Vaudreuil-Dorion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vaudreuil-Dorion clear sky chart from 2005-11-06 to 2025-01-22.

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	16% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	105290
	Night	18% 11% 4 8% 5% 4 4 4 5% 6% 31%	104087
Transparency	Day	49% 7% 13% 21% 9% 1	108753
	Night	53% 6% 12% 19% 9% 1	108713
Seeing	Day	20% 11% 28% 24% 13% 4	14737
	Night	22% 10% 29% 28% 10% 1	23845

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% 17% 5% 12% 6% 4 4 3 5% 5% 22%	2597
	11th to 20th	Day	15% 12% 6% 10% 6% 5% 5% 4 6% 7% 24%	2600
	21st to end	Day	14% 16% 5% 10% 5% 5% 5% 4 6% 6% 23%	2780
February	1st to 10th	Day	15% 16% 4 11% 5% 5% 5% 4 6% 5% 25%	1688
	11th to 20th	Day	14% 12% 3 10% 7% 5% 5% 5% 5% 6% 28%	1750
	21st to end	Day	18% 15% 4 10% 5% 5% 4 4 5% 5% 27%	1570
March	1st to 10th	Day	20% 12% 5% 10% 6% 4 4 3 4 6% 26%	3116
	11th to 20th	Day	12% 15% 5% 12% 6% 5% 4 3 5% 5% 27%	3310
	21st to end	Day	15% 7% 3 8% 5% 4 5% 3 5% 5% 40%	4152
April	1st to 10th	Day	21% 11% 3 7% 5% 4 4 3 5% 5% 32%	2280
	11th to 20th	Day	20% 8% 2 7% 6% 4 3 4 5% 5% 36%	2254
	21st to end	Day	21% 9% 3 7% 6% 4 3 3 5% 6% 32%	2417
May	1st to 10th	Day	19% 9% 3 9% 5% 4 5% 4 6% 7% 30%	4389
	11th to 20th	Day	18% 8% 3 8% 5% 4 4 4 5% 6% 34%	4398
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 7% 8% 37%	4837
June	1st to 10th	Day	20% 8% 3 7% 4 5% 5% 5% 6% 6% 31%	2660
	11th to 20th	Day	14% 6% 3 7% 5% 5% 6% 4 6% 8% 38%	2660
	21st to end	Day	19% 8% 3 6% 5% 5% 5% 4 6% 7% 32%	2660
July	1st to 10th	Day	11% 6% 2 7% 6% 5% 6% 4 7% 8% 37%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 5% 7% 9% 38%	4440
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 45%	4814
August	1st to 10th	Day	15% 6% 2 8% 5% 5% 5% 5% 7% 9% 33%	4423
	11th to 20th	Day	13% 6% 3 7% 5% 4 5% 4 5% 9% 40%	3981
	21st to end	Day	16% 5% 2 5% 4 4 4 4 7% 9% 41%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 43%	2280
	11th to 20th	Day	13% 4 2 5% 4 4 3 4 5% 7% 49%	2212
	21st to end	Day	17% 5% 2 6% 4 4 4 4 5% 7% 41%	2090
October	1st to 10th	Day	19% 7% 3 7% 5% 5% 3 3 5% 6% 37%	1943
	11th to 20th	Day	18% 7% 3 9% 6% 6% 5% 3 5% 6% 31%	1874
	21st to end	Day	23% 11% 4 6% 5% 3 5% 3 5% 7% 28%	1881
November	1st to 10th	Day	17% 10% 3 7% 4 4 4 4 6% 7% 33%	1761
	11th to 20th	Day	16% 11% 3 7% 5% 5% 5% 4 6% 7% 30%	1707
	21st to end	Day	22% 12% 3 8% 6% 5% 6% 4 6% 7% 22%	1600
December	1st to 10th	Day	21% 20% 5% 10% 5% 4 4 4 5% 5% 17%	2600
	11th to 20th	Day	18% 13% 5% 9% 6% 6% 5% 4 4 4 25%	2986
	21st to end	Day	24% 13% 4 10% 5% 5% 5% 3 5% 5% 21%	3960
January	1st to 10th	Night	17% 17% 6% 10% 5% 5% 4 3 5% 6% 22%	4569
	11th to 20th	Night	12% 13% 5% 13% 7% 7% 6% 4 6% 6% 20%	4580
	21st to end	Night	16% 18% 5% 10% 6% 5% 4 3 3 5% 24%	4899
February	1st to 10th	Night	14% 15% 5% 11% 7% 6% 5% 4 5% 6% 22%	2489
