Arco
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arco clear sky chart from 2005-11-06 to 2024-03-01.

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
58%
23731
20%
80526
17%
23658
64%
23658
30%
46893

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 10thNight
53%
747
16%
4332
9%
736
58%
736
11%
2594
January11th to 20thNight
55%
751
15%
4377
14%
740
62%
740
13%
2863
January21st to endNight
53%
826
9%
4626
12%
814
59%
814
11%
3248
February1st to 10thNight
44%
760
13%
2470
9%
760
51%
760
23%
1624
February11th to 20thNight
47%
743
16%
2319
10%
740
56%
740
25%
1497
February21st to endNight
47%
628
15%
1884
10%
628
54%
628
26%
1215
March1st to 10thNight
53%
722
16%
2125
12%
722
58%
722
28%
1358
March11th to 20thNight
56%
720
20%
1980
14%
720
62%
720
36%
1173
March21st to endNight
51%
792
15%
2178
10%
792
55%
792
29%
1424
April1st to 10thNight
54%
720
20%
1872
10%
720
60%
720
35%
1191
April11th to 20thNight
47%
545
23%
1613
12%
545
54%
545
33%
960
April21st to endNight
53%
540
23%
1620
15%
540
59%
540
35%
929
May1st to 10thNight
54%
540
21%
1620
16%
540
57%
540
38%
910
May11th to 20thNight
55%
531
19%
1594
16%
531
59%
531
34%
931
May21st to endNight
55%
520
15%
1635
15%
520
58%
520
28%
1010
June1st to 10thNight
67%
360
19%
1260
22%
360
73%
360
31%
698
June11th to 20thNight
58%
360
23%
1260
21%
360
68%
360
36%
643
June21st to endNight
77%
360
30%
1260
37%
360
82%
360
54%
527
July1st to 10thNight
77%
350
25%
1369
35%
350
83%
350
55%
523
July11th to 20thNight
84%
348
31%
1392
44%
348
89%
348
64%
474
July21st to endNight
76%
492
30%
1581
32%
465
80%
465
56%
681
August1st to 10thNight
70%
537
27%
1602
24%
534
72%
534
47%
808
August11th to 20thNight
78%
534
37%
1602
31%
534
80%
534
61%
724
August21st to endNight
71%
594
36%
1782
28%
594
74%
594
53%
852
September1st to 10thNight
75%
713
33%
1894
23%
713
79%
713
60%
950
September11th to 20thNight
73%
720
33%
1980
27%
720
76%
720
55%
1000
September21st to endNight
67%
720
33%
1980
26%
720
72%
720
50%
1043
October1st to 10thNight
64%
720
26%
2024
19%
720
69%
720
44%
1110
October11th to 20thNight
64%
720
30%
2160
24%
720
71%
720
47%
1101
October21st to endNight
60%
792
25%
2538
20%
792
68%
792
39%
1358
November1st to 10thNight
59%
740
24%
2405
23%
740
63%
740
33%
1381
November11th to 20thNight
54%
760
20%
2470
14%
760
63%
760
32%
1425
November21st to endNight
58%
943
19%
2653
13%
943
63%
943
36%
1576
December1st to 10thNight
50%
950
14%
2660
9%
950
55%
950
26%
1792
December11th to 20thNight
49%
948
13%
3397
9%
948
52%
948
18%
2347
December21st to endNight
47%
985
8%
5012
7%
979
52%
979
14%
2953

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
46%35%5%35%5%6%8%50%
78300
Night
47%36%5%35%5%6%8%49%
81114
TransparencyDay
29%8%15%21%18%9%
78008
Night
31%9%16%21%16%7%
80927
SeeingDay
8%10%26%33%18%4
14025
Night
6%322%44%21%4
23781

