Sechelt
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sechelt clear sky chart from 2005-11-06 to 2025-03-12.

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	21% 9% 3 7% 5% 4 4 4 5% 6% 33%	112268
	Night	25% 10% 3 7% 4 4 4 3 5% 5% 29%	115373
Transparency	Day	51% 10% 13% 17% 8% 1	112013
	Night	56% 7% 12% 16% 8% 1	115274
Seeing	Day	23% 6% 18% 27% 21% 5%	15834
	Night	30% 5% 15% 24% 20% 5%	24137

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% 13% 4 7% 5% 5% 5% 3 4 4 14%	3179
	11th to 20th	Day	19% 12% 3 9% 6% 5% 5% 4 6% 7% 23%	3159
	21st to end	Day	36% 12% 3 7% 4 4 4 3 4 3 19%	3912
February	1st to 10th	Day	30% 13% 4 9% 6% 5% 4 4 5% 6% 15%	1800
	11th to 20th	Day	26% 11% 3 8% 5% 5% 6% 3 6% 6% 20%	1755
	21st to end	Day	24% 11% 3 10% 7% 6% 5% 4 5% 7% 19%	1485
March	1st to 10th	Day	24% 13% 4 11% 7% 6% 6% 4 5% 5% 15%	3381
	11th to 20th	Day	21% 10% 3 7% 5% 4 4 4 6% 7% 29%	3503
	21st to end	Day	22% 13% 4 10% 6% 5% 4 3 6% 6% 22%	3881
April	1st to 10th	Day	26% 11% 3 8% 5% 4 5% 4 5% 7% 21%	2280
	11th to 20th	Day	21% 9% 4 8% 5% 5% 4 4 6% 6% 28%	2389
	21st to end	Day	22% 10% 4 7% 5% 4 4 3 5% 6% 29%	2498
May	1st to 10th	Day	13% 9% 3 7% 4 4 4 3 4 6% 44%	4420
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 5% 8% 12% 37%	4377
	21st to end	Day	25% 8% 3 6% 5% 5% 5% 4 6% 7% 28%	5026
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 4 6% 8% 29%	2850
	11th to 20th	Day	17% 8% 2 7% 6% 5% 6% 4 7% 8% 30%	2850
	21st to end	Day	14% 6% 3 7% 5% 4 4 3 6% 8% 40%	2850
July	1st to 10th	Day	6% 4 1 4 2 3 3 2 4 5% 66%	4740
	11th to 20th	Day	6% 2 1 2 2 2 3 2 3 6% 71%	4740
	21st to end	Day	10% 4 2 5% 3 4 4 3 5% 7% 52%	4983
August	1st to 10th	Day	6% 3 1 2 2 2 3 3 4 6% 69%	4314
	11th to 20th	Day	12% 7% 3 6% 4 4 5% 4 6% 8% 42%	4026
	21st to end	Day	14% 5% 2 6% 4 4 5% 4 6% 8% 42%	4469
September	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 5% 8% 47%	2280
	11th to 20th	Day	18% 7% 3 6% 5% 3 4 4 5% 7% 38%	2238
	21st to end	Day	22% 6% 2 6% 5% 5% 4 4 6% 8% 32%	2025
October	1st to 10th	Day	23% 8% 3 7% 4 5% 5% 4 6% 7% 27%	3180
	11th to 20th	Day	32% 8% 3 7% 5% 4 5% 4 5% 6% 22%	3161
	21st to end	Day	29% 10% 3 8% 5% 6% 5% 4 6% 7% 17%	3150
November	1st to 10th	Day	37% 9% 3 8% 4 4 5% 4 4 4 16%	1568
	11th to 20th	Day	33% 13% 3 7% 4 4 4 3 6% 5% 17%	1600
	21st to end	Day	35% 12% 3 7% 6% 4 4 4 4 4 17%	1600
December	1st to 10th	Day	23% 13% 3 9% 5% 4 5% 4 5% 6% 23%	2456
	11th to 20th	Day	42% 14% 4 8% 4 4 4 4 3 3 10%	2645
	21st to end	Day	38% 15% 4 9% 5% 5% 4 3 4 3 10%	3498
January	1st to 10th	Night	34% 13% 5% 10% 5% 4 4 3 3 4 14%	6766
	11th to 20th	Night	21% 9% 3 8% 5% 5% 4 4 7% 7% 27%	6739
	21st to end	Night	35% 11% 3 7% 4 4 4 3 4 4 23%	7043
February	1st to 10th	Night	30% 13% 4 8% 5% 4 4 3 5% 5% 19%	2600
	11th to 20th	Night	25% 12% 3 9% 4 4 4 4 5% 5% 26%	2532
