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 2026-07-16.

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	19% 9% 3 7% 4 4 4 4 5% 7% 34%	142010
	Night	24% 10% 3 7% 4 4 4 3 5% 6% 30%	139355
Transparency	Day	51% 9% 14% 17% 8% 1	141712
	Night	55% 7% 13% 16% 8% 1	139235
Seeing	Day	23% 6% 19% 27% 20% 5%	17693
	Night	29% 6% 15% 25% 20% 5%	25738

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	38% 13% 4 7% 5% 5% 4 3 4 4 13%	4125
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 4 6% 6% 29%	4119
	21st to end	Day	35% 12% 4 7% 4 4 4 3 4 4 19%	5080
February	1st to 10th	Day	30% 13% 4 9% 6% 5% 4 4 5% 6% 15%	1890
	11th to 20th	Day	25% 12% 4 8% 5% 5% 6% 3 6% 6% 20%	1845
	21st to end	Day	23% 12% 3 10% 6% 7% 5% 4 5% 7% 19%	1557
March	1st to 10th	Day	24% 13% 4 11% 6% 5% 5% 4 5% 5% 17%	4812
	11th to 20th	Day	22% 13% 4 8% 5% 4 5% 4 6% 6% 23%	5110
	21st to end	Day	24% 13% 4 11% 7% 6% 5% 4 5% 6% 17%	5691
April	1st to 10th	Day	25% 10% 3 8% 5% 4 5% 4 6% 7% 22%	2520
	11th to 20th	Day	20% 9% 3 8% 5% 5% 5% 4 6% 6% 28%	2644
	21st to end	Day	21% 9% 3 7% 5% 4 4 3 5% 6% 32%	2762
May	1st to 10th	Day	10% 8% 3 7% 4 4 4 4 5% 6% 46%	8195
	11th to 20th	Day	13% 8% 3 8% 4 4 5% 4 8% 11% 30%	8160
	21st to end	Day	17% 6% 2 6% 5% 5% 5% 4 6% 8% 35%	9388
June	1st to 10th	Day	19% 8% 3 7% 5% 5% 4 4 6% 9% 31%	3150
	11th to 20th	Day	15% 8% 2 7% 6% 5% 6% 4 7% 8% 32%	3150
	21st to end	Day	14% 6% 3 7% 5% 4 5% 4 6% 8% 39%	3150
July	1st to 10th	Day	8% 4 1 4 3 3 3 2 4 6% 61%	6930
	11th to 20th	Day	4 3 1 2 2 2 3 2 3 6% 71%	6856
	21st to end	Day	7% 4 2 4 3 4 3 3 4 6% 60%	7151
August	1st to 10th	Day	6% 3 1 2 2 2 3 3 4 6% 68%	4451
	11th to 20th	Day	12% 7% 3 6% 4 4 5% 4 6% 8% 42%	4156
	21st to end	Day	14% 5% 2 6% 4 4 5% 4 6% 8% 43%	4610
September	1st to 10th	Day	10% 6% 2 6% 4 4 4 5% 5% 8% 47%	2400
	11th to 20th	Day	17% 6% 3 6% 5% 4 5% 4 5% 7% 38%	2356
	21st to end	Day	22% 6% 2 6% 5% 5% 4 4 6% 8% 32%	2131
October	1st to 10th	Day	23% 8% 3 8% 4 5% 5% 4 6% 7% 27%	3280
	11th to 20th	Day	32% 8% 3 7% 5% 4 5% 4 4 6% 22%	3261
	21st to end	Day	29% 10% 3 8% 5% 6% 5% 4 6% 7% 17%	3251
November	1st to 10th	Day	37% 9% 3 8% 5% 4 5% 5% 4 4 16%	1648
	11th to 20th	Day	33% 13% 3 7% 4 4 4 3 6% 5% 17%	1680
	21st to end	Day	35% 12% 3 7% 6% 4 4 4 4 4 16%	1680
December	1st to 10th	Day	24% 13% 3 9% 5% 4 5% 4 5% 6% 23%	2531
	11th to 20th	Day	42% 14% 4 8% 4 4 4 4 3 3 10%	2715
	21st to end	Day	38% 15% 4 9% 5% 5% 4 3 4 3 10%	3575
January	1st to 10th	Night	35% 13% 5% 10% 5% 4 4 3 4 4 13%	8770
	11th to 20th	Night	23% 7% 3 7% 4 5% 5% 4 6% 6% 31%	8779
	21st to end	Night	33% 10% 3 7% 4 4 5% 3 4 4 24%	9102
February	1st to 10th	Night	30% 13% 4 8% 5% 4 4 3 5% 5% 19%	2730
	11th to 20th	Night	24% 12% 3 9% 5% 4 4 4 5% 5% 26%	2662
	21st to end	Night	29% 13% 4 7% 5% 5% 3 3 4 5% 23%	2249
