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 2024-10-25.

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	16% 11% 4 9% 5% 5% 5% 4 5% 6% 30%	101500
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 31%	97311
Transparency	Day	52% 7% 11% 19% 9% 1	101261
	Night	51% 8% 12% 19% 10% 1	97170
Seeing	Day	24% 19% 31% 18% 6% 2	14471
	Night	22% 15% 31% 23% 8% 1	23398

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% 17% 6% 14% 6% 5% 4 4 5% 5% 22%	2517
	11th to 20th	Day	10% 15% 7% 16% 9% 5% 4 3 3 5% 23%	2520
	21st to end	Day	9% 14% 7% 15% 6% 6% 5% 5% 6% 5% 22%	2772
February	1st to 10th	Day	9% 18% 6% 12% 7% 7% 4 3 4 6% 24%	1662
	11th to 20th	Day	10% 17% 6% 11% 6% 5% 5% 3 5% 6% 28%	1732
	21st to end	Day	14% 18% 6% 9% 7% 5% 5% 3 4 4 26%	1570
March	1st to 10th	Day	15% 19% 4 10% 6% 6% 4 3 4 4 24%	3116
	11th to 20th	Day	10% 17% 6% 14% 7% 4 5% 3 4 5% 25%	3310
	21st to end	Day	12% 13% 2 8% 5% 4 5% 4 6% 6% 36%	4152
April	1st to 10th	Day	18% 16% 3 8% 6% 4 3 3 4 5% 29%	2280
	11th to 20th	Day	22% 9% 3 7% 4 4 4 3 5% 5% 33%	2254
	21st to end	Day	20% 12% 4 8% 5% 4 4 4 5% 6% 30%	2438
May	1st to 10th	Day	20% 11% 3 7% 5% 4 4 4 5% 6% 30%	4426
	11th to 20th	Day	18% 8% 2 7% 5% 5% 5% 4 7% 8% 30%	4398
	21st to end	Day	17% 7% 3 8% 5% 5% 6% 4 5% 8% 33%	4837
June	1st to 10th	Day	23% 9% 2 7% 5% 5% 5% 4 6% 6% 27%	2660
	11th to 20th	Day	16% 7% 3 8% 6% 6% 5% 5% 6% 7% 32%	2660
	21st to end	Day	23% 9% 3 7% 6% 5% 5% 4 6% 6% 26%	2660
July	1st to 10th	Day	14% 7% 3 9% 6% 6% 6% 5% 7% 8% 29%	4440
	11th to 20th	Day	14% 5% 2 7% 5% 6% 7% 5% 7% 8% 34%	4440
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 6% 7% 42%	4814
August	1st to 10th	Day	14% 6% 2 8% 6% 7% 6% 6% 7% 9% 29%	4423
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 5% 7% 8% 32%	4054
	21st to end	Day	15% 5% 3 7% 5% 6% 5% 4 5% 8% 37%	4180
September	1st to 10th	Day	15% 5% 2 6% 6% 5% 4 4 6% 7% 39%	2280
	11th to 20th	Day	14% 6% 2 6% 4 5% 4 4 6% 7% 42%	2214
	21st to end	Day	19% 8% 2 6% 4 4 4 3 5% 6% 38%	2090
October	1st to 10th	Day	21% 10% 3 6% 4 4 4 3 5% 7% 32%	1936
	11th to 20th	Day	21% 13% 4 8% 5% 5% 5% 4 5% 5% 26%	1862
	21st to end	Day	24% 13% 3 8% 5% 5% 4 3 4 5% 25%	1825
November	1st to 10th	Day	15% 14% 4 6% 5% 5% 4 4 6% 6% 31%	1671
	11th to 20th	Day	18% 14% 6% 10% 6% 5% 4 3 5% 6% 24%	1589
	21st to end	Day	18% 17% 5% 10% 6% 5% 5% 4 4 4 22%	1520
December	1st to 10th	Day	21% 19% 5% 10% 5% 4 3 3 4 4 21%	1520
	11th to 20th	Day	17% 17% 5% 12% 6% 4 4 3 4 5% 22%	1906
	21st to end	Day	19% 19% 6% 10% 4 4 4 2 4 5% 22%	2772
January	1st to 10th	Night	13% 15% 6% 13% 6% 5% 5% 5% 5% 5% 23%	4429
	11th to 20th	Night	8% 13% 6% 15% 10% 6% 5% 4 4 6% 23%	4440
	21st to end	Night	8% 14% 7% 17% 8% 6% 6% 4 5% 6% 20%	4884
February	1st to 10th	Night	10% 14% 5% 12% 7% 6% 5% 4 5% 6% 26%	2514
	11th to 20th	Night	9% 14% 6% 12% 6% 5% 5% 4 5% 7% 28%	2333
	21st to end	Night	11% 14% 5% 9% 5% 5% 5% 5% 6% 7% 28%	1884
March	1st to 10th	Night	17% 16% 4 8% 5% 4 4 3 5% 5% 29%	3724
	11th to 20th	Night	12% 18% 6% 11% 5% 4 4 3 4 5% 27%	3647
	21st to end	Night	12% 10% 5% 11% 6% 5% 5% 3 5% 5% 35%	3480
April	1st to 10th	Night	20% 13% 3 7% 4 5% 4 3 5% 6% 31%	1900
