Burnaby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burnaby clear sky chart from 2005-11-06 to 2025-11-03.

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	23% 8% 3 6% 4 4 4 3 5% 6% 34%	130885
	Night	28% 9% 3 6% 4 4 4 3 4 5% 31%	127857
Transparency	Day	33% 39% 10% 12% 5% 1	130592
	Night	36% 39% 9% 11% 4 1	127727
Seeing	Day	26% 7% 17% 26% 18% 6%	16669
	Night	33% 5% 10% 26% 21% 5%	24778

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	41% 11% 3 8% 6% 4 4 3 4 5% 10%	3179
	11th to 20th	Day	23% 10% 3 6% 4 4 4 3 5% 8% 30%	3159
	21st to end	Day	47% 7% 2 5% 3 2 2 2 3 5% 22%	4021
February	1st to 10th	Day	34% 11% 4 7% 6% 5% 4 3 6% 5% 17%	1800
	11th to 20th	Day	33% 10% 3 7% 5% 4 3 3 3 6% 22%	1755
	21st to end	Day	28% 13% 4 8% 5% 5% 5% 3 4 5% 21%	1502
March	1st to 10th	Day	28% 15% 4 9% 6% 4 4 3 5% 5% 16%	4666
	11th to 20th	Day	27% 12% 3 8% 5% 4 4 3 4 6% 25%	5000
	21st to end	Day	33% 12% 4 7% 5% 5% 4 3 4 5% 16%	5633
April	1st to 10th	Day	30% 11% 4 7% 5% 5% 5% 4 6% 6% 18%	2400
	11th to 20th	Day	23% 10% 3 7% 5% 5% 4 3 5% 5% 28%	2469
	21st to end	Day	26% 10% 3 6% 4 4 4 3 6% 6% 27%	2660
May	1st to 10th	Day	15% 8% 3 6% 4 3 4 3 5% 6% 43%	6320
	11th to 20th	Day	19% 8% 3 7% 4 5% 5% 4 6% 8% 31%	6277
	21st to end	Day	24% 7% 2 6% 4 4 5% 4 7% 8% 28%	7036
June	1st to 10th	Day	22% 9% 3 7% 4 5% 4 3 6% 6% 32%	3000
	11th to 20th	Day	22% 10% 3 9% 5% 5% 5% 4 6% 7% 26%	3000
	21st to end	Day	16% 9% 3 7% 4 4 5% 4 5% 7% 36%	3000
July	1st to 10th	Day	9% 4 2 4 3 3 3 3 4 5% 60%	6780
	11th to 20th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	6780
	21st to end	Day	9% 4 1 4 2 3 3 3 4 7% 60%	6994
August	1st to 10th	Day	7% 3 1 4 2 2 3 2 4 5% 67%	4511
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 45%	4156
	21st to end	Day	16% 7% 2 6% 4 3 4 4 5% 7% 42%	4551
September	1st to 10th	Day	15% 6% 2 6% 3 4 3 4 5% 6% 47%	2400
	11th to 20th	Day	21% 7% 3 6% 4 4 3 3 5% 6% 39%	2400
	21st to end	Day	26% 7% 2 5% 4 4 4 3 5% 6% 35%	2102
October	1st to 10th	Day	25% 8% 3 7% 5% 5% 4 3 5% 6% 29%	3280
	11th to 20th	Day	37% 8% 2 6% 3 4 4 3 5% 6% 24%	3261
	21st to end	Day	33% 10% 3 9% 5% 4 4 4 6% 6% 16%	3279
November	1st to 10th	Day	42% 9% 3 8% 3 4 4 3 4 4 17%	1584
	11th to 20th	Day	41% 10% 3 7% 5% 4 3 3 3 4 20%	1600
	21st to end	Day	42% 10% 4 5% 4 3 4 3 4 5% 18%	1600
December	1st to 10th	Day	26% 10% 3 8% 6% 4 5% 4 6% 7% 20%	2587
	11th to 20th	Day	44% 14% 4 8% 4 4 3 3 3 4 10%	2645
	21st to end	Day	45% 13% 4 8% 5% 4 4 3 3 3 8%	3498
January	1st to 10th	Night	41% 12% 4 9% 4 4 3 2 3 4 15%	6766
	11th to 20th	Night	24% 7% 2 5% 3 4 4 4 5% 9% 31%	6739
	21st to end	Night	41% 9% 2 5% 3 2 3 2 3 4 26%	6920
February	1st to 10th	Night	34% 11% 3 8% 5% 4 5% 3 4 5% 20%	2600
	11th to 20th	Night	31% 11% 2 7% 4 3 4 2 4 5% 25%	2532
