Powell River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Powell River clear sky chart from 2005-11-06 to 2024-11-30.

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	20% 9% 3 7% 4 4 4 3 5% 6% 35%	105759
	Night	25% 10% 3 7% 5% 4 4 3 4 5% 29%	102424
Transparency	Day	50% 9% 15% 18% 7% 1	105501
	Night	57% 8% 13% 15% 6% 1	102328
Seeing	Day	25% 11% 23% 24% 14% 3	15716
	Night	32% 8% 18% 24% 16% 3	23715

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	37% 15% 3 7% 5% 4 4 4 5% 5% 12%	2219
	11th to 20th	Day	29% 14% 5% 7% 5% 5% 5% 4 5% 6% 16%	2199
	21st to end	Day	48% 13% 3 9% 4 4 3 2 3 3 8%	2647
February	1st to 10th	Day	33% 13% 3 8% 4 5% 5% 4 4 4 17%	1710
	11th to 20th	Day	26% 12% 3 8% 5% 5% 5% 3 4 5% 23%	1665
	21st to end	Day	25% 11% 3 8% 6% 6% 5% 4 5% 6% 22%	1413
March	1st to 10th	Day	22% 13% 5% 10% 6% 6% 5% 5% 6% 4 18%	3278
	11th to 20th	Day	21% 11% 3 8% 5% 5% 4 4 5% 5% 29%	3490
	21st to end	Day	21% 11% 3 8% 5% 5% 5% 4 5% 7% 26%	3844
April	1st to 10th	Day	23% 12% 3 8% 5% 5% 5% 3 4 7% 23%	2280
	11th to 20th	Day	21% 9% 3 7% 5% 4 5% 4 6% 6% 30%	2433
	21st to end	Day	23% 9% 3 7% 5% 4 4 4 5% 5% 31%	2476
May	1st to 10th	Day	14% 7% 3 7% 4 4 4 3 4 6% 43%	4420
	11th to 20th	Day	12% 7% 2 6% 4 5% 4 4 7% 11% 37%	4377
	21st to end	Day	24% 9% 3 7% 5% 4 4 4 5% 6% 30%	5146
June	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 6% 7% 32%	2850
	11th to 20th	Day	14% 7% 3 8% 6% 6% 5% 4 7% 8% 33%	2850
	21st to end	Day	14% 6% 3 6% 5% 4 4 4 6% 7% 41%	2850
July	1st to 10th	Day	7% 3 1 3 3 2 2 2 4 5% 67%	4740
	11th to 20th	Day	6% 3 1 2 2 2 2 2 3 5% 72%	4740
	21st to end	Day	8% 5% 2 5% 3 4 4 3 5% 7% 53%	5082
August	1st to 10th	Day	5% 2 1 3 2 2 3 3 3 6% 71%	4262
	11th to 20th	Day	10% 6% 3 6% 4 5% 5% 4 6% 9% 42%	4026
	21st to end	Day	14% 6% 2 5% 4 4 4 4 5% 7% 46%	4521
September	1st to 10th	Day	10% 5% 2 4 4 3 4 4 5% 8% 50%	2285
	11th to 20th	Day	18% 7% 2 7% 4 4 4 3 6% 6% 39%	2200
	21st to end	Day	23% 7% 3 6% 5% 4 4 4 5% 6% 32%	2052
October	1st to 10th	Day	24% 8% 3 9% 6% 6% 5% 4 5% 6% 24%	3180
	11th to 20th	Day	31% 9% 3 7% 5% 4 5% 3 5% 6% 23%	3161
	21st to end	Day	26% 13% 3 10% 6% 5% 4 4 4 6% 18%	3119
November	1st to 10th	Day	35% 12% 4 9% 4 4 4 4 3 4 17%	1568
	11th to 20th	Day	32% 14% 3 8% 6% 4 4 4 4 4 17%	1600
	21st to end	Day	34% 12% 4 10% 6% 5% 4 3 3 4 16%	1595
December	1st to 10th	Day	29% 13% 4 8% 5% 4 3 4 4 6% 20%	1354
	11th to 20th	Day	41% 13% 4 11% 4 4 4 2 2 3 11%	1685
	21st to end	Day	36% 14% 4 9% 6% 5% 3 4 4 4 12%	2442
January	1st to 10th	Night	35% 13% 3 10% 5% 4 5% 4 4 4 13%	4726
	11th to 20th	Night	31% 10% 3 6% 4 4 4 4 5% 6% 21%	4699
	21st to end	Night	46% 15% 4 8% 4 4 3 2 2 3 9%	5008
February	1st to 10th	Night	32% 14% 4 7% 5% 4 3 3 3 5% 20%	2470
	11th to 20th	Night	26% 13% 3 7% 4 3 4 3 4 5% 28%	2402
	21st to end	Night	28% 14% 4 7% 5% 4 3 3 4 6% 23%	2041
