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 2024-02-25.

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	17% 11% 4 8% 7% 4 5% 5% 5% 6% 30%	78227
	Night	15% 11% 4 8% 7% 3 5% 5% 5% 7% 31%	81067
Transparency	Day	53% 7% 10% 18% 10% 1	77932
	Night	51% 8% 11% 19% 10% 1	80896
Seeing	Day	24% 19% 32% 18% 6% 2	13502
	Night	22% 15% 31% 23% 8% 1	22649

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% 16% 7% 12% 7% 4 4 5% 4 5% 22%	2517
	11th to 20th	Day	10% 15% 7% 14% 12% 4 4 3 3 5% 23%	2520
	21st to end	Day	9% 13% 7% 13% 8% 4 5% 6% 5% 6% 22%	2772
February	1st to 10th	Day	9% 17% 6% 10% 8% 5% 6% 4 4 6% 25%	1662
	11th to 20th	Day	10% 16% 7% 10% 6% 3 5% 4 5% 5% 28%	1732
	21st to end	Day	14% 17% 7% 8% 7% 4 5% 4 4 4 26%	1520
March	1st to 10th	Day	12% 13% 6% 9% 9% 5% 5% 4 5% 5% 28%	1797
	11th to 20th	Day	13% 13% 5% 9% 8% 3 4 5% 5% 6% 29%	1880
	21st to end	Day	17% 11% 3 7% 6% 3 4 5% 5% 6% 34%	2362
April	1st to 10th	Day	19% 15% 4 7% 7% 3 4 4 4 5% 29%	2160
	11th to 20th	Day	22% 9% 3 6% 5% 3 4 4 4 5% 34%	2134
	21st to end	Day	21% 11% 4 6% 6% 3 4 5% 4 6% 30%	2309
May	1st to 10th	Day	20% 11% 3 6% 6% 4 4 4 5% 6% 32%	2520
	11th to 20th	Day	20% 7% 3 6% 7% 4 4 5% 6% 5% 33%	2478
	21st to end	Day	20% 7% 3 6% 6% 4 5% 5% 5% 8% 32%	2725
June	1st to 10th	Day	24% 8% 3 5% 6% 4 5% 5% 6% 7% 27%	2520
	11th to 20th	Day	17% 6% 3 7% 7% 4 6% 5% 6% 7% 32%	2520
	21st to end	Day	23% 8% 4 6% 7% 3 5% 5% 6% 6% 26%	2520
July	1st to 10th	Day	14% 6% 3 6% 6% 4 6% 6% 6% 9% 34%	2520
	11th to 20th	Day	15% 6% 3 6% 7% 3 6% 6% 8% 9% 33%	2520
	21st to end	Day	13% 7% 3 7% 6% 3 7% 6% 7% 9% 32%	2744
August	1st to 10th	Day	14% 7% 2 8% 7% 5% 6% 7% 7% 9% 29%	2506
	11th to 20th	Day	14% 7% 3 6% 6% 3 6% 7% 7% 9% 33%	2316
	21st to end	Day	13% 6% 3 6% 6% 3 5% 5% 5% 8% 39%	2376
September	1st to 10th	Day	15% 5% 3 6% 7% 4 5% 4 5% 7% 39%	2160
	11th to 20th	Day	15% 5% 3 6% 5% 4 4 5% 6% 7% 41%	2098
	21st to end	Day	19% 8% 2 5% 5% 3 4 4 5% 6% 39%	1980
October	1st to 10th	Day	22% 9% 3 4 5% 2 5% 4 5% 7% 32%	1835
	11th to 20th	Day	22% 12% 4 7% 7% 3 5% 5% 5% 5% 24%	1764
	21st to end	Day	25% 12% 3 7% 6% 3 5% 4 4 5% 25%	1782
November	1st to 10th	Day	15% 13% 4 5% 5% 4 5% 4 6% 6% 31%	1671
	11th to 20th	Day	19% 13% 6% 9% 7% 4 4 4 5% 6% 24%	1589
	21st to end	Day	18% 16% 6% 9% 6% 4 5% 4 4 5% 22%	1520
December	1st to 10th	Day	21% 18% 7% 9% 6% 3 3 4 4 4 21%	1520
	11th to 20th	Day	17% 16% 6% 11% 8% 3 4 4 4 6% 23%	1906
	21st to end	Day	20% 19% 6% 9% 5% 3 4 3 4 5% 23%	2772
January	1st to 10th	Night	13% 14% 6% 11% 7% 4 5% 5% 5% 5% 23%	4429
	11th to 20th	Night	9% 12% 7% 13% 12% 5% 5% 5% 4 6% 23%	4440
	21st to end	Night	9% 14% 7% 14% 10% 5% 6% 5% 4 6% 20%	4884
February	1st to 10th	Night	10% 13% 6% 11% 8% 4 6% 5% 5% 6% 27%	2514
	11th to 20th	Night	9% 13% 6% 11% 6% 4 5% 5% 5% 7% 28%	2333
