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 2024-01-22.

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 5% 5% 3 4 4 5% 7% 45%	74949
	Night	14% 5% 2 4 4 2 3 4 4 7% 50%	75016
Transparency	Day	38% 5% 9% 20% 18% 9%	74674
	Night	35% 5% 10% 20% 18% 12%	74811
Seeing	Day	15% 7% 23% 30% 21% 4	13676
	Night	17% 6% 24% 35% 15% 1	23759

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	16% 5% 2 4 3 2 3 3 4 6% 51%	1707
	11th to 20th	Day	19% 6% 3 5% 3 2 3 3 3 5% 48%	1710
	21st to end	Day	16% 6% 2 4 4 2 3 4 3 6% 50%	1962
February	1st to 10th	Day	20% 8% 2 5% 4 2 3 3 3 5% 47%	1800
	11th to 20th	Day	20% 7% 2 4 4 2 4 4 4 6% 43%	1749
	21st to end	Day	20% 7% 1 4 3 2 3 3 4 6% 49%	1480
March	1st to 10th	Day	21% 7% 2 5% 5% 2 3 3 5% 5% 41%	1934
	11th to 20th	Day	17% 6% 2 5% 5% 2 4 4 4 6% 45%	1980
	21st to end	Day	19% 6% 2 4 4 2 3 3 5% 6% 46%	2178
April	1st to 10th	Day	15% 6% 4 5% 6% 2 5% 4 4 5% 44%	1980
	11th to 20th	Day	21% 6% 3 5% 4 2 3 4 4 5% 43%	1977
	21st to end	Day	17% 7% 2 5% 5% 3 4 3 4 5% 44%	2263
May	1st to 10th	Day	17% 6% 3 6% 5% 3 5% 4 5% 5% 39%	2340
	11th to 20th	Day	15% 7% 3 6% 6% 3 5% 4 5% 7% 37%	2302
	21st to end	Day	16% 7% 4 5% 6% 4 6% 6% 6% 8% 34%	2531
June	1st to 10th	Day	5% 5% 2 4 6% 4 6% 6% 7% 8% 46%	2340
	11th to 20th	Day	7% 5% 3 5% 6% 4 6% 5% 7% 9% 44%	2340
	21st to end	Day	8% 6% 4 6% 8% 5% 6% 7% 7% 8% 37%	2340
July	1st to 10th	Day	12% 6% 3 6% 6% 4 6% 7% 5% 9% 37%	2340
	11th to 20th	Day	5% 4 2 4 5% 3 6% 6% 6% 10% 49%	2340
	21st to end	Day	6% 3 2 4 5% 3 5% 5% 7% 12% 48%	2546
August	1st to 10th	Day	2 2 1 3 4 3 4 4 5% 10% 60%	2265
	11th to 20th	Day	6% 4 2 4 5% 3 5% 5% 7% 10% 50%	2123
	21st to end	Day	6% 4 3 6% 7% 4 6% 5% 6% 10% 42%	2296
September	1st to 10th	Day	9% 7% 3 6% 6% 5% 6% 5% 5% 7% 41%	1980
	11th to 20th	Day	11% 5% 3 6% 6% 5% 6% 6% 7% 8% 38%	1980
	21st to end	Day	8% 5% 2 5% 5% 3 4 5% 7% 8% 47%	1980
October	1st to 10th	Day	8% 4 2 4 5% 3 5% 4 6% 6% 53%	1980
	11th to 20th	Day	14% 5% 2 4 5% 3 4 4 4 5% 49%	1889
	21st to end	Day	12% 4 2 4 3 2 3 3 4 5% 57%	1980
November	1st to 10th	Day	14% 8% 4 6% 5% 3 4 3 4 6% 43%	1858
	11th to 20th	Day	14% 6% 2 5% 5% 3 4 4 4 5% 48%	1763
	21st to end	Day	19% 6% 2 5% 5% 3 4 3 4 5% 44%	1710
December	1st to 10th	Day	17% 6% 3 5% 4 3 4 3 4 6% 46%	1710
	11th to 20th	Day	19% 7% 2 5% 4 3 4 4 5% 5% 44%	2161
	21st to end	Day	17% 6% 2 3 3 2 3 3 3 5% 54%	3135
January	1st to 10th	Night	18% 4 2 3 3 2 4 3 4 5% 52%	2458
	11th to 20th	Night	18% 6% 2 4 4 2 3 3 3 5% 51%	2470
	21st to end	Night	20% 5% 2 4 4 3 4 3 4 5% 48%	2442
February	1st to 10th	Night	19% 6% 2 4 3 2 3 3 4 5% 48%	2160
	11th to 20th	Night	20% 7% 2 4 3 2 2 3 3 6% 48%	2098
	21st to end	Night	22% 5% 2 4 4 1 3 4 4 6% 45%	1776
March	1st to 10th	Night	19% 6% 2 5% 4 2 4 3 4 5% 44%	2024
