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 2024-09-14.

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 6% 4 4 4 3 4 6% 33%	101205
	Night	29% 10% 3 6% 4 3 3 3 4 5% 31%	96769
Transparency	Day	54% 6% 13% 17% 8% 1	100953
	Night	57% 5% 12% 16% 8% 2	96667
Seeing	Day	24% 4 16% 26% 24% 7%	15233
	Night	31% 4 13% 24% 22% 6%	23334

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	45% 13% 4 7% 5% 4 3 2 3 4 10%	2219
	11th to 20th	Day	32% 14% 3 6% 3 3 2 2 3 6% 26%	2199
	21st to end	Day	59% 9% 2 5% 3 3 2 2 3 3 9%	2769
February	1st to 10th	Day	35% 12% 5% 7% 5% 4 3 4 4 6% 16%	1710
	11th to 20th	Day	32% 11% 3 8% 4 4 4 3 4 5% 22%	1665
	21st to end	Day	26% 14% 4 8% 5% 6% 5% 2 3 5% 20%	1420
March	1st to 10th	Day	27% 16% 5% 9% 6% 4 4 3 5% 4 15%	3256
	11th to 20th	Day	25% 11% 3 6% 4 3 4 2 3 5% 32%	3490
	21st to end	Day	29% 15% 4 8% 5% 4 4 3 4 5% 20%	3912
April	1st to 10th	Day	28% 14% 3 8% 4 6% 5% 4 6% 6% 16%	2280
	11th to 20th	Day	24% 12% 3 8% 5% 5% 4 4 5% 6% 24%	2357
	21st to end	Day	26% 12% 3 7% 4 4 5% 3 5% 7% 23%	2521
May	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 5% 5% 39%	4420
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 5% 7% 9% 34%	4377
	21st to end	Day	29% 9% 3 7% 5% 4 5% 4 6% 7% 22%	4939
June	1st to 10th	Day	23% 9% 4 8% 5% 4 4 4 5% 6% 28%	2850
	11th to 20th	Day	22% 10% 3 9% 5% 4 6% 4 5% 7% 23%	2850
	21st to end	Day	16% 8% 2 7% 5% 5% 5% 4 6% 7% 35%	2850
July	1st to 10th	Day	7% 4 2 4 3 3 3 3 4 5% 63%	4740
	11th to 20th	Day	7% 3 1 3 2 2 3 2 4 5% 69%	4740
	21st to end	Day	12% 5% 2 5% 3 3 3 3 6% 8% 50%	4900
August	1st to 10th	Day	6% 3 2 3 2 2 2 2 4 5% 67%	4352
	11th to 20th	Day	14% 7% 2 8% 5% 4 4 4 5% 6% 41%	4026
	21st to end	Day	18% 6% 3 7% 4 4 3 3 5% 7% 41%	4433
September	1st to 10th	Day	14% 7% 2 7% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	20% 8% 3 7% 4 4 4 3 4 5% 38%	2189
	21st to end	Day	27% 6% 2 6% 3 3 4 3 5% 7% 34%	1900
October	1st to 10th	Day	26% 8% 3 7% 3 3 3 3 5% 6% 34%	1800
	11th to 20th	Day	34% 9% 3 6% 4 4 4 3 5% 6% 23%	1800
	21st to end	Day	37% 10% 3 6% 3 3 3 2 5% 6% 22%	1828
November	1st to 10th	Day	43% 9% 3 7% 4 4 3 2 4 4 16%	1488
	11th to 20th	Day	40% 13% 3 6% 3 4 2 3 3 4 19%	1520
	21st to end	Day	41% 10% 4 6% 2 3 4 3 4 4 19%	1520
December	1st to 10th	Day	34% 15% 3 5% 3 3 4 3 3 4 23%	1478
	11th to 20th	Day	42% 15% 3 7% 4 3 3 3 3 4 14%	1685
	21st to end	Day	46% 14% 3 7% 4 3 4 3 3 3 10%	2442
January	1st to 10th	Night	43% 14% 4 8% 4 4 3 2 3 4 13%	4726
	11th to 20th	Night	34% 8% 3 6% 4 4 3 2 4 8% 23%	4699
	21st to end	Night	56% 12% 2 5% 3 2 2 2 2 3 12%	4884
February	1st to 10th	Night	35% 12% 4 7% 4 4 3 3 4 4 19%	2470
	11th to 20th	Night	29% 13% 4 7% 4 3 4 3 3 5% 24%	2402
	21st to end	Night	30% 13% 4 6% 4 3 4 3 4 4 25%	2033
