Ophelia Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ophelia 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	12% 6% 2 6% 4 4 4 4 6% 8% 43%	127013
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	124340
Transparency	Day	23% 39% 9% 15% 11% 2	130602
	Night	24% 38% 7% 16% 12% 3	128820
Seeing	Day	15% 4 16% 31% 25% 9%	16620
	Night	17% 6% 22% 33% 19% 3	26181

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% 4 1 4 3 3 3 2 5% 7% 54%	3674
	11th to 20th	Day	11% 8% 2 6% 5% 4 3 3 4 5% 49%	4060
	21st to end	Day	12% 7% 3 9% 5% 5% 4 4 5% 6% 42%	4466
February	1st to 10th	Day	13% 8% 3 6% 5% 4 4 4 7% 7% 39%	1800
	11th to 20th	Day	20% 6% 2 5% 4 3 4 3 4 6% 44%	1893
	21st to end	Day	16% 8% 2 6% 5% 4 5% 4 5% 6% 40%	1650
March	1st to 10th	Day	17% 6% 2 6% 4 4 4 4 6% 8% 39%	4709
	11th to 20th	Day	10% 7% 2 4 3 3 4 2 5% 7% 52%	4980
	21st to end	Day	15% 8% 2 5% 4 4 4 3 5% 7% 43%	5648
April	1st to 10th	Day	12% 7% 2 5% 4 3 4 3 6% 7% 48%	2400
	11th to 20th	Day	10% 6% 2 5% 4 5% 4 3 5% 6% 49%	2374
	21st to end	Day	14% 6% 2 6% 3 4 4 4 5% 8% 45%	2400
May	1st to 10th	Day	15% 8% 3 6% 5% 4 5% 4 6% 10% 34%	5467
	11th to 20th	Day	18% 7% 2 6% 5% 5% 5% 4 6% 9% 34%	6221
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 7% 9% 41%	6934
June	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 7% 11% 44%	2800
	11th to 20th	Day	10% 4 1 5% 4 5% 5% 4 7% 11% 45%	2800
	21st to end	Day	7% 4 2 4 4 5% 5% 5% 7% 10% 47%	2800
July	1st to 10th	Day	6% 4 2 6% 4 4 5% 5% 7% 12% 43%	6360
	11th to 20th	Day	10% 6% 3 7% 6% 6% 6% 5% 9% 12% 31%	6222
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 8% 11% 42%	6424
August	1st to 10th	Day	13% 8% 3 7% 4 5% 5% 4 8% 11% 33%	4234
	11th to 20th	Day	10% 5% 2 8% 6% 6% 5% 4 6% 9% 39%	3854
	21st to end	Day	9% 4 1 4 3 4 4 3 6% 9% 52%	4312
September	1st to 10th	Day	13% 5% 2 5% 3 4 4 4 6% 8% 47%	2400
	11th to 20th	Day	12% 7% 2 7% 4 3 4 4 5% 7% 46%	2400
	21st to end	Day	20% 8% 3 6% 3 4 4 3 5% 6% 38%	2143
October	1st to 10th	Day	14% 5% 2 6% 4 4 4 3 5% 6% 47%	2000
	11th to 20th	Day	17% 5% 2 4 4 2 3 3 4 6% 51%	2000
	21st to end	Day	12% 6% 2 5% 4 3 4 3 4 7% 49%	2200
November	1st to 10th	Day	14% 6% 1 5% 3 3 3 2 4 7% 52%	1914
	11th to 20th	Day	13% 6% 2 6% 4 3 4 3 6% 6% 47%	1890
	21st to end	Day	14% 4 2 5% 4 3 4 3 5% 5% 50%	1786
December	1st to 10th	Day	11% 6% 2 5% 3 3 3 2 5% 7% 54%	2680
	11th to 20th	Day	18% 7% 3 6% 3 3 3 3 3 5% 46%	3070
	21st to end	Day	12% 5% 2 5% 4 4 4 4 5% 8% 47%	4048
January	1st to 10th	Night	12% 6% 2 5% 4 4 3 3 4 6% 50%	6290
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 3 5% 53%	5900
	21st to end	Night	14% 8% 3 6% 3 3 3 2 4 5% 47%	6490
February	1st to 10th	Night	15% 9% 2 6% 3 3 3 3 5% 6% 43%	2600
	11th to 20th	Night	20% 7% 3 4 4 3 3 3 5% 6% 42%	2392
	21st to end	Night	17% 8% 2 4 3 3 4 3 5% 5% 46%	1980
