Observatoire de La Sitelle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de La Sitelle clear sky chart from 2005-11-06 to 2024-11-08.

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% 11% 4 9% 5% 5% 5% 4 5% 6% 30%	101591
	Night	15% 12% 4 9% 6% 5% 4 3 5% 6% 30%	97506
Transparency	Day	50% 8% 13% 19% 9% 1	105041
	Night	50% 8% 13% 18% 9% 1	102145
Seeing	Day	23% 19% 32% 18% 6% 2	14516
	Night	21% 16% 31% 23% 8% 1	23476

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% 17% 7% 15% 7% 4 4 3 5% 5% 18%	2517
	11th to 20th	Day	11% 14% 7% 19% 11% 6% 3 3 3 4 21%	2520
	21st to end	Day	10% 16% 8% 15% 5% 5% 6% 5% 6% 5% 21%	2772
February	1st to 10th	Day	10% 18% 6% 12% 8% 5% 4 3 4 6% 23%	1676
	11th to 20th	Day	11% 17% 6% 12% 6% 5% 4 3 5% 5% 25%	1728
	21st to end	Day	14% 19% 6% 9% 7% 5% 5% 4 4 5% 24%	1570
March	1st to 10th	Day	16% 18% 5% 11% 7% 5% 4 3 4 5% 24%	3116
	11th to 20th	Day	11% 19% 6% 13% 6% 4 5% 3 4 5% 24%	3320
	21st to end	Day	13% 11% 3 8% 5% 5% 5% 3 5% 6% 36%	4131
April	1st to 10th	Day	18% 15% 4 9% 5% 4 3 3 4 6% 29%	2280
	11th to 20th	Day	21% 10% 3 8% 5% 3 5% 3 4 5% 33%	2254
	21st to end	Day	21% 11% 4 9% 4 4 4 4 4 5% 30%	2431
May	1st to 10th	Day	21% 11% 3 8% 5% 4 5% 3 5% 6% 29%	4426
	11th to 20th	Day	18% 7% 3 7% 6% 5% 5% 4 7% 8% 29%	4398
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 5% 7% 33%	4837
June	1st to 10th	Day	23% 9% 3 8% 6% 5% 5% 4 6% 6% 26%	2660
	11th to 20th	Day	16% 8% 3 7% 6% 6% 5% 5% 6% 7% 32%	2660
	21st to end	Day	22% 10% 3 7% 5% 5% 5% 4 6% 6% 26%	2660
July	1st to 10th	Day	13% 7% 3 8% 6% 6% 6% 4 7% 8% 30%	4440
	11th to 20th	Day	15% 6% 2 6% 6% 5% 6% 5% 7% 8% 34%	4440
	21st to end	Day	12% 6% 3 6% 4 5% 4 4 6% 7% 43%	4814
August	1st to 10th	Day	15% 7% 2 8% 6% 6% 6% 5% 7% 8% 29%	4423
	11th to 20th	Day	16% 7% 3 7% 4 5% 6% 5% 6% 8% 33%	4027
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	4180
September	1st to 10th	Day	16% 6% 3 7% 4 4 4 4 6% 7% 40%	2280
	11th to 20th	Day	15% 5% 3 5% 4 4 4 4 6% 6% 43%	2220
	21st to end	Day	19% 8% 3 6% 4 4 3 4 5% 6% 38%	2090
October	1st to 10th	Day	21% 9% 3 7% 4 4 5% 3 6% 7% 32%	1929
	11th to 20th	Day	22% 11% 4 8% 6% 5% 4 4 5% 5% 25%	1872
	21st to end	Day	24% 11% 4 9% 5% 4 4 3 4 5% 25%	1881
November	1st to 10th	Day	15% 13% 4 8% 5% 5% 4 3 5% 6% 31%	1734
	11th to 20th	Day	18% 15% 5% 10% 6% 4 3 4 5% 5% 23%	1587
	21st to end	Day	19% 17% 5% 11% 5% 4 5% 4 5% 4 21%	1520
December	1st to 10th	Day	21% 20% 6% 11% 5% 4 3 3 4 5% 18%	1520
	11th to 20th	Day	18% 17% 6% 11% 6% 4 4 3 5% 5% 21%	1906
	21st to end	Day	20% 19% 6% 11% 5% 3 3 3 4 5% 20%	2772
January	1st to 10th	Night	13% 18% 7% 13% 6% 4 4 4 6% 5% 21%	4429
	11th to 20th	Night	10% 13% 6% 15% 10% 7% 5% 3 4 5% 21%	4440
	21st to end	Night	10% 14% 8% 16% 8% 6% 5% 3 5% 6% 19%	4884
February	1st to 10th	Night	11% 15% 5% 12% 7% 5% 5% 4 5% 5% 25%	2502
	11th to 20th	Night	10% 14% 6% 12% 6% 5% 5% 3 6% 6% 27%	2337
