Sechelt
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sechelt clear sky chart from 2005-11-06 to 2024-02-10.

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
40%
22715
9%
80885
8%
22592
43%
22592
13%
61545

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 10thNight
20%
838
8%
4704
6%
816
23%
816
4%
3916
January11th to 20thNight
28%
841
10%
4676
5%
820
30%
820
5%
3408
January21st to endNight
28%
875
4%
4936
7%
848
31%
848
4%
4436
February1st to 10thNight
28%
758
9%
2462
5%
758
33%
758
9%
2029
February11th to 20thNight
35%
700
9%
2274
8%
700
38%
700
11%
1799
February21st to endNight
30%
592
10%
1924
8%
592
34%
592
12%
1493
March1st to 10thNight
33%
720
7%
2081
6%
720
34%
720
12%
1688
March11th to 20thNight
30%
720
9%
1980
6%
720
31%
720
11%
1634
March21st to endNight
32%
792
7%
2147
3%
792
34%
792
10%
1818
April1st to 10thNight
38%
720
7%
1800
3%
720
39%
720
14%
1460
April11th to 20thNight
39%
579
12%
1647
8%
579
41%
579
15%
1272
April21st to endNight
42%
513
11%
1593
8%
513
45%
513
15%
1190
May1st to 10thNight
52%
360
12%
1440
18%
360
55%
360
18%
942
May11th to 20thNight
56%
354
10%
1416
17%
354
58%
354
15%
964
May21st to endNight
52%
389
7%
1436
10%
388
54%
388
16%
995
June1st to 10thNight
48%
360
3%
1260
4%
360
48%
360
15%
907
June11th to 20thNight
49%
360
3%
1260
1%
360
50%
360
15%
914
June21st to endNight
62%
360
6%
1260
2%
360
63%
360
21%
817
July1st to 10thNight
64%
350
6%
1225
4%
350
65%
350
27%
725
July11th to 20thNight
72%
348
12%
1218
14%
348
73%
348
33%
649
July21st to endNight
80%
394
16%
1384
23%
372
82%
372
40%
661
August1st to 10thNight
76%
403
16%
1469
22%
401
77%
401
35%
735
August11th to 20thNight
80%
534
20%
1602
20%
534
81%
534
41%
868
August21st to endNight
63%
619
19%
1807
16%
619
64%
619
29%
1138
September1st to 10thNight
69%
720
20%
1800
11%
720
71%
720
39%
1121
September11th to 20thNight
55%
720
18%
1836
11%
720
57%
720
26%
1296
September21st to endNight
49%
720
15%
2040
11%
720
51%
720
22%
1433
October1st to 10thNight
52%
720
11%
2160
11%
720
53%
720
23%
1486
October11th to 20thNight
42%
720
11%
2160
10%
720
45%
720
16%
1627
October21st to endNight
34%
792
11%
2536
8%
792
38%
792
13%
1927
November1st to 10thNight
26%
740
6%
2590
5%
740
28%
740
7%
2154
November11th to 20thNight
28%
760
7%
2660
6%
760
31%
760
9%
2156
November21st to endNight
26%
760
7%
2660
5%
760
30%
760
9%
2150
December1st to 10thNight
32%
802
9%
2750
7%
802
34%
802
9%
2208
December11th to 20thNight
20%
850
3%
3516
2%
849
22%
849
5%
3092
December21st to endNight
18%
932
5%
5176
4%
905
24%
905
4%
4437

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
23%8%36%5%345%5%7%31%
77779
Night
27%9%36%5%3445%6%27%
81135
TransparencyDay
54%10%13%15%7%1
77485
Night
58%8%12%14%7%1
81009
SeeingDay
23%5%18%27%22%5%
14427
Night
30%5%16%24%20%5%
22743

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 10thDay
40%11%35%5%44445%14%
2219
11th to 20thDay
28%14%49%7%445%6%6%15%
2199