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 10thDay
29%7%12%8%47%6%7%8%31%
2539
11th to 20thDay
37%39%8%46%5%7%8%39%
2540
21st to endDay
6%20%5%9%6%3435%8%32%
2990
February1st to 10thDay
37%47%6%47%5%8%9%40%
1710
11th to 20thDay
38%49%7%47%6%7%9%35%
1748
21st to endDay
26%48%6%47%6%7%12%38%
1570
March1st to 10thDay
38%37%6%36%6%8%11%39%
1839
11th to 20thDay
48%34446%5%7%9%44%
1980
21st to endDay
5%8%47%7%5%6%6%9%10%35%
2178
April1st to 10thDay
5%7%45%6%45%5%8%9%41%
2083
11th to 20thDay
5%6%46%5%35%5%6%8%47%
2294
21st to endDay
5%9%26%5%35%5%6%9%45%
2340
May1st to 10thDay
6%6%36%6%45%6%6%8%46%
2340
11th to 20thDay
6%6%36%7%36%6%8%9%41%
2301
21st to endDay
9%7%37%6%36%6%7%10%36%
2633
June1st to 10thDay
6%5%26%5%35%5%8%11%45%
2700
11th to 20thDay
6%5%245%345%6%8%51%
2700
21st to endDay
221343445%6%66%
2700
July1st to 10thDay
211233446%8%65%
2546
11th to 20thDay
2212213345%76%
2520
21st to endDay
431342445%5%63%
2641
August1st to 10thDay
5%4133335%5%8%59%
2328
11th to 20thDay
221222345%7%71%
2299
21st to endDay
421332335%7%68%
2574
September1st to 10thDay
3312323446%70%
2062
11th to 20thDay
5%41332345%7%62%
1980
21st to endDay
6%5%23323346%64%
1980
October1st to 10thDay
8%6%2443445%6%52%
1936
11th to 20thDay
3424435%45%7%58%
1800
21st to endDay
4423435%5%6%9%55%
1814
November1st to 10thDay
5%6%35%5%36%36%9%49%
1674
11th to 20thDay
25%36%5%45%5%7%10%49%
1696
21st to endDay
37%36%5%445%7%7%50%
1520
December1st to 10thDay
39%37%6%45%7%5%8%44%
1518
11th to 20thDay
411%48%6%46%6%6%9%36%
1685
21st to endDay
48%49%6%445%5%7%45%
2542
January1st to 10thNight
38%5%9%7%46%6%6%8%39%
4406
11th to 20thNight
39%49%7%46%6%6%8%38%
4420
21st to endNight
5%19%6%8%5%245%5%7%33%
4670
February1st to 10thNight
48%46%6%45%7%6%9%41%
2470
11th to 20thNight
48%36%7%45%6%6%8%43%
2318
21st to endNight
27%38%6%47%6%7%8%41%
1884
March1st to 10thNight
39%46%5%36%6%8%8%43%
2125
11th to 20thNight
45%25%4346%7%11%49%
1980
21st to endNight
5%7%36%6%45%6%7%9%43%
2178
April1st to 10thNight
5%7%345%35%5%7%8%46%
1872
11th to 20thNight
46%26%5%45%46%8%49%
1613
21st to endNight
5%6%35%5%35%5%6%7%50%
1620
May1st to 10thNight
46%35%5%35%5%6%6%54%
1620
11th to 20thNight
6%426%6%35%6%7%10%45%
1594
21st to endNight
10%6%25%6%445%6%9%41%
1635
June1st to 10thNight
6%3145%36%7%7%10%48%
1260
11th to 20thNight
6%3245%35%5%5%8%54%
1260
21st to endNight
221332345%6%68%
1260
July1st to 10thNight
221332336%8%68%
1409
11th to 20thNight
1112113446%76%
1440
21st to endNight
2313423447%68%
1674
August1st to 10thNight
33144345%5%8%58%
1611
11th to 20thNight
221221345%7%70%
1602
21st to endNight
321332345%7%66%
1782
September1st to 10thNight
3312223336%71%
1894
11th to 20thNight
5%31332345%6%65%
1980
21st to endNight
7%323323345%66%
1980
October1st to 10thNight
7%41442345%7%57%
2024
11th to 20thNight
442432345%7%61%
2160
21st to endNight
4424435%5%6%9%55%
2538
November1st to 10thNight
6%5%25%435%6%6%9%48%
2405
11th to 20thNight
36%245%36%5%7%9%50%
2470
21st to endNight
36%25%5%35%5%6%8%52%
2653
December1st to 10thNight
47%37%6%45%6%6%8%43%
2660
11th to 20thNight
5%10%5%7%6%46%5%7%8%36%
3506
21st to endNight
39%48%6%45%5%6%7%43%
5141

