Monroe Robotic Observatory
Clear Sky Chart
History

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

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	10% 5% 2 5% 3 3 4 3 5% 7% 53%	127611
	Night	9% 5% 2 4 3 3 3 3 4 6% 57%	124693
Transparency	Day	31% 4 9% 25% 23% 8%	131328
	Night	28% 3 9% 24% 25% 11%	129039
Seeing	Day	13% 10% 26% 29% 18% 4	16853
	Night	12% 9% 31% 33% 13% 1	26839

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	12% 8% 2 5% 3 3 3 2 4 5% 53%	4167
	11th to 20th	Day	7% 5% 1 3 2 2 2 2 4 6% 67%	4170
	21st to end	Day	18% 8% 2 5% 3 2 2 2 4 4 50%	4587
February	1st to 10th	Day	14% 7% 2 6% 4 3 3 2 3 6% 49%	1920
	11th to 20th	Day	13% 7% 2 5% 5% 4 3 3 4 5% 49%	1949
	21st to end	Day	18% 8% 2 5% 3 2 2 2 3 3 53%	1650
March	1st to 10th	Day	13% 6% 1 4 3 3 3 3 4 5% 54%	4926
	11th to 20th	Day	9% 5% 2 5% 4 3 4 3 4 5% 58%	4980
	21st to end	Day	11% 7% 2 5% 4 4 4 4 5% 7% 46%	5462
April	1st to 10th	Day	12% 6% 2 4 4 3 4 3 4 6% 53%	2200
	11th to 20th	Day	12% 5% 2 6% 3 3 4 4 5% 6% 50%	2280
	21st to end	Day	11% 6% 2 6% 5% 4 4 3 5% 6% 47%	2600
May	1st to 10th	Day	15% 7% 3 6% 4 4 4 3 6% 6% 42%	5862
	11th to 20th	Day	12% 6% 2 5% 3 4 4 3 5% 7% 48%	5862
	21st to end	Day	12% 7% 3 7% 5% 4 5% 3 6% 8% 41%	6434
June	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 4 7% 8% 50%	2600
	11th to 20th	Day	6% 3 2 5% 4 4 5% 4 6% 9% 53%	2600
	21st to end	Day	4 3 1 4 3 4 4 3 6% 9% 59%	2600
July	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 4 6% 9% 42%	5900
	11th to 20th	Day	3 3 2 4 4 4 4 3 5% 9% 59%	5900
	21st to end	Day	3 3 1 4 3 4 4 4 6% 9% 61%	6422
August	1st to 10th	Day	2 2 1 4 3 3 4 3 5% 7% 65%	4234
	11th to 20th	Day	4 2 1 4 3 3 3 3 6% 10% 60%	4171
	21st to end	Day	3 2 1 3 3 3 4 4 6% 10% 60%	4236
September	1st to 10th	Day	10% 4 2 4 4 3 3 3 4 7% 56%	2200
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 6% 8% 49%	2200
	21st to end	Day	8% 3 1 4 2 3 3 4 5% 8% 59%	2200
October	1st to 10th	Day	5% 3 1 5% 3 4 3 3 4 5% 64%	2160
	11th to 20th	Day	10% 4 1 3 2 3 3 2 3 5% 65%	2000
	21st to end	Day	13% 5% 2 4 2 2 3 1 3 4 61%	2200
November	1st to 10th	Day	11% 4 2 5% 2 3 3 2 3 5% 60%	2058
	11th to 20th	Day	6% 3 1 3 3 2 2 2 3 6% 66%	1893
	21st to end	Day	12% 6% 2 5% 3 3 3 2 3 4 58%	1890
December	1st to 10th	Day	12% 9% 2 5% 3 3 3 2 4 5% 53%	3030
	11th to 20th	Day	14% 7% 2 6% 3 3 3 3 3 4 51%	3481
	21st to end	Day	15% 9% 3 5% 3 3 3 2 4 4 49%	4587
January	1st to 10th	Night	13% 5% 2 5% 3 3 3 3 4 6% 54%	6018
	11th to 20th	Night	6% 3 1 2 2 2 2 2 3 5% 70%	6030
	21st to end	Night	19% 8% 2 5% 3 2 2 2 3 4 49%	6633
February	1st to 10th	Night	12% 7% 3 5% 4 3 3 3 4 4 53%	2496
	11th to 20th	Night	14% 7% 2 5% 3 3 4 2 4 5% 51%	2338
	21st to end	Night	12% 7% 2 5% 3 2 3 3 4 4 55%	1980
March	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 4 5% 51%	4928
