Vanier
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vanier clear sky chart from 2005-11-06 to 2024-12-06.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	101643
	Night	19% 12% 4 8% 5% 4 4 3 5% 6% 30%	98096
Transparency	Day	51% 7% 14% 19% 8% 1	105103
	Night	55% 6% 12% 18% 8% 1	102713
Seeing	Day	23% 14% 29% 22% 10% 2	15320
	Night	24% 11% 28% 28% 8% 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	14% 17% 6% 13% 6% 4 4 3 5% 6% 22%	2517
	11th to 20th	Day	10% 15% 7% 14% 6% 6% 4 3 4 5% 27%	2520
	21st to end	Day	10% 13% 5% 9% 5% 4 4 4 5% 7% 34%	2772
February	1st to 10th	Day	11% 14% 6% 12% 6% 5% 5% 4 6% 6% 25%	1520
	11th to 20th	Day	14% 14% 6% 10% 5% 5% 4 4 5% 6% 27%	1833
	21st to end	Day	13% 14% 5% 10% 7% 4 4 4 4 7% 28%	1570
March	1st to 10th	Day	20% 11% 4 9% 5% 4 4 3 4 6% 30%	3116
	11th to 20th	Day	15% 18% 4 8% 5% 4 4 3 5% 6% 27%	3318
	21st to end	Day	14% 13% 4 7% 4 5% 4 3 4 5% 37%	4056
April	1st to 10th	Day	21% 13% 3 7% 5% 5% 4 3 5% 5% 29%	2280
	11th to 20th	Day	20% 6% 3 6% 5% 5% 4 3 5% 6% 37%	2347
	21st to end	Day	24% 8% 3 7% 4 4 4 3 4 6% 31%	2470
May	1st to 10th	Day	22% 7% 2 7% 4 4 4 3 5% 7% 36%	4200
	11th to 20th	Day	18% 6% 3 7% 5% 5% 6% 4 6% 8% 32%	4398
	21st to end	Day	18% 7% 2 8% 6% 5% 6% 4 6% 7% 32%	4891
June	1st to 10th	Day	19% 6% 3 7% 5% 5% 6% 4 8% 7% 28%	2850
	11th to 20th	Day	19% 7% 3 6% 5% 4 5% 4 6% 8% 34%	2850
	21st to end	Day	23% 8% 3 8% 6% 5% 5% 4 5% 7% 27%	2850
July	1st to 10th	Day	15% 8% 3 8% 5% 6% 5% 4 7% 9% 30%	4506
	11th to 20th	Day	17% 6% 3 7% 5% 5% 6% 5% 7% 9% 32%	4440
	21st to end	Day	14% 5% 2 6% 5% 4 5% 4 7% 8% 40%	4814
August	1st to 10th	Day	15% 5% 2 7% 5% 6% 6% 5% 7% 10% 31%	4399
	11th to 20th	Day	20% 6% 2 7% 5% 6% 4 4 6% 9% 29%	4045
	21st to end	Day	21% 5% 2 6% 4 5% 3 3 5% 6% 38%	4342
September	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 5% 9% 38%	2280
	11th to 20th	Day	18% 5% 2 4 3 3 3 2 5% 8% 46%	2110
	21st to end	Day	21% 7% 2 7% 3 4 4 3 5% 6% 37%	2090
October	1st to 10th	Day	20% 8% 3 6% 5% 4 5% 4 5% 7% 33%	2087
	11th to 20th	Day	24% 9% 3 7% 6% 5% 5% 4 6% 7% 25%	1738
	21st to end	Day	27% 10% 4 7% 4 4 4 4 5% 5% 25%	1881
November	1st to 10th	Day	20% 11% 3 8% 5% 5% 4 3 4 6% 31%	1761
	11th to 20th	Day	22% 12% 5% 8% 5% 4 5% 3 5% 4 27%	1800
	21st to end	Day	24% 16% 5% 8% 4 4 4 4 4 5% 22%	1439
December	1st to 10th	Day	22% 19% 4 8% 5% 5% 4 3 5% 4 20%	1365
	11th to 20th	Day	21% 15% 3 9% 6% 5% 3 3 4 5% 27%	1668
	21st to end	Day	22% 19% 4 8% 4 4 3 3 4 4 26%	2520
January	1st to 10th	Night	15% 20% 6% 14% 6% 4 3 2 3 4 22%	4429
	11th to 20th	Night	12% 16% 5% 13% 6% 5% 5% 4 4 5% 24%	4440
	21st to end	Night	11% 14% 4 11% 7% 6% 5% 4 6% 6% 26%	4884
February	1st to 10th	Night	12% 13% 5% 11% 8% 5% 5% 4 5% 5% 27%	2660
	11th to 20th	Night	13% 17% 5% 11% 6% 4 4 3 5% 6% 26%	2229
	21st to end	Night	15% 14% 4 10% 5% 5% 4 3 5% 6% 29%	1884
