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 2025-11-03.

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	18% 13% 5% 10% 6% 5% 5% 3 5% 6% 24%	126225
	Night	17% 15% 5% 12% 7% 5% 5% 3 4 5% 23%	123827
Transparency	Day	59% 7% 11% 16% 7% 1	129706
	Night	63% 6% 10% 14% 7% 1	128434
Seeing	Day	29% 20% 28% 16% 6% 1	16202
	Night	26% 18% 27% 21% 7% 1	24996

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% 18% 10% 18% 13% 8% 6% 2 3 2 7%	3597
	11th to 20th	Day	7% 14% 7% 29% 17% 6% 4 3 2 2 10%	3570
	21st to end	Day	7% 17% 8% 18% 8% 10% 8% 3 3 3 15%	3960
February	1st to 10th	Day	12% 19% 7% 17% 12% 7% 4 2 3 2 15%	1666
	11th to 20th	Day	12% 19% 9% 18% 9% 6% 4 3 3 4 14%	1948
	21st to end	Day	10% 20% 4 14% 9% 8% 4 4 4 4 18%	1650
March	1st to 10th	Day	16% 17% 6% 15% 8% 4 5% 3 3 3 18%	4476
	11th to 20th	Day	13% 18% 5% 11% 6% 5% 4 3 4 6% 24%	4782
	21st to end	Day	20% 17% 7% 12% 5% 4 3 2 3 4 23%	5780
April	1st to 10th	Day	20% 21% 5% 10% 6% 2 3 2 3 4 24%	2400
	11th to 20th	Day	18% 17% 5% 8% 4 4 3 2 3 5% 31%	2452
	21st to end	Day	22% 17% 4 8% 4 4 4 3 4 4 26%	2600
May	1st to 10th	Day	29% 14% 4 8% 6% 5% 5% 3 4 4 19%	5886
	11th to 20th	Day	21% 10% 3 8% 6% 5% 5% 4 6% 6% 26%	6306
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 4 6% 7% 27%	6949
June	1st to 10th	Day	29% 10% 3 6% 4 4 5% 4 6% 7% 23%	2808
	11th to 20th	Day	20% 9% 2 6% 5% 5% 5% 4 5% 8% 30%	2997
	21st to end	Day	24% 10% 4 7% 5% 5% 5% 3 5% 7% 24%	2800
July	1st to 10th	Day	18% 8% 4 9% 6% 6% 6% 5% 7% 8% 24%	6360
	11th to 20th	Day	17% 8% 2 7% 5% 5% 6% 4 7% 8% 30%	6360
	21st to end	Day	17% 8% 2 5% 4 5% 5% 4 6% 8% 36%	6926
August	1st to 10th	Day	20% 8% 3 8% 5% 6% 6% 4 6% 8% 26%	4448
	11th to 20th	Day	21% 10% 3 8% 5% 5% 6% 5% 7% 8% 23%	4175
	21st to end	Day	21% 8% 3 5% 4 4 4 4 6% 7% 32%	4423
September	1st to 10th	Day	19% 7% 3 7% 4 3 5% 3 5% 6% 38%	2400
	11th to 20th	Day	19% 8% 2 6% 3 4 4 3 5% 7% 40%	2209
	21st to end	Day	19% 11% 3 6% 4 4 4 3 6% 8% 32%	2200
October	1st to 10th	Day	21% 13% 2 6% 4 4 5% 3 6% 7% 30%	2200
	11th to 20th	Day	18% 18% 5% 8% 5% 5% 5% 3 5% 6% 24%	1865
	21st to end	Day	23% 23% 5% 7% 5% 3 3 3 3 4 21%	1980
November	1st to 10th	Day	18% 21% 5% 8% 5% 3 4 3 4 4 25%	1779
	11th to 20th	Day	16% 19% 7% 12% 7% 3 4 3 3 5% 21%	1800
	21st to end	Day	16% 21% 8% 12% 6% 4 3 2 4 5% 16%	1639
December	1st to 10th	Day	14% 22% 9% 21% 11% 5% 3 2 2 2 10%	2280
	11th to 20th	Day	15% 19% 9% 15% 6% 5% 4 3 3 3 19%	2618
	21st to end	Day	16% 21% 6% 14% 6% 4 5% 3 3 4 17%	3936
January	1st to 10th	Night	10% 17% 9% 24% 13% 8% 6% 2 3 2 6%	6349
	11th to 20th	Night	8% 18% 8% 25% 15% 8% 4 3 2 2 7%	6315
	21st to end	Night	8% 14% 9% 17% 9% 10% 7% 4 4 4 14%	6996
February	1st to 10th	Night	11% 17% 7% 16% 11% 6% 6% 2 4 4 16%	2731
	11th to 20th	Night	10% 19% 6% 19% 9% 7% 5% 2 3 3 14%	2338
