Squamish
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Squamish 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
29%
14853
8%
47967
5%
14822
32%
14822
11%
37655

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
22%
750
10%
2686
7%
746
26%
746
8%
2220
January16th to endNight
20%
784
7%
2775
4%
784
24%
784
7%
2266
February1st to 15thNight
18%
701
5%
2288
3%
699
22%
699
8%
1914
February16th to endNight
19%
632
9%
2050
4%
632
26%
632
10%
1632
March1st to 15thNight
15%
720
4%
2058
2%
720
17%
720
6%
1821
March16th to endNight
16%
768
4%
2076
2%
768
18%
768
7%
1834
April1st to 15thNight
25%
704
4%
1784
2%
704
26%
704
10%
1524
April16th to endNight
25%
501
5%
1581
3%
501
27%
501
10%
1312
May1st to 15thNight
44%
360
9%
1440
12%
360
46%
360
13%
1038
May16th to endNight
38%
375
5%
1431
7%
374
40%
374
12%
1088
June1st to 15thNight
33%
360
1%
1260
1%
360
33%
360
13%
961
June16th to endNight
38%
360
3%
1260
1%
360
38%
360
11%
964
July1st to 15thNight
64%
340
7%
1190
5%
340
65%
340
29%
679
July16th to endNight
68%
376
12%
1304
17%
354
71%
354
31%
700
August1st to 15thNight
72%
426
13%
1498
17%
424
73%
424
32%
812
August16th to endNight
61%
603
15%
1749
13%
603
61%
603
28%
1122
September1st to 15thNight
58%
720
19%
1800
10%
720
60%
720
37%
1137
September16th to endNight
38%
716
14%
1978
10%
716
40%
716
17%
1485
October1st to 15thNight
31%
720
9%
2160
8%
720
34%
720
16%
1620
October16th to endNight
23%
768
6%
2418
4%
768
26%
768
8%
2009
November1st to 15thNight
10%
760
4%
2660
2%
760
13%
760
4%
2366
November16th to endNight
16%
780
5%
2730
3%
780
19%
780
6%
2296
December1st to 15thNight
18%
806
7%
2841
4%
806
23%
806
8%
2289
December16th to endNight
7%
823
6%
2950
1%
823
12%
823
4%
2566

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
29%12%35%42333425%
48910
Night
29%13%35%42333426%
48118
Cloud CoverDay
28%15%35%42333425%
48910
Night
27%15%35%42333425%
48121
TransparencyDay
63%5%9%13%6%1
48565
Night
62%5%10%12%6%1
47967
SeeingDay
34%12%25%19%6%1
6447
Night
36%6%22%21%11%1
14856

