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 2024-01-31.

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% 13% 5% 8% 7% 3 5% 4 5% 6% 25%	74631
	Night	18% 15% 6% 10% 7% 4 5% 4 4 5% 24%	75469
Transparency	Day	60% 6% 10% 15% 7% 1	74336
	Night	62% 6% 10% 15% 7% 1	75299
Seeing	Day	29% 20% 28% 16% 6% 1	13850
	Night	26% 18% 27% 20% 7% 1	22845

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% 19% 10% 14% 12% 5% 5% 3 4 3 11%	1517
	11th to 20th	Day	15% 18% 7% 14% 12% 4 5% 4 3 3 15%	1520
	21st to end	Day	9% 14% 9% 13% 11% 5% 7% 5% 4 4 18%	1664
February	1st to 10th	Day	13% 19% 8% 14% 13% 6% 5% 3 3 2 14%	1499
	11th to 20th	Day	13% 18% 10% 16% 9% 4 5% 4 3 4 14%	1748
	21st to end	Day	11% 20% 6% 12% 9% 6% 6% 4 4 4 18%	1480
March	1st to 10th	Day	12% 18% 8% 12% 9% 4 4 4 3 4 22%	1797
	11th to 20th	Day	15% 15% 7% 9% 8% 4 4 4 3 5% 25%	1894
	21st to end	Day	17% 18% 8% 11% 6% 3 4 3 3 3 25%	2298
April	1st to 10th	Day	21% 18% 7% 9% 6% 2 3 2 4 4 24%	2160
	11th to 20th	Day	18% 15% 5% 7% 4 3 3 3 3 5% 33%	2204
	21st to end	Day	23% 17% 4 8% 5% 2 4 4 4 4 25%	2340
May	1st to 10th	Day	24% 13% 4 6% 6% 3 4 3 4 4 29%	2340
	11th to 20th	Day	22% 11% 3 6% 6% 3 4 4 5% 5% 31%	2466
	21st to end	Day	21% 8% 3 7% 6% 4 5% 5% 6% 9% 27%	2725
June	1st to 10th	Day	30% 9% 3 6% 5% 3 4 5% 5% 7% 23%	2527
	11th to 20th	Day	21% 8% 3 6% 6% 3 5% 4 5% 8% 30%	2698
	21st to end	Day	24% 9% 4 7% 6% 4 5% 4 5% 7% 24%	2520
July	1st to 10th	Day	19% 7% 3 6% 6% 4 5% 5% 6% 8% 31%	2520
	11th to 20th	Day	19% 8% 3 6% 7% 4 6% 6% 7% 8% 27%	2520
	21st to end	Day	22% 8% 3 6% 6% 4 5% 6% 6% 8% 25%	2744
August	1st to 10th	Day	20% 8% 3 7% 6% 3 6% 6% 6% 8% 27%	2449
	11th to 20th	Day	19% 8% 3 6% 6% 3 5% 6% 7% 9% 29%	2304
	21st to end	Day	22% 8% 2 4 5% 3 4 5% 6% 7% 33%	2442
September	1st to 10th	Day	20% 7% 3 6% 5% 2 5% 4 5% 6% 36%	2160
	11th to 20th	Day	21% 7% 2 5% 4 3 4 3 5% 7% 38%	1989
	21st to end	Day	20% 10% 3 5% 5% 3 5% 4 6% 8% 32%	1980
October	1st to 10th	Day	23% 12% 3 5% 4 3 5% 5% 6% 7% 27%	1980
	11th to 20th	Day	19% 16% 5% 8% 6% 3 5% 5% 5% 5% 23%	1679
	21st to end	Day	24% 23% 6% 6% 5% 2 3 4 3 4 19%	1782
November	1st to 10th	Day	19% 20% 5% 8% 5% 2 4 5% 4 4 26%	1671
	11th to 20th	Day	17% 17% 9% 11% 7% 3 4 4 4 5% 20%	1710
	21st to end	Day	16% 19% 8% 11% 8% 3 4 3 4 5% 18%	1558
December	1st to 10th	Day	18% 23% 11% 14% 6% 4 2 3 2 3 14%	1330
	11th to 20th	Day	17% 19% 8% 12% 7% 3 6% 3 3 4 19%	1668
	21st to end	Day	20% 22% 7% 12% 9% 3 4 3 2 3 14%	2748
January	1st to 10th	Night	12% 22% 9% 16% 11% 5% 5% 4 4 3 10%	2649
