Laval-West
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Laval-West clear sky chart from 2005-11-06 to 2024-02-25.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	78229
	Night	18% 10% 4 7% 6% 3 5% 4 5% 6% 32%	81060
Transparency	Day	50% 7% 12% 20% 10% 1	77934
	Night	53% 6% 11% 19% 10% 1	80889
Seeing	Day	21% 9% 27% 25% 13% 4	13568
	Night	23% 7% 28% 31% 11% 1	22725

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	16% 14% 5% 11% 8% 4 4 4 5% 5% 23%	2517
	11th to 20th	Day	15% 12% 6% 9% 7% 4 5% 5% 6% 6% 26%	2520
	21st to end	Day	14% 15% 5% 9% 6% 4 6% 5% 5% 6% 24%	2772
February	1st to 10th	Day	14% 14% 5% 10% 6% 4 5% 5% 4 6% 26%	1675
	11th to 20th	Day	14% 10% 5% 10% 7% 3 6% 6% 6% 6% 28%	1755
	21st to end	Day	19% 13% 5% 9% 6% 3 4 4 4 5% 28%	1520
March	1st to 10th	Day	16% 11% 5% 9% 7% 4 5% 4 4 5% 30%	1797
	11th to 20th	Day	16% 10% 4 7% 6% 4 5% 4 6% 5% 32%	1872
	21st to end	Day	19% 9% 4 6% 5% 3 4 4 5% 6% 35%	2367
April	1st to 10th	Day	22% 8% 4 7% 6% 3 4 4 4 5% 32%	2160
	11th to 20th	Day	20% 7% 3 6% 5% 3 4 4 5% 6% 37%	2134
	21st to end	Day	21% 10% 3 7% 6% 2 4 4 4 6% 32%	2299
May	1st to 10th	Day	18% 7% 3 7% 6% 3 6% 5% 5% 7% 34%	2492
	11th to 20th	Day	17% 7% 3 5% 6% 3 5% 5% 4 7% 38%	2478
	21st to end	Day	17% 6% 2 6% 6% 3 5% 4 6% 9% 36%	2725
June	1st to 10th	Day	21% 7% 3 6% 6% 3 5% 5% 5% 7% 31%	2520
	11th to 20th	Day	14% 6% 3 6% 6% 3 5% 5% 6% 8% 38%	2520
	21st to end	Day	19% 7% 3 6% 6% 4 5% 5% 6% 8% 31%	2520
July	1st to 10th	Day	11% 5% 2 5% 6% 3 6% 6% 6% 8% 42%	2520
	11th to 20th	Day	12% 6% 2 4 5% 4 5% 6% 8% 10% 37%	2520
	21st to end	Day	11% 6% 3 6% 4 3 6% 6% 7% 10% 38%	2744
August	1st to 10th	Day	11% 6% 2 6% 6% 4 5% 6% 7% 9% 37%	2506
	11th to 20th	Day	9% 6% 2 6% 6% 4 5% 5% 6% 9% 42%	2280
	21st to end	Day	12% 5% 2 5% 6% 3 5% 5% 7% 9% 42%	2376
September	1st to 10th	Day	11% 6% 2 5% 6% 4 5% 6% 7% 9% 40%	2160
	11th to 20th	Day	14% 5% 2 4 4 2 4 4 6% 7% 48%	2088
	21st to end	Day	15% 6% 3 5% 5% 3 4 4 5% 7% 42%	1980
October	1st to 10th	Day	19% 8% 3 6% 5% 3 5% 5% 5% 6% 36%	1850
	11th to 20th	Day	18% 8% 3 6% 8% 5% 6% 5% 6% 7% 28%	1766
	21st to end	Day	25% 9% 4 5% 6% 3 4 4 5% 6% 29%	1782
November	1st to 10th	Day	17% 9% 4 5% 5% 3 6% 5% 6% 7% 34%	1671
	11th to 20th	Day	18% 10% 4 7% 5% 3 5% 4 6% 7% 29%	1625
	21st to end	Day	22% 10% 4 6% 6% 4 6% 5% 6% 7% 25%	1520
December	1st to 10th	Day	25% 13% 6% 8% 6% 3 5% 4 5% 6% 19%	1520
	11th to 20th	Day	21% 13% 5% 8% 5% 3 5% 4 5% 5% 27%	1906
	21st to end	Day	28% 14% 5% 9% 6% 3 4 4 3 4 20%	2772
January	1st to 10th	Night	17% 14% 6% 9% 6% 4 5% 4 5% 6% 23%	4429
	11th to 20th	Night	12% 13% 5% 11% 9% 5% 6% 5% 5% 7% 23%	4440
	21st to end	Night	16% 15% 6% 9% 8% 4 5% 4 4 5% 24%	4884
February	1st to 10th	Night	14% 14% 6% 10% 8% 4 6% 5% 5% 7% 23%	2504
	11th to 20th	Night	14% 10% 5% 8% 7% 4 6% 5% 6% 7% 29%	2309