March	1st to 10th	Night	26% 12% 3 8% 5% 4 5% 4 5% 6% 22%	5283
	11th to 20th	Night	23% 12% 3 9% 5% 4 4 4 5% 6% 26%	5109
	21st to end	Night	29% 13% 5% 10% 6% 4 4 3 4 4 17%	5526
April	1st to 10th	Night	23% 11% 3 7% 6% 6% 5% 4 5% 6% 24%	2100
	11th to 20th	Night	17% 11% 4 8% 7% 4 5% 4 4 8% 29%	1924
	21st to end	Night	22% 9% 3 7% 4 4 4 4 5% 7% 31%	1857
May	1st to 10th	Night	12% 8% 2 5% 3 3 4 2 5% 6% 50%	4724
	11th to 20th	Night	13% 8% 3 8% 6% 5% 5% 4 6% 9% 33%	4700
	21st to end	Night	17% 9% 3 10% 5% 5% 5% 3 5% 7% 31%	4768
June	1st to 10th	Night	19% 10% 3 8% 5% 5% 5% 3 5% 4 33%	1470
	11th to 20th	Night	15% 10% 3 8% 6% 5% 5% 3 5% 8% 33%	1470
	21st to end	Night	13% 7% 2 7% 4 4 5% 4 6% 7% 41%	1470
July	1st to 10th	Night	7% 4 2 5% 4 3 4 3 4 7% 57%	3250
	11th to 20th	Night	3 2 1 2 2 2 3 2 5% 5% 73%	3215
	21st to end	Night	7% 3 2 4 3 3 4 3 4 6% 61%	3690
August	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 73%	2699
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 5% 7% 44%	2902
	21st to end	Night	14% 5% 2 6% 5% 4 4 4 5% 5% 47%	3300
September	1st to 10th	Night	8% 3 2 5% 3 4 4 3 5% 7% 56%	2000
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 5% 6% 42%	2040
	21st to end	Night	22% 7% 3 7% 3 3 3 3 4 6% 38%	2268
October	1st to 10th	Night	25% 9% 3 7% 4 4 5% 3 6% 6% 29%	3920
	11th to 20th	Night	29% 9% 3 7% 4 4 4 3 4 6% 27%	3897
	21st to end	Night	29% 9% 3 7% 4 5% 4 4 5% 6% 25%	4533
November	1st to 10th	Night	37% 10% 3 8% 5% 4 3 3 4 5% 18%	2870
	11th to 20th	Night	34% 11% 3 7% 5% 4 4 4 5% 4 19%	2940
	21st to end	Night	34% 11% 3 8% 5% 4 4 4 4 5% 20%	2940
December	1st to 10th	Night	25% 12% 3 8% 4 5% 5% 4 5% 6% 22%	4865
	11th to 20th	Night	41% 14% 4 7% 4 4 4 3 4 4 11%	5710
	21st to end	Night	35% 15% 4 10% 5% 4 4 3 4 4 13%	7623

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	74% 7% 9% 7% 3 1	4125
	11th to 20th	Day	49% 8% 12% 16% 14% 1	4140
	21st to end	Day	69% 4 5% 15% 7%	5081
February	1st to 10th	Day	69% 9% 8% 8% 3 3	1890
	11th to 20th	Day	62% 7% 11% 13% 5% 1	1854
	21st to end	Day	65% 10% 10% 9% 4 2	1557
March	1st to 10th	Day	65% 11% 10% 9% 4	4812
	11th to 20th	Day	62% 8% 9% 17% 4	5110
	21st to end	Day	69% 10% 12% 7% 2	5691
April	1st to 10th	Day	63% 12% 11% 11% 4	2520
	11th to 20th	Day	56% 10% 11% 14% 8% 2	2644
	21st to end	Day	56% 9% 11% 15% 7% 1	2762
May	1st to 10th	Day	41% 8% 15% 24% 12% 1	8195
	11th to 20th	Day	46% 14% 19% 17% 3	8163
	21st to end	Day	47% 12% 18% 17% 5%	9389
June	1st to 10th	Day	52% 10% 16% 14% 5% 2	3150
	11th to 20th	Day	52% 13% 15% 15% 5%	3150
	21st to end	Day	46% 10% 17% 18% 8% 1	3150
July	1st to 10th	Day	28% 9% 16% 22% 17% 7%	6856
	11th to 20th	Day	17% 8% 19% 34% 21% 1	6775
	21st to end	Day	26% 9% 27% 26% 11% 2	6949
August	1st to 10th	Day	20% 7% 13% 46% 14% 1	4434
	11th to 20th	Day	43% 11% 19% 16% 8% 2	4195
	21st to end	Day	42% 9% 17% 22% 9% 1	4609