21st to endDay
46%13%46%6%345%337%
2716
February1st to 10thDay
31%12%47%6%45%45%6%15%
1702
11th to 20thDay
27%10%47%6%36%5%6%6%20%
1575
21st to endDay
22%11%38%7%5%6%5%5%8%20%
1332
March1st to 10thDay
28%11%48%6%45%45%6%20%
1874
11th to 20thDay
30%11%5%8%7%34345%19%
1980
21st to endDay
27%10%48%7%4445%5%22%
2209
April1st to 10thDay
26%10%37%7%35%5%48%22%
2160
11th to 20thDay
22%8%47%6%46%46%7%26%
2261
21st to endDay
22%9%46%5%3445%7%30%
2366
May1st to 10thDay
16%7%37%6%35%46%7%37%
2520
11th to 20thDay
16%7%36%6%36%6%6%9%32%
2477
21st to endDay
18%7%36%6%35%5%6%7%33%
2838
June1st to 10thDay
20%8%36%5%445%6%9%30%
2700
11th to 20thDay
17%7%36%6%46%6%7%8%30%
2700
21st to endDay
15%5%36%5%3446%8%41%
2700
July1st to 10thDay
10%5%36%43445%7%49%
2700
11th to 20thDay
11%423434448%53%
2700
21st to endDay
7%413423347%62%
2850
August1st to 10thDay
10%423433446%56%
2459
11th to 20thDay
7%5%35%4245%5%7%55%
2298
21st to endDay
10%425%5%445%6%9%46%
2548
September1st to 10thDay
11%6%25%4345%5%8%46%
2160
11th to 20thDay
18%6%36%5%245%5%7%38%
2121
21st to endDay
22%6%25%6%35%5%6%8%33%
1919
October1st to 10thDay
24%8%35%5%36%5%6%7%31%
1800
11th to 20thDay
30%9%46%5%35%45%7%22%
1800
21st to endDay
31%8%36%5%35%46%6%22%
1815
November1st to 10thDay
37%9%37%5%25%5%5%5%17%
1488
11th to 20thDay
34%12%46%43446%5%18%
1520
21st to endDay
36%10%46%6%335%4418%
1520
December1st to 10thDay
29%14%48%6%34446%20%
1426
11th to 20thDay
37%13%5%8%6%35%5%4410%
1685
21st to endDay
38%16%47%5%3444411%
2442
January1st to 10thNight
36%13%5%8%6%3443414%
4726
11th to 20thNight
30%10%48%6%445%7%8%16%
4699
21st to endNight
46%14%46%5%3333410%
4936
February1st to 10thNight
32%12%47%5%4445%5%19%
2462
11th to 20thNight
25%11%48%5%345%5%5%25%
2272
21st to endNight
28%10%46%5%45%346%24%
1924
March1st to 10thNight
29%10%38%6%35%5%5%5%22%
2081
11th to 20thNight
32%10%47%5%33346%22%
1979
21st to endNight
28%9%48%7%35%5%5%6%20%
2147
April1st to 10thNight
25%11%36%6%45%5%5%6%24%
1800
11th to 20thNight
20%9%5%7%8%36%5%5%7%26%
1647
21st to endNight
23%9%36%5%35%45%8%29%
1593
May1st to 10thNight
18%6%35%5%35%5%5%6%39%
1440
11th to 20thNight
17%8%46%6%46%5%7%8%31%
1416
21st to endNight
16%7%38%6%45%5%5%7%33%
1436
June1st to 10thNight
20%10%38%6%45%345%33%
1260
11th to 20thNight
17%9%47%6%445%5%8%30%
1260
21st to endNight
12%5%36%5%35%5%6%7%42%
1260
July1st to 10thNight
10%6%26%5%34436%51%
1260
11th to 20thNight
7%4245%3436%7%54%
1260
21st to endNight
6%32333435%6%63%
1465
August1st to 10thNight
6%42442335%6%61%
1477
11th to 20thNight
5%314325%45%8%59%
1602
21st to endNight
12%4246%445%5%7%46%
1807
September1st to 10thNight
9%32443445%7%55%
1800
11th to 20thNight
18%6%35%4345%46%41%
1836
21st to endNight
21%7%36%423446%39%
2040
October1st to 10thNight
21%7%35%5%3435%6%39%
2160
11th to 20thNight
29%8%25%444445%30%
2160
21st to endNight
32%8%26%5%34445%28%
2536
November1st to 10thNight
37%9%46%6%33445%18%
2590
11th to 20thNight
34%10%36%6%35%45%5%21%
