Comox
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Comox 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	16% 9% 3 7% 5% 4 5% 4 5% 6% 35%	135812
	Night	20% 11% 3 7% 5% 4 4 3 5% 6% 32%	136037
Transparency	Day	49% 5% 17% 21% 8% 1	135510
	Night	54% 4 15% 19% 8% 1	135918
Seeing	Day	19% 7% 21% 26% 19% 7%	17677
	Night	24% 5% 15% 29% 22% 5%	25734

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	27% 19% 5% 10% 6% 5% 4 3 4 5% 12%	4125
	11th to 20th	Day	16% 10% 4 8% 6% 4 3 3 5% 7% 33%	4119
	21st to end	Day	33% 13% 3 8% 4 4 3 3 3 4 22%	4965
February	1st to 10th	Day	22% 16% 5% 9% 5% 5% 6% 4 6% 5% 18%	1890
	11th to 20th	Day	20% 14% 4 7% 5% 4 4 4 5% 5% 27%	1845
	21st to end	Day	19% 13% 4 8% 7% 6% 6% 5% 6% 5% 21%	1557
March	1st to 10th	Day	20% 15% 3 9% 5% 5% 6% 4 5% 6% 22%	4829
	11th to 20th	Day	15% 13% 4 9% 6% 6% 6% 4 5% 6% 26%	5110
	21st to end	Day	20% 14% 4 10% 6% 6% 6% 4 6% 6% 18%	5607
April	1st to 10th	Day	19% 12% 4 9% 6% 5% 5% 4 6% 6% 25%	2525
	11th to 20th	Day	16% 10% 3 8% 6% 5% 6% 5% 7% 6% 28%	2698
	21st to end	Day	17% 10% 3 8% 5% 4 4 3 5% 7% 33%	2730
May	1st to 10th	Day	11% 8% 3 8% 6% 5% 5% 4 5% 6% 40%	6432
	11th to 20th	Day	13% 9% 3 8% 5% 4 5% 4 6% 9% 33%	6417
	21st to end	Day	17% 10% 3 8% 6% 5% 5% 4 6% 7% 28%	7569
June	1st to 10th	Day	16% 8% 3 8% 5% 5% 6% 4 6% 7% 31%	3001
	11th to 20th	Day	13% 6% 3 8% 7% 6% 6% 6% 8% 9% 26%	3000
	21st to end	Day	14% 7% 3 8% 5% 5% 5% 4 6% 6% 37%	3000
July	1st to 10th	Day	7% 4 2 4 4 3 3 3 4 6% 60%	6780
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 5% 73%	6780
	21st to end	Day	5% 3 1 4 3 3 3 3 4 7% 62%	7330
August	1st to 10th	Day	6% 2 1 3 2 2 2 2 4 6% 69%	4357
	11th to 20th	Day	10% 6% 2 5% 4 4 4 4 7% 9% 43%	4156
	21st to end	Day	12% 5% 2 6% 4 4 5% 3 5% 6% 49%	4664
September	1st to 10th	Day	9% 3 2 5% 4 3 4 4 6% 7% 54%	2420
	11th to 20th	Day	16% 6% 2 6% 3 4 4 3 5% 6% 42%	2294
	21st to end	Day	18% 7% 3 7% 4 4 5% 3 6% 7% 36%	2175
October	1st to 10th	Day	19% 10% 4 9% 5% 5% 5% 3 5% 6% 29%	3280
	11th to 20th	Day	22% 8% 4 8% 5% 5% 5% 4 5% 6% 29%	3261
	21st to end	Day	21% 9% 3 9% 6% 6% 5% 5% 6% 7% 23%	3225
November	1st to 10th	Day	28% 11% 3 8% 5% 6% 5% 4 5% 5% 20%	1648
	11th to 20th	Day	24% 14% 4 8% 4 5% 5% 5% 6% 6% 20%	1680
	21st to end	Day	26% 12% 4 8% 6% 5% 5% 3 5% 5% 21%	1680
December	1st to 10th	Day	19% 16% 6% 9% 5% 5% 5% 2 4 5% 23%	2373
	11th to 20th	Day	35% 14% 3 9% 4 5% 4 3 4 4 15%	2715
	21st to end	Day	33% 16% 5% 10% 5% 4 4 3 4 4 12%	3575
January	1st to 10th	Night	28% 18% 5% 10% 5% 5% 4 3 4 5% 14%	8770
	11th to 20th	Night	17% 10% 3 7% 5% 4 4 3 5% 7% 35%	8779
	21st to end	Night	29% 12% 3 6% 3 4 4 4 4 4 27%	9202
February	1st to 10th	Night	21% 14% 4 8% 6% 5% 6% 3 5% 5% 23%	2730
	11th to 20th	Night	20% 12% 3 6% 4 4 5% 3 5% 7% 31%	2662
	21st to end	Night	18% 15% 4 8% 5% 6% 5% 4 5% 4 26%	2249
