Maier Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maier Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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% 6% 2 6% 4 4 4 3 5% 7% 45%	105238
	Night	16% 6% 2 5% 3 3 3 3 4 6% 49%	104275
Transparency	Day	37% 5% 9% 21% 19% 10%	109069
	Night	35% 5% 10% 20% 19% 12%	108558
Seeing	Day	16% 8% 23% 29% 20% 4	15008
	Night	18% 7% 24% 35% 15% 1	25062

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	15% 7% 2 4 2 3 3 2 4 5% 51%	2937
	11th to 20th	Day	17% 6% 2 4 2 2 2 2 4 5% 55%	2940
	21st to end	Day	19% 8% 2 4 3 2 3 3 4 9% 43%	3441
February	1st to 10th	Day	20% 8% 2 5% 3 3 3 2 3 4 46%	1900
	11th to 20th	Day	19% 7% 2 4 4 3 4 3 4 5% 44%	1849
	21st to end	Day	19% 7% 1 4 2 3 2 2 4 5% 49%	1570
March	1st to 10th	Day	17% 8% 3 7% 4 4 3 2 5% 5% 43%	3367
	11th to 20th	Day	22% 10% 3 8% 5% 4 4 3 3 4 32%	3480
	21st to end	Day	19% 6% 2 5% 3 3 3 3 5% 6% 46%	3814
April	1st to 10th	Day	14% 7% 3 6% 5% 4 4 3 4 5% 44%	2090
	11th to 20th	Day	21% 7% 2 5% 4 3 3 4 5% 5% 42%	2089
	21st to end	Day	17% 8% 2 6% 5% 4 4 3 5% 5% 43%	2389
May	1st to 10th	Day	24% 9% 3 7% 4 4 4 3 5% 5% 31%	4082
	11th to 20th	Day	15% 6% 3 6% 4 4 4 4 5% 7% 42%	4082
	21st to end	Day	11% 6% 3 6% 5% 5% 5% 5% 6% 9% 38%	4477
June	1st to 10th	Day	6% 5% 2 5% 5% 6% 6% 4 7% 8% 46%	2470
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	2470
	21st to end	Day	7% 7% 2 7% 7% 6% 5% 5% 7% 8% 37%	2470
July	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 5% 5% 8% 46%	4120
	11th to 20th	Day	6% 5% 2 5% 4 5% 6% 5% 6% 11% 45%	4120
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 4 8% 10% 37%	4465
August	1st to 10th	Day	2 2 1 3 3 3 4 3 5% 9% 67%	3985
	11th to 20th	Day	4 2 1 4 3 4 4 4 8% 12% 56%	3726
	21st to end	Day	5% 4 2 6% 5% 5% 5% 4 7% 11% 46%	4030
September	1st to 10th	Day	9% 8% 3 7% 5% 6% 5% 4 6% 7% 41%	2090
	11th to 20th	Day	11% 6% 3 7% 5% 6% 5% 5% 7% 8% 39%	2090
	21st to end	Day	8% 5% 2 6% 4 4 4 4 7% 8% 48%	2090
October	1st to 10th	Day	7% 4 2 5% 4 4 4 4 6% 6% 55%	2090
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 4 5% 50%	1993
	21st to end	Day	12% 4 2 5% 3 3 3 3 4 5% 57%	2090
November	1st to 10th	Day	15% 8% 3 7% 4 4 3 3 4 6% 43%	1958
	11th to 20th	Day	13% 6% 2 5% 5% 4 4 3 5% 5% 49%	1855
	21st to end	Day	18% 6% 2 6% 4 4 4 2 4 5% 45%	1800
December	1st to 10th	Day	28% 8% 3 6% 3 3 2 2 3 5% 37%	2940
	11th to 20th	Day	20% 7% 2 6% 3 3 3 3 4 5% 44%	3391
	21st to end	Day	16% 5% 2 3 2 2 3 2 3 4 58%	4488
January	1st to 10th	Night	19% 5% 1 3 2 3 3 2 4 5% 51%	4238
	11th to 20th	Night	14% 4 1 3 2 2 2 1 3 4 65%	4250
	21st to end	Night	23% 6% 2 6% 3 3 3 2 4 6% 43%	4276
February	1st to 10th	Night	20% 6% 2 4 3 3 3 3 4 5% 48%	2280
	11th to 20th	Night	20% 8% 2 4 2 2 3 2 3 6% 48%	2218
	21st to end	Night	21% 6% 2 5% 4 2 2 3 5% 5% 45%	1884
