Site d'observation Chemin Jordan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Site d'observation Chemin Jordan clear sky chart from 2005-11-06 to 2025-12-03.

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% 12% 4 9% 5% 5% 5% 3 5% 6% 27%	127113
	Night	19% 15% 5% 11% 5% 4 4 3 4 5% 25%	123594
Transparency	Day	57% 6% 11% 18% 7% 1	130568
	Night	61% 5% 9% 16% 8% 1	128226
Seeing	Day	28% 16% 28% 18% 7% 2	16009
	Night	27% 15% 25% 24% 9% 1	24929

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	14% 24% 8% 19% 6% 6% 3 2 3 3 11%	3597
	11th to 20th	Day	10% 17% 9% 24% 11% 6% 4 3 4 3 9%	3570
	21st to end	Day	12% 20% 8% 13% 6% 10% 5% 3 4 4 15%	3960
February	1st to 10th	Day	15% 18% 6% 15% 9% 6% 4 3 4 3 17%	1715
	11th to 20th	Day	14% 20% 7% 14% 8% 4 5% 4 4 3 18%	1918
	21st to end	Day	14% 20% 6% 11% 7% 6% 4 3 4 5% 21%	1650
March	1st to 10th	Day	20% 17% 7% 13% 5% 4 5% 2 3 4 19%	4476
	11th to 20th	Day	13% 18% 5% 10% 5% 4 4 4 5% 5% 27%	4648
	21st to end	Day	21% 15% 6% 10% 5% 3 4 3 4 4 26%	5970
April	1st to 10th	Day	22% 17% 4 9% 4 4 4 2 4 4 26%	2400
	11th to 20th	Day	21% 14% 3 8% 4 4 4 3 4 5% 32%	2374
	21st to end	Day	25% 11% 4 7% 5% 5% 4 3 5% 5% 28%	2600
May	1st to 10th	Day	31% 12% 3 8% 5% 4 4 3 4 5% 20%	6065
	11th to 20th	Day	21% 8% 3 8% 6% 5% 6% 4 6% 7% 26%	6318
	21st to end	Day	22% 10% 3 6% 4 4 4 4 6% 7% 29%	6949
June	1st to 10th	Day	28% 7% 2 6% 4 5% 4 4 5% 8% 27%	2800
	11th to 20th	Day	19% 6% 3 6% 5% 4 5% 4 7% 7% 35%	2800
	21st to end	Day	25% 7% 3 6% 5% 5% 5% 4 6% 6% 28%	2800
July	1st to 10th	Day	16% 7% 2 7% 5% 6% 6% 6% 8% 9% 28%	6360
	11th to 20th	Day	15% 6% 2 6% 5% 5% 6% 5% 7% 9% 34%	6360
	21st to end	Day	15% 6% 2 5% 4 5% 4 4 6% 9% 39%	6926
August	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 8% 29%	4563
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 4 6% 8% 31%	4102
	21st to end	Day	19% 7% 2 5% 3 4 4 4 5% 8% 38%	4312
September	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 7% 42%	2400
	11th to 20th	Day	18% 7% 1 5% 3 3 4 2 4 6% 47%	2270
	21st to end	Day	20% 7% 2 5% 4 4 4 4 6% 8% 37%	2200
October	1st to 10th	Day	24% 8% 2 6% 5% 5% 5% 3 5% 5% 31%	2132
	11th to 20th	Day	23% 11% 3 7% 5% 4 5% 4 5% 5% 29%	1915
	21st to end	Day	27% 18% 3 7% 4 4 3 3 3 4 23%	1980
November	1st to 10th	Day	20% 17% 4 7% 5% 3 4 3 4 5% 27%	1851
	11th to 20th	Day	18% 21% 5% 10% 5% 4 4 3 3 4 24%	1890
	21st to end	Day	20% 21% 7% 10% 5% 4 3 3 5% 5% 17%	1680
December	1st to 10th	Day	17% 23% 7% 20% 7% 5% 3 2 3 3 10%	2616
	11th to 20th	Day	20% 19% 7% 13% 5% 3 4 2 4 4 19%	2986
	21st to end	Day	19% 19% 5% 13% 6% 5% 5% 3 4 4 18%	3960
January	1st to 10th	Night	13% 22% 10% 22% 6% 5% 3 2 3 3 12%	6349
	11th to 20th	Night	10% 21% 9% 22% 8% 6% 4 3 3 3 11%	6315
	21st to end	Night	12% 19% 6% 15% 8% 6% 5% 3 3 4 18%	6996
February	1st to 10th	Night	15% 20% 6% 16% 7% 5% 4 3 4 4 17%	2680
