Observatoire Alphonse-Tardif à St-Nérée
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Alphonse-Tardif à St-Nérée clear sky chart from 2005-11-06 to 2026-04-17.

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	18% 12% 4 9% 5% 5% 4 4 5% 6% 28%	131026
	Night	18% 14% 5% 10% 6% 4 4 3 4 5% 26%	131159
Transparency	Day	55% 7% 13% 18% 7% 1	134481
	Night	58% 6% 11% 16% 7% 1	135793
Seeing	Day	26% 17% 30% 19% 7% 1	17157
	Night	26% 14% 30% 23% 6%	25726

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	13% 19% 7% 14% 6% 4 4 3 4 4 21%	4661
	11th to 20th	Day	10% 18% 9% 20% 11% 6% 4 2 3 3 14%	4650
	21st to end	Day	5% 11% 8% 13% 8% 6% 6% 5% 7% 7% 24%	5124
February	1st to 10th	Day	12% 16% 5% 12% 8% 6% 5% 3 5% 6% 23%	1713
	11th to 20th	Day	14% 18% 6% 13% 6% 5% 4 2 3 4 25%	2006
	21st to end	Day	12% 16% 6% 11% 7% 5% 4 3 5% 6% 26%	1730
March	1st to 10th	Day	17% 18% 6% 11% 5% 5% 5% 2 4 4 22%	4576
	11th to 20th	Day	15% 16% 4 9% 5% 5% 4 4 5% 6% 27%	4902
	21st to end	Day	19% 16% 4 8% 4 4 3 3 4 4 29%	5861
April	1st to 10th	Day	24% 15% 4 8% 4 3 4 2 4 6% 26%	2520
	11th to 20th	Day	20% 15% 3 7% 3 4 3 3 3 5% 35%	2568
	21st to end	Day	23% 12% 3 8% 4 3 4 3 4 6% 30%	2600
May	1st to 10th	Day	25% 10% 3 7% 4 5% 4 4 5% 6% 26%	5931
	11th to 20th	Day	22% 8% 3 8% 5% 5% 5% 4 6% 7% 27%	6318
	21st to end	Day	21% 9% 3 8% 5% 5% 5% 4 5% 6% 28%	7151
June	1st to 10th	Day	22% 9% 3 7% 5% 5% 5% 5% 7% 7% 25%	3000
	11th to 20th	Day	20% 7% 2 6% 5% 5% 5% 4 6% 7% 33%	3000
	21st to end	Day	25% 9% 3 8% 6% 5% 4 4 5% 6% 26%	3000
July	1st to 10th	Day	19% 9% 3 8% 6% 5% 5% 4 6% 7% 27%	6574
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 5% 7% 8% 32%	6360
	21st to end	Day	14% 7% 2 6% 4 4 4 4 6% 8% 40%	6926
August	1st to 10th	Day	17% 7% 2 7% 5% 5% 5% 5% 7% 9% 30%	4481
	11th to 20th	Day	19% 7% 3 8% 5% 5% 5% 4 6% 7% 29%	4175
	21st to end	Day	20% 9% 2 7% 4 4 4 3 4 6% 36%	4524
September	1st to 10th	Day	20% 7% 2 7% 4 4 4 3 6% 8% 37%	2399
	11th to 20th	Day	20% 6% 2 4 3 3 3 3 5% 5% 46%	2200
	21st to end	Day	22% 7% 2 6% 4 4 4 3 5% 6% 38%	2200
October	1st to 10th	Day	21% 9% 3 6% 4 4 4 4 5% 7% 34%	2200
	11th to 20th	Day	23% 13% 4 7% 5% 5% 4 4 4 5% 25%	1835
	21st to end	Day	28% 15% 3 7% 4 4 3 3 5% 6% 22%	1980
November	1st to 10th	Day	20% 16% 4 8% 5% 4 4 3 5% 4 26%	1851
	11th to 20th	Day	21% 18% 6% 9% 4 4 3 3 4 4 23%	1879
	21st to end	Day	22% 21% 7% 10% 4 3 3 2 3 5% 19%	1512
December	1st to 10th	Day	18% 18% 6% 12% 5% 5% 4 3 5% 5% 19%	2350
	11th to 20th	Day	20% 18% 6% 9% 6% 4 3 2 4 4 24%	2688
	21st to end	Day	20% 17% 5% 11% 5% 5% 5% 3 4 5% 20%	3581
January	1st to 10th	Night	13% 20% 6% 14% 7% 5% 5% 3 4 4 20%	8234
	11th to 20th	Night	10% 21% 9% 21% 8% 5% 4 2 3 3 14%	8235
	21st to end	Night	6% 12% 7% 16% 8% 7% 6% 4 6% 6% 22%	9057
February	1st to 10th	Night	11% 15% 6% 14% 8% 4 4 3 5% 4 26%	2905
