Observatoire de Walter Laperle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Walter Laperle 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
24%
14671
12%
46840
7%
14640
31%
14640
13%
34195

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
11%
720
6%
2506
2%
716
16%
716
5%
2056
January16th to endNight
16%
768
8%
2679
5%
768
22%
768
8%
2066
February1st to 15thNight
12%
704
8%
2287
3%
701
18%
701
7%
1860
February16th to endNight
17%
631
11%
1904
4%
631
25%
631
10%
1483
March1st to 15thNight
16%
720
12%
2148
6%
720
23%
720
11%
1652
March16th to endNight
24%
768
18%
1999
7%
768
31%
768
17%
1441
April1st to 15thNight
20%
718
15%
1796
4%
718
26%
718
17%
1356
April16th to endNight
23%
651
16%
1731
3%
651
32%
651
17%
1240
May1st to 15thNight
24%
378
16%
1458
11%
378
37%
378
12%
977
May16th to endNight
27%
374
12%
1497
7%
374
39%
374
14%
979
June1st to 15thNight
27%
360
9%
1440
6%
360
36%
360
11%
1006
June16th to endNight
35%
360
9%
1440
8%
360
44%
360
16%
903
July1st to 15thNight
41%
340
14%
1360
17%
340
49%
340
23%
768
July16th to endNight
40%
376
12%
1418
12%
354
51%
354
22%
834
August1st to 15thNight
47%
393
15%
1464
12%
391
53%
391
20%
898
August16th to endNight
42%
753
19%
1899
9%
753
48%
753
32%
1233
September1st to 15thNight
42%
720
15%
1800
7%
720
44%
720
27%
1239
September16th to endNight
43%
665
20%
1810
14%
665
47%
665
28%
1179
October1st to 15thNight
27%
660
17%
1966
11%
660
35%
660
17%
1388
October16th to endNight
19%
704
9%
2233
5%
704
25%
704
10%
1732
November1st to 15thNight
23%
700
14%
2277
10%
700
30%
700
12%
1663
November16th to endNight
17%
720
11%
2520
6%
720
24%
720
8%
1929
December1st to 15thNight
13%
720
6%
2520
2%
720
17%
720
5%
2076
December16th to endNight
8%
768
6%
2688
2%
768
13%
768
4%
2237

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%8%36%5%35%446%32%
47945
Night
19%10%46%5%34445%30%
47009
Cloud CoverDay
19%9%36%5%34446%31%
47954
Night
19%10%47%5%34445%29%
47015
TransparencyDay
51%5%12%19%9%1
47632
Night
55%5%11%18%8%
46840
SeeingDay
21%18%26%19%10%3
5563
Night
21%24%23%21%8%
14672

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%15%5%9%8%35%43317%
1432
16th to endDay
14%17%5%8%6%45%5%5%6%19%
1542
February1st to 15thDay
16%13%5%11%9%46%5%45%18%
1575
16th to endDay
18%14%5%7%6%3434425%
1569
March1st to 15thDay
18%13%5%8%6%3433427%
1799
16th to endDay
19%8%45%423335%37%
2224
April1st to 15thDay
22%10%36%6%2334432%
2152
16th to endDay
19%8%24424446%36%
2229
May1st to 15thDay
21%7%25%5%34446%35%
2504
16th to endDay
18%6%35%5%2445%7%36%
2618
June1st to 15thDay
22%6%36%5%34447%31%
2520
16th to endDay
19%5%25%5%36%5%6%8%32%
2520
July1st to 15thDay
13%425%5%35%5%5%7%40%
2520
16th to endDay
12%425%5%37%5%6%9%36%
2654
August1st to 15thDay
13%5%26%6%35%5%5%8%36%
2481
16th to endDay
11%424435%6%5%9%44%
2292
September1st to 15thDay
17%5%15%424347%43%
2160
16th to endDay
16%6%24324347%44%
1856
October1st to 15thDay
21%8%25%5%2435%6%33%
1663
16th to endDay
27%12%36%5%2444424%
1638
November1st to 15thDay
16%9%47%5%345%5%7%30%
1581
16th to endDay
22%13%48%5%34345%24%
1440
December1st to 15thDay
25%15%6%8%6%45%35%5%14%
1440
16th to endDay
27%17%5%8%5%25%345%14%
1536
January1st to 15thNight
19%17%7%11%7%35%44416%
2506
16th to endNight
15%16%6%8%7%45%445%22%
2679
February1st to 15thNight
15%14%8%14%8%3443418%
2285
16th to endNight
17%13%6%8%6%3444424%
1904
March1st to 15thNight
21%12%46%7%2423428%
2135
16th to endNight
19%11%35%5%2324437%
1999
April1st to 15thNight
25%8%35%5%24345%31%
1796
16th to endNight
21%8%25%424245%37%
1731
May1st to 15thNight
23%5%36%5%24346%34%
1458
16th to endNight
21%425%5%3446%7%35%
1495
June1st to 15thNight
24%6%25%5%345%6%8%27%
1440
16th to endNight
16%5%25%4245%6%9%37%
1440
July1st to 15thNight
11%3245%35%47%9%42%
1440
16th to endNight
10%5%23435%6%7%10%41%
1514
August1st to 15thNight
12%5%26%4335%7%8%39%
1474
16th to endNight
14%41443345%6%47%
1899
September1st to 15thNight
17%5%25%5%2435%6%41%
1800
16th to endNight
18%314333345%46%
1810
October1st to 15thNight
21%8%35%423446%34%
1966
16th to endNight
27%10%37%5%3333425%
2233
November1st to 15thNight
22%9%45%5%34446%29%
2277
16th to endNight
23%12%5%7%6%24445%24%
2520
December1st to 15thNight
23%18%6%8%6%2444416%
2520
16th to endNight
26%17%5%7%5%3433317%
2688