	11th to 20th	Night	14% 17% 7% 14% 8% 5% 4 3 3 4 19%	2368
	21st to end	Night	14% 20% 6% 12% 7% 5% 4 2 3 4 24%	1980
March	1st to 10th	Night	19% 17% 6% 10% 6% 5% 4 3 4 4 24%	5364
	11th to 20th	Night	15% 19% 5% 10% 5% 5% 4 3 4 6% 25%	5308
	21st to end	Night	17% 20% 5% 11% 4 4 3 2 2 4 26%	4962
April	1st to 10th	Night	23% 14% 4 9% 5% 4 3 3 4 5% 26%	2000
	11th to 20th	Night	25% 12% 3 7% 4 4 4 3 3 5% 30%	1975
	21st to end	Night	23% 13% 3 6% 3 3 4 3 4 5% 32%	1800
May	1st to 10th	Night	28% 13% 3 9% 4 4 4 3 4 6% 22%	3917
	11th to 20th	Night	24% 9% 3 8% 5% 4 4 3 5% 6% 30%	3575
	21st to end	Night	21% 12% 3 7% 5% 4 4 4 4 6% 31%	3926
June	1st to 10th	Night	27% 8% 3 6% 3 4 4 4 5% 8% 29%	1600
	11th to 20th	Night	20% 6% 2 6% 4 5% 5% 4 5% 7% 36%	1600
	21st to end	Night	22% 8% 2 6% 4 5% 5% 4 7% 8% 30%	1600
July	1st to 10th	Night	16% 7% 2 8% 6% 6% 6% 5% 6% 8% 30%	3600
	11th to 20th	Night	19% 7% 3 7% 4 4 4 3 5% 7% 37%	3600
	21st to end	Night	15% 7% 2 7% 5% 5% 5% 4 5% 7% 39%	3926
August	1st to 10th	Night	24% 6% 3 7% 4 4 3 3 4 7% 34%	2586
	11th to 20th	Night	17% 9% 3 8% 5% 5% 6% 3 5% 6% 33%	2898
	21st to end	Night	19% 6% 3 5% 4 4 5% 3 5% 6% 41%	3586
September	1st to 10th	Night	19% 5% 2 6% 5% 4 4 3 5% 6% 42%	2000
	11th to 20th	Night	16% 6% 1 5% 3 4 3 3 5% 6% 47%	2128
	21st to end	Night	22% 6% 2 5% 4 4 4 3 5% 6% 41%	2200
October	1st to 10th	Night	22% 8% 3 7% 4 3 4 3 5% 6% 35%	2265
	11th to 20th	Night	23% 11% 3 8% 4 4 4 3 4 5% 30%	2483
	21st to end	Night	28% 14% 3 7% 4 4 4 4 4 5% 25%	2860
November	1st to 10th	Night	22% 15% 4 7% 4 4 5% 3 4 5% 26%	2667
	11th to 20th	Night	20% 18% 5% 8% 5% 3 3 3 4 4 26%	2730
	21st to end	Night	21% 21% 6% 11% 5% 4 3 3 3 4 20%	2937
December	1st to 10th	Night	16% 27% 12% 15% 5% 4 3 2 3 3 9%	4609
	11th to 20th	Night	21% 22% 6% 14% 5% 4 3 2 3 2 16%	5208
	21st to end	Night	20% 20% 6% 11% 5% 4 4 2 3 4 21%	6996

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	80% 4 8% 7% 1	3598
	11th to 20th	Day	80% 5% 6% 6% 3	3600
	21st to end	Day	73% 5% 7% 10% 4	3960
February	1st to 10th	Day	73% 4 6% 11% 5% 1	1715
	11th to 20th	Day	71% 5% 8% 11% 4 1	1927
	21st to end	Day	67% 4 9% 13% 6% 1	1650
March	1st to 10th	Day	71% 4 8% 9% 6% 2	4479
	11th to 20th	Day	58% 6% 12% 13% 10% 1	4648
	21st to end	Day	62% 4 6% 13% 14% 1	5970
April	1st to 10th	Day	63% 4 7% 17% 8% 1	2400
	11th to 20th	Day	56% 4 7% 18% 13% 1	2374
	21st to end	Day	59% 4 9% 16% 9% 2	2600
May	1st to 10th	Day	66% 6% 7% 15% 5% 1	6076
	11th to 20th	Day	55% 8% 13% 15% 8% 1	6322
	21st to end	Day	51% 8% 11% 20% 9% 1	6949
June	1st to 10th	Day	55% 6% 11% 19% 8% 1	2800
	11th to 20th	Day	47% 6% 12% 23% 10% 2	2800
	21st to end	Day	55% 6% 11% 19% 8% 1	2800
July	1st to 10th	Day	48% 8% 15% 22% 7%	6290
	11th to 20th	Day	43% 9% 13% 27% 8%	6285
	21st to end	Day	40% 8% 13% 32% 7%	6728
