Prince Rupert
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prince Rupert 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	36% 13% 3 7% 4 4 4 3 4 5% 18%	135901
	Night	37% 15% 3 7% 4 4 3 2 3 4 17%	135909
Transparency	Day	73% 5% 8% 8% 4 1	135588
	Night	74% 4 7% 8% 5% 1	135800
Seeing	Day	46% 10% 18% 18% 8% 1	18392
	Night	47% 8% 15% 19% 10% 1	25797

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	36% 18% 4 7% 4 4 4 3 4 4 13%	3527
	11th to 20th	Day	36% 11% 2 4 3 3 3 2 5% 6% 25%	3957
	21st to end	Day	49% 12% 2 6% 3 3 2 2 2 3 15%	4926
February	1st to 10th	Day	39% 13% 3 7% 4 2 3 2 2 3 23%	1680
	11th to 20th	Day	32% 15% 3 6% 3 3 3 2 3 5% 24%	1698
	21st to end	Day	29% 20% 2 7% 4 4 2 3 3 4 23%	1675
March	1st to 10th	Day	31% 17% 3 7% 5% 4 3 3 4 5% 18%	4596
	11th to 20th	Day	30% 21% 4 9% 5% 4 5% 4 5% 4 11%	4917
	21st to end	Day	25% 13% 3 8% 5% 4 4 4 5% 6% 23%	5873
April	1st to 10th	Day	34% 17% 4 8% 4 3 4 2 5% 4 16%	2572
	11th to 20th	Day	30% 14% 4 8% 5% 4 4 3 3 4 20%	2698
	21st to end	Day	29% 14% 3 8% 6% 4 4 3 4 4 21%	2813
May	1st to 10th	Day	32% 12% 4 8% 5% 5% 4 3 5% 6% 17%	6745
	11th to 20th	Day	34% 14% 4 8% 5% 4 4 3 5% 6% 14%	6886
	21st to end	Day	40% 13% 3 8% 4 3 3 2 5% 5% 12%	7570
June	1st to 10th	Day	35% 11% 3 8% 5% 4 4 4 4 4 17%	3166
	11th to 20th	Day	34% 12% 4 9% 5% 4 4 4 5% 6% 14%	3200
	21st to end	Day	38% 10% 3 8% 5% 4 4 3 4 4 17%	3200
July	1st to 10th	Day	29% 10% 3 6% 4 4 4 3 4 6% 28%	7240
	11th to 20th	Day	35% 12% 3 9% 5% 4 5% 3 4 6% 15%	7070
	21st to end	Day	34% 13% 4 9% 5% 4 4 3 4 5% 14%	7375
August	1st to 10th	Day	21% 6% 2 5% 3 4 4 4 6% 9% 36%	4590
	11th to 20th	Day	30% 11% 3 7% 4 3 3 3 4 5% 26%	4428
	21st to end	Day	41% 9% 3 7% 4 3 3 3 5% 7% 17%	4664
September	1st to 10th	Day	38% 10% 3 7% 4 4 4 3 4 6% 16%	2482
	11th to 20th	Day	35% 10% 4 8% 4 4 3 2 4 4 23%	2253
	21st to end	Day	52% 10% 3 6% 4 3 2 2 3 4 12%	2200
October	1st to 10th	Day	42% 11% 3 7% 4 3 4 3 5% 5% 15%	3386
	11th to 20th	Day	47% 13% 3 8% 4 4 3 2 3 3 8%	2933
	21st to end	Day	35% 14% 3 7% 4 3 4 3 4 4 19%	3200
November	1st to 10th	Day	48% 11% 3 8% 4 4 3 3 2 3 11%	1614
	11th to 20th	Day	40% 16% 4 8% 4 4 3 2 3 3 13%	1470
	21st to end	Day	43% 17% 3 6% 3 3 3 2 2 3 14%	1470
December	1st to 10th	Day	48% 12% 3 5% 3 4 3 2 3 3 14%	2360
	11th to 20th	Day	38% 15% 4 9% 4 3 3 2 3 3 15%	2409
	21st to end	Day	47% 19% 4 9% 3 3 2 2 2 2 8%	3058
January	1st to 10th	Night	39% 17% 3 7% 4 3 3 2 3 4 14%	9368
	11th to 20th	Night	37% 11% 2 4 3 3 3 3 4 5% 24%	8926
	21st to end	Night	47% 14% 3 6% 3 2 3 2 3 3 14%	9273
February	1st to 10th	Night	39% 13% 3 5% 3 3 2 3 3 3 22%	2940
	11th to 20th	Night	34% 16% 3 5% 4 3 3 3 3 4 22%	2809
	21st to end	Night	27% 20% 3 7% 3 4 3 2 3 4 24%	2128
