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 2024-01-14.

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% 7% 3 5% 5% 3 4 4 5% 6% 34%	74738
	Night	29% 8% 3 5% 5% 3 4 4 4 5% 31%	75027
Transparency	Day	51% 9% 16% 16% 7% 1	74425
	Night	57% 7% 13% 15% 7% 1	74858
Seeing	Day	22% 4 17% 29% 23% 5%	14298
	Night	31% 4 15% 25% 21% 5%	22601

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	48% 9% 3 5% 4 2 3 3 3 3 15%	1329
	11th to 20th	Day	36% 11% 4 5% 5% 2 4 4 4 6% 18%	1281
	21st to end	Day	37% 11% 2 6% 5% 3 4 3 5% 5% 18%	1564
February	1st to 10th	Day	33% 10% 4 6% 5% 4 4 5% 6% 5% 18%	1620
	11th to 20th	Day	29% 10% 3 5% 5% 3 5% 5% 5% 6% 25%	1575
	21st to end	Day	25% 10% 4 6% 5% 4 6% 4 5% 6% 25%	1332
March	1st to 10th	Day	30% 9% 3 6% 5% 3 4 5% 5% 6% 22%	1875
	11th to 20th	Day	34% 10% 3 6% 7% 3 4 3 3 4 22%	1980
	21st to end	Day	28% 10% 4 7% 6% 3 4 3 4 5% 25%	2220
April	1st to 10th	Day	27% 9% 3 7% 6% 3 5% 5% 6% 6% 23%	2160
	11th to 20th	Day	25% 7% 4 6% 5% 3 5% 5% 6% 6% 28%	2241
	21st to end	Day	24% 8% 3 6% 5% 3 5% 4 5% 5% 31%	2380
May	1st to 10th	Day	16% 6% 3 6% 7% 3 5% 5% 6% 7% 37%	2520
	11th to 20th	Day	16% 6% 3 6% 7% 3 4 5% 6% 8% 35%	2477
	21st to end	Day	17% 7% 4 7% 5% 4 5% 5% 5% 7% 35%	2809
June	1st to 10th	Day	21% 7% 2 6% 6% 3 5% 4 6% 7% 33%	2700
	11th to 20th	Day	19% 7% 3 6% 6% 3 5% 6% 6% 7% 31%	2700
	21st to end	Day	15% 5% 2 4 6% 3 5% 4 6% 7% 43%	2700
July	1st to 10th	Day	11% 4 3 4 4 2 4 4 5% 6% 51%	2700
	11th to 20th	Day	10% 5% 2 3 4 2 4 4 5% 7% 55%	2700
	21st to end	Day	8% 3 1 3 3 2 3 3 4 6% 65%	2825
August	1st to 10th	Day	10% 3 2 5% 4 2 3 4 5% 5% 58%	2474
	11th to 20th	Day	8% 4 2 4 4 2 3 3 5% 6% 58%	2298
	21st to end	Day	11% 4 2 4 5% 3 4 4 6% 8% 49%	2534
September	1st to 10th	Day	13% 4 2 5% 3 3 4 4 5% 6% 50%	2160
	11th to 20th	Day	20% 6% 3 4 5% 3 3 4 4 5% 43%	2139
	21st to end	Day	25% 4 2 4 4 3 4 4 4 7% 40%	1907
October	1st to 10th	Day	26% 7% 2 4 3 2 3 4 5% 7% 37%	1800
	11th to 20th	Day	33% 7% 3 5% 5% 3 4 5% 4 6% 26%	1800
	21st to end	Day	35% 8% 2 6% 4 2 3 3 5% 5% 27%	1824
November	1st to 10th	Day	42% 8% 3 5% 4 2 4 4 3 4 21%	1488
	11th to 20th	Day	39% 8% 3 5% 4 2 4 4 4 4 23%	1520
	21st to end	Day	42% 8% 3 5% 5% 3 3 4 4 3 22%	1520
December	1st to 10th	Day	33% 10% 4 7% 4 3 4 4 3 5% 25%	1459
	11th to 20th	Day	40% 12% 4 7% 5% 2 3 3 3 4 16%	1685
	21st to end	Day	47% 11% 3 7% 4 2 3 2 2 4 13%	2442
January	1st to 10th	Night	44% 10% 3 6% 5% 2 3 3 3 4 16%	2836
	11th to 20th	Night	40% 9% 3 5% 4 3 4 3 5% 6% 19%	2751
	21st to end	Night	33% 11% 3 6% 5% 2 4 4 4 5% 22%	2786
February	1st to 10th	Night	34% 9% 4 6% 4 3 4 4 4 5% 21%	2340
