Chilliwack Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chilliwack Lake clear sky chart from 2005-11-05 to 2018-02-14.

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
21%
15078
7%
48699
4%
15049
25%
15049
10%
38594

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
14%
819
8%
2885
4%
815
21%
815
8%
2371
January16th to endNight
14%
832
7%
2912
4%
832
18%
832
6%
2414
February1st to 15thNight
8%
757
5%
2498
2%
756
12%
756
5%
2145
February16th to endNight
12%
632
8%
2005
2%
632
20%
632
7%
1656
March1st to 15thNight
10%
720
2%
2106
1%
720
12%
720
5%
1842
March16th to endNight
10%
768
4%
2040
1%
768
12%
768
6%
1813
April1st to 15thNight
15%
719
4%
1799
2%
719
16%
719
8%
1577
April16th to endNight
19%
513
6%
1593
3%
513
22%
513
8%
1342
May1st to 15thNight
30%
360
9%
1440
11%
360
35%
360
10%
1072
May16th to endNight
29%
374
4%
1496
7%
374
31%
374
7%
1188
June1st to 15thNight
28%
360
1%
1305
1%
360
29%
360
9%
1036
June16th to endNight
32%
360
4%
1260
1%
360
33%
360
12%
936
July1st to 15thNight
53%
340
6%
1190
5%
340
55%
340
26%
700
July16th to endNight
51%
376
13%
1396
16%
354
60%
354
28%
723
August1st to 15thNight
61%
382
15%
1454
19%
380
64%
380
29%
760
August16th to endNight
49%
648
17%
1794
12%
648
53%
648
28%
1135
September1st to 15thNight
42%
720
18%
1800
8%
720
45%
720
30%
1178
September16th to endNight
33%
716
16%
1960
9%
716
37%
716
17%
1468
October1st to 15thNight
24%
720
9%
2160
6%
720
28%
720
13%
1631
October16th to endNight
17%
768
7%
2418
4%
768
22%
768
8%
1985
November1st to 15thNight
6%
760
3%
2634
1%
760
8%
760
3%
2368
November16th to endNight
9%
780
3%
2730
1%
780
12%
780
4%
2328
December1st to 15thNight
12%
780
7%
2730
2%
780
18%
780
7%
2213
December16th to endNight
4%
874
5%
3094
1%
874
9%
874
4%
2713

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%17%46%5%2333423%
49400
Night
20%18%46%5%24345%23%
48855
Cloud CoverDay
20%18%5%7%5%3333423%
49400
Night
18%18%5%7%6%34445%22%
48858
TransparencyDay
63%5%9%13%6%1
49060
Night
63%6%10%12%6%1
48699
SeeingDay
27%25%25%16%41
6314
Night
24%25%24%18%6%
15082

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
27%18%5%8%42423318%
1381
16th to endDay
21%23%5%6%5%2434418%
1664
February1st to 15thDay
25%20%6%7%6%23335%14%
1665
16th to endDay
13%28%8%9%6%2332217%
1469
March1st to 15thDay
18%28%10%11%5%2332210%
1854
16th to endDay
19%31%9%9%6%333327%
2184
April1st to 15thDay
20%36%6%7%5%242328%
2149
16th to endDay
23%29%5%6%43443311%
2364
May1st to 15thDay
21%21%35%5%34345%21%
2511
16th to endDay
33%14%46%5%33345%14%
2615
June1st to 15thDay
38%12%45%5%2323315%
2652
16th to endDay
33%11%46%5%2333420%
2700
July1st to 15thDay
17%6%25%42333444%
2700
16th to endDay
13%6%24423445%48%
2675
August1st to 15thDay
14%5%1443345%7%44%
2496
16th to endDay
16%6%25%5%245%47%39%
2407
September1st to 15thDay
15%6%25%323335%49%
2160
16th to endDay
26%9%36%423435%30%
1997
October1st to 15thDay
24%11%46%5%35%345%26%
1800
16th to endDay
31%12%36%5%2435%320%
1806
November1st to 15thDay
34%24%5%7%3243329%
1552
16th to endDay
23%24%5%6%5%24235%16%
1560
December1st to 15thDay
15%24%7%9%5%2332421%
1560
16th to endDay
20%28%9%8%5%2222214%
1479
January1st to 15thNight
28%20%5%6%422235%17%
2885
16th to endNight
20%23%5%7%6%23345%15%
2912
February1st to 15thNight
24%21%6%8%5%2434414%
2486
16th to endNight
15%26%5%8%6%3423419%
2005
March1st to 15thNight
19%25%7%8%5%4433413%
2106
16th to endNight
20%27%7%6%7%3442313%
2036
April1st to 15thNight
14%31%6%7%6%2433413%
1799
16th to endNight
21%22%47%5%2445%416%
1593
May1st to 15thNight
17%15%36%5%35%446%25%
1439
16th to endNight
26%10%37%6%35%45%6%20%
1496
June1st to 15thNight
29%9%37%5%34445%22%
1305
16th to endNight
21%11%36%5%25%45%5%28%
1260
July1st to 15thNight
10%5%33424446%50%
1260
16th to endNight
10%4235%23245%54%
1491
August1st to 15thNight
9%414313346%56%
1462
16th to endNight
9%5%245%3446%8%44%
1794
September1st to 15thNight
11%6%25%5%23345%50%
1800
16th to endNight
23%9%25%5%24346%30%
1960
October1st to 15thNight
23%11%36%5%34335%29%
2160
16th to endNight
28%14%37%5%35%44419%
2418
November1st to 15thNight
33%19%49%5%2323310%
2634
16th to endNight
23%25%5%7%5%3432414%
2730
December1st to 15thNight
17%22%6%6%6%34445%18%
2730
16th to endNight
20%28%7%7%6%2333312%
3094

