TheDamObservatory-Lake Tschida
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TheDamObservatory-Lake Tschida clear sky chart from 2005-11-06 to 2025-05-11.

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	8% 7% 3 7% 5% 4 5% 4 6% 7% 44%	117128
	Night	7% 8% 3 8% 5% 4 5% 4 6% 7% 43%	120609
Transparency	Day	38% 5% 14% 27% 14% 2	116871
	Night	39% 5% 15% 26% 14% 2	120456
Seeing	Day	13% 9% 30% 30% 15% 3	16706
	Night	11% 9% 33% 35% 11% 1	26802

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	4 9% 6% 13% 8% 6% 6% 4 6% 7% 30%	3638
	11th to 20th	Day	2 9% 3 13% 6% 6% 8% 5% 9% 10% 27%	3640
	21st to end	Day	3 8% 6% 12% 7% 5% 5% 3 4 5% 41%	4004
February	1st to 10th	Day	8% 12% 5% 10% 7% 6% 5% 3 5% 6% 33%	1624
	11th to 20th	Day	5% 12% 5% 11% 6% 4 6% 5% 6% 7% 34%	1926
	21st to end	Day	5% 12% 4 11% 8% 5% 5% 4 5% 6% 35%	1650
March	1st to 10th	Day	5% 8% 4 9% 5% 4 5% 3 5% 8% 45%	4500
	11th to 20th	Day	5% 8% 4 8% 5% 5% 5% 4 8% 10% 38%	4712
	21st to end	Day	14% 16% 4 11% 6% 4 5% 3 5% 6% 26%	5831
April	1st to 10th	Day	9% 10% 3 8% 5% 5% 5% 4 7% 8% 37%	2400
	11th to 20th	Day	14% 10% 4 9% 5% 5% 4 4 6% 6% 33%	2441
	21st to end	Day	16% 10% 3 7% 4 4 4 4 5% 6% 37%	2600
May	1st to 10th	Day	15% 8% 2 6% 4 4 4 4 6% 7% 41%	4363
	11th to 20th	Day	10% 6% 2 6% 4 5% 4 4 6% 8% 44%	4390
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 4 6% 8% 41%	4825
June	1st to 10th	Day	13% 5% 2 5% 5% 4 4 4 6% 8% 45%	2774
	11th to 20th	Day	10% 5% 2 5% 6% 5% 4 4 6% 9% 45%	2850
	21st to end	Day	7% 4 2 4 4 3 4 4 6% 8% 53%	2776
July	1st to 10th	Day	6% 4 1 5% 5% 5% 5% 5% 8% 10% 46%	4430
	11th to 20th	Day	4 3 1 3 3 3 3 3 5% 8% 63%	4430
	21st to end	Day	4 3 1 5% 4 4 5% 4 6% 8% 55%	4802
August	1st to 10th	Day	10% 5% 2 5% 3 4 3 3 5% 7% 53%	4411
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 7% 7% 44%	4078
	21st to end	Day	7% 4 2 4 3 3 3 3 5% 7% 59%	4262
September	1st to 10th	Day	9% 4 2 4 3 4 4 3 5% 5% 58%	2280
	11th to 20th	Day	9% 5% 1 5% 3 3 3 3 5% 7% 55%	2148
	21st to end	Day	11% 6% 1 5% 3 3 2 2 4 6% 56%	2090
October	1st to 10th	Day	9% 4 1 4 2 2 3 3 5% 7% 60%	3423
	11th to 20th	Day	9% 6% 2 4 3 2 3 2 4 9% 54%	2910
	21st to end	Day	8% 9% 3 5% 3 4 4 3 6% 8% 46%	3091
November	1st to 10th	Day	10% 11% 2 6% 4 4 4 3 6% 7% 42%	1763
	11th to 20th	Day	6% 8% 4 8% 7% 4 4 4 6% 8% 40%	1780
	21st to end	Day	5% 8% 4 9% 6% 6% 5% 4 6% 8% 38%	1515
December	1st to 10th	Day	5% 12% 6% 12% 6% 4 4 3 5% 6% 37%	2290
	11th to 20th	Day	6% 13% 4 13% 7% 7% 7% 4 6% 7% 26%	2643
	21st to end	Day	6% 9% 4 10% 6% 5% 4 3 5% 6% 41%	3838
January	1st to 10th	Night	4 13% 5% 15% 9% 5% 5% 3 5% 5% 31%	6327
	11th to 20th	Night	3 8% 3 11% 6% 7% 10% 6% 9% 8% 30%	6340
	21st to end	Night	2 8% 5% 11% 5% 5% 5% 4 5% 7% 43%	6974
February	1st to 10th	Night	8% 12% 5% 9% 7% 6% 5% 5% 5% 7% 31%	2795
	11th to 20th	Night	5% 8% 4 10% 7% 5% 5% 4 6% 7% 39%	2359
