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Vancouver
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vancouver clear sky chart from 2005-11-05 to 2018-03-11.

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
43%
15222
9%
49071
8%
15194
45%
15194
14%
36858

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%
825
9%
2911
8%
821
31%
821
9%
2366
January16th to endNight
32%
851
6%
2976
7%
851
33%
851
8%
2430
February1st to 15thNight
32%
759
6%
2483
6%
759
34%
759
9%
2048
February16th to endNight
36%
684
12%
2216
10%
684
40%
684
13%
1686
March1st to 15thNight
28%
764
4%
2182
4%
764
28%
764
9%
1845
March16th to endNight
32%
768
6%
2078
4%
768
33%
768
10%
1775
April1st to 15thNight
40%
711
8%
1791
4%
711
41%
711
15%
1446
April16th to endNight
42%
507
8%
1587
7%
507
43%
507
12%
1230
May1st to 15thNight
58%
359
12%
1439
19%
359
59%
359
19%
915
May16th to endNight
57%
374
6%
1452
10%
374
58%
374
16%
984
June1st to 15thNight
55%
360
3%
1260
2%
360
55%
360
18%
871
June16th to endNight
57%
360
5%
1260
2%
360
57%
360
18%
866
July1st to 15thNight
77%
340
9%
1190
9%
340
77%
340
35%
632
July16th to endNight
80%
376
15%
1321
22%
354
83%
354
41%
634
August1st to 15thNight
80%
434
16%
1507
22%
432
80%
432
39%
745
August16th to endNight
72%
606
19%
1752
17%
606
73%
606
37%
1017
September1st to 15thNight
76%
720
21%
1800
13%
720
77%
720
46%
1055
September16th to endNight
51%
716
17%
1978
14%
716
52%
716
21%
1426
October1st to 15thNight
51%
720
10%
2160
10%
720
52%
720
21%
1513
October16th to endNight
39%
768
7%
2403
7%
768
40%
768
11%
1915
November1st to 15thNight
26%
760
4%
2660
5%
760
27%
760
6%
2272
November16th to endNight
27%
780
5%
2730
4%
780
30%
780
7%
2263
December1st to 15thNight
33%
800
7%
2815
6%
800
35%
800
9%
2290
December16th to endNight
24%
880
7%
3120
5%
880
27%
880
7%
2634

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
25%7%35%424445%32%
49587
Night
28%7%25%423345%30%
49224
Cloud CoverDay
26%7%35%423446%30%
49587
Night
29%7%25%423345%30%
49227
TransparencyDay
55%8%13%15%6%1
49243
Night
57%6%12%15%6%1
49072
SeeingDay
25%315%27%22%6%
6643
Night
31%5%9%24%22%6%
15229

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
44%8%36%422345%14%
1358
16th to endDay
39%9%36%5%2344416%
1599
February1st to 15thDay
37%8%36%5%33345%16%
1711
16th to endDay
25%10%35%5%245%5%5%25%
1544
March1st to 15thDay
38%10%36%5%3443415%
2011
16th to endDay
32%10%36%7%2433420%
2145
April1st to 15thDay
24%9%37%6%35%5%5%6%21%
2155
16th to endDay
24%8%45%5%24446%27%
2372
May1st to 15thDay
17%7%36%43445%6%36%
2511
16th to endDay
19%7%37%5%35%45%7%30%
2657
June1st to 15thDay
20%5%27%5%25%45%6%33%
2700
16th to endDay
19%7%25%5%3446%7%34%
2700
July1st to 15thDay
10%423413346%55%
2700
16th to endDay
10%312313345%59%
2757
August1st to 15thDay
10%414413245%57%
2442
16th to endDay
10%423324447%51%
2449
September1st to 15thDay
12%5%245%23346%50%
2160
16th to endDay
25%6%25%42345%5%32%
1980
October1st to 15thDay
28%6%35%423446%30%
1800
16th to endDay
36%8%46%423346%19%
1820
November1st to 15thDay
47%7%23413335%17%
1528
16th to endDay
41%9%34423345%17%
1560
December1st to 15thDay
33%10%35%5%2443322%
1472
16th to endDay
45%8%35%5%2333216%
1456
January1st to 15thNight
41%8%2441333421%
2911
16th to endNight
36%9%35%424446%18%
2976
February1st to 15thNight
36%9%36%43333420%
2471
16th to endNight
28%8%35%423335%29%
2216
March1st to 15thNight
39%9%35%5%2333320%
2182
16th to endNight
33%8%36%6%3434420%
2074
April1st to 15thNight
26%9%36%5%35%345%25%
1791
16th to endNight
24%9%36%5%3345%5%26%
1587
May1st to 15thNight
17%325%5%335%5%6%39%
1439
16th to endNight
16%7%36%5%25%45%7%34%
1452
June1st to 15thNight
20%6%26%5%34345%38%
1260
16th to endNight
16%6%25%5%46%5%47%36%
1260
July1st to 15thNight
7%3135%13336%60%
1260
16th to endNight
5%313222346%63%
1412
August1st to 15thNight
6%22313447%61%
1515
16th to endNight
9%32332235%8%52%
1752
September1st to 15thNight
8%212223346%61%
1800
16th to endNight
23%5%25%5%23345%38%
1978
October1st to 15thNight
22%6%25%32334440%
2160
16th to endNight
35%6%25%323346%25%
2403
November1st to 15thNight
43%7%35%5%2333317%
2660
16th to endNight
38%8%35%42432320%
2730
December1st to 15thNight
34%11%35%42343422%
2815
16th to endNight
42%11%25%41322319%
3120

