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 2024-03-18.

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	17% 9% 4 7% 6% 4 5% 5% 5% 7% 32%	78221
	Night	20% 10% 3 7% 6% 3 5% 5% 5% 6% 31%	81521
Transparency	Day	50% 11% 16% 16% 6% 1	77930
	Night	53% 9% 14% 16% 7% 1	81392
Seeing	Day	18% 5% 16% 29% 25% 7%	14492
	Night	23% 6% 16% 25% 23% 7%	22894

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% 10% 7% 4 4 4 5% 5% 12%	2219
	11th to 20th	Day	25% 15% 5% 7% 6% 3 4 4 5% 7% 19%	2199
	21st to end	Day	40% 16% 5% 7% 6% 3 4 4 3 3 8%	2832
February	1st to 10th	Day	24% 15% 5% 9% 6% 4 5% 5% 5% 5% 18%	1710
	11th to 20th	Day	21% 14% 3 8% 7% 4 5% 5% 5% 6% 22%	1665
	21st to end	Day	17% 13% 6% 8% 8% 5% 7% 6% 5% 7% 19%	1413
March	1st to 10th	Day	18% 12% 5% 10% 8% 4 6% 6% 6% 7% 19%	1990
	11th to 20th	Day	21% 11% 6% 7% 7% 4 5% 5% 5% 6% 23%	2059
	21st to end	Day	20% 10% 5% 9% 7% 4 6% 5% 5% 7% 23%	2214
April	1st to 10th	Day	18% 11% 4 7% 8% 4 6% 6% 8% 7% 21%	2160
	11th to 20th	Day	16% 10% 4 8% 7% 4 7% 6% 6% 7% 25%	2238
	21st to end	Day	17% 9% 3 7% 7% 4 6% 4 7% 7% 28%	2362
May	1st to 10th	Day	11% 6% 4 6% 7% 5% 6% 6% 7% 7% 35%	2520
	11th to 20th	Day	12% 7% 3 7% 6% 4 6% 6% 6% 8% 34%	2477
	21st to end	Day	12% 9% 4 8% 5% 4 5% 6% 6% 8% 34%	2785
June	1st to 10th	Day	15% 8% 3 7% 5% 3 6% 6% 7% 8% 32%	2700
	11th to 20th	Day	12% 7% 3 7% 7% 5% 7% 7% 7% 9% 29%	2700
	21st to end	Day	10% 5% 2 5% 6% 3 6% 6% 7% 9% 41%	2700
July	1st to 10th	Day	8% 4 2 5% 5% 3 5% 5% 5% 6% 52%	2700
	11th to 20th	Day	6% 3 2 3 5% 2 4 5% 5% 7% 58%	2700
	21st to end	Day	4 2 1 3 3 2 4 3 5% 7% 65%	2804
August	1st to 10th	Day	6% 4 2 4 4 3 4 5% 5% 7% 57%	2450
	11th to 20th	Day	5% 4 2 4 4 2 4 4 5% 7% 58%	2298
	21st to end	Day	7% 5% 2 5% 6% 3 4 6% 6% 8% 48%	2532
September	1st to 10th	Day	8% 5% 2 5% 4 3 5% 4 5% 7% 51%	2160
	11th to 20th	Day	13% 7% 3 6% 5% 3 5% 5% 5% 6% 43%	2132
	21st to end	Day	15% 6% 3 7% 5% 3 4 6% 5% 7% 39%	1913
October	1st to 10th	Day	18% 7% 3 6% 5% 2 5% 5% 5% 7% 36%	1800
	11th to 20th	Day	21% 11% 4 7% 6% 4 4 5% 5% 7% 26%	1800
	21st to end	Day	24% 11% 3 8% 5% 3 4 4 5% 7% 26%	1846
November	1st to 10th	Day	25% 14% 5% 7% 7% 5% 6% 5% 5% 5% 16%	1488
	11th to 20th	Day	24% 11% 6% 8% 7% 4 5% 4 4 5% 21%	1520
	21st to end	Day	27% 9% 5% 9% 7% 5% 5% 5% 5% 5% 18%	1520
December	1st to 10th	Day	22% 16% 5% 7% 7% 3 4 4 4 5% 23%	1488
	11th to 20th	Day	27% 14% 4 9% 7% 4 7% 6% 5% 5% 12%	1685
	21st to end	Day	26% 16% 6% 11% 8% 3 5% 4 5% 5% 12%	2442
January	1st to 10th	Night	26% 15% 5% 9% 8% 4 6% 5% 4 4 14%	4726
	11th to 20th	Night	26% 11% 4 7% 6% 3 4 4 4 7% 24%	4699
	21st to end	Night	38% 14% 3 8% 5% 3 4 4 4 5% 13%	4824
February	1st to 10th	Night	25% 12% 5% 8% 6% 3 5% 4 6% 5% 21%	2470
	11th to 20th	Night	21% 12% 4 7% 6% 3 4 5% 4 5% 28%	2402
	21st to end	Night	22% 11% 5% 6% 7% 3 4 5% 4 6% 27%	2041
