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 2024-01-13.

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	13% 5% 2 4 5% 3 4 5% 6% 8% 44%	74697
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 43%	75052
Transparency	Day	37% 5% 13% 25% 16% 3	74407
	Night	40% 5% 12% 24% 17% 3	74861
Seeing	Day	16% 4 15% 31% 26% 9%	14015
	Night	17% 6% 22% 33% 19% 3	23624

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% 6% 2 4 6% 3 4 4 5% 9% 43%	1545
	11th to 20th	Day	16% 8% 3 5% 5% 2 3 5% 6% 7% 41%	1644
	21st to end	Day	16% 6% 3 5% 5% 3 3 4 5% 7% 44%	1782
February	1st to 10th	Day	13% 8% 3 5% 6% 3 4 5% 7% 7% 38%	1620
	11th to 20th	Day	19% 5% 2 5% 4 2 3 3 4 6% 46%	1698
	21st to end	Day	17% 8% 2 5% 6% 3 5% 5% 6% 6% 38%	1480
March	1st to 10th	Day	14% 5% 2 4 3 2 3 4 4 7% 50%	1890
	11th to 20th	Day	17% 6% 2 4 4 3 4 4 5% 8% 43%	1980
	21st to end	Day	16% 6% 2 4 6% 3 5% 4 5% 6% 42%	2250
April	1st to 10th	Day	12% 6% 2 4 4 2 3 4 6% 7% 49%	2160
	11th to 20th	Day	10% 5% 2 5% 5% 4 4 4 5% 7% 50%	2134
	21st to end	Day	14% 6% 2 5% 4 2 5% 4 5% 8% 45%	2160
May	1st to 10th	Day	13% 7% 3 4 5% 3 4 4 5% 9% 42%	2180
	11th to 20th	Day	15% 6% 2 4 5% 3 4 4 6% 8% 40%	2437
	21st to end	Day	13% 5% 2 4 5% 3 5% 5% 5% 10% 45%	2725
June	1st to 10th	Day	10% 4 2 4 4 3 4 5% 7% 11% 45%	2520
	11th to 20th	Day	10% 3 2 4 5% 4 4 6% 7% 11% 44%	2520
	21st to end	Day	7% 4 2 3 5% 4 5% 6% 7% 11% 46%	2520
July	1st to 10th	Day	7% 5% 3 5% 6% 3 5% 6% 6% 11% 44%	2520
	11th to 20th	Day	6% 3 2 4 5% 4 6% 6% 9% 12% 44%	2466
	21st to end	Day	7% 4 2 5% 6% 4 6% 7% 9% 10% 40%	2547
August	1st to 10th	Day	9% 6% 2 5% 5% 3 6% 5% 8% 11% 41%	2327
	11th to 20th	Day	11% 5% 2 6% 6% 4 5% 6% 6% 10% 40%	2130
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 45%	2376
September	1st to 10th	Day	13% 5% 2 4 4 3 4 5% 5% 9% 46%	2160
	11th to 20th	Day	12% 6% 3 6% 5% 2 3 5% 5% 7% 47%	2160
	21st to end	Day	19% 7% 4 5% 4 3 4 4 5% 6% 40%	1930
October	1st to 10th	Day	15% 5% 2 5% 4 3 4 4 5% 6% 46%	1800
	11th to 20th	Day	17% 5% 2 3 4 2 3 4 4 6% 50%	1800
	21st to end	Day	12% 6% 2 5% 5% 3 4 5% 4 7% 47%	1980
November	1st to 10th	Day	14% 6% 2 4 4 2 4 3 4 7% 51%	1728
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 4 5% 6% 47%	1710
	21st to end	Day	15% 4 2 4 5% 2 4 4 5% 5% 50%	1616
December	1st to 10th	Day	16% 7% 3 5% 4 3 4 3 5% 8% 43%	1520
	11th to 20th	Day	16% 6% 2 5% 4 2 3 4 3 5% 50%	1910
	21st to end	Day	16% 6% 3 5% 5% 3 4 4 4 8% 42%	2772
January	1st to 10th	Night	15% 6% 2 5% 5% 3 4 4 5% 8% 44%	2616
	11th to 20th	Night	17% 6% 2 5% 5% 3 5% 5% 5% 7% 39%	2378
	21st to end	Night	16% 7% 2 4 4 2 4 4 4 7% 46%	2574
February	1st to 10th	Night	16% 9% 2 5% 4 2 4 4 5% 6% 42%	2340
	11th to 20th	Night	19% 7% 3 4 4 3 3 4 5% 6% 42%	2147
	21st to end	Night	18% 7% 2 4 4 2 4 4 4 5% 46%	1776
