Ponte di Legno Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ponte di Legno Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
28%
15735
12%
48419
7%
15694
33%
15694
14%
35661

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
9%
975
4%
2838
1%
970
12%
970
4%
2520
January16th to endNight
13%
850
7%
2622
3%
850
18%
850
6%
2238
February1st to 15thNight
14%
701
6%
2287
2%
701
18%
701
7%
1911
February16th to endNight
19%
631
11%
1973
4%
631
26%
631
10%
1531
March1st to 15thNight
22%
720
14%
2028
7%
720
28%
720
15%
1491
March16th to endNight
30%
768
20%
2112
10%
768
37%
768
20%
1425
April1st to 15thNight
25%
654
17%
1797
6%
654
33%
654
20%
1245
April16th to endNight
30%
540
19%
1620
7%
540
40%
540
19%
1085
May1st to 15thNight
39%
532
15%
1612
11%
532
44%
532
19%
1084
May16th to endNight
40%
374
15%
1497
12%
374
50%
374
19%
856
June1st to 15thNight
39%
360
13%
1266
11%
360
47%
360
20%
783
June16th to endNight
46%
360
13%
1260
12%
360
53%
360
23%
751
July1st to 15thNight
57%
340
18%
1190
19%
340
62%
340
33%
615
July16th to endNight
50%
530
16%
1486
14%
497
58%
497
30%
893
August1st to 15thNight
55%
539
18%
1609
14%
536
60%
536
30%
935
August16th to endNight
55%
573
20%
1719
12%
573
61%
573
31%
1013
September1st to 15thNight
48%
711
16%
1869
9%
711
53%
711
31%
1210
September16th to endNight
46%
717
20%
1980
13%
717
50%
717
27%
1301
October1st to 15thNight
32%
720
14%
2139
11%
720
37%
720
17%
1533
October16th to endNight
20%
768
9%
2360
4%
768
27%
768
10%
1873
November1st to 15thNight
22%
760
12%
2563
10%
760
27%
760
11%
1940
November16th to endNight
15%
780
7%
2730
4%
780
19%
780
6%
2226
December1st to 15thNight
10%
792
2%
2742
1%
792
11%
792
4%
2420
December16th to endNight
7%
1040
4%
3120
0%
1040
10%
1040
4%
2782

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
15%10%47%5%3445%6%32%
49103
Night
16%12%5%8%6%34446%27%
48588
Cloud CoverDay
14%10%47%5%3445%6%32%
49113
Night
16%11%5%8%6%3445%6%27%
48592
TransparencyDay
51%312%21%10%
48790
Night
57%311%18%8%
48419
SeeingDay
18%15%24%23%13%5%
6170
Night
19%22%21%23%11%1
15739

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%19%9%13%9%35%3437%
1426
16th to endDay
14%19%10%13%10%45%4239%
1704
February1st to 15thDay
13%17%8%14%10%4433415%
1575
16th to endDay
14%16%6%9%9%45%445%18%
1497
March1st to 15thDay
13%10%47%6%35%5%5%5%30%
1921
16th to endDay
13%8%37%6%345%5%6%36%
2112
April1st to 15thDay
21%9%35%434446%33%
2160
16th to endDay
17%8%2432335%7%40%
2340
May1st to 15thDay
16%6%45%424447%39%
2337
16th to endDay
11%5%245%2435%7%47%
2618
June1st to 15thDay
13%5%244345%6%8%39%
2691
16th to endDay
11%6%35%425%5%6%9%40%
2700
July1st to 15thDay
9%42442446%8%48%
2700
16th to endDay
8%4244235%6%9%46%
2575
August1st to 15thDay
9%5%2443445%8%48%
2340
16th to endDay
11%6%35%43446%8%41%
2480
September1st to 15thDay
13%5%25%5%2445%7%41%
2079
16th to endDay
16%5%25%5%2445%7%40%
1980
October1st to 15thDay
21%9%36%5%24345%32%
1820
16th to endDay
30%12%48%6%2443419%
1863
November1st to 15thDay
20%11%5%8%8%45%45%6%19%
1623
16th to endDay
21%21%5%8%7%345%35%12%
1560
December1st to 15thDay
19%25%9%12%8%343246%
1546
16th to endDay
21%22%8%13%8%23335%7%
1456
January1st to 15thNight
20%18%8%12%9%35%5%437%
2838
16th to endNight
14%17%9%13%10%45%5%3411%
2622
February1st to 15thNight
12%18%9%13%9%45%335%14%
2285
16th to endNight
14%13%7%11%7%35%45%6%19%
1973
March1st to 15thNight
15%12%5%8%6%3435%6%29%
2016
16th to endNight
14%8%47%434345%39%
2112
April1st to 15thNight
20%9%44324346%35%
1797
16th to endNight
18%6%35%42345%6%37%
1620
May1st to 15thNight
15%8%45%6%25%446%36%
1612
16th to endNight
11%5%245%45%5%6%7%42%
1495
June1st to 15thNight
12%7%346%25%5%5%8%38%
1266
16th to endNight
8%5%25%6%246%5%9%41%
1260
July1st to 15thNight
8%213435%36%9%50%
1260
16th to endNight
8%4235%35%5%6%7%47%
1590
August1st to 15thNight
7%5%145%245%6%7%47%
1620
16th to endNight
10%425%42445%7%46%
1719
September1st to 15thNight
12%5%245%3446%7%42%
1869
16th to endNight
13%6%35%5%35%446%41%
1980
October1st to 15thNight
21%7%37%5%34446%29%
2139
16th to endNight
26%12%47%6%34445%19%
2360
November1st to 15thNight
19%14%49%6%34446%21%
2563
16th to endNight
24%18%48%6%34445%14%
2730
December1st to 15thNight
19%24%9%13%7%344337%
2742
16th to endNight
22%21%9%13%6%333238%
3120