March	1st to 10th	Night	19% 10% 3 7% 7% 4 5% 5% 6% 6% 26%	2185
	11th to 20th	Night	18% 11% 4 7% 6% 4 6% 6% 6% 6% 28%	2066
	21st to end	Night	19% 10% 5% 9% 8% 4 5% 5% 6% 7% 23%	2142
April	1st to 10th	Night	17% 9% 4 8% 7% 4 6% 4 6% 8% 28%	1800
	11th to 20th	Night	16% 9% 3 6% 6% 4 7% 5% 6% 8% 33%	1669
	21st to end	Night	14% 9% 3 6% 7% 3 6% 6% 6% 7% 33%	1598
May	1st to 10th	Night	11% 5% 2 4 5% 4 6% 7% 5% 7% 44%	1440
	11th to 20th	Night	10% 6% 3 6% 6% 2 5% 5% 7% 9% 40%	1416
	21st to end	Night	12% 6% 3 6% 5% 4 5% 6% 6% 9% 39%	1487
June	1st to 10th	Night	14% 7% 3 5% 6% 4 5% 6% 6% 6% 38%	1260
	11th to 20th	Night	10% 5% 2 6% 5% 3 7% 5% 10% 9% 37%	1260
	21st to end	Night	7% 4 1 5% 4 3 6% 6% 7% 11% 48%	1260
July	1st to 10th	Night	6% 4 2 4 5% 3 5% 4 4 7% 56%	1260
	11th to 20th	Night	3 3 2 3 3 1 4 4 5% 7% 64%	1260
	21st to end	Night	3 1 1 2 2 2 3 3 4 6% 73%	1510
August	1st to 10th	Night	5% 3 1 3 3 3 3 4 4 6% 65%	1488
	11th to 20th	Night	2 3 1 3 3 2 3 3 5% 8% 66%	1602
	21st to end	Night	6% 3 2 4 4 3 4 5% 7% 8% 54%	1823
September	1st to 10th	Night	5% 3 2 3 4 3 3 5% 5% 7% 61%	1800
	11th to 20th	Night	12% 6% 2 5% 6% 3 4 4 4 7% 47%	1826
	21st to end	Night	13% 7% 2 6% 5% 3 4 5% 5% 7% 43%	2047
October	1st to 10th	Night	15% 7% 2 6% 5% 3 4 5% 5% 5% 44%	2160
	11th to 20th	Night	20% 9% 3 5% 5% 3 4 5% 5% 6% 36%	2160
	21st to end	Night	24% 8% 3 5% 5% 3 4 5% 4 5% 33%	2508
November	1st to 10th	Night	27% 11% 3 7% 7% 4 5% 6% 4 5% 21%	2590
	11th to 20th	Night	25% 10% 4 6% 6% 3 5% 5% 5% 5% 26%	2660
	21st to end	Night	24% 10% 4 8% 7% 4 6% 5% 5% 5% 23%	2660
December	1st to 10th	Night	21% 13% 5% 8% 7% 4 6% 5% 4 5% 23%	2688
	11th to 20th	Night	29% 15% 5% 8% 7% 4 5% 4 5% 4 14%	3520
	21st to end	Night	27% 14% 5% 9% 7% 4 4 4 4 4 18%	5214

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	72% 13% 6% 7% 3	2219
	11th to 20th	Day	63% 7% 15% 9% 5% 1	2220
	21st to end	Day	80% 8% 5% 5% 1	2832
February	1st to 10th	Day	68% 10% 9% 9% 4 1	1710
	11th to 20th	Day	64% 8% 10% 13% 4 1	1674
	21st to end	Day	61% 10% 14% 10% 3 1	1413
March	1st to 10th	Day	61% 11% 14% 10% 4	1990
	11th to 20th	Day	61% 9% 12% 13% 4 1	2059
	21st to end	Day	61% 10% 16% 11% 2	2214
April	1st to 10th	Day	56% 14% 16% 12% 2	2160
	11th to 20th	Day	54% 11% 14% 13% 8% 1	2238
	21st to end	Day	51% 13% 14% 14% 7% 1	2362
May	1st to 10th	Day	43% 13% 19% 17% 7% 1	2520
	11th to 20th	Day	45% 11% 20% 18% 6% 1	2480
	21st to end	Day	44% 13% 21% 19% 3	2786
June	1st to 10th	Day	46% 10% 21% 15% 5% 2	2700
	11th to 20th	Day	46% 12% 24% 14% 3	2700
	21st to end	Day	37% 11% 22% 20% 8% 2	2700
July	1st to 10th	Day	30% 11% 19% 25% 11% 3	2626
	11th to 20th	Day	24% 11% 23% 30% 11% 1	2619
	21st to end	Day	15% 9% 23% 35% 15% 3	2648
August	1st to 10th	Day	24% 11% 21% 30% 12% 2	2433
	11th to 20th	Day	25% 10% 22% 26% 14% 2	2298
	21st to end	Day	30% 12% 24% 26% 6% 1	2532