March	1st to 10th	Night	17% 7% 2 5% 4 4 4 2 4 5% 46%	5126
	11th to 20th	Night	13% 7% 3 4 3 3 3 3 5% 6% 50%	4980
	21st to end	Night	15% 8% 3 6% 3 3 3 3 4 6% 46%	5270
April	1st to 10th	Night	15% 7% 3 6% 5% 4 4 4 6% 7% 40%	2000
	11th to 20th	Night	12% 5% 2 6% 5% 3 4 3 5% 7% 48%	1975
	21st to end	Night	15% 6% 1 6% 4 3 5% 3 6% 7% 45%	2000
May	1st to 10th	Night	15% 7% 3 8% 5% 5% 5% 4 6% 9% 32%	4457
	11th to 20th	Night	21% 8% 3 7% 4 4 4 4 6% 7% 32%	3672
	21st to end	Night	15% 7% 2 7% 4 3 5% 3 6% 9% 39%	3920
June	1st to 10th	Night	12% 5% 2 5% 6% 5% 5% 4 6% 8% 42%	1600
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 5% 6% 11% 40%	1600
	21st to end	Night	7% 5% 2 6% 5% 4 7% 4 7% 11% 43%	1600
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 38%	3598
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 5% 9% 13% 32%	3730
	21st to end	Night	9% 6% 2 8% 5% 5% 6% 5% 7% 10% 37%	4427
August	1st to 10th	Night	16% 8% 3 6% 5% 4 5% 4 8% 10% 31%	2915
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 4 6% 9% 40%	3161
	21st to end	Night	10% 4 2 5% 4 4 4 3 5% 8% 51%	3586
September	1st to 10th	Night	14% 5% 2 6% 4 4 4 3 5% 8% 48%	2000
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 46%	2000
	21st to end	Night	21% 7% 2 6% 4 5% 4 4 6% 7% 35%	2254
October	1st to 10th	Night	15% 6% 2 5% 4 3 4 4 6% 7% 45%	2400
	11th to 20th	Night	17% 5% 2 5% 3 3 3 3 4 5% 50%	2400
	21st to end	Night	15% 6% 2 5% 3 2 3 3 5% 6% 50%	2640
November	1st to 10th	Night	14% 6% 2 5% 4 3 3 2 5% 6% 49%	2602
	11th to 20th	Night	16% 7% 2 5% 5% 4 4 3 4 5% 46%	2730
	21st to end	Night	12% 5% 2 4 3 4 4 3 5% 7% 50%	2830
December	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 53%	4720
	11th to 20th	Night	18% 6% 3 7% 4 4 4 3 5% 6% 38%	5345
	21st to end	Night	11% 8% 3 6% 3 3 4 4 6% 7% 46%	7150

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	22% 27% 3 21% 21% 7%	3675
	11th to 20th	Day	27% 27% 4 16% 21% 6%	4060
	21st to end	Day	32% 29% 7% 21% 9% 1	4466
February	1st to 10th	Day	17% 62% 5% 11% 4 1	1800
	11th to 20th	Day	19% 61% 3 8% 7% 2	1902
	21st to end	Day	17% 62% 5% 7% 7% 2	1650
March	1st to 10th	Day	32% 31% 7% 10% 15% 5%	4709
	11th to 20th	Day	21% 30% 6% 19% 18% 6%	4980
	21st to end	Day	29% 30% 8% 13% 14% 6%	5648
April	1st to 10th	Day	16% 62% 4 9% 7% 1	2400
	11th to 20th	Day	13% 62% 6% 10% 7% 2	2374
	21st to end	Day	15% 62% 5% 11% 5% 2	2400
May	1st to 10th	Day	34% 33% 12% 14% 6% 1	5499
	11th to 20th	Day	34% 32% 10% 18% 6%	6225
	21st to end	Day	28% 31% 10% 18% 11% 2	6949
June	1st to 10th	Day	14% 64% 5% 10% 6% 1	2800
	11th to 20th	Day	11% 63% 7% 10% 8% 1	2800
	21st to end	Day	11% 61% 8% 11% 8%	2800
July	1st to 10th	Day	23% 33% 18% 15% 9% 2	6290
	11th to 20th	Day	35% 33% 18% 13% 2	6147
	21st to end	Day	25% 30% 13% 16% 16%	6240
August	1st to 10th	Day	31% 39% 12% 15% 3	4221
	11th to 20th	Day	24% 40% 9% 19% 8%	3890