August	1st to 10th	Day	51% 8% 15% 20% 6%	4549
	11th to 20th	Day	50% 7% 18% 20% 5%	4141
	21st to end	Day	43% 7% 17% 18% 13% 1	4312
September	1st to 10th	Day	42% 6% 13% 29% 10% 1	2400
	11th to 20th	Day	39% 4 11% 31% 14%	2270
	21st to end	Day	44% 6% 15% 24% 11% 1	2200
October	1st to 10th	Day	47% 6% 15% 25% 8%	3470
	11th to 20th	Day	54% 5% 14% 21% 7%	3092
	21st to end	Day	54% 5% 15% 20% 6% 1	3180
November	1st to 10th	Day	60% 6% 10% 17% 7%	1851
	11th to 20th	Day	66% 4 9% 12% 7% 1	1890
	21st to end	Day	70% 5% 12% 9% 4	1680
December	1st to 10th	Day	81% 4 7% 6% 1	2616
	11th to 20th	Day	70% 3 7% 15% 5%	2986
	21st to end	Day	71% 5% 6% 10% 8%	3960
January	1st to 10th	Night	80% 5% 8% 6% 1	6349
	11th to 20th	Night	79% 5% 7% 6% 2	6360
	21st to end	Night	71% 5% 9% 7% 8% 1	6996
February	1st to 10th	Night	73% 4 6% 11% 5%	2680
	11th to 20th	Night	70% 4 8% 12% 5%	2370
	21st to end	Night	66% 4 8% 14% 8% 1	1980
March	1st to 10th	Night	66% 4 9% 12% 8% 2	5374
	11th to 20th	Night	59% 7% 12% 13% 8% 1	5309
	21st to end	Night	64% 4 5% 17% 9% 1	4962
April	1st to 10th	Night	62% 4 7% 16% 11% 1	2000
	11th to 20th	Night	57% 5% 6% 19% 13%	1975
	21st to end	Night	55% 5% 7% 18% 13% 2	1800
May	1st to 10th	Night	63% 6% 8% 15% 6% 1	3923
	11th to 20th	Night	53% 8% 10% 20% 7% 1	3576
	21st to end	Night	53% 7% 8% 19% 12% 1	3927
June	1st to 10th	Night	54% 5% 10% 21% 9% 1	1600
	11th to 20th	Night	47% 7% 11% 21% 12% 2	1600
	21st to end	Night	50% 9% 13% 18% 10% 1	1600
July	1st to 10th	Night	48% 8% 16% 20% 8%	3560
	11th to 20th	Night	45% 7% 12% 27% 8%	3552
	21st to end	Night	43% 7% 14% 25% 10%	3809
August	1st to 10th	Night	50% 7% 13% 24% 6%	2576
	11th to 20th	Night	50% 8% 15% 19% 8%	2925
	21st to end	Night	43% 7% 12% 23% 13% 1	3586
September	1st to 10th	Night	42% 6% 12% 28% 11% 1	2000
	11th to 20th	Night	38% 5% 15% 31% 12%	2128
	21st to end	Night	45% 6% 11% 24% 14% 1	2200
October	1st to 10th	Night	52% 5% 10% 23% 10%	3707
	11th to 20th	Night	53% 4 10% 22% 10%	4045
	21st to end	Night	55% 6% 13% 17% 9% 1	4610
November	1st to 10th	Night	59% 6% 11% 16% 7% 1	2667
	11th to 20th	Night	63% 4 9% 13% 9% 2	2730
	21st to end	Night	69% 4 10% 12% 4	2937
December	1st to 10th	Night	82% 4 6% 6% 1	4609
	11th to 20th	Night	76% 4 5% 11% 5%	5208
	21st to end	Night	70% 5% 7% 11% 7%	6996

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	33% 19% 30% 13% 6% 1	200
	11th to 20th	Day	29% 26% 31% 11% 3 1	200
	21st to end	Day	28% 23% 30% 15% 4	220
February	1st to 10th	Day	36% 31% 26% 5% 2	257
	11th to 20th	Day	34% 27% 27% 10% 2	466
	21st to end	Day	33% 19% 31% 15% 2	414
March	1st to 10th	Day	35% 19% 27% 16% 3	500
	11th to 20th	Day	33% 22% 28% 13% 3 1	500
	21st to end	Day	36% 21% 22% 15% 5% 1	550
April	1st to 10th	Day	39% 17% 24% 15% 4 1	500
	11th to 20th	Day	38% 19% 22% 13% 6% 2	492
	21st to end	Day	34% 18% 29% 12% 6% 2	500