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
21%15%5%10%9%45%42316%
1432
16th to endDay
13%18%6%9%6%345%5%6%19%
1542
February1st to 15thDay
16%13%5%12%9%46%445%17%
1575
16th to endDay
17%16%5%8%7%35%33424%
1569
March1st to 15thDay
18%13%6%8%6%3434426%
1809
16th to endDay
20%10%36%41333437%
2223
April1st to 15thDay
22%11%36%433335%31%
2152
16th to endDay
20%9%24424346%36%
2229
May1st to 15thDay
21%7%25%5%25%35%6%34%
2504
16th to endDay
18%6%35%3345%5%8%35%
2618
June1st to 15thDay
24%6%35%5%24446%30%
2520
16th to endDay
19%6%25%5%345%6%8%32%
2520
July1st to 15thDay
14%5%245%35%5%5%7%39%
2520
16th to endDay
12%5%346%36%5%6%9%35%
2654
August1st to 15thDay
13%6%26%6%45%5%6%8%34%
2481
16th to endDay
11%4244345%6%9%42%
2292
September1st to 15thDay
17%5%25%423337%42%
2160
16th to endDay
15%6%24423437%43%
1856
October1st to 15thDay
22%7%245%24446%33%
1663
16th to endDay
28%12%35%6%2434424%
1638
November1st to 15thDay
17%9%46%6%335%47%29%
1581
16th to endDay
22%14%5%7%5%34435%24%
1440
December1st to 15thDay
24%16%6%7%8%24445%15%
1440
16th to endDay
27%17%5%8%5%3443414%
1536
January1st to 15thNight
18%17%7%12%7%35%43416%
2506
16th to endNight
15%17%6%8%7%45%44421%
2679
February1st to 15thNight
14%15%7%14%9%3433418%
2278
16th to endNight
17%14%6%9%6%35%44423%
1904
March1st to 15thNight
20%13%46%7%3423427%
2148
16th to endNight
19%10%36%42423436%
1999
April1st to 15thNight
25%8%36%5%33345%30%
1796
16th to endNight
21%7%35%5%24345%36%
1731
May1st to 15thNight
23%5%36%5%24345%34%
1458
16th to endNight
20%425%5%3445%7%34%
1495
June1st to 15thNight
25%7%245%3445%8%28%
1440
16th to endNight
16%5%244335%7%8%36%
1440
July1st to 15thNight
10%324445%47%9%42%
1440
16th to endNight
11%424425%6%6%9%41%
1514
August1st to 15thNight
12%435%5%235%6%10%38%
1474
16th to endNight
14%42442345%6%46%
1899
September1st to 15thNight
16%5%35%434445%42%
1800
16th to endNight
18%413423445%46%
1810
October1st to 15thNight
21%8%345%25%446%34%
1966
16th to endNight
28%10%36%6%34435%24%
2233
November1st to 15thNight
21%11%35%5%3445%5%28%
2277
16th to endNight
22%12%5%8%5%33435%25%
2520
December1st to 15thNight
23%18%6%8%5%3444316%
2520
16th to endNight
25%18%5%8%5%3443217%
2688

