Clemens Sauer Homestead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clemens Sauer Homestead Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	7% 4 2 5% 3 3 3 3 5% 6% 58%	119711
	Night	7% 5% 2 4 3 3 3 3 5% 7% 60%	118817
Transparency	Day	27% 5% 8% 21% 24% 16%	123629
	Night	24% 5% 9% 21% 24% 18%	123017
Seeing	Day	9% 6% 25% 33% 22% 6%	15635
	Night	8% 6% 33% 38% 13% 1	25665

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	9% 5% 2 5% 2 2 3 2 3 6% 60%	4077
	11th to 20th	Day	6% 4 2 3 2 2 2 2 3 5% 69%	4374
	21st to end	Day	14% 6% 2 5% 4 3 3 2 4 5% 55%	4994
February	1st to 10th	Day	9% 6% 2 5% 3 2 3 2 5% 6% 57%	2000
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 3 6% 56%	1949
	21st to end	Day	9% 4 1 3 3 3 3 4 5% 6% 59%	1650
March	1st to 10th	Day	6% 4 2 5% 4 3 4 3 4 5% 61%	4500
	11th to 20th	Day	12% 5% 2 5% 3 2 3 3 4 5% 56%	4935
	21st to end	Day	5% 5% 2 6% 3 4 4 3 5% 6% 57%	5462
April	1st to 10th	Day	6% 4 2 5% 4 3 3 3 5% 6% 60%	2360
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 4 5% 55%	2374
	21st to end	Day	8% 6% 2 4 3 3 3 2 4 5% 60%	2400
May	1st to 10th	Day	9% 6% 2 5% 3 4 3 3 5% 6% 53%	5761
	11th to 20th	Day	9% 5% 2 6% 3 3 4 3 5% 6% 54%	5862
	21st to end	Day	8% 5% 2 5% 3 4 4 4 6% 8% 50%	6434
June	1st to 10th	Day	3 4 1 3 4 3 4 3 6% 9% 60%	2588
	11th to 20th	Day	4 4 1 4 3 3 4 3 5% 8% 60%	2470
	21st to end	Day	5% 4 1 4 4 5% 4 4 7% 7% 55%	2470
July	1st to 10th	Day	4 3 1 5% 5% 4 5% 4 6% 7% 56%	4120
	11th to 20th	Day	2 2 1 3 3 4 4 3 6% 8% 64%	4120
	21st to end	Day	5% 3 1 5% 4 5% 4 4 5% 8% 56%	4288
August	1st to 10th	Day	1 1 1 2 2 3 4 3 4 7% 72%	3785
	11th to 20th	Day	4 2 1 3 3 2 3 2 5% 7% 67%	3726
	21st to end	Day	4 4 1 5% 4 4 5% 4 6% 10% 51%	4180
September	1st to 10th	Day	10% 6% 2 5% 4 5% 4 3 5% 7% 48%	2172
	11th to 20th	Day	10% 5% 3 6% 6% 5% 4 3 6% 7% 46%	2090
	21st to end	Day	8% 3 1 5% 3 4 5% 3 5% 7% 54%	2090
October	1st to 10th	Day	5% 4 2 4 4 3 3 3 5% 7% 60%	2090
	11th to 20th	Day	9% 4 2 4 3 3 3 2 4 5% 62%	2090
	21st to end	Day	11% 4 2 4 3 1 2 2 3 4 64%	2118
November	1st to 10th	Day	9% 6% 1 6% 2 2 3 3 4 7% 58%	1763
	11th to 20th	Day	6% 4 2 4 3 4 3 3 5% 5% 62%	1800
	21st to end	Day	9% 6% 2 4 3 3 3 3 4 6% 56%	1800
December	1st to 10th	Day	17% 7% 3 6% 3 3 2 2 3 4 49%	2940
	11th to 20th	Day	8% 6% 3 6% 4 4 5% 3 5% 4 52%	3391
	21st to end	Day	7% 5% 2 4 2 2 2 2 3 4 68%	4488
January	1st to 10th	Night	7% 6% 2 5% 3 3 3 3 4 5% 61%	5888
	11th to 20th	Night	5% 4 1 3 1 2 2 2 3 5% 72%	5647
	21st to end	Night	14% 8% 2 5% 3 3 3 2 3 5% 52%	5984
February	1st to 10th	Night	8% 5% 2 5% 3 2 3 3 4 6% 59%	2400
	11th to 20th	Night	11% 6% 2 5% 3 4 3 3 5% 5% 54%	2338
	21st to end	Night	8% 5% 2 4 3 3 3 3 5% 6% 58%	1980
March	1st to 10th	Night	4 4 1 4 3 3 4 3 5% 8% 62%	5374
