Salt Spring Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salt Spring Island clear sky chart from 2005-11-06 to 2025-07-06.

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	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	123736
	Night	18% 10% 3 8% 5% 4 4 4 5% 6% 32%	123789
Transparency	Day	48% 9% 17% 18% 8% 1	123484
	Night	52% 7% 14% 18% 8% 1	123684
Seeing	Day	18% 6% 16% 29% 25% 7%	16272
	Night	23% 6% 16% 25% 23% 6%	24448

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	30% 15% 5% 11% 6% 5% 4 3 5% 5% 11%	3179
	11th to 20th	Day	18% 13% 5% 9% 5% 4 4 4 5% 8% 25%	3159
	21st to end	Day	30% 14% 4 9% 5% 4 4 3 4 4 17%	4084
February	1st to 10th	Day	22% 16% 4 10% 6% 6% 4 4 5% 5% 18%	1800
	11th to 20th	Day	22% 14% 3 9% 6% 5% 5% 4 5% 6% 22%	1755
	21st to end	Day	18% 14% 5% 9% 7% 7% 5% 5% 5% 6% 18%	1485
March	1st to 10th	Day	18% 13% 5% 11% 6% 6% 6% 4 6% 6% 18%	4733
	11th to 20th	Day	17% 12% 4 8% 5% 6% 5% 4 6% 6% 27%	5000
	21st to end	Day	20% 13% 4 11% 6% 6% 6% 4 5% 6% 17%	5573
April	1st to 10th	Day	17% 12% 4 9% 6% 6% 6% 5% 8% 7% 20%	2400
	11th to 20th	Day	15% 10% 3 8% 6% 5% 7% 5% 6% 7% 27%	2491
	21st to end	Day	17% 10% 3 7% 6% 5% 6% 3 7% 7% 29%	2625
May	1st to 10th	Day	10% 7% 3 6% 5% 5% 4 4 5% 7% 45%	6320
	11th to 20th	Day	11% 9% 3 8% 5% 5% 6% 4 6% 10% 32%	6277
	21st to end	Day	14% 8% 3 9% 5% 5% 6% 5% 6% 8% 31%	7077
June	1st to 10th	Day	13% 8% 3 8% 4 5% 5% 4 7% 8% 34%	3000
	11th to 20th	Day	11% 8% 3 9% 6% 6% 7% 6% 7% 9% 29%	3000
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	3000
July	1st to 10th	Day	4 3 1 4 3 3 3 3 4 4 69%	4816
	11th to 20th	Day	3 2 1 2 3 2 2 3 4 5% 73%	4740
	21st to end	Day	7% 4 1 4 3 3 4 3 5% 7% 58%	4895
August	1st to 10th	Day	3 2 1 3 3 3 3 3 4 6% 70%	4292
	11th to 20th	Day	7% 6% 2 7% 5% 4 5% 3 6% 8% 46%	4026
	21st to end	Day	10% 6% 3 7% 5% 4 5% 4 5% 7% 45%	4440
September	1st to 10th	Day	7% 5% 2 5% 3 4 5% 3 6% 8% 52%	2280
	11th to 20th	Day	13% 8% 2 7% 4 4 4 4 5% 6% 42%	2250
	21st to end	Day	15% 7% 3 8% 5% 4 4 5% 5% 7% 39%	2019
October	1st to 10th	Day	15% 8% 3 9% 5% 4 6% 5% 7% 7% 29%	3180
	11th to 20th	Day	24% 11% 4 9% 5% 5% 4 3 5% 6% 26%	3161
	21st to end	Day	21% 13% 4 9% 6% 5% 4 3 5% 7% 23%	3208
November	1st to 10th	Day	25% 15% 4 9% 6% 6% 5% 4 5% 5% 16%	1568
	11th to 20th	Day	24% 13% 5% 10% 6% 5% 5% 3 4 5% 21%	1600
	21st to end	Day	27% 11% 5% 10% 7% 5% 5% 4 5% 5% 17%	1600
December	1st to 10th	Day	18% 14% 5% 10% 6% 4 4 4 5% 6% 24%	2560
	11th to 20th	Day	31% 14% 4 9% 5% 6% 5% 4 5% 5% 12%	2645
	21st to end	Day	28% 17% 6% 13% 7% 5% 4 3 4 4 10%	3498
January	1st to 10th	Night	28% 17% 5% 10% 6% 5% 5% 4 4 4 12%	6766
	11th to 20th	Night	18% 10% 3 8% 5% 4 4 4 5% 7% 32%	6739
	21st to end	Night	29% 13% 3 7% 4 4 4 3 4 5% 24%	6876
February	1st to 10th	Night	23% 13% 4 10% 5% 5% 5% 3 6% 5% 21%	2600
	11th to 20th	Night	21% 13% 4 8% 5% 4 4 4 4 5% 28%	2532
