Observatoires du Mont Megantic
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoires du Mont Megantic clear sky chart from 2005-11-06 to 2024-11-06.

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	19% 14% 4 10% 6% 5% 4 3 5% 6% 25%	101158
	Night	18% 15% 5% 11% 6% 5% 4 3 4 5% 24%	97898
Transparency	Day	59% 7% 11% 16% 7% 1	104657
	Night	62% 6% 10% 14% 7% 1	102489
Seeing	Day	29% 20% 28% 16% 6% 1	14938
	Night	26% 18% 27% 21% 7% 1	23748

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% 20% 9% 16% 11% 7% 5% 3 5% 3 10%	2517
	11th to 20th	Day	9% 15% 6% 25% 14% 7% 3 2 3 3 14%	2520
	21st to end	Day	10% 18% 9% 17% 7% 7% 5% 3 4 4 16%	2772
February	1st to 10th	Day	12% 20% 7% 16% 11% 6% 4 2 3 2 16%	1582
	11th to 20th	Day	11% 20% 9% 17% 8% 6% 4 3 3 4 14%	1848
	21st to end	Day	11% 21% 4 13% 8% 7% 4 4 5% 4 18%	1570
March	1st to 10th	Day	19% 18% 5% 12% 6% 4 4 3 3 4 22%	3116
	11th to 20th	Day	15% 24% 7% 14% 5% 4 3 2 3 3 19%	3338
	21st to end	Day	17% 17% 6% 13% 4 3 3 2 3 4 27%	4032
April	1st to 10th	Day	20% 20% 5% 10% 6% 2 3 2 3 4 24%	2280
	11th to 20th	Day	17% 17% 5% 8% 4 4 3 2 3 5% 32%	2328
	21st to end	Day	22% 17% 4 8% 4 4 4 3 4 4 26%	2470
May	1st to 10th	Day	24% 13% 3 8% 5% 5% 5% 4 4 5% 25%	4106
	11th to 20th	Day	21% 10% 3 8% 6% 5% 5% 4 6% 6% 26%	4386
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 6% 9% 29%	4837
June	1st to 10th	Day	29% 10% 3 6% 4 4 5% 4 6% 7% 23%	2668
	11th to 20th	Day	20% 9% 2 6% 5% 5% 5% 4 5% 8% 30%	2847
	21st to end	Day	25% 10% 4 7% 5% 5% 5% 3 5% 7% 23%	2660
July	1st to 10th	Day	16% 7% 3 8% 5% 6% 6% 5% 7% 8% 29%	4440
	11th to 20th	Day	18% 8% 3 8% 6% 5% 6% 4 7% 8% 27%	4440
	21st to end	Day	18% 8% 3 6% 5% 5% 4 4 6% 7% 35%	4814
August	1st to 10th	Day	21% 8% 3 8% 5% 6% 6% 5% 6% 7% 24%	4311
	11th to 20th	Day	21% 10% 3 8% 5% 5% 6% 5% 7% 8% 22%	4045
	21st to end	Day	22% 8% 3 5% 4 4 4 4 6% 7% 33%	4288
September	1st to 10th	Day	19% 7% 3 7% 5% 3 5% 3 5% 6% 37%	2280
	11th to 20th	Day	20% 7% 2 6% 3 4 4 3 5% 7% 39%	2099
	21st to end	Day	20% 11% 3 6% 4 4 4 3 6% 8% 32%	2090
October	1st to 10th	Day	22% 13% 2 6% 4 4 5% 3 6% 7% 27%	2090
	11th to 20th	Day	18% 18% 5% 8% 5% 5% 5% 3 5% 6% 24%	1772
	21st to end	Day	22% 24% 5% 7% 4 3 3 3 3 4 21%	1881
November	1st to 10th	Day	18% 21% 5% 8% 5% 3 4 3 4 4 26%	1717
	11th to 20th	Day	17% 19% 7% 12% 7% 3 4 3 4 5% 20%	1710
	21st to end	Day	16% 20% 8% 13% 6% 5% 3 3 4 5% 17%	1558
December	1st to 10th	Day	18% 25% 9% 15% 5% 4 2 2 2 3 13%	1330
	11th to 20th	Day	16% 21% 7% 14% 6% 5% 4 3 3 4 18%	1668
	21st to end	Day	20% 22% 7% 15% 6% 4 3 3 2 3 14%	2748
January	1st to 10th	Night	12% 19% 9% 20% 12% 6% 5% 2 3 3 9%	4429
	11th to 20th	Night	10% 17% 7% 20% 14% 8% 5% 3 3 2 9%	4440
	21st to end	Night	11% 18% 10% 18% 8% 8% 5% 3 3 4 13%	4884
February	1st to 10th	Night	11% 17% 7% 16% 11% 6% 6% 2 4 4 16%	2596
