University of British Columbia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the University of British Columbia clear sky chart from 2005-11-06 to 2024-01-16.

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
44%
22592
9%
74840
9%
22539
46%
22539
14%
56153

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
24%
850
7%
2836
7%
846
25%
846
6%
2438
January11th to 20thNight
33%
829
5%
2787
5%
829
35%
829
8%
2318
January21st to endNight
36%
808
8%
2775
9%
808
37%
808
9%
2253
February1st to 10thNight
33%
720
8%
2340
6%
720
35%
720
9%
1914
February11th to 20thNight
38%
700
9%
2274
9%
700
39%
700
12%
1783
February21st to endNight
35%
592
11%
1920
9%
592
39%
592
14%
1474
March1st to 10thNight
36%
720
8%
2088
7%
720
36%
720
13%
1673
March11th to 20thNight
34%
720
8%
1980
7%
720
35%
720
13%
1618
March21st to endNight
35%
792
6%
2132
4%
792
35%
792
11%
1801
April1st to 10thNight
41%
720
7%
1800
4%
720
41%
720
15%
1458
April11th to 20thNight
43%
605
11%
1673
8%
605
44%
605
16%
1279
April21st to endNight
45%
496
9%
1576
8%
496
46%
496
13%
1183
May1st to 10thNight
57%
360
12%
1440
18%
360
59%
360
19%
906
May11th to 20thNight
61%
354
10%
1416
18%
354
62%
354
18%
918
May21st to endNight
57%
388
6%
1478
10%
388
58%
388
16%
1006
June1st to 10thNight
53%
360
3%
1260
3%
360
53%
360
17%
893
June11th to 20thNight
53%
360
3%
1260
2%
360
53%
360
16%
899
June21st to endNight
69%
360
6%
1260
3%
360
69%
360
23%
787
July1st to 10thNight
67%
350
8%
1225
6%
350
68%
350
29%
707
July11th to 20thNight
75%
348
14%
1218
17%
348
76%
348
36%
641
July21st to endNight
83%
394
18%
1421
28%
372
86%
372
45%
626
August1st to 10thNight
78%
385
17%
1451
26%
383
78%
383
37%
705
August11th to 20thNight
83%
534
22%
1602
23%
534
83%
534
46%
818
August21st to endNight
67%
638
19%
1826
17%
638
68%
638
32%
1124
September1st to 10thNight
74%
720
19%
1800
12%
720
74%
720
40%
1111
September11th to 20thNight
59%
720
18%
1812
11%
720
60%
720
27%
1265
September21st to endNight
52%
720
16%
2056
13%
720
54%
720
23%
1438
October1st to 10thNight
55%
720
10%
2160
11%
720
56%
720
22%
1492
October11th to 20thNight
45%
720
10%
2160
10%
720
46%
720
16%
1622
October21st to endNight
38%
792
10%
2523
9%
792
41%
792
13%
1937
November1st to 10thNight
32%
740
5%
2590
7%
740
32%
740
8%
2143
November11th to 20thNight
33%
760
7%
2660
7%
760
35%
760
9%
2124
November21st to endNight
30%
760
6%
2660
6%
760
32%
760
8%
2163
December1st to 10thNight
35%
778
9%
2698
9%
778
37%
778
9%
2166
December11th to 20thNight
24%
850
2%
3516
2%
849
25%
849
5%
3109
December21st to endNight
22%
929
4%
5167
5%
905
26%
905
4%
4361

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
22%7%36%5%3445%6%34%
74762
Night
27%8%36%5%34446%30%
75057
TransparencyDay
51%10%15%16%7%1
74450
Night
55%8%13%15%7%1
74887
SeeingDay
22%39%26%29%11%
14278
Night
30%411%24%23%8%
22603

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
44%10%46%5%3344413%
1329
11th to 20thDay
