Lac-Megantic
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac-Megantic clear sky chart from 2005-11-06 to 2024-08-15.

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	17% 13% 4 10% 6% 5% 4 4 5% 6% 26%	95246
	Night	16% 14% 5% 11% 6% 5% 5% 3 4 5% 25%	93442
Transparency	Day	59% 6% 10% 17% 7% 1	94965
	Night	61% 6% 10% 15% 7% 1	93278
Seeing	Day	29% 20% 28% 16% 6% 1	14834
	Night	26% 18% 28% 21% 7% 1	23458

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% 8% 16% 11% 6% 6% 3 4 5% 11%	2517
	11th to 20th	Day	9% 15% 6% 23% 14% 6% 3 2 3 3 15%	2520
	21st to end	Day	10% 17% 9% 17% 7% 7% 5% 3 4 4 18%	2772
February	1st to 10th	Day	11% 18% 7% 15% 11% 7% 4 3 4 3 16%	1575
	11th to 20th	Day	11% 19% 8% 16% 8% 6% 5% 4 3 4 15%	1848
	21st to end	Day	10% 19% 4 14% 7% 8% 5% 3 4 5% 19%	1570
March	1st to 10th	Day	20% 16% 4 11% 6% 5% 3 2 4 4 23%	3116
	11th to 20th	Day	15% 23% 7% 15% 6% 4 4 2 3 3 19%	3348
	21st to end	Day	16% 18% 5% 12% 5% 4 3 2 3 4 28%	4004
April	1st to 10th	Day	19% 18% 5% 10% 6% 4 3 3 4 4 24%	2280
	11th to 20th	Day	16% 16% 3 8% 5% 4 4 2 4 6% 32%	2342
	21st to end	Day	22% 16% 3 8% 4 4 3 3 4 5% 27%	2470
May	1st to 10th	Day	22% 12% 3 8% 6% 6% 4 4 5% 5% 26%	4106
	11th to 20th	Day	20% 9% 3 8% 5% 6% 5% 4 5% 7% 28%	4361
	21st to end	Day	15% 8% 3 8% 6% 5% 5% 5% 7% 9% 29%	4837
June	1st to 10th	Day	28% 9% 3 6% 4 4 4 4 7% 7% 24%	2764
	11th to 20th	Day	19% 8% 3 7% 4 5% 6% 4 6% 8% 31%	2850
	21st to end	Day	22% 10% 3 8% 5% 5% 5% 4 6% 6% 25%	2759
July	1st to 10th	Day	14% 7% 3 8% 5% 5% 6% 5% 7% 10% 29%	4440
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 5% 7% 8% 30%	4440
	21st to end	Day	16% 8% 3 7% 5% 5% 4 4 5% 7% 37%	4814
August	1st to 10th	Day	20% 7% 2 8% 7% 6% 5% 4 7% 9% 26%	2576
	11th to 20th	Day	17% 8% 2 8% 5% 5% 5% 4 7% 8% 31%	2359
	21st to end	Day	18% 8% 3 6% 5% 4 5% 4 6% 6% 34%	2461
September	1st to 10th	Day	19% 7% 3 6% 4 4 4 4 6% 8% 36%	2159
	11th to 20th	Day	19% 9% 2 6% 3 3 4 3 5% 6% 41%	1980
	21st to end	Day	19% 9% 2 7% 4 3 4 4 5% 9% 34%	1980
October	1st to 10th	Day	21% 13% 3 5% 4 4 3 4 6% 7% 29%	1980
	11th to 20th	Day	16% 16% 4 9% 6% 5% 5% 3 6% 5% 25%	1681
	21st to end	Day	23% 22% 4 8% 4 4 4 3 4 5% 20%	1782
November	1st to 10th	Day	16% 19% 5% 8% 5% 5% 3 4 4 4 27%	1671
	11th to 20th	Day	15% 18% 8% 11% 6% 3 5% 3 4 5% 21%	1710
	21st to end	Day	16% 16% 8% 13% 6% 5% 4 4 4 4 19%	1517
December	1st to 10th	Day	17% 24% 8% 15% 6% 5% 3 2 2 3 14%	1330
	11th to 20th	Day	17% 17% 8% 12% 6% 5% 4 4 3 4 19%	1668
	21st to end	Day	20% 22% 5% 15% 7% 4 3 2 3 3 15%	2659
January	1st to 10th	Night	12% 16% 9% 20% 12% 6% 4 3 4 3 11%	4429
	11th to 20th	Night	10% 17% 6% 19% 14% 8% 5% 4 3 3 10%	4440
	21st to end	Night	10% 17% 8% 17% 7% 8% 6% 4 4 4 14%	4884
February	1st to 10th	Night	10% 15% 7% 14% 10% 8% 6% 4 4 4 19%	2599
