Strohbehn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strohbehn Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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% 8% 4 7% 6% 3 5% 5% 5% 7% 37%	78453
	Night	12% 8% 4 8% 6% 3 4 4 5% 7% 40%	80884
Transparency	Day	45% 6% 13% 22% 12% 1	78165
	Night	44% 6% 13% 23% 13% 2	80693
Seeing	Day	15% 10% 30% 28% 13% 3	14838
	Night	15% 9% 34% 31% 10% 1	24924

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	6% 14% 7% 18% 13% 5% 5% 5% 5% 5% 19%	2527
	11th to 20th	Day	8% 14% 5% 11% 8% 4 9% 6% 7% 8% 21%	2800
	21st to end	Day	13% 14% 10% 14% 10% 3 5% 4 5% 5% 18%	3135
February	1st to 10th	Day	10% 11% 5% 11% 7% 5% 5% 5% 5% 8% 26%	1710
	11th to 20th	Day	11% 9% 5% 8% 6% 3 6% 5% 5% 8% 33%	1664
	21st to end	Day	15% 8% 5% 9% 7% 3 4 5% 5% 5% 32%	1448
March	1st to 10th	Day	14% 11% 6% 8% 6% 4 4 4 5% 6% 33%	1980
	11th to 20th	Day	15% 8% 4 9% 6% 3 5% 4 5% 8% 32%	1980
	21st to end	Day	19% 14% 6% 6% 5% 3 4 4 5% 6% 27%	2178
April	1st to 10th	Day	18% 10% 4 6% 6% 3 4 4 5% 7% 33%	2143
	11th to 20th	Day	18% 9% 4 8% 6% 3 4 3 4 6% 34%	2134
	21st to end	Day	21% 9% 3 6% 5% 3 4 4 5% 6% 35%	2322
May	1st to 10th	Day	21% 7% 3 6% 6% 3 5% 5% 6% 7% 31%	2340
	11th to 20th	Day	19% 7% 4 5% 5% 2 4 5% 4 7% 37%	2450
	21st to end	Day	17% 7% 3 6% 5% 2 6% 4 5% 8% 36%	2725
June	1st to 10th	Day	11% 6% 2 5% 4 2 5% 5% 7% 8% 45%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 3 4 5% 6% 9% 44%	2520
	21st to end	Day	10% 5% 3 6% 6% 4 6% 6% 6% 8% 41%	2520
July	1st to 10th	Day	8% 4 1 4 5% 3 5% 5% 6% 10% 49%	2520
	11th to 20th	Day	6% 3 2 4 5% 3 4 4 6% 8% 53%	2520
	21st to end	Day	7% 3 2 5% 5% 3 6% 6% 7% 10% 47%	2546
August	1st to 10th	Day	8% 6% 3 6% 7% 3 5% 6% 6% 8% 43%	2328
	11th to 20th	Day	10% 4 2 5% 6% 3 5% 5% 6% 7% 46%	2301
	21st to end	Day	8% 5% 2 5% 5% 3 4 4 5% 8% 51%	2448
September	1st to 10th	Day	11% 5% 3 5% 5% 2 4 4 4 7% 51%	2160
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 4 5% 7% 50%	2088
	21st to end	Day	11% 5% 2 5% 5% 3 4 3 6% 6% 49%	1921
October	1st to 10th	Day	16% 6% 3 5% 5% 3 4 3 5% 7% 44%	1800
	11th to 20th	Day	15% 6% 3 6% 5% 3 4 4 5% 5% 45%	1800
	21st to end	Day	17% 9% 4 5% 5% 3 3 4 5% 6% 40%	1980
November	1st to 10th	Day	10% 6% 2 6% 5% 2 4 5% 5% 8% 47%	1684
	11th to 20th	Day	13% 9% 5% 8% 6% 2 4 4 5% 7% 37%	1520
	21st to end	Day	14% 9% 4 5% 5% 2 4 4 5% 7% 40%	1520
December	1st to 10th	Day	12% 11% 4 8% 8% 4 5% 5% 5% 9% 30%	1520
	11th to 20th	Day	12% 11% 4 9% 7% 4 4 5% 5% 7% 31%	1918
	21st to end	Day	19% 14% 7% 16% 6% 3 3 3 4 4 19%	2783
January	1st to 10th	Night	9% 12% 6% 20% 10% 4 4 5% 4 5% 22%	4428
	11th to 20th	Night	8% 13% 5% 10% 8% 4 6% 6% 9% 8% 23%	4152
	21st to end	Night	14% 14% 7% 14% 7% 3 5% 5% 4 6% 22%	4532
February	1st to 10th	Night	9% 12% 6% 11% 8% 3 5% 4 5% 5% 32%	2470
	11th to 20th	Night	11% 9% 4 7% 6% 4 5% 5% 5% 7% 39%	2403