33%11%45%6%44346%19%
1295
21st to endDay
35%10%47%6%4445%6%16%
1579
February1st to 10thDay
34%8%46%5%45%5%5%6%18%
1620
11th to 20thDay
28%9%36%6%35%447%24%
1575
21st to endDay
23%10%48%6%46%446%25%
1336
March1st to 10thDay
28%10%37%6%35%6%5%6%22%
1871
11th to 20thDay
31%11%47%6%34335%23%
1980
21st to endDay
26%10%38%6%35%436%26%
2223
April1st to 10thDay
24%10%37%6%46%5%6%6%24%
2160
11th to 20thDay
21%8%47%5%45%5%6%6%29%
2233
21st to endDay
19%9%46%6%4445%6%32%
2382
May1st to 10thDay
13%7%37%6%35%6%5%7%38%
2520
11th to 20thDay
15%7%36%6%45%5%6%8%37%
2477
21st to endDay
15%8%37%6%45%5%5%7%36%
2795
June1st to 10thDay
19%7%36%6%3445%8%35%
2700
11th to 20thDay
17%7%36%6%35%5%6%8%32%
2700
21st to endDay
13%5%26%5%35%46%7%42%
2700
July1st to 10thDay
10%5%24425%45%7%53%
2700
11th to 20thDay
9%42432435%7%57%
2700
21st to endDay
7%22332335%6%66%
2811
August1st to 10thDay
8%424433346%59%
2477
11th to 20thDay
7%42442345%6%59%
2298
21st to endDay
10%425%5%3445%8%50%
2529
September1st to 10thDay
11%5%35%5%34447%49%
2160
11th to 20thDay
17%6%36%6%335%5%7%40%
2146
21st to endDay
22%5%26%5%3446%6%38%
1904
October1st to 10thDay
23%6%25%435%448%34%
1800
11th to 20thDay
32%8%36%5%345%5%7%24%
1800
21st to endDay
32%8%36%5%3445%6%25%
1829
November1st to 10thDay
39%10%25%435%445%20%
1488
11th to 20thDay
35%10%46%5%2444422%
1520
21st to endDay
39%9%35%5%2445%420%
1520
December1st to 10thDay
32%11%45%5%26%445%22%
1478
11th to 20thDay
35%12%49%8%2343414%
1685
21st to endDay
41%12%47%6%4343412%
2442
January1st to 10thNight
42%11%46%5%3443416%
2836
11th to 20thNight
37%10%45%434446%19%
2787
21st to endNight
32%10%47%5%34446%21%
2775
February1st to 10thNight
33%10%46%5%35%446%20%
2340
11th to 20thNight
28%13%37%433345%26%
2272
21st to endNight
27%10%38%6%34445%26%
1920
March1st to 10thNight
29%10%37%5%345%46%24%
2088
11th to 20thNight
32%10%36%6%34445%23%
1979
21st to endNight
29%11%48%7%35%45%5%20%
2132
April1st to 10thNight
26%10%46%6%45%5%47%24%
1800
11th to 20thNight
22%8%48%6%35%5%5%6%28%
1673
21st to endNight
21%9%48%7%3447%7%27%
1576
May1st to 10thNight
15%5%35%6%35%5%5%7%41%
1440
11th to 20thNight
16%6%35%5%45%5%7%7%37%
1416
21st to endNight
17%7%46%6%35%5%6%6%35%
1478
June1st to 10thNight
21%6%37%6%45%46%6%34%
1260
11th to 20thNight
16%8%47%7%27%6%6%8%31%
1260
21st to endNight
11%5%25%6%46%6%6%9%42%
1260
July1st to 10thNight
11%5%25%5%24445%54%
1260
11th to 20thNight
6%42442345%7%59%
1260
21st to endNight
4213433346%67%
1505
August1st to 10thNight
7%323433346%64%
1459
11th to 20thNight
6%21332345%8%63%
1602
21st to endNight
9%5%26%5%345%7%9%47%
1826
September1st to 10thNight
9%4234245%5%6%56%
1800
11th to 20thNight
18%5%36%42445%6%43%
1812
21st to endNight
20%7%25%5%33446%41%
2056
October1st to 10thNight
19%6%36%434446%41%
2160
11th to 20thNight
29%8%35%434446%32%
2160
21st to endNight
34%7%35%433446%29%
2523
November1st to 10thNight
37%10%46%5%34445%19%
2590
11th to 20thNight
35%9%445%45%43424%