	11th to 20th	Night	8% 4 2 3 2 3 2 3 4 6% 62%	4980
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 6% 50%	5467
April	1st to 10th	Night	9% 5% 2 5% 4 3 4 3 5% 8% 53%	2200
	11th to 20th	Night	11% 6% 1 4 4 4 4 3 4 7% 53%	2063
	21st to end	Night	10% 5% 2 6% 3 3 3 3 5% 7% 53%	1800
May	1st to 10th	Night	15% 8% 2 6% 4 3 3 3 5% 6% 45%	4053
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 7% 8% 51%	4053
	21st to end	Night	10% 5% 2 5% 3 3 4 4 6% 8% 49%	4443
June	1st to 10th	Night	4 3 1 3 3 3 4 4 6% 9% 58%	1800
	11th to 20th	Night	4 3 1 3 3 3 4 3 6% 10% 62%	1800
	21st to end	Night	2 2 3 4 3 3 3 5% 8% 67%	1800
July	1st to 10th	Night	5% 5% 2 7% 5% 5% 4 4 6% 10% 46%	4078
	11th to 20th	Night	2 2 1 3 2 3 3 3 5% 8% 67%	4077
	21st to end	Night	2 2 1 3 3 2 3 3 6% 8% 66%	4449
August	1st to 10th	Night	2 1 1 2 2 2 2 2 5% 8% 73%	2926
	11th to 20th	Night	3 2 1 2 2 2 2 3 5% 11% 67%	2888
	21st to end	Night	2 2 1 4 3 3 3 3 5% 9% 65%	3663
September	1st to 10th	Night	8% 4 1 4 3 3 3 3 4 6% 61%	2200
	11th to 20th	Night	8% 5% 1 6% 4 4 4 3 5% 7% 54%	2200
	21st to end	Night	6% 3 1 4 2 3 3 3 5% 7% 64%	2200
October	1st to 10th	Night	6% 3 1 3 3 3 3 2 4 7% 65%	2217
	11th to 20th	Night	9% 4 1 4 2 2 2 2 4 4 66%	2400
	21st to end	Night	13% 5% 1 4 2 2 2 2 3 4 62%	2640
November	1st to 10th	Night	10% 4 1 3 3 2 3 3 3 5% 63%	2460
	11th to 20th	Night	6% 4 2 3 3 3 2 3 4 6% 64%	2724
	21st to end	Night	13% 5% 2 4 3 3 3 3 4 5% 56%	2730
December	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 3 5% 58%	4380
	11th to 20th	Night	14% 6% 2 6% 3 3 3 2 3 4 55%	4946
	21st to end	Night	14% 7% 2 5% 3 2 2 2 3 4 53%	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	34% 3 7% 27% 25% 4	4168
	11th to 20th	Day	22% 2 7% 22% 41% 7%	4170
	21st to end	Day	41% 2 4 19% 23% 11%	4587
February	1st to 10th	Day	40% 3 6% 20% 23% 8%	1920
	11th to 20th	Day	40% 4 6% 22% 20% 8%	1959
	21st to end	Day	38% 2 4 15% 27% 13%	1650
March	1st to 10th	Day	33% 3 7% 16% 23% 19%	4926
	11th to 20th	Day	30% 5% 8% 17% 21% 20%	4980
	21st to end	Day	37% 4 10% 23% 20% 5%	5464
April	1st to 10th	Day	35% 3 10% 23% 20% 10%	2200
	11th to 20th	Day	35% 5% 9% 20% 20% 10%	2280
	21st to end	Day	36% 6% 9% 24% 21% 4	2600
May	1st to 10th	Day	42% 4 10% 23% 14% 6%	5900
	11th to 20th	Day	37% 5% 10% 22% 22% 4	5866
	21st to end	Day	42% 5% 12% 21% 13% 6%	6447
June	1st to 10th	Day	31% 7% 15% 28% 16% 3	2600
	11th to 20th	Day	28% 5% 14% 27% 22% 4	2600
	21st to end	Day	23% 6% 14% 27% 26% 4	2600
July	1st to 10th	Day	39% 4 13% 30% 12% 1	5836
	11th to 20th	Day	22% 4 13% 35% 25% 2	5831
	21st to end	Day	20% 5% 14% 34% 25% 1	6240
August	1st to 10th	Day	18% 3 12% 27% 31% 9%	4220
	11th to 20th	Day	21% 4 13% 40% 21% 2	4210
	21st to end	Day	20% 5% 18% 38% 15% 3	4235
September	1st to 10th	Day	29% 4 10% 23% 23% 11%	2200
