Bowen Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bowen Island clear sky chart from 2005-11-06 to 2026-01-02.

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	22% 8% 2 6% 4 4 4 3 5% 6% 37%	131357
	Night	27% 9% 3 6% 4 4 3 3 4 5% 32%	128670
Transparency	Day	49% 7% 17% 18% 7% 1	131062
	Night	55% 6% 15% 17% 6% 1	128543
Seeing	Day	22% 4 16% 28% 23% 6%	16876
	Night	30% 4 15% 25% 21% 5%	25076

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	40% 11% 4 9% 4 5% 4 3 4 4 14%	3186
	11th to 20th	Day	22% 9% 3 5% 4 3 4 3 6% 8% 33%	3159
	21st to end	Day	47% 6% 1 4 2 4 3 2 3 4 22%	3970
February	1st to 10th	Day	31% 11% 4 8% 4 5% 4 5% 6% 6% 18%	1800
	11th to 20th	Day	29% 11% 3 6% 4 4 4 4 5% 5% 25%	1755
	21st to end	Day	26% 10% 4 7% 5% 5% 5% 4 5% 6% 23%	1485
March	1st to 10th	Day	26% 13% 4 9% 6% 5% 4 3 5% 6% 19%	4710
	11th to 20th	Day	26% 12% 3 7% 5% 4 4 3 4 5% 27%	5000
	21st to end	Day	32% 11% 4 8% 5% 4 4 3 4 5% 19%	5605
April	1st to 10th	Day	26% 10% 3 8% 5% 4 4 4 6% 6% 22%	2400
	11th to 20th	Day	22% 8% 3 7% 4 4 5% 4 6% 6% 32%	2494
	21st to end	Day	24% 9% 2 6% 4 4 4 3 5% 5% 32%	2645
May	1st to 10th	Day	13% 8% 2 6% 5% 4 4 3 5% 6% 46%	6320
	11th to 20th	Day	17% 7% 3 7% 5% 4 4 4 7% 9% 33%	6277
	21st to end	Day	22% 7% 2 6% 4 5% 5% 4 6% 9% 31%	7129
June	1st to 10th	Day	20% 7% 2 7% 5% 4 4 3 6% 7% 34%	3000
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 5% 6% 7% 32%	3000
	21st to end	Day	15% 7% 2 5% 5% 5% 4 4 6% 7% 41%	3000
July	1st to 10th	Day	8% 4 2 4 3 3 3 3 4 5% 62%	6780
	11th to 20th	Day	4 3 1 2 2 2 2 2 4 6% 72%	6780
	21st to end	Day	9% 4 1 4 3 2 2 2 4 6% 62%	7070
August	1st to 10th	Day	6% 2 1 3 2 2 3 2 4 6% 68%	4480
	11th to 20th	Day	12% 7% 2 7% 4 3 4 3 5% 7% 47%	4156
	21st to end	Day	15% 6% 2 5% 4 3 4 3 5% 7% 46%	4583
September	1st to 10th	Day	12% 4 2 5% 3 4 4 3 5% 6% 51%	2400
	11th to 20th	Day	19% 6% 2 5% 4 4 3 3 5% 5% 43%	2376
	21st to end	Day	25% 5% 2 4 4 4 4 3 4 7% 38%	2118
October	1st to 10th	Day	25% 8% 3 7% 5% 4 4 3 5% 6% 30%	3280
	11th to 20th	Day	35% 7% 2 5% 4 3 4 4 4 6% 26%	3261
	21st to end	Day	31% 10% 3 9% 4 5% 3 3 5% 6% 21%	3260
November	1st to 10th	Day	41% 9% 3 6% 3 3 4 4 3 4 20%	1648
	11th to 20th	Day	38% 10% 3 5% 4 3 4 3 4 5% 22%	1680
	21st to end	Day	42% 9% 2 6% 4 3 3 3 4 4 20%	1680
December	1st to 10th	Day	26% 10% 3 9% 6% 4 4 3 3 6% 27%	2580
	11th to 20th	Day	46% 12% 4 8% 4 4 2 3 3 4 12%	2715
	21st to end	Day	46% 12% 3 9% 4 4 3 2 2 4 11%	3575
January	1st to 10th	Night	40% 11% 3 8% 4 4 4 2 3 4 16%	6781
	11th to 20th	Night	24% 8% 2 6% 4 4 4 3 6% 8% 32%	6739
	21st to end	Night	41% 7% 2 4 3 3 3 3 3 4 26%	6984
February	1st to 10th	Night	32% 11% 4 8% 4 5% 4 3 4 5% 21%	2600
	11th to 20th	Night	28% 13% 3 7% 4 4 4 3 4 5% 28%	2532
	21st to end	Night	30% 11% 3 7% 5% 3 2 3 5% 4 25%	2145