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%39%11%4
1433
16th to endDay
62%413%12%5%
1542
February1st to 15thDay
65%5%10%15%2
1577
16th to endDay
61%411%13%8%
1569
March1st to 15thDay
61%312%13%7%
1809
16th to endDay
48%49%17%15%3
2224
April1st to 15thDay
55%36%20%11%2
2152
16th to endDay
47%49%19%13%4
2229
May1st to 15thDay
49%411%18%14%1
2504
16th to endDay
46%6%12%21%12%1
2622
June1st to 15thDay
52%5%11%20%9%
2520
16th to endDay
47%7%13%20%10%
2520
July1st to 15thDay
38%6%14%28%11%
2371
16th to endDay
40%8%17%23%8%
2487
August1st to 15thDay
44%7%16%22%7%
2467
16th to endDay
34%6%18%27%11%
2292
September1st to 15thDay
40%413%27%12%
2160
16th to endDay
39%5%12%32%10%
1856
October1st to 15thDay
50%5%13%21%9%
1663
16th to endDay
61%5%12%13%5%
1638
November1st to 15thDay
51%7%13%18%8%
1581
16th to endDay
62%5%10%14%6%
1440
December1st to 15thDay
70%6%10%10%1
1440
16th to endDay
71%5%11%8%3
1536
January1st to 15thNight
70%410%9%4
2506
16th to endNight
63%411%14%5%
2679
February1st to 15thNight
68%410%12%3
2287
16th to endNight
61%5%10%14%8%
1904
March1st to 15thNight
60%49%16%7%
2148
16th to endNight
51%39%18%13%4
1999
April1st to 15thNight
55%38%19%12%
1796
16th to endNight
49%48%18%15%3
1731
May1st to 15thNight
51%38%15%16%3
1458
16th to endNight
47%6%10%21%12%1
1497
June1st to 15thNight
52%7%12%17%9%
1440
16th to endNight
42%7%15%22%12%
1440
July1st to 15thNight
34%6%15%28%15%
1360
16th to endNight
35%8%17%23%14%
1418
August1st to 15thNight
38%8%19%22%10%
1464
16th to endNight
35%5%15%28%13%
1899
September1st to 15thNight
43%411%26%13%
1800
16th to endNight
39%5%10%32%11%
1810
October1st to 15thNight
49%5%10%23%9%
1966
16th to endNight
61%5%11%15%5%
2233
November1st to 15thNight
55%6%12%15%8%2
2277
16th to endNight
62%5%11%15%5%
2520
December1st to 15thNight
70%5%10%12%1
2520
16th to endNight
70%5%10%9%3
2688

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
30%16%20%26%6%
60
16th to endDay
33%10%38%13%3
65
February1st to 15thDay
33%25%35%41
90
16th to endDay
28%25%26%17%3
228
March1st to 15thDay
22%26%30%14%5%
270
16th to endDay
24%24%24%17%6%2
288
April1st to 15thDay
28%24%30%9%6%
270
16th to endDay
18%27%24%16%11%1
270
May1st to 15thDay
28%21%22%16%7%3
288
16th to endDay
19%23%31%13%11%
331
June1st to 15thDay
24%19%29%21%41
315
16th to endDay
18%18%29%21%10%1
315
July1st to 15thDay
16%11%29%28%11%3
305
16th to endDay
12%15%25%30%13%2
326
August1st to 15thDay
14%12%24%31%13%4
313
16th to endDay
11%11%28%24%15%9%
332
September1st to 15thDay
16%10%26%19%17%10%
315
16th to endDay
15%15%24%18%15%10%
259
October1st to 15thDay
21%20%21%17%15%3
255
16th to endDay
32%20%19%21%4
249
November1st to 15thDay
20%23%24%16%14%
235
16th to endDay
36%10%30%18%5%
60
December1st to 15thDay
28%16%31%21%1
60
16th to endDay
42%17%32%7%
64
January1st to 15thNight
23%29%27%16%3
720
16th to endNight
22%29%24%19%4
768
February1st to 15thNight
21%30%25%18%3
704
16th to endNight
21%27%26%18%4
631
March1st to 15thNight
25%28%25%16%4
720
16th to endNight
22%25%22%24%5%
768
April1st to 15thNight
24%26%24%21%3
718
16th to endNight
21%27%21%20%7%
651
May1st to 15thNight
21%25%21%22%8%1
378
16th to endNight
15%23%29%22%9%
375
June1st to 15thNight
21%23%21%27%6%
360
16th to endNight
15%22%20%28%10%1
360
July1st to 15thNight
11%16%25%30%15%
340
16th to endNight
10%20%24%32%11%1
376
August1st to 15thNight
12%12%17%35%19%2
393
16th to endNight
13%13%24%28%18%1
753
September1st to 15thNight
16%13%22%32%12%2
720
16th to endNight
18%14%20%24%19%2
665
October1st to 15thNight
24%19%22%21%10%
660
16th to endNight
28%20%23%20%5%
704
November1st to 15thNight
20%25%25%18%9%
700
16th to endNight
23%31%20%15%8%
720
December1st to 15thNight
30%29%22%15%3
720
16th to endNight
32%28%24%10%3
768
Page generated at 2017-09-18 08:38:20. Version ac04

Copyright 2017 A. Danko


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