Chilliwack
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chilliwack clear sky chart from 2005-11-06 to 2024-02-05.

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
37%
22563
9%
80611
8%
22443
40%
22443
13%
60313

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%
844
7%
4705
7%
816
25%
816
4%
3959
January11th to 20thNight
27%
810
14%
4504
6%
788
31%
788
7%
3042
January21st to endNight
23%
833
5%
4862
6%
814
28%
814
5%
4114
February1st to 10thNight
20%
738
7%
2416
3%
738
25%
738
8%
1970
February11th to 20thNight
22%
700
8%
2274
4%
700
28%
700
9%
1844
February21st to endNight
27%
592
13%
1870
8%
592
33%
592
11%
1453
March1st to 10thNight
32%
720
8%
2146
6%
720
34%
720
13%
1671
March11th to 20thNight
29%
720
8%
1980
5%
720
32%
720
12%
1595
March21st to endNight
26%
792
5%
2088
2%
792
27%
792
11%
1742
April1st to 10thNight
32%
720
6%
1800
3%
720
33%
720
13%
1490
April11th to 20thNight
35%
670
10%
1738
5%
670
37%
670
15%
1379
April21st to endNight
32%
446
7%
1526
5%
446
34%
446
11%
1187
May1st to 10thNight
48%
360
9%
1440
13%
360
50%
360
15%
991
May11th to 20thNight
55%
354
9%
1416
16%
354
57%
354
15%
953
May21st to endNight
54%
388
6%
1552
9%
388
56%
388
16%
1053
June1st to 10thNight
46%
360
3%
1284
3%
360
46%
360
15%
923
June11th to 20thNight
41%
360
1%
1260
1%
360
41%
360
12%
970
June21st to endNight
61%
360
5%
1260
3%
360
61%
360
24%
775
July1st to 10thNight
65%
350
6%
1225
6%
350
65%
350
28%
716
July11th to 20thNight
67%
348
13%
1236
17%
348
68%
348
33%
669
July21st to endNight
83%
394
17%
1488
29%
372
85%
372
43%
654
August1st to 10thNight
77%
358
16%
1424
25%
356
78%
356
35%
678
August11th to 20thNight
77%
501
21%
1569
22%
501
78%
501
44%
801
August21st to endNight
65%
688
18%
1876
14%
688
66%
688
33%
1178
September1st to 10thNight
61%
720
17%
1800
10%
720
62%
720
36%
1155
September11th to 20thNight
52%
720
18%
1800
11%
720
53%
720
28%
1248
September21st to endNight
49%
720
16%
2048
13%
720
52%
720
23%
1434
October1st to 10thNight
44%
720
10%
2160
9%
720
46%
720
20%
1529
October11th to 20thNight
38%
720
11%
2160
10%
720
41%
720
16%
1618
October21st to endNight
27%
792
10%
2528
7%
792
33%
792
13%
1920
November1st to 10thNight
22%
740
7%
2575
5%
740
26%
740
8%
2100
November11th to 20thNight
21%
760
8%
2660
5%
760
25%
760
8%
2140
November21st to endNight
21%
760
7%
2660
3%
760
26%
760
7%
2156
December1st to 10thNight
28%
760
11%
2660
6%
760
35%
760
12%
1999
December11th to 20thNight
17%
814
4%
3432
3%
813
20%
813
5%
2894
December21st to endNight
14%
931
4%
5189
3%
905
20%
905
4%
4313

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
23%10%37%6%34445%30%
77898
Night
26%11%36%5%34445%28%
80907
TransparencyDay
58%414%16%7%1
77612
Night
60%413%14%7%1
80773
SeeingDay
27%11%26%24%10%2
14081
Night
31%6%17%26%17%2
22585

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
35%19%47%5%3433313%
2219
11th to 20thDay
25%12%5%8%6%3333427%