March	1st to 10th	Night	29% 18% 4 6% 4 4 4 3 3 5% 22%	3617
	11th to 20th	Night	26% 10% 2 5% 3 3 3 3 4 5% 35%	3489
	21st to end	Night	33% 15% 4 8% 4 4 3 2 3 4 21%	3741
April	1st to 10th	Night	29% 13% 3 7% 6% 4 4 2 5% 5% 22%	1900
	11th to 20th	Night	22% 13% 3 7% 5% 4 5% 3 4 6% 27%	1771
	21st to end	Night	25% 11% 3 7% 5% 5% 4 4 5% 6% 25%	1658
May	1st to 10th	Night	17% 8% 2 6% 4 3 3 4 4 4 46%	2540
	11th to 20th	Night	12% 6% 2 5% 3 4 4 4 7% 9% 44%	2516
	21st to end	Night	25% 11% 4 9% 5% 4 4 2 4 5% 27%	2619
June	1st to 10th	Night	24% 9% 3 6% 5% 4 4 4 5% 6% 32%	1330
	11th to 20th	Night	18% 11% 4 7% 4 5% 5% 4 6% 7% 29%	1330
	21st to end	Night	15% 6% 2 7% 5% 5% 4 4 5% 7% 41%	1330
July	1st to 10th	Night	6% 3 1 4 3 3 3 2 3 6% 66%	2220
	11th to 20th	Night	5% 3 1 2 2 2 2 2 3 4 74%	2220
	21st to end	Night	10% 5% 2 4 3 3 3 4 6% 6% 55%	2650
August	1st to 10th	Night	5% 2 1 2 2 2 2 2 4 6% 72%	2578
	11th to 20th	Night	10% 6% 3 6% 3 4 3 3 6% 7% 49%	2812
	21st to end	Night	15% 6% 2 7% 4 3 4 3 5% 6% 43%	3236
September	1st to 10th	Night	9% 4 2 5% 3 4 4 3 5% 7% 55%	1900
	11th to 20th	Night	22% 6% 2 6% 4 2 3 4 5% 5% 41%	1848
	21st to end	Night	23% 8% 3 6% 3 4 3 2 3 5% 39%	2060
October	1st to 10th	Night	22% 7% 2 7% 3 4 4 3 4 4 39%	2160
	11th to 20th	Night	34% 8% 2 6% 3 3 4 3 3 5% 30%	2160
	21st to end	Night	37% 9% 2 5% 3 3 3 2 4 5% 27%	2528
November	1st to 10th	Night	41% 12% 3 6% 4 3 3 3 3 4 18%	2590
	11th to 20th	Night	38% 11% 3 7% 3 3 3 2 3 4 22%	2660
	21st to end	Night	39% 11% 3 7% 4 3 3 2 4 4 21%	2660
December	1st to 10th	Night	34% 12% 3 6% 4 3 3 3 3 4 24%	2698
	11th to 20th	Night	46% 14% 2 7% 4 3 2 3 3 4 12%	3520
	21st to end	Night	46% 15% 3 6% 3 3 2 1 3 3 15%	5214

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% 5% 7% 7% 2 1	2219
	11th to 20th	Day	63% 5% 11% 11% 5% 5%	2220
	21st to end	Day	83% 3 5% 7% 2	2769
February	1st to 10th	Day	72% 5% 9% 8% 4 2	1710
	11th to 20th	Day	66% 6% 9% 12% 6% 1	1674
	21st to end	Day	69% 4 11% 11% 3 2	1420
March	1st to 10th	Day	67% 9% 11% 9% 4	3256
	11th to 20th	Day	56% 7% 11% 24% 2 1	3490
	21st to end	Day	68% 4 15% 9% 3	3912
April	1st to 10th	Day	69% 7% 13% 9% 2	2280
	11th to 20th	Day	62% 6% 11% 12% 7% 2	2357
	21st to end	Day	64% 6% 12% 12% 6%	2521
May	1st to 10th	Day	47% 6% 16% 23% 7%	4420
	11th to 20th	Day	45% 8% 22% 21% 4	4380
	21st to end	Day	62% 7% 16% 13% 2	4940
June	1st to 10th	Day	59% 5% 18% 13% 4 2	2850
	11th to 20th	Day	62% 7% 16% 12% 3	2850
	21st to end	Day	50% 7% 16% 17% 8% 1	2850
July	1st to 10th	Day	25% 6% 11% 25% 24% 9%	4666
	11th to 20th	Day	21% 4 14% 38% 21% 2	4659
	21st to end	Day	32% 10% 20% 23% 13% 2	4745
August	1st to 10th	Day	22% 5% 10% 47% 15% 1	4335
	11th to 20th	Day	43% 9% 21% 17% 8% 1	4065
	21st to end	Day	45% 7% 18% 19% 11% 1	4432
September	1st to 10th	Day	41% 6% 14% 23% 11% 4	2280
