Observatoire St-gabriel Lalemant
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire St-gabriel Lalemant clear sky chart from 2005-11-05 to 2017-09-17.

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
27%
14616
10%
46815
6%
14586
33%
14586
14%
34845

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%
730
9%
2565
3%
726
20%
726
8%
2031
January16th to endNight
23%
768
10%
2688
4%
768
31%
768
11%
2015
February1st to 15thNight
20%
702
8%
2371
3%
701
27%
701
12%
1801
February16th to endNight
21%
631
11%
1893
5%
631
28%
631
12%
1487
March1st to 15thNight
22%
720
12%
2130
8%
720
28%
720
15%
1599
March16th to endNight
28%
768
16%
2067
7%
768
34%
768
19%
1533
April1st to 15thNight
24%
678
14%
1756
6%
678
28%
678
16%
1379
April16th to endNight
30%
540
15%
1620
8%
540
36%
540
17%
1153
May1st to 15thNight
31%
489
10%
1569
8%
489
35%
489
15%
1145
May16th to endNight
28%
375
9%
1372
7%
374
36%
374
12%
1020
June1st to 15thNight
36%
360
7%
1260
5%
360
39%
360
14%
911
June16th to endNight
36%
360
6%
1260
4%
360
39%
360
15%
907
July1st to 15thNight
38%
340
7%
1223
6%
340
42%
340
18%
833
July16th to endNight
48%
376
8%
1418
10%
354
51%
354
17%
940
August1st to 15thNight
50%
444
9%
1515
10%
442
52%
442
18%
1045
August16th to endNight
42%
585
13%
1731
9%
585
45%
585
23%
1172
September1st to 15thNight
37%
720
10%
1877
4%
720
39%
720
25%
1344
September16th to endNight
35%
665
16%
1836
10%
665
40%
665
27%
1230
October1st to 15thNight
29%
660
15%
1906
7%
660
37%
660
20%
1358
October16th to endNight
22%
704
7%
2288
4%
704
26%
704
12%
1757
November1st to 15thNight
24%
701
13%
2283
9%
701
30%
701
12%
1713
November16th to endNight
24%
750
9%
2607
6%
750
29%
750
10%
2025
December1st to 15thNight
14%
750
5%
2700
1%
750
20%
750
7%
2180
December16th to endNight
17%
800
9%
2880
3%
800
24%
800
8%
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
17%8%36%5%3445%7%32%
47970
Night
18%10%46%6%34446%30%
46977
TransparencyDay
53%6%14%17%7%
47651
Night
56%6%12%16%6%
46815
SeeingDay
24%10%28%23%9%2
6321
Night
23%10%30%25%8%
14618

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
15%13%47%6%45%5%5%7%25%
1373
16th to endDay
9%10%6%8%8%35%6%6%7%25%
1536
February1st to 15thDay
8%13%5%9%9%45%5%6%6%25%
1485
16th to endDay
15%13%5%8%6%36%5%46%25%
1580
March1st to 15thDay
17%11%5%6%5%3445%5%30%
1820
16th to endDay
15%11%46%5%23446%33%
2156
April1st to 15thDay
21%11%36%424346%31%
2191
16th to endDay
22%8%345%24346%35%
2340
May1st to 15thDay
21%7%35%5%24446%35%
2391
16th to endDay
23%6%35%5%26%45%6%30%
2743
June1st to 15thDay
21%6%34435%5%6%8%30%
2700
16th to endDay
19%6%25%5%35%6%6%7%29%
2700
July1st to 15thDay
14%5%25%4345%6%9%36%
2663
16th to endDay
14%6%35%435%5%5%8%36%
2654
August1st to 15thDay
13%425%436%5%7%10%36%
2422
16th to endDay
12%5%15%4235%5%7%44%
2469
September1st to 15thDay
19%4244235%46%42%
2082
16th to endDay
16%423324346%47%
1830
October1st to 15thDay
20%5%36%5%3445%7%34%
1722
16th to endDay
25%10%36%435%45%5%26%
1584
November1st to 15thDay
20%7%36%6%345%46%31%
1572
16th to endDay
20%12%48%6%33345%27%
1353
December1st to 15thDay
22%14%5%6%7%3435%422%
1260
16th to endDay
20%14%6%6%5%4444423%
1344
January1st to 15thNight
14%15%5%9%6%44445%23%
2565
16th to endNight
11%11%5%8%8%46%5%6%6%24%
2688
February1st to 15thNight
8%12%49%10%46%5%5%6%25%
2370
16th to endNight
17%14%6%8%7%2434427%
1893
March1st to 15thNight
17%10%47%7%35%35%5%29%
2117
16th to endNight
16%12%46%5%24335%34%
2067
April1st to 15thNight
23%12%47%5%2444427%
1756
16th to endNight
26%6%25%424235%35%
1620
May1st to 15thNight
24%9%35%42445%430%
1569
16th to endNight
25%7%36%5%2445%5%29%
1370
June1st to 15thNight
21%8%45%6%245%46%30%
1260
16th to endNight
18%7%26%6%345%7%5%31%
1260
July1st to 15thNight
17%6%46%42437%7%34%
1295
16th to endNight
14%6%24446%5%6%8%35%
1514
August1st to 15thNight
14%5%25%6%36%6%5%7%36%
1525
16th to endNight
15%5%245%3446%7%39%
1731
September1st to 15thNight
18%5%25%5%3445%6%38%
1877
16th to endNight
19%5%23223346%45%
1836
October1st to 15thNight
18%9%34433446%36%
1906
16th to endNight
26%11%35%424446%26%
2288
November1st to 15thNight
21%9%35%5%34447%30%
2283
16th to endNight
18%12%5%8%6%245%45%25%
2607
December1st to 15thNight
20%16%5%9%5%34336%21%
2700
16th to endNight
20%14%5%6%6%34445%23%
2880

