Messier 110 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Messier 110 Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	11% 6% 2 5% 4 4 4 3 5% 7% 49%	127449
	Night	11% 5% 2 5% 3 3 3 3 5% 7% 54%	124189
Transparency	Day	33% 5% 11% 25% 21% 5%	131101
	Night	30% 4 10% 26% 23% 7%	128600
Seeing	Day	13% 9% 27% 29% 18% 4	17011
	Night	13% 10% 31% 32% 13% 1	26918

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	14% 9% 4 7% 3 3 3 2 4 6% 45%	4086
	11th to 20th	Day	7% 6% 2 6% 5% 3 3 3 4 5% 57%	4080
	21st to end	Day	16% 11% 3 5% 2 2 3 2 3 4 49%	4488
February	1st to 10th	Day	15% 10% 3 7% 5% 2 3 3 4 5% 42%	1800
	11th to 20th	Day	14% 7% 2 7% 4 4 3 2 5% 6% 47%	1900
	21st to end	Day	14% 8% 2 5% 4 4 4 3 5% 5% 46%	1676
March	1st to 10th	Day	11% 6% 2 5% 3 2 3 2 4 5% 56%	4936
	11th to 20th	Day	8% 6% 2 4 3 3 3 3 5% 7% 57%	4980
	21st to end	Day	11% 8% 3 7% 5% 5% 5% 4 6% 8% 39%	5462
April	1st to 10th	Day	11% 6% 2 5% 4 3 4 4 6% 7% 47%	2201
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 7% 45%	2374
	21st to end	Day	18% 7% 2 7% 4 3 3 3 5% 6% 41%	2585
May	1st to 10th	Day	19% 8% 3 6% 4 4 4 3 5% 5% 40%	5862
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 6% 6% 48%	5862
	21st to end	Day	18% 7% 3 7% 5% 4 5% 4 6% 7% 36%	6434
June	1st to 10th	Day	6% 4 2 6% 5% 4 5% 5% 7% 9% 48%	2600
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 3 6% 8% 50%	2600
	21st to end	Day	5% 3 1 3 3 4 4 4 6% 7% 59%	2600
July	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 8% 10% 43%	5900
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 6% 9% 50%	5900
	21st to end	Day	4 3 1 4 4 4 4 4 7% 11% 53%	6422
August	1st to 10th	Day	5% 4 1 4 3 3 4 4 6% 9% 57%	4234
	11th to 20th	Day	7% 3 2 5% 4 4 4 4 7% 9% 49%	4171
	21st to end	Day	5% 3 2 4 4 3 4 4 6% 9% 57%	4457
September	1st to 10th	Day	11% 4 1 5% 4 4 4 4 4 6% 53%	2238
	11th to 20th	Day	10% 6% 2 5% 3 4 4 4 7% 7% 48%	2200
	21st to end	Day	9% 4 1 4 3 4 4 3 5% 6% 57%	2200
October	1st to 10th	Day	9% 3 2 4 3 3 4 2 5% 7% 59%	2075
	11th to 20th	Day	11% 3 1 4 2 2 2 2 4 5% 63%	2000
	21st to end	Day	16% 6% 1 4 2 3 3 2 4 5% 54%	2200
November	1st to 10th	Day	10% 4 1 4 3 3 3 3 3 6% 60%	2048
	11th to 20th	Day	11% 5% 2 3 3 2 3 2 4 6% 61%	1890
	21st to end	Day	14% 7% 2 3 2 2 2 2 5% 5% 55%	1890
December	1st to 10th	Day	9% 8% 2 6% 3 3 3 3 3 6% 55%	3030
	11th to 20th	Day	11% 6% 2 6% 3 3 3 3 4 5% 54%	3481
	21st to end	Day	19% 14% 4 6% 4 3 3 3 4 4 35%	4587
January	1st to 10th	Night	14% 7% 2 7% 4 3 3 3 5% 6% 47%	5902
	11th to 20th	Night	6% 4 1 5% 3 4 4 3 5% 7% 59%	5900
	21st to end	Night	17% 7% 2 5% 3 2 3 2 3 5% 50%	6490
February	1st to 10th	Night	14% 9% 2 6% 4 3 3 3 5% 6% 46%	2600
	11th to 20th	Night	14% 8% 3 6% 3 3 2 2 4 6% 49%	2403
	21st to end	Night	12% 7% 2 5% 4 4 4 3 3 4 52%	1952