	11th to 20th	Day	50% 5% 11% 17% 14% 2	2189
	21st to end	Day	52% 7% 15% 16% 8% 2	1900
October	1st to 10th	Day	53% 5% 15% 18% 9%	1800
	11th to 20th	Day	63% 7% 11% 15% 4 1	1800
	21st to end	Day	64% 6% 11% 11% 7% 1	1828
November	1st to 10th	Day	74% 4 8% 9% 4 1	1488
	11th to 20th	Day	72% 3 8% 9% 6% 2	1520
	21st to end	Day	70% 4 7% 11% 7% 1	1520
December	1st to 10th	Day	66% 5% 8% 12% 8% 1	1478
	11th to 20th	Day	77% 4 7% 8% 2 2	1688
	21st to end	Day	80% 5% 6% 7% 2 1	2442
January	1st to 10th	Night	76% 5% 5% 11% 2 1	4726
	11th to 20th	Night	59% 5% 14% 12% 8% 3	4740
	21st to end	Night	81% 3 5% 8% 2 1	4884
February	1st to 10th	Night	69% 5% 10% 10% 4 2	2470
	11th to 20th	Night	64% 7% 10% 11% 7% 2	2404
	21st to end	Night	62% 4 11% 14% 6% 2	2033
March	1st to 10th	Night	65% 6% 9% 13% 7%	3617
	11th to 20th	Night	53% 6% 13% 23% 5% 1	3490
	21st to end	Night	70% 5% 12% 10% 2	3741
April	1st to 10th	Night	65% 5% 14% 13% 3	1900
	11th to 20th	Night	58% 6% 11% 15% 7% 2	1771
	21st to end	Night	61% 5% 12% 14% 8%	1658
May	1st to 10th	Night	41% 7% 15% 26% 10%	2540
	11th to 20th	Night	34% 11% 25% 25% 5%	2516
	21st to end	Night	59% 6% 18% 13% 3	2619
June	1st to 10th	Night	54% 6% 18% 15% 4 3	1330
	11th to 20th	Night	53% 8% 20% 14% 4	1330
	21st to end	Night	43% 8% 20% 16% 8% 3	1330
July	1st to 10th	Night	22% 4 12% 30% 22% 10%	2185
	11th to 20th	Night	16% 4 14% 39% 26% 2	2178
	21st to end	Night	29% 7% 16% 29% 15% 3	2566
August	1st to 10th	Night	16% 4 15% 38% 27% 2	2570
	11th to 20th	Night	34% 10% 28% 17% 8% 3	2839
	21st to end	Night	41% 6% 20% 23% 10% 1	3236
September	1st to 10th	Night	31% 7% 17% 26% 14% 5%	1900
	11th to 20th	Night	45% 7% 12% 16% 16% 4	1848
	21st to end	Night	50% 5% 15% 20% 8% 2	2060
October	1st to 10th	Night	49% 6% 14% 19% 11% 1	2160
	11th to 20th	Night	59% 4 13% 17% 6%	2160
	21st to end	Night	61% 6% 10% 14% 9%	2528
November	1st to 10th	Night	73% 4 9% 9% 4 1	2590
	11th to 20th	Night	69% 4 9% 10% 6% 2	2660
	21st to end	Night	70% 3 9% 9% 8% 1	2660
December	1st to 10th	Night	65% 5% 11% 11% 7% 1	2698
	11th to 20th	Night	78% 4 7% 6% 4 1	3516
	21st to end	Night	77% 3 6% 9% 4 1	5214

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	44% 7% 9% 19% 12% 8%	180
	11th to 20th	Day	45% 8% 14% 12% 16% 5%	180
	21st to end	Day	49% 4 12% 18% 15% 4	224
February	1st to 10th	Day	39% 6% 16% 22% 15% 2	370
	11th to 20th	Day	37% 2 21% 22% 16% 2	365
	21st to end	Day	29% 8% 18% 28% 13% 4	312
March	1st to 10th	Day	32% 6% 16% 26% 15% 5%	460
	11th to 20th	Day	32% 5% 16% 22% 21% 5%	460
	21st to end	Day	35% 8% 16% 24% 14% 4	506
April	1st to 10th	Day	29% 6% 22% 22% 18% 3	460
	11th to 20th	Day	27% 6% 18% 24% 19% 6%	452
	21st to end	Day	25% 5% 24% 25% 18% 4	460
May	1st to 10th	Day	16% 5% 18% 29% 27% 5%	463
	11th to 20th	Day	15% 5% 13% 28% 30% 9%	488