	21st to end	Day	14% 38% 10% 21% 16% 1	4312
September	1st to 10th	Day	15% 59% 9% 11% 5% 1	2400
	11th to 20th	Day	17% 58% 5% 11% 7% 2	2400
	21st to end	Day	24% 58% 3 11% 3 1	2143
October	1st to 10th	Day	19% 38% 7% 15% 18% 3	3260
	11th to 20th	Day	14% 36% 3 13% 26% 8%	3240
	21st to end	Day	9% 35% 6% 20% 20% 9%	3538
November	1st to 10th	Day	17% 53% 5% 13% 9% 3	1914
	11th to 20th	Day	17% 55% 5% 9% 12% 3	1890
	21st to end	Day	16% 54% 4 14% 10% 1	1786
December	1st to 10th	Day	21% 36% 6% 22% 13% 3	2680
	11th to 20th	Day	30% 31% 9% 15% 12% 3	3066
	21st to end	Day	27% 28% 11% 23% 11% 1	4048
January	1st to 10th	Night	27% 26% 3 16% 22% 5%	6290
	11th to 20th	Night	24% 26% 3 20% 21% 5%	5900
	21st to end	Night	30% 29% 5% 22% 13% 2	6490
February	1st to 10th	Night	17% 62% 7% 10% 5% 1	2600
	11th to 20th	Night	18% 60% 3 8% 8% 2	2394
	21st to end	Night	15% 62% 4 9% 7% 3	1980
March	1st to 10th	Night	31% 30% 4 15% 13% 7%	5126
	11th to 20th	Night	23% 29% 7% 17% 18% 6%	4980
	21st to end	Night	28% 30% 5% 18% 13% 6%	5270
April	1st to 10th	Night	19% 63% 3 7% 8% 1	2000
	11th to 20th	Night	15% 62% 4 10% 7% 2	1975
	21st to end	Night	17% 62% 5% 8% 7% 1	2000
May	1st to 10th	Night	37% 31% 11% 15% 4 1	4487
	11th to 20th	Night	38% 31% 9% 16% 6%	3673
	21st to end	Night	32% 32% 9% 18% 10%	3927
June	1st to 10th	Night	17% 63% 4 8% 6% 1	1600
	11th to 20th	Night	13% 64% 6% 10% 7% 1	1600
	21st to end	Night	11% 63% 6% 11% 7% 2	1600
July	1st to 10th	Night	31% 32% 14% 13% 10% 1	3560
	11th to 20th	Night	34% 32% 21% 12% 2	3685
	21st to end	Night	30% 31% 10% 18% 12%	4297
August	1st to 10th	Night	34% 38% 10% 14% 3	2904
	11th to 20th	Night	24% 40% 12% 18% 7%	3191
	21st to end	Night	16% 37% 6% 19% 21% 1	3586
September	1st to 10th	Night	14% 59% 9% 11% 5% 2	2000
	11th to 20th	Night	16% 59% 4 11% 8% 2	2000
	21st to end	Night	26% 57% 6% 8% 3	2254
October	1st to 10th	Night	23% 37% 7% 14% 16% 3	3920
	11th to 20th	Night	13% 36% 5% 15% 24% 7%	3899
	21st to end	Night	9% 35% 4 25% 18% 9%	4252
November	1st to 10th	Night	19% 53% 5% 11% 10% 2	2602
	11th to 20th	Night	18% 54% 4 9% 10% 5%	2730
	21st to end	Night	14% 54% 5% 13% 12% 1	2830
December	1st to 10th	Night	19% 35% 7% 20% 17% 2	4720
	11th to 20th	Night	33% 32% 8% 15% 8% 4	5348
	21st to end	Night	28% 27% 10% 23% 11% 1	7150

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	17% 8% 26% 40% 8%	217
	11th to 20th	Day	17% 9% 33% 33% 8% 1	300
	21st to end	Day	17% 4 23% 45% 11% 1	330
February	1st to 10th	Day	17% 6% 22% 40% 14%	300
	11th to 20th	Day	25% 6% 32% 29% 7%	441
	21st to end	Day	22% 5% 27% 36% 10%	414
March	1st to 10th	Day	17% 6% 27% 35% 12% 2	500
	11th to 20th	Day	18% 6% 24% 39% 11% 2	500
	21st to end	Day	19% 4 23% 39% 13% 2	550
April	1st to 10th	Day	15% 5% 27% 36% 15% 2	500
	11th to 20th	Day	10% 4 22% 39% 21% 4	492