March	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 4 4 53%	4919
	11th to 20th	Night	8% 4 1 3 2 3 2 3 5% 6% 63%	4980
	21st to end	Night	11% 5% 2 6% 4 4 4 3 5% 8% 48%	5467
April	1st to 10th	Night	12% 5% 2 4 4 3 3 3 5% 7% 54%	2196
	11th to 20th	Night	14% 5% 1 5% 3 2 3 2 5% 7% 51%	1975
	21st to end	Night	14% 7% 2 5% 4 3 3 2 5% 6% 48%	1810
May	1st to 10th	Night	16% 7% 2 5% 4 4 3 3 4 6% 46%	4053
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 50%	4053
	21st to end	Night	16% 5% 2 5% 3 3 3 4 5% 8% 47%	4443
June	1st to 10th	Night	6% 5% 2 4 4 4 4 4 5% 8% 54%	1800
	11th to 20th	Night	5% 3 1 4 3 3 4 4 7% 11% 54%	1800
	21st to end	Night	3 3 1 4 2 3 4 3 6% 8% 63%	1800
July	1st to 10th	Night	5% 3 2 4 4 4 5% 4 8% 11% 48%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 4 5% 9% 59%	4077
	21st to end	Night	4 3 1 3 2 3 4 4 6% 10% 61%	4449
August	1st to 10th	Night	3 2 1 3 3 3 3 4 7% 8% 62%	2926
	11th to 20th	Night	5% 3 2 5% 5% 5% 5% 4 6% 9% 53%	2888
	21st to end	Night	3 3 1 4 3 3 4 3 5% 8% 64%	3443
September	1st to 10th	Night	9% 5% 1 4 3 3 3 3 4 6% 59%	2158
	11th to 20th	Night	10% 5% 2 5% 4 5% 4 4 5% 8% 50%	2200
	21st to end	Night	8% 3 2 4 3 3 4 3 4 6% 60%	2200
October	1st to 10th	Night	7% 3 1 4 3 2 2 3 4 6% 63%	2303
	11th to 20th	Night	11% 4 1 3 2 3 3 2 4 5% 62%	2400
	21st to end	Night	14% 5% 2 4 3 3 2 2 3 4 58%	2640
November	1st to 10th	Night	10% 5% 1 3 2 2 3 3 4 5% 63%	2465
	11th to 20th	Night	10% 5% 2 3 3 3 3 2 4 6% 60%	2730
	21st to end	Night	14% 5% 2 4 3 3 3 2 4 6% 54%	2730
December	1st to 10th	Night	8% 6% 2 5% 3 3 3 3 4 5% 59%	4380
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 3 4 55%	4946
	21st to end	Night	19% 10% 3 5% 3 3 2 3 4 5% 44%	6633

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	43% 4 10% 25% 17% 2	4087
	11th to 20th	Day	30% 4 11% 23% 26% 6%	4080
	21st to end	Day	41% 3 6% 21% 26% 3	4488
February	1st to 10th	Day	45% 4 10% 22% 16% 4	1800
	11th to 20th	Day	40% 3 9% 26% 18% 4	1910
	21st to end	Day	40% 3 7% 21% 20% 9%	1676
March	1st to 10th	Day	33% 3 6% 21% 20% 18%	4936
	11th to 20th	Day	28% 5% 8% 20% 22% 16%	4980
	21st to end	Day	43% 6% 10% 29% 11% 1	5464
April	1st to 10th	Day	35% 6% 11% 23% 19% 6%	2201
	11th to 20th	Day	38% 6% 11% 21% 17% 6%	2374
	21st to end	Day	44% 7% 9% 22% 16% 2	2585
May	1st to 10th	Day	46% 5% 9% 21% 16% 3	5900
	11th to 20th	Day	34% 8% 11% 22% 22% 5%	5866
	21st to end	Day	46% 8% 11% 15% 17% 3	6447
June	1st to 10th	Day	30% 9% 14% 27% 17% 3	2600
	11th to 20th	Day	33% 6% 13% 27% 18% 3	2600
	21st to end	Day	22% 7% 14% 29% 22% 5%	2600
July	1st to 10th	Day	32% 9% 16% 26% 16% 2	5836
	11th to 20th	Day	29% 7% 12% 28% 22% 2	5831
	21st to end	Day	22% 8% 19% 35% 15%	6240
August	1st to 10th	Day	22% 6% 13% 28% 24% 6%	4220
	11th to 20th	Day	29% 8% 19% 25% 17% 2	4210
	21st to end	Day	25% 7% 13% 37% 15% 4	4456
