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 2024-11-12.

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% 2 6% 4 4 4 3 5% 6% 37%	105587
	Night	28% 9% 3 6% 4 3 3 3 4 5% 32%	102185
Transparency	Day	49% 8% 16% 17% 8% 1	105334
	Night	55% 6% 14% 16% 7% 1	102084
Seeing	Day	22% 4 17% 28% 23% 5%	15474
	Night	31% 4 15% 25% 21% 5%	23581

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	45% 12% 3 8% 3 4 3 2 4 3 13%	2219
	11th to 20th	Day	31% 13% 3 6% 5% 3 3 3 4 6% 25%	2199
	21st to end	Day	60% 8% 2 5% 3 3 2 2 3 3 11%	2760
February	1st to 10th	Day	33% 10% 4 7% 4 5% 4 5% 5% 5% 17%	1710
	11th to 20th	Day	28% 11% 3 6% 4 4 4 4 5% 5% 25%	1665
	21st to end	Day	25% 10% 4 7% 5% 5% 5% 4 5% 6% 24%	1413
March	1st to 10th	Day	27% 13% 3 7% 5% 4 4 4 6% 7% 19%	3278
	11th to 20th	Day	24% 9% 2 7% 5% 4 4 3 4 5% 35%	3490
	21st to end	Day	27% 12% 4 8% 4 4 4 3 4 5% 26%	3905
April	1st to 10th	Day	26% 10% 3 8% 5% 4 4 4 6% 6% 22%	2280
	11th to 20th	Day	23% 8% 3 7% 4 4 5% 4 6% 6% 30%	2368
	21st to end	Day	25% 9% 2 7% 4 5% 4 3 5% 5% 31%	2513
May	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 5% 45%	4420
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 5% 8% 10% 39%	4377
	21st to end	Day	26% 8% 3 6% 4 4 4 4 6% 7% 28%	4969
June	1st to 10th	Day	21% 7% 2 7% 5% 4 5% 3 6% 7% 32%	2850
	11th to 20th	Day	19% 8% 3 6% 5% 4 5% 5% 6% 7% 32%	2850
	21st to end	Day	15% 6% 2 5% 5% 5% 4 4 6% 7% 41%	2850
July	1st to 10th	Day	7% 4 2 4 2 2 2 2 4 4 66%	4740
	11th to 20th	Day	6% 3 1 2 2 2 2 2 4 6% 71%	4740
	21st to end	Day	12% 4 2 5% 3 3 3 2 4 6% 56%	4930
August	1st to 10th	Day	6% 2 1 3 2 2 2 2 4 6% 69%	4342
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 5% 7% 47%	4026
	21st to end	Day	16% 6% 2 5% 4 3 4 3 5% 6% 46%	4442
September	1st to 10th	Day	12% 4 2 5% 3 4 4 3 5% 6% 51%	2280
	11th to 20th	Day	19% 6% 3 5% 4 4 3 3 4 5% 43%	2257
	21st to end	Day	25% 5% 2 4 3 4 4 3 4 7% 39%	2012
October	1st to 10th	Day	25% 8% 3 7% 5% 4 4 3 5% 6% 31%	3180
	11th to 20th	Day	35% 7% 2 5% 4 3 4 4 4 6% 25%	3161
	21st to end	Day	30% 10% 4 9% 4 5% 3 3 5% 6% 21%	3159
November	1st to 10th	Day	42% 9% 3 6% 3 3 4 4 3 4 20%	1568
	11th to 20th	Day	38% 9% 3 5% 4 3 4 3 4 5% 23%	1528
	21st to end	Day	41% 9% 2 6% 4 3 3 3 4 3 22%	1520
December	1st to 10th	Day	32% 12% 2 7% 4 3 3 3 3 4 25%	1459
	11th to 20th	Day	40% 12% 4 8% 4 4 3 3 3 4 16%	1685
	21st to end	Day	47% 11% 3 8% 4 3 3 2 2 4 13%	2442
January	1st to 10th	Night	41% 12% 3 8% 5% 3 4 2 3 3 15%	4726
	11th to 20th	Night	34% 9% 2 7% 4 4 3 3 5% 7% 23%	4699
	21st to end	Night	55% 10% 2 5% 3 2 2 2 3 3 12%	4892
February	1st to 10th	Night	33% 10% 4 7% 4 5% 4 3 4 5% 20%	2470
	11th to 20th	Night	28% 13% 3 7% 4 3 4 3 4 5% 28%	2402
	21st to end	Night	29% 10% 3 6% 5% 3 2 3 5% 5% 26%	2041
March	1st to 10th	Night	31% 14% 3 6% 4 4 3 3 4 5% 23%	3595
