Shawnigan Lake School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shawnigan Lake School Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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 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
45%
14631
11%
47070
9%
14604
48%
14604
17%
33147

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
29%
748
9%
2686
7%
746
33%
746
9%
2164
January16th to endNight
37%
781
9%
2718
8%
781
39%
781
11%
2095
February1st to 15thNight
30%
696
7%
2288
4%
696
35%
696
10%
1821
February16th to endNight
37%
632
12%
2053
10%
632
41%
632
14%
1517
March1st to 15thNight
30%
720
7%
2038
5%
720
32%
720
11%
1673
March16th to endNight
31%
768
8%
2091
4%
768
33%
768
12%
1660
April1st to 15thNight
42%
702
10%
1782
5%
702
44%
702
18%
1334
April16th to endNight
46%
532
11%
1612
7%
532
49%
532
19%
1142
May1st to 15thNight
57%
359
14%
1439
20%
359
61%
359
20%
876
May16th to endNight
61%
375
8%
1457
11%
374
64%
374
19%
901
June1st to 15thNight
55%
360
5%
1260
4%
360
56%
360
24%
772
June16th to endNight
58%
360
7%
1260
4%
360
59%
360
27%
737
July1st to 15thNight
76%
340
12%
1190
12%
340
77%
340
44%
565
July16th to endNight
82%
376
17%
1322
24%
354
85%
354
49%
561
August1st to 15thNight
80%
466
17%
1540
21%
464
81%
464
44%
737
August16th to endNight
74%
600
23%
1746
19%
600
75%
600
45%
919
September1st to 15thNight
78%
720
24%
1800
15%
720
78%
720
52%
991
September16th to endNight
56%
716
19%
1985
14%
716
57%
716
27%
1303
October1st to 15thNight
53%
720
11%
2160
10%
720
55%
720
24%
1444
October16th to endNight
39%
708
8%
2201
6%
708
43%
708
14%
1661
November1st to 15thNight
27%
700
7%
2450
5%
700
31%
700
8%
1979
November16th to endNight
33%
720
8%
2520
6%
720
38%
720
10%
1939
December1st to 15thNight
30%
732
6%
2592
4%
732
34%
732
9%
2042
December16th to endNight
24%
800
8%
2880
4%
800
29%
800
8%
2314

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
17%10%47%6%35%45%6%28%
48382
Night
17%8%36%5%35%45%6%33%
47223
Cloud CoverDay
15%9%37%6%35%5%5%6%30%
48382
Night
16%8%35%5%35%45%6%34%
47226
TransparencyDay
53%7%14%17%5%
48038
Night
50%6%15%18%7%1
47071
SeeingDay
19%11%24%25%15%3
6318
Night
20%9%14%27%22%5%
14642