September	1st to 10th	Day	37% 9% 17% 23% 11% 3	2400
	11th to 20th	Day	46% 9% 13% 18% 12% 2	2356
	21st to end	Day	50% 11% 15% 15% 9% 1	2131
October	1st to 10th	Day	57% 9% 16% 13% 5%	3280
	11th to 20th	Day	62% 7% 12% 12% 6%	3261
	21st to end	Day	66% 9% 11% 9% 4	3251
November	1st to 10th	Day	70% 8% 9% 7% 5% 1	1648
	11th to 20th	Day	68% 8% 9% 8% 5% 2	1680
	21st to end	Day	68% 6% 8% 10% 6% 1	1680
December	1st to 10th	Day	60% 7% 10% 17% 6% 1	2531
	11th to 20th	Day	78% 7% 7% 6% 1 1	2718
	21st to end	Day	81% 6% 6% 4 1 1	3575
January	1st to 10th	Night	75% 5% 7% 9% 4	8770
	11th to 20th	Night	47% 8% 13% 16% 15% 1	8820
	21st to end	Night	63% 5% 7% 18% 6%	9102
February	1st to 10th	Night	66% 7% 8% 10% 6% 2	2730
	11th to 20th	Night	61% 7% 11% 12% 8% 1	2664
	21st to end	Night	63% 7% 10% 12% 7% 2	2249
March	1st to 10th	Night	60% 10% 12% 12% 7%	5283
	11th to 20th	Night	58% 9% 10% 17% 6%	5110
	21st to end	Night	70% 8% 11% 8% 3	5526
April	1st to 10th	Night	60% 9% 12% 16% 3	2100
	11th to 20th	Night	53% 9% 10% 17% 9% 2	1924
	21st to end	Night	51% 9% 13% 18% 9%	1857
May	1st to 10th	Night	38% 5% 16% 27% 14%	4721
	11th to 20th	Night	44% 10% 20% 22% 4	4700
	21st to end	Night	50% 7% 20% 18% 4	4772
June	1st to 10th	Night	52% 7% 15% 16% 6% 4	1470
	11th to 20th	Night	48% 9% 17% 19% 7%	1470
	21st to end	Night	42% 9% 19% 19% 8% 3	1470
July	1st to 10th	Night	25% 7% 20% 23% 18% 7%	3215
	11th to 20th	Night	13% 5% 21% 33% 24% 4	3173
	21st to end	Night	23% 6% 27% 27% 14% 3	3587
August	1st to 10th	Night	16% 4 14% 39% 25% 2	2691
	11th to 20th	Night	37% 10% 25% 15% 9% 3	2929
	21st to end	Night	39% 7% 18% 24% 10% 1	3300
September	1st to 10th	Night	28% 8% 18% 27% 14% 4	2000
	11th to 20th	Night	42% 8% 12% 18% 15% 4	2040
	21st to end	Night	48% 8% 16% 18% 9% 2	2268
October	1st to 10th	Night	54% 8% 16% 15% 7%	3920
	11th to 20th	Night	60% 5% 11% 17% 7%	3897
	21st to end	Night	61% 7% 12% 15% 5%	4533
November	1st to 10th	Night	70% 7% 9% 8% 4 1	2870
	11th to 20th	Night	67% 7% 9% 10% 5% 2	2940
	21st to end	Night	67% 7% 9% 9% 7% 1	2940
December	1st to 10th	Night	61% 6% 11% 16% 4 1	4865
	11th to 20th	Night	78% 6% 7% 7% 3	5706
	21st to end	Night	77% 7% 6% 7% 2	7623

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% 8% 20% 18% 7% 5%	220
	11th to 20th	Day	35% 8% 24% 18% 14% 3	220
	21st to end	Day	43% 6% 17% 21% 10% 3	295
February	1st to 10th	Day	36% 9% 24% 21% 9% 2	430
	11th to 20th	Day	31% 6% 26% 24% 12% 1	425
	21st to end	Day	30% 13% 24% 21% 10% 3	355
March	1st to 10th	Day	32% 10% 18% 23% 16% 1	532
	11th to 20th	Day	31% 11% 16% 23% 15% 3	540
	21st to end	Day	31% 8% 26% 23% 10% 2	594
April	1st to 10th	Day	29% 8% 23% 24% 14% 2	540
	11th to 20th	Day	22% 8% 27% 23% 15% 4	532
	21st to end	Day	23% 7% 24% 27% 14% 4	540
May	1st to 10th	Day	15% 5% 20% 33% 24% 3	543