	11th to 20th	Night	12% 19% 6% 12% 6% 5% 5% 2 4 5% 23%	2498
	21st to end	Night	13% 18% 5% 10% 5% 4 3 3 4 5% 29%	2076
March	1st to 10th	Night	21% 16% 5% 11% 5% 3 5% 2 3 5% 25%	5484
	11th to 20th	Night	14% 15% 4 11% 6% 6% 6% 4 6% 6% 21%	5263
	21st to end	Night	19% 18% 4 9% 4 4 3 3 3 5% 28%	5311
April	1st to 10th	Night	23% 17% 4 8% 4 3 3 3 4 4 27%	2100
	11th to 20th	Night	22% 12% 3 6% 5% 4 4 3 4 6% 30%	1913
	21st to end	Night	25% 12% 4 8% 3 4 3 3 3 5% 31%	1800
May	1st to 10th	Night	24% 10% 3 7% 5% 5% 4 4 5% 6% 28%	4040
	11th to 20th	Night	24% 9% 3 7% 4 4 5% 3 4 6% 30%	3575
	21st to end	Night	21% 7% 2 5% 4 4 5% 4 6% 7% 34%	3733
June	1st to 10th	Night	22% 11% 2 7% 6% 5% 5% 4 6% 5% 27%	1400
	11th to 20th	Night	17% 9% 3 6% 4 5% 4 5% 5% 7% 34%	1400
	21st to end	Night	23% 10% 3 7% 6% 4 5% 4 4 6% 29%	1400
July	1st to 10th	Night	19% 9% 4 7% 5% 4 5% 4 6% 8% 29%	3378
	11th to 20th	Night	25% 7% 2 7% 5% 4 4 3 5% 7% 32%	3600
	21st to end	Night	14% 6% 2 6% 5% 6% 6% 4 6% 7% 37%	3926
August	1st to 10th	Night	21% 7% 2 6% 4 5% 5% 4 5% 7% 32%	2637
	11th to 20th	Night	19% 8% 3 8% 6% 6% 6% 4 6% 7% 28%	2872
	21st to end	Night	19% 9% 3 6% 4 4 4 4 5% 6% 36%	3371
September	1st to 10th	Night	20% 7% 2 7% 5% 4 4 3 5% 6% 38%	2000
	11th to 20th	Night	18% 7% 3 6% 4 3 3 3 5% 6% 43%	2200
	21st to end	Night	21% 7% 3 6% 4 4 4 3 4 5% 39%	2200
October	1st to 10th	Night	21% 9% 3 6% 4 3 4 3 4 6% 37%	2200
	11th to 20th	Night	25% 12% 3 8% 4 4 3 3 4 5% 29%	2558
	21st to end	Night	25% 14% 3 7% 4 4 4 3 4 6% 26%	2860
November	1st to 10th	Night	22% 16% 3 9% 5% 4 4 3 4 5% 26%	2667
	11th to 20th	Night	20% 14% 6% 10% 5% 4 3 3 4 5% 26%	2740
	21st to end	Night	20% 22% 6% 9% 4 3 3 3 4 4 21%	3103
December	1st to 10th	Night	16% 18% 9% 15% 8% 5% 4 3 4 4 15%	5060
	11th to 20th	Night	19% 20% 6% 12% 6% 4 3 2 4 4 22%	5741
	21st to end	Night	19% 20% 5% 9% 5% 4 4 3 3 3 25%	7622

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% 7% 8% 15% 6%	4662
	11th to 20th	Day	72% 7% 5% 10% 4 1	4680
	21st to end	Day	54% 8% 10% 16% 11%	5124
February	1st to 10th	Day	63% 5% 8% 15% 8% 1	1713
	11th to 20th	Day	64% 4 9% 15% 7% 1	2015
	21st to end	Day	60% 4 8% 19% 7% 2	1730
March	1st to 10th	Day	62% 7% 8% 11% 9% 2	4579
	11th to 20th	Day	54% 9% 14% 15% 8%	4902
	21st to end	Day	58% 4 7% 17% 12% 2	5861
April	1st to 10th	Day	61% 4 10% 15% 9% 2	2520
	11th to 20th	Day	53% 5% 9% 21% 11% 2	2568
	21st to end	Day	56% 5% 9% 17% 11% 2	2600
May	1st to 10th	Day	56% 7% 9% 18% 9% 1	5942
	11th to 20th	Day	52% 10% 15% 16% 5% 2	6322
	21st to end	Day	53% 9% 11% 17% 8% 2	7151
June	1st to 10th	Day	53% 9% 13% 18% 7% 1	3000
	11th to 20th	Day	48% 9% 15% 19% 9% 1	3000
	21st to end	Day	58% 7% 11% 16% 8%	3000
July	1st to 10th	Day	54% 7% 14% 20% 5%	6504
	11th to 20th	Day	45% 8% 19% 24% 3	6285
	21st to end	Day	41% 7% 19% 26% 7%	6728