2323
21st to endDay
37%15%49%6%3333414%
2794
February1st to 10thDay
32%15%46%6%33336%18%
1633
11th to 20thDay
27%14%46%6%45%436%22%
1575
21st to endDay
24%18%5%7%5%46%44321%
1386
March1st to 10thDay
24%15%49%7%45%44420%
1812
11th to 20thDay
27%14%48%7%45%435%18%
1980
21st to endDay
27%13%49%7%45%6%5%417%
2268
April1st to 10thDay
25%15%48%7%36%446%17%
2160
11th to 20thDay
24%12%48%6%46%46%5%20%
2170
21st to endDay
24%13%47%7%35%5%5%5%21%
2432
May1st to 10thDay
21%9%47%7%45%5%46%29%
2520
11th to 20thDay
18%8%36%7%36%6%7%6%31%
2477
21st to endDay
24%9%48%6%44445%27%
2723
June1st to 10thDay
27%8%47%6%445%5%6%25%
2672
11th to 20thDay
29%10%48%7%45%45%6%18%
2700
21st to endDay
17%9%46%6%345%5%6%35%
2700
July1st to 10thDay
14%6%35%4245%5%5%48%
2700
11th to 20thDay
12%6%2442445%6%51%
2680
21st to endDay
10%323323336%61%
2741
August1st to 10thDay
11%5%24324448%53%
2507
11th to 20thDay
9%42332445%7%57%
2328
21st to endDay
15%6%25%5%3445%8%44%
2480
September1st to 10thDay
13%6%35%5%34446%48%
2160
11th to 20thDay
18%8%36%6%34445%40%
2160
21st to endDay
24%7%35%5%3344439%
1909
October1st to 10thDay
23%10%25%5%44345%36%
1800
11th to 20thDay
29%8%36%5%3345%6%28%
1800
21st to endDay
32%10%26%6%34345%26%
1828
November1st to 10thDay
35%11%47%5%44445%18%
1502
11th to 20thDay
35%11%38%43333323%
1520
21st to endDay
34%13%47%5%2434419%
1520
December1st to 10thDay
28%13%37%5%3433427%
1520
11th to 20thDay
28%14%5%9%6%3344420%
1757
21st to endDay
30%15%5%8%7%45%445%13%
2442
January1st to 10thNight
35%19%5%8%6%2333314%
4726
11th to 20thNight
28%13%34333347%29%
4572
21st to endNight
34%14%5%9%7%3433414%
4862
February1st to 10thNight
32%13%37%5%35%34420%
2416
11th to 20thNight
27%19%46%6%3433422%
2272
21st to endNight
25%15%47%5%24445%25%
1870
March1st to 10thNight
26%13%36%6%34346%25%
2146
11th to 20thNight
27%13%48%6%34446%21%
1979
21st to endNight
28%15%47%6%34435%20%
2088
April1st to 10thNight
24%14%39%6%46%45%6%20%
1800
11th to 20thNight
23%10%47%6%46%5%5%5%25%
1738
21st to endNight
28%10%48%6%3446%6%21%
1526
May1st to 10thNight
20%8%36%5%45%445%35%
1440
11th to 20thNight
16%7%36%6%45%6%6%8%32%
1416
21st to endNight
21%8%36%5%35%45%6%34%
1552
June1st to 10thNight
19%7%38%8%46%5%5%6%29%
1284
11th to 20thNight
23%8%5%9%7%35%6%6%6%23%
1260
21st to endNight
15%5%25%5%3445%8%43%
1260
July1st to 10thNight
13%6%3442335%5%51%
1260
11th to 20thNight
10%6%23423346%58%
1278
21st to endNight
8%212333445%66%
1576
August1st to 10thNight
9%423323346%61%
1432
11th to 20thNight
7%414322347%63%
1569
21st to endNight
11%5%25%5%3445%9%46%
1876
September1st to 10thNight
12%425%5%3445%7%50%
1800
11th to 20thNight
18%6%35%6%3435%6%42%
1800
21st to endNight
20%7%25%6%35%445%39%
2048
October1st to 10thNight
21%7%36%5%35%45%5%36%
2160
11th to 20thNight
29%9%35%43435%6%29%
2160
21st to endNight
32%10%35%5%24435%28%
2528
November1st to 10thNight
35%11%37%6%34445%18%
2575
11th to 20thNight
