Twillingate Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twillingate Astronomical Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
21%
14871
7%
46443
3%
14828
25%
14828
10%
38055

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
6%
748
4%
2656
1%
746
10%
746
3%
2382
January16th to endNight
7%
800
5%
2688
1%
800
12%
800
4%
2392
February1st to 15thNight
11%
734
4%
2410
0%
731
15%
731
6%
2059
February16th to endNight
15%
636
8%
1927
1%
636
20%
636
9%
1563
March1st to 15thNight
19%
691
9%
2131
3%
691
24%
691
9%
1734
March16th to endNight
19%
576
9%
2063
6%
576
26%
576
9%
1661
April1st to 15thNight
19%
539
10%
1733
7%
539
26%
539
11%
1377
April16th to endNight
23%
540
10%
1620
6%
540
27%
540
13%
1262
May1st to 15thNight
29%
540
7%
1486
3%
540
31%
540
13%
1207
May16th to endNight
28%
561
6%
1309
3%
560
29%
560
14%
1082
June1st to 15thNight
29%
540
2%
1260
1%
540
29%
540
13%
1061
June16th to endNight
34%
540
3%
1260
2%
540
35%
540
19%
998
July1st to 15thNight
40%
510
4%
1190
3%
510
41%
510
25%
870
July16th to endNight
38%
565
6%
1350
3%
532
40%
532
18%
1058
August1st to 15thNight
38%
528
8%
1453
4%
524
40%
524
18%
1095
August16th to endNight
43%
525
11%
1575
9%
525
46%
525
19%
1121
September1st to 15thNight
35%
495
11%
1694
10%
495
40%
495
17%
1200
September16th to endNight
30%
493
12%
1815
9%
493
36%
493
15%
1287
October1st to 15thNight
26%
544
13%
1936
8%
544
32%
544
12%
1479
October16th to endNight
17%
736
8%
2288
4%
736
21%
736
9%
1868
November1st to 15thNight
17%
730
8%
2355
4%
730
21%
730
8%
1937
November16th to endNight
11%
750
6%
2664
1%
750
16%
750
5%
2249
December1st to 15thNight
12%
750
4%
2700
1%
750
15%
750
4%
2425
December16th to endNight
6%
800
1%
2880
0%
800
7%
800
2%
2688

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%
47542
Night
24%14%5%9%7%34345%18%
46603
TransparencyDay
62%411%15%5%
47220
Night
69%49%12%4
46443
SeeingDay
30%8%22%24%11%2
8033
Night
31%9%25%24%8%1
14873