	11th to 20th	Night	9% 17% 7% 17% 9% 8% 5% 3 3 4 16%	2218
	21st to end	Night	11% 17% 5% 12% 8% 6% 6% 3 4 4 25%	1884
March	1st to 10th	Night	20% 19% 5% 9% 5% 3 5% 2 3 4 24%	3724
	11th to 20th	Night	13% 21% 8% 13% 6% 4 4 2 4 4 22%	3610
	21st to end	Night	19% 17% 5% 11% 6% 3 3 2 3 4 26%	3612
April	1st to 10th	Night	20% 16% 5% 9% 5% 4 4 3 4 5% 27%	1900
	11th to 20th	Night	19% 13% 3 7% 5% 3 4 3 4 6% 32%	1787
	21st to end	Night	20% 14% 4 8% 4 3 4 3 5% 6% 29%	1710
May	1st to 10th	Night	24% 11% 3 6% 4 4 5% 4 6% 7% 26%	2834
	11th to 20th	Night	18% 11% 2 8% 5% 5% 4 3 5% 5% 32%	2559
	21st to end	Night	18% 7% 2 5% 4 4 4 4 6% 10% 34%	2738
June	1st to 10th	Night	27% 9% 2 6% 5% 4 4 3 4 7% 27%	1410
	11th to 20th	Night	19% 8% 3 6% 4 4 4 4 6% 8% 34%	1330
	21st to end	Night	19% 9% 3 7% 5% 5% 5% 5% 6% 6% 30%	1413
July	1st to 10th	Night	12% 8% 4 9% 6% 6% 6% 5% 6% 8% 31%	2520
	11th to 20th	Night	17% 7% 4 7% 5% 5% 5% 5% 6% 7% 32%	2520
	21st to end	Night	13% 9% 3 7% 4 5% 5% 4 6% 7% 39%	2739
August	1st to 10th	Night	16% 7% 2 6% 4 4 5% 4 6% 8% 37%	1562
	11th to 20th	Night	14% 8% 3 7% 4 5% 5% 5% 7% 7% 35%	1641
	21st to end	Night	16% 7% 2 7% 4 4 5% 3 4 7% 41%	1893
September	1st to 10th	Night	16% 8% 2 7% 4 4 4 3 5% 6% 41%	1800
	11th to 20th	Night	18% 7% 2 6% 3 3 4 4 5% 5% 43%	1980
	21st to end	Night	19% 8% 2 5% 3 3 4 3 4 7% 42%	1980
October	1st to 10th	Night	18% 10% 3 6% 4 5% 4 4 5% 7% 35%	1980
	11th to 20th	Night	20% 13% 3 8% 5% 5% 5% 3 5% 5% 28%	2276
	21st to end	Night	23% 17% 4 8% 3 4 5% 3 4 5% 23%	2574
November	1st to 10th	Night	19% 16% 5% 9% 5% 4 5% 3 4 5% 25%	2407
	11th to 20th	Night	15% 15% 7% 11% 6% 4 3 3 5% 5% 25%	2470
	21st to end	Night	14% 16% 8% 14% 8% 5% 4 3 4 5% 20%	2657
December	1st to 10th	Night	17% 21% 7% 15% 8% 5% 4 3 5% 3 12%	2850
	11th to 20th	Night	17% 18% 8% 17% 8% 6% 4 3 4 4 12%	3531
	21st to end	Night	21% 19% 7% 11% 6% 3 3 2 3 4 20%	4981

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% 5% 9% 8% 2	2518
	11th to 20th	Day	76% 3 5% 12% 4 1	2520
	21st to end	Day	69% 6% 8% 8% 8% 2	2772
February	1st to 10th	Day	74% 3 5% 9% 8% 1	1575
	11th to 20th	Day	74% 3 7% 9% 6% 1	1857
	21st to end	Day	67% 4 8% 13% 6% 2	1570
March	1st to 10th	Day	66% 4 7% 12% 9% 2	3119
	11th to 20th	Day	71% 4 7% 10% 7% 1	3348
	21st to end	Day	61% 4 6% 14% 14% 2	4004
April	1st to 10th	Day	65% 3 8% 13% 8% 2	2280
	11th to 20th	Day	55% 4 8% 20% 12% 1	2342
	21st to end	Day	61% 4 8% 14% 10% 3	2470
May	1st to 10th	Day	59% 6% 10% 16% 8% 1	4120
	11th to 20th	Day	55% 8% 15% 15% 6% 1	4365
	21st to end	Day	48% 9% 12% 21% 10%	4837
June	1st to 10th	Day	58% 7% 9% 20% 5%	2764
	11th to 20th	Day	50% 7% 12% 21% 9% 1	2850
	21st to end	Day	58% 8% 10% 18% 6%	2759
July	1st to 10th	Day	46% 9% 15% 23% 7%	4370
	11th to 20th	Day	47% 9% 14% 26% 4	4365
	21st to end	Day	47% 7% 12% 27% 6%	4661
August	1st to 10th	Day	53% 9% 14% 20% 4	2562