	21st to end	Night	31% 12% 3 7% 4 3 4 3 5% 4 26%	2127
March	1st to 10th	Night	28% 14% 3 7% 4 4 4 3 4 5% 23%	5227
	11th to 20th	Night	28% 12% 3 7% 4 3 4 3 4 5% 28%	4999
	21st to end	Night	39% 12% 4 8% 4 3 3 3 3 4 17%	5341
April	1st to 10th	Night	30% 11% 4 7% 5% 5% 5% 3 5% 5% 22%	2000
	11th to 20th	Night	21% 11% 3 7% 5% 4 4 3 5% 6% 30%	1878
	21st to end	Night	25% 9% 3 7% 5% 4 4 3 5% 6% 29%	1738
May	1st to 10th	Night	17% 7% 3 6% 3 3 3 2 4 5% 49%	3640
	11th to 20th	Night	15% 7% 3 7% 4 4 4 4 7% 8% 37%	3616
	21st to end	Night	19% 9% 3 9% 6% 5% 5% 3 4 6% 30%	3834
June	1st to 10th	Night	23% 7% 3 6% 4 4 4 3 6% 6% 34%	1400
	11th to 20th	Night	17% 10% 4 7% 5% 5% 4 5% 4 8% 31%	1400
	21st to end	Night	15% 6% 3 6% 5% 4 4 4 5% 8% 41%	1400
July	1st to 10th	Night	10% 4 1 3 3 2 3 2 3 6% 62%	3180
	11th to 20th	Night	4 2 1 2 1 1 2 2 3 5% 77%	3180
	21st to end	Night	7% 3 2 4 2 3 3 3 5% 7% 61%	3846
August	1st to 10th	Night	5% 3 1 2 2 2 2 2 3 6% 72%	2636
	11th to 20th	Night	11% 6% 3 5% 3 3 3 3 5% 7% 51%	2902
	21st to end	Night	14% 5% 2 6% 4 4 4 3 6% 7% 46%	3361
September	1st to 10th	Night	9% 4 1 5% 3 4 4 3 5% 7% 56%	2000
	11th to 20th	Night	20% 6% 2 5% 5% 3 3 3 4 5% 44%	2000
	21st to end	Night	24% 7% 2 6% 3 3 3 2 4 5% 39%	2294
October	1st to 10th	Night	21% 8% 3 7% 5% 5% 5% 4 5% 5% 32%	3920
	11th to 20th	Night	32% 8% 3 6% 3 3 3 3 4 5% 29%	3897
	21st to end	Night	34% 9% 3 7% 4 3 3 2 4 5% 24%	4519
November	1st to 10th	Night	41% 10% 3 7% 4 4 3 3 4 3 18%	2758
	11th to 20th	Night	40% 10% 3 5% 4 3 4 2 3 4 22%	2800
	21st to end	Night	39% 10% 3 6% 5% 4 3 3 4 4 20%	2800
December	1st to 10th	Night	29% 9% 3 8% 6% 5% 6% 4 6% 5% 20%	4589
	11th to 20th	Night	46% 12% 3 7% 4 4 3 3 3 4 11%	5560
	21st to end	Night	44% 14% 3 8% 4 3 3 2 3 3 13%	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	58% 27% 7% 7% 1	3179
	11th to 20th	Day	36% 28% 13% 14% 6% 2	3180
	21st to end	Day	50% 27% 5% 14% 4	4021
February	1st to 10th	Day	26% 62% 3 4 2 3	1800
	11th to 20th	Day	27% 61% 4 6% 1 1	1764
	21st to end	Day	25% 62% 5% 5% 2 1	1502
March	1st to 10th	Day	52% 29% 8% 9% 2	4666
	11th to 20th	Day	44% 31% 7% 16% 1	5000
	21st to end	Day	53% 30% 10% 5% 2	5633
April	1st to 10th	Day	26% 64% 5% 6% 1	2400
	11th to 20th	Day	23% 62% 5% 7% 2 1	2469
	21st to end	Day	22% 63% 5% 7% 3	2660
May	1st to 10th	Day	29% 29% 12% 20% 9%	6320
	11th to 20th	Day	39% 32% 14% 13% 2	6280
	21st to end	Day	39% 30% 16% 13% 2	7037
June	1st to 10th	Day	19% 62% 8% 9% 3	3000
	11th to 20th	Day	21% 63% 7% 7% 3	3000
	21st to end	Day	19% 61% 9% 8% 3	3000
July	1st to 10th	Day	19% 28% 14% 18% 16% 6%	6706
	11th to 20th	Day	11% 27% 16% 28% 18% 1	6699
	21st to end	Day	19% 29% 26% 20% 6%	6798
August	1st to 10th	Day	10% 36% 8% 32% 13% 1	4494
	11th to 20th	Day	28% 41% 17% 10% 4 1	4195
	21st to end	Day	29% 39% 11% 11% 9%	4550