	21st to end	Day	17% 5% 17% 32% 21% 8%	603
June	1st to 10th	Day	18% 4 18% 31% 26% 3	680
	11th to 20th	Day	18% 5% 21% 28% 23% 4	680
	21st to end	Day	15% 2 16% 32% 29% 6%	680
July	1st to 10th	Day	12% 1 15% 31% 33% 8%	671
	11th to 20th	Day	7% 2 14% 33% 36% 8%	668
	21st to end	Day	6% 2 10% 29% 40% 11%	602
August	1st to 10th	Day	10% 2 10% 25% 39% 14%	487
	11th to 20th	Day	9% 2 9% 31% 38% 12%	477
	21st to end	Day	13% 2 17% 32% 27% 9%	539
September	1st to 10th	Day	14% 2 16% 33% 27% 8%	490
	11th to 20th	Day	21% 4 15% 25% 26% 9%	463
	21st to end	Day	25% 3 16% 24% 25% 7%	450
October	1st to 10th	Day	28% 4 14% 26% 20% 9%	450
	11th to 20th	Day	37% 4 14% 18% 18% 9%	450
	21st to end	Day	36% 9% 14% 21% 14% 5%	365
November	1st to 10th	Day	37% 7% 18% 19% 14% 4	180
	11th to 20th	Day	42% 4 12% 14% 17% 11%	180
	21st to end	Day	42% 7% 14% 14% 11% 11%	180
December	1st to 10th	Day	48% 4 16% 8% 13% 11%	180
	11th to 20th	Day	40% 8% 12% 20% 16% 3	180
	21st to end	Day	44% 6% 13% 24% 10% 3	198
January	1st to 10th	Night	49% 6% 13% 17% 11% 4	850
	11th to 20th	Night	43% 5% 11% 20% 18% 2	850
	21st to end	Night	42% 4 14% 23% 14% 3	852
February	1st to 10th	Night	37% 5% 17% 25% 14% 3	760
	11th to 20th	Night	36% 4 17% 27% 15% 2	744
	21st to end	Night	34% 5% 18% 23% 16% 4	628
March	1st to 10th	Night	35% 6% 16% 20% 19% 3	760
	11th to 20th	Night	37% 4 15% 23% 17% 4	760
	21st to end	Night	36% 4 16% 22% 16% 5%	836
April	1st to 10th	Night	32% 5% 13% 28% 18% 4	760
	11th to 20th	Night	25% 5% 17% 30% 18% 4	643
	21st to end	Night	27% 4 16% 32% 17% 4	518
May	1st to 10th	Night	19% 2 13% 31% 30% 6%	380
	11th to 20th	Night	19% 3 9% 25% 34% 10%	374
	21st to end	Night	20% 3 11% 29% 31% 6%	411
June	1st to 10th	Night	23% 5% 8% 29% 30% 4	380
	11th to 20th	Night	18% 4 16% 32% 24% 6%	380
	21st to end	Night	14% 2 8% 31% 38% 6%	380
July	1st to 10th	Night	12% 1 9% 28% 41% 9%	370
	11th to 20th	Night	9% 2 8% 26% 45% 10%	368
	21st to end	Night	7% 1 6% 23% 48% 15%	416
August	1st to 10th	Night	8% 1 6% 20% 45% 19%	401
	11th to 20th	Night	9% 4 21% 50% 17%	564
	21st to end	Night	14% 3 9% 23% 40% 11%	678
September	1st to 10th	Night	10% 2 7% 31% 39% 11%	760
	11th to 20th	Night	22% 3 9% 19% 32% 16%	736
	21st to end	Night	25% 3 11% 25% 29% 7%	720
October	1st to 10th	Night	23% 3 13% 25% 27% 9%	720
	11th to 20th	Night	36% 3 12% 23% 21% 6%	720
	21st to end	Night	39% 3 13% 26% 14% 5%	792
November	1st to 10th	Night	42% 6% 13% 23% 15% 1	740
	11th to 20th	Night	41% 5% 14% 22% 13% 4	760
	21st to end	Night	42% 4 15% 19% 16% 4	760
December	1st to 10th	Night	36% 4 15% 25% 16% 4	778
	11th to 20th	Night	52% 4 13% 22% 8% 1	850
	21st to end	Night	47% 7% 17% 18% 9% 1	935

Page generated at 2024-09-11 07:00:05. Version ac07

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