Boundary Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boundary Bay clear sky chart from 2005-11-06 to 2024-01-17.

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
42%
22592
10%
74840
9%
22537
45%
22537
16%
54723

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%
850
8%
2836
6%
846
23%
846
7%
2386
January11th to 20thNight
29%
834
7%
2802
5%
834
32%
834
10%
2255
January21st to endNight
31%
794
9%
2746
8%
794
33%
794
10%
2186
February1st to 10thNight
27%
720
9%
2340
5%
720
32%
720
9%
1885
February11th to 20thNight
30%
700
11%
2274
8%
700
35%
700
12%
1767
February21st to endNight
31%
592
12%
1908
8%
592
37%
592
13%
1450
March1st to 10thNight
32%
720
9%
2097
7%
720
35%
720
14%
1632
March11th to 20thNight
33%
720
10%
1979
7%
720
35%
720
14%
1569
March21st to endNight
32%
792
7%
2124
4%
792
33%
792
12%
1770
April1st to 10thNight
40%
720
8%
1800
4%
720
41%
720
16%
1432
April11th to 20thNight
42%
621
13%
1689
8%
621
45%
621
17%
1273
April21st to endNight
45%
493
9%
1573
8%
493
47%
493
14%
1181
May1st to 10thNight
55%
360
14%
1440
20%
360
58%
360
19%
888
May11th to 20thNight
62%
354
12%
1416
20%
354
63%
354
20%
862
May21st to endNight
59%
389
7%
1508
11%
388
60%
388
19%
969
June1st to 10thNight
54%
360
4%
1260
4%
360
54%
360
19%
861
June11th to 20thNight
51%
360
3%
1260
2%
360
51%
360
17%
882
June21st to endNight
67%
360
7%
1260
4%
360
68%
360
28%
739
July1st to 10thNight
71%
350
9%
1225
8%
350
72%
350
33%
671
July11th to 20thNight
75%
348
16%
1218
20%
348
76%
348
38%
623
July21st to endNight
82%
394
20%
1446
31%
372
85%
372
49%
599
August1st to 10thNight
76%
381
18%
1447
26%
379
77%
379
40%
676
August11th to 20thNight
82%
534
23%
1602
24%
534
83%
534
49%
798
August21st to endNight
67%
652
21%
1840
18%
652
68%
652
35%
1096
September1st to 10thNight
75%
720
21%
1800
13%
720
75%
720
45%
1078
September11th to 20thNight
56%
720
19%
1800
11%
720
58%
720
30%
1237
September21st to endNight
52%
720
18%
2065
14%
720
54%
720
25%
1389
October1st to 10thNight
53%
720
11%
2160
11%
720
54%
720
23%
1461
October11th to 20thNight
43%
720
11%
2160
10%
720
46%
720
17%
1578
October21st to endNight
35%
792
11%
2514
10%
792
39%
792
14%
1871
November1st to 10thNight
29%
740
7%
2590
7%
740
32%
740
9%
2101
November11th to 20thNight
30%
760
8%
2660
6%
760
33%
760
9%
2083
November21st to endNight
28%
760
7%
2660
5%
760
32%
760
8%
2155
December1st to 10thNight
34%
762
10%
2664
9%
762
37%
762
11%
2048
December11th to 20thNight
21%
850
3%
3516
2%
849
23%
849
5%
3058
December21st to endNight
19%
930
5%
5161
4%
905
24%
905
4%
4214

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
20%8%36%5%3445%7%33%
74776
Night
25%9%36%5%3445%6%30%
75065
TransparencyDay
52%5%16%18%7%1
74465
Night
56%5%13%17%7%1
74894
SeeingDay
22%5%14%26%24%9%
14229
Night
29%6%12%25%22%6%
22601

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
41%10%47%7%3443412%
1329
11th to 20thDay
30%12%49%7%46%445%16%
1302