March	1st to 10th	Night	19% 14% 3 8% 6% 5% 5% 3 5% 6% 26%	5274
	11th to 20th	Night	11% 9% 3 9% 6% 6% 7% 4 6% 8% 32%	5109
	21st to end	Night	22% 15% 4 8% 5% 5% 5% 4 5% 5% 22%	5610
April	1st to 10th	Night	17% 11% 3 7% 5% 4 5% 5% 7% 8% 28%	2092
	11th to 20th	Night	15% 10% 3 7% 5% 6% 5% 3 6% 8% 32%	1871
	21st to end	Night	16% 9% 2 7% 5% 4 5% 3 6% 7% 35%	1890
May	1st to 10th	Night	13% 7% 2 5% 3 4 4 3 5% 6% 46%	3749
	11th to 20th	Night	13% 6% 3 7% 6% 5% 6% 4 6% 7% 37%	3682
	21st to end	Night	18% 12% 3 8% 5% 5% 5% 4 6% 6% 27%	3547
June	1st to 10th	Night	15% 7% 2 8% 5% 5% 5% 5% 7% 6% 36%	1400
	11th to 20th	Night	16% 8% 2 7% 6% 6% 5% 4 6% 7% 32%	1400
	21st to end	Night	16% 6% 3 5% 4 5% 4 3 5% 8% 41%	1400
July	1st to 10th	Night	7% 4 2 4 3 3 3 4 6% 7% 58%	3180
	11th to 20th	Night	3 2 1 1 2 1 2 2 4 5% 77%	3180
	21st to end	Night	6% 3 1 4 3 3 4 3 5% 7% 60%	3511
August	1st to 10th	Night	6% 3 1 3 2 2 2 2 3 5% 71%	2796
	11th to 20th	Night	11% 5% 2 6% 4 4 5% 3 6% 10% 44%	2902
	21st to end	Night	13% 6% 2 6% 4 4 4 3 5% 4 48%	3245
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 4 7% 55%	1980
	11th to 20th	Night	15% 7% 2 6% 5% 4 4 4 5% 6% 43%	2104
	21st to end	Night	17% 7% 3 7% 4 4 4 3 4 6% 41%	2225
October	1st to 10th	Night	17% 8% 4 9% 6% 5% 6% 3 5% 6% 31%	3920
	11th to 20th	Night	20% 9% 3 9% 5% 5% 5% 3 5% 6% 29%	3897
	21st to end	Night	20% 9% 3 8% 5% 5% 5% 4 5% 7% 30%	4574
November	1st to 10th	Night	28% 11% 3 7% 5% 5% 5% 4 5% 5% 21%	2870
	11th to 20th	Night	24% 11% 3 8% 6% 6% 6% 4 6% 5% 23%	2940
	21st to end	Night	25% 11% 3 8% 5% 5% 5% 4 5% 6% 23%	2940
December	1st to 10th	Night	21% 18% 5% 10% 5% 5% 5% 3 4 5% 20%	5024
	11th to 20th	Night	34% 17% 4 9% 5% 4 4 3 4 4 12%	5710
	21st to end	Night	33% 14% 4 8% 4 4 4 3 4 5% 17%	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	75% 4 7% 11% 3	4125
	11th to 20th	Day	52% 6% 13% 22% 8% 1	4140
	21st to end	Day	68% 3 10% 15% 3	4966
February	1st to 10th	Day	66% 6% 9% 12% 5% 1	1890
	11th to 20th	Day	60% 3 13% 16% 6%	1854
	21st to end	Day	61% 7% 12% 11% 7% 2	1557
March	1st to 10th	Day	62% 4 11% 16% 6%	4829
	11th to 20th	Day	58% 5% 10% 19% 7%	5110
	21st to end	Day	65% 6% 13% 12% 3	5607
April	1st to 10th	Day	59% 6% 14% 17% 4	2525
	11th to 20th	Day	55% 5% 12% 18% 8% 2	2698
	21st to end	Day	53% 3 13% 21% 9% 1	2730
May	1st to 10th	Day	45% 5% 16% 25% 8%	6432
	11th to 20th	Day	47% 6% 22% 22% 3	6420
	21st to end	Day	54% 5% 20% 16% 5% 1	7570
June	1st to 10th	Day	51% 5% 16% 19% 7% 2	3001
	11th to 20th	Day	51% 8% 19% 18% 4 1	3000
	21st to end	Day	47% 5% 21% 20% 7% 1	3000
July	1st to 10th	Day	25% 5% 22% 27% 17% 5%	6706
	11th to 20th	Day	15% 3 23% 41% 17% 1	6699
	21st to end	Day	22% 5% 33% 28% 11% 1	7124
August	1st to 10th	Day	17% 3 16% 47% 17%	4340
	11th to 20th	Day	36% 8% 30% 17% 8% 1	4195
	21st to end	Day	36% 5% 27% 24% 8% 1	4663