	11th to 20th	Night	17% 8% 4 6% 5% 5% 3 4 5% 6% 36%	1875
	21st to end	Night	20% 10% 3 8% 4 4 4 4 5% 6% 34%	1746
May	1st to 10th	Night	18% 10% 4 8% 6% 5% 4 3 5% 6% 30%	2524
	11th to 20th	Night	20% 7% 3 6% 4 4 3 3 5% 7% 38%	2495
	21st to end	Night	18% 7% 3 7% 5% 6% 5% 4 5% 8% 31%	2738
June	1st to 10th	Night	17% 8% 2 8% 6% 5% 3 4 6% 9% 32%	1520
	11th to 20th	Night	18% 7% 3 4 5% 3 5% 4 6% 8% 37%	1520
	21st to end	Night	20% 7% 2 5% 5% 5% 4 4 7% 7% 34%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 6% 5% 5% 6% 8% 34%	2520
	11th to 20th	Night	15% 6% 2 5% 4 5% 4 4 6% 8% 41%	2520
	21st to end	Night	10% 5% 1 6% 4 4 4 3 7% 8% 48%	2739
August	1st to 10th	Night	11% 6% 3 7% 5% 6% 4 4 6% 7% 39%	2506
	11th to 20th	Night	15% 7% 2 8% 5% 4 4 3 5% 6% 39%	2738
	21st to end	Night	17% 6% 2 7% 4 4 4 4 5% 8% 40%	3476
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 6% 7% 47%	1900
	11th to 20th	Night	14% 6% 2 4 3 4 4 3 5% 7% 48%	1965
	21st to end	Night	16% 7% 2 6% 3 3 4 3 5% 7% 43%	2090
October	1st to 10th	Night	17% 9% 3 7% 5% 4 4 3 4 6% 39%	2242
	11th to 20th	Night	20% 9% 3 9% 4 4 4 4 5% 6% 32%	2318
	21st to end	Night	21% 10% 4 8% 5% 4 4 3 5% 7% 27%	2637
November	1st to 10th	Night	16% 11% 3 8% 6% 4 5% 5% 5% 7% 30%	2407
	11th to 20th	Night	16% 11% 4 10% 7% 5% 5% 4 6% 8% 26%	2588
	21st to end	Night	17% 16% 5% 10% 7% 4 4 3 5% 5% 25%	2660
December	1st to 10th	Night	17% 15% 6% 13% 7% 5% 5% 4 5% 5% 17%	2660
	11th to 20th	Night	18% 16% 5% 10% 6% 4 4 3 5% 5% 25%	3288
	21st to end	Night	20% 19% 6% 10% 5% 4 4 3 4 5% 20%	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	1570
March	1st to 10th	Day	63% 5% 6% 13% 11% 2	3119
	11th to 20th	Day	59% 8% 9% 11% 10% 4	3310
	21st to end	Day	47% 5% 10% 18% 17% 3	4152
April	1st to 10th	Day	57% 5% 9% 16% 11% 3	2280
	11th to 20th	Day	52% 6% 9% 21% 11% 2	2254
	21st to end	Day	55% 6% 7% 17% 12% 3	2438
May	1st to 10th	Day	53% 7% 9% 20% 9% 1	4440
	11th to 20th	Day	48% 10% 17% 16% 8% 1	4402
	21st to end	Day	47% 9% 10% 20% 14% 1	4837
June	1st to 10th	Day	54% 8% 10% 17% 10% 1	2660
	11th to 20th	Day	48% 8% 12% 20% 11% 3	2660
	21st to end	Day	57% 8% 10% 16% 9%	2660
July	1st to 10th	Day	48% 8% 13% 23% 8%	4370
	11th to 20th	Day	42% 8% 18% 25% 6%	4365
	21st to end	Day	39% 7% 15% 29% 10%	4661
August	1st to 10th	Day	47% 9% 16% 21% 6%	4409
	11th to 20th	Day	45% 9% 17% 24% 5%	4096
	21st to end	Day	44% 8% 14% 21% 13% 1	4180
September	1st to 10th	Day	41% 8% 13% 24% 13%	2280
	11th to 20th	Day	39% 8% 14% 29% 10% 1	2214
	21st to end	Day	46% 7% 11% 24% 11%	2090
October	1st to 10th	Day	50% 7% 11% 21% 10% 1	1936
	11th to 20th	Day	57% 9% 11% 18% 5% 1	1862
	21st to end	Day	59% 7% 12% 13% 8% 1	1825
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	53% 6% 10% 17% 12% 2	1884
March	1st to 10th	Night	56% 6% 10% 13% 11% 3	3734
	11th to 20th	Night	57% 7% 9% 13% 13% 1	3648
	21st to end	Night	49% 5% 9% 19% 14% 4	3480
April	1st to 10th	Night	54% 4 9% 17% 14% 2	1900
	11th to 20th	Night	47% 6% 11% 21% 14% 2	1875
	21st to end	Night	49% 7% 9% 19% 13% 2	1746
May	1st to 10th	Night	52% 8% 11% 18% 8% 2	2530
	11th to 20th	Night	44% 9% 16% 17% 12% 2	2496