21st to endDay
35%10%5%8%6%36%45%5%14%
1603
February1st to 10thDay
31%11%47%7%3446%6%16%
1620
11th to 20thDay
27%10%38%7%35%447%21%
1575
21st to endDay
23%11%5%8%6%35%5%6%6%24%
1347
March1st to 10thDay
26%12%48%7%4445%6%21%
1862
11th to 20thDay
29%10%48%7%34345%23%
1980
21st to endDay
24%11%49%6%345%5%6%24%
2232
April1st to 10thDay
24%9%46%6%46%6%6%7%22%
2160
11th to 20thDay
20%8%47%7%45%5%6%7%28%
2219
21st to endDay
19%10%47%6%35%45%7%30%
2386
May1st to 10thDay
13%7%37%7%45%46%7%38%
2520
11th to 20thDay
14%7%36%5%45%46%8%37%
2477
21st to endDay
15%8%47%6%35%5%5%7%36%
2764
June1st to 10thDay
19%7%36%7%345%5%7%35%
2700
11th to 20thDay
17%7%37%5%35%5%6%8%32%
2700
21st to endDay
11%6%36%5%35%5%5%9%42%
2700
July1st to 10thDay
10%43442445%6%53%
2700
11th to 20thDay
8%424424447%56%
2700
21st to endDay
5%31321435%7%65%
2786
August1st to 10thDay
8%42432335%6%59%
2482
11th to 20thDay
7%5%2432435%7%58%
2298
21st to endDay
9%5%245%345%6%8%48%
2516
September1st to 10thDay
11%6%35%5%3445%8%46%
2160
11th to 20thDay
16%7%46%5%3446%8%39%
2156
21st to endDay
21%7%25%5%345%48%36%
1895
October1st to 10thDay
21%9%36%5%35%46%7%31%
1800
11th to 20thDay
28%9%38%6%35%5%5%7%22%
1800
21st to endDay
30%10%46%5%34447%24%
1841
November1st to 10thDay
35%9%27%6%45%44419%
1488
11th to 20thDay
32%10%47%6%33445%21%
1520
21st to endDay
35%10%47%6%44445%17%
1520
December1st to 10thDay
30%13%47%5%2444423%
1511
11th to 20thDay
33%14%5%10%6%3444412%
1685
21st to endDay
33%15%5%10%7%45%43410%
2442
January1st to 10thNight
38%11%46%7%3434416%
2836
11th to 20thNight
35%10%36%5%34445%19%
2802
21st to endNight
30%12%48%5%2445%7%20%
2746
February1st to 10thNight
32%11%46%5%2445%6%20%
2340
11th to 20thNight
27%13%48%5%23445%25%
2272
21st to endNight
26%11%46%5%345%5%5%26%
1908
March1st to 10thNight
28%10%47%6%35%446%24%
2097
11th to 20thNight
31%9%45%435%45%6%23%
1979
21st to endNight
29%11%5%8%7%4435%5%20%
2124
April1st to 10thNight
25%10%37%6%45%5%5%7%24%
1800
11th to 20thNight
21%10%36%5%36%5%5%6%29%
1689
21st to endNight
20%9%49%6%45%5%7%6%27%
1573
May1st to 10thNight
14%6%46%5%345%5%7%40%
1440
11th to 20thNight
14%6%35%6%35%6%6%8%38%
1416
21st to endNight
15%6%37%5%45%5%6%7%36%
1508
June1st to 10thNight
19%8%36%5%3446%7%33%
1260
11th to 20thNight
13%9%39%6%45%5%5%9%31%
1260
21st to endNight
10%5%26%5%35%5%6%9%43%
1260
July1st to 10thNight
10%425%423446%55%
1260
11th to 20thNight
7%324324445%61%
1260
21st to endNight
4213422346%69%
1531
August1st to 10thNight
7%413323346%64%
1455
11th to 20thNight
6%31322335%8%63%
1602
21st to endNight
8%425%6%345%7%9%47%
1840
September1st to 10thNight
8%313435%45%7%57%
1800
11th to 20thNight
17%5%246%3445%6%43%
1800
21st to endNight
18%5%36%43445%6%40%
2065
October1st to 10thNight
18%6%36%5%35%45%7%38%
2160
11th to 20thNight
28%7%35%4345%5%6%31%
2160
21st to endNight
30%8%36%5%33447%27%
2514
November1st to 10thNight
35%8%47%5%35%5%45%18%
2590
11th to 20thNight
34%9%35%5%34446%22%