	11th to 20th	Day	34% 5% 11% 21% 21% 7%	2200
	21st to end	Day	24% 4 8% 25% 29% 12%	2200
October	1st to 10th	Day	15% 3 5% 14% 38% 24%	3524
	11th to 20th	Day	17% 2 5% 22% 36% 18%	3240
	21st to end	Day	25% 2 4 31% 28% 10%	3538
November	1st to 10th	Day	29% 3 7% 23% 27% 10%	2058
	11th to 20th	Day	22% 2 9% 24% 31% 12%	1893
	21st to end	Day	32% 2 5% 22% 28% 10%	1890
December	1st to 10th	Day	36% 2 4 32% 22% 3	3030
	11th to 20th	Day	40% 2 5% 14% 31% 9%	3479
	21st to end	Day	40% 2 5% 25% 21% 7%	4587
January	1st to 10th	Night	33% 2 7% 27% 26% 5%	6018
	11th to 20th	Night	19% 2 7% 20% 38% 14%	6030
	21st to end	Night	41% 2 4 15% 25% 13%	6633
February	1st to 10th	Night	35% 3 8% 20% 22% 11%	2496
	11th to 20th	Night	37% 3 8% 20% 23% 10%	2338
	21st to end	Night	35% 3 6% 17% 23% 18%	1980
March	1st to 10th	Night	37% 3 5% 14% 23% 19%	4928
	11th to 20th	Night	25% 3 7% 22% 17% 26%	4980
	21st to end	Night	35% 4 9% 18% 29% 5%	5467
April	1st to 10th	Night	31% 4 10% 20% 21% 14%	2200
	11th to 20th	Night	32% 5% 8% 19% 22% 13%	2063
	21st to end	Night	31% 4 12% 24% 24% 5%	1800
May	1st to 10th	Night	43% 4 11% 20% 17% 5%	4080
	11th to 20th	Night	31% 4 13% 22% 22% 8%	4054
	21st to end	Night	32% 5% 16% 24% 13% 9%	4452
June	1st to 10th	Night	22% 8% 13% 33% 19% 4	1800
	11th to 20th	Night	19% 5% 15% 31% 24% 7%	1800
	21st to end	Night	16% 5% 14% 30% 29% 7%	1800
July	1st to 10th	Night	33% 4 16% 32% 13% 2	4035
	11th to 20th	Night	16% 3 12% 38% 27% 3	4026
	21st to end	Night	17% 4 14% 36% 26% 2	4320
August	1st to 10th	Night	12% 3 8% 32% 38% 7%	2916
	11th to 20th	Night	13% 4 12% 40% 25% 6%	2915
	21st to end	Night	18% 4 19% 36% 20% 4	3663
September	1st to 10th	Night	25% 4 10% 22% 29% 11%	2200
	11th to 20th	Night	29% 6% 9% 22% 22% 11%	2200
	21st to end	Night	20% 4 8% 25% 28% 15%	2200
October	1st to 10th	Night	13% 2 6% 14% 36% 29%	3620
	11th to 20th	Night	16% 2 5% 18% 36% 23%	3899
	21st to end	Night	25% 2 4 29% 27% 14%	4252
November	1st to 10th	Night	26% 3 6% 22% 28% 15%	2460
	11th to 20th	Night	22% 3 8% 24% 29% 15%	2724
	21st to end	Night	32% 3 7% 18% 29% 11%	2730
December	1st to 10th	Night	31% 3 5% 26% 27% 7%	4380
	11th to 20th	Night	36% 2 5% 16% 27% 14%	4947
	21st to end	Night	37% 2 6% 22% 26% 8%	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	22% 18% 36% 20% 4	330
	11th to 20th	Day	21% 22% 36% 16% 5% 1	330
	21st to end	Day	19% 21% 37% 16% 5% 1	363
February	1st to 10th	Day	24% 18% 39% 17% 3	300
	11th to 20th	Day	25% 22% 40% 10% 3	300
	21st to end	Day	29% 23% 32% 10% 5%	249
March	1st to 10th	Day	23% 23% 33% 17% 3 1	300
	11th to 20th	Day	25% 22% 41% 8% 4 1	300
	21st to end	Day	20% 21% 42% 15% 2 1	330
April	1st to 10th	Day	24% 21% 32% 20% 3	300
	11th to 20th	Day	20% 20% 42% 15% 3	398
	21st to end	Day	16% 19% 39% 19% 5% 2	700
