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 2026-08-30.

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	12% 8% 3 8% 5% 4 4 4 6% 7% 39%	144381
	Night	11% 8% 3 8% 5% 4 4 3 5% 7% 42%	138160
Transparency	Day	43% 6% 13% 25% 13% 1	147982
	Night	41% 5% 13% 25% 15% 2	142639
Seeing	Day	15% 10% 31% 28% 13% 3	18450
	Night	15% 10% 34% 31% 10% 1	28205

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% 6% 22% 9% 6% 4 3 4 4 22%	4691
	11th to 20th	Day	4 10% 4 13% 6% 7% 8% 6% 7% 8% 27%	5232
	21st to end	Day	7% 11% 6% 12% 6% 6% 6% 4 5% 5% 30%	5812
February	1st to 10th	Day	10% 12% 5% 12% 7% 6% 5% 4 6% 7% 26%	1890
	11th to 20th	Day	10% 11% 5% 9% 5% 4 6% 4 5% 8% 33%	1844
	21st to end	Day	14% 9% 4 10% 6% 5% 3 4 5% 5% 35%	1651
March	1st to 10th	Day	14% 9% 4 7% 3 3 3 2 4 5% 46%	5046
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 5% 8% 46%	5090
	21st to end	Day	21% 13% 7% 8% 4 4 4 3 4 6% 25%	5583
April	1st to 10th	Day	18% 12% 4 7% 4 4 4 3 5% 6% 33%	2501
	11th to 20th	Day	18% 10% 3 8% 5% 5% 3 3 5% 6% 35%	2494
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 5% 6% 35%	2709
May	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	7617
	11th to 20th	Day	16% 7% 2 5% 4 3 3 3 4 6% 46%	8139
	21st to end	Day	16% 8% 3 8% 5% 4 5% 4 6% 7% 36%	9047
June	1st to 10th	Day	11% 7% 2 6% 4 3 4 4 7% 8% 44%	2940
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 4 6% 8% 44%	2940
	21st to end	Day	10% 6% 3 6% 5% 5% 5% 5% 6% 7% 41%	2940
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 4 7% 10% 39%	8280
	11th to 20th	Day	7% 4 2 5% 3 3 3 3 5% 7% 59%	8266
	21st to end	Day	8% 4 2 7% 5% 5% 5% 5% 7% 9% 43%	8337
August	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 9% 44%	4364
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 5% 7% 8% 38%	4301
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 6% 8% 49%	4542
September	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 5% 7% 52%	2400
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 5% 8% 48%	2320
	21st to end	Day	10% 5% 2 5% 4 4 4 3 6% 6% 50%	2133
October	1st to 10th	Day	14% 6% 2 5% 4 4 3 3 5% 6% 47%	2000
	11th to 20th	Day	15% 6% 3 7% 4 4 4 3 5% 5% 46%	2000
	21st to end	Day	16% 9% 4 6% 4 3 4 3 5% 6% 41%	2200
November	1st to 10th	Day	11% 7% 2 7% 3 3 4 4 6% 8% 46%	1864
	11th to 20th	Day	13% 10% 4 8% 5% 4 4 3 6% 6% 37%	1680
	21st to end	Day	13% 10% 4 7% 4 4 4 3 5% 7% 38%	1680
December	1st to 10th	Day	7% 8% 4 7% 7% 5% 4 4 5% 8% 41%	2690
	11th to 20th	Day	14% 12% 4 13% 9% 6% 4 4 5% 6% 23%	3088
	21st to end	Day	20% 16% 8% 16% 5% 4 3 2 3 4 17%	4070
January	1st to 10th	Night	8% 12% 5% 19% 7% 5% 4 4 5% 6% 25%	8232
	11th to 20th	Night	5% 9% 3 10% 7% 7% 8% 5% 8% 8% 29%	7740
	21st to end	Night	8% 10% 5% 12% 6% 4 5% 3 5% 7% 36%	8402
February	1st to 10th	Night	9% 13% 5% 12% 7% 4 5% 4 5% 5% 32%	2730