2660
21st to endNight
32%10%5%7%6%4444420%
2660
December1st to 10thNight
30%9%37%6%34447%22%
2664
11th to 20thNight
39%14%5%7%6%3343412%
3520
21st to endNight
34%15%48%6%3433416%
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
77%47%7%41
1329
11th to 20thDay
70%7%9%9%41
1302
21st to endDay
72%410%11%3
1603
February1st to 10thDay
68%5%11%9%43
1620
11th to 20thDay
65%5%10%13%6%
1584
21st to endDay
60%6%13%14%43
1347
March1st to 10thDay
64%5%13%13%5%
1862
11th to 20thDay
66%411%14%41
1980
21st to endDay
63%416%14%3
2232
April1st to 10thDay
60%6%18%12%4
2160
11th to 20thDay
56%6%12%17%9%1
2219
21st to endDay
54%5%16%16%8%1
2386
May1st to 10thDay
46%7%18%21%8%1
2520
11th to 20thDay
45%6%21%21%6%1
2480
21st to endDay
48%6%21%21%4
2765
June1st to 10thDay
49%6%20%19%5%2
2700
11th to 20thDay
49%6%23%18%4
2700
21st to endDay
40%6%23%21%8%2
2700
July1st to 10thDay
33%5%20%26%12%4
2626
11th to 20thDay
29%5%23%30%11%2
2619
21st to endDay
18%5%22%36%15%4
2631
August1st to 10thDay
28%5%21%31%13%2
2465
11th to 20thDay
26%6%24%27%14%2
2298
21st to endDay
35%5%22%29%8%1
2516
September1st to 10thDay
37%6%19%24%11%4
2160
11th to 20thDay
45%416%20%13%2
2156
21st to endDay
48%6%15%20%10%1
1895
October1st to 10thDay
51%6%16%18%8%
1800
11th to 20thDay
60%7%15%14%31
1800
21st to endDay
62%6%11%12%8%1
1841
November1st to 10thDay
68%412%11%41
1488
11th to 20thDay
66%5%11%12%5%2
1520
21st to endDay
69%49%11%6%1
1520
December1st to 10thDay
67%5%7%13%8%
1511
11th to 20thDay
75%410%7%31
1688
21st to endDay
78%49%7%1
2442
January1st to 10thNight
73%48%10%41
2836
11th to 20thNight
67%5%12%11%41
2802
21st to endNight
66%5%9%15%31
2746
February1st to 10thNight
66%6%11%11%43
2340
11th to 20thNight
63%5%10%14%7%1
2274
21st to endNight
60%5%10%16%7%2
1908
March1st to 10thNight
62%413%15%5%
2097
11th to 20thNight
64%411%14%6%1
1980
21st to endNight
68%5%13%12%2
2124
April1st to 10thNight
61%5%13%18%4
1800
11th to 20thNight
55%6%11%18%7%2
1689
21st to endNight
59%5%12%14%9%
1573
May1st to 10thNight
44%5%18%21%11%1
1440
11th to 20thNight
42%6%21%21%9%
1416
21st to endNight
46%6%21%20%6%
1508
June1st to 10thNight
50%5%18%19%5%3
1260
11th to 20thNight
51%6%19%19%3
1260
21st to endNight
37%5%24%21%10%3
1260
July1st to 10thNight
32%5%16%30%14%4
1225
11th to 20thNight
27%420%31%16%2
1218
21st to endNight
17%414%36%24%5%
1446
August1st to 10thNight
23%5%19%30%19%3
1447
11th to 20thNight
21%423%31%15%6%
1602
21st to endNight
33%5%19%31%11%1
1840
September1st to 10thNight
26%7%19%29%14%5%
1800
11th to 20thNight
43%5%13%18%17%4
1800
21st to endNight
45%5%15%25%9%2
2065
October1st to 10thNight
47%5%15%22%11%
2160
11th to 20thNight
55%5%15%19%6%
2160
21st to endNight
58%5%12%16%9%
2514
November1st to 10thNight
68%5%10%12%31
2590
11th to 20thNight
64%6%12%10%6%2
2660
21st to endNight
70%49%10%7%1
2660
December1st to 10thNight
62%6%12%12%7%1
2664
11th to 20thNight
78%48%6%41
3516
21st to endNight
