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 2024-11-11.

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 8% 5% 5% 4 4 5% 6% 28%	101516
	Night	20% 14% 4 10% 5% 4 4 3 4 5% 27%	97657
Transparency	Day	56% 6% 12% 18% 7% 1	104989
	Night	60% 6% 10% 17% 8% 1	102273
Seeing	Day	28% 16% 28% 18% 8% 2	14689
	Night	27% 15% 24% 24% 9% 1	23599

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% 24% 7% 16% 5% 4 4 3 4 3 14%	2517
	11th to 20th	Day	13% 18% 8% 18% 9% 5% 4 4 5% 4 12%	2520
	21st to end	Day	14% 23% 7% 13% 5% 8% 4 3 4 4 14%	2772
February	1st to 10th	Day	16% 18% 6% 14% 10% 6% 4 3 4 3 17%	1629
	11th to 20th	Day	14% 21% 7% 13% 8% 4 5% 4 4 3 18%	1819
	21st to end	Day	14% 20% 6% 11% 7% 6% 4 3 4 5% 21%	1570
March	1st to 10th	Day	22% 15% 4 11% 6% 4 4 3 4 5% 22%	3116
	11th to 20th	Day	14% 24% 6% 12% 6% 4 3 2 4 4 21%	3246
	21st to end	Day	19% 13% 6% 10% 4 3 3 2 3 4 32%	4166
April	1st to 10th	Day	23% 16% 4 9% 4 4 4 3 4 4 26%	2280
	11th to 20th	Day	21% 13% 3 7% 4 4 4 3 4 5% 32%	2254
	21st to end	Day	26% 11% 4 7% 5% 5% 4 3 4 5% 28%	2470
May	1st to 10th	Day	25% 11% 3 7% 5% 5% 5% 4 5% 6% 26%	4229
	11th to 20th	Day	20% 8% 3 8% 6% 5% 6% 4 6% 7% 27%	4398
	21st to end	Day	16% 8% 3 7% 4 5% 5% 4 7% 8% 33%	4837
June	1st to 10th	Day	28% 7% 2 6% 4 5% 4 4 5% 8% 27%	2660
	11th to 20th	Day	19% 6% 3 6% 4 4 4 4 7% 7% 35%	2660
	21st to end	Day	26% 7% 3 6% 5% 5% 5% 4 6% 6% 28%	2660
July	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	16% 7% 3 6% 5% 5% 6% 5% 7% 9% 31%	4440
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 8% 38%	4814
August	1st to 10th	Day	20% 8% 4 7% 5% 5% 5% 4 6% 8% 28%	4423
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 4 6% 8% 31%	3974
	21st to end	Day	19% 7% 2 5% 3 3 4 4 5% 8% 39%	4180
September	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 6% 7% 41%	2280
	11th to 20th	Day	19% 7% 1 5% 3 3 4 2 5% 6% 45%	2157
	21st to end	Day	20% 7% 3 5% 4 4 4 4 6% 8% 37%	2090
October	1st to 10th	Day	26% 9% 2 6% 5% 5% 5% 3 5% 5% 28%	2026
	11th to 20th	Day	23% 11% 2 7% 5% 4 5% 4 5% 5% 29%	1819
	21st to end	Day	27% 18% 3 7% 4 4 3 2 3 5% 24%	1881
November	1st to 10th	Day	20% 15% 4 7% 5% 3 4 3 4 5% 28%	1761
	11th to 20th	Day	19% 19% 5% 10% 5% 4 4 4 3 4 23%	1710
	21st to end	Day	20% 20% 6% 10% 5% 4 3 3 5% 5% 18%	1520
December	1st to 10th	Day	23% 23% 6% 11% 7% 3 4 2 3 3 15%	1520
	11th to 20th	Day	20% 20% 7% 10% 5% 4 4 2 3 5% 19%	1906
	21st to end	Day	23% 20% 4 13% 6% 5% 5% 2 3 3 15%	2772
January	1st to 10th	Night	16% 22% 8% 16% 6% 5% 3 3 3 4 14%	4429
	11th to 20th	Night	13% 19% 8% 19% 8% 6% 4 3 3 3 14%	4440
	21st to end	Night	16% 22% 7% 13% 6% 5% 3 2 3 3 19%	4884
February	1st to 10th	Night	15% 20% 6% 15% 7% 5% 4 3 4 4 17%	2546
	11th to 20th	Night	15% 17% 7% 13% 8% 5% 4 3 3 4 20%	2247
