Alma
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alma clear sky chart from 2005-11-06 to 2024-01-10.

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
43%
24567
25%
74188
14%
24508
52%
24508
35%
42385

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
37%
950
25%
2646
13%
946
47%
946
36%
1568
January11th to 20thNight
38%
900
25%
2463
12%
900
47%
900
34%
1486
January21st to endNight
32%
990
28%
2574
11%
990
43%
990
35%
1604
February1st to 10thNight
31%
850
20%
2290
7%
850
40%
850
29%
1495
February11th to 20thNight
33%
704
24%
2098
11%
700
43%
700
31%
1258
February21st to endNight
33%
592
28%
1776
9%
592
48%
592
32%
1013
March1st to 10thNight
34%
707
24%
2147
9%
707
46%
707
34%
1193
March11th to 20thNight
34%
540
25%
1980
17%
540
47%
540
27%
1116
March21st to endNight
27%
594
17%
2178
9%
594
39%
594
22%
1318
April1st to 10thNight
27%
540
20%
1847
10%
540
42%
540
27%
1060
April11th to 20thNight
30%
533
20%
1708
11%
533
43%
533
26%
1038
April21st to endNight
39%
540
23%
1620
16%
540
50%
540
30%
958
May1st to 10thNight
35%
540
15%
1620
10%
540
43%
540
26%
1037
May11th to 20thNight
36%
531
18%
1593
12%
531
45%
531
31%
959
May21st to endNight
38%
583
15%
1746
9%
582
43%
582
26%
1130
June1st to 10thNight
54%
540
20%
1544
11%
540
59%
540
41%
858
June11th to 20thNight
45%
540
21%
1440
9%
540
51%
540
40%
857
June21st to endNight
52%
540
22%
1440
11%
540
57%
540
44%
821
July1st to 10thNight
59%
525
19%
1400
12%
525
62%
525
39%
841
July11th to 20thNight
70%
522
25%
1415
17%
522
74%
522
51%
746
July21st to endNight
67%
591
23%
1673
22%
558
70%
558
43%
905
August1st to 10thNight
68%
537
20%
1601
20%
534
71%
534
39%
896
August11th to 20thNight
61%
534
27%
1600
26%
534
68%
534
40%
889
August21st to endNight
64%
594
28%
1928
29%
594
71%
594
44%
965
September1st to 10thNight
58%
540
28%
1890
25%
540
68%
540
42%
916
September11th to 20thNight
52%
540
30%
1980
24%
540
65%
540
38%
973
September21st to endNight
49%
540
31%
1980
26%
540
59%
540
39%
947
October1st to 10thNight
45%
540
31%
1980
25%
540
56%
540
31%
1046
October11th to 20thNight
39%
687
31%
2127
15%
687
51%
687
42%
1079
October21st to endNight
42%
940
29%
2524
13%
940
50%
940
42%
1415
November1st to 10thNight
48%
925
32%
2405
14%
925
57%
925
51%
1263
November11th to 20thNight
42%
950
34%
2470
14%
950
54%
950
44%
1403
November21st to endNight
46%
950
29%
2470
15%
950
54%
950
42%
1420
December1st to 10thNight
41%
950
27%
2470
12%
950
51%
950
40%
1456
December11th to 20thNight
38%
949
31%
2845
12%
948
49%
948
36%
1541
December21st to endNight
36%
1039
18%
4720
12%
1026
49%
1026
19%
2915

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
9%5%2442445%7%53%
74994
Night
8%5%2442445%7%53%
74675
TransparencyDay
31%6%14%27%19%3
74711
Night
30%6%13%27%20%5%
74481
SeeingDay
11%8%31%33%15%3
14531
Night
11%8%34%37%10%
24575

