Camp Onas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp Onas clear sky chart from 2005-11-06 to 2025-10-19.

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	16% 7% 2 6% 4 4 4 4 5% 7% 40%	126745
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	122964
Transparency	Day	43% 3 11% 24% 16% 3	130260
	Night	42% 3 11% 24% 17% 3	127536
Seeing	Day	22% 16% 29% 21% 10% 3	16198
	Night	20% 15% 30% 25% 9% 1	25400

By Month

Percentage Cloud Cover NE (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	13% 8% 2 6% 3 4 3 4 4 5% 49%	3597
	11th to 20th	Day	13% 9% 3 11% 5% 5% 4 3 4 5% 38%	3616
	21st to end	Day	17% 9% 4 7% 4 4 3 3 4 5% 40%	4466
February	1st to 10th	Day	17% 8% 3 6% 6% 4 5% 4 6% 7% 37%	1800
	11th to 20th	Day	16% 10% 3 8% 5% 4 4 3 5% 5% 39%	1898
	21st to end	Day	19% 9% 3 6% 4 4 4 3 4 5% 39%	1650
March	1st to 10th	Day	21% 7% 2 5% 3 3 3 3 4 5% 43%	4476
	11th to 20th	Day	12% 7% 2 6% 5% 5% 5% 4 5% 6% 43%	4968
	21st to end	Day	18% 6% 2 5% 4 3 4 3 5% 7% 43%	5804
April	1st to 10th	Day	18% 8% 3 7% 5% 4 4 3 5% 5% 39%	2400
	11th to 20th	Day	17% 7% 2 5% 5% 4 4 3 5% 8% 40%	2374
	21st to end	Day	16% 6% 2 6% 5% 5% 4 4 6% 7% 40%	2400
May	1st to 10th	Day	27% 7% 2 6% 4 4 4 4 5% 8% 29%	5894
	11th to 20th	Day	24% 9% 3 6% 4 4 3 3 5% 6% 33%	6318
	21st to end	Day	20% 6% 2 6% 3 4 4 4 6% 8% 36%	6949
June	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 5% 6% 9% 38%	2800
	11th to 20th	Day	15% 7% 2 6% 6% 5% 5% 4 6% 8% 37%	2800
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 8% 41%	2800
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 4 7% 10% 38%	6360
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 11% 33%	6360
	21st to end	Day	12% 6% 2 7% 4 5% 5% 4 5% 9% 41%	6885
August	1st to 10th	Day	21% 5% 2 6% 5% 4 5% 4 6% 8% 33%	4234
	11th to 20th	Day	13% 6% 2 5% 4 5% 5% 4 6% 10% 42%	3859
	21st to end	Day	12% 5% 2 5% 3 3 4 3 5% 8% 49%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 44%	2400
	11th to 20th	Day	13% 4 2 4 3 3 3 3 5% 8% 51%	2364
	21st to end	Day	19% 6% 2 8% 5% 4 4 3 5% 6% 38%	2200
October	1st to 10th	Day	18% 6% 2 5% 3 4 4 3 4 6% 44%	2008
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 6% 47%	1980
	21st to end	Day	19% 7% 2 5% 3 4 4 3 4 6% 44%	2007
November	1st to 10th	Day	13% 6% 2 5% 3 2 3 3 4 6% 52%	1761
	11th to 20th	Day	16% 5% 2 4 3 3 4 4 5% 6% 47%	1800