	11th to 20th	Night	10% 10% 4 8% 5% 5% 5% 4 5% 6% 39%	2663
	21st to end	Night	11% 8% 4 9% 5% 4 4 3 5% 6% 40%	2171
March	1st to 10th	Night	15% 7% 3 5% 3 3 3 2 4 5% 51%	5029
	11th to 20th	Night	9% 7% 2 5% 3 4 4 3 6% 8% 48%	5090
	21st to end	Night	21% 10% 4 11% 5% 4 4 3 4 5% 30%	5588
April	1st to 10th	Night	15% 8% 3 7% 5% 4 4 3 5% 6% 40%	2118
	11th to 20th	Night	15% 8% 3 6% 5% 5% 4 4 5% 7% 39%	2075
	21st to end	Night	18% 9% 3 6% 4 3 3 3 5% 6% 41%	1907
May	1st to 10th	Night	13% 5% 2 5% 4 3 4 3 5% 6% 50%	5266
	11th to 20th	Night	13% 6% 2 6% 3 3 3 3 4 5% 52%	4752
	21st to end	Night	18% 8% 3 7% 4 3 4 3 4 6% 40%	5139
June	1st to 10th	Night	8% 4 2 5% 4 5% 5% 4 7% 9% 47%	1680
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 6% 9% 48%	1680
	21st to end	Night	9% 5% 2 5% 4 4 4 3 6% 9% 48%	1680
July	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	4708
	11th to 20th	Night	5% 4 1 3 3 3 3 3 5% 7% 63%	4707
	21st to end	Night	9% 4 2 5% 4 4 5% 4 7% 9% 46%	5767
August	1st to 10th	Night	6% 4 2 6% 4 4 4 4 6% 8% 51%	3016
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 8% 53%	2978
	21st to end	Night	9% 5% 2 5% 3 3 3 3 5% 7% 56%	3544
September	1st to 10th	Night	8% 5% 2 5% 3 3 4 3 5% 6% 56%	2000
	11th to 20th	Night	10% 5% 2 5% 3 3 4 2 5% 8% 54%	2077
	21st to end	Night	9% 5% 1 4 3 4 3 3 5% 7% 57%	2246
October	1st to 10th	Night	12% 6% 2 5% 3 3 3 2 4 6% 52%	2400
	11th to 20th	Night	15% 7% 2 5% 4 4 4 3 5% 6% 46%	2400
	21st to end	Night	16% 8% 2 6% 4 4 3 3 4 5% 44%	2640
November	1st to 10th	Night	11% 7% 2 6% 4 3 4 4 5% 7% 48%	2646
	11th to 20th	Night	12% 10% 3 8% 4 4 4 3 5% 6% 41%	2940
	21st to end	Night	13% 10% 4 8% 3 4 4 3 4 6% 42%	2940
December	1st to 10th	Night	6% 8% 3 9% 6% 5% 4 4 6% 8% 42%	4720
	11th to 20th	Night	12% 11% 4 12% 6% 5% 4 3 4 5% 33%	5339
	21st to end	Night	19% 17% 8% 16% 5% 3 3 2 3 4 19%	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	64% 5% 11% 13% 6%	4692
	11th to 20th	Day	53% 4 10% 20% 14% 1	5232
	21st to end	Day	55% 4 13% 21% 7% 1	5812
February	1st to 10th	Day	55% 5% 14% 17% 7% 1	1890
	11th to 20th	Day	49% 6% 12% 21% 10% 2	1853
	21st to end	Day	50% 5% 13% 20% 10% 2	1651
March	1st to 10th	Day	42% 4 10% 28% 13% 2	5046
	11th to 20th	Day	36% 4 11% 32% 16% 2	5090
	21st to end	Day	60% 6% 14% 15% 4 1	5585
April	1st to 10th	Day	51% 6% 12% 22% 9% 1	2501
	11th to 20th	Day	50% 5% 11% 20% 13% 1	2494
	21st to end	Day	50% 6% 11% 21% 12% 1	2709
May	1st to 10th	Day	38% 5% 10% 27% 19% 1	7655
	11th to 20th	Day	39% 5% 8% 28% 17% 3	8143
	21st to end	Day	46% 6% 11% 23% 13% 1	9061
June	1st to 10th	Day	35% 7% 15% 26% 15% 1	2940
	11th to 20th	Day	36% 7% 13% 23% 19% 2	2940
	21st to end	Day	39% 9% 15% 22% 14% 2	2940
July	1st to 10th	Day	40% 6% 17% 29% 7% 1	8211
	11th to 20th	Day	25% 5% 12% 35% 20% 2	8191
	21st to end	Day	35% 8% 19% 27% 10% 1	8155
August	1st to 10th	Day	35% 7% 16% 27% 14% 1	4350