	21st to end	Night	21% 13% 4 8% 6% 4 4 4 4 6% 26%	2145
March	1st to 10th	Night	16% 11% 4 10% 6% 5% 5% 4 6% 7% 25%	5156
	11th to 20th	Night	14% 11% 3 8% 5% 5% 5% 4 6% 7% 33%	4999
	21st to end	Night	24% 13% 5% 10% 6% 5% 4 3 5% 5% 20%	5402
April	1st to 10th	Night	16% 10% 4 9% 7% 5% 5% 3 6% 8% 26%	2000
	11th to 20th	Night	14% 9% 3 6% 5% 6% 5% 4 5% 8% 35%	1856
	21st to end	Night	14% 9% 3 7% 6% 5% 5% 4 6% 7% 33%	1775
May	1st to 10th	Night	12% 6% 2 5% 3 4 4 3 4 5% 50%	3640
	11th to 20th	Night	11% 8% 3 7% 4 4 4 4 7% 8% 40%	3616
	21st to end	Night	13% 8% 3 8% 6% 6% 6% 5% 6% 8% 31%	3795
June	1st to 10th	Night	13% 8% 2 6% 5% 5% 4 5% 6% 6% 40%	1400
	11th to 20th	Night	10% 6% 2 7% 4 6% 5% 5% 10% 9% 38%	1400
	21st to end	Night	7% 4 2 7% 3 5% 5% 5% 7% 10% 46%	1400
July	1st to 10th	Night	3 3 1 3 3 3 4 3 4 5% 69%	2255
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	2220
	21st to end	Night	6% 4 1 5% 3 3 3 3 5% 6% 61%	2654
August	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 74%	2641
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 7% 50%	2812
	21st to end	Night	10% 3 2 5% 3 4 4 4 6% 8% 51%	3229
September	1st to 10th	Night	5% 3 2 3 3 4 3 4 5% 7% 61%	1900
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 4 7% 47%	1928
	21st to end	Night	13% 7% 2 7% 4 4 4 4 5% 7% 42%	2161
October	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 3 5% 6% 41%	3800
	11th to 20th	Night	21% 9% 3 7% 5% 4 5% 4 5% 6% 31%	3777
	21st to end	Night	22% 11% 4 8% 4 4 4 3 4 6% 29%	4351
November	1st to 10th	Night	28% 12% 3 9% 6% 5% 5% 4 4 5% 21%	2730
	11th to 20th	Night	25% 12% 3 7% 5% 5% 4 4 5% 5% 25%	2800
	21st to end	Night	23% 12% 4 9% 7% 5% 5% 4 5% 5% 22%	2800
December	1st to 10th	Night	17% 12% 6% 10% 6% 6% 5% 4 5% 6% 22%	4616
	11th to 20th	Night	33% 16% 4 10% 5% 5% 4 3 4 4 12%	5560
	21st to end	Night	26% 14% 4 10% 6% 5% 5% 4 4 5% 16%	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	73% 10% 6% 9% 2	3179
	11th to 20th	Day	56% 6% 18% 14% 4 1	3180
	21st to end	Day	71% 6% 9% 11% 3	4084
February	1st to 10th	Day	68% 10% 9% 9% 4 1	1800
	11th to 20th	Day	64% 8% 10% 14% 4 1	1764
	21st to end	Day	63% 10% 13% 10% 3 1	1485
March	1st to 10th	Day	60% 12% 12% 12% 5%	4733
	11th to 20th	Day	55% 8% 12% 20% 5%	5000
	21st to end	Day	64% 9% 17% 8% 2	5573
April	1st to 10th	Day	56% 14% 16% 12% 2	2400
	11th to 20th	Day	51% 11% 14% 14% 9% 2	2491
	21st to end	Day	50% 12% 15% 15% 7% 1	2625
May	1st to 10th	Day	37% 7% 19% 25% 11% 1	6320
	11th to 20th	Day	43% 10% 24% 19% 4	6280
	21st to end	Day	45% 11% 23% 17% 3 1	7078
June	1st to 10th	Day	44% 10% 22% 16% 6% 2	3000
	11th to 20th	Day	45% 12% 24% 15% 4	3000
	21st to end	Day	38% 10% 23% 19% 7% 2	3000
July	1st to 10th	Day	19% 7% 12% 29% 25% 9%	4742
	11th to 20th	Day	14% 6% 14% 38% 26% 2	4659
	21st to end	Day	24% 6% 27% 26% 14% 3	4740
August	1st to 10th	Day	16% 7% 15% 44% 17% 1	4275