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
41%14%35%31132318%
1253
16th to endDay
33%18%45%42323418%
1445
February1st to 15thDay
34%17%45%323325%18%
1576
16th to endDay
22%22%46%43344418%
1424
March1st to 15thDay
39%20%36%5%1222311%
1902
16th to endDay
34%23%36%5%2332211%
2148
April1st to 15thDay
30%20%47%6%3333412%
2161
16th to endDay
32%17%5%7%5%3333313%
2379
May1st to 15thDay
24%12%5%7%5%24445%23%
2511
16th to endDay
31%11%36%5%35%445%19%
2678
June1st to 15thDay
35%10%36%423345%19%
2700
16th to endDay
32%10%47%5%2334422%
2700
July1st to 15thDay
15%426%434345%45%
2700
16th to endDay
16%5%23324346%46%
2773
August1st to 15thDay
14%5%23323447%47%
2454
16th to endDay
16%5%245%23447%41%
2453
September1st to 15thDay
13%6%24423346%47%
2160
16th to endDay
30%8%35%5%2333428%
1980
October1st to 15thDay
32%6%35%41333330%
1800
16th to endDay
41%10%35%41322420%
1806
November1st to 15thDay
48%13%3431322213%
1528
16th to endDay
39%16%25%32322317%
1560
December1st to 15thDay
30%17%4442321325%
1447
16th to endDay
36%27%4421312115%
1372
January1st to 15thNight
38%15%3432233319%
2686
16th to endNight
34%16%35%412246%17%
2775
February1st to 15thNight
32%17%35%423245%16%
2276
16th to endNight
24%21%36%42323423%
2050
March1st to 15thNight
37%21%35%31322314%
2058
16th to endNight
35%20%25%42333315%
2072
April1st to 15thNight
26%19%45%5%3434319%
1784
16th to endNight
28%14%45%5%23345%21%
1581
May1st to 15thNight
20%7%25%425%6%37%32%
1439
16th to endNight
22%9%47%5%25%45%7%26%
1431
June1st to 15thNight
26%9%36%6%13345%28%
1260
16th to endNight
24%8%37%5%25%35%329%
1260
July1st to 15thNight
11%31232435%6%53%
1260
16th to endNight
12%423223345%56%
1394
August1st to 15thNight
12%4121235%46%55%
1506
16th to endNight
13%5%1443445%8%45%
1749
September1st to 15thNight
11%41331235%5%56%
1800
16th to endNight
29%8%34423335%31%
1978
October1st to 15thNight
27%9%1342445%332%
2160
16th to endNight
38%10%25%42342319%
2418
November1st to 15thNight
48%14%2442232311%
2660
16th to endNight
38%15%35%42222219%
2730
December1st to 15thNight
30%16%45%32343421%
2841
16th to endNight
36%23%45%31222315%
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
37%19%3421234317%
1253
16th to endDay
30%20%45%42222419%
1445
February1st to 15thDay
31%20%44323225%18%
1576
16th to endDay
18%25%6%7%5%3334418%
1424
March1st to 15thDay
34%26%45%42222311%
1902
16th to endDay
30%28%5%6%5%2322210%
2148
April1st to 15thDay
27%26%5%7%42332411%
2161
16th to endDay
29%23%5%8%42333312%
2379
May1st to 15thDay
23%15%5%7%5%2335%421%
2511
16th to endDay
32%12%36%5%34445%17%
2678
June1st to 15thDay
36%12%45%423345%16%
2700
16th to endDay
34%10%46%5%2323421%
2700
July1st to 15thDay
15%6%24424345%44%
2700
16th to endDay
18%5%24323446%45%
2773
August1st to 15thDay
15%5%24323347%47%
2454
16th to endDay
16%6%25%43345%6%40%
2453
September1st to 15thDay
15%5%2432435%5%46%
2160
16th to endDay
32%10%2442323428%
1980
October1st to 15thDay
32%9%25%31333330%
1800
16th to endDay
42%11%25%412225%19%
1806
November1st to 15thDay
46%17%25%31222213%
1528
16th to endDay
35%20%3442232217%
1560
December1st to 15thDay
26%19%46%32322225%
1447
16th to endDay
30%29%6%6%31221114%
1372
January1st to 15thNight
35%18%25%22334319%
2685
16th to endNight
30%19%35%323247%17%
2775
February1st to 15thNight
29%20%45%423346%16%
2276
16th to endNight
20%25%36%42223323%
2050
March1st to 15thNight
33%24%36%32332214%
2058
16th to endNight
31%24%35%42323414%
2076
April1st to 15thNight
23%23%45%5%3333418%
1784
16th to endNight
26%18%37%5%22335%20%
1581
May1st to 15thNight
19%10%24435%5%47%31%
1439
16th to endNight
24%10%36%5%2445%7%25%
1431
June1st to 15thNight
27%10%37%43443426%
1260
16th to endNight
26%7%36%6%345%45%27%
1260
July1st to 15thNight
11%324423347%52%
1260
16th to endNight
13%5%22212446%55%
1394
August1st to 15thNight
12%3132135%46%55%
1506
16th to endNight
13%5%244345%5%8%44%
1749
September1st to 15thNight
13%31222346%5%53%
1800
16th to endNight
28%9%35%323336%30%
1978
October1st to 15thNight
26%10%25%41344431%