March	1st to 10th	Night	20% 9% 2 6% 4 4 4 3 3 5% 40%	3487
	11th to 20th	Night	23% 11% 3 7% 4 4 3 3 4 5% 33%	3480
	21st to end	Night	20% 7% 2 5% 3 3 3 3 5% 5% 45%	3817
April	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 5% 8% 45%	2090
	11th to 20th	Night	21% 8% 2 5% 4 3 3 2 3 5% 45%	2036
	21st to end	Night	21% 7% 2 5% 4 2 3 3 4 4 45%	1790
May	1st to 10th	Night	27% 8% 2 5% 3 3 3 3 4 5% 36%	2823
	11th to 20th	Night	15% 6% 2 5% 4 4 3 3 6% 5% 49%	2823
	21st to end	Night	15% 6% 2 5% 3 4 4 3 5% 9% 43%	3090
June	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 9% 59%	1710
	11th to 20th	Night	5% 5% 1 4 3 3 4 4 5% 10% 55%	1710
	21st to end	Night	8% 7% 2 4 4 4 4 4 7% 9% 49%	1710
July	1st to 10th	Night	6% 4 2 4 4 3 4 4 6% 10% 52%	2850
	11th to 20th	Night	5% 4 1 5% 4 4 5% 5% 7% 10% 49%	2850
	21st to end	Night	14% 7% 2 5% 4 4 4 4 6% 9% 41%	3098
August	1st to 10th	Night	2 1 1 2 2 2 3 2 4 8% 73%	2950
	11th to 20th	Night	3 3 1 3 3 3 4 4 7% 12% 57%	3113
	21st to end	Night	6% 4 1 5% 3 3 4 4 6% 10% 54%	3632
September	1st to 10th	Night	9% 6% 2 5% 4 4 5% 3 5% 8% 48%	2090
	11th to 20th	Night	11% 6% 3 7% 4 3 5% 3 6% 8% 45%	2090
	21st to end	Night	8% 5% 2 6% 3 3 4 4 6% 8% 50%	2090
October	1st to 10th	Night	7% 4 1 4 3 3 3 4 4 7% 59%	2090
	11th to 20th	Night	15% 4 1 5% 3 3 3 2 4 5% 55%	2166
	21st to end	Night	15% 4 2 4 2 2 2 2 3 3 61%	2508
November	1st to 10th	Night	15% 7% 2 6% 3 3 3 2 3 5% 51%	2340
	11th to 20th	Night	12% 6% 2 4 3 3 4 3 4 6% 54%	2540
	21st to end	Night	19% 6% 2 4 3 3 3 3 4 6% 47%	2600
December	1st to 10th	Night	27% 8% 3 6% 4 3 3 2 3 5% 36%	4250
	11th to 20th	Night	24% 8% 2 5% 2 2 2 2 3 4 47%	4816
	21st to end	Night	20% 5% 2 3 2 2 2 2 3 4 56%	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	36% 2 3 17% 25% 16%	2938
	11th to 20th	Day	34% 2 5% 15% 25% 19%	2940
	21st to end	Day	41% 3 5% 12% 29% 10%	3441
February	1st to 10th	Day	43% 3 4 13% 21% 16%	1900
	11th to 20th	Day	42% 4 6% 17% 18% 13%	1859
	21st to end	Day	39% 4 6% 17% 19% 16%	1570
March	1st to 10th	Day	44% 5% 6% 16% 20% 10%	3367
	11th to 20th	Day	55% 5% 5% 9% 16% 9%	3480
	21st to end	Day	38% 4 9% 17% 19% 13%	3814
April	1st to 10th	Day	43% 5% 7% 16% 17% 12%	2090
	11th to 20th	Day	44% 5% 6% 16% 17% 12%	2089
	21st to end	Day	44% 4 6% 19% 18% 10%	2389
May	1st to 10th	Day	53% 6% 8% 14% 13% 6%	4120
	11th to 20th	Day	40% 7% 8% 19% 19% 7%	4086
	21st to end	Day	39% 7% 10% 31% 12% 1	4489
June	1st to 10th	Day	32% 8% 12% 25% 20% 3	2470
	11th to 20th	Day	34% 7% 11% 25% 18% 5%	2470
	21st to end	Day	41% 8% 10% 24% 14% 3	2470
July	1st to 10th	Day	34% 6% 15% 37% 7% 1	4056
	11th to 20th	Day	31% 7% 17% 29% 15% 1	4051
	21st to end	Day	39% 8% 16% 28% 9%	4325
August	1st to 10th	Day	15% 5% 11% 44% 24% 1	3971
	11th to 20th	Day	20% 7% 22% 36% 12% 2	3762
	21st to end	Day	31% 10% 16% 24% 18% 2	4029
