Courtenay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Courtenay clear sky chart from 2005-11-05 to 2017-11-30.

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%
14790
10%
47711
8%
14761
48%
14761
17%
34307

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
33%
750
9%
2686
8%
746
36%
746
10%
2148
January16th to endNight
36%
795
8%
2792
8%
795
38%
795
10%
2208
February1st to 15thNight
33%
698
7%
2288
6%
698
35%
698
11%
1827
February16th to endNight
42%
632
13%
2053
11%
632
46%
632
17%
1461
March1st to 15thNight
32%
720
7%
2045
3%
720
36%
720
14%
1605
March16th to endNight
38%
768
9%
2112
6%
768
40%
768
16%
1655
April1st to 15thNight
44%
647
10%
1733
5%
647
47%
647
20%
1284
April16th to endNight
45%
540
11%
1620
9%
540
47%
540
19%
1162
May1st to 15thNight
54%
370
12%
1450
16%
370
58%
370
17%
961
May16th to endNight
45%
375
6%
1363
7%
374
48%
374
16%
943
June1st to 15thNight
53%
360
2%
1260
2%
360
54%
360
19%
830
June16th to endNight
50%
360
4%
1260
1%
360
51%
360
18%
845
July1st to 15thNight
70%
340
6%
1190
4%
340
72%
340
32%
651
July16th to endNight
78%
376
12%
1248
16%
354
80%
354
40%
616
August1st to 15thNight
77%
486
14%
1560
17%
484
77%
484
37%
850
August16th to endNight
73%
573
17%
1719
16%
573
75%
573
36%
976
September1st to 15thNight
71%
707
22%
1791
14%
707
73%
707
45%
1050
September16th to endNight
51%
716
16%
1994
11%
716
53%
716
25%
1353
October1st to 15thNight
53%
720
12%
2160
11%
720
55%
720
25%
1419
October16th to endNight
40%
768
9%
2423
7%
768
44%
768
14%
1829
November1st to 15thNight
28%
760
6%
2660
3%
760
32%
760
9%
2131
November16th to endNight
34%
780
8%
2730
5%
780
38%
780
10%
2124
December1st to 15thNight
32%
749
7%
2694
4%
749
36%
749
9%
2119
December16th to endNight
28%
800
9%
2880
5%
800
34%
800
10%
2260

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%9%36%6%35%5%5%6%29%
48736
Night
18%9%36%5%35%5%5%6%29%
47857
Cloud CoverDay
18%7%36%5%35%5%5%7%32%
48736
Night
21%8%36%5%35%45%6%30%
47860
TransparencyDay
51%5%18%17%5%
48385
Night
54%416%17%6%
47712
SeeingDay
19%5%20%25%19%7%
6622
Night
24%313%28%23%6%
14797