2160
16th to endNight
37%11%35%42433319%
2418
November1st to 15thNight
46%17%3341222311%
2660
16th to endNight
34%20%3442222218%
2730
December1st to 15thNight
26%19%45%42333422%
2841
16th to endNight
31%28%5%5%31222214%
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
71%36%10%5%2
1253
16th to endDay
70%48%9%32
1445
February1st to 15thDay
71%49%7%5%1
1576
16th to endDay
69%5%8%11%4
1424
March1st to 15thDay
80%46%6%1
1902
16th to endDay
81%37%7%
2148
April1st to 15thDay
78%5%6%7%1
2161
16th to endDay
78%5%6%6%2
2379
May1st to 15thDay
65%7%10%12%4
2511
16th to endDay
70%7%9%10%2
2682
June1st to 15thDay
70%6%11%7%2
2700
16th to endDay
67%410%12%4
2700
July1st to 15thDay
43%6%13%21%12%1
2541
16th to endDay
38%7%14%24%12%1
2600
August1st to 15thDay
37%8%14%26%10%1
2437
16th to endDay
43%7%17%22%7%1
2453
September1st to 15thDay
39%6%11%21%16%3
2160
16th to endDay
61%5%8%14%8%2
1980
October1st to 15thDay
59%5%11%13%9%
1800
16th to endDay
71%39%10%4
1806
November1st to 15thDay
79%45%431
1528
16th to endDay
74%447%6%2
1560
December1st to 15thDay
66%46%11%8%2
1447
16th to endDay
80%347%21
1372
January1st to 15thNight
70%5%5%11%5%2
2686
16th to endNight
68%6%7%10%43
2775
February1st to 15thNight
70%5%8%8%41
2288
16th to endNight
66%410%12%5%1
2050
March1st to 15thNight
77%46%9%2
2058
16th to endNight
76%5%9%7%
2076
April1st to 15thNight
70%6%10%10%2
1784
16th to endNight
67%7%11%10%2
1581
May1st to 15thNight
52%9%16%16%4
1440
16th to endNight
58%7%15%14%3
1431
June1st to 15thNight
61%5%19%8%31
1260
16th to endNight
58%9%11%16%31
1260
July1st to 15thNight
33%6%20%23%14%1
1190
16th to endNight
29%7%17%30%13%2
1304
August1st to 15thNight
29%7%21%26%12%2
1498
16th to endNight
37%7%20%21%8%3
1749
September1st to 15thNight
30%8%15%24%17%3
1800
16th to endNight
56%5%11%16%6%3
1978
October1st to 15thNight
55%7%11%14%11%
2160
16th to endNight
70%5%8%10%5%
2418
November1st to 15thNight
80%45%5%21
2660
16th to endNight
73%36%6%7%1
2730
December1st to 15thNight
67%5%8%9%6%2
2841
16th to endNight
77%446%5%1
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
18%6%30%23%16%5%
60
16th to endDay
53%7%14%18%7%
71
February1st to 15thDay
44%11%24%13%6%
236
16th to endDay
37%15%21%20%4
212
March1st to 15thDay
54%19%17%7%1
270
16th to endDay
51%15%20%7%4
288
April1st to 15thDay
49%15%16%12%5%
269
16th to endDay
42%17%20%17%11
270
May1st to 15thDay
35%15%27%16%4
288
16th to endDay
36%7%24%20%8%1
393
June1st to 15thDay
40%13%23%16%5%1
495
16th to endDay
33%14%26%20%41
495
July1st to 15thDay
20%10%31%30%5%1
475
16th to endDay
18%10%32%30%5%2
442
August1st to 15thDay
15%8%25%33%12%5%
315
16th to endDay
15%13%32%26%8%2
332
September1st to 15thDay
22%13%30%25%6%1
315
16th to endDay
33%10%26%18%8%2
315
October1st to 15thDay
39%10%27%16%41
315
16th to endDay
51%6%19%14%6%1
249
November1st to 15thDay
54%12%17%12%3
90
16th to endDay
51%10%15%7%7%7%
90
December1st to 15thDay
42%218%17%16%2
90
16th to endDay
41%6%31%11%8%
72
January1st to 15thNight
43%7%21%20%5%1
750
16th to endNight
40%10%24%18%5%
784
February1st to 15thNight
40%6%29%20%2
704
16th to endNight
34%11%28%17%7%
632
March1st to 15thNight
48%10%21%13%5%
720
16th to endNight
45%8%24%15%5%
768
April1st to 15thNight
38%7%22%24%7%
704
16th to endNight
37%426%21%8%
501
May1st to 15thNight
25%321%30%17%1
360
16th to endNight
32%120%29%15%
375
June1st to 15thNight
32%423%18%19%1
360
16th to endNight
28%5%19%30%16%1
360
July1st to 15thNight
11%214%38%31%1
340
16th to endNight
13%211%29%38%4
376
August1st to 15thNight
14%7%32%40%4
426
16th to endNight
19%213%30%33%2
603
September1st to 15thNight
16%220%28%29%3
720
16th to endNight
32%418%25%16%1
716
October1st to 15thNight
31%5%26%21%13%1
720
16th to endNight
44%5%22%19%5%1
768
November1st to 15thNight
57%7%20%12%1
760
16th to endNight
44%12%21%14%5%1
780
December1st to 15thNight
38%9%29%17%4
806
16th to endNight
48%10%29%10%
823
Page generated at 2017-12-21 04:04:49. Version ac04

Copyright 2017 A. Danko


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