73%39%11%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
41%7%20%15%12%6%
180
11th to 20thDay
38%13%14%16%13%5%
172
21st to endDay
46%413%18%13%6%
203
February1st to 10thDay
41%7%16%20%15%1
340
11th to 20thDay
36%7%15%24%16%3
335
21st to endDay
27%9%19%29%12%5%
288
March1st to 10thDay
31%6%15%28%16%5%
420
11th to 20thDay
30%7%16%21%19%7%
420
21st to endDay
32%6%19%21%19%4
462
April1st to 10thDay
29%9%15%24%19%5%
420
11th to 20thDay
24%320%27%19%7%
412
21st to endDay
21%5%20%30%19%5%
420
May1st to 10thDay
15%414%36%26%5%
423
11th to 20thDay
16%49%28%31%12%
448
21st to endDay
14%414%30%26%11%
526
June1st to 10thDay
19%215%32%25%7%
630
11th to 20thDay
17%418%35%21%6%
630
21st to endDay
12%314%28%33%10%
630
July1st to 10thDay
12%211%29%35%12%
621
11th to 20thDay
6%311%34%35%11%
618
21st to endDay
5%18%26%42%17%
532
August1st to 10thDay
9%36%23%38%20%
447
11th to 20thDay
6%25%32%38%17%
437
21st to endDay
10%213%32%31%12%
495
September1st to 10thDay
15%312%32%29%9%
450
11th to 20thDay
17%410%29%29%10%
450
21st to endDay
24%316%23%25%10%
450
October1st to 10thDay
25%5%13%22%22%13%
450
11th to 20thDay
32%5%12%20%20%11%
450
21st to endDay
32%8%17%22%15%6%
372
November1st to 10thDay
37%420%22%13%4
180
11th to 20thDay
33%12%14%12%17%12%
180
21st to endDay
37%9%16%19%9%10%
180
December1st to 10thDay
40%8%18%13%11%9%
180
11th to 20thDay
42%9%11%23%13%2
180
21st to endDay
37%7%23%22%9%2
198
January1st to 10thNight
44%9%16%17%10%3
850
11th to 20thNight
42%6%12%21%16%3
834
21st to endNight
37%7%13%23%17%3
794
February1st to 10thNight
38%8%18%23%11%3
720
11th to 20thNight
34%8%17%26%15%2
704
21st to endNight
31%9%18%25%13%4
592
March1st to 10thNight
33%7%18%21%18%3
720
11th to 20thNight
35%7%16%24%15%3
720
21st to endNight
34%8%12%25%16%5%
792
April1st to 10thNight
32%5%11%28%19%5%
720
11th to 20thNight
24%6%14%30%18%7%
621
21st to endNight
26%6%12%31%20%5%
493
May1st to 10thNight
19%312%26%34%5%
360
11th to 20thNight
17%25%29%38%8%
354
21st to endNight
19%35%30%35%7%
389
June1st to 10thNight
21%5%9%29%31%4
360
11th to 20thNight
18%410%36%26%5%
360
21st to endNight
13%37%34%35%9%
360
July1st to 10thNight
13%15%27%45%8%
350
11th to 20thNight
7%36%31%43%9%
348
21st to endNight
416%26%48%15%
394
August1st to 10thNight
9%25%18%44%22%
381
11th to 20thNight
7%2423%47%17%
534
21st to endNight
10%27%24%44%12%
652
September1st to 10thNight
11%16%34%36%13%
720
11th to 20thNight
19%411%18%32%17%
720
21st to endNight
22%214%25%30%7%
720
October1st to 10thNight
22%411%25%27%11%
720
11th to 20thNight
32%413%23%21%9%
720
21st to endNight
35%7%14%26%15%4
792
November1st to 10thNight
41%6%14%26%12%1
740
11th to 20thNight
38%7%17%22%12%4
760
21st to endNight
38%8%12%24%14%4
760
December1st to 10thNight
33%7%14%27%16%3
762
11th to 20thNight
47%8%14%21%8%1
850
21st to endNight
46%7%19%19%8%1
935
Page generated at 2024-01-14 06:55:04. Version ac07

Copyright 2024 Attilla Danko


Boundary Bay Clear Sky Chart |Charts Home