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 2025-04-26.

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% 6% 5% 5% 4 5% 6% 29%	113620
	Night	14% 12% 4 10% 6% 5% 4 4 5% 6% 30%	114985
Transparency	Day	52% 7% 11% 18% 10% 1	117100
	Night	52% 7% 11% 18% 10% 1	119656
Seeing	Day	24% 19% 31% 17% 6% 2	15004
	Night	22% 16% 31% 23% 8% 1	24126

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	11% 19% 7% 14% 6% 5% 5% 4 4 5% 19%	3597
	11th to 20th	Day	8% 16% 7% 16% 10% 6% 4 3 4 5% 21%	3570
	21st to end	Day	6% 12% 7% 18% 6% 5% 5% 4 5% 5% 26%	3960
February	1st to 10th	Day	8% 18% 6% 12% 8% 7% 5% 3 4 6% 25%	1750
	11th to 20th	Day	9% 18% 6% 12% 6% 5% 5% 3 4 5% 27%	1826
	21st to end	Day	13% 18% 6% 9% 6% 5% 5% 3 4 4 26%	1650
March	1st to 10th	Day	16% 19% 5% 12% 7% 6% 4 3 4 3 23%	4476
	11th to 20th	Day	9% 14% 5% 12% 6% 4 5% 3 5% 6% 29%	4740
	21st to end	Day	15% 14% 4 9% 5% 4 4 3 5% 5% 33%	5942
April	1st to 10th	Day	18% 16% 3 8% 6% 4 3 3 4 5% 30%	2400
	11th to 20th	Day	22% 10% 3 7% 4 4 4 3 5% 5% 33%	2374
	21st to end	Day	20% 13% 4 7% 5% 4 4 4 5% 5% 29%	2501
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	23% 13% 3 8% 5% 5% 4 3 4 6% 26%	1881
November	1st to 10th	Day	15% 14% 4 6% 5% 6% 4 4 6% 6% 31%	1761
	11th to 20th	Day	18% 14% 6% 10% 6% 5% 4 4 5% 6% 25%	1672
	21st to end	Day	18% 17% 6% 11% 6% 5% 5% 3 4 4 21%	1600
December	1st to 10th	Day	17% 18% 9% 13% 5% 4 3 4 4 4 18%	2600
	11th to 20th	Day	15% 16% 6% 13% 6% 4 4 3 4 5% 23%	2986
	21st to end	Day	17% 16% 6% 9% 5% 4 4 3 4 5% 26%	3960
January	1st to 10th	Night	10% 20% 8% 16% 6% 5% 4 4 4 5% 19%	6349
	11th to 20th	Night	6% 14% 7% 18% 10% 6% 5% 3 4 6% 20%	6315
	21st to end	Night	6% 12% 7% 18% 9% 6% 6% 4 4 5% 23%	6996
February	1st to 10th	Night	9% 14% 5% 12% 7% 6% 5% 4 5% 6% 27%	2646
	11th to 20th	Night	9% 14% 6% 12% 6% 5% 5% 4 5% 7% 27%	2459
	21st to end	Night	11% 15% 5% 10% 5% 5% 5% 5% 6% 7% 27%	1980
March	1st to 10th	Night	18% 17% 5% 10% 5% 4 4 3 4 5% 25%	5364
	11th to 20th	Night	9% 14% 5% 10% 5% 5% 5% 4 6% 7% 29%	5217
	21st to end	Night	14% 11% 5% 10% 6% 5% 5% 3 5% 6% 30%	4990
April	1st to 10th	Night	20% 13% 3 7% 4 5% 4 3 5% 6% 31%	2000
	11th to 20th	Night	17% 8% 4 7% 5% 5% 3 4 6% 6% 36%	1975
	21st to end	Night	20% 10% 3 8% 4 4 4 4 5% 6% 33%	1800
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%	2717
November	1st to 10th	Night	16% 11% 4 8% 6% 5% 5% 5% 5% 7% 30%	2537
	11th to 20th	Night	16% 11% 4 10% 7% 5% 5% 4 6% 8% 26%	2725
	21st to end	Night	16% 16% 5% 10% 7% 4 4 3 5% 5% 24%	2800
December	1st to 10th	Night	15% 14% 5% 14% 8% 6% 6% 5% 5% 6% 17%	4580
	11th to 20th	Night	19% 15% 5% 11% 7% 4 4 3 3 4 24%	5208
	21st to end	Night	18% 20% 6% 9% 5% 3 3 2 4 6% 25%	6996

