Whistler
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whistler clear sky chart from 2005-11-05 to 2017-12-20.

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
28%
14824
6%
47970
5%
14796
30%
14796
10%
38761

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
23%
750
7%
2686
5%
746
26%
746
7%
2272
January16th to endNight
18%
785
4%
2793
4%
785
20%
785
5%
2413
February1st to 15thNight
18%
698
4%
2294
3%
698
20%
698
6%
1995
February16th to endNight
21%
632
7%
2050
4%
632
26%
632
9%
1692
March1st to 15thNight
14%
720
2%
2066
1%
720
15%
720
6%
1865
March16th to endNight
16%
768
4%
2070
2%
768
17%
768
6%
1854
April1st to 15thNight
23%
705
4%
1785
2%
705
24%
705
8%
1550
April16th to endNight
24%
489
4%
1569
3%
489
25%
489
7%
1352
May1st to 15thNight
42%
359
7%
1440
9%
359
45%
359
11%
1081
May16th to endNight
38%
374
4%
1421
5%
374
39%
374
9%
1141
June1st to 15thNight
35%
360
1%
1260
0%
360
36%
360
12%
974
June16th to endNight
33%
360
2%
1260
0%
360
34%
360
10%
993
July1st to 15thNight
58%
340
5%
1190
3%
340
59%
340
29%
680
July16th to endNight
64%
376
10%
1299
14%
354
66%
354
30%
724
August1st to 15thNight
66%
409
14%
1481
18%
407
69%
407
30%
807
August16th to endNight
53%
603
16%
1749
13%
603
55%
603
27%
1116
September1st to 15thNight
51%
720
17%
1800
10%
720
53%
720
34%
1170
September16th to endNight
35%
716
13%
1976
9%
716
37%
716
17%
1495
October1st to 15thNight
28%
720
8%
2160
6%
720
30%
720
15%
1644
October16th to endNight
21%
768
5%
2427
3%
768
24%
768
7%
2066
November1st to 15thNight
9%
760
4%
2660
2%
760
12%
760
3%
2433
November16th to endNight
17%
780
3%
2730
2%
780
18%
780
5%
2395
December1st to 15thNight
21%
809
5%
2854
2%
809
24%
809
6%
2396
December16th to endNight
11%
823
3%
2950
2%
823
13%
823
4%
2653

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
18%18%5%7%5%34345%22%
48903
Night
15%18%6%8%6%34445%22%
48120
Cloud CoverDay
16%18%6%8%6%34345%21%
48903
Night
14%18%6%9%6%34445%20%
48123
TransparencyDay
65%6%9%11%5%
48557
Night
64%7%10%11%5%
47970
SeeingDay
26%17%26%20%6%1
6439
Night
25%11%27%23%10%
14832

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
22%24%7%5%5%2333416%
1253
16th to endDay
14%27%7%9%44323416%
1431
February1st to 15thDay
17%26%7%7%6%23335%14%
1569
16th to endDay
8%25%10%11%6%33445%15%
1424
March1st to 15thDay
15%31%7%11%6%332349%
1893
16th to endDay
13%33%8%10%6%344338%
2153
April1st to 15thDay
15%29%8%10%8%333339%
2161
16th to endDay
18%28%7%9%7%3433410%
2391
May1st to 15thDay
15%21%5%8%6%34446%18%
2511
16th to endDay
25%17%49%5%34445%15%
2687
June1st to 15thDay
29%14%46%7%3445%5%14%
2700
16th to endDay
26%13%5%7%6%33335%19%
2700
July1st to 15thDay
14%7%345%24446%42%
2700
16th to endDay
14%6%34424447%42%
2781
August1st to 15thDay
11%6%25%424447%46%
2469
16th to endDay
14%7%25%5%345%47%39%
2453
September1st to 15thDay
13%6%25%42335%5%47%
2160
16th to endDay
25%13%36%424335%26%
1980
October1st to 15thDay
22%13%47%5%34335%26%
1800
16th to endDay
23%20%5%7%5%2334418%
1793
November1st to 15thDay
23%28%7%6%5%2333311%
1528
16th to endDay
18%26%7%7%7%3433413%
1560
December1st to 15thDay
13%21%8%7%5%35%43323%
1434
16th to endDay
15%29%8%12%6%3332310%
1372
January1st to 15thNight
21%24%6%7%5%23335%17%
2686
16th to endNight
16%22%7%9%7%35%446%12%
2793
February1st to 15thNight
16%23%7%8%6%45%445%12%
2282
16th to endNight
10%21%9%10%6%34335%20%
2050
March1st to 15thNight
13%26%9%10%8%44335%12%
2066
16th to endNight
12%28%8%11%6%3343412%
2066
April1st to 15thNight
10%23%7%8%8%45%346%15%
1785
16th to endNight
13%20%6%10%7%45%5%46%15%
1569
May1st to 15thNight
13%14%46%5%35%5%5%7%27%
1439
16th to endNight
17%13%48%7%345%47%21%
1421
June1st to 15thNight
18%12%46%5%36%35%7%25%
1260
16th to endNight
18%10%48%6%45%345%26%
1260
July1st to 15thNight
7%435%42445%7%51%
1260
16th to endNight
9%434334446%52%
1388
August1st to 15thNight
8%41332336%7%54%
1489
16th to endNight
9%5%25%5%2346%8%45%
1749
September1st to 15thNight
8%5%25%5%245%5%7%49%
1800
16th to endNight
19%11%46%42445%6%29%
1976
October1st to 15thNight
18%13%47%6%34335%28%
2160
16th to endNight
23%18%48%6%3444415%
2427
November1st to 15thNight
27%25%6%8%6%3432210%
2660
16th to endNight
18%26%6%9%7%3444411%
2730
December1st to 15thNight
14%21%6%9%7%35%446%17%
2854
16th to endNight
15%27%9%11%6%3443410%
2950