March	1st to 10th	Night	23% 13% 4 9% 6% 6% 5% 4 4 6% 20%	3592
	11th to 20th	Night	19% 10% 3 9% 5% 4 4 5% 5% 5% 31%	3489
	21st to end	Night	24% 12% 5% 9% 6% 5% 3 3 4 5% 24%	3809
April	1st to 10th	Night	24% 12% 3 9% 5% 5% 5% 4 5% 6% 23%	1900
	11th to 20th	Night	21% 11% 3 6% 5% 5% 5% 4 6% 6% 28%	1693
	21st to end	Night	23% 9% 3 7% 5% 5% 5% 3 6% 5% 29%	1702
May	1st to 10th	Night	15% 8% 3 7% 4 3 3 3 4 5% 46%	2540
	11th to 20th	Night	14% 5% 2 5% 3 4 5% 4 6% 9% 42%	2516
	21st to end	Night	23% 10% 3 9% 5% 4 4 4 5% 6% 26%	2427
June	1st to 10th	Night	18% 11% 3 9% 5% 5% 5% 4 6% 5% 30%	1330
	11th to 20th	Night	17% 9% 3 7% 5% 5% 5% 3 5% 6% 32%	1330
	21st to end	Night	17% 7% 2 5% 4 4 4 4 5% 8% 41%	1330
July	1st to 10th	Night	7% 4 1 4 3 3 4 3 4 5% 62%	2220
	11th to 20th	Night	5% 3 1 3 2 3 2 2 5% 6% 70%	2220
	21st to end	Night	10% 5% 2 7% 5% 4 4 4 5% 5% 50%	2468
August	1st to 10th	Night	5% 3 1 2 2 2 2 2 4 6% 70%	2656
	11th to 20th	Night	8% 6% 3 7% 4 5% 6% 3 6% 7% 45%	2812
	21st to end	Night	14% 8% 3 6% 4 4 4 3 4 5% 46%	3146
September	1st to 10th	Night	9% 5% 2 5% 4 3 4 3 5% 7% 55%	1894
	11th to 20th	Night	18% 8% 2 6% 5% 3 4 4 5% 5% 41%	1976
	21st to end	Night	22% 7% 3 6% 4 3 3 3 5% 6% 39%	2128
October	1st to 10th	Night	26% 9% 3 8% 5% 5% 4 3 5% 5% 27%	3800
	11th to 20th	Night	32% 8% 3 7% 3 4 4 3 5% 6% 25%	3777
	21st to end	Night	26% 10% 4 8% 5% 5% 4 4 5% 6% 23%	4438
November	1st to 10th	Night	36% 10% 4 8% 5% 4 4 3 4 5% 17%	2730
	11th to 20th	Night	32% 11% 4 9% 6% 5% 3 4 4 4 19%	2800
	21st to end	Night	32% 11% 4 10% 5% 3 4 3 4 5% 19%	2800
December	1st to 10th	Night	29% 13% 3 9% 5% 4 4 3 3 4 23%	2821
	11th to 20th	Night	43% 15% 4 7% 4 3 3 3 3 3 11%	3520
	21st to end	Night	37% 14% 4 10% 4 4 3 3 3 3 15%	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	72% 7% 7% 10% 3	2219
	11th to 20th	Day	64% 10% 10% 9% 6%	2220
	21st to end	Day	83% 6% 5% 5% 1	2647
February	1st to 10th	Day	69% 9% 8% 7% 4 3	1710
	11th to 20th	Day	63% 7% 12% 12% 4 2	1674
	21st to end	Day	64% 7% 12% 9% 6% 2	1413
March	1st to 10th	Day	64% 10% 12% 9% 5%	3278
	11th to 20th	Day	56% 9% 12% 20% 3 1	3490
	21st to end	Day	58% 11% 16% 11% 3	3844
April	1st to 10th	Day	63% 9% 13% 10% 4	2280
	11th to 20th	Day	57% 8% 12% 13% 8% 2	2433
	21st to end	Day	57% 8% 14% 13% 8%	2476
May	1st to 10th	Day	42% 9% 17% 23% 8%	4420
	11th to 20th	Day	40% 13% 21% 22% 5%	4380
	21st to end	Day	57% 9% 15% 13% 6%	5147
June	1st to 10th	Day	52% 10% 17% 14% 5% 2	2850
	11th to 20th	Day	50% 11% 19% 15% 4 1	2850
	21st to end	Day	45% 7% 20% 19% 7% 1	2850
July	1st to 10th	Day	21% 6% 14% 26% 24% 9%	4666
	11th to 20th	Day	18% 5% 17% 39% 19% 2	4659
	21st to end	Day	31% 8% 19% 27% 13% 2	4921
August	1st to 10th	Day	16% 6% 15% 47% 14% 1	4245
	11th to 20th	Day	39% 10% 24% 17% 8% 2	4065
	21st to end	Day	38% 9% 23% 22% 7%	4520