	21st to end	Night	11% 14% 5% 9% 6% 3 5% 6% 6% 7% 29%	1831
March	1st to 10th	Night	13% 13% 5% 8% 7% 4 6% 5% 6% 6% 28%	2150
	11th to 20th	Night	14% 13% 6% 7% 6% 4 5% 4 6% 6% 30%	2077
	21st to end	Night	13% 9% 5% 7% 6% 3 5% 5% 5% 6% 37%	1994
April	1st to 10th	Night	21% 12% 4 6% 5% 4 4 4 5% 6% 31%	1800
	11th to 20th	Night	16% 6% 4 5% 5% 4 4 5% 5% 7% 38%	1775
	21st to end	Night	20% 9% 4 8% 4 3 4 4 5% 6% 33%	1655
May	1st to 10th	Night	20% 8% 3 5% 5% 3 5% 3 4 8% 36%	1450
	11th to 20th	Night	19% 7% 3 6% 6% 3 3 3 4 8% 39%	1415
	21st to end	Night	18% 6% 3 6% 5% 3 5% 5% 5% 8% 37%	1550
June	1st to 10th	Night	17% 7% 3 7% 7% 3 4 5% 6% 9% 32%	1440
	11th to 20th	Night	18% 6% 3 4 6% 3 4 5% 6% 8% 37%	1440
	21st to end	Night	19% 6% 3 5% 5% 3 5% 5% 6% 8% 35%	1440
July	1st to 10th	Night	11% 5% 2 4 6% 4 4 6% 5% 9% 44%	1440
	11th to 20th	Night	12% 6% 2 4 5% 4 6% 5% 6% 8% 42%	1440
	21st to end	Night	12% 5% 2 6% 5% 3 5% 4 7% 9% 42%	1574
August	1st to 10th	Night	11% 6% 3 4 6% 3 5% 6% 7% 9% 42%	1432
	11th to 20th	Night	12% 6% 2 6% 6% 3 5% 5% 5% 8% 44%	1562
	21st to end	Night	14% 6% 2 4 4 3 4 5% 5% 9% 43%	1980
September	1st to 10th	Night	12% 5% 2 5% 5% 3 4 4 6% 8% 46%	1800
	11th to 20th	Night	15% 5% 2 4 3 3 4 4 5% 8% 46%	1861
	21st to end	Night	17% 7% 2 5% 4 2 4 4 5% 7% 44%	1980
October	1st to 10th	Night	17% 8% 3 6% 5% 3 4 4 4 6% 40%	2124
	11th to 20th	Night	21% 9% 3 7% 6% 2 5% 5% 5% 6% 31%	2196
	21st to end	Night	22% 10% 4 7% 7% 4 4 5% 5% 7% 27%	2574
November	1st to 10th	Night	16% 10% 4 7% 7% 3 6% 5% 5% 7% 30%	2407
	11th to 20th	Night	16% 10% 4 9% 8% 4 5% 4 6% 8% 26%	2588
	21st to end	Night	17% 14% 5% 9% 8% 3 4 4 5% 6% 25%	2660
December	1st to 10th	Night	17% 14% 7% 12% 7% 4 5% 5% 5% 6% 18%	2660
	11th to 20th	Night	18% 15% 6% 9% 7% 3 4 4 5% 5% 25%	3288
	21st to end	Night	20% 19% 6% 9% 6% 3 4 4 4 5% 21%	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	63% 7% 8% 16% 5%	2518
	11th to 20th	Day	62% 10% 5% 14% 8% 1	2520
	21st to end	Day	60% 8% 9% 14% 7% 2	2772
February	1st to 10th	Day	61% 5% 7% 17% 8% 2	1662
	11th to 20th	Day	57% 6% 11% 14% 11% 1	1741
	21st to end	Day	61% 5% 7% 15% 9% 3	1520
March	1st to 10th	Day	59% 5% 7% 16% 11% 3	1800
	11th to 20th	Day	56% 6% 9% 13% 13% 3	1880
	21st to end	Day	52% 5% 9% 18% 13% 4	2362
April	1st to 10th	Day	57% 4 9% 15% 11% 3	2160
	11th to 20th	Day	52% 6% 9% 21% 12% 2	2134
	21st to end	Day	55% 6% 7% 17% 12% 3	2309
May	1st to 10th	Day	53% 6% 7% 20% 12% 3	2520
	11th to 20th	Day	50% 6% 9% 18% 15% 3	2482
	21st to end	Day	50% 7% 10% 18% 13% 2	2725
June	1st to 10th	Day	54% 8% 10% 17% 10% 1	2520
	11th to 20th	Day	48% 8% 11% 20% 11% 3	2520
	21st to end	Day	56% 8% 10% 16% 9%	2520
July	1st to 10th	Day	44% 8% 13% 24% 10%	2450
	11th to 20th	Day	44% 8% 15% 23% 10%	2445
	21st to end	Day	46% 10% 15% 21% 8%	2591
August	1st to 10th	Day	48% 11% 15% 22% 4	2492
