USAO JMOERC Habitat Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the USAO JMOERC Habitat Area clear sky chart from 2005-11-06 to 2025-12-03.

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	9% 5% 2 5% 3 3 4 3 5% 7% 54%	127017
	Night	9% 5% 2 4 3 3 3 3 5% 7% 58%	123976
Transparency	Day	30% 3 9% 25% 24% 8%	130747
	Night	27% 3 9% 25% 27% 10%	128309
Seeing	Day	12% 8% 26% 31% 18% 5%	16785
	Night	11% 8% 31% 35% 13% 1	26665

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	10% 7% 3 6% 4 3 3 3 5% 6% 50%	4077
	11th to 20th	Day	6% 6% 2 3 2 2 3 2 3 4 67%	4080
	21st to end	Day	14% 8% 4 4 3 2 2 2 3 5% 52%	4488
February	1st to 10th	Day	11% 9% 2 7% 3 3 3 2 4 4 52%	1940
	11th to 20th	Day	11% 6% 2 5% 3 4 4 2 5% 5% 53%	1949
	21st to end	Day	12% 8% 3 5% 3 3 3 2 3 5% 53%	1650
March	1st to 10th	Day	11% 5% 2 4 3 3 3 2 4 5% 58%	4797
	11th to 20th	Day	7% 6% 2 5% 4 3 4 3 5% 6% 56%	4980
	21st to end	Day	10% 8% 3 6% 4 3 4 3 5% 7% 47%	5462
April	1st to 10th	Day	10% 5% 2 4 4 3 3 3 5% 7% 55%	2200
	11th to 20th	Day	12% 5% 2 6% 3 3 3 3 4 6% 51%	2368
	21st to end	Day	14% 5% 2 4 4 4 3 3 5% 6% 49%	2600
May	1st to 10th	Day	16% 8% 2 6% 4 4 4 3 5% 6% 41%	5862
	11th to 20th	Day	9% 5% 2 5% 4 3 4 3 5% 7% 52%	5862
	21st to end	Day	11% 7% 3 7% 5% 4 4 3 5% 6% 45%	6434
June	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 49%	2600
	11th to 20th	Day	5% 4 2 4 3 4 4 4 7% 8% 56%	2600
	21st to end	Day	5% 3 1 4 3 4 4 3 5% 8% 61%	2600
July	1st to 10th	Day	8% 5% 2 7% 6% 5% 6% 5% 7% 8% 41%	5900
	11th to 20th	Day	4 3 1 5% 3 4 4 4 6% 9% 56%	5900
	21st to end	Day	2 2 1 3 3 4 4 4 6% 9% 62%	6422
August	1st to 10th	Day	4 3 2 4 3 4 5% 4 5% 9% 58%	4234
	11th to 20th	Day	4 3 2 4 4 4 4 3 6% 10% 57%	4171
	21st to end	Day	4 3 1 3 2 3 4 4 6% 9% 62%	4286
September	1st to 10th	Day	8% 4 1 5% 3 4 4 3 5% 6% 58%	2200
	11th to 20th	Day	11% 4 2 5% 4 5% 4 4 5% 7% 50%	2200
	21st to end	Day	8% 4 2 4 3 3 3 3 5% 7% 59%	2200
October	1st to 10th	Day	8% 3 2 4 3 3 3 3 4 6% 61%	2195
	11th to 20th	Day	10% 3 1 3 2 3 3 2 3 4 68%	2000
	21st to end	Day	12% 5% 1 3 2 3 2 2 3 4 61%	2200
November	1st to 10th	Day	9% 4 1 3 2 3 3 2 4 6% 63%	1943
	11th to 20th	Day	7% 3 1 3 3 2 3 2 4 5% 67%	1890
	21st to end	Day	11% 4 2 3 3 2 3 3 4 5% 61%	1890
December	1st to 10th	Day	6% 5% 2 5% 3 3 3 3 4 7% 58%	2958
	11th to 20th	Day	9% 4 2 4 3 3 3 4 4 5% 58%	3391
	21st to end	Day	15% 8% 3 6% 4 4 3 3 4 5% 45%	4488
January	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 4 5% 51%	5888
	11th to 20th	Night	4 3 1 3 2 3 3 3 4 6% 67%	5900
	21st to end	Night	14% 8% 2 4 2 2 3 2 4 5% 53%	6490
February	1st to 10th	Night	12% 7% 3 5% 3 3 2 3 4 5% 55%	2477
	11th to 20th	Night	11% 7% 2 5% 3 3 2 3 4 7% 53%	2338
	21st to end	Night	10% 6% 3 5% 3 3 3 3 5% 6% 55%	1980
March	1st to 10th	Night	9% 5% 2 5% 3 3 3 2 4 6% 58%	5062