	11th to 20th	Night	10% 20% 7% 19% 8% 7% 6% 2 3 4 15%	2218
	21st to end	Night	11% 18% 7% 13% 8% 7% 6% 3 3 4 22%	1884
March	1st to 10th	Night	20% 20% 4 9% 4 4 5% 2 3 4 24%	3724
	11th to 20th	Night	12% 25% 8% 12% 6% 5% 4 3 3 3 20%	3620
	21st to end	Night	20% 19% 5% 11% 6% 3 3 2 3 3 26%	3598
April	1st to 10th	Night	20% 19% 5% 9% 4 4 3 3 4 4 26%	1900
	11th to 20th	Night	21% 15% 3 7% 4 3 4 4 4 5% 30%	1800
	21st to end	Night	22% 15% 4 6% 4 4 4 3 4 6% 28%	1710
May	1st to 10th	Night	25% 12% 3 7% 3 5% 5% 4 6% 6% 25%	2834
	11th to 20th	Night	19% 10% 3 8% 6% 5% 4 3 5% 6% 31%	2537
	21st to end	Night	20% 6% 3 6% 4 5% 4 4 6% 8% 34%	2738
June	1st to 10th	Night	28% 10% 3 6% 4 4 4 3 5% 7% 26%	1501
	11th to 20th	Night	20% 9% 3 6% 4 4 4 4 6% 7% 35%	1330
	21st to end	Night	22% 9% 3 7% 6% 5% 5% 4 5% 6% 29%	1508
July	1st to 10th	Night	17% 10% 3 8% 6% 5% 5% 4 5% 7% 30%	2520
	11th to 20th	Night	23% 9% 2 7% 4 4 5% 4 5% 7% 30%	2520
	21st to end	Night	17% 7% 2 7% 5% 5% 5% 4 5% 6% 36%	2739
August	1st to 10th	Night	25% 9% 3 7% 5% 3 5% 4 5% 6% 28%	2587
	11th to 20th	Night	19% 9% 3 9% 5% 5% 6% 5% 5% 7% 28%	2782
	21st to end	Night	19% 8% 3 6% 4 4 3 3 5% 6% 39%	3366
September	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 4 5% 40%	1900
	11th to 20th	Night	19% 7% 2 5% 3 4 4 4 5% 5% 43%	2080
	21st to end	Night	20% 8% 2 5% 4 3 3 3 5% 6% 40%	2090
October	1st to 10th	Night	19% 11% 4 7% 4 4 4 3 4 6% 33%	2090
	11th to 20th	Night	21% 17% 3 9% 5% 5% 4 4 4 4 26%	2404
	21st to end	Night	24% 19% 3 8% 4 3 4 3 4 4 23%	2717
November	1st to 10th	Night	21% 19% 5% 9% 5% 4 3 2 4 5% 23%	2483
	11th to 20th	Night	16% 18% 7% 13% 5% 3 4 3 3 5% 23%	2470
	21st to end	Night	15% 20% 9% 14% 7% 5% 3 2 4 4 19%	2616
December	1st to 10th	Night	18% 23% 8% 15% 7% 5% 3 2 3 3 11%	2850
	11th to 20th	Night	16% 22% 8% 17% 8% 5% 3 2 3 3 12%	3531
	21st to end	Night	20% 21% 7% 13% 6% 4 4 2 3 3 17%	4902

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	76% 7% 9% 6% 2	2518
	11th to 20th	Day	76% 5% 4 11% 3 1	2520
	21st to end	Day	70% 7% 8% 7% 6% 2	2772
February	1st to 10th	Day	75% 4 5% 9% 6% 1	1582
	11th to 20th	Day	75% 3 8% 9% 5% 1	1857
	21st to end	Day	67% 5% 7% 12% 6% 2	1570
March	1st to 10th	Day	66% 5% 8% 10% 8% 2	3119
	11th to 20th	Day	70% 5% 7% 10% 6% 1	3338
	21st to end	Day	62% 4 6% 14% 13% 2	4032
April	1st to 10th	Day	65% 3 9% 13% 7% 2	2280
	11th to 20th	Day	56% 4 8% 19% 11% 1	2328
	21st to end	Day	61% 6% 7% 14% 9% 3	2470
May	1st to 10th	Day	59% 8% 10% 15% 7% 1	4120
	11th to 20th	Day	54% 11% 16% 13% 5% 1	4390
	21st to end	Day	47% 11% 14% 19% 9%	4837
June	1st to 10th	Day	58% 8% 10% 18% 5%	2668
	11th to 20th	Day	50% 7% 13% 20% 9% 1	2847
	21st to end	Day	59% 8% 11% 16% 6%	2660
July	1st to 10th	Day	49% 8% 15% 21% 7%	4370
	11th to 20th	Day	50% 8% 15% 23% 3	4365
	21st to end	Day	47% 8% 13% 26% 6%	4661