	21st to end	Night	12% 9% 4 8% 7% 4 4 4 4 5% 39%	1917
March	1st to 10th	Night	14% 8% 5% 6% 5% 3 3 4 4 6% 41%	1980
	11th to 20th	Night	14% 9% 4 7% 4 3 4 4 5% 7% 39%	1980
	21st to end	Night	18% 11% 5% 9% 5% 3 4 4 4 6% 31%	2178
April	1st to 10th	Night	15% 7% 3 6% 6% 3 5% 4 5% 7% 41%	1816
	11th to 20th	Night	17% 9% 2 5% 5% 3 5% 5% 5% 6% 38%	1775
	21st to end	Night	17% 8% 3 5% 5% 2 3 4 4 6% 42%	1635
May	1st to 10th	Night	17% 6% 2 6% 5% 2 4 4 6% 7% 41%	1620
	11th to 20th	Night	15% 6% 2 5% 5% 3 5% 5% 4 8% 42%	1444
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 7% 8% 42%	1551
June	1st to 10th	Night	7% 3 2 5% 5% 3 6% 5% 7% 10% 48%	1440
	11th to 20th	Night	9% 5% 2 4 4 3 4 4 6% 9% 49%	1440
	21st to end	Night	8% 4 3 4 4 3 4 4 7% 9% 50%	1440
July	1st to 10th	Night	4 3 1 3 5% 2 5% 5% 5% 9% 58%	1440
	11th to 20th	Night	5% 3 1 3 4 2 4 5% 6% 8% 60%	1440
	21st to end	Night	4 3 1 3 4 2 4 5% 7% 9% 58%	1769
August	1st to 10th	Night	7% 4 2 4 5% 3 5% 5% 6% 7% 52%	1611
	11th to 20th	Night	8% 5% 2 4 4 3 4 3 4 8% 56%	1600
	21st to end	Night	7% 5% 2 4 4 3 3 4 4 6% 57%	1908
September	1st to 10th	Night	9% 4 2 4 4 3 4 4 5% 6% 55%	1800
	11th to 20th	Night	11% 4 2 3 3 2 3 3 5% 7% 56%	1869
	21st to end	Night	10% 4 2 3 4 3 3 3 5% 7% 56%	2020
October	1st to 10th	Night	12% 6% 3 4 4 3 3 4 4 6% 51%	2160
	11th to 20th	Night	15% 7% 2 5% 5% 4 4 4 4 6% 45%	2160
	21st to end	Night	16% 8% 2 5% 5% 3 3 4 4 5% 45%	2376
November	1st to 10th	Night	10% 6% 3 4 4 2 4 5% 5% 7% 50%	2387
	11th to 20th	Night	12% 9% 3 8% 4 3 4 4 5% 6% 41%	2660
	21st to end	Night	13% 9% 3 6% 4 3 4 4 4 5% 44%	2660
December	1st to 10th	Night	10% 10% 4 9% 7% 4 5% 5% 5% 7% 34%	2660
	11th to 20th	Night	12% 11% 4 8% 6% 4 5% 5% 5% 6% 35%	3279
	21st to end	Night	19% 15% 7% 14% 7% 3 3 4 3 4 22%	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	65% 7% 11% 11% 6%	2528
	11th to 20th	Day	59% 5% 10% 20% 6%	2800
	21st to end	Day	67% 5% 11% 13% 3 1	3135
February	1st to 10th	Day	55% 6% 14% 17% 7% 1	1710
	11th to 20th	Day	49% 6% 12% 22% 10% 2	1673
	21st to end	Day	53% 5% 13% 18% 10% 2	1448
March	1st to 10th	Day	51% 6% 14% 20% 7% 2	1980
	11th to 20th	Day	51% 5% 13% 21% 9% 1	1980
	21st to end	Day	57% 7% 13% 16% 7% 1	2178
April	1st to 10th	Day	51% 6% 13% 21% 9% 1	2143
	11th to 20th	Day	52% 4 10% 20% 13% 1	2134
	21st to end	Day	50% 6% 11% 22% 11% 1	2322
May	1st to 10th	Day	51% 6% 13% 20% 9% 1	2340
	11th to 20th	Day	47% 7% 11% 24% 10% 2	2454
	21st to end	Day	47% 7% 13% 18% 12% 2	2725
June	1st to 10th	Day	35% 7% 16% 25% 16% 1	2520
	11th to 20th	Day	36% 8% 14% 23% 18% 2	2520
	21st to end	Day	38% 9% 15% 22% 14% 2	2520
July	1st to 10th	Day	30% 7% 16% 31% 13% 2	2451
	11th to 20th	Day	29% 8% 16% 26% 17% 4	2445
	21st to end	Day	29% 9% 18% 27% 15% 3	2405
August	1st to 10th	Day	38% 8% 15% 25% 12% 2	2314
