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 2026-02-01.

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	20% 12% 4 9% 5% 5% 4 3 5% 6% 28%	127234
	Night	17% 13% 4 10% 6% 4 4 3 4 6% 28%	124831
Transparency	Day	55% 7% 12% 16% 8% 1	130676
	Night	55% 7% 12% 17% 9% 1	129477
Seeing	Day	27% 18% 30% 17% 6% 1	16740
	Night	24% 14% 29% 25% 8% 1	25351

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% 18% 7% 14% 6% 5% 4 3 4 6% 21%	3677
	11th to 20th	Day	8% 16% 7% 20% 10% 7% 3 2 3 2 22%	3650
	21st to end	Day	6% 9% 7% 15% 5% 5% 4 4 6% 6% 33%	4048
February	1st to 10th	Day	8% 15% 6% 16% 8% 7% 5% 3 4 4 25%	1600
	11th to 20th	Day	12% 16% 7% 15% 7% 5% 4 3 5% 4 23%	1919
	21st to end	Day	12% 16% 5% 13% 7% 4 4 3 5% 5% 26%	1650
March	1st to 10th	Day	19% 19% 5% 12% 5% 3 2 2 3 3 24%	4476
	11th to 20th	Day	16% 19% 4 10% 4 4 4 3 4 5% 27%	4745
	21st to end	Day	17% 17% 5% 9% 4 3 3 2 3 5% 32%	5822
April	1st to 10th	Day	21% 17% 4 9% 4 4 3 2 4 5% 26%	2400
	11th to 20th	Day	21% 14% 3 7% 4 3 4 3 4 5% 32%	2472
	21st to end	Day	25% 12% 3 7% 5% 3 4 3 5% 5% 28%	2600
May	1st to 10th	Day	28% 10% 3 6% 4 3 4 4 5% 5% 27%	6061
	11th to 20th	Day	23% 8% 3 7% 5% 5% 5% 4 5% 7% 29%	6318
	21st to end	Day	22% 10% 3 8% 5% 6% 5% 4 5% 6% 26%	7077
June	1st to 10th	Day	24% 8% 3 8% 5% 5% 6% 4 6% 8% 24%	3000
	11th to 20th	Day	24% 9% 3 5% 5% 5% 4 4 6% 6% 30%	3000
	21st to end	Day	28% 10% 3 8% 6% 4 4 3 5% 6% 24%	3000
July	1st to 10th	Day	21% 8% 3 8% 6% 6% 6% 4 7% 8% 23%	6504
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 7% 8% 27%	6360
	21st to end	Day	15% 5% 2 6% 5% 5% 7% 5% 6% 8% 35%	6926
August	1st to 10th	Day	19% 7% 3 7% 5% 6% 6% 5% 8% 8% 27%	4547
	11th to 20th	Day	24% 7% 3 8% 6% 5% 6% 4 6% 7% 25%	4175
	21st to end	Day	23% 7% 2 7% 5% 4 5% 3 6% 7% 32%	4482
September	1st to 10th	Day	23% 8% 3 6% 4 5% 5% 4 6% 6% 33%	2400
	11th to 20th	Day	19% 6% 2 5% 4 4 4 3 4 7% 43%	2225
	21st to end	Day	26% 7% 2 6% 4 3 3 3 5% 6% 34%	2200
October	1st to 10th	Day	24% 10% 2 6% 4 4 4 4 4 5% 32%	2190
	11th to 20th	Day	26% 14% 4 7% 4 4 4 3 4 6% 24%	1829
	21st to end	Day	28% 15% 3 7% 4 4 3 3 4 5% 23%	1980
November	1st to 10th	Day	21% 17% 4 8% 4 4 3 3 4 5% 26%	1851
	11th to 20th	Day	20% 19% 6% 10% 4 4 3 2 4 4 24%	1879
	21st to end	Day	18% 22% 6% 10% 6% 3 4 3 4 4 19%	1490
December	1st to 10th	Day	17% 16% 7% 13% 7% 5% 4 3 4 4 19%	2350
	11th to 20th	Day	19% 14% 6% 11% 6% 4 3 2 3 4 26%	2688
	21st to end	Day	16% 17% 7% 9% 4 3 4 3 4 5% 27%	3643
January	1st to 10th	Night	11% 20% 7% 15% 8% 4 4 2 3 4 21%	6489
	11th to 20th	Night	8% 16% 8% 20% 11% 6% 3 3 4 3 18%	6455
	21st to end	Night	5% 10% 6% 15% 8% 6% 6% 4 7% 7% 26%	7150
February	1st to 10th	Night	9% 14% 5% 13% 8% 5% 4 4 4 6% 27%	2801
	11th to 20th	Night	10% 19% 6% 12% 6% 6% 5% 3 4 6% 24%	2363
	21st to end	Night	12% 16% 5% 11% 7% 4 4 4 5% 5% 27%	1980
