Notre-Dame-de-la-Merci
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Notre-Dame-de-la-Merci clear sky chart from 2005-11-06 to 2026-08-30.

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	15% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	144441
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 30%	137781
Transparency	Day	52% 7% 11% 19% 10% 1	147875
	Night	52% 7% 11% 19% 10% 1	142423
Seeing	Day	24% 19% 32% 17% 6% 2	16766
	Night	22% 16% 31% 23% 8% 1	25645

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	10% 17% 6% 15% 6% 5% 5% 4 5% 6% 21%	4661
	11th to 20th	Day	7% 18% 8% 18% 10% 5% 4 3 3 4 20%	4650
	21st to end	Day	5% 11% 7% 18% 7% 6% 5% 4 5% 6% 26%	5124
February	1st to 10th	Day	8% 17% 5% 13% 7% 7% 5% 3 4 6% 26%	1838
	11th to 20th	Day	9% 17% 6% 11% 6% 5% 5% 3 5% 6% 28%	1920
	21st to end	Day	13% 18% 6% 9% 6% 6% 5% 3 4 4 26%	1730
March	1st to 10th	Day	16% 19% 5% 12% 7% 6% 4 3 4 3 23%	4576
	11th to 20th	Day	9% 14% 5% 12% 6% 4 5% 3 5% 6% 29%	4844
	21st to end	Day	15% 14% 4 9% 5% 4 4 3 5% 5% 32%	6073
April	1st to 10th	Day	18% 16% 3 8% 5% 4 3 3 4 5% 29%	2520
	11th to 20th	Day	22% 10% 3 8% 4 4 4 3 5% 5% 32%	2494
	21st to end	Day	20% 12% 4 7% 5% 4 4 4 5% 6% 30%	2695
May	1st to 10th	Day	21% 12% 4 8% 6% 5% 5% 4 5% 6% 23%	8237
	11th to 20th	Day	20% 10% 2 8% 5% 5% 5% 4 6% 7% 27%	8221
	21st to end	Day	21% 9% 3 7% 5% 5% 5% 4 5% 6% 29%	9060
June	1st to 10th	Day	23% 9% 2 6% 5% 5% 5% 4 6% 7% 28%	2940
	11th to 20th	Day	16% 6% 3 8% 7% 6% 6% 5% 7% 7% 31%	2940
	21st to end	Day	22% 8% 3 7% 6% 5% 5% 4 6% 6% 27%	2940
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 4 7% 8% 34%	8280
	11th to 20th	Day	11% 4 2 6% 5% 5% 6% 5% 8% 9% 40%	8280
	21st to end	Day	12% 6% 3 6% 4 5% 6% 5% 7% 10% 37%	8993
August	1st to 10th	Day	14% 6% 2 8% 5% 7% 6% 6% 7% 9% 30%	4703
	11th to 20th	Day	15% 8% 3 7% 4 4 5% 5% 7% 8% 33%	4314
	21st to end	Day	15% 5% 3 7% 5% 6% 5% 4 6% 8% 36%	4420
September	1st to 10th	Day	14% 5% 2 6% 6% 5% 4 4 6% 7% 39%	2400
	11th to 20th	Day	13% 5% 2 6% 4 5% 4 4 6% 7% 44%	2330
	21st to end	Day	19% 8% 2 6% 4 4 4 3 5% 6% 39%	2200
October	1st to 10th	Day	21% 9% 3 5% 4 4 4 3 5% 7% 34%	2038
	11th to 20th	Day	20% 13% 4 8% 5% 5% 4 4 5% 5% 27%	1960
	21st to end	Day	23% 13% 3 8% 5% 5% 4 3 4 6% 26%	1980
November	1st to 10th	Day	15% 15% 5% 6% 5% 6% 4 4 5% 6% 30%	1851
	11th to 20th	Day	17% 14% 6% 10% 6% 5% 4 4 5% 6% 24%	1755
	21st to end	Day	18% 17% 6% 11% 6% 5% 4 3 4 4 20%	1680
December	1st to 10th	Day	17% 18% 9% 13% 5% 4 4 4 4 4 18%	2680
	11th to 20th	Day	15% 16% 6% 13% 6% 4 4 3 5% 5% 23%	3066
	21st to end	Day	17% 16% 6% 10% 5% 4 4 3 4 4 25%	4048
January	1st to 10th	Night	9% 18% 7% 15% 6% 6% 5% 4 5% 5% 20%	8234
	11th to 20th	Night	7% 16% 8% 19% 11% 6% 5% 3 4 5% 17%	8235
	21st to end	Night	5% 10% 6% 17% 9% 7% 7% 4 6% 6% 23%	9057
February	1st to 10th	Night	9% 13% 5% 13% 7% 6% 5% 4 5% 6% 27%	2778