	21st to end	Night	11% 18% 7% 14% 8% 7% 5% 3 3 4 21%	1980
March	1st to 10th	Night	18% 18% 6% 15% 5% 5% 7% 2 3 3 18%	5364
	11th to 20th	Night	12% 20% 6% 11% 6% 5% 4 3 4 5% 23%	5176
	21st to end	Night	18% 18% 6% 11% 6% 4 3 2 4 3 24%	5150
April	1st to 10th	Night	21% 18% 5% 9% 4 4 3 3 4 3 26%	2000
	11th to 20th	Night	20% 16% 3 7% 4 3 4 4 4 5% 30%	1896
	21st to end	Night	22% 15% 4 6% 4 4 4 3 4 6% 28%	1800
May	1st to 10th	Night	28% 13% 3 8% 3 4 4 4 5% 5% 21%	4054
	11th to 20th	Night	22% 11% 3 7% 5% 5% 4 3 5% 6% 29%	3631
	21st to end	Night	23% 8% 3 6% 4 5% 4 4 5% 7% 31%	3926
June	1st to 10th	Night	27% 10% 3 6% 4 4 4 3 6% 6% 26%	1580
	11th to 20th	Night	20% 9% 3 7% 4 4 4 4 6% 7% 34%	1400
	21st to end	Night	21% 9% 2 7% 5% 5% 5% 4 5% 6% 29%	1588
July	1st to 10th	Night	19% 10% 4 9% 6% 5% 5% 4 5% 7% 27%	3600
	11th to 20th	Night	22% 8% 2 6% 4 4 5% 4 5% 7% 34%	3600
	21st to end	Night	15% 8% 3 6% 5% 5% 6% 5% 6% 7% 36%	3926
August	1st to 10th	Night	25% 9% 3 7% 5% 3 5% 4 5% 6% 30%	2669
	11th to 20th	Night	18% 9% 3 9% 5% 5% 6% 4 5% 7% 29%	2872
	21st to end	Night	19% 9% 3 6% 4 4 3 3 5% 6% 39%	3472
September	1st to 10th	Night	18% 8% 2 7% 4 4 4 3 4 5% 40%	2000
	11th to 20th	Night	18% 7% 2 5% 3 4 4 4 5% 5% 44%	2190
	21st to end	Night	20% 8% 2 6% 4 3 4 3 5% 6% 40%	2200
October	1st to 10th	Night	19% 11% 4 7% 4 4 4 3 4 6% 35%	2200
	11th to 20th	Night	21% 16% 3 9% 5% 5% 4 4 4 4 26%	2531
	21st to end	Night	24% 19% 4 8% 4 3 4 3 4 4 23%	2860
November	1st to 10th	Night	21% 19% 5% 9% 5% 4 3 2 4 5% 23%	2564
	11th to 20th	Night	17% 18% 7% 12% 5% 3 3 3 3 5% 24%	2600
	21st to end	Night	15% 21% 9% 13% 7% 4 3 2 4 4 18%	2754
December	1st to 10th	Night	14% 21% 11% 24% 10% 5% 3 2 2 2 8%	4910
	11th to 20th	Night	16% 21% 7% 17% 9% 4 3 2 3 3 13%	5591
	21st to end	Night	17% 20% 6% 12% 6% 4 5% 2 4 4 20%	7014

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	82% 6% 7% 5% 1	3598
	11th to 20th	Day	80% 5% 4 8% 2 1	3600
	21st to end	Day	72% 7% 6% 7% 7% 1	3960
February	1st to 10th	Day	76% 3 5% 8% 6% 1	1666
	11th to 20th	Day	75% 3 8% 9% 4 1	1957
	21st to end	Day	68% 5% 7% 12% 6% 2	1650
March	1st to 10th	Day	70% 5% 6% 8% 7% 4	4479
	11th to 20th	Day	61% 5% 13% 12% 8% 1	4782
	21st to end	Day	65% 4 6% 12% 12% 1	5780
April	1st to 10th	Day	65% 3 8% 14% 8% 2	2400
	11th to 20th	Day	57% 4 8% 19% 11% 1	2452
	21st to end	Day	61% 5% 7% 15% 9% 2	2600
May	1st to 10th	Day	67% 7% 8% 13% 5%	5897
	11th to 20th	Day	55% 10% 13% 14% 6% 2	6310
	21st to end	Day	52% 9% 12% 18% 8% 1	6949
June	1st to 10th	Day	58% 8% 10% 18% 6%	2808
	11th to 20th	Day	50% 7% 13% 20% 8% 1	2997
	21st to end	Day	58% 8% 11% 17% 6%	2800
July	1st to 10th	Day	54% 8% 15% 17% 6%	6290
	11th to 20th	Day	47% 9% 14% 25% 5%	6285
	21st to end	Day	44% 8% 14% 28% 6%	6728
August	1st to 10th	Day	54% 8% 15% 19% 4	4434
