Rue de Renard Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rue de Renard Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	13% 8% 3 7% 5% 4 4 4 5% 7% 40%	119223
	Night	14% 8% 3 7% 4 4 4 3 5% 6% 42%	119092
Transparency	Day	42% 6% 10% 23% 17% 3	122926
	Night	41% 5% 9% 23% 18% 4	123529
Seeing	Day	18% 11% 24% 24% 16% 7%	16112
	Night	18% 9% 25% 28% 17% 2	25955

By Month

Percentage Cloud Cover SE (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% 11% 9% 11% 5% 5% 5% 4 4 4 28%	3617
	11th to 20th	Day	15% 9% 4 11% 6% 4 5% 2 3 5% 37%	3620
	21st to end	Day	21% 10% 6% 5% 4 3 3 3 4 5% 37%	4662
February	1st to 10th	Day	17% 12% 4 8% 4 4 4 3 5% 6% 35%	2000
	11th to 20th	Day	19% 10% 4 8% 5% 4 3 3 4 5% 35%	1948
	21st to end	Day	16% 11% 4 7% 5% 4 4 4 5% 5% 36%	1650
March	1st to 10th	Day	18% 12% 4 7% 4 4 3 3 4 5% 37%	4480
	11th to 20th	Day	13% 10% 2 6% 4 3 3 2 4 6% 47%	4701
	21st to end	Day	12% 8% 3 8% 4 4 4 3 5% 6% 41%	5870
April	1st to 10th	Day	15% 6% 2 6% 5% 4 4 4 5% 7% 42%	2400
	11th to 20th	Day	13% 8% 3 6% 5% 5% 4 3 6% 5% 41%	2374
	21st to end	Day	16% 7% 2 6% 4 5% 4 3 5% 7% 41%	2443
May	1st to 10th	Day	18% 9% 3 9% 6% 5% 5% 4 6% 8% 27%	5862
	11th to 20th	Day	16% 8% 3 8% 5% 5% 5% 4 5% 9% 33%	5861
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 6% 7% 38%	6433
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 4 7% 8% 45%	2753
	11th to 20th	Day	5% 4 1 5% 4 5% 6% 5% 7% 10% 47%	2660
	21st to end	Day	5% 5% 2 5% 5% 6% 6% 4 8% 11% 43%	2660
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 5% 6% 11% 38%	4440
	11th to 20th	Day	7% 5% 2 6% 5% 4 5% 5% 7% 11% 43%	4440
	21st to end	Day	13% 10% 4 9% 7% 6% 5% 5% 7% 8% 27%	4574
August	1st to 10th	Day	6% 4 2 4 4 4 4 3 6% 10% 53%	3923
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 8% 10% 40%	3729
	21st to end	Day	5% 3 2 5% 4 4 4 4 6% 9% 54%	4180
September	1st to 10th	Day	10% 6% 2 7% 5% 4 4 5% 5% 9% 43%	2280
	11th to 20th	Day	12% 4 3 6% 5% 4 5% 4 5% 7% 46%	2090
	21st to end	Day	12% 6% 2 6% 3 4 4 3 5% 6% 49%	2090
October	1st to 10th	Day	10% 5% 2 4 3 3 4 3 5% 6% 56%	2090
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 3 6% 53%	1995
	21st to end	Day	19% 7% 2 5% 3 2 3 3 4 5% 46%	1900
November	1st to 10th	Day	12% 6% 2 6% 4 3 3 2 3 5% 55%	1762
	11th to 20th	Day	15% 8% 3 5% 4 3 3 2 5% 6% 46%	1800
	21st to end	Day	16% 10% 3 6% 3 3 4 3 5% 5% 44%	1800
December	1st to 10th	Day	16% 10% 2 7% 3 3 3 2 4 5% 43%	2930
	11th to 20th	Day	18% 13% 5% 9% 4 5% 4 3 4 5% 32%	3224
	21st to end	Day	18% 14% 4 9% 5% 4 4 3 5% 6% 26%	3982
January	1st to 10th	Night	16% 13% 4 11% 4 3 4 3 4 5% 32%	6348
	11th to 20th	Night	17% 12% 4 8% 5% 4 3 2 2 3 37%	6360
	21st to end	Night	20% 11% 4 6% 3 3 3 2 3 6% 39%	6281
February	1st to 10th	Night	22% 11% 4 8% 4 4 3 3 4 5% 32%	2400
	11th to 20th	Night	21% 8% 4 8% 5% 4 3 3 3 5% 35%	2338
