Observatoire de l'Aigle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de l'Aigle clear sky chart from 2005-11-06 to 2024-11-28.

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	20% 12% 4 8% 5% 5% 4 3 5% 6% 28%	101619
	Night	18% 13% 4 9% 5% 4 4 3 4 6% 29%	97938
Transparency	Day	53% 8% 13% 16% 8% 1	105079
	Night	53% 8% 13% 17% 8% 1	102568
Seeing	Day	26% 18% 30% 18% 7% 1	15319
	Night	24% 13% 29% 25% 8% 1	23790

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	12% 17% 6% 14% 7% 5% 4 4 5% 6% 20%	2517
	11th to 20th	Day	10% 14% 7% 18% 8% 6% 3 3 3 3 25%	2520
	21st to end	Day	9% 12% 8% 12% 4 4 4 4 5% 5% 33%	2772
February	1st to 10th	Day	8% 15% 6% 16% 7% 7% 5% 3 4 4 25%	1520
	11th to 20th	Day	12% 15% 7% 15% 7% 5% 4 3 5% 4 23%	1819
	21st to end	Day	12% 16% 5% 13% 7% 4 4 3 5% 5% 25%	1570
March	1st to 10th	Day	18% 17% 4 10% 5% 4 3 3 4 4 28%	3116
	11th to 20th	Day	15% 24% 5% 10% 4 4 4 3 3 4 24%	3315
	21st to end	Day	14% 16% 5% 9% 5% 3 4 2 3 5% 34%	4060
April	1st to 10th	Day	22% 18% 4 9% 4 4 3 2 4 5% 26%	2280
	11th to 20th	Day	21% 14% 3 7% 4 3 4 3 3 5% 33%	2347
	21st to end	Day	25% 12% 3 7% 5% 4 4 3 5% 5% 28%	2470
May	1st to 10th	Day	22% 9% 3 7% 4 4 4 4 5% 6% 32%	4225
	11th to 20th	Day	20% 8% 3 6% 5% 5% 5% 4 6% 8% 29%	4398
	21st to end	Day	22% 7% 2 7% 5% 6% 6% 4 6% 6% 29%	4923
June	1st to 10th	Day	23% 9% 3 8% 5% 5% 6% 4 6% 7% 24%	2850
	11th to 20th	Day	24% 9% 3 6% 5% 5% 4 4 5% 6% 31%	2850
	21st to end	Day	28% 10% 3 8% 6% 4 4 3 5% 6% 23%	2850
July	1st to 10th	Day	19% 9% 3 8% 6% 6% 6% 4 6% 7% 26%	4542
	11th to 20th	Day	22% 8% 3 7% 5% 6% 6% 4 7% 7% 24%	4440
	21st to end	Day	18% 6% 2 6% 5% 5% 6% 4 6% 7% 34%	4814
August	1st to 10th	Day	19% 7% 3 7% 5% 6% 6% 5% 8% 8% 25%	4407
	11th to 20th	Day	24% 7% 3 8% 6% 5% 6% 4 6% 7% 23%	4045
	21st to end	Day	23% 7% 2 7% 4 4 5% 3 6% 7% 32%	4345
September	1st to 10th	Day	23% 8% 3 6% 4 5% 5% 4 5% 6% 32%	2280
	11th to 20th	Day	20% 6% 2 5% 4 4 4 3 4 7% 42%	2114
	21st to end	Day	27% 8% 2 6% 4 3 3 3 5% 6% 33%	2090
October	1st to 10th	Day	25% 10% 2 7% 5% 4 4 4 4 5% 30%	2081
	11th to 20th	Day	27% 15% 4 7% 4 4 4 3 4 6% 23%	1738
	21st to end	Day	29% 15% 3 7% 4 4 3 3 4 5% 23%	1881
November	1st to 10th	Day	21% 17% 4 8% 4 4 3 3 4 5% 27%	1761
	11th to 20th	Day	21% 18% 5% 10% 4 4 3 2 4 4 24%	1790
	21st to end	Day	19% 21% 6% 9% 6% 4 4 3 4 4 20%	1398
December	1st to 10th	Day	22% 19% 6% 9% 6% 4 4 2 2 4 21%	1330
	11th to 20th	Day	20% 16% 4 10% 5% 5% 4 2 4 4 26%	1668
	21st to end	Day	17% 18% 8% 8% 4 3 3 3 4 5% 25%	2493
January	1st to 10th	Night	12% 19% 7% 15% 8% 4 4 3 4 4 22%	4429
	11th to 20th	Night	10% 15% 6% 15% 11% 7% 3 3 4 4 23%	4440
	21st to end	Night	7% 14% 7% 14% 6% 5% 5% 4 6% 6% 25%	4884
February	1st to 10th	Night	9% 14% 5% 12% 8% 5% 4 4 4 6% 27%	2660
	11th to 20th	Night	10% 19% 5% 12% 6% 6% 5% 3 4 6% 24%	2243
