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 2026-10-14.

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% 7% 3 7% 5% 4 4 4 6% 8% 40%	148761
	Night	14% 8% 3 7% 4 4 4 3 5% 7% 42%	143149
Transparency	Day	41% 6% 11% 24% 16% 2	152422
	Night	41% 5% 10% 23% 18% 3	147563
Seeing	Day	18% 11% 24% 24% 17% 7%	18020
	Night	18% 9% 25% 29% 17% 2	27690

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% 8% 11% 5% 5% 4 4 4 4 30%	4691
	11th to 20th	Day	12% 8% 3 10% 5% 3 4 2 3 5% 44%	4710
	21st to end	Day	21% 10% 5% 6% 5% 4 4 3 3 5% 35%	6046
February	1st to 10th	Day	16% 12% 4 8% 4 3 4 3 5% 6% 35%	2100
	11th to 20th	Day	19% 9% 4 8% 5% 5% 3 3 4 5% 35%	2048
	21st to end	Day	16% 11% 4 8% 5% 4 4 4 5% 6% 35%	1730
March	1st to 10th	Day	18% 12% 4 7% 4 4 3 3 4 5% 37%	4580
	11th to 20th	Day	12% 10% 2 6% 4 3 3 2 4 6% 47%	4805
	21st to end	Day	12% 8% 3 8% 4 4 4 3 5% 6% 42%	6000
April	1st to 10th	Day	14% 6% 2 6% 5% 4 4 4 5% 8% 43%	2520
	11th to 20th	Day	13% 8% 3 6% 5% 5% 4 3 6% 6% 41%	2494
	21st to end	Day	16% 7% 2 6% 4 5% 4 3 5% 7% 41%	2565
May	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	7616
	11th to 20th	Day	15% 7% 3 7% 5% 4 5% 4 5% 8% 38%	7626
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 30%	8391
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 4 7% 8% 45%	2904
	11th to 20th	Day	6% 5% 2 5% 4 5% 6% 5% 7% 10% 46%	2940
	21st to end	Day	6% 5% 2 5% 5% 6% 6% 4 8% 11% 44%	2940
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 6% 4 6% 11% 36%	8280
	11th to 20th	Day	7% 5% 2 7% 6% 6% 6% 6% 9% 12% 33%	8280
	21st to end	Day	8% 6% 3 8% 6% 6% 6% 6% 8% 12% 33%	8557
August	1st to 10th	Day	8% 4 2 6% 4 4 5% 4 6% 9% 48%	5757
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 10% 43%	5486
	21st to end	Day	4 3 1 4 3 3 4 3 5% 9% 61%	6080
September	1st to 10th	Day	10% 6% 2 7% 5% 4 4 5% 6% 8% 44%	2520
	11th to 20th	Day	11% 4 3 6% 5% 4 5% 3 5% 7% 48%	2310
	21st to end	Day	12% 6% 2 6% 4 4 4 3 5% 6% 48%	2310
October	1st to 10th	Day	10% 5% 2 4 4 3 4 3 5% 6% 56%	2310
	11th to 20th	Day	12% 4 2 5% 4 4 3 3 3 6% 54%	2133
	21st to end	Day	20% 7% 2 5% 3 2 3 3 4 5% 46%	2000
November	1st to 10th	Day	12% 6% 2 6% 4 3 3 2 4 5% 54%	1852
	11th to 20th	Day	15% 8% 3 5% 4 3 3 2 5% 6% 46%	1890
	21st to end	Day	16% 10% 3 6% 3 3 4 3 4 5% 43%	1890
December	1st to 10th	Day	16% 10% 3 7% 3 3 3 2 4 5% 43%	3020
	11th to 20th	Day	17% 12% 5% 9% 4 5% 4 3 4 5% 33%	3310
	21st to end	Day	18% 14% 5% 9% 5% 5% 4 3 5% 6% 26%	4070
January	1st to 10th	Night	16% 12% 4 9% 4 3 4 3 4 5% 36%	8232
	11th to 20th	Night	15% 11% 4 9% 5% 4 3 2 3 4 40%	8280
	21st to end	Night	18% 12% 4 7% 4 3 3 3 3 5% 37%	8126
February	1st to 10th	Night	22% 11% 4 9% 4 4 3 3 4 4 32%	2520
	11th to 20th	Night	21% 8% 3 8% 5% 3 3 3 3 6% 35%	2458
	21st to end	Night	21% 9% 4 8% 4 3 3 3 4 4 36%	2076
