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 2024-02-05.

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	38% 12% 4 6% 5% 3 4 4 4 4 17%	77470
	Night	40% 14% 3 6% 5% 3 3 3 3 4 17%	81345
Transparency	Day	75% 5% 9% 7% 3 1	77159
	Night	75% 4 8% 7% 4 2	81236
Seeing	Day	46% 9% 17% 18% 8% 1	15262
	Night	48% 8% 15% 19% 10% 1	22805

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	34% 17% 5% 6% 5% 3 4 4 4 4 12%	1899
	11th to 20th	Day	38% 13% 3 5% 4 2 3 3 3 4 21%	2107
	21st to end	Day	62% 12% 3 6% 3 1 2 1 1 2 8%	2647
February	1st to 10th	Day	41% 11% 3 6% 4 2 3 3 2 3 21%	1473
	11th to 20th	Day	36% 15% 4 5% 4 2 2 3 3 5% 21%	1450
	21st to end	Day	28% 17% 4 5% 5% 3 3 4 3 4 25%	1432
March	1st to 10th	Day	30% 16% 3 6% 6% 3 3 4 4 4 21%	1800
	11th to 20th	Day	33% 20% 5% 7% 5% 3 4 4 4 4 12%	1903
	21st to end	Day	32% 15% 4 6% 6% 3 4 4 4 5% 18%	2283
April	1st to 10th	Day	37% 15% 5% 6% 5% 2 3 3 4 4 16%	2204
	11th to 20th	Day	34% 12% 5% 8% 5% 2 4 4 3 4 19%	2308
	21st to end	Day	33% 13% 4 6% 6% 3 5% 4 3 4 19%	2411
May	1st to 10th	Day	33% 12% 4 7% 7% 3 5% 4 4 5% 17%	2623
	11th to 20th	Day	29% 11% 4 7% 5% 3 5% 4 5% 6% 21%	2656
	21st to end	Day	32% 11% 4 6% 5% 3 4 4 5% 6% 20%	2917
June	1st to 10th	Day	36% 10% 4 7% 6% 3 5% 4 4 5% 17%	2848
	11th to 20th	Day	36% 11% 4 8% 5% 3 4 4 5% 6% 14%	2880
	21st to end	Day	38% 8% 4 8% 5% 3 4 4 4 4 17%	2880
July	1st to 10th	Day	31% 10% 4 6% 5% 3 4 4 5% 6% 21%	2880
	11th to 20th	Day	37% 10% 4 7% 5% 3 4 4 4 6% 17%	2822
	21st to end	Day	39% 8% 4 6% 5% 2 4 3 3 5% 20%	2938
August	1st to 10th	Day	30% 9% 3 6% 5% 3 3 4 6% 7% 25%	2533
	11th to 20th	Day	35% 9% 3 6% 5% 3 4 4 5% 5% 22%	2454
	21st to end	Day	45% 9% 3 5% 4 2 3 3 4 5% 15%	2574
September	1st to 10th	Day	40% 9% 3 6% 4 3 4 4 5% 6% 16%	2234
	11th to 20th	Day	34% 9% 4 6% 5% 3 3 4 4 5% 24%	2029
	21st to end	Day	52% 9% 3 5% 5% 2 2 3 3 4 12%	1980
October	1st to 10th	Day	38% 9% 2 5% 5% 3 4 4 5% 4 20%	1867
	11th to 20th	Day	47% 12% 3 6% 5% 3 4 4 4 3 10%	1620
	21st to end	Day	43% 11% 3 5% 4 2 3 3 4 4 19%	1782
November	1st to 10th	Day	49% 10% 3 7% 5% 3 3 3 2 3 12%	1458
	11th to 20th	Day	42% 14% 4 7% 5% 2 3 3 3 3 13%	1330
	21st to end	Day	44% 16% 3 6% 3 2 3 3 2 3 14%	1330
December	1st to 10th	Day	37% 12% 3 4 5% 4 3 4 4 4 20%	1330
	11th to 20th	Day	46% 14% 4 6% 4 2 2 2 2 3 15%	1498
	21st to end	Day	47% 18% 3 7% 4 2 2 2 2 2 10%	2090
January	1st to 10th	Night	43% 19% 4 6% 4 2 2 2 3 3 12%	5046
	11th to 20th	Night	38% 10% 2 4 3 2 3 3 4 4 25%	4790
	21st to end	Night	60% 13% 3 4 4 1 2 2 2 2 8%	5014
February	1st to 10th	Night	41% 12% 3 4 4 3 2 3 3 3 21%	2581
	11th to 20th	Night	37% 16% 3 5% 4 2 3 4 3 4 19%	2397
	21st to end	Night	27% 18% 3 6% 3 3 3 3 3 4 26%	1821