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
46%8%35%323335%14%
1358
16th to endDay
40%8%25%5%2344416%
1599
February1st to 15thDay
39%8%36%5%24245%16%
1711
16th to endDay
27%10%45%5%34446%23%
1544
March1st to 15thDay
40%11%36%5%2342414%
2011
16th to endDay
33%10%47%5%3443418%
2145
April1st to 15thDay
27%9%47%5%35%5%5%5%19%
2155
16th to endDay
26%9%36%5%3445%6%23%
2372
May1st to 15thDay
19%8%35%6%24446%33%
2511
16th to endDay
20%8%37%5%35%46%7%27%
2657
June1st to 15thDay
22%7%36%5%2445%6%30%
2700
16th to endDay
20%6%37%5%3436%7%31%
2700
July1st to 15thDay
11%42342335%6%53%
2700
16th to endDay
11%313323335%57%
2757
August1st to 15thDay
10%5%14423336%55%
2442
16th to endDay
12%424323447%49%
2449
September1st to 15thDay
14%5%245%13246%50%
2160
16th to endDay
27%6%345%24346%31%
1980
October1st to 15thDay
27%8%36%323446%29%
1800
16th to endDay
37%8%36%5%23247%18%
1820
November1st to 15thDay
49%6%2442333414%
1528
16th to endDay
43%8%35%5%2234416%
1560
December1st to 15thDay
34%10%36%42444421%
1472
16th to endDay
44%11%3441332315%
1456
January1st to 15thNight
43%8%2432223421%
2910
16th to endNight
37%9%35%423345%19%
2976
February1st to 15thNight
37%9%35%5%24335%19%
2471
16th to endNight
29%10%25%42334429%
2216
March1st to 15thNight
41%8%25%42333419%
2182
16th to endNight
35%8%36%5%3444419%
2078
April1st to 15thNight
27%9%36%5%34345%24%
1791
16th to endNight
25%10%36%6%24435%26%
1587
May1st to 15thNight
18%435%5%345%5%7%38%
1439
16th to endNight
16%7%35%5%35%5%5%7%34%
1452
June1st to 15thNight
22%6%26%434336%36%
1260
16th to endNight
16%6%35%5%36%447%35%
1260
July1st to 15thNight
7%313323336%60%
1260
16th to endNight
7%213313345%64%
1412
August1st to 15thNight
6%313313246%62%
1515
16th to endNight
9%41331246%8%52%
1752
September1st to 15thNight
9%212423346%61%
1800
16th to endNight
23%6%25%5%13345%37%
1978
October1st to 15thNight
23%6%2442334439%
2160
16th to endNight
36%7%25%423346%24%
2403
November1st to 15thNight
45%6%36%42323316%
2660
16th to endNight
40%8%36%5%2332320%
2730
December1st to 15thNight
35%10%35%42433422%
2815
16th to endNight
44%11%2432222318%
3120