	21st to end	Night	29% 12% 4 7% 5% 5% 3 3 4 5% 23%	2145
March	1st to 10th	Night	26% 13% 3 9% 4 4 5% 3 5% 5% 21%	3695
	11th to 20th	Night	22% 9% 3 8% 4 4 4 3 5% 6% 32%	3504
	21st to end	Night	25% 14% 5% 10% 6% 4 4 3 4 4 21%	3772
April	1st to 10th	Night	24% 11% 3 7% 6% 6% 5% 4 5% 6% 23%	1900
	11th to 20th	Night	19% 10% 4 8% 7% 4 5% 4 4 7% 28%	1739
	21st to end	Night	23% 10% 3 7% 4 5% 4 4 5% 7% 28%	1681
May	1st to 10th	Night	14% 10% 3 6% 4 3 4 2 4 5% 46%	2540
	11th to 20th	Night	12% 6% 2 4 4 4 4 4 7% 11% 42%	2516
	21st to end	Night	21% 11% 4 12% 6% 5% 4 3 4 5% 26%	2548
June	1st to 10th	Night	20% 11% 3 8% 5% 5% 5% 2 5% 5% 32%	1330
	11th to 20th	Night	16% 10% 4 8% 6% 5% 5% 3 5% 8% 30%	1330
	21st to end	Night	12% 7% 3 7% 5% 4 5% 3 6% 6% 41%	1330
July	1st to 10th	Night	6% 4 2 5% 3 3 3 3 4 6% 63%	2220
	11th to 20th	Night	4 3 1 2 3 2 2 2 4 5% 72%	2220
	21st to end	Night	9% 4 2 5% 4 4 5% 4 5% 6% 53%	2567
August	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 73%	2616
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 5% 7% 44%	2812
	21st to end	Night	14% 5% 2 6% 5% 4 4 4 5% 5% 46%	3199
September	1st to 10th	Night	8% 3 2 5% 3 4 4 3 5% 7% 56%	1900
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 4 6% 41%	1938
	21st to end	Night	21% 7% 3 7% 4 4 3 3 4 6% 38%	2154
October	1st to 10th	Night	25% 9% 3 7% 4 4 5% 3 6% 6% 29%	3800
	11th to 20th	Night	30% 9% 3 7% 4 4 4 3 4 6% 27%	3777
	21st to end	Night	29% 9% 3 7% 4 5% 4 4 5% 6% 25%	4392
November	1st to 10th	Night	37% 10% 3 8% 5% 4 3 3 4 5% 18%	2730
	11th to 20th	Night	34% 11% 3 7% 5% 4 4 4 5% 4 20%	2800
	21st to end	Night	34% 11% 3 8% 5% 4 4 4 4 5% 20%	2800
December	1st to 10th	Night	25% 12% 3 7% 4 5% 5% 4 5% 7% 23%	4720
	11th to 20th	Night	41% 14% 4 8% 4 4 4 3 4 4 11%	5560
	21st to end	Night	35% 15% 4 10% 5% 4 4 3 4 3 13%	7458

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	70% 8% 10% 8% 3 1	3179
	11th to 20th	Day	52% 10% 14% 14% 9% 1	3180
	21st to end	Day	68% 5% 6% 15% 6%	3912
February	1st to 10th	Day	69% 9% 9% 8% 3 3	1800
	11th to 20th	Day	62% 8% 11% 13% 5% 1	1764
	21st to end	Day	65% 10% 10% 9% 4 2	1485
March	1st to 10th	Day	64% 13% 12% 8% 4	3381
	11th to 20th	Day	54% 9% 10% 22% 5% 1	3503
	21st to end	Day	61% 11% 15% 10% 3	3881
April	1st to 10th	Day	64% 11% 11% 10% 4	2280
	11th to 20th	Day	57% 10% 10% 13% 8% 2	2389
	21st to end	Day	59% 9% 10% 14% 8% 1	2498
May	1st to 10th	Day	43% 9% 15% 21% 11%	4420
	11th to 20th	Day	38% 19% 17% 21% 5%	4380
	21st to end	Day	55% 16% 13% 14% 3	5027
June	1st to 10th	Day	54% 10% 16% 13% 4 2	2850
	11th to 20th	Day	54% 13% 15% 13% 5%	2850
	21st to end	Day	46% 10% 17% 18% 8% 2	2850
July	1st to 10th	Day	24% 7% 11% 24% 23% 10%	4666
	11th to 20th	Day	18% 7% 15% 37% 23% 1	4659
	21st to end	Day	32% 10% 20% 24% 12% 3	4825
August	1st to 10th	Day	19% 7% 13% 47% 14% 1	4297
	11th to 20th	Day	43% 11% 20% 16% 8% 2	4065
