Bella Bella
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bella Bella 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	34% 12% 3 7% 4 4 4 3 4 5% 20%	136009
	Night	38% 12% 3 7% 4 3 3 2 4 4 20%	135854
Transparency	Day	68% 4 12% 12% 4 1	135705
	Night	70% 3 10% 11% 4 1	135736
Seeing	Day	37% 9% 17% 20% 13% 4	18160
	Night	43% 8% 10% 19% 15% 5%	25815

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	43% 19% 5% 8% 3 3 3 2 3 4 7%	4125
	11th to 20th	Day	37% 9% 2 4 3 2 3 3 4 6% 28%	4119
	21st to end	Day	48% 11% 2 6% 3 2 3 2 3 4 14%	4945
February	1st to 10th	Day	46% 11% 3 7% 3 2 2 2 3 3 19%	1680
	11th to 20th	Day	33% 13% 3 6% 3 3 3 3 3 5% 24%	1840
	21st to end	Day	35% 16% 3 6% 4 3 3 3 2 2 23%	1625
March	1st to 10th	Day	33% 15% 3 7% 4 4 4 3 4 5% 18%	4596
	11th to 20th	Day	32% 20% 4 9% 6% 5% 4 3 3 3 11%	5106
	21st to end	Day	30% 13% 4 7% 5% 5% 4 3 4 4 20%	5623
April	1st to 10th	Day	35% 16% 4 8% 5% 4 3 3 4 4 16%	2624
	11th to 20th	Day	32% 12% 3 7% 4 4 3 3 5% 6% 21%	2698
	21st to end	Day	33% 10% 3 7% 6% 4 4 3 4 6% 22%	2730
May	1st to 10th	Day	31% 11% 4 7% 4 4 4 3 5% 6% 22%	6531
	11th to 20th	Day	34% 11% 3 7% 4 5% 4 4 5% 6% 19%	6886
	21st to end	Day	37% 11% 3 7% 4 4 4 3 4 5% 17%	7570
June	1st to 10th	Day	35% 11% 3 6% 5% 4 4 3 4 5% 19%	3001
	11th to 20th	Day	37% 11% 4 8% 4 4 4 3 4 5% 16%	3000
	21st to end	Day	39% 11% 3 6% 4 4 3 2 4 5% 19%	3000
July	1st to 10th	Day	23% 7% 2 6% 4 4 4 3 5% 8% 34%	6780
	11th to 20th	Day	23% 10% 3 6% 4 4 4 4 6% 7% 29%	6780
	21st to end	Day	27% 10% 4 8% 5% 4 4 3 5% 6% 22%	7375
August	1st to 10th	Day	15% 6% 3 5% 3 4 4 3 5% 7% 44%	4591
	11th to 20th	Day	26% 12% 4 9% 4 3 3 3 4 6% 26%	4196
	21st to end	Day	29% 10% 3 7% 4 4 4 3 5% 7% 22%	4664
September	1st to 10th	Day	32% 10% 4 7% 5% 3 4 3 4 7% 22%	2516
	11th to 20th	Day	31% 10% 4 8% 4 4 3 3 5% 5% 23%	2200
	21st to end	Day	42% 11% 3 7% 5% 4 3 2 4 5% 14%	2200
October	1st to 10th	Day	41% 11% 3 8% 4 4 3 3 4 4 16%	3392
	11th to 20th	Day	42% 9% 4 9% 5% 5% 4 3 4 5% 11%	3041
	21st to end	Day	35% 11% 3 8% 5% 4 4 3 4 5% 18%	3200
November	1st to 10th	Day	50% 10% 3 7% 4 2 3 2 2 3 14%	1668
	11th to 20th	Day	48% 14% 4 6% 4 3 3 2 2 2 12%	1587
	21st to end	Day	45% 11% 3 7% 4 4 2 3 2 2 16%	1470
December	1st to 10th	Day	50% 11% 2 5% 3 3 2 2 3 4 15%	2360
	11th to 20th	Day	50% 15% 3 6% 4 3 3 2 3 2 10%	2715
	21st to end	Day	49% 16% 4 9% 4 3 2 2 2 2 8%	3575
January	1st to 10th	Night	46% 17% 4 7% 3 3 3 2 3 3 9%	8770
	11th to 20th	Night	37% 8% 2 5% 3 3 4 3 4 6% 26%	8779
	21st to end	Night	48% 11% 3 5% 3 2 2 1 3 5% 18%	9242
February	1st to 10th	Night	46% 11% 2 5% 4 2 2 2 3 3 19%	2940
	11th to 20th	Night	36% 13% 3 6% 4 2 3 2 4 4 24%	2667
	21st to end	Night	35% 15% 2 6% 4 3 2 3 3 5% 23%	2180