	11th to 20th	Night	19% 7% 3 5% 4 2 3 3 4 5% 45%	1980
	21st to end	Night	18% 7% 2 4 3 2 3 3 5% 6% 48%	2178
April	1st to 10th	Night	15% 5% 3 5% 4 3 4 3 5% 8% 45%	1980
	11th to 20th	Night	20% 7% 3 4 4 2 3 2 3 5% 46%	1928
	21st to end	Night	20% 5% 2 5% 4 2 3 4 4 4 46%	1696
May	1st to 10th	Night	15% 7% 3 4 5% 3 4 4 4 7% 45%	1620
	11th to 20th	Night	14% 6% 3 4 5% 3 4 3 6% 7% 45%	1593
	21st to end	Night	15% 6% 3 5% 3 3 4 4 5% 11% 42%	1745
June	1st to 10th	Night	6% 4 1 4 3 3 3 4 4 9% 60%	1620
	11th to 20th	Night	5% 4 2 3 4 3 4 5% 5% 10% 57%	1620
	21st to end	Night	8% 6% 2 4 4 3 4 5% 6% 9% 48%	1620
July	1st to 10th	Night	10% 5% 3 4 4 3 4 6% 6% 10% 46%	1620
	11th to 20th	Night	3 2 1 4 4 2 4 5% 6% 11% 58%	1620
	21st to end	Night	6% 3 2 2 4 2 4 5% 6% 11% 57%	1772
August	1st to 10th	Night	2 2 1 2 3 2 3 4 4 9% 68%	1669
	11th to 20th	Night	5% 3 2 3 5% 2 5% 4 7% 12% 51%	1778
	21st to end	Night	7% 3 2 4 5% 3 4 5% 7% 10% 48%	2060
September	1st to 10th	Night	9% 6% 3 4 5% 2 5% 5% 5% 8% 48%	1980
	11th to 20th	Night	11% 6% 3 6% 5% 2 5% 5% 6% 8% 44%	1980
	21st to end	Night	9% 5% 2 5% 4 2 4 5% 6% 9% 50%	1980
October	1st to 10th	Night	7% 4 2 3 4 2 4 5% 4 7% 58%	1980
	11th to 20th	Night	15% 4 2 4 3 3 3 3 4 5% 53%	2052
	21st to end	Night	15% 4 2 4 3 2 2 2 3 4 61%	2376
November	1st to 10th	Night	13% 7% 2 5% 4 2 3 3 3 5% 53%	2220
	11th to 20th	Night	13% 6% 2 3 3 2 4 4 4 6% 53%	2413
	21st to end	Night	20% 6% 2 4 3 2 3 3 4 6% 46%	2470
December	1st to 10th	Night	16% 6% 2 4 3 2 3 4 4 6% 50%	2470
	11th to 20th	Night	19% 7% 2 5% 4 2 3 3 3 5% 46%	3036
	21st to end	Night	20% 5% 2 3 2 2 2 3 3 5% 52%	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	37% 3 4 18% 22% 16%	1708
	11th to 20th	Day	42% 3 5% 15% 19% 17%	1710
	21st to end	Day	37% 3 6% 14% 25% 16%	1962
February	1st to 10th	Day	42% 3 5% 13% 21% 16%	1800
	11th to 20th	Day	43% 4 6% 17% 18% 13%	1759
	21st to end	Day	40% 3 6% 16% 19% 16%	1480
March	1st to 10th	Day	46% 4 8% 14% 17% 12%	1934
	11th to 20th	Day	41% 4 7% 14% 18% 16%	1980
	21st to end	Day	40% 4 9% 16% 18% 13%	2178
April	1st to 10th	Day	43% 5% 7% 17% 18% 11%	1980
	11th to 20th	Day	44% 4 6% 16% 18% 13%	1977
	21st to end	Day	43% 4 5% 19% 18% 11%	2263
May	1st to 10th	Day	45% 5% 8% 16% 18% 7%	2340
	11th to 20th	Day	46% 5% 8% 19% 18% 5%	2306
	21st to end	Day	48% 7% 9% 20% 16% 1	2531
June	1st to 10th	Day	32% 8% 12% 25% 20% 3	2340
	11th to 20th	Day	34% 7% 11% 26% 18% 5%	2340
	21st to end	Day	42% 8% 10% 23% 13% 3	2340
July	1st to 10th	Day	43% 8% 13% 24% 10% 2	2276
	11th to 20th	Day	29% 7% 17% 27% 18% 2	2271
	21st to end	Day	26% 7% 19% 34% 13% 1	2405
August	1st to 10th	Day	20% 6% 16% 39% 19% 1	2251
	11th to 20th	Day	29% 8% 16% 30% 13% 4	2123
	21st to end	Day	36% 8% 15% 25% 13% 3	2296
September	1st to 10th	Day	42% 6% 9% 20% 16% 7%	1980
