Observatoire du Geai Bleu
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Geai Bleu clear sky chart from 2005-11-06 to 2024-11-05.

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	16% 9% 3 7% 5% 5% 5% 4 6% 7% 34%	101555
	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 34%	97472
Transparency	Day	48% 7% 14% 21% 10% 1	105018
	Night	50% 6% 13% 20% 10% 1	102098
Seeing	Day	20% 11% 29% 25% 12% 3	14554
	Night	22% 8% 30% 30% 10% 1	23487

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% 14% 5% 10% 6% 5% 4 4 5% 5% 26%	2517
	11th to 20th	Day	13% 14% 5% 9% 6% 4 4 4 5% 6% 30%	2520
	21st to end	Day	12% 14% 5% 11% 7% 5% 4 4 5% 6% 25%	2772
February	1st to 10th	Day	14% 16% 4 9% 6% 4 5% 4 5% 6% 28%	1654
	11th to 20th	Day	12% 12% 5% 11% 6% 6% 5% 4 5% 6% 29%	1758
	21st to end	Day	16% 15% 4 10% 6% 4 4 3 5% 5% 28%	1570
March	1st to 10th	Day	19% 11% 3 10% 5% 6% 5% 3 5% 5% 27%	3116
	11th to 20th	Day	12% 16% 5% 10% 6% 6% 4 3 4 6% 29%	3274
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 3 5% 6% 38%	4166
April	1st to 10th	Day	20% 11% 3 7% 5% 4 5% 3 4 5% 32%	2280
	11th to 20th	Day	21% 7% 2 6% 5% 5% 4 3 5% 6% 37%	2254
	21st to end	Day	21% 9% 3 7% 5% 4 4 3 4 6% 33%	2441
May	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 5% 7% 31%	4381
	11th to 20th	Day	18% 7% 3 8% 5% 5% 5% 3 6% 8% 32%	4398
	21st to end	Day	15% 5% 3 6% 5% 5% 5% 4 7% 8% 37%	4837
June	1st to 10th	Day	20% 8% 2 7% 5% 5% 5% 4 6% 8% 30%	2660
	11th to 20th	Day	14% 6% 2 7% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	20% 8% 3 7% 6% 5% 5% 5% 5% 7% 29%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 5% 6% 9% 35%	4440
	11th to 20th	Day	13% 5% 3 6% 5% 5% 6% 5% 8% 9% 37%	4440
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 8% 45%	4814
August	1st to 10th	Day	14% 5% 2 7% 6% 6% 6% 5% 7% 10% 32%	4423
	11th to 20th	Day	14% 6% 2 7% 5% 4 5% 4 7% 9% 37%	4025
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 6% 8% 41%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 5% 6% 8% 43%	2280
	11th to 20th	Day	13% 5% 3 4 3 4 4 3 6% 6% 50%	2199
	21st to end	Day	17% 6% 2 6% 5% 4 3 3 5% 7% 43%	2090
October	1st to 10th	Day	19% 7% 2 6% 4 4 5% 3 5% 8% 37%	1963
	11th to 20th	Day	19% 7% 4 7% 6% 5% 6% 4 6% 6% 31%	1851
	21st to end	Day	22% 10% 3 7% 4 4 4 3 5% 5% 32%	1881
November	1st to 10th	Day	15% 9% 3 7% 5% 4 4 4 6% 7% 36%	1708
	11th to 20th	Day	18% 11% 4 7% 4 4 5% 4 5% 7% 32%	1625
	21st to end	Day	20% 11% 2 8% 5% 5% 6% 4 6% 7% 27%	1520
December	1st to 10th	Day	24% 14% 4 9% 5% 4 5% 3 4 5% 23%	1520
	11th to 20th	Day	21% 15% 4 8% 3 4 4 3 4 5% 29%	1906
	21st to end	Day	27% 16% 5% 9% 4 3 3 3 4 4 23%	2772
January	1st to 10th	Night	16% 15% 4 9% 6% 5% 5% 4 5% 5% 26%	4429
	11th to 20th	Night	11% 12% 5% 11% 7% 6% 6% 4 5% 6% 27%	4440
	21st to end	Night	13% 15% 5% 11% 6% 5% 5% 4 5% 6% 26%	4884
February	1st to 10th	Night	13% 14% 5% 11% 6% 5% 4 4 5% 5% 26%	2523