March	1st to 10th	Night	14% 5% 2 5% 4 2 4 4 5% 5% 49%	2066
	11th to 20th	Night	19% 5% 2 4 4 2 4 4 7% 7% 41%	1980
	21st to end	Night	16% 8% 4 6% 4 2 3 3 5% 7% 42%	2106
April	1st to 10th	Night	14% 6% 3 5% 6% 3 5% 4 6% 8% 41%	1800
	11th to 20th	Night	12% 5% 2 5% 5% 2 4 4 5% 7% 50%	1775
	21st to end	Night	17% 5% 2 5% 4 2 5% 4 5% 7% 45%	1800
May	1st to 10th	Night	14% 7% 3 5% 6% 4 4 5% 6% 9% 39%	1795
	11th to 20th	Night	15% 7% 3 6% 6% 3 5% 4 5% 7% 41%	1456
	21st to end	Night	13% 7% 2 5% 4 2 4 5% 6% 10% 41%	1550
June	1st to 10th	Night	13% 5% 2 4 6% 3 6% 4 6% 9% 43%	1440
	11th to 20th	Night	10% 4 2 5% 6% 3 6% 6% 6% 11% 40%	1440
	21st to end	Night	7% 4 3 6% 6% 4 6% 6% 7% 11% 42%	1440
July	1st to 10th	Night	8% 5% 2 6% 6% 4 5% 6% 7% 11% 40%	1440
	11th to 20th	Night	4 4 2 5% 5% 4 6% 6% 8% 11% 44%	1489
	21st to end	Night	7% 4 3 6% 6% 3 7% 6% 7% 10% 41%	1771
August	1st to 10th	Night	8% 5% 2 5% 6% 4 7% 7% 9% 11% 36%	1611
	11th to 20th	Night	10% 6% 4 6% 5% 4 5% 6% 7% 9% 39%	1752
	21st to end	Night	10% 5% 3 5% 7% 3 5% 5% 6% 10% 41%	1980
September	1st to 10th	Night	14% 4 2 5% 5% 2 4 4 5% 8% 48%	1800
	11th to 20th	Night	9% 5% 2 5% 5% 3 4 5% 6% 8% 47%	1800
	21st to end	Night	20% 6% 2 5% 5% 4 5% 4 5% 7% 37%	2027
October	1st to 10th	Night	16% 5% 1 5% 5% 3 3 4 5% 7% 44%	2160
	11th to 20th	Night	17% 5% 2 4 4 2 3 3 4 5% 50%	2160
	21st to end	Night	16% 6% 2 4 4 2 3 4 5% 7% 48%	2376
November	1st to 10th	Night	14% 6% 2 4 5% 2 3 3 5% 7% 49%	2348
	11th to 20th	Night	16% 6% 2 4 5% 3 4 4 4 5% 47%	2470
	21st to end	Night	12% 5% 2 4 4 3 5% 4 5% 7% 50%	2560
December	1st to 10th	Night	17% 7% 3 6% 5% 3 4 4 5% 6% 41%	2660
	11th to 20th	Night	17% 5% 3 5% 5% 3 4 4 4 7% 43%	3285
	21st to end	Night	13% 7% 3 5% 4 3 3 5% 6% 7% 42%	4884

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	41% 5% 10% 26% 14% 4	1546
	11th to 20th	Day	42% 5% 12% 24% 15% 2	1644
	21st to end	Day	41% 3 10% 26% 16% 4	1782
February	1st to 10th	Day	44% 4 11% 26% 13% 2	1620
	11th to 20th	Day	41% 3 8% 23% 19% 5%	1707
	21st to end	Day	46% 5% 11% 19% 16% 4	1480
March	1st to 10th	Day	36% 4 11% 25% 21% 3	1890
	11th to 20th	Day	39% 5% 11% 22% 18% 5%	1980
	21st to end	Day	42% 5% 12% 20% 18% 4	2250
April	1st to 10th	Day	33% 5% 13% 24% 19% 6%	2160
	11th to 20th	Day	35% 4 11% 24% 21% 5%	2134
	21st to end	Day	37% 4 13% 24% 17% 5%	2160
May	1st to 10th	Day	39% 5% 13% 25% 15% 3	2180
	11th to 20th	Day	40% 6% 15% 24% 12% 2	2441
	21st to end	Day	35% 6% 17% 28% 12% 1	2725
June	1st to 10th	Day	32% 6% 18% 29% 13% 2	2520
	11th to 20th	Day	32% 8% 18% 24% 15% 2	2520
	21st to end	Day	31% 7% 17% 26% 18% 1	2520
July	1st to 10th	Day	34% 8% 17% 24% 15% 3	2450
	11th to 20th	Day	28% 9% 20% 29% 12% 2	2391
	21st to end	Day	34% 8% 17% 23% 16% 2	2405
August	1st to 10th	Day	34% 7% 18% 27% 11% 2	2314
	11th to 20th	Day	38% 7% 17% 23% 14% 1	2130