	11th to 20th	Day	41% 7% 11% 19% 17% 4	1980
	21st to end	Day	34% 6% 10% 20% 18% 11%	1980
October	1st to 10th	Day	30% 6% 11% 19% 25% 9%	1980
	11th to 20th	Day	37% 5% 8% 16% 19% 16%	1889
	21st to end	Day	31% 3 5% 15% 25% 21%	1980
November	1st to 10th	Day	43% 3 6% 19% 17% 11%	1858
	11th to 20th	Day	39% 3 8% 16% 21% 14%	1763
	21st to end	Day	45% 3 5% 14% 20% 13%	1710
December	1st to 10th	Day	40% 3 8% 20% 19% 10%	1710
	11th to 20th	Day	43% 5% 6% 10% 22% 15%	2159
	21st to end	Day	35% 3 4 16% 27% 14%	3135
January	1st to 10th	Night	35% 3 6% 16% 22% 19%	2458
	11th to 20th	Night	39% 2 5% 17% 21% 17%	2470
	21st to end	Night	41% 2 4 14% 20% 19%	2442
February	1st to 10th	Night	40% 3 6% 13% 21% 18%	2160
	11th to 20th	Night	41% 3 5% 16% 19% 16%	2098
	21st to end	Night	42% 3 6% 16% 17% 16%	1776
March	1st to 10th	Night	43% 4 8% 16% 18% 11%	2024
	11th to 20th	Night	43% 4 8% 13% 15% 17%	1980
	21st to end	Night	38% 3 11% 15% 18% 14%	2178
April	1st to 10th	Night	38% 4 9% 19% 16% 13%	1980
	11th to 20th	Night	42% 3 8% 14% 17% 16%	1928
	21st to end	Night	42% 4 8% 19% 16% 11%	1696
May	1st to 10th	Night	39% 5% 10% 20% 17% 10%	1620
	11th to 20th	Night	38% 5% 10% 25% 17% 5%	1594
	21st to end	Night	38% 6% 14% 26% 14% 1	1746
June	1st to 10th	Night	24% 5% 16% 30% 22% 3	1620
	11th to 20th	Night	25% 6% 14% 31% 20% 5%	1620
	21st to end	Night	31% 6% 17% 28% 14% 3	1620
July	1st to 10th	Night	31% 9% 21% 29% 9% 1	1575
	11th to 20th	Night	18% 10% 21% 31% 18% 1	1566
	21st to end	Night	20% 8% 26% 34% 10% 1	1673
August	1st to 10th	Night	13% 7% 23% 40% 17% 1	1659
	11th to 20th	Night	25% 10% 22% 31% 11% 2	1778
	21st to end	Night	29% 9% 22% 26% 11% 3	2060
September	1st to 10th	Night	34% 6% 16% 21% 16% 7%	1980
	11th to 20th	Night	37% 8% 15% 22% 14% 5%	1980
	21st to end	Night	31% 7% 13% 21% 18% 11%	1980
October	1st to 10th	Night	26% 5% 12% 25% 20% 11%	1980
	11th to 20th	Night	33% 4 9% 17% 19% 17%	2052
	21st to end	Night	31% 2 6% 15% 24% 22%	2376
November	1st to 10th	Night	35% 4 7% 19% 21% 14%	2220
	11th to 20th	Night	34% 4 9% 18% 20% 15%	2413
	21st to end	Night	40% 4 6% 16% 20% 14%	2470
December	1st to 10th	Night	37% 3 8% 20% 20% 12%	2470
	11th to 20th	Night	42% 4 5% 12% 18% 19%	3037
	21st to end	Night	36% 3 4 14% 28% 14%	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	23% 17% 36% 18% 6%	270
	11th to 20th	Day	27% 14% 29% 22% 6% 1	270
	21st to end	Day	20% 17% 39% 19% 4 1	267
February	1st to 10th	Day	33% 15% 28% 18% 7%	240
	11th to 20th	Day	30% 19% 32% 15% 3	240
	21st to end	Day	28% 19% 40% 12% 1	198
March	1st to 10th	Day	26% 18% 39% 15% 2	240
	11th to 20th	Day	22% 17% 41% 15% 5%	240
	21st to end	Day	21% 16% 41% 17% 5% 1	264
April	1st to 10th	Day	22% 15% 44% 15% 3	240
	11th to 20th	Day	26% 15% 35% 20% 4	255
