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 2024-11-02.

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	7% 4 2 5% 3 3 4 3 5% 7% 57%	100822
	Night	6% 5% 2 4 3 3 3 3 5% 7% 60%	98286
Transparency	Day	27% 5% 9% 21% 23% 13%	100638
	Night	24% 5% 10% 22% 23% 15%	98141
Seeing	Day	8% 6% 24% 33% 23% 6%	14868
	Night	8% 6% 33% 39% 13% 1	24804

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 2 2 3 5% 63%	2847
	11th to 20th	Day	6% 4 2 3 2 2 2 2 4 6% 67%	3046
	21st to end	Day	8% 6% 2 6% 4 3 4 2 5% 6% 55%	3487
February	1st to 10th	Day	8% 6% 2 5% 3 3 3 2 5% 6% 56%	1900
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 3 6% 55%	1849
	21st to end	Day	10% 4 1 3 3 3 3 4 5% 5% 59%	1570
March	1st to 10th	Day	8% 6% 2 6% 5% 4 4 3 4 6% 52%	3130
	11th to 20th	Day	17% 8% 3 6% 4 3 4 3 4 5% 43%	3448
	21st to end	Day	5% 5% 2 6% 3 4 4 3 6% 6% 55%	3814
April	1st to 10th	Day	6% 4 2 5% 4 3 3 3 6% 6% 59%	2242
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 4 5% 55%	2254
	21st to end	Day	8% 6% 2 4 3 3 2 2 4 5% 61%	2280
May	1st to 10th	Day	10% 7% 2 5% 3 3 3 3 5% 6% 52%	4009
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 4 6% 53%	4082
	21st to end	Day	6% 4 2 5% 4 4 4 3 5% 7% 55%	4477
June	1st to 10th	Day	3 4 1 3 3 3 4 3 6% 9% 61%	2470
	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 1 4 3 2 2 2 3 4 64%	2118
November	1st to 10th	Day	9% 5% 1 5% 2 2 3 3 4 7% 58%	1682
	11th to 20th	Day	6% 4 2 5% 3 4 3 3 5% 5% 60%	1710
	21st to end	Day	10% 6% 2 5% 3 3 3 3 4 6% 55%	1710
December	1st to 10th	Day	11% 5% 2 4 3 3 3 3 4 6% 55%	1710
	11th to 20th	Day	7% 6% 3 5% 3 4 4 3 6% 5% 54%	2161
	21st to end	Day	9% 5% 1 4 2 2 2 2 3 5% 64%	3135
January	1st to 10th	Night	6% 5% 2 5% 3 3 3 2 4 5% 62%	4108
	11th to 20th	Night	6% 5% 1 3 2 2 3 2 3 5% 68%	3951
	21st to end	Night	10% 7% 2 5% 3 3 3 2 4 7% 55%	4180
February	1st to 10th	Night	8% 5% 2 5% 3 2 3 3 4 7% 58%	2280
	11th to 20th	Night	11% 6% 2 5% 3 4 3 2 5% 5% 54%	2218
	21st to end	Night	8% 5% 2 4 3 3 2 3 5% 6% 58%	1884
March	1st to 10th	Night	6% 5% 2 4 3 3 5% 3 5% 7% 57%	3734
	11th to 20th	Night	13% 8% 3 5% 3 4 4 3 4 6% 47%	3512
	21st to end	Night	4 6% 2 5% 3 4 4 4 5% 6% 56%	3817
April	1st to 10th	Night	4 4 1 4 3 3 3 3 6% 8% 60%	1933
	11th to 20th	Night	8% 6% 2 5% 3 4 3 3 5% 7% 56%	1877
	21st to end	Night	6% 5% 1 3 3 2 3 2 4 5% 64%	1900
May	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 5% 5% 52%	2893
	11th to 20th	Night	8% 4 2 4 2 3 4 3 5% 7% 59%	2823
	21st to end	Night	5% 4 2 4 3 3 4 3 6% 8% 57%	3090
June	1st to 10th	Night	2 2 1 3 2 2 4 4 7% 10% 62%	1710
	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 4 5% 62%	2431
	11th to 20th	Night	6% 4 2 4 3 3 3 3 5% 5% 63%	2470
	21st to end	Night	9% 6% 1 5% 3 3 3 3 5% 6% 55%	2470
December	1st to 10th	Night	8% 5% 2 4 3 3 4 3 4 6% 58%	2470
	11th to 20th	Night	7% 6% 2 6% 4 4 4 3 4 5% 54%	3036
	21st to end	Night	8% 7% 2 4 3 3 2 2 4 5% 60%	4532