March	1st to 10th	Night	29% 12% 3 6% 4 4 4 3 4 5% 24%	5170
	11th to 20th	Night	27% 11% 3 7% 4 4 4 3 4 5% 28%	4999
	21st to end	Night	38% 12% 3 7% 4 4 3 2 3 4 18%	5369
April	1st to 10th	Night	27% 11% 3 7% 6% 5% 4 4 6% 6% 23%	2000
	11th to 20th	Night	19% 11% 4 6% 5% 4 4 4 5% 6% 30%	1851
	21st to end	Night	24% 8% 3 7% 5% 4 4 3 5% 6% 31%	1755
May	1st to 10th	Night	16% 8% 3 5% 3 3 3 2 4 4 49%	3640
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 4 6% 9% 37%	3616
	21st to end	Night	18% 10% 4 9% 7% 6% 4 4 4 5% 30%	3742
June	1st to 10th	Night	21% 7% 3 7% 4 4 4 4 5% 5% 36%	1400
	11th to 20th	Night	16% 9% 3 7% 5% 5% 6% 4 7% 7% 33%	1400
	21st to end	Night	12% 7% 2 8% 5% 4 4 5% 5% 7% 42%	1400
July	1st to 10th	Night	8% 4 1 4 3 3 2 3 4 6% 62%	3180
	11th to 20th	Night	3 1 1 2 1 2 2 2 3 5% 77%	3180
	21st to end	Night	8% 4 1 4 2 2 3 2 5% 6% 61%	3758
August	1st to 10th	Night	5% 2 1 2 2 2 2 2 3 5% 74%	2669
	11th to 20th	Night	10% 5% 2 6% 4 3 4 4 5% 7% 49%	2902
	21st to end	Night	13% 5% 2 6% 4 4 5% 3 4 6% 46%	3329
September	1st to 10th	Night	9% 4 2 4 4 3 3 3 5% 6% 58%	2000
	11th to 20th	Night	20% 6% 2 5% 3 3 3 3 5% 6% 44%	2020
	21st to end	Night	23% 7% 2 6% 3 4 3 3 4 5% 39%	2281
October	1st to 10th	Night	22% 8% 3 8% 5% 4 4 3 5% 6% 32%	3920
	11th to 20th	Night	32% 8% 3 6% 4 3 4 2 4 5% 30%	3897
	21st to end	Night	33% 10% 3 6% 4 4 3 3 4 5% 27%	4526
November	1st to 10th	Night	39% 11% 3 7% 4 4 4 2 4 5% 18%	2870
	11th to 20th	Night	37% 9% 2 5% 5% 4 4 3 4 3 24%	2940
	21st to end	Night	38% 9% 2 7% 5% 3 3 2 3 4 22%	2940
December	1st to 10th	Night	30% 11% 2 6% 4 4 3 3 5% 7% 25%	4802
	11th to 20th	Night	46% 12% 3 7% 5% 3 3 2 3 4 13%	5710
	21st to end	Night	45% 14% 3 7% 4 3 3 2 3 3 13%	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	74% 6% 9% 9% 2	3186
	11th to 20th	Day	50% 8% 17% 15% 8% 1	3180
	21st to end	Day	67% 5% 8% 16% 3	3970
February	1st to 10th	Day	66% 9% 11% 8% 3 3	1800
	11th to 20th	Day	62% 9% 10% 13% 6% 1	1764
	21st to end	Day	63% 9% 13% 10% 4 1	1485
March	1st to 10th	Day	64% 8% 13% 11% 3	4710
	11th to 20th	Day	60% 6% 11% 19% 3 1	5000
	21st to end	Day	67% 8% 16% 7% 2	5605
April	1st to 10th	Day	61% 10% 16% 10% 3	2400
	11th to 20th	Day	53% 9% 14% 15% 9% 1	2494
	21st to end	Day	54% 8% 16% 14% 7% 1	2645
May	1st to 10th	Day	39% 7% 19% 22% 12% 1	6320
	11th to 20th	Day	46% 9% 23% 18% 4	6280
	21st to end	Day	50% 9% 22% 17% 3	7130
June	1st to 10th	Day	48% 9% 21% 15% 6% 2	3000
	11th to 20th	Day	49% 13% 21% 13% 4	3000
	21st to end	Day	43% 10% 21% 17% 8% 2	3000
July	1st to 10th	Day	26% 7% 19% 24% 17% 6%	6706
	11th to 20th	Day	16% 5% 23% 36% 18% 2	6699
	21st to end	Day	24% 6% 33% 26% 10% 1	6872
August	1st to 10th	Day	19% 6% 15% 47% 12% 1	4463
	11th to 20th	Day	37% 7% 29% 17% 9% 1	4195
	21st to end	Day	39% 8% 21% 21% 11% 1	4582