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
23%19%6%7%5%3433318%
1381
16th to endDay
17%24%5%8%6%3334417%
1664
February1st to 15thDay
21%21%7%9%6%23345%14%
1665
16th to endDay
11%27%10%9%6%3333317%
1469
March1st to 15thDay
14%30%9%11%7%333339%
1854
16th to endDay
15%31%10%10%7%333337%
2184
April1st to 15thDay
17%34%8%8%6%243238%
2149
16th to endDay
20%28%6%9%43343411%
2364
May1st to 15thDay
19%21%37%433446%20%
2511
16th to endDay
30%16%5%6%5%3344414%
2615
June1st to 15thDay
34%15%46%5%2323416%
2652
16th to endDay
31%12%36%6%3334321%
2700
July1st to 15thDay
15%6%35%42434445%
2700
16th to endDay
11%5%35%424346%48%
2675
August1st to 15thDay
13%6%2442345%7%46%
2496
16th to endDay
14%7%35%5%2446%6%40%
2407
September1st to 15thDay
14%7%24423235%49%
2160
16th to endDay
25%9%36%5%3433429%
1997
October1st to 15thDay
22%12%46%6%34345%24%
1800
16th to endDay
28%14%38%5%3333420%
1806
November1st to 15thDay
30%25%6%6%5%233339%
1552
16th to endDay
19%23%7%8%5%34335%15%
1560
December1st to 15thDay
12%24%8%8%6%3443320%
1560
16th to endDay
16%27%9%11%6%2322214%
1479
January1st to 15thNight
24%20%6%8%423245%15%
2884
16th to endNight
17%24%6%9%6%34447%13%
2912
February1st to 15thNight
20%23%7%9%7%3433413%
2486
16th to endNight
11%25%8%10%7%33435%16%
2005
March1st to 15thNight
15%25%8%9%7%36%335%12%
2106
16th to endNight
16%27%9%8%6%3442312%
2040
April1st to 15thNight
13%29%7%8%7%3433413%
1799
16th to endNight
18%22%49%6%2444416%
1593
May1st to 15thNight
15%17%36%6%445%46%25%
1439
16th to endNight
23%12%36%7%45%45%6%20%
1496
June1st to 15thNight
26%12%45%7%33445%21%
1305
16th to endNight
19%12%26%5%3445%6%28%
1260
July1st to 15thNight
11%413425%445%51%
1260
16th to endNight
9%323424345%54%
1491
August1st to 15thNight
7%6%24313346%57%
1462
16th to endNight
8%425%5%25%45%8%45%
1794
September1st to 15thNight
10%6%35%5%23335%50%
1800
16th to endNight
21%10%36%6%24436%30%
1960
October1st to 15thNight
20%13%46%5%24445%28%
2160
16th to endNight
25%15%48%7%3444419%
2418
November1st to 15thNight
28%21%7%9%5%333338%
2634
16th to endNight
19%25%6%8%7%3434313%
2730
December1st to 15thNight
14%23%5%9%6%24445%17%
2730
16th to endNight
18%27%8%10%6%3333311%
3094