	11th to 20th	Day	49% 9% 15% 18% 8%	2359
	21st to end	Day	48% 8% 12% 21% 11%	2461
September	1st to 10th	Day	45% 8% 13% 23% 11%	2159
	11th to 20th	Day	45% 5% 11% 26% 13% 1	1980
	21st to end	Day	48% 6% 12% 23% 10% 1	1980
October	1st to 10th	Day	53% 5% 12% 20% 9%	1980
	11th to 20th	Day	60% 6% 13% 16% 5%	1681
	21st to end	Day	68% 4 8% 12% 6% 1	1782
November	1st to 10th	Day	61% 5% 10% 15% 8% 1	1671
	11th to 20th	Day	67% 5% 8% 13% 6% 2	1710
	21st to end	Day	67% 6% 10% 13% 3	1517
December	1st to 10th	Day	78% 3 6% 7% 5%	1330
	11th to 20th	Day	69% 4 6% 10% 10% 1	1668
	21st to end	Day	76% 4 5% 9% 6% 1	2659
January	1st to 10th	Night	78% 6% 6% 7% 2	4429
	11th to 20th	Night	80% 5% 5% 8% 2	4440
	21st to end	Night	73% 5% 7% 7% 5% 1	4884
February	1st to 10th	Night	69% 6% 7% 11% 7% 1	2599
	11th to 20th	Night	73% 4 8% 9% 5% 1	2220
	21st to end	Night	65% 5% 6% 14% 9% 1	1884
March	1st to 10th	Night	65% 4 8% 14% 6% 2	3734
	11th to 20th	Night	68% 6% 7% 11% 7% 1	3611
	21st to end	Night	64% 4 5% 14% 12% 2	3612
April	1st to 10th	Night	61% 4 7% 14% 12% 1	1900
	11th to 20th	Night	54% 6% 8% 19% 12% 1	1787
	21st to end	Night	57% 7% 9% 16% 10% 2	1710
May	1st to 10th	Night	55% 9% 14% 16% 7% 1	2840
	11th to 20th	Night	52% 8% 12% 21% 6% 1	2560
	21st to end	Night	45% 8% 16% 19% 12%	2739
June	1st to 10th	Night	57% 6% 11% 20% 6%	1410
	11th to 20th	Night	47% 7% 12% 22% 10% 1	1330
	21st to end	Night	53% 9% 12% 19% 8%	1413
July	1st to 10th	Night	48% 9% 16% 19% 8%	2480
	11th to 20th	Night	46% 11% 15% 23% 5%	2472
	21st to end	Night	44% 8% 16% 26% 5%	2651
August	1st to 10th	Night	43% 9% 20% 24% 4	1552
	11th to 20th	Night	44% 11% 16% 22% 7%	1641
	21st to end	Night	43% 8% 14% 25% 10%	1893
September	1st to 10th	Night	44% 7% 13% 26% 10%	1800
	11th to 20th	Night	43% 6% 14% 27% 10% 1	1980
	21st to end	Night	43% 8% 11% 25% 11% 1	1980
October	1st to 10th	Night	49% 7% 10% 21% 12% 1	1980
	11th to 20th	Night	58% 7% 11% 18% 5%	2276
	21st to end	Night	64% 6% 8% 13% 7% 1	2574
November	1st to 10th	Night	62% 5% 10% 15% 7% 1	2407
	11th to 20th	Night	63% 5% 10% 13% 8% 1	2470
	21st to end	Night	69% 5% 10% 11% 4	2657
December	1st to 10th	Night	76% 5% 8% 8% 3	2850
	11th to 20th	Night	77% 4 6% 8% 6%	3532
	21st to end	Night	70% 5% 8% 11% 6%	4981

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% 28% 31% 11%	180
	11th to 20th	Day	37% 24% 27% 9% 2 1	180
	21st to end	Day	26% 22% 37% 11% 3 1	198
February	1st to 10th	Day	34% 30% 25% 9% 1	235
	11th to 20th	Day	31% 33% 28% 7% 1	456
	21st to end	Day	35% 26% 25% 13% 2	382
March	1st to 10th	Day	32% 24% 30% 11% 3	460
	11th to 20th	Day	32% 26% 25% 13% 4	460
	21st to end	Day	34% 23% 24% 13% 7% 1	506
April	1st to 10th	Day	39% 21% 24% 12% 4 1	460
	11th to 20th	Day	35% 25% 22% 12% 5% 1	452
	21st to end	Day	37% 22% 26% 10% 3 2	460