March	1st to 10th	Night	18% 16% 5% 11% 6% 4 4 3 5% 5% 23%	5364
	11th to 20th	Night	14% 17% 4 10% 5% 5% 5% 4 6% 6% 23%	5214
	21st to end	Night	17% 16% 5% 9% 4 4 4 3 4 5% 30%	5106
April	1st to 10th	Night	21% 17% 5% 7% 4 4 4 3 4 5% 28%	2000
	11th to 20th	Night	20% 11% 3 6% 4 5% 4 4 5% 7% 31%	1875
	21st to end	Night	23% 12% 3 8% 4 3 3 2 4 5% 33%	1800
May	1st to 10th	Night	27% 8% 3 6% 4 5% 4 3 4 5% 32%	3921
	11th to 20th	Night	24% 8% 3 6% 4 4 3 4 4 6% 33%	3575
	21st to end	Night	20% 8% 2 6% 4 4 4 4 5% 7% 35%	3799
June	1st to 10th	Night	21% 9% 2 7% 6% 4 5% 4 6% 7% 29%	1400
	11th to 20th	Night	21% 7% 3 6% 4 4 4 3 5% 7% 36%	1400
	21st to end	Night	26% 8% 3 8% 5% 3 4 3 4 6% 30%	1400
July	1st to 10th	Night	18% 8% 3 7% 5% 5% 5% 5% 7% 8% 30%	3457
	11th to 20th	Night	23% 8% 3 7% 4 4 4 4 6% 7% 31%	3600
	21st to end	Night	14% 6% 2 6% 4 4 4 4 5% 8% 44%	3926
August	1st to 10th	Night	20% 7% 3 7% 4 4 4 4 5% 7% 37%	2586
	11th to 20th	Night	22% 7% 3 5% 5% 5% 5% 3 6% 7% 32%	2855
	21st to end	Night	20% 9% 3 8% 5% 5% 4 4 4 6% 34%	3413
September	1st to 10th	Night	21% 7% 2 5% 4 3 4 3 4 7% 41%	2000
	11th to 20th	Night	20% 6% 2 5% 3 3 4 3 5% 6% 43%	2175
	21st to end	Night	23% 8% 2 5% 3 3 3 3 4 6% 40%	2200
October	1st to 10th	Night	23% 9% 2 5% 4 4 4 3 5% 6% 37%	2206
	11th to 20th	Night	27% 9% 2 6% 4 4 4 3 4 6% 31%	2570
	21st to end	Night	26% 15% 2 6% 4 3 4 4 5% 6% 25%	2860
November	1st to 10th	Night	21% 14% 5% 8% 4 4 4 3 4 6% 27%	2667
	11th to 20th	Night	20% 14% 5% 9% 4 3 4 3 5% 6% 27%	2738
	21st to end	Night	20% 18% 7% 10% 5% 4 3 3 4 5% 21%	3128
December	1st to 10th	Night	13% 15% 7% 16% 9% 7% 4 2 4 4 19%	5060
	11th to 20th	Night	20% 17% 5% 11% 8% 4 3 2 3 4 22%	5741
	21st to end	Night	18% 18% 6% 10% 4 4 3 2 3 3 28%	7557

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	60% 9% 10% 12% 9%	3678
	11th to 20th	Day	65% 8% 7% 12% 7% 2	3680
	21st to end	Day	47% 8% 8% 18% 19% 1	4048
February	1st to 10th	Day	60% 6% 9% 14% 9% 3	1600
	11th to 20th	Day	61% 6% 10% 12% 8% 2	1928
	21st to end	Day	58% 5% 9% 16% 8% 3	1650
March	1st to 10th	Day	62% 7% 7% 11% 9% 5%	4479
	11th to 20th	Day	55% 7% 15% 13% 9% 1	4745
	21st to end	Day	55% 5% 6% 15% 14% 4	5822
April	1st to 10th	Day	59% 5% 10% 13% 10% 4	2400
	11th to 20th	Day	51% 6% 10% 19% 11% 2	2472
	21st to end	Day	55% 6% 11% 15% 11% 2	2600
May	1st to 10th	Day	54% 7% 12% 15% 11% 1	6072
	11th to 20th	Day	51% 10% 17% 15% 5% 3	6322
	21st to end	Day	54% 9% 11% 14% 10% 2	7077
June	1st to 10th	Day	54% 10% 12% 17% 6% 1	3000
	11th to 20th	Day	50% 8% 15% 16% 9% 1	3000
	21st to end	Day	59% 7% 12% 13% 8% 1	3000
July	1st to 10th	Day	57% 6% 14% 17% 6%	6434
	11th to 20th	Day	52% 7% 18% 20% 4	6285
	21st to end	Day	44% 7% 16% 26% 7%	6728
August	1st to 10th	Day	51% 9% 18% 17% 5%	4533
	11th to 20th	Day	55% 7% 18% 15% 4	4214