August	1st to 10th	Day	48% 9% 20% 19% 5%	4467
	11th to 20th	Day	51% 9% 21% 14% 5%	4214
	21st to end	Day	49% 7% 16% 18% 10% 1	4524
September	1st to 10th	Day	44% 7% 16% 23% 10% 1	2399
	11th to 20th	Day	40% 5% 16% 28% 10%	2200
	21st to end	Day	46% 6% 13% 25% 9%	2200
October	1st to 10th	Day	52% 6% 11% 25% 5%	3590
	11th to 20th	Day	55% 7% 15% 22% 1	2960
	21st to end	Day	55% 5% 16% 18% 6%	3180
November	1st to 10th	Day	60% 6% 12% 16% 5%	1851
	11th to 20th	Day	65% 5% 9% 15% 6%	1879
	21st to end	Day	69% 5% 11% 12% 3	1512
December	1st to 10th	Day	67% 5% 12% 10% 6%	2350
	11th to 20th	Day	64% 4 8% 17% 7%	2688
	21st to end	Day	63% 8% 9% 10% 8% 1	3581
January	1st to 10th	Night	67% 6% 9% 12% 5%	8234
	11th to 20th	Night	74% 6% 6% 10% 3	8280
	21st to end	Night	59% 6% 11% 13% 11%	9057
February	1st to 10th	Night	61% 5% 9% 16% 8% 1	2905
	11th to 20th	Night	64% 5% 8% 15% 8% 1	2500
	21st to end	Night	58% 4 8% 17% 11% 1	2076
March	1st to 10th	Night	64% 4 8% 12% 11% 1	5494
	11th to 20th	Night	60% 8% 14% 12% 6% 1	5264
	21st to end	Night	60% 5% 6% 18% 11% 1	5311
April	1st to 10th	Night	60% 4 9% 13% 12% 2	2100
	11th to 20th	Night	53% 5% 10% 19% 11% 2	1913
	21st to end	Night	56% 6% 7% 17% 12% 2	1800
May	1st to 10th	Night	55% 7% 10% 16% 11% 1	4046
	11th to 20th	Night	53% 8% 12% 19% 8%	3576
	21st to end	Night	46% 8% 16% 16% 12% 2	3734
June	1st to 10th	Night	55% 7% 12% 18% 8%	1400
	11th to 20th	Night	47% 9% 13% 20% 10% 2	1400
	21st to end	Night	55% 8% 11% 16% 9%	1400
July	1st to 10th	Night	51% 7% 18% 19% 5%	3339
	11th to 20th	Night	49% 7% 19% 21% 3	3552
	21st to end	Night	43% 9% 18% 22% 8%	3809
August	1st to 10th	Night	49% 7% 17% 22% 4	2627
	11th to 20th	Night	53% 10% 18% 15% 4	2899
	21st to end	Night	47% 7% 15% 19% 11% 1	3371
September	1st to 10th	Night	46% 7% 13% 23% 10% 1	2000
	11th to 20th	Night	42% 7% 17% 26% 8%	2200
	21st to end	Night	46% 7% 11% 24% 12%	2200
October	1st to 10th	Night	47% 6% 11% 27% 7%	3590
	11th to 20th	Night	56% 5% 13% 23% 3	4172
	21st to end	Night	54% 5% 17% 16% 8%	4610
November	1st to 10th	Night	60% 6% 12% 17% 5%	2667
	11th to 20th	Night	59% 7% 11% 14% 9%	2740
	21st to end	Night	68% 5% 11% 12% 5%	3103
December	1st to 10th	Night	72% 6% 10% 10% 2	5060
	11th to 20th	Night	66% 4 7% 19% 4	5742
	21st to end	Night	64% 4 8% 15% 8%	7622

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% 25% 30% 15% 2	220
	11th to 20th	Day	29% 27% 31% 9% 4	220
	21st to end	Day	18% 28% 36% 13% 4	242
February	1st to 10th	Day	26% 24% 31% 15% 4	253
	11th to 20th	Day	25% 28% 35% 11% 2	514
	21st to end	Day	25% 22% 34% 16% 2	446
March	1st to 10th	Day	30% 23% 27% 16% 3 1	540
	11th to 20th	Day	28% 22% 31% 13% 6% 1	540
	21st to end	Day	30% 22% 26% 15% 6% 1	594
April	1st to 10th	Day	35% 20% 26% 14% 4	540
	11th to 20th	Day	31% 20% 27% 16% 5% 1	516
	21st to end	Day	31% 20% 29% 15% 4 1	500
