West Vancouver
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Vancouver clear sky chart from 2005-11-06 to 2026-06-01.

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	24% 9% 3 7% 4 4 4 3 5% 6% 32%	135842
	Night	29% 10% 3 6% 4 3 3 3 4 5% 30%	136015
Transparency	Day	54% 7% 14% 17% 8% 1	135549
	Night	57% 6% 12% 16% 8% 1	135886
Seeing	Day	24% 4 16% 26% 23% 6%	17358
	Night	31% 4 12% 25% 22% 6%	25598

By Month

Percentage Cloud Cover NW (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	43% 14% 4 8% 5% 4 3 3 4 4 9%	4125
	11th to 20th	Day	23% 10% 3 6% 3 3 3 3 4 8% 35%	4119
	21st to end	Day	44% 7% 2 6% 4 3 2 2 3 4 23%	5175
February	1st to 10th	Day	33% 13% 4 8% 5% 4 4 4 4 7% 15%	1890
	11th to 20th	Day	31% 12% 3 8% 5% 4 4 3 3 5% 22%	1845
	21st to end	Day	28% 14% 4 8% 5% 6% 5% 2 3 4 19%	1565
March	1st to 10th	Day	28% 17% 5% 9% 5% 5% 4 3 4 4 15%	4792
	11th to 20th	Day	29% 14% 3 8% 5% 4 4 3 3 5% 23%	5110
	21st to end	Day	33% 14% 4 8% 5% 5% 4 3 4 5% 15%	5736
April	1st to 10th	Day	28% 13% 3 7% 4 6% 5% 4 6% 6% 17%	2520
	11th to 20th	Day	23% 11% 3 8% 5% 5% 4 4 5% 6% 24%	2609
	21st to end	Day	25% 11% 3 7% 4 4 4 3 5% 6% 26%	2787
May	1st to 10th	Day	14% 9% 3 7% 4 4 4 3 4 6% 41%	6460
	11th to 20th	Day	19% 9% 3 8% 5% 4 4 4 7% 8% 28%	6417
	21st to end	Day	24% 8% 2 6% 4 4 5% 4 7% 8% 26%	7243
June	1st to 10th	Day	22% 9% 3 7% 5% 4 4 4 5% 6% 30%	3001
	11th to 20th	Day	22% 10% 4 9% 5% 5% 6% 4 6% 7% 23%	3000
	21st to end	Day	16% 9% 2 8% 5% 5% 5% 4 6% 7% 35%	3000
July	1st to 10th	Day	9% 4 2 5% 3 4 3 3 4 5% 58%	6780
	11th to 20th	Day	5% 3 1 3 2 2 3 2 4 6% 68%	6780
	21st to end	Day	9% 4 1 4 3 3 3 3 5% 8% 56%	7040
August	1st to 10th	Day	6% 3 2 4 2 2 2 2 4 5% 66%	4490
	11th to 20th	Day	14% 7% 2 8% 5% 4 4 4 5% 6% 41%	4156
	21st to end	Day	18% 6% 3 7% 4 4 3 3 5% 7% 42%	4573
September	1st to 10th	Day	13% 7% 2 7% 4 4 4 3 5% 7% 45%	2400
	11th to 20th	Day	20% 8% 3 7% 4 4 4 3 4 6% 37%	2389
	21st to end	Day	27% 7% 2 6% 3 4 4 3 5% 7% 33%	2110
October	1st to 10th	Day	26% 8% 3 9% 4 5% 4 3 5% 6% 27%	3280
	11th to 20th	Day	38% 7% 2 5% 4 4 4 4 5% 5% 21%	3261
	21st to end	Day	35% 12% 4 9% 5% 4 4 3 6% 5% 15%	3277
November	1st to 10th	Day	42% 9% 3 7% 4 4 4 3 4 5% 15%	1648
	11th to 20th	Day	41% 12% 3 6% 4 4 2 3 3 4 17%	1680