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%6%7%4
1358
16th to endDay
71%6%10%9%1
1599
February1st to 15thDay
71%6%9%7%42
1711
16th to endDay
60%8%12%13%4
1544
March1st to 15thDay
74%6%9%7%1
2011
16th to endDay
70%7%9%10%1
2145
April1st to 15thDay
65%10%10%12%2
2155
16th to endDay
60%9%12%12%4
2372
May1st to 15thDay
49%9%14%18%7%
2511
16th to endDay
54%10%15%16%3
2661
June1st to 15thDay
53%10%15%14%41
2700
16th to endDay
51%10%15%16%5%
2700
July1st to 15thDay
32%7%17%26%12%3
2541
16th to endDay
27%9%18%29%12%1
2585
August1st to 15thDay
30%8%18%29%10%2
2425
16th to endDay
33%10%20%26%7%1
2449
September1st to 15thDay
36%6%15%22%15%2
2160
16th to endDay
54%8%11%16%7%
1980
October1st to 15thDay
55%8%14%14%6%
1800
16th to endDay
67%8%10%8%3
1820
November1st to 15thDay
74%7%6%7%21
1528
16th to endDay
71%6%7%9%5%
1560
December1st to 15thDay
68%6%6%10%6%1
1472
16th to endDay
76%46%8%21
1456
January1st to 15thNight
68%5%7%13%4
2911
16th to endNight
68%6%10%11%21
2976
February1st to 15thNight
68%6%10%8%32
2483
16th to endNight
58%6%10%16%6%
2216
March1st to 15thNight
70%6%9%10%2
2182
16th to endNight
68%8%9%11%2
2078
April1st to 15thNight
61%6%11%16%3
1791
16th to endNight
60%7%13%13%5%
1587
May1st to 15thNight
44%7%18%18%10%1
1440
16th to endNight
46%9%20%17%5%
1452
June1st to 15thNight
49%6%20%16%42
1260
16th to endNight
47%9%16%18%6%2
1260
July1st to 15thNight
27%6%15%31%15%3
1190
16th to endNight
22%6%19%34%15%3
1321
August1st to 15thNight
24%5%22%30%13%3
1507
16th to endNight
28%7%21%27%11%3
1752
September1st to 15thNight
24%6%18%26%19%4
1800
16th to endNight
49%7%11%22%7%2
1978
October1st to 15thNight
48%6%15%19%9%
2160
16th to endNight
62%7%12%11%5%
2403
November1st to 15thNight
73%5%8%7%21
2660
16th to endNight
70%5%9%8%6%
2730
December1st to 15thNight
66%6%9%10%5%1
2815
16th to endNight
72%5%7%9%41
3120

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
34%1223%16%22%
90
16th to endDay
60%49%9%15%
116
February1st to 15thDay
45%48%22%16%2
281
16th to endDay
32%7%19%21%14%5%
252
March1st to 15thDay
44%5%17%18%9%4
312
16th to endDay
39%7%17%20%11%2
288
April1st to 15thDay
30%7%16%22%19%4
269
16th to endDay
27%422%27%14%2
270
May1st to 15thDay
20%5%20%28%21%3
288
16th to endDay
17%316%26%26%9%
372
June1st to 15thDay
18%320%30%21%5%
495
16th to endDay
16%320%33%23%3
495
July1st to 15thDay
9%211%37%34%5%
475
16th to endDay
6%112%37%36%5%
426
August1st to 15thDay
12%7%32%34%12%
315
16th to endDay
10%213%33%30%9%
332
September1st to 15thDay
14%118%29%28%7%
315
16th to endDay
25%213%27%20%9%
315
October1st to 15thDay
32%214%27%18%4
315
16th to endDay
39%5%12%21%15%5%
256
November1st to 15thDay
53%7%12%15%8%2
90
16th to endDay
54%37%12%8%13%
90
December1st to 15thDay
43%28%10%23%12%
90
16th to endDay
47%25%28%12%4
96
January1st to 15thNight
44%6%9%17%16%5%
825
16th to endNight
41%6%10%24%13%3
851
February1st to 15thNight
40%5%11%24%15%2
764
16th to endNight
31%6%14%27%15%3
684
March1st to 15thNight
41%8%12%20%14%2
764
16th to endNight
38%6%12%23%15%4
768
April1st to 15thNight
28%6%11%28%20%4
711
16th to endNight
28%5%11%32%16%5%
507
May1st to 15thNight
18%37%33%31%6%
360
16th to endNight
18%25%28%37%7%
375
June1st to 15thNight
19%5%8%27%32%6%
360
16th to endNight
18%310%28%33%5%
360
July1st to 15thNight
9%1427%47%9%
340
16th to endNight
7%2325%47%13%
376
August1st to 15thNight
9%1217%48%20%
434
16th to endNight
12%15%21%45%13%
606
September1st to 15thNight
10%1427%39%17%
720
16th to endNight
25%47%25%27%9%
716
October1st to 15thNight
27%211%27%24%6%
720
16th to endNight
38%48%25%19%4
768
November1st to 15thNight
46%8%10%24%9%
760
16th to endNight
40%7%13%20%12%5%
780
December1st to 15thNight
39%5%11%25%14%4
800
16th to endNight
48%6%13%22%8%
880
Page generated at 2018-03-12 10:28:02. Version ac04

Copyright 2018 A. Danko


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