	21st to end	Night	11% 16% 5% 10% 5% 5% 5% 4 6% 6% 27%	1884
March	1st to 10th	Night	17% 14% 4 10% 5% 4 5% 3 4 5% 29%	3724
	11th to 20th	Night	12% 19% 6% 11% 5% 4 4 3 4 5% 26%	3624
	21st to end	Night	12% 11% 4 9% 7% 5% 5% 3 5% 5% 35%	3500
April	1st to 10th	Night	20% 12% 3 8% 5% 4 3 3 5% 7% 29%	1900
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 6% 5% 36%	1875
	21st to end	Night	19% 10% 3 8% 4 4 4 3 6% 5% 34%	1758
May	1st to 10th	Night	18% 11% 4 8% 6% 5% 5% 3 5% 7% 30%	2521
	11th to 20th	Night	20% 8% 3 6% 5% 3 4 3 5% 7% 37%	2495
	21st to end	Night	17% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	2738
June	1st to 10th	Night	19% 8% 3 6% 5% 5% 4 4 7% 7% 31%	1520
	11th to 20th	Night	18% 7% 3 6% 5% 3 5% 4 5% 8% 38%	1520
	21st to end	Night	21% 8% 2 6% 5% 4 4 4 6% 6% 35%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 5% 5% 5% 5% 7% 35%	2520
	11th to 20th	Night	15% 6% 2 7% 3 4 5% 4 6% 7% 41%	2520
	21st to end	Night	11% 5% 2 5% 3 4 5% 5% 6% 7% 47%	2739
August	1st to 10th	Night	12% 6% 3 9% 5% 4 4 4 7% 8% 39%	2506
	11th to 20th	Night	15% 8% 3 7% 4 3 4 4 5% 6% 41%	2765
	21st to end	Night	17% 6% 2 6% 4 4 4 4 5% 6% 41%	3476
September	1st to 10th	Night	12% 7% 2 5% 3 4 4 4 5% 7% 46%	1900
	11th to 20th	Night	15% 4 2 6% 3 3 3 3 5% 8% 48%	1959
	21st to end	Night	18% 6% 2 5% 4 3 3 4 5% 7% 43%	2090
October	1st to 10th	Night	16% 9% 3 6% 5% 5% 4 3 5% 6% 38%	2249
	11th to 20th	Night	20% 10% 3 8% 5% 4 5% 4 4 6% 32%	2308
	21st to end	Night	22% 10% 3 9% 6% 4 4 3 5% 7% 27%	2717
November	1st to 10th	Night	17% 10% 4 9% 6% 5% 5% 4 6% 6% 28%	2505
	11th to 20th	Night	16% 12% 5% 10% 6% 5% 4 4 5% 7% 26%	2589
	21st to end	Night	17% 17% 5% 11% 5% 4 4 3 4 5% 24%	2660
December	1st to 10th	Night	17% 16% 7% 14% 7% 5% 5% 4 4 5% 17%	2660
	11th to 20th	Night	18% 16% 5% 12% 7% 5% 4 3 3 4 24%	3288
	21st to end	Night	21% 21% 6% 10% 5% 4 3 3 4 5% 20%	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	64% 8% 11% 12% 4	2518
	11th to 20th	Day	62% 10% 5% 13% 8% 1	2520
	21st to end	Day	61% 9% 10% 12% 6% 1	2772
February	1st to 10th	Day	61% 5% 8% 16% 7% 2	1676
	11th to 20th	Day	58% 6% 11% 14% 10% 1	1737
	21st to end	Day	61% 5% 8% 14% 8% 3	1570
March	1st to 10th	Day	61% 8% 7% 13% 10% 1	3119
	11th to 20th	Day	57% 10% 10% 11% 10% 3	3320
	21st to end	Day	44% 7% 10% 19% 17% 3	4131
April	1st to 10th	Day	55% 6% 9% 16% 11% 3	2280
	11th to 20th	Day	51% 7% 9% 20% 11% 2	2254
	21st to end	Day	55% 6% 8% 16% 11% 3	2431
May	1st to 10th	Day	52% 9% 10% 19% 9% 1	4440
	11th to 20th	Day	46% 12% 19% 14% 8% 1	4402
	21st to end	Day	45% 10% 12% 18% 14% 1	4837
June	1st to 10th	Day	54% 8% 11% 16% 10% 1	2660
	11th to 20th	Day	47% 8% 13% 18% 11% 3	2660
	21st to end	Day	57% 8% 10% 16% 9%	2660
July	1st to 10th	Day	47% 9% 14% 23% 8%	4370
	11th to 20th	Day	43% 8% 18% 25% 6%	4365
	21st to end	Day	39% 7% 15% 29% 10%	4661