	21st to end	Night	14% 19% 6% 11% 6% 5% 5% 2 3 5% 24%	1884
March	1st to 10th	Night	22% 14% 4 7% 5% 4 4 3 4 5% 28%	3724
	11th to 20th	Night	16% 24% 5% 10% 5% 4 3 2 3 4 24%	3710
	21st to end	Night	16% 19% 6% 10% 4 3 3 2 2 4 30%	3466
April	1st to 10th	Night	23% 14% 4 8% 5% 4 3 3 4 5% 26%	1900
	11th to 20th	Night	24% 11% 3 7% 4 4 4 3 3 5% 31%	1875
	21st to end	Night	23% 13% 3 6% 4 3 4 3 4 5% 32%	1710
May	1st to 10th	Night	25% 11% 3 8% 4 4 4 4 4 6% 26%	2739
	11th to 20th	Night	22% 9% 3 8% 4 4 4 3 5% 6% 33%	2495
	21st to end	Night	18% 7% 2 6% 5% 4 4 4 5% 8% 36%	2738
June	1st to 10th	Night	27% 8% 3 6% 3 3 4 4 5% 8% 29%	1520
	11th to 20th	Night	20% 6% 2 5% 4 5% 5% 4 5% 8% 36%	1520
	21st to end	Night	22% 8% 2 6% 4 5% 5% 4 7% 7% 30%	1520
July	1st to 10th	Night	17% 8% 2 8% 5% 5% 5% 5% 5% 7% 32%	2520
	11th to 20th	Night	18% 7% 2 7% 4 5% 5% 4 6% 7% 35%	2520
	21st to end	Night	18% 7% 2 7% 5% 5% 4 4 4 6% 37%	2739
August	1st to 10th	Night	25% 7% 3 8% 4 4 3 3 4 7% 32%	2506
	11th to 20th	Night	18% 9% 3 8% 5% 5% 6% 3 5% 7% 32%	2807
	21st to end	Night	19% 6% 3 5% 4 4 5% 3 5% 6% 41%	3476
September	1st to 10th	Night	20% 5% 2 6% 5% 4 4 3 5% 6% 41%	1900
	11th to 20th	Night	16% 6% 1 5% 3 4 3 3 5% 6% 46%	2021
	21st to end	Night	22% 5% 2 5% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Night	23% 8% 3 7% 4 3 4 4 5% 6% 33%	2152
	11th to 20th	Night	24% 11% 3 8% 4 4 4 3 4 5% 29%	2359
	21st to end	Night	28% 13% 3 7% 4 4 4 4 4 5% 25%	2717
November	1st to 10th	Night	21% 15% 4 7% 5% 4 5% 3 5% 5% 27%	2537
	11th to 20th	Night	21% 17% 4 9% 6% 3 4 3 4 5% 26%	2477
	21st to end	Night	21% 20% 5% 11% 5% 4 3 3 3 4 21%	2657
December	1st to 10th	Night	22% 25% 6% 11% 5% 4 4 3 4 4 13%	2660
	11th to 20th	Night	22% 21% 7% 13% 5% 5% 4 2 3 3 15%	3288
	21st to end	Night	24% 21% 6% 13% 5% 4 3 2 3 3 16%	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	75% 5% 11% 8% 1	2518
	11th to 20th	Day	75% 5% 8% 7% 4	2520
	21st to end	Day	74% 5% 8% 9% 3 1	2772
February	1st to 10th	Day	73% 4 6% 12% 4 1	1629
	11th to 20th	Day	71% 5% 8% 12% 4 1	1828
	21st to end	Day	66% 4 9% 12% 7% 1	1570
March	1st to 10th	Day	66% 5% 10% 12% 7% 1	3119
	11th to 20th	Day	66% 5% 9% 10% 9% 1	3246
	21st to end	Day	58% 3 6% 16% 16% 1	4166
April	1st to 10th	Day	63% 4 7% 17% 8% 1	2280
	11th to 20th	Day	56% 4 7% 19% 13% 1	2254
	21st to end	Day	59% 4 9% 16% 9% 3	2470
May	1st to 10th	Day	58% 6% 9% 18% 7% 1	4243
	11th to 20th	Day	54% 9% 14% 15% 7% 1	4402
	21st to end	Day	44% 9% 13% 23% 10% 1	4837
June	1st to 10th	Day	55% 6% 11% 19% 8% 1	2660
	11th to 20th	Day	47% 6% 12% 23% 10% 2	2660
	21st to end	Day	56% 6% 12% 18% 7% 1	2660
July	1st to 10th	Day	44% 7% 15% 25% 8%	4370
	11th to 20th	Day	46% 9% 14% 27% 4	4365
	21st to end	Day	44% 8% 12% 29% 6%	4661
August	1st to 10th	Day	52% 7% 15% 19% 6%	4409
	11th to 20th	Day	51% 7% 18% 19% 5%	4013
