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 2005-11-05 to 2017-08-12.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
46%
14371
10%
46377
8%
14345
48%
14345
16%
33748

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
30%
748
9%
2686
7%
746
34%
746
8%
2191
January16th to endNight
35%
781
8%
2730
7%
781
38%
781
10%
2192
February1st to 15thNight
35%
696
7%
2288
5%
696
38%
696
9%
1864
February16th to endNight
38%
632
12%
2053
10%
632
42%
632
14%
1521
March1st to 15thNight
31%
720
6%
2040
4%
720
34%
720
10%
1694
March16th to endNight
36%
768
8%
2088
4%
768
38%
768
12%
1707
April1st to 15thNight
44%
704
9%
1784
4%
704
46%
704
19%
1353
April16th to endNight
49%
525
11%
1605
10%
525
51%
525
17%
1176
May1st to 15thNight
58%
359
14%
1439
21%
359
62%
359
21%
876
May16th to endNight
62%
374
7%
1452
12%
374
63%
374
18%
948
June1st to 15thNight
58%
360
3%
1260
3%
360
58%
360
21%
824
June16th to endNight
63%
360
7%
1260
4%
360
63%
360
23%
797
July1st to 15thNight
79%
340
11%
1190
11%
340
80%
340
39%
605
July16th to endNight
84%
376
16%
1319
23%
354
87%
354
44%
590
August1st to 15thNight
82%
445
17%
1495
21%
443
82%
443
43%
731
August16th to endNight
74%
550
20%
1600
18%
550
74%
550
39%
884
September1st to 15thNight
77%
660
23%
1650
14%
660
78%
660
49%
931
September16th to endNight
55%
656
18%
1817
14%
656
57%
656
26%
1232
October1st to 15thNight
51%
660
11%
1980
10%
660
53%
660
23%
1356
October16th to endNight
39%
704
7%
2193
6%
704
43%
704
13%
1704
November1st to 15thNight
28%
700
6%
2450
6%
700
31%
700
8%
2015
November16th to endNight
33%
720
7%
2520
5%
720
36%
720
9%
2023
December1st to 15thNight
28%
733
5%
2598
4%
733
31%
733
8%
2150
December16th to endNight
22%
800
7%
2880
3%
800
27%
800
7%
2384

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 ForecastData
Points
Cloud CoverDay
16%8%36%6%35%5%5%6%31%
47631
Night
18%8%36%5%35%45%6%33%
46530
Cloud CoverDay
17%8%36%5%35%5%5%6%32%
47631
Night
20%8%35%5%3445%6%32%
46533
TransparencyDay
50%10%16%15%5%
47287
Night
52%7%14%17%6%1
46378
SeeingDay
18%314%28%26%8%
6048
Night
23%5%16%25%22%7%
14383

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
27%12%5%9%7%35%44414%
1253
16th to endDay
25%14%5%10%6%46%5%35%12%
1492
February1st to 15thDay
28%14%47%5%345%5%417%
1576
16th to endDay
16%12%5%7%7%46%5%5%6%20%
1421
March1st to 15thDay
23%12%5%9%7%45%5%5%5%14%
1917
16th to endDay
21%11%5%9%7%35%445%20%
2136
April1st to 15thDay
16%9%47%8%45%6%7%7%19%
2163
16th to endDay
17%9%47%7%47%5%6%6%23%
2355
May1st to 15thDay
12%6%36%6%45%5%6%6%35%
2511
16th to endDay
13%8%48%5%46%6%5%8%28%
2657
June1st to 15thDay
12%6%37%6%35%6%7%8%32%
2700
16th to endDay
13%5%25%6%46%6%7%8%33%
2700
July1st to 15thDay
6%324424446%55%
2700
16th to endDay
6%21332445%7%59%
2757
August1st to 15thDay
7%313423446%55%
2372
16th to endDay
6%5%15%6%35%5%5%8%47%
2249
September1st to 15thDay
7%41442445%7%52%
1980
16th to endDay
18%6%26%5%33447%35%
1812
October1st to 15thDay
20%9%36%6%3445%6%28%
1650
16th to endDay
24%13%47%5%34447%21%
1678
November1st to 15thDay
29%12%45%5%34445%18%
1408
16th to endDay
26%9%5%7%8%45%5%45%17%
1440
December1st to 15thDay
22%15%47%7%2444421%
1360
16th to endDay
26%12%48%6%37%445%15%
1344
January1st to 15thNight
27%11%37%6%35%33422%
2686
16th to endNight
24%10%37%5%35%5%46%21%
2730
February1st to 15thNight
25%11%47%5%25%45%5%21%
2276
16th to endNight
19%8%46%6%245%46%30%
2053
March1st to 15thNight
23%10%36%6%36%6%5%5%21%
2040
16th to endNight
20%8%48%7%35%5%6%6%22%
2084
April1st to 15thNight
16%7%37%6%35%5%5%7%30%
1784
16th to endNight
16%8%25%5%36%5%5%8%31%
1605
May1st to 15thNight
12%5%23435%5%5%7%42%
1439
16th to endNight
9%5%36%5%36%5%7%9%36%
1452
June1st to 15thNight
10%6%35%6%45%46%7%39%
1260
16th to endNight
10%414436%5%8%9%40%
1260
July1st to 15thNight
4312323346%63%
1260
16th to endNight
4212214235%68%
1410
August1st to 15thNight
323323345%65%
1503
16th to endNight
5%31432346%7%57%
1600
September1st to 15thNight
6%212323446%64%
1650
16th to endNight
13%6%25%5%2445%8%40%
1817
October1st to 15thNight
17%7%25%4235%45%40%
1980
16th to endNight
25%7%26%5%3445%6%27%
2193
November1st to 15thNight
28%9%47%6%345%45%19%
2450
16th to endNight
24%9%46%7%35%445%23%
2520
December1st to 15thNight
21%14%5%8%7%46%44418%
2598
16th to endNight
26%13%5%7%5%3444420%
2880