	21st to end	Night	16% 14% 5% 7% 6% 3 4 3 4 5% 32%	1831
March	1st to 10th	Night	17% 12% 5% 9% 6% 3 4 4 5% 6% 29%	2150
	11th to 20th	Night	17% 13% 4 7% 6% 3 4 4 4 6% 32%	2085
	21st to end	Night	18% 9% 4 7% 5% 3 4 3 4 4 38%	1988
April	1st to 10th	Night	24% 9% 4 5% 5% 3 4 4 5% 6% 31%	1800
	11th to 20th	Night	23% 7% 3 5% 5% 2 4 4 5% 6% 36%	1775
	21st to end	Night	21% 9% 2 7% 5% 3 4 4 5% 6% 33%	1661
May	1st to 10th	Night	20% 9% 3 7% 4 2 5% 4 5% 7% 35%	1484
	11th to 20th	Night	20% 7% 2 5% 5% 3 5% 4 5% 6% 39%	1415
	21st to end	Night	15% 6% 3 5% 5% 3 5% 5% 5% 8% 40%	1550
June	1st to 10th	Night	20% 7% 3 6% 6% 3 5% 5% 6% 8% 31%	1440
	11th to 20th	Night	16% 6% 3 6% 5% 3 3 5% 6% 8% 39%	1440
	21st to end	Night	17% 6% 3 7% 6% 4 4 6% 6% 7% 35%	1440
July	1st to 10th	Night	11% 4 2 5% 5% 3 5% 6% 6% 9% 43%	1440
	11th to 20th	Night	11% 4 3 6% 6% 3 5% 5% 6% 11% 40%	1440
	21st to end	Night	11% 5% 4 5% 4 3 4 5% 7% 9% 42%	1574
August	1st to 10th	Night	12% 5% 2 5% 4 3 5% 5% 6% 9% 44%	1432
	11th to 20th	Night	12% 5% 3 6% 5% 3 5% 4 6% 8% 44%	1598
	21st to end	Night	13% 5% 2 5% 4 3 4 5% 6% 8% 43%	1980
September	1st to 10th	Night	12% 4 3 6% 6% 4 4 5% 5% 8% 43%	1800
	11th to 20th	Night	14% 6% 3 5% 3 2 2 3 4 8% 48%	1870
	21st to end	Night	17% 4 2 5% 5% 3 4 4 5% 7% 43%	1980
October	1st to 10th	Night	18% 6% 2 6% 5% 3 6% 5% 5% 7% 38%	2106
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 4 4 7% 34%	2192
	21st to end	Night	22% 9% 3 7% 6% 3 5% 5% 5% 5% 30%	2574
November	1st to 10th	Night	19% 9% 3 5% 6% 3 5% 5% 5% 7% 33%	2407
	11th to 20th	Night	19% 9% 3 8% 5% 3 4 5% 6% 6% 32%	2550
	21st to end	Night	22% 12% 4 7% 6% 4 4 4 4 5% 27%	2660
December	1st to 10th	Night	21% 15% 5% 8% 7% 3 5% 5% 5% 5% 22%	2660
	11th to 20th	Night	22% 15% 5% 7% 5% 3 4 4 4 5% 26%	3288
	21st to end	Night	29% 16% 4 8% 5% 2 3 3 4 4 22%	4884

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	61% 10% 11% 13% 4 1	2518
	11th to 20th	Day	55% 7% 14% 15% 8%	2520
	21st to end	Day	59% 7% 13% 14% 5%	2772
February	1st to 10th	Day	59% 4 10% 20% 5% 2	1675
	11th to 20th	Day	55% 7% 11% 16% 9% 1	1764
	21st to end	Day	59% 4 9% 16% 10% 2	1520
March	1st to 10th	Day	57% 5% 9% 18% 10% 2	1800
	11th to 20th	Day	52% 5% 12% 16% 13% 3	1872
	21st to end	Day	50% 6% 9% 18% 14% 3	2367
April	1st to 10th	Day	55% 5% 8% 18% 13% 2	2160
	11th to 20th	Day	48% 6% 7% 22% 15% 2	2134
	21st to end	Day	53% 6% 9% 17% 12% 4	2299
May	1st to 10th	Day	49% 5% 8% 20% 15% 2	2492
	11th to 20th	Day	45% 6% 10% 20% 16% 3	2482
	21st to end	Day	45% 7% 13% 20% 14% 2	2725
June	1st to 10th	Day	50% 7% 11% 19% 12% 2	2520
	11th to 20th	Day	43% 7% 10% 23% 14% 3	2520
	21st to end	Day	51% 7% 11% 20% 10% 1	2520
July	1st to 10th	Day	37% 9% 12% 28% 13% 1	2450
	11th to 20th	Day	38% 8% 15% 29% 10%	2445
	21st to end	Day	40% 8% 16% 27% 9%	2591
August	1st to 10th	Day	41% 9% 16% 26% 9%	2492