	11th to 20th	Night	14% 10% 5% 10% 5% 5% 5% 4 5% 5% 32%	2307
	21st to end	Night	15% 13% 4 10% 5% 3 4 3 4 6% 32%	1884
March	1st to 10th	Night	20% 13% 4 7% 4 4 4 3 4 5% 33%	3724
	11th to 20th	Night	15% 17% 5% 10% 5% 4 4 3 4 4 29%	3667
	21st to end	Night	13% 10% 5% 9% 5% 5% 5% 3 4 5% 38%	3466
April	1st to 10th	Night	23% 10% 3 7% 4 4 4 3 4 7% 31%	1900
	11th to 20th	Night	20% 8% 2 7% 4 3 4 4 5% 5% 36%	1875
	21st to end	Night	21% 9% 3 6% 4 3 4 3 5% 5% 37%	1737
May	1st to 10th	Night	21% 9% 3 7% 4 4 4 4 5% 6% 32%	2588
	11th to 20th	Night	21% 7% 3 6% 4 4 4 4 6% 8% 34%	2495
	21st to end	Night	16% 8% 3 7% 5% 5% 4 3 6% 9% 35%	2738
June	1st to 10th	Night	20% 6% 3 7% 4 5% 5% 4 5% 8% 34%	1520
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 7% 7% 38%	1520
	21st to end	Night	19% 8% 2 7% 5% 4 4 4 6% 7% 34%	1520
July	1st to 10th	Night	11% 7% 2 8% 5% 5% 6% 5% 7% 8% 34%	2520
	11th to 20th	Night	14% 5% 2 5% 5% 4 5% 4 6% 8% 42%	2520
	21st to end	Night	10% 6% 2 6% 4 4 4 4 7% 8% 45%	2739
August	1st to 10th	Night	13% 6% 3 8% 5% 5% 6% 4 6% 7% 38%	2506
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 3 6% 6% 40%	2754
	21st to end	Night	17% 7% 3 7% 4 4 4 4 5% 7% 40%	3476
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 5% 7% 47%	1900
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 5% 7% 51%	1981
	21st to end	Night	16% 5% 2 6% 4 3 3 3 5% 7% 45%	2090
October	1st to 10th	Night	18% 7% 3 6% 4 5% 4 3 4 5% 42%	2213
	11th to 20th	Night	19% 9% 3 7% 4 4 5% 3 5% 6% 37%	2327
	21st to end	Night	21% 9% 3 7% 5% 4 4 3 5% 6% 33%	2717
November	1st to 10th	Night	17% 9% 4 7% 5% 4 5% 4 5% 6% 34%	2470
	11th to 20th	Night	19% 10% 3 7% 4 4 4 4 4 6% 35%	2550
	21st to end	Night	22% 13% 3 8% 5% 4 4 3 3 5% 31%	2660
December	1st to 10th	Night	21% 13% 5% 10% 6% 4 5% 4 5% 6% 23%	2660
	11th to 20th	Night	23% 14% 5% 8% 5% 3 3 3 4 5% 29%	3288
	21st to end	Night	26% 16% 5% 9% 4 3 3 2 4 4 23%	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	57% 9% 14% 14% 5% 1	2518
	11th to 20th	Day	53% 7% 14% 18% 8%	2520
	21st to end	Day	58% 8% 13% 14% 7% 1	2772
February	1st to 10th	Day	58% 4 10% 19% 7% 2	1654
	11th to 20th	Day	56% 6% 13% 14% 10% 1	1767
	21st to end	Day	58% 4 10% 16% 9% 2	1570
March	1st to 10th	Day	58% 6% 9% 16% 9% 1	3119
	11th to 20th	Day	55% 6% 13% 11% 11% 3	3274
	21st to end	Day	45% 5% 11% 19% 17% 2	4166
April	1st to 10th	Day	55% 4 9% 18% 12% 2	2280
	11th to 20th	Day	49% 5% 8% 22% 13% 2	2254
	21st to end	Day	53% 6% 9% 17% 12% 3	2441
May	1st to 10th	Day	50% 8% 10% 21% 10% 1	4395
	11th to 20th	Day	48% 8% 17% 16% 9% 2	4402
	21st to end	Day	42% 8% 12% 22% 15% 1	4837
June	1st to 10th	Day	50% 7% 12% 18% 11% 2	2660
	11th to 20th	Day	42% 8% 12% 22% 13% 3	2660
	21st to end	Day	52% 7% 12% 17% 10% 1	2660
July	1st to 10th	Day	43% 7% 15% 25% 10% 1	4370
	11th to 20th	Day	40% 8% 17% 27% 8%	4365
	21st to end	Day	35% 8% 15% 32% 10%	4661