	11th to 20th	Night	13% 17% 8% 15% 12% 5% 7% 4 4 3 11%	2660
	21st to end	Night	10% 14% 8% 15% 11% 7% 8% 5% 4 4 15%	2919
February	1st to 10th	Night	11% 17% 8% 14% 12% 5% 7% 3 4 4 15%	2459
	11th to 20th	Night	11% 19% 8% 16% 10% 5% 7% 4 3 4 15%	2098
	21st to end	Night	12% 17% 7% 12% 9% 5% 7% 4 2 4 21%	1776
March	1st to 10th	Night	13% 18% 8% 11% 7% 4 5% 3 3 4 22%	2150
	11th to 20th	Night	15% 16% 6% 10% 6% 4 5% 4 3 5% 25%	2064
	21st to end	Night	17% 17% 7% 10% 6% 3 4 2 4 4 28%	2056
April	1st to 10th	Night	21% 18% 5% 8% 4 3 4 3 4 3 25%	1800
	11th to 20th	Night	21% 14% 4 6% 4 2 4 4 4 5% 32%	1705
	21st to end	Night	23% 14% 4 5% 5% 3 4 4 4 6% 27%	1620
May	1st to 10th	Night	24% 13% 4 6% 4 3 4 5% 5% 6% 28%	1620
	11th to 20th	Night	20% 10% 4 6% 6% 4 5% 4 4 5% 32%	1443
	21st to end	Night	22% 7% 3 6% 5% 4 4 4 6% 7% 32%	1550
June	1st to 10th	Night	28% 9% 4 6% 5% 3 4 4 5% 6% 26%	1422
	11th to 20th	Night	20% 8% 3 5% 4 3 4 4 5% 7% 35%	1260
	21st to end	Night	21% 7% 3 7% 6% 4 5% 5% 6% 6% 30%	1428
July	1st to 10th	Night	17% 8% 3 5% 6% 3 5% 5% 6% 7% 34%	1440
	11th to 20th	Night	15% 6% 2 6% 6% 4 6% 7% 6% 10% 31%	1440
	21st to end	Night	17% 7% 3 5% 5% 4 7% 6% 5% 7% 33%	1574
August	1st to 10th	Night	17% 6% 2 5% 5% 2 5% 6% 7% 8% 35%	1471
	11th to 20th	Night	17% 8% 3 8% 6% 2 5% 4 5% 7% 35%	1596
	21st to end	Night	18% 8% 3 6% 5% 3 3 4 4 7% 39%	1912
September	1st to 10th	Night	19% 8% 3 6% 5% 3 4 4 4 6% 39%	1800
	11th to 20th	Night	20% 7% 2 4 4 3 4 5% 5% 6% 41%	1970
	21st to end	Night	21% 8% 2 4 4 2 4 3 4 6% 41%	1980
October	1st to 10th	Night	20% 11% 4 6% 5% 3 5% 5% 4 6% 33%	1980
	11th to 20th	Night	22% 15% 3 8% 6% 3 4 5% 4 4 25%	2277
	21st to end	Night	26% 19% 3 7% 5% 2 4 4 4 5% 22%	2574
November	1st to 10th	Night	21% 18% 6% 8% 6% 3 4 3 4 5% 23%	2407
	11th to 20th	Night	17% 16% 8% 11% 6% 3 4 4 3 5% 24%	2470
	21st to end	Night	15% 18% 9% 12% 9% 3 4 3 4 4 19%	2616
December	1st to 10th	Night	19% 21% 9% 14% 8% 4 4 3 3 3 12%	2850
	11th to 20th	Night	16% 20% 10% 15% 10% 4 4 3 3 3 12%	3531
	21st to end	Night	20% 20% 7% 12% 7% 3 4 3 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	79% 4 8% 6% 3	1518
	11th to 20th	Day	74% 4 5% 11% 4 1	1520
	21st to end	Day	68% 6% 8% 10% 7% 1	1664
February	1st to 10th	Day	77% 3 5% 8% 5% 1	1499
	11th to 20th	Day	75% 3 8% 9% 5% 1	1757
	21st to end	Day	69% 5% 7% 12% 6% 2	1480
March	1st to 10th	Day	67% 5% 8% 13% 5% 3	1800
	11th to 20th	Day	62% 5% 9% 11% 10% 2	1894
	21st to end	Day	66% 3 7% 14% 8% 2	2298
April	1st to 10th	Day	66% 3 9% 13% 7% 2	2160
	11th to 20th	Day	56% 4 8% 19% 12% 1	2204