	11th to 20th	Day	35% 6% 31% 18% 8% 1	4065
	21st to end	Day	38% 8% 23% 23% 8% 1	4439
September	1st to 10th	Day	30% 10% 21% 24% 12% 3	2280
	11th to 20th	Day	41% 10% 17% 19% 12% 2	2250
	21st to end	Day	45% 9% 17% 18% 10% 1	2019
October	1st to 10th	Day	50% 9% 16% 20% 5%	3180
	11th to 20th	Day	59% 7% 12% 15% 6%	3161
	21st to end	Day	60% 7% 14% 14% 5%	3208
November	1st to 10th	Day	68% 8% 11% 8% 4 1	1568
	11th to 20th	Day	65% 8% 11% 12% 4 1	1600
	21st to end	Day	67% 11% 9% 10% 3 1	1600
December	1st to 10th	Day	61% 6% 11% 16% 5%	2560
	11th to 20th	Day	72% 8% 11% 7% 2	2648
	21st to end	Day	75% 8% 9% 6% 2	3498
January	1st to 10th	Night	73% 7% 8% 9% 2	6766
	11th to 20th	Night	50% 6% 20% 18% 5% 1	6780
	21st to end	Night	65% 6% 9% 15% 4	6876
February	1st to 10th	Night	65% 8% 12% 9% 5% 1	2600
	11th to 20th	Night	58% 8% 12% 15% 6% 1	2534
	21st to end	Night	58% 8% 10% 15% 7% 1	2145
March	1st to 10th	Night	52% 11% 13% 16% 8%	5156
	11th to 20th	Night	49% 9% 13% 24% 5%	5000
	21st to end	Night	64% 8% 13% 12% 2	5402
April	1st to 10th	Night	55% 9% 17% 16% 4	2000
	11th to 20th	Night	46% 8% 14% 20% 9% 2	1856
	21st to end	Night	49% 8% 15% 18% 10% 1	1775
May	1st to 10th	Night	35% 7% 13% 29% 15% 1	3637
	11th to 20th	Night	41% 7% 24% 22% 6%	3616
	21st to end	Night	50% 8% 20% 20% 3	3795
June	1st to 10th	Night	43% 9% 17% 21% 8% 3	1400
	11th to 20th	Night	38% 12% 22% 23% 5%	1400
	21st to end	Night	33% 8% 22% 24% 9% 3	1400
July	1st to 10th	Night	19% 5% 11% 30% 23% 12%	2220
	11th to 20th	Night	12% 5% 12% 35% 34% 2	2178
	21st to end	Night	25% 5% 16% 30% 22% 2	2570
August	1st to 10th	Night	14% 5% 14% 37% 29% 2	2633
	11th to 20th	Night	34% 4 30% 19% 9% 3	2839
	21st to end	Night	30% 7% 23% 29% 10% 1	3229
September	1st to 10th	Night	22% 8% 19% 29% 17% 5%	1900
	11th to 20th	Night	38% 7% 15% 19% 16% 5%	1928
	21st to end	Night	40% 8% 16% 24% 10% 2	2161
October	1st to 10th	Night	45% 5% 21% 21% 9%	3800
	11th to 20th	Night	54% 5% 14% 21% 5%	3777
	21st to end	Night	55% 7% 14% 17% 7%	4351
November	1st to 10th	Night	65% 8% 11% 12% 4 1	2730
	11th to 20th	Night	61% 8% 13% 11% 6% 2	2800
	21st to end	Night	65% 9% 10% 10% 6%	2800
December	1st to 10th	Night	60% 8% 12% 16% 4	4616
	11th to 20th	Night	75% 7% 10% 6% 2	5556
	21st to end	Night	67% 7% 12% 12% 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	36% 9% 28% 17% 7% 5%	200
	11th to 20th	Day	33% 15% 17% 20% 16% 1	200
	21st to end	Day	35% 8% 20% 21% 12% 4	283
February	1st to 10th	Day	29% 12% 25% 21% 13% 1	400
	11th to 20th	Day	32% 8% 24% 25% 10% 2	395
	21st to end	Day	26% 11% 21% 28% 11% 3	331
March	1st to 10th	Day	26% 9% 19% 27% 17% 3	500
	11th to 20th	Day	25% 7% 20% 27% 17% 4	500
	21st to end	Day	27% 7% 21% 26% 15% 4	550
April	1st to 10th	Day	22% 10% 20% 28% 17% 3	500
	11th to 20th	Day	18% 7% 26% 27% 17% 5%	492
	21st to end	Day	21% 5% 16% 33% 20% 5%	500