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 10thDay
45%15%16%18%6%1
2539
11th to 20thDay
38%14%19%19%8%2
2540
21st to endDay
52%10%16%16%5%1
2990
February1st to 10thDay
35%16%21%21%6%1
1710
11th to 20thDay
40%12%22%18%8%1
1757
21st to endDay
33%15%20%21%9%2
1570
March1st to 10thDay
34%12%21%22%10%1
1839
11th to 20thDay
33%11%19%25%11%1
1980
21st to endDay
38%13%21%19%8%1
2178
April1st to 10thDay
33%12%20%21%13%1
2083
11th to 20thDay
33%8%15%26%16%2
2297
21st to endDay
32%8%15%28%16%1
2340
May1st to 10thDay
31%8%14%26%19%2
2340
11th to 20thDay
34%8%13%28%14%2
2304
21st to endDay
36%11%16%25%12%2
2633
June1st to 10thDay
30%8%16%26%18%2
2700
11th to 20thDay
26%6%12%20%23%13%
2700
21st to endDay
14%5%8%20%35%18%
2700
July1st to 10thDay
13%5%8%17%32%25%
2477
11th to 20thDay
10%25%14%27%41%
2445
21st to endDay
19%47%13%24%34%
2494
August1st to 10thDay
20%5%10%17%26%22%
2313
11th to 20thDay
12%36%21%36%22%
2299
21st to endDay
16%38%20%32%21%
2574
September1st to 10thDay
16%37%17%30%27%
2062
11th to 20thDay
20%6%10%23%28%13%
1980
21st to endDay
21%49%28%28%10%
1980
October1st to 10thDay
31%7%13%25%19%5%
1936
11th to 20thDay
23%7%17%33%17%4
1800
21st to endDay
22%9%22%27%19%2
1814
November1st to 10thDay
34%7%19%22%16%1
1674
11th to 20thDay
29%13%23%25%8%2
1696
21st to endDay
32%8%25%24%11%2
1520
December1st to 10thDay
41%12%18%20%8%2
1518
11th to 20thDay
43%13%21%19%5%
1684
21st to endDay
37%10%20%17%14%2
2542
January1st to 10thNight
41%11%17%20%10%1
4406
11th to 20thNight
43%13%17%16%8%3
4420
21st to endNight
48%13%16%15%6%1
4670
February1st to 10thNight
39%12%21%21%7%2
2470
11th to 20thNight
36%11%19%23%9%2
2319
21st to endNight
37%10%20%22%8%3
1884
March1st to 10thNight
35%11%20%25%8%2
2125
11th to 20thNight
27%10%23%23%16%2
1980
21st to endNight
36%10%21%24%8%1
2178
April1st to 10thNight
31%10%17%22%17%3
1872
11th to 20thNight
33%6%15%28%16%2
1613
21st to endNight
29%7%15%28%20%1
1620
May1st to 10thNight
27%7%11%31%21%3
1620
11th to 20thNight
29%8%15%27%19%2
1595
21st to endNight
37%7%16%25%13%2
1635
June1st to 10thNight
26%11%16%23%20%3
1260
11th to 20thNight
25%7%10%19%25%14%
1260
21st to endNight
15%48%21%29%24%
1260
July1st to 10thNight
14%38%17%31%27%
1369
11th to 20thNight
10%35%13%25%45%
1392
21st to endNight
15%47%13%24%37%
1581
August1st to 10thNight
21%5%10%16%20%27%
1602
11th to 20thNight
14%45%18%32%28%
1602
21st to endNight
17%5%8%15%27%28%
1782
September1st to 10thNight
15%5%6%12%32%30%
1894
11th to 20thNight
18%410%24%26%18%
1980
21st to endNight
21%5%9%22%32%12%
1980
October1st to 10thNight
25%5%13%26%23%7%
2024
11th to 20thNight
21%5%14%34%22%4
2160
21st to endNight
23%9%18%27%21%2
2538
November1st to 10thNight
30%8%18%24%17%3
2405
11th to 20thNight
29%10%21%26%11%3
2470
21st to endNight
30%8%21%26%14%2
2653
December1st to 10thNight
37%13%21%18%10%2
2660
11th to 20thNight
43%11%19%21%5%1
3507
21st to endNight
38%11%19%17%13%2
5141