September	1st to 10th	Day	32% 5% 10% 22% 21% 9%	2238
	11th to 20th	Day	32% 8% 12% 22% 21% 5%	2200
	21st to end	Day	28% 5% 8% 21% 30% 7%	2200
October	1st to 10th	Day	18% 4 8% 16% 42% 13%	3374
	11th to 20th	Day	15% 2 5% 24% 38% 16%	3240
	21st to end	Day	27% 3 7% 28% 29% 6%	3538
November	1st to 10th	Day	27% 4 6% 28% 27% 8%	2048
	11th to 20th	Day	27% 3 9% 28% 26% 8%	1890
	21st to end	Day	33% 3 9% 25% 25% 5%	1890
December	1st to 10th	Day	32% 4 7% 36% 20% 1	3030
	11th to 20th	Day	34% 3 6% 26% 28% 4	3479
	21st to end	Day	53% 3 8% 21% 12% 2	4587
January	1st to 10th	Night	38% 3 11% 29% 15% 3	5902
	11th to 20th	Night	25% 5% 12% 22% 31% 6%	5900
	21st to end	Night	39% 3 8% 19% 28% 4	6490
February	1st to 10th	Night	40% 4 11% 22% 18% 5%	2600
	11th to 20th	Night	38% 3 8% 26% 19% 5%	2403
	21st to end	Night	37% 3 7% 19% 24% 10%	1952
March	1st to 10th	Night	35% 3 6% 19% 22% 14%	4919
	11th to 20th	Night	22% 3 7% 23% 26% 18%	4980
	21st to end	Night	35% 5% 11% 32% 15% 2	5467
April	1st to 10th	Night	32% 4 11% 22% 23% 9%	2196
	11th to 20th	Night	34% 4 11% 23% 20% 9%	1975
	21st to end	Night	37% 5% 10% 23% 21% 3	1810
May	1st to 10th	Night	40% 6% 12% 18% 21% 3	4080
	11th to 20th	Night	34% 6% 10% 23% 20% 7%	4054
	21st to end	Night	35% 6% 15% 22% 18% 4	4452
June	1st to 10th	Night	27% 8% 15% 29% 19% 3	1800
	11th to 20th	Night	24% 6% 14% 33% 20% 4	1800
	21st to end	Night	18% 6% 15% 30% 25% 7%	1800
July	1st to 10th	Night	25% 9% 19% 29% 15% 3	4035
	11th to 20th	Night	21% 6% 12% 34% 26% 2	4026
	21st to end	Night	18% 5% 16% 39% 21% 1	4320
August	1st to 10th	Night	17% 6% 13% 32% 25% 7%	2916
	11th to 20th	Night	27% 7% 16% 26% 21% 3	2915
	21st to end	Night	18% 6% 11% 41% 18% 6%	3443
September	1st to 10th	Night	28% 4 9% 26% 23% 11%	2158
	11th to 20th	Night	32% 6% 10% 21% 25% 6%	2200
	21st to end	Night	26% 4 8% 24% 31% 7%	2200
October	1st to 10th	Night	15% 3 6% 13% 40% 22%	3771
	11th to 20th	Night	19% 2 5% 19% 37% 18%	3899
	21st to end	Night	26% 4 7% 26% 29% 9%	4252
November	1st to 10th	Night	25% 3 8% 24% 30% 9%	2465
	11th to 20th	Night	28% 3 7% 26% 27% 9%	2730
	21st to end	Night	33% 4 7% 23% 27% 6%	2730
December	1st to 10th	Night	28% 3 10% 37% 18% 3	4380
	11th to 20th	Night	35% 3 6% 24% 26% 6%	4947
	21st to end	Night	44% 3 8% 26% 15% 4	6633

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	21% 14% 35% 24% 6%	303
	11th to 20th	Day	22% 15% 42% 17% 3 1	300
	21st to end	Day	17% 15% 41% 20% 6%	330
February	1st to 10th	Day	24% 15% 39% 19% 3	300
	11th to 20th	Day	20% 20% 41% 17% 2	300
	21st to end	Day	22% 21% 37% 15% 4	249
March	1st to 10th	Day	18% 19% 39% 18% 5%	300
	11th to 20th	Day	20% 19% 41% 17% 2	300
	21st to end	Day	18% 25% 35% 18% 4	330
April	1st to 10th	Day	16% 22% 39% 18% 6%	301
	11th to 20th	Day	21% 17% 38% 20% 4	492
