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 2024-11-06.

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	24% 9% 3 6% 4 4 4 3 5% 6% 34%	105520
	Night	29% 9% 3 6% 4 3 3 3 4 5% 31%	102139
Transparency	Day	29% 47% 8% 11% 5% 1	105269
	Night	31% 46% 7% 10% 5% 1	102036
Seeing	Day	27% 6% 17% 26% 18% 6%	15378
	Night	33% 5% 10% 26% 21% 5%	23531

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	46% 10% 3 7% 5% 4 3 3 4 4 10%	2219
	11th to 20th	Day	32% 13% 4 5% 4 3 3 2 3 5% 26%	2199
	21st to end	Day	59% 9% 2 5% 3 2 3 2 3 3 9%	2797
February	1st to 10th	Day	35% 11% 4 7% 6% 5% 3 2 5% 5% 17%	1710
	11th to 20th	Day	33% 10% 3 7% 5% 4 3 3 3 6% 22%	1665
	21st to end	Day	27% 13% 4 8% 5% 5% 5% 3 4 6% 22%	1429
March	1st to 10th	Day	27% 16% 4 7% 6% 4 4 4 4 5% 18%	3247
	11th to 20th	Day	26% 9% 3 6% 4 3 3 3 3 6% 33%	3490
	21st to end	Day	29% 13% 3 7% 5% 4 3 3 4 6% 22%	3933
April	1st to 10th	Day	29% 11% 4 7% 5% 5% 5% 4 6% 6% 19%	2280
	11th to 20th	Day	24% 11% 4 7% 5% 5% 4 3 5% 5% 27%	2344
	21st to end	Day	27% 11% 3 7% 4 4 4 3 6% 6% 26%	2527
May	1st to 10th	Day	17% 9% 3 5% 4 3 4 3 5% 5% 41%	4420
	11th to 20th	Day	13% 7% 3 6% 4 5% 4 5% 7% 9% 37%	4377
	21st to end	Day	29% 9% 3 7% 5% 5% 4 4 6% 6% 24%	4904
June	1st to 10th	Day	23% 9% 3 7% 4 5% 4 3 6% 6% 30%	2850
	11th to 20th	Day	22% 10% 3 8% 5% 4 5% 4 6% 6% 26%	2850
	21st to end	Day	15% 8% 3 7% 4 4 5% 4 5% 7% 37%	2850
July	1st to 10th	Day	8% 4 2 4 3 2 3 3 4 4 64%	4740
	11th to 20th	Day	7% 3 1 3 2 2 2 2 3 5% 70%	4740
	21st to end	Day	12% 5% 2 4 3 3 3 3 5% 7% 54%	4868
August	1st to 10th	Day	6% 3 1 4 2 2 3 2 4 5% 68%	4372
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 45%	4026
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 7% 42%	4411
September	1st to 10th	Day	16% 6% 2 6% 3 3 3 3 4 6% 47%	2280
	11th to 20th	Day	21% 7% 3 6% 4 4 3 3 5% 6% 38%	2280
	21st to end	Day	26% 7% 2 5% 4 4 4 3 5% 6% 35%	1997
October	1st to 10th	Day	25% 7% 3 7% 5% 5% 4 3 6% 6% 29%	3180
	11th to 20th	Day	37% 8% 2 6% 3 4 4 3 5% 6% 23%	3161
	21st to end	Day	32% 10% 3 9% 5% 4 4 4 6% 6% 16%	3178
November	1st to 10th	Day	42% 9% 3 7% 3 4 3 2 4 4 17%	1528
	11th to 20th	Day	42% 10% 2 7% 4 3 2 3 3 4 20%	1520
	21st to end	Day	42% 9% 4 5% 4 3 3 3 4 4 18%	1520
December	1st to 10th	Day	34% 14% 2 5% 4 3 3 3 3 4 25%	1501
	11th to 20th	Day	39% 15% 3 8% 4 4 4 3 4 4 12%	1685
	21st to end	Day	46% 13% 4 7% 5% 4 3 2 3 3 10%	2442
January	1st to 10th	Night	43% 13% 3 8% 4 4 3 2 3 4 14%	4726
	11th to 20th	Night	35% 8% 2 5% 3 3 4 3 5% 8% 24%	4699
	21st to end	Night	54% 11% 3 5% 3 2 2 2 3 3 12%	4856
February	1st to 10th	Night	35% 11% 3 7% 4 4 4 3 4 5% 20%	2470
	11th to 20th	Night	31% 12% 2 7% 4 3 4 2 4 5% 25%	2402
	21st to end	Night	30% 12% 3 7% 4 3 4 3 5% 4 27%	2024