March	1st to 10th	Night	34% 14% 4 7% 4 4 4 3 4 5% 19%	5498
	11th to 20th	Night	29% 21% 4 9% 5% 4 5% 3 4 3 13%	5112
	21st to end	Night	30% 14% 3 8% 4 4 3 3 4 6% 20%	5577
April	1st to 10th	Night	31% 16% 4 8% 5% 3 3 2 4 4 21%	1996
	11th to 20th	Night	32% 13% 3 6% 4 2 2 3 5% 5% 24%	1871
	21st to end	Night	32% 11% 3 6% 3 4 3 2 3 5% 29%	1890
May	1st to 10th	Night	24% 12% 4 8% 4 4 5% 3 5% 7% 24%	3655
	11th to 20th	Night	34% 11% 3 7% 4 4 4 4 4 4 21%	3229
	21st to end	Night	40% 10% 3 7% 4 4 3 3 4 4 18%	3547
June	1st to 10th	Night	36% 10% 3 5% 4 4 3 2 4 4 24%	1400
	11th to 20th	Night	35% 9% 3 6% 3 4 4 4 6% 6% 20%	1400
	21st to end	Night	37% 10% 2 6% 4 3 3 3 4 5% 23%	1400
July	1st to 10th	Night	21% 8% 3 7% 4 3 3 2 4 4 40%	3180
	11th to 20th	Night	25% 12% 3 6% 4 3 3 3 4 6% 30%	3180
	21st to end	Night	23% 10% 3 8% 5% 4 4 3 5% 6% 28%	3468
August	1st to 10th	Night	15% 8% 2 6% 3 4 3 3 5% 6% 45%	2567
	11th to 20th	Night	26% 10% 3 7% 4 3 3 3 5% 6% 29%	2862
	21st to end	Night	29% 8% 3 7% 5% 5% 4 3 3 5% 27%	3245
September	1st to 10th	Night	28% 10% 3 8% 5% 3 3 3 4 5% 28%	1880
	11th to 20th	Night	30% 9% 3 6% 4 3 3 2 3 5% 30%	2200
	21st to end	Night	45% 11% 3 7% 4 4 3 2 3 4 15%	2200
October	1st to 10th	Night	49% 10% 3 6% 3 3 2 2 3 3 15%	3807
	11th to 20th	Night	46% 12% 4 8% 5% 3 2 2 3 3 11%	4109
	21st to end	Night	36% 10% 3 7% 3 3 4 3 4 7% 20%	4601
November	1st to 10th	Night	47% 13% 3 6% 4 4 3 2 2 2 13%	2850
	11th to 20th	Night	47% 14% 3 7% 4 3 2 2 3 3 12%	3029
	21st to end	Night	45% 13% 3 7% 4 3 2 2 2 3 16%	3150
December	1st to 10th	Night	51% 11% 2 6% 3 2 2 2 2 4 14%	5040
	11th to 20th	Night	45% 15% 4 7% 4 3 3 2 3 3 12%	5710
	21st to end	Night	46% 17% 3 8% 3 3 3 2 3 3 9%	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	84% 2 5% 8% 2	4125
	11th to 20th	Day	59% 2 6% 17% 11% 5%	4140
	21st to end	Day	76% 2 9% 9% 4 1	4946
February	1st to 10th	Day	73% 1 5% 6% 9% 6%	1680
	11th to 20th	Day	66% 3 7% 15% 8% 2	1849
	21st to end	Day	69% 3 7% 10% 8% 4	1625
March	1st to 10th	Day	70% 4 8% 9% 8% 1	4596
	11th to 20th	Day	80% 2 6% 7% 6% 1	5106
	21st to end	Day	68% 3 10% 12% 5% 1	5623
April	1st to 10th	Day	76% 3 9% 8% 4 1	2624
	11th to 20th	Day	66% 3 9% 12% 8% 2	2698
	21st to end	Day	67% 2 12% 13% 4 1	2730
May	1st to 10th	Day	64% 5% 16% 13% 2	6531
	11th to 20th	Day	68% 4 16% 11% 1	6889
	21st to end	Day	73% 4 10% 9% 4	7571
June	1st to 10th	Day	70% 4 13% 10% 2 2	3001
	11th to 20th	Day	74% 4 13% 8% 1	3000
	21st to end	Day	70% 3 15% 10% 2	3000
July	1st to 10th	Day	50% 6% 15% 19% 8% 2	6706
	11th to 20th	Day	54% 8% 24% 13% 1	6699
	21st to end	Day	62% 8% 20% 8% 1	7168
August	1st to 10th	Day	38% 4 17% 38% 3	4573
	11th to 20th	Day	64% 5% 15% 13% 2	4235
	21st to end	Day	62% 9% 16% 12% 1	4663
September	1st to 10th	Day	64% 4 17% 11% 3	2516
