Nanaimo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nanaimo 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
43%
14370
10%
46385
7%
14341
46%
14341
16%
33360

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
32%
750
9%
2686
8%
746
35%
746
9%
2140
January16th to endNight
36%
786
8%
2751
9%
786
38%
786
11%
2134
February1st to 15thNight
30%
697
7%
2288
4%
697
34%
697
10%
1839
February16th to endNight
38%
632
13%
2053
11%
632
43%
632
16%
1478
March1st to 15thNight
30%
720
8%
2043
4%
720
33%
720
12%
1659
March16th to endNight
34%
768
8%
2096
4%
768
37%
768
13%
1668
April1st to 15thNight
42%
688
9%
1768
3%
688
45%
688
18%
1338
April16th to endNight
45%
531
11%
1611
8%
531
48%
531
17%
1177
May1st to 15thNight
50%
359
13%
1439
14%
359
57%
359
19%
886
May16th to endNight
52%
375
7%
1424
9%
374
55%
374
17%
955
June1st to 15thNight
50%
360
3%
1260
2%
360
52%
360
20%
829
June16th to endNight
53%
360
6%
1260
2%
360
54%
360
22%
794
July1st to 15thNight
66%
340
9%
1190
6%
340
70%
340
38%
603
July16th to endNight
74%
376
14%
1296
17%
354
79%
354
44%
588
August1st to 15thNight
74%
451
16%
1501
18%
449
76%
449
43%
730
August16th to endNight
69%
539
19%
1589
14%
539
72%
539
38%
892
September1st to 15thNight
70%
660
23%
1650
13%
660
74%
660
46%
956
September16th to endNight
46%
656
17%
1820
11%
656
50%
656
25%
1244
October1st to 15thNight
49%
660
12%
1980
9%
660
52%
660
24%
1320
October16th to endNight
36%
704
8%
2202
6%
704
40%
704
13%
1701
November1st to 15thNight
26%
700
6%
2450
4%
700
30%
700
8%
1991
November16th to endNight
32%
720
7%
2520
4%
720
37%
720
9%
2001
December1st to 15thNight
31%
738
5%
2628
4%
738
33%
738
8%
2124
December16th to endNight
24%
800
7%
2880
4%
800
29%
800
8%
2313

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%9%36%5%35%5%5%6%31%
47618
Night
17%8%36%5%35%5%5%6%32%
46536
Cloud CoverDay
17%8%36%5%35%45%7%32%
47618
Night
19%8%35%5%3445%6%32%
46539
TransparencyDay
52%7%17%16%5%
47272
Night
52%6%15%17%6%1
46386
SeeingDay
19%7%22%29%17%3
6108
Night
22%7%16%27%20%5%
14378