	11th to 20th	Night	10% 6% 2 4 3 3 3 2 4 6% 58%	5026
	21st to end	Night	4 5% 2 4 3 3 4 3 5% 6% 60%	5467
April	1st to 10th	Night	5% 4 1 4 3 3 3 3 6% 7% 59%	2035
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 4 6% 57%	1977
	21st to end	Night	7% 5% 1 3 3 2 3 3 4 5% 63%	2000
May	1st to 10th	Night	10% 6% 2 6% 3 3 4 3 5% 5% 53%	4151
	11th to 20th	Night	6% 3 1 4 3 3 4 3 6% 8% 59%	4053
	21st to end	Night	6% 5% 2 5% 4 4 4 4 7% 9% 51%	4443
June	1st to 10th	Night	2 2 1 3 2 3 4 4 7% 10% 61%	1796
	11th to 20th	Night	2 2 1 2 3 3 4 3 7% 10% 64%	1710
	21st to end	Night	3 4 1 3 3 3 3 3 5% 8% 62%	1710
July	1st to 10th	Night	3 2 1 4 3 3 4 3 6% 8% 62%	2850
	11th to 20th	Night	1 1 2 1 1 2 3 4 7% 76%	2850
	21st to end	Night	3 3 1 4 3 3 3 3 6% 7% 63%	3270
August	1st to 10th	Night	1 1 1 2 2 3 3 3 4 7% 73%	3155
	11th to 20th	Night	3 2 1 3 2 3 3 3 6% 9% 66%	3113
	21st to end	Night	3 3 1 4 3 4 5% 4 7% 12% 54%	3487
September	1st to 10th	Night	7% 4 2 4 4 4 3 4 5% 7% 56%	2006
	11th to 20th	Night	7% 5% 1 5% 3 4 4 4 6% 7% 53%	2090
	21st to end	Night	8% 5% 1 4 3 3 3 3 4 8% 58%	2090
October	1st to 10th	Night	4 3 1 3 2 3 3 3 4 7% 66%	2090
	11th to 20th	Night	10% 4 2 3 2 2 3 2 4 5% 63%	2090
	21st to end	Night	8% 4 2 4 3 2 2 2 4 4 66%	2456
November	1st to 10th	Night	9% 5% 1 4 2 3 3 2 3 5% 62%	2535
	11th to 20th	Night	6% 4 2 4 3 3 2 3 5% 5% 63%	2600
	21st to end	Night	9% 6% 1 5% 4 3 3 3 5% 6% 56%	2600
December	1st to 10th	Night	16% 8% 3 5% 3 3 3 3 4 5% 48%	4250
	11th to 20th	Night	6% 6% 2 5% 4 3 4 3 5% 6% 56%	4816
	21st to end	Night	6% 7% 2 4 2 2 2 2 4 5% 63%	6490

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	26% 3 4 21% 27% 19%	4078
	11th to 20th	Day	20% 2 6% 21% 30% 20%	4374
	21st to end	Day	33% 3 5% 14% 27% 18%	4994
February	1st to 10th	Day	29% 3 6% 14% 24% 24%	2000
	11th to 20th	Day	31% 4 6% 21% 20% 18%	1959
	21st to end	Day	27% 4 5% 14% 28% 22%	1650
March	1st to 10th	Day	27% 3 4 13% 20% 32%	4500
	11th to 20th	Day	31% 4 4 8% 19% 33%	4935
	21st to end	Day	27% 5% 6% 15% 25% 22%	5464
April	1st to 10th	Day	25% 5% 7% 18% 23% 22%	2360
	11th to 20th	Day	30% 6% 7% 15% 21% 20%	2374
	21st to end	Day	27% 4 8% 20% 23% 17%	2400
May	1st to 10th	Day	32% 6% 7% 12% 22% 22%	5798
	11th to 20th	Day	31% 4 7% 13% 27% 18%	5866
	21st to end	Day	31% 7% 10% 23% 17% 12%	6447
June	1st to 10th	Day	19% 7% 12% 33% 23% 6%	2588
	11th to 20th	Day	23% 6% 11% 26% 26% 9%	2470
	21st to end	Day	27% 7% 12% 24% 22% 7%	2470
July	1st to 10th	Day	25% 7% 14% 36% 16% 1	4056
	11th to 20th	Day	17% 6% 16% 36% 22% 3	4051
	21st to end	Day	25% 7% 12% 28% 24% 4	4153
August	1st to 10th	Day	13% 4 11% 35% 33% 3	3772
	11th to 20th	Day	17% 5% 15% 42% 19% 2	3762
	21st to end	Day	27% 9% 17% 22% 22% 3	4179
September	1st to 10th	Day	36% 6% 10% 20% 19% 9%	2172