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
18%19%9%15%9%45%4427%
1426
16th to endDay
13%20%9%14%11%45%3438%
1704
February1st to 15thDay
12%17%9%13%9%5%5%44413%
1575
16th to endDay
14%15%6%10%9%45%345%18%
1497
March1st to 15thDay
13%10%5%7%7%35%5%5%5%30%
1932
16th to endDay
12%8%47%6%345%5%6%35%
2111
April1st to 15thDay
20%8%46%424346%33%
2160
16th to endDay
17%8%2432336%7%39%
2340
May1st to 15thDay
16%6%45%32435%7%40%
2337
16th to endDay
11%41443445%8%46%
2618
June1st to 15thDay
12%5%34435%46%8%40%
2691
16th to endDay
12%5%25%435%46%8%42%
2700
July1st to 15thDay
8%42442445%9%48%
2700
16th to endDay
8%425%425%46%9%46%
2575
August1st to 15thDay
9%5%2443445%8%48%
2340
16th to endDay
11%7%25%5%2445%8%41%
2480
September1st to 15thDay
14%5%345%34447%41%
2079
16th to endDay
15%6%25%43445%7%40%
1980
October1st to 15thDay
20%9%45%5%33436%32%
1820
16th to endDay
29%12%5%8%444335%18%
1863
November1st to 15thDay
19%14%5%6%6%36%45%6%21%
1623
16th to endDay
19%21%6%9%7%44445%12%
1560
December1st to 15thDay
17%23%10%13%8%443346%
1546
16th to endDay
21%21%10%14%6%234446%
1456
January1st to 15thNight
19%18%8%13%9%35%5%338%
2838
16th to endNight
14%16%9%14%10%5%5%34411%
2622
February1st to 15thNight
12%17%9%13%9%45%435%13%
2278
16th to endNight
13%12%7%12%8%36%5%45%20%
1973
March1st to 15thNight
14%13%48%6%34345%29%
2028
16th to endNight
14%9%46%5%2335%5%38%
2112
April1st to 15thNight
21%8%45%413346%36%
1797
16th to endNight
17%7%35%42435%7%37%
1620
May1st to 15thNight
15%7%45%6%3435%6%36%
1611
16th to endNight
11%5%25%5%345%6%5%43%
1495
June1st to 15thNight
12%6%35%5%36%45%9%37%
1266
16th to endNight
8%5%15%5%45%5%6%8%42%
1260
July1st to 15thNight
7%41342446%9%50%
1260
16th to endNight
7%4245%345%7%6%47%
1590
August1st to 15thNight
8%4244345%6%7%47%
1620
16th to endNight
9%5%26%4335%5%8%46%
1719
September1st to 15thNight
12%425%4345%6%7%43%
1869
16th to endNight
12%7%36%43435%6%41%
1980
October1st to 15thNight
20%8%26%6%35%45%7%29%
2139
16th to endNight
25%11%48%6%44445%19%
2360
November1st to 15thNight
19%12%5%8%7%35%447%21%
2563
16th to endNight
23%16%5%8%7%34346%14%
2730
December1st to 15thNight
19%22%9%12%8%443437%
2742
16th to endNight
21%21%9%13%7%443337%
3120