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
19%16%10%13%11%443339%
1280
16th to endDay
18%14%7%14%14%7%5%4246%
1536
February1st to 15thDay
17%14%410%14%45%5%46%12%
1449
16th to endDay
17%17%7%11%9%45%5%3314%
1545
March1st to 15thDay
21%11%6%8%7%45%43423%
1818
16th to endDay
23%15%49%7%2345%419%
2160
April1st to 15thDay
21%13%5%5%6%25%45%6%23%
2215
16th to endDay
21%14%5%6%5%23335%28%
2340
May1st to 15thDay
23%13%47%6%3334424%
2464
16th to endDay
27%11%36%42345%6%24%
2805
June1st to 15thDay
30%11%35%5%25%445%21%
2700
16th to endDay
25%10%36%5%3445%5%26%
2700
July1st to 15thDay
17%6%35%43445%8%34%
2700
16th to endDay
20%8%36%6%3446%6%29%
2721
August1st to 15thDay
22%10%36%5%2445%6%29%
2411
16th to endDay
19%7%25%4345%6%8%31%
2275
September1st to 15thDay
23%7%35%424347%32%
1934
16th to endDay
22%6%35%424447%32%
1815
October1st to 15thDay
27%9%36%42433427%
1691
16th to endDay
31%18%35%5%23335%17%
1584
November1st to 15thDay
22%19%6%7%6%34335%17%
1502
16th to endDay
23%16%9%10%5%2343416%
1293
December1st to 15thDay
21%16%8%15%10%2233311%
1260
16th to endDay
23%18%9%15%13%222224
1344
January1st to 15thNight
18%18%9%12%13%45%3436%
2656
16th to endNight
18%13%6%17%13%5%33349%
2688
February1st to 15thNight
18%12%5%14%14%4433413%
2410
16th to endNight
18%15%6%10%7%34445%17%
1927
March1st to 15thNight
19%13%5%10%8%46%446%17%
2118
16th to endNight
25%14%5%9%6%35%34417%
2063
April1st to 15thNight
24%15%6%8%5%33346%19%
1733
16th to endNight
25%14%5%6%422245%24%
1620
May1st to 15thNight
28%14%47%5%2334421%
1486
16th to endNight
32%12%44434345%21%
1307
June1st to 15thNight
33%10%47%323446%17%
1260
16th to endNight
29%11%35%314346%26%
1260
July1st to 15thNight
19%8%35%5%35%45%7%31%
1260
16th to endNight
23%9%36%6%34345%27%
1444
August1st to 15thNight
22%10%35%6%34446%28%
1464
16th to endNight
24%7%35%424447%31%
1575
September1st to 15thNight
25%8%25%424446%32%
1694
16th to endNight
23%9%27%42335%7%29%
1815
October1st to 15thNight
29%11%36%5%33336%24%
1936
16th to endNight
32%18%36%32223419%
2288
November1st to 15thNight
26%19%47%5%33345%17%
2355
16th to endNight
23%19%9%8%5%23345%13%
2664
December1st to 15thNight
21%18%8%15%9%333338%
2700
16th to endNight
24%17%12%14%12%332125%
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
81%37%5%1
1281
16th to endDay
81%446%2
1536
February1st to 15thDay
71%39%8%5%
1453
16th to endDay
73%36%10%4
1545
March1st to 15thDay
64%39%13%7%
1828
16th to endDay
67%47%14%5%
2160
April1st to 15thDay
61%211%16%7%
2215
16th to endDay
60%37%19%8%
2340
May1st to 15thDay
63%311%16%5%
2464
16th to endDay
60%412%17%5%
2809
June1st to 15thDay
64%411%15%3
2700
16th to endDay
59%49%18%7%1
2700
July1st to 15thDay
46%418%23%6%
2542
16th to endDay
53%5%15%20%5%
2552
August1st to 15thDay
54%416%19%4
2397
16th to endDay
48%5%19%19%5%
2275
September1st to 15thDay
51%414%20%7%
1934
16th to endDay
50%418%21%5%
1815
October1st to 15thDay
60%311%16%7%
1691
16th to endDay
69%37%14%4
1584
November1st to 15thDay
70%5%10%10%3
1502
16th to endDay
71%5%8%9%4
1293
December1st to 15thDay
79%37%7%2
1260
16th to endDay
87%2341
1344
January1st to 15thNight
81%35%5%2
2656
16th to endNight
79%45%7%3
2688
February1st to 15thNight
75%37%9%3
2410
16th to endNight
68%39%11%5%
1927
March1st to 15thNight
68%48%12%5%
2131
16th to endNight
69%36%13%7%
2063
April1st to 15thNight
66%37%15%6%
1733
16th to endNight
63%38%15%8%
1620
May1st to 15thNight
67%39%14%41
1486
16th to endNight
66%49%13%6%
1309
June1st to 15thNight
65%6%11%12%4
1260
16th to endNight
60%310%18%6%
1260
July1st to 15thNight
49%417%23%5%
1190
16th to endNight
58%5%12%18%5%
1350
August1st to 15thNight
55%6%15%17%5%
1453
16th to endNight
52%415%20%7%
1575
September1st to 15thNight
53%413%22%5%
1694
16th to endNight
54%5%14%18%7%
1815
October1st to 15thNight
62%411%14%6%
1936
16th to endNight
70%26%14%4
2288
November1st to 15thNight
69%49%12%4
2355
16th to endNight
74%48%9%2
2664
December1st to 15thNight
82%36%6%1
2700
16th to endNight
88%2341
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
24%18%37%16%3
240
16th to endDay
25%17%34%19%3
256
February1st to 15thDay
24%14%35%19%5%
236
16th to endDay
20%13%33%23%5%3
212
March1st to 15thDay
27%11%28%20%9%2
240
16th to endDay
29%14%23%20%9%2
264
April1st to 15thDay
32%7%27%22%5%3
332
16th to endDay
33%6%23%22%11%2
450
May1st to 15thDay
33%417%23%16%4
468
16th to endDay
36%316%28%12%2
519
June1st to 15thDay
37%5%12%25%15%4
495
16th to endDay
30%121%27%14%4
495
July1st to 15thDay
24%222%28%18%4
475
16th to endDay
25%315%30%22%2
514
August1st to 15thDay
26%416%31%14%5%
473
16th to endDay
25%216%29%21%6%
443
September1st to 15thDay
32%7%17%30%8%3
261
16th to endDay
25%7%29%25%10%1
224
October1st to 15thDay
32%10%24%18%11%2
225
16th to endDay
46%12%22%13%4
240
November1st to 15thDay
35%12%27%16%5%1
235
16th to endDay
34%14%27%19%4
240
December1st to 15thDay
28%16%32%19%3
240
16th to endDay
25%19%32%16%31
256
January1st to 15thNight
28%16%33%18%3
750
16th to endNight
25%17%36%15%5%
800
February1st to 15thNight
25%14%32%21%4
734
16th to endNight
27%7%34%19%7%2
636
March1st to 15thNight
25%12%29%22%8%1
691
16th to endNight
32%8%26%24%6%
576
April1st to 15thNight
31%8%28%22%7%1
539
16th to endNight
34%424%25%10%1
540
May1st to 15thNight
35%415%28%14%2
540
16th to endNight
38%419%26%9%1
561
June1st to 15thNight
37%414%29%13%1
540
16th to endNight
35%415%27%15%2
540
July1st to 15thNight
24%421%33%14%1
510
16th to endNight
28%316%33%16%1
565
August1st to 15thNight
27%317%32%17%1
528
16th to endNight
27%315%33%18%2
525
September1st to 15thNight
29%323%33%9%
495
16th to endNight
31%5%26%28%6%
493
October1st to 15thNight
38%5%23%24%8%
544
16th to endNight
43%10%20%20%5%
736
November1st to 15thNight
34%12%25%20%6%
730
16th to endNight
33%14%29%18%3
750
December1st to 15thNight
30%15%30%18%4
750
16th to endNight
29%16%29%17%6%1
800
Page generated at 2017-08-13 15:46:54. Version ac04

Copyright 2017 A. Danko


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