2660
21st to endNight
36%10%36%6%34345%21%
2660
December1st to 10thNight
32%11%36%5%34345%23%
2698
11th to 20thNight
44%12%5%6%5%2333413%
3520
21st to endNight
41%13%47%43333316%
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
75%8%7%5%41
1329
11th to 20thDay
70%8%10%8%31
1295
21st to endDay
70%9%9%10%2
1579
February1st to 10thDay
68%10%9%8%32
1620
11th to 20thDay
63%9%10%11%6%
1584
21st to endDay
61%10%12%12%42
1336
March1st to 10thDay
63%11%13%10%4
1871
11th to 20thDay
66%8%9%12%41
1980
21st to endDay
63%10%13%11%3
2223
April1st to 10thDay
61%11%15%10%3
2160
11th to 20thDay
55%10%12%14%8%1
2233
21st to endDay
54%10%14%13%7%1
2382
May1st to 10thDay
46%11%18%17%7%1
2520
11th to 20thDay
45%12%18%19%6%
2480
21st to endDay
48%12%17%19%4
2796
June1st to 10thDay
49%10%18%15%5%2
2700
11th to 20thDay
50%15%19%13%4
2700
21st to endDay
40%11%21%18%8%2
2700
July1st to 10thDay
33%10%18%24%11%4
2626
11th to 20thDay
29%10%21%29%10%1
2619
21st to endDay
18%10%21%32%15%3
2655
August1st to 10thDay
28%9%20%29%12%2
2460
11th to 20thDay
27%11%21%25%15%2
2298
21st to endDay
33%12%21%26%7%1
2529
September1st to 10thDay
38%9%16%23%11%3
2160
11th to 20thDay
44%10%14%17%13%2
2146
21st to endDay
46%11%15%17%9%1
1904
October1st to 10thDay
49%11%16%16%8%
1800
11th to 20thDay
60%11%14%11%31
1800
21st to endDay
62%9%11%12%6%1
1829
November1st to 10thDay
67%9%11%8%41
1488
11th to 20thDay
66%9%10%8%42
1520
21st to endDay
66%9%10%8%6%1
1520
December1st to 10thDay
65%8%8%12%7%1
1478
11th to 20thDay
72%11%8%6%21
1688
21st to endDay
76%9%8%5%1
2442
January1st to 10thNight
73%7%7%9%41
2836
11th to 20thNight
67%9%11%9%31
2787
21st to endNight
65%9%9%13%31
2775
February1st to 10thNight
66%7%12%9%42
2340
11th to 20thNight
61%8%12%12%7%1
2274
21st to endNight
59%7%12%15%6%2
1920
March1st to 10thNight
61%8%14%13%4
2088
11th to 20thNight
62%8%11%12%6%1
1980
21st to endNight
66%9%11%11%2
2132
April1st to 10thNight
61%8%13%16%3
1800
11th to 20thNight
54%10%13%15%7%2
1673
21st to endNight
54%11%14%12%9%
1576
May1st to 10thNight
41%9%20%19%9%1
1440
11th to 20thNight
42%11%20%19%7%1
1416
21st to endNight
45%11%18%19%6%
1478
June1st to 10thNight
49%9%17%17%43
1260
11th to 20thNight
48%11%18%19%3
1260
21st to endNight
37%11%21%19%9%3
1260
July1st to 10thNight
32%8%15%28%14%3
1225
11th to 20thNight
25%9%21%30%13%2
1218
21st to endNight
18%6%15%35%22%4
1421
August1st to 10thNight
22%8%19%29%19%3
1451
11th to 20thNight
19%8%25%28%14%6%
1602
21st to endNight
32%10%19%29%10%1
1826
September1st to 10thNight
27%9%18%28%13%5%
1800
11th to 20thNight
42%9%12%17%16%5%
1812
21st to endNight
46%8%15%22%8%2
2056
October1st to 10thNight
45%9%16%20%10%
2160
11th to 20thNight
55%8%15%16%6%
2160
21st to endNight
58%8%11%14%8%
2523
November1st to 10thNight
67%8%11%9%31
2590
11th to 20thNight
64%8%12%9%5%2
2660
21st to endNight
67%7%11%8%7%
2660
December1st to 10thNight
64%8%11%11%5%1
2698
11th to 20thNight
76%8%8%5%4
3516
21st to endNight