March	1st to 10th	Night	24% 12% 3 7% 4 3 6% 3 4 5% 29%	3724
	11th to 20th	Night	18% 17% 4 10% 5% 5% 4 4 4 5% 24%	3640
	21st to end	Night	18% 14% 5% 9% 5% 4 4 3 3 5% 33%	3572
April	1st to 10th	Night	22% 14% 4 7% 4 4 3 3 4 5% 29%	1900
	11th to 20th	Night	21% 8% 3 7% 4 4 4 4 5% 7% 34%	1782
	21st to end	Night	23% 11% 2 7% 5% 3 3 3 4 5% 35%	1710
May	1st to 10th	Night	22% 7% 3 6% 5% 4 5% 4 4 6% 34%	2770
	11th to 20th	Night	23% 8% 3 7% 5% 4 4 3 5% 7% 32%	2495
	21st to end	Night	19% 5% 2 6% 5% 4 5% 3 6% 8% 36%	2681
June	1st to 10th	Night	21% 8% 3 7% 5% 4 5% 5% 5% 8% 28%	1330
	11th to 20th	Night	20% 6% 3 6% 4 5% 3 4 6% 7% 37%	1330
	21st to end	Night	22% 9% 4 8% 5% 4 5% 3 4 7% 30%	1330
July	1st to 10th	Night	15% 8% 2 7% 5% 6% 6% 4 7% 8% 32%	2450
	11th to 20th	Night	21% 7% 2 6% 5% 4 4 4 5% 7% 34%	2520
	21st to end	Night	14% 5% 2 7% 4 5% 5% 3 5% 7% 42%	2739
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 5% 7% 34%	2506
	11th to 20th	Night	19% 7% 3 8% 5% 5% 5% 4 6% 7% 31%	2774
	21st to end	Night	21% 6% 3 7% 5% 5% 5% 3 5% 6% 34%	3311
September	1st to 10th	Night	19% 6% 2 7% 5% 3 4 3 4 7% 41%	1900
	11th to 20th	Night	18% 7% 2 5% 4 4 3 3 5% 6% 44%	2069
	21st to end	Night	20% 7% 3 5% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Night	19% 8% 2 7% 4 4 4 4 5% 6% 36%	2090
	11th to 20th	Night	26% 8% 3 7% 5% 5% 4 3 5% 4 31%	2441
	21st to end	Night	25% 11% 3 7% 4 4 3 3 5% 7% 30%	2717
November	1st to 10th	Night	20% 11% 3 7% 5% 5% 4 3 6% 6% 31%	2537
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 4 4 6% 32%	2600
	21st to end	Night	23% 15% 5% 8% 4 5% 5% 3 4 5% 24%	2959
December	1st to 10th	Night	23% 16% 5% 10% 6% 5% 5% 3 4 4 19%	2932
	11th to 20th	Night	21% 14% 4 10% 6% 4 4 3 4 6% 25%	3531
	21st to end	Night	24% 20% 4 8% 4 3 3 3 3 3 25%	5140

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	64% 6% 11% 15% 4 1	2518
	11th to 20th	Day	61% 7% 9% 17% 5% 1	2520
	21st to end	Day	51% 6% 11% 23% 9%	2772
February	1st to 10th	Day	59% 5% 12% 15% 8% 2	1520
	11th to 20th	Day	59% 5% 13% 13% 9% 1	1842
	21st to end	Day	56% 5% 10% 18% 8% 2	1570
March	1st to 10th	Day	54% 7% 11% 16% 9% 2	3119
	11th to 20th	Day	57% 6% 11% 17% 7% 1	3318
	21st to end	Day	50% 5% 10% 19% 13% 4	4056
April	1st to 10th	Day	57% 4 11% 14% 10% 3	2280
	11th to 20th	Day	47% 5% 11% 23% 11% 2	2347
	21st to end	Day	54% 6% 10% 17% 11% 2	2470
May	1st to 10th	Day	47% 6% 14% 17% 15% 1	4214
	11th to 20th	Day	47% 9% 18% 19% 7% 1	4402
	21st to end	Day	48% 8% 10% 20% 13% 1	4891
June	1st to 10th	Day	50% 10% 12% 19% 7% 1	2850
	11th to 20th	Day	46% 8% 14% 20% 11% 2	2850
	21st to end	Day	56% 7% 11% 16% 9%	2850
July	1st to 10th	Day	47% 9% 15% 23% 7%	4436
	11th to 20th	Day	45% 8% 21% 21% 4	4365
	21st to end	Day	40% 8% 20% 25% 8%	4661
August	1st to 10th	Day	45% 9% 19% 20% 6%	4385
