Observatoire Astronomique de Laval
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Astronomique de Laval clear sky chart from 2005-11-05 to 2018-02-22.

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
35%
15264
14%
48916
10%
15232
41%
15232
18%
34557

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
21%
780
10%
2716
6%
776
27%
776
10%
2100
January16th to endNight
26%
832
11%
2912
7%
832
33%
832
12%
2154
February1st to 15thNight
25%
764
10%
2508
6%
761
31%
761
12%
1945
February16th to endNight
28%
659
14%
1976
8%
659
36%
659
16%
1465
March1st to 15thNight
29%
720
14%
2160
10%
720
34%
720
16%
1603
March16th to endNight
37%
768
20%
1998
11%
768
43%
768
25%
1405
April1st to 15thNight
31%
718
16%
1796
5%
718
36%
718
21%
1342
April16th to endNight
32%
620
17%
1700
6%
620
39%
620
23%
1201
May1st to 15thNight
33%
396
16%
1476
13%
396
42%
396
17%
987
May16th to endNight
36%
375
12%
1497
13%
374
43%
374
17%
997
June1st to 15thNight
41%
360
9%
1440
9%
360
48%
360
15%
996
June16th to endNight
45%
360
8%
1440
11%
360
49%
360
18%
924
July1st to 15thNight
55%
340
13%
1360
19%
340
59%
340
25%
779
July16th to endNight
57%
376
12%
1418
16%
354
59%
354
24%
820
August1st to 15thNight
58%
363
14%
1434
17%
361
60%
361
21%
878
August16th to endNight
57%
756
19%
1902
11%
756
59%
756
37%
1216
September1st to 15thNight
53%
720
14%
1800
8%
720
55%
720
30%
1243
September16th to endNight
53%
717
22%
1972
16%
717
57%
717
34%
1241
October1st to 15thNight
38%
720
20%
2118
12%
720
48%
720
24%
1426
October16th to endNight
31%
768
13%
2465
10%
768
37%
768
16%
1776
November1st to 15thNight
31%
760
18%
2472
13%
760
40%
760
18%
1739
November16th to endNight
27%
780
14%
2714
10%
780
34%
780
13%
1982
December1st to 15thNight
22%
780
10%
2730
4%
780
29%
780
11%
2092
December16th to endNight
17%
832
12%
2912
5%
832
26%
832
10%
2246

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%7%36%5%3445%6%34%
49342
Night
18%9%36%5%24446%33%
49085
Cloud CoverDay
18%8%36%5%3445%6%33%
49352
Night
19%9%36%5%34446%32%
49090
TransparencyDay
49%5%12%20%10%1
49029
Night
52%5%11%20%10%1
48916
SeeingDay
21%5%24%26%16%5%
6013
Night
23%5%27%31%11%
15264

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
21%14%47%6%4443423%
1552
16th to endDay
13%13%48%7%36%446%29%
1664
February1st to 15thDay
15%13%5%8%7%35%5%45%25%
1681
16th to endDay
17%13%5%7%5%2444428%
1644
March1st to 15thDay
17%11%48%6%46%34428%
1790
16th to endDay
18%8%35%414335%39%
2224
April1st to 15thDay
22%8%35%6%2433433%
2152
16th to endDay
20%6%26%5%24435%38%
2259
May1st to 15thDay
22%5%36%5%3445%5%33%
2486
16th to endDay
20%5%25%5%25%46%7%32%
2618
June1st to 15thDay
22%6%25%5%345%46%31%
2520
16th to endDay
18%6%25%6%36%5%5%9%30%
2520
July1st to 15thDay
13%4246%36%6%6%7%38%
2520
16th to endDay
12%426%5%35%6%6%9%38%
2654
August1st to 15thDay
13%5%26%6%45%5%6%7%35%
2502
16th to endDay
10%324425%46%7%47%
2297
September1st to 15thDay
16%5%25%42445%7%42%
2160
16th to endDay
14%423424337%50%
1987
October1st to 15thDay
21%6%25%5%2445%6%35%
1841
16th to endDay
23%8%36%5%34445%29%
1758
November1st to 15thDay
16%9%36%5%2446%6%33%
1716
16th to endDay
23%9%35%5%25%435%30%
1573
December1st to 15thDay
25%10%5%7%6%2444423%
1560
16th to endDay
25%13%46%5%33445%24%
1664
January1st to 15thNight
18%15%6%8%6%34445%22%
2716
16th to endNight
13%13%5%8%7%35%45%5%27%
2912
February1st to 15thNight
13%13%6%11%7%35%445%23%
2506
16th to endNight
18%12%47%5%35%35%429%
1976
March1st to 15thNight
21%11%46%434436%29%
2147
16th to endNight
16%10%35%434335%39%
1998
April1st to 15thNight
26%7%36%423335%32%
1796
16th to endNight
23%6%24423345%37%
1700
May1st to 15thNight
21%6%27%5%14336%34%
1476
16th to endNight
20%6%34435%45%7%34%
1495
June1st to 15thNight
25%7%3443446%6%30%
1440
16th to endNight
17%5%25%4345%6%8%36%
1440
July1st to 15thNight
11%4145%25%5%7%8%42%
1440
16th to endNight
11%4245%35%5%6%10%41%
1514
August1st to 15thNight
12%5%35%5%2446%8%40%
1444
16th to endNight
13%41342435%7%48%
1902
September1st to 15thNight
16%426%435%446%42%
1800
16th to endNight
15%424313346%49%
1972
October1st to 15thNight
17%6%35%424445%40%
2118
16th to endNight
24%8%36%424345%31%
2465
November1st to 15thNight
21%7%36%5%33445%34%
2472
16th to endNight
22%12%38%5%2333429%
2714
December1st to 15thNight
22%13%47%6%23435%24%
2730
16th to endNight
22%15%5%8%5%3333424%
2912