March	1st to 10th	Night	24% 20% 4 8% 5% 4 4 3 4 4 19%	5498
	11th to 20th	Night	27% 22% 5% 9% 5% 5% 5% 4 4 4 11%	5294
	21st to end	Night	23% 16% 3 8% 5% 4 4 3 4 5% 25%	5329
April	1st to 10th	Night	31% 18% 4 8% 4 4 3 3 3 3 18%	2048
	11th to 20th	Night	29% 17% 3 7% 3 4 4 3 5% 4 21%	1871
	21st to end	Night	29% 14% 3 6% 4 4 3 2 5% 6% 23%	1806
May	1st to 10th	Night	33% 15% 3 8% 5% 5% 4 3 3 5% 17%	3443
	11th to 20th	Night	40% 14% 3 7% 4 4 4 2 4 4 14%	3229
	21st to end	Night	40% 14% 4 9% 5% 4 4 2 3 4 13%	3547
June	1st to 10th	Night	36% 11% 3 7% 6% 5% 4 2 3 3 19%	1231
	11th to 20th	Night	35% 12% 4 8% 4 4 4 4 5% 6% 16%	1200
	21st to end	Night	35% 13% 3 7% 7% 5% 5% 3 3 5% 14%	1200
July	1st to 10th	Night	33% 9% 3 5% 4 2 3 2 4 4 30%	2720
	11th to 20th	Night	38% 13% 3 7% 4 4 4 3 4 5% 15%	2876
	21st to end	Night	37% 12% 4 7% 4 4 3 2 4 6% 17%	3468
August	1st to 10th	Night	19% 9% 3 7% 5% 5% 3 3 5% 6% 35%	2567
	11th to 20th	Night	33% 8% 2 6% 4 4 3 3 3 5% 28%	2629
	21st to end	Night	46% 11% 3 8% 4 2 3 2 3 3 15%	3245
September	1st to 10th	Night	37% 12% 4 8% 4 3 4 3 3 4 19%	1915
	11th to 20th	Night	36% 10% 2 6% 4 3 4 3 3 5% 25%	2147
	21st to end	Night	51% 10% 3 7% 4 3 3 2 2 3 12%	2200
October	1st to 10th	Night	43% 12% 4 7% 4 3 3 2 3 3 14%	3808
	11th to 20th	Night	47% 13% 4 8% 4 3 3 2 3 4 9%	4215
	21st to end	Night	34% 13% 3 9% 4 4 3 2 3 4 20%	4601
November	1st to 10th	Night	46% 14% 4 6% 4 4 3 2 2 3 13%	2900
	11th to 20th	Night	40% 19% 4 7% 4 4 3 3 3 4 11%	3150
	21st to end	Night	42% 17% 3 7% 4 3 3 2 3 3 13%	3150
December	1st to 10th	Night	50% 13% 3 5% 3 3 3 2 3 3 12%	5040
	11th to 20th	Night	36% 19% 4 8% 4 3 3 2 3 3 14%	5998
	21st to end	Night	43% 20% 4 8% 4 4 3 2 2 2 7%	8140

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	77% 5% 2 8% 7% 1	3527
	11th to 20th	Day	62% 3 6% 12% 12% 4	3978
	21st to end	Day	78% 2 4 6% 7% 2	4927
February	1st to 10th	Day	70% 2 5% 6% 9% 7%	1680
	11th to 20th	Day	67% 4 8% 10% 9% 3	1706
	21st to end	Day	68% 4 6% 12% 8% 2	1675
March	1st to 10th	Day	70% 4 5% 13% 7% 1	4596
	11th to 20th	Day	77% 6% 5% 7% 5%	4917
	21st to end	Day	65% 4 8% 17% 6%	5873
April	1st to 10th	Day	78% 4 8% 8% 2	2572
	11th to 20th	Day	72% 5% 6% 11% 6% 1	2698
	21st to end	Day	73% 4 9% 9% 4	2813
May	1st to 10th	Day	74% 7% 9% 9% 1	6745
	11th to 20th	Day	76% 7% 10% 5% 1	6889
	21st to end	Day	80% 5% 7% 7% 1	7571
June	1st to 10th	Day	75% 6% 11% 6% 2	3166
	11th to 20th	Day	77% 6% 10% 6%	3200
	21st to end	Day	77% 6% 11% 5%	3200
July	1st to 10th	Day	62% 7% 11% 14% 6%	7161
	11th to 20th	Day	74% 7% 14% 4	6983
	21st to end	Day	75% 8% 13% 4	7168
August	1st to 10th	Day	45% 6% 15% 15% 19%	4572
	11th to 20th	Day	63% 6% 12% 14% 6%	4470
	21st to end	Day	73% 7% 13% 6% 2	4663