	21st to end	Day	43% 7% 17% 18% 14% 1	4180
September	1st to 10th	Day	43% 6% 13% 27% 10% 1	2280
	11th to 20th	Day	40% 4 12% 31% 13%	2157
	21st to end	Day	44% 6% 15% 24% 9% 1	2090
October	1st to 10th	Day	48% 6% 15% 24% 7%	3364
	11th to 20th	Day	54% 5% 14% 21% 6%	2996
	21st to end	Day	54% 5% 15% 20% 6% 1	3081
November	1st to 10th	Day	58% 6% 11% 18% 7%	1761
	11th to 20th	Day	66% 5% 10% 11% 7% 2	1710
	21st to end	Day	68% 5% 13% 10% 4	1520
December	1st to 10th	Day	75% 5% 9% 9% 2	1520
	11th to 20th	Day	70% 3 8% 14% 5%	1906
	21st to end	Day	76% 5% 7% 10% 3	2772
January	1st to 10th	Night	75% 6% 11% 6% 2	4429
	11th to 20th	Night	75% 6% 8% 8% 3	4440
	21st to end	Night	72% 5% 10% 8% 4 1	4884
February	1st to 10th	Night	73% 4 6% 11% 5%	2546
	11th to 20th	Night	70% 4 7% 13% 5%	2249
	21st to end	Night	64% 4 8% 14% 8% 1	1884
March	1st to 10th	Night	60% 4 10% 16% 8% 2	3734
	11th to 20th	Night	64% 6% 6% 13% 10% 1	3711
	21st to end	Night	61% 4 5% 18% 11% 2	3466
April	1st to 10th	Night	61% 4 7% 16% 11% 1	1900
	11th to 20th	Night	56% 6% 6% 19% 13%	1875
	21st to end	Night	55% 5% 7% 17% 13% 2	1710
May	1st to 10th	Night	58% 7% 8% 17% 9% 2	2745
	11th to 20th	Night	51% 8% 12% 20% 9% 1	2496
	21st to end	Night	45% 8% 11% 20% 16% 1	2739
June	1st to 10th	Night	54% 5% 10% 21% 9% 1	1520
	11th to 20th	Night	46% 7% 12% 21% 12% 2	1520
	21st to end	Night	50% 8% 14% 18% 9% 1	1520
July	1st to 10th	Night	49% 7% 12% 21% 11%	2480
	11th to 20th	Night	45% 8% 13% 27% 7%	2472
	21st to end	Night	47% 7% 14% 22% 11%	2651
August	1st to 10th	Night	52% 7% 13% 23% 6%	2496
	11th to 20th	Night	51% 8% 16% 19% 7%	2834
	21st to end	Night	43% 7% 12% 23% 13% 1	3476
September	1st to 10th	Night	43% 6% 12% 26% 11% 1	1900
	11th to 20th	Night	38% 5% 15% 31% 11%	2021
	21st to end	Night	44% 6% 12% 24% 13% 1	2090
October	1st to 10th	Night	53% 5% 10% 23% 9%	3594
	11th to 20th	Night	53% 4 10% 22% 10%	3921
	21st to end	Night	54% 6% 13% 17% 9% 1	4467
November	1st to 10th	Night	59% 6% 11% 16% 7% 1	2537
	11th to 20th	Night	62% 4 9% 14% 8% 2	2477
	21st to end	Night	69% 5% 10% 13% 4	2657
December	1st to 10th	Night	77% 4 7% 9% 2	2660
	11th to 20th	Night	76% 4 6% 11% 4	3288
	21st to end	Night	75% 5% 7% 11% 2	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	34% 17% 29% 14% 6% 1	180
	11th to 20th	Day	31% 26% 29% 11% 3 1	180
	21st to end	Day	25% 23% 31% 16% 5% 1	198
February	1st to 10th	Day	37% 29% 25% 6% 2	231
	11th to 20th	Day	33% 28% 27% 10% 2	427
	21st to end	Day	33% 18% 31% 16% 2	382
March	1st to 10th	Day	34% 20% 26% 17% 3	460
	11th to 20th	Day	32% 22% 28% 13% 3 1	460
	21st to end	Day	35% 20% 22% 15% 6% 1	506
April	1st to 10th	Day	37% 17% 25% 16% 4 1	460
	11th to 20th	Day	36% 20% 23% 13% 7% 2	452
	21st to end	Day	34% 18% 28% 12% 6% 2	460
May	1st to 10th	Day	35% 16% 27% 14% 7% 2	463