	21st to end	Day	50% 6% 16% 16% 12%	4482
September	1st to 10th	Day	47% 8% 16% 21% 8%	2400
	11th to 20th	Day	40% 6% 17% 27% 9%	2225
	21st to end	Day	49% 7% 12% 22% 10%	2200
October	1st to 10th	Day	56% 6% 10% 22% 6%	3567
	11th to 20th	Day	55% 7% 13% 22% 3	2954
	21st to end	Day	58% 6% 16% 13% 6%	3180
November	1st to 10th	Day	58% 7% 12% 17% 6%	1851
	11th to 20th	Day	62% 6% 10% 15% 6% 1	1879
	21st to end	Day	66% 8% 10% 11% 4 1	1490
December	1st to 10th	Day	67% 5% 8% 11% 8%	2350
	11th to 20th	Day	63% 5% 7% 15% 11%	2688
	21st to end	Day	58% 7% 8% 12% 13% 3	3643
January	1st to 10th	Night	66% 7% 8% 12% 6%	6489
	11th to 20th	Night	67% 7% 9% 12% 4 1	6500
	21st to end	Night	51% 9% 8% 16% 16% 1	7150
February	1st to 10th	Night	56% 6% 9% 17% 10% 1	2801
	11th to 20th	Night	59% 7% 11% 12% 10% 1	2365
	21st to end	Night	56% 6% 9% 15% 12% 2	1980
March	1st to 10th	Night	61% 6% 9% 11% 12% 1	5374
	11th to 20th	Night	58% 8% 13% 12% 7% 2	5215
	21st to end	Night	56% 5% 7% 20% 10% 2	5106
April	1st to 10th	Night	57% 6% 10% 12% 12% 3	2000
	11th to 20th	Night	49% 7% 11% 20% 11% 2	1875
	21st to end	Night	52% 7% 10% 16% 13% 2	1800
May	1st to 10th	Night	54% 6% 9% 16% 13% 2	3927
	11th to 20th	Night	50% 9% 14% 19% 8% 1	3576
	21st to end	Night	46% 7% 13% 18% 14% 2	3800
June	1st to 10th	Night	51% 9% 13% 18% 8% 1	1400
	11th to 20th	Night	46% 8% 14% 20% 11% 2	1400
	21st to end	Night	55% 8% 11% 16% 11%	1400
July	1st to 10th	Night	50% 6% 21% 18% 5%	3417
	11th to 20th	Night	50% 7% 20% 20% 3	3552
	21st to end	Night	39% 6% 21% 26% 8%	3809
August	1st to 10th	Night	47% 6% 18% 22% 7%	2576
	11th to 20th	Night	49% 9% 20% 15% 5% 1	2882
	21st to end	Night	50% 7% 12% 22% 8%	3413
September	1st to 10th	Night	42% 8% 15% 24% 10% 1	2000
	11th to 20th	Night	42% 8% 17% 27% 7%	2175
	21st to end	Night	44% 6% 14% 24% 11%	2200
October	1st to 10th	Night	50% 5% 11% 27% 7%	3609
	11th to 20th	Night	52% 7% 11% 24% 5%	4184
	21st to end	Night	53% 8% 15% 15% 8%	4610
November	1st to 10th	Night	55% 7% 14% 17% 6% 1	2667
	11th to 20th	Night	54% 8% 12% 15% 10%	2738
	21st to end	Night	65% 7% 10% 11% 6% 1	3128
December	1st to 10th	Night	67% 6% 9% 13% 4	5060
	11th to 20th	Night	65% 5% 7% 14% 8%	5742
	21st to end	Night	61% 5% 7% 13% 11% 3	7557

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	25% 22% 35% 15% 4	220
	11th to 20th	Day	28% 21% 31% 15% 4	220
	21st to end	Day	15% 25% 42% 13% 4 1	242
February	1st to 10th	Day	28% 31% 33% 7% 2 1	200
	11th to 20th	Day	23% 29% 34% 11% 3	477
	21st to end	Day	24% 26% 33% 14% 3	414
March	1st to 10th	Day	25% 23% 33% 15% 4	500
	11th to 20th	Day	27% 23% 31% 13% 5% 1	500
	21st to end	Day	27% 25% 26% 16% 5% 1	550
April	1st to 10th	Day	32% 21% 28% 14% 5%	500
	11th to 20th	Day	31% 18% 29% 16% 4 2	492
	21st to end	Day	32% 21% 33% 10% 3 1	500