	11th to 20th	Day	64% 4 11% 16% 5%	2200
	21st to end	Day	76% 3 9% 9% 3	2200
October	1st to 10th	Day	74% 3 9% 9% 3 1	3392
	11th to 20th	Day	76% 4 9% 9% 2	3041
	21st to end	Day	70% 4 7% 12% 8%	3200
November	1st to 10th	Day	79% 2 5% 9% 4 1	1668
	11th to 20th	Day	82% 2 5% 5% 5% 1	1587
	21st to end	Day	76% 2 5% 9% 6% 2	1470
December	1st to 10th	Day	74% 3 8% 9% 4 1	2360
	11th to 20th	Day	83% 2 5% 6% 3 2	2718
	21st to end	Day	86% 2 4 4 2 1	3575
January	1st to 10th	Night	83% 2 4 7% 3	8770
	11th to 20th	Night	60% 3 8% 16% 9% 4	8820
	21st to end	Night	73% 2 9% 12% 4	9242
February	1st to 10th	Night	73% 2 4 8% 7% 5%	2940
	11th to 20th	Night	67% 2 8% 13% 8% 3	2669
	21st to end	Night	68% 2 9% 12% 7% 3	2180
March	1st to 10th	Night	69% 3 8% 12% 6% 1	5498
	11th to 20th	Night	77% 3 7% 8% 4 1	5113
	21st to end	Night	68% 3 10% 13% 4 2	5577
April	1st to 10th	Night	69% 4 13% 9% 5% 1	1996
	11th to 20th	Night	64% 2 10% 14% 8% 2	1871
	21st to end	Night	62% 2 14% 17% 3 1	1890
May	1st to 10th	Night	60% 5% 18% 15% 2	3652
	11th to 20th	Night	68% 5% 16% 9% 1	3229
	21st to end	Night	72% 3 13% 7% 3 1	3547
June	1st to 10th	Night	66% 4 15% 12% 1 2	1400
	11th to 20th	Night	67% 5% 18% 9% 1	1400
	21st to end	Night	66% 3 18% 11% 2	1400
July	1st to 10th	Night	48% 4 14% 25% 8%	3145
	11th to 20th	Night	56% 7% 24% 12%	3138
	21st to end	Night	57% 10% 24% 8% 1	3370
August	1st to 10th	Night	40% 4 21% 34% 2	2560
	11th to 20th	Night	59% 7% 18% 14% 2	2889
	21st to end	Night	62% 6% 18% 13% 1	3245
September	1st to 10th	Night	60% 4 20% 12% 3 1	1880
	11th to 20th	Night	58% 4 15% 18% 5%	2200
	21st to end	Night	78% 3 7% 8% 3 1	2200
October	1st to 10th	Night	77% 2 9% 8% 3 1	3807
	11th to 20th	Night	81% 3 7% 6% 2	4109
	21st to end	Night	65% 5% 12% 11% 7%	4601
November	1st to 10th	Night	80% 2 6% 6% 5% 1	2850
	11th to 20th	Night	80% 2 5% 7% 5% 1	3029
	21st to end	Night	76% 1 6% 9% 6% 1	3150
December	1st to 10th	Night	76% 3 8% 7% 5% 1	5040
	11th to 20th	Night	79% 3 5% 8% 4 1	5706
	21st to end	Night	82% 3 6% 5% 2 1	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	51% 14% 17% 10% 5% 3	220
	11th to 20th	Day	51% 11% 11% 14% 10% 2	220
	21st to end	Day	53% 8% 14% 14% 8% 3	389
February	1st to 10th	Day	49% 10% 20% 13% 7% 1	430
	11th to 20th	Day	36% 15% 19% 16% 12% 2	425
	21st to end	Day	46% 16% 18% 10% 8% 1	355
March	1st to 10th	Day	38% 12% 21% 18% 9% 2	430
	11th to 20th	Day	42% 15% 14% 17% 10% 1	539
	21st to end	Day	40% 9% 17% 17% 14% 3	594
April	1st to 10th	Day	42% 12% 18% 17% 8% 3	540
	11th to 20th	Day	31% 10% 20% 21% 13% 5%	532
	21st to end	Day	32% 9% 21% 18% 15% 5%	540
May	1st to 10th	Day	31% 9% 18% 26% 14% 3	647
	11th to 20th	Day	30% 7% 20% 27% 13% 3	775
	21st to end	Day	33% 10% 22% 24% 9% 2	845