August	1st to 10th	Day	47% 9% 17% 21% 6%	4409
	11th to 20th	Day	44% 9% 16% 25% 5%	4069
	21st to end	Day	44% 7% 15% 21% 13% 1	4180
September	1st to 10th	Day	41% 8% 14% 25% 13%	2280
	11th to 20th	Day	38% 8% 15% 28% 11% 1	2220
	21st to end	Day	45% 7% 12% 25% 11%	2090
October	1st to 10th	Day	46% 7% 13% 26% 8%	3202
	11th to 20th	Day	47% 8% 13% 24% 7%	3088
	21st to end	Day	48% 6% 21% 15% 9% 1	3081
November	1st to 10th	Day	51% 8% 14% 18% 9% 1	1734
	11th to 20th	Day	57% 9% 12% 13% 9%	1587
	21st to end	Day	61% 10% 11% 13% 5% 1	1520
December	1st to 10th	Day	66% 7% 10% 11% 6%	1520
	11th to 20th	Day	61% 8% 11% 13% 7%	1906
	21st to end	Day	65% 7% 8% 13% 7%	2772
January	1st to 10th	Night	59% 11% 13% 13% 4	4429
	11th to 20th	Night	56% 13% 13% 12% 5% 1	4440
	21st to end	Night	61% 11% 10% 11% 7% 1	4884
February	1st to 10th	Night	58% 7% 10% 17% 7% 1	2502
	11th to 20th	Night	53% 9% 11% 18% 9% 1	2339
	21st to end	Night	54% 7% 10% 16% 11% 2	1884
March	1st to 10th	Night	54% 8% 10% 13% 11% 3	3734
	11th to 20th	Night	55% 9% 10% 13% 12% 1	3625
	21st to end	Night	47% 7% 10% 19% 13% 4	3500
April	1st to 10th	Night	53% 5% 10% 18% 13% 2	1900
	11th to 20th	Night	46% 7% 11% 20% 14% 2	1875
	21st to end	Night	49% 7% 10% 18% 13% 3	1758
May	1st to 10th	Night	48% 12% 12% 17% 8% 2	2527
	11th to 20th	Night	42% 10% 19% 15% 12% 2	2496
	21st to end	Night	46% 10% 11% 18% 13% 2	2739
June	1st to 10th	Night	47% 9% 13% 20% 11%	1520
	11th to 20th	Night	45% 7% 11% 22% 13% 2	1520
	21st to end	Night	48% 9% 12% 19% 12% 1	1520
July	1st to 10th	Night	45% 8% 18% 19% 10%	2480
	11th to 20th	Night	39% 8% 20% 28% 6%	2472
	21st to end	Night	33% 8% 20% 27% 12%	2651
August	1st to 10th	Night	41% 8% 16% 27% 7%	2496
	11th to 20th	Night	41% 7% 19% 25% 7%	2789
	21st to end	Night	42% 7% 16% 23% 11% 2	3476
September	1st to 10th	Night	34% 9% 16% 26% 14% 1	1900
	11th to 20th	Night	33% 7% 17% 31% 10% 1	1959
	21st to end	Night	39% 8% 13% 28% 12%	2090
October	1st to 10th	Night	44% 6% 13% 24% 12% 1	3756
	11th to 20th	Night	44% 7% 12% 27% 10%	3831
	21st to end	Night	46% 7% 18% 16% 11% 2	4467
November	1st to 10th	Night	51% 9% 14% 19% 6% 1	2505
	11th to 20th	Night	52% 9% 13% 16% 8% 2	2589
	21st to end	Night	58% 9% 12% 16% 6% 1	2660
December	1st to 10th	Night	65% 9% 10% 11% 4	2660
	11th to 20th	Night	61% 8% 9% 15% 7% 1	3288
	21st to end	Night	64% 7% 8% 14% 6%	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	17% 26% 39% 17% 2	180
	11th to 20th	Day	27% 21% 34% 13% 5% 1	180
	21st to end	Day	18% 22% 40% 14% 4 1	198
February	1st to 10th	Day	33% 30% 30% 6% 2	254
	11th to 20th	Day	25% 29% 39% 7% 1	335
	21st to end	Day	29% 26% 30% 14% 2	382
March	1st to 10th	Day	27% 22% 33% 15% 3	460
	11th to 20th	Day	25% 25% 33% 13% 3	460
	21st to end	Day	30% 24% 26% 14% 5% 1	506
April	1st to 10th	Day	30% 19% 33% 13% 4 1	460
	11th to 20th	Day	34% 21% 24% 13% 7% 1	452