	11th to 20th	Day	42% 7% 15% 24% 11% 1	4340
	21st to end	Day	32% 6% 15% 27% 17% 2	4541
September	1st to 10th	Day	32% 6% 13% 27% 20% 2	2400
	11th to 20th	Day	34% 6% 14% 31% 15%	2320
	21st to end	Day	34% 6% 11% 29% 20% 1	2133
October	1st to 10th	Day	23% 3 7% 30% 35% 2	3260
	11th to 20th	Day	30% 4 13% 27% 25% 2	3240
	21st to end	Day	41% 4 9% 30% 14% 3	3538
November	1st to 10th	Day	36% 7% 15% 24% 16% 2	1864
	11th to 20th	Day	46% 6% 13% 22% 13% 1	1680
	21st to end	Day	46% 5% 16% 23% 11% 1	1680
December	1st to 10th	Day	40% 6% 14% 31% 7% 1	2690
	11th to 20th	Day	61% 5% 14% 14% 6%	3085
	21st to end	Day	72% 4 8% 12% 4	4070
January	1st to 10th	Night	59% 5% 13% 15% 7% 1	8233
	11th to 20th	Night	49% 4 13% 16% 16% 1	7740
	21st to end	Night	48% 4 14% 22% 12%	8402
February	1st to 10th	Night	53% 5% 12% 20% 9% 1	2730
	11th to 20th	Night	45% 5% 11% 24% 13% 2	2664
	21st to end	Night	44% 4 13% 21% 15% 2	2171
March	1st to 10th	Night	36% 4 9% 31% 17% 2	5029
	11th to 20th	Night	34% 4 10% 32% 17% 4	5090
	21st to end	Night	57% 6% 13% 16% 6% 1	5588
April	1st to 10th	Night	43% 6% 11% 25% 13% 1	2118
	11th to 20th	Night	44% 5% 12% 20% 17% 3	2075
	21st to end	Night	43% 5% 12% 23% 14% 2	1907
May	1st to 10th	Night	34% 4 8% 27% 25% 1	5293
	11th to 20th	Night	36% 5% 9% 25% 19% 6%	4753
	21st to end	Night	45% 6% 9% 24% 14% 2	5149
June	1st to 10th	Night	31% 9% 15% 28% 15% 3	1680
	11th to 20th	Night	32% 7% 14% 21% 22% 5%	1680
	21st to end	Night	32% 7% 15% 26% 17% 3	1680
July	1st to 10th	Night	33% 7% 17% 29% 12% 1	4670
	11th to 20th	Night	22% 5% 15% 34% 22% 3	4662
	21st to end	Night	33% 7% 19% 28% 12% 1	5639
August	1st to 10th	Night	29% 7% 15% 33% 14% 2	3006
	11th to 20th	Night	30% 6% 17% 32% 13% 2	3005
	21st to end	Night	29% 5% 16% 29% 19% 3	3544
September	1st to 10th	Night	28% 5% 12% 27% 25% 3	2000
	11th to 20th	Night	30% 5% 13% 31% 20%	2077
	21st to end	Night	28% 5% 11% 28% 25% 3	2246
October	1st to 10th	Night	22% 3 7% 27% 39% 3	3920
	11th to 20th	Night	27% 3 10% 28% 25% 6%	3899
	21st to end	Night	42% 4 10% 26% 16% 2	4252
November	1st to 10th	Night	34% 5% 15% 26% 17% 3	2646
	11th to 20th	Night	43% 6% 13% 25% 13% 1	2940
	21st to end	Night	45% 3 13% 26% 12% 2	2940
December	1st to 10th	Night	40% 4 14% 34% 8%	4720
	11th to 20th	Night	52% 4 14% 24% 5%	5341
	21st to end	Night	70% 4 10% 12% 5%	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	15% 14% 38% 25% 8% 1	330
	11th to 20th	Day	16% 15% 45% 21% 2 1	330
	21st to end	Day	18% 12% 41% 23% 4 2	363
February	1st to 10th	Day	13% 21% 41% 21% 3 1	330
	11th to 20th	Day	14% 20% 37% 23% 5% 1	330
	21st to end	Day	21% 16% 41% 20% 2	273
March	1st to 10th	Day	18% 13% 47% 15% 5% 1	330
	11th to 20th	Day	23% 16% 33% 21% 7%	330
	21st to end	Day	31% 20% 29% 17% 3	363
April	1st to 10th	Day	28% 13% 36% 20% 3	521
	11th to 20th	Day	23% 18% 30% 22% 7% 1	532