2660
21st to endNight
36%9%36%5%345%45%20%
2660
December1st to 10thNight
29%12%47%6%45%45%5%21%
2750
11th to 20thNight
42%14%46%5%3343411%
3520
21st to endNight
37%15%5%8%6%3333314%
5214

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 10thDay
70%10%9%7%41
2219
11th to 20thDay
62%10%11%7%8%1
2220
21st to endDay
82%5%7%5%1
2716
February1st to 10thDay
69%8%9%8%32
1702
11th to 20thDay
62%8%11%13%5%1
1584
21st to endDay
63%10%11%10%42
1332
March1st to 10thDay
65%10%11%9%4
1874
11th to 20thDay
70%7%8%11%41
1980
21st to endDay
65%9%11%11%3
2209
April1st to 10thDay
64%11%11%10%4
2160
11th to 20thDay
59%10%10%13%7%1
2261
21st to endDay
59%9%10%13%8%1
2366
May1st to 10thDay
50%11%15%17%6%1
2520
11th to 20thDay
51%10%14%20%5%1
2480
21st to endDay
52%11%13%20%4
2839
June1st to 10thDay
54%10%16%13%42
2700
11th to 20thDay
55%13%15%12%5%
2700
21st to endDay
44%10%17%18%8%2
2700
July1st to 10thDay
38%10%16%23%10%3
2626
11th to 20thDay
30%11%19%29%10%1
2619
21st to endDay
23%9%19%32%13%4
2691
August1st to 10thDay
31%11%16%28%12%2
2442
11th to 20thDay
28%10%20%26%14%3
2298
21st to endDay
36%12%18%27%6%1
2548
September1st to 10thDay
38%9%16%23%11%3
2160
11th to 20thDay
46%8%12%18%13%2
2121
21st to endDay
48%12%14%15%9%1
1919
October1st to 10thDay
50%10%16%15%10%
1800
11th to 20thDay
60%10%13%12%41
1800
21st to endDay
61%7%13%11%7%1
1815
November1st to 10thDay
69%8%9%7%5%1
1488
11th to 20thDay
67%8%9%8%6%2
1520
21st to endDay
67%6%8%11%7%1
1520
December1st to 10thDay
65%7%9%11%6%1
1426
11th to 20thDay
74%9%8%6%21
1688
21st to endDay
76%7%7%6%21
2442
January1st to 10thNight
73%6%7%10%31
4726
11th to 20thNight
60%8%14%10%7%1
4740
21st to endNight
80%6%5%7%21
4936
February1st to 10thNight
67%7%8%10%5%2
2462
11th to 20thNight
62%8%11%12%7%1
2274
21st to endNight
60%7%11%14%7%2
1924
March1st to 10thNight
62%9%12%12%5%
2081
11th to 20thNight
66%6%9%12%6%1
1980
21st to endNight
66%10%11%11%3
2147
April1st to 10thNight
60%9%12%16%3
1800
11th to 20thNight
56%9%9%17%8%1
1647
21st to endNight
54%9%11%16%9%
1593
May1st to 10thNight
45%9%17%22%7%
1440
11th to 20thNight
47%11%18%19%5%1
1416
21st to endNight
48%9%17%20%5%
1436
June1st to 10thNight
53%7%15%17%44
1260
11th to 20thNight
52%9%18%15%5%
1260
21st to endNight
40%10%18%19%9%3
1260
July1st to 10thNight
35%8%16%25%13%4
1225
11th to 20thNight
28%8%24%28%11%2
1218
21st to endNight
21%8%16%32%19%5%
1384
August1st to 10thNight
25%7%19%28%18%3
1469
11th to 20thNight
21%11%23%24%16%6%
1602
21st to endNight
35%10%17%29%9%1
1807
September1st to 10thNight
29%8%17%27%15%3
1800
11th to 20thNight
44%8%11%16%16%5%
1836
21st to endNight
46%8%15%20%9%2
2040
October1st to 10thNight
45%8%15%20%12%1
2160
11th to 20thNight
57%6%13%17%7%
2160
21st to endNight
60%6%11%15%8%
2536
November1st to 10thNight
69%7%10%8%5%1
2590
11th to 20thNight
66%8%10%10%5%2
2660
21st to endNight
66%7%9%9%7%1
2660
December1st to 10thNight
66%6%9%12%6%1
2750
11th to 20thNight
77%6%7%5%4