	21st to end	Day	42% 10% 4 6% 3 3 3 3 4 4 18%	1680
December	1st to 10th	Day	28% 10% 3 7% 4 4 5% 4 5% 7% 22%	2614
	11th to 20th	Day	48% 14% 3 7% 4 3 3 3 3 4 10%	2715
	21st to end	Day	46% 14% 4 8% 4 3 4 2 3 3 8%	3575
January	1st to 10th	Night	42% 14% 4 8% 4 4 3 2 3 4 12%	8770
	11th to 20th	Night	26% 6% 3 6% 3 3 3 3 5% 7% 36%	8779
	21st to end	Night	40% 8% 2 5% 3 2 2 2 3 4 29%	9006
February	1st to 10th	Night	34% 13% 4 7% 4 4 3 3 4 4 19%	2730
	11th to 20th	Night	29% 13% 4 7% 4 3 4 3 3 5% 25%	2662
	21st to end	Night	32% 13% 4 6% 4 3 4 3 4 4 24%	2240
March	1st to 10th	Night	28% 16% 4 7% 4 4 4 3 4 5% 21%	5321
	11th to 20th	Night	30% 13% 3 6% 3 4 4 3 4 4 26%	5109
	21st to end	Night	40% 13% 4 7% 4 3 3 2 3 4 16%	5481
April	1st to 10th	Night	29% 13% 3 7% 6% 4 4 3 5% 5% 22%	2100
	11th to 20th	Night	21% 12% 4 8% 5% 3 5% 4 5% 6% 27%	1959
	21st to end	Night	23% 10% 3 7% 5% 5% 4 3 5% 6% 29%	1832
May	1st to 10th	Night	17% 9% 2 5% 3 3 3 3 4 4 48%	3720
	11th to 20th	Night	15% 7% 3 8% 4 5% 4 4 7% 8% 35%	3696
	21st to end	Night	20% 10% 4 10% 5% 5% 4 3 5% 7% 28%	3857
June	1st to 10th	Night	23% 8% 3 6% 5% 4 4 4 5% 6% 33%	1400
	11th to 20th	Night	17% 11% 4 7% 5% 5% 5% 4 6% 7% 29%	1400
	21st to end	Night	15% 6% 2 7% 5% 4 4 4 5% 7% 41%	1400
July	1st to 10th	Night	9% 4 2 4 3 3 3 2 4 6% 61%	3180
	11th to 20th	Night	4 2 1 2 2 2 2 2 3 5% 76%	3180
	21st to end	Night	7% 4 1 4 2 3 3 3 5% 6% 60%	3801
August	1st to 10th	Night	5% 2 1 2 2 2 2 2 4 6% 71%	2659
	11th to 20th	Night	10% 6% 3 6% 3 4 3 3 6% 7% 48%	2902
	21st to end	Night	15% 6% 2 7% 4 4 4 3 5% 6% 44%	3338
September	1st to 10th	Night	9% 4 2 5% 3 4 4 3 5% 7% 54%	2000
	11th to 20th	Night	21% 6% 2 6% 4 2 3 4 5% 5% 42%	2010
	21st to end	Night	24% 8% 3 6% 4 4 3 2 4 5% 38%	2290
October	1st to 10th	Night	24% 9% 3 8% 5% 4 4 4 5% 5% 29%	3920
	11th to 20th	Night	34% 8% 3 6% 3 3 4 3 3 5% 28%	3897
	21st to end	Night	36% 12% 3 7% 4 3 3 2 4 5% 22%	4525
November	1st to 10th	Night	41% 12% 3 7% 4 4 3 3 3 4 17%	2870
	11th to 20th	Night	40% 11% 3 7% 3 3 3 2 3 4 21%	2940
	21st to end	Night	39% 11% 3 7% 4 3 3 2 4 4 20%	2940
December	1st to 10th	Night	29% 11% 3 6% 3 4 4 3 5% 6% 26%	4768
	11th to 20th	Night	46% 14% 3 7% 4 4 3 2 3 4 10%	5710
	21st to end	Night	46% 17% 3 7% 3 3 2 2 3 3 11%	7623

