Mont St-Alex
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mont St-Alex 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
33%
15034
13%
48040
9%
15003
38%
15003
16%
34945

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
19%
720
8%
2506
4%
716
23%
716
7%
2043
January16th to endNight
23%
768
9%
2688
7%
768
28%
768
10%
2100
February1st to 15thNight
20%
704
7%
2302
5%
701
24%
701
9%
1876
February16th to endNight
26%
631
10%
1893
6%
631
31%
631
13%
1473
March1st to 15thNight
29%
720
14%
2160
11%
720
34%
720
15%
1640
March16th to endNight
32%
768
20%
2003
10%
768
38%
768
22%
1459
April1st to 15thNight
27%
718
15%
1796
5%
718
32%
718
18%
1389
April16th to endNight
30%
609
17%
1689
7%
609
37%
609
22%
1188
May1st to 15thNight
33%
426
17%
1506
14%
426
41%
426
18%
1008
May16th to endNight
39%
374
13%
1497
12%
374
47%
374
17%
983
June1st to 15thNight
35%
360
9%
1440
10%
360
42%
360
14%
1003
June16th to endNight
45%
360
10%
1440
14%
360
51%
360
20%
896
July1st to 15thNight
56%
340
12%
1360
19%
340
60%
340
23%
807
July16th to endNight
58%
376
13%
1418
17%
354
61%
354
23%
842
August1st to 15thNight
56%
386
14%
1457
16%
384
58%
384
22%
902
August16th to endNight
58%
741
19%
1887
12%
741
59%
741
34%
1216
September1st to 15thNight
53%
720
15%
1806
9%
720
53%
720
31%
1229
September16th to endNight
48%
717
22%
1980
16%
717
52%
717
32%
1260
October1st to 15thNight
37%
720
17%
2094
11%
720
44%
720
22%
1447
October16th to endNight
26%
768
11%
2477
8%
768
31%
768
14%
1852
November1st to 15thNight
30%
760
16%
2472
12%
760
36%
760
15%
1793
November16th to endNight
24%
780
12%
2684
9%
780
30%
780
12%
2034
December1st to 15thNight
18%
780
6%
2730
3%
780
22%
780
7%
2238
December16th to endNight
13%
788
8%
2755
3%
788
19%
788
7%
2267

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
19%9%36%5%3445%6%31%
48811
Night
20%10%47%5%34345%29%
48210
Cloud CoverDay
19%9%36%5%3445%6%30%
48821
Night
20%11%47%5%24445%29%
48215
TransparencyDay
53%312%21%8%
48499
Night
56%310%19%8%
48040
SeeingDay
25%6%23%24%15%5%
5907
Night
26%6%24%29%11%1
15035

By Month

Percentage Cloud Cover NE (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%17%6%8%6%35%435%17%
1432
16th to endDay
13%16%5%9%6%3446%7%22%
1536
February1st to 15thDay
15%15%7%10%7%36%5%3420%
1556
16th to endDay
18%13%6%7%7%3445%5%22%
1580
March1st to 15thDay
18%13%5%8%7%35%33426%
1790
16th to endDay
20%8%47%423345%34%
2220
April1st to 15thDay
23%11%35%42444431%
2152
16th to endDay
20%7%345%34346%36%
2271
May1st to 15thDay
22%6%36%5%34447%33%
2457
16th to endDay
19%6%36%5%35%45%7%32%
2618
June1st to 15thDay
26%6%25%5%2446%6%29%
2520
16th to endDay
19%6%25%445%5%5%7%32%
2520
July1st to 15thDay
14%5%26%435%5%6%8%36%
2520
16th to endDay
13%5%245%35%6%7%8%35%
2654
August1st to 15thDay
13%6%36%7%45%6%6%8%32%
2481
16th to endDay
12%5%1443436%8%44%
2312
September1st to 15thDay
18%6%24422447%42%
2154
16th to endDay
14%5%2432335%8%46%
1980
October1st to 15thDay
22%8%25%42435%6%32%
1863
16th to endDay
26%10%26%433445%26%
1746
November1st to 15thDay
19%13%35%43445%6%29%
1716
16th to endDay
22%13%5%6%6%3445%424%
1605
December1st to 15thDay
24%15%5%8%6%3444417%
1560
16th to endDay
27%18%7%9%5%2332414%
1568
January1st to 15thNight
19%16%6%11%7%3433417%
2506
16th to endNight
14%15%6%10%8%3443423%
2688
February1st to 15thNight
16%14%7%13%8%4434416%
2301
16th to endNight
18%14%5%9%6%35%335%24%
1893
March1st to 15thNight
23%12%47%6%2333427%
2147
16th to endNight
19%11%4442433435%
2003
April1st to 15thNight
26%8%46%5%3424429%
1796
16th to endNight
22%9%25%314335%37%
1689
May1st to 15thNight
21%7%46%423335%36%
1506
16th to endNight
21%6%245%335%6%7%32%
1495
June1st to 15thNight
29%5%25%5%24447%28%
1440
16th to endNight
18%6%234245%6%10%35%
1440
July1st to 15thNight
12%425%5%35%5%6%9%37%
1440
16th to endNight
12%426%446%5%6%8%39%
1514
August1st to 15thNight
14%5%15%6%35%46%8%37%
1467
16th to endNight
12%6%244235%5%7%46%
1887
September1st to 15thNight
16%6%25%5%23446%41%
1806
16th to endNight
18%5%2331335%6%46%
1980
October1st to 15thNight
20%7%26%5%3335%5%35%
2094
16th to endNight
28%10%36%5%23345%27%
2477
November1st to 15thNight
21%10%36%5%25%446%28%
2472
16th to endNight
24%12%48%5%2433426%
2684
December1st to 15thNight
24%16%6%9%6%3433417%
2730
16th to endNight
23%21%6%9%6%2322418%
2755