September	1st to 10th	Day	34% 10% 18% 23% 11% 4	2400
	11th to 20th	Day	44% 9% 14% 18% 13% 2	2376
	21st to end	Day	48% 9% 17% 16% 8% 1	2118
October	1st to 10th	Day	54% 7% 18% 16% 5%	3280
	11th to 20th	Day	60% 6% 13% 15% 5%	3261
	21st to end	Day	64% 7% 13% 12% 4	3260
November	1st to 10th	Day	68% 7% 12% 9% 4 1	1648
	11th to 20th	Day	68% 7% 9% 9% 4 2	1680
	21st to end	Day	69% 6% 10% 9% 6% 1	1680
December	1st to 10th	Day	58% 9% 12% 15% 5% 1	2580
	11th to 20th	Day	78% 4 9% 6% 2 1	2718
	21st to end	Day	79% 5% 9% 5% 2	3575
January	1st to 10th	Night	74% 5% 8% 11% 2	6781
	11th to 20th	Night	48% 9% 20% 17% 6% 1	6780
	21st to end	Night	63% 5% 11% 18% 2	6984
February	1st to 10th	Night	66% 7% 10% 10% 5% 2	2600
	11th to 20th	Night	61% 8% 11% 13% 7% 1	2534
	21st to end	Night	61% 7% 11% 13% 6% 2	2145
March	1st to 10th	Night	60% 7% 16% 12% 6%	5170
	11th to 20th	Night	57% 5% 14% 21% 3	5000
	21st to end	Night	71% 6% 12% 10% 2	5369
April	1st to 10th	Night	62% 6% 15% 14% 2	2000
	11th to 20th	Night	53% 7% 13% 16% 9% 2	1851
	21st to end	Night	55% 6% 16% 15% 8%	1755
May	1st to 10th	Night	39% 4 16% 27% 13%	3637
	11th to 20th	Night	42% 9% 23% 20% 5%	3616
	21st to end	Night	56% 6% 18% 17% 2	3742
June	1st to 10th	Night	50% 6% 20% 16% 6% 2	1400
	11th to 20th	Night	49% 9% 19% 18% 5%	1400
	21st to end	Night	41% 9% 21% 18% 8% 3	1400
July	1st to 10th	Night	26% 4 19% 29% 17% 4	3145
	11th to 20th	Night	12% 4 24% 37% 22% 2	3138
	21st to end	Night	25% 4 27% 29% 12% 2	3652
August	1st to 10th	Night	15% 4 16% 43% 21% 2	2661
	11th to 20th	Night	35% 5% 31% 17% 8% 3	2929
	21st to end	Night	39% 6% 23% 22% 10% 1	3329
September	1st to 10th	Night	28% 8% 20% 28% 13% 4	2000
	11th to 20th	Night	42% 7% 15% 17% 15% 4	2020
	21st to end	Night	48% 6% 16% 21% 7% 2	2281
October	1st to 10th	Night	54% 5% 19% 15% 6%	3920
	11th to 20th	Night	59% 4 12% 20% 5%	3897
	21st to end	Night	60% 6% 15% 15% 5%	4526
November	1st to 10th	Night	70% 5% 11% 9% 4 1	2870
	11th to 20th	Night	67% 6% 10% 10% 5% 2	2940
	21st to end	Night	68% 6% 10% 9% 7% 1	2940
December	1st to 10th	Night	60% 8% 14% 13% 4 1	4802
	11th to 20th	Night	78% 5% 8% 6% 3	5706
	21st to end	Night	76% 5% 9% 8% 2	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	39% 8% 15% 23% 9% 6%	202
	11th to 20th	Day	37% 10% 18% 19% 17% 1	200
	21st to end	Day	43% 6% 13% 23% 12% 4	256
February	1st to 10th	Day	35% 6% 20% 25% 13% 1	400
	11th to 20th	Day	34% 3 21% 26% 15% 1	395
	21st to end	Day	29% 9% 20% 26% 13% 3	331
March	1st to 10th	Day	29% 6% 19% 28% 14% 3	500
	11th to 20th	Day	30% 5% 19% 24% 19% 3	500
	21st to end	Day	33% 7% 20% 26% 13% 1	550
April	1st to 10th	Day	28% 7% 23% 24% 16% 2	500
	11th to 20th	Day	24% 5% 23% 28% 16% 4	492
	21st to end	Day	23% 5% 22% 28% 18% 4	500
May	1st to 10th	Day	15% 4 19% 36% 24% 3	503
	11th to 20th	Day	17% 3 13% 32% 29% 5%	528