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
6%8%25%5%24347%53%
1510
11th to 20thDay
8%7%35%42447%8%49%
1492
21st to endDay
7%7%25%5%2436%7%50%
1782
February1st to 10thDay
7%8%5%6%5%445%6%6%43%
1686
11th to 20thDay
5%6%36%6%35%5%48%48%
1749
21st to endDay
7%6%2443445%8%52%
1480
March1st to 10thDay
7%6%2442445%7%57%
1810
11th to 20thDay
12%7%24423447%49%
1980
21st to endDay
12%8%46%5%2446%6%44%
2178
April1st to 10thDay
10%5%34423448%53%
2110
11th to 20thDay
12%6%35%5%3445%8%46%
2198
21st to endDay
16%5%2443445%8%45%
2340
May1st to 10thDay
13%7%35%43446%9%44%
2340
11th to 20thDay
14%6%2442345%8%46%
2302
21st to endDay
10%6%35%6%35%5%7%9%42%
2531
June1st to 10thDay
5%32332346%11%59%
2411
11th to 20thDay
7%32343446%9%55%
2520
21st to endDay
5%3234335%5%7%59%
2520
July1st to 10thDay
5%324435%5%6%9%54%
2520
11th to 20thDay
32144346%7%8%58%
2494
21st to endDay
6%3234345%7%10%53%
2546
August1st to 10thDay
6%4245%35%5%7%10%48%
2328
11th to 20thDay
5%323325%47%9%56%
2301
21st to endDay
7%42342435%6%60%
2425
September1st to 10thDay
11%414324446%58%
2070
11th to 20thDay
9%414423336%59%
1980
21st to endDay
8%313323336%63%
1980
October1st to 10thDay
16%423222246%57%
1980
11th to 20thDay
9%423223245%63%
1814
21st to endDay
11%6%34222345%58%
1828
November1st to 10thDay
7%31342435%6%61%
1673
11th to 20thDay
7%5%23324345%61%
1710
21st to endDay
9%7%34324436%55%
1710
December1st to 10thDay
7%6%26%42445%7%54%
1710
11th to 20thDay
8%7%25%424348%52%
2161
21st to endDay
12%12%411%5%24435%38%
2825
January1st to 10thNight
5%9%36%5%2345%8%51%
2646
11th to 20thNight
6%7%36%5%34447%52%
2463
21st to endNight
6%6%35%5%35%45%7%50%
2574
February1st to 10thNight
8%8%45%5%25%5%46%47%
2290
11th to 20thNight
5%8%35%5%345%6%8%48%
2098
21st to endNight
6%6%26%5%35%345%55%
1776
March1st to 10thNight
9%6%2432435%6%56%
2147
11th to 20thNight
12%7%34323446%52%
1980
21st to endNight
12%7%36%5%35%5%6%7%43%
2178
April1st to 10thNight
9%6%25%5%3445%7%50%
1847
11th to 20thNight
13%5%35%425%45%9%45%
1708
21st to endNight
12%5%2443445%8%50%
1620
May1st to 10thNight
14%5%25%435%5%6%9%42%
1620
11th to 20thNight
13%5%245%2345%8%49%
1593
21st to endNight
14%5%2443447%10%42%
1745
June1st to 10thNight
5%3143345%8%10%55%
1544
11th to 20thNight
8%4234245%7%10%52%
1440
21st to endNight
43245%346%6%11%55%
1440
July1st to 10thNight
6%4245%345%7%10%49%
1440
11th to 20thNight
2323425%6%6%10%57%
1463
21st to endNight
43145%35%5%8%10%53%
1772
August1st to 10thNight
5%324435%5%5%11%52%
1611
11th to 20thNight
5%324435%46%9%55%
1600
21st to endNight
5%21332445%8%62%
1928
September1st to 10thNight
7%313323347%62%
1890
11th to 20thNight
7%5%13323446%61%
1980
21st to endNight
7%41432335%6%62%
1980
October1st to 10thNight
13%42432335%7%54%
1980
11th to 20thNight
9%413322347%63%
2127
21st to endNight
10%423312445%61%
2524
November1st to 10thNight
442232345%7%65%
2405
11th to 20thNight
7%324423346%61%
2470
21st to endNight
8%6%1332335%6%59%
2470
December1st to 10thNight
5%6%4442445%6%57%
2470
11th to 20thNight
7%5%2442445%7%57%
3036
21st to endNight
12%13%36%5%23346%43%
4820