	11th to 20th	Day	44% 11% 16% 21% 8%	2316
	21st to end	Day	41% 8% 15% 24% 12% 1	2376
September	1st to 10th	Day	42% 9% 13% 23% 13%	2160
	11th to 20th	Day	40% 8% 13% 28% 10% 1	2098
	21st to end	Day	46% 7% 11% 25% 11%	1980
October	1st to 10th	Day	50% 7% 11% 20% 11% 1	1835
	11th to 20th	Day	58% 9% 10% 17% 5% 1	1764
	21st to end	Day	60% 7% 11% 13% 8% 1	1782
November	1st to 10th	Day	51% 7% 13% 18% 10% 1	1671
	11th to 20th	Day	59% 8% 10% 13% 9% 1	1589
	21st to end	Day	61% 9% 10% 13% 6% 1	1520
December	1st to 10th	Day	65% 7% 9% 12% 7%	1520
	11th to 20th	Day	61% 6% 10% 14% 8%	1906
	21st to end	Day	65% 5% 7% 14% 8%	2772
January	1st to 10th	Night	58% 10% 11% 15% 5%	4429
	11th to 20th	Night	58% 11% 10% 15% 5% 2	4440
	21st to end	Night	60% 11% 8% 11% 9% 1	4884
February	1st to 10th	Night	58% 6% 9% 18% 8% 1	2514
	11th to 20th	Night	54% 7% 10% 18% 10% 1	2335
	21st to end	Night	52% 6% 9% 17% 13% 2	1831
March	1st to 10th	Night	56% 7% 8% 16% 11% 2	2160
	11th to 20th	Night	53% 6% 10% 15% 14% 2	2078
	21st to end	Night	47% 5% 9% 19% 15% 4	1994
April	1st to 10th	Night	54% 4 9% 17% 13% 2	1800
	11th to 20th	Night	45% 6% 11% 22% 14% 2	1775
	21st to end	Night	50% 7% 9% 19% 13% 2	1655
May	1st to 10th	Night	50% 4 9% 19% 14% 4	1450
	11th to 20th	Night	45% 7% 9% 19% 16% 3	1416
	21st to end	Night	44% 8% 13% 20% 13% 2	1551
June	1st to 10th	Night	48% 8% 13% 21% 11%	1440
	11th to 20th	Night	44% 9% 10% 21% 12% 3	1440
	21st to end	Night	46% 10% 13% 20% 12%	1440
July	1st to 10th	Night	36% 8% 18% 26% 12% 1	1400
	11th to 20th	Night	38% 10% 16% 26% 9% 1	1392
	21st to end	Night	37% 10% 19% 25% 10%	1486
August	1st to 10th	Night	36% 10% 20% 26% 8%	1422
	11th to 20th	Night	37% 9% 18% 25% 11%	1562
	21st to end	Night	37% 9% 16% 27% 10%	1980
September	1st to 10th	Night	36% 9% 14% 27% 14%	1800
	11th to 20th	Night	35% 7% 15% 31% 10% 1	1861
	21st to end	Night	39% 7% 12% 30% 12%	1980
October	1st to 10th	Night	47% 7% 9% 24% 13% 1	2124
	11th to 20th	Night	50% 9% 12% 21% 8%	2196
	21st to end	Night	55% 8% 11% 17% 8% 1	2574
November	1st to 10th	Night	50% 9% 14% 20% 7% 1	2407
	11th to 20th	Night	53% 9% 12% 17% 8% 2	2588
	21st to end	Night	58% 7% 10% 17% 8% 1	2660
December	1st to 10th	Night	65% 8% 9% 12% 5%	2660
	11th to 20th	Night	60% 7% 8% 16% 8% 1	3288
	21st to end	Night	64% 6% 7% 14% 7% 1	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	22% 21% 38% 17% 3	180
	11th to 20th	Day	28% 16% 39% 11% 6% 1	180
	21st to end	Day	19% 22% 40% 16% 3 1	198
February	1st to 10th	Day	29% 30% 32% 7% 2	247
	11th to 20th	Day	25% 27% 40% 8% 1	339
	21st to end	Day	27% 26% 32% 12% 2	362
March	1st to 10th	Day	26% 22% 34% 15% 3	420
	11th to 20th	Day	26% 23% 33% 14% 3 1	420
	21st to end	Day	30% 24% 26% 13% 6% 1	462
April	1st to 10th	Day	29% 20% 32% 13% 6% 1	420
	11th to 20th	Day	33% 19% 24% 15% 8% 1	412