	11th to 20th	Night	14% 10% 4 10% 6% 5% 5% 4 6% 6% 29%	2314
	21st to end	Night	15% 14% 4 11% 4 4 4 4 4 5% 31%	1884
March	1st to 10th	Night	21% 11% 3 8% 5% 4 4 3 4 5% 32%	3724
	11th to 20th	Night	19% 17% 4 9% 5% 4 4 3 5% 4 27%	3645
	21st to end	Night	13% 11% 3 8% 5% 5% 4 3 4 5% 39%	3480
April	1st to 10th	Night	23% 9% 3 7% 5% 4 4 4 5% 6% 31%	1900
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 4 6% 34%	1875
	21st to end	Night	21% 9% 4 7% 4 3 4 4 5% 6% 34%	1762
May	1st to 10th	Night	22% 10% 3 7% 5% 4 4 3 5% 7% 30%	2580
	11th to 20th	Night	23% 7% 2 6% 4 4 4 2 4 6% 37%	2495
	21st to end	Night	15% 7% 3 7% 5% 5% 4 3 5% 9% 38%	2738
June	1st to 10th	Night	20% 7% 3 6% 6% 5% 6% 4 6% 9% 29%	1520
	11th to 20th	Night	16% 6% 3 6% 4 4 4 5% 5% 8% 40%	1520
	21st to end	Night	18% 7% 3 6% 5% 5% 4 5% 5% 7% 35%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 5% 5% 4 6% 7% 35%	2520
	11th to 20th	Night	14% 5% 2 6% 5% 4 5% 5% 6% 8% 41%	2520
	21st to end	Night	11% 7% 3 6% 5% 4 4 4 6% 7% 44%	2739
August	1st to 10th	Night	14% 8% 3 7% 4 3 5% 4 6% 7% 39%	2506
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 3 5% 7% 39%	2812
	21st to end	Night	16% 5% 3 7% 5% 4 4 4 5% 7% 40%	3476
September	1st to 10th	Night	12% 5% 3 7% 5% 4 4 3 6% 7% 43%	1900
	11th to 20th	Night	15% 6% 2 5% 3 2 3 2 4 8% 49%	1966
	21st to end	Night	16% 6% 2 5% 4 4 4 4 5% 7% 42%	2090
October	1st to 10th	Night	18% 6% 3 7% 5% 5% 5% 4 5% 7% 36%	2232
	11th to 20th	Night	20% 7% 3 8% 5% 4 4 4 5% 5% 35%	2304
	21st to end	Night	22% 9% 3 7% 5% 6% 4 3 4 6% 30%	2717
November	1st to 10th	Night	19% 9% 3 8% 5% 4 4 3 6% 7% 32%	2537
	11th to 20th	Night	18% 11% 3 8% 5% 4 4 3 5% 5% 33%	2690
	21st to end	Night	22% 11% 4 9% 6% 5% 4 3 5% 5% 25%	2800
December	1st to 10th	Night	18% 17% 5% 12% 6% 5% 5% 4 5% 4 18%	4580
	11th to 20th	Night	23% 14% 4 9% 5% 4 4 4 5% 5% 23%	5208
	21st to end	Night	25% 15% 4 9% 4 3 3 5% 5% 4 22%	6996

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	62% 9% 15% 12% 3	2598
	11th to 20th	Day	59% 8% 14% 12% 6%	2600
	21st to end	Day	61% 9% 14% 11% 4 1	2780
February	1st to 10th	Day	61% 6% 11% 16% 4 1	1688
	11th to 20th	Day	56% 6% 14% 16% 7% 1	1759
	21st to end	Day	58% 6% 11% 15% 9% 2	1570
March	1st to 10th	Day	58% 6% 10% 18% 7% 1	3119
	11th to 20th	Day	56% 6% 12% 14% 10% 2	3310
	21st to end	Day	45% 6% 10% 21% 17% 2	4152
April	1st to 10th	Day	52% 6% 8% 20% 12% 2	2280
	11th to 20th	Day	47% 6% 9% 21% 15% 2	2254
	21st to end	Day	52% 5% 10% 17% 12% 4	2417
May	1st to 10th	Day	52% 8% 11% 19% 9% 1	4403
	11th to 20th	Day	47% 8% 15% 19% 9% 1	4402
	21st to end	Day	41% 8% 13% 24% 12% 1	4837
June	1st to 10th	Day	49% 8% 11% 18% 12% 1	2660
	11th to 20th	Day	43% 7% 12% 23% 14% 2	2660
	21st to end	Day	50% 8% 12% 20% 10% 1	2660
July	1st to 10th	Day	41% 7% 14% 28% 10%	4370
	11th to 20th	Day	39% 7% 16% 31% 7%	4365
	21st to end	Day	36% 8% 13% 33% 9%	4661