September	1st to 10th	Day	32% 11% 20% 24% 11% 3	2160
	11th to 20th	Day	41% 10% 16% 19% 13% 2	2132
	21st to end	Day	45% 9% 17% 18% 10% 1	1913
October	1st to 10th	Day	46% 12% 16% 17% 8%	1800
	11th to 20th	Day	58% 11% 14% 14% 3	1800
	21st to end	Day	58% 10% 12% 12% 7%	1846
November	1st to 10th	Day	67% 8% 12% 8% 4 1	1488
	11th to 20th	Day	65% 8% 10% 11% 4 2	1520
	21st to end	Day	66% 11% 9% 11% 3 1	1520
December	1st to 10th	Day	64% 9% 8% 12% 6%	1488
	11th to 20th	Day	70% 12% 11% 5% 2 1	1688
	21st to end	Day	73% 10% 9% 6% 3	2442
January	1st to 10th	Night	71% 10% 8% 8% 3	4726
	11th to 20th	Night	59% 7% 15% 12% 5% 1	4740
	21st to end	Night	75% 8% 6% 9% 2	4824
February	1st to 10th	Night	65% 8% 12% 9% 5% 1	2470
	11th to 20th	Night	58% 8% 13% 15% 7%	2404
	21st to end	Night	58% 8% 10% 15% 7% 2	2041
March	1st to 10th	Night	56% 11% 12% 16% 6%	2185
	11th to 20th	Night	56% 9% 11% 17% 5% 1	2067
	21st to end	Night	60% 9% 14% 14% 2	2142
April	1st to 10th	Night	54% 8% 17% 17% 4	1800
	11th to 20th	Night	49% 8% 13% 20% 9% 1	1669
	21st to end	Night	50% 9% 14% 17% 10% 1	1598
May	1st to 10th	Night	37% 11% 18% 22% 11% 1	1440
	11th to 20th	Night	40% 9% 19% 23% 9% 1	1416
	21st to end	Night	43% 9% 20% 22% 6%	1487
June	1st to 10th	Night	45% 9% 17% 21% 6% 3	1260
	11th to 20th	Night	38% 13% 23% 21% 5%	1260
	21st to end	Night	31% 9% 23% 24% 10% 4	1260
July	1st to 10th	Night	29% 8% 16% 28% 14% 4	1225
	11th to 20th	Night	21% 8% 20% 31% 17% 2	1218
	21st to end	Night	13% 7% 15% 34% 27% 4	1426
August	1st to 10th	Night	22% 7% 18% 30% 18% 4	1480
	11th to 20th	Night	17% 7% 24% 30% 16% 6%	1602
	21st to end	Night	26% 9% 22% 32% 10% 1	1823
September	1st to 10th	Night	23% 9% 19% 29% 16% 4	1800
	11th to 20th	Night	38% 7% 15% 19% 17% 5%	1826
	21st to end	Night	40% 8% 16% 24% 10% 2	2047
October	1st to 10th	Night	43% 7% 16% 22% 12%	2160
	11th to 20th	Night	50% 7% 17% 18% 8%	2160
	21st to end	Night	53% 9% 13% 15% 10%	2508
November	1st to 10th	Night	64% 9% 11% 12% 4 1	2590
	11th to 20th	Night	60% 9% 13% 11% 6% 2	2660
	21st to end	Night	64% 9% 10% 11% 6%	2660
December	1st to 10th	Night	63% 9% 11% 13% 5% 1	2688
	11th to 20th	Night	71% 11% 10% 6% 3	3516
	21st to end	Night	68% 9% 9% 10% 3	5214

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	34% 9% 26% 17% 7% 6%	180
	11th to 20th	Day	37% 13% 16% 19% 16%	180
	21st to end	Day	38% 8% 20% 20% 12% 2	257
February	1st to 10th	Day	30% 12% 25% 20% 13% 1	370
	11th to 20th	Day	31% 8% 25% 25% 8% 2	365
	21st to end	Day	25% 12% 21% 28% 12% 3	307
March	1st to 10th	Day	26% 8% 20% 27% 16% 3	460
	11th to 20th	Day	24% 6% 20% 28% 17% 4	449
	21st to end	Day	27% 6% 21% 26% 15% 4	462
April	1st to 10th	Day	23% 10% 20% 27% 16% 3	420
	11th to 20th	Day	21% 5% 23% 28% 18% 5%	412
	21st to end	Day	21% 5% 16% 35% 18% 5%	420
May	1st to 10th	Day	11% 5% 13% 38% 29% 4	423