	21st to end	Day	30% 20% 33% 12% 4 1	420
May	1st to 10th	Day	28% 22% 32% 15% 2 2	423
	11th to 20th	Day	25% 21% 31% 15% 6% 1	447
	21st to end	Day	23% 22% 33% 17% 4 1	485
June	1st to 10th	Day	26% 18% 36% 15% 5%	450
	11th to 20th	Day	20% 20% 30% 18% 10% 1	450
	21st to end	Day	24% 16% 31% 20% 7% 1	450
July	1st to 10th	Day	16% 10% 38% 26% 7% 2	445
	11th to 20th	Day	16% 12% 38% 28% 6% 1	444
	21st to end	Day	16% 12% 33% 28% 9% 2	488
August	1st to 10th	Day	14% 14% 31% 29% 10% 2	446
	11th to 20th	Day	14% 10% 33% 27% 10% 6%	439
	21st to end	Day	16% 17% 31% 19% 11% 6%	495
September	1st to 10th	Day	18% 14% 33% 20% 10% 5%	450
	11th to 20th	Day	16% 15% 28% 24% 11% 6%	450
	21st to end	Day	22% 16% 25% 20% 12% 5%	450
October	1st to 10th	Day	28% 17% 26% 18% 10% 2	450
	11th to 20th	Day	27% 21% 27% 17% 6% 1	432
	21st to end	Day	32% 17% 32% 16% 4	396
November	1st to 10th	Day	28% 21% 29% 18% 4 1	365
	11th to 20th	Day	26% 23% 31% 14% 5%	249
	21st to end	Day	28% 27% 30% 12% 3 1	180
December	1st to 10th	Day	29% 21% 30% 14% 5% 1	180
	11th to 20th	Day	24% 31% 34% 8% 2	180
	21st to end	Day	32% 25% 28% 10% 4 1	198
January	1st to 10th	Night	25% 19% 35% 17% 4	760
	11th to 20th	Night	23% 20% 31% 21% 5%	760
	21st to end	Night	14% 17% 40% 22% 6% 1	836
February	1st to 10th	Night	17% 22% 37% 20% 4	760
	11th to 20th	Night	19% 21% 38% 18% 3	743
	21st to end	Night	21% 20% 35% 22% 2	611
March	1st to 10th	Night	25% 19% 35% 18% 3	720
	11th to 20th	Night	23% 21% 33% 17% 5% 1	720
	21st to end	Night	21% 18% 32% 23% 6% 1	792
April	1st to 10th	Night	28% 17% 30% 20% 5%	720
	11th to 20th	Night	23% 17% 30% 23% 6% 1	711
	21st to end	Night	26% 17% 31% 19% 6%	575
May	1st to 10th	Night	24% 13% 33% 22% 7% 1	370
	11th to 20th	Night	22% 13% 31% 27% 7%	354
	21st to end	Night	21% 12% 37% 21% 9%	389
June	1st to 10th	Night	22% 9% 35% 28% 5%	360
	11th to 20th	Night	24% 9% 25% 30% 12% 1	360
	21st to end	Night	19% 8% 25% 34% 14% 1	360
July	1st to 10th	Night	12% 9% 30% 34% 15%	350
	11th to 20th	Night	12% 6% 27% 41% 14% 1	348
	21st to end	Night	12% 6% 28% 40% 12% 1	394
August	1st to 10th	Night	13% 6% 20% 44% 17%	358
	11th to 20th	Night	13% 5% 24% 34% 22% 1	498
	21st to end	Night	16% 10% 28% 27% 18% 2	792
September	1st to 10th	Night	15% 8% 31% 33% 13% 1	720
	11th to 20th	Night	18% 8% 26% 30% 17% 1	720
	21st to end	Night	20% 11% 28% 24% 15% 2	720
October	1st to 10th	Night	23% 14% 26% 24% 13% 1	720
	11th to 20th	Night	25% 15% 30% 21% 9%	720
	21st to end	Night	28% 14% 31% 22% 5%	792
November	1st to 10th	Night	23% 19% 28% 22% 6% 1	740
	11th to 20th	Night	24% 18% 30% 19% 8% 1	760
	21st to end	Night	26% 23% 28% 18% 5% 1	760
December	1st to 10th	Night	26% 18% 32% 19% 5% 1	760
	11th to 20th	Night	28% 19% 31% 18% 4 1	760
	21st to end	Night	31% 19% 30% 16% 4	836

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