September	1st to 10th	Day	29% 6% 25% 27% 11% 2	2420
	11th to 20th	Day	43% 4 18% 21% 13% 1	2294
	21st to end	Day	48% 5% 18% 19% 9% 1	2175
October	1st to 10th	Day	54% 5% 18% 17% 6%	3280
	11th to 20th	Day	57% 5% 14% 21% 4	3261
	21st to end	Day	57% 8% 15% 15% 5%	3225
November	1st to 10th	Day	66% 4 11% 11% 6% 1	1648
	11th to 20th	Day	65% 6% 10% 14% 5% 1	1680
	21st to end	Day	66% 5% 12% 11% 5% 1	1680
December	1st to 10th	Day	64% 4 13% 13% 5%	2373
	11th to 20th	Day	74% 4 9% 9% 3	2718
	21st to end	Day	76% 3 9% 8% 2 1	3575
January	1st to 10th	Night	74% 3 8% 11% 4	8770
	11th to 20th	Night	49% 5% 14% 18% 13% 1	8820
	21st to end	Night	61% 4 12% 20% 4	9202
February	1st to 10th	Night	64% 4 11% 13% 8% 1	2730
	11th to 20th	Night	55% 4 13% 18% 8% 1	2664
	21st to end	Night	60% 6% 10% 15% 8% 2	2249
March	1st to 10th	Night	60% 3 11% 17% 9%	5274
	11th to 20th	Night	50% 4 12% 26% 7%	5110
	21st to end	Night	65% 3 13% 13% 5%	5610
April	1st to 10th	Night	53% 5% 15% 20% 7% 1	2092
	11th to 20th	Night	50% 4 13% 21% 10% 2	1871
	21st to end	Night	50% 3 14% 25% 8% 1	1890
May	1st to 10th	Night	40% 3 15% 31% 11%	3746
	11th to 20th	Night	45% 5% 24% 19% 4 2	3682
	21st to end	Night	57% 5% 14% 20% 4 1	3547
June	1st to 10th	Night	49% 5% 20% 18% 7% 2	1400
	11th to 20th	Night	51% 4 20% 18% 6%	1400
	21st to end	Night	43% 5% 23% 21% 7% 2	1400
July	1st to 10th	Night	26% 4 25% 23% 17% 5%	3145
	11th to 20th	Night	11% 4 27% 38% 18% 1	3138
	21st to end	Night	22% 5% 35% 27% 10% 1	3413
August	1st to 10th	Night	19% 3 11% 43% 23% 1	2788
	11th to 20th	Night	35% 8% 29% 17% 9% 2	2929
	21st to end	Night	38% 5% 24% 23% 9% 1	3245
September	1st to 10th	Night	30% 4 19% 32% 14% 2	1980
	11th to 20th	Night	43% 4 15% 20% 15% 2	2104
	21st to end	Night	45% 3 19% 20% 10% 2	2225
October	1st to 10th	Night	52% 7% 17% 17% 7%	3920
	11th to 20th	Night	55% 4 16% 20% 4	3897
	21st to end	Night	54% 6% 17% 18% 5%	4574
November	1st to 10th	Night	66% 4 13% 12% 5% 1	2870
	11th to 20th	Night	64% 5% 13% 12% 5% 1	2940
	21st to end	Night	63% 5% 12% 14% 5% 1	2940
December	1st to 10th	Night	66% 5% 13% 13% 3	5024
	11th to 20th	Night	77% 3 9% 7% 3	5706
	21st to end	Night	70% 4 10% 12% 4	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	40% 7% 21% 20% 6% 5%	220
	11th to 20th	Day	34% 5% 20% 20% 16% 5%	220
	21st to end	Day	31% 7% 21% 20% 16% 5%	347
February	1st to 10th	Day	28% 8% 26% 23% 12% 3	430
	11th to 20th	Day	25% 9% 24% 24% 15% 2	425
	21st to end	Day	29% 11% 26% 21% 9% 4	355
March	1st to 10th	Day	24% 12% 23% 25% 13% 4	505
	11th to 20th	Day	28% 11% 24% 20% 14% 3	540
	21st to end	Day	26% 12% 25% 22% 12% 4	594
April	1st to 10th	Day	22% 14% 27% 22% 12% 4	540
	11th to 20th	Day	18% 11% 25% 25% 15% 5%	532
	21st to end	Day	22% 10% 23% 26% 13% 6%	540
May	1st to 10th	Day	15% 8% 23% 29% 19% 5%	543
	11th to 20th	Day	16% 6% 23% 28% 20% 7%	568