March	1st to 10th	Night	30% 16% 3 6% 4 4 3 3 4 4 22%	3626
	11th to 20th	Night	26% 8% 2 6% 3 3 4 2 4 6% 36%	3489
	21st to end	Night	34% 13% 4 8% 4 4 3 3 3 4 21%	3719
April	1st to 10th	Night	30% 11% 3 7% 5% 5% 5% 3 5% 5% 23%	1900
	11th to 20th	Night	22% 12% 3 7% 5% 4 4 3 5% 6% 29%	1783
	21st to end	Night	25% 10% 4 7% 5% 4 4 3 5% 5% 27%	1651
May	1st to 10th	Night	18% 7% 2 5% 3 3 4 3 4 5% 47%	2540
	11th to 20th	Night	11% 5% 2 5% 4 4 3 4 6% 8% 46%	2516
	21st to end	Night	24% 10% 3 8% 5% 5% 4 3 4 5% 28%	2666
June	1st to 10th	Night	24% 7% 3 6% 5% 4 4 3 6% 6% 32%	1330
	11th to 20th	Night	17% 10% 4 7% 5% 5% 4 5% 4 8% 30%	1330
	21st to end	Night	14% 6% 3 6% 5% 4 4 4 5% 7% 41%	1330
July	1st to 10th	Night	6% 3 1 3 3 2 3 2 3 7% 66%	2220
	11th to 20th	Night	6% 2 1 2 2 2 2 2 3 4 75%	2220
	21st to end	Night	9% 4 2 5% 3 3 4 3 5% 6% 56%	2681
August	1st to 10th	Night	4 3 1 2 2 2 2 2 3 6% 73%	2555
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 5% 7% 51%	2812
	21st to end	Night	14% 5% 2 6% 4 4 4 3 6% 7% 45%	3259
September	1st to 10th	Night	9% 4 1 5% 3 4 4 3 5% 7% 56%	1900
	11th to 20th	Night	21% 6% 2 5% 5% 3 3 3 4 5% 44%	1900
	21st to end	Night	24% 7% 2 6% 3 3 4 2 4 6% 40%	2179
October	1st to 10th	Night	21% 8% 3 7% 5% 5% 5% 4 5% 5% 32%	3800
	11th to 20th	Night	32% 8% 3 6% 3 3 3 3 4 5% 28%	3777
	21st to end	Night	35% 10% 3 7% 4 3 3 2 4 5% 24%	4378
November	1st to 10th	Night	42% 9% 3 7% 4 4 3 3 4 4 19%	2672
	11th to 20th	Night	39% 9% 3 5% 4 3 4 3 3 4 23%	2660
	21st to end	Night	39% 10% 3 6% 5% 4 3 3 3 4 21%	2660
December	1st to 10th	Night	34% 10% 2 6% 4 4 3 2 3 5% 26%	2675
	11th to 20th	Night	47% 13% 3 6% 3 3 3 3 3 3 13%	3520
	21st to end	Night	46% 13% 3 7% 3 3 2 2 2 3 16%	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	51% 36% 6% 5% 2	2219
	11th to 20th	Day	40% 36% 9% 7% 4 3	2220
	21st to end	Day	57% 38% 2 3	2797
February	1st to 10th	Day	25% 65% 3 3 2 2	1710
	11th to 20th	Day	25% 64% 4 5% 1 1	1674
	21st to end	Day	22% 65% 5% 5% 2 1	1429
March	1st to 10th	Day	43% 39% 9% 6% 3	3247
	11th to 20th	Day	29% 42% 7% 20% 2	3490
	21st to end	Day	41% 40% 11% 6% 2	3933
April	1st to 10th	Day	24% 66% 4 5% 1	2280
	11th to 20th	Day	22% 65% 4 5% 2 1	2344
	21st to end	Day	22% 65% 4 6% 3	2527
May	1st to 10th	Day	26% 39% 9% 17% 8%	4420
	11th to 20th	Day	26% 41% 16% 14% 3	4380
	21st to end	Day	41% 40% 12% 7% 1	4905
June	1st to 10th	Day	19% 65% 6% 7% 2	2850
	11th to 20th	Day	19% 66% 6% 7% 3	2850
	21st to end	Day	17% 64% 8% 8% 3	2850
July	1st to 10th	Day	13% 36% 5% 18% 20% 8%	4666
	11th to 20th	Day	8% 35% 7% 30% 18% 1	4659
	21st to end	Day	22% 38% 16% 16% 6% 1	4714
August	1st to 10th	Day	9% 37% 7% 33% 13% 1	4355
	11th to 20th	Day	27% 42% 17% 10% 4	4065
	21st to end	Day	29% 40% 11% 11% 8%	4410
September	1st to 10th	Day	20% 61% 5% 9% 4 1	2280