	21st to end	Day	15% 4 17% 35% 23% 6%	669
June	1st to 10th	Day	17% 4 15% 35% 26% 3	730
	11th to 20th	Day	16% 4 18% 34% 22% 5%	730
	21st to end	Day	15% 2 14% 33% 29% 7%	730
July	1st to 10th	Day	12% 2 12% 32% 34% 8%	721
	11th to 20th	Day	7% 1 12% 33% 40% 7%	718
	21st to end	Day	6% 1 9% 28% 44% 11%	667
August	1st to 10th	Day	9% 2 9% 22% 41% 15%	527
	11th to 20th	Day	9% 2 9% 31% 38% 10%	517
	21st to end	Day	11% 2 15% 32% 30% 10%	583
September	1st to 10th	Day	12% 3 15% 36% 23% 11%	530
	11th to 20th	Day	19% 4 15% 27% 26% 8%	530
	21st to end	Day	24% 3 20% 25% 23% 5%	530
October	1st to 10th	Day	26% 4 18% 26% 21% 6%	530
	11th to 20th	Day	35% 5% 15% 20% 18% 7%	530
	21st to end	Day	34% 9% 19% 23% 11% 3	435
November	1st to 10th	Day	39% 8% 19% 20% 12% 1	220
	11th to 20th	Day	38% 5% 16% 19% 16% 6%	220
	21st to end	Day	43% 8% 19% 14% 10% 7%	220
December	1st to 10th	Day	43% 3 18% 12% 18% 7%	220
	11th to 20th	Day	43% 7% 16% 22% 10% 2	220
	21st to end	Day	44% 7% 17% 23% 9% 1	242
January	1st to 10th	Night	48% 6% 16% 16% 12% 2	905
	11th to 20th	Night	41% 4 14% 24% 17% 1	900
	21st to end	Night	39% 4 17% 24% 15% 2	907
February	1st to 10th	Night	35% 6% 19% 27% 12% 2	800
	11th to 20th	Night	34% 5% 19% 29% 13% 2	784
	21st to end	Night	33% 7% 22% 22% 13% 3	660
March	1st to 10th	Night	33% 5% 19% 25% 17% 3	800
	11th to 20th	Night	36% 5% 18% 24% 16% 2	800
	21st to end	Night	36% 5% 16% 24% 15% 4	880
April	1st to 10th	Night	29% 5% 15% 31% 16% 4	800
	11th to 20th	Night	25% 5% 22% 29% 17% 3	663
	21st to end	Night	27% 4 17% 31% 18% 3	555
May	1st to 10th	Night	18% 2 16% 33% 26% 7%	400
	11th to 20th	Night	19% 4 9% 27% 34% 8%	394
	21st to end	Night	18% 5% 11% 30% 31% 5%	433
June	1st to 10th	Night	22% 4 11% 32% 27% 4	400
	11th to 20th	Night	18% 5% 13% 34% 23% 7%	400
	21st to end	Night	14% 2 8% 34% 35% 8%	400
July	1st to 10th	Night	12% 2 8% 26% 43% 9%	390
	11th to 20th	Night	7% 1 10% 29% 42% 12%	388
	21st to end	Night	8% 1 5% 22% 49% 15%	438
August	1st to 10th	Night	9% 2 4 19% 45% 21%	432
	11th to 20th	Night	8% 1 5% 25% 47% 14%	594
	21st to end	Night	12% 2 11% 25% 38% 11%	705
September	1st to 10th	Night	10% 2 8% 32% 35% 13%	800
	11th to 20th	Night	21% 3 10% 21% 32% 13%	800
	21st to end	Night	26% 4 13% 26% 27% 5%	800
October	1st to 10th	Night	23% 3 15% 27% 26% 7%	800
	11th to 20th	Night	33% 3 16% 24% 20% 5%	800
	21st to end	Night	38% 6% 15% 24% 13% 3	880
November	1st to 10th	Night	42% 6% 16% 26% 9%	820
	11th to 20th	Night	41% 5% 20% 22% 10% 2	840
	21st to end	Night	43% 3 18% 20% 13% 3	840
December	1st to 10th	Night	37% 5% 16% 26% 14% 2	873
	11th to 20th	Night	50% 7% 16% 20% 7% 1	950
	21st to end	Night	45% 8% 21% 20% 6%	1045

Page generated at 2025-12-29 22:14:08. Version ac07

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