March	1st to 10th	Night	28% 18% 4 5% 6% 3 4 4 4 4 20%	2160
	11th to 20th	Night	30% 21% 6% 7% 6% 3 4 4 3 3 12%	2056
	21st to end	Night	32% 18% 4 7% 5% 3 4 2 3 5% 16%	2070
April	1st to 10th	Night	33% 16% 4 7% 5% 3 4 4 2 3 18%	1756
	11th to 20th	Night	31% 15% 3 7% 4 2 4 4 4 4 20%	1601
	21st to end	Night	31% 14% 4 5% 6% 3 3 4 4 6% 20%	1548
May	1st to 10th	Night	34% 11% 4 7% 6% 4 5% 4 3 5% 17%	1337
	11th to 20th	Night	28% 10% 4 7% 5% 4 5% 4 5% 6% 22%	1239
	21st to end	Night	33% 10% 3 7% 6% 3 4 3 4 5% 20%	1358
June	1st to 10th	Night	38% 10% 3 6% 7% 4 4 3 3 4 20%	1109
	11th to 20th	Night	37% 10% 4 7% 5% 3 5% 4 5% 6% 14%	1080
	21st to end	Night	34% 12% 4 7% 7% 4 5% 6% 3 5% 14%	1080
July	1st to 10th	Night	31% 11% 4 6% 5% 2 4 4 5% 5% 23%	1080
	11th to 20th	Night	35% 9% 3 7% 6% 4 4 4 5% 7% 17%	1138
	21st to end	Night	36% 10% 4 5% 4 2 4 3 4 6% 20%	1379
August	1st to 10th	Night	27% 11% 3 6% 6% 3 4 4 6% 6% 23%	1404
	11th to 20th	Night	33% 10% 3 7% 6% 4 4 5% 3 6% 21%	1446
	21st to end	Night	44% 9% 3 7% 5% 2 3 3 3 3 19%	1782
September	1st to 10th	Night	39% 10% 4 7% 4 2 3 3 3 4 19%	1723
	11th to 20th	Night	35% 9% 2 5% 5% 2 3 4 3 5% 27%	1931
	21st to end	Night	52% 10% 3 6% 4 2 3 2 2 3 13%	1980
October	1st to 10th	Night	35% 8% 3 6% 5% 3 4 4 4 5% 22%	2090
	11th to 20th	Night	45% 11% 4 6% 5% 3 3 4 3 4 12%	2340
	21st to end	Night	42% 11% 3 6% 5% 3 3 3 3 4 19%	2574
November	1st to 10th	Night	46% 13% 4 5% 4 3 4 2 2 2 14%	2616
	11th to 20th	Night	41% 17% 4 6% 4 3 3 3 3 4 12%	2850
	21st to end	Night	45% 15% 4 6% 4 2 3 3 3 4 12%	2850
December	1st to 10th	Night	34% 16% 3 6% 4 3 4 4 4 4 19%	2850
	11th to 20th	Night	41% 15% 4 6% 5% 2 3 3 2 3 16%	3703
	21st to end	Night	46% 19% 3 6% 4 2 3 3 2 3 10%	5566

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	76% 6% 4 9% 5%	1899
	11th to 20th	Day	69% 4 6% 4 10% 8%	2128
	21st to end	Day	89% 1 2 4 3 1	2647
February	1st to 10th	Day	71% 2 5% 7% 9% 5%	1473
	11th to 20th	Day	71% 4 8% 8% 9% 1	1458
	21st to end	Day	66% 3 6% 13% 9% 2	1432
March	1st to 10th	Day	70% 3 7% 11% 7% 3	1800
	11th to 20th	Day	81% 2 7% 7% 3	1903
	21st to end	Day	74% 4 10% 9% 4	2283
April	1st to 10th	Day	78% 3 8% 7% 3	2204
	11th to 20th	Day	73% 4 6% 11% 6%	2308
	21st to end	Day	76% 3 7% 9% 5%	2411
May	1st to 10th	Day	74% 6% 11% 7% 2	2623
	11th to 20th	Day	69% 7% 12% 9% 3	2659
	21st to end	Day	71% 7% 12% 8% 1	2918
June	1st to 10th	Day	76% 6% 10% 5% 3	2848
	11th to 20th	Day	78% 6% 10% 5%	2880
	21st to end	Day	77% 6% 12% 4	2880
July	1st to 10th	Day	69% 8% 12% 9% 1	2801
	11th to 20th	Day	76% 8% 11% 5% 1	2735
	21st to end	Day	72% 7% 12% 8% 1	2775
August	1st to 10th	Day	63% 8% 17% 9% 3	2515
	11th to 20th	Day	69% 7% 13% 8% 2	2454
	21st to end	Day	77% 7% 10% 4 1	2574
