	11th to 20th	Night	19% 14% 4 9% 5% 5% 4 3 4 5% 29%	2851
	21st to end	Night	22% 17% 6% 8% 5% 4 4 3 4 4 21%	2940
December	1st to 10th	Night	19% 26% 7% 14% 6% 4 4 3 3 3 11%	4720
	11th to 20th	Night	23% 19% 6% 11% 5% 4 3 2 3 3 21%	5348
	21st to end	Night	23% 18% 5% 12% 5% 4 3 2 4 4 18%	7150

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	74% 7% 7% 10% 2	4662
	11th to 20th	Day	77% 6% 6% 5% 6% 1	4680
	21st to end	Day	75% 5% 6% 7% 6% 1	5300
February	1st to 10th	Day	69% 6% 7% 15% 3 1	1890
	11th to 20th	Day	66% 6% 9% 12% 6% 1	1915
	21st to end	Day	68% 6% 8% 11% 6% 1	1730
March	1st to 10th	Day	63% 5% 9% 12% 7% 2	4579
	11th to 20th	Day	56% 8% 14% 13% 8% 1	4986
	21st to end	Day	55% 6% 6% 16% 16% 2	5977
April	1st to 10th	Day	58% 5% 7% 19% 11% 2	2412
	11th to 20th	Day	52% 5% 7% 18% 15% 2	2374
	21st to end	Day	54% 5% 9% 15% 13% 3	2487
May	1st to 10th	Day	63% 7% 8% 15% 6% 1	6357
	11th to 20th	Day	54% 8% 11% 17% 9% 1	6322
	21st to end	Day	51% 8% 11% 21% 8% 1	6949
June	1st to 10th	Day	51% 9% 12% 17% 11% 1	2800
	11th to 20th	Day	44% 8% 12% 24% 10% 2	2800
	21st to end	Day	51% 8% 11% 20% 10% 1	2800
July	1st to 10th	Day	43% 7% 13% 27% 10%	6290
	11th to 20th	Day	39% 8% 13% 27% 12%	6285
	21st to end	Day	37% 7% 12% 37% 7%	6728
August	1st to 10th	Day	46% 7% 14% 23% 9%	4524
	11th to 20th	Day	44% 8% 16% 25% 6%	4063
	21st to end	Day	42% 7% 17% 24% 10%	4312
September	1st to 10th	Day	40% 8% 14% 27% 12% 1	2400
	11th to 20th	Day	37% 7% 12% 30% 15% 1	2365
	21st to end	Day	45% 8% 13% 24% 10%	2190
October	1st to 10th	Day	47% 5% 12% 26% 10%	3260
	11th to 20th	Day	51% 5% 14% 23% 7% 1	3240
	21st to end	Day	49% 5% 17% 22% 6% 1	3223
November	1st to 10th	Day	55% 7% 12% 19% 6% 1	1851
	11th to 20th	Day	59% 7% 11% 13% 8% 2	1766
	21st to end	Day	68% 8% 11% 9% 4	1680
December	1st to 10th	Day	77% 6% 9% 6% 1	2680
	11th to 20th	Day	68% 7% 7% 12% 5%	3066
	21st to end	Day	69% 5% 7% 14% 5%	4048
January	1st to 10th	Night	74% 6% 8% 8% 3	8234
	11th to 20th	Night	78% 7% 5% 6% 4	8280
	21st to end	Night	73% 5% 6% 9% 6%	8877
February	1st to 10th	Night	71% 5% 8% 10% 5%	2730
	11th to 20th	Night	64% 6% 9% 16% 5%	2601
	21st to end	Night	63% 7% 9% 15% 7%	2076
March	1st to 10th	Night	61% 5% 7% 16% 10% 2	5494
	11th to 20th	Night	53% 8% 17% 14% 6% 2	5189
	21st to end	Night	60% 5% 5% 19% 10% 2	5196
April	1st to 10th	Night	58% 5% 8% 18% 10% 1	2011
	11th to 20th	Night	54% 5% 9% 18% 12% 1	1975
	21st to end	Night	54% 5% 8% 17% 12% 3	1921
May	1st to 10th	Night	60% 9% 9% 13% 8% 1	3608
	11th to 20th	Night	51% 9% 11% 17% 11% 1	3576
	21st to end	Night	52% 6% 11% 18% 12% 1	3927
June	1st to 10th	Night	50% 10% 14% 16% 10% 1	1600
	11th to 20th	Night	43% 7% 14% 19% 15% 1	1600
	21st to end	Night	51% 8% 12% 18% 11%	1600
July	1st to 10th	Night	43% 6% 16% 22% 12% 1	3560
	11th to 20th	Night	40% 6% 14% 27% 12% 1	3552
	21st to end	Night	39% 7% 12% 30% 12%	3809
August	1st to 10th	Night	46% 7% 15% 23% 9%	2599
	11th to 20th	Night	45% 7% 15% 24% 8% 1	3019
	21st to end	Night	41% 6% 15% 26% 10% 1	3586
September	1st to 10th	Night	41% 6% 13% 27% 12% 1	2000
	11th to 20th	Night	34% 7% 14% 31% 13%	2034
	21st to end	Night	44% 7% 11% 25% 12% 1	2206
October	1st to 10th	Night	46% 6% 12% 25% 10% 1	3920
	11th to 20th	Night	47% 6% 15% 21% 10% 1	3899
	21st to end	Night	52% 6% 16% 19% 6% 1	4565
November	1st to 10th	Night	54% 7% 13% 17% 8% 1	2667
	11th to 20th	Night	57% 7% 12% 15% 7% 2	2851
	21st to end	Night	67% 7% 11% 11% 4	2940
December	1st to 10th	Night	79% 6% 8% 7% 1	4720
	11th to 20th	Night	69% 5% 7% 12% 6%	5348
	21st to end	Night	70% 6% 7% 10% 6% 1	7150