September	1st to 10th	Day	42% 6% 9% 19% 16% 8%	2090
	11th to 20th	Day	40% 7% 10% 19% 18% 5%	2090
	21st to end	Day	33% 6% 10% 20% 18% 13%	2090
October	1st to 10th	Day	18% 4 6% 11% 25% 36%	3480
	11th to 20th	Day	27% 4 7% 18% 23% 21%	3285
	21st to end	Day	29% 3 5% 17% 32% 14%	3428
November	1st to 10th	Day	43% 3 6% 18% 17% 12%	1958
	11th to 20th	Day	37% 3 7% 16% 20% 15%	1855
	21st to end	Day	44% 3 5% 15% 20% 13%	1800
December	1st to 10th	Day	52% 2 5% 18% 13% 10%	2940
	11th to 20th	Day	42% 5% 7% 12% 20% 13%	3389
	21st to end	Day	32% 3 3 17% 27% 17%	4488
January	1st to 10th	Night	35% 3 4 16% 21% 21%	4238
	11th to 20th	Night	27% 2 4 17% 28% 22%	4250
	21st to end	Night	44% 2 4 12% 25% 12%	4276
February	1st to 10th	Night	40% 3 6% 13% 21% 18%	2280
	11th to 20th	Night	41% 3 5% 16% 19% 16%	2218
	21st to end	Night	41% 3 6% 16% 18% 16%	1884
March	1st to 10th	Night	46% 5% 6% 16% 18% 10%	3487
	11th to 20th	Night	53% 6% 7% 11% 12% 11%	3480
	21st to end	Night	41% 4 9% 15% 20% 11%	3817
April	1st to 10th	Night	38% 4 9% 18% 16% 14%	2090
	11th to 20th	Night	43% 3 8% 14% 17% 16%	2036
	21st to end	Night	43% 4 8% 19% 16% 10%	1790
May	1st to 10th	Night	50% 5% 8% 17% 13% 7%	2850
	11th to 20th	Night	35% 6% 10% 22% 20% 7%	2824
	21st to end	Night	38% 6% 13% 30% 12% 2	3099
June	1st to 10th	Night	24% 5% 16% 31% 21% 3	1710
	11th to 20th	Night	25% 6% 14% 29% 21% 5%	1710
	21st to end	Night	31% 6% 17% 28% 15% 3	1710
July	1st to 10th	Night	25% 8% 24% 36% 6% 1	2805
	11th to 20th	Night	27% 9% 19% 30% 14% 1	2796
	21st to end	Night	39% 8% 22% 25% 7% 1	2999
August	1st to 10th	Night	11% 5% 16% 47% 20%	2940
	11th to 20th	Night	20% 7% 31% 33% 8% 1	3143
	21st to end	Night	25% 11% 21% 25% 15% 2	3632
September	1st to 10th	Night	35% 6% 15% 20% 16% 8%	2090
	11th to 20th	Night	37% 8% 14% 22% 15% 5%	2090
	21st to end	Night	30% 6% 13% 20% 17% 12%	2090
October	1st to 10th	Night	16% 3 7% 16% 21% 37%	3480
	11th to 20th	Night	23% 3 9% 16% 30% 18%	3587
	21st to end	Night	28% 2 6% 18% 32% 16%	4120
November	1st to 10th	Night	37% 4 7% 18% 20% 14%	2340
	11th to 20th	Night	33% 4 8% 18% 21% 17%	2540
	21st to end	Night	39% 4 7% 17% 19% 14%	2600
December	1st to 10th	Night	53% 2 5% 15% 13% 11%	4250
	11th to 20th	Night	44% 3 5% 10% 20% 18%	4817
	21st to end	Night	35% 3 3 13% 28% 18%	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	25% 16% 36% 18% 6%	300
	11th to 20th	Day	27% 18% 27% 22% 6% 1	300
	21st to end	Day	21% 16% 38% 19% 6% 1	300
February	1st to 10th	Day	33% 16% 26% 19% 6%	270
	11th to 20th	Day	30% 20% 32% 15% 3	270
	21st to end	Day	28% 18% 42% 12% 1	225
March	1st to 10th	Day	25% 18% 40% 15% 1	270
	11th to 20th	Day	21% 17% 43% 15% 5%	270
	21st to end	Day	22% 17% 39% 17% 4 1	297
April	1st to 10th	Day	23% 17% 42% 16% 3	270
	11th to 20th	Day	25% 16% 35% 20% 3	287
	21st to end	Day	21% 12% 40% 22% 5%	569