	21st to end	Day	15% 7% 2 4 4 4 4 3 6% 7% 44%	1659
December	1st to 10th	Day	15% 8% 2 6% 4 3 4 4 6% 7% 42%	2600
	11th to 20th	Day	22% 9% 2 5% 3 3 3 3 4 6% 41%	2986
	21st to end	Day	17% 6% 3 7% 5% 4 5% 4 6% 6% 37%	3960
January	1st to 10th	Night	13% 6% 2 6% 4 3 4 3 4 6% 50%	6349
	11th to 20th	Night	14% 8% 3 7% 4 4 4 3 4 6% 46%	6255
	21st to end	Night	18% 8% 2 5% 4 3 4 3 4 5% 43%	6490
February	1st to 10th	Night	17% 9% 3 5% 5% 4 3 4 5% 6% 40%	2600
	11th to 20th	Night	18% 9% 2 7% 4 4 3 3 4 5% 41%	2387
	21st to end	Night	18% 8% 2 5% 4 3 4 4 5% 6% 41%	1980
March	1st to 10th	Night	19% 8% 2 5% 3 3 4 3 4 5% 44%	5364
	11th to 20th	Night	13% 8% 2 5% 3 3 3 3 4 5% 50%	4988
	21st to end	Night	17% 8% 2 6% 4 4 4 3 4 5% 43%	5113
April	1st to 10th	Night	18% 6% 3 6% 4 5% 4 4 6% 6% 38%	2000
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 4 5% 7% 39%	1975
	21st to end	Night	18% 6% 1 5% 3 2 3 3 5% 8% 44%	2000
May	1st to 10th	Night	26% 8% 3 6% 4 3 4 4 6% 8% 28%	4090
	11th to 20th	Night	24% 9% 3 6% 4 4 4 3 5% 6% 33%	3575
	21st to end	Night	22% 6% 2 6% 4 4 3 3 6% 8% 36%	3926
June	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 5% 7% 42%	1600
	11th to 20th	Night	14% 5% 2 6% 5% 4 5% 5% 7% 8% 40%	1600
	21st to end	Night	11% 4 2 5% 5% 5% 6% 4 7% 9% 43%	1600
July	1st to 10th	Night	10% 6% 3 8% 6% 6% 5% 4 7% 9% 37%	3600
	11th to 20th	Night	13% 8% 3 8% 5% 4 5% 5% 7% 10% 31%	3600
	21st to end	Night	12% 6% 2 5% 4 4 4 4 6% 8% 44%	3963
August	1st to 10th	Night	22% 6% 2 6% 4 4 5% 4 6% 7% 34%	2915
	11th to 20th	Night	14% 7% 2 6% 5% 5% 5% 4 6% 7% 41%	3157
	21st to end	Night	11% 5% 2 5% 4 3 4 4 6% 8% 49%	3586
September	1st to 10th	Night	15% 6% 3 5% 4 4 4 3 4 6% 47%	2000
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 4 7% 52%	2035
	21st to end	Night	18% 7% 2 6% 4 4 4 3 5% 7% 41%	2200
October	1st to 10th	Night	18% 6% 3 6% 3 4 3 3 4 6% 44%	2390
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 5% 5% 50%	2377
	21st to end	Night	20% 6% 2 4 3 2 3 3 4 6% 46%	2589
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 4 6% 53%	2537
	11th to 20th	Night	18% 6% 2 4 3 3 4 3 3 4 48%	2600
	21st to end	Night	14% 6% 2 6% 4 4 4 3 7% 7% 43%	2739
December	1st to 10th	Night	13% 8% 3 6% 4 3 4 3 4 6% 46%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 3 3 4 5% 41%	5208
	21st to end	Night	20% 9% 3 7% 4 3 3 3 4 5% 40%	6996