	21st to end	Night	12% 15% 5% 11% 7% 4 4 4 5% 5% 28%	1884
March	1st to 10th	Night	20% 15% 4 8% 5% 4 5% 3 4 5% 27%	3724
	11th to 20th	Night	14% 21% 5% 11% 5% 5% 5% 3 4 5% 23%	3644
	21st to end	Night	15% 14% 5% 9% 5% 4 5% 3 4 5% 32%	3568
April	1st to 10th	Night	21% 17% 4 7% 4 4 4 3 4 5% 28%	1900
	11th to 20th	Night	20% 11% 3 6% 4 5% 4 3 5% 7% 32%	1780
	21st to end	Night	22% 12% 3 8% 4 3 3 2 4 6% 33%	1710
May	1st to 10th	Night	23% 7% 2 6% 4 5% 4 3 4 6% 36%	2743
	11th to 20th	Night	22% 8% 3 6% 4 4 3 3 4 6% 36%	2495
	21st to end	Night	22% 5% 2 6% 4 4 4 4 5% 8% 36%	2650
June	1st to 10th	Night	20% 10% 2 7% 6% 4 5% 5% 5% 7% 29%	1330
	11th to 20th	Night	20% 7% 2 6% 5% 4 4 3 5% 7% 37%	1330
	21st to end	Night	26% 8% 2 8% 5% 4 4 3 4 6% 30%	1330
July	1st to 10th	Night	17% 7% 3 7% 6% 5% 5% 5% 6% 8% 31%	2416
	11th to 20th	Night	22% 8% 3 7% 4 4 5% 4 6% 7% 30%	2520
	21st to end	Night	15% 6% 2 5% 3 4 3 4 5% 8% 45%	2739
August	1st to 10th	Night	20% 7% 3 7% 4 4 4 4 5% 7% 36%	2506
	11th to 20th	Night	23% 7% 3 5% 5% 5% 6% 3 6% 7% 31%	2766
	21st to end	Night	19% 8% 3 8% 5% 5% 4 4 4 6% 34%	3308
September	1st to 10th	Night	21% 7% 2 5% 4 3 4 3 4 6% 40%	1900
	11th to 20th	Night	21% 6% 2 5% 3 3 4 3 5% 6% 42%	2066
	21st to end	Night	23% 8% 3 5% 3 3 3 3 3 6% 40%	2090
October	1st to 10th	Night	23% 9% 2 6% 4 4 4 3 4 6% 35%	2095
	11th to 20th	Night	28% 10% 2 6% 4 3 4 3 4 5% 30%	2441
	21st to end	Night	26% 14% 2 5% 4 3 4 4 5% 6% 25%	2717
November	1st to 10th	Night	20% 13% 4 8% 4 4 4 3 4 6% 28%	2537
	11th to 20th	Night	20% 13% 4 9% 5% 3 4 3 5% 6% 28%	2607
	21st to end	Night	21% 17% 6% 9% 5% 4 3 3 4 5% 22%	2935
December	1st to 10th	Night	19% 19% 6% 11% 6% 5% 3 3 4 4 19%	2850
	11th to 20th	Night	20% 16% 5% 10% 6% 4 4 3 4 5% 23%	3531
	21st to end	Night	19% 20% 7% 9% 4 4 3 2 3 4 25%	5170

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	57% 12% 14% 12% 4 1	2518
	11th to 20th	Day	59% 10% 10% 13% 7% 1	2520
	21st to end	Day	46% 11% 11% 20% 12% 1	2772
February	1st to 10th	Day	60% 6% 9% 14% 9% 2	1520
	11th to 20th	Day	61% 6% 10% 12% 9% 2	1828
	21st to end	Day	59% 5% 9% 16% 8% 3	1570
March	1st to 10th	Day	56% 9% 10% 15% 8% 3	3119
	11th to 20th	Day	57% 9% 12% 13% 7% 1	3315
	21st to end	Day	51% 7% 8% 17% 12% 5%	4060
April	1st to 10th	Day	60% 5% 10% 12% 9% 4	2280
	11th to 20th	Day	51% 6% 11% 20% 10% 2	2347
	21st to end	Day	55% 6% 11% 15% 10% 3	2470
May	1st to 10th	Day	47% 9% 15% 16% 12% 1	4239
	11th to 20th	Day	46% 12% 20% 16% 6% 1	4402
	21st to end	Day	48% 11% 12% 16% 12% 1	4923
June	1st to 10th	Day	54% 11% 12% 17% 6% 1	2850
	11th to 20th	Day	50% 8% 16% 16% 9% 1	2850
	21st to end	Day	60% 7% 11% 14% 8%	2850
July	1st to 10th	Day	55% 7% 15% 16% 7%	4472
	11th to 20th	Day	54% 8% 17% 17% 4	4365
	21st to end	Day	46% 9% 16% 23% 6%	4661
August	1st to 10th	Day	52% 9% 18% 16% 4	4393
