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 2025-02-06.

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% 12% 3 7% 4 4 4 3 4 5% 18%	111710
	Night	38% 15% 3 7% 4 3 3 2 3 4 17%	115180
Transparency	Day	72% 5% 9% 9% 4 1	111441
	Night	74% 4 7% 8% 5% 1	115095
Seeing	Day	46% 9% 17% 18% 8% 1	16601
	Night	47% 8% 15% 19% 10% 1	24116

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% 18% 4 7% 5% 4 4 3 4 4 10%	2719
	11th to 20th	Day	39% 12% 3 5% 3 3 3 3 4 4 20%	3039
	21st to end	Day	49% 12% 2 7% 3 3 2 2 2 3 15%	3801
February	1st to 10th	Day	39% 12% 3 7% 4 2 3 2 2 3 23%	1561
	11th to 20th	Day	34% 15% 3 6% 3 3 3 3 3 5% 23%	1532
	21st to end	Day	26% 20% 2 6% 4 4 2 3 3 4 24%	1519
March	1st to 10th	Day	28% 14% 3 7% 5% 4 3 3 4 6% 23%	3126
	11th to 20th	Day	32% 18% 4 8% 5% 4 5% 4 4 4 12%	3357
	21st to end	Day	26% 12% 3 7% 5% 4 4 3 5% 5% 28%	4007
April	1st to 10th	Day	36% 16% 4 8% 4 3 3 2 5% 4 15%	2327
	11th to 20th	Day	31% 14% 4 8% 5% 4 4 3 3 4 21%	2438
	21st to end	Day	31% 14% 3 8% 6% 4 4 3 3 4 20%	2545
May	1st to 10th	Day	28% 12% 3 8% 5% 5% 4 3 5% 6% 21%	4611
	11th to 20th	Day	34% 12% 3 8% 4 4 4 3 5% 6% 15%	4696
	21st to end	Day	34% 14% 3 7% 4 4 3 3 5% 6% 16%	5161
June	1st to 10th	Day	36% 11% 3 8% 5% 4 4 4 4 4 16%	3007
	11th to 20th	Day	35% 12% 4 8% 5% 4 4 4 5% 6% 13%	3040
	21st to end	Day	37% 10% 3 8% 5% 4 4 3 5% 4 17%	3040
July	1st to 10th	Day	27% 9% 3 6% 3 4 3 3 4 6% 33%	5060
	11th to 20th	Day	33% 12% 4 9% 5% 5% 5% 4 4 6% 13%	4946
	21st to end	Day	41% 12% 4 7% 4 4 3 2 3 4 14%	5138
August	1st to 10th	Day	20% 6% 2 5% 3 4 4 4 6% 9% 38%	4449
	11th to 20th	Day	30% 11% 3 7% 4 3 3 3 4 6% 27%	4290
	21st to end	Day	42% 9% 3 6% 4 3 3 3 4 6% 17%	4521
September	1st to 10th	Day	40% 9% 3 7% 4 3 4 3 4 6% 16%	2358
	11th to 20th	Day	34% 9% 4 8% 4 4 3 3 4 4 23%	2141
	21st to end	Day	53% 10% 3 6% 4 3 2 2 3 4 11%	2090
October	1st to 10th	Day	43% 11% 3 7% 4 3 3 3 4 4 14%	3283
	11th to 20th	Day	48% 13% 3 8% 4 4 3 2 3 3 8%	2843
	21st to end	Day	35% 14% 3 7% 4 3 4 3 3 4 20%	3101
November	1st to 10th	Day	48% 11% 3 8% 4 4 2 3 2 3 12%	1536
	11th to 20th	Day	40% 16% 4 8% 5% 4 3 2 3 3 13%	1400
	21st to end	Day	44% 17% 3 6% 3 2 3 2 2 3 14%	1400
December	1st to 10th	Day	48% 12% 3 5% 3 4 3 2 3 3 14%	2290
	11th to 20th	Day	38% 15% 4 9% 4 3 3 2 3 3 15%	2346
	21st to end	Day	47% 20% 4 9% 3 3 2 2 2 2 7%	2992
January	1st to 10th	Night	42% 18% 4 7% 4 3 3 2 3 3 11%	7226
	11th to 20th	Night	36% 13% 2 5% 3 3 3 3 4 4 23%	6858
	21st to end	Night	50% 15% 3 6% 3 2 2 2 2 2 13%	7167
February	1st to 10th	Night	39% 13% 3 5% 3 3 2 3 3 3 22%	2730
	11th to 20th	Night	35% 16% 3 5% 4 3 3 3 3 4 21%	2535
	21st to end	Night	26% 20% 3 6% 3 4 3 3 3 4 26%	1932