May	1st to 10th	Day	11% 5% 14% 38% 29% 4	503
	11th to 20th	Day	14% 3 10% 33% 29% 11%	528
	21st to end	Day	14% 4 13% 32% 27% 9%	643
June	1st to 10th	Day	15% 5% 14% 34% 26% 6%	730
	11th to 20th	Day	12% 5% 16% 38% 23% 7%	730
	21st to end	Day	11% 2 12% 32% 34% 8%	730
July	1st to 10th	Day	9% 2 9% 30% 37% 14%	697
	11th to 20th	Day	4 2 9% 33% 40% 13%	668
	21st to end	Day	6% 1 6% 27% 48% 13%	597
August	1st to 10th	Day	6% 1 6% 28% 42% 17%	487
	11th to 20th	Day	5% 2 7% 31% 41% 13%	477
	21st to end	Day	8% 3 14% 33% 34% 8%	539
September	1st to 10th	Day	10% 2 14% 38% 31% 7%	490
	11th to 20th	Day	18% 3 16% 32% 23% 8%	490
	21st to end	Day	18% 5% 19% 30% 24% 4	490
October	1st to 10th	Day	20% 7% 18% 26% 23% 6%	490
	11th to 20th	Day	28% 7% 17% 24% 19% 6%	490
	21st to end	Day	27% 10% 24% 25% 12% 3	422
November	1st to 10th	Day	30% 11% 25% 23% 12% 1	200
	11th to 20th	Day	30% 8% 21% 20% 18% 5%	200
	21st to end	Day	33% 9% 20% 21% 11% 7%	200
December	1st to 10th	Day	34% 7% 16% 19% 21% 4	200
	11th to 20th	Day	34% 9% 22% 22% 14% 1	200
	21st to end	Day	35% 15% 22% 19% 9%	220
January	1st to 10th	Night	38% 10% 20% 18% 11% 2	900
	11th to 20th	Night	34% 8% 15% 23% 18% 2	900
	21st to end	Night	32% 7% 17% 24% 16% 3	896
February	1st to 10th	Night	30% 9% 21% 25% 13% 3	800
	11th to 20th	Night	26% 8% 19% 28% 18% 2	784
	21st to end	Night	27% 13% 19% 24% 13% 4	660
March	1st to 10th	Night	24% 8% 20% 27% 16% 5%	800
	11th to 20th	Night	25% 8% 22% 24% 17% 4	800
	21st to end	Night	28% 8% 15% 26% 18% 5%	880
April	1st to 10th	Night	21% 8% 17% 28% 22% 5%	800
	11th to 20th	Night	18% 7% 22% 29% 20% 5%	668
	21st to end	Night	18% 5% 16% 33% 23% 5%	575
May	1st to 10th	Night	12% 2 18% 31% 30% 8%	400
	11th to 20th	Night	14% 3 11% 27% 34% 11%	394
	21st to end	Night	14% 3 9% 33% 34% 7%	433
June	1st to 10th	Night	17% 4 12% 31% 30% 6%	400
	11th to 20th	Night	10% 5% 15% 33% 31% 7%	400
	21st to end	Night	10% 4 10% 31% 37% 8%	400
July	1st to 10th	Night	8% 2 7% 25% 43% 15%	380
	11th to 20th	Night	5% 2 7% 29% 43% 15%	368
	21st to end	Night	5% 1 4 22% 50% 17%	416
August	1st to 10th	Night	6% 2 5% 19% 44% 24%	438
	11th to 20th	Night	6% 1 5% 22% 48% 18%	564
	21st to end	Night	10% 2 10% 27% 40% 12%	671
September	1st to 10th	Night	8% 1 8% 32% 38% 14%	760
	11th to 20th	Night	14% 5% 11% 20% 31% 19%	760
	21st to end	Night	17% 3 16% 26% 30% 8%	760
October	1st to 10th	Night	17% 3 16% 27% 26% 11%	760
	11th to 20th	Night	28% 4 16% 22% 24% 7%	760
	21st to end	Night	29% 6% 19% 26% 15% 5%	836
November	1st to 10th	Night	34% 7% 18% 27% 14% 1	780
	11th to 20th	Night	30% 9% 20% 24% 13% 3	800
	21st to end	Night	30% 9% 19% 23% 14% 4	800
December	1st to 10th	Night	26% 10% 18% 27% 17% 3	815
	11th to 20th	Night	38% 11% 22% 19% 9% 1	900
	21st to end	Night	37% 12% 22% 20% 7% 1	990

Page generated at 2025-07-02 22:30:15. Version ac07

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