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
26%13%5%9%7%45%44415%
1253
16th to endDay
22%13%5%8%7%46%446%14%
1505
February1st to 15thDay
25%17%49%6%2445%6%14%
1576
16th to endDay
17%15%48%7%45%5%6%7%18%
1421
March1st to 15thDay
23%14%6%10%8%45%5%45%11%
1920
16th to endDay
23%16%5%9%8%46%34314%
2133
April1st to 15thDay
19%14%49%8%46%5%5%5%15%
2164
16th to endDay
20%13%5%8%6%5%4445%19%
2346
May1st to 15thDay
16%9%37%7%46%5%5%6%26%
2511
16th to endDay
18%11%47%7%46%5%5%7%21%
2652
June1st to 15thDay
16%10%37%6%46%5%5%7%25%
2700
16th to endDay
14%8%38%7%45%5%6%6%28%
2700
July1st to 15thDay
8%5%25%424446%49%
2700
16th to endDay
8%42332445%6%54%
2754
August1st to 15thDay
9%5%25%5%24446%47%
2409
16th to endDay
7%5%26%6%35%46%9%43%
2456
September1st to 15thDay
8%5%2442335%8%50%
2160
16th to endDay
18%7%36%6%3445%6%33%
1974
October1st to 15thDay
20%10%26%6%36%45%6%28%
1800
16th to endDay
24%10%37%6%25%46%7%21%
1691
November1st to 15thDay
29%10%5%9%6%345%4316%
1408
16th to endDay
25%13%48%5%26%5%5%5%17%
1440
December1st to 15thDay
20%15%5%7%7%45%445%19%
1365
16th to endDay
27%16%46%435%5%4416%
1344
January1st to 15thNight
26%11%46%5%46%34421%
2686
16th to endNight
21%11%36%6%45%5%5%7%21%
2718
February1st to 15thNight
23%12%47%7%34446%21%
2276
16th to endNight
17%10%36%6%45%46%7%28%
2053
March1st to 15thNight
21%10%36%8%47%6%5%6%20%
2038
16th to endNight
18%12%47%6%46%5%5%7%21%
2087
April1st to 15thNight
16%8%27%6%35%5%5%7%29%
1782
16th to endNight
17%8%35%5%35%45%7%31%
1612
May1st to 15thNight
12%5%25%6%25%46%6%42%
1439
16th to endNight
9%6%36%5%35%6%7%9%36%
1457
June1st to 15thNight
11%6%25%7%24347%43%
1260
16th to endNight
8%325%5%35%6%6%11%41%
1260
July1st to 15thNight
5%313312237%64%
1260
16th to endNight
412112247%69%
1413
August1st to 15thNight
3213314347%64%
1548
16th to endNight
5%31231435%8%58%
1746
September1st to 15thNight
5%22323346%64%
1800
16th to endNight
13%7%245%2346%8%39%
1985
October1st to 15thNight
16%5%35%5%35%44440%
2160
16th to endNight
24%8%26%6%3445%6%25%
2201
November1st to 15thNight
27%9%47%6%45%445%19%
2450
16th to endNight
23%9%47%6%45%445%24%
2520
December1st to 15thNight
19%14%5%7%6%45%5%4421%
2592
16th to endNight
26%13%47%6%35%44419%
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
25%13%5%8%7%35%5%35%15%
1253
16th to endDay
21%15%5%9%8%45%35%414%
1505
February1st to 15thDay
25%15%48%6%2445%6%15%
1576
16th to endDay
15%13%5%8%8%46%45%8%18%
1421
March1st to 15thDay
23%12%5%10%7%45%5%6%5%14%
1920
16th to endDay
21%13%49%9%36%44417%
2133
April1st to 15thDay
18%9%5%9%7%47%6%5%6%19%
2164
16th to endDay
18%10%48%7%5%5%5%6%5%21%
2346
May1st to 15thDay
13%7%47%6%46%5%6%6%31%
2511
16th to endDay
14%9%38%6%36%6%6%8%25%
2652
June1st to 15thDay
12%7%37%6%36%5%6%7%30%
2700
16th to endDay
12%7%36%7%35%5%7%7%31%
2700
July1st to 15thDay
7%42442445%7%53%
2700
16th to endDay
6%313324446%58%
2754
August1st to 15thDay
6%415%42445%7%51%
2409
16th to endDay
6%3245%345%6%9%48%
2456
September1st to 15thDay
6%325%42336%9%51%
2160
16th to endDay
17%6%26%5%345%5%6%35%
1974
October1st to 15thDay
18%10%37%6%4445%6%29%
1800
16th to endDay
21%11%5%8%6%345%5%6%22%
1691
November1st to 15thDay
28%10%48%6%35%5%4418%
1408
16th to endDay
24%12%5%7%7%3445%6%17%
1440
December1st to 15thDay
20%14%47%7%26%45%420%
1365
16th to endDay
25%13%48%6%345%5%5%16%
1344
January1st to 15thNight
25%11%36%5%45%44422%
2685
16th to endNight
21%10%36%6%35%5%5%7%22%
2718
February1st to 15thNight
23%12%36%6%35%5%46%22%
2276
16th to endNight
17%10%46%5%3446%6%29%
2053
March1st to 15thNight
20%10%46%7%45%6%6%5%21%
2038
16th to endNight
17%10%48%7%36%5%6%6%23%
2091
April1st to 15thNight
15%8%26%7%35%46%7%31%
1782
16th to endNight
17%7%25%6%35%5%5%8%32%
1612
May1st to 15thNight
11%5%25%435%5%5%5%44%
1439
16th to endNight
8%5%36%435%7%6%9%38%
1457
June1st to 15thNight
10%6%36%435%45%6%43%
1260
16th to endNight
8%423335%5%5%12%43%
1260
July1st to 15thNight
5%313223336%65%
1260
16th to endNight
412113237%70%
1413
August1st to 15thNight
2212413446%65%
1548
16th to endNight
5%31331335%8%60%
1746
September1st to 15thNight
5%212223346%65%
1800
16th to endNight
13%5%25%5%345%5%9%40%
1985
October1st to 15thNight