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	78% 6% 6% 7% 2	4125
	11th to 20th	Day	49% 7% 11% 18% 13% 3	4140
	21st to end	Day	67% 4 5% 16% 8%	5176
February	1st to 10th	Day	71% 5% 9% 8% 4 2	1890
	11th to 20th	Day	65% 6% 9% 13% 6% 1	1854
	21st to end	Day	70% 5% 10% 10% 3 2	1565
March	1st to 10th	Day	69% 8% 9% 10% 4	4792
	11th to 20th	Day	64% 7% 8% 18% 2 1	5110
	21st to end	Day	73% 6% 11% 8% 2	5736
April	1st to 10th	Day	67% 8% 14% 10% 2	2520
	11th to 20th	Day	60% 7% 11% 13% 8% 1	2609
	21st to end	Day	61% 6% 13% 14% 6%	2787
May	1st to 10th	Day	44% 6% 17% 23% 9%	6460
	11th to 20th	Day	52% 10% 18% 17% 3	6420
	21st to end	Day	54% 9% 18% 16% 2	7244
June	1st to 10th	Day	56% 5% 19% 14% 4 2	3001
	11th to 20th	Day	62% 7% 16% 12% 3	3000
	21st to end	Day	51% 8% 16% 16% 8% 1	3000
July	1st to 10th	Day	28% 8% 18% 22% 18% 6%	6706
	11th to 20th	Day	19% 7% 19% 33% 20% 1	6699
	21st to end	Day	26% 10% 28% 23% 12% 2	6843
August	1st to 10th	Day	22% 5% 11% 46% 15% 1	4473
	11th to 20th	Day	43% 9% 21% 17% 8% 1	4195
	21st to end	Day	44% 7% 18% 19% 11% 1	4572
September	1st to 10th	Day	40% 7% 15% 23% 11% 4	2400
	11th to 20th	Day	49% 6% 11% 18% 14% 2	2389
	21st to end	Day	53% 7% 15% 16% 8% 2	2110
October	1st to 10th	Day	59% 7% 14% 15% 5%	3280
	11th to 20th	Day	63% 9% 9% 12% 6%	3261
	21st to end	Day	70% 9% 8% 9% 4 1	3277
November	1st to 10th	Day	73% 5% 8% 9% 4 1	1648
	11th to 20th	Day	73% 4 7% 8% 5% 2	1680
	21st to end	Day	71% 4 7% 10% 6% 1	1680
December	1st to 10th	Day	59% 7% 9% 17% 8% 1	2614
	11th to 20th	Day	81% 5% 6% 6% 2 1	2718
	21st to end	Day	83% 5% 5% 5% 2	3575
January	1st to 10th	Night	77% 6% 5% 9% 3	8770
	11th to 20th	Night	46% 7% 13% 18% 14% 2	8820
	21st to end	Night	62% 4 7% 19% 8%	9006
February	1st to 10th	Night	69% 5% 9% 9% 5% 3	2730
	11th to 20th	Night	63% 7% 9% 12% 8% 2	2664
	21st to end	Night	64% 4 11% 13% 6% 2	2240
March	1st to 10th	Night	64% 8% 9% 12% 7%	5321
	11th to 20th	Night	62% 6% 9% 18% 4	5110
	21st to end	Night	73% 5% 11% 8% 2	5481
April	1st to 10th	Night	64% 5% 14% 13% 3	2100
	11th to 20th	Night	57% 7% 11% 16% 7% 2	1959
	21st to end	Night	57% 5% 14% 16% 8%	1832
May	1st to 10th	Night	40% 6% 14% 26% 13%	3717
	11th to 20th	Night	43% 11% 21% 21% 4	3696
	21st to end	Night	55% 7% 19% 16% 3	3857
June	1st to 10th	Night	52% 6% 19% 14% 6% 3	1400
	11th to 20th	Night	53% 8% 19% 15% 5%	1400
	21st to end	Night	44% 9% 20% 16% 8% 3	1400
July	1st to 10th	Night	25% 6% 20% 26% 16% 7%	3145
	11th to 20th	Night	12% 6% 22% 33% 24% 3	3138
	21st to end	Night	23% 7% 25% 28% 14% 2	3693
August	1st to 10th	Night	16% 4 15% 37% 26% 2	2651
	11th to 20th	Night	34% 11% 27% 16% 8% 4	2929
	21st to end	Night	40% 6% 20% 23% 10% 1	3338
September	1st to 10th	Night	30% 7% 18% 26% 13% 5%	2000
	11th to 20th	Night	44% 8% 12% 17% 15% 4	2010
	21st to end	Night	51% 5% 15% 19% 8% 2	2290
October	1st to 10th	Night	56% 8% 15% 14% 6%	3920
	11th to 20th	Night	61% 5% 9% 16% 9%	3897
	21st to end	Night	66% 7% 8% 14% 5%	4525
November	1st to 10th	Night	73% 4 8% 9% 4 1	2870
	11th to 20th	Night	70% 4 9% 9% 6% 2	2940
	21st to end	Night	70% 4 8% 9% 8% 1	2940
December	1st to 10th	Night	59% 7% 12% 16% 5% 1	4768
	11th to 20th	Night	80% 5% 6% 6% 2 1	5706
	21st to end	Night	80% 5% 5% 7% 3	7623

