Alma
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alma clear sky chart from 2005-11-05 to 2017-09-10.

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
45%
15931
24%
46672
14%
15885
54%
15885
36%
26761

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
40%
900
25%
2506
14%
895
49%
895
36%
1460
January16th to endNight
36%
960
29%
2518
13%
960
46%
960
39%
1488
February1st to 15thNight
33%
787
19%
2199
8%
783
42%
783
28%
1421
February16th to endNight
37%
632
27%
1894
10%
632
51%
632
33%
1087
March1st to 15thNight
37%
651
23%
2091
13%
651
46%
651
31%
1188
March16th to endNight
30%
576
20%
2112
13%
576
42%
576
26%
1217
April1st to 15thNight
30%
539
18%
1828
11%
539
42%
539
25%
1105
April16th to endNight
35%
540
20%
1632
14%
540
45%
540
27%
1018
May1st to 15thNight
40%
540
18%
1620
13%
540
48%
540
29%
1000
May16th to endNight
39%
562
17%
1685
9%
561
47%
561
29%
1041
June1st to 15thNight
44%
540
16%
1509
6%
540
49%
540
36%
897
June16th to endNight
59%
540
23%
1440
12%
540
63%
540
51%
778
July1st to 15thNight
64%
510
19%
1360
11%
510
68%
510
43%
785
July16th to endNight
71%
564
23%
1552
20%
531
73%
531
44%
830
August1st to 15thNight
69%
539
21%
1610
23%
536
72%
536
39%
898
August16th to endNight
64%
573
27%
1817
27%
573
71%
573
42%
955
September1st to 15thNight
54%
525
24%
1865
21%
525
64%
525
36%
976
September16th to endNight
56%
492
31%
1815
28%
492
65%
492
40%
860
October1st to 15thNight
45%
531
31%
1851
23%
531
53%
531
32%
987
October16th to endNight
48%
795
30%
2203
15%
795
57%
795
45%
1180
November1st to 15thNight
50%
875
34%
2275
15%
875
60%
875
50%
1212
November16th to endNight
47%
900
32%
2340
16%
900
56%
900
45%
1307
December1st to 15thNight
39%
900
23%
2340
11%
900
47%
900
35%
1457
December16th to endNight
40%
960
26%
2610
12%
960
51%
960
33%
1614

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
8%42442445%7%52%
47952
Night
8%42432345%7%53%
46856
Cloud CoverDay
8%5%2442445%7%52%
47950
Night
7%42432345%7%53%
46856
TransparencyDay
31%5%14%27%17%3
47639
Night
29%5%14%26%19%4
46672
SeeingDay
11%6%30%34%15%2
5917
Night
10%7%32%37%11%
15936

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
7%7%24425%35%6%51%
1432
16th to endDay
6%6%25%31235%7%54%
1702
February1st to 15thDay
7%8%45%5%24446%43%
1673
16th to endDay
6%6%14435%448%50%
1580
March1st to 15thDay
6%5%1332345%8%55%
1867
16th to endDay
12%7%3442345%7%47%
2112
April1st to 15thDay
12%5%24423347%48%
2117
16th to endDay
18%6%24434446%40%
2326
May1st to 15thDay
12%5%2342445%8%45%
2331
16th to endDay
12%5%2442335%8%47%
2430
June1st to 15thDay
8%32332345%9%54%
2448
16th to endDay
331332445%8%60%
2520
July1st to 15thDay
5%3134245%7%8%53%
2520
16th to endDay
421242446%9%56%
2508
August1st to 15thDay
7%324435%47%8%47%
2340
16th to endDay
6%32332435%7%58%
2383
September1st to 15thDay
10%6%14424345%52%
1982
16th to endDay
7%33223436%61%
1815
October1st to 15thDay
15%322212246%56%
1768
16th to endDay
9%41322324460%
1667
November1st to 15thDay
7%213423346%59%
1583
16th to endDay
8%6%23224435%57%
1620
December1st to 15thDay
8%7%25%424447%48%
1620
16th to endDay
8%7%37%423447%47%
1608
January1st to 15thNight
47%24413447%53%
2506
16th to endNight
6%5%24323346%55%
2518
February1st to 15thNight
8%7%4442445%6%46%
2189
16th to endNight
5%5%24435%345%54%
1894
March1st to 15thNight
8%6%24324345%53%
2091
16th to endNight
11%6%24424446%48%
2112
April1st to 15thNight
11%6%25%42345%6%45%
1828
16th to endNight
15%42432445%8%44%
1632
May1st to 15thNight
12%41442345%7%47%
1619
16th to endNight
14%31332436%9%46%
1683
June1st to 15thNight
7%3134245%7%8%50%
1509
16th to endNight
42241446%10%58%
1440
July1st to 15thNight
43244245%6%10%50%
1440
16th to endNight
32133245%6%10%55%
1659
August1st to 15thNight
5%214425%5%5%10%52%
1620
16th to endNight
5%213324448%60%
1817
September1st to 15thNight
7%41332345%7%56%
1865
16th to endNight
6%3322335%6%63%
1815
October1st to 15thNight
12%41331225%6%55%
1851
16th to endNight
9%212312345%62%
2203
November1st to 15thNight
5%212223337%65%
2275
16th to endNight
8%412313245%61%
2340
December1st to 15thNight
8%6%2442445%6%51%
2340
16th to endNight
8%6%25%42345%7%49%
2610