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
24%14%46%7%35%5%5%418%
1253
16th to endDay
21%14%5%9%6%47%5%6%413%
1469
February1st to 15thDay
25%15%47%5%2445%5%17%
1576
16th to endDay
18%11%36%7%36%5%7%7%21%
1421
March1st to 15thDay
22%13%48%7%5%6%6%46%13%
1915
16th to endDay
22%11%5%9%7%46%5%35%20%
2127
April1st to 15thDay
18%10%38%8%46%6%6%6%19%
2179
16th to endDay
18%10%48%7%45%6%5%6%22%
2349
May1st to 15thDay
13%7%36%5%36%5%6%8%33%
2511
16th to endDay
17%9%47%6%35%46%8%26%
2686
June1st to 15thDay
14%7%47%5%36%5%5%7%30%
2700
16th to endDay
14%7%37%6%46%5%48%31%
2700
July1st to 15thDay
8%42442445%7%51%
2700
16th to endDay
6%32431345%6%57%
2784
August1st to 15thDay
8%42432345%6%54%
2364
16th to endDay
7%5%26%425%46%9%46%
2260
September1st to 15thDay
7%42333445%7%52%
1980
16th to endDay
17%6%27%5%2345%5%37%
1807
October1st to 15thDay
20%9%36%5%245%47%29%
1650
16th to endDay
24%11%37%5%345%48%22%
1666
November1st to 15thDay
28%9%5%6%6%45%335%20%
1408
16th to endDay
22%11%5%8%6%35%5%4420%
1440
December1st to 15thDay
21%14%47%7%345%45%21%
1329
16th to endDay
26%16%28%435%5%4416%
1344
January1st to 15thNight
23%12%46%6%35%445%23%
2686
16th to endNight
21%11%47%7%3446%7%21%
2751
February1st to 15thNight
24%10%47%6%35%45%6%20%
2276
16th to endNight
18%9%35%5%35%5%47%30%
2053
March1st to 15thNight
21%9%46%7%46%5%6%6%21%
2043
16th to endNight
17%10%48%6%46%6%6%6%22%
2092
April1st to 15thNight
14%9%36%5%46%6%5%7%29%
1768
16th to endNight
17%8%35%5%47%46%8%30%
1611
May1st to 15thNight
11%5%35%6%35%6%48%38%
1439
16th to endNight
11%7%37%6%45%5%6%8%34%
1424
June1st to 15thNight
11%7%26%6%35%5%5%6%39%
1260
16th to endNight
10%5%25%436%7%6%8%39%
1260
July1st to 15thNight
4312433446%61%
1260
16th to endNight
4223313445%65%
1385
August1st to 15thNight
4213422345%63%
1509
16th to endNight
7%31242446%9%53%
1589
September1st to 15thNight
7%22323445%64%
1650
16th to endNight
16%7%25%434348%39%
1820
October1st to 15thNight
15%7%25%5%24446%40%
1980
16th to endNight
26%9%25%5%34446%26%
2202
November1st to 15thNight
27%10%46%7%36%44420%
2450
16th to endNight
21%10%37%6%35%5%5%5%22%
2520
December1st to 15thNight
20%14%5%8%7%35%5%4420%
2628
16th to endNight
25%13%47%6%345%5%421%
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
27%12%48%5%35%445%16%
1253
16th to endDay
24%14%5%9%7%37%5%6%411%
1469
February1st to 15thDay
28%14%45%5%35%345%17%
1576
16th to endDay
19%9%46%6%36%5%7%8%22%
1421
March1st to 15thDay
23%12%49%7%45%5%5%414%
1915
16th to endDay
21%11%5%8%6%46%5%3421%
2127
April1st to 15thDay
18%8%47%8%46%6%5%7%20%
2179
16th to endDay
17%9%47%7%46%5%5%7%24%
2349
May1st to 15thDay
12%6%35%5%35%6%6%8%35%
2511
16th to endDay
16%8%26%6%36%45%9%28%
2686
June1st to 15thDay
13%7%37%6%35%5%6%7%33%
2700
16th to endDay
13%7%36%7%36%5%5%7%33%
2700
July1st to 15thDay
7%32342445%7%53%
2700
16th to endDay
6%323323437%59%
2784
August1st to 15thDay
7%413424446%55%
2364
16th to endDay
7%425%5%2445%9%47%
2260
September1st to 15thDay
7%414425%45%7%52%
1980
16th to endDay
18%6%26%6%24446%36%
1807
October1st to 15thDay
21%10%36%42346%6%29%
1650
16th to endDay
26%10%35%6%3445%7%21%
1666
November1st to 15thDay
30%10%45%6%34345%20%
1408
16th to endDay
26%12%47%5%35%5%45%19%
1440
December1st to 15thDay
23%14%6%6%6%35%436%19%
1329
16th to endDay
29%14%46%6%35%5%3416%
1344
January1st to 15thNight
25%12%36%7%34435%22%
2685
16th to endNight
24%11%37%6%2446%8%20%
2751
February1st to 15thNight
26%10%37%6%35%46%5%20%
2276
16th to endNight
20%9%36%5%3445%6%31%
2053
March1st to 15thNight
23%11%37%6%45%5%5%5%21%
2043
16th to endNight
20%10%47%6%46%5%5%6%23%
2096
April1st to 15thNight
16%8%36%6%37%5%5%7%28%
1768
16th to endNight
17%7%36%6%35%6%5%7%30%
1611
May1st to 15thNight
11%5%26%5%35%6%5%8%39%
1439
16th to endNight
11%7%37%7%3446%8%33%
1424
June1st to 15thNight
12%6%36%7%35%46%6%37%
1260
16th to endNight
10%5%25%5%36%6%5%9%38%
1260
July1st to 15thNight
4313323346%61%
1260
16th to endNight
4213213347%64%
1385
August1st to 15thNight
4223413336%63%
1509
16th to endNight
7%3133345%6%8%53%
1589
September1st to 15thNight
7%22323445%63%
1650
16th to endNight
16%7%25%434448%38%
1820
October1st to 15thNight