August	1st to 10th	Day	46% 7% 18% 21% 8%	4409
	11th to 20th	Day	42% 8% 19% 25% 6%	4067
	21st to end	Day	41% 7% 16% 21% 15% 1	4180
September	1st to 10th	Day	36% 8% 15% 28% 12% 1	2280
	11th to 20th	Day	34% 7% 14% 31% 14% 1	2199
	21st to end	Day	43% 5% 15% 26% 11%	2090
October	1st to 10th	Day	45% 6% 14% 26% 9%	3262
	11th to 20th	Day	43% 6% 18% 26% 7%	3054
	21st to end	Day	42% 5% 21% 22% 10% 1	3081
November	1st to 10th	Day	46% 7% 15% 21% 10% 1	1708
	11th to 20th	Day	52% 6% 13% 18% 11% 1	1625
	21st to end	Day	56% 7% 15% 16% 6% 1	1520
December	1st to 10th	Day	64% 5% 11% 14% 5%	1520
	11th to 20th	Day	58% 6% 11% 18% 7%	1906
	21st to end	Day	66% 6% 11% 11% 6%	2772
January	1st to 10th	Night	59% 7% 16% 13% 5%	4429
	11th to 20th	Night	55% 10% 14% 16% 5% 1	4440
	21st to end	Night	59% 8% 13% 12% 7% 1	4884
February	1st to 10th	Night	60% 6% 10% 16% 8% 1	2523
	11th to 20th	Night	53% 6% 11% 19% 10% 1	2309
	21st to end	Night	55% 5% 9% 16% 13% 2	1884
March	1st to 10th	Night	53% 7% 10% 17% 9% 4	3734
	11th to 20th	Night	57% 6% 10% 13% 13% 2	3668
	21st to end	Night	47% 5% 9% 21% 15% 3	3466
April	1st to 10th	Night	53% 4 9% 18% 14% 2	1900
	11th to 20th	Night	50% 5% 8% 21% 14% 2	1875
	21st to end	Night	49% 5% 9% 20% 13% 4	1737
May	1st to 10th	Night	51% 8% 11% 18% 9% 3	2594
	11th to 20th	Night	46% 9% 13% 17% 11% 2	2496
	21st to end	Night	45% 7% 11% 19% 17% 1	2739
June	1st to 10th	Night	49% 6% 11% 20% 13% 1	1520
	11th to 20th	Night	43% 7% 12% 21% 13% 3	1520
	21st to end	Night	48% 8% 11% 18% 14% 1	1520
July	1st to 10th	Night	44% 7% 16% 20% 12% 1	2480
	11th to 20th	Night	39% 7% 19% 27% 8%	2472
	21st to end	Night	36% 7% 20% 25% 13%	2651
August	1st to 10th	Night	45% 7% 13% 25% 9%	2496
	11th to 20th	Night	43% 8% 17% 24% 7%	2778
	21st to end	Night	44% 8% 13% 21% 13% 1	3476
September	1st to 10th	Night	37% 7% 15% 25% 16% 1	1900
	11th to 20th	Night	34% 6% 14% 32% 12% 1	1981
	21st to end	Night	39% 7% 11% 28% 14%	2090
October	1st to 10th	Night	44% 6% 14% 25% 10% 1	3694
	11th to 20th	Night	43% 5% 12% 31% 9%	3863
	21st to end	Night	45% 5% 17% 18% 13% 2	4467
November	1st to 10th	Night	50% 6% 13% 21% 9% 1	2470
	11th to 20th	Night	51% 6% 13% 19% 10% 1	2550
	21st to end	Night	58% 6% 11% 18% 8%	2660
December	1st to 10th	Night	62% 6% 12% 15% 5%	2660
	11th to 20th	Night	59% 5% 10% 18% 7% 1	3288
	21st to end	Night	65% 5% 9% 15% 5%	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	22% 14% 31% 24% 9%	180
	11th to 20th	Day	24% 14% 32% 25% 4 1	180
	21st to end	Day	19% 11% 35% 26% 8% 2	198
February	1st to 10th	Day	28% 21% 33% 17% 2	244
	11th to 20th	Day	18% 13% 41% 22% 5%	365
	21st to end	Day	27% 11% 33% 24% 5%	382
March	1st to 10th	Day	24% 10% 32% 25% 8%	460
	11th to 20th	Day	20% 14% 35% 25% 5% 1	460
	21st to end	Day	26% 12% 33% 20% 8% 1	506
April	1st to 10th	Day	26% 15% 27% 22% 8% 2	460
	11th to 20th	Day	27% 17% 23% 22% 8% 2	452