September	1st to 10th	Day	20% 59% 6% 10% 4 1	2400
	11th to 20th	Day	23% 58% 5% 8% 6%	2400
	21st to end	Day	23% 58% 7% 8% 4	2102
October	1st to 10th	Day	39% 38% 11% 10% 2	3280
	11th to 20th	Day	41% 37% 8% 9% 5%	3261
	21st to end	Day	45% 40% 6% 8% 2	3279
November	1st to 10th	Day	32% 56% 5% 5% 1	1584
	11th to 20th	Day	29% 57% 5% 6% 2 2	1600
	21st to end	Day	27% 57% 4 6% 4 1	1600
December	1st to 10th	Day	36% 40% 8% 13% 2	2587
	11th to 20th	Day	58% 31% 4 4 1	2648
	21st to end	Day	64% 27% 5% 4 1	3498
January	1st to 10th	Night	57% 26% 6% 9% 2	6766
	11th to 20th	Night	32% 31% 14% 16% 6% 2	6780
	21st to end	Night	47% 29% 9% 13% 2	6920
February	1st to 10th	Night	26% 62% 3 4 3 3	2600
	11th to 20th	Night	27% 61% 4 4 3 1	2534
	21st to end	Night	21% 62% 5% 7% 2 2	2127
March	1st to 10th	Night	47% 31% 6% 10% 6%	5227
	11th to 20th	Night	41% 30% 10% 16% 3	5000
	21st to end	Night	55% 29% 10% 5% 1	5341
April	1st to 10th	Night	25% 62% 4 7% 1	2000
	11th to 20th	Night	21% 63% 5% 7% 3 1	1878
	21st to end	Night	21% 61% 7% 6% 4	1738
May	1st to 10th	Night	29% 28% 10% 23% 10%	3637
	11th to 20th	Night	33% 32% 18% 13% 3	3616
	21st to end	Night	42% 29% 14% 13% 1	3834
June	1st to 10th	Night	18% 62% 8% 8% 3 1	1400
	11th to 20th	Night	18% 62% 8% 9% 3	1400
	21st to end	Night	17% 62% 9% 8% 4	1400
July	1st to 10th	Night	17% 27% 15% 22% 15% 5%	3145
	11th to 20th	Night	6% 26% 17% 30% 19% 2	3138
	21st to end	Night	18% 27% 21% 23% 9%	3737
August	1st to 10th	Night	7% 35% 9% 29% 18% 1	2628
	11th to 20th	Night	27% 39% 19% 11% 3 1	2929
	21st to end	Night	26% 39% 14% 13% 8% 1	3361
September	1st to 10th	Night	17% 59% 9% 9% 6% 1	2000
	11th to 20th	Night	21% 58% 7% 7% 5% 1	2000
	21st to end	Night	22% 57% 7% 10% 4	2294
October	1st to 10th	Night	37% 40% 13% 8% 2	3920
	11th to 20th	Night	41% 37% 6% 11% 5%	3897
	21st to end	Night	42% 39% 7% 9% 3	4519
November	1st to 10th	Night	33% 55% 5% 5% 2	2758
	11th to 20th	Night	29% 57% 4 6% 3 2	2800
	21st to end	Night	29% 57% 4 4 6%	2800
December	1st to 10th	Night	38% 43% 10% 6% 3	4589
	11th to 20th	Night	56% 33% 5% 5% 1	5556
	21st to end	Night	60% 28% 5% 6% 2	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	47% 6% 12% 20% 10% 7%	200
	11th to 20th	Day	46% 9% 8% 17% 15% 7%	200
	21st to end	Day	46% 7% 10% 14% 16% 7%	240
February	1st to 10th	Day	41% 6% 17% 21% 15% 2	400
	11th to 20th	Day	38% 6% 17% 21% 16% 2	395
	21st to end	Day	35% 10% 22% 21% 9% 3	341
March	1st to 10th	Day	34% 7% 20% 22% 14% 3	500
	11th to 20th	Day	37% 7% 14% 20% 18% 4	500
	21st to end	Day	38% 9% 19% 21% 11% 3	550
April	1st to 10th	Day	33% 9% 18% 22% 15% 3	500
	11th to 20th	Day	26% 8% 24% 23% 15% 5%	492
	21st to end	Day	28% 7% 22% 25% 13% 5%	500
May	1st to 10th	Day	18% 9% 19% 30% 19% 4	503
	11th to 20th	Day	24% 5% 16% 27% 19% 8%	528