	21st to end	Day	62% 6% 8% 14% 9% 3	2340
May	1st to 10th	Day	58% 5% 7% 18% 11% 1	2340
	11th to 20th	Day	54% 6% 12% 17% 9% 1	2470
	21st to end	Day	54% 9% 13% 16% 9% 1	2725
June	1st to 10th	Day	59% 8% 10% 17% 5% 1	2527
	11th to 20th	Day	51% 7% 13% 20% 8% 1	2698
	21st to end	Day	58% 8% 12% 16% 6%	2520
July	1st to 10th	Day	50% 8% 15% 21% 7%	2450
	11th to 20th	Day	52% 8% 14% 20% 6%	2445
	21st to end	Day	55% 9% 13% 18% 5%	2591
August	1st to 10th	Day	52% 9% 16% 20% 3	2435
	11th to 20th	Day	49% 10% 16% 17% 7%	2304
	21st to end	Day	48% 8% 13% 19% 11%	2442
September	1st to 10th	Day	48% 7% 14% 22% 9% 1	2160
	11th to 20th	Day	46% 5% 11% 26% 12% 1	1989
	21st to end	Day	49% 8% 11% 22% 10% 1	1980
October	1st to 10th	Day	55% 7% 13% 17% 9%	1980
	11th to 20th	Day	61% 7% 13% 15% 5%	1679
	21st to end	Day	69% 5% 9% 11% 6% 1	1782
November	1st to 10th	Day	61% 6% 10% 15% 7% 1	1671
	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	80% 4 6% 7% 3	2649
	11th to 20th	Night	78% 5% 6% 7% 3 1	2660
	21st to end	Night	71% 6% 7% 9% 5% 1	2919
February	1st to 10th	Night	73% 5% 7% 10% 5% 1	2459
	11th to 20th	Night	74% 5% 6% 9% 5% 1	2100
	21st to end	Night	68% 5% 5% 13% 9% 1	1776
March	1st to 10th	Night	66% 4 8% 14% 6% 2	2160
	11th to 20th	Night	62% 7% 9% 11% 10% 2	2065
	21st to end	Night	61% 4 7% 17% 8% 3	2056
April	1st to 10th	Night	63% 5% 7% 14% 10% 1	1800
	11th to 20th	Night	53% 6% 10% 18% 11% 1	1705
	21st to end	Night	58% 7% 10% 15% 9% 2	1620
May	1st to 10th	Night	55% 7% 9% 16% 12% 1	1620
	11th to 20th	Night	53% 7% 11% 17% 10% 1	1444
	21st to end	Night	51% 8% 13% 19% 10% 1	1551
June	1st to 10th	Night	57% 6% 11% 18% 6%	1422
	11th to 20th	Night	47% 9% 12% 22% 9% 2	1260
	21st to end	Night	54% 8% 12% 19% 7%	1428
July	1st to 10th	Night	46% 9% 16% 20% 9%	1400
	11th to 20th	Night	45% 10% 17% 22% 7%	1392
	21st to end	Night	48% 10% 13% 22% 7%	1486
August	1st to 10th	Night	43% 10% 19% 23% 5%	1461
	11th to 20th	Night	46% 11% 16% 20% 7%	1596
	21st to end	Night	44% 7% 15% 24% 9%	1912
September	1st to 10th	Night	46% 7% 14% 24% 9%	1800
	11th to 20th	Night	43% 6% 14% 26% 9% 1	1970
	21st to end	Night	45% 6% 13% 24% 11% 1	1980
October	1st to 10th	Night	51% 7% 11% 20% 11% 1	1980
	11th to 20th	Night	60% 8% 11% 16% 5%	2277
	21st to end	Night	65% 6% 9% 12% 6% 1	2574
November	1st to 10th	Night	64% 5% 11% 14% 6% 1	2407
	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% 26% 35% 14% 3 1	196
February	1st to 10th	Day	39% 29% 24% 7% 1	209
	11th to 20th	Day	30% 31% 31% 6% 2	416
	21st to end	Day	33% 26% 27% 12% 2	346