	21st to end	Day	20% 12% 40% 23% 5%	523
May	1st to 10th	Day	20% 13% 34% 27% 7%	603
	11th to 20th	Day	19% 9% 30% 30% 9% 2	625
	21st to end	Day	18% 6% 28% 35% 13% 1	679
June	1st to 10th	Day	8% 3 16% 44% 26% 3	630
	11th to 20th	Day	8% 1 17% 50% 22% 2	630
	21st to end	Day	11% 2 13% 37% 30% 6%	630
July	1st to 10th	Day	11% 1 12% 32% 35% 9%	621
	11th to 20th	Day	5% 1 7% 36% 45% 6%	618
	21st to end	Day	5% 1 5% 36% 44% 9%	684
August	1st to 10th	Day	4 1 7% 32% 45% 11%	563
	11th to 20th	Day	8% 5% 39% 37% 10%	437
	21st to end	Day	5% 2 7% 31% 40% 16%	415
September	1st to 10th	Day	13% 9% 23% 43% 11%	270
	11th to 20th	Day	8% 5% 31% 44% 12%	270
	21st to end	Day	10% 1 10% 30% 35% 13%	270
October	1st to 10th	Day	7% 3 16% 37% 32% 5%	270
	11th to 20th	Day	13% 5% 21% 42% 17% 3	270
	21st to end	Day	23% 12% 24% 28% 11% 2	297
November	1st to 10th	Day	20% 7% 27% 30% 12% 4	270
	11th to 20th	Day	23% 12% 27% 25% 11% 2	270
	21st to end	Day	27% 16% 33% 15% 7% 1	270
December	1st to 10th	Day	17% 11% 34% 26% 7% 4	270
	11th to 20th	Day	26% 14% 32% 23% 6%	270
	21st to end	Day	24% 10% 41% 18% 6% 1	297
January	1st to 10th	Night	21% 8% 26% 35% 10% 1	950
	11th to 20th	Night	24% 10% 27% 31% 8%	950
	21st to end	Night	24% 9% 26% 34% 7%	842
February	1st to 10th	Night	25% 11% 29% 28% 7%	720
	11th to 20th	Night	28% 12% 30% 26% 5%	704
	21st to end	Night	28% 13% 36% 22% 2	592
March	1st to 10th	Night	24% 11% 36% 26% 3	584
	11th to 20th	Night	23% 9% 32% 31% 5%	540
	21st to end	Night	20% 10% 40% 26% 3 1	594
April	1st to 10th	Night	17% 11% 42% 26% 4	540
	11th to 20th	Night	24% 10% 37% 27% 3	533
	21st to end	Night	23% 8% 36% 26% 6% 1	540
May	1st to 10th	Night	19% 8% 43% 26% 4	540
	11th to 20th	Night	17% 6% 35% 32% 9%	531
	21st to end	Night	18% 6% 30% 36% 10%	584
June	1st to 10th	Night	8% 2 24% 44% 21% 1	540
	11th to 20th	Night	7% 2 33% 46% 12% 1	540
	21st to end	Night	9% 1 20% 41% 24% 3	540
July	1st to 10th	Night	11% 1 16% 42% 27% 3	525
	11th to 20th	Night	4 1 11% 53% 28% 3	522
	21st to end	Night	7% 1 9% 52% 29% 3	591
August	1st to 10th	Night	2 10% 51% 34% 4	537
	11th to 20th	Night	6% 1 10% 49% 31% 4	534
	21st to end	Night	8% 1 6% 41% 40% 5%	594
September	1st to 10th	Night	11% 1 9% 39% 35% 5%	540
	11th to 20th	Night	13% 1 10% 37% 35% 5%	540
	21st to end	Night	10% 2 13% 35% 35% 5%	540
October	1st to 10th	Night	9% 2 14% 45% 27% 5%	540
	11th to 20th	Night	15% 4 20% 39% 20% 3	612
	21st to end	Night	18% 7% 22% 32% 19% 2	792
November	1st to 10th	Night	15% 5% 20% 38% 20% 2	740
	11th to 20th	Night	16% 7% 22% 37% 16% 2	893
	21st to end	Night	23% 9% 25% 29% 13% 1	950
December	1st to 10th	Night	22% 7% 24% 34% 12% 1	950
	11th to 20th	Night	26% 9% 24% 32% 9%	950
	21st to end	Night	22% 8% 27% 33% 9%	1045

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