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 10thDay
9%6%14%40%24%7%
180
11th to 20thDay
8%212%44%22%11%
180
21st to endDay
6%315%45%22%9%
254
February1st to 10thDay
7%6%31%40%14%2
270
11th to 20thDay
6%6%29%39%16%5%
353
21st to endDay
5%10%29%35%19%3
382
March1st to 10thDay
7%6%31%40%15%1
421
11th to 20thDay
8%9%24%32%24%3
420
21st to endDay
10%12%28%34%14%2
462
April1st to 10thDay
9%13%23%35%18%1
420
11th to 20thDay
8%19%33%26%11%2
412
21st to endDay
10%15%32%26%14%4
420
May1st to 10thDay
10%12%29%33%13%2
423
11th to 20thDay
13%12%26%27%17%4
448
21st to endDay
14%12%21%23%21%8%
529
June1st to 10thDay
9%13%20%30%23%6%
630
11th to 20thDay
12%16%28%26%14%4
630
21st to endDay
39%26%37%21%4
630
July1st to 10thDay
412%27%35%19%3
472
11th to 20thDay
314%37%31%13%2
444
21st to endDay
410%31%32%19%4
487
August1st to 10thDay
7%10%30%30%20%3
447
11th to 20thDay
49%21%36%23%7%
437
21st to endDay
411%29%32%20%4
495
September1st to 10thDay
5%11%29%31%18%6%
450
11th to 20thDay
8%12%27%28%19%6%
450
21st to endDay
9%11%26%31%18%5%
450
October1st to 10thDay
11%8%26%32%20%4
406
11th to 20thDay
6%11%23%27%24%9%
270
21st to endDay
9%12%26%35%16%2
297
November1st to 10thDay
11%12%22%36%14%5%
270
11th to 20thDay
27%28%38%18%7%
270
21st to endDay
8%424%41%20%4
270
December1st to 10thDay
6%421%43%20%7%
268
11th to 20thDay
11%314%47%22%3
180
21st to endDay
11%413%44%22%7%
198
January1st to 10thNight
7%220%45%21%4
760
11th to 20thNight
7%321%43%21%6%
760
21st to endNight
8%121%47%17%6%
836
February1st to 10thNight
8%231%42%16%2
760
11th to 20thNight
8%329%41%17%3
744
21st to endNight
4429%42%18%3
628
March1st to 10thNight
6%225%49%16%2
722
11th to 20thNight
6%5%25%44%17%3
720
21st to endNight
9%5%24%45%15%2
792
April1st to 10thNight
8%5%26%44%15%2
720
11th to 20thNight
6%434%40%14%2
545
21st to endNight
7%427%43%17%2
540
May1st to 10thNight
5%7%27%40%18%2
540
11th to 20thNight
9%424%34%26%3
531
21st to endNight
12%5%19%34%26%3
522
June1st to 10thNight
5%418%43%28%3
360
11th to 20thNight
7%424%44%19%2
360
21st to endNight
3114%55%24%3
360
July1st to 10thNight
4114%50%30%2
350
11th to 20thNight
1111%64%23%
348
21st to endNight
3113%47%33%3
492
August1st to 10thNight
4316%49%26%2
537
11th to 20thNight
2114%50%30%3
534
21st to endNight
3217%46%27%4
594
September1st to 10thNight
5%114%46%29%6%
713
11th to 20thNight
6%115%40%29%8%
720
21st to endNight
8%217%36%29%8%
720
October1st to 10thNight
9%316%43%23%4
720
11th to 20thNight
6%420%41%24%5%
720
21st to endNight
6%324%43%19%5%
792
November1st to 10thNight
8%320%43%23%3
740
11th to 20thNight
5%230%44%16%3
760
21st to endNight
6%324%44%19%4
943
December1st to 10thNight
7%224%47%16%2
950
11th to 20thNight
7%324%48%15%3
950
21st to endNight
7%5%25%47%13%3
998
Page generated at 2024-02-27 04:30:14. Version ac07

Copyright © 2024 Attilla Danko.


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