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 2024-11-03.

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 7% 5% 5% 5% 4 5% 6% 36%	101708
	Night	18% 10% 3 7% 5% 4 4 4 5% 6% 34%	97367
Transparency	Day	46% 10% 17% 18% 8% 1	101456
	Night	50% 8% 14% 18% 8% 1	97265
Seeing	Day	18% 5% 16% 29% 25% 7%	15456
	Night	23% 6% 16% 25% 23% 7%	23573

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% 16% 5% 11% 6% 5% 5% 2 5% 5% 12%	2219
	11th to 20th	Day	25% 15% 4 8% 5% 4 4 3 5% 7% 19%	2199
	21st to end	Day	40% 17% 5% 8% 5% 4 4 3 3 3 8%	2832
February	1st to 10th	Day	23% 15% 4 10% 5% 5% 4 4 5% 5% 18%	1710
	11th to 20th	Day	21% 14% 4 9% 6% 5% 5% 4 5% 6% 22%	1665
	21st to end	Day	17% 14% 6% 9% 7% 7% 6% 5% 5% 6% 18%	1413
March	1st to 10th	Day	15% 12% 4 11% 7% 7% 7% 5% 7% 7% 17%	3288
	11th to 20th	Day	15% 9% 4 7% 5% 5% 5% 4 6% 6% 34%	3490
	21st to end	Day	20% 12% 4 10% 6% 5% 5% 4 5% 6% 23%	3886
April	1st to 10th	Day	17% 12% 4 9% 6% 6% 6% 5% 8% 7% 20%	2280
	11th to 20th	Day	15% 11% 3 9% 6% 6% 6% 5% 6% 6% 26%	2365
	21st to end	Day	17% 10% 3 8% 6% 5% 6% 3 7% 7% 28%	2494
May	1st to 10th	Day	12% 8% 2 5% 5% 5% 4 4 6% 6% 42%	4420
	11th to 20th	Day	8% 6% 2 7% 4 5% 5% 4 6% 11% 40%	4377
	21st to end	Day	17% 10% 4 10% 5% 5% 5% 5% 6% 7% 27%	4931
June	1st to 10th	Day	14% 9% 3 8% 5% 5% 6% 4 7% 8% 32%	2850
	11th to 20th	Day	12% 8% 3 8% 6% 6% 7% 6% 7% 8% 29%	2850
	21st to end	Day	10% 5% 2 7% 5% 5% 5% 5% 7% 8% 40%	2850
July	1st to 10th	Day	5% 3 1 4 3 3 3 3 4 4 69%	4740
	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	18% 8% 3 7% 4 4 5% 4 5% 7% 35%	1900
	11th to 20th	Day	21% 12% 3 8% 5% 5% 4 4 5% 7% 26%	1900
	21st to end	Day	24% 12% 3 8% 5% 5% 3 3 5% 7% 25%	1948
November	1st to 10th	Day	25% 14% 4 9% 6% 6% 5% 4 5% 5% 16%	1504
	11th to 20th	Day	24% 13% 5% 10% 6% 5% 5% 3 4 5% 21%	1520
	21st to end	Day	27% 11% 5% 9% 7% 6% 4 4 5% 5% 18%	1520
December	1st to 10th	Day	22% 17% 4 8% 6% 4 4 3 4 5% 23%	1488
	11th to 20th	Day	27% 15% 4 10% 6% 6% 6% 5% 5% 5% 12%	1685
	21st to end	Day	26% 16% 6% 12% 7% 5% 5% 3 5% 5% 11%	2442
January	1st to 10th	Night	26% 16% 5% 10% 6% 6% 5% 4 4 4 14%	4726
	11th to 20th	Night	25% 12% 3 8% 5% 4 4 3 4 6% 24%	4699
	21st to end	Night	38% 14% 3 8% 4 4 4 3 4 5% 13%	4824
February	1st to 10th	Night	24% 13% 4 9% 5% 5% 5% 3 6% 5% 20%	2470
	11th to 20th	Night	21% 13% 4 8% 5% 4 4 4 4 5% 28%	2402
	21st to end	Night	21% 13% 4 7% 6% 4 4 4 4 6% 27%	2041
March	1st to 10th	Night	18% 12% 4 10% 6% 5% 6% 4 6% 6% 22%	3581
	11th to 20th	Night	11% 8% 2 6% 5% 4 5% 4 6% 8% 40%	3489
	21st to end	Night	20% 12% 5% 10% 6% 5% 4 3 5% 6% 24%	3767
April	1st to 10th	Night	17% 10% 3 9% 6% 5% 5% 4 6% 8% 27%	1900
	11th to 20th	Night	15% 9% 3 6% 5% 6% 5% 4 5% 7% 34%	1762
	21st to end	Night	15% 9% 3 7% 6% 5% 5% 4 6% 7% 32%	1686
May	1st to 10th	Night	11% 6% 2 5% 3 5% 5% 4 5% 5% 49%	2540
	11th to 20th	Night	7% 5% 2 6% 4 3 4 3 6% 8% 52%	2516
	21st to end	Night	15% 9% 3 8% 6% 6% 5% 5% 5% 6% 31%	2641
June	1st to 10th	Night	14% 8% 2 7% 5% 5% 4 5% 6% 6% 38%	1330
	11th to 20th	Night	9% 6% 2 7% 4 6% 5% 4 10% 9% 38%	1330
	21st to end	Night	7% 4 2 6% 3 4 5% 5% 7% 10% 47%	1330
July	1st to 10th	Night	3 3 1 3 3 3 4 3 4 5% 69%	2220
	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	15% 7% 2 7% 4 4 4 3 4 5% 44%	2280
	11th to 20th	Night	20% 9% 3 6% 4 4 5% 4 5% 6% 35%	2280
	21st to end	Night	24% 8% 3 7% 4 5% 4 4 4 5% 32%	2648
November	1st to 10th	Night	28% 12% 3 8% 6% 5% 5% 4 4 5% 21%	2618