	21st to end	Day	23% 18% 29% 21% 8% 1	685
May	1st to 10th	Day	17% 12% 37% 25% 8% 1	703
	11th to 20th	Day	16% 11% 32% 25% 11% 4	725
	21st to end	Day	17% 9% 31% 22% 15% 5%	789
June	1st to 10th	Day	7% 5% 22% 37% 24% 5%	730
	11th to 20th	Day	8% 3 25% 39% 22% 4	730
	21st to end	Day	5% 2 23% 43% 23% 5%	730
July	1st to 10th	Day	7% 2 15% 33% 31% 12%	721
	11th to 20th	Day	3 2 13% 39% 35% 7%	718
	21st to end	Day	7% 1 9% 33% 36% 13%	794
August	1st to 10th	Day	6% 2 12% 45% 30% 5%	726
	11th to 20th	Day	7% 2 15% 36% 32% 8%	715
	21st to end	Day	7% 3 10% 33% 37% 9%	676
September	1st to 10th	Day	11% 3 9% 31% 33% 12%	368
	11th to 20th	Day	6% 1 16% 39% 29% 9%	330
	21st to end	Day	13% 4 20% 32% 24% 7%	330
October	1st to 10th	Day	7% 6% 27% 32% 22% 6%	330
	11th to 20th	Day	8% 12% 36% 30% 13% 1	330
	21st to end	Day	23% 13% 29% 25% 9% 1	363
November	1st to 10th	Day	14% 11% 41% 25% 8% 2	330
	11th to 20th	Day	15% 13% 38% 21% 11% 2	330
	21st to end	Day	20% 17% 35% 22% 6% 1	330
December	1st to 10th	Day	14% 15% 45% 18% 8% 1	330
	11th to 20th	Day	17% 15% 39% 22% 6% 1	330
	21st to end	Day	15% 22% 39% 18% 5%	363
January	1st to 10th	Night	14% 13% 40% 27% 5%	1006
	11th to 20th	Night	14% 17% 38% 26% 5%	1000
	21st to end	Night	14% 15% 39% 28% 4	1100
February	1st to 10th	Night	19% 15% 39% 25% 3	1000
	11th to 20th	Night	18% 19% 35% 25% 3	848
	21st to end	Night	16% 16% 38% 26% 3	632
March	1st to 10th	Night	16% 13% 37% 31% 4	600
	11th to 20th	Night	20% 13% 39% 25% 4	600
	21st to end	Night	19% 13% 41% 23% 4	660
April	1st to 10th	Night	15% 15% 40% 25% 4	600
	11th to 20th	Night	18% 12% 40% 25% 6%	593
	21st to end	Night	17% 11% 39% 26% 7% 1	600
May	1st to 10th	Night	16% 8% 40% 30% 6%	600
	11th to 20th	Night	15% 8% 30% 33% 14% 1	591
	21st to end	Night	12% 5% 30% 34% 17% 2	650
June	1st to 10th	Night	7% 3 23% 42% 24% 1	600
	11th to 20th	Night	6% 3 27% 45% 19% 1	600
	21st to end	Night	4 1 26% 50% 19% 1	600
July	1st to 10th	Night	5% 1 15% 45% 31% 3	585
	11th to 20th	Night	3 1 13% 49% 30% 3	582
	21st to end	Night	6% 1 12% 42% 38% 2	657
August	1st to 10th	Night	3 2 14% 51% 28% 2	597
	11th to 20th	Night	5% 1 14% 43% 34% 3	594
	21st to end	Night	5% 1 12% 41% 39% 3	660
September	1st to 10th	Night	10% 2 14% 43% 31% 1	600
	11th to 20th	Night	11% 2 18% 39% 27% 3	600
	21st to end	Night	10% 4 19% 38% 25% 3	600
October	1st to 10th	Night	8% 3 29% 36% 22% 3	703
	11th to 20th	Night	13% 8% 37% 31% 11% 1	800
	21st to end	Night	17% 13% 29% 31% 10% 1	880
November	1st to 10th	Night	12% 9% 38% 29% 12% 1	825
	11th to 20th	Night	13% 13% 36% 31% 8%	1050
	21st to end	Night	16% 15% 32% 28% 9%	1050
December	1st to 10th	Night	15% 15% 35% 29% 5%	1050
	11th to 20th	Night	18% 12% 37% 27% 6%	1050
	21st to end	Night	17% 17% 34% 28% 4	1155

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