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
33%417%26%17%2
1511
11th to 20thDay
34%6%15%27%14%4
1492
21st to endDay
33%5%18%29%13%2
1782
February1st to 10thDay
41%6%17%21%12%4
1686
11th to 20thDay
35%6%15%25%16%4
1759
21st to endDay
31%5%15%26%18%5%
1480
March1st to 10thDay
28%5%15%25%23%4
1810
11th to 20thDay
36%5%12%25%18%4
1980
21st to endDay
41%6%16%24%11%1
2178
April1st to 10thDay
31%6%15%26%19%3
2110
11th to 20thDay
37%6%15%24%15%3
2201
21st to endDay
36%7%13%28%14%1
2340
May1st to 10thDay
37%8%15%24%14%2
2340
11th to 20thDay
36%7%18%27%11%
2306
21st to endDay
37%10%18%21%11%2
2531
June1st to 10thDay
21%7%19%36%15%2
2411
11th to 20thDay
26%8%15%28%19%5%
2520
21st to endDay
23%6%13%30%23%5%
2520
July1st to 10thDay
26%7%13%28%22%3
2451
11th to 20thDay
20%8%14%29%24%5%
2419
21st to endDay
23%8%18%32%18%1
2405
August1st to 10thDay
29%10%19%27%13%2
2314
11th to 20thDay
24%7%14%34%18%3
2301
21st to endDay
25%6%11%26%25%7%
2425
September1st to 10thDay
28%5%11%23%25%8%
2070
11th to 20thDay
27%5%11%27%25%4
1980
21st to endDay
23%410%33%27%2
1980
October1st to 10thDay
31%49%28%26%3
1980
11th to 20thDay
26%48%31%23%8%
1814
21st to endDay
30%410%27%24%6%
1828
November1st to 10thDay
24%412%31%24%4
1673
11th to 20thDay
25%411%28%28%4
1710
21st to endDay
33%411%25%23%5%
1710
December1st to 10thDay
30%5%14%29%19%2
1710
11th to 20thDay
32%414%35%14%
2159
21st to endDay
49%6%9%21%14%2
2825
January1st to 10thNight
32%413%31%18%2
2646
11th to 20thNight
33%5%13%28%20%2
2463
21st to endNight
33%5%16%26%16%3
2574
February1st to 10thNight
38%6%13%22%15%5%
2290
11th to 20thNight
34%6%12%31%15%2
2098
21st to endNight
30%5%13%21%23%7%
1776
March1st to 10thNight
30%411%26%23%6%
2147
11th to 20thNight
34%6%10%25%20%6%
1980
21st to endNight
39%7%16%22%14%2
2178
April1st to 10thNight
33%7%13%22%21%4
1847
11th to 20thNight
36%7%15%23%17%2
1708
21st to endNight
33%6%14%27%18%2
1620
May1st to 10thNight
38%8%16%19%16%2
1620
11th to 20thNight
34%6%18%26%15%1
1594
21st to endNight
37%10%18%22%11%2
1746
June1st to 10thNight
22%9%20%29%17%3
1544
11th to 20thNight
28%7%15%25%19%6%
1440
21st to endNight
24%7%16%27%22%5%
1440
July1st to 10thNight
27%9%15%27%17%5%
1400
11th to 20thNight
18%7%18%29%20%7%
1415
21st to endNight
23%8%16%33%17%3
1673
August1st to 10thNight
26%8%21%29%13%2
1601
11th to 20thNight
25%8%14%32%17%4
1600
21st to endNight
20%7%13%26%25%9%
1928
September1st to 10thNight
22%5%11%25%26%11%
1890
11th to 20thNight
24%6%10%27%27%7%
1980
21st to endNight
23%5%10%27%30%5%
1980
October1st to 10thNight
30%5%10%25%25%5%
1980
11th to 20thNight
23%49%27%26%10%
2127
21st to endNight
26%412%25%23%10%
2524
November1st to 10thNight
19%411%30%28%8%
2405
11th to 20thNight
26%49%28%28%6%
2470
21st to endNight
27%411%26%26%5%
2470
December1st to 10thNight
28%5%14%29%20%3
2470
11th to 20thNight
27%5%12%36%19%2
3037
21st to endNight
42%6%11%27%13%2
4820