	21st to end	Day	42% 9% 17% 22% 8% 1	4468
September	1st to 10th	Day	37% 9% 16% 23% 12% 4	2280
	11th to 20th	Day	47% 8% 13% 18% 13% 2	2238
	21st to end	Day	49% 12% 14% 15% 9% 1	2025
October	1st to 10th	Day	56% 9% 16% 13% 6%	3180
	11th to 20th	Day	63% 7% 12% 11% 6%	3161
	21st to end	Day	66% 9% 11% 9% 4	3150
November	1st to 10th	Day	70% 8% 9% 7% 5% 1	1568
	11th to 20th	Day	67% 8% 9% 9% 6% 2	1600
	21st to end	Day	68% 6% 8% 11% 6% 1	1600
December	1st to 10th	Day	59% 7% 10% 17% 6% 1	2456
	11th to 20th	Day	78% 7% 7% 6% 1 1	2648
	21st to end	Day	81% 6% 6% 5% 1 1	3498
January	1st to 10th	Night	73% 5% 6% 10% 4	6766
	11th to 20th	Night	50% 10% 16% 16% 8% 1	6780
	21st to end	Night	65% 5% 8% 17% 5%	7043
February	1st to 10th	Night	66% 7% 8% 10% 6% 3	2600
	11th to 20th	Night	61% 7% 11% 12% 7% 1	2534
	21st to end	Night	62% 7% 11% 13% 6% 2	2145
March	1st to 10th	Night	61% 10% 11% 11% 7%	3695
	11th to 20th	Night	50% 10% 12% 21% 7%	3505
	21st to end	Night	65% 10% 11% 11% 3	3772
April	1st to 10th	Night	60% 10% 12% 15% 3	1900
	11th to 20th	Night	54% 9% 9% 17% 9% 2	1739
	21st to end	Night	55% 9% 11% 15% 9%	1681
May	1st to 10th	Night	41% 6% 16% 25% 11%	2540
	11th to 20th	Night	33% 11% 23% 26% 7% 1	2516
	21st to end	Night	57% 9% 16% 14% 3	2548
June	1st to 10th	Night	53% 7% 15% 17% 5% 3	1330
	11th to 20th	Night	51% 9% 18% 16% 6%	1330
	21st to end	Night	42% 10% 18% 18% 9% 3	1330
July	1st to 10th	Night	22% 6% 11% 26% 25% 10%	2185
	11th to 20th	Night	16% 4 14% 37% 26% 2	2178
	21st to end	Night	29% 8% 18% 27% 15% 4	2486
August	1st to 10th	Night	15% 4 14% 40% 26% 2	2608
	11th to 20th	Night	37% 10% 26% 15% 9% 3	2839
	21st to end	Night	40% 7% 18% 24% 10%	3199
September	1st to 10th	Night	29% 8% 16% 27% 15% 5%	1900
	11th to 20th	Night	44% 8% 12% 17% 15% 4	1938
	21st to end	Night	47% 8% 15% 19% 9% 2	2154
October	1st to 10th	Night	55% 8% 15% 14% 7%	3800
	11th to 20th	Night	60% 5% 11% 17% 7%	3777
	21st to end	Night	60% 7% 12% 15% 5%	4392
November	1st to 10th	Night	70% 7% 10% 8% 5% 1	2730
	11th to 20th	Night	67% 8% 9% 10% 5% 2	2800
	21st to end	Night	67% 7% 9% 9% 7% 1	2800
December	1st to 10th	Night	61% 6% 11% 17% 5% 1	4720
	11th to 20th	Night	78% 6% 7% 7% 3	5556
	21st to end	Night	78% 6% 6% 7% 2	7458

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	44% 7% 20% 19% 7% 5%	200
	11th to 20th	Day	35% 9% 25% 18% 13% 1	200
	21st to end	Day	43% 6% 17% 21% 10% 3	270
February	1st to 10th	Day	35% 9% 24% 20% 10% 2	400
	11th to 20th	Day	32% 5% 26% 24% 12% 1	395
	21st to end	Day	29% 12% 23% 21% 11% 3	331
March	1st to 10th	Day	31% 10% 19% 23% 16% 1	493
	11th to 20th	Day	28% 10% 16% 25% 18% 3	465
	21st to end	Day	30% 8% 25% 24% 11% 3	506
April	1st to 10th	Day	30% 8% 24% 22% 14% 2	460
	11th to 20th	Day	24% 7% 27% 22% 15% 5%	452
	21st to end	Day	25% 7% 24% 27% 15% 3	460