August	1st to 10th	Day	46% 7% 16% 22% 8%	4409
	11th to 20th	Day	41% 7% 17% 28% 7%	4023
	21st to end	Day	38% 7% 19% 22% 14%	4180
September	1st to 10th	Day	37% 8% 14% 28% 13%	2280
	11th to 20th	Day	35% 6% 13% 30% 14% 1	2212
	21st to end	Day	41% 7% 15% 26% 10% 1	2090
October	1st to 10th	Day	45% 7% 14% 26% 8%	3229
	11th to 20th	Day	43% 6% 19% 25% 6%	3090
	21st to end	Day	46% 5% 20% 23% 6%	3081
November	1st to 10th	Day	50% 7% 14% 21% 8% 1	1761
	11th to 20th	Day	54% 6% 12% 17% 11% 1	1707
	21st to end	Day	62% 8% 13% 13% 4	1600
December	1st to 10th	Day	70% 5% 11% 13% 1	2600
	11th to 20th	Day	60% 8% 10% 16% 7%	2986
	21st to end	Day	65% 6% 9% 15% 4	3960
January	1st to 10th	Night	65% 8% 13% 10% 4	4569
	11th to 20th	Night	62% 9% 12% 11% 5%	4580
	21st to end	Night	64% 6% 13% 11% 6%	4899
February	1st to 10th	Night	65% 5% 9% 14% 6% 1	2489
	11th to 20th	Night	55% 6% 12% 18% 8% 1	2316
	21st to end	Night	56% 4 9% 17% 12% 1	1884
March	1st to 10th	Night	54% 5% 9% 21% 9% 3	3734
	11th to 20th	Night	59% 7% 9% 14% 9% 2	3646
	21st to end	Night	48% 5% 8% 23% 14% 3	3480
April	1st to 10th	Night	54% 4 10% 17% 13% 1	1900
	11th to 20th	Night	52% 6% 9% 19% 12% 1	1875
	21st to end	Night	52% 4 9% 18% 13% 4	1762
May	1st to 10th	Night	53% 8% 10% 18% 9% 3	2586
	11th to 20th	Night	47% 7% 13% 19% 12% 2	2496
	21st to end	Night	43% 7% 11% 20% 18% 1	2739
June	1st to 10th	Night	50% 8% 11% 19% 11% 1	1520
	11th to 20th	Night	43% 6% 13% 21% 15% 2	1520
	21st to end	Night	47% 7% 13% 20% 12% 1	1520
July	1st to 10th	Night	46% 7% 13% 20% 14%	2480
	11th to 20th	Night	38% 6% 18% 29% 8%	2472
	21st to end	Night	39% 7% 17% 24% 13%	2651
August	1st to 10th	Night	46% 6% 14% 26% 8%	2496
	11th to 20th	Night	45% 6% 19% 22% 8%	2836
	21st to end	Night	41% 7% 15% 22% 13% 1	3476
September	1st to 10th	Night	39% 7% 12% 27% 15% 1	1900
	11th to 20th	Night	36% 6% 13% 32% 13% 1	1966
	21st to end	Night	42% 7% 12% 25% 14%	2090
October	1st to 10th	Night	45% 6% 14% 26% 9%	3726
	11th to 20th	Night	45% 5% 13% 28% 9%	3827
	21st to end	Night	49% 5% 15% 19% 11% 1	4467
November	1st to 10th	Night	53% 6% 12% 19% 8% 1	2537
	11th to 20th	Night	53% 5% 12% 19% 9% 1	2690
	21st to end	Night	61% 7% 12% 15% 5%	2800
December	1st to 10th	Night	71% 5% 12% 10% 2	4580
	11th to 20th	Night	63% 4 8% 14% 10%	5208
	21st to end	Night	65% 5% 9% 14% 7%	6996

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	27% 12% 32% 22% 7% 1	200
	11th to 20th	Day	27% 16% 33% 20% 5% 1	200
	21st to end	Day	21% 12% 35% 25% 7% 1	200
February	1st to 10th	Day	26% 19% 36% 15% 4	260
	11th to 20th	Day	19% 13% 45% 19% 3	357
	21st to end	Day	27% 13% 29% 29% 3	382
March	1st to 10th	Day	22% 13% 35% 23% 7%	460
	11th to 20th	Day	18% 18% 36% 20% 8% 1	460
	21st to end	Day	26% 13% 30% 18% 11% 2	506
April	1st to 10th	Day	28% 13% 28% 20% 10% 1	460
	11th to 20th	Day	24% 16% 28% 19% 10% 3	452
	21st to end	Day	25% 12% 31% 20% 10% 2	460