	11th to 20th	Night	28% 12% 3 6% 4 2 4 4 4 5% 27%	2272
	21st to end	Night	28% 10% 4 6% 6% 3 3 4 5% 5% 27%	1924
March	1st to 10th	Night	33% 10% 3 5% 5% 3 4 4 5% 6% 24%	2084
	11th to 20th	Night	34% 9% 4 6% 5% 2 4 3 4 5% 23%	1979
	21st to end	Night	32% 11% 3 7% 6% 3 4 4 4 5% 20%	2135
April	1st to 10th	Night	28% 10% 3 6% 6% 3 5% 5% 5% 6% 24%	1800
	11th to 20th	Night	21% 11% 4 6% 6% 3 5% 5% 6% 6% 28%	1665
	21st to end	Night	25% 8% 3 7% 5% 3 5% 4 5% 6% 30%	1580
May	1st to 10th	Night	17% 4 2 5% 6% 3 5% 5% 7% 6% 41%	1440
	11th to 20th	Night	16% 6% 3 5% 6% 3 5% 5% 6% 9% 35%	1416
	21st to end	Night	16% 8% 3 7% 6% 3 5% 4 5% 7% 36%	1462
June	1st to 10th	Night	21% 7% 4 7% 5% 4 5% 4 5% 5% 34%	1260
	11th to 20th	Night	17% 8% 3 7% 6% 3 6% 6% 6% 7% 32%	1260
	21st to end	Night	12% 5% 2 6% 6% 3 4 6% 6% 7% 43%	1260
July	1st to 10th	Night	11% 4 2 5% 5% 2 4 3 4 6% 53%	1260
	11th to 20th	Night	8% 3 2 4 3 2 4 4 5% 7% 58%	1260
	21st to end	Night	7% 3 2 3 3 1 3 4 4 6% 65%	1491
August	1st to 10th	Night	8% 3 1 3 3 2 4 3 4 5% 64%	1462
	11th to 20th	Night	6% 3 1 3 3 3 3 4 5% 8% 62%	1602
	21st to end	Night	10% 4 3 5% 5% 4 4 5% 6% 7% 47%	1822
September	1st to 10th	Night	10% 4 2 4 4 3 3 4 5% 6% 57%	1800
	11th to 20th	Night	21% 5% 2 4 3 2 4 4 5% 5% 43%	1818
	21st to end	Night	22% 7% 2 5% 4 3 4 3 4 5% 40%	2052
October	1st to 10th	Night	21% 7% 2 5% 5% 3 4 3 5% 6% 41%	2160
	11th to 20th	Night	32% 6% 2 5% 3 2 4 3 3 5% 33%	2160
	21st to end	Night	37% 6% 2 4 4 2 3 3 4 5% 29%	2529
November	1st to 10th	Night	40% 10% 3 6% 5% 3 3 3 3 5% 19%	2590
	11th to 20th	Night	36% 9% 3 5% 5% 3 4 4 4 3 25%	2660
	21st to end	Night	39% 8% 2 5% 6% 2 4 3 3 4 23%	2660
December	1st to 10th	Night	34% 11% 3 6% 4 3 4 4 3 5% 25%	2717
	11th to 20th	Night	46% 11% 3 6% 5% 3 3 3 3 4 14%	3520
	21st to end	Night	48% 12% 3 5% 4 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% 7% 6% 5% 1	1329
	11th to 20th	Day	68% 7% 9% 9% 4 2	1281
	21st to end	Day	69% 8% 10% 11% 2	1564
February	1st to 10th	Day	67% 9% 11% 7% 3 3	1620
	11th to 20th	Day	62% 9% 10% 12% 7%	1584
	21st to end	Day	61% 9% 14% 11% 4 2	1332
March	1st to 10th	Day	62% 10% 15% 10% 4	1875
	11th to 20th	Day	67% 6% 10% 12% 4 1	1980
	21st to end	Day	62% 10% 14% 12% 2	2220
April	1st to 10th	Day	61% 10% 16% 10% 4	2160
	11th to 20th	Day	56% 9% 14% 13% 8%	2241
	21st to end	Day	55% 9% 15% 13% 7% 1	2380
May	1st to 10th	Day	46% 12% 18% 18% 6% 1	2520
	11th to 20th	Day	47% 10% 19% 18% 5%	2480
	21st to end	Day	48% 12% 18% 19% 4	2810
June	1st to 10th	Day	50% 9% 20% 14% 5% 2	2700
	11th to 20th	Day	50% 14% 21% 12% 4	2700
	21st to end	Day	41% 11% 20% 17% 9% 2	2700
