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 2018-01-12.

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
43%
16326
21%
48348
14%
16279
50%
16279
27%
30748

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
25%
956
18%
2662
7%
951
34%
951
22%
1836
January16th to endNight
24%
960
18%
2547
6%
960
33%
960
22%
1809
February1st to 15thNight
22%
770
15%
2178
5%
767
30%
767
20%
1526
February16th to endNight
24%
631
19%
1893
7%
631
34%
631
21%
1273
March1st to 15thNight
23%
720
16%
2160
7%
720
30%
720
19%
1490
March16th to endNight
34%
584
15%
1997
11%
584
41%
584
19%
1331
April1st to 15thNight
34%
539
21%
1797
13%
539
47%
539
26%
1095
April16th to endNight
40%
540
21%
1800
17%
540
48%
540
26%
1133
May1st to 15thNight
42%
540
17%
1637
11%
539
49%
539
23%
1102
May16th to endNight
55%
563
20%
1530
14%
561
59%
561
30%
1010
June1st to 15thNight
66%
540
21%
1440
16%
540
69%
540
40%
853
June16th to endNight
65%
540
22%
1440
17%
540
69%
540
39%
864
July1st to 15thNight
69%
510
20%
1360
16%
510
71%
510
40%
815
July16th to endNight
76%
564
25%
1417
21%
531
78%
531
43%
818
August1st to 15thNight
77%
539
23%
1736
26%
536
78%
536
39%
937
August16th to endNight
74%
573
26%
1910
29%
573
77%
573
37%
1022
September1st to 15thNight
69%
540
28%
1800
30%
540
72%
540
35%
1009
September16th to endNight
61%
706
32%
1969
25%
706
65%
706
37%
1173
October1st to 15thNight
54%
720
29%
2082
21%
720
60%
720
36%
1241
October16th to endNight
38%
768
27%
2377
19%
768
48%
768
30%
1415
November1st to 15thNight
39%
760
28%
2471
19%
760
51%
760
30%
1406
November16th to endNight
34%
780
24%
2535
17%
780
45%
780
26%
1556
December1st to 15thNight
30%
943
15%
2698
8%
943
36%
943
21%
1901
December16th to endNight
22%
1040
16%
2912
5%
1040
32%
1040
18%
2133

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
12%6%25%5%3445%7%41%
49000
Night
13%6%35%424447%44%
48523
TransparencyDay
40%6%12%23%14%2
48679
Night
39%5%10%23%17%3
48350
SeeingDay
13%5%22%26%21%10%
6216
Night
16%7%27%30%16%2
16326

By Month

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
15%9%38%5%345%35%35%
1520
16th to endDay
12%8%36%6%23447%38%
1674
February1st to 15thDay
15%8%5%6%424447%35%
1684
16th to endDay
11%10%46%5%35%5%6%6%34%
1580
March1st to 15thDay
17%8%25%434345%38%
1803
16th to endDay
18%9%36%5%345%46%32%
2233
April1st to 15thDay
15%6%24323347%43%
2151
16th to endDay
17%6%25%5%24447%38%
2160
May1st to 15thDay
18%5%25%5%3445%7%35%
2313
16th to endDay
10%6%25%5%36%5%6%8%39%
2581
June1st to 15thDay
7%3245%35%6%6%8%47%
2520
16th to endDay
7%325%5%35%6%6%9%44%
2520
July1st to 15thDay
8%4245%35%5%6%10%42%
2520
16th to endDay
4315%6%35%6%6%11%46%
2655
August1st to 15thDay
6%425%5%36%5%7%9%43%
2211
16th to endDay
6%425%5%35%5%7%8%44%
2292
September1st to 15thDay
10%6%25%5%335%5%6%45%
2158
16th to endDay
8%425%5%3445%7%48%
1980
October1st to 15thDay
12%6%2442435%6%47%
1875
16th to endDay
13%5%2342335%5%50%
1845
November1st to 15thDay
12%5%25%324445%50%
1717
16th to endDay
17%7%35%5%23235%44%
1755
December1st to 15thDay
17%9%36%42445%5%36%
1589
16th to endDay
18%11%45%423446%33%
1664
January1st to 15thNight
15%7%47%433346%37%
2662
16th to endNight
13%9%47%5%24445%36%
2547
February1st to 15thNight
15%8%46%5%24446%35%
2169
16th to endNight
14%8%37%5%24335%40%
1893
March1st to 15thNight
17%8%46%5%24435%37%
2160
16th to endNight
17%6%35%43445%7%36%
1997
April1st to 15thNight
13%5%24434346%46%
1797
16th to endNight
16%7%2442435%7%41%
1800
May1st to 15thNight
16%5%35%5%34346%40%
1637
16th to endNight
7%5%26%5%35%5%6%9%42%
1529
June1st to 15thNight
7%413425%35%7%53%
1440
16th to endNight
5%423425%5%6%11%48%
1440
July1st to 15thNight
7%41342346%10%51%
1440
16th to endNight
42135%345%6%9%52%
1513
August1st to 15thNight
5%31343437%9%53%
1745
16th to endNight
4325%42345%9%53%
1910
September1st to 15thNight
9%42442435%6%52%
1800
16th to endNight
8%5%15%324447%52%
1969
October1st to 15thNight
11%423424346%52%
2082
16th to endNight
15%5%14322345%51%
2377
November1st to 15thNight
11%5%24423346%50%
2471
16th to endNight
17%6%34323246%46%
2535
December1st to 15thNight
20%8%45%324446%34%
2698
16th to endNight
20%10%46%423335%32%
2912