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%14%5%8%6%25%43422%
1552
16th to endDay
13%13%48%6%35%446%29%
1664
February1st to 15thDay
15%13%5%8%7%35%445%24%
1681
16th to endDay
18%13%5%7%7%2445%428%
1644
March1st to 15thDay
18%9%48%7%36%35%428%
1800
16th to endDay
18%8%45%5%2434438%
2224
April1st to 15thDay
23%9%35%5%3434432%
2152
16th to endDay
20%6%36%424335%38%
2259
May1st to 15thDay
21%6%36%4345%5%5%33%
2486
16th to endDay
20%6%245%345%5%7%33%
2618
June1st to 15thDay
23%6%25%5%3345%8%31%
2520
16th to endDay
17%7%25%6%36%46%8%31%
2520
July1st to 15thDay
12%4246%36%6%6%8%38%
2520
16th to endDay
12%425%5%35%5%6%9%37%
2654
August1st to 15thDay
12%6%26%6%35%5%6%8%35%
2502
16th to endDay
9%423435%45%8%46%
2297
September1st to 15thDay
16%425%42445%7%42%
2160
16th to endDay
13%423423347%49%
1987
October1st to 15thDay
20%7%35%5%34446%34%
1841
16th to endDay
23%9%36%6%3444429%
1758
November1st to 15thDay
17%8%46%5%2446%7%32%
1716
16th to endDay
23%8%36%5%25%435%30%
1573
December1st to 15thDay
26%10%47%6%34445%22%
1560
16th to endDay
25%14%47%424345%22%
1664
January1st to 15thNight
18%15%5%8%6%3444422%
2716
16th to endNight
14%13%5%8%7%45%45%5%26%
2912
February1st to 15thNight
14%13%7%10%8%35%44423%
2499
16th to endNight
18%12%5%7%5%25%44429%
1976
March1st to 15thNight
21%11%37%434345%29%
2160
16th to endNight
16%9%36%43424439%
1997
April1st to 15thNight
26%8%35%424335%32%
1796
16th to endNight
23%6%245%23445%36%
1700
May1st to 15thNight
21%6%37%5%34335%35%
1476
16th to endNight
20%5%35%425%5%5%7%34%
1495
June1st to 15thNight
25%6%35%425%45%7%30%
1440
16th to endNight
17%426%5%245%6%9%35%
1440
July1st to 15thNight
11%414435%5%6%9%41%
1440
16th to endNight
11%4245%345%7%10%41%
1514
August1st to 15thNight
13%5%25%5%2446%8%40%
1444
16th to endNight
13%41342445%7%47%
1902
September1st to 15thNight
16%5%25%434447%42%
1800
16th to endNight
16%423323347%48%
1972
October1st to 15thNight
16%6%36%43435%6%39%
2118
16th to endNight
25%7%36%434345%31%
2465
November1st to 15thNight
21%7%36%5%3444434%
2472
16th to endNight
22%12%47%42333429%
2714
December1st to 15thNight
22%13%48%5%34335%24%
2730
16th to endNight
23%16%48%42433423%
2912