	11th to 20th	Day	22% 60% 5% 6% 6%	2280
	21st to end	Day	21% 60% 6% 8% 4	1997
October	1st to 10th	Day	38% 39% 11% 10% 2	3180
	11th to 20th	Day	41% 38% 8% 8% 4	3161
	21st to end	Day	44% 41% 6% 8% 2	3178
November	1st to 10th	Day	30% 57% 6% 6% 1	1528
	11th to 20th	Day	26% 60% 4 6% 3 2	1520
	21st to end	Day	24% 60% 4 7% 5% 1	1520
December	1st to 10th	Day	27% 59% 3 8% 4	1501
	11th to 20th	Day	44% 47% 3 4 2 1	1688
	21st to end	Day	55% 36% 4 4 1 1	2442
January	1st to 10th	Night	50% 36% 5% 8% 2	4726
	11th to 20th	Night	35% 38% 10% 9% 6% 3	4740
	21st to end	Night	55% 38% 3 3	4856
February	1st to 10th	Night	25% 65% 3 3 2 2	2470
	11th to 20th	Night	25% 64% 4 3 3 1	2404
	21st to end	Night	18% 65% 5% 7% 2 2	2024
March	1st to 10th	Night	41% 40% 4 9% 6%	3626
	11th to 20th	Night	26% 40% 11% 19% 4	3490
	21st to end	Night	44% 40% 8% 7% 1	3719
April	1st to 10th	Night	23% 65% 4 7% 2	1900
	11th to 20th	Night	21% 66% 4 6% 2 1	1783
	21st to end	Night	21% 64% 5% 5% 4	1651
May	1st to 10th	Night	24% 39% 9% 19% 8% 1	2540
	11th to 20th	Night	20% 42% 19% 15% 5%	2516
	21st to end	Night	40% 38% 12% 8% 2	2666
June	1st to 10th	Night	18% 65% 7% 8% 2 1	1330
	11th to 20th	Night	17% 65% 8% 8% 3	1330
	21st to end	Night	15% 65% 9% 7% 4	1330
July	1st to 10th	Night	9% 36% 5% 24% 20% 6%	2185
	11th to 20th	Night	6% 35% 6% 33% 19% 1	2178
	21st to end	Night	22% 37% 11% 19% 11% 1	2596
August	1st to 10th	Night	6% 36% 9% 30% 18% 1	2547
	11th to 20th	Night	26% 40% 19% 11% 3 1	2839
	21st to end	Night	27% 40% 13% 12% 7%	3259
September	1st to 10th	Night	16% 61% 8% 8% 6% 1	1900
	11th to 20th	Night	21% 60% 6% 6% 5% 1	1900
	21st to end	Night	20% 60% 7% 9% 4	2179
October	1st to 10th	Night	37% 41% 12% 8% 2	3800
	11th to 20th	Night	41% 38% 6% 11% 4	3777
	21st to end	Night	42% 40% 7% 9% 3	4378
November	1st to 10th	Night	31% 57% 6% 5% 2	2672
	11th to 20th	Night	26% 59% 4 6% 3 2	2660
	21st to end	Night	27% 59% 3 4 6%	2660
December	1st to 10th	Night	27% 60% 3 6% 4 1	2675
	11th to 20th	Night	44% 48% 4 3 2	3516
	21st to end	Night	52% 36% 3 6% 3	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	48% 4 13% 18% 9% 7%	180
	11th to 20th	Day	51% 9% 7% 13% 14% 6%	180
	21st to end	Day	48% 7% 9% 14% 16% 5%	217
February	1st to 10th	Day	43% 5% 15% 21% 14% 2	370
	11th to 20th	Day	39% 6% 16% 21% 16% 2	365
	21st to end	Day	34% 10% 22% 22% 9% 3	316
March	1st to 10th	Day	35% 7% 19% 22% 14% 4	460
	11th to 20th	Day	36% 6% 15% 20% 19% 5%	460
	21st to end	Day	36% 9% 19% 21% 12% 3	506
April	1st to 10th	Day	33% 8% 19% 22% 15% 2	460
	11th to 20th	Day	27% 8% 23% 22% 15% 6%	452
	21st to end	Day	29% 8% 22% 25% 12% 5%	460
May	1st to 10th	Day	19% 8% 19% 30% 20% 4	463
	11th to 20th	Day	23% 5% 16% 29% 20% 8%	488
	21st to end	Day	21% 7% 23% 27% 16% 7%	581