	21st to end	Night	20% 10% 4 8% 4 3 3 3 4 5% 36%	1980
March	1st to 10th	Night	18% 12% 3 7% 4 3 3 3 5% 5% 36%	5373
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 5% 6% 49%	5257
	21st to end	Night	15% 8% 3 8% 5% 4 4 3 4 7% 39%	5100
April	1st to 10th	Night	14% 5% 2 6% 4 3 5% 4 5% 7% 45%	2000
	11th to 20th	Night	14% 7% 2 6% 3 3 4 3 6% 7% 45%	1975
	21st to end	Night	14% 7% 3 6% 5% 5% 4 4 5% 9% 38%	1955
May	1st to 10th	Night	17% 10% 3 7% 4 4 4 4 7% 8% 31%	4033
	11th to 20th	Night	14% 8% 3 8% 5% 6% 5% 5% 6% 8% 32%	4032
	21st to end	Night	11% 6% 2 7% 5% 5% 5% 5% 6% 8% 38%	4421
June	1st to 10th	Night	10% 6% 2 5% 4 5% 4 4 6% 9% 45%	1626
	11th to 20th	Night	5% 3 2 4 4 4 4 5% 8% 10% 53%	1520
	21st to end	Night	3 3 1 4 3 4 5% 4 8% 14% 51%	1520
July	1st to 10th	Night	6% 5% 2 5% 4 5% 5% 4 7% 11% 46%	2530
	11th to 20th	Night	7% 4 2 4 3 4 3 4 6% 9% 54%	2530
	21st to end	Night	9% 8% 3 10% 6% 6% 7% 5% 7% 8% 30%	2965
August	1st to 10th	Night	6% 4 1 4 3 3 4 3 5% 7% 60%	3002
	11th to 20th	Night	4 3 2 6% 4 4 5% 4 8% 9% 49%	3100
	21st to end	Night	4 3 1 4 3 3 4 3 5% 8% 62%	3476
September	1st to 10th	Night	11% 5% 2 4 4 4 4 3 5% 6% 51%	1900
	11th to 20th	Night	10% 4 3 6% 3 4 4 4 5% 6% 50%	2071
	21st to end	Night	11% 5% 2 4 4 2 4 3 5% 7% 53%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 2 3 4 6% 61%	2090
	11th to 20th	Night	16% 5% 2 5% 3 3 3 2 4 4 53%	2181
	21st to end	Night	17% 7% 2 5% 3 4 3 3 3 6% 47%	2698
November	1st to 10th	Night	13% 5% 2 5% 3 4 3 3 3 6% 52%	2536
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 5% 6% 49%	2600
	21st to end	Night	17% 8% 2 6% 3 3 3 3 4 6% 46%	2600
December	1st to 10th	Night	19% 11% 3 7% 3 3 3 2 4 4 41%	4250
	11th to 20th	Night	19% 10% 3 6% 4 3 4 3 5% 5% 39%	4958
	21st to end	Night	21% 14% 5% 9% 5% 5% 4 3 4 5% 25%	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	59% 4 10% 18% 9% 1	3618
	11th to 20th	Day	51% 3 6% 22% 16% 2	3620
	21st to end	Day	51% 3 8% 19% 15% 4	4662
February	1st to 10th	Day	51% 3 10% 22% 12% 2	2000
	11th to 20th	Day	54% 4 7% 20% 12% 4	1958
	21st to end	Day	49% 5% 9% 17% 16% 5%	1650
March	1st to 10th	Day	51% 3 4 18% 19% 5%	4480
	11th to 20th	Day	39% 4 7% 26% 20% 4	4701
	21st to end	Day	43% 5% 10% 26% 15% 1	5872
April	1st to 10th	Day	41% 5% 11% 23% 19% 2	2400
	11th to 20th	Day	43% 5% 9% 22% 18% 3	2374
	21st to end	Day	43% 6% 10% 26% 13% 2	2443
May	1st to 10th	Day	54% 7% 12% 17% 9%	5897
	11th to 20th	Day	48% 8% 12% 21% 10%	5865
	21st to end	Day	43% 7% 11% 20% 16% 3	6447
June	1st to 10th	Day	35% 7% 12% 23% 19% 3	2753
	11th to 20th	Day	30% 9% 14% 25% 20% 2	2660
	21st to end	Day	32% 9% 15% 24% 16% 5%	2660
July	1st to 10th	Day	38% 8% 14% 26% 12% 2	4371
	11th to 20th	Day	31% 9% 14% 33% 12% 2	4365
	21st to end	Day	52% 8% 12% 19% 7% 1	4429
August	1st to 10th	Day	25% 7% 15% 31% 21% 1	3910
	11th to 20th	Day	36% 8% 12% 25% 18% 1	3765