38%10%35%5%34335%22%
2660
21st to endNight
35%13%36%5%3443421%
2660
December1st to 10thNight
27%11%36%5%34446%28%
2660
11th to 20thNight
34%15%5%7%6%3344415%
3444
21st to endNight
33%16%48%6%4444414%
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
78%27%9%31
2219
11th to 20thDay
63%312%13%44
2345
21st to endDay
77%28%9%3
2794
February1st to 10thDay
70%5%8%9%7%1
1633
11th to 20thDay
66%410%12%6%1
1584
21st to endDay
69%49%12%42
1386
March1st to 10thDay
69%311%12%5%1
1812
11th to 20thDay
71%310%11%41
1980
21st to endDay
72%413%10%1
2268
April1st to 10thDay
70%5%13%10%1
2160
11th to 20thDay
67%410%9%8%1
2170
21st to endDay
67%413%9%7%
2432
May1st to 10thDay
58%5%15%16%5%1
2520
11th to 20thDay
53%5%20%16%6%
2480
21st to endDay
60%5%16%16%2
2724
June1st to 10thDay
62%416%13%33
2672
11th to 20thDay
68%416%10%2
2700
21st to endDay
51%418%18%8%1
2700
July1st to 10thDay
40%5%16%25%12%2
2626
11th to 20thDay
36%418%29%11%2
2599
21st to endDay
26%317%36%14%4
2589
August1st to 10thDay
33%419%29%12%2
2490
11th to 20thDay
28%5%21%27%15%3
2328
21st to endDay
41%421%26%8%1
2480
September1st to 10thDay
39%5%16%23%12%5%
2160
11th to 20thDay
48%312%16%18%3
2160
21st to endDay
50%416%17%11%2
1909
October1st to 10thDay
53%315%18%11%
1800
11th to 20thDay
58%5%12%16%7%1
1800
21st to endDay
63%313%13%8%
1828
November1st to 10thDay
71%310%12%31
1502
11th to 20thDay
71%29%11%5%2
1520
21st to endDay
69%47%11%8%1
1520
December1st to 10thDay
65%5%9%11%10%1
1520
11th to 20thDay
70%311%12%41
1760
21st to endDay
75%212%8%3
2442
January1st to 10thNight
78%27%11%2
4726
11th to 20thNight
58%314%15%5%5%
4612
21st to endNight
77%39%8%31
4862
February1st to 10thNight
70%410%10%5%2
2416
11th to 20thNight
69%49%11%6%1
2274
21st to endNight
64%410%16%6%1
1870
March1st to 10thNight
63%414%13%6%1
2146
11th to 20thNight
66%413%12%5%
1980
21st to endNight
69%417%9%1
2088
April1st to 10thNight
66%5%15%11%2
1800
11th to 20thNight
62%5%12%12%7%2
1738
21st to endNight
65%414%12%5%1
1526
May1st to 10thNight
53%5%19%15%6%1
1440
11th to 20thNight
49%7%22%16%5%
1416
21st to endNight
51%5%21%19%3
1552
June1st to 10thNight
57%418%14%42
1284
11th to 20thNight
62%6%19%11%2
1260
21st to endNight
41%5%27%19%5%3
1260
July1st to 10thNight
38%419%23%14%2
1225
11th to 20thNight
32%320%30%13%2
1236
21st to endNight
22%317%33%20%5%
1488
August1st to 10thNight
26%423%27%17%3
1424
11th to 20thNight
23%5%25%27%15%5%
1569
21st to endNight
37%5%21%28%9%1
1876
September1st to 10thNight
36%5%18%24%14%4
1800
11th to 20thNight
46%314%17%15%5%
1800
21st to endNight
49%417%18%10%2
2048
October1st to 10thNight
52%414%20%9%1
2160
11th to 20thNight
59%413%15%8%1
2160
21st to endNight
62%312%15%9%
2528
November1st to 10thNight
70%410%12%4
2575
11th to 20thNight
69%410%9%6%2
2660
21st to endNight
69%47%9%9%1
2660
December1st to 10thNight
60%5%13%13%8%1
2660
11th to 20thNight
75%410%7%41
3440
21st to endNight