September	1st to 10th	Day	34% 9% 18% 25% 12% 2	2285
	11th to 20th	Day	46% 9% 15% 16% 13% 1	2200
	21st to end	Day	51% 9% 15% 16% 8%	2052
October	1st to 10th	Day	58% 10% 15% 13% 5%	3180
	11th to 20th	Day	63% 8% 12% 14% 3	3161
	21st to end	Day	67% 8% 11% 10% 3	3119
November	1st to 10th	Day	72% 7% 9% 7% 5% 1	1568
	11th to 20th	Day	70% 8% 9% 8% 4 1	1600
	21st to end	Day	71% 7% 9% 8% 4 1	1595
December	1st to 10th	Day	64% 8% 11% 10% 5% 2	1354
	11th to 20th	Day	78% 7% 6% 5% 3 1	1688
	21st to end	Day	75% 7% 8% 5% 3 1	2442
January	1st to 10th	Night	74% 7% 8% 7% 3	4726
	11th to 20th	Night	60% 9% 13% 10% 6% 2	4740
	21st to end	Night	82% 5% 6% 5% 2	5008
February	1st to 10th	Night	69% 7% 8% 9% 4 2	2470
	11th to 20th	Night	61% 7% 13% 12% 6% 1	2404
	21st to end	Night	64% 5% 10% 14% 6% 2	2041
March	1st to 10th	Night	63% 9% 11% 13% 5%	3592
	11th to 20th	Night	53% 9% 13% 21% 3	3490
	21st to end	Night	63% 10% 11% 12% 4	3809
April	1st to 10th	Night	61% 9% 14% 13% 3	1900
	11th to 20th	Night	57% 9% 10% 15% 8% 2	1693
	21st to end	Night	57% 8% 12% 16% 6%	1702
May	1st to 10th	Night	40% 8% 17% 26% 9%	2540
	11th to 20th	Night	37% 10% 23% 24% 5%	2516
	21st to end	Night	58% 10% 14% 14% 4	2427
June	1st to 10th	Night	54% 9% 17% 13% 6% 2	1330
	11th to 20th	Night	52% 10% 19% 14% 5%	1330
	21st to end	Night	42% 10% 19% 20% 6% 2	1330
July	1st to 10th	Night	23% 5% 14% 28% 22% 7%	2185
	11th to 20th	Night	18% 4 18% 42% 17% 1	2178
	21st to end	Night	35% 6% 16% 27% 14% 2	2390
August	1st to 10th	Night	17% 6% 11% 46% 19% 1	2648
	11th to 20th	Night	37% 11% 28% 15% 9% 1	2839
	21st to end	Night	40% 8% 22% 24% 6%	3146
September	1st to 10th	Night	30% 7% 18% 30% 12% 2	1894
	11th to 20th	Night	45% 8% 14% 15% 15% 3	1976
	21st to end	Night	47% 7% 19% 17% 9% 1	2128
October	1st to 10th	Night	58% 7% 15% 13% 6%	3800
	11th to 20th	Night	61% 6% 14% 17% 2	3777
	21st to end	Night	61% 8% 14% 13% 4	4438
November	1st to 10th	Night	70% 9% 9% 7% 4 1	2730
	11th to 20th	Night	69% 8% 9% 8% 4 1	2800
	21st to end	Night	68% 7% 10% 9% 5% 1	2800
December	1st to 10th	Night	65% 7% 12% 10% 5% 1	2821
	11th to 20th	Night	79% 6% 6% 5% 3 1	3516
	21st to end	Night	75% 7% 8% 8% 2 1	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	40% 12% 21% 14% 8% 5%	180
	11th to 20th	Day	43% 10% 21% 15% 11%	180
	21st to end	Day	41% 12% 18% 18% 8% 3	267
February	1st to 10th	Day	42% 12% 23% 16% 7%	370
	11th to 20th	Day	31% 12% 31% 19% 8%	365
	21st to end	Day	35% 12% 28% 17% 8% 1	307
March	1st to 10th	Day	32% 13% 21% 21% 10% 3	438
	11th to 20th	Day	32% 14% 18% 20% 14% 2	460
	21st to end	Day	33% 16% 24% 19% 7% 1	506
April	1st to 10th	Day	31% 17% 27% 17% 7% 1	460
	11th to 20th	Day	27% 17% 26% 17% 11% 2	452
	21st to end	Day	27% 15% 30% 17% 9% 2	460
May	1st to 10th	Day	19% 13% 24% 32% 11% 1	463