	21st to end	Night	48% 9% 11% 19% 13% 1	2739
June	1st to 10th	Night	48% 8% 13% 21% 11%	1520
	11th to 20th	Night	44% 8% 11% 21% 13% 3	1520
	21st to end	Night	47% 9% 12% 19% 12% 1	1520
July	1st to 10th	Night	45% 8% 18% 19% 9% 1	2480
	11th to 20th	Night	38% 8% 21% 27% 5%	2472
	21st to end	Night	33% 8% 20% 27% 12%	2651
August	1st to 10th	Night	41% 8% 17% 26% 7%	2496
	11th to 20th	Night	41% 7% 20% 25% 7%	2762
	21st to end	Night	42% 8% 14% 23% 11% 1	3476
September	1st to 10th	Night	35% 9% 14% 27% 14%	1900
	11th to 20th	Night	34% 7% 16% 31% 11% 1	1965
	21st to end	Night	40% 7% 12% 29% 12%	2090
October	1st to 10th	Night	46% 7% 10% 24% 13% 1	2242
	11th to 20th	Night	49% 9% 12% 21% 8%	2318
	21st to end	Night	54% 8% 12% 17% 8% 1	2637
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% 13% 2	382
March	1st to 10th	Day	27% 21% 33% 16% 3	460
	11th to 20th	Day	25% 23% 34% 14% 3 1	460
	21st to end	Day	29% 25% 27% 12% 5% 1	506
April	1st to 10th	Day	29% 21% 31% 13% 6% 1	460
	11th to 20th	Day	34% 20% 24% 13% 7% 1	452
	21st to end	Day	31% 21% 33% 12% 4 1	460
May	1st to 10th	Day	28% 22% 32% 14% 2 2	463
	11th to 20th	Day	24% 20% 31% 17% 7% 1	487
	21st to end	Day	24% 21% 33% 17% 4 1	529
June	1st to 10th	Day	25% 18% 35% 17% 5%	490
	11th to 20th	Day	20% 21% 30% 18% 10% 1	490
	21st to end	Day	26% 17% 30% 19% 7% 1	490
July	1st to 10th	Day	16% 11% 39% 25% 7% 2	485
	11th to 20th	Day	17% 13% 37% 27% 6% 1	484
	21st to end	Day	16% 12% 33% 29% 9% 2	532
August	1st to 10th	Day	14% 14% 31% 29% 10% 2	486
	11th to 20th	Day	15% 10% 32% 27% 11% 6%	479
	21st to end	Day	16% 16% 31% 20% 11% 6%	539
September	1st to 10th	Day	18% 15% 32% 20% 10% 5%	490
	11th to 20th	Day	15% 14% 26% 25% 14% 6%	490
	21st to end	Day	22% 16% 25% 21% 12% 5%	490
October	1st to 10th	Day	27% 16% 26% 19% 10% 2	490
	11th to 20th	Day	27% 21% 28% 16% 7% 1	470
	21st to end	Day	31% 17% 31% 16% 4	411
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% 36% 22% 2	628
March	1st to 10th	Night	26% 18% 34% 19% 3	760
	11th to 20th	Night	23% 21% 33% 17% 5% 1	760
	21st to end	Night	21% 18% 33% 22% 5% 1	836
April	1st to 10th	Night	28% 17% 30% 20% 5%	760
	11th to 20th	Night	25% 18% 30% 22% 5% 1	751
	21st to end	Night	26% 17% 32% 19% 6%	606
May	1st to 10th	Night	23% 13% 33% 23% 6% 1	390
	11th to 20th	Night	21% 13% 30% 28% 8%	374
	21st to end	Night	21% 12% 37% 21% 9%	411
June	1st to 10th	Night	22% 10% 34% 29% 6%	380
	11th to 20th	Night	24% 8% 24% 31% 12% 1	380
	21st to end	Night	21% 8% 25% 33% 13% 1	380
July	1st to 10th	Night	12% 8% 30% 35% 14%	370
	11th to 20th	Night	13% 5% 27% 40% 13% 1	368
	21st to end	Night	12% 7% 27% 40% 12% 1	416
August	1st to 10th	Night	13% 6% 20% 44% 16%	378
	11th to 20th	Night	14% 6% 23% 34% 23% 1	527
	21st to end	Night	16% 10% 28% 27% 17% 2	836
September	1st to 10th	Night	14% 8% 31% 34% 12% 1	760
	11th to 20th	Night	17% 8% 25% 30% 19% 2	760
	21st to end	Night	20% 11% 28% 24% 16% 2	760
October	1st to 10th	Night	22% 14% 26% 23% 13% 1	760
	11th to 20th	Night	25% 16% 30% 21% 9%	760
	21st to end	Night	27% 15% 30% 22% 5%	812
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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