	21st to end	Day	23% 16% 32% 22% 6% 2	729
May	1st to 10th	Day	19% 14% 33% 22% 11% 1	753
	11th to 20th	Day	23% 12% 29% 22% 11% 2	775
	21st to end	Day	18% 9% 29% 28% 13% 2	844
June	1st to 10th	Day	8% 8% 28% 32% 21% 3	780
	11th to 20th	Day	11% 7% 32% 32% 14% 3	780
	21st to end	Day	11% 7% 36% 29% 13% 3	780
July	1st to 10th	Day	7% 4 20% 36% 24% 9%	771
	11th to 20th	Day	7% 3 26% 35% 23% 7%	768
	21st to end	Day	6% 3 24% 40% 23% 4	849
August	1st to 10th	Day	9% 3 21% 39% 22% 6%	776
	11th to 20th	Day	12% 4 21% 34% 24% 6%	765
	21st to end	Day	9% 4 23% 39% 21% 6%	702
September	1st to 10th	Day	12% 6% 24% 34% 18% 5%	530
	11th to 20th	Day	9% 4 25% 38% 19% 6%	450
	21st to end	Day	9% 11% 29% 33% 14% 5%	330
October	1st to 10th	Day	16% 9% 28% 25% 17% 4	330
	11th to 20th	Day	18% 20% 36% 19% 6% 1	330
	21st to end	Day	20% 16% 36% 19% 7% 1	363
November	1st to 10th	Day	16% 12% 44% 20% 6% 2	330
	11th to 20th	Day	18% 22% 35% 18% 5% 1	330
	21st to end	Day	21% 15% 40% 20% 5% 1	330
December	1st to 10th	Day	10% 16% 44% 22% 8% 1	330
	11th to 20th	Day	17% 14% 37% 23% 8%	330
	21st to end	Day	24% 17% 39% 18% 2 1	363
January	1st to 10th	Night	12% 13% 39% 28% 7%	1050
	11th to 20th	Night	15% 13% 39% 27% 6%	1050
	21st to end	Night	17% 12% 39% 27% 6%	1155
February	1st to 10th	Night	16% 12% 41% 27% 5%	1050
	11th to 20th	Night	16% 13% 40% 26% 4	1029
	21st to end	Night	15% 13% 43% 23% 5% 1	787
March	1st to 10th	Night	18% 12% 39% 23% 7% 1	630
	11th to 20th	Night	19% 11% 40% 23% 7%	630
	21st to end	Night	22% 13% 39% 19% 6% 1	693
April	1st to 10th	Night	17% 16% 41% 22% 3	630
	11th to 20th	Night	19% 14% 38% 23% 5% 1	623
	21st to end	Night	21% 11% 35% 25% 6% 1	630
May	1st to 10th	Night	17% 9% 33% 31% 9%	630
	11th to 20th	Night	16% 9% 33% 31% 10%	621
	21st to end	Night	16% 6% 29% 36% 12%	683
June	1st to 10th	Night	9% 6% 30% 40% 15%	630
	11th to 20th	Night	11% 6% 29% 44% 10%	630
	21st to end	Night	9% 4 31% 42% 13% 1	630
July	1st to 10th	Night	6% 2 17% 46% 27% 2	615
	11th to 20th	Night	5% 3 23% 43% 24% 3	612
	21st to end	Night	7% 2 16% 52% 21% 2	690
August	1st to 10th	Night	8% 3 19% 47% 23% 1	627
	11th to 20th	Night	9% 3 20% 42% 24% 3	624
	21st to end	Night	9% 3 21% 43% 22% 3	687
September	1st to 10th	Night	9% 5% 24% 38% 22% 2	600
	11th to 20th	Night	12% 2 26% 41% 18% 1	600
	21st to end	Night	10% 7% 31% 36% 15% 1	646
October	1st to 10th	Night	15% 8% 32% 33% 12% 1	800
	11th to 20th	Night	17% 11% 38% 28% 6%	800
	21st to end	Night	19% 12% 35% 26% 7%	880
November	1st to 10th	Night	13% 11% 39% 29% 7%	888
	11th to 20th	Night	16% 14% 41% 23% 5%	1050
	21st to end	Night	17% 13% 36% 26% 8%	1050
December	1st to 10th	Night	15% 11% 41% 26% 6%	1050
	11th to 20th	Night	20% 10% 35% 28% 6%	1050
	21st to end	Night	24% 12% 37% 23% 5%	1155

Page generated at 2026-08-27 03:07:14. Version ac07

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