Port Coquitlam
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Coquitlam clear sky chart from 2005-11-06 to 2025-07-21.

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	28% 10% 3 7% 4 4 4 3 4 5% 29%	123906
	Night	31% 11% 3 6% 4 3 3 3 4 5% 28%	123925
Transparency	Day	57% 6% 13% 16% 7% 1	123655
	Night	59% 6% 12% 15% 7% 1	123819
Seeing	Day	31% 8% 21% 24% 13% 4	16225
	Night	36% 5% 16% 25% 17% 2	24401

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	42% 14% 4 7% 5% 4 3 3 3 4 11%	3179
	11th to 20th	Day	22% 11% 4 6% 3 4 4 3 3 5% 34%	3159
	21st to end	Day	47% 7% 2 5% 3 2 2 2 2 2 25%	4026
February	1st to 10th	Day	35% 13% 3 9% 4 4 3 3 4 5% 17%	1800
	11th to 20th	Day	33% 14% 3 7% 4 3 4 2 4 5% 22%	1755
	21st to end	Day	28% 18% 4 9% 5% 5% 4 2 3 4 19%	1510
March	1st to 10th	Day	30% 20% 5% 9% 5% 4 4 3 3 4 14%	4643
	11th to 20th	Day	29% 17% 4 8% 5% 4 3 2 3 3 23%	5000
	21st to end	Day	36% 14% 4 8% 5% 4 4 3 4 5% 14%	5651
April	1st to 10th	Day	33% 13% 3 8% 6% 5% 5% 4 5% 5% 14%	2400
	11th to 20th	Day	25% 13% 3 8% 6% 4 5% 3 5% 5% 23%	2459
	21st to end	Day	29% 12% 4 7% 4 5% 4 3 5% 5% 21%	2670
May	1st to 10th	Day	18% 11% 3 6% 4 4 3 3 4 6% 38%	6320
	11th to 20th	Day	25% 10% 3 8% 5% 4 5% 4 6% 7% 24%	6277
	21st to end	Day	28% 9% 3 7% 4 4 5% 4 6% 7% 22%	7010
June	1st to 10th	Day	28% 8% 3 7% 5% 4 4 4 4 7% 27%	3000
	11th to 20th	Day	29% 11% 4 8% 6% 5% 5% 3 4 5% 20%	3000
	21st to end	Day	22% 9% 3 7% 5% 5% 4 3 5% 6% 32%	3000
July	1st to 10th	Day	10% 4 2 5% 3 3 3 3 4 5% 58%	4890
	11th to 20th	Day	8% 4 1 3 2 2 3 2 3 4 67%	4890
	21st to end	Day	16% 5% 2 5% 3 3 3 2 6% 7% 49%	4858
August	1st to 10th	Day	8% 4 2 4 2 2 2 2 4 6% 64%	4384
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 38%	4026
	21st to end	Day	23% 6% 2 6% 4 4 4 3 4 7% 37%	4406
September	1st to 10th	Day	19% 7% 2 6% 3 4 3 2 4 6% 43%	2280
	11th to 20th	Day	22% 8% 3 8% 5% 3 4 3 4 4 37%	2280
	21st to end	Day	30% 7% 2 6% 4 4 3 3 4 5% 33%	2001
October	1st to 10th	Day	29% 9% 3 7% 4 4 4 3 5% 6% 26%	3180
	11th to 20th	Day	41% 7% 2 6% 4 4 4 3 4 4 21%	3161
	21st to end	Day	38% 14% 4 8% 3 4 3 3 5% 4 14%	3178
November	1st to 10th	Day	45% 10% 3 8% 4 4 3 2 3 4 15%	1568
	11th to 20th	Day	44% 11% 3 6% 4 2 2 2 3 3 20%	1600
	21st to end	Day	43% 11% 3 5% 3 3 2 4 4 4 18%	1600
December	1st to 10th	Day	27% 11% 3 7% 4 4 4 3 5% 9% 23%	2602
	11th to 20th	Day	49% 15% 4 7% 3 3 2 2 3 3 10%	2645
	21st to end	Day	49% 16% 3 8% 4 3 3 2 3 2 7%	3498
January	1st to 10th	Night	41% 14% 4 8% 4 3 3 2 3 3 15%	6766
	11th to 20th	Night	24% 8% 2 6% 3 3 4 3 5% 8% 33%	6739
	21st to end	Night	44% 9% 2 4 2 2 2 2 2 3 28%	6927
February	1st to 10th	Night	35% 13% 3 7% 5% 4 3 3 3 5% 19%	2600
	11th to 20th	Night	31% 15% 3 7% 5% 3 3 3 3 4 24%	2532
	21st to end	Night	32% 13% 3 6% 5% 2 3 3 5% 5% 24%	2119