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
6%7%24415%45%6%51%
1432
16th to endDay
6%6%2431325%7%54%
1702
February1st to 15thDay
7%8%445%35%447%43%
1673
16th to endDay
6%5%245%24448%50%
1580
March1st to 15thDay
6%6%1332235%8%55%
1867
16th to endDay
12%7%2441335%7%46%
2110
April1st to 15thDay
11%5%24433447%47%
2117
16th to endDay
17%6%25%424447%39%
2326
May1st to 15thDay
11%5%2442445%9%45%
2331
16th to endDay
12%5%2442345%7%47%
2430
June1st to 15thDay
7%31342335%9%53%
2448
16th to endDay
221342445%8%59%
2520
July1st to 15thDay
5%3134245%6%8%52%
2520
16th to endDay
421332446%9%56%
2508
August1st to 15thDay
7%324435%47%9%47%
2340
16th to endDay
6%31331435%6%58%
2383
September1st to 15thDay
10%5%24423345%52%
1982
16th to endDay
6%33223336%61%
1815
October1st to 15thDay
14%412222246%55%
1768
16th to endDay
9%423223235%60%
1667
November1st to 15thDay
7%214423347%58%
1583
16th to endDay
7%6%23224435%57%
1620
December1st to 15thDay
8%7%35%423437%48%
1620
16th to endDay
8%7%37%423347%47%
1608
January1st to 15thNight
47%25%42335%7%53%
2506
16th to endNight
6%5%24423346%55%
2518
February1st to 15thNight
8%7%44424446%46%
2189
16th to endNight
5%5%2443435%5%54%
1894
March1st to 15thNight
8%6%2433335%5%53%
2091
16th to endNight
11%6%2432345%6%49%
2112
April1st to 15thNight
11%5%25%43445%6%45%
1828
16th to endNight
14%42432445%8%44%
1632
May1st to 15thNight
11%42442445%7%47%
1619
16th to endNight
14%41432336%9%45%
1683
June1st to 15thNight
7%3144345%7%8%50%
1509
16th to endNight
42231446%11%58%
1440
July1st to 15thNight
33243345%7%10%50%
1440
16th to endNight
32143245%7%10%55%
1659
August1st to 15thNight
4213425%5%6%10%51%
1620
16th to endNight
4213324448%60%
1817
September1st to 15thNight
7%41341345%7%56%
1865
16th to endNight
6%313213345%63%
1815
October1st to 15thNight
11%423312346%55%
1851
16th to endNight
8%212322345%62%
2203
November1st to 15thNight
5%213213336%65%
2275
16th to endNight
7%412213246%61%
2340
December1st to 15thNight
8%6%2442345%6%51%
2340
16th to endNight
8%7%25%41435%7%49%
2610