May	1st to 10th	Day	30% 17% 32% 16% 5% 1	503
	11th to 20th	Day	24% 13% 31% 22% 9% 1	527
	21st to end	Day	25% 15% 34% 18% 7%	658
June	1st to 10th	Day	25% 14% 33% 20% 7%	730
	11th to 20th	Day	22% 13% 30% 27% 8%	730
	21st to end	Day	29% 9% 29% 22% 9% 1	730
July	1st to 10th	Day	23% 13% 31% 25% 8%	622
	11th to 20th	Day	20% 16% 35% 20% 8% 1	524
	21st to end	Day	21% 11% 36% 23% 8% 1	576
August	1st to 10th	Day	21% 11% 29% 26% 10% 2	526
	11th to 20th	Day	19% 10% 28% 28% 13% 2	519
	21st to end	Day	22% 16% 23% 23% 12% 4	583
September	1st to 10th	Day	22% 14% 28% 23% 11% 3	530
	11th to 20th	Day	21% 12% 28% 24% 13% 2	530
	21st to end	Day	22% 15% 29% 19% 10% 5%	530
October	1st to 10th	Day	23% 17% 29% 21% 8% 2	530
	11th to 20th	Day	31% 17% 26% 17% 8% 1	423
	21st to end	Day	36% 17% 31% 12% 5%	462
November	1st to 10th	Day	33% 19% 31% 13% 3 1	425
	11th to 20th	Day	30% 20% 28% 17% 5%	430
	21st to end	Day	36% 19% 32% 13%	262
December	1st to 10th	Day	30% 20% 29% 17% 3 1	220
	11th to 20th	Day	32% 25% 30% 9% 3 1	220
	21st to end	Day	33% 21% 29% 14% 2	242
January	1st to 10th	Night	26% 21% 34% 17% 2	840
	11th to 20th	Night	25% 22% 32% 18% 3	840
	21st to end	Night	18% 20% 35% 23% 4	924
February	1st to 10th	Night	18% 20% 37% 19% 5%	840
	11th to 20th	Night	24% 20% 39% 13% 4	823
	21st to end	Night	23% 19% 33% 20% 4	692
March	1st to 10th	Night	26% 16% 35% 19% 4	840
	11th to 20th	Night	26% 18% 34% 18% 5%	840
	21st to end	Night	25% 15% 32% 21% 6% 1	924
April	1st to 10th	Night	31% 17% 28% 20% 5%	840
	11th to 20th	Night	29% 12% 32% 22% 5% 1	693
	21st to end	Night	31% 13% 28% 23% 7%	600
May	1st to 10th	Night	28% 11% 30% 25% 6%	599
	11th to 20th	Night	26% 7% 29% 29% 9% 1	394
	21st to end	Night	25% 10% 32% 27% 6%	433
June	1st to 10th	Night	27% 6% 28% 31% 7%	400
	11th to 20th	Night	21% 7% 26% 36% 10%	400
	21st to end	Night	25% 8% 31% 29% 8%	400
July	1st to 10th	Night	20% 7% 35% 28% 10%	390
	11th to 20th	Night	20% 5% 30% 34% 11% 1	388
	21st to end	Night	16% 7% 27% 39% 9%	438
August	1st to 10th	Night	18% 4 26% 36% 15%	423
	11th to 20th	Night	20% 6% 23% 37% 13% 1	592
	21st to end	Night	20% 7% 27% 32% 11% 2	743
September	1st to 10th	Night	24% 7% 29% 28% 11% 1	800
	11th to 20th	Night	22% 7% 27% 30% 13% 1	800
	21st to end	Night	22% 11% 27% 27% 12% 1	800
October	1st to 10th	Night	25% 10% 31% 26% 7% 1	800
	11th to 20th	Night	30% 14% 28% 22% 6% 1	800
	21st to end	Night	35% 13% 30% 17% 6%	880
November	1st to 10th	Night	34% 14% 29% 20% 3	820
	11th to 20th	Night	28% 18% 27% 19% 7% 1	846
	21st to end	Night	33% 16% 30% 15% 4 1	950
December	1st to 10th	Night	32% 16% 31% 15% 5%	950
	11th to 20th	Night	26% 25% 28% 16% 5%	950
	21st to end	Night	32% 20% 29% 16% 3	1034

Page generated at 2026-04-14 02:44:31. Version ac07

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