Arco
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arco clear sky chart from 2005-11-05 to 2018-02-13.

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
61%
15919
20%
48782
17%
15886
65%
15886
34%
28539

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
59%
776
11%
2716
10%
776
63%
776
19%
1841
January16th to endNight
59%
832
16%
2830
15%
832
63%
832
23%
1822
February1st to 15thNight
53%
747
12%
2444
10%
744
57%
744
24%
1593
February16th to endNight
50%
632
15%
1900
10%
632
57%
632
25%
1249
March1st to 15thNight
58%
720
14%
2073
11%
720
61%
720
29%
1314
March16th to endNight
53%
768
17%
2112
11%
768
57%
768
32%
1331
April1st to 15thNight
55%
666
19%
1794
11%
666
59%
666
33%
1141
April16th to endNight
53%
540
23%
1620
16%
540
56%
540
34%
942
May1st to 15thNight
55%
539
20%
1619
17%
539
58%
539
39%
898
May16th to endNight
56%
519
16%
1609
17%
519
58%
519
29%
983
June1st to 15thNight
68%
360
18%
1260
21%
360
72%
360
31%
706
June16th to endNight
76%
360
30%
1260
36%
360
81%
360
56%
516
July1st to 15thNight
85%
340
23%
1340
36%
340
89%
340
54%
522
July16th to endNight
82%
441
30%
1476
37%
414
85%
414
60%
582
August1st to 15thNight
76%
539
29%
1611
26%
536
77%
536
53%
778
August16th to endNight
76%
573
37%
1719
30%
573
77%
573
55%
814
September1st to 15thNight
77%
716
30%
1924
22%
716
80%
716
57%
981
September16th to endNight
71%
716
34%
1980
28%
716
74%
716
49%
1043
October1st to 15thNight
65%
720
26%
2070
21%
720
69%
720
43%
1122
October16th to endNight
66%
768
27%
2413
24%
768
71%
768
40%
1302
November1st to 15thNight
60%
760
20%
2470
20%
760
63%
760
33%
1427
November16th to endNight
57%
905
18%
2660
13%
905
64%
905
33%
1612
December1st to 15thNight
54%
975
11%
2795
8%
975
57%
975
24%
1897
December16th to endNight
51%
1007
12%
3087
9%
1007
55%
1007
21%
2123

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
45%2443446%8%49%
49259
Night
45%244245%6%8%50%
48961
TransparencyDay
29%8%15%21%17%8%
48936
Night
30%8%16%22%15%7%
48784
SeeingDay
7%10%28%30%18%4
6078
Night
6%220%42%23%4
15931

By Month

Percentage Cloud Cover SW (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
37%5%7%5%25%5%6%9%40%
1552
16th to endDay
412%36%7%35%47%9%36%
1745
February1st to 15thDay
25%38%5%46%5%7%10%39%
1683
16th to endDay
47%47%5%36%5%7%11%36%
1573
March1st to 15thDay
38%46%5%46%5%7%10%37%
1885
16th to endDay
5%6%36%6%46%5%8%9%36%
2112
April1st to 15thDay
5%8%45%5%35%47%9%39%
2150
16th to endDay
6%7%25%5%345%5%9%44%
2340
May1st to 15thDay
5%425%5%35%5%6%7%46%
2331
16th to endDay
9%7%46%6%25%6%7%9%34%
2499
June1st to 15thDay
7%5%26%5%35%5%7%9%40%
2700
16th to endDay
221232345%6%66%
2700
July1st to 15thDay
32232436%8%64%
2537
16th to endDay
3212323345%67%
2590
August1st to 15thDay
33123235%47%62%
2340
16th to endDay
3112213347%68%
2483
September1st to 15thDay
4212223346%65%
2034
16th to endDay
6%41332235%6%62%
1980
October1st to 15thDay
6%5%235%2345%7%51%
1890
16th to endDay
3214335%5%6%8%54%
1809
November1st to 15thDay
35%35%5%25%35%8%49%
1719
16th to endDay
36%25%4345%7%9%45%
1615
December1st to 15thDay
38%38%5%345%5%8%41%
1494
16th to endDay
5%10%36%6%345%5%7%40%
1498
January1st to 15thNight
36%36%6%46%7%6%9%40%
2716
16th to endNight
49%35%4245%5%9%43%
2830
February1st to 15thNight
36%36%5%35%6%7%9%41%
2433
16th to endNight
47%36%6%35%6%6%8%41%
1900
March1st to 15thNight
26%345%36%7%8%8%43%
2073
16th to endNight
5%5%25%435%5%7%10%45%
2112
April1st to 15thNight
6%7%24425%5%6%9%45%
1794
16th to endNight
45%35%5%3445%6%50%
1620
May1st to 15thNight
35%24425%5%5%6%54%
1619
16th to endNight
8%5%246%35%6%6%8%42%
1609
June1st to 15thNight
6%2145%36%5%5%9%48%
1260
16th to endNight
122212347%69%
1260
July1st to 15thNight
21212246%8%66%
1420
16th to endNight
112222335%73%
1577
August1st to 15thNight
3213323447%63%
1620
16th to endNight
2212323347%67%
1719
September1st to 15thNight
332223336%67%
1924
16th to endNight
6%31231234464%
1980
October1st to 15thNight
6%31432335%7%57%
2070
16th to endNight
5%3133245%5%8%56%
2413
November1st to 15thNight
45%244345%6%9%48%
2470
16th to endNight
35%145%35%5%7%9%48%
2660
December1st to 15thNight
47%36%6%45%5%5%8%42%
2795
16th to endNight
5%10%5%6%5%36%5%6%7%38%
3087