September	1st to 10th	Day	73% 8% 9% 9% 1	2482
	11th to 20th	Day	68% 5% 10% 12% 5%	2253
	21st to end	Day	83% 3 6% 5% 2	2200
October	1st to 10th	Day	77% 5% 7% 8% 2	3386
	11th to 20th	Day	86% 4 4 5% 2	2933
	21st to end	Day	72% 4 8% 10% 5% 1	3200
November	1st to 10th	Day	83% 3 4 5% 3 1	1614
	11th to 20th	Day	81% 4 6% 5% 4 1	1470
	21st to end	Day	79% 2 5% 6% 7% 2	1470
December	1st to 10th	Day	79% 3 8% 7% 3 1	2360
	11th to 20th	Day	78% 3 4 6% 7% 2	2412
	21st to end	Day	88% 2 3 4 2 1	3058
January	1st to 10th	Night	77% 3 5% 8% 6% 1	9368
	11th to 20th	Night	64% 3 6% 12% 10% 5%	8967
	21st to end	Night	79% 3 4 7% 6% 2	9273
February	1st to 10th	Night	69% 3 4 8% 7% 8%	2940
	11th to 20th	Night	68% 3 7% 11% 9% 2	2812
	21st to end	Night	67% 3 8% 10% 8% 3	2128
March	1st to 10th	Night	69% 4 6% 11% 7% 2	5498
	11th to 20th	Night	79% 5% 5% 5% 5%	5295
	21st to end	Night	63% 5% 6% 20% 6%	5329
April	1st to 10th	Night	75% 4 10% 8% 4	2048
	11th to 20th	Night	68% 5% 7% 13% 6% 2	1871
	21st to end	Night	66% 6% 13% 11% 4	1806
May	1st to 10th	Night	74% 8% 8% 9% 1	3440
	11th to 20th	Night	77% 6% 9% 6% 2	3229
	21st to end	Night	79% 5% 7% 7% 1	3547
June	1st to 10th	Night	70% 8% 11% 8% 3	1231
	11th to 20th	Night	73% 8% 12% 7% 1	1200
	21st to end	Night	76% 8% 11% 4	1200
July	1st to 10th	Night	61% 6% 12% 12% 8%	2690
	11th to 20th	Night	74% 9% 11% 5%	2840
	21st to end	Night	73% 8% 13% 5% 1	3370
August	1st to 10th	Night	44% 8% 13% 16% 18%	2560
	11th to 20th	Night	63% 8% 12% 12% 5%	2653
	21st to end	Night	78% 5% 8% 8% 1	3245
September	1st to 10th	Night	73% 5% 13% 7% 2	1915
	11th to 20th	Night	66% 6% 11% 13% 5%	2147
	21st to end	Night	83% 3 5% 6% 3 1	2200
October	1st to 10th	Night	79% 4 7% 7% 3	3808
	11th to 20th	Night	83% 4 6% 5% 2 1	4215
	21st to end	Night	73% 4 6% 11% 6%	4601
November	1st to 10th	Night	81% 3 5% 5% 4 1	2900
	11th to 20th	Night	82% 3 5% 5% 3 2	3150
	21st to end	Night	80% 2 5% 5% 6% 2	3150
December	1st to 10th	Night	79% 4 6% 7% 3 1	5040
	11th to 20th	Night	78% 3 5% 7% 6% 1	5994
	21st to end	Night	87% 3 4 4 2 1	8140

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	47% 13% 17% 16% 6%	220
	11th to 20th	Day	54% 12% 16% 10% 6% 1	220
	21st to end	Day	56% 8% 20% 10% 5% 1	383
February	1st to 10th	Day	48% 14% 20% 12% 6% 1	430
	11th to 20th	Day	43% 12% 20% 17% 6% 2	425
	21st to end	Day	45% 18% 22% 10% 5% 1	355
March	1st to 10th	Day	38% 13% 23% 18% 6% 1	430
	11th to 20th	Day	46% 14% 21% 12% 6% 1	494
	21st to end	Day	41% 13% 18% 20% 6% 2	594
April	1st to 10th	Day	47% 14% 19% 14% 5% 1	540
	11th to 20th	Day	40% 12% 16% 21% 9% 2	532
	21st to end	Day	44% 12% 21% 15% 7% 1	623
May	1st to 10th	Day	42% 10% 21% 21% 6% 1	753
	11th to 20th	Day	36% 11% 21% 21% 10% 2	775