3516
21st to endNight
75%6%6%9%31
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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
44%6%18%19%7%6%
180
11th to 20thDay
38%9%24%17%12%1
180
21st to endDay
46%6%18%20%9%2
245
February1st to 10thDay
38%9%23%20%11%1
368
11th to 20thDay
34%5%27%22%11%1
335
21st to endDay
26%11%25%23%12%3
280
March1st to 10thDay
31%8%20%23%17%1
414
11th to 20thDay
29%11%16%25%15%3
420
21st to endDay
30%7%24%25%10%3
462
April1st to 10thDay
31%8%25%20%14%2
420
11th to 20thDay
26%6%26%21%16%5%
412
21st to endDay
24%6%24%27%15%3
420
May1st to 10thDay
16%319%35%24%3
423
11th to 20thDay
17%413%31%28%7%
448
21st to endDay
15%5%15%34%25%6%
600
June1st to 10thDay
21%418%29%24%3
630
11th to 20thDay
16%421%33%22%3
630
21st to endDay
14%216%32%30%6%
630
July1st to 10thDay
14%214%29%33%8%
621
11th to 20thDay
8%314%34%33%8%
618
21st to endDay
7%28%30%43%10%
596
August1st to 10thDay
11%210%26%36%16%
447
11th to 20thDay
8%29%30%37%14%
437
21st to endDay
14%315%33%31%5%
495
September1st to 10thDay
16%419%33%22%6%
450
11th to 20thDay
25%5%14%23%23%9%
450
21st to endDay
24%5%21%26%18%6%
450
October1st to 10thDay
30%5%16%22%20%7%
450
11th to 20thDay
36%5%18%18%17%6%
450
21st to endDay
33%10%22%23%9%4
368
November1st to 10thDay
38%7%29%18%8%
180
11th to 20thDay
39%7%16%19%14%5%
180
21st to endDay
43%11%19%11%10%5%
180
December1st to 10thDay
41%7%23%13%12%6%
180
11th to 20thDay
38%9%20%22%8%2
180
21st to endDay
44%9%20%21%6%1
198
January1st to 10thNight
46%8%17%17%10%2
850
11th to 20thNight
41%6%14%21%17%
850
21st to endNight
41%7%16%21%14%1
875
February1st to 10thNight
37%7%18%25%12%1
758
11th to 20thNight
31%5%20%30%13%1
704
21st to endNight
33%9%19%22%14%3
592
March1st to 10thNight
33%7%18%23%16%3
720
11th to 20thNight
38%6%18%21%15%3
720
21st to endNight
33%6%18%23%17%4
792
April1st to 10thNight
30%5%17%25%17%5%
720
11th to 20thNight
22%7%21%26%21%2
579
21st to endNight
27%416%30%20%3
513
May1st to 10thNight
18%317%29%26%7%
360
11th to 20thNight
19%49%24%33%10%
354
21st to endNight
19%312%31%27%9%
389
June1st to 10thNight
25%48%30%28%5%
360
11th to 20thNight
20%413%32%22%9%
360
21st to endNight
15%29%32%34%8%
360
July1st to 10thNight
13%111%23%38%15%
350
11th to 20thNight
8%29%29%38%14%
348
21st to endNight
8%17%19%47%18%
394
August1st to 10thNight
9%15%22%41%22%
403
11th to 20thNight
7%1425%49%13%
534
21st to endNight
15%211%24%39%9%
619
September1st to 10thNight
10%210%32%35%11%
720
11th to 20thNight
21%313%17%31%14%
720
21st to endNight
25%315%24%28%5%
720
October1st to 10thNight
23%315%26%25%7%
720
11th to 20thNight
35%313%23%21%5%
720
21st to endNight
36%7%18%24%13%3
792
November1st to 10thNight
41%7%18%25%8%1
740
11th to 20thNight
37%7%19%23%12%2
760
21st to endNight
41%6%19%20%11%3
760
December1st to 10thNight
35%7%17%25%15%1
802
11th to 20thNight
48%5%19%20%7%
850
21st to endNight
42%10%23%19%6%
935
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