Percentage Cloud Cover SE (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%18%5%9%6%4443415%
1432
16th to endDay
13%16%6%9%7%35%46%5%21%
1536
February1st to 15thDay
14%16%8%11%7%35%5%4418%
1556
16th to endDay
17%15%6%7%7%35%445%22%
1580
March1st to 15thDay
18%13%5%7%7%35%335%25%
1800
16th to endDay
21%8%46%5%23346%33%
2220
April1st to 15thDay
23%11%35%5%2444430%
2152
16th to endDay
22%7%25%5%34346%35%
2271
May1st to 15thDay
22%6%36%5%35%347%32%
2457
16th to endDay
20%6%36%5%25%45%7%31%
2618
June1st to 15thDay
27%5%25%42436%6%29%
2520
16th to endDay
20%5%25%435%6%5%8%31%
2520
July1st to 15thDay
14%6%25%5%35%5%6%9%35%
2520
16th to endDay
13%5%25%6%35%6%7%8%34%
2654
August1st to 15thDay
14%6%36%7%45%6%6%8%30%
2481
16th to endDay
12%5%1443446%8%43%
2312
September1st to 15thDay
19%5%25%423446%40%
2154
16th to endDay
14%5%2442435%7%46%
1980
October1st to 15thDay
23%8%26%43336%6%31%
1863
16th to endDay
27%10%35%5%3345%426%
1746
November1st to 15thDay
21%12%35%424446%29%
1716
16th to endDay
22%13%47%6%3444423%
1605
December1st to 15thDay
24%16%5%7%7%3434417%
1560
16th to endDay
27%19%6%8%6%2332413%
1568
January1st to 15thNight
19%17%6%12%7%35%43416%
2506
16th to endNight
15%15%7%9%7%45%5%3422%
2688
February1st to 15thNight
16%14%7%14%8%35%33416%
2294
16th to endNight
16%15%5%10%6%35%33424%
1893
March1st to 15thNight
23%13%46%6%3333427%
2160
16th to endNight
19%12%35%5%2432434%
2002
April1st to 15thNight
25%10%47%6%2334428%
1796
16th to endNight
23%8%25%413335%37%
1689
May1st to 15thNight
21%7%36%5%23336%35%
1506
16th to endNight
21%6%245%25%5%6%7%32%
1495
June1st to 15thNight
28%6%26%5%2445%7%27%
1440
16th to endNight
19%5%143345%6%9%35%
1440
July1st to 15thNight
13%326%6%36%5%7%10%36%
1440
16th to endNight
13%425%436%6%6%8%38%
1514
August1st to 15thNight
14%5%25%5%45%46%9%37%
1467
16th to endNight
13%5%245%3345%7%45%
1887
September1st to 15thNight
17%6%15%6%23447%41%
1806
16th to endNight
19%423323346%46%
1980
October1st to 15thNight
20%7%27%5%2345%6%34%
2094
16th to endNight
29%9%37%5%23345%25%
2477
November1st to 15thNight
21%11%36%5%25%446%27%
2472
16th to endNight
24%12%48%5%2434424%
2684
December1st to 15thNight
25%17%6%8%7%2443417%
2730
16th to endNight
23%21%6%9%6%2322317%
2755

