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 2017-09-20.

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%
15210
12%
46783
7%
15169
33%
15169
14%
34345

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
7%
900
3%
2619
0%
895
10%
895
4%
2337
January16th to endNight
14%
825
8%
2553
4%
825
19%
825
6%
2177
February1st to 15thNight
14%
701
6%
2287
2%
701
18%
701
7%
1911
February16th to endNight
20%
631
10%
1973
4%
631
26%
631
10%
1531
March1st to 15thNight
22%
720
13%
2028
7%
720
28%
720
15%
1491
March16th to endNight
30%
768
20%
2112
10%
768
38%
768
20%
1425
April1st to 15thNight
25%
654
17%
1797
6%
654
32%
654
20%
1245
April16th to endNight
29%
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
51%
374
19%
856
June1st to 15thNight
40%
360
13%
1266
11%
360
48%
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
49%
530
16%
1486
14%
497
57%
497
30%
893
August1st to 15thNight
55%
539
18%
1609
14%
536
59%
536
30%
935
August16th to endNight
55%
573
20%
1719
12%
573
61%
573
31%
1013
September1st to 15thNight
49%
711
17%
1869
9%
711
53%
711
31%
1210
September16th to endNight
45%
677
19%
1870
12%
677
49%
677
27%
1235
October1st to 15thNight
31%
660
14%
1961
11%
660
36%
660
17%
1408
October16th to endNight
20%
704
9%
2163
4%
704
26%
704
10%
1730
November1st to 15thNight
24%
700
13%
2361
11%
700
28%
700
12%
1763
November16th to endNight
17%
720
7%
2520
5%
720
20%
720
6%
2061
December1st to 15thNight
9%
731
2%
2531
1%
731
10%
731
4%
2232
December16th to endNight
7%
960
4%
2880
1%
960
11%
960
3%
2574

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%9%47%5%3445%6%33%
48052
Night
16%12%5%8%6%34446%27%
46952
Cloud CoverDay
14%9%47%5%3445%6%33%
48062
Night
16%11%5%8%6%3445%6%27%
46956
TransparencyDay
51%312%21%10%
47739
Night
57%211%18%8%
46783
SeeingDay
18%14%24%24%13%5%
5829
Night
19%22%21%23%11%1
15214

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%14%9%45%3337%
1316
16th to endDay
15%19%10%13%10%45%4239%
1669
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%6%25%5%2445%7%39%
1859
October1st to 15thDay
21%9%36%6%34345%31%
1669
16th to endDay
30%12%48%6%2443417%
1708
November1st to 15thDay
19%10%5%8%8%45%45%6%20%
1495
16th to endDay
21%21%5%8%8%245%35%12%
1440
December1st to 15thDay
19%24%8%12%9%343236%
1427
16th to endDay
22%23%9%13%7%23325%6%
1344
January1st to 15thNight
20%19%8%13%9%344437%
2619
16th to endNight
15%17%9%13%10%35%5%3411%
2553
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
14%6%35%5%24446%41%
1870
October1st to 15thNight
22%7%37%6%34446%28%
1961
16th to endNight
27%12%47%6%34445%18%
2163
November1st to 15thNight
19%13%48%6%34446%22%
2361
16th to endNight
24%19%5%8%6%34435%14%
2520
December1st to 15thNight
20%24%9%12%6%344337%
2531
16th to endNight
23%22%9%13%6%333238%
2880

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%14%10%443427%
1316
16th to endDay
13%20%9%14%11%45%3438%
1669
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
16%6%25%43445%7%39%
1859
October1st to 15thDay
20%10%46%5%33445%31%
1669
16th to endDay
30%12%48%444335%16%
1708
November1st to 15thDay
18%14%5%6%6%36%5%5%6%22%
1495
16th to endDay
19%21%6%9%7%34445%12%
1440
December1st to 15thDay
18%22%10%13%8%443246%
1427
16th to endDay
22%22%10%14%6%224446%
1344
January1st to 15thNight
20%18%8%13%9%35%4338%
2619
16th to endNight
14%16%9%14%10%45%34411%
2553
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
13%7%36%434346%41%
1870
October1st to 15thNight
20%9%26%6%35%45%7%28%
1961
16th to endNight
26%12%48%6%34445%18%
2163
November1st to 15thNight
19%11%5%8%7%35%45%7%22%
2361
16th to endNight
23%17%5%8%7%34346%14%
2520
December1st to 15thNight
20%22%9%12%8%343437%
2531
16th to endNight
22%22%8%13%6%343337%
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
82%26%8%
1317
16th to endDay
80%25%8%2
1669
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
43%415%27%7%
1859
October1st to 15thDay
54%39%21%10%
1669
16th to endDay
70%310%11%3
1708
November1st to 15thDay
62%411%15%6%
1495
16th to endDay
74%210%8%2
1440
December1st to 15thDay
82%18%5%1
1427
16th to endDay
82%18%6%
1344
January1st to 15thNight
80%26%7%1
2619
16th to endNight
75%28%9%3
2553
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%28%10%
1870
October1st to 15thNight
55%211%21%9%
1961
16th to endNight
66%311%14%4
2163
November1st to 15thNight
61%313%16%4
2361
16th to endNight
72%212%10%1
2520
December1st to 15thNight
81%110%5%1
2531
16th to endNight
82%16%7%1
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
25%15%33%18%7%
71
16th to endDay
33%6%33%17%9%
96
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
17%12%17%26%17%8%
270
October1st to 15thDay
22%14%23%25%11%2
255
16th to endDay
34%14%25%19%6%
220
November1st to 15thDay
16%16%34%22%9%1
75
16th to endDay
23%21%28%25%1
60
December1st to 15thDay
30%18%30%16%5%
60
16th to endDay
32%35%26%4
64
January1st to 15thNight
22%31%25%13%5%
900
16th to endNight
18%28%23%22%6%1
825
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%19%24%22%6%
677
October1st to 15thNight
22%17%20%23%13%2
660
16th to endNight
30%19%22%21%5%
704
November1st to 15thNight
21%24%22%19%10%2
700
16th to endNight
28%28%19%16%7%
720
December1st to 15thNight
29%30%24%11%3
731
16th to endNight
28%30%22%13%4
960
Page generated at 2017-09-21 07:18:20. Version ac04

Copyright 2017 A. Danko


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