16%7%24434446%40%
1980
16th to endNight
27%9%245%34346%26%
2202
November1st to 15thNight
30%10%45%6%35%44420%
2450
16th to endNight
22%10%47%6%35%45%5%21%
2520
December1st to 15thNight
23%14%5%7%7%3444419%
2628
16th to endNight
27%13%46%6%3444420%
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
69%6%10%10%3
1253
16th to endDay
71%8%9%7%11
1469
February1st to 15thDay
69%5%10%9%3
1576
16th to endDay
57%7%18%12%3
1421
March1st to 15thDay
71%6%12%7%1
1915
16th to endDay
67%5%14%11%1
2127
April1st to 15thDay
62%7%16%11%2
2179
16th to endDay
59%7%14%14%4
2349
May1st to 15thDay
46%8%20%17%6%
2511
16th to endDay
53%9%21%14%2
2690
June1st to 15thDay
50%8%21%14%41
2700
16th to endDay
49%8%20%15%4
2700
July1st to 15thDay
31%7%22%25%10%2
2541
16th to endDay
24%8%25%28%11%1
2610
August1st to 15thDay
30%7%22%27%10%1
2347
16th to endDay
33%8%25%24%7%
2260
September1st to 15thDay
29%7%20%25%15%1
1980
16th to endDay
48%7%15%18%8%
1807
October1st to 15thDay
54%7%16%16%5%
1650
16th to endDay
60%8%16%11%3
1666
November1st to 15thDay
68%5%12%9%3
1408
16th to endDay
66%6%9%13%4
1440
December1st to 15thDay
67%6%11%11%3
1329
16th to endDay
71%5%8%9%3
1344
January1st to 15thNight
65%6%10%12%5%
2686
16th to endNight
61%6%12%13%31
2751
February1st to 15thNight
64%6%12%11%3
2288
16th to endNight
53%5%15%18%6%
2053
March1st to 15thNight
63%6%12%13%3
2043
16th to endNight
60%7%14%14%3
2096
April1st to 15thNight
53%6%15%18%5%
1768
16th to endNight
51%8%15%17%6%
1611
May1st to 15thNight
41%6%18%21%10%
1440
16th to endNight
47%8%21%19%4
1424
June1st to 15thNight
45%6%23%18%42
1260
16th to endNight
41%7%20%23%5%1
1260
July1st to 15thNight
24%6%23%27%14%3
1190
16th to endNight
18%6%24%32%16%1
1296
August1st to 15thNight
22%424%28%16%3
1501
16th to endNight
26%7%23%31%8%2
1589
September1st to 15thNight
22%7%17%27%20%4
1650
16th to endNight
44%6%15%21%8%2
1820
October1st to 15thNight
44%5%19%19%9%
1980
16th to endNight
59%7%14%13%5%
2202
November1st to 15thNight
67%6%12%9%21
2450
16th to endNight
63%7%10%11%6%
2520
December1st to 15thNight
67%6%12%10%2
2628
16th to endNight
66%6%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
18%116%15%25%23%
60
16th to endDay
38%12%18%22%5%1
106
February1st to 15thDay
36%6%22%23%9%
236
16th to endDay
28%11%25%21%11%1
211
March1st to 15thDay
35%16%25%17%5%
268
16th to endDay
28%15%29%18%6%1
288
April1st to 15thDay
22%10%31%23%11%1
269
16th to endDay
19%9%33%24%11%
270
May1st to 15thDay
20%7%26%27%17%1
288
16th to endDay
16%5%18%32%19%7%
401
June1st to 15thDay
13%7%23%36%16%2
495
16th to endDay
15%5%23%36%16%2
495
July1st to 15thDay
9%418%33%29%5%
475
16th to endDay
5%317%38%31%3
453
August1st to 15thDay
10%12%39%29%8%
300
16th to endDay
11%420%37%25%
268
September1st to 15thDay
9%6%22%29%30%1
255
16th to endDay
20%7%23%30%14%3
255
October1st to 15thDay
29%9%24%23%12%
255
16th to endDay
32%7%26%21%7%3
216
November1st to 15thDay
38%18%20%20%3
60
16th to endDay
31%11%16%8%16%15%
60
December1st to 15thDay
40%18%16%8%15%1
60
16th to endDay
34%7%20%23%9%4
64
January1st to 15thNight
30%10%14%23%17%3
750
16th to endNight
30%8%14%25%19%2
786
February1st to 15thNight
30%7%16%26%16%2
704
16th to endNight
23%7%19%28%17%3
632
March1st to 15thNight
28%10%22%23%12%3
720
16th to endNight
24%8%21%24%15%4
768
April1st to 15thNight
19%9%17%29%19%4
688
16th to endNight
21%5%16%34%19%2
531
May1st to 15thNight
14%419%28%26%6%
360
16th to endNight
13%6%10%33%28%8%
375
June1st to 15thNight
13%5%16%37%20%6%
360
16th to endNight
13%319%35%23%5%
360
July1st to 15thNight
6%315%31%35%8%
340
16th to endNight
5%211%28%42%9%
376
August1st to 15thNight
6%7%30%41%13%
451
16th to endNight
9%111%31%36%8%
539
September1st to 15thNight
8%312%26%35%12%
660
16th to endNight
20%417%26%22%8%
656
October1st to 15thNight
21%5%17%28%22%5%
660
16th to endNight
32%5%16%24%15%4
704
November1st to 15thNight
33%10%19%25%9%1
700
16th to endNight
28%10%16%23%16%4
720
December1st to 15thNight
29%11%14%26%15%1
738
16th to endNight
33%10%22%22%8%1
800
Page generated at 2017-08-13 11:16:38. Version ac04

Copyright 2017 A. Danko


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