March	1st to 10th	Night	29% 19% 3 7% 4 4 3 3 3 4 21%	5249
	11th to 20th	Night	31% 15% 3 7% 3 3 3 3 3 4 24%	4999
	21st to end	Night	43% 13% 4 6% 3 3 3 2 3 4 16%	5323
April	1st to 10th	Night	30% 14% 3 7% 5% 5% 3 3 5% 5% 20%	2000
	11th to 20th	Night	23% 12% 4 8% 5% 4 4 3 5% 6% 27%	1889
	21st to end	Night	27% 11% 4 7% 6% 5% 4 2 4 6% 25%	1730
May	1st to 10th	Night	18% 10% 3 6% 4 3 2 2 3 4 46%	3640
	11th to 20th	Night	20% 9% 3 7% 4 4 4 4 6% 8% 33%	3616
	21st to end	Night	23% 10% 3 8% 5% 5% 5% 3 5% 6% 27%	3862
June	1st to 10th	Night	24% 7% 2 7% 5% 4 4 4 5% 5% 31%	1400
	11th to 20th	Night	20% 13% 3 8% 5% 5% 3 4 6% 7% 26%	1400
	21st to end	Night	18% 8% 2 6% 5% 3 4 4 6% 7% 38%	1400
July	1st to 10th	Night	7% 3 2 3 4 2 3 2 4 6% 64%	2290
	11th to 20th	Night	6% 2 1 3 2 2 2 2 3 4 74%	2290
	21st to end	Night	12% 4 1 4 3 3 3 3 5% 6% 56%	2694
August	1st to 10th	Night	5% 3 1 2 2 2 2 3 5% 7% 69%	2546
	11th to 20th	Night	13% 6% 3 6% 3 4 3 3 5% 6% 48%	2812
	21st to end	Night	18% 6% 2 6% 4 3 4 3 5% 7% 41%	3264
September	1st to 10th	Night	12% 4 2 6% 3 4 3 3 5% 5% 53%	1900
	11th to 20th	Night	23% 6% 2 5% 4 3 4 2 4 5% 41%	1900
	21st to end	Night	27% 7% 3 6% 4 3 3 3 3 6% 36%	2176
October	1st to 10th	Night	26% 12% 3 7% 5% 4 4 3 4 5% 27%	3800
	11th to 20th	Night	38% 8% 2 5% 3 3 3 3 5% 5% 25%	3777
	21st to end	Night	39% 13% 3 7% 3 3 3 2 3 4 21%	4377
November	1st to 10th	Night	44% 11% 3 6% 4 3 3 2 3 4 17%	2730
	11th to 20th	Night	43% 11% 3 5% 4 2 3 2 3 3 21%	2800
	21st to end	Night	40% 11% 3 6% 4 3 3 3 3 3 20%	2800
December	1st to 10th	Night	30% 10% 3 6% 4 4 4 3 6% 6% 26%	4560
	11th to 20th	Night	47% 15% 3 6% 4 3 3 2 3 3 11%	5560
	21st to end	Night	51% 16% 3 6% 3 2 2 1 2 3 10%	7458

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	76% 6% 8% 7% 2	3179
	11th to 20th	Day	54% 6% 15% 16% 7% 3	3180
	21st to end	Day	68% 3 6% 16% 7%	4026
February	1st to 10th	Day	70% 6% 9% 8% 4 3	1800
	11th to 20th	Day	67% 5% 9% 12% 6% 1	1764
	21st to end	Day	70% 5% 9% 10% 3 2	1510
March	1st to 10th	Day	72% 6% 8% 10% 3	4643
	11th to 20th	Day	66% 6% 9% 17% 2	5000
	21st to end	Day	73% 6% 11% 8% 2	5651
April	1st to 10th	Day	71% 7% 12% 8% 2	2400
	11th to 20th	Day	62% 6% 12% 11% 7% 2	2459
	21st to end	Day	64% 7% 12% 12% 6%	2670
May	1st to 10th	Day	46% 5% 18% 21% 9%	6320
	11th to 20th	Day	55% 9% 20% 13% 3	6280
	21st to end	Day	58% 8% 18% 14% 2	7011
June	1st to 10th	Day	58% 6% 17% 13% 5% 2	3000
	11th to 20th	Day	65% 7% 15% 10% 3	3000
	21st to end	Day	53% 7% 17% 15% 8% 1	3000
July	1st to 10th	Day	28% 7% 11% 25% 22% 8%	4816
	11th to 20th	Day	22% 4 14% 40% 18% 1	4809
	21st to end	Day	34% 7% 22% 24% 11% 2	4704
August	1st to 10th	Day	23% 5% 12% 43% 15% 1	4367
	11th to 20th	Day	45% 8% 20% 17% 8% 1	4065
	21st to end	Day	46% 7% 17% 20% 9% 1	4405