March	1st to 10th	Day	29% 27% 30% 10% 4	420
	11th to 20th	Day	31% 30% 22% 13% 4	420
	21st to end	Day	34% 22% 23% 14% 8%	462
April	1st to 10th	Day	41% 17% 24% 12% 5%	420
	11th to 20th	Day	33% 23% 25% 12% 5% 2	412
	21st to end	Day	37% 21% 25% 11% 4 1	420
May	1st to 10th	Day	40% 17% 26% 12% 3 1	423
	11th to 20th	Day	28% 18% 32% 17% 4 1	447
	21st to end	Day	23% 23% 30% 19% 5% 1	485
June	1st to 10th	Day	35% 18% 29% 13% 4	457
	11th to 20th	Day	24% 15% 27% 23% 9%	628
	21st to end	Day	28% 16% 32% 17% 7% 1	450
July	1st to 10th	Day	22% 13% 33% 24% 7% 1	445
	11th to 20th	Day	21% 14% 37% 20% 8% 1	444
	21st to end	Day	24% 12% 33% 24% 5% 1	488
August	1st to 10th	Day	20% 15% 29% 25% 10% 1	446
	11th to 20th	Day	21% 10% 31% 25% 10% 3	439
	21st to end	Day	25% 16% 25% 19% 10% 5%	495
September	1st to 10th	Day	22% 13% 30% 20% 12% 3	450
	11th to 20th	Day	24% 12% 25% 19% 15% 6%	450
	21st to end	Day	21% 16% 27% 21% 11% 4	450
October	1st to 10th	Day	28% 18% 22% 20% 9% 4	450
	11th to 20th	Day	30% 20% 27% 13% 8% 1	378
	21st to end	Day	40% 22% 21% 14% 3	396
November	1st to 10th	Day	35% 20% 28% 13% 4	365
	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	835
February	1st to 10th	Night	22% 28% 34% 13% 3	720
	11th to 20th	Night	23% 27% 34% 13% 2	703
	21st to end	Night	25% 24% 33% 17% 2	592
March	1st to 10th	Night	27% 20% 33% 17% 2	720
	11th to 20th	Night	27% 24% 28% 16% 5% 1	720
	21st to end	Night	27% 20% 26% 20% 6% 1	792
April	1st to 10th	Night	33% 21% 25% 17% 4	720
	11th to 20th	Night	30% 17% 27% 20% 6% 1	641
	21st to end	Night	31% 20% 26% 18% 4 1	540
May	1st to 10th	Night	29% 15% 30% 18% 7% 1	540
	11th to 20th	Night	23% 14% 31% 26% 6%	382
	21st to end	Night	24% 11% 30% 27% 7%	389
June	1st to 10th	Night	31% 8% 28% 23% 9%	360
	11th to 20th	Night	24% 7% 24% 33% 13%	360
	21st to end	Night	21% 8% 28% 32% 10%	360
July	1st to 10th	Night	17% 7% 31% 33% 10% 1	350
	11th to 20th	Night	16% 8% 28% 34% 12% 1	348
	21st to end	Night	19% 7% 22% 40% 12%	394
August	1st to 10th	Night	19% 4 20% 37% 19% 1	397
	11th to 20th	Night	18% 7% 23% 35% 17% 1	532
	21st to end	Night	21% 8% 24% 29% 16% 2	724
September	1st to 10th	Night	21% 8% 26% 31% 13% 1	720
	11th to 20th	Night	24% 9% 21% 27% 17% 2	720
	21st to end	Night	24% 11% 25% 24% 14% 2	720
October	1st to 10th	Night	27% 11% 25% 25% 12% 1	720
	11th to 20th	Night	30% 15% 25% 21% 8% 2	720
	21st to end	Night	35% 19% 25% 16% 4	792
November	1st to 10th	Night	34% 17% 25% 18% 6%	740
	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

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