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
25%15%45%6%45%445%17%
1253
16th to endDay
22%15%5%7%6%44346%18%
1428
February1st to 15thDay
26%14%46%6%35%5%46%17%
1576
16th to endDay
19%11%36%6%47%5%5%6%23%
1421
March1st to 15thDay
24%12%47%7%46%6%5%415%
1914
16th to endDay
20%12%49%9%46%6%45%17%
2112
April1st to 15thDay
19%10%48%7%47%6%5%6%18%
2211
16th to endDay
20%10%5%8%6%35%5%5%5%21%
2340
May1st to 15thDay
14%7%37%6%36%6%5%7%31%
2499
16th to endDay
17%7%47%7%46%5%6%7%23%
2747
June1st to 15thDay
14%8%38%8%46%5%5%7%26%
2700
16th to endDay
16%7%49%8%46%5%6%5%25%
2700
July1st to 15thDay
9%425%5%25%45%7%46%
2700
16th to endDay
8%324435%5%5%6%50%
2837
August1st to 15thDay
6%413425%5%5%7%51%
2391
16th to endDay
8%425%5%35%46%8%44%
2483
September1st to 15thDay
8%4145%3345%6%52%
2166
16th to endDay
18%6%36%6%35%45%7%32%
1965
October1st to 15thDay
21%8%36%6%35%44431%
1800
16th to endDay
27%9%37%5%25%45%6%22%
1800
November1st to 15thDay
27%10%46%6%36%5%5%418%
1528
16th to endDay
25%10%37%6%35%6%5%6%19%
1555
December1st to 15thDay
22%14%6%5%5%35%44423%
1266
16th to endDay
25%16%5%8%6%2444417%
1344
January1st to 15thNight
24%12%47%5%35%445%21%
2686
16th to endNight
23%12%47%6%36%5%5%5%19%
2792
February1st to 15thNight
23%13%38%5%35%6%46%18%
2276
16th to endNight
16%10%36%5%35%5%5%6%31%
2053
March1st to 15thNight
21%10%37%6%46%6%6%6%21%
2045
16th to endNight
16%9%47%8%5%7%5%6%6%20%
2108
April1st to 15thNight
16%11%36%7%45%5%7%7%26%
1733
16th to endNight
17%6%36%6%46%45%8%28%
1620
May1st to 15thNight
14%7%446%46%6%6%7%31%
1450
16th to endNight
12%8%48%7%45%5%6%7%28%
1363
June1st to 15thNight
14%6%27%5%46%45%8%33%
1260
16th to endNight
13%6%38%6%47%5%5%7%30%
1260
July1st to 15thNight
6%314445%6%6%6%49%
1260
16th to endNight
6%224325%348%56%
1332
August1st to 15thNight
7%4143345%46%54%
1568
16th to endNight
6%314425%5%7%8%48%
1719
September1st to 15thNight
7%313424447%56%
1791
16th to endNight
16%8%25%6%3345%6%37%
1994
October1st to 15thNight
17%6%246%3446%6%38%
2160
16th to endNight
26%9%36%434445%26%
2423
November1st to 15thNight
29%10%36%6%35%5%45%18%
2660
16th to endNight
23%10%46%5%46%45%5%22%
2730
December1st to 15thNight
23%14%5%7%5%35%44421%
2694
16th to endNight
25%12%37%436%445%21%
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
30%13%5%6%5%34346%15%
1253
16th to endDay
27%14%5%6%5%46%5%46%14%
1428
February1st to 15thDay
29%12%38%5%335%45%19%
1576
16th to endDay
21%8%36%6%27%5%5%8%23%
1421
March1st to 15thDay
27%9%47%6%36%5%6%5%15%
1914
16th to endDay
21%9%47%8%46%6%5%5%19%
2112
April1st to 15thDay
18%9%37%6%46%6%7%7%22%
2211
16th to endDay
19%8%38%7%35%5%5%7%25%
2340
May1st to 15thDay
15%5%35%4346%6%8%35%
2499
16th to endDay
16%7%36%5%35%5%5%8%30%
2747
June1st to 15thDay
13%5%36%7%35%6%6%9%32%
2700
16th to endDay
14%6%37%6%46%5%6%7%30%
2700
July1st to 15thDay
8%42432445%8%52%
2700
16th to endDay
7%3133235%5%7%56%
2837
August1st to 15thDay
5%41332336%8%57%
2391
16th to endDay
8%4144345%6%8%48%
2483
September1st to 15thDay
8%31342435%7%55%
2166
16th to endDay
18%6%26%5%346%5%6%33%
1965
October1st to 15thDay
21%8%37%5%3444433%
1800
16th to endDay
27%8%36%6%45%445%22%
1800
November1st to 15thDay
31%9%47%5%35%44419%
1528
16th to endDay
29%10%36%5%37%5%5%5%18%
1555
December1st to 15thDay
26%12%48%5%3433423%
1266
16th to endDay
30%13%5%6%7%36%43315%
1344
January1st to 15thNight
27%12%46%6%3433420%
2685
16th to endNight
27%12%46%6%35%5%45%18%
2792
February1st to 15thNight
27%13%35%5%35%45%5%18%
2276
16th to endNight
20%8%26%5%345%46%30%
2053
March1st to 15thNight
25%7%46%7%36%6%5%5%20%
2045
16th to endNight
19%9%38%7%46%5%6%6%21%
2112
April1st to 15thNight
18%9%46%6%345%6%9%25%
1733
16th to endNight
18%7%36%6%36%5%5%9%29%
1620
May1st to 15thNight
16%7%26%6%36%5%6%7%33%
1450
16th to endNight
13%7%47%6%46%6%5%8%28%
1363
June1st to 15thNight
13%7%38%435%5%5%6%36%
1260
16th to endNight
13%7%38%6%36%45%7%32%
1260
July1st to 15thNight
6%423436%46%8%51%
1260
16th to endNight
8%313323447%57%
1332
August1st to 15thNight
7%413424446%56%
1568
16th to endNight
6%3244245%6%8%50%
1719
September1st to 15thNight
7%314324346%57%
1791
16th to endNight
18%8%26%42345%6%38%