September	1st to 10th	Day	74% 8% 9% 7% 1	2234
	11th to 20th	Day	66% 5% 11% 12% 5%	2029
	21st to end	Day	83% 3 6% 5% 3	1980
October	1st to 10th	Day	70% 5% 9% 11% 4 1	1867
	11th to 20th	Day	83% 4 6% 6% 1	1620
	21st to end	Day	72% 4 9% 11% 4 1	1782
November	1st to 10th	Day	82% 3 4 6% 3 1	1458
	11th to 20th	Day	80% 4 6% 5% 4 1	1330
	21st to end	Day	80% 2 5% 5% 7% 2	1330
December	1st to 10th	Day	71% 4 8% 11% 6% 1	1330
	11th to 20th	Day	79% 2 5% 6% 5% 3	1501
	21st to end	Day	85% 2 3 4 4 2	2090
January	1st to 10th	Night	81% 4 5% 7% 2	5046
	11th to 20th	Night	64% 3 6% 6% 11% 10%	4831
	21st to end	Night	87% 2 3 5% 2 1	5014
February	1st to 10th	Night	72% 3 4 8% 7% 6%	2581
	11th to 20th	Night	72% 3 7% 10% 7% 1	2400
	21st to end	Night	64% 3 8% 11% 10% 3	1821
March	1st to 10th	Night	69% 4 8% 9% 7% 3	2160
	11th to 20th	Night	80% 4 5% 6% 5%	2057
	21st to end	Night	75% 5% 8% 9% 3	2070
April	1st to 10th	Night	75% 4 9% 8% 4	1756
	11th to 20th	Night	70% 5% 6% 13% 6% 1	1601
	21st to end	Night	70% 5% 10% 10% 4	1548
May	1st to 10th	Night	75% 7% 11% 6% 2 1	1337
	11th to 20th	Night	68% 7% 13% 7% 5% 1	1239
	21st to end	Night	69% 7% 12% 10% 3	1358
June	1st to 10th	Night	70% 8% 11% 8% 3 1	1109
	11th to 20th	Night	74% 8% 12% 4 1	1080
	21st to end	Night	75% 9% 11% 5%	1080
July	1st to 10th	Night	65% 11% 14% 9% 1	1050
	11th to 20th	Night	73% 10% 12% 5% 1	1102
	21st to end	Night	67% 8% 15% 8% 2	1302
August	1st to 10th	Night	60% 11% 18% 9% 2	1397
	11th to 20th	Night	68% 10% 14% 7% 2	1446
	21st to end	Night	74% 6% 11% 8% 1	1782
September	1st to 10th	Night	72% 5% 14% 7% 2	1723
	11th to 20th	Night	63% 6% 11% 14% 5%	1931
	21st to end	Night	83% 3 5% 6% 3 1	1980
October	1st to 10th	Night	67% 6% 12% 10% 5% 1	2090
	11th to 20th	Night	80% 5% 8% 6% 1 1	2340
	21st to end	Night	74% 3 7% 11% 5% 1	2574
November	1st to 10th	Night	80% 4 5% 6% 4 1	2616
	11th to 20th	Night	82% 3 6% 5% 3 2	2850
	21st to end	Night	81% 2 5% 4 6% 2	2850
December	1st to 10th	Night	71% 4 7% 10% 6% 2	2850
	11th to 20th	Night	77% 3 6% 6% 7% 2	3699
	21st to end	Night	85% 3 4 4 3 2	5566

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	46% 13% 19% 16% 6%	180
	11th to 20th	Day	56% 14% 18% 6% 5% 2	180
	21st to end	Day	58% 9% 18% 9% 6%	325
February	1st to 10th	Day	48% 14% 20% 10% 6% 1	353
	11th to 20th	Day	48% 10% 21% 14% 4 2	335
	21st to end	Day	43% 16% 23% 11% 6% 1	280
March	1st to 10th	Day	34% 15% 24% 19% 6% 2	340
	11th to 20th	Day	47% 13% 20% 12% 7% 1	386
	21st to end	Day	43% 12% 18% 20% 6% 2	462
April	1st to 10th	Day	48% 12% 18% 15% 6% 1	420
	11th to 20th	Day	41% 11% 15% 21% 10% 2	412
	21st to end	Day	50% 10% 18% 15% 6% 1	491
May	1st to 10th	Day	41% 10% 20% 23% 5% 1	603
	11th to 20th	Day	32% 10% 21% 24% 12% 2	625