	11th to 20th	Day	37% 8% 17% 26% 11%	2280
	21st to end	Day	37% 7% 15% 26% 14%	2376
September	1st to 10th	Day	38% 7% 15% 27% 13% 1	2160
	11th to 20th	Day	34% 7% 12% 32% 15% 1	2088
	21st to end	Day	41% 6% 14% 28% 10% 1	1980
October	1st to 10th	Day	49% 5% 12% 22% 11%	1850
	11th to 20th	Day	54% 8% 12% 20% 7%	1766
	21st to end	Day	56% 5% 12% 18% 8% 1	1782
November	1st to 10th	Day	48% 6% 14% 22% 8% 1	1671
	11th to 20th	Day	53% 6% 12% 17% 11% 1	1625
	21st to end	Day	57% 9% 14% 15% 6%	1520
December	1st to 10th	Day	67% 5% 11% 13% 4	1520
	11th to 20th	Day	60% 5% 13% 17% 5%	1906
	21st to end	Day	69% 6% 10% 10% 5%	2772
January	1st to 10th	Night	61% 7% 14% 12% 4	4429
	11th to 20th	Night	58% 7% 14% 14% 5% 1	4440
	21st to end	Night	62% 6% 12% 13% 6% 1	4884
February	1st to 10th	Night	62% 5% 11% 16% 6% 1	2504
	11th to 20th	Night	53% 5% 11% 21% 9% 1	2311
	21st to end	Night	56% 5% 8% 17% 13% 1	1831
March	1st to 10th	Night	57% 4 9% 17% 11% 2	2160
	11th to 20th	Night	55% 4 9% 16% 13% 3	2086
	21st to end	Night	50% 4 7% 20% 14% 4	1988
April	1st to 10th	Night	54% 4 8% 19% 14% 2	1800
	11th to 20th	Night	51% 4 7% 21% 15% 2	1775
	21st to end	Night	51% 4 9% 18% 13% 4	1661
May	1st to 10th	Night	51% 3 7% 19% 15% 5%	1484
	11th to 20th	Night	46% 5% 8% 18% 18% 4	1416
	21st to end	Night	43% 7% 11% 20% 17% 2	1551
June	1st to 10th	Night	50% 7% 10% 21% 12% 1	1440
	11th to 20th	Night	42% 6% 12% 22% 15% 3	1440
	21st to end	Night	47% 8% 12% 20% 13%	1440
July	1st to 10th	Night	36% 7% 13% 25% 17% 1	1400
	11th to 20th	Night	36% 9% 15% 28% 12%	1392
	21st to end	Night	36% 9% 18% 25% 12%	1486
August	1st to 10th	Night	37% 7% 17% 26% 12%	1422
	11th to 20th	Night	38% 7% 17% 25% 12%	1598
	21st to end	Night	37% 8% 15% 26% 13% 1	1980
September	1st to 10th	Night	39% 6% 13% 26% 15% 1	1800
	11th to 20th	Night	37% 4 13% 32% 12% 1	1870
	21st to end	Night	41% 6% 12% 27% 14%	1980
October	1st to 10th	Night	46% 6% 10% 25% 12% 1	2106
	11th to 20th	Night	51% 5% 12% 24% 8%	2192
	21st to end	Night	56% 5% 13% 17% 9% 1	2574
November	1st to 10th	Night	51% 5% 12% 21% 9% 1	2407
	11th to 20th	Night	52% 5% 13% 19% 10% 1	2550
	21st to end	Night	59% 5% 12% 17% 6%	2660
December	1st to 10th	Night	65% 6% 11% 15% 4	2660
	11th to 20th	Night	62% 4 9% 18% 7%	3288
	21st to end	Night	67% 5% 9% 15% 5%	4884

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	26% 11% 27% 26% 11%	180
	11th to 20th	Day	29% 13% 28% 22% 7% 1	180
	21st to end	Day	21% 12% 32% 26% 8% 2	198
February	1st to 10th	Day	29% 17% 34% 16% 3	254
	11th to 20th	Day	22% 12% 39% 22% 4	362
	21st to end	Day	29% 9% 31% 29% 2	362
March	1st to 10th	Day	24% 11% 31% 25% 8%	420
	11th to 20th	Day	21% 10% 33% 27% 6% 2	420
	21st to end	Day	27% 10% 30% 21% 10% 3	462
April	1st to 10th	Day	25% 13% 28% 21% 9% 3	420
	11th to 20th	Day	27% 14% 24% 22% 11% 3	412
	21st to end	Day	28% 11% 28% 21% 10% 3	420