May	1st to 10th	Day	16% 4 18% 34% 24% 3	463
	11th to 20th	Day	16% 4 14% 32% 27% 7%	488
	21st to end	Day	17% 5% 16% 33% 23% 6%	651
June	1st to 10th	Day	21% 4 19% 29% 24% 3	680
	11th to 20th	Day	16% 5% 20% 33% 22% 3	680
	21st to end	Day	15% 3 16% 33% 28% 6%	680
July	1st to 10th	Day	13% 2 16% 29% 33% 7%	671
	11th to 20th	Day	8% 3 13% 36% 33% 8%	668
	21st to end	Day	8% 2 10% 30% 41% 10%	646
August	1st to 10th	Day	10% 2 9% 28% 36% 15%	487
	11th to 20th	Day	9% 3 9% 29% 37% 13%	477
	21st to end	Day	15% 4 14% 33% 29% 5%	539
September	1st to 10th	Day	15% 3 18% 33% 24% 7%	490
	11th to 20th	Day	25% 6% 15% 23% 22% 9%	490
	21st to end	Day	25% 6% 21% 26% 18% 6%	490
October	1st to 10th	Day	29% 5% 17% 23% 19% 7%	490
	11th to 20th	Day	37% 5% 19% 18% 16% 6%	490
	21st to end	Day	32% 9% 22% 23% 9% 4	402
November	1st to 10th	Day	39% 9% 28% 18% 7%	200
	11th to 20th	Day	38% 8% 17% 20% 14% 5%	200
	21st to end	Day	42% 11% 20% 13% 10% 5%	200
December	1st to 10th	Day	38% 7% 21% 14% 15% 7%	200
	11th to 20th	Day	40% 10% 20% 21% 8% 2	200
	21st to end	Day	45% 8% 20% 20% 6%	220
January	1st to 10th	Night	46% 7% 17% 18% 10% 2	900
	11th to 20th	Night	39% 6% 14% 22% 18%	900
	21st to end	Night	39% 7% 16% 23% 14% 1	923
February	1st to 10th	Night	35% 7% 19% 26% 12% 1	800
	11th to 20th	Night	30% 5% 20% 31% 14% 1	784
	21st to end	Night	35% 9% 18% 22% 13% 3	660
March	1st to 10th	Night	32% 7% 19% 23% 16% 3	800
	11th to 20th	Night	37% 6% 17% 21% 17% 2	766
	21st to end	Night	33% 6% 18% 23% 17% 4	836
April	1st to 10th	Night	29% 6% 17% 26% 17% 5%	760
	11th to 20th	Night	22% 8% 21% 27% 20% 2	611
	21st to end	Night	27% 4 16% 30% 19% 3	541
May	1st to 10th	Night	17% 4 17% 29% 27% 7%	380
	11th to 20th	Night	19% 4 9% 26% 32% 9%	374
	21st to end	Night	19% 3 12% 30% 26% 9%	411
June	1st to 10th	Night	25% 4 9% 30% 27% 4	380
	11th to 20th	Night	19% 5% 13% 32% 22% 9%	380
	21st to end	Night	15% 3 9% 32% 34% 8%	380
July	1st to 10th	Night	12% 1 10% 25% 38% 14%	370
	11th to 20th	Night	8% 2 9% 29% 40% 13%	368
	21st to end	Night	8% 2 7% 20% 46% 17%	416
August	1st to 10th	Night	8% 1 5% 21% 43% 22%	426
	11th to 20th	Night	8% 1 5% 24% 48% 13%	564
	21st to end	Night	15% 2 11% 24% 39% 8%	654
September	1st to 10th	Night	10% 2 10% 31% 37% 11%	760
	11th to 20th	Night	21% 4 12% 19% 31% 14%	760
	21st to end	Night	25% 3 15% 25% 26% 5%	760
October	1st to 10th	Night	24% 3 15% 27% 24% 7%	760
	11th to 20th	Night	35% 4 13% 24% 21% 4	760
	21st to end	Night	36% 7% 18% 24% 12% 3	836
November	1st to 10th	Night	41% 8% 17% 25% 8% 1	780
	11th to 20th	Night	38% 7% 19% 22% 12% 2	800
	21st to end	Night	40% 6% 19% 21% 12% 3	800
December	1st to 10th	Night	34% 7% 16% 25% 16% 2	847
	11th to 20th	Night	47% 6% 19% 20% 7%	900
	21st to end	Night	42% 10% 23% 19% 6%	990

Page generated at 2025-03-09 05:08:46. Version ac07

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