	11th to 20th	Day	55% 10% 16% 15% 4	4214
	21st to end	Day	48% 7% 14% 18% 11% 2	4423
September	1st to 10th	Day	46% 6% 14% 25% 9%	2400
	11th to 20th	Day	44% 5% 12% 27% 12% 1	2209
	21st to end	Day	48% 8% 11% 21% 11% 1	2200
October	1st to 10th	Day	51% 7% 15% 19% 9%	3590
	11th to 20th	Day	57% 6% 10% 21% 6%	3016
	21st to end	Day	57% 4 14% 17% 8%	3180
November	1st to 10th	Day	61% 6% 10% 15% 7% 1	1779
	11th to 20th	Day	66% 6% 7% 11% 7% 2	1800
	21st to end	Day	70% 6% 10% 12% 2	1639
December	1st to 10th	Day	82% 4 6% 5% 3	2280
	11th to 20th	Day	68% 5% 7% 12% 8% 1	2618
	21st to end	Day	71% 5% 5% 9% 8% 3	3936
January	1st to 10th	Night	83% 5% 6% 4 1	6349
	11th to 20th	Night	85% 4 4 5% 2	6360
	21st to end	Night	69% 8% 7% 7% 8% 1	6996
February	1st to 10th	Night	72% 5% 7% 10% 5% 1	2731
	11th to 20th	Night	75% 5% 7% 9% 5% 1	2340
	21st to end	Night	67% 5% 5% 13% 8% 1	1980
March	1st to 10th	Night	71% 4 8% 10% 5% 2	5374
	11th to 20th	Night	63% 6% 12% 11% 7% 1	5177
	21st to end	Night	64% 4 5% 13% 12% 1	5150
April	1st to 10th	Night	62% 5% 7% 15% 10% 1	2000
	11th to 20th	Night	55% 7% 10% 17% 11% 1	1896
	21st to end	Night	57% 7% 10% 15% 9% 2	1800
May	1st to 10th	Night	61% 9% 12% 11% 6%	4060
	11th to 20th	Night	54% 9% 14% 18% 5% 1	3632
	21st to end	Night	51% 8% 14% 16% 12%	3927
June	1st to 10th	Night	57% 6% 12% 18% 7%	1580
	11th to 20th	Night	47% 9% 13% 21% 9% 2	1400
	21st to end	Night	54% 8% 11% 19% 8%	1588
July	1st to 10th	Night	55% 7% 15% 18% 5%	3560
	11th to 20th	Night	48% 7% 15% 24% 6%	3552
	21st to end	Night	45% 9% 14% 26% 6%	3809
August	1st to 10th	Night	54% 7% 14% 21% 4	2659
	11th to 20th	Night	52% 10% 16% 16% 6%	2899
	21st to end	Night	45% 7% 14% 21% 13% 1	3472
September	1st to 10th	Night	45% 7% 13% 25% 9%	2000
	11th to 20th	Night	41% 6% 14% 28% 11% 1	2190
	21st to end	Night	45% 6% 13% 24% 11% 1	2200
October	1st to 10th	Night	49% 6% 12% 21% 11%	3590
	11th to 20th	Night	57% 5% 9% 20% 8%	4119
	21st to end	Night	56% 6% 13% 15% 8% 2	4610
November	1st to 10th	Night	64% 5% 11% 14% 6% 1	2564
	11th to 20th	Night	64% 5% 9% 12% 8% 2	2600
	21st to end	Night	71% 5% 11% 9% 4	2754
December	1st to 10th	Night	85% 4 5% 5% 1	4910
	11th to 20th	Night	77% 4 4 8% 6%	5592
	21st to end	Night	68% 6% 8% 10% 8% 2	7014

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% 27% 34% 9%	200
	11th to 20th	Day	32% 27% 26% 13% 2 1	200
	21st to end	Day	26% 26% 34% 11% 2	220
February	1st to 10th	Day	36% 30% 25% 7% 1	256
	11th to 20th	Day	32% 29% 31% 6% 2	496
	21st to end	Day	31% 26% 29% 12% 1	414
March	1st to 10th	Day	31% 26% 29% 10% 3	500
	11th to 20th	Day	32% 30% 22% 12% 3	500
	21st to end	Day	35% 23% 23% 12% 6%	550
April	1st to 10th	Day	42% 17% 25% 11% 5%	500
	11th to 20th	Day	35% 24% 23% 12% 4 1	492
	21st to end	Day	37% 22% 26% 11% 4 1	500
