Observatoire de La Sérénité
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de La Sérénité clear sky chart from 2005-11-06 to 2024-03-01.

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	19% 10% 4 7% 6% 3 5% 5% 5% 7% 30%	78064
	Night	19% 11% 4 7% 6% 3 4 4 5% 6% 30%	81339
Transparency	Day	54% 4 13% 20% 9% 1	77769
	Night	56% 3 11% 19% 9% 1	81169
Seeing	Day	26% 12% 29% 22% 9% 2	14195
	Night	25% 10% 27% 28% 9% 1	22926

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	16% 16% 7% 10% 8% 4 4 4 5% 6% 21%	2517
	11th to 20th	Day	10% 15% 8% 14% 9% 3 4 4 4 4 26%	2520
	21st to end	Day	10% 13% 5% 9% 6% 3 4 5% 5% 6% 33%	2772
February	1st to 10th	Day	11% 14% 7% 10% 9% 4 5% 5% 4 6% 25%	1520
	11th to 20th	Day	14% 15% 6% 10% 6% 3 5% 5% 4 5% 26%	1832
	21st to end	Day	14% 14% 6% 10% 8% 3 5% 4 4 7% 27%	1570
March	1st to 10th	Day	15% 12% 5% 8% 6% 3 4 4 5% 6% 30%	1797
	11th to 20th	Day	17% 12% 6% 6% 6% 2 5% 5% 4 6% 30%	1881
	21st to end	Day	15% 11% 4 7% 7% 3 6% 6% 4 5% 32%	2317
April	1st to 10th	Day	22% 12% 4 7% 7% 3 4 4 4 5% 28%	2160
	11th to 20th	Day	21% 7% 3 6% 5% 3 3 3 5% 6% 37%	2215
	21st to end	Day	25% 8% 4 6% 6% 3 3 4 4 6% 31%	2340
May	1st to 10th	Day	23% 8% 3 6% 6% 3 5% 4 5% 6% 33%	2400
	11th to 20th	Day	19% 7% 3 6% 7% 4 5% 5% 5% 7% 33%	2478
	21st to end	Day	22% 7% 3 6% 6% 3 6% 5% 5% 6% 32%	2738
June	1st to 10th	Day	20% 6% 3 6% 7% 3 7% 6% 7% 8% 26%	2700
	11th to 20th	Day	20% 6% 3 6% 5% 4 5% 6% 6% 7% 34%	2700
	21st to end	Day	23% 8% 3 7% 6% 4 5% 5% 5% 7% 26%	2700
July	1st to 10th	Day	15% 6% 3 7% 6% 4 6% 6% 7% 9% 31%	2542
	11th to 20th	Day	16% 6% 3 7% 6% 4 5% 6% 7% 10% 31%	2520
	21st to end	Day	16% 7% 4 6% 6% 3 7% 5% 8% 8% 31%	2744
August	1st to 10th	Day	18% 6% 3 7% 6% 4 6% 6% 7% 10% 28%	2502
	11th to 20th	Day	17% 6% 2 6% 6% 3 5% 5% 7% 8% 35%	2304
	21st to end	Day	17% 7% 2 6% 5% 3 4 6% 5% 8% 36%	2460
September	1st to 10th	Day	18% 7% 3 5% 5% 3 4 5% 6% 8% 36%	2160
	11th to 20th	Day	19% 5% 2 4 4 3 3 3 5% 7% 44%	2006
	21st to end	Day	23% 7% 2 5% 4 2 4 4 4 7% 38%	1980
October	1st to 10th	Day	22% 6% 3 6% 5% 3 5% 6% 4 6% 33%	1972
	11th to 20th	Day	26% 8% 3 8% 6% 4 4 4 6% 6% 23%	1652
	21st to end	Day	29% 11% 3 6% 6% 3 5% 3 5% 4 25%	1782
November	1st to 10th	Day	21% 10% 4 6% 7% 3 5% 3 5% 5% 31%	1671
	11th to 20th	Day	23% 13% 5% 8% 5% 3 5% 4 5% 5% 25%	1706
	21st to end	Day	24% 15% 5% 8% 6% 3 4 5% 4 4 22%	1375
December	1st to 10th	Day	25% 17% 4 7% 7% 3 4 3 4 4 22%	1330
	11th to 20th	Day	22% 12% 5% 9% 7% 3 3 3 3 4 27%	1668
	21st to end	Day	22% 18% 5% 7% 6% 2 3 3 4 4 26%	2533
January	1st to 10th	Night	16% 19% 6% 11% 8% 3 4 3 3 4 22%	4429
	11th to 20th	Night	13% 16% 6% 11% 7% 4 5% 4 4 5% 25%	4440
	21st to end	Night	11% 14% 5% 9% 8% 4 5% 5% 6% 6% 26%	4884
February	1st to 10th	Night	12% 13% 6% 10% 8% 3 5% 5% 4 6% 28%	2660
	11th to 20th	Night	13% 16% 6% 9% 8% 3 5% 4 4 5% 26%	2231