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
33%417%27%14%2
1433
16th to endDay
29%418%29%14%3
1702
February1st to 15thDay
40%6%17%23%8%2
1674
16th to endDay
31%418%24%17%3
1580
March1st to 15thDay
27%5%17%24%21%3
1867
16th to endDay
37%6%15%24%13%2
2112
April1st to 15thDay
35%5%14%27%14%1
2117
16th to endDay
43%6%14%23%11%
2326
May1st to 15thDay
35%7%14%26%14%1
2331
16th to endDay
35%8%17%24%11%2
2434
June1st to 15thDay
27%5%17%30%14%3
2448
16th to endDay
21%6%13%30%22%5%
2520
July1st to 15thDay
27%6%13%27%19%4
2371
16th to endDay
21%7%16%33%18%2
2352
August1st to 15thDay
31%8%17%26%13%2
2326
16th to endDay
25%6%12%30%20%4
2383
September1st to 15thDay
34%411%22%20%6%
1982
16th to endDay
24%411%34%23%1
1815
October1st to 15thDay
31%39%27%24%3
1768
16th to endDay
27%39%32%22%4
1667
November1st to 15thDay
25%311%27%27%3
1583
16th to endDay
29%313%29%19%4
1620
December1st to 15thDay
35%5%18%26%12%1
1620
16th to endDay
38%414%25%15%1
1608
January1st to 15thNight
29%414%30%18%2
2506
16th to endNight
30%315%27%19%2
2518
February1st to 15thNight
38%6%13%26%11%3
2199
16th to endNight
30%5%14%26%17%5%
1894
March1st to 15thNight
32%5%10%23%21%6%
2091
16th to endNight
35%5%15%23%16%3
2112
April1st to 15thNight
36%6%13%22%18%2
1828
16th to endNight
37%6%16%22%15%1
1632
May1st to 15thNight
35%7%15%21%17%1
1620
16th to endNight
34%8%17%22%14%2
1685
June1st to 15thNight
28%8%19%25%14%3
1509
16th to endNight
19%6%15%28%23%5%
1440
July1st to 15thNight
24%8%16%26%17%6%
1360
16th to endNight
21%7%17%30%18%4
1552
August1st to 15thNight
25%7%19%29%13%3
1610
16th to endNight
23%6%13%28%20%7%
1817
September1st to 15thNight
26%6%12%24%19%10%
1865
16th to endNight
22%5%10%27%29%4
1815
October1st to 15thNight
29%48%24%25%6%
1851
16th to endNight
23%312%28%25%6%
2203
November1st to 15thNight
21%38%28%29%8%
2275
16th to endNight
25%312%27%25%5%
2340
December1st to 15thNight
33%5%16%29%14%1
2340
16th to endNight
34%5%16%23%17%2
2610

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
15%11%37%33%2
90
16th to endDay
16%8%45%20%7%1
96
February1st to 15thDay
13%6%47%27%31
90
16th to endDay
420%38%20%14%
81
March1st to 15thDay
11%8%45%24%8%1
90
16th to endDay
21%12%31%21%12%
96
April1st to 15thDay
13%17%38%23%7%
236
16th to endDay
24%11%31%24%7%
436
May1st to 15thDay
11%9%34%29%12%1
468
16th to endDay
18%7%34%27%11%1
517
June1st to 15thDay
8%431%35%16%3
495
16th to endDay
4432%38%18%1
495
July1st to 15thDay
7%221%43%21%3
475
16th to endDay
4118%45%27%2
515
August1st to 15thDay
6%118%46%25%2
493
16th to endDay
6%425%40%19%3
423
September1st to 15thDay
7%5%35%32%17%2
179
16th to endDay
13%232%27%20%4
90
October1st to 15thDay
14%328%36%14%2
90
16th to endDay
9%228%41%14%4
96
November1st to 15thDay
8%5%21%40%16%7%
90
16th to endDay
26%14%30%20%7%1
90
December1st to 15thDay
13%10%48%21%6%
90
16th to endDay
13%13%44%23%4
96
January1st to 15thNight
8%10%35%37%8%
900
16th to endNight
10%10%38%35%6%
960
February1st to 15thNight
11%8%41%32%5%
791
16th to endNight
9%10%38%34%7%
632
March1st to 15thNight
12%10%36%33%7%
651
16th to endNight
15%10%39%26%6%
576
April1st to 15thNight
13%10%42%28%4
539
16th to endNight
17%10%33%29%8%
540
May1st to 15thNight
15%6%33%34%9%
540
16th to endNight
15%5%36%31%9%
563
June1st to 15thNight
8%7%35%36%10%
540
16th to endNight
4330%49%12%
540
July1st to 15thNight
5%122%47%21%
510
16th to endNight
417%53%22%
564
August1st to 15thNight
6%115%54%21%
539
16th to endNight
6%222%42%24%1
573
September1st to 15thNight
8%231%42%13%1
525
16th to endNight
8%5%28%37%19%1
492
October1st to 15thNight
14%8%28%35%12%
531
16th to endNight
10%7%29%38%12%
795
November1st to 15thNight
7%8%30%42%10%
875
16th to endNight
10%8%32%37%10%
900
December1st to 15thNight
11%9%36%35%7%
900
16th to endNight
12%9%32%38%7%
960
Page generated at 2017-09-11 18:35:21. Version ac04

Copyright 2017 A. Danko


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