August	1st to 10th	Day	56% 8% 14% 18% 4	4297
	11th to 20th	Day	56% 10% 16% 14% 4	4084
	21st to end	Day	48% 7% 14% 18% 11% 2	4288
September	1st to 10th	Day	47% 6% 14% 23% 9%	2280
	11th to 20th	Day	45% 5% 12% 26% 12% 1	2099
	21st to end	Day	49% 8% 11% 21% 10% 1	2090
October	1st to 10th	Day	52% 7% 15% 18% 8%	3480
	11th to 20th	Day	57% 6% 10% 20% 6%	2923
	21st to end	Day	57% 4 14% 17% 8%	3081
November	1st to 10th	Day	62% 6% 10% 15% 7% 1	1717
	11th to 20th	Day	67% 6% 8% 11% 6% 2	1710
	21st to end	Day	69% 7% 10% 12% 2	1558
December	1st to 10th	Day	78% 4 6% 7% 5%	1330
	11th to 20th	Day	70% 5% 6% 12% 6% 1	1668
	21st to end	Day	76% 5% 5% 9% 5%	2748
January	1st to 10th	Night	78% 7% 7% 6% 2	4429
	11th to 20th	Night	81% 6% 5% 6% 2	4440
	21st to end	Night	74% 6% 7% 7% 4 1	4884
February	1st to 10th	Night	72% 5% 7% 10% 5% 1	2596
	11th to 20th	Night	74% 5% 7% 9% 5% 1	2220
	21st to end	Night	67% 5% 6% 13% 8% 1	1884
March	1st to 10th	Night	64% 5% 10% 14% 5% 2	3734
	11th to 20th	Night	69% 6% 7% 11% 6% 1	3621
	21st to end	Night	65% 4 5% 14% 11% 2	3598
April	1st to 10th	Night	62% 5% 7% 15% 10% 1	1900
	11th to 20th	Night	54% 7% 10% 17% 11% 1	1800
	21st to end	Night	57% 7% 10% 15% 10% 2	1710
May	1st to 10th	Night	54% 11% 15% 14% 7% 1	2840
	11th to 20th	Night	51% 9% 16% 17% 6% 1	2538
	21st to end	Night	45% 10% 15% 17% 13%	2739
June	1st to 10th	Night	57% 6% 12% 19% 6%	1501
	11th to 20th	Night	46% 9% 13% 22% 9% 2	1330
	21st to end	Night	55% 8% 11% 18% 7%	1508
July	1st to 10th	Night	52% 7% 15% 19% 7%	2480
	11th to 20th	Night	51% 8% 15% 21% 5%	2472
	21st to end	Night	46% 9% 12% 26% 6%	2651
August	1st to 10th	Night	55% 7% 14% 20% 3	2577
	11th to 20th	Night	53% 10% 16% 15% 5%	2809
	21st to end	Night	45% 7% 14% 21% 13% 1	3366
September	1st to 10th	Night	46% 7% 14% 24% 10%	1900
	11th to 20th	Night	42% 6% 14% 27% 10% 1	2080
	21st to end	Night	45% 6% 13% 24% 11% 1	2090
October	1st to 10th	Night	51% 6% 12% 20% 11%	3480
	11th to 20th	Night	57% 5% 9% 20% 8%	3992
	21st to end	Night	56% 6% 13% 15% 8% 2	4467
November	1st to 10th	Night	64% 5% 11% 14% 6% 1	2483
	11th to 20th	Night	64% 5% 10% 12% 7% 2	2470
	21st to end	Night	70% 5% 11% 10% 4	2616
December	1st to 10th	Night	79% 4 6% 8% 3	2850
	11th to 20th	Night	77% 5% 5% 7% 5%	3532
	21st to end	Night	72% 6% 9% 9% 5%	4902

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	31% 26% 33% 10%	180
	11th to 20th	Day	33% 27% 25% 13% 1 1	180
	21st to end	Day	22% 25% 37% 13% 3 1	198
February	1st to 10th	Day	37% 30% 24% 7% 1	232
	11th to 20th	Day	31% 30% 30% 6% 2	456
	21st to end	Day	32% 26% 29% 12% 2	382
March	1st to 10th	Day	31% 25% 30% 11% 3	460
	11th to 20th	Day	32% 30% 22% 13% 4	460
	21st to end	Day	35% 23% 23% 12% 7%	506
April	1st to 10th	Day	41% 17% 24% 12% 5%	460
	11th to 20th	Day	34% 24% 24% 12% 4 2	452
	21st to end	Day	36% 22% 26% 11% 4 1	460