	11th to 20th	Day	36% 7% 11% 20% 20% 6%	2090
	21st to end	Day	29% 5% 11% 20% 21% 14%	2090
October	1st to 10th	Day	14% 3 6% 14% 24% 38%	3480
	11th to 20th	Day	27% 3 5% 16% 21% 28%	3458
	21st to end	Day	22% 2 3 21% 39% 13%	3459
November	1st to 10th	Day	28% 3 9% 22% 21% 16%	1763
	11th to 20th	Day	25% 3 9% 19% 23% 21%	1800
	21st to end	Day	30% 5% 5% 18% 27% 16%	1800
December	1st to 10th	Day	40% 3 5% 16% 24% 12%	2940
	11th to 20th	Day	35% 4 6% 13% 26% 15%	3389
	21st to end	Day	23% 2 3 19% 30% 23%	4488
January	1st to 10th	Night	26% 3 5% 19% 30% 17%	5888
	11th to 20th	Night	18% 2 4 20% 30% 27%	5647
	21st to end	Night	35% 4 5% 14% 23% 19%	5984
February	1st to 10th	Night	26% 4 7% 14% 26% 23%	2400
	11th to 20th	Night	32% 4 6% 17% 21% 20%	2338
	21st to end	Night	26% 4 6% 12% 26% 24%	1980
March	1st to 10th	Night	20% 5% 6% 16% 27% 27%	5374
	11th to 20th	Night	28% 5% 5% 11% 17% 34%	5026
	21st to end	Night	24% 5% 8% 16% 23% 23%	5467
April	1st to 10th	Night	23% 5% 11% 21% 17% 23%	2035
	11th to 20th	Night	27% 6% 10% 19% 19% 20%	1977
	21st to end	Night	24% 5% 10% 24% 22% 15%	2000
May	1st to 10th	Night	32% 7% 9% 17% 18% 18%	4177
	11th to 20th	Night	22% 6% 11% 18% 26% 18%	4054
	21st to end	Night	28% 7% 13% 24% 16% 12%	4452
June	1st to 10th	Night	16% 8% 18% 32% 22% 4	1796
	11th to 20th	Night	15% 6% 14% 31% 26% 8%	1710
	21st to end	Night	20% 6% 15% 27% 25% 8%	1710
July	1st to 10th	Night	20% 7% 18% 38% 16% 2	2805
	11th to 20th	Night	9% 4 14% 42% 25% 5%	2796
	21st to end	Night	19% 5% 15% 33% 26% 2	3166
August	1st to 10th	Night	12% 4 12% 30% 38% 5%	3144
	11th to 20th	Night	15% 6% 17% 43% 18% 2	3143
	21st to end	Night	22% 10% 20% 26% 20% 3	3487
September	1st to 10th	Night	26% 8% 13% 24% 20% 10%	2006
	11th to 20th	Night	28% 8% 15% 21% 22% 6%	2090
	21st to end	Night	24% 6% 13% 24% 18% 17%	2090
October	1st to 10th	Night	12% 3 7% 15% 23% 39%	3480
	11th to 20th	Night	24% 3 7% 15% 24% 28%	3460
	21st to end	Night	18% 3 4 26% 33% 16%	4043
November	1st to 10th	Night	26% 4 8% 19% 24% 18%	2535
	11th to 20th	Night	23% 4 8% 20% 23% 21%	2600
	21st to end	Night	29% 5% 7% 17% 25% 18%	2600
December	1st to 10th	Night	39% 3 5% 19% 19% 15%	4250
	11th to 20th	Night	31% 3 6% 17% 25% 18%	4817
	21st to end	Night	25% 3 4 19% 28% 20%	6490

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	10% 10% 41% 29% 7% 2	300
	11th to 20th	Day	13% 10% 35% 30% 9% 2	300
	21st to end	Day	11% 11% 38% 29% 10% 1	330
February	1st to 10th	Day	18% 10% 35% 23% 14%	300
	11th to 20th	Day	13% 10% 49% 23% 5%	300
	21st to end	Day	15% 10% 49% 22% 5%	249
March	1st to 10th	Day	13% 9% 46% 27% 4	300
	11th to 20th	Day	14% 16% 37% 23% 8% 1	300
	21st to end	Day	7% 13% 47% 24% 8%	330
April	1st to 10th	Day	8% 15% 43% 28% 6%	460