	21st to end	Night	15% 13% 6% 9% 6% 3 4 4 4 6% 29%	1884
March	1st to 10th	Night	15% 12% 4 7% 8% 4 6% 5% 4 6% 30%	2157
	11th to 20th	Night	18% 13% 4 7% 6% 4 5% 5% 4 6% 29%	2077
	21st to end	Night	17% 11% 3 7% 5% 3 4 4 4 6% 36%	2036
April	1st to 10th	Night	23% 13% 5% 7% 5% 3 4 4 5% 4 28%	1800
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 5% 5% 6% 35%	1693
	21st to end	Night	24% 9% 4 7% 5% 3 3 3 3 6% 34%	1620
May	1st to 10th	Night	24% 7% 3 6% 5% 3 5% 5% 5% 4 33%	1576
	11th to 20th	Night	22% 7% 3 6% 5% 3 5% 4 4 5% 36%	1415
	21st to end	Night	23% 5% 3 5% 5% 3 5% 4 5% 7% 36%	1533
June	1st to 10th	Night	22% 7% 3 6% 7% 3 5% 5% 6% 8% 28%	1260
	11th to 20th	Night	21% 5% 3 5% 4 3 4 5% 6% 7% 37%	1260
	21st to end	Night	23% 7% 4 7% 6% 3 4 4 5% 8% 30%	1260
July	1st to 10th	Night	17% 6% 3 6% 5% 3 5% 5% 5% 8% 37%	1412
	11th to 20th	Night	18% 6% 2 6% 5% 2 6% 5% 6% 8% 36%	1440
	21st to end	Night	17% 6% 3 7% 5% 3 6% 5% 6% 8% 35%	1574
August	1st to 10th	Night	16% 4 2 5% 5% 4 5% 5% 8% 8% 39%	1432
	11th to 20th	Night	16% 6% 4 7% 6% 3 6% 5% 6% 7% 34%	1583
	21st to end	Night	17% 6% 2 5% 5% 3 4 5% 4 7% 40%	1894
September	1st to 10th	Night	19% 6% 2 5% 6% 3 4 4 5% 8% 40%	1800
	11th to 20th	Night	20% 5% 2 5% 4 3 3 4 5% 5% 43%	1953
	21st to end	Night	21% 5% 2 6% 4 2 4 4 4 6% 42%	1980
October	1st to 10th	Night	20% 6% 3 6% 5% 3 5% 4 6% 5% 38%	1987
	11th to 20th	Night	25% 9% 3 6% 6% 3 4 5% 5% 5% 30%	2308
	21st to end	Night	27% 10% 3 5% 5% 3 4 4 5% 5% 29%	2574
November	1st to 10th	Night	21% 10% 3 6% 5% 4 4 4 4 7% 31%	2407
	11th to 20th	Night	21% 10% 4 7% 6% 3 4 4 4 6% 31%	2471
	21st to end	Night	23% 14% 5% 8% 6% 3 5% 3 4 5% 25%	2802
December	1st to 10th	Night	24% 16% 5% 9% 7% 3 5% 4 4 4 20%	2850
	11th to 20th	Night	22% 13% 5% 9% 7% 3 4 4 4 5% 25%	3531
	21st to end	Night	24% 19% 5% 8% 5% 2 3 3 4 3 25%	5126

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	64% 2 12% 16% 5% 1	2518
	11th to 20th	Day	63% 2 10% 19% 6% 1	2520
	21st to end	Day	51% 2 12% 25% 9% 1	2772
February	1st to 10th	Day	59% 4 10% 16% 9% 2	1520
	11th to 20th	Day	60% 3 12% 15% 10% 1	1841
	21st to end	Day	58% 2 9% 19% 9% 2	1570
March	1st to 10th	Day	54% 4 11% 17% 12% 2	1800
	11th to 20th	Day	54% 5% 9% 19% 12% 2	1881
	21st to end	Day	52% 3 11% 19% 12% 3	2317
April	1st to 10th	Day	59% 2 12% 14% 9% 4	2160
	11th to 20th	Day	48% 2 11% 25% 11% 3	2215
	21st to end	Day	55% 3 11% 17% 12% 2	2340
May	1st to 10th	Day	51% 3 12% 19% 14% 2	2400
	11th to 20th	Day	51% 3 11% 21% 11% 1	2482
	21st to end	Day	52% 5% 11% 19% 12% 1	2738
June	1st to 10th	Day	53% 5% 13% 19% 8% 2	2700
	11th to 20th	Day	48% 5% 14% 20% 11% 2	2700
	21st to end	Day	57% 4 13% 17% 9%	2700
July	1st to 10th	Day	47% 6% 18% 23% 6%	2472
	11th to 20th	Day	47% 4 19% 23% 7%	2445
	21st to end	Day	50% 4 18% 20% 7%	2591
August	1st to 10th	Day	50% 6% 21% 20% 3	2488