September	1st to 10th	Day	43% 7% 13% 22% 11% 4	2280
	11th to 20th	Day	50% 6% 10% 17% 13% 2	2280
	21st to end	Day	54% 6% 15% 15% 9% 1	2001
October	1st to 10th	Day	59% 5% 15% 14% 6%	3180
	11th to 20th	Day	65% 7% 12% 11% 6%	3161
	21st to end	Day	71% 6% 9% 9% 4 1	3178
November	1st to 10th	Day	74% 5% 8% 9% 3 1	1568
	11th to 20th	Day	72% 4 8% 9% 5% 2	1600
	21st to end	Day	71% 5% 6% 10% 7% 1	1600
December	1st to 10th	Day	58% 6% 12% 17% 8%	2602
	11th to 20th	Day	80% 5% 6% 6% 2 1	2648
	21st to end	Day	83% 5% 6% 5% 1	3498
January	1st to 10th	Night	75% 5% 7% 9% 4	6766
	11th to 20th	Night	49% 7% 17% 17% 7% 3	6780
	21st to end	Night	64% 3 8% 18% 6% 1	6927
February	1st to 10th	Night	68% 6% 11% 8% 5% 3	2600
	11th to 20th	Night	65% 7% 9% 10% 8% 2	2534
	21st to end	Night	64% 4 11% 13% 6% 2	2119
March	1st to 10th	Night	67% 5% 9% 11% 7%	5249
	11th to 20th	Night	63% 7% 11% 16% 4	5000
	21st to end	Night	74% 6% 12% 7% 2	5323
April	1st to 10th	Night	66% 5% 14% 12% 2	2000
	11th to 20th	Night	58% 7% 12% 14% 7% 2	1889
	21st to end	Night	60% 7% 13% 13% 6% 1	1730
May	1st to 10th	Night	43% 4 16% 25% 11% 1	3637
	11th to 20th	Night	48% 9% 23% 16% 4	3616
	21st to end	Night	57% 8% 17% 16% 2	3862
June	1st to 10th	Night	54% 7% 17% 14% 5% 3	1400
	11th to 20th	Night	56% 9% 18% 14% 4	1400
	21st to end	Night	45% 9% 20% 16% 8% 3	1400
July	1st to 10th	Night	23% 5% 13% 32% 20% 7%	2255
	11th to 20th	Night	17% 4 14% 43% 21% 1	2248
	21st to end	Night	28% 7% 17% 29% 17% 3	2609
August	1st to 10th	Night	16% 4 17% 38% 23% 2	2538
	11th to 20th	Night	36% 7% 28% 18% 8% 4	2839
	21st to end	Night	43% 7% 20% 20% 9% 1	3264
September	1st to 10th	Night	33% 8% 17% 23% 14% 5%	1900
	11th to 20th	Night	47% 5% 12% 16% 15% 4	1900
	21st to end	Night	52% 6% 14% 18% 8% 2	2176
October	1st to 10th	Night	59% 5% 17% 12% 6%	3800
	11th to 20th	Night	62% 5% 10% 15% 7%	3777
	21st to end	Night	69% 4 8% 13% 5%	4377
November	1st to 10th	Night	73% 4 9% 9% 4 1	2730
	11th to 20th	Night	70% 5% 8% 9% 6% 2	2800
	21st to end	Night	69% 5% 8% 8% 9% 1	2800
December	1st to 10th	Night	58% 7% 14% 15% 5% 1	4560
	11th to 20th	Night	80% 5% 6% 6% 3 1	5556
	21st to end	Night	82% 4 5% 6% 3	7458

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	49% 5% 16% 16% 10% 5%	200
	11th to 20th	Day	49% 10% 13% 16% 12% 2	200
	21st to end	Day	51% 4 13% 17% 13% 2	230
February	1st to 10th	Day	44% 7% 21% 18% 9% 1	400
	11th to 20th	Day	41% 7% 21% 22% 8% 2	395
	21st to end	Day	38% 11% 25% 17% 7% 2	344
March	1st to 10th	Day	41% 7% 22% 20% 9% 2	500
	11th to 20th	Day	42% 8% 15% 19% 15% 2	500
	21st to end	Day	44% 10% 21% 16% 8% 2	550
April	1st to 10th	Day	38% 11% 20% 20% 10% 1	500
	11th to 20th	Day	30% 11% 24% 21% 11% 3	492
	21st to end	Day	32% 10% 25% 20% 10% 2	500
May	1st to 10th	Day	25% 10% 22% 28% 12% 3	503