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
21%24%6%8%5%2424413%
1253
16th to endDay
14%26%8%10%6%34235%13%
1431
February1st to 15thDay
18%25%7%9%5%34335%12%
1569
16th to endDay
7%25%10%12%6%3443414%
1424
March1st to 15thDay
15%30%9%10%7%243439%
1893
16th to endDay
13%31%9%12%6%344327%
2153
April1st to 15thDay
13%29%9%11%7%444339%
2161
16th to endDay
16%27%8%11%7%343349%
2391
May1st to 15thDay
13%19%6%10%7%34446%17%
2511
16th to endDay
21%19%6%8%7%34445%14%
2687
June1st to 15thDay
25%16%5%8%6%3445%5%14%
2700
16th to endDay
22%15%6%8%6%34445%17%
2700
July1st to 15thDay
12%7%35%425%347%41%
2700
16th to endDay
12%7%35%434447%41%
2781
August1st to 15thDay
10%6%35%5%3445%7%45%
2469
16th to endDay
12%8%35%5%3446%7%37%
2453
September1st to 15thDay
12%7%25%5%23346%46%
2160
16th to endDay
23%14%46%5%34335%25%
1980
October1st to 15thDay
20%14%48%6%2443425%
1800
16th to endDay
23%20%5%8%5%24336%16%
1793
November1st to 15thDay
23%27%8%8%5%2243210%
1528
16th to endDay
17%27%8%8%7%2334312%
1560
December1st to 15thDay
13%22%7%7%6%46%43420%
1434
16th to endDay
15%28%10%12%8%323338%
1372
January1st to 15thNight
20%24%7%6%5%24337%12%
2685
16th to endNight
15%23%7%12%6%44246%9%
2793
February1st to 15thNight
16%23%7%9%8%45%345%10%
2282
16th to endNight
9%22%8%11%7%44345%18%
2050
March1st to 15thNight
12%27%9%10%8%35%33411%
2066
16th to endNight
11%28%9%11%7%4433411%
2070
April1st to 15thNight
9%21%9%10%8%5%5%445%15%
1785
16th to endNight
13%18%6%9%8%6%5%5%5%5%14%
1569
May1st to 15thNight
13%12%5%8%5%35%5%5%7%27%
1439
16th to endNight
17%13%49%7%4446%7%20%
1421
June1st to 15thNight
16%13%48%5%35%5%47%24%
1260
16th to endNight
16%10%5%7%7%5%5%446%25%
1260
July1st to 15thNight
6%5%25%5%235%5%6%51%
1260
16th to endNight
7%5%35%32345%6%51%
1388
August1st to 15thNight
6%42432335%8%53%
1489
16th to endNight
8%5%26%6%245%6%8%44%
1749
September1st to 15thNight
7%5%25%5%335%6%6%48%
1800
16th to endNight
17%10%47%5%345%6%5%28%
1976
October1st to 15thNight
18%14%47%6%3444428%
2160
16th to endNight
21%19%5%10%6%35%445%14%
2427
November1st to 15thNight
26%25%6%9%6%343229%
2660
16th to endNight
18%27%6%9%8%4433310%
2730
December1st to 15thNight
14%21%7%10%7%35%446%14%
2854
16th to endNight
15%28%9%11%7%343447%
2950