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	33% 15% 35% 12% 4	220
	11th to 20th	Day	35% 25% 27% 10% 2	220
	21st to end	Day	25% 26% 32% 16% 1	273
February	1st to 10th	Day	36% 26% 30% 7% 1	330
	11th to 20th	Day	30% 33% 31% 6%	393
	21st to end	Day	35% 24% 31% 9% 1	446
March	1st to 10th	Day	32% 23% 29% 13% 3	540
	11th to 20th	Day	36% 21% 29% 12% 2	540
	21st to end	Day	36% 23% 24% 10% 5%	594
April	1st to 10th	Day	38% 20% 27% 12% 4	504
	11th to 20th	Day	36% 20% 24% 14% 4 2	492
	21st to end	Day	36% 21% 26% 11% 5% 1	500
May	1st to 10th	Day	30% 18% 28% 17% 6% 1	503
	11th to 20th	Day	23% 19% 30% 19% 9% 1	527
	21st to end	Day	22% 17% 27% 25% 9%	573
June	1st to 10th	Day	28% 15% 31% 18% 6% 1	530
	11th to 20th	Day	19% 16% 35% 21% 7% 2	530
	21st to end	Day	26% 16% 33% 15% 8% 1	530
July	1st to 10th	Day	16% 11% 34% 26% 11% 2	525
	11th to 20th	Day	15% 12% 33% 28% 9% 2	524
	21st to end	Day	16% 11% 35% 28% 9% 1	576
August	1st to 10th	Day	16% 10% 29% 30% 13% 2	526
	11th to 20th	Day	18% 9% 28% 29% 13% 4	519
	21st to end	Day	16% 13% 34% 23% 10% 4	583
September	1st to 10th	Day	19% 12% 29% 22% 11% 6%	530
	11th to 20th	Day	13% 10% 25% 27% 15% 9%	530
	21st to end	Day	19% 13% 29% 24% 11% 3	530
October	1st to 10th	Day	25% 16% 25% 19% 10% 4	530
	11th to 20th	Day	28% 20% 30% 15% 5% 1	530
	21st to end	Day	37% 17% 26% 16% 4	478
November	1st to 10th	Day	32% 19% 28% 16% 5%	425
	11th to 20th	Day	29% 25% 26% 13% 5% 2	306
	21st to end	Day	34% 23% 31% 9% 3	220
December	1st to 10th	Day	37% 15% 30% 17% 2	220
	11th to 20th	Day	34% 32% 25% 7% 2	220
	21st to end	Day	39% 20% 27% 12% 3	242
January	1st to 10th	Night	32% 20% 32% 14% 2	840
	11th to 20th	Night	31% 23% 27% 15% 3	840
	21st to end	Night	23% 22% 31% 19% 4	924
February	1st to 10th	Night	28% 22% 33% 15% 2	840
	11th to 20th	Night	26% 21% 37% 13% 2	823
	21st to end	Night	29% 19% 34% 16% 3	692
March	1st to 10th	Night	30% 20% 30% 19% 2	840
	11th to 20th	Night	31% 20% 30% 16% 3	840
	21st to end	Night	31% 18% 27% 19% 5% 1	924
April	1st to 10th	Night	31% 18% 29% 19% 2	805
	11th to 20th	Night	32% 18% 27% 16% 7%	791
	21st to end	Night	32% 14% 31% 19% 6%	721
May	1st to 10th	Night	28% 13% 31% 22% 5% 1	408
	11th to 20th	Night	21% 11% 35% 27% 6% 1	394
	21st to end	Night	18% 12% 35% 27% 8%	433
June	1st to 10th	Night	24% 10% 28% 32% 6%	400
	11th to 20th	Night	21% 11% 30% 28% 11% 1	400
	21st to end	Night	20% 9% 34% 28% 9% 1	400
July	1st to 10th	Night	13% 7% 32% 39% 8% 1	390
	11th to 20th	Night	12% 6% 32% 36% 13%	388
	21st to end	Night	13% 7% 34% 37% 7% 1	438
August	1st to 10th	Night	16% 6% 26% 38% 14%	408
	11th to 20th	Night	20% 6% 22% 35% 17% 1	659
	21st to end	Night	17% 7% 33% 29% 13% 1	880
September	1st to 10th	Night	18% 10% 28% 30% 14% 1	800
	11th to 20th	Night	16% 9% 23% 31% 19% 4	800
	21st to end	Night	19% 13% 25% 26% 16% 1	800
October	1st to 10th	Night	26% 11% 29% 21% 12% 1	800
	11th to 20th	Night	27% 15% 29% 22% 7%	800
	21st to end	Night	34% 16% 26% 21% 3	880
November	1st to 10th	Night	31% 17% 29% 17% 5%	820
	11th to 20th	Night	30% 20% 27% 15% 8%	840
	21st to end	Night	33% 21% 26% 15% 5%	840
December	1st to 10th	Night	35% 21% 25% 16% 3	840
	11th to 20th	Night	32% 22% 29% 13% 3 1	840
	21st to end	Night	37% 18% 27% 15% 3	924

Page generated at 2026-03-30 02:18:43. Version ac07

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