	11th to 20th	Night	9% 14% 6% 12% 6% 5% 5% 4 5% 7% 28%	2585
	21st to end	Night	10% 14% 5% 11% 5% 5% 5% 5% 6% 7% 27%	2076
March	1st to 10th	Night	17% 17% 5% 10% 5% 4 4 3 4 5% 26%	5484
	11th to 20th	Night	10% 14% 5% 10% 5% 5% 5% 4 6% 7% 29%	5332
	21st to end	Night	14% 11% 5% 11% 6% 5% 5% 3 5% 6% 30%	5101
April	1st to 10th	Night	20% 13% 3 7% 4 5% 4 3 5% 6% 30%	2100
	11th to 20th	Night	16% 8% 4 7% 5% 5% 3 4 5% 6% 35%	2075
	21st to end	Night	20% 9% 3 8% 4 4 4 4 4 6% 35%	1930
May	1st to 10th	Night	19% 11% 4 9% 5% 5% 5% 4 5% 7% 27%	4684
	11th to 20th	Night	21% 9% 3 7% 4 4 4 3 5% 7% 33%	4639
	21st to end	Night	22% 9% 3 7% 4 5% 4 4 5% 7% 29%	5114
June	1st to 10th	Night	16% 8% 2 8% 6% 5% 3 4 6% 8% 34%	1680
	11th to 20th	Night	18% 7% 3 5% 5% 3 5% 4 5% 8% 37%	1680
	21st to end	Night	19% 7% 2 5% 5% 5% 4 5% 7% 7% 35%	1680
July	1st to 10th	Night	14% 5% 2 6% 5% 5% 5% 5% 7% 9% 37%	4680
	11th to 20th	Night	11% 7% 2 5% 4 4 4 4 6% 8% 46%	4680
	21st to end	Night	12% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	5084
August	1st to 10th	Night	11% 6% 3 7% 5% 5% 4 4 6% 7% 40%	2666
	11th to 20th	Night	15% 7% 2 8% 5% 4 4 3 5% 6% 40%	2915
	21st to end	Night	17% 6% 2 7% 4 4 4 4 5% 8% 40%	3677
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 6% 7% 48%	2000
	11th to 20th	Night	14% 5% 2 4 3 4 4 3 5% 7% 49%	2069
	21st to end	Night	16% 7% 2 6% 3 3 4 3 5% 7% 43%	2200
October	1st to 10th	Night	16% 8% 3 7% 4 4 3 3 4 6% 41%	2360
	11th to 20th	Night	19% 9% 3 9% 4 4 4 4 6% 6% 33%	2440
	21st to end	Night	21% 10% 3 8% 5% 5% 4 3 5% 7% 28%	2860
November	1st to 10th	Night	16% 11% 4 8% 6% 4 5% 5% 5% 7% 29%	2667
	11th to 20th	Night	15% 11% 4 10% 7% 5% 5% 4 6% 7% 26%	2861
	21st to end	Night	16% 16% 6% 10% 7% 4 4 3 5% 5% 23%	2940
December	1st to 10th	Night	14% 14% 5% 14% 8% 6% 6% 5% 5% 6% 17%	4720
	11th to 20th	Night	19% 15% 5% 11% 7% 5% 4 3 4 4 24%	5348
	21st to end	Night	17% 20% 6% 10% 5% 3 3 2 4 6% 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	62% 6% 8% 17% 7%	4662
	11th to 20th	Day	67% 6% 3 11% 10% 2	4680
	21st to end	Day	58% 6% 7% 14% 14% 1	5124
February	1st to 10th	Day	60% 5% 6% 18% 8% 2	1838
	11th to 20th	Day	57% 6% 10% 15% 12% 1	1929
	21st to end	Day	60% 5% 7% 15% 10% 3	1730
March	1st to 10th	Day	65% 4 6% 10% 11% 4	4579
	11th to 20th	Day	53% 7% 14% 12% 11% 3	4844
	21st to end	Day	54% 4 7% 14% 18% 2	6073
April	1st to 10th	Day	57% 4 9% 16% 12% 3	2520
	11th to 20th	Day	53% 5% 8% 20% 11% 2	2494
	21st to end	Day	55% 6% 7% 18% 12% 3	2695
May	1st to 10th	Day	59% 6% 8% 18% 9% 1	8249
	11th to 20th	Day	52% 8% 14% 18% 7% 2	8225
	21st to end	Day	53% 7% 9% 19% 11% 1	9061
June	1st to 10th	Day	53% 8% 9% 18% 11% 1	2940
	11th to 20th	Day	48% 8% 12% 21% 10% 2	2940
	21st to end	Day	55% 8% 11% 17% 9% 1	2940
July	1st to 10th	Day	45% 7% 13% 24% 11%	8210
	11th to 20th	Day	35% 7% 17% 30% 10%	8205
	21st to end	Day	40% 7% 17% 27% 8%	8795