	11th to 20th	Day	37% 7% 14% 28% 14% 1	2301
	21st to end	Day	31% 7% 13% 27% 19% 3	2448
September	1st to 10th	Day	33% 6% 13% 26% 20% 2	2160
	11th to 20th	Day	33% 6% 14% 31% 15%	2088
	21st to end	Day	35% 6% 11% 28% 19% 1	1921
October	1st to 10th	Day	40% 5% 12% 25% 16% 1	1800
	11th to 20th	Day	41% 5% 11% 23% 18% 2	1800
	21st to end	Day	44% 5% 12% 22% 15% 1	1980
November	1st to 10th	Day	35% 7% 15% 24% 17% 2	1684
	11th to 20th	Day	46% 6% 13% 22% 13% 1	1520
	21st to end	Day	45% 5% 16% 23% 11% 1	1520
December	1st to 10th	Day	50% 8% 17% 16% 8% 2	1520
	11th to 20th	Day	51% 6% 19% 18% 6%	1915
	21st to end	Day	69% 5% 9% 12% 5% 1	2783
January	1st to 10th	Night	64% 5% 9% 13% 8% 1	4428
	11th to 20th	Night	55% 5% 13% 16% 9% 1	4152
	21st to end	Night	63% 5% 11% 13% 6%	4532
February	1st to 10th	Night	53% 5% 11% 20% 9% 1	2470
	11th to 20th	Night	45% 6% 12% 24% 13% 2	2404
	21st to end	Night	47% 4 12% 20% 14% 3	1917
March	1st to 10th	Night	43% 6% 14% 26% 9% 2	1980
	11th to 20th	Night	44% 6% 13% 22% 14% 1	1980
	21st to end	Night	55% 6% 13% 17% 7% 2	2178
April	1st to 10th	Night	42% 7% 12% 25% 13% 1	1816
	11th to 20th	Night	46% 5% 11% 19% 17% 3	1775
	21st to end	Night	43% 5% 12% 24% 14% 2	1635
May	1st to 10th	Night	42% 7% 14% 22% 14% 1	1620
	11th to 20th	Night	40% 8% 13% 25% 13% 1	1445
	21st to end	Night	38% 8% 15% 22% 14% 3	1552
June	1st to 10th	Night	30% 9% 16% 27% 16% 2	1440
	11th to 20th	Night	31% 7% 15% 21% 21% 6%	1440
	21st to end	Night	30% 7% 16% 27% 16% 3	1440
July	1st to 10th	Night	23% 7% 15% 33% 20% 3	1400
	11th to 20th	Night	21% 7% 18% 33% 17% 4	1392
	21st to end	Night	20% 6% 19% 30% 22% 3	1671
August	1st to 10th	Night	30% 9% 14% 29% 14% 4	1601
	11th to 20th	Night	28% 6% 13% 34% 17% 3	1600
	21st to end	Night	28% 6% 12% 26% 22% 5%	1908
September	1st to 10th	Night	29% 5% 12% 24% 26% 3	1800
	11th to 20th	Night	29% 5% 13% 32% 21% 1	1869
	21st to end	Night	28% 5% 12% 30% 23% 2	2020
October	1st to 10th	Night	34% 4 12% 28% 20% 3	2160
	11th to 20th	Night	39% 5% 11% 23% 18% 3	2160
	21st to end	Night	41% 5% 12% 22% 18% 1	2376
November	1st to 10th	Night	33% 5% 15% 25% 18% 3	2387
	11th to 20th	Night	43% 6% 13% 25% 13% 1	2660
	21st to end	Night	43% 3 13% 26% 12% 2	2660
December	1st to 10th	Night	50% 5% 14% 22% 8% 1	2660
	11th to 20th	Night	49% 5% 16% 24% 6% 1	3281
	21st to end	Night	67% 4 9% 14% 6%	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	16% 14% 36% 24% 9% 1	270
	11th to 20th	Day	19% 13% 43% 23% 2 1	270
	21st to end	Day	21% 11% 38% 24% 4 2	297
February	1st to 10th	Day	14% 20% 42% 21% 2 1	270
	11th to 20th	Day	13% 21% 37% 23% 5% 1	270
	21st to end	Day	22% 14% 40% 21% 2	210
March	1st to 10th	Day	16% 16% 46% 15% 6% 1	240
	11th to 20th	Day	24% 13% 35% 21% 7%	240
	21st to end	Day	34% 19% 23% 19% 4	264
April	1st to 10th	Day	27% 12% 35% 21% 4	403