	11th to 20th	Day	45% 4 19% 23% 7%	2304
	21st to end	Day	46% 4 15% 26% 9%	2460
September	1st to 10th	Day	46% 3 16% 25% 10%	2160
	11th to 20th	Day	40% 2 18% 29% 10%	2006
	21st to end	Day	48% 3 15% 25% 9%	1980
October	1st to 10th	Day	51% 3 13% 24% 9%	1972
	11th to 20th	Day	59% 4 16% 17% 3	1652
	21st to end	Day	62% 4 10% 18% 5% 1	1782
November	1st to 10th	Day	56% 4 12% 20% 8%	1671
	11th to 20th	Day	61% 3 10% 19% 6% 1	1706
	21st to end	Day	64% 4 11% 14% 6% 1	1375
December	1st to 10th	Day	66% 3 10% 15% 6%	1330
	11th to 20th	Day	62% 3 6% 20% 9%	1668
	21st to end	Day	63% 3 12% 14% 7% 2	2533
January	1st to 10th	Night	68% 3 9% 13% 6% 1	4429
	11th to 20th	Night	64% 2 9% 20% 5% 1	4440
	21st to end	Night	58% 3 11% 18% 9% 1	4884
February	1st to 10th	Night	58% 3 8% 20% 10% 1	2660
	11th to 20th	Night	61% 3 10% 15% 10% 1	2233
	21st to end	Night	57% 2 8% 18% 12% 2	1884
March	1st to 10th	Night	57% 3 10% 17% 11% 2	2167
	11th to 20th	Night	56% 4 8% 16% 12% 3	2078
	21st to end	Night	51% 5% 9% 19% 11% 4	2036
April	1st to 10th	Night	60% 2 8% 15% 13% 3	1800
	11th to 20th	Night	48% 4 8% 24% 14% 2	1693
	21st to end	Night	54% 4 8% 18% 14% 2	1620
May	1st to 10th	Night	53% 4 10% 17% 14% 2	1576
	11th to 20th	Night	51% 3 9% 20% 15% 2	1416
	21st to end	Night	48% 5% 11% 19% 15% 1	1534
June	1st to 10th	Night	53% 4 13% 20% 9% 1	1260
	11th to 20th	Night	47% 5% 11% 23% 11% 3	1260
	21st to end	Night	54% 4 13% 17% 12%	1260
July	1st to 10th	Night	45% 4 20% 22% 9%	1372
	11th to 20th	Night	45% 5% 18% 24% 7% 1	1392
	21st to end	Night	47% 6% 17% 21% 8%	1486
August	1st to 10th	Night	41% 6% 20% 27% 5%	1422
	11th to 20th	Night	47% 5% 21% 19% 7%	1583
	21st to end	Night	43% 5% 13% 31% 9%	1894
September	1st to 10th	Night	45% 4 14% 25% 12% 1	1800
	11th to 20th	Night	44% 3 18% 27% 8% 1	1953
	21st to end	Night	45% 3 12% 27% 12%	1980
October	1st to 10th	Night	47% 4 10% 26% 12% 1	1987
	11th to 20th	Night	57% 4 14% 20% 6%	2308
	21st to end	Night	57% 3 13% 18% 8%	2574
November	1st to 10th	Night	54% 4 13% 21% 7% 1	2407
	11th to 20th	Night	55% 4 12% 18% 10%	2471
	21st to end	Night	63% 3 10% 17% 7% 1	2802
December	1st to 10th	Night	69% 3 10% 14% 5%	2850
	11th to 20th	Night	63% 3 7% 18% 9%	3532
	21st to end	Night	66% 2 8% 16% 7% 2	5126

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	27% 14% 32% 22% 4 2	180
	11th to 20th	Day	27% 22% 32% 14% 4	180
	21st to end	Day	20% 20% 32% 22% 5% 1	198
February	1st to 10th	Day	28% 21% 35% 15% 1 1	180
	11th to 20th	Day	23% 21% 37% 16% 4 1	443
	21st to end	Day	25% 20% 28% 21% 6%	382
March	1st to 10th	Day	25% 18% 32% 18% 7% 1	420
	11th to 20th	Day	26% 16% 32% 17% 7% 1	420
	21st to end	Day	24% 16% 23% 24% 11% 2	462
April	1st to 10th	Day	30% 12% 30% 19% 9%	420
	11th to 20th	Day	27% 13% 28% 22% 9% 1	412
	21st to end	Day	33% 10% 31% 19% 5% 1	420