15%6%25%5%34445%41%
2160
16th to endNight
23%8%36%5%345%5%6%26%
2201
November1st to 15thNight
27%9%36%7%46%5%35%20%
2450
16th to endNight
22%9%46%6%35%446%24%
2520
December1st to 15thNight
20%13%48%6%35%45%5%21%
2592
16th to endNight
24%13%47%435%44421%
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
72%6%6%9%4
1253
16th to endDay
71%410%10%2
1505
February1st to 15thDay
71%5%10%8%4
1576
16th to endDay
63%6%12%12%4
1421
March1st to 15thDay
73%6%10%7%1
1920
16th to endDay
72%5%9%10%1
2133
April1st to 15thDay
64%9%10%12%2
2164
16th to endDay
60%9%12%12%3
2346
May1st to 15thDay
52%9%13%17%6%
2511
16th to endDay
55%9%16%15%1
2656
June1st to 15thDay
49%11%19%14%4
2700
16th to endDay
48%9%19%17%4
2700
July1st to 15thDay
31%8%17%28%11%2
2541
16th to endDay
23%9%22%33%11%1
2582
August1st to 15thDay
30%8%18%30%9%2
2392
16th to endDay
31%8%22%28%7%1
2456
September1st to 15thDay
29%7%18%26%16%1
2160
16th to endDay
49%7%15%18%7%1
1974
October1st to 15thDay
55%7%13%16%6%
1800
16th to endDay
62%5%16%11%3
1691
November1st to 15thDay
69%5%9%10%31
1408
16th to endDay
69%411%12%2
1440
December1st to 15thDay
68%6%11%10%3
1365
16th to endDay
70%410%9%3
1344
January1st to 15thNight
66%6%9%12%5%
2686
16th to endNight
61%6%11%13%5%1
2718
February1st to 15thNight
63%6%13%11%4
2288
16th to endNight
56%5%14%17%5%
2053
March1st to 15thNight
63%8%11%13%3
2038
16th to endNight
61%6%14%15%3
2091
April1st to 15thNight
50%8%15%20%5%
1782
16th to endNight
49%7%16%20%5%
1612
May1st to 15thNight
40%6%16%23%10%
1440
16th to endNight
39%9%22%23%4
1457
June1st to 15thNight
41%425%23%41
1260
16th to endNight
34%7%26%23%5%2
1260
July1st to 15thNight
21%420%34%13%5%
1190
16th to endNight
15%6%23%36%16%2
1322
August1st to 15thNight
19%6%22%33%13%4
1540
16th to endNight
22%5%24%32%11%3
1746
September1st to 15thNight
20%419%27%20%6%
1800
16th to endNight
40%6%16%22%11%2
1985
October1st to 15thNight
44%5%17%19%11%
2160
16th to endNight
56%6%16%14%6%
2201
November1st to 15thNight
67%5%10%11%31
2450
16th to endNight
61%5%13%11%7%
2520
December1st to 15thNight
64%5%13%11%3
2592
16th to endNight
67%5%11%11%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
23%6%18%16%26%8%
60
16th to endDay
42%15%18%13%9%1
111
February1st to 15thDay
38%17%22%15%5%
236
16th to endDay
26%24%23%17%7%1
211
March1st to 15thDay
37%25%20%13%2
270
16th to endDay
31%20%25%16%41
288
April1st to 15thDay
24%15%28%18%10%1
269
16th to endDay
22%17%28%19%10%1
270
May1st to 15thDay
20%11%27%27%11%2
288
16th to endDay
16%8%24%28%17%4
367
June1st to 15thDay
12%10%28%28%16%2
495
16th to endDay
12%11%30%27%16%2
495
July1st to 15thDay
9%5%18%34%28%4
475
16th to endDay
6%421%33%26%6%
423
August1st to 15thDay
8%5%13%32%28%11%
315
16th to endDay
7%5%21%35%21%8%
332
September1st to 15thDay
11%427%29%23%3
315
16th to endDay
20%10%24%24%17%2
315
October1st to 15thDay
26%10%24%22%14%1
315
16th to endDay
26%18%24%19%8%2
224
November1st to 15thDay
43%11%28%11%5%
60
16th to endDay
26%13%21%11%11%15%
60
December1st to 15thDay
36%16%20%21%31
60
16th to endDay
29%14%25%18%9%3
64
January1st to 15thNight
31%13%15%20%15%3
750
16th to endNight
27%8%14%25%19%3
781
February1st to 15thNight
28%14%14%22%17%2
704
16th to endNight
20%13%17%27%17%3
632
March1st to 15thNight
26%16%18%21%13%2
720
16th to endNight
22%14%19%27%12%3
768
April1st to 15thNight
18%11%16%28%20%4
702
16th to endNight
20%7%16%35%16%2
532
May1st to 15thNight
13%6%14%37%22%5%
360
16th to endNight
10%315%35%30%5%
375
June1st to 15thNight
12%6%18%28%29%3
360
16th to endNight
9%7%17%35%23%6%
360
July1st to 15thNight
428%32%43%8%
340
16th to endNight
318%28%45%12%
376
August1st to 15thNight
41423%49%17%
466
16th to endNight
7%310%26%41%11%
600
September1st to 15thNight
6%26%29%37%16%
720
16th to endNight
17%313%28%28%9%
716
October1st to 15thNight
19%5%13%31%23%6%
720
16th to endNight
28%6%14%25%17%6%
708
November1st to 15thNight
31%13%17%26%9%1
700
16th to endNight
26%11%17%21%17%5%
720
December1st to 15thNight
27%13%14%28%14%1
732
16th to endNight
30%13%20%25%8%1
800
Page generated at 2017-10-17 13:35:25. Version ac04

Copyright 2017 A. Danko


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