May	1st to 10th	Day	41% 17% 26% 12% 3 1	503
	11th to 20th	Day	28% 18% 30% 18% 5% 2	527
	21st to end	Day	24% 23% 31% 18% 4 1	573
June	1st to 10th	Day	33% 18% 31% 13% 4 1	538
	11th to 20th	Day	24% 16% 28% 22% 9%	727
	21st to end	Day	29% 17% 32% 16% 6% 1	530
July	1st to 10th	Day	22% 15% 35% 21% 6% 1	525
	11th to 20th	Day	20% 15% 38% 19% 7% 1	524
	21st to end	Day	23% 14% 33% 24% 5% 1	576
August	1st to 10th	Day	19% 15% 30% 25% 10% 1	526
	11th to 20th	Day	21% 10% 30% 24% 12% 3	519
	21st to end	Day	24% 16% 27% 20% 9% 4	583
September	1st to 10th	Day	22% 13% 30% 20% 11% 3	530
	11th to 20th	Day	21% 11% 25% 21% 16% 7%	530
	21st to end	Day	22% 15% 27% 21% 11% 4	530
October	1st to 10th	Day	26% 18% 24% 20% 9% 3	530
	11th to 20th	Day	30% 21% 26% 14% 8% 1	442
	21st to end	Day	38% 24% 21% 15% 3	462
November	1st to 10th	Day	36% 20% 27% 12% 3	401
	11th to 20th	Day	28% 24% 31% 11% 5% 2	400
	21st to end	Day	34% 25% 26% 11% 3 1	278
December	1st to 10th	Day	30% 28% 28% 13% 2	200
	11th to 20th	Day	38% 28% 26% 7% 2 1	200
	21st to end	Day	35% 26% 27% 7% 5%	220
January	1st to 10th	Night	25% 29% 34% 11% 2	800
	11th to 20th	Night	24% 28% 29% 15% 3	800
	21st to end	Night	18% 27% 35% 16% 4 1	880
February	1st to 10th	Night	22% 27% 34% 14% 3	800
	11th to 20th	Night	23% 28% 34% 13% 2	783
	21st to end	Night	24% 24% 34% 16% 2	660
March	1st to 10th	Night	28% 21% 33% 16% 2	800
	11th to 20th	Night	27% 25% 28% 16% 4 1	800
	21st to end	Night	28% 21% 26% 20% 5% 1	880
April	1st to 10th	Night	33% 21% 25% 17% 4	800
	11th to 20th	Night	30% 18% 27% 19% 5% 1	712
	21st to end	Night	32% 20% 26% 18% 4 1	600
May	1st to 10th	Night	29% 16% 30% 19% 6% 1	600
	11th to 20th	Night	23% 14% 30% 26% 7%	424
	21st to end	Night	24% 11% 30% 27% 7%	433
June	1st to 10th	Night	31% 8% 28% 24% 9%	400
	11th to 20th	Night	24% 9% 23% 32% 12%	400
	21st to end	Night	22% 9% 29% 32% 9%	400
July	1st to 10th	Night	17% 8% 30% 35% 9% 1	390
	11th to 20th	Night	18% 9% 26% 35% 11% 1	388
	21st to end	Night	18% 7% 21% 42% 12%	438
August	1st to 10th	Night	20% 4 19% 37% 19% 1	442
	11th to 20th	Night	17% 8% 22% 34% 18% 1	592
	21st to end	Night	21% 8% 24% 30% 16% 2	805
September	1st to 10th	Night	22% 8% 25% 31% 13% 1	800
	11th to 20th	Night	22% 8% 20% 28% 20% 2	800
	21st to end	Night	24% 11% 25% 25% 14% 1	800
October	1st to 10th	Night	25% 11% 25% 25% 13% 1	800
	11th to 20th	Night	30% 15% 25% 22% 7% 2	800
	21st to end	Night	34% 19% 26% 17% 4	880
November	1st to 10th	Night	33% 19% 24% 18% 5%	789
	11th to 20th	Night	27% 22% 28% 15% 7% 2	800
	21st to end	Night	30% 24% 26% 15% 4 1	817
December	1st to 10th	Night	30% 25% 27% 14% 3	900
	11th to 20th	Night	31% 25% 25% 14% 4	900
	21st to end	Night	34% 24% 26% 14% 2	883

Page generated at 2025-10-31 02:02:40. Version ac07

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