	21st to end	Night	6% 10% 4 8% 5% 5% 4 4 5% 7% 41%	1980
March	1st to 10th	Night	6% 8% 3 8% 4 5% 5% 3 5% 7% 46%	5374
	11th to 20th	Night	6% 7% 2 7% 5% 4 5% 4 7% 10% 43%	5259
	21st to end	Night	13% 14% 5% 11% 6% 4 5% 4 5% 7% 26%	5099
April	1st to 10th	Night	8% 8% 3 7% 5% 4 6% 5% 8% 7% 39%	2000
	11th to 20th	Night	11% 9% 5% 8% 5% 4 5% 4 7% 7% 35%	1906
	21st to end	Night	13% 6% 3 6% 5% 4 4 4 5% 7% 42%	1800
May	1st to 10th	Night	12% 6% 2 5% 5% 5% 4 4 6% 6% 46%	2822
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 7% 7% 42%	2521
	21st to end	Night	14% 6% 2 4 4 3 5% 4 7% 9% 45%	2762
June	1st to 10th	Night	9% 4 2 4 4 3 4 4 8% 10% 50%	1400
	11th to 20th	Night	10% 4 2 6% 4 5% 5% 4 7% 7% 46%	1330
	21st to end	Night	5% 4 2 4 3 3 4 3 8% 9% 57%	1397
July	1st to 10th	Night	5% 3 2 5% 4 4 4 4 8% 11% 52%	2540
	11th to 20th	Night	2 3 1 4 3 3 4 4 6% 8% 63%	2540
	21st to end	Night	4 3 2 4 3 3 4 4 6% 9% 59%	2761
August	1st to 10th	Night	6% 4 1 4 3 4 4 3 6% 6% 59%	2528
	11th to 20th	Night	7% 5% 2 5% 4 4 4 4 5% 8% 53%	2761
	21st to end	Night	7% 4 1 4 3 3 3 3 6% 7% 59%	3389
September	1st to 10th	Night	7% 3 1 4 2 2 3 3 5% 7% 63%	1900
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 5% 8% 55%	2031
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 7% 55%	2090
October	1st to 10th	Night	10% 4 1 4 2 3 3 3 4 7% 60%	3535
	11th to 20th	Night	7% 7% 2 5% 3 3 5% 4 6% 9% 49%	3987
	21st to end	Night	9% 8% 3 6% 4 3 4 3 5% 7% 48%	4467
November	1st to 10th	Night	7% 9% 4 7% 5% 4 4 4 6% 8% 43%	2535
	11th to 20th	Night	6% 8% 3 9% 6% 5% 5% 4 5% 8% 41%	2618
	21st to end	Night	6% 8% 4 8% 5% 4 5% 4 6% 8% 42%	2883
December	1st to 10th	Night	5% 10% 5% 12% 6% 5% 6% 3 5% 6% 37%	4900
	11th to 20th	Night	6% 9% 4 10% 7% 6% 6% 4 6% 8% 33%	5564
	21st to end	Night	8% 10% 3 10% 6% 6% 5% 4 5% 6% 37%	7135

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	53% 5% 16% 19% 6%	3639
	11th to 20th	Day	49% 5% 15% 14% 18% 1	3640
	21st to end	Day	46% 4 16% 27% 6%	4004
February	1st to 10th	Day	53% 4 12% 20% 10% 1	1624
	11th to 20th	Day	49% 4 12% 24% 10% 2	1936
	21st to end	Day	48% 5% 14% 22% 10% 1	1650
March	1st to 10th	Day	38% 5% 12% 31% 14%	4500
	11th to 20th	Day	39% 6% 16% 27% 12%	4712
	21st to end	Day	60% 5% 14% 15% 6%	5831
April	1st to 10th	Day	43% 5% 15% 23% 12% 2	2400
	11th to 20th	Day	50% 5% 11% 22% 11% 1	2444
	21st to end	Day	48% 5% 13% 24% 10% 1	2600
May	1st to 10th	Day	41% 4 12% 28% 13% 1	4363
	11th to 20th	Day	35% 6% 13% 30% 14% 1	4394
	21st to end	Day	40% 6% 17% 30% 7%	4825
June	1st to 10th	Day	36% 5% 17% 29% 11% 1	2774
	11th to 20th	Day	36% 6% 16% 28% 12% 2	2850
	21st to end	Day	27% 6% 19% 30% 15% 1	2776
July	1st to 10th	Day	28% 8% 18% 32% 10% 2	4361
	11th to 20th	Day	19% 5% 11% 33% 27% 5%	4355
	21st to end	Day	24% 6% 14% 34% 19% 2	4651
August	1st to 10th	Day	31% 5% 12% 31% 16% 5%	4396