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
70%28%14%3
1433
16th to endDay
61%314%15%4
1536
February1st to 15thDay
68%210%16%1
1559
16th to endDay
63%212%13%6%
1580
March1st to 15thDay
62%310%16%6%
1800
16th to endDay
52%28%22%11%1
2220
April1st to 15thDay
57%28%19%10%1
2152
16th to endDay
50%210%21%11%3
2271
May1st to 15thDay
52%212%19%13%
2457
16th to endDay
51%412%20%10%1
2622
June1st to 15thDay
54%411%20%8%
2520
16th to endDay
49%5%11%24%8%
2520
July1st to 15thDay
41%5%14%29%8%
2371
16th to endDay
43%419%25%7%
2487
August1st to 15thDay
48%418%21%6%
2467
16th to endDay
36%318%30%11%
2312
September1st to 15thDay
43%312%27%11%
2154
16th to endDay
36%413%33%11%
1980
October1st to 15thDay
53%312%22%7%
1863
16th to endDay
59%313%18%4
1746
November1st to 15thDay
55%413%17%8%
1716
16th to endDay
63%311%14%6%
1605
December1st to 15thDay
70%312%12%1
1560
16th to endDay
74%39%8%3
1568
January1st to 15thNight
71%38%13%3
2506
16th to endNight
66%39%15%6%
2688
February1st to 15thNight
70%28%13%3
2302
16th to endNight
64%210%13%8%
1893
March1st to 15thNight
60%38%19%7%1
2160
16th to endNight
53%27%18%14%3
2003
April1st to 15thNight
59%25%18%12%1
1796
16th to endNight
49%37%19%15%3
1689
May1st to 15thNight
51%25%19%16%3
1506
16th to endNight
49%49%22%11%2
1497
June1st to 15thNight
55%410%20%7%1
1440
16th to endNight
43%5%13%23%12%1
1440
July1st to 15thNight
39%5%13%28%11%
1360
16th to endNight
39%5%15%25%12%
1418
August1st to 15thNight
42%5%18%23%10%
1457
16th to endNight
37%414%28%13%
1887
September1st to 15thNight
42%312%27%12%
1806
16th to endNight
39%311%30%14%
1980
October1st to 15thNight
49%312%23%10%
2094
16th to endNight
60%311%18%6%
2477
November1st to 15thNight
56%411%18%6%2
2472
16th to endNight
63%210%16%6%
2684
December1st to 15thNight
71%39%13%1
2730
16th to endNight
72%29%10%4
2755

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
28%10%16%28%15%1
60
16th to endDay
37%6%29%18%43
64
February1st to 15thDay
30%15%29%14%9%
108
16th to endDay
28%8%29%24%8%
239
March1st to 15thDay
30%7%27%28%5%
270
16th to endDay
28%6%25%23%11%4
288
April1st to 15thDay
32%8%24%22%10%2
270
16th to endDay
25%7%28%18%14%6%
270
May1st to 15thDay
31%6%23%22%11%5%
288
16th to endDay
21%6%31%21%16%2
331
June1st to 15thDay
32%417%28%13%2
315
16th to endDay
22%327%30%12%3
315
July1st to 15thDay
18%124%32%16%6%
305
16th to endDay
18%212%37%24%5%
326
August1st to 15thDay
20%217%29%21%7%
313
16th to endDay
16%416%25%24%12%
332
September1st to 15thDay
18%217%24%22%14%
315
16th to endDay
13%322%21%26%12%
314
October1st to 15thDay
21%6%30%18%18%4
315
16th to endDay
38%8%20%21%10%
292
November1st to 15thDay
30%7%23%23%12%2
280
16th to endDay
33%15%23%14%11%1
135
December1st to 15thDay
33%7%22%26%7%2
90
16th to endDay
47%8%22%20%1
72
January1st to 15thNight
26%10%30%24%5%1
720
16th to endNight
23%9%27%28%8%
768
February1st to 15thNight
24%7%30%30%7%
704
16th to endNight
26%8%28%28%7%
631
March1st to 15thNight
30%9%23%29%6%
720
16th to endNight
26%7%26%27%10%1
768
April1st to 15thNight
30%8%24%28%7%
718
16th to endNight
27%9%26%25%11%
609
May1st to 15thNight
25%329%26%13%1
426
16th to endNight
24%426%34%9%1
375
June1st to 15thNight
33%319%30%13%
360
16th to endNight
20%223%38%14%
360
July1st to 15thNight
10%122%44%18%2
340
16th to endNight
14%115%50%17%
376
August1st to 15thNight
17%214%39%25%2
386
16th to endNight
16%214%37%26%2
741
September1st to 15thNight
19%316%40%17%2
720
16th to endNight
21%419%28%22%3
717
October1st to 15thNight
24%325%28%15%1
720
16th to endNight
35%5%25%24%8%
768
November1st to 15thNight
27%8%26%26%10%1
760
16th to endNight
32%9%25%20%10%1
780
December1st to 15thNight
35%9%27%22%5%
780
16th to endNight
36%7%28%20%6%1
788
Page generated at 2017-12-21 07:04:44. Version ac04

Copyright 2017 A. Danko


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