	11th to 20th	Day	17% 6% 16% 32% 24% 6%	568
	21st to end	Day	16% 6% 19% 32% 22% 5%	752
June	1st to 10th	Day	20% 6% 20% 29% 22% 3	780
	11th to 20th	Day	14% 7% 22% 32% 22% 3	780
	21st to end	Day	15% 3 17% 33% 27% 6%	780
July	1st to 10th	Day	13% 2 18% 29% 30% 7%	771
	11th to 20th	Day	8% 3 16% 35% 31% 7%	744
	21st to end	Day	7% 3 10% 30% 40% 9%	696
August	1st to 10th	Day	9% 3 10% 28% 34% 15%	527
	11th to 20th	Day	10% 3 12% 29% 34% 12%	517
	21st to end	Day	14% 3 14% 33% 29% 6%	583
September	1st to 10th	Day	14% 3 18% 33% 25% 7%	530
	11th to 20th	Day	24% 6% 15% 25% 22% 9%	530
	21st to end	Day	26% 6% 22% 25% 16% 5%	530
October	1st to 10th	Day	28% 6% 18% 23% 18% 6%	530
	11th to 20th	Day	35% 7% 18% 18% 16% 5%	530
	21st to end	Day	33% 9% 22% 24% 8% 3	437
November	1st to 10th	Day	39% 10% 28% 17% 7%	220
	11th to 20th	Day	38% 8% 17% 20% 13% 4	220
	21st to end	Day	43% 10% 19% 13% 10% 5%	220
December	1st to 10th	Day	39% 7% 20% 14% 13% 6%	220
	11th to 20th	Day	44% 9% 20% 19% 7% 2	220
	21st to end	Day	45% 8% 20% 21% 6%	242
January	1st to 10th	Night	45% 8% 17% 19% 10% 2	950
	11th to 20th	Night	39% 6% 14% 23% 18% 1	950
	21st to end	Night	39% 6% 15% 23% 15% 1	971
February	1st to 10th	Night	35% 7% 19% 26% 12% 1	840
	11th to 20th	Night	30% 5% 19% 31% 14% 1	824
	21st to end	Night	35% 9% 18% 22% 13% 3	692
March	1st to 10th	Night	33% 7% 18% 23% 16% 3	840
	11th to 20th	Night	37% 7% 18% 20% 16% 2	840
	21st to end	Night	32% 7% 19% 23% 16% 3	924
April	1st to 10th	Night	28% 5% 17% 27% 18% 5%	840
	11th to 20th	Night	21% 8% 21% 28% 20% 2	676
	21st to end	Night	26% 4 17% 31% 20% 3	597
May	1st to 10th	Night	17% 4 16% 30% 26% 7%	420
	11th to 20th	Night	20% 5% 10% 28% 30% 8%	414
	21st to end	Night	19% 4 11% 31% 27% 8%	455
June	1st to 10th	Night	24% 5% 10% 31% 26% 4	420
	11th to 20th	Night	18% 6% 13% 33% 23% 8%	420
	21st to end	Night	16% 3 9% 32% 34% 7%	420
July	1st to 10th	Night	12% 1 10% 27% 36% 13%	410
	11th to 20th	Night	7% 2 9% 31% 38% 12%	398
	21st to end	Night	8% 2 7% 20% 47% 17%	438
August	1st to 10th	Night	9% 1 5% 21% 43% 21%	449
	11th to 20th	Night	9% 2 6% 24% 47% 13%	594
	21st to end	Night	14% 2 11% 24% 40% 9%	689
September	1st to 10th	Night	10% 2 9% 31% 37% 11%	800
	11th to 20th	Night	20% 4 13% 19% 31% 13%	800
	21st to end	Night	27% 3 15% 25% 25% 5%	800
October	1st to 10th	Night	24% 4 15% 28% 24% 7%	800
	11th to 20th	Night	34% 4 13% 24% 20% 4	800
	21st to end	Night	36% 7% 18% 24% 12% 3	880
November	1st to 10th	Night	41% 7% 17% 25% 8%	820
	11th to 20th	Night	38% 7% 18% 23% 11% 2	840
	21st to end	Night	40% 6% 18% 22% 11% 3	840
December	1st to 10th	Night	35% 7% 16% 25% 15% 1	892
	11th to 20th	Night	48% 6% 19% 20% 7%	950
	21st to end	Night	41% 11% 23% 20% 6%	1045

Page generated at 2026-07-13 00:14:49. Version ac07

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