March	1st to 10th	Night	18% 12% 3 7% 4 3 4 3 5% 5% 35%	5493
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 5% 6% 49%	5373
	21st to end	Night	14% 7% 3 8% 5% 4 4 3 5% 7% 39%	5213
April	1st to 10th	Night	14% 5% 2 5% 4 3 5% 4 5% 7% 46%	2100
	11th to 20th	Night	14% 7% 2 6% 4 3 4 3 6% 7% 45%	2075
	21st to end	Night	14% 7% 3 7% 5% 5% 4 4 5% 8% 39%	2053
May	1st to 10th	Night	16% 9% 3 8% 4 5% 4 4 6% 8% 34%	5237
	11th to 20th	Night	12% 7% 3 8% 5% 5% 5% 4 6% 7% 37%	5234
	21st to end	Night	15% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	5761
June	1st to 10th	Night	10% 5% 2 5% 3 5% 4 4 6% 9% 46%	1710
	11th to 20th	Night	5% 4 2 5% 4 4 4 4 7% 10% 51%	1680
	21st to end	Night	4 3 1 4 3 4 5% 4 8% 13% 51%	1680
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 4 6% 10% 44%	4708
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 5% 8% 11% 42%	4707
	21st to end	Night	7% 6% 2 8% 6% 5% 7% 5% 8% 11% 35%	5513
August	1st to 10th	Night	7% 5% 2 5% 4 3 4 3 5% 7% 54%	4388
	11th to 20th	Night	4 2 2 4 3 3 4 4 7% 9% 56%	4560
	21st to end	Night	4 3 1 3 3 3 4 3 5% 8% 63%	5046
September	1st to 10th	Night	10% 5% 2 4 4 4 4 3 5% 6% 52%	2100
	11th to 20th	Night	9% 4 3 6% 3 4 4 4 5% 6% 51%	2289
	21st to end	Night	12% 5% 2 4 4 3 4 3 5% 7% 53%	2310
October	1st to 10th	Night	9% 4 2 4 3 3 2 3 4 5% 61%	2310
	11th to 20th	Night	15% 5% 2 5% 3 3 3 2 3 4 55%	2330
	21st to end	Night	18% 7% 2 5% 3 4 3 3 3 5% 46%	2840
November	1st to 10th	Night	13% 5% 2 5% 3 4 3 3 3 6% 52%	2666
	11th to 20th	Night	14% 7% 2 5% 4 3 3 2 5% 6% 50%	2730
	21st to end	Night	18% 8% 2 6% 3 2 3 2 4 6% 45%	2730
December	1st to 10th	Night	19% 11% 3 8% 3 3 3 2 4 4 41%	4380
	11th to 20th	Night	19% 10% 3 6% 4 3 4 3 5% 5% 39%	5091
	21st to end	Night	21% 14% 5% 9% 5% 5% 4 3 4 5% 25%	7150

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% 3 11% 20% 7% 1	4692
	11th to 20th	Day	45% 2 6% 27% 19% 1	4710
	21st to end	Day	53% 2 8% 20% 12% 4	6046
February	1st to 10th	Day	51% 3 10% 23% 12% 2	2100
	11th to 20th	Day	53% 4 7% 20% 12% 3	2058
	21st to end	Day	50% 4 9% 17% 15% 5%	1730
March	1st to 10th	Day	51% 3 4 18% 19% 5%	4580
	11th to 20th	Day	39% 4 7% 26% 20% 4	4805
	21st to end	Day	42% 5% 10% 27% 15% 1	6002
April	1st to 10th	Day	40% 5% 12% 23% 18% 2	2520
	11th to 20th	Day	43% 5% 9% 22% 18% 3	2494
	21st to end	Day	42% 6% 11% 26% 14% 2	2565
May	1st to 10th	Day	49% 6% 12% 21% 10% 1	7651
	11th to 20th	Day	44% 7% 12% 21% 15% 1	7630
	21st to end	Day	51% 7% 10% 17% 13% 2	8405
June	1st to 10th	Day	35% 7% 12% 23% 20% 3	2904
	11th to 20th	Day	31% 8% 14% 26% 18% 2	2940
	21st to end	Day	31% 8% 15% 25% 16% 4	2940
July	1st to 10th	Day	40% 8% 13% 27% 12% 1	8211
	11th to 20th	Day	37% 12% 18% 25% 7% 1	8205
	21st to end	Day	40% 9% 20% 23% 7% 1	8370
August	1st to 10th	Day	30% 7% 15% 28% 20% 1	5744
	11th to 20th	Day	34% 7% 16% 27% 16% 1	5522