	21st to end	Day	34% 6% 16% 25% 14% 4	2376
September	1st to 10th	Day	35% 6% 17% 22% 16% 4	2160
	11th to 20th	Day	35% 5% 10% 28% 20% 3	2160
	21st to end	Day	44% 5% 8% 23% 17% 3	1930
October	1st to 10th	Day	38% 4 11% 25% 19% 3	1800
	11th to 20th	Day	36% 4 8% 27% 21% 4	1800
	21st to end	Day	37% 4 7% 26% 21% 5%	1980
November	1st to 10th	Day	35% 3 9% 27% 20% 5%	1728
	11th to 20th	Day	38% 4 11% 19% 22% 5%	1710
	21st to end	Day	37% 3 9% 28% 19% 4	1616
December	1st to 10th	Day	41% 4 13% 25% 14% 3	1520
	11th to 20th	Day	39% 3 8% 28% 16% 5%	1906
	21st to end	Day	42% 5% 12% 28% 13% 1	2772
January	1st to 10th	Night	40% 4 9% 22% 19% 5%	2616
	11th to 20th	Night	45% 5% 11% 23% 14% 2	2378
	21st to end	Night	40% 3 8% 26% 19% 4	2574
February	1st to 10th	Night	43% 3 11% 25% 17% 2	2340
	11th to 20th	Night	43% 4 7% 22% 18% 5%	2149
	21st to end	Night	41% 3 9% 22% 19% 5%	1776
March	1st to 10th	Night	37% 4 9% 27% 19% 3	2066
	11th to 20th	Night	42% 4 11% 22% 18% 4	1980
	21st to end	Night	43% 4 9% 22% 17% 5%	2106
April	1st to 10th	Night	42% 4 10% 19% 20% 5%	1800
	11th to 20th	Night	35% 4 11% 22% 22% 5%	1775
	21st to end	Night	39% 4 13% 24% 15% 5%	1800
May	1st to 10th	Night	42% 6% 12% 23% 14% 3	1795
	11th to 20th	Night	43% 6% 14% 20% 16% 1	1457
	21st to end	Night	38% 7% 14% 27% 12% 1	1551
June	1st to 10th	Night	38% 6% 13% 26% 16% 1	1440
	11th to 20th	Night	38% 7% 15% 24% 14% 2	1440
	21st to end	Night	36% 7% 16% 22% 17% 2	1440
July	1st to 10th	Night	38% 7% 19% 20% 14% 3	1400
	11th to 20th	Night	30% 10% 19% 29% 11% 1	1441
	21st to end	Night	35% 8% 16% 28% 13%	1672
August	1st to 10th	Night	39% 9% 18% 23% 11%	1600
	11th to 20th	Night	39% 8% 17% 22% 13% 1	1752
	21st to end	Night	38% 6% 16% 22% 15% 2	1980
September	1st to 10th	Night	36% 5% 17% 21% 17% 4	1800
	11th to 20th	Night	34% 6% 11% 27% 21% 2	1800
	21st to end	Night	46% 7% 8% 18% 17% 3	2027
October	1st to 10th	Night	39% 6% 10% 24% 18% 3	2160
	11th to 20th	Night	38% 4 7% 25% 23% 4	2160
	21st to end	Night	37% 4 8% 26% 21% 4	2376
November	1st to 10th	Night	37% 4 10% 26% 19% 4	2348
	11th to 20th	Night	41% 3 9% 20% 20% 6%	2470
	21st to end	Night	35% 3 9% 28% 21% 4	2560
December	1st to 10th	Night	44% 5% 11% 24% 14% 3	2660
	11th to 20th	Night	42% 4 10% 22% 18% 4	3288
	21st to end	Night	39% 5% 14% 28% 12% 2	4884

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	18% 4 25% 43% 9% 1	193
	11th to 20th	Day	17% 8% 30% 34% 9% 1	248
	21st to end	Day	19% 4 23% 42% 10% 1	264
February	1st to 10th	Day	19% 7% 21% 40% 13%	240
	11th to 20th	Day	25% 5% 30% 33% 7%	366
	21st to end	Day	23% 4 28% 36% 8% 1	346
March	1st to 10th	Day	17% 6% 28% 35% 13% 1	420
	11th to 20th	Day	20% 6% 24% 38% 10% 2	420
	21st to end	Day	19% 4 22% 38% 15% 2	462
April	1st to 10th	Day	15% 4 27% 35% 16% 3	420
	11th to 20th	Day	9% 3 22% 38% 23% 5%	412