	21st to end	Day	42% 8% 21% 19% 8% 1	680
June	1st to 10th	Day	50% 8% 17% 19% 6% 1	630
	11th to 20th	Day	47% 8% 18% 20% 7% 1	630
	21st to end	Day	42% 6% 18% 22% 10% 2	630
July	1st to 10th	Day	38% 7% 14% 25% 14% 2	621
	11th to 20th	Day	48% 7% 14% 21% 9% 2	618
	21st to end	Day	45% 5% 16% 21% 10% 2	684
August	1st to 10th	Day	37% 5% 15% 27% 14% 2	626
	11th to 20th	Day	45% 5% 18% 22% 9% 1	593
	21st to end	Day	55% 7% 13% 15% 9% 1	495
September	1st to 10th	Day	51% 6% 14% 19% 8%	450
	11th to 20th	Day	43% 8% 13% 21% 13% 3	450
	21st to end	Day	60% 11% 11% 12% 5%	450
October	1st to 10th	Day	44% 7% 17% 17% 13% 2	423
	11th to 20th	Day	57% 8% 16% 12% 7%	360
	21st to end	Day	47% 9% 17% 18% 9% 1	396
November	1st to 10th	Day	59% 10% 14% 10% 6%	216
	11th to 20th	Day	56% 8% 16% 14% 6% 1	180
	21st to end	Day	56% 10% 11% 15% 7% 2	180
December	1st to 10th	Day	43% 12% 17% 13% 13% 1	180
	11th to 20th	Day	48% 14% 20% 13% 6%	180
	21st to end	Day	45% 11% 17% 19% 8% 1	198
January	1st to 10th	Night	56% 11% 15% 14% 5%	850
	11th to 20th	Night	58% 10% 17% 11% 3	850
	21st to end	Night	57% 8% 16% 12% 6%	935
February	1st to 10th	Night	50% 9% 19% 16% 6%	822
	11th to 20th	Night	47% 8% 19% 19% 5% 1	762
	21st to end	Night	36% 14% 24% 19% 7%	592
March	1st to 10th	Night	40% 10% 19% 21% 9% 1	720
	11th to 20th	Night	46% 9% 19% 19% 7%	720
	21st to end	Night	44% 8% 14% 23% 10% 2	684
April	1st to 10th	Night	45% 6% 16% 18% 13% 1	540
	11th to 20th	Night	41% 8% 17% 21% 13% 1	533
	21st to end	Night	43% 6% 15% 24% 11% 1	540
May	1st to 10th	Night	40% 6% 15% 22% 16% 2	437
	11th to 20th	Night	32% 8% 12% 31% 16% 2	354
	21st to end	Night	38% 6% 8% 30% 17% 1	389
June	1st to 10th	Night	42% 4 11% 20% 20% 2	360
	11th to 20th	Night	41% 6% 8% 23% 19% 3	360
	21st to end	Night	43% 5% 9% 25% 17% 2	360
July	1st to 10th	Night	32% 7% 8% 27% 23% 3	350
	11th to 20th	Night	41% 5% 4 24% 26% 2	348
	21st to end	Night	42% 5% 8% 22% 20% 3	394
August	1st to 10th	Night	32% 5% 7% 22% 30% 4	509
	11th to 20th	Night	39% 5% 7% 24% 22% 3	534
	21st to end	Night	53% 3 7% 22% 15% 1	594
September	1st to 10th	Night	46% 5% 9% 25% 16% 1	540
	11th to 20th	Night	40% 6% 11% 20% 20% 3	671
	21st to end	Night	59% 7% 13% 12% 8% 1	720
October	1st to 10th	Night	43% 4 15% 24% 12% 2	720
	11th to 20th	Night	55% 6% 14% 17% 8%	720
	21st to end	Night	53% 6% 16% 18% 7%	792
November	1st to 10th	Night	60% 8% 17% 11% 4	770
	11th to 20th	Night	56% 9% 16% 15% 4	850
	21st to end	Night	59% 8% 16% 11% 5%	850
December	1st to 10th	Night	45% 10% 19% 18% 7%	850
	11th to 20th	Night	48% 10% 21% 17% 4	850
	21st to end	Night	51% 11% 19% 14% 4	935

Page generated at 2024-02-02 02:20:26. Version ac07

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