June	1st to 10th	Day	24% 7% 21% 31% 15% 3	680
	11th to 20th	Day	22% 9% 25% 28% 14% 2	680
	21st to end	Day	16% 8% 19% 30% 22% 5%	680
July	1st to 10th	Day	15% 4 18% 35% 24% 5%	671
	11th to 20th	Day	9% 6% 18% 37% 25% 5%	668
	21st to end	Day	9% 3 15% 38% 26% 8%	583
August	1st to 10th	Day	14% 5% 13% 28% 29% 11%	487
	11th to 20th	Day	10% 3 12% 36% 31% 8%	477
	21st to end	Day	16% 5% 20% 31% 18% 10%	539
September	1st to 10th	Day	18% 5% 19% 30% 20% 8%	490
	11th to 20th	Day	21% 7% 14% 28% 25% 5%	490
	21st to end	Day	27% 5% 17% 23% 21% 7%	490
October	1st to 10th	Day	29% 5% 15% 23% 20% 8%	490
	11th to 20th	Day	38% 6% 12% 18% 18% 8%	490
	21st to end	Day	38% 8% 15% 23% 12% 5%	397
November	1st to 10th	Day	42% 8% 13% 19% 16% 2	190
	11th to 20th	Day	47% 7% 6% 13% 15% 12%	180
	21st to end	Day	45% 7% 13% 14% 9% 12%	180
December	1st to 10th	Day	48% 6% 13% 8% 13% 12%	180
	11th to 20th	Day	47% 5% 13% 16% 16% 3	180
	21st to end	Day	45% 6% 14% 23% 10% 3	198
January	1st to 10th	Night	51% 7% 12% 18% 10% 3	850
	11th to 20th	Night	46% 5% 9% 22% 15% 2	850
	21st to end	Night	45% 6% 9% 24% 14% 3	843
February	1st to 10th	Night	42% 5% 15% 25% 12% 1	760
	11th to 20th	Night	38% 6% 13% 28% 14% 1	744
	21st to end	Night	37% 7% 15% 25% 14% 2	628
March	1st to 10th	Night	39% 7% 12% 22% 18% 2	760
	11th to 20th	Night	40% 6% 12% 25% 14% 3	760
	21st to end	Night	39% 6% 11% 24% 17% 3	836
April	1st to 10th	Night	35% 6% 11% 28% 17% 3	760
	11th to 20th	Night	27% 8% 14% 29% 17% 5%	655
	21st to end	Night	30% 6% 12% 34% 15% 3	511
May	1st to 10th	Night	21% 2 11% 34% 29% 3	380
	11th to 20th	Night	18% 5% 6% 29% 35% 7%	374
	21st to end	Night	21% 3 6% 35% 31% 4	411
June	1st to 10th	Night	26% 3 7% 33% 27% 4	380
	11th to 20th	Night	20% 6% 14% 31% 25% 4	380
	21st to end	Night	16% 3 10% 31% 35% 5%	380
July	1st to 10th	Night	11% 4 6% 32% 43% 5%	370
	11th to 20th	Night	10% 2 5% 31% 43% 8%	368
	21st to end	Night	7% 1 5% 29% 47% 12%	416
August	1st to 10th	Night	11% 3 1 22% 47% 16%	391
	11th to 20th	Night	9% 1 2 24% 49% 15%	564
	21st to end	Night	14% 5% 6% 25% 40% 10%	688
September	1st to 10th	Night	12% 2 5% 34% 38% 9%	760
	11th to 20th	Night	22% 4 8% 22% 33% 11%	760
	21st to end	Night	27% 4 8% 29% 27% 5%	760
October	1st to 10th	Night	26% 4 11% 26% 27% 7%	760
	11th to 20th	Night	37% 4 10% 25% 19% 5%	760
	21st to end	Night	40% 5% 11% 28% 12% 5%	836
November	1st to 10th	Night	48% 5% 12% 23% 12%	764
	11th to 20th	Night	45% 6% 13% 20% 12% 4	760
	21st to end	Night	42% 6% 12% 21% 14% 4	760
December	1st to 10th	Night	38% 4 11% 27% 16% 4	767
	11th to 20th	Night	54% 6% 10% 21% 8% 1	850
	21st to end	Night	51% 7% 13% 21% 9% 1	935

Page generated at 2024-11-03 10:19:02. Version ac07

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