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
59%7%14%13%5%
1374
16th to endDay
57%8%13%13%7%
1536
February1st to 15thDay
59%7%14%12%5%1
1488
16th to endDay
60%5%11%14%7%
1580
March1st to 15thDay
56%6%9%14%10%1
1830
16th to endDay
54%5%10%17%10%1
2156
April1st to 15thDay
57%310%16%9%3
2191
16th to endDay
51%411%17%13%2
2340
May1st to 15thDay
52%5%12%17%11%
2391
16th to endDay
56%7%11%17%6%
2747
June1st to 15thDay
52%7%14%17%7%
2700
16th to endDay
53%8%15%15%7%
2700
July1st to 15thDay
43%9%19%20%5%
2507
16th to endDay
48%9%17%17%6%
2487
August1st to 15thDay
45%9%23%17%4
2408
16th to endDay
39%8%20%25%6%
2469
September1st to 15thDay
43%6%17%22%9%
2082
16th to endDay
40%5%17%24%10%
1830
October1st to 15thDay
53%6%12%19%8%
1722
16th to endDay
62%6%12%14%4
1584
November1st to 15thDay
55%7%13%18%4
1572
16th to endDay
61%6%13%15%3
1353
December1st to 15thDay
66%5%11%11%3
1260
16th to endDay
65%6%10%13%4
1344
January1st to 15thNight
64%6%10%13%5%
2565
16th to endNight
58%6%12%15%6%
2688
February1st to 15thNight
59%6%13%15%5%
2371
16th to endNight
63%410%14%7%
1893
March1st to 15thNight
57%5%11%16%9%
2130
16th to endNight
52%5%10%20%9%1
2067
April1st to 15thNight
60%46%14%12%2
1756
16th to endNight
51%5%8%19%13%1
1620
May1st to 15thNight
56%5%10%15%10%1
1569
16th to endNight
56%7%9%15%8%
1372
June1st to 15thNight
55%6%11%18%6%1
1260
16th to endNight
52%8%14%16%7%
1260
July1st to 15thNight
47%8%18%20%5%
1223
16th to endNight
44%10%17%19%8%
1418
August1st to 15thNight
44%11%19%20%4
1515
16th to endNight
42%8%20%22%5%
1731
September1st to 15thNight
46%6%16%20%8%
1877
16th to endNight
41%6%15%25%9%
1836
October1st to 15thNight
50%5%13%23%7%
1906
16th to endNight
60%5%14%14%4
2288
November1st to 15thNight
56%8%14%14%6%
2283
16th to endNight
61%7%11%14%4
2607
December1st to 15thNight
67%6%13%10%2
2700
16th to endNight
64%6%11%12%5%
2880

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
21%28%38%11%
60
16th to endDay
21%15%32%18%10%
64
February1st to 15thDay
20%13%31%26%8%
146
16th to endDay
25%11%34%20%7%
239
March1st to 15thDay
25%14%28%21%8%1
270
16th to endDay
20%12%29%20%12%4
288
April1st to 15thDay
31%13%26%21%5%2
270
16th to endDay
28%12%27%24%43
270
May1st to 15thDay
34%7%26%21%7%2
288
16th to endDay
26%11%33%19%7%1
456
June1st to 15thDay
26%8%29%22%11%1
495
16th to endDay
21%9%28%28%11%
495
July1st to 15thDay
21%7%29%26%12%2
441
16th to endDay
20%326%33%13%1
326
August1st to 15thDay
15%6%30%27%15%5%
313
16th to endDay
21%8%27%21%17%4
332
September1st to 15thDay
23%11%23%25%13%3
315
16th to endDay
18%10%32%23%10%4
259
October1st to 15thDay
23%10%30%22%9%3
242
16th to endDay
36%15%24%15%6%1
240
November1st to 15thDay
27%17%25%23%42
235
16th to endDay
32%16%21%20%7%1
153
December1st to 15thDay
35%6%41%13%11
60
16th to endDay
39%29%25%6%
64
January1st to 15thNight
23%16%36%19%3
730
16th to endNight
16%13%35%26%6%
768
February1st to 15thNight
15%12%38%26%6%
704
16th to endNight
24%12%32%23%5%
631
March1st to 15thNight
22%11%37%21%6%
720
16th to endNight
21%11%32%24%9%1
768
April1st to 15thNight
29%9%29%24%6%
678
16th to endNight
31%9%25%25%8%
540
May1st to 15thNight
26%9%27%25%10%
489
16th to endNight
29%8%27%27%8%
375
June1st to 15thNight
23%7%23%34%10%
360
16th to endNight
20%5%32%32%9%
360
July1st to 15thNight
17%7%30%29%13%
340
16th to endNight
16%225%43%11%
376
August1st to 15thNight
17%320%35%20%1
444
16th to endNight
18%5%25%36%12%1
585
September1st to 15thNight
20%6%30%29%11%1
720
16th to endNight
21%6%34%26%9%1
665
October1st to 15thNight
23%10%31%25%6%1
660
16th to endNight
32%9%30%19%7%
704
November1st to 15thNight
26%14%28%21%6%
701
16th to endNight
24%16%28%22%7%1
750
December1st to 15thNight
27%16%33%18%4
750
16th to endNight
28%16%29%18%6%
800
Page generated at 2017-09-18 08:38:23. Version ac04

Copyright 2017 A. Danko


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