	11th to 20th	Day	24% 16% 31% 18% 10% 2	487
	21st to end	Day	20% 18% 33% 22% 6% 1	529
June	1st to 10th	Day	32% 13% 31% 16% 8% 1	490
	11th to 20th	Day	23% 13% 32% 22% 10% 1	490
	21st to end	Day	28% 13% 33% 18% 6% 2	490
July	1st to 10th	Day	18% 11% 30% 29% 11% 1	485
	11th to 20th	Day	18% 12% 33% 26% 8% 3	484
	21st to end	Day	19% 10% 34% 28% 8% 2	532
August	1st to 10th	Day	19% 10% 30% 26% 14% 1	486
	11th to 20th	Day	22% 6% 28% 26% 14% 4	479
	21st to end	Day	20% 14% 25% 24% 12% 6%	539
September	1st to 10th	Day	21% 12% 27% 22% 12% 6%	490
	11th to 20th	Day	19% 11% 21% 22% 19% 8%	490
	21st to end	Day	19% 13% 25% 27% 10% 6%	490
October	1st to 10th	Day	29% 13% 24% 17% 13% 3	490
	11th to 20th	Day	32% 19% 23% 17% 9% 1	447
	21st to end	Day	39% 16% 24% 16% 5%	429
November	1st to 10th	Day	35% 19% 25% 15% 5% 1	395
	11th to 20th	Day	35% 21% 21% 14% 6% 1	370
	21st to end	Day	34% 20% 28% 15% 3	180
December	1st to 10th	Day	34% 20% 29% 12% 5%	180
	11th to 20th	Day	36% 22% 31% 9% 1 1	180
	21st to end	Day	39% 22% 24% 12% 3	198
January	1st to 10th	Night	29% 23% 27% 18% 3	760
	11th to 20th	Night	28% 23% 26% 18% 5%	760
	21st to end	Night	22% 21% 29% 23% 6%	836
February	1st to 10th	Night	26% 21% 28% 20% 4	760
	11th to 20th	Night	25% 21% 31% 19% 3	743
	21st to end	Night	27% 19% 30% 22% 2	628
March	1st to 10th	Night	29% 17% 27% 23% 4	760
	11th to 20th	Night	31% 19% 24% 20% 7%	760
	21st to end	Night	30% 18% 23% 21% 7% 1	836
April	1st to 10th	Night	31% 16% 26% 22% 4	760
	11th to 20th	Night	34% 15% 23% 21% 7%	751
	21st to end	Night	32% 15% 26% 20% 6%	570
May	1st to 10th	Night	27% 13% 28% 23% 9% 1	514
	11th to 20th	Night	24% 10% 29% 28% 8% 1	374
	21st to end	Night	20% 10% 27% 34% 8% 1	411
June	1st to 10th	Night	30% 8% 22% 31% 9% 1	380
	11th to 20th	Night	23% 7% 24% 32% 13% 1	380
	21st to end	Night	23% 8% 22% 37% 9% 1	380
July	1st to 10th	Night	16% 5% 29% 36% 13% 1	370
	11th to 20th	Night	12% 7% 21% 42% 16% 2	368
	21st to end	Night	18% 6% 20% 43% 14%	416
August	1st to 10th	Night	19% 6% 16% 37% 21% 1	378
	11th to 20th	Night	18% 7% 17% 38% 19% 2	573
	21st to end	Night	18% 7% 21% 34% 19% 2	836
September	1st to 10th	Night	20% 9% 23% 33% 14% 2	760
	11th to 20th	Night	20% 7% 17% 30% 24% 2	760
	21st to end	Night	23% 10% 24% 23% 17% 2	760
October	1st to 10th	Night	27% 12% 22% 26% 12% 1	760
	11th to 20th	Night	31% 13% 22% 24% 9% 1	760
	21st to end	Night	36% 14% 26% 20% 4	836
November	1st to 10th	Night	32% 17% 27% 19% 6% 1	780
	11th to 20th	Night	30% 20% 23% 17% 8% 2	763
	21st to end	Night	32% 22% 23% 16% 6% 1	760
December	1st to 10th	Night	37% 21% 22% 15% 5%	760
	11th to 20th	Night	31% 20% 26% 17% 6% 1	760
	21st to end	Night	35% 19% 24% 19% 3	836

Page generated at 2024-11-08 06:44:50. Version ac07

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