	11th to 20th	Day	22% 15% 30% 24% 8% 1	412
	21st to end	Day	23% 15% 31% 23% 7% 2	582
May	1st to 10th	Day	22% 14% 33% 22% 9% 1	603
	11th to 20th	Day	24% 12% 28% 21% 11% 3	625
	21st to end	Day	19% 8% 27% 29% 14% 3	679
June	1st to 10th	Day	7% 7% 27% 33% 23% 4	630
	11th to 20th	Day	11% 5% 31% 34% 15% 3	630
	21st to end	Day	10% 7% 35% 30% 15% 3	630
July	1st to 10th	Day	7% 3 19% 36% 25% 10%	621
	11th to 20th	Day	7% 3 27% 36% 21% 6%	618
	21st to end	Day	6% 2 24% 40% 24% 4	684
August	1st to 10th	Day	8% 4 19% 39% 24% 6%	626
	11th to 20th	Day	11% 3 20% 34% 25% 7%	615
	21st to end	Day	10% 4 22% 38% 21% 6%	567
September	1st to 10th	Day	14% 5% 24% 35% 17% 5%	450
	11th to 20th	Day	9% 4 26% 37% 18% 7%	378
	21st to end	Day	10% 13% 31% 31% 12% 2	270
October	1st to 10th	Day	19% 8% 26% 26% 18% 3	270
	11th to 20th	Day	18% 21% 34% 19% 7% 1	270
	21st to end	Day	22% 16% 33% 19% 9% 2	297
November	1st to 10th	Day	14% 12% 43% 22% 7% 2	270
	11th to 20th	Day	16% 23% 35% 20% 6% 1	270
	21st to end	Day	21% 13% 41% 21% 4 1	270
December	1st to 10th	Day	10% 14% 46% 21% 8% 1	270
	11th to 20th	Day	16% 12% 38% 25% 9%	270
	21st to end	Day	22% 20% 39% 17% 2	297
January	1st to 10th	Night	12% 13% 40% 27% 7%	950
	11th to 20th	Night	16% 12% 38% 28% 6%	950
	21st to end	Night	18% 12% 37% 27% 6%	1045
February	1st to 10th	Night	16% 10% 40% 28% 5%	950
	11th to 20th	Night	16% 13% 39% 27% 5% 1	929
	21st to end	Night	16% 14% 39% 24% 6% 1	697
March	1st to 10th	Night	18% 12% 37% 24% 8% 1	540
	11th to 20th	Night	20% 10% 38% 25% 8%	540
	21st to end	Night	22% 13% 36% 21% 7% 1	594
April	1st to 10th	Night	17% 16% 41% 23% 3	540
	11th to 20th	Night	20% 12% 38% 23% 6% 1	533
	21st to end	Night	20% 10% 35% 26% 7% 1	540
May	1st to 10th	Night	19% 9% 33% 29% 9%	540
	11th to 20th	Night	16% 8% 34% 32% 10% 1	531
	21st to end	Night	15% 6% 30% 35% 14% 1	584
June	1st to 10th	Night	7% 5% 28% 41% 17% 1	540
	11th to 20th	Night	11% 5% 27% 46% 11%	540
	21st to end	Night	9% 3 31% 42% 15% 1	540
July	1st to 10th	Night	6% 1 16% 46% 28% 2	525
	11th to 20th	Night	5% 3 25% 43% 22% 3	522
	21st to end	Night	4 1 16% 54% 23% 1	591
August	1st to 10th	Night	7% 2 19% 47% 24% 1	537
	11th to 20th	Night	9% 3 20% 40% 25% 3	534
	21st to end	Night	9% 3 23% 40% 21% 3	594
September	1st to 10th	Night	10% 5% 24% 38% 21% 2	540
	11th to 20th	Night	12% 2 27% 40% 18% 1	540
	21st to end	Night	11% 7% 34% 34% 13% 1	580
October	1st to 10th	Night	15% 7% 34% 32% 11% 1	720
	11th to 20th	Night	18% 12% 36% 28% 6%	720
	21st to end	Night	19% 11% 34% 27% 8%	792
November	1st to 10th	Night	13% 11% 39% 29% 8%	801
	11th to 20th	Night	16% 14% 42% 22% 6%	950
	21st to end	Night	17% 13% 36% 26% 8%	950
December	1st to 10th	Night	15% 11% 41% 27% 6%	950
	11th to 20th	Night	20% 9% 35% 30% 6%	950
	21st to end	Night	23% 12% 37% 23% 4	1045

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