May	1st to 10th	Day	23% 10% 33% 22% 9% 3	463
	11th to 20th	Day	17% 10% 31% 24% 14% 4	487
	21st to end	Day	16% 11% 29% 26% 14% 3	529
June	1st to 10th	Day	23% 10% 21% 29% 12% 4	490
	11th to 20th	Day	14% 10% 28% 28% 19% 2	490
	21st to end	Day	22% 8% 28% 23% 13% 5%	490
July	1st to 10th	Day	12% 7% 26% 29% 20% 7%	485
	11th to 20th	Day	14% 7% 26% 30% 19% 5%	484
	21st to end	Day	12% 7% 23% 34% 19% 5%	532
August	1st to 10th	Day	16% 6% 20% 31% 20% 7%	486
	11th to 20th	Day	13% 4 22% 33% 19% 8%	479
	21st to end	Day	14% 9% 24% 26% 19% 9%	539
September	1st to 10th	Day	12% 10% 27% 24% 19% 8%	490
	11th to 20th	Day	14% 8% 20% 22% 23% 14%	490
	21st to end	Day	16% 7% 28% 24% 19% 7%	490
October	1st to 10th	Day	22% 10% 25% 22% 15% 6%	490
	11th to 20th	Day	21% 13% 29% 24% 12% 2	475
	21st to end	Day	31% 12% 25% 23% 8%	429
November	1st to 10th	Day	25% 15% 28% 23% 9% 1	395
	11th to 20th	Day	24% 19% 30% 19% 7% 1	307
	21st to end	Day	26% 20% 28% 22% 5% 1	200
December	1st to 10th	Day	29% 12% 28% 22% 7% 2	200
	11th to 20th	Day	23% 17% 38% 18% 3 1	200
	21st to end	Day	30% 14% 28% 20% 6% 3	220
January	1st to 10th	Night	26% 14% 32% 24% 5%	800
	11th to 20th	Night	26% 12% 34% 23% 6%	800
	21st to end	Night	20% 11% 35% 27% 7% 1	841
February	1st to 10th	Night	21% 13% 36% 24% 5% 1	760
	11th to 20th	Night	19% 14% 37% 26% 4	743
	21st to end	Night	22% 11% 36% 29% 4	628
March	1st to 10th	Night	24% 11% 34% 26% 5%	760
	11th to 20th	Night	25% 12% 33% 25% 5%	760
	21st to end	Night	24% 10% 30% 27% 9% 1	836
April	1st to 10th	Night	26% 12% 29% 26% 6%	760
	11th to 20th	Night	26% 11% 32% 24% 6%	751
	21st to end	Night	25% 10% 31% 25% 9%	622
May	1st to 10th	Night	27% 7% 29% 27% 10% 1	420
	11th to 20th	Night	19% 7% 31% 32% 10% 1	374
	21st to end	Night	17% 5% 33% 34% 11%	411
June	1st to 10th	Night	22% 7% 27% 33% 9% 1	380
	11th to 20th	Night	19% 5% 27% 34% 14% 1	380
	21st to end	Night	18% 7% 28% 28% 18% 1	380
July	1st to 10th	Night	12% 4 25% 40% 18% 1	370
	11th to 20th	Night	10% 5% 26% 41% 17% 2	368
	21st to end	Night	13% 4 24% 42% 17% 2	416
August	1st to 10th	Night	16% 3 18% 43% 20% 1	378
	11th to 20th	Night	15% 3 21% 34% 23% 3	575
	21st to end	Night	17% 2 23% 36% 20% 2	836
September	1st to 10th	Night	13% 5% 26% 37% 18% 1	760
	11th to 20th	Night	18% 5% 16% 36% 21% 4	760
	21st to end	Night	18% 6% 26% 29% 19% 2	760
October	1st to 10th	Night	21% 8% 26% 29% 16% 1	760
	11th to 20th	Night	23% 10% 28% 28% 11%	760
	21st to end	Night	26% 12% 31% 26% 5%	836
November	1st to 10th	Night	24% 15% 29% 24% 8%	780
	11th to 20th	Night	25% 13% 32% 19% 9% 1	800
	21st to end	Night	27% 14% 31% 19% 9%	800
December	1st to 10th	Night	31% 13% 31% 21% 5%	800
	11th to 20th	Night	29% 15% 29% 20% 5% 1	800
	21st to end	Night	34% 12% 29% 20% 5% 1	880

Page generated at 2025-01-19 03:06:47. Version ac07

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