	21st to end	Day	16% 5% 17% 33% 26% 3	500
May	1st to 10th	Day	18% 4 16% 35% 21% 6%	503
	11th to 20th	Day	19% 2 13% 32% 28% 6%	527
	21st to end	Day	18% 3 8% 28% 31% 12%	573
June	1st to 10th	Day	11% 2 8% 31% 36% 12%	530
	11th to 20th	Day	11% 1 9% 28% 37% 14%	530
	21st to end	Day	10% 2 6% 29% 38% 15%	530
July	1st to 10th	Day	9% 2 4 24% 40% 20%	525
	11th to 20th	Day	5% 2 2 20% 49% 21%	524
	21st to end	Day	10% 2 4 25% 43% 16%	576
August	1st to 10th	Day	12% 2 6% 27% 40% 13%	526
	11th to 20th	Day	11% 4 5% 24% 39% 18%	519
	21st to end	Day	10% 2 5% 28% 36% 20%	583
September	1st to 10th	Day	15% 1 7% 25% 32% 20%	530
	11th to 20th	Day	15% 2 8% 23% 35% 18%	530
	21st to end	Day	24% 5% 11% 28% 23% 8%	530
October	1st to 10th	Day	18% 3 9% 28% 27% 16%	530
	11th to 20th	Day	18% 5% 19% 27% 24% 8%	530
	21st to end	Day	14% 5% 21% 31% 22% 7%	583
November	1st to 10th	Day	16% 5% 21% 31% 20% 6%	459
	11th to 20th	Day	13% 10% 29% 32% 14% 2	430
	21st to end	Day	15% 7% 26% 31% 18% 2	326
December	1st to 10th	Day	19% 5% 25% 40% 11% 1	220
	11th to 20th	Day	21% 5% 24% 36% 13%	220
	21st to end	Day	17% 6% 24% 40% 12% 1	242
January	1st to 10th	Night	18% 13% 37% 27% 6%	805
	11th to 20th	Night	20% 10% 31% 31% 9%	800
	21st to end	Night	21% 10% 34% 32% 4	880
February	1st to 10th	Night	19% 7% 31% 37% 5% 1	800
	11th to 20th	Night	22% 11% 36% 27% 4	783
	21st to end	Night	19% 10% 30% 35% 5% 1	660
March	1st to 10th	Night	18% 9% 31% 34% 8% 1	800
	11th to 20th	Night	19% 6% 30% 33% 9% 2	800
	21st to end	Night	19% 5% 30% 38% 8% 1	880
April	1st to 10th	Night	18% 6% 33% 32% 10% 1	800
	11th to 20th	Night	14% 5% 26% 39% 15% 1	791
	21st to end	Night	18% 5% 21% 40% 15% 2	800
May	1st to 10th	Night	18% 5% 21% 40% 15% 2	793
	11th to 20th	Night	18% 4 21% 37% 20% 1	439
	21st to end	Night	15% 3 11% 32% 33% 6%	433
June	1st to 10th	Night	13% 3 14% 34% 33% 4	400
	11th to 20th	Night	12% 3 10% 37% 33% 6%	400
	21st to end	Night	7% 3 9% 40% 36% 5%	400
July	1st to 10th	Night	10% 3 4 37% 38% 8%	390
	11th to 20th	Night	6% 2 4 34% 45% 9%	443
	21st to end	Night	8% 3 6% 37% 41% 5%	657
August	1st to 10th	Night	11% 2 6% 37% 38% 7%	597
	11th to 20th	Night	13% 3 7% 33% 38% 7%	766
	21st to end	Night	11% 2 6% 33% 39% 9%	880
September	1st to 10th	Night	15% 2 8% 31% 34% 10%	800
	11th to 20th	Night	13% 2 9% 29% 39% 9%	800
	21st to end	Night	25% 4 12% 30% 26% 3	800
October	1st to 10th	Night	19% 3 16% 27% 26% 9%	800
	11th to 20th	Night	19% 7% 21% 30% 20% 3	800
	21st to end	Night	18% 7% 24% 29% 19% 4	880
November	1st to 10th	Night	17% 6% 22% 31% 19% 4	820
	11th to 20th	Night	19% 9% 27% 31% 12% 1	840
	21st to end	Night	14% 11% 28% 32% 14% 2	840
December	1st to 10th	Night	20% 9% 32% 27% 10% 2	840
	11th to 20th	Night	18% 8% 36% 29% 9%	840
	21st to end	Night	17% 9% 30% 33% 11%	924

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