	11th to 20th	Day	14% 2 9% 31% 31% 12%	448
	21st to end	Day	13% 3 10% 34% 29% 11%	547
June	1st to 10th	Day	17% 3 14% 33% 26% 7%	630
	11th to 20th	Day	12% 4 16% 39% 23% 6%	630
	21st to end	Day	10% 1 12% 32% 36% 8%	630
July	1st to 10th	Day	10% 2 8% 29% 37% 14%	621
	11th to 20th	Day	4 2 9% 33% 39% 13%	618
	21st to end	Day	5% 1 5% 26% 50% 13%	550
August	1st to 10th	Day	6% 2 6% 28% 41% 18%	447
	11th to 20th	Day	5% 1 7% 32% 42% 13%	437
	21st to end	Day	8% 2 13% 33% 35% 9%	495
September	1st to 10th	Day	10% 2 14% 39% 28% 6%	450
	11th to 20th	Day	18% 3 16% 31% 24% 9%	450
	21st to end	Day	18% 5% 20% 30% 24% 4	450
October	1st to 10th	Day	21% 6% 17% 26% 24% 6%	450
	11th to 20th	Day	26% 7% 18% 24% 19% 6%	450
	21st to end	Day	27% 10% 24% 24% 11% 3	386
November	1st to 10th	Day	29% 11% 25% 23% 11% 1	180
	11th to 20th	Day	31% 7% 19% 20% 18% 5%	180
	21st to end	Day	32% 9% 19% 22% 11% 7%	180
December	1st to 10th	Day	37% 7% 17% 18% 18% 3	180
	11th to 20th	Day	32% 9% 21% 24% 14% 1	180
	21st to end	Day	34% 15% 22% 20% 9% 1	198
January	1st to 10th	Night	37% 11% 21% 18% 11% 2	850
	11th to 20th	Night	36% 8% 14% 22% 18% 2	850
	21st to end	Night	33% 7% 17% 24% 15% 3	851
February	1st to 10th	Night	31% 9% 21% 24% 13% 3	760
	11th to 20th	Night	26% 8% 19% 28% 17% 1	744
	21st to end	Night	27% 13% 19% 24% 13% 4	628
March	1st to 10th	Night	24% 8% 21% 28% 15% 5%	760
	11th to 20th	Night	25% 8% 21% 25% 17% 5%	752
	21st to end	Night	27% 9% 15% 27% 18% 5%	792
April	1st to 10th	Night	22% 8% 17% 27% 21% 5%	720
	11th to 20th	Night	19% 5% 21% 29% 20% 5%	601
	21st to end	Night	18% 5% 16% 33% 23% 5%	518
May	1st to 10th	Night	13% 1 18% 30% 30% 8%	360
	11th to 20th	Night	14% 2 10% 25% 36% 12%	354
	21st to end	Night	13% 3 8% 32% 36% 8%	389
June	1st to 10th	Night	18% 3 9% 32% 30% 7%	360
	11th to 20th	Night	10% 4 14% 34% 30% 7%	360
	21st to end	Night	10% 4 10% 31% 38% 9%	360
July	1st to 10th	Night	9% 2 7% 24% 43% 15%	350
	11th to 20th	Night	5% 2 7% 30% 42% 15%	348
	21st to end	Night	4 1 4 23% 51% 18%	394
August	1st to 10th	Night	6% 2 6% 20% 42% 25%	414
	11th to 20th	Night	5% 1 5% 22% 50% 17%	534
	21st to end	Night	9% 2 10% 27% 40% 13%	635
September	1st to 10th	Night	8% 1 8% 32% 37% 13%	720
	11th to 20th	Night	14% 5% 11% 20% 32% 19%	720
	21st to end	Night	17% 3 16% 26% 30% 9%	720
October	1st to 10th	Night	18% 3 16% 26% 27% 11%	720
	11th to 20th	Night	27% 4 16% 21% 24% 8%	720
	21st to end	Night	29% 6% 18% 26% 15% 5%	792
November	1st to 10th	Night	33% 7% 18% 27% 14% 1	740
	11th to 20th	Night	30% 9% 20% 24% 13% 4	760
	21st to end	Night	30% 9% 19% 23% 14% 4	760
December	1st to 10th	Night	26% 10% 18% 27% 16% 3	773
	11th to 20th	Night	37% 11% 22% 19% 10% 1	850
	21st to end	Night	38% 11% 22% 20% 8% 1	935

Page generated at 2024-03-15 11:01:39. Version ac07

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