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	39% 2 8% 28% 22% 2	3598
	11th to 20th	Day	49% 2 8% 21% 14% 6%	3646
	21st to end	Day	48% 2 11% 23% 15% 1	4466
February	1st to 10th	Day	46% 4 13% 23% 12% 2	1800
	11th to 20th	Day	48% 3 8% 24% 15% 2	1907
	21st to end	Day	49% 3 8% 24% 12% 3	1650
March	1st to 10th	Day	45% 2 7% 24% 15% 7%	4479
	11th to 20th	Day	41% 2 10% 29% 12% 5%	4968
	21st to end	Day	43% 2 10% 16% 24% 5%	5804
April	1st to 10th	Day	47% 4 8% 21% 14% 5%	2400
	11th to 20th	Day	43% 4 12% 21% 17% 4	2374
	21st to end	Day	43% 4 9% 22% 17% 4	2400
May	1st to 10th	Day	54% 3 13% 18% 10% 1	5905
	11th to 20th	Day	54% 3 8% 23% 12% 1	6322
	21st to end	Day	46% 4 10% 24% 15% 1	6949
June	1st to 10th	Day	42% 6% 13% 23% 15% 1	2800
	11th to 20th	Day	44% 5% 14% 23% 11% 2	2800
	21st to end	Day	39% 5% 15% 25% 15% 1	2800
July	1st to 10th	Day	41% 6% 14% 22% 16% 1	6290
	11th to 20th	Day	45% 4 17% 23% 10% 1	6285
	21st to end	Day	41% 3 10% 22% 23% 1	6687
August	1st to 10th	Day	48% 5% 13% 24% 10%	4221
	11th to 20th	Day	39% 3 13% 30% 14% 1	3895
	21st to end	Day	35% 3 10% 30% 20% 2	4312
September	1st to 10th	Day	39% 5% 11% 22% 21% 3	2400
	11th to 20th	Day	33% 3 9% 27% 24% 3	2364
	21st to end	Day	48% 3 8% 19% 19% 2	2200
October	1st to 10th	Day	38% 3 8% 21% 25% 5%	3268
	11th to 20th	Day	29% 2 10% 27% 26% 5%	3220
	21st to end	Day	27% 2 13% 25% 28% 4	3284
November	1st to 10th	Day	35% 3 13% 25% 21% 3	1761
	11th to 20th	Day	38% 3 9% 27% 20% 3	1800
	21st to end	Day	40% 3 13% 30% 12% 2	1659
December	1st to 10th	Day	43% 2 16% 26% 11% 2	2600
	11th to 20th	Day	47% 2 13% 26% 11% 2	2986
	21st to end	Day	48% 2 10% 24% 15% 1	3960
January	1st to 10th	Night	38% 2 8% 27% 21% 4	6349
	11th to 20th	Night	42% 2 12% 23% 15% 6%	6300
	21st to end	Night	45% 2 9% 23% 18% 3	6490
February	1st to 10th	Night	45% 3 13% 26% 11% 2	2600
	11th to 20th	Night	46% 4 8% 21% 18% 4	2389
	21st to end	Night	44% 3 7% 24% 18% 4	1980
March	1st to 10th	Night	44% 2 8% 24% 13% 9%	5374
	11th to 20th	Night	38% 2 14% 27% 14% 5%	4989
	21st to end	Night	45% 2 6% 17% 24% 5%	5113
April	1st to 10th	Night	46% 4 10% 21% 16% 4	2000
	11th to 20th	Night	44% 4 9% 21% 19% 2	1975
	21st to end	Night	39% 5% 9% 23% 20% 5%	2000
May	1st to 10th	Night	55% 3 12% 18% 10% 2	4096
	11th to 20th	Night	54% 3 12% 17% 13% 1	3576
	21st to end	Night	46% 4 12% 24% 12% 2	3927
June	1st to 10th	Night	41% 6% 10% 22% 20% 2	1600
	11th to 20th	Night	40% 7% 14% 26% 13% 1	1600
	21st to end	Night	37% 5% 14% 28% 15% 1	1600
July	1st to 10th	Night	43% 6% 15% 19% 16% 2	3560
	11th to 20th	Night	48% 4 15% 21% 10% 1	3552
	21st to end	Night	38% 4 13% 23% 21% 1	3846
August	1st to 10th	Night	49% 4 18% 18% 10% 1	2904
	11th to 20th	Night	43% 3 12% 26% 15% 1	3187
	21st to end	Night	34% 3 9% 31% 21% 1	3586
September	1st to 10th	Night	40% 5% 10% 21% 22% 2	2000
	11th to 20th	Night	34% 3 10% 24% 26% 4	2035
	21st to end	Night	44% 3 8% 22% 22% 1	2200
October	1st to 10th	Night	42% 2 8% 24% 21% 2	3910
	11th to 20th	Night	28% 2 9% 30% 28% 4	3876
	21st to end	Night	29% 2 11% 33% 22% 3	4262
November	1st to 10th	Night	32% 4 12% 25% 22% 4	2537
	11th to 20th	Night	40% 3 9% 24% 20% 4	2600
	21st to end	Night	40% 3 12% 28% 15% 2	2739
December	1st to 10th	Night	42% 2 12% 31% 12% 2	4580
	11th to 20th	Night	46% 3 10% 25% 13% 3	5208
	21st to end	Night	48% 2 9% 21% 17% 2	6996