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	45% 6% 10% 19% 13% 6%	220
	11th to 20th	Day	40% 7% 13% 16% 16% 7%	220
	21st to end	Day	46% 3 12% 16% 18% 5%	272
February	1st to 10th	Day	38% 5% 16% 23% 16% 2	430
	11th to 20th	Day	36% 2 20% 23% 17% 2	425
	21st to end	Day	32% 7% 19% 26% 12% 4	361
March	1st to 10th	Day	33% 6% 17% 24% 15% 4	540
	11th to 20th	Day	36% 6% 16% 19% 19% 4	540
	21st to end	Day	35% 8% 17% 23% 13% 4	594
April	1st to 10th	Day	30% 5% 21% 22% 18% 4	540
	11th to 20th	Day	24% 7% 19% 24% 19% 6%	532
	21st to end	Day	23% 5% 25% 25% 17% 5%	540
May	1st to 10th	Day	15% 6% 20% 30% 25% 5%	543
	11th to 20th	Day	17% 5% 16% 28% 26% 8%	568
	21st to end	Day	16% 5% 20% 32% 20% 7%	699
June	1st to 10th	Day	17% 4 19% 32% 25% 3	731
	11th to 20th	Day	18% 4 21% 29% 24% 4	730
	21st to end	Day	15% 2 16% 33% 28% 6%	730
July	1st to 10th	Day	12% 1 15% 32% 32% 8%	721
	11th to 20th	Day	7% 2 15% 35% 34% 7%	718
	21st to end	Day	6% 2 10% 30% 40% 11%	650
August	1st to 10th	Day	11% 2 10% 25% 38% 13%	527
	11th to 20th	Day	9% 2 11% 31% 36% 11%	517
	21st to end	Day	12% 2 17% 31% 28% 10%	583
September	1st to 10th	Day	13% 2 15% 33% 28% 9%	530
	11th to 20th	Day	22% 4 14% 25% 26% 9%	530
	21st to end	Day	26% 4 17% 25% 23% 6%	530
October	1st to 10th	Day	29% 4 15% 25% 19% 8%	530
	11th to 20th	Day	37% 5% 15% 18% 18% 8%	530
	21st to end	Day	39% 8% 14% 23% 13% 5%	435
November	1st to 10th	Day	37% 7% 18% 20% 14% 3	220
	11th to 20th	Day	44% 5% 11% 15% 15% 10%	220
	21st to end	Day	47% 6% 12% 14% 10% 10%	220
December	1st to 10th	Day	46% 3 15% 9% 15% 11%	220
	11th to 20th	Day	45% 7% 13% 17% 14% 3	220
	21st to end	Day	47% 5% 12% 22% 11% 3	242
January	1st to 10th	Night	49% 6% 12% 19% 11% 3	950
	11th to 20th	Night	41% 5% 11% 22% 19% 3	950
	21st to end	Night	40% 4 13% 24% 16% 4	943
February	1st to 10th	Night	37% 5% 16% 26% 14% 3	840
	11th to 20th	Night	35% 3 16% 27% 17% 2	824
	21st to end	Night	36% 5% 18% 23% 15% 3	692
March	1st to 10th	Night	35% 6% 16% 21% 20% 3	840
	11th to 20th	Night	40% 4 15% 22% 15% 4	840
	21st to end	Night	36% 4 17% 23% 16% 5%	924
April	1st to 10th	Night	32% 5% 12% 28% 19% 5%	840
	11th to 20th	Night	24% 6% 16% 31% 18% 5%	711
	21st to end	Night	25% 4 16% 33% 17% 5%	572
May	1st to 10th	Night	18% 2 12% 32% 31% 6%	420
	11th to 20th	Night	20% 3 10% 27% 31% 9%	414
	21st to end	Night	20% 3 11% 30% 32% 6%	455
June	1st to 10th	Night	22% 5% 8% 31% 30% 5%	400
	11th to 20th	Night	18% 4 16% 32% 25% 6%	400
	21st to end	Night	15% 3 8% 31% 39% 6%	400
July	1st to 10th	Night	12% 1 9% 28% 41% 9%	390
	11th to 20th	Night	8% 2 8% 28% 44% 10%	388
	21st to end	Night	7% 2 6% 23% 47% 15%	438
August	1st to 10th	Night	9% 1 6% 21% 45% 19%	422
	11th to 20th	Night	9% 4 22% 49% 16%	594
	21st to end	Night	14% 2 9% 23% 41% 11%	714
September	1st to 10th	Night	10% 2 7% 31% 39% 12%	800
	11th to 20th	Night	21% 3 9% 21% 33% 15%	800
	21st to end	Night	26% 3 12% 26% 28% 6%	800
October	1st to 10th	Night	24% 3 12% 27% 26% 9%	800
	11th to 20th	Night	35% 3 13% 23% 22% 5%	800
	21st to end	Night	40% 3 12% 26% 13% 5%	880
November	1st to 10th	Night	43% 5% 13% 24% 14% 1	820
	11th to 20th	Night	43% 5% 13% 23% 13% 3	840
	21st to end	Night	43% 4 14% 20% 16% 4	840
December	1st to 10th	Night	37% 3 14% 24% 17% 4	862
	11th to 20th	Night	53% 5% 13% 21% 8% 1	950
	21st to end	Night	47% 7% 17% 19% 9% 1	1045

Page generated at 2026-05-28 22:53:29. Version ac07

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