	21st to end	Day	21% 6% 10% 39% 22% 2	6079
September	1st to 10th	Day	36% 7% 11% 22% 20% 4	2520
	11th to 20th	Day	35% 7% 9% 25% 22% 2	2310
	21st to end	Day	35% 5% 8% 23% 23% 5%	2310
October	1st to 10th	Day	20% 3 5% 18% 46% 7%	3700
	11th to 20th	Day	23% 3 7% 27% 32% 8%	3438
	21st to end	Day	30% 3 6% 27% 27% 7%	3212
November	1st to 10th	Day	34% 4 8% 25% 24% 5%	1852
	11th to 20th	Day	40% 3 8% 24% 21% 5%	1890
	21st to end	Day	45% 3 7% 25% 17% 3	1890
December	1st to 10th	Day	45% 3 8% 26% 18% 1	3020
	11th to 20th	Day	55% 4 9% 19% 12% 2	3307
	21st to end	Day	58% 5% 12% 18% 7%	4070
January	1st to 10th	Night	51% 3 12% 24% 9% 1	8233
	11th to 20th	Night	50% 2 4 22% 19% 3	8280
	21st to end	Night	51% 3 7% 20% 16% 3	8126
February	1st to 10th	Night	57% 3 8% 18% 12% 1	2520
	11th to 20th	Night	52% 4 6% 21% 14% 3	2459
	21st to end	Night	52% 4 8% 18% 15% 3	2076
March	1st to 10th	Night	51% 4 7% 16% 19% 4	5493
	11th to 20th	Night	36% 4 9% 23% 19% 9%	5373
	21st to end	Night	45% 4 10% 24% 14% 2	5213
April	1st to 10th	Night	37% 5% 13% 25% 18% 3	2100
	11th to 20th	Night	38% 5% 11% 19% 21% 6%	2075
	21st to end	Night	42% 7% 9% 23% 17% 2	2053
May	1st to 10th	Night	46% 6% 12% 23% 11% 1	5264
	11th to 20th	Night	44% 8% 12% 20% 15% 1	5235
	21st to end	Night	48% 9% 12% 19% 12% 1	5771
June	1st to 10th	Night	34% 6% 12% 24% 20% 4	1710
	11th to 20th	Night	25% 7% 16% 23% 24% 3	1680
	21st to end	Night	23% 10% 17% 25% 19% 6%	1680
July	1st to 10th	Night	33% 9% 13% 27% 16% 2	4670
	11th to 20th	Night	33% 11% 19% 26% 10% 2	4662
	21st to end	Night	39% 9% 20% 23% 8% 1	5387
August	1st to 10th	Night	29% 6% 13% 32% 20% 1	4377
	11th to 20th	Night	22% 6% 20% 35% 15% 1	4590
	21st to end	Night	19% 5% 10% 39% 25% 2	5046
September	1st to 10th	Night	31% 6% 10% 24% 24% 5%	2100
	11th to 20th	Night	32% 6% 9% 25% 24% 4	2289
	21st to end	Night	32% 5% 9% 22% 26% 6%	2310
October	1st to 10th	Night	19% 3 5% 16% 48% 10%	3700
	11th to 20th	Night	22% 2 6% 24% 37% 9%	3764
	21st to end	Night	30% 3 7% 22% 27% 11%	4578
November	1st to 10th	Night	34% 4 8% 25% 24% 5%	2666
	11th to 20th	Night	36% 3 8% 24% 20% 8%	2730
	21st to end	Night	42% 3 9% 25% 19% 3	2730
December	1st to 10th	Night	48% 4 8% 22% 18% 1	4380
	11th to 20th	Night	47% 4 9% 21% 17% 1	5093
	21st to end	Night	62% 4 8% 17% 7% 1	7150

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	27% 22% 31% 16% 5%	330
	11th to 20th	Day	30% 26% 30% 11% 3	330
	21st to end	Day	27% 24% 38% 9% 3	363
February	1st to 10th	Day	25% 24% 32% 15% 2 1	330
	11th to 20th	Day	33% 25% 32% 7% 2	330
	21st to end	Day	32% 23% 30% 13% 3	273
March	1st to 10th	Day	30% 20% 35% 12% 3	330
	11th to 20th	Day	29% 23% 31% 12% 4 1	411
	21st to end	Day	26% 20% 34% 14% 6%	594
April	1st to 10th	Day	22% 20% 28% 22% 8%	540
	11th to 20th	Day	23% 16% 29% 21% 10% 1	532
	21st to end	Day	22% 15% 34% 18% 9% 2	540