June	1st to 10th	Day	37% 11% 18% 21% 11% 2	731
	11th to 20th	Day	35% 9% 20% 20% 12% 3	730
	21st to end	Day	38% 6% 14% 25% 14% 4	730
July	1st to 10th	Day	26% 7% 16% 26% 20% 5%	721
	11th to 20th	Day	29% 7% 18% 24% 18% 5%	718
	21st to end	Day	29% 6% 13% 25% 20% 7%	794
August	1st to 10th	Day	24% 4 13% 25% 26% 6%	726
	11th to 20th	Day	28% 7% 13% 29% 17% 5%	545
	21st to end	Day	37% 7% 13% 20% 17% 7%	583
September	1st to 10th	Day	36% 7% 13% 21% 15% 8%	530
	11th to 20th	Day	34% 8% 13% 22% 18% 4	530
	21st to end	Day	44% 9% 18% 15% 9% 4	530
October	1st to 10th	Day	36% 11% 12% 19% 15% 6%	530
	11th to 20th	Day	42% 11% 17% 18% 9% 4	457
	21st to end	Day	42% 12% 18% 16% 10% 2	462
November	1st to 10th	Day	50% 11% 18% 12% 9%	240
	11th to 20th	Day	49% 13% 15% 12% 6% 5%	220
	21st to end	Day	46% 14% 15% 12% 8% 5%	220
December	1st to 10th	Day	45% 13% 10% 17% 11% 4	220
	11th to 20th	Day	54% 7% 11% 18% 8% 2	220
	21st to end	Day	56% 9% 13% 15% 6% 1	242
January	1st to 10th	Night	54% 12% 12% 12% 9% 2	950
	11th to 20th	Night	54% 9% 12% 16% 8% 1	950
	21st to end	Night	52% 6% 11% 17% 11% 3	1045
February	1st to 10th	Night	51% 11% 13% 18% 7% 1	950
	11th to 20th	Night	42% 11% 12% 20% 12% 3	827
	21st to end	Night	46% 11% 13% 19% 9% 2	692
March	1st to 10th	Night	40% 11% 16% 19% 12% 1	840
	11th to 20th	Night	46% 11% 12% 19% 11% 1	840
	21st to end	Night	43% 9% 11% 18% 16% 3	916
April	1st to 10th	Night	39% 7% 10% 22% 18% 4	630
	11th to 20th	Night	37% 6% 12% 24% 17% 4	623
	21st to end	Night	36% 7% 9% 25% 21% 3	630
May	1st to 10th	Night	33% 6% 7% 24% 25% 5%	499
	11th to 20th	Night	31% 5% 12% 27% 21% 5%	414
	21st to end	Night	33% 4 6% 26% 26% 5%	455
June	1st to 10th	Night	38% 4 8% 17% 27% 7%	400
	11th to 20th	Night	37% 5% 5% 20% 24% 9%	400
	21st to end	Night	41% 3 5% 21% 23% 7%	400
July	1st to 10th	Night	31% 2 5% 20% 31% 13%	390
	11th to 20th	Night	31% 4 6% 18% 30% 12%	388
	21st to end	Night	26% 6% 4 17% 35% 12%	438
August	1st to 10th	Night	26% 5% 3 14% 31% 20%	567
	11th to 20th	Night	29% 2 4 17% 35% 13%	594
	21st to end	Night	38% 4 5% 18% 28% 7%	660
September	1st to 10th	Night	31% 6% 7% 20% 23% 12%	635
	11th to 20th	Night	32% 7% 7% 19% 23% 12%	800
	21st to end	Night	48% 9% 9% 18% 15% 3	800
October	1st to 10th	Night	41% 6% 10% 21% 18% 5%	800
	11th to 20th	Night	46% 7% 11% 17% 14% 5%	800
	21st to end	Night	47% 8% 11% 21% 10% 3	880
November	1st to 10th	Night	55% 8% 13% 16% 6% 1	820
	11th to 20th	Night	53% 11% 11% 16% 7% 2	887
	21st to end	Night	51% 11% 11% 16% 9% 2	950
December	1st to 10th	Night	46% 9% 13% 18% 11% 3	950
	11th to 20th	Night	48% 13% 13% 16% 8% 2	950
	21st to end	Night	53% 11% 13% 17% 6% 1	1045

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

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