	11th to 20th	Night	24% 8% 3 6% 4 3 4 2 4 5% 36%	3489
	21st to end	Night	33% 13% 3 8% 5% 4 3 3 3 4 21%	3747
April	1st to 10th	Night	27% 11% 3 7% 6% 5% 4 4 5% 6% 23%	1900
	11th to 20th	Night	20% 12% 4 6% 5% 4 4 3 6% 6% 29%	1758
	21st to end	Night	24% 9% 3 7% 5% 4 4 4 5% 6% 29%	1667
May	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 5% 4 47%	2540
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 6% 10% 47%	2516
	21st to end	Night	21% 10% 3 9% 6% 5% 4 3 4 5% 29%	2602
June	1st to 10th	Night	22% 8% 3 7% 4 5% 4 4 5% 4 34%	1330
	11th to 20th	Night	16% 9% 3 7% 5% 5% 6% 4 7% 7% 32%	1330
	21st to end	Night	12% 6% 2 8% 5% 4 4 5% 5% 7% 42%	1330
July	1st to 10th	Night	6% 3 1 4 3 2 2 3 3 6% 66%	2220
	11th to 20th	Night	4 2 1 3 2 2 2 2 3 4 75%	2220
	21st to end	Night	11% 5% 2 5% 3 2 3 3 5% 6% 55%	2621
August	1st to 10th	Night	5% 2 1 2 2 2 2 2 4 5% 74%	2587
	11th to 20th	Night	10% 5% 2 6% 4 3 4 4 5% 7% 49%	2812
	21st to end	Night	14% 6% 3 6% 4 4 5% 3 4 6% 45%	3228
September	1st to 10th	Night	9% 4 2 4 4 4 3 3 5% 6% 58%	1900
	11th to 20th	Night	21% 6% 2 5% 3 3 3 3 5% 5% 43%	1919
	21st to end	Night	23% 7% 2 6% 3 4 3 3 4 5% 39%	2167
October	1st to 10th	Night	23% 8% 3 8% 5% 4 4 3 5% 6% 32%	3800
	11th to 20th	Night	32% 8% 3 6% 4 4 4 3 4 5% 29%	3777
	21st to end	Night	33% 10% 3 6% 4 4 3 3 4 5% 27%	4385
November	1st to 10th	Night	40% 10% 3 7% 4 4 3 2 3 5% 18%	2730
	11th to 20th	Night	37% 9% 2 5% 5% 4 4 3 4 3 25%	2674
	21st to end	Night	38% 9% 2 6% 5% 3 3 2 3 4 23%	2660
December	1st to 10th	Night	33% 12% 3 6% 4 3 4 3 3 5% 25%	2717
	11th to 20th	Night	46% 12% 3 7% 4 3 3 2 3 4 14%	3520
	21st to end	Night	48% 13% 3 5% 3 2 2 2 3 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	74% 7% 9% 6% 3 1	2219
	11th to 20th	Day	61% 5% 14% 10% 7% 1	2220
	21st to end	Day	81% 5% 6% 6% 1	2760
February	1st to 10th	Day	67% 9% 11% 8% 3 3	1710
	11th to 20th	Day	62% 10% 10% 12% 6% 1	1674
	21st to end	Day	61% 9% 13% 11% 4 2	1413
March	1st to 10th	Day	61% 10% 16% 9% 4	3278
	11th to 20th	Day	52% 8% 12% 23% 4 1	3490
	21st to end	Day	61% 9% 18% 10% 3	3905
April	1st to 10th	Day	61% 11% 16% 9% 4	2280
	11th to 20th	Day	55% 9% 14% 13% 9% 1	2368
	21st to end	Day	55% 8% 15% 13% 7% 1	2513
May	1st to 10th	Day	40% 8% 19% 20% 11% 1	4420
	11th to 20th	Day	38% 12% 25% 20% 5%	4380
	21st to end	Day	55% 11% 18% 13% 2	4970
June	1st to 10th	Day	50% 9% 20% 14% 5% 2	2850
	11th to 20th	Day	49% 13% 21% 13% 4	2850
	21st to end	Day	42% 10% 20% 17% 8% 2	2850
July	1st to 10th	Day	22% 7% 12% 26% 23% 8%	4666
	11th to 20th	Day	17% 5% 18% 38% 20% 1	4659
	21st to end	Day	29% 7% 23% 26% 13% 2	4774
August	1st to 10th	Day	18% 6% 15% 48% 12% 1	4325
	11th to 20th	Day	37% 7% 30% 17% 8% 2	4065
	21st to end	Day	40% 8% 21% 21% 10% 1	4441