May	1st to 10th	Day	14% 12% 40% 28% 6% 1	703
	11th to 20th	Day	18% 10% 37% 24% 10% 2	725
	21st to end	Day	14% 8% 34% 30% 10% 3	789
June	1st to 10th	Day	7% 3 20% 40% 23% 6%	730
	11th to 20th	Day	7% 3 24% 40% 21% 4	730
	21st to end	Day	4 2 17% 42% 28% 7%	730
July	1st to 10th	Day	6% 1 12% 40% 32% 9%	721
	11th to 20th	Day	3 2 11% 38% 39% 8%	718
	21st to end	Day	3 2 8% 38% 39% 11%	794
August	1st to 10th	Day	4 2 9% 39% 37% 10%	726
	11th to 20th	Day	7% 1 9% 41% 35% 7%	715
	21st to end	Day	6% 8% 36% 39% 11%	546
September	1st to 10th	Day	9% 2 9% 34% 33% 12%	330
	11th to 20th	Day	7% 2 10% 39% 31% 11%	330
	21st to end	Day	12% 3 13% 41% 21% 9%	330
October	1st to 10th	Day	2 4 28% 32% 28% 6%	330
	11th to 20th	Day	11% 10% 30% 32% 15% 1	330
	21st to end	Day	24% 11% 28% 26% 10% 1	363
November	1st to 10th	Day	19% 11% 34% 25% 8% 3	330
	11th to 20th	Day	12% 13% 38% 24% 9% 3	330
	21st to end	Day	19% 19% 34% 21% 5% 2	330
December	1st to 10th	Day	16% 16% 37% 23% 6% 2	330
	11th to 20th	Day	20% 13% 44% 17% 6%	330
	21st to end	Day	19% 20% 36% 21% 3	363
January	1st to 10th	Night	14% 14% 36% 29% 6%	1050
	11th to 20th	Night	15% 16% 36% 27% 6%	1050
	21st to end	Night	15% 14% 36% 30% 5%	1155
February	1st to 10th	Night	18% 13% 40% 25% 3	896
	11th to 20th	Night	19% 18% 38% 22% 3	784
	21st to end	Night	19% 20% 38% 21% 2	660
March	1st to 10th	Night	19% 15% 36% 27% 4	609
	11th to 20th	Night	16% 13% 44% 23% 5%	600
	21st to end	Night	14% 15% 42% 25% 4	660
April	1st to 10th	Night	13% 17% 43% 24% 4	600
	11th to 20th	Night	15% 17% 38% 26% 4	593
	21st to end	Night	13% 12% 44% 23% 8% 1	600
May	1st to 10th	Night	12% 9% 41% 31% 7% 1	600
	11th to 20th	Night	13% 8% 38% 28% 12% 1	591
	21st to end	Night	8% 6% 34% 35% 15% 1	650
June	1st to 10th	Night	4 4 25% 41% 25% 2	600
	11th to 20th	Night	4 2 29% 50% 15%	600
	21st to end	Night	2 1 23% 47% 24% 3	600
July	1st to 10th	Night	5% 1 13% 45% 33% 3	585
	11th to 20th	Night	3 1 15% 46% 34% 2	582
	21st to end	Night	1 1 11% 46% 37% 4	657
August	1st to 10th	Night	2 1 10% 53% 32% 3	597
	11th to 20th	Night	7% 1 10% 45% 33% 4	594
	21st to end	Night	4 1 8% 49% 33% 6%	660
September	1st to 10th	Night	8% 2 10% 43% 34% 3	600
	11th to 20th	Night	10% 1 13% 44% 29% 3	600
	21st to end	Night	7% 1 20% 43% 26% 3	600
October	1st to 10th	Night	7% 4 25% 36% 25% 2	617
	11th to 20th	Night	12% 7% 31% 38% 12% 1	800
	21st to end	Night	18% 9% 31% 30% 11% 1	880
November	1st to 10th	Night	11% 7% 35% 35% 11% 1	820
	11th to 20th	Night	9% 12% 36% 31% 11% 1	1044
	21st to end	Night	17% 12% 36% 26% 9%	1050
December	1st to 10th	Night	14% 12% 38% 31% 6%	1050
	11th to 20th	Night	18% 11% 38% 28% 6%	1050
	21st to end	Night	19% 13% 38% 25% 6%	1155

Page generated at 2026-01-29 00:21:46. Version ac07

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