	21st to end	Day	17% 5% 18% 33% 25% 2	420
May	1st to 10th	Day	17% 4 17% 34% 23% 5%	423
	11th to 20th	Day	19% 2 13% 32% 29% 6%	447
	21st to end	Day	19% 3 6% 25% 34% 13%	485
June	1st to 10th	Day	12% 2 6% 30% 37% 13%	450
	11th to 20th	Day	11% 1 9% 29% 34% 15%	450
	21st to end	Day	11% 2 6% 30% 39% 12%	450
July	1st to 10th	Day	10% 2 3 26% 37% 22%	445
	11th to 20th	Day	5% 2 2 19% 50% 23%	444
	21st to end	Day	10% 2 3 26% 43% 15%	488
August	1st to 10th	Day	10% 2 5% 27% 41% 15%	446
	11th to 20th	Day	11% 3 5% 23% 38% 20%	439
	21st to end	Day	11% 1 4 26% 36% 21%	495
September	1st to 10th	Day	16% 1 6% 23% 32% 22%	450
	11th to 20th	Day	14% 1 8% 24% 34% 19%	450
	21st to end	Day	24% 5% 11% 27% 25% 8%	450
October	1st to 10th	Day	20% 3 8% 28% 26% 14%	450
	11th to 20th	Day	17% 4 18% 27% 25% 9%	450
	21st to end	Day	14% 5% 21% 32% 23% 5%	495
November	1st to 10th	Day	18% 5% 21% 29% 21% 7%	393
	11th to 20th	Day	15% 8% 29% 29% 16% 2	370
	21st to end	Day	17% 8% 24% 29% 20% 3	276
December	1st to 10th	Day	18% 4 26% 39% 12% 1	180
	11th to 20th	Day	21% 5% 24% 35% 14% 1	180
	21st to end	Day	19% 5% 22% 40% 13% 1	198
January	1st to 10th	Night	18% 12% 36% 28% 6%	760
	11th to 20th	Night	20% 9% 30% 32% 10%	732
	21st to end	Night	21% 10% 34% 32% 4	792
February	1st to 10th	Night	19% 7% 32% 35% 5% 1	720
	11th to 20th	Night	22% 11% 36% 28% 4	703
	21st to end	Night	21% 10% 30% 34% 5%	592
March	1st to 10th	Night	17% 8% 32% 34% 8% 1	720
	11th to 20th	Night	20% 6% 30% 33% 9% 3	720
	21st to end	Night	19% 5% 29% 38% 8% 1	792
April	1st to 10th	Night	17% 6% 34% 32% 11% 1	720
	11th to 20th	Night	14% 4 25% 39% 17% 1	711
	21st to end	Night	19% 4 22% 39% 14% 2	720
May	1st to 10th	Night	18% 5% 22% 39% 14% 2	715
	11th to 20th	Night	17% 4 19% 38% 20% 1	395
	21st to end	Night	15% 2 10% 31% 36% 6%	389
June	1st to 10th	Night	14% 2 15% 32% 34% 4	360
	11th to 20th	Night	11% 3 10% 38% 32% 6%	360
	21st to end	Night	8% 4 10% 39% 35% 5%	360
July	1st to 10th	Night	9% 3 4 38% 37% 9%	350
	11th to 20th	Night	5% 3 3 33% 47% 9%	397
	21st to end	Night	8% 2 6% 37% 42% 5%	591
August	1st to 10th	Night	9% 1 5% 37% 41% 7%	537
	11th to 20th	Night	13% 3 6% 32% 39% 8%	688
	21st to end	Night	12% 2 6% 31% 40% 10%	792
September	1st to 10th	Night	16% 2 7% 28% 36% 11%	720
	11th to 20th	Night	13% 2 9% 28% 40% 9%	720
	21st to end	Night	24% 3 12% 31% 27% 4	720
October	1st to 10th	Night	20% 3 17% 26% 26% 8%	720
	11th to 20th	Night	19% 6% 20% 30% 22% 2	720
	21st to end	Night	19% 7% 24% 29% 18% 4	792
November	1st to 10th	Night	18% 6% 22% 30% 19% 5%	740
	11th to 20th	Night	19% 8% 26% 31% 14% 1	760
	21st to end	Night	14% 11% 27% 32% 15% 2	760
December	1st to 10th	Night	21% 8% 32% 27% 10% 2	760
	11th to 20th	Night	18% 8% 36% 29% 9%	760
	21st to end	Night	18% 8% 29% 34% 11%	836

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