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
75%5%5%8%31
1253
16th to endDay
73%6%8%5%32
1431
February1st to 15thDay
73%7%8%5%41
1569
16th to endDay
73%5%8%8%4
1424
March1st to 15thDay
80%5%5%5%1
1893
16th to endDay
83%5%5%4
2153
April1st to 15thDay
81%46%6%1
2161
16th to endDay
80%47%6%1
2391
May1st to 15thDay
66%6%10%10%4
2511
16th to endDay
70%7%10%9%1
2691
June1st to 15thDay
70%6%11%7%2
2700
16th to endDay
68%6%9%10%4
2700
July1st to 15thDay
43%5%14%21%13%1
2541
16th to endDay
41%6%13%23%13%1
2607
August1st to 15thDay
38%7%14%27%10%1
2452
16th to endDay
43%7%14%24%8%1
2453
September1st to 15thDay
39%6%12%22%16%2
2160
16th to endDay
62%5%9%12%7%2
1980
October1st to 15thDay
62%5%10%13%8%
1800
16th to endDay
70%6%9%9%3
1793
November1st to 15thDay
79%5%5%5%21
1528
16th to endDay
76%5%6%5%31
1560
December1st to 15thDay
68%6%9%7%6%1
1434
16th to endDay
82%44421
1372
January1st to 15thNight
72%6%7%8%41
2686
16th to endNight
73%7%8%5%3
2793
February1st to 15thNight
72%8%8%5%4
2294
16th to endNight
67%6%9%12%3
2050
March1st to 15thNight
77%6%7%6%1
2066
16th to endNight
77%5%9%5%
2070
April1st to 15thNight
71%7%9%9%1
1785
16th to endNight
70%8%10%7%2
1569
May1st to 15thNight
56%9%15%13%4
1440
16th to endNight
63%9%13%11%1
1421
June1st to 15thNight
60%7%19%8%4
1260
16th to endNight
61%9%11%14%2
1260
July1st to 15thNight
32%7%21%23%13%2
1190
16th to endNight
30%8%19%30%10%1
1299
August1st to 15thNight
29%8%18%30%10%2
1481
16th to endNight
36%8%20%23%8%1
1749
September1st to 15thNight
33%8%14%24%16%1
1800
16th to endNight
55%6%11%16%7%2
1976
October1st to 15thNight
58%5%11%16%7%
2160
16th to endNight
71%6%7%9%4
2427
November1st to 15thNight
82%5%3421
2660
16th to endNight
77%5%7%441
2730
December1st to 15thNight
69%8%9%6%41
2854
16th to endNight
79%6%5%431
2950

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
6%5%33%31%18%5%
60
16th to endDay
39%14%20%17%6%3
64
February1st to 15thDay
29%20%25%16%6%
229
16th to endDay
17%24%29%18%8%1
212
March1st to 15thDay
35%28%24%10%
270
16th to endDay
37%21%25%10%4
288
April1st to 15thDay
31%23%23%15%41
269
16th to endDay
33%23%19%17%41
270
May1st to 15thDay
26%18%23%22%6%1
288
16th to endDay
27%8%25%26%9%2
402
June1st to 15thDay
31%16%25%17%8%1
495
16th to endDay
27%16%29%20%41
495
July1st to 15thDay
17%12%31%30%6%1
475
16th to endDay
14%11%33%32%5%2
450
August1st to 15thDay
13%9%28%28%13%4
315
16th to endDay
14%16%34%25%7%1
332
September1st to 15thDay
19%19%28%22%8%1
315
16th to endDay
30%15%25%19%8%
315
October1st to 15thDay
32%19%27%13%5%
315
16th to endDay
41%16%18%16%6%
238
November1st to 15thDay
42%21%20%11%5%
90
16th to endDay
40%16%22%10%46%
90
December1st to 15thDay
27%14%12%22%17%5%
90
16th to endDay
19%20%36%15%6%1
72
January1st to 15thNight
33%15%24%20%6%
750
16th to endNight
27%16%28%19%6%
785
February1st to 15thNight
30%13%29%20%6%
704
16th to endNight
19%16%32%22%8%
632
March1st to 15thNight
31%16%31%15%5%
720
16th to endNight
28%15%30%18%7%
768
April1st to 15thNight
23%12%30%23%7%1
705
16th to endNight
24%10%32%24%7%
489
May1st to 15thNight
20%7%21%31%16%1
360
16th to endNight
24%5%21%33%15%
375
June1st to 15thNight
20%7%28%30%11%1
360
16th to endNight
21%9%26%30%12%
360
July1st to 15thNight
8%421%40%23%
340
16th to endNight
7%416%43%26%
376
August1st to 15thNight
8%216%39%32%1
409
16th to endNight
12%6%21%34%23%
603
September1st to 15thNight
11%5%27%27%25%3
720
16th to endNight
25%8%25%24%14%1
716
October1st to 15thNight
26%7%30%22%11%
720
16th to endNight
34%14%23%19%7%
768
November1st to 15thNight
42%15%26%12%2
760
16th to endNight
34%16%23%17%6%1
780
December1st to 15thNight
25%14%32%20%6%
809
16th to endNight
31%15%34%14%2
823
Page generated at 2017-12-21 04:04:50. Version ac04

Copyright 2017 A. Danko


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