May	1st to 10th	Day	30% 20% 30% 15% 5% 1	503
	11th to 20th	Day	25% 18% 30% 20% 5% 1	527
	21st to end	Day	29% 21% 29% 15% 5%	623
June	1st to 10th	Day	25% 17% 30% 22% 7%	730
	11th to 20th	Day	27% 17% 26% 21% 8%	730
	21st to end	Day	31% 13% 27% 21% 7% 1	730
July	1st to 10th	Day	23% 15% 32% 20% 9%	591
	11th to 20th	Day	23% 13% 37% 19% 7% 1	524
	21st to end	Day	21% 16% 34% 22% 8% 1	576
August	1st to 10th	Day	22% 11% 33% 21% 10% 2	526
	11th to 20th	Day	22% 9% 29% 27% 11% 3	519
	21st to end	Day	25% 15% 25% 20% 11% 4	583
September	1st to 10th	Day	24% 16% 27% 21% 10% 3	530
	11th to 20th	Day	22% 13% 29% 21% 12% 3	530
	21st to end	Day	26% 14% 28% 18% 10% 4	530
October	1st to 10th	Day	26% 15% 31% 18% 9% 1	530
	11th to 20th	Day	32% 18% 26% 16% 7% 1	435
	21st to end	Day	39% 19% 23% 15% 4	462
November	1st to 10th	Day	36% 20% 24% 16% 3 1	425
	11th to 20th	Day	28% 20% 27% 17% 7% 1	419
	21st to end	Day	33% 25% 30% 10% 1	220
December	1st to 10th	Day	27% 20% 30% 16% 6%	220
	11th to 20th	Day	32% 25% 29% 9% 5%	220
	21st to end	Day	28% 23% 31% 13% 5%	242
January	1st to 10th	Night	22% 18% 35% 21% 4	840
	11th to 20th	Night	23% 19% 31% 20% 7%	840
	21st to end	Night	14% 15% 38% 27% 5% 1	924
February	1st to 10th	Night	17% 18% 37% 24% 4	801
	11th to 20th	Night	21% 17% 39% 18% 4	783
	21st to end	Night	21% 17% 35% 23% 4	660
March	1st to 10th	Night	22% 15% 37% 24% 3	800
	11th to 20th	Night	21% 19% 34% 19% 5% 1	800
	21st to end	Night	22% 18% 31% 23% 6% 1	880
April	1st to 10th	Night	30% 15% 31% 19% 5%	800
	11th to 20th	Night	26% 13% 32% 23% 5%	691
	21st to end	Night	31% 16% 29% 19% 5% 1	600
May	1st to 10th	Night	27% 12% 32% 23% 5%	545
	11th to 20th	Night	23% 11% 28% 29% 9%	394
	21st to end	Night	27% 8% 30% 26% 8%	433
June	1st to 10th	Night	24% 9% 27% 33% 7%	400
	11th to 20th	Night	22% 8% 25% 35% 10% 1	400
	21st to end	Night	29% 5% 25% 33% 9% 1	400
July	1st to 10th	Night	20% 6% 26% 37% 10% 1	390
	11th to 20th	Night	21% 4 24% 37% 13% 1	388
	21st to end	Night	18% 6% 23% 39% 13% 1	438
August	1st to 10th	Night	19% 4 19% 40% 18%	398
	11th to 20th	Night	19% 6% 23% 34% 17% 1	575
	21st to end	Night	21% 9% 23% 30% 16% 2	772
September	1st to 10th	Night	21% 8% 25% 32% 12% 1	800
	11th to 20th	Night	21% 8% 24% 30% 17% 2	800
	21st to end	Night	25% 10% 23% 29% 13% 1	800
October	1st to 10th	Night	26% 11% 24% 29% 10% 1	800
	11th to 20th	Night	30% 10% 26% 24% 9%	800
	21st to end	Night	34% 13% 27% 20% 5%	880
November	1st to 10th	Night	30% 15% 25% 23% 5% 1	820
	11th to 20th	Night	26% 18% 25% 23% 8% 1	840
	21st to end	Night	29% 20% 27% 19% 4 1	939
December	1st to 10th	Night	28% 15% 28% 23% 7%	950
	11th to 20th	Night	25% 21% 27% 21% 5% 1	950
	21st to end	Night	27% 18% 32% 17% 5%	1020

Page generated at 2026-01-29 01:21:47. Version ac07

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