May	1st to 10th	Day	23% 9% 31% 25% 10% 3	423
	11th to 20th	Day	20% 8% 30% 26% 11% 5%	447
	21st to end	Day	18% 8% 33% 24% 13% 3	485
June	1st to 10th	Day	24% 10% 25% 27% 12% 3	450
	11th to 20th	Day	17% 9% 22% 32% 16% 4	450
	21st to end	Day	20% 6% 24% 28% 17% 4	450
July	1st to 10th	Day	11% 7% 22% 32% 20% 7%	445
	11th to 20th	Day	13% 5% 26% 32% 19% 5%	444
	21st to end	Day	14% 5% 22% 34% 20% 5%	488
August	1st to 10th	Day	15% 3 21% 33% 21% 8%	446
	11th to 20th	Day	11% 5% 19% 30% 23% 13%	439
	21st to end	Day	14% 7% 24% 24% 22% 9%	495
September	1st to 10th	Day	12% 6% 24% 30% 18% 10%	450
	11th to 20th	Day	15% 7% 22% 25% 20% 12%	450
	21st to end	Day	18% 7% 26% 24% 20% 6%	450
October	1st to 10th	Day	22% 9% 27% 22% 14% 6%	450
	11th to 20th	Day	21% 11% 31% 22% 13% 2	432
	21st to end	Day	34% 11% 24% 23% 8% 1	396
November	1st to 10th	Day	27% 12% 24% 25% 11% 1	365
	11th to 20th	Day	22% 14% 34% 20% 8% 1	285
	21st to end	Day	28% 13% 28% 23% 7% 1	180
December	1st to 10th	Day	31% 9% 26% 26% 8% 2	180
	11th to 20th	Day	25% 13% 37% 19% 4 1	180
	21st to end	Day	31% 16% 29% 17% 7% 1	198
January	1st to 10th	Night	26% 10% 30% 28% 5%	760
	11th to 20th	Night	25% 9% 34% 26% 5%	760
	21st to end	Night	19% 7% 36% 29% 8%	836
February	1st to 10th	Night	21% 7% 36% 28% 6% 1	760
	11th to 20th	Night	21% 10% 36% 28% 5%	743
	21st to end	Night	24% 8% 32% 32% 4	611
March	1st to 10th	Night	24% 9% 31% 29% 6%	720
	11th to 20th	Night	27% 8% 31% 26% 8%	720
	21st to end	Night	23% 7% 28% 33% 8% 1	792
April	1st to 10th	Night	27% 8% 27% 31% 6%	720
	11th to 20th	Night	26% 9% 29% 28% 7% 1	711
	21st to end	Night	27% 8% 29% 27% 9%	581
May	1st to 10th	Night	22% 6% 31% 30% 8% 2	404
	11th to 20th	Night	23% 5% 28% 36% 8% 1	354
	21st to end	Night	18% 5% 32% 35% 10% 1	389
June	1st to 10th	Night	25% 4 23% 34% 13% 1	360
	11th to 20th	Night	19% 4 26% 36% 14% 1	360
	21st to end	Night	18% 5% 24% 36% 16% 1	360
July	1st to 10th	Night	11% 3 26% 41% 17% 1	350
	11th to 20th	Night	12% 3 20% 47% 17% 1	348
	21st to end	Night	13% 3 18% 46% 20% 1	394
August	1st to 10th	Night	16% 2 12% 46% 23% 1	358
	11th to 20th	Night	15% 2 18% 37% 26% 2	534
	21st to end	Night	16% 3 20% 36% 23% 2	792
September	1st to 10th	Night	14% 3 22% 42% 18% 1	720
	11th to 20th	Night	18% 4 18% 37% 21% 2	720
	21st to end	Night	19% 3 25% 32% 19% 2	720
October	1st to 10th	Night	21% 6% 27% 33% 13% 1	720
	11th to 20th	Night	23% 7% 27% 31% 11% 1	720
	21st to end	Night	28% 7% 30% 29% 6%	792
November	1st to 10th	Night	25% 9% 29% 28% 9%	740
	11th to 20th	Night	24% 9% 33% 24% 10% 1	760
	21st to end	Night	30% 10% 28% 24% 8% 1	760
December	1st to 10th	Night	30% 8% 31% 24% 6%	760
	11th to 20th	Night	29% 10% 33% 21% 6% 1	760
	21st to end	Night	33% 11% 30% 21% 5% 1	836

Page generated at 2024-02-22 06:05:46. Version ac07

Copyright 2024 Attilla Danko