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
50%5%10%19%12%1
1521
16th to endDay
45%5%12%27%8%
1674
February1st to 15thDay
47%5%12%24%9%1
1686
16th to endDay
47%5%13%22%10%
1580
March1st to 15thDay
47%5%11%22%10%2
1803
16th to endDay
51%6%13%20%7%
2235
April1st to 15thDay
39%5%11%26%16%1
2151
16th to endDay
45%5%10%24%11%2
2160
May1st to 15thDay
46%7%12%23%9%
2313
16th to endDay
41%8%14%18%14%2
2585
June1st to 15thDay
31%7%15%24%18%2
2520
16th to endDay
33%8%15%20%17%3
2520
July1st to 15thDay
35%8%11%25%14%4
2371
16th to endDay
28%9%14%28%17%2
2488
August1st to 15thDay
34%7%12%26%16%1
2197
16th to endDay
32%8%15%20%17%5%
2292
September1st to 15thDay
37%6%10%21%20%4
2158
16th to endDay
34%5%9%25%21%3
1980
October1st to 15thDay
36%410%24%19%3
1875
16th to endDay
34%48%28%20%1
1845
November1st to 15thDay
36%411%23%18%6%
1717
16th to endDay
44%29%27%13%2
1755
December1st to 15thDay
47%6%13%20%11%
1589
16th to endDay
52%411%20%9%1
1664
January1st to 15thNight
47%49%23%14%1
2662
16th to endNight
48%412%23%10%
2547
February1st to 15thNight
49%411%21%12%1
2178
16th to endNight
46%413%23%12%
1893
March1st to 15thNight
49%49%20%13%2
2160
16th to endNight
47%5%13%21%11%1
1997
April1st to 15thNight
38%410%24%19%2
1797
16th to endNight
41%49%25%15%3
1800
May1st to 15thNight
44%6%11%22%13%
1638
16th to endNight
36%9%12%20%16%4
1531
June1st to 15thNight
29%6%12%26%23%1
1440
16th to endNight
28%7%14%22%21%6%
1440
July1st to 15thNight
28%6%12%28%17%6%
1360
16th to endNight
26%6%14%31%18%3
1417
August1st to 15thNight
26%6%14%26%22%3
1736
16th to endNight
26%7%12%23%23%6%
1910
September1st to 15thNight
31%48%26%21%7%
1800
16th to endNight
31%5%6%25%25%6%
1969
October1st to 15thNight
33%49%23%23%6%
2082
16th to endNight
36%38%27%19%4
2377
November1st to 15thNight
34%39%23%22%6%
2471
16th to endNight
40%39%26%18%1
2535
December1st to 15thNight
49%411%21%12%
2698
16th to endNight
54%410%20%9%1
2912

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
29%12%35%13%8%
123
16th to endDay
11%22%42%21%1
96
February1st to 15thDay
21%15%42%16%4
90
16th to endDay
22%18%24%27%7%
81
March1st to 15thDay
31%10%41%10%7%
90
16th to endDay
24%12%32%21%8%
219
April1st to 15thDay
15%12%30%26%13%1
270
16th to endDay
22%7%27%24%13%5%
270
May1st to 15thDay
17%9%27%28%11%5%
288
16th to endDay
11%428%27%18%9%
481
June1st to 15thDay
8%219%28%28%12%
495
16th to endDay
9%226%32%21%8%
495
July1st to 15thDay
12%114%33%23%14%
475
16th to endDay
5%17%29%34%22%
515
August1st to 15thDay
9%19%20%36%23%
364
16th to endDay
6%110%24%40%17%
332
September1st to 15thDay
13%212%21%33%16%
315
16th to endDay
10%312%25%28%19%
314
October1st to 15thDay
16%320%29%24%4
210
16th to endDay
18%8%25%30%15%2
144
November1st to 15thDay
14%8%22%27%17%8%
135
16th to endDay
25%9%31%23%8%
135
December1st to 15thDay
12%17%37%20%7%4
135
16th to endDay
29%11%43%11%3
144
January1st to 15thNight
20%15%34%24%4
956
16th to endNight
19%13%37%26%2
960
February1st to 15thNight
21%12%37%26%2
770
16th to endNight
18%12%39%26%1
631
March1st to 15thNight
23%10%38%23%4
720
16th to endNight
20%6%32%30%8%
584
April1st to 15thNight
14%12%34%26%11%
539
16th to endNight
19%429%31%12%1
540
May1st to 15thNight
17%426%36%13%1
540
16th to endNight
9%125%37%23%2
563
June1st to 15thNight
9%217%42%27%2
540
16th to endNight
7%19%43%25%2
540
July1st to 15thNight
9%12%39%33%4
510
16th to endNight
5%8%34%42%7%
564
August1st to 15thNight
5%17%34%43%7%
539
16th to endNight
6%10%32%45%4
573
September1st to 15thNight
11%111%35%31%8%
540
16th to endNight
10%317%29%32%7%
706
October1st to 15thNight
13%423%30%24%4
720
16th to endNight
18%8%31%30%10%
768
November1st to 15thNight
13%8%32%30%14%
760
16th to endNight
21%9%30%28%9%
780
December1st to 15thNight
25%11%30%26%6%
943
16th to endNight
27%9%35%24%3
1040
Page generated at 2018-01-12 21:01:37. Version ac04

Copyright 2018 A. Danko


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