	11th to 20th	Day	30% 6% 20% 24% 16% 4	528
	21st to end	Day	25% 8% 28% 23% 11% 5%	615
June	1st to 10th	Day	27% 8% 26% 27% 11% 2	730
	11th to 20th	Day	30% 12% 25% 23% 9% 1	730
	21st to end	Day	24% 8% 23% 26% 17% 3	730
July	1st to 10th	Day	18% 5% 25% 35% 14% 3	721
	11th to 20th	Day	13% 8% 23% 37% 15% 3	718
	21st to end	Day	13% 5% 19% 39% 18% 6%	573
August	1st to 10th	Day	16% 6% 17% 33% 20% 8%	487
	11th to 20th	Day	14% 2 21% 34% 23% 7%	477
	21st to end	Day	20% 8% 22% 27% 16% 6%	539
September	1st to 10th	Day	22% 6% 23% 29% 15% 5%	490
	11th to 20th	Day	26% 7% 19% 28% 17% 3	490
	21st to end	Day	31% 8% 16% 24% 16% 5%	490
October	1st to 10th	Day	32% 5% 20% 21% 18% 4	490
	11th to 20th	Day	42% 7% 13% 20% 15% 4	490
	21st to end	Day	44% 8% 18% 19% 9% 4	393
November	1st to 10th	Day	45% 8% 17% 20% 10% 1	200
	11th to 20th	Day	50% 7% 11% 12% 13% 9%	200
	21st to end	Day	49% 8% 16% 11% 7% 10%	200
December	1st to 10th	Day	48% 7% 11% 10% 16% 9%	200
	11th to 20th	Day	53% 6% 15% 16% 8% 4	200
	21st to end	Day	53% 5% 14% 22% 6% 1	220
January	1st to 10th	Night	53% 6% 15% 19% 7% 1	900
	11th to 20th	Night	44% 4 16% 25% 10%	900
	21st to end	Night	46% 6% 16% 22% 10%	880
February	1st to 10th	Night	42% 5% 23% 23% 7% 1	800
	11th to 20th	Night	39% 7% 20% 25% 10%	784
	21st to end	Night	38% 9% 20% 22% 10%	660
March	1st to 10th	Night	41% 7% 17% 22% 13% 1	800
	11th to 20th	Night	44% 7% 15% 22% 11% 1	800
	21st to end	Night	45% 5% 16% 21% 12% 1	880
April	1st to 10th	Night	36% 5% 18% 27% 12% 2	800
	11th to 20th	Night	29% 7% 22% 28% 12% 2	701
	21st to end	Night	35% 4 18% 29% 12% 2	530
May	1st to 10th	Night	22% 2 20% 33% 23% 1	400
	11th to 20th	Night	22% 5% 8% 35% 27% 4	394
	21st to end	Night	23% 3 13% 36% 24% 1	433
June	1st to 10th	Night	28% 4 11% 36% 20% 2	400
	11th to 20th	Night	26% 5% 18% 28% 21% 3	400
	21st to end	Night	19% 5% 14% 30% 30% 3	400
July	1st to 10th	Night	12% 3 11% 35% 38% 2	390
	11th to 20th	Night	11% 2 9% 33% 40% 6%	388
	21st to end	Night	8% 1 8% 29% 49% 6%	416
August	1st to 10th	Night	12% 2 4 25% 48% 9%	382
	11th to 20th	Night	9% 1 6% 28% 45% 11%	564
	21st to end	Night	17% 2 12% 28% 36% 4	693
September	1st to 10th	Night	14% 1 12% 37% 33% 3	760
	11th to 20th	Night	25% 3 12% 25% 31% 5%	760
	21st to end	Night	33% 3 13% 29% 21% 2	760
October	1st to 10th	Night	30% 4 14% 27% 22% 3	760
	11th to 20th	Night	41% 3 14% 26% 14% 2	760
	21st to end	Night	43% 3 19% 24% 9% 2	836
November	1st to 10th	Night	49% 6% 19% 21% 5%	780
	11th to 20th	Night	51% 6% 18% 17% 9% 1	800
	21st to end	Night	46% 6% 18% 18% 10% 2	800
December	1st to 10th	Night	39% 5% 18% 26% 12% 1	800
	11th to 20th	Night	55% 7% 16% 17% 4 1	900
	21st to end	Night	53% 8% 19% 17% 3	990

Page generated at 2025-07-17 22:10:01. Version ac07

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