August	1st to 10th	Day	46% 9% 17% 21% 6%	4689
	11th to 20th	Day	44% 9% 17% 25% 5%	4356
	21st to end	Day	44% 8% 14% 21% 12% 1	4420
September	1st to 10th	Day	40% 8% 14% 25% 13%	2400
	11th to 20th	Day	37% 7% 13% 30% 11% 1	2330
	21st to end	Day	45% 7% 11% 24% 12%	2200
October	1st to 10th	Day	45% 7% 13% 26% 8% 1	3311
	11th to 20th	Day	46% 7% 13% 25% 8%	3176
	21st to end	Day	48% 6% 21% 16% 9% 1	3180
November	1st to 10th	Day	53% 6% 13% 18% 9% 1	1851
	11th to 20th	Day	58% 8% 10% 13% 10% 1	1755
	21st to end	Day	63% 9% 10% 12% 6% 1	1680
December	1st to 10th	Day	67% 6% 9% 13% 5%	2680
	11th to 20th	Day	61% 5% 8% 16% 10%	3066
	21st to end	Day	62% 4 7% 15% 11%	4048
January	1st to 10th	Night	62% 7% 9% 16% 6% 1	8234
	11th to 20th	Night	67% 7% 7% 12% 6% 1	8280
	21st to end	Night	57% 8% 8% 12% 15% 1	9057
February	1st to 10th	Night	57% 6% 9% 18% 9% 2	2778
	11th to 20th	Night	54% 6% 10% 18% 10% 1	2587
	21st to end	Night	53% 7% 10% 17% 12% 2	2076
March	1st to 10th	Night	61% 5% 8% 11% 13% 3	5494
	11th to 20th	Night	51% 7% 12% 15% 12% 3	5333
	21st to end	Night	53% 5% 8% 20% 12% 3	5101
April	1st to 10th	Night	54% 4 9% 17% 13% 2	2100
	11th to 20th	Night	47% 6% 11% 21% 14% 2	2075
	21st to end	Night	49% 6% 9% 19% 14% 2	1930
May	1st to 10th	Night	55% 7% 11% 17% 8% 1	4690
	11th to 20th	Night	48% 7% 13% 21% 9% 1	4640
	21st to end	Night	53% 6% 10% 18% 12% 1	5115
June	1st to 10th	Night	47% 7% 12% 21% 13%	1680
	11th to 20th	Night	44% 8% 11% 21% 13% 2	1680
	21st to end	Night	46% 9% 13% 20% 12% 1	1680
July	1st to 10th	Night	41% 7% 19% 23% 10%	4640
	11th to 20th	Night	33% 7% 20% 32% 7%	4632
	21st to end	Night	38% 8% 17% 28% 9%	4967
August	1st to 10th	Night	40% 8% 17% 26% 8%	2656
	11th to 20th	Night	40% 7% 20% 25% 8%	2939
	21st to end	Night	42% 8% 15% 24% 11% 1	3677
September	1st to 10th	Night	34% 9% 15% 28% 14%	2000
	11th to 20th	Night	34% 7% 16% 32% 11% 1	2069
	21st to end	Night	40% 7% 12% 29% 13%	2200
October	1st to 10th	Night	43% 6% 13% 24% 12% 1	3854
	11th to 20th	Night	43% 8% 13% 26% 10%	3963
	21st to end	Night	47% 6% 17% 17% 10% 2	4610
November	1st to 10th	Night	51% 8% 13% 20% 6% 1	2667
	11th to 20th	Night	53% 9% 12% 17% 9% 1	2861
	21st to end	Night	60% 7% 9% 16% 7% 1	2940
December	1st to 10th	Night	62% 8% 14% 12% 5%	4720
	11th to 20th	Night	62% 6% 6% 15% 10% 1	5348
	21st to end	Night	61% 5% 5% 13% 15% 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	21% 22% 39% 15% 3	220
	11th to 20th	Day	29% 20% 37% 10% 5%	220
	21st to end	Day	21% 21% 39% 16% 2 1	242
February	1st to 10th	Day	26% 29% 35% 8% 2	303
	11th to 20th	Day	25% 27% 38% 10% 1	407
	21st to end	Day	27% 24% 35% 12% 2	446
March	1st to 10th	Day	27% 23% 32% 14% 3	540
	11th to 20th	Day	27% 23% 33% 13% 3 1	540
	21st to end	Day	30% 26% 26% 12% 5% 1	594
April	1st to 10th	Day	31% 22% 29% 11% 5% 1	540
	11th to 20th	Day	37% 19% 22% 14% 7% 1	532
