Observatoire Obaska
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Obaska clear sky chart from 2005-11-05 to 2017-12-04.

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%
15092
9%
47673
6%
15060
28%
15060
12%
37351

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
14%
881
5%
2666
3%
876
16%
876
4%
2367
January16th to endNight
21%
768
6%
2658
4%
768
24%
768
6%
2259
February1st to 15thNight
23%
703
8%
2287
5%
701
28%
701
9%
1880
February16th to endNight
16%
631
7%
2019
3%
631
22%
631
8%
1691
March1st to 15thNight
22%
720
10%
2061
7%
720
27%
720
12%
1652
March16th to endNight
27%
768
17%
2064
9%
768
33%
768
19%
1532
April1st to 15thNight
24%
718
13%
1796
5%
718
28%
718
16%
1396
April16th to endNight
26%
538
16%
1618
9%
538
33%
538
19%
1149
May1st to 15thNight
32%
360
14%
1440
15%
360
40%
360
15%
982
May16th to endNight
29%
375
8%
1497
7%
374
38%
374
14%
1048
June1st to 15thNight
30%
360
7%
1310
5%
360
34%
360
13%
945
June16th to endNight
42%
360
7%
1260
5%
360
43%
360
20%
828
July1st to 15thNight
38%
340
7%
1190
7%
340
40%
340
20%
783
July16th to endNight
49%
376
9%
1396
13%
354
49%
354
18%
919
August1st to 15thNight
39%
431
10%
1502
9%
429
44%
429
15%
1075
August16th to endNight
41%
635
14%
1781
9%
635
44%
635
24%
1218
September1st to 15thNight
34%
720
10%
1800
4%
720
36%
720
22%
1320
September16th to endNight
34%
717
15%
1979
9%
717
38%
717
22%
1396
October1st to 15thNight
24%
720
12%
2160
8%
720
29%
720
15%
1629
October16th to endNight
17%
768
8%
2394
5%
768
21%
768
8%
2002
November1st to 15thNight
14%
760
8%
2644
5%
760
19%
760
8%
2151
November16th to endNight
13%
780
6%
2730
3%
780
16%
780
5%
2338
December1st to 15thNight
11%
736
4%
2574
1%
736
14%
736
5%
2240
December16th to endNight
13%
927
5%
2847
4%
927
15%
927
4%
2551

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
22%12%47%6%34445%23%
48829
Night
20%13%5%8%6%35%445%23%
47832
TransparencyDay
62%49%15%6%
48506
Night
63%410%14%6%
47673
SeeingDay
29%11%29%19%8%1
6035
Night
28%10%28%23%8%
15093

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%17%7%13%9%16%5%438%
1271
16th to endDay
15%18%6%11%9%46%6%5%411%
1565
February1st to 15thDay
10%13%6%14%11%6%7%45%7%12%
1575
16th to endDay
15%18%7%11%8%45%33317%
1453
March1st to 15thDay
16%14%5%8%6%35%445%25%
1885
16th to endDay
14%15%46%4345%45%31%
2160
April1st to 15thDay
23%15%5%6%42334325%
2152
16th to endDay
21%11%46%5%33345%31%
2349
May1st to 15thDay
21%10%35%435%45%5%29%
2511
16th to endDay
25%9%35%323335%32%
2618
June1st to 15thDay
23%8%25%435%45%8%26%
2648
16th to endDay
20%6%37%6%45%5%5%7%29%
2700
July1st to 15thDay
20%7%27%6%35%6%5%8%26%
2700
16th to endDay
21%6%36%5%35%5%5%7%28%
2675
August1st to 15thDay
25%8%37%5%35%45%6%25%
2446
16th to endDay
22%6%37%6%445%5%7%26%
2408
September1st to 15thDay
24%7%35%5%34447%30%
2160
16th to endDay
26%7%25%424347%31%
1980
October1st to 15thDay
25%14%36%5%22346%25%
1800
16th to endDay
33%20%36%43233313%
1830
November1st to 15thDay
25%20%7%8%5%2322319%
1541
16th to endDay
26%20%8%11%7%3322210%
1560
December1st to 15thDay
20%24%8%11%7%3432410%
1468
16th to endDay
20%19%8%12%8%34435%9%
1374
January1st to 15thNight
22%17%8%12%7%36%4329%
2666
16th to endNight
13%16%8%12%8%5%8%6%4411%
2658
February1st to 15thNight
11%13%6%12%10%5%8%6%5%5%14%
2285
16th to endNight
15%16%7%11%8%46%6%5%315%
2019
March1st to 15thNight
17%16%5%6%7%46%5%5%5%19%
2049
16th to endNight
16%11%46%435%44432%
2064
April1st to 15thNight
22%11%5%8%32443429%
1796
16th to endNight
20%9%46%424345%35%
1618
May1st to 15thNight
17%10%5%6%5%24445%32%
1440
16th to endNight
23%8%35%5%35%45%8%29%
1495
June1st to 15thNight
21%7%37%6%35%5%45%28%
1310
16th to endNight
15%5%27%6%3445%7%36%
1260
July1st to 15thNight
18%6%245%2447%8%34%
1260
16th to endNight
15%5%35%6%35%45%7%37%
1491
August1st to 15thNight
21%7%27%5%445%6%6%29%
1512
16th to endNight
14%7%35%5%245%47%38%
1781
September1st to 15thNight
21%7%35%5%34345%36%
1800
16th to endNight
24%7%24422345%37%
1979
October1st to 15thNight
24%10%36%5%34345%27%
2160
16th to endNight
33%17%35%42334417%
2394
November1st to 15thNight
23%17%7%8%5%24335%19%
2644
16th to endNight
27%20%6%8%5%2422414%
2730
December1st to 15thNight
21%22%8%12%7%2432311%
2574
16th to endNight
20%21%8%12%8%35%4229%
2847