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%35%8%
1427
16th to endDay
80%25%8%2
1704
February1st to 15thDay
73%28%12%2
1577
16th to endDay
67%38%14%6%
1497
March1st to 15thDay
53%412%20%9%
1932
16th to endDay
47%312%19%14%1
2112
April1st to 15thDay
52%28%22%12%1
2160
16th to endDay
43%311%24%15%2
2340
May1st to 15thDay
43%38%25%15%2
2337
16th to endDay
35%315%26%16%1
2622
June1st to 15thDay
40%313%28%13%
2691
16th to endDay
38%414%27%12%
2700
July1st to 15thDay
31%216%31%16%2
2541
16th to endDay
33%415%30%14%
2416
August1st to 15thDay
33%418%28%14%
2327
16th to endDay
39%415%27%11%1
2480
September1st to 15thDay
40%315%29%10%
2079
16th to endDay
42%415%29%7%
1980
October1st to 15thDay
53%39%21%10%
1820
16th to endDay
69%310%12%4
1863
November1st to 15thDay
63%311%15%5%
1623
16th to endDay
74%210%9%2
1560
December1st to 15thDay
82%18%6%1
1546
16th to endDay
81%17%7%
1456
January1st to 15thNight
79%27%7%1
2838
16th to endNight
75%28%9%2
2622
February1st to 15thNight
73%28%12%2
2287
16th to endNight
65%210%14%6%
1973
March1st to 15thNight
55%211%20%8%
2028
16th to endNight
46%210%21%16%2
2112
April1st to 15thNight
49%38%24%12%1
1797
16th to endNight
46%38%20%19%2
1620
May1st to 15thNight
48%37%22%16%2
1612
16th to endNight
39%213%24%17%2
1497
June1st to 15thNight
42%49%25%16%1
1266
16th to endNight
38%313%29%14%
1260
July1st to 15thNight
28%314%30%19%3
1190
16th to endNight
34%5%13%27%17%
1486
August1st to 15thNight
33%416%28%15%1
1609
16th to endNight
34%316%29%13%1
1719
September1st to 15thNight
38%415%28%13%
1869
16th to endNight
43%313%30%10%
1980
October1st to 15thNight
54%210%22%9%
2139
16th to endNight
66%211%14%4
2360
November1st to 15thNight
62%312%16%4
2563
16th to endNight
71%212%10%1
2730
December1st to 15thNight
81%19%5%1
2742
16th to endNight
81%17%7%1
3120

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
27%17%32%16%4
106
16th to endDay
31%11%32%17%8%
109
February1st to 15thDay
25%23%34%14%2
90
16th to endDay
22%25%33%16%2
81
March1st to 15thDay
16%24%27%24%5%
222
16th to endDay
21%18%23%23%9%3
288
April1st to 15thDay
22%19%27%18%8%2
270
16th to endDay
24%16%27%16%10%4
270
May1st to 15thDay
20%14%22%21%13%5%
288
16th to endDay
13%16%24%25%13%6%
331
June1st to 15thDay
14%16%27%26%12%2
486
16th to endDay
14%17%25%26%11%4
495
July1st to 15thDay
11%10%23%29%18%5%
475
16th to endDay
10%12%23%28%18%5%
402
August1st to 15thDay
13%7%16%31%20%11%
313
16th to endDay
19%7%18%23%20%10%
332
September1st to 15thDay
13%7%20%24%21%12%
315
16th to endDay
15%12%17%25%21%8%
314
October1st to 15thDay
23%13%24%23%11%3
315
16th to endDay
32%15%26%18%5%
279
November1st to 15thDay
25%18%30%18%6%
113
16th to endDay
25%23%32%17%1
90
December1st to 15thDay
31%18%30%14%5%
90
16th to endDay
28%30%35%6%
96
January1st to 15thNight
23%30%25%14%5%
975
16th to endNight
18%29%23%22%6%1
850
February1st to 15thNight
18%28%27%20%4
704
16th to endNight
17%22%29%22%7%
631
March1st to 15thNight
17%26%24%22%7%
720
16th to endNight
18%23%22%24%10%1
768
April1st to 15thNight
19%24%24%24%5%1
654
16th to endNight
20%23%20%21%12%
540
May1st to 15thNight
15%19%15%29%17%2
532
16th to endNight
12%21%19%30%15%1
375
June1st to 15thNight
14%20%17%32%14%
360
16th to endNight
9%19%16%31%23%
360
July1st to 15thNight
9%14%13%40%19%2
340
16th to endNight
10%17%15%34%20%2
530
August1st to 15thNight
10%11%13%33%27%3
539
16th to endNight
11%11%15%31%25%5%
573
September1st to 15thNight
12%13%18%26%19%9%
711
16th to endNight
14%13%18%24%22%6%
717
October1st to 15thNight
22%16%21%24%12%2
720
16th to endNight
30%18%23%21%5%
768
November1st to 15thNight
23%23%22%18%9%1
760
16th to endNight
28%27%19%16%6%
780
December1st to 15thNight
28%29%26%12%3
792
16th to endNight
27%29%24%14%4
1040
Page generated at 2018-01-21 12:19:25. Version ac04

Copyright 2018 A. Danko


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