72%8%8%9%3
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
39%413%22%13%8%
180
11th to 20thDay
42%416%16%16%5%
170
21st to endDay
44%49%21%18%4
208
February1st to 10thDay
39%412%26%16%2
340
11th to 20thDay
34%313%30%17%3
335
21st to endDay
27%214%32%17%8%
282
March1st to 10thDay
30%212%29%20%7%
420
11th to 20thDay
31%314%22%23%7%
420
21st to endDay
32%415%25%18%6%
462
April1st to 10thDay
27%416%24%21%7%
420
11th to 20thDay
27%311%30%19%10%
412
21st to endDay
20%411%33%24%7%
420
May1st to 10thDay
15%310%30%34%9%
423
11th to 20thDay
15%2427%35%17%
448
21st to endDay
14%46%28%34%14%
557
June1st to 10thDay
18%27%31%32%10%
630
11th to 20thDay
18%29%30%32%10%
630
21st to endDay
13%27%25%39%14%
630
July1st to 10thDay
12%1426%40%17%
621
11th to 20thDay
7%27%24%45%16%
618
21st to endDay
5%2419%49%22%
557
August1st to 10thDay
11%1418%39%26%
447
11th to 20thDay
6%2423%46%19%
437
21st to endDay
11%29%26%40%13%
495
September1st to 10thDay
13%38%33%33%10%
450
11th to 20thDay
19%48%24%31%14%
450
21st to endDay
21%212%26%28%11%
450
October1st to 10thDay
27%39%25%23%12%
450
11th to 20thDay
36%411%18%22%10%
450
21st to endDay
34%6%15%25%16%5%
368
November1st to 10thDay
41%414%24%13%4
180
11th to 20thDay
37%314%17%19%9%
180
21st to endDay
40%5%13%20%12%9%
180
December1st to 10thDay
43%313%16%16%9%
180
11th to 20thDay
37%7%12%26%17%2
180
21st to endDay
42%5%7%33%9%4
198
January1st to 10thNight
47%6%11%19%13%4
850
11th to 20thNight
42%410%20%22%2
829
21st to endNight
38%312%25%17%5%
808
February1st to 10thNight
36%5%13%27%16%3
720
11th to 20thNight
35%314%28%17%3
704
21st to endNight
29%416%28%17%5%
592
March1st to 10thNight
33%414%24%20%5%
720
11th to 20thNight
35%5%14%23%17%6%
720
21st to endNight
34%5%11%24%19%7%
792
April1st to 10thNight
31%311%28%22%6%
720
11th to 20thNight
24%5%14%28%21%7%
605
21st to endNight
25%49%32%24%6%
496
May1st to 10thNight
17%211%29%31%9%
360
11th to 20thNight
18%28%21%36%14%
354
21st to endNight
19%46%25%38%9%
389
June1st to 10thNight
22%28%28%33%8%
360
11th to 20thNight
15%6%11%33%26%8%
360
21st to endNight
13%15%30%41%11%
360
July1st to 10thNight
13%26%23%39%17%
350
11th to 20thNight
7%17%26%43%16%
348
21st to endNight
5%2419%50%20%
394
August1st to 10thNight
9%1418%44%25%
385
11th to 20thNight
7%224%47%20%
534
21st to endNight
12%29%22%40%15%
638
September1st to 10thNight
11%36%28%35%18%
720
11th to 20thNight
20%28%20%28%21%
720
21st to endNight
24%311%23%29%11%
720
October1st to 10thNight
22%210%28%25%13%
720
11th to 20thNight
33%211%23%22%9%
720
21st to endNight
37%5%12%24%16%6%
792
November1st to 10thNight
41%5%11%25%16%1
740
11th to 20thNight
38%5%16%23%14%5%
760
21st to endNight
41%413%23%15%5%
760
December1st to 10thNight
36%5%12%24%19%4
778
11th to 20thNight
49%5%11%23%12%1
850
21st to endNight
46%6%16%20%10%2
935
Page generated at 2024-01-13 06:37:55. Version ac07

Copyright 2024 Attilla Danko


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