	21st to end	Day	26% 7% 10% 34% 21% 3	4179
September	1st to 10th	Day	37% 7% 11% 21% 19% 4	2280
	11th to 20th	Day	37% 7% 10% 23% 22% 2	2090
	21st to end	Day	35% 5% 8% 24% 22% 5%	2090
October	1st to 10th	Day	19% 3 6% 18% 47% 7%	3480
	11th to 20th	Day	24% 3 7% 27% 32% 8%	3300
	21st to end	Day	30% 3 6% 27% 27% 7%	3112
November	1st to 10th	Day	34% 4 8% 25% 24% 5%	1762
	11th to 20th	Day	40% 3 8% 24% 21% 5%	1800
	21st to end	Day	44% 3 7% 25% 17% 3	1800
December	1st to 10th	Day	44% 3 7% 27% 18% 1	2930
	11th to 20th	Day	55% 4 8% 19% 12% 2	3221
	21st to end	Day	57% 5% 11% 19% 7%	3982
January	1st to 10th	Night	54% 3 10% 22% 10% 1	6348
	11th to 20th	Night	54% 3 4 20% 16% 3	6360
	21st to end	Night	49% 3 7% 20% 18% 3	6281
February	1st to 10th	Night	57% 3 8% 18% 12% 1	2400
	11th to 20th	Night	52% 4 7% 19% 15% 3	2339
	21st to end	Night	52% 4 8% 17% 15% 3	1980
March	1st to 10th	Night	50% 4 6% 16% 19% 4	5373
	11th to 20th	Night	36% 4 9% 23% 20% 9%	5257
	21st to end	Night	45% 4 10% 24% 15% 2	5100
April	1st to 10th	Night	37% 5% 11% 25% 18% 3	2000
	11th to 20th	Night	39% 5% 10% 19% 21% 6%	1975
	21st to end	Night	42% 7% 10% 22% 17% 2	1955
May	1st to 10th	Night	48% 7% 12% 22% 10% 1	4060
	11th to 20th	Night	48% 9% 12% 20% 10%	4033
	21st to end	Night	40% 9% 13% 22% 15% 1	4429
June	1st to 10th	Night	34% 6% 13% 24% 19% 3	1626
	11th to 20th	Night	23% 7% 17% 24% 25% 4	1520
	21st to end	Night	22% 10% 18% 25% 18% 6%	1520
July	1st to 10th	Night	31% 8% 13% 30% 16% 3	2490
	11th to 20th	Night	26% 7% 12% 35% 17% 3	2482
	21st to end	Night	49% 10% 12% 19% 9% 1	2870
August	1st to 10th	Night	23% 6% 12% 38% 21% 1	2991
	11th to 20th	Night	28% 8% 17% 29% 17% 1	3130
	21st to end	Night	21% 6% 10% 35% 25% 3	3476
September	1st to 10th	Night	32% 7% 10% 24% 23% 5%	1900
	11th to 20th	Night	33% 5% 9% 24% 24% 5%	2071
	21st to end	Night	31% 5% 8% 22% 26% 6%	2090
October	1st to 10th	Night	18% 3 5% 16% 49% 9%	3480
	11th to 20th	Night	22% 2 6% 24% 37% 9%	3615
	21st to end	Night	30% 3 7% 22% 27% 11%	4436
November	1st to 10th	Night	35% 4 7% 24% 25% 6%	2536
	11th to 20th	Night	36% 4 8% 23% 21% 8%	2600
	21st to end	Night	41% 3 8% 25% 19% 3	2600
December	1st to 10th	Night	47% 4 8% 22% 18% 1	4250
	11th to 20th	Night	48% 4 9% 22% 17% 2	4960
	21st to end	Night	62% 4 8% 17% 7% 1	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	26% 22% 32% 16% 4	300
	11th to 20th	Day	29% 27% 30% 11% 3	300
	21st to end	Day	25% 24% 39% 9% 3	330
February	1st to 10th	Day	25% 25% 32% 15% 2 1	300
	11th to 20th	Day	33% 26% 31% 7% 2	300
	21st to end	Day	31% 23% 31% 12% 3	249
March	1st to 10th	Day	31% 19% 34% 13% 3	300
	11th to 20th	Day	29% 22% 31% 13% 5% 1	377
	21st to end	Day	27% 20% 31% 14% 6%	550
April	1st to 10th	Day	22% 20% 26% 22% 8%	500
	11th to 20th	Day	23% 15% 28% 22% 10% 1	492
	21st to end	Day	22% 15% 33% 18% 10% 2	500