May	1st to 10th	Day	40% 17% 26% 13% 3 1	463
	11th to 20th	Day	27% 17% 31% 18% 5% 1	487
	21st to end	Day	23% 23% 32% 18% 4 1	529
June	1st to 10th	Day	34% 18% 30% 14% 5% 1	498
	11th to 20th	Day	24% 15% 28% 23% 9%	677
	21st to end	Day	30% 17% 31% 16% 6% 1	490
July	1st to 10th	Day	22% 14% 35% 23% 6% 1	485
	11th to 20th	Day	20% 14% 38% 19% 7% 1	484
	21st to end	Day	23% 13% 33% 24% 5% 1	532
August	1st to 10th	Day	21% 16% 30% 24% 9% 1	486
	11th to 20th	Day	22% 11% 30% 24% 10% 3	479
	21st to end	Day	24% 16% 26% 20% 10% 5%	539
September	1st to 10th	Day	23% 13% 31% 20% 11% 3	490
	11th to 20th	Day	22% 11% 24% 21% 16% 6%	490
	21st to end	Day	21% 15% 27% 21% 12% 4	490
October	1st to 10th	Day	27% 18% 23% 19% 9% 3	490
	11th to 20th	Day	30% 20% 26% 13% 9% 1	410
	21st to end	Day	38% 24% 21% 14% 3	429
November	1st to 10th	Day	35% 20% 29% 12% 4	381
	11th to 20th	Day	27% 24% 31% 11% 6% 2	370
	21st to end	Day	32% 25% 27% 12% 4 1	255
December	1st to 10th	Day	31% 28% 26% 13% 2	180
	11th to 20th	Day	37% 29% 25% 6% 2 1	180
	21st to end	Day	36% 28% 27% 7% 2 1	198
January	1st to 10th	Night	25% 28% 33% 11% 2	760
	11th to 20th	Night	25% 28% 29% 15% 3	760
	21st to end	Night	18% 26% 35% 17% 4 1	836
February	1st to 10th	Night	21% 28% 35% 14% 3	760
	11th to 20th	Night	23% 28% 34% 13% 2	743
	21st to end	Night	24% 24% 34% 16% 2	628
March	1st to 10th	Night	28% 20% 33% 17% 2	760
	11th to 20th	Night	27% 24% 28% 16% 4 1	760
	21st to end	Night	28% 20% 26% 19% 6% 1	836
April	1st to 10th	Night	32% 21% 25% 17% 4	760
	11th to 20th	Night	30% 18% 27% 19% 5% 1	676
	21st to end	Night	31% 21% 26% 18% 4 1	570
May	1st to 10th	Night	29% 15% 30% 19% 6% 1	570
	11th to 20th	Night	22% 14% 30% 27% 7%	403
	21st to end	Night	24% 11% 31% 27% 7%	411
June	1st to 10th	Night	32% 8% 27% 24% 9%	380
	11th to 20th	Night	23% 7% 23% 33% 13%	380
	21st to end	Night	22% 8% 28% 32% 10%	380
July	1st to 10th	Night	17% 8% 30% 35% 10% 1	370
	11th to 20th	Night	18% 8% 26% 35% 12% 1	368
	21st to end	Night	19% 6% 21% 41% 12%	416
August	1st to 10th	Night	21% 4 20% 36% 19% 1	420
	11th to 20th	Night	17% 8% 23% 35% 17% 1	562
	21st to end	Night	21% 8% 24% 29% 16% 2	765
September	1st to 10th	Night	22% 8% 26% 31% 13% 1	760
	11th to 20th	Night	23% 8% 20% 27% 20% 2	760
	21st to end	Night	24% 11% 24% 25% 15% 1	760
October	1st to 10th	Night	26% 11% 25% 25% 12% 1	760
	11th to 20th	Night	30% 15% 24% 21% 7% 2	760
	21st to end	Night	35% 19% 25% 17% 4	836
November	1st to 10th	Night	34% 18% 25% 17% 6%	764
	11th to 20th	Night	27% 22% 28% 14% 7% 2	760
	21st to end	Night	30% 24% 26% 16% 4 1	775
December	1st to 10th	Night	31% 25% 26% 14% 3	850
	11th to 20th	Night	30% 25% 26% 14% 4	850
	21st to end	Night	35% 25% 26% 13% 2	839

Page generated at 2024-11-03 13:19:01. Version ac07

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