	21st to end	Day	45% 10% 19% 17% 7% 1	845
June	1st to 10th	Day	48% 9% 17% 19% 6% 1	731
	11th to 20th	Day	44% 10% 18% 20% 7% 1	730
	21st to end	Day	44% 7% 17% 21% 9% 2	730
July	1st to 10th	Day	38% 8% 15% 23% 13% 2	721
	11th to 20th	Day	47% 8% 15% 20% 8% 2	718
	21st to end	Day	44% 7% 17% 21% 10% 2	794
August	1st to 10th	Day	37% 4 17% 27% 13% 2	726
	11th to 20th	Day	46% 6% 18% 21% 8% 1	689
	21st to end	Day	51% 7% 13% 16% 10% 3	583
September	1st to 10th	Day	47% 6% 17% 21% 9%	530
	11th to 20th	Day	45% 8% 14% 18% 11% 2	530
	21st to end	Day	61% 11% 12% 12% 4	530
October	1st to 10th	Day	45% 7% 18% 17% 11% 1	497
	11th to 20th	Day	57% 8% 17% 11% 6%	420
	21st to end	Day	48% 8% 18% 17% 8%	462
November	1st to 10th	Day	62% 10% 13% 10% 5%	260
	11th to 20th	Day	56% 8% 17% 14% 5%	220
	21st to end	Day	55% 12% 12% 13% 7% 1	220
December	1st to 10th	Day	49% 11% 16% 13% 11% 1	220
	11th to 20th	Day	45% 15% 19% 15% 5%	220
	21st to end	Day	48% 10% 17% 18% 7%	242
January	1st to 10th	Night	55% 11% 16% 13% 4	950
	11th to 20th	Night	57% 9% 18% 13% 3	950
	21st to end	Night	55% 9% 17% 13% 6%	1045
February	1st to 10th	Night	49% 9% 20% 16% 6%	950
	11th to 20th	Night	44% 9% 21% 20% 5% 1	904
	21st to end	Night	38% 16% 22% 18% 7%	692
March	1st to 10th	Night	41% 10% 20% 21% 8%	840
	11th to 20th	Night	44% 11% 18% 20% 7%	840
	21st to end	Night	41% 9% 15% 23% 10% 2	798
April	1st to 10th	Night	44% 8% 17% 19% 12% 1	630
	11th to 20th	Night	39% 9% 17% 22% 13% 1	623
	21st to end	Night	40% 6% 16% 25% 12% 1	630
May	1st to 10th	Night	40% 7% 14% 23% 15% 1	509
	11th to 20th	Night	35% 8% 12% 27% 16% 2	414
	21st to end	Night	40% 7% 9% 27% 16%	455
June	1st to 10th	Night	42% 5% 13% 21% 18% 2	400
	11th to 20th	Night	39% 6% 8% 24% 20% 3	400
	21st to end	Night	45% 5% 9% 24% 17% 2	400
July	1st to 10th	Night	33% 7% 8% 27% 23% 3	390
	11th to 20th	Night	40% 5% 4 25% 24% 2	388
	21st to end	Night	41% 6% 8% 23% 20% 3	438
August	1st to 10th	Night	32% 5% 7% 23% 29% 4	567
	11th to 20th	Night	40% 7% 7% 24% 20% 3	594
	21st to end	Night	50% 3 7% 21% 17% 2	660
September	1st to 10th	Night	44% 5% 9% 24% 17% 1	600
	11th to 20th	Night	43% 6% 11% 20% 18% 3	747
	21st to end	Night	61% 7% 13% 11% 7% 1	800
October	1st to 10th	Night	45% 5% 15% 23% 11% 1	800
	11th to 20th	Night	55% 6% 15% 16% 7%	800
	21st to end	Night	53% 7% 15% 17% 7%	880
November	1st to 10th	Night	61% 9% 16% 11% 3	858
	11th to 20th	Night	57% 9% 16% 15% 3	950
	21st to end	Night	58% 9% 17% 11% 5%	950
December	1st to 10th	Night	50% 9% 17% 17% 7%	950
	11th to 20th	Night	49% 9% 20% 18% 4	950
	21st to end	Night	52% 11% 20% 14% 3	1045

Page generated at 2026-05-28 22:53:31. Version ac07

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