	11th to 20th	Day	37% 6% 16% 28% 12% 1	4117
	21st to end	Day	25% 4 13% 33% 22% 2	4261
September	1st to 10th	Day	28% 3 11% 34% 21% 3	2280
	11th to 20th	Day	30% 4 14% 32% 18% 2	2148
	21st to end	Day	31% 3 11% 33% 20% 3	2090
October	1st to 10th	Day	26% 3 10% 31% 24% 7%	3423
	11th to 20th	Day	29% 3 11% 38% 18% 1	2910
	21st to end	Day	36% 5% 12% 24% 21% 2	3091
November	1st to 10th	Day	41% 5% 14% 23% 15% 1	1763
	11th to 20th	Day	41% 5% 16% 26% 10% 2	1780
	21st to end	Day	43% 6% 18% 23% 10% 1	1515
December	1st to 10th	Day	49% 4 16% 23% 7% 2	2290
	11th to 20th	Day	55% 7% 15% 18% 5%	2640
	21st to end	Day	44% 4 9% 31% 11% 1	3838
January	1st to 10th	Night	56% 3 14% 19% 8% 1	6327
	11th to 20th	Night	47% 5% 16% 17% 14% 1	6340
	21st to end	Night	40% 5% 20% 25% 9%	6974
February	1st to 10th	Night	51% 5% 12% 19% 12% 1	2795
	11th to 20th	Night	43% 5% 12% 26% 12% 2	2359
	21st to end	Night	43% 4 14% 25% 13% 2	1980
March	1st to 10th	Night	38% 5% 12% 29% 15% 1	5374
	11th to 20th	Night	35% 6% 18% 29% 11%	5259
	21st to end	Night	55% 5% 15% 18% 6%	5099
April	1st to 10th	Night	40% 6% 12% 26% 14% 3	2000
	11th to 20th	Night	46% 5% 10% 23% 14% 2	1906
	21st to end	Night	41% 6% 13% 26% 14% 1	1800
May	1st to 10th	Night	37% 5% 12% 28% 13% 4	2822
	11th to 20th	Night	36% 7% 17% 26% 14%	2522
	21st to end	Night	34% 7% 20% 27% 11% 1	2762
June	1st to 10th	Night	28% 6% 18% 33% 13% 3	1400
	11th to 20th	Night	34% 8% 18% 25% 13% 2	1330
	21st to end	Night	22% 5% 20% 34% 17% 2	1397
July	1st to 10th	Night	26% 7% 18% 36% 11% 3	2500
	11th to 20th	Night	18% 6% 13% 34% 25% 4	2492
	21st to end	Night	22% 5% 18% 32% 19% 4	2674
August	1st to 10th	Night	25% 5% 13% 29% 21% 7%	2520
	11th to 20th	Night	30% 5% 19% 31% 13% 2	2788
	21st to end	Night	25% 5% 10% 34% 22% 4	3389
September	1st to 10th	Night	22% 4 10% 35% 25% 5%	1900
	11th to 20th	Night	28% 4 15% 31% 19% 2	2031
	21st to end	Night	30% 4 11% 32% 20% 2	2090
October	1st to 10th	Night	26% 3 8% 25% 32% 6%	3535
	11th to 20th	Night	32% 4 10% 36% 17% 1	3987
	21st to end	Night	37% 4 11% 29% 17% 2	4467
November	1st to 10th	Night	39% 5% 12% 25% 17% 2	2535
	11th to 20th	Night	42% 4 14% 25% 12% 2	2618
	21st to end	Night	39% 6% 18% 27% 10% 1	2883
December	1st to 10th	Night	48% 5% 20% 20% 6%	4900
	11th to 20th	Night	47% 7% 22% 19% 5%	5566
	21st to end	Night	49% 4 11% 23% 13% 1	7135

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	8% 10% 34% 30% 12% 5%	300
	11th to 20th	Day	10% 13% 39% 26% 7% 5%	300
	21st to end	Day	8% 14% 41% 22% 13% 2	330
February	1st to 10th	Day	11% 14% 39% 30% 5%	300
	11th to 20th	Day	12% 8% 43% 28% 8% 1	300
	21st to end	Day	13% 10% 35% 33% 8%	249
March	1st to 10th	Day	17% 10% 36% 27% 8% 3	300
	11th to 20th	Day	11% 12% 38% 28% 10% 2	300
	21st to end	Day	16% 11% 31% 27% 11% 3	490
April	1st to 10th	Day	15% 17% 35% 25% 8%	500
	11th to 20th	Day	19% 14% 35% 25% 6% 1	562