	21st to end	Day	20% 7% 23% 26% 16% 7%	628
June	1st to 10th	Day	22% 7% 20% 32% 15% 4	730
	11th to 20th	Day	22% 9% 24% 28% 15% 2	730
	21st to end	Day	17% 8% 19% 30% 22% 5%	730
July	1st to 10th	Day	14% 4 19% 35% 24% 5%	721
	11th to 20th	Day	9% 6% 19% 37% 24% 5%	718
	21st to end	Day	9% 3 15% 38% 27% 8%	630
August	1st to 10th	Day	14% 5% 14% 28% 30% 10%	527
	11th to 20th	Day	11% 3 13% 35% 29% 8%	517
	21st to end	Day	15% 5% 19% 31% 19% 11%	583
September	1st to 10th	Day	17% 5% 18% 30% 22% 8%	530
	11th to 20th	Day	20% 7% 15% 27% 25% 6%	530
	21st to end	Day	27% 5% 18% 23% 20% 6%	530
October	1st to 10th	Day	29% 6% 16% 22% 19% 8%	530
	11th to 20th	Day	36% 8% 14% 17% 17% 7%	530
	21st to end	Day	39% 8% 15% 22% 11% 5%	432
November	1st to 10th	Day	42% 7% 14% 19% 17% 1	204
	11th to 20th	Day	46% 9% 8% 13% 15% 11%	200
	21st to end	Day	46% 8% 13% 14% 10% 12%	200
December	1st to 10th	Day	45% 5% 13% 8% 16% 14%	200
	11th to 20th	Day	49% 5% 14% 15% 15% 3	200
	21st to end	Day	46% 7% 14% 21% 10% 2	220
January	1st to 10th	Night	50% 7% 12% 19% 10% 2	900
	11th to 20th	Night	44% 5% 9% 24% 16% 2	900
	21st to end	Night	44% 6% 9% 24% 15% 3	887
February	1st to 10th	Night	41% 5% 15% 26% 12% 2	800
	11th to 20th	Night	38% 6% 13% 28% 14% 1	784
	21st to end	Night	37% 7% 15% 25% 13% 2	660
March	1st to 10th	Night	38% 7% 12% 22% 19% 2	800
	11th to 20th	Night	41% 6% 12% 24% 14% 3	800
	21st to end	Night	40% 6% 11% 23% 16% 3	880
April	1st to 10th	Night	35% 6% 11% 28% 17% 3	800
	11th to 20th	Night	26% 8% 14% 31% 17% 5%	690
	21st to end	Night	29% 5% 11% 33% 17% 4	538
May	1st to 10th	Night	20% 2 11% 35% 28% 3	400
	11th to 20th	Night	19% 5% 7% 28% 34% 7%	394
	21st to end	Night	20% 3 6% 36% 31% 4	433
June	1st to 10th	Night	25% 4 7% 33% 28% 4	400
	11th to 20th	Night	19% 6% 14% 31% 26% 5%	400
	21st to end	Night	16% 4 10% 30% 36% 5%	400
July	1st to 10th	Night	11% 3 7% 32% 43% 5%	390
	11th to 20th	Night	10% 2 6% 32% 43% 8%	388
	21st to end	Night	6% 1 5% 28% 47% 12%	438
August	1st to 10th	Night	11% 3 1 23% 47% 15%	412
	11th to 20th	Night	10% 2 3 25% 47% 14%	594
	21st to end	Night	13% 4 6% 25% 41% 10%	724
September	1st to 10th	Night	12% 2 5% 33% 37% 11%	800
	11th to 20th	Night	21% 5% 8% 22% 34% 11%	800
	21st to end	Night	27% 4 8% 29% 27% 5%	800
October	1st to 10th	Night	26% 4 11% 26% 27% 6%	800
	11th to 20th	Night	36% 4 12% 25% 19% 5%	800
	21st to end	Night	40% 5% 11% 28% 12% 5%	880
November	1st to 10th	Night	47% 5% 13% 23% 12%	788
	11th to 20th	Night	46% 7% 13% 20% 12% 4	800
	21st to end	Night	42% 6% 12% 21% 14% 5%	800
December	1st to 10th	Night	38% 4 11% 27% 16% 4	808
	11th to 20th	Night	54% 6% 10% 21% 8% 1	900
	21st to end	Night	50% 8% 14% 20% 8% 1	990

Page generated at 2025-10-30 23:02:40. Version ac07

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