March	1st to 10th	Night	22% 18% 4 8% 5% 4 5% 3 4 4 23%	3738
	11th to 20th	Night	30% 20% 4 8% 5% 5% 5% 4 4 3 11%	3618
	21st to end	Night	23% 15% 3 8% 5% 4 4 2 4 4 29%	3637
April	1st to 10th	Night	32% 18% 4 8% 4 4 3 3 3 3 18%	1853
	11th to 20th	Night	29% 17% 3 8% 3 4 4 3 5% 4 22%	1691
	21st to end	Night	30% 15% 4 7% 5% 4 4 2 5% 5% 20%	1634
May	1st to 10th	Night	27% 13% 3 8% 5% 5% 5% 4 4 5% 22%	2353
	11th to 20th	Night	40% 13% 3 7% 5% 4 4 2 4 4 16%	2199
	21st to end	Night	32% 14% 3 10% 6% 3 4 2 3 4 18%	2414
June	1st to 10th	Night	37% 11% 3 6% 6% 4 4 2 3 3 19%	1170
	11th to 20th	Night	35% 12% 4 8% 4 4 4 4 5% 6% 15%	1140
	21st to end	Night	33% 13% 4 7% 7% 5% 5% 4 3 5% 14%	1140
July	1st to 10th	Night	29% 8% 3 4 3 2 3 2 5% 5% 35%	1900
	11th to 20th	Night	36% 13% 4 8% 5% 5% 4 3 4 5% 14%	2014
	21st to end	Night	41% 12% 3 7% 4 3 3 2 4 5% 15%	2414
August	1st to 10th	Night	19% 9% 3 7% 5% 5% 3 3 5% 6% 36%	2488
	11th to 20th	Night	32% 8% 2 6% 4 4 3 3 3 5% 29%	2548
	21st to end	Night	47% 11% 3 7% 4 2 3 2 3 3 14%	3146
September	1st to 10th	Night	38% 11% 4 8% 4 3 4 3 3 4 19%	1819
	11th to 20th	Night	35% 10% 2 6% 4 3 4 3 4 5% 26%	2039
	21st to end	Night	52% 10% 3 7% 4 3 2 2 2 3 12%	2090
October	1st to 10th	Night	44% 12% 4 7% 4 3 3 3 3 3 13%	3691
	11th to 20th	Night	48% 13% 4 8% 4 3 3 2 3 4 9%	4085
	21st to end	Night	34% 13% 3 9% 4 4 3 2 3 4 21%	4458
November	1st to 10th	Night	46% 14% 3 6% 4 4 3 2 2 3 13%	2758
	11th to 20th	Night	40% 19% 4 7% 4 4 3 3 3 4 11%	3000
	21st to end	Night	43% 17% 3 7% 3 3 3 2 3 3 13%	3000
December	1st to 10th	Night	49% 13% 3 5% 3 3 3 2 3 3 12%	4890
	11th to 20th	Night	37% 18% 4 8% 4 3 3 2 3 3 15%	5841
	21st to end	Night	43% 20% 4 8% 4 4 3 2 2 2 7%	7964

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	79% 5% 3 9% 4	2719
	11th to 20th	Day	69% 3 7% 9% 7% 5%	3060
	21st to end	Day	79% 2 5% 5% 6% 2	3801
February	1st to 10th	Day	70% 2 5% 6% 9% 7%	1561
	11th to 20th	Day	68% 4 8% 10% 8% 2	1540
	21st to end	Day	65% 4 7% 13% 9% 2	1519
March	1st to 10th	Day	64% 4 6% 16% 9% 2	3126
	11th to 20th	Day	75% 6% 7% 8% 4	3357
	21st to end	Day	62% 4 8% 17% 9%	4007
April	1st to 10th	Day	78% 3 8% 8% 3	2327
	11th to 20th	Day	72% 4 5% 11% 7% 1	2438
	21st to end	Day	75% 4 7% 9% 5%	2545
May	1st to 10th	Day	68% 8% 11% 12% 1	4611
	11th to 20th	Day	75% 8% 10% 6% 2	4699
	21st to end	Day	75% 5% 9% 10% 1	5162
June	1st to 10th	Day	75% 6% 10% 5% 3	3007
	11th to 20th	Day	78% 6% 11% 5%	3040
	21st to end	Day	77% 7% 12% 4	3040
July	1st to 10th	Day	56% 6% 13% 17% 8%	4981
	11th to 20th	Day	76% 9% 12% 3	4859
	21st to end	Day	79% 6% 8% 6%	4976
August	1st to 10th	Day	43% 6% 15% 16% 19%	4431
	11th to 20th	Day	63% 6% 12% 14% 6%	4332
	21st to end	Day	75% 7% 12% 5% 1	4520