	21st to end	Day	16% 6% 23% 30% 20% 5%	844
June	1st to 10th	Day	19% 9% 22% 24% 22% 5%	731
	11th to 20th	Day	15% 8% 25% 28% 20% 5%	730
	21st to end	Day	14% 7% 19% 30% 23% 7%	730
July	1st to 10th	Day	11% 3 18% 33% 28% 8%	721
	11th to 20th	Day	7% 4 21% 33% 26% 9%	718
	21st to end	Day	6% 5% 16% 29% 30% 15%	774
August	1st to 10th	Day	11% 1 12% 29% 28% 18%	527
	11th to 20th	Day	8% 4 16% 30% 28% 14%	517
	21st to end	Day	10% 5% 19% 32% 24% 10%	583
September	1st to 10th	Day	11% 5% 18% 30% 26% 10%	530
	11th to 20th	Day	19% 6% 19% 25% 22% 9%	530
	21st to end	Day	21% 10% 23% 22% 19% 6%	530
October	1st to 10th	Day	24% 9% 20% 22% 18% 8%	530
	11th to 20th	Day	27% 6% 25% 19% 17% 7%	530
	21st to end	Day	28% 10% 21% 24% 12% 5%	451
November	1st to 10th	Day	28% 10% 24% 23% 12% 3	220
	11th to 20th	Day	30% 9% 17% 19% 16% 10%	220
	21st to end	Day	34% 5% 22% 19% 9% 11%	220
December	1st to 10th	Day	32% 5% 18% 21% 13% 11%	220
	11th to 20th	Day	33% 6% 17% 25% 14% 5%	220
	21st to end	Day	36% 5% 20% 25% 12% 2	242
January	1st to 10th	Night	40% 7% 18% 22% 10% 4	950
	11th to 20th	Night	33% 5% 12% 29% 17% 3	950
	21st to end	Night	34% 3 15% 25% 18% 5%	1018
February	1st to 10th	Night	28% 5% 18% 34% 14% 2	840
	11th to 20th	Night	26% 4 17% 33% 18% 2	824
	21st to end	Night	26% 7% 21% 28% 15% 3	692
March	1st to 10th	Night	23% 5% 22% 28% 17% 5%	840
	11th to 20th	Night	23% 9% 23% 27% 16% 3	840
	21st to end	Night	25% 7% 18% 27% 19% 5%	924
April	1st to 10th	Night	21% 8% 15% 31% 20% 4	824
	11th to 20th	Night	18% 6% 20% 36% 18% 2	623
	21st to end	Night	20% 3 18% 33% 21% 4	630
May	1st to 10th	Night	18% 3 12% 36% 26% 5%	436
	11th to 20th	Night	15% 4 14% 35% 24% 8%	414
	21st to end	Night	19% 4 14% 31% 27% 5%	455
June	1st to 10th	Night	16% 3 14% 39% 25% 4	400
	11th to 20th	Night	18% 3 15% 33% 26% 6%	400
	21st to end	Night	18% 4 10% 35% 28% 6%	400
July	1st to 10th	Night	9% 2 9% 31% 40% 9%	390
	11th to 20th	Night	9% 2 11% 33% 38% 9%	388
	21st to end	Night	7% 2 4 30% 44% 13%	438
August	1st to 10th	Night	11% 2 4 24% 44% 16%	507
	11th to 20th	Night	7% 2 6% 28% 48% 9%	594
	21st to end	Night	11% 3 9% 30% 40% 7%	660
September	1st to 10th	Night	11% 2 6% 34% 36% 10%	780
	11th to 20th	Night	17% 3 11% 22% 32% 16%	800
	21st to end	Night	22% 5% 13% 29% 24% 7%	800
October	1st to 10th	Night	21% 4 12% 30% 28% 5%	800
	11th to 20th	Night	27% 3 14% 29% 21% 7%	800
	21st to end	Night	27% 6% 18% 29% 16% 3	880
November	1st to 10th	Night	35% 5% 18% 29% 12% 1	820
	11th to 20th	Night	31% 4 17% 30% 15% 3	840
	21st to end	Night	31% 5% 18% 27% 15% 5%	840
December	1st to 10th	Night	31% 7% 14% 26% 19% 4	942
	11th to 20th	Night	38% 4 18% 26% 11% 3	950
	21st to end	Night	36% 5% 22% 25% 10% 1	1045

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

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