77%29%8%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
38%12%24%14%8%3
180
11th to 20thDay
36%9%21%21%12%2
180
21st to endDay
36%10%22%24%9%1
198
February1st to 10thDay
45%15%17%18%5%
329
11th to 20thDay
39%13%28%16%41
335
21st to endDay
34%16%27%16%6%1
304
March1st to 10thDay
32%15%27%18%7%
420
11th to 20thDay
32%11%25%20%10%1
420
21st to endDay
35%15%24%19%6%1
462
April1st to 10thDay
37%12%26%17%7%1
420
11th to 20thDay
30%17%27%17%8%1
412
21st to endDay
33%16%25%18%7%2
420
May1st to 10thDay
23%13%31%26%6%1
423
11th to 20thDay
22%10%23%28%13%3
448
21st to endDay
27%13%25%22%10%3
485
June1st to 10thDay
25%15%30%22%7%1
602
11th to 20thDay
29%14%30%22%5%1
630
21st to endDay
20%12%27%27%13%2
630
July1st to 10thDay
19%8%30%31%10%2
621
11th to 20thDay
12%11%29%34%12%2
598
21st to endDay
8%8%31%34%15%5%
487
August1st to 10thDay
13%9%24%32%15%7%
447
11th to 20thDay
11%6%27%33%17%7%
437
21st to endDay
16%11%28%28%13%4
495
September1st to 10thDay
17%12%29%30%10%3
450
11th to 20thDay
23%8%24%29%14%3
450
21st to endDay
26%11%24%23%13%2
450
October1st to 10thDay
27%10%19%25%16%3
450
11th to 20thDay
35%8%19%23%12%3
450
21st to endDay
37%9%24%19%9%2
343
November1st to 10thDay
33%9%30%21%6%1
187
11th to 20thDay
40%8%22%17%10%3
180
21st to endDay
39%8%25%16%10%2
180
December1st to 10thDay
40%8%19%18%10%4
180
11th to 20thDay
41%7%25%21%43
180
21st to endDay
43%9%25%19%31
198
January1st to 10thNight
44%9%20%17%9%1
850
11th to 20thNight
41%7%17%23%11%
814
21st to endNight
38%6%23%24%8%1
836
February1st to 10thNight
39%9%23%24%5%
738
11th to 20thNight
38%9%20%25%8%
704
21st to endNight
33%13%19%24%10%1
592
March1st to 10thNight
33%7%19%24%16%1
720
11th to 20thNight
34%8%20%23%14%1
720
21st to endNight
35%9%20%24%10%2
792
April1st to 10thNight
32%5%20%29%12%2
720
11th to 20thNight
30%6%21%31%11%1
670
21st to endNight
35%5%17%31%11%2
446
May1st to 10thNight
24%6%14%34%20%1
360
11th to 20thNight
19%410%32%30%4
354
21st to endNight
25%5%6%35%27%2
389
June1st to 10thNight
23%316%35%22%3
360
11th to 20thNight
26%413%29%23%4
360
21st to endNight
18%410%34%31%3
360
July1st to 10thNight
16%37%32%38%4
350
11th to 20thNight
12%5%7%31%39%6%
348
21st to endNight
9%1333%47%7%
394
August1st to 10thNight
13%1326%47%10%
358
11th to 20thNight
9%25%32%45%7%
501
21st to endNight
13%311%35%35%4
688
September1st to 10thNight
14%314%37%29%3
720
11th to 20thNight
21%412%25%33%5%
720
21st to endNight
24%414%31%25%2
720
October1st to 10thNight
24%5%17%29%23%1
720
11th to 20thNight
35%5%15%27%17%2
720
21st to endNight
38%8%19%23%9%2
792
November1st to 10thNight
42%6%24%24%4
740
11th to 20thNight
44%6%22%16%10%1
760
21st to endNight
43%11%17%19%9%1
760
December1st to 10thNight
32%9%24%25%9%1
760
11th to 20thNight
44%7%25%19%5%
814
21st to endNight
45%9%22%20%4
935
Page generated at 2024-02-02 02:20:28. Version ac07

Copyright 2024 Attilla Danko


Chilliwack Clear Sky Chart |Charts Home