	11th to 20th	Night	25% 11% 3 7% 5% 5% 4 4 5% 5% 26%	2660
	21st to end	Night	23% 11% 4 9% 6% 5% 5% 4 5% 5% 23%	2660
December	1st to 10th	Night	20% 15% 4 8% 7% 6% 5% 4 4 5% 22%	2688
	11th to 20th	Night	29% 16% 4 9% 6% 5% 4 3 5% 4 14%	3520
	21st to end	Night	27% 15% 4 10% 6% 5% 4 3 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	56% 16% 13% 9% 5%	3288
	11th to 20th	Day	48% 10% 14% 23% 4 1	3490
	21st to end	Day	58% 12% 18% 10% 3	3886
April	1st to 10th	Day	56% 14% 16% 11% 2	2280
	11th to 20th	Day	52% 11% 14% 13% 9% 2	2365
	21st to end	Day	51% 13% 14% 15% 7% 1	2494
May	1st to 10th	Day	38% 10% 19% 24% 9% 1	4420
	11th to 20th	Day	34% 13% 27% 21% 5%	4380
	21st to end	Day	50% 14% 20% 13% 3	4932
June	1st to 10th	Day	46% 11% 21% 15% 5% 2	2850
	11th to 20th	Day	45% 12% 24% 15% 4	2850
	21st to end	Day	38% 11% 22% 20% 8% 2	2850
July	1st to 10th	Day	19% 7% 11% 29% 25% 9%	4666
	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	47% 12% 16% 17% 8%	1900
	11th to 20th	Day	59% 11% 13% 14% 3	1900
	21st to end	Day	59% 9% 13% 12% 7%	1948
November	1st to 10th	Day	67% 8% 12% 9% 4 1	1504
	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	55% 15% 11% 13% 6%	3581
	11th to 20th	Night	40% 11% 17% 26% 6% 1	3490
	21st to end	Night	60% 10% 15% 14% 2	3767
April	1st to 10th	Night	54% 9% 17% 16% 4	1900
	11th to 20th	Night	48% 8% 13% 19% 9% 2	1762
	21st to end	Night	51% 9% 14% 16% 10% 1	1686
May	1st to 10th	Night	34% 9% 15% 26% 15% 1	2540
	11th to 20th	Night	28% 9% 27% 27% 8%	2516
	21st to end	Night	51% 10% 18% 17% 4	2641
June	1st to 10th	Night	44% 9% 16% 21% 7% 3	1330
	11th to 20th	Night	38% 12% 23% 21% 6%	1330
	21st to end	Night	33% 8% 22% 24% 10% 3	1330
July	1st to 10th	Night	19% 5% 10% 30% 23% 13%	2185
	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	43% 7% 17% 21% 11%	2280
	11th to 20th	Night	50% 7% 17% 19% 7%	2280
	21st to end	Night	53% 9% 13% 16% 9%	2648
November	1st to 10th	Night	64% 9% 11% 12% 4 1	2618
	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	23% 6% 20% 28% 18% 4	460
	21st to end	Day	26% 7% 21% 26% 16% 4	506
April	1st to 10th	Day	22% 10% 20% 28% 16% 3	460
	11th to 20th	Day	20% 6% 25% 29% 16% 5%	452
	21st to end	Day	23% 5% 17% 33% 18% 5%	460
May	1st to 10th	Day	11% 5% 14% 38% 29% 3	463
	11th to 20th	Day	13% 3 10% 33% 30% 11%	488
	21st to end	Day	15% 4 11% 33% 28% 10%	595
June	1st to 10th	Day	16% 4 14% 33% 26% 7%	680
	11th to 20th	Day	12% 4 16% 38% 23% 7%	680
	21st to end	Day	10% 2 13% 32% 35% 8%	680
July	1st to 10th	Day	9% 2 9% 30% 37% 13%	671
	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% 24% 12% 3	422
November	1st to 10th	Day	30% 11% 24% 23% 11% 1	184
	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	24% 8% 20% 25% 18% 4	760
	21st to end	Night	27% 8% 15% 27% 18% 5%	836
April	1st to 10th	Night	21% 8% 17% 27% 21% 5%	760
	11th to 20th	Night	18% 7% 21% 29% 20% 5%	634
	21st to end	Night	19% 5% 16% 34% 22% 5%	546
May	1st to 10th	Night	12% 2 17% 31% 30% 8%	380
	11th to 20th	Night	14% 2 11% 26% 35% 12%	374
	21st to end	Night	14% 3 8% 33% 35% 7%	411
June	1st to 10th	Night	18% 3 11% 32% 30% 7%	380
	11th to 20th	Night	10% 4 15% 33% 31% 7%	380
	21st to end	Night	9% 4 11% 32% 36% 8%	380
July	1st to 10th	Night	8% 2 7% 25% 42% 15%	370
	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% 18% 26% 15% 5%	836
November	1st to 10th	Night	34% 7% 18% 27% 14% 1	748
	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 2024-10-31 00:39:20. Version ac07

Copyright © 2024 Attilla Danko.