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	24% 4 4 15% 28% 25%	2848
	11th to 20th	Day	20% 3 7% 17% 33% 19%	3046
	21st to end	Day	30% 5% 7% 17% 29% 12%	3487
February	1st to 10th	Day	29% 3 7% 15% 24% 22%	1900
	11th to 20th	Day	31% 4 6% 20% 21% 19%	1859
	21st to end	Day	26% 4 5% 14% 29% 22%	1570
March	1st to 10th	Day	33% 4 6% 11% 23% 23%	3130
	11th to 20th	Day	43% 6% 6% 12% 19% 15%	3448
	21st to end	Day	26% 6% 8% 15% 22% 22%	3814
April	1st to 10th	Day	25% 5% 7% 18% 23% 22%	2242
	11th to 20th	Day	30% 6% 8% 15% 21% 20%	2254
	21st to end	Day	27% 4 8% 20% 24% 17%	2280
May	1st to 10th	Day	32% 6% 8% 12% 19% 23%	4046
	11th to 20th	Day	33% 5% 8% 18% 24% 14%	4086
	21st to end	Day	27% 8% 12% 21% 17% 16%	4489
June	1st to 10th	Day	19% 7% 12% 32% 24% 6%	2470
	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	24% 6% 9% 23% 23% 14%	2090
	11th to 20th	Day	27% 4 7% 16% 25% 21%	2090
	21st to end	Day	26% 3 4 16% 32% 19%	2118
November	1st to 10th	Day	28% 3 9% 23% 21% 15%	1682
	11th to 20th	Day	26% 3 10% 18% 24% 19%	1710
	21st to end	Day	31% 5% 5% 17% 27% 16%	1710
December	1st to 10th	Day	31% 4 7% 18% 26% 13%	1710
	11th to 20th	Day	30% 4 8% 15% 23% 19%	2159
	21st to end	Day	25% 3 4 18% 28% 23%	3135
January	1st to 10th	Night	24% 4 5% 15% 29% 23%	4108
	11th to 20th	Night	21% 3 4 20% 27% 25%	3951
	21st to end	Night	30% 5% 7% 17% 27% 15%	4180
February	1st to 10th	Night	27% 4 8% 14% 26% 21%	2280
	11th to 20th	Night	32% 4 6% 15% 22% 21%	2218
	21st to end	Night	26% 5% 7% 13% 26% 24%	1884
March	1st to 10th	Night	24% 6% 8% 14% 29% 19%	3734
	11th to 20th	Night	37% 7% 7% 15% 20% 15%	3512
	21st to end	Night	26% 7% 9% 19% 18% 22%	3817
April	1st to 10th	Night	23% 5% 11% 22% 17% 23%	1933
	11th to 20th	Night	27% 6% 10% 18% 18% 20%	1877
	21st to end	Night	23% 5% 9% 24% 23% 15%	1900
May	1st to 10th	Night	31% 8% 9% 15% 20% 17%	2921
	11th to 20th	Night	24% 7% 11% 22% 21% 15%	2824
	21st to end	Night	24% 8% 13% 25% 16% 15%	3099
June	1st to 10th	Night	15% 8% 18% 32% 23% 4	1710
	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	19% 5% 11% 25% 23% 17%	2090
	11th to 20th	Night	26% 3 9% 17% 25% 21%	2090
	21st to end	Night	23% 4 6% 17% 28% 22%	2456
November	1st to 10th	Night	26% 4 8% 20% 25% 18%	2431
	11th to 20th	Night	24% 4 8% 21% 24% 20%	2470
	21st to end	Night	30% 5% 7% 16% 25% 18%	2470
December	1st to 10th	Night	27% 4 7% 21% 24% 16%	2470
	11th to 20th	Night	33% 4 6% 16% 22% 20%	3037
	21st to end	Night	27% 4 5% 15% 28% 21%	4532

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% 30% 7% 2	270
	11th to 20th	Day	14% 11% 33% 30% 10% 2	270
	21st to end	Day	9% 11% 38% 31% 10% 1	297
February	1st to 10th	Day	17% 11% 38% 21% 12%	270
	11th to 20th	Day	14% 10% 47% 23% 6%	270
	21st to end	Day	16% 10% 52% 20% 3	225
March	1st to 10th	Day	13% 8% 48% 27% 4	270
	11th to 20th	Day	15% 14% 37% 23% 9% 1	270
	21st to end	Day	8% 14% 47% 23% 8%	297
April	1st to 10th	Day	8% 14% 45% 28% 5%	422
	11th to 20th	Day	10% 16% 40% 28% 5%	452
	21st to end	Day	9% 12% 41% 30% 6% 1	460
May	1st to 10th	Day	9% 9% 40% 33% 9%	605
	11th to 20th	Day	13% 7% 34% 32% 13% 2	675
	21st to end	Day	10% 4 33% 40% 12% 1	734
June	1st to 10th	Day	3 4 18% 48% 25% 3	680
	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	14% 7% 27% 37% 14% 1	273
	11th to 20th	Day	15% 9% 26% 29% 17% 4	270
	21st to end	Day	13% 14% 36% 24% 9% 3	270
December	1st to 10th	Day	15% 6% 29% 34% 13% 3	270
	11th to 20th	Day	10% 11% 40% 27% 10% 1	270
	21st to end	Day	15% 9% 39% 30% 8%	297
January	1st to 10th	Night	11% 6% 41% 35% 7%	950
	11th to 20th	Night	10% 9% 38% 37% 7%	846
	21st to end	Night	12% 8% 41% 31% 8%	836
February	1st to 10th	Night	10% 10% 45% 29% 6%	760
	11th to 20th	Night	14% 10% 46% 26% 4	744
	21st to end	Night	11% 13% 50% 25% 2	628
March	1st to 10th	Night	12% 12% 49% 24% 4	760
	11th to 20th	Night	12% 10% 47% 28% 3	589
	21st to end	Night	6% 14% 54% 23% 2	627
April	1st to 10th	Night	5% 9% 55% 28% 4	570
	11th to 20th	Night	9% 10% 53% 25% 3	563
	21st to end	Night	7% 9% 54% 26% 3	570
May	1st to 10th	Night	6% 8% 55% 27% 4	570
	11th to 20th	Night	9% 7% 39% 35% 8% 1	561
	21st to end	Night	7% 4 43% 36% 9% 1	617
June	1st to 10th	Night	2 2 29% 54% 12% 1	570
	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	11% 3 31% 39% 15% 1	935
	11th to 20th	Night	7% 6% 35% 39% 13% 1	950
	21st to end	Night	12% 7% 36% 33% 11% 1	950
December	1st to 10th	Night	11% 6% 35% 39% 9% 1	950
	11th to 20th	Night	12% 9% 38% 35% 6%	950
	21st to end	Night	11% 6% 41% 35% 7% 1	1045

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