	11th to 20th	Day	56% 8% 19% 14% 4	4084
	21st to end	Day	50% 6% 16% 16% 12%	4345
September	1st to 10th	Day	48% 8% 16% 20% 9%	2280
	11th to 20th	Day	41% 6% 18% 26% 9% 1	2114
	21st to end	Day	50% 8% 12% 21% 9%	2090
October	1st to 10th	Day	58% 6% 10% 21% 5%	3458
	11th to 20th	Day	56% 7% 13% 22% 3	2863
	21st to end	Day	58% 6% 16% 13% 6%	3081
November	1st to 10th	Day	57% 7% 12% 17% 6%	1761
	11th to 20th	Day	61% 6% 10% 16% 6% 1	1790
	21st to end	Day	65% 8% 11% 11% 4 1	1398
December	1st to 10th	Day	67% 6% 9% 11% 6%	1330
	11th to 20th	Day	60% 7% 9% 15% 9%	1668
	21st to end	Day	58% 9% 10% 14% 7% 2	2493
January	1st to 10th	Night	63% 9% 10% 12% 5% 1	4429
	11th to 20th	Night	59% 10% 11% 14% 5% 1	4440
	21st to end	Night	52% 12% 10% 14% 11% 1	4884
February	1st to 10th	Night	56% 6% 9% 18% 10% 1	2660
	11th to 20th	Night	59% 7% 11% 12% 10% 1	2245
	21st to end	Night	55% 6% 9% 15% 12% 2	1884
March	1st to 10th	Night	56% 8% 12% 14% 8% 2	3734
	11th to 20th	Night	59% 9% 12% 13% 6% 1	3645
	21st to end	Night	53% 7% 9% 20% 9% 2	3568
April	1st to 10th	Night	57% 6% 10% 12% 12% 3	1900
	11th to 20th	Night	48% 7% 11% 21% 11% 2	1780
	21st to end	Night	52% 7% 10% 16% 13% 2	1710
May	1st to 10th	Night	48% 8% 12% 20% 11% 1	2749
	11th to 20th	Night	45% 12% 15% 18% 9% 1	2496
	21st to end	Night	43% 9% 15% 17% 15% 1	2651
June	1st to 10th	Night	52% 10% 13% 17% 8% 1	1330
	11th to 20th	Night	45% 8% 14% 20% 11% 3	1330
	21st to end	Night	55% 8% 11% 16% 10%	1330
July	1st to 10th	Night	49% 7% 20% 18% 5%	2376
	11th to 20th	Night	51% 8% 19% 18% 4	2472
	21st to end	Night	38% 7% 25% 22% 9%	2651
August	1st to 10th	Night	48% 6% 18% 22% 6%	2496
	11th to 20th	Night	50% 10% 21% 15% 5%	2793
	21st to end	Night	50% 7% 13% 22% 8%	3308
September	1st to 10th	Night	43% 8% 15% 22% 11% 1	1900
	11th to 20th	Night	42% 8% 17% 26% 7%	2066
	21st to end	Night	45% 7% 14% 23% 11%	2090
October	1st to 10th	Night	51% 5% 10% 26% 7%	3498
	11th to 20th	Night	53% 7% 11% 24% 5%	4055
	21st to end	Night	52% 9% 16% 14% 8%	4467
November	1st to 10th	Night	54% 7% 15% 18% 6% 1	2537
	11th to 20th	Night	53% 9% 13% 15% 10%	2607
	21st to end	Night	64% 7% 11% 12% 6% 1	2935
December	1st to 10th	Night	68% 7% 9% 11% 5% 1	2850
	11th to 20th	Night	60% 7% 11% 13% 9% 1	3532
	21st to end	Night	62% 7% 9% 13% 7% 2	5170

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	24% 21% 34% 17% 4	180
	11th to 20th	Day	27% 21% 33% 16% 2	180
	21st to end	Day	14% 23% 43% 15% 5% 1	198
February	1st to 10th	Day	27% 29% 34% 8% 1 1	180
	11th to 20th	Day	20% 29% 35% 12% 3	437
	21st to end	Day	24% 26% 32% 15% 3	382
March	1st to 10th	Day	23% 23% 33% 15% 4	460
	11th to 20th	Day	27% 22% 31% 14% 6% 1	460
	21st to end	Day	24% 27% 26% 16% 6% 1	506
April	1st to 10th	Day	30% 22% 28% 15% 5%	460
	11th to 20th	Day	31% 18% 29% 16% 4 2	452
	21st to end	Day	30% 21% 33% 11% 4 1	460
