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 2017-08-12.

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%
14319
7%
46322
4%
14290
24%
14290
9%
36727

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
13%
746
9%
2662
4%
742
20%
742
7%
2198
January16th to endNight
15%
768
8%
2688
5%
768
19%
768
7%
2197
February1st to 15thNight
9%
701
4%
2314
2%
700
12%
700
5%
1988
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%
372
15%
1420
20%
370
64%
370
29%
743
August16th to endNight
46%
594
15%
1644
10%
594
50%
594
26%
1063
September1st to 15thNight
40%
660
18%
1650
8%
660
44%
660
29%
1093
September16th to endNight
31%
656
15%
1796
8%
656
36%
656
17%
1343
October1st to 15thNight
23%
660
10%
1980
7%
660
27%
660
13%
1488
October16th to endNight
15%
704
5%
2216
2%
704
20%
704
7%
1853
November1st to 15thNight
6%
700
4%
2426
1%
700
8%
700
4%
2171
November16th to endNight
10%
720
4%
2520
1%
720
13%
720
5%
2119
December1st to 15thNight
8%
720
6%
2520
1%
720
14%
720
6%
2083
December16th to endNight
4%
796
4%
2856
0%
796
9%
796
4%
2503

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%5%6%5%2333423%
47675
Night
20%18%47%5%24345%23%
46478
Cloud CoverDay
20%18%5%7%5%3333423%
47675
Night
18%18%5%7%6%34445%22%
46481
TransparencyDay
64%5%9%13%6%1
47335
Night
63%6%10%12%6%1
46322
SeeingDay
27%25%25%15%41
5777
Night
24%25%24%18%6%
14323

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
28%17%6%8%42424317%
1274
16th to endDay
21%22%5%5%5%2434419%
1536
February1st to 15thDay
22%21%6%8%6%23345%14%
1549
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%1442345%7%45%
2445
16th to endDay
17%7%25%5%245%47%37%
2206
September1st to 15thDay
16%7%25%322335%48%
1980
16th to endDay
26%9%35%423435%31%
1831
October1st to 15thDay
24%11%36%5%35%345%25%
1650
16th to endDay
32%12%36%5%2435%319%
1656
November1st to 15thDay
36%23%5%6%2243339%
1430
16th to endDay
22%23%5%6%5%2433417%
1440
December1st to 15thDay
15%26%8%9%5%2323419%
1440
16th to endDay
18%29%9%9%5%2222314%
1365
January1st to 15thNight
28%20%5%6%422235%16%
2662
16th to endNight
20%21%5%7%6%24445%16%
2688
February1st to 15thNight
22%21%6%8%6%2444414%
2302
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%
1428
16th to endNight
10%5%25%5%35%46%8%42%
1644
September1st to 15thNight
12%6%25%5%2334449%
1650
16th to endNight
23%8%26%6%24346%30%
1796
October1st to 15thNight
23%11%36%5%33335%29%
1980
16th to endNight
28%14%37%6%35%44417%
2216
November1st to 15thNight
34%19%48%5%2323310%
2426
16th to endNight
23%24%5%7%5%3432415%
2520
December1st to 15thNight
18%23%6%7%5%34445%16%
2520
16th to endNight
19%28%7%8%6%2333312%
2856

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
24%19%6%7%5%3433318%
1274
16th to endDay
17%23%5%7%6%3335%5%18%
1536
February1st to 15thDay
20%21%7%9%6%23345%13%
1549
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%
2445
16th to endDay
16%7%36%5%2445%6%38%
2206
September1st to 15thDay
15%8%24423235%48%
1980
16th to endDay
25%9%36%434335%30%
1831
October1st to 15thDay
23%12%46%6%35%345%25%
1650
16th to endDay
29%14%38%5%3333419%
1656
November1st to 15thDay
31%25%6%5%5%233339%
1430
16th to endDay
18%23%7%8%5%34335%16%
1440
December1st to 15thDay
13%26%8%8%6%3432418%
1440
16th to endDay
15%28%9%10%7%3322213%
1365
January1st to 15thNight
25%20%6%8%5%23345%15%
2661
16th to endNight
17%22%6%9%6%34447%14%
2688
February1st to 15thNight
20%23%6%9%7%3433412%
2302
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%24313336%57%
1428
16th to endNight
9%5%25%5%35%46%8%43%
1644
September1st to 15thNight
11%7%25%5%2433449%
1650
16th to endNight
22%9%35%5%24436%30%
1796
October1st to 15thNight
22%13%45%6%24345%29%
1980
16th to endNight
26%15%48%7%3444417%
2216
November1st to 15thNight
29%21%6%9%5%333349%
2426
16th to endNight
19%25%6%8%6%3433314%
2520
December1st to 15thNight
15%24%5%10%6%24445%15%
2520
16th to endNight
17%27%8%10%6%3333311%
2856

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%36%12%41
1274
16th to endDay
67%5%7%9%6%2
1536
February1st to 15thDay
72%7%7%7%41
1549
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
35%7%17%23%11%2
2428
16th to endDay
45%7%12%24%8%1
2206
September1st to 15thDay
40%5%10%23%17%2
1980
16th to endDay
57%49%15%10%2
1831
October1st to 15thDay
60%6%10%13%8%
1650
16th to endDay
69%5%9%12%4
1656
November1st to 15thDay
81%5%5%5%11
1430
16th to endDay
70%6%5%8%5%2
1440
December1st to 15thDay
71%5%6%10%5%
1440
16th to endDay
78%5%45%5%
1365
January1st to 15thNight
71%36%10%5%1
2662
16th to endNight
69%46%9%5%3
2688
February1st to 15thNight
75%46%7%41
2314
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
28%7%20%26%14%2
1420
16th to endNight
36%8%18%25%10%1
1644
September1st to 15thNight
37%6%12%20%20%2
1650
16th to endNight
54%5%10%16%9%3
1796
October1st to 15thNight
57%5%10%16%8%
1980
16th to endNight
68%7%7%10%5%
2216
November1st to 15thNight
79%5%6%421
2426
16th to endNight
73%46%7%6%2
2520
December1st to 15thNight
69%6%9%10%4
2520
16th to endNight
77%5%5%5%41
2856

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
8%13%35%25%16%1
60
16th to endDay
34%23%25%14%3
64
February1st to 15thDay
33%31%21%11%
209
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
14%17%28%26%11%2
300
16th to endDay
16%22%33%22%3
268
September1st to 15thDay
27%23%22%18%7%1
255
16th to endDay
26%23%25%18%5%
255
October1st to 15thDay
30%27%23%12%5%
255
16th to endDay
33%16%27%17%4
168
November1st to 15thDay
42%28%25%4
64
16th to endDay
23%26%23%10%10%6%
60
December1st to 15thDay
30%26%33%6%3
60
16th to endDay
20%23%39%17%
64
January1st to 15thNight
29%28%25%15%1
746
16th to endNight
23%30%27%15%2
768
February1st to 15thNight
28%29%26%13%2
704
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%
372
16th to endNight
12%14%21%37%14%
594
September1st to 15thNight
14%15%25%21%21%1
660
16th to endNight
26%16%22%24%10%
656
October1st to 15thNight
30%17%25%21%5%
660
16th to endNight
35%19%25%16%3
704
November1st to 15thNight
35%29%26%7%1
700
16th to endNight
30%32%22%10%2
720
December1st to 15thNight
25%32%31%10%
720
16th to endNight
25%35%30%8%
796
Page generated at 2017-08-13 11:16:31. Version ac04

Copyright 2017 A. Danko


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