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
10%10%39%30%8%3
267
11th to 20thDay
16%13%33%29%9%
240
21st to endDay
12%9%49%22%7%
264
February1st to 10thDay
13%13%48%22%4
240
11th to 20thDay
12%10%44%28%5%2
240
21st to endDay
11%17%47%21%4
198
March1st to 10thDay
13%11%45%23%7%
240
11th to 20thDay
21%11%32%23%12%1
240
21st to endDay
22%11%39%22%6%1
264
April1st to 10thDay
15%17%37%25%5%1
370
11th to 20thDay
14%16%39%25%5%
479
21st to endDay
20%13%35%22%9%2
600
May1st to 10thDay
15%10%31%31%12%1
603
11th to 20thDay
20%6%32%27%13%3
625
21st to endDay
16%8%33%29%13%2
679
June1st to 10thDay
46%24%37%22%7%
630
11th to 20thDay
7%433%36%16%2
630
21st to endDay
5%8%28%40%18%1
630
July1st to 10thDay
6%322%41%25%4
621
11th to 20thDay
4321%43%25%5%
618
21st to endDay
5%219%43%26%5%
684
August1st to 10thDay
5%217%46%25%4
626
11th to 20thDay
6%322%44%22%3
615
21st to endDay
9%220%42%22%5%
544
September1st to 10thDay
12%427%38%18%3
360
11th to 20thDay
5%6%27%35%22%6%
270
21st to endDay
14%11%26%30%17%2
270
October1st to 10thDay
20%8%23%31%14%4
270
11th to 20thDay
415%38%27%11%4
270
21st to endDay
18%14%31%26%10%1
297
November1st to 10thDay
11%12%34%28%11%4
270
11th to 20thDay
12%10%39%27%10%1
270
21st to endDay
19%13%32%25%9%3
270
December1st to 10thDay
9%7%41%34%8%1
270
11th to 20thDay
14%9%40%30%6%
270
21st to endDay
17%11%40%25%6%
297
January1st to 10thNight
10%8%37%36%8%
950
11th to 20thNight
10%12%34%35%8%
900
21st to endNight
10%9%44%31%6%
990
February1st to 10thNight
12%9%42%31%6%
850
11th to 20thNight
9%10%43%33%5%
704
21st to endNight
10%13%39%33%5%
592
March1st to 10thNight
13%11%38%33%5%
707
11th to 20thNight
16%10%36%29%8%1
540
21st to endNight
18%12%39%25%6%
594
April1st to 10thNight
12%12%46%26%4
540
11th to 20thNight
15%13%40%28%5%
533
21st to endNight
15%13%31%33%9%
540
May1st to 10thNight
16%9%36%31%8%
540
11th to 20thNight
16%6%37%32%9%1
531
21st to endNight
17%7%34%32%10%1
584
June1st to 10thNight
5%6%31%42%14%2
540
11th to 20thNight
10%5%36%38%11%
540
21st to endNight
5%5%34%46%11%
540
July1st to 10thNight
7%424%44%21%1
525
11th to 20thNight
3221%55%19%1
522
21st to endNight
6%119%51%23%1
591
August1st to 10thNight
6%217%52%22%1
537
11th to 20thNight
6%425%47%18%1
534
21st to endNight
6%224%47%19%2
594
September1st to 10thNight
8%329%49%10%2
540
11th to 20thNight
10%331%38%17%
540
21st to endNight
8%8%33%36%14%1
540
October1st to 10thNight
15%8%29%36%11%
540
11th to 20thNight
12%10%36%34%8%
687
21st to endNight
13%10%32%33%12%1
940
November1st to 10thNight
7%9%33%42%9%
925
11th to 20thNight
10%9%35%37%8%
950
21st to endNight
11%9%32%37%11%1
950
December1st to 10thNight
9%9%37%39%6%
950
11th to 20thNight
12%8%36%35%8%
950
21st to endNight
15%9%35%35%5%
1045
Page generated at 2024-01-07 09:06:51. Version ac07

Copyright 2024 Attilla Danko


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