July	1st to 10th	Day	33% 12% 19% 23% 11% 3	2626
	11th to 20th	Day	29% 9% 23% 28% 10% 1	2619
	21st to end	Day	20% 10% 21% 31% 15% 3	2668
August	1st to 10th	Day	29% 10% 19% 29% 11% 2	2457
	11th to 20th	Day	28% 9% 21% 24% 15% 3	2298
	21st to end	Day	34% 11% 22% 26% 6% 1	2534
September	1st to 10th	Day	36% 10% 16% 24% 11% 3	2160
	11th to 20th	Day	44% 9% 13% 18% 14% 2	2139
	21st to end	Day	47% 9% 18% 16% 8% 2	1907
October	1st to 10th	Day	49% 9% 17% 17% 8%	1800
	11th to 20th	Day	59% 10% 15% 12% 3 1	1800
	21st to end	Day	60% 8% 12% 12% 6% 1	1824
November	1st to 10th	Day	67% 7% 12% 9% 4 1	1488
	11th to 20th	Day	67% 8% 9% 10% 4 2	1520
	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% 7% 10% 4 1	2836
	11th to 20th	Night	67% 8% 11% 8% 4 1	2751
	21st to end	Night	66% 7% 9% 14% 3 1	2786
February	1st to 10th	Night	66% 7% 11% 10% 4 2	2340
	11th to 20th	Night	61% 8% 11% 13% 7% 1	2274
	21st to end	Night	60% 7% 11% 14% 6% 2	1924
March	1st to 10th	Night	61% 7% 14% 13% 4	2084
	11th to 20th	Night	65% 6% 10% 13% 4 1	1980
	21st to end	Night	67% 7% 12% 11% 3	2135
April	1st to 10th	Night	61% 6% 15% 15% 3	1800
	11th to 20th	Night	56% 7% 13% 15% 8% 1	1665
	21st to end	Night	57% 6% 14% 14% 9%	1580
May	1st to 10th	Night	43% 8% 20% 20% 9% 1	1440
	11th to 20th	Night	45% 9% 21% 19% 6% 1	1416
	21st to end	Night	48% 9% 18% 19% 6%	1462
June	1st to 10th	Night	52% 6% 18% 16% 5% 3	1260
	11th to 20th	Night	50% 10% 20% 16% 5%	1260
	21st to end	Night	39% 8% 22% 19% 9% 3	1260
July	1st to 10th	Night	34% 6% 16% 27% 14% 3	1225
	11th to 20th	Night	26% 7% 23% 29% 13% 2	1218
	21st to end	Night	19% 6% 16% 34% 21% 4	1408
August	1st to 10th	Night	24% 6% 19% 29% 18% 3	1454
	11th to 20th	Night	21% 7% 25% 27% 15% 5%	1602
	21st to end	Night	33% 8% 21% 28% 9% 1	1822
September	1st to 10th	Night	28% 9% 18% 28% 13% 4	1800
	11th to 20th	Night	43% 8% 13% 16% 16% 4	1818
	21st to end	Night	47% 6% 16% 22% 8% 2	2052
October	1st to 10th	Night	45% 7% 16% 20% 11% 1	2160
	11th to 20th	Night	56% 6% 14% 18% 5%	2160
	21st to end	Night	58% 7% 13% 15% 8%	2529
November	1st to 10th	Night	69% 5% 12% 9% 4 1	2590
	11th to 20th	Night	65% 7% 11% 10% 5% 2	2660
	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	42% 10% 19% 14% 14% 1	166
	21st to end	Day	41% 6% 14% 24% 13% 2	208
February	1st to 10th	Day	39% 6% 21% 22% 11%	340
	11th to 20th	Day	36% 2 23% 25% 12% 1	335
	21st to end	Day	26% 8% 21% 29% 14% 3	280
March	1st to 10th	Day	31% 5% 20% 27% 14% 3	420
	11th to 20th	Day	30% 6% 20% 24% 16% 4	420
	21st to end	Day	31% 6% 21% 27% 14% 1	462
April	1st to 10th	Day	29% 7% 24% 22% 16% 2	420