	11th to 20th	Day	50% 8% 20% 17% 5%	4084
	21st to end	Day	45% 8% 15% 19% 13% 1	4342
September	1st to 10th	Day	42% 7% 16% 24% 10%	2280
	11th to 20th	Day	37% 6% 17% 30% 10%	2110
	21st to end	Day	46% 6% 14% 25% 8%	2090
October	1st to 10th	Day	54% 7% 11% 23% 5%	3464
	11th to 20th	Day	52% 8% 18% 21% 2	2863
	21st to end	Day	53% 6% 17% 16% 7%	3081
November	1st to 10th	Day	55% 6% 11% 20% 7%	1761
	11th to 20th	Day	60% 5% 9% 19% 6% 1	1800
	21st to end	Day	65% 5% 12% 12% 5%	1439
December	1st to 10th	Day	67% 5% 11% 13% 4	1365
	11th to 20th	Day	61% 5% 8% 18% 7%	1668
	21st to end	Day	63% 6% 11% 12% 6% 2	2520
January	1st to 10th	Night	66% 6% 10% 12% 5%	4429
	11th to 20th	Night	62% 5% 10% 19% 4 1	4440
	21st to end	Night	57% 6% 12% 17% 8% 1	4884
February	1st to 10th	Night	59% 5% 10% 17% 8% 1	2660
	11th to 20th	Night	60% 5% 11% 15% 9% 1	2231
	21st to end	Night	56% 5% 9% 16% 13% 1	1884
March	1st to 10th	Night	59% 5% 12% 15% 8% 2	3734
	11th to 20th	Night	63% 6% 9% 15% 7% 1	3641
	21st to end	Night	57% 4 8% 21% 9% 2	3572
April	1st to 10th	Night	57% 4 9% 15% 12% 2	1900
	11th to 20th	Night	50% 5% 10% 20% 12% 2	1782
	21st to end	Night	53% 5% 8% 17% 15% 2	1710
May	1st to 10th	Night	50% 6% 12% 19% 11% 1	2776
	11th to 20th	Night	48% 9% 13% 17% 12% 1	2496
	21st to end	Night	45% 7% 12% 18% 17% 1	2682
June	1st to 10th	Night	52% 7% 13% 19% 8% 1	1330
	11th to 20th	Night	46% 7% 12% 20% 12% 3	1330
	21st to end	Night	55% 6% 12% 17% 10%	1330
July	1st to 10th	Night	48% 8% 19% 19% 7%	2410
	11th to 20th	Night	48% 8% 19% 21% 4	2472
	21st to end	Night	41% 8% 21% 22% 8%	2651
August	1st to 10th	Night	48% 8% 16% 23% 6%	2496
	11th to 20th	Night	51% 10% 18% 16% 5%	2801
	21st to end	Night	50% 6% 13% 20% 11%	3311
September	1st to 10th	Night	44% 6% 14% 23% 11% 1	1900
	11th to 20th	Night	40% 6% 17% 28% 8% 1	2069
	21st to end	Night	45% 6% 11% 26% 12%	2090
October	1st to 10th	Night	50% 6% 11% 26% 7%	3480
	11th to 20th	Night	54% 6% 13% 23% 3	4055
	21st to end	Night	51% 6% 18% 15% 10%	4467
November	1st to 10th	Night	54% 6% 13% 20% 6% 1	2537
	11th to 20th	Night	54% 7% 13% 18% 9%	2600
	21st to end	Night	64% 6% 11% 14% 6% 1	2959
December	1st to 10th	Night	68% 5% 11% 12% 4	2932
	11th to 20th	Night	62% 5% 9% 15% 8%	3532
	21st to end	Night	65% 5% 8% 15% 6% 1	5140

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% 19% 31% 17% 4 1	180
	11th to 20th	Day	28% 23% 31% 13% 5%	180
	21st to end	Day	15% 21% 37% 22% 4 1	198
February	1st to 10th	Day	24% 24% 34% 14% 3 1	180
	11th to 20th	Day	22% 20% 37% 17% 4	449
	21st to end	Day	22% 22% 29% 22% 5%	382
March	1st to 10th	Day	24% 19% 30% 21% 7% 1	460
	11th to 20th	Day	23% 18% 33% 18% 7% 2	460
	21st to end	Day	23% 17% 27% 22% 10% 1	506
April	1st to 10th	Day	27% 16% 29% 19% 8%	460
	11th to 20th	Day	25% 12% 31% 22% 9% 1	452
	21st to end	Day	28% 16% 32% 16% 6% 2	460