May	1st to 10th	Day	28% 21% 31% 15% 5% 1	463
	11th to 20th	Day	23% 19% 32% 19% 6% 1	487
	21st to end	Day	28% 22% 29% 16% 5%	576
June	1st to 10th	Day	24% 17% 30% 22% 7%	680
	11th to 20th	Day	25% 17% 26% 22% 9%	680
	21st to end	Day	30% 12% 27% 22% 7% 1	680
July	1st to 10th	Day	22% 14% 33% 20% 10%	548
	11th to 20th	Day	22% 12% 37% 20% 7% 1	484
	21st to end	Day	21% 13% 34% 23% 8% 1	532
August	1st to 10th	Day	23% 12% 33% 21% 10% 2	486
	11th to 20th	Day	23% 9% 28% 28% 11% 3	479
	21st to end	Day	24% 16% 25% 19% 11% 5%	539
September	1st to 10th	Day	24% 16% 27% 21% 10% 3	490
	11th to 20th	Day	22% 12% 29% 22% 12% 2	490
	21st to end	Day	25% 14% 28% 19% 10% 4	490
October	1st to 10th	Day	27% 15% 30% 18% 9% 1	490
	11th to 20th	Day	34% 18% 24% 16% 7% 1	404
	21st to end	Day	39% 19% 24% 15% 4	429
November	1st to 10th	Day	35% 18% 25% 17% 4 1	395
	11th to 20th	Day	28% 19% 28% 18% 7% 1	390
	21st to end	Day	32% 24% 31% 11% 2	194
December	1st to 10th	Day	29% 17% 28% 17% 7% 1	180
	11th to 20th	Day	31% 24% 30% 11% 4 1	180
	21st to end	Day	28% 25% 31% 12% 5%	198
January	1st to 10th	Night	21% 17% 36% 21% 4	760
	11th to 20th	Night	23% 19% 31% 21% 6%	760
	21st to end	Night	15% 14% 38% 27% 5% 1	836
February	1st to 10th	Night	17% 17% 37% 25% 5%	760
	11th to 20th	Night	20% 17% 40% 18% 4	743
	21st to end	Night	20% 18% 34% 23% 4	628
March	1st to 10th	Night	21% 14% 37% 25% 3	760
	11th to 20th	Night	21% 20% 33% 19% 6% 1	760
	21st to end	Night	21% 18% 32% 23% 6% 1	836
April	1st to 10th	Night	29% 15% 31% 20% 5%	760
	11th to 20th	Night	27% 13% 31% 24% 5%	656
	21st to end	Night	30% 15% 29% 20% 5% 1	570
May	1st to 10th	Night	27% 12% 32% 24% 5%	518
	11th to 20th	Night	22% 11% 28% 30% 9%	374
	21st to end	Night	28% 8% 31% 25% 8%	411
June	1st to 10th	Night	24% 9% 26% 33% 8%	380
	11th to 20th	Night	21% 8% 25% 35% 10% 1	380
	21st to end	Night	29% 4 24% 33% 9% 1	380
July	1st to 10th	Night	20% 6% 26% 36% 11% 1	370
	11th to 20th	Night	21% 4 24% 37% 13% 1	368
	21st to end	Night	19% 5% 21% 41% 14% 1	416
August	1st to 10th	Night	20% 4 19% 39% 18%	378
	11th to 20th	Night	20% 6% 23% 34% 17% 1	546
	21st to end	Night	20% 8% 24% 30% 16% 2	733
September	1st to 10th	Night	22% 8% 26% 32% 12% 1	760
	11th to 20th	Night	22% 8% 24% 29% 16% 2	760
	21st to end	Night	25% 9% 23% 29% 13% 1	760
October	1st to 10th	Night	27% 10% 23% 29% 10% 1	760
	11th to 20th	Night	31% 10% 26% 23% 9%	760
	21st to end	Night	34% 14% 27% 20% 5%	836
November	1st to 10th	Night	29% 15% 25% 24% 6% 1	780
	11th to 20th	Night	26% 18% 24% 23% 8% 1	800
	21st to end	Night	29% 19% 28% 20% 4 1	876
December	1st to 10th	Night	29% 14% 27% 22% 7%	850
	11th to 20th	Night	24% 20% 28% 22% 5% 1	850
	21st to end	Night	27% 19% 31% 18% 5%	915

Page generated at 2024-11-25 00:22:14. Version ac07

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