	21st to end	Day	32% 21% 32% 11% 4 1	540
May	1st to 10th	Day	29% 22% 31% 13% 2 1	543
	11th to 20th	Day	25% 22% 30% 16% 6% 1	567
	21st to end	Day	26% 22% 31% 16% 4 1	617
June	1st to 10th	Day	25% 18% 34% 17% 5% 1	570
	11th to 20th	Day	22% 20% 31% 17% 9% 1	570
	21st to end	Day	24% 17% 32% 19% 7% 1	570
July	1st to 10th	Day	16% 13% 39% 24% 7% 2	565
	11th to 20th	Day	16% 14% 38% 25% 5% 1	564
	21st to end	Day	16% 14% 32% 27% 9% 2	620
August	1st to 10th	Day	14% 13% 32% 29% 10% 2	566
	11th to 20th	Day	15% 9% 34% 25% 11% 5%	559
	21st to end	Day	17% 16% 30% 21% 11% 5%	619
September	1st to 10th	Day	18% 15% 32% 20% 10% 5%	530
	11th to 20th	Day	14% 13% 26% 25% 15% 7%	530
	21st to end	Day	22% 15% 25% 21% 12% 5%	530
October	1st to 10th	Day	25% 16% 27% 20% 9% 2	530
	11th to 20th	Day	26% 20% 29% 17% 6% 1	508
	21st to end	Day	31% 17% 31% 16% 4	462
November	1st to 10th	Day	31% 20% 29% 17% 3 1	425
	11th to 20th	Day	26% 22% 30% 16% 5%	295
	21st to end	Day	30% 28% 30% 10% 3	220
December	1st to 10th	Day	27% 21% 32% 14% 5% 1	220
	11th to 20th	Day	25% 28% 37% 8% 2	220
	21st to end	Day	30% 23% 31% 10% 4 2	242
January	1st to 10th	Night	24% 20% 36% 17% 4	840
	11th to 20th	Night	23% 21% 30% 21% 5%	840
	21st to end	Night	14% 18% 40% 22% 6% 1	924
February	1st to 10th	Night	16% 22% 37% 20% 5%	840
	11th to 20th	Night	19% 21% 38% 18% 3	823
	21st to end	Night	20% 19% 36% 23% 2	692
March	1st to 10th	Night	27% 19% 33% 18% 3	840
	11th to 20th	Night	24% 20% 34% 16% 5% 1	840
	21st to end	Night	22% 18% 32% 21% 5% 1	924
April	1st to 10th	Night	28% 17% 30% 20% 4	840
	11th to 20th	Night	25% 18% 30% 22% 5%	831
	21st to end	Night	27% 17% 31% 19% 6%	670
May	1st to 10th	Night	24% 13% 33% 22% 6% 1	431
	11th to 20th	Night	22% 12% 31% 27% 8%	414
	21st to end	Night	24% 11% 36% 21% 8%	455
June	1st to 10th	Night	21% 10% 33% 30% 6%	420
	11th to 20th	Night	24% 10% 25% 31% 11%	420
	21st to end	Night	20% 8% 24% 35% 12%	420
July	1st to 10th	Night	12% 8% 32% 35% 13%	410
	11th to 20th	Night	13% 6% 27% 41% 12% 1	408
	21st to end	Night	13% 8% 26% 40% 12% 1	460
August	1st to 10th	Night	13% 6% 21% 44% 16%	418
	11th to 20th	Night	13% 6% 24% 35% 22% 1	584
	21st to end	Night	17% 9% 27% 27% 17% 2	917
September	1st to 10th	Night	14% 8% 31% 34% 13% 1	800
	11th to 20th	Night	16% 8% 24% 31% 19% 2	800
	21st to end	Night	20% 11% 28% 24% 16% 2	800
October	1st to 10th	Night	22% 14% 27% 24% 14% 1	800
	11th to 20th	Night	24% 16% 30% 21% 9%	800
	21st to end	Night	27% 15% 30% 23% 5%	880
November	1st to 10th	Night	24% 19% 28% 22% 6% 1	820
	11th to 20th	Night	24% 18% 30% 18% 8% 1	840
	21st to end	Night	26% 24% 27% 17% 5% 1	840
December	1st to 10th	Night	25% 18% 32% 19% 5%	840
	11th to 20th	Night	28% 20% 30% 17% 5% 1	840
	21st to end	Night	31% 19% 29% 17% 4	924

Page generated at 2026-08-27 04:07:13. Version ac07

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