May	1st to 10th	Day	37% 17% 29% 13% 3 1	463
	11th to 20th	Day	26% 22% 27% 19% 6% 1	487
	21st to end	Day	22% 24% 34% 15% 4 1	529
June	1st to 10th	Day	33% 17% 29% 14% 6% 1	594
	11th to 20th	Day	23% 18% 26% 24% 9% 1	680
	21st to end	Day	25% 17% 31% 17% 9% 1	589
July	1st to 10th	Day	20% 16% 35% 22% 7%	485
	11th to 20th	Day	21% 15% 39% 17% 8% 1	484
	21st to end	Day	21% 12% 36% 25% 5% 1	532
August	1st to 10th	Day	21% 15% 31% 22% 10% 1	486
	11th to 20th	Day	18% 15% 29% 26% 9% 3	456
	21st to end	Day	26% 16% 24% 20% 11% 4	495
September	1st to 10th	Day	24% 14% 27% 22% 10% 4	450
	11th to 20th	Day	24% 13% 25% 19% 13% 6%	450
	21st to end	Day	21% 15% 28% 21% 11% 4	450
October	1st to 10th	Day	27% 16% 24% 18% 10% 4	450
	11th to 20th	Day	30% 19% 26% 15% 8% 2	372
	21st to end	Day	37% 22% 22% 15% 4	396
November	1st to 10th	Day	33% 21% 26% 15% 4	365
	11th to 20th	Day	28% 24% 30% 11% 6% 1	370
	21st to end	Day	32% 25% 26% 13% 2 1	264
December	1st to 10th	Day	32% 28% 26% 11% 3	180
	11th to 20th	Day	38% 27% 24% 6% 3 1	180
	21st to end	Day	36% 34% 20% 9% 1 1	198
January	1st to 10th	Night	25% 27% 33% 13% 2	760
	11th to 20th	Night	26% 26% 29% 16% 3	760
	21st to end	Night	19% 26% 33% 18% 3 1	836
February	1st to 10th	Night	22% 26% 35% 15% 2	760
	11th to 20th	Night	25% 27% 31% 15% 2	743
	21st to end	Night	26% 23% 34% 15% 2	628
March	1st to 10th	Night	26% 21% 33% 18% 2	760
	11th to 20th	Night	27% 24% 27% 18% 4	760
	21st to end	Night	28% 19% 26% 21% 5% 1	836
April	1st to 10th	Night	31% 21% 27% 17% 4	760
	11th to 20th	Night	28% 16% 27% 23% 5%	663
	21st to end	Night	31% 20% 26% 19% 4 1	570
May	1st to 10th	Night	29% 13% 29% 21% 6% 1	570
	11th to 20th	Night	22% 14% 29% 29% 5% 1	412
	21st to end	Night	22% 13% 31% 27% 7% 1	411
June	1st to 10th	Night	30% 9% 29% 25% 7%	380
	11th to 20th	Night	23% 7% 24% 32% 14%	380
	21st to end	Night	20% 11% 27% 31% 10%	380
July	1st to 10th	Night	16% 9% 30% 33% 11% 1	370
	11th to 20th	Night	17% 7% 27% 35% 13% 1	368
	21st to end	Night	20% 5% 23% 37% 14%	416
August	1st to 10th	Night	20% 5% 21% 37% 17% 1	428
	11th to 20th	Night	16% 9% 26% 32% 16% 1	547
	21st to end	Night	19% 9% 26% 30% 15% 2	705
September	1st to 10th	Night	20% 9% 25% 31% 13% 1	720
	11th to 20th	Night	23% 9% 22% 27% 17% 2	720
	21st to end	Night	24% 11% 26% 23% 14% 2	720
October	1st to 10th	Night	25% 12% 24% 28% 11% 1	720
	11th to 20th	Night	30% 16% 24% 21% 8% 2	720
	21st to end	Night	34% 19% 26% 17% 4	792
November	1st to 10th	Night	33% 16% 27% 19% 5%	740
	11th to 20th	Night	27% 22% 26% 16% 8% 1	760
	21st to end	Night	29% 23% 27% 15% 4 1	800
December	1st to 10th	Night	32% 23% 28% 14% 4	850
	11th to 20th	Night	30% 25% 25% 15% 5%	850
	21st to end	Night	35% 24% 25% 13% 3	863

Page generated at 2024-08-12 09:52:48. Version ac07

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