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	66% 6% 7% 16% 5%	3598
	11th to 20th	Day	63% 8% 4 14% 8% 3	3600
	21st to end	Day	58% 7% 7% 14% 13% 2	3960
February	1st to 10th	Day	61% 5% 7% 16% 8% 2	1750
	11th to 20th	Day	58% 6% 10% 14% 11% 1	1835
	21st to end	Day	61% 5% 7% 15% 10% 3	1650
March	1st to 10th	Day	66% 4 6% 10% 11% 3	4479
	11th to 20th	Day	53% 7% 14% 12% 11% 3	4740
	21st to end	Day	53% 4 7% 15% 18% 2	5942
April	1st to 10th	Day	56% 4 9% 16% 12% 3	2400
	11th to 20th	Day	52% 6% 8% 20% 12% 2	2374
	21st to end	Day	56% 6% 7% 17% 11% 3	2501
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	46% 7% 13% 25% 8% 1	3209
	11th to 20th	Day	47% 7% 13% 25% 7%	3078
	21st to end	Day	47% 6% 21% 15% 9% 1	3081
November	1st to 10th	Day	52% 7% 13% 18% 10% 1	1761
	11th to 20th	Day	58% 8% 10% 13% 10% 1	1672
	21st to end	Day	62% 9% 10% 13% 5% 1	1600
December	1st to 10th	Day	68% 6% 10% 13% 4	2600
	11th to 20th	Day	61% 5% 8% 17% 10%	2986
	21st to end	Day	62% 4 7% 15% 11%	3960
January	1st to 10th	Night	64% 8% 9% 14% 5%	6349
	11th to 20th	Night	63% 8% 9% 14% 5% 1	6360
	21st to end	Night	59% 8% 7% 10% 15% 1	6996
February	1st to 10th	Night	57% 6% 9% 17% 9% 1	2646
	11th to 20th	Night	55% 6% 10% 18% 9% 1	2461
	21st to end	Night	53% 7% 10% 17% 12% 2	1980
March	1st to 10th	Night	61% 5% 7% 11% 13% 3	5374
	11th to 20th	Night	51% 7% 12% 15% 12% 3	5218
	21st to end	Night	52% 5% 8% 20% 12% 3	4990
April	1st to 10th	Night	54% 4 9% 17% 14% 2	2000
	11th to 20th	Night	47% 6% 11% 21% 14% 2	1975
	21st to end	Night	50% 7% 9% 19% 13% 2	1800
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	44% 7% 13% 24% 12%	3736
	11th to 20th	Night	44% 8% 13% 26% 9%	3841
	21st to end	Night	47% 6% 18% 17% 10% 2	4467
November	1st to 10th	Night	50% 9% 13% 20% 7% 1	2537
	11th to 20th	Night	53% 9% 11% 16% 9% 2	2725
	21st to end	Night	59% 7% 10% 16% 7% 1	2800
December	1st to 10th	Night	62% 8% 14% 12% 4	4580
	11th to 20th	Night	62% 6% 6% 15% 10% 1	5208
	21st to end	Night	61% 5% 5% 13% 15% 1	6996

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% 22% 40% 15% 3	200
	11th to 20th	Day	28% 18% 39% 11% 5% 1	200
	21st to end	Day	20% 23% 40% 15% 2 1	220
February	1st to 10th	Day	29% 31% 31% 7% 1	275
	11th to 20th	Day	26% 27% 39% 8% 1	373
	21st to end	Day	27% 26% 33% 12% 2	414
March	1st to 10th	Day	28% 21% 33% 15% 3	500
	11th to 20th	Day	25% 24% 34% 13% 3 1	500
	21st to end	Day	30% 25% 27% 12% 5% 1	550
April	1st to 10th	Day	31% 22% 29% 12% 5% 1	500
	11th to 20th	Day	36% 20% 23% 13% 7% 1	492
	21st to end	Day	31% 20% 33% 11% 4 1	480
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% 18% 31% 16% 4	429
November	1st to 10th	Day	30% 20% 29% 17% 3 1	395
	11th to 20th	Day	26% 23% 30% 16% 5%	272
	21st to end	Day	29% 27% 31% 11% 3 1	200
December	1st to 10th	Day	29% 21% 31% 14% 5% 1	200
	11th to 20th	Day	26% 30% 34% 9% 2	200
	21st to end	Day	31% 23% 30% 10% 4 2	220
January	1st to 10th	Night	24% 21% 35% 16% 4	800
	11th to 20th	Night	22% 21% 31% 22% 5%	800
	21st to end	Night	14% 18% 40% 22% 6% 1	880
February	1st to 10th	Night	17% 23% 37% 20% 4	800
	11th to 20th	Night	20% 22% 38% 17% 3	783
	21st to end	Night	20% 20% 36% 22% 2	660
March	1st to 10th	Night	27% 18% 33% 19% 3	800
	11th to 20th	Night	23% 20% 34% 17% 5% 1	800
	21st to end	Night	22% 18% 32% 22% 5% 1	880
April	1st to 10th	Night	28% 17% 30% 20% 5%	800
	11th to 20th	Night	25% 17% 30% 22% 5% 1	791
	21st to end	Night	27% 17% 31% 19% 6%	626
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%	836
November	1st to 10th	Night	24% 19% 28% 22% 6% 1	780
	11th to 20th	Night	24% 18% 30% 19% 8% 1	800
	21st to end	Night	27% 24% 27% 17% 5% 1	800
December	1st to 10th	Night	25% 18% 32% 19% 6% 1	800
	11th to 20th	Night	28% 19% 30% 18% 5% 1	800
	21st to end	Night	31% 19% 29% 17% 5%	880

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