May	1st to 10th	Day	23% 15% 28% 22% 8% 3	543
	11th to 20th	Day	19% 12% 25% 28% 10% 6%	567
	21st to end	Day	15% 7% 23% 30% 16% 10%	617
June	1st to 10th	Day	12% 6% 22% 26% 23% 10%	744
	11th to 20th	Day	7% 5% 20% 31% 27% 10%	780
	21st to end	Day	7% 4 23% 31% 23% 13%	780
July	1st to 10th	Day	11% 2 14% 29% 26% 18%	771
	11th to 20th	Day	7% 4 16% 31% 28% 14%	768
	21st to end	Day	10% 3 14% 30% 27% 15%	697
August	1st to 10th	Day	13% 3 13% 31% 27% 13%	566
	11th to 20th	Day	12% 2 18% 32% 28% 9%	559
	21st to end	Day	9% 3 11% 27% 35% 16%	627
September	1st to 10th	Day	11% 3 16% 26% 32% 13%	570
	11th to 20th	Day	10% 2 12% 27% 33% 15%	570
	21st to end	Day	16% 8% 21% 24% 21% 9%	570
October	1st to 10th	Day	12% 4 21% 34% 23% 7%	570
	11th to 20th	Day	14% 13% 30% 26% 13% 5%	442
	21st to end	Day	28% 13% 30% 22% 6% 1	363
November	1st to 10th	Day	18% 12% 36% 21% 10% 3	330
	11th to 20th	Day	22% 20% 28% 23% 6% 1	330
	21st to end	Day	27% 14% 31% 19% 7% 2	330
December	1st to 10th	Day	26% 20% 31% 17% 5% 1	330
	11th to 20th	Day	25% 17% 33% 20% 5%	330
	21st to end	Day	28% 21% 32% 16% 2	363
January	1st to 10th	Night	25% 17% 30% 24% 4	1050
	11th to 20th	Night	28% 17% 33% 18% 4	1050
	21st to end	Night	24% 16% 35% 22% 2	1011
February	1st to 10th	Night	27% 14% 34% 22% 2	840
	11th to 20th	Night	30% 16% 33% 20% 2	823
	21st to end	Night	26% 18% 35% 19% 2	692
March	1st to 10th	Night	25% 15% 30% 26% 4	840
	11th to 20th	Night	24% 13% 34% 23% 5%	840
	21st to end	Night	22% 13% 32% 27% 6%	756
April	1st to 10th	Night	18% 13% 31% 30% 7% 1	630
	11th to 20th	Night	19% 10% 33% 27% 11% 1	623
	21st to end	Night	17% 9% 31% 32% 10% 1	630
May	1st to 10th	Night	20% 7% 29% 28% 14% 1	630
	11th to 20th	Night	14% 6% 24% 34% 19% 3	621
	21st to end	Night	10% 4 19% 35% 28% 4	683
June	1st to 10th	Night	11% 4 19% 36% 28% 3	630
	11th to 20th	Night	6% 3 15% 41% 33% 2	630
	21st to end	Night	4 2 15% 40% 34% 5%	630
July	1st to 10th	Night	9% 1 11% 29% 41% 9%	615
	11th to 20th	Night	8% 2 10% 28% 45% 7%	612
	21st to end	Night	10% 2 12% 33% 36% 7%	690
August	1st to 10th	Night	8% 1 10% 32% 42% 7%	627
	11th to 20th	Night	7% 13% 38% 38% 5%	624
	21st to end	Night	7% 1 9% 32% 44% 7%	693
September	1st to 10th	Night	12% 2 11% 33% 37% 5%	630
	11th to 20th	Night	10% 3 9% 32% 39% 7%	819
	21st to end	Night	13% 4 20% 31% 28% 5%	840
October	1st to 10th	Night	12% 4 17% 34% 28% 5%	840
	11th to 20th	Night	18% 7% 24% 33% 18% 1	813
	21st to end	Night	22% 8% 29% 27% 13% 1	880
November	1st to 10th	Night	15% 9% 28% 32% 15% 1	820
	11th to 20th	Night	17% 12% 31% 29% 10%	840
	21st to end	Night	23% 13% 24% 27% 12%	840
December	1st to 10th	Night	28% 11% 27% 28% 6%	840
	11th to 20th	Night	24% 13% 30% 25% 7% 1	903
	21st to end	Night	29% 15% 30% 23% 4	1155

Page generated at 2026-10-11 04:06:32. Version ac07

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