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
40%12%22%17%5%1
1552
16th to endDay
45%10%18%16%6%2
1745
February1st to 15thDay
36%15%23%18%6%
1683
16th to endDay
37%13%19%20%6%1
1573
March1st to 15thDay
36%13%20%21%7%
1885
16th to endDay
37%12%20%20%8%
2112
April1st to 15thDay
37%10%18%21%11%
2150
16th to endDay
33%7%14%26%17%
2340
May1st to 15thDay
30%7%12%29%18%1
2331
16th to endDay
38%9%14%23%12%2
2502
June1st to 15thDay
35%7%13%21%18%4
2700
16th to endDay
15%47%18%36%18%
2700
July1st to 15thDay
14%48%16%29%25%
2388
16th to endDay
15%36%12%21%39%
2428
August1st to 15thDay
17%48%16%28%24%
2325
16th to endDay
14%38%21%31%20%
2483
September1st to 15thDay
18%48%18%33%15%
2034
16th to endDay
21%411%28%24%8%
1980
October1st to 15thDay
30%7%16%27%15%3
1890
16th to endDay
23%9%19%29%17%
1809
November1st to 15thDay
34%9%20%22%12%1
1719
16th to endDay
32%10%27%21%6%2
1615
December1st to 15thDay
43%11%20%19%4
1494
16th to endDay
42%12%22%14%6%1
1498
January1st to 15thNight
40%13%19%19%5%1
2716
16th to endNight
39%10%18%21%7%2
2830
February1st to 15thNight
37%11%22%21%5%
2444
16th to endNight
38%10%20%22%5%1
1900
March1st to 15thNight
32%11%22%23%8%1
2073
16th to endNight
32%9%20%26%9%1
2112
April1st to 15thNight
33%8%16%25%14%1
1794
16th to endNight
32%5%13%28%18%1
1620
May1st to 15thNight
26%5%11%32%21%1
1620
16th to endNight
36%6%13%24%15%2
1610
June1st to 15thNight
29%8%12%20%21%6%
1260
16th to endNight
14%37%17%33%24%
1260
July1st to 15thNight
14%38%18%27%27%
1340
16th to endNight
12%25%11%22%44%
1476
August1st to 15thNight
18%48%16%22%30%
1611
16th to endNight
16%46%16%28%27%
1719
September1st to 15thNight
16%5%7%15%33%20%
1924
16th to endNight
22%39%26%27%9%
1980
October1st to 15thNight
25%415%29%19%4
2070
16th to endNight
24%7%15%29%21%1
2413
November1st to 15thNight
31%7%20%24%13%3
2470
16th to endNight
29%10%22%23%11%2
2660
December1st to 15thNight
38%12%23%18%7%
2795
16th to endNight
44%9%20%17%6%1
3087

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
11%27%35%28%14%
90
16th to endDay
7%215%42%22%8%
115
February1st to 15thDay
3329%36%20%7%
126
16th to endDay
7%8%25%39%15%3
232
March1st to 15thDay
6%10%30%33%19%
270
16th to endDay
9%16%34%29%11%
288
April1st to 15thDay
7%19%27%27%15%2
269
16th to endDay
11%16%39%21%10%1
270
May1st to 15thDay
9%12%34%27%12%3
288
16th to endDay
14%11%18%28%20%6%
360
June1st to 15thDay
7%13%25%28%20%4
495
16th to endDay
311%26%30%23%5%
495
July1st to 15thDay
49%32%28%20%4
322
16th to endDay
311%39%27%14%3
327
August1st to 15thDay
39%31%31%19%4
315
16th to endDay
10%31%29%19%7%
332
September1st to 15thDay
5%14%24%26%18%9%
315
16th to endDay
9%8%25%29%20%5%
315
October1st to 15thDay
8%8%31%28%16%6%
225
16th to endDay
8%6%23%31%25%4
144
November1st to 15thDay
10%6%17%30%26%8%
135
16th to endDay
10%5%28%43%10%1
135
December1st to 15thDay
10%320%44%14%6%
119
16th to endDay
11%212%53%16%4
96
January1st to 15thNight
7%118%42%24%5%
780
16th to endNight
9%217%41%21%7%
832
February1st to 15thNight
8%123%43%19%3
752
16th to endNight
5%328%41%17%3
632
March1st to 15thNight
4225%43%20%3
720
16th to endNight
6%5%26%42%16%1
768
April1st to 15thNight
7%5%25%40%18%2
666
16th to endNight
6%328%43%15%2
540
May1st to 15thNight
6%5%27%37%22%1
540
16th to endNight
10%319%36%26%3
521
June1st to 15thNight
5%316%48%25%1
360
16th to endNight
217%47%27%3
360
July1st to 15thNight
28%50%36%1
340
16th to endNight
111%49%34%2
441
August1st to 15thNight
3112%47%32%2
539
16th to endNight
2114%45%31%5%
573
September1st to 15thNight
5%12%37%34%9%
716
16th to endNight
8%111%34%31%11%
716
October1st to 15thNight
7%217%42%25%5%
720
16th to endNight
5%119%41%25%5%
768
November1st to 15thNight
5%124%39%25%3
760
16th to endNight
4225%43%17%4
905
December1st to 15thNight
7%222%47%17%2
975
16th to endNight
9%323%47%13%2
1007
Page generated at 2018-02-13 18:46:03. Version ac04

Copyright 2018 A. Danko


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