September	1st to 10th	Day	35% 10% 17% 24% 11% 4	2280
	11th to 20th	Day	45% 9% 13% 17% 13% 2	2257
	21st to end	Day	48% 9% 17% 16% 8% 1	2012
October	1st to 10th	Day	54% 7% 18% 17% 5%	3180
	11th to 20th	Day	61% 7% 13% 14% 5%	3161
	21st to end	Day	64% 7% 13% 12% 4	3159
November	1st to 10th	Day	67% 7% 12% 9% 4 1	1568
	11th to 20th	Day	67% 8% 9% 9% 4 2	1528
	21st to end	Day	68% 6% 10% 9% 6% 1	1520
December	1st to 10th	Day	64% 7% 9% 11% 7% 1	1459
	11th to 20th	Day	75% 6% 10% 6% 2 1	1688
	21st to end	Day	77% 6% 8% 6% 2 1	2442
January	1st to 10th	Night	73% 6% 8% 10% 2	4726
	11th to 20th	Night	58% 8% 16% 10% 6% 1	4740
	21st to end	Night	79% 5% 6% 8% 2 1	4892
February	1st to 10th	Night	67% 7% 11% 9% 4 2	2470
	11th to 20th	Night	61% 8% 11% 12% 7% 1	2404
	21st to end	Night	60% 7% 11% 14% 6% 2	2041
March	1st to 10th	Night	62% 8% 13% 11% 5%	3595
	11th to 20th	Night	49% 6% 16% 24% 4	3490
	21st to end	Night	67% 7% 12% 12% 2	3747
April	1st to 10th	Night	61% 7% 15% 14% 3	1900
	11th to 20th	Night	55% 6% 13% 15% 9% 2	1758
	21st to end	Night	57% 6% 14% 14% 9%	1667
May	1st to 10th	Night	40% 6% 16% 27% 11%	2540
	11th to 20th	Night	32% 10% 27% 24% 7%	2516
	21st to end	Night	57% 8% 18% 14% 3	2602
June	1st to 10th	Night	52% 6% 19% 15% 5% 3	1330
	11th to 20th	Night	49% 10% 20% 17% 5%	1330
	21st to end	Night	40% 8% 21% 18% 9% 3	1330
July	1st to 10th	Night	22% 5% 11% 33% 24% 6%	2185
	11th to 20th	Night	15% 4 14% 43% 22% 1	2178
	21st to end	Night	30% 6% 16% 29% 16% 2	2538
August	1st to 10th	Night	14% 4 15% 44% 21% 2	2579
	11th to 20th	Night	35% 5% 31% 18% 8% 3	2839
	21st to end	Night	40% 6% 23% 22% 9%	3228
September	1st to 10th	Night	28% 9% 18% 28% 13% 4	1900
	11th to 20th	Night	43% 7% 14% 16% 16% 4	1919
	21st to end	Night	48% 6% 16% 21% 7% 2	2167
October	1st to 10th	Night	55% 6% 19% 14% 6%	3800
	11th to 20th	Night	59% 4 12% 20% 5%	3777
	21st to end	Night	60% 6% 15% 15% 5%	4385
November	1st to 10th	Night	70% 5% 11% 9% 4 1	2730
	11th to 20th	Night	65% 7% 11% 10% 5% 2	2674
	21st to end	Night	67% 6% 10% 9% 7% 1	2660
December	1st to 10th	Night	64% 6% 11% 12% 6% 1	2717
	11th to 20th	Night	77% 6% 8% 5% 4	3516
	21st to end	Night	74% 5% 9% 8% 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	39% 9% 16% 20% 9% 7%	180
	11th to 20th	Day	41% 10% 18% 16% 14% 1	180
	21st to end	Day	45% 6% 14% 22% 11% 2	232
February	1st to 10th	Day	38% 7% 20% 23% 12% 1	370
	11th to 20th	Day	34% 3 22% 26% 13% 1	365
	21st to end	Day	28% 9% 20% 27% 13% 3	307
March	1st to 10th	Day	29% 7% 20% 27% 14% 3	460
	11th to 20th	Day	29% 5% 19% 25% 19% 3	460
	21st to end	Day	31% 7% 20% 26% 14% 2	506
April	1st to 10th	Day	28% 7% 23% 25% 15% 2	460
	11th to 20th	Day	26% 5% 23% 27% 14% 5%	452
	21st to end	Day	23% 6% 23% 29% 17% 2	460
May	1st to 10th	Day	15% 4 19% 36% 23% 2	463