May	1st to 10th	Day	27% 16% 33% 18% 5% 1	463
	11th to 20th	Day	20% 13% 32% 24% 9% 2	487
	21st to end	Day	23% 18% 31% 19% 7% 1	557
June	1st to 10th	Day	22% 14% 29% 26% 9% 1	680
	11th to 20th	Day	20% 11% 28% 27% 13% 1	680
	21st to end	Day	26% 10% 26% 24% 11% 2	680
July	1st to 10th	Day	18% 12% 30% 26% 12% 2	525
	11th to 20th	Day	15% 11% 32% 28% 12% 2	484
	21st to end	Day	15% 9% 33% 28% 12% 2	532
August	1st to 10th	Day	17% 8% 28% 27% 15% 4	486
	11th to 20th	Day	19% 5% 27% 27% 18% 4	479
	21st to end	Day	21% 10% 25% 21% 16% 7%	539
September	1st to 10th	Day	18% 12% 27% 26% 13% 3	490
	11th to 20th	Day	18% 11% 27% 22% 18% 5%	490
	21st to end	Day	20% 13% 24% 23% 14% 6%	490
October	1st to 10th	Day	22% 13% 26% 25% 10% 3	490
	11th to 20th	Day	29% 14% 27% 18% 10% 1	404
	21st to end	Day	33% 15% 28% 18% 6%	429
November	1st to 10th	Day	31% 15% 24% 23% 7% 1	395
	11th to 20th	Day	28% 16% 30% 18% 9%	400
	21st to end	Day	33% 18% 30% 16% 3	205
December	1st to 10th	Day	32% 11% 28% 21% 6% 3	190
	11th to 20th	Day	31% 18% 29% 17% 3 2	180
	21st to end	Day	34% 17% 32% 13% 4 1	198
January	1st to 10th	Night	26% 16% 32% 22% 4	760
	11th to 20th	Night	25% 15% 30% 25% 4	760
	21st to end	Night	17% 12% 34% 30% 6% 1	836
February	1st to 10th	Night	19% 12% 34% 28% 6%	760
	11th to 20th	Night	21% 15% 39% 20% 4 1	743
	21st to end	Night	24% 12% 33% 27% 4	628
March	1st to 10th	Night	23% 11% 35% 26% 6%	760
	11th to 20th	Night	25% 14% 32% 22% 7% 1	760
	21st to end	Night	23% 10% 30% 29% 7% 1	836
April	1st to 10th	Night	29% 13% 26% 26% 6%	760
	11th to 20th	Night	26% 9% 34% 24% 6%	658
	21st to end	Night	28% 11% 30% 24% 6%	570
May	1st to 10th	Night	25% 10% 33% 27% 6%	532
	11th to 20th	Night	25% 9% 27% 32% 7%	374
	21st to end	Night	27% 6% 30% 29% 8%	411
June	1st to 10th	Night	25% 7% 27% 35% 5% 1	380
	11th to 20th	Night	19% 7% 25% 37% 12%	380
	21st to end	Night	24% 6% 23% 37% 9%	380
July	1st to 10th	Night	17% 5% 30% 37% 11% 1	370
	11th to 20th	Night	19% 3 22% 41% 14% 1	368
	21st to end	Night	16% 5% 18% 46% 14%	416
August	1st to 10th	Night	19% 4 14% 47% 16% 1	378
	11th to 20th	Night	17% 5% 21% 40% 16% 1	554
	21st to end	Night	19% 5% 24% 32% 18% 2	736
September	1st to 10th	Night	20% 5% 25% 34% 15% 1	760
	11th to 20th	Night	20% 6% 23% 31% 18% 2	760
	21st to end	Night	22% 6% 25% 31% 15% 1	760
October	1st to 10th	Night	22% 9% 26% 33% 9% 1	760
	11th to 20th	Night	29% 10% 24% 27% 9% 1	760
	21st to end	Night	30% 12% 29% 25% 4	836
November	1st to 10th	Night	27% 13% 26% 26% 9%	780
	11th to 20th	Night	25% 13% 27% 26% 8% 1	800
	21st to end	Night	31% 13% 30% 19% 6%	883
December	1st to 10th	Night	30% 12% 28% 23% 8% 1	878
	11th to 20th	Night	25% 18% 28% 22% 6% 1	850
	21st to end	Night	33% 16% 29% 18% 4 1	908

Page generated at 2024-12-03 06:45:14. Version ac07

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