September	1st to 10th	Day	74% 8% 9% 8% 1	2358
	11th to 20th	Day	68% 5% 11% 12% 5%	2141
	21st to end	Day	83% 3 6% 5% 2	2090
October	1st to 10th	Day	78% 5% 6% 7% 2	3283
	11th to 20th	Day	86% 4 4 5% 1	2843
	21st to end	Day	72% 4 8% 10% 5% 1	3101
November	1st to 10th	Day	82% 3 4 5% 3 1	1536
	11th to 20th	Day	80% 4 6% 5% 4 1	1400
	21st to end	Day	79% 2 5% 6% 6% 2	1400
December	1st to 10th	Day	78% 3 8% 7% 3 1	2290
	11th to 20th	Day	78% 3 4 6% 7% 2	2349
	21st to end	Day	88% 2 3 4 2 1	2992
January	1st to 10th	Night	81% 3 6% 8% 2	7226
	11th to 20th	Night	67% 3 6% 9% 8% 7%	6899
	21st to end	Night	83% 3 4 6% 4 1	7167
February	1st to 10th	Night	69% 3 4 8% 8% 8%	2730
	11th to 20th	Night	70% 3 7% 11% 8% 2	2538
	21st to end	Night	64% 3 9% 11% 9% 3	1932
March	1st to 10th	Night	63% 5% 7% 12% 10% 3	3738
	11th to 20th	Night	79% 6% 7% 6% 3	3619
	21st to end	Night	60% 5% 7% 20% 8%	3637
April	1st to 10th	Night	75% 4 9% 8% 4	1853
	11th to 20th	Night	68% 4 6% 13% 6% 2	1691
	21st to end	Night	69% 6% 10% 11% 4	1634
May	1st to 10th	Night	67% 9% 10% 12% 1	2353
	11th to 20th	Night	76% 7% 10% 4 3	2199
	21st to end	Night	73% 5% 10% 10% 2	2414
June	1st to 10th	Night	71% 8% 11% 8% 3 1	1170
	11th to 20th	Night	74% 8% 12% 5% 1	1140
	21st to end	Night	76% 9% 11% 4	1140
July	1st to 10th	Night	54% 8% 14% 14% 10%	1870
	11th to 20th	Night	75% 10% 12% 3	1978
	21st to end	Night	74% 9% 10% 7% 1	2337
August	1st to 10th	Night	43% 8% 14% 16% 19%	2481
	11th to 20th	Night	62% 8% 12% 13% 5%	2572
	21st to end	Night	79% 5% 8% 7% 1	3146
September	1st to 10th	Night	73% 5% 13% 7% 2	1819
	11th to 20th	Night	65% 6% 11% 13% 5%	2039
	21st to end	Night	83% 3 5% 5% 3 1	2090
October	1st to 10th	Night	79% 4 7% 6% 3	3691
	11th to 20th	Night	84% 4 5% 4 2	4085
	21st to end	Night	72% 4 6% 11% 6%	4458
November	1st to 10th	Night	81% 3 5% 6% 4 1	2758
	11th to 20th	Night	82% 3 6% 5% 3 2	3000
	21st to end	Night	81% 2 5% 5% 6% 2	3000
December	1st to 10th	Night	79% 4 6% 7% 4 1	4890
	11th to 20th	Night	77% 3 5% 7% 7% 1	5837
	21st to end	Night	87% 3 4 4 2 1	7964

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% 14% 19% 15% 6%	200
	11th to 20th	Day	56% 14% 17% 8% 5% 2	200
	21st to end	Day	55% 9% 20% 10% 6%	354
February	1st to 10th	Day	47% 14% 21% 11% 6% 1	386
	11th to 20th	Day	45% 12% 21% 16% 5% 2	365
	21st to end	Day	41% 18% 23% 11% 6% 1	307
March	1st to 10th	Day	34% 14% 24% 20% 6% 2	370
	11th to 20th	Day	46% 13% 21% 13% 7% 1	422
	21st to end	Day	41% 11% 17% 22% 7% 2	506
April	1st to 10th	Day	48% 13% 17% 14% 5% 1	460
	11th to 20th	Day	40% 12% 15% 22% 10% 2	452
	21st to end	Day	48% 11% 19% 15% 6% 1	535
May	1st to 10th	Day	41% 10% 21% 22% 5% 1	653
	11th to 20th	Day	34% 10% 21% 22% 11% 2	675