	11th to 20th	Night	6% 3 1 3 2 2 3 3 4 6% 66%	4980
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 8% 49%	5467
April	1st to 10th	Night	10% 5% 1 4 3 3 2 3 5% 6% 59%	2200
	11th to 20th	Night	12% 4 2 3 4 3 3 3 4 7% 55%	1976
	21st to end	Night	13% 3 2 4 3 3 4 3 5% 7% 53%	1800
May	1st to 10th	Night	16% 7% 2 5% 3 3 3 2 4 6% 48%	4053
	11th to 20th	Night	9% 4 2 5% 3 4 4 3 5% 7% 56%	4053
	21st to end	Night	10% 5% 2 4 3 3 4 3 6% 7% 53%	4443
June	1st to 10th	Night	6% 3 1 3 3 3 4 3 6% 9% 58%	1800
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 9% 59%	1800
	21st to end	Night	3 3 1 3 2 2 3 3 5% 10% 66%	1800
July	1st to 10th	Night	5% 5% 2 7% 5% 4 5% 4 7% 10% 46%	4078
	11th to 20th	Night	3 2 1 3 2 3 4 3 6% 12% 61%	4077
	21st to end	Night	3 1 1 3 2 2 3 3 6% 10% 66%	4449
August	1st to 10th	Night	2 1 1 3 3 3 4 3 6% 10% 66%	2926
	11th to 20th	Night	4 2 1 4 4 3 5% 4 7% 9% 56%	2888
	21st to end	Night	4 2 1 3 2 3 3 3 5% 10% 64%	3614
September	1st to 10th	Night	6% 4 1 5% 3 3 4 3 4 6% 60%	2200
	11th to 20th	Night	11% 5% 2 6% 4 2 4 3 5% 6% 52%	2200
	21st to end	Night	7% 4 2 3 2 2 3 3 5% 6% 62%	2200
October	1st to 10th	Night	7% 2 1 3 3 3 3 3 4 6% 64%	2200
	11th to 20th	Night	8% 4 2 3 2 3 2 2 3 5% 65%	2384
	21st to end	Night	11% 5% 1 2 2 2 2 2 3 4 64%	2640
November	1st to 10th	Night	8% 3 1 3 2 3 2 2 4 5% 66%	2570
	11th to 20th	Night	5% 4 2 4 3 3 3 3 4 5% 65%	2730
	21st to end	Night	10% 5% 2 4 3 3 3 2 4 5% 58%	2730
December	1st to 10th	Night	6% 5% 1 3 2 3 3 2 4 6% 64%	4277
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 3 5% 60%	4816
	21st to end	Night	15% 8% 2 4 3 2 3 2 4 4 52%	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	37% 2 9% 27% 22% 3	4078
	11th to 20th	Day	23% 1 9% 21% 38% 8%	4080
	21st to end	Day	38% 1 4 19% 29% 8%	4488
February	1st to 10th	Day	37% 3 7% 23% 25% 6%	1940
	11th to 20th	Day	34% 2 7% 28% 23% 6%	1959
	21st to end	Day	37% 1 4 18% 29% 11%	1650
March	1st to 10th	Day	31% 2 5% 15% 22% 25%	4797
	11th to 20th	Day	30% 1 8% 18% 24% 18%	4980
	21st to end	Day	37% 3 9% 27% 20% 4	5464
April	1st to 10th	Day	31% 3 11% 25% 21% 9%	2200
	11th to 20th	Day	35% 3 8% 23% 22% 9%	2368
	21st to end	Day	36% 3 10% 27% 21% 4	2600
May	1st to 10th	Day	44% 4 11% 20% 16% 5%	5900
	11th to 20th	Day	33% 3 11% 23% 23% 8%	5866
	21st to end	Day	40% 3 11% 23% 16% 8%	6447
June	1st to 10th	Day	31% 4 18% 28% 16% 4	2600
	11th to 20th	Day	25% 4 13% 29% 25% 5%	2600
	21st to end	Day	22% 5% 13% 28% 25% 7%	2600
July	1st to 10th	Day	38% 6% 11% 24% 17% 4	5836
	11th to 20th	Day	24% 4 10% 31% 25% 5%	5831
	21st to end	Day	18% 4 14% 36% 25% 3	6240
August	1st to 10th	Day	23% 4 10% 26% 27% 11%	4220
	11th to 20th	Day	24% 4 13% 32% 22% 5%	4210
	21st to end	Day	20% 5% 12% 39% 20% 4	4285
September	1st to 10th	Day	27% 4 8% 24% 26% 11%	2200