	21st to end	Day	23% 10% 27% 25% 14% 2	700
May	1st to 10th	Day	15% 9% 29% 31% 13% 3	703
	11th to 20th	Day	16% 9% 27% 30% 15% 3	676
	21st to end	Day	15% 10% 28% 25% 18% 5%	734
June	1st to 10th	Day	12% 9% 24% 29% 21% 5%	680
	11th to 20th	Day	13% 9% 36% 28% 12% 3	680
	21st to end	Day	10% 9% 25% 34% 18% 3	680
July	1st to 10th	Day	6% 6% 25% 37% 21% 4	671
	11th to 20th	Day	6% 6% 28% 39% 19% 3	668
	21st to end	Day	5% 4 25% 42% 22% 3	739
August	1st to 10th	Day	8% 4 25% 35% 23% 5%	676
	11th to 20th	Day	9% 4 23% 35% 23% 6%	665
	21st to end	Day	9% 6% 23% 35% 22% 5%	595
September	1st to 10th	Day	11% 8% 28% 29% 19% 6%	490
	11th to 20th	Day	11% 6% 29% 33% 18% 4	358
	21st to end	Day	18% 8% 31% 25% 14% 3	300
October	1st to 10th	Day	20% 9% 23% 26% 17% 5%	300
	11th to 20th	Day	14% 14% 37% 20% 15% 1	300
	21st to end	Day	17% 15% 35% 24% 6% 2	330
November	1st to 10th	Day	21% 9% 33% 23% 12% 3	300
	11th to 20th	Day	13% 14% 35% 25% 11% 2	300
	21st to end	Day	10% 16% 31% 32% 10% 1	300
December	1st to 10th	Day	13% 12% 39% 26% 9% 1	300
	11th to 20th	Day	14% 11% 43% 27% 4 1	300
	21st to end	Day	11% 11% 39% 26% 10% 3	330
January	1st to 10th	Night	9% 11% 39% 30% 10% 1	1000
	11th to 20th	Night	11% 15% 37% 28% 9% 1	1000
	21st to end	Night	9% 13% 38% 32% 8%	1100
February	1st to 10th	Night	12% 12% 36% 31% 8% 1	995
	11th to 20th	Night	8% 8% 41% 32% 10% 1	784
	21st to end	Night	11% 7% 34% 38% 10% 1	660
March	1st to 10th	Night	12% 11% 36% 31% 8% 2	800
	11th to 20th	Night	14% 7% 36% 32% 10% 2	723
	21st to end	Night	18% 7% 33% 31% 11% 1	660
April	1st to 10th	Night	10% 10% 38% 34% 7%	600
	11th to 20th	Night	15% 9% 41% 25% 9% 1	593
	21st to end	Night	16% 10% 28% 33% 12% 1	600
May	1st to 10th	Night	13% 6% 29% 39% 14%	600
	11th to 20th	Night	14% 5% 28% 41% 11% 1	563
	21st to end	Night	17% 5% 31% 34% 13%	617
June	1st to 10th	Night	10% 7% 28% 40% 15%	570
	11th to 20th	Night	13% 7% 34% 34% 12%	570
	21st to end	Night	6% 5% 28% 46% 13%	570
July	1st to 10th	Night	6% 2 27% 47% 17%	555
	11th to 20th	Night	5% 3 29% 50% 13%	552
	21st to end	Night	4 4 22% 53% 16% 1	624
August	1st to 10th	Night	6% 2 25% 51% 15% 1	567
	11th to 20th	Night	8% 2 26% 45% 17% 2	564
	21st to end	Night	6% 3 28% 44% 17% 1	627
September	1st to 10th	Night	9% 3 24% 45% 17% 1	570
	11th to 20th	Night	9% 5% 29% 41% 15% 1	570
	21st to end	Night	14% 6% 32% 36% 11% 1	570
October	1st to 10th	Night	18% 8% 25% 38% 11% 1	599
	11th to 20th	Night	14% 10% 28% 35% 12% 1	879
	21st to end	Night	14% 12% 35% 29% 9% 1	1045
November	1st to 10th	Night	12% 10% 37% 33% 8% 1	975
	11th to 20th	Night	10% 11% 39% 29% 10%	1000
	21st to end	Night	10% 13% 37% 33% 7%	1000
December	1st to 10th	Night	13% 10% 36% 32% 8% 1	1000
	11th to 20th	Night	12% 12% 35% 33% 8% 1	1000
	21st to end	Night	15% 11% 33% 31% 10%	1100

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