	11th to 20th	Day	20% 7% 25% 30% 15% 2	488
	21st to end	Day	19% 11% 29% 27% 13% 2	720
June	1st to 10th	Day	25% 16% 24% 24% 11% 1	680
	11th to 20th	Day	18% 14% 32% 23% 12% 1	680
	21st to end	Day	18% 10% 25% 31% 15% 2	680
July	1st to 10th	Day	15% 8% 25% 31% 18% 2	671
	11th to 20th	Day	10% 8% 25% 35% 20% 3	668
	21st to end	Day	7% 7% 20% 35% 27% 3	707
August	1st to 10th	Day	10% 4 19% 32% 27% 8%	487
	11th to 20th	Day	10% 4 21% 35% 26% 5%	477
	21st to end	Day	17% 10% 19% 34% 18% 3	539
September	1st to 10th	Day	14% 9% 26% 29% 17% 5%	490
	11th to 20th	Day	26% 10% 18% 24% 19% 3	490
	21st to end	Day	27% 13% 19% 24% 15% 2	490
October	1st to 10th	Day	32% 8% 21% 20% 17% 3	490
	11th to 20th	Day	36% 11% 19% 15% 14% 4	490
	21st to end	Day	35% 13% 22% 17% 9% 4	404
November	1st to 10th	Day	41% 12% 26% 12% 10%	200
	11th to 20th	Day	39% 13% 18% 11% 14% 6%	200
	21st to end	Day	46% 12% 14% 13% 11% 5%	199
December	1st to 10th	Day	36% 12% 20% 12% 14% 6%	180
	11th to 20th	Day	46% 9% 17% 17% 10% 1	180
	21st to end	Day	41% 12% 19% 22% 5% 2	198
January	1st to 10th	Night	47% 10% 17% 14% 9% 2	850
	11th to 20th	Night	43% 7% 16% 21% 13%	850
	21st to end	Night	41% 7% 19% 20% 12% 2	906
February	1st to 10th	Night	41% 10% 18% 24% 8%	760
	11th to 20th	Night	32% 10% 19% 29% 10% 1	744
	21st to end	Night	36% 12% 17% 23% 9% 3	628
March	1st to 10th	Night	33% 11% 22% 20% 13% 2	760
	11th to 20th	Night	36% 12% 18% 20% 13% 1	760
	21st to end	Night	35% 9% 19% 20% 15% 2	836
April	1st to 10th	Night	31% 8% 21% 25% 13% 2	760
	11th to 20th	Night	27% 10% 25% 25% 12% 2	565
	21st to end	Night	28% 9% 22% 26% 13% 2	562
May	1st to 10th	Night	19% 7% 24% 31% 17% 2	380
	11th to 20th	Night	21% 6% 18% 33% 20% 2	374
	21st to end	Night	20% 8% 20% 32% 19% 1	411
June	1st to 10th	Night	24% 9% 17% 35% 13% 2	380
	11th to 20th	Night	22% 6% 24% 32% 16% 1	380
	21st to end	Night	21% 4 19% 32% 22% 2	380
July	1st to 10th	Night	12% 7% 17% 32% 28% 4	370
	11th to 20th	Night	10% 5% 20% 36% 27% 2	368
	21st to end	Night	8% 3 16% 38% 29% 6%	416
August	1st to 10th	Night	9% 5% 11% 30% 37% 9%	453
	11th to 20th	Night	9% 1 14% 35% 34% 6%	564
	21st to end	Night	17% 5% 17% 31% 27% 4	627
September	1st to 10th	Night	12% 4 16% 33% 27% 7%	754
	11th to 20th	Night	22% 8% 13% 20% 28% 9%	760
	21st to end	Night	28% 7% 18% 22% 20% 4	760
October	1st to 10th	Night	30% 7% 14% 23% 23% 3	760
	11th to 20th	Night	37% 5% 16% 21% 17% 4	760
	21st to end	Night	39% 9% 17% 20% 11% 3	836
November	1st to 10th	Night	44% 9% 19% 20% 8%	780
	11th to 20th	Night	41% 9% 23% 16% 10% 1	800
	21st to end	Night	39% 9% 20% 19% 11% 2	800
December	1st to 10th	Night	36% 8% 21% 21% 12% 3	836
	11th to 20th	Night	48% 10% 16% 17% 8% 1	850
	21st to end	Night	46% 9% 23% 18% 4	935

Page generated at 2024-11-27 14:30:53. Version ac07

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