May	1st to 10th	Day	36% 17% 26% 13% 6% 2	503
	11th to 20th	Day	25% 15% 30% 19% 9% 2	527
	21st to end	Day	22% 18% 33% 21% 5% 1	573
June	1st to 10th	Day	32% 13% 32% 15% 7% 1	530
	11th to 20th	Day	23% 13% 32% 21% 9% 1	530
	21st to end	Day	27% 14% 34% 18% 6% 2	530
July	1st to 10th	Day	17% 12% 31% 28% 10% 1	525
	11th to 20th	Day	17% 12% 34% 26% 8% 3	524
	21st to end	Day	19% 11% 34% 27% 8% 1	576
August	1st to 10th	Day	17% 10% 30% 27% 15% 1	526
	11th to 20th	Day	21% 6% 29% 25% 14% 3	519
	21st to end	Day	20% 14% 26% 23% 11% 5%	583
September	1st to 10th	Day	20% 12% 27% 23% 12% 6%	530
	11th to 20th	Day	18% 11% 22% 22% 20% 8%	530
	21st to end	Day	20% 14% 25% 26% 10% 5%	530
October	1st to 10th	Day	28% 13% 25% 18% 13% 3	530
	11th to 20th	Day	32% 19% 22% 18% 8% 1	483
	21st to end	Day	39% 16% 24% 15% 5%	462
November	1st to 10th	Day	36% 20% 24% 15% 4	425
	11th to 20th	Day	35% 20% 23% 15% 7% 1	430
	21st to end	Day	35% 21% 28% 13% 2	220
December	1st to 10th	Day	33% 21% 30% 11% 5%	204
	11th to 20th	Day	37% 22% 31% 9% 1 1	200
	21st to end	Day	37% 20% 26% 12% 4	220
January	1st to 10th	Night	29% 24% 28% 17% 3	800
	11th to 20th	Night	28% 22% 26% 18% 5%	800
	21st to end	Night	21% 21% 30% 22% 5%	880
February	1st to 10th	Night	27% 22% 28% 20% 4	800
	11th to 20th	Night	26% 22% 31% 18% 3	783
	21st to end	Night	27% 18% 30% 22% 2	660
March	1st to 10th	Night	29% 18% 27% 22% 4	800
	11th to 20th	Night	30% 20% 24% 20% 6%	800
	21st to end	Night	30% 18% 23% 21% 7% 1	880
April	1st to 10th	Night	32% 17% 26% 22% 4	800
	11th to 20th	Night	34% 15% 23% 20% 7%	791
	21st to end	Night	32% 15% 26% 20% 6%	600
May	1st to 10th	Night	28% 13% 28% 22% 9% 1	541
	11th to 20th	Night	24% 10% 28% 27% 9% 1	394
	21st to end	Night	22% 10% 27% 33% 8% 1	433
June	1st to 10th	Night	29% 9% 23% 30% 8% 1	400
	11th to 20th	Night	24% 8% 25% 31% 13% 1	400
	21st to end	Night	23% 8% 24% 36% 9% 1	400
July	1st to 10th	Night	16% 4 29% 37% 13% 1	390
	11th to 20th	Night	12% 7% 20% 43% 15% 2	388
	21st to end	Night	17% 6% 20% 43% 13%	438
August	1st to 10th	Night	18% 6% 16% 38% 21% 1	398
	11th to 20th	Night	17% 7% 17% 38% 20% 1	604
	21st to end	Night	18% 8% 21% 33% 18% 2	880
September	1st to 10th	Night	20% 8% 23% 33% 15% 2	800
	11th to 20th	Night	20% 7% 16% 31% 25% 2	800
	21st to end	Night	23% 10% 25% 23% 17% 2	800
October	1st to 10th	Night	26% 12% 22% 27% 12% 1	800
	11th to 20th	Night	30% 13% 23% 25% 9% 1	800
	21st to end	Night	36% 13% 26% 20% 5%	880
November	1st to 10th	Night	33% 16% 26% 19% 5% 1	820
	11th to 20th	Night	30% 20% 23% 18% 8% 1	840
	21st to end	Night	33% 22% 24% 16% 5% 1	840
December	1st to 10th	Night	36% 21% 23% 15% 5%	809
	11th to 20th	Night	33% 20% 26% 16% 5% 1	800
	21st to end	Night	34% 19% 24% 19% 3	880

Page generated at 2025-11-30 01:00:54. Version ac07

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