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
31%12%5%7%6%4434414%
1253
16th to endDay
26%15%5%9%7%45%435%12%
1492
February1st to 15thDay
28%14%47%6%3434417%
1576
16th to endDay
19%12%47%6%45%5%5%6%21%
1421
March1st to 15thDay
26%12%5%9%6%35%5%5%5%13%
1917
16th to endDay
22%11%5%9%7%36%445%21%
2136
April1st to 15thDay
17%9%48%7%45%6%6%9%20%
2163
16th to endDay
17%8%47%6%46%6%6%6%25%
2355
May1st to 15thDay
12%7%25%6%46%6%6%7%36%
2511
16th to endDay
13%7%38%6%45%5%5%8%31%
2657
June1st to 15thDay
13%6%36%6%35%5%6%7%34%
2700
16th to endDay
14%5%26%5%35%5%6%8%35%
2700
July1st to 15thDay
6%31432445%6%56%
2700
16th to endDay
6%21221345%6%61%
2757
August1st to 15thDay
7%413323347%57%
2372
16th to endDay
6%4246%445%5%8%47%
2249
September1st to 15thDay
7%5%2442445%8%51%
1980
16th to endDay
18%7%26%5%34447%35%
1812
October1st to 15thDay
22%9%46%5%335%6%7%26%
1650
16th to endDay
25%13%37%43445%7%20%
1678
November1st to 15thDay
32%12%445%35%35%419%
1408
16th to endDay
27%10%5%8%7%35%5%45%16%
1440
December1st to 15thDay
25%15%47%6%35%44320%
1360
16th to endDay
28%11%48%6%46%45%5%15%
1344
January1st to 15thNight
30%10%36%5%45%33421%
2685
16th to endNight
26%10%36%6%35%45%6%21%
2730
February1st to 15thNight
27%11%36%5%35%446%21%
2276
16th to endNight
21%9%35%6%3445%6%29%
2053
March1st to 15thNight
26%9%46%6%35%5%5%5%21%
2040
16th to endNight
22%8%47%7%445%5%6%21%
2088
April1st to 15thNight
16%8%38%5%36%45%7%29%
1784
16th to endNight
18%7%36%5%35%6%5%7%29%
1605
May1st to 15thNight
12%5%245%26%45%7%43%
1439
16th to endNight
10%7%37%6%35%5%7%8%35%
1452
June1st to 15thNight
11%6%35%7%345%5%6%38%
1260
16th to endNight
10%4246%26%6%7%10%39%
1260
July1st to 15thNight
5%313423335%63%
1260
16th to endNight
3212214246%67%
1410
August1st to 15thNight
321233335%5%65%
1503
16th to endNight
6%41332346%7%56%
1600
September1st to 15thNight
6%212313436%63%
1650
16th to endNight
14%6%35%5%2445%7%40%
1817
October1st to 15thNight
19%7%2432444440%
1980
16th to endNight
26%8%25%5%345%5%5%26%
2193
November1st to 15thNight
31%9%46%5%345%45%19%
2450
16th to endNight
25%10%5%6%6%44445%22%
2520
December1st to 15thNight
24%14%49%6%35%44417%
2598
16th to endNight
29%13%5%6%5%3444320%
2880