	11th to 20th	Day	28% 4 22% 26% 15% 5%	412
	21st to end	Day	22% 5% 23% 30% 17% 2	420
May	1st to 10th	Day	15% 4 20% 37% 22% 2	423
	11th to 20th	Day	16% 3 11% 32% 32% 6%	448
	21st to end	Day	13% 4 17% 35% 24% 7%	571
June	1st to 10th	Day	18% 3 15% 36% 24% 3	630
	11th to 20th	Day	18% 4 19% 35% 22% 3	630
	21st to end	Day	14% 2 13% 35% 29% 6%	630
July	1st to 10th	Day	12% 2 12% 33% 34% 7%	621
	11th to 20th	Day	8% 1 12% 36% 38% 5%	618
	21st to end	Day	5% 1 9% 30% 45% 9%	571
August	1st to 10th	Day	10% 3 10% 25% 40% 13%	447
	11th to 20th	Day	8% 2 9% 33% 39% 9%	437
	21st to end	Day	11% 2 16% 34% 30% 7%	495
September	1st to 10th	Day	14% 3 17% 40% 21% 5%	450
	11th to 20th	Day	20% 4 16% 28% 25% 7%	450
	21st to end	Day	22% 4 20% 25% 24% 5%	450
October	1st to 10th	Day	27% 3 17% 26% 20% 6%	450
	11th to 20th	Day	36% 5% 14% 21% 18% 7%	450
	21st to end	Day	34% 9% 19% 22% 12% 3	366
November	1st to 10th	Day	38% 9% 19% 20% 12% 1	180
	11th to 20th	Day	39% 3 16% 17% 17% 7%	180
	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	44% 5% 13% 21% 17%	817
	21st to end	Night	38% 4 18% 24% 15% 1	814
February	1st to 10th	Night	37% 5% 20% 25% 12% 1	720
	11th to 20th	Night	35% 5% 19% 29% 12% 1	704
	21st to end	Night	30% 6% 23% 23% 14% 4	592
March	1st to 10th	Night	33% 4 19% 25% 16% 3	720
	11th to 20th	Night	38% 5% 18% 23% 14% 2	720
	21st to end	Night	36% 4 16% 24% 16% 4	792
April	1st to 10th	Night	31% 5% 15% 30% 16% 4	720
	11th to 20th	Night	27% 4 21% 27% 18% 3	597
	21st to end	Night	28% 3 18% 31% 18% 2	500
May	1st to 10th	Night	18% 1 16% 33% 26% 7%	360
	11th to 20th	Night	18% 3 8% 27% 36% 8%	354
	21st to end	Night	18% 4 11% 31% 31% 5%	389
June	1st to 10th	Night	23% 4 11% 31% 27% 4	360
	11th to 20th	Night	18% 5% 14% 35% 22% 6%	360
	21st to end	Night	14% 2 8% 34% 35% 7%	360
July	1st to 10th	Night	12% 2 9% 26% 42% 9%	350
	11th to 20th	Night	8% 1 10% 30% 42% 10%	348
	21st to end	Night	7% 1 5% 22% 50% 15%	394
August	1st to 10th	Night	10% 2 5% 20% 44% 20%	388
	11th to 20th	Night	8% 4 25% 49% 13%	534
	21st to end	Night	12% 2 12% 26% 39% 9%	634
September	1st to 10th	Night	11% 2 8% 34% 35% 10%	720
	11th to 20th	Night	21% 3 11% 21% 31% 13%	720
	21st to end	Night	25% 4 13% 25% 27% 6%	720
October	1st to 10th	Night	23% 3 15% 26% 26% 7%	720
	11th to 20th	Night	33% 3 15% 23% 20% 5%	720
	21st to end	Night	39% 6% 15% 24% 13% 3	792
November	1st to 10th	Night	42% 5% 17% 26% 9%	740
	11th to 20th	Night	40% 4 21% 21% 11% 2	760
	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 2024-01-11 01:22:41. Version ac07

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