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	26% 33% 28% 13% 1 1	200
	11th to 20th	Day	32% 30% 27% 8% 2	210
	21st to end	Day	23% 33% 28% 12% 4	330
February	1st to 10th	Day	29% 29% 32% 7% 3	300
	11th to 20th	Day	33% 27% 30% 9% 1	446
	21st to end	Day	33% 23% 28% 13% 3	414
March	1st to 10th	Day	29% 24% 30% 14% 3	500
	11th to 20th	Day	25% 27% 32% 13% 2 1	500
	21st to end	Day	28% 27% 31% 10% 4 1	550
April	1st to 10th	Day	28% 27% 28% 13% 4 1	500
	11th to 20th	Day	27% 24% 29% 12% 6% 2	492
	21st to end	Day	27% 17% 34% 16% 5% 1	500
May	1st to 10th	Day	31% 20% 28% 14% 5% 2	503
	11th to 20th	Day	24% 15% 32% 20% 6% 1	527
	21st to end	Day	21% 10% 28% 25% 13% 2	573
June	1st to 10th	Day	17% 14% 30% 25% 11% 3	530
	11th to 20th	Day	19% 15% 26% 26% 12% 3	530
	21st to end	Day	16% 11% 32% 27% 12% 2	530
July	1st to 10th	Day	11% 7% 23% 32% 20% 6%	525
	11th to 20th	Day	10% 5% 26% 31% 22% 6%	524
	21st to end	Day	14% 6% 32% 32% 13% 3	576
August	1st to 10th	Day	12% 7% 27% 30% 18% 6%	526
	11th to 20th	Day	15% 6% 20% 34% 18% 6%	519
	21st to end	Day	13% 5% 30% 29% 15% 8%	583
September	1st to 10th	Day	18% 10% 24% 26% 15% 7%	530
	11th to 20th	Day	15% 5% 27% 27% 17% 9%	530
	21st to end	Day	24% 12% 25% 25% 11% 4	530
October	1st to 10th	Day	24% 9% 26% 21% 13% 7%	530
	11th to 20th	Day	19% 17% 30% 23% 8% 2	522
	21st to end	Day	22% 16% 34% 15% 11% 1	494
November	1st to 10th	Day	19% 14% 31% 23% 11% 2	395
	11th to 20th	Day	22% 22% 32% 19% 5% 1	400
	21st to end	Day	24% 24% 33% 14% 4	259
December	1st to 10th	Day	28% 28% 30% 9% 5%	200
	11th to 20th	Day	32% 29% 23% 13% 4	200
	21st to end	Day	27% 22% 30% 14% 7%	220
January	1st to 10th	Night	20% 27% 35% 15% 2	800
	11th to 20th	Night	27% 21% 30% 20% 3	800
	21st to end	Night	20% 25% 35% 19% 1	880
February	1st to 10th	Night	23% 20% 36% 20% 1	800
	11th to 20th	Night	26% 28% 33% 12% 1	783
	21st to end	Night	25% 24% 33% 15% 2	660
March	1st to 10th	Night	24% 25% 30% 19% 3	800
	11th to 20th	Night	23% 24% 32% 17% 4 1	800
	21st to end	Night	23% 20% 37% 16% 4	880
April	1st to 10th	Night	22% 24% 34% 17% 4	800
	11th to 20th	Night	23% 17% 35% 19% 6%	791
	21st to end	Night	23% 15% 33% 24% 5%	800
May	1st to 10th	Night	27% 13% 30% 24% 6%	623
	11th to 20th	Night	22% 11% 36% 22% 10%	394
	21st to end	Night	18% 6% 25% 37% 12% 2	433
June	1st to 10th	Night	17% 7% 28% 36% 12%	400
	11th to 20th	Night	15% 6% 29% 39% 10% 1	400
	21st to end	Night	12% 3 27% 46% 12% 1	400
July	1st to 10th	Night	12% 4 25% 40% 17% 2	390
	11th to 20th	Night	10% 3 26% 40% 20% 1	388
	21st to end	Night	11% 5% 24% 39% 21% 2	450
August	1st to 10th	Night	14% 2 17% 42% 24% 2	597
	11th to 20th	Night	14% 3 16% 39% 25% 2	762
	21st to end	Night	15% 4 18% 39% 22% 2	880
September	1st to 10th	Night	18% 3 27% 34% 17% 2	800
	11th to 20th	Night	14% 5% 21% 35% 21% 4	800
	21st to end	Night	21% 7% 22% 32% 16% 1	800
October	1st to 10th	Night	21% 9% 26% 24% 18% 3	800
	11th to 20th	Night	19% 13% 29% 29% 11%	793
	21st to end	Night	23% 15% 31% 23% 8%	836
November	1st to 10th	Night	15% 15% 33% 26% 10% 1	780
	11th to 20th	Night	22% 19% 28% 24% 7%	800
	21st to end	Night	18% 21% 33% 22% 5% 1	800
December	1st to 10th	Night	26% 20% 30% 19% 5% 1	800
	11th to 20th	Night	22% 19% 35% 20% 4	800
	21st to end	Night	22% 20% 33% 22% 3	880

Page generated at 2025-10-16 01:50:30. Version ac07

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