	21st to end	Day	30% 20% 34% 12% 3 1	460
May	1st to 10th	Day	26% 23% 33% 14% 3 1	463
	11th to 20th	Day	24% 20% 31% 19% 6% 1	487
	21st to end	Day	24% 20% 32% 19% 5%	529
June	1st to 10th	Day	25% 17% 36% 16% 6% 1	490
	11th to 20th	Day	18% 21% 33% 17% 10% 1	490
	21st to end	Day	25% 17% 32% 19% 6% 1	490
July	1st to 10th	Day	14% 12% 39% 25% 8% 2	485
	11th to 20th	Day	16% 13% 37% 27% 6% 1	484
	21st to end	Day	15% 12% 36% 27% 9% 1	532
August	1st to 10th	Day	17% 11% 31% 29% 10% 1	486
	11th to 20th	Day	14% 11% 30% 27% 12% 5%	479
	21st to end	Day	16% 17% 30% 20% 10% 6%	539
September	1st to 10th	Day	18% 12% 34% 21% 10% 5%	490
	11th to 20th	Day	13% 14% 27% 25% 14% 7%	490
	21st to end	Day	22% 16% 25% 22% 12% 4	490
October	1st to 10th	Day	26% 18% 26% 18% 10% 2	490
	11th to 20th	Day	27% 23% 27% 16% 6% 1	475
	21st to end	Day	31% 17% 33% 16% 3	429
November	1st to 10th	Day	30% 20% 29% 17% 3 1	386
	11th to 20th	Day	25% 26% 31% 13% 6%	247
	21st to end	Day	28% 28% 29% 12% 2	180
December	1st to 10th	Day	30% 21% 28% 16% 5%	180
	11th to 20th	Day	25% 29% 36% 8% 2	180
	21st to end	Day	34% 26% 24% 11% 4 1	198
January	1st to 10th	Night	23% 20% 35% 17% 4	760
	11th to 20th	Night	22% 22% 31% 21% 4	760
	21st to end	Night	15% 17% 40% 22% 5% 1	836
February	1st to 10th	Night	18% 22% 38% 19% 4	760
	11th to 20th	Night	20% 21% 40% 15% 3	743
	21st to end	Night	21% 19% 36% 21% 2	628
March	1st to 10th	Night	24% 19% 35% 19% 3	760
	11th to 20th	Night	23% 22% 34% 17% 4 1	760
	21st to end	Night	21% 18% 33% 22% 5% 1	836
April	1st to 10th	Night	27% 19% 29% 21% 5%	760
	11th to 20th	Night	24% 18% 30% 22% 5% 1	751
	21st to end	Night	25% 17% 32% 19% 7%	618
May	1st to 10th	Night	22% 13% 35% 22% 6% 2	387
	11th to 20th	Night	21% 15% 29% 29% 6% 1	374
	21st to end	Night	19% 12% 41% 21% 7%	411
June	1st to 10th	Night	22% 8% 36% 26% 7%	380
	11th to 20th	Night	22% 9% 26% 32% 11% 1	380
	21st to end	Night	21% 7% 28% 30% 13% 1	380
July	1st to 10th	Night	14% 7% 31% 35% 13% 1	370
	11th to 20th	Night	11% 7% 27% 40% 14% 1	368
	21st to end	Night	13% 6% 27% 41% 13% 1	416
August	1st to 10th	Night	13% 5% 22% 44% 15%	378
	11th to 20th	Night	13% 6% 25% 33% 22% 1	541
	21st to end	Night	15% 9% 30% 29% 16% 2	836
September	1st to 10th	Night	15% 7% 33% 33% 11% 1	760
	11th to 20th	Night	14% 10% 25% 31% 18% 2	760
	21st to end	Night	20% 12% 26% 26% 15% 2	760
October	1st to 10th	Night	21% 14% 28% 25% 12% 1	760
	11th to 20th	Night	25% 16% 29% 22% 8% 1	760
	21st to end	Night	28% 15% 31% 21% 5%	836
November	1st to 10th	Night	23% 19% 30% 21% 6% 1	771
	11th to 20th	Night	23% 19% 31% 19% 8% 1	760
	21st to end	Night	26% 24% 28% 17% 4 1	760
December	1st to 10th	Night	26% 20% 31% 17% 5%	760
	11th to 20th	Night	27% 21% 30% 18% 4 1	760
	21st to end	Night	31% 20% 30% 15% 4	836

Page generated at 2024-11-05 08:15:51. Version ac07

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