	11th to 20th	Day	10% 16% 39% 29% 5%	492
	21st to end	Day	9% 12% 43% 29% 6% 1	500
May	1st to 10th	Day	9% 9% 40% 33% 9%	653
	11th to 20th	Day	12% 7% 35% 32% 12% 2	725
	21st to end	Day	10% 4 33% 40% 12% 1	789
June	1st to 10th	Day	3 4 18% 48% 24% 3	726
	11th to 20th	Day	4 1 21% 48% 21% 4	680
	21st to end	Day	5% 2 11% 44% 31% 7%	680
July	1st to 10th	Day	5% 2 7% 36% 39% 11%	671
	11th to 20th	Day	2 3 41% 43% 11%	668
	21st to end	Day	3 3 32% 47% 15%	637
August	1st to 10th	Day	2 3 27% 50% 18%	487
	11th to 20th	Day	7% 6% 26% 44% 17%	477
	21st to end	Day	4 2 5% 26% 42% 21%	539
September	1st to 10th	Day	10% 5% 26% 41% 18%	382
	11th to 20th	Day	7% 6% 25% 43% 19%	300
	21st to end	Day	12% 2 6% 25% 37% 18%	300
October	1st to 10th	Day	3 2 13% 37% 36% 9%	300
	11th to 20th	Day	12% 2 18% 43% 22% 2	300
	21st to end	Day	13% 6% 29% 28% 19% 4	330
November	1st to 10th	Day	13% 8% 29% 35% 13% 1	300
	11th to 20th	Day	15% 9% 27% 28% 17% 5%	300
	21st to end	Day	12% 12% 37% 25% 10% 3	300
December	1st to 10th	Day	16% 7% 29% 33% 12% 3	300
	11th to 20th	Day	10% 10% 39% 28% 12% 2	300
	21st to end	Day	15% 9% 38% 29% 9%	330
January	1st to 10th	Night	10% 6% 41% 35% 7%	1000
	11th to 20th	Night	9% 9% 39% 36% 7%	890
	21st to end	Night	12% 9% 41% 31% 7%	880
February	1st to 10th	Night	11% 9% 45% 29% 6%	800
	11th to 20th	Night	14% 11% 46% 26% 4	784
	21st to end	Night	11% 12% 50% 25% 2	660
March	1st to 10th	Night	11% 12% 48% 25% 4	800
	11th to 20th	Night	11% 11% 47% 28% 3	620
	21st to end	Night	6% 14% 54% 24% 2	660
April	1st to 10th	Night	5% 10% 54% 27% 4	600
	11th to 20th	Night	9% 11% 53% 25% 3	593
	21st to end	Night	7% 10% 54% 25% 3	600
May	1st to 10th	Night	6% 8% 55% 28% 4	600
	11th to 20th	Night	9% 7% 40% 36% 7% 1	591
	21st to end	Night	7% 4 44% 35% 9% 1	650
June	1st to 10th	Night	2 2 30% 53% 11% 1	599
	11th to 20th	Night	2 1 36% 54% 8%	570
	21st to end	Night	5% 1 18% 55% 20% 1	570
July	1st to 10th	Night	6% 1 9% 54% 28% 1	555
	11th to 20th	Night	3 1 8% 59% 28% 1	552
	21st to end	Night	1 5% 61% 31% 1	624
August	1st to 10th	Night	2 4 53% 39% 2	567
	11th to 20th	Night	5% 1 6% 53% 32% 3	564
	21st to end	Night	4 2 8% 42% 40% 4	627
September	1st to 10th	Night	5% 1 8% 46% 35% 3	570
	11th to 20th	Night	8% 1 9% 47% 34% 2	570
	21st to end	Night	8% 2 15% 47% 27% 2	570
October	1st to 10th	Night	4 2 21% 52% 20%	570
	11th to 20th	Night	12% 4 26% 45% 12% 1	570
	21st to end	Night	9% 6% 30% 39% 15% 2	784
November	1st to 10th	Night	12% 4 30% 39% 14% 1	975
	11th to 20th	Night	7% 6% 35% 39% 12% 1	1000
	21st to end	Night	12% 7% 36% 33% 12% 1	1000
December	1st to 10th	Night	12% 6% 34% 39% 8% 1	1000
	11th to 20th	Night	12% 9% 38% 35% 6%	1000
	21st to end	Night	11% 6% 41% 34% 7% 1	1100

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