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
64%49%14%6%
1553
16th to endDay
55%5%12%17%7%
1664
February1st to 15thDay
60%411%18%4
1683
16th to endDay
58%410%15%9%1
1644
March1st to 15thDay
58%312%15%9%1
1800
16th to endDay
48%310%18%15%3
2224
April1st to 15thDay
54%37%19%12%2
2152
16th to endDay
49%48%19%14%3
2259
May1st to 15thDay
52%48%18%13%1
2486
16th to endDay
47%6%13%18%12%1
2622
June1st to 15thDay
51%6%11%19%10%1
2520
16th to endDay
49%6%11%21%8%1
2520
July1st to 15thDay
40%7%13%25%12%
2371
16th to endDay
40%7%17%24%8%
2487
August1st to 15thDay
44%7%17%22%7%
2488
16th to endDay
33%5%17%28%13%
2297
September1st to 15thDay
40%5%13%27%12%
2160
16th to endDay
35%312%33%12%
1987
October1st to 15thDay
48%5%12%23%9%
1841
16th to endDay
56%5%13%18%6%
1758
November1st to 15thDay
49%5%14%20%9%
1716
16th to endDay
55%5%12%17%8%
1573
December1st to 15thDay
63%412%14%4
1560
16th to endDay
63%410%11%8%
1664
January1st to 15thNight
63%410%15%5%
2716
16th to endNight
57%6%10%16%8%
2912
February1st to 15thNight
63%49%17%5%
2508
16th to endNight
57%410%17%10%
1976
March1st to 15thNight
57%49%17%9%1
2160
16th to endNight
48%39%18%16%3
1998
April1st to 15thNight
54%26%20%14%1
1796
16th to endNight
49%37%19%15%4
1700
May1st to 15thNight
51%37%17%14%4
1476
16th to endNight
49%5%10%19%13%2
1497
June1st to 15thNight
52%5%10%19%10%
1440
16th to endNight
43%8%12%19%14%1
1440
July1st to 15thNight
35%6%14%27%15%
1360
16th to endNight
35%7%19%23%13%
1418
August1st to 15thNight
40%7%17%22%11%
1434
16th to endNight
34%5%17%29%12%
1902
September1st to 15thNight
41%5%12%25%13%1
1800
16th to endNight
36%5%12%31%14%
1972
October1st to 15thNight
44%6%10%26%11%
2118
16th to endNight
54%412%20%7%
2465
November1st to 15thNight
52%412%20%9%2
2472
16th to endNight
58%310%19%6%
2714
December1st to 15thNight
62%411%16%4
2730
16th to endNight
64%39%13%7%
2912

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
23%8%20%35%12%
90
16th to endDay
25%11%34%19%7%2
96
February1st to 15thDay
34%9%26%26%2
131
16th to endDay
28%5%27%30%7%
265
March1st to 15thDay
22%9%29%28%9%
270
16th to endDay
22%429%27%12%3
288
April1st to 15thDay
26%12%24%23%9%3
270
16th to endDay
22%5%27%26%12%5%
270
May1st to 15thDay
26%5%26%23%12%5%
288
16th to endDay
21%7%26%23%16%3
331
June1st to 15thDay
27%6%21%26%13%4
315
16th to endDay
18%5%22%33%17%3
315
July1st to 15thDay
14%222%30%22%6%
305
16th to endDay
16%14%35%25%7%
326
August1st to 15thDay
14%218%28%24%10%
313
16th to endDay
9%318%28%22%17%
332
September1st to 15thDay
15%219%24%25%13%
315
16th to endDay
13%5%22%20%23%14%
314
October1st to 15thDay
20%426%26%17%5%
315
16th to endDay
28%8%25%24%12%
295
November1st to 15thDay
25%7%24%25%15%2
280
16th to endDay
33%6%23%24%11%
103
December1st to 15thDay
27%5%32%22%10%2
90
16th to endDay
33%9%37%13%6%
96
January1st to 15thNight
25%9%29%27%7%
780
16th to endNight
20%8%33%28%7%1
832
February1st to 15thNight
20%6%33%31%7%
764
16th to endNight
25%5%31%31%6%
659
March1st to 15thNight
27%5%31%29%6%
720
16th to endNight
21%428%34%10%
768
April1st to 15thNight
28%7%25%32%5%
718
16th to endNight
26%6%31%25%9%
620
May1st to 15thNight
23%5%29%30%10%
396
16th to endNight
22%330%34%8%
375
June1st to 15thNight
28%320%34%11%
360
16th to endNight
18%227%37%14%
360
July1st to 15thNight
10%323%40%21%
340
16th to endNight
12%220%46%17%1
376
August1st to 15thNight
15%214%41%24%1
363
16th to endNight
15%119%35%26%2
756
September1st to 15thNight
18%218%41%18%1
720
16th to endNight
17%321%32%23%2
717
October1st to 15thNight
20%427%32%13%
720
16th to endNight
30%7%25%27%8%
768
November1st to 15thNight
25%6%28%28%11%
760
16th to endNight
28%7%27%23%12%
780
December1st to 15thNight
29%8%29%26%6%
780
16th to endNight
31%7%32%22%6%
832
Page generated at 2018-02-23 11:21:38. Version ac04

Copyright 2018 A. Danko


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