	11th to 20th	Day	34% 4 9% 23% 23% 7%	2200
	21st to end	Day	25% 3 7% 26% 30% 8%	2200
October	1st to 10th	Day	17% 1 6% 14% 41% 20%	3572
	11th to 20th	Day	18% 2 6% 24% 33% 17%	3240
	21st to end	Day	22% 2 6% 29% 32% 8%	3538
November	1st to 10th	Day	25% 2 7% 24% 31% 11%	1943
	11th to 20th	Day	22% 2 6% 27% 31% 11%	1890
	21st to end	Day	27% 3 5% 27% 28% 10%	1890
December	1st to 10th	Day	28% 2 8% 34% 24% 4	2958
	11th to 20th	Day	29% 2 5% 22% 32% 10%	3389
	21st to end	Day	42% 2 5% 26% 20% 5%	4488
January	1st to 10th	Night	37% 2 7% 28% 22% 4	5888
	11th to 20th	Night	20% 2 11% 20% 35% 13%	5900
	21st to end	Night	36% 1 6% 18% 29% 9%	6490
February	1st to 10th	Night	35% 2 7% 22% 26% 9%	2477
	11th to 20th	Night	33% 3 8% 24% 23% 9%	2338
	21st to end	Night	33% 2 5% 19% 26% 16%	1980
March	1st to 10th	Night	29% 2 4 17% 25% 23%	5062
	11th to 20th	Night	21% 1 5% 23% 23% 27%	4980
	21st to end	Night	33% 3 11% 23% 27% 4	5467
April	1st to 10th	Night	28% 3 9% 23% 24% 14%	2200
	11th to 20th	Night	30% 4 10% 23% 21% 12%	1976
	21st to end	Night	32% 4 12% 26% 22% 5%	1800
May	1st to 10th	Night	39% 3 13% 19% 21% 5%	4080
	11th to 20th	Night	28% 3 11% 24% 22% 11%	4054
	21st to end	Night	31% 5% 14% 20% 19% 11%	4452
June	1st to 10th	Night	23% 4 17% 33% 19% 5%	1800
	11th to 20th	Night	23% 4 15% 29% 24% 7%	1800
	21st to end	Night	17% 4 12% 29% 29% 9%	1800
July	1st to 10th	Night	32% 6% 16% 28% 15% 3	4035
	11th to 20th	Night	17% 4 12% 36% 26% 5%	4026
	21st to end	Night	15% 3 14% 36% 29% 3	4320
August	1st to 10th	Night	15% 3 11% 27% 35% 9%	2916
	11th to 20th	Night	23% 4 10% 34% 25% 4	2915
	21st to end	Night	17% 4 14% 38% 22% 5%	3614
September	1st to 10th	Night	26% 4 8% 23% 27% 12%	2200
	11th to 20th	Night	32% 4 8% 21% 26% 9%	2200
	21st to end	Night	23% 3 6% 26% 31% 12%	2200
October	1st to 10th	Night	15% 2 6% 15% 38% 22%	3590
	11th to 20th	Night	18% 2 6% 19% 36% 20%	3883
	21st to end	Night	20% 2 6% 28% 34% 11%	4252
November	1st to 10th	Night	22% 2 7% 23% 33% 14%	2570
	11th to 20th	Night	23% 2 6% 25% 32% 12%	2730
	21st to end	Night	30% 2 6% 22% 28% 12%	2730
December	1st to 10th	Night	23% 2 6% 35% 28% 5%	4277
	11th to 20th	Night	28% 2 5% 23% 32% 10%	4817
	21st to end	Night	37% 2 5% 25% 23% 7%	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	14% 16% 36% 24% 10% 1	300
	11th to 20th	Day	18% 18% 34% 25% 5% 1	300
	21st to end	Day	15% 13% 42% 21% 9% 1	330
February	1st to 10th	Day	20% 16% 38% 22% 4	300
	11th to 20th	Day	16% 21% 43% 17% 3	300
	21st to end	Day	21% 18% 37% 20% 3	249
March	1st to 10th	Day	19% 17% 37% 21% 5%	300
	11th to 20th	Day	20% 18% 39% 17% 5% 1	300
	21st to end	Day	18% 17% 41% 18% 5% 1	330
April	1st to 10th	Day	18% 18% 32% 23% 9%	300
	11th to 20th	Day	20% 18% 38% 21% 3	486
	21st to end	Day	20% 15% 32% 25% 7% 2	700