	21st to end	Day	28% 12% 31% 20% 8% 2	460
May	1st to 10th	Day	23% 11% 33% 23% 8% 2	463
	11th to 20th	Day	19% 10% 30% 25% 14% 2	487
	21st to end	Day	18% 12% 32% 25% 10% 2	529
June	1st to 10th	Day	23% 10% 27% 27% 11% 2	490
	11th to 20th	Day	15% 12% 27% 31% 13% 2	490
	21st to end	Day	22% 10% 23% 28% 13% 3	490
July	1st to 10th	Day	14% 6% 27% 31% 18% 5%	485
	11th to 20th	Day	15% 7% 26% 32% 16% 4	484
	21st to end	Day	12% 5% 27% 34% 18% 4	532
August	1st to 10th	Day	16% 6% 22% 33% 19% 5%	486
	11th to 20th	Day	11% 4 21% 32% 21% 11%	479
	21st to end	Day	14% 8% 25% 25% 18% 9%	539
September	1st to 10th	Day	13% 7% 27% 28% 17% 7%	490
	11th to 20th	Day	12% 8% 21% 28% 19% 12%	490
	21st to end	Day	18% 9% 26% 23% 18% 6%	490
October	1st to 10th	Day	21% 11% 27% 23% 14% 4	490
	11th to 20th	Day	20% 13% 32% 22% 12% 2	463
	21st to end	Day	29% 10% 28% 23% 8%	429
November	1st to 10th	Day	24% 14% 28% 24% 9% 1	378
	11th to 20th	Day	26% 12% 32% 19% 10% 1	285
	21st to end	Day	27% 14% 30% 18% 11% 1	180
December	1st to 10th	Day	29% 11% 23% 24% 10% 2	180
	11th to 20th	Day	23% 14% 35% 23% 3 1	180
	21st to end	Day	33% 15% 29% 15% 7% 1	198
January	1st to 10th	Night	25% 11% 31% 27% 6%	760
	11th to 20th	Night	24% 10% 33% 26% 7%	760
	21st to end	Night	17% 8% 36% 31% 7% 1	836
February	1st to 10th	Night	21% 9% 37% 28% 5% 1	760
	11th to 20th	Night	19% 10% 37% 28% 5% 1	743
	21st to end	Night	22% 9% 34% 31% 4	628
March	1st to 10th	Night	25% 8% 32% 29% 5%	760
	11th to 20th	Night	25% 11% 32% 26% 7%	760
	21st to end	Night	21% 8% 33% 31% 7%	836
April	1st to 10th	Night	27% 10% 28% 28% 6%	760
	11th to 20th	Night	25% 11% 32% 27% 6%	751
	21st to end	Night	28% 8% 32% 24% 7%	597
May	1st to 10th	Night	24% 7% 31% 30% 7% 1	428
	11th to 20th	Night	22% 7% 30% 32% 9% 1	374
	21st to end	Night	18% 8% 36% 30% 8%	411
June	1st to 10th	Night	24% 4 25% 38% 9%	380
	11th to 20th	Night	18% 7% 27% 34% 12% 1	380
	21st to end	Night	22% 3 26% 34% 14%	380
July	1st to 10th	Night	11% 6% 26% 40% 16% 1	370
	11th to 20th	Night	12% 4 22% 45% 16%	368
	21st to end	Night	13% 3 22% 46% 16% 1	416
August	1st to 10th	Night	13% 5% 14% 48% 20% 1	378
	11th to 20th	Night	14% 4 21% 36% 23% 2	543
	21st to end	Night	15% 4 23% 35% 21% 2	836
September	1st to 10th	Night	15% 4 25% 39% 16% 1	760
	11th to 20th	Night	16% 4 20% 35% 22% 2	760
	21st to end	Night	18% 5% 27% 32% 16% 2	760
October	1st to 10th	Night	22% 5% 27% 34% 11% 1	760
	11th to 20th	Night	23% 8% 28% 30% 10% 1	760
	21st to end	Night	27% 9% 31% 27% 7%	836
November	1st to 10th	Night	23% 10% 30% 28% 8% 1	760
	11th to 20th	Night	23% 10% 34% 23% 10% 1	760
	21st to end	Night	28% 10% 31% 22% 8% 1	760
December	1st to 10th	Night	29% 8% 32% 24% 7%	760
	11th to 20th	Night	28% 11% 31% 24% 5% 1	760
	21st to end	Night	33% 9% 32% 20% 6%	836

Page generated at 2024-11-03 02:11:17. Version ac07

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