1994
October1st to 15thNight
18%6%145%34446%40%
2160
16th to endNight
28%8%35%423445%27%
2423
November1st to 15thNight
34%8%35%6%35%44419%
2660
16th to endNight
26%11%36%6%36%445%21%
2730
December1st to 15thNight
28%11%47%5%2443421%
2694
16th to endNight
30%11%36%5%34445%20%
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
70%410%9%4
1253
16th to endDay
70%410%9%21
1428
February1st to 15thDay
67%5%13%9%4
1576
16th to endDay
59%5%15%14%4
1421
March1st to 15thDay
67%5%13%10%2
1914
16th to endDay
65%5%12%14%1
2112
April1st to 15thDay
59%7%13%16%2
2211
16th to endDay
59%412%16%6%
2340
May1st to 15thDay
47%6%19%20%5%
2499
16th to endDay
52%6%20%18%2
2751
June1st to 15thDay
48%8%19%18%4
2700
16th to endDay
52%6%20%16%3
2700
July1st to 15thDay
32%5%24%26%10%1
2541
16th to endDay
26%5%26%30%9%
2658
August1st to 15thDay
26%6%25%29%9%1
2374
16th to endDay
32%5%29%24%6%1
2483
September1st to 15thDay
29%5%23%25%14%
2166
16th to endDay
49%5%17%19%7%
1965
October1st to 15thDay
55%416%14%7%
1800
16th to endDay
63%5%14%12%4
1800
November1st to 15thDay
66%412%11%3
1528
16th to endDay
66%5%12%11%3
1555
December1st to 15thDay
65%314%10%5%
1266
16th to endDay
71%39%10%21
1344
January1st to 15thNight
66%411%11%6%
2686
16th to endNight
65%411%12%31
2792
February1st to 15thNight
65%412%12%31
2288
16th to endNight
53%414%20%6%
2053
March1st to 15thNight
61%5%16%13%4
2045
16th to endNight
61%414%15%3
2112
April1st to 15thNight
52%6%15%19%5%
1733
16th to endNight
53%314%21%6%
1620
May1st to 15thNight
49%415%21%8%
1451
16th to endNight
51%5%19%18%4
1363
June1st to 15thNight
47%5%25%15%5%1
1260
16th to endNight
49%418%21%31
1260
July1st to 15thNight
31%5%23%25%11%2
1190
16th to endNight
24%5%28%31%9%1
1248
August1st to 15thNight
28%5%22%31%9%2
1560
16th to endNight
29%6%26%27%7%1
1719
September1st to 15thNight
27%417%30%18%1
1791
16th to endNight
46%318%20%8%2
1994
October1st to 15thNight
43%418%21%10%
2160
16th to endNight
58%5%17%13%4
2423
November1st to 15thNight
67%413%9%4
2660
16th to endNight
64%5%11%13%5%
2730
December1st to 15thNight
66%312%11%4
2694
16th to endNight
65%411%12%5%
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%10%11%18%23%13%
60
16th to endDay
37%224%16%16%2
124
February1st to 15thDay
36%6%18%23%12%1
236
16th to endDay
26%7%21%24%15%5%
211
March1st to 15thDay
33%13%32%13%6%1
264
16th to endDay
31%10%26%18%9%4
288
April1st to 15thDay
20%10%27%22%13%5%
269
16th to endDay
24%10%26%22%12%3
270
May1st to 15thDay
20%6%20%27%19%5%
288
16th to endDay
17%417%30%22%8%
463
June1st to 15thDay
16%6%21%24%25%5%
495
16th to endDay
17%5%20%28%21%6%
495
July1st to 15thDay
8%318%30%29%9%
475
16th to endDay
6%416%30%28%13%
506
August1st to 15thDay
8%112%32%24%19%
315
16th to endDay
9%218%31%25%12%
332
September1st to 15thDay
9%221%27%25%13%
315
16th to endDay
20%6%22%24%19%6%
315
October1st to 15thDay
25%6%22%22%18%4
315
16th to endDay
32%7%19%22%12%6%
283
November1st to 15thDay
30%6%24%21%14%3
90
16th to endDay
34%416%13%13%16%
89
December1st to 15thDay
40%113%26%10%8%
60
16th to endDay
25%315%35%15%4
64
January1st to 15thNight
34%5%14%23%16%4
750
16th to endNight
32%312%26%19%7%
795
February1st to 15thNight
31%313%31%17%2
704
16th to endNight
23%416%32%18%4
632
March1st to 15thNight
28%7%20%25%14%3
720
16th to endNight
24%420%27%17%6%
768
April1st to 15thNight
20%5%14%32%22%4
647
16th to endNight
21%216%36%19%3
540
May1st to 15thNight
18%311%34%23%8%
371
16th to endNight
17%413%26%31%8%
375
June1st to 15thNight
14%312%33%29%6%
360
16th to endNight
18%312%34%25%6%
360
July1st to 15thNight
6%29%27%40%13%
340
16th to endNight
8%1326%43%16%
376
August1st to 15thNight
9%1121%48%17%
486
16th to endNight
9%6%28%46%8%
573
September1st to 15thNight
10%6%27%36%19%
707
16th to endNight
21%311%25%26%11%
716
October1st to 15thNight
21%310%32%25%7%
720
16th to endNight
30%213%27%18%6%
768
November1st to 15thNight
37%318%26%12%1
760
16th to endNight
31%416%26%15%4
780
December1st to 15thNight
34%5%12%26%17%3
749
16th to endNight
35%322%25%11%1
800
Page generated at 2017-12-01 09:13:39. Version ac04

Copyright 2017 A. Danko


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