May	1st to 10th	Day	14% 10% 39% 29% 8% 1	703
	11th to 20th	Day	16% 8% 32% 28% 14% 2	725
	21st to end	Day	14% 7% 34% 25% 16% 4	789
June	1st to 10th	Day	8% 4 21% 39% 23% 6%	730
	11th to 20th	Day	6% 3 25% 43% 18% 4	730
	21st to end	Day	4 2 19% 47% 22% 6%	730
July	1st to 10th	Day	6% 2 12% 36% 34% 11%	721
	11th to 20th	Day	4 1 13% 40% 34% 8%	718
	21st to end	Day	3 2 8% 37% 37% 13%	794
August	1st to 10th	Day	5% 1 10% 43% 34% 7%	726
	11th to 20th	Day	8% 1 12% 35% 35% 9%	715
	21st to end	Day	7% 2 7% 35% 36% 12%	570
September	1st to 10th	Day	9% 2 12% 33% 30% 14%	330
	11th to 20th	Day	5% 13% 40% 31% 10%	330
	21st to end	Day	12% 5% 13% 38% 21% 11%	330
October	1st to 10th	Day	8% 4 25% 35% 20% 8%	330
	11th to 20th	Day	10% 11% 28% 36% 14% 1	330
	21st to end	Day	22% 9% 29% 26% 11% 2	363
November	1st to 10th	Day	17% 8% 34% 29% 11% 2	330
	11th to 20th	Day	13% 10% 37% 28% 9% 2	330
	21st to end	Day	17% 11% 40% 22% 10% 1	330
December	1st to 10th	Day	10% 14% 38% 25% 12% 1	306
	11th to 20th	Day	15% 13% 38% 24% 10% 1	300
	21st to end	Day	23% 14% 34% 24% 5%	330
January	1st to 10th	Night	12% 10% 40% 30% 7% 1	1000
	11th to 20th	Night	13% 14% 33% 35% 6%	1000
	21st to end	Night	12% 10% 39% 33% 6%	1100
February	1st to 10th	Night	15% 12% 41% 27% 5%	877
	11th to 20th	Night	16% 15% 38% 26% 5%	784
	21st to end	Night	16% 14% 40% 27% 3	660
March	1st to 10th	Night	12% 13% 37% 34% 4	670
	11th to 20th	Night	16% 12% 39% 27% 6%	600
	21st to end	Night	11% 15% 43% 25% 5%	660
April	1st to 10th	Night	14% 16% 42% 24% 5%	600
	11th to 20th	Night	14% 12% 44% 25% 5%	593
	21st to end	Night	15% 10% 41% 27% 7% 1	600
May	1st to 10th	Night	12% 10% 41% 30% 7%	600
	11th to 20th	Night	12% 7% 35% 33% 12% 1	591
	21st to end	Night	7% 5% 36% 35% 14% 3	650
June	1st to 10th	Night	7% 3 24% 43% 21% 2	600
	11th to 20th	Night	6% 3 29% 49% 13%	600
	21st to end	Night	3 1 27% 49% 19% 2	600
July	1st to 10th	Night	5% 1 14% 46% 31% 2	585
	11th to 20th	Night	2 1 13% 50% 32% 2	582
	21st to end	Night	4 8% 52% 33% 2	657
August	1st to 10th	Night	2 1 14% 50% 31% 2	597
	11th to 20th	Night	6% 2 14% 44% 32% 2	594
	21st to end	Night	3 1 9% 46% 38% 2	660
September	1st to 10th	Night	8% 2 14% 45% 29% 2	600
	11th to 20th	Night	13% 2 18% 38% 26% 3	600
	21st to end	Night	9% 3 19% 44% 22% 3	600
October	1st to 10th	Night	8% 5% 26% 38% 22% 1	600
	11th to 20th	Night	11% 7% 33% 36% 12%	784
	21st to end	Night	16% 9% 32% 31% 12% 1	880
November	1st to 10th	Night	10% 6% 35% 36% 11% 1	930
	11th to 20th	Night	8% 12% 33% 36% 11%	1050
	21st to end	Night	14% 11% 34% 30% 10%	1050
December	1st to 10th	Night	11% 11% 35% 36% 7%	1011
	11th to 20th	Night	16% 9% 37% 30% 7%	1000
	21st to end	Night	15% 11% 35% 31% 7%	1100

Page generated at 2025-11-30 00:00:57. Version ac07

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