May	1st to 10th	Day	23% 14% 27% 23% 9% 3	503
	11th to 20th	Day	19% 11% 24% 28% 11% 6%	527
	21st to end	Day	13% 7% 23% 30% 16% 11%	573
June	1st to 10th	Day	12% 6% 22% 25% 24% 11%	692
	11th to 20th	Day	5% 5% 19% 33% 28% 11%	680
	21st to end	Day	6% 3 24% 31% 23% 12%	680
July	1st to 10th	Day	12% 2 14% 30% 24% 18%	671
	11th to 20th	Day	8% 3 16% 30% 28% 15%	668
	21st to end	Day	11% 3 14% 29% 27% 15%	601
August	1st to 10th	Day	13% 2 13% 31% 26% 15%	486
	11th to 20th	Day	13% 2 19% 32% 26% 9%	479
	21st to end	Day	10% 2 11% 24% 35% 18%	539
September	1st to 10th	Day	12% 2 16% 24% 34% 12%	490
	11th to 20th	Day	12% 2 13% 27% 32% 14%	490
	21st to end	Day	17% 8% 19% 22% 23% 10%	490
October	1st to 10th	Day	11% 4 21% 32% 24% 8%	490
	11th to 20th	Day	14% 14% 31% 24% 13% 5%	395
	21st to end	Day	27% 12% 30% 23% 6% 2	330
November	1st to 10th	Day	18% 12% 36% 21% 11% 3	300
	11th to 20th	Day	20% 19% 29% 24% 6% 1	300
	21st to end	Day	27% 13% 30% 21% 8% 2	300
December	1st to 10th	Day	26% 20% 28% 18% 6% 1	300
	11th to 20th	Day	25% 16% 32% 21% 6%	300
	21st to end	Day	28% 21% 32% 17% 2	330
January	1st to 10th	Night	25% 17% 30% 24% 4	1000
	11th to 20th	Night	29% 17% 32% 18% 4	1000
	21st to end	Night	24% 16% 36% 22% 2	963
February	1st to 10th	Night	28% 14% 33% 22% 2	800
	11th to 20th	Night	29% 16% 33% 19% 2	783
	21st to end	Night	26% 18% 35% 19% 2	660
March	1st to 10th	Night	25% 15% 30% 27% 4	800
	11th to 20th	Night	23% 14% 33% 24% 6%	800
	21st to end	Night	23% 12% 30% 28% 7%	720
April	1st to 10th	Night	19% 13% 31% 30% 7% 1	600
	11th to 20th	Night	19% 9% 32% 27% 11% 1	593
	21st to end	Night	17% 9% 31% 32% 10% 1	600
May	1st to 10th	Night	20% 7% 28% 28% 15% 1	600
	11th to 20th	Night	15% 6% 22% 34% 20% 3	591
	21st to end	Night	8% 3 20% 36% 29% 4	650
June	1st to 10th	Night	12% 4 18% 36% 28% 3	599
	11th to 20th	Night	6% 2 14% 42% 34% 2	570
	21st to end	Night	4 2 16% 40% 34% 5%	570
July	1st to 10th	Night	9% 1 11% 30% 39% 10%	555
	11th to 20th	Night	9% 2 10% 28% 45% 7%	552
	21st to end	Night	10% 2 12% 34% 36% 7%	624
August	1st to 10th	Night	8% 1 9% 32% 43% 7%	567
	11th to 20th	Night	7% 13% 37% 38% 5%	564
	21st to end	Night	8% 1 9% 30% 45% 7%	627
September	1st to 10th	Night	13% 2 11% 32% 36% 5%	570
	11th to 20th	Night	10% 3 10% 31% 38% 7%	741
	21st to end	Night	13% 4 20% 30% 29% 5%	760
October	1st to 10th	Night	12% 4 17% 32% 29% 5%	760
	11th to 20th	Night	19% 7% 25% 31% 18% 1	760
	21st to end	Night	21% 8% 30% 27% 14% 1	836
November	1st to 10th	Night	16% 9% 26% 33% 16% 1	780
	11th to 20th	Night	18% 12% 32% 28% 11%	800
	21st to end	Night	22% 14% 24% 27% 12% 1	800
December	1st to 10th	Night	28% 11% 27% 28% 6%	800
	11th to 20th	Night	24% 13% 29% 26% 8% 1	860
	21st to end	Night	29% 15% 29% 24% 4	1100

Page generated at 2025-06-07 09:28:13. Version ac07

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