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
71%46%12%41
1381
16th to endDay
69%5%7%9%6%2
1664
February1st to 15thDay
72%7%6%7%5%1
1665
16th to endDay
72%48%9%3
1469
March1st to 15thDay
80%5%7%5%1
1854
16th to endDay
82%47%4
2184
April1st to 15thDay
81%5%6%5%1
2149
16th to endDay
76%5%9%42
2364
May1st to 15thDay
64%6%12%11%4
2511
16th to endDay
71%8%10%9%1
2619
June1st to 15thDay
72%5%9%8%21
2652
16th to endDay
67%410%14%3
2700
July1st to 15thDay
43%6%10%24%12%2
2541
16th to endDay
35%6%12%27%15%2
2507
August1st to 15thDay
36%7%18%23%11%2
2479
16th to endDay
43%7%13%25%8%1
2407
September1st to 15thDay
39%5%9%23%18%3
2160
16th to endDay
58%49%15%10%2
1997
October1st to 15thDay
60%6%10%13%8%
1800
16th to endDay
67%48%12%5%
1806
November1st to 15thDay
80%5%5%411
1552
16th to endDay
71%6%5%8%5%2
1560
December1st to 15thDay
69%5%7%10%6%1
1560
16th to endDay
78%5%46%5%
1479
January1st to 15thNight
71%36%11%5%1
2885
16th to endNight
71%46%8%5%2
2912
February1st to 15thNight
75%46%7%42
2498
16th to endNight
70%38%13%21
2005
March1st to 15thNight
74%6%10%6%1
2106
16th to endNight
76%5%9%7%
2040
April1st to 15thNight
73%6%10%7%1
1799
16th to endNight
67%8%10%9%2
1593
May1st to 15thNight
57%8%13%13%6%
1440
16th to endNight
61%10%13%10%2
1496
June1st to 15thNight
63%7%13%11%3
1305
16th to endNight
53%9%15%16%3
1260
July1st to 15thNight
33%8%16%26%13%2
1190
16th to endNight
28%6%16%27%17%2
1396
August1st to 15thNight
27%7%20%26%14%2
1454
16th to endNight
34%8%18%25%10%1
1794
September1st to 15thNight
36%6%12%20%21%2
1800
16th to endNight
55%5%10%16%9%2
1960
October1st to 15thNight
57%6%10%16%9%
2160
16th to endNight
67%6%7%11%7%
2418
November1st to 15thNight
80%5%5%421
2634
16th to endNight
74%46%6%5%1
2730
December1st to 15thNight
67%6%9%10%41
2730
16th to endNight
78%45%5%5%1
3094

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
14%15%30%20%18%1
90
16th to endDay
38%29%17%12%2
96
February1st to 15thDay
34%31%21%10%
247
16th to endDay
26%28%27%11%5%
219
March1st to 15thDay
37%36%20%4
270
16th to endDay
29%38%21%8%1
288
April1st to 15thDay
37%29%20%8%21
269
16th to endDay
35%30%20%10%31
270
May1st to 15thDay
30%27%22%15%21
288
16th to endDay
33%23%19%14%8%2
330
June1st to 15thDay
33%23%22%15%4
447
16th to endDay
28%27%25%15%31
495
July1st to 15thDay
17%21%31%25%31
475
16th to endDay
12%25%31%23%34
344
August1st to 15thDay
13%17%27%27%10%2
315
16th to endDay
13%21%32%24%6%
332
September1st to 15thDay
22%22%25%21%6%1
315
16th to endDay
27%20%25%18%6%1
315
October1st to 15thDay
29%25%25%13%41
315
16th to endDay
32%18%26%19%3
222
November1st to 15thDay
37%28%27%5%11
96
16th to endDay
33%24%23%7%6%4
90
December1st to 15thDay
23%18%28%16%12%
90
16th to endDay
28%22%36%12%
96
January1st to 15thNight
30%26%25%16%1
819
16th to endNight
24%30%28%14%2
832
February1st to 15thNight
29%28%25%13%2
760
16th to endNight
21%31%29%15%2
632
March1st to 15thNight
23%35%25%11%3
720
16th to endNight
27%31%25%11%2
768
April1st to 15thNight
26%29%22%16%4
719
16th to endNight
25%27%25%15%5%
513
May1st to 15thNight
19%22%21%24%11%
360
16th to endNight
24%20%16%27%10%
375
June1st to 15thNight
23%21%20%22%11%
360
16th to endNight
22%20%18%28%10%
360
July1st to 15thNight
12%16%15%37%17%
340
16th to endNight
6%19%19%32%22%
376
August1st to 15thNight
10%11%12%33%31%
382
16th to endNight
11%12%20%37%16%
648
September1st to 15thNight
13%14%26%23%21%1
720
16th to endNight
26%15%21%24%11%
716
October1st to 15thNight
29%16%26%22%5%
720
16th to endNight
34%18%25%17%3
768
November1st to 15thNight
35%29%26%7%1
760
16th to endNight
30%32%23%10%2
780
December1st to 15thNight
25%30%30%13%1
780
16th to endNight
26%33%31%8%
874
Page generated at 2018-02-15 07:58:39. Version ac04

Copyright 2018 A. Danko


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