May	1st to 10th	Day	27% 17% 33% 16% 6% 1	423
	11th to 20th	Day	22% 12% 34% 22% 8% 2	447
	21st to end	Day	27% 18% 31% 17% 7% 1	498
June	1st to 10th	Day	25% 12% 30% 24% 9%	630
	11th to 20th	Day	24% 11% 27% 25% 12% 1	630
	21st to end	Day	29% 7% 27% 23% 12% 2	630
July	1st to 10th	Day	20% 10% 31% 24% 13% 1	467
	11th to 20th	Day	19% 8% 32% 28% 10% 2	444
	21st to end	Day	20% 8% 32% 28% 11% 2	488
August	1st to 10th	Day	22% 4 32% 24% 14% 4	446
	11th to 20th	Day	19% 5% 26% 30% 17% 3	439
	21st to end	Day	24% 9% 24% 21% 13% 8%	495
September	1st to 10th	Day	22% 10% 26% 25% 14% 3	450
	11th to 20th	Day	22% 10% 28% 20% 15% 4	450
	21st to end	Day	24% 11% 23% 23% 13% 6%	450
October	1st to 10th	Day	24% 11% 27% 24% 11% 3	450
	11th to 20th	Day	35% 9% 24% 20% 11% 1	376
	21st to end	Day	38% 12% 27% 17% 5%	396
November	1st to 10th	Day	32% 12% 24% 23% 8% 1	365
	11th to 20th	Day	31% 13% 27% 20% 9% 1	366
	21st to end	Day	33% 16% 29% 17% 6%	180
December	1st to 10th	Day	34% 8% 27% 22% 7% 3	180
	11th to 20th	Day	32% 18% 29% 16% 3 2	180
	21st to end	Day	32% 18% 30% 15% 5%	198
January	1st to 10th	Night	26% 16% 30% 24% 5%	760
	11th to 20th	Night	27% 14% 29% 24% 6% 1	760
	21st to end	Night	17% 13% 32% 30% 7% 1	836
February	1st to 10th	Night	20% 13% 33% 28% 6%	760
	11th to 20th	Night	23% 15% 36% 21% 5% 1	743
	21st to end	Night	25% 11% 31% 27% 5%	628
March	1st to 10th	Night	22% 10% 35% 27% 6%	723
	11th to 20th	Night	26% 14% 30% 22% 6% 1	720
	21st to end	Night	24% 10% 27% 30% 8% 1	792
April	1st to 10th	Night	30% 11% 26% 26% 6% 1	720
	11th to 20th	Night	27% 7% 33% 26% 7%	629
	21st to end	Night	30% 10% 30% 23% 7%	540
May	1st to 10th	Night	26% 9% 30% 28% 6%	496
	11th to 20th	Night	24% 9% 28% 32% 7%	354
	21st to end	Night	26% 4 32% 28% 9%	389
June	1st to 10th	Night	26% 5% 27% 34% 7%	360
	11th to 20th	Night	21% 4 25% 38% 13%	360
	21st to end	Night	25% 4 22% 37% 10% 1	360
July	1st to 10th	Night	20% 3 27% 38% 11% 1	350
	11th to 20th	Night	19% 4 20% 41% 16%	348
	21st to end	Night	19% 3 16% 45% 16% 1	394
August	1st to 10th	Night	20% 4 13% 46% 18%	358
	11th to 20th	Night	19% 3 21% 39% 16% 2	519
	21st to end	Night	21% 4 23% 33% 18% 2	706
September	1st to 10th	Night	22% 3 25% 33% 15% 1	720
	11th to 20th	Night	22% 5% 22% 31% 17% 2	720
	21st to end	Night	25% 5% 25% 29% 14% 2	720
October	1st to 10th	Night	24% 7% 26% 33% 9% 1	720
	11th to 20th	Night	30% 7% 24% 27% 11% 1	720
	21st to end	Night	33% 10% 28% 24% 5%	792
November	1st to 10th	Night	29% 11% 24% 28% 9% 1	740
	11th to 20th	Night	27% 13% 24% 26% 8% 1	760
	21st to end	Night	31% 12% 29% 21% 6% 1	827
December	1st to 10th	Night	32% 11% 26% 22% 8% 1	850
	11th to 20th	Night	27% 17% 27% 23% 6% 1	850
	21st to end	Night	33% 14% 28% 19% 5% 1	902

Page generated at 2024-02-27 06:30:12. Version ac07

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