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
73%7%7%7%3
1253
16th to endDay
74%7%7%7%2
1492
February1st to 15thDay
69%9%7%8%4
1576
16th to endDay
61%8%13%13%3
1421
March1st to 15thDay
70%9%11%6%1
1917
16th to endDay
65%8%13%10%1
2136
April1st to 15thDay
58%13%14%11%2
2163
16th to endDay
54%12%14%13%4
2355
May1st to 15thDay
45%11%18%16%7%
2511
16th to endDay
48%12%20%15%2
2661
June1st to 15thDay
45%11%21%14%4
2700
16th to endDay
43%11%22%17%4
2700
July1st to 15thDay
26%11%21%25%11%2
2541
16th to endDay
20%9%25%31%11%1
2585
August1st to 15thDay
27%9%21%29%9%2
2355
16th to endDay
32%10%23%24%7%1
2249
September1st to 15thDay
30%11%20%22%14%1
1980
16th to endDay
48%9%15%17%8%
1812
October1st to 15thDay
55%11%13%12%6%
1650
16th to endDay
62%11%13%8%3
1678
November1st to 15thDay
68%7%10%9%31
1408
16th to endDay
68%8%9%11%2
1440
December1st to 15thDay
69%6%8%10%5%
1360
16th to endDay
69%8%9%7%3
1344
January1st to 15thNight
67%6%9%10%5%
2686
16th to endNight
63%8%10%12%31
2730
February1st to 15thNight
64%8%10%11%41
2288
16th to endNight
54%8%13%17%5%
2053
March1st to 15thNight
64%8%10%12%3
2040
16th to endNight
61%9%11%14%2
2088
April1st to 15thNight
53%7%15%17%4
1784
16th to endNight
52%8%13%19%6%
1605
May1st to 15thNight
38%9%17%21%12%1
1440
16th to endNight
43%9%21%20%4
1452
June1st to 15thNight
43%8%20%21%42
1260
16th to endNight
38%9%20%22%6%2
1260
July1st to 15thNight
24%6%16%32%15%4
1190
16th to endNight
18%6%20%31%19%2
1319
August1st to 15thNight
20%6%22%30%15%4
1495
16th to endNight
25%8%21%31%9%3
1600
September1st to 15thNight
21%6%19%27%19%5%
1650
16th to endNight
41%7%15%23%9%2
1817
October1st to 15thNight
47%5%17%19%10%
1980
16th to endNight
58%8%15%12%4
2193
November1st to 15thNight
66%8%11%9%21
2450
16th to endNight
64%8%10%10%6%
2520
December1st to 15thNight
68%7%10%10%3
2598
16th to endNight
68%7%9%9%4
2880

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%325%13%31%10%
60
16th to endDay
43%418%20%8%2
101
February1st to 15thDay
38%5%19%20%16%
236
16th to endDay
24%10%21%25%12%6%
211
March1st to 15thDay
38%8%22%18%10%1
270
16th to endDay
29%6%25%25%9%3
288
April1st to 15thDay
21%5%20%30%18%5%
269
16th to endDay
21%216%38%17%4
270
May1st to 15thDay
14%315%34%26%5%
288
16th to endDay
13%28%26%33%15%
372
June1st to 15thDay
12%213%32%30%8%
495
16th to endDay
13%213%32%32%6%
495
July1st to 15thDay
6%5%31%40%14%
475
16th to endDay
5%16%28%44%13%
426
August1st to 15thDay
8%1327%41%18%
300
16th to endDay
7%19%30%40%10%
268
September1st to 15thDay
10%112%34%27%13%
255
16th to endDay
21%118%32%20%5%
255
October1st to 15thDay
27%5%18%24%20%2
255
16th to endDay
32%420%25%14%3
215
November1st to 15thDay
41%325%25%5%
60
16th to endDay
31%5%8%23%18%13%
60
December1st to 15thDay
41%5%23%18%11%
60
16th to endDay
25%10%20%31%12%
64
January1st to 15thNight
35%7%16%20%16%3
750
16th to endNight
30%5%18%23%18%3
781
February1st to 15thNight
28%8%16%25%17%2
704
16th to endNight
24%7%20%27%16%4
632
March1st to 15thNight
29%8%22%22%12%4
720
16th to endNight
27%7%18%28%14%4
768
April1st to 15thNight
18%7%17%27%22%5%
704
16th to endNight
21%313%32%24%4
525
May1st to 15thNight
15%116%29%28%9%
360
16th to endNight
12%210%29%35%10%
375
June1st to 15thNight
14%310%30%31%9%
360
16th to endNight
11%211%35%31%7%
360
July1st to 15thNight
6%6%23%45%16%
340
16th to endNight
5%15%22%47%18%
376
August1st to 15thNight
5%419%46%24%
445
16th to endNight
9%17%24%42%15%
550
September1st to 15thNight
8%7%24%36%22%
660
16th to endNight
17%314%24%27%12%
656
October1st to 15thNight
23%215%27%22%9%
660
16th to endNight
30%416%24%17%6%
704
November1st to 15thNight
34%6%21%24%11%1
700
16th to endNight
30%8%19%22%14%5%
720
December1st to 15thNight
30%8%20%24%13%2
733
16th to endNight
35%8%26%20%8%1
800
Page generated at 2017-08-13 11:16:24. Version ac04

Copyright 2017 A. Danko


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