May	1st to 10th	Day	22% 13% 33% 26% 6%	653
	11th to 20th	Day	18% 10% 31% 30% 9% 2	675
	21st to end	Day	17% 7% 29% 33% 12% 1	734
June	1st to 10th	Day	9% 3 16% 44% 25% 3	680
	11th to 20th	Day	9% 1 17% 49% 21% 2	680
	21st to end	Day	11% 2 14% 37% 29% 6%	680
July	1st to 10th	Day	10% 1 12% 32% 35% 9%	671
	11th to 20th	Day	7% 1 7% 35% 44% 6%	668
	21st to end	Day	6% 1 7% 35% 42% 9%	739
August	1st to 10th	Day	3 1 7% 32% 45% 12%	609
	11th to 20th	Day	7% 6% 40% 37% 9%	477
	21st to end	Day	5% 2 7% 31% 40% 15%	454
September	1st to 10th	Day	13% 13% 24% 40% 10%	300
	11th to 20th	Day	7% 5% 34% 42% 11%	300
	21st to end	Day	9% 1 11% 32% 34% 13%	300
October	1st to 10th	Day	6% 3 16% 38% 31% 5%	300
	11th to 20th	Day	11% 4 20% 44% 18% 3	300
	21st to end	Day	22% 11% 24% 28% 11% 4	330
November	1st to 10th	Day	20% 8% 29% 28% 12% 4	300
	11th to 20th	Day	21% 11% 30% 24% 12% 2	300
	21st to end	Day	26% 16% 33% 16% 8% 2	300
December	1st to 10th	Day	21% 12% 33% 24% 7% 4	300
	11th to 20th	Day	26% 13% 31% 24% 6% 1	300
	21st to end	Day	22% 11% 40% 19% 7% 1	330
January	1st to 10th	Night	22% 9% 26% 34% 10% 1	1000
	11th to 20th	Night	23% 10% 28% 30% 8%	1000
	21st to end	Night	24% 10% 26% 34% 6%	885
February	1st to 10th	Night	26% 11% 28% 28% 7%	760
	11th to 20th	Night	28% 12% 30% 26% 4	744
	21st to end	Night	27% 13% 36% 23% 2	628
March	1st to 10th	Night	24% 11% 36% 25% 3	616
	11th to 20th	Night	24% 10% 32% 29% 5%	570
	21st to end	Night	21% 11% 40% 25% 3	627
April	1st to 10th	Night	17% 13% 41% 26% 4	570
	11th to 20th	Night	24% 11% 36% 26% 3	563
	21st to end	Night	24% 8% 35% 26% 6% 1	570
May	1st to 10th	Night	21% 8% 42% 25% 4	570
	11th to 20th	Night	17% 7% 35% 32% 9%	561
	21st to end	Night	18% 8% 30% 34% 10%	617
June	1st to 10th	Night	8% 2 24% 43% 20% 2	570
	11th to 20th	Night	7% 3 33% 45% 11% 1	570
	21st to end	Night	10% 2 20% 41% 24% 3	570
July	1st to 10th	Night	11% 1 15% 43% 26% 3	555
	11th to 20th	Night	5% 1 11% 53% 28% 3	552
	21st to end	Night	8% 2 9% 50% 28% 3	624
August	1st to 10th	Night	2 1 10% 50% 34% 4	567
	11th to 20th	Night	6% 1 10% 51% 30% 4	564
	21st to end	Night	8% 1 6% 41% 39% 5%	627
September	1st to 10th	Night	11% 1 9% 39% 34% 5%	570
	11th to 20th	Night	13% 1 9% 38% 35% 4	570
	21st to end	Night	9% 2 14% 36% 35% 5%	570
October	1st to 10th	Night	8% 2 13% 46% 27% 5%	570
	11th to 20th	Night	14% 4 20% 40% 20% 2	646
	21st to end	Night	18% 7% 21% 32% 20% 2	836
November	1st to 10th	Night	16% 6% 21% 37% 19% 2	780
	11th to 20th	Night	16% 7% 22% 37% 16% 1	940
	21st to end	Night	22% 10% 25% 30% 12% 1	1000
December	1st to 10th	Night	23% 7% 24% 33% 12% 1	1000
	11th to 20th	Night	27% 9% 24% 32% 9%	1000
	21st to end	Night	22% 8% 26% 34% 9%	1100

Page generated at 2025-01-19 02:06:49. Version ac07

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