	21st to end	Day	43% 9% 20% 19% 7% 1	735
June	1st to 10th	Day	50% 8% 16% 20% 6% 1	680
	11th to 20th	Day	46% 8% 17% 20% 7% 1	680
	21st to end	Day	42% 7% 18% 22% 10% 2	680
July	1st to 10th	Day	37% 7% 15% 25% 13% 2	671
	11th to 20th	Day	46% 8% 15% 21% 8% 2	668
	21st to end	Day	46% 6% 16% 20% 10% 1	739
August	1st to 10th	Day	35% 4 16% 28% 14% 3	676
	11th to 20th	Day	45% 6% 18% 22% 9% 1	641
	21st to end	Day	55% 7% 13% 14% 9% 1	539
September	1st to 10th	Day	50% 6% 16% 20% 8%	490
	11th to 20th	Day	44% 8% 13% 20% 12% 3	490
	21st to end	Day	62% 11% 11% 12% 5%	490
October	1st to 10th	Day	47% 7% 16% 17% 12% 2	460
	11th to 20th	Day	58% 8% 16% 11% 6%	390
	21st to end	Day	47% 9% 17% 17% 9%	429
November	1st to 10th	Day	61% 9% 13% 11% 5%	238
	11th to 20th	Day	54% 9% 18% 15% 5% 1	200
	21st to end	Day	55% 12% 10% 14% 8% 2	200
December	1st to 10th	Day	45% 12% 17% 13% 12% 1	200
	11th to 20th	Day	46% 15% 20% 14% 6%	200
	21st to end	Day	49% 10% 16% 17% 8%	220
January	1st to 10th	Night	56% 10% 16% 13% 5%	900
	11th to 20th	Night	58% 10% 18% 12% 3	900
	21st to end	Night	56% 8% 17% 13% 6%	990
February	1st to 10th	Night	48% 10% 19% 16% 7%	875
	11th to 20th	Night	45% 9% 22% 19% 5% 1	810
	21st to end	Night	36% 15% 23% 19% 8%	628
March	1st to 10th	Night	39% 10% 20% 22% 9% 1	760
	11th to 20th	Night	45% 11% 18% 20% 6%	760
	21st to end	Night	42% 8% 14% 23% 11% 2	722
April	1st to 10th	Night	45% 7% 17% 18% 12% 1	570
	11th to 20th	Night	39% 8% 17% 22% 13% 1	563
	21st to end	Night	42% 6% 16% 24% 11% 1	570
May	1st to 10th	Night	39% 7% 15% 23% 16% 2	461
	11th to 20th	Night	33% 8% 11% 29% 16% 2	374
	21st to end	Night	38% 6% 9% 29% 17%	411
June	1st to 10th	Night	43% 4 12% 20% 19% 2	380
	11th to 20th	Night	40% 6% 8% 23% 20% 3	380
	21st to end	Night	43% 5% 9% 24% 17% 2	380
July	1st to 10th	Night	32% 7% 8% 27% 24% 3	370
	11th to 20th	Night	40% 5% 4 24% 25% 2	368
	21st to end	Night	42% 6% 8% 22% 19% 3	416
August	1st to 10th	Night	31% 5% 6% 23% 31% 4	538
	11th to 20th	Night	39% 6% 7% 24% 21% 3	564
	21st to end	Night	53% 3 8% 22% 14% 1	627
September	1st to 10th	Night	45% 5% 9% 25% 16% 1	570
	11th to 20th	Night	41% 6% 11% 21% 19% 3	709
	21st to end	Night	60% 7% 13% 11% 7% 1	760
October	1st to 10th	Night	45% 4 15% 23% 11% 1	760
	11th to 20th	Night	56% 6% 14% 16% 8%	760
	21st to end	Night	52% 7% 16% 18% 7%	836
November	1st to 10th	Night	60% 9% 16% 11% 4	814
	11th to 20th	Night	56% 9% 16% 15% 3	900
	21st to end	Night	59% 8% 16% 11% 5%	900
December	1st to 10th	Night	47% 10% 18% 18% 7%	900
	11th to 20th	Night	48% 9% 20% 18% 4	900
	21st to end	Night	52% 11% 19% 14% 4	990

Page generated at 2025-02-03 00:05:52. Version ac07

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