	11th to 20th	Day	15% 3 12% 33% 31% 6%	488
	21st to end	Day	15% 5% 17% 34% 22% 6%	620
June	1st to 10th	Day	18% 4 16% 35% 24% 3	680
	11th to 20th	Day	17% 4 19% 34% 21% 4	680
	21st to end	Day	14% 2 14% 34% 29% 7%	680
July	1st to 10th	Day	12% 2 12% 33% 35% 7%	671
	11th to 20th	Day	7% 1 11% 34% 39% 7%	668
	21st to end	Day	6% 1 9% 30% 44% 9%	619
August	1st to 10th	Day	9% 2 9% 23% 41% 15%	487
	11th to 20th	Day	8% 2 9% 32% 39% 10%	477
	21st to end	Day	12% 2 16% 34% 29% 8%	539
September	1st to 10th	Day	13% 3 16% 37% 22% 9%	490
	11th to 20th	Day	20% 4 17% 27% 25% 7%	490
	21st to end	Day	23% 3 19% 25% 24% 5%	490
October	1st to 10th	Day	26% 3 17% 26% 21% 6%	490
	11th to 20th	Day	36% 5% 13% 21% 18% 7%	490
	21st to end	Day	33% 10% 19% 23% 13% 4	400
November	1st to 10th	Day	40% 9% 19% 20% 12% 1	200
	11th to 20th	Day	38% 3 16% 17% 18% 7%	182
	21st to end	Day	42% 7% 21% 13% 9% 8%	180
December	1st to 10th	Day	44% 4 18% 12% 16% 6%	180
	11th to 20th	Day	38% 7% 18% 23% 11% 2	180
	21st to end	Day	42% 6% 18% 26% 8% 1	198
January	1st to 10th	Night	49% 6% 17% 15% 11% 2	850
	11th to 20th	Night	43% 4 14% 22% 16%	850
	21st to end	Night	40% 4 17% 23% 14% 1	861
February	1st to 10th	Night	36% 6% 19% 26% 12% 1	760
	11th to 20th	Night	34% 5% 19% 29% 12% 1	744
	21st to end	Night	32% 7% 22% 22% 14% 4	628
March	1st to 10th	Night	33% 5% 19% 25% 16% 2	760
	11th to 20th	Night	36% 5% 18% 23% 16% 2	760
	21st to end	Night	36% 5% 16% 24% 15% 4	836
April	1st to 10th	Night	30% 5% 15% 31% 16% 4	760
	11th to 20th	Night	26% 5% 22% 29% 17% 3	630
	21st to end	Night	28% 4 18% 31% 17% 2	527
May	1st to 10th	Night	18% 2 16% 32% 26% 7%	380
	11th to 20th	Night	18% 3 9% 28% 35% 7%	374
	21st to end	Night	18% 5% 11% 31% 30% 5%	411
June	1st to 10th	Night	23% 4 11% 32% 26% 4	380
	11th to 20th	Night	17% 5% 14% 36% 22% 7%	380
	21st to end	Night	14% 2 8% 34% 36% 7%	380
July	1st to 10th	Night	12% 2 9% 26% 43% 9%	370
	11th to 20th	Night	8% 1 10% 28% 42% 12%	368
	21st to end	Night	8% 1 5% 23% 49% 14%	416
August	1st to 10th	Night	9% 2 4 19% 45% 21%	410
	11th to 20th	Night	8% 1 4 25% 48% 14%	564
	21st to end	Night	13% 2 11% 26% 38% 10%	670
September	1st to 10th	Night	10% 2 8% 33% 35% 12%	760
	11th to 20th	Night	21% 3 11% 21% 31% 13%	760
	21st to end	Night	25% 4 13% 25% 27% 6%	760
October	1st to 10th	Night	23% 4 15% 26% 26% 6%	760
	11th to 20th	Night	33% 3 15% 23% 20% 5%	760
	21st to end	Night	38% 6% 15% 25% 13% 3	836
November	1st to 10th	Night	43% 6% 16% 26% 9%	780
	11th to 20th	Night	41% 4 21% 21% 11% 2	764
	21st to end	Night	43% 2 19% 20% 12% 3	760
December	1st to 10th	Night	36% 5% 17% 27% 14% 1	787
	11th to 20th	Night	50% 6% 16% 21% 7%	850
	21st to end	Night	47% 8% 20% 19% 6%	935

Page generated at 2024-11-08 19:45:38. Version ac07

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