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
79%38%7%1
1272
16th to endDay
74%35%11%5%
1565
February1st to 15thDay
71%47%11%4
1577
16th to endDay
71%26%15%4
1453
March1st to 15thDay
61%46%15%10%
1896
16th to endDay
54%47%20%10%2
2160
April1st to 15thDay
62%37%13%10%2
2152
16th to endDay
56%29%16%12%1
2349
May1st to 15thDay
55%38%18%11%1
2511
16th to endDay
55%47%20%10%
2622
June1st to 15thDay
55%410%19%9%
2648
16th to endDay
53%5%10%20%8%1
2700
July1st to 15thDay
52%6%13%19%7%
2541
16th to endDay
57%6%11%19%5%
2507
August1st to 15thDay
59%6%13%17%3
2432
16th to endDay
56%5%14%17%6%
2408
September1st to 15thDay
54%5%14%17%6%1
2160
16th to endDay
54%5%12%21%5%
1980
October1st to 15thDay
61%313%14%6%
1800
16th to endDay
76%37%8%3
1830
November1st to 15thDay
71%311%9%3
1541
16th to endDay
82%25%7%2
1560
December1st to 15thDay
80%35%9%1
1468
16th to endDay
78%37%7%2
1374
January1st to 15thNight
80%26%8%1
2666
16th to endNight
75%36%9%4
2658
February1st to 15thNight
69%48%10%6%
2287
16th to endNight
71%46%12%4
2019
March1st to 15thNight
65%48%12%9%
2061
16th to endNight
54%48%20%10%1
2064
April1st to 15thNight
58%47%16%11%2
1796
16th to endNight
52%47%19%14%1
1618
May1st to 15thNight
52%48%18%13%2
1440
16th to endNight
53%5%10%19%10%
1497
June1st to 15thNight
55%6%8%17%11%1
1310
16th to endNight
45%5%12%23%10%1
1260
July1st to 15thNight
45%6%15%24%8%
1190
16th to endNight
47%6%15%23%6%
1396
August1st to 15thNight
53%6%14%21%3
1502
16th to endNight
44%6%20%23%5%
1781
September1st to 15thNight
50%416%19%8%
1800
16th to endNight
49%415%24%6%
1979
October1st to 15thNight
58%413%15%6%1
2160
16th to endNight
71%410%11%3
2394
November1st to 15thNight
69%412%10%3
2644
16th to endNight
75%48%8%3
2730
December1st to 15thNight
79%27%8%1
2574
16th to endNight
81%35%6%3
2847

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
31%18%33%11%5%
60
16th to endDay
39%7%30%14%8%
69
February1st to 15thDay
24%14%44%13%21
90
16th to endDay
25%16%38%17%1
112
March1st to 15thDay
26%16%32%18%6%
270
16th to endDay
23%13%36%18%7%1
288
April1st to 15thDay
33%11%28%17%5%3
270
16th to endDay
27%18%27%17%7%2
270
May1st to 15thDay
31%11%29%18%8%
288
16th to endDay
31%12%27%21%5%2
331
June1st to 15thDay
32%12%28%17%7%1
443
16th to endDay
20%11%31%26%7%2
495
July1st to 15thDay
24%9%30%24%8%2
475
16th to endDay
23%6%33%20%11%3
346
August1st to 15thDay
32%326%20%12%3
313
16th to endDay
31%6%25%19%12%3
332
September1st to 15thDay
25%7%27%25%9%4
315
16th to endDay
26%8%31%21%10%1
314
October1st to 15thDay
31%12%30%16%7%
315
16th to endDay
42%13%19%15%6%
313
November1st to 15thDay
41%15%29%9%3
105
16th to endDay
46%15%28%7%1
90
December1st to 15thDay
34%13%32%14%21
67
16th to endDay
42%14%32%7%3
64
January1st to 15thNight
33%11%30%20%4
881
16th to endNight
21%12%31%22%12%
768
February1st to 15thNight
18%12%35%26%7%
704
16th to endNight
24%13%34%22%5%
631
March1st to 15thNight
28%17%25%21%5%
720
16th to endNight
23%12%30%23%8%1
768
April1st to 15thNight
29%14%25%23%6%
718
16th to endNight
26%12%31%22%6%1
538
May1st to 15thNight
24%5%31%28%9%
360
16th to endNight
28%6%31%26%6%
375
June1st to 15thNight
25%7%29%25%10%
360
16th to endNight
16%6%27%34%14%
360
July1st to 15thNight
18%432%33%10%
340
16th to endNight
16%322%41%15%1
376
August1st to 15thNight
23%423%29%17%2
431
16th to endNight
19%6%26%28%16%1
635
September1st to 15thNight
28%6%25%22%14%1
720
16th to endNight
28%7%24%26%11%
717
October1st to 15thNight
29%11%29%21%7%
720
16th to endNight
44%9%23%16%5%1
768
November1st to 15thNight
34%12%30%14%6%
760
16th to endNight
40%12%26%15%4
780
December1st to 15thNight
36%12%26%17%5%1
736
16th to endNight
33%13%25%19%5%2
927
Page generated at 2017-12-05 10:18:58. Version ac04

Copyright 2017 A. Danko


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