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 2018-02-22.

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
20%
15626
14%
48810
5%
15581
30%
15581
14%
34420

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
10%
825
13%
2909
1%
821
25%
821
9%
2019
January16th to endNight
13%
834
17%
2714
2%
834
30%
834
12%
1842
February1st to 15thNight
12%
764
12%
2481
2%
761
24%
761
11%
1717
February16th to endNight
14%
659
14%
2116
3%
659
27%
659
10%
1532
March1st to 15thNight
15%
720
16%
1995
5%
720
26%
720
14%
1446
March16th to endNight
16%
768
16%
2112
4%
768
26%
768
16%
1510
April1st to 15thNight
17%
566
14%
1790
6%
566
26%
566
13%
1300
April16th to endNight
21%
540
14%
1620
6%
540
29%
540
15%
1158
May1st to 15thNight
22%
540
10%
1542
5%
540
27%
540
13%
1156
May16th to endNight
21%
561
9%
1496
3%
560
27%
560
14%
1147
June1st to 15thNight
23%
412
7%
1312
4%
412
27%
412
11%
1005
June16th to endNight
32%
360
7%
1260
3%
360
37%
360
11%
922
July1st to 15thNight
35%
340
9%
1190
8%
340
40%
340
17%
789
July16th to endNight
31%
533
8%
1450
6%
500
36%
500
14%
1110
August1st to 15thNight
36%
539
10%
1608
7%
535
39%
535
17%
1153
August16th to endNight
40%
573
15%
1752
7%
573
45%
573
23%
1143
September1st to 15thNight
32%
559
16%
1819
10%
559
39%
559
21%
1152
September16th to endNight
33%
717
22%
1995
11%
717
43%
717
27%
1266
October1st to 15thNight
26%
720
19%
2160
7%
720
36%
720
20%
1429
October16th to endNight
19%
768
16%
2322
5%
768
29%
768
14%
1635
November1st to 15thNight
22%
798
15%
2632
7%
798
31%
798
14%
1822
November16th to endNight
17%
825
15%
2730
5%
825
29%
825
11%
1923
December1st to 15thNight
11%
825
14%
2730
1%
825
26%
825
8%
1976
December16th to endNight
8%
880
13%
3075
2%
880
22%
880
7%
2268

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
19%9%36%5%34446%30%
49446
Night
19%8%35%5%3445%6%32%
48977
TransparencyDay
52%411%20%9%
49131
Night
52%412%20%9%
48810
SeeingDay
23%22%26%19%7%1
7617
Night
21%27%25%19%6%
15626

By Month

Percentage Cloud Cover NE (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
14%14%47%6%23445%32%
1358
16th to endDay
16%10%47%435%446%32%
1861
February1st to 15thDay
14%12%47%5%345%45%30%
1710
16th to endDay
12%16%5%8%7%33445%28%
1501
March1st to 15thDay
17%11%5%7%7%34345%30%
1953
16th to endDay
14%10%5%8%7%34345%32%
2112
April1st to 15thDay
18%12%5%7%6%34445%26%
2156
16th to endDay
21%8%37%6%24437%29%
2340
May1st to 15thDay
23%10%5%7%5%25%44426%
2410
16th to endDay
22%10%37%5%2445%6%26%
2618
June1st to 15thDay
26%8%36%6%35%45%6%23%
2658
16th to endDay
24%8%36%5%24349%26%
2700
July1st to 15thDay
17%6%35%5%345%6%9%32%
2700
16th to endDay
19%7%36%6%36%5%5%7%27%
2604
August1st to 15thDay
17%5%27%5%36%45%9%30%
2340
16th to endDay
14%6%25%6%246%6%7%36%
2450
September1st to 15thDay
17%6%26%5%3445%6%37%
2139
16th to endDay
16%5%25%323337%45%
1964
October1st to 15thDay
17%8%25%424347%39%
1800
16th to endDay
21%6%38%5%24446%33%
1899
November1st to 15thDay
22%9%25%5%33336%32%
1555
16th to endDay
18%10%47%6%35%345%31%
1560
December1st to 15thDay
27%11%35%324337%27%
1560
16th to endDay
19%14%6%5%5%2335%5%28%
1498
January1st to 15thNight
16%9%36%6%35%5%5%7%32%
2909
16th to endNight
16%9%36%6%25%346%34%
2714
February1st to 15thNight
17%10%35%5%35%5%5%7%31%
2480
16th to endNight
15%13%6%7%6%24445%28%
2116
March1st to 15thNight
17%10%36%6%3445%5%30%
1983
16th to endNight
15%11%46%5%34345%33%
2112
April1st to 15thNight
22%9%46%5%3445%5%27%
1790
16th to endNight
20%8%25%5%45%445%31%
1620
May1st to 15thNight
21%8%35%8%35%45%5%27%
1542
16th to endNight
19%8%36%5%36%5%6%6%26%
1494
June1st to 15thNight
25%9%5%6%5%35%446%23%
1312
16th to endNight
22%8%35%437%5%5%6%26%
1260
July1st to 15thNight
13%8%37%6%26%5%6%7%33%
1260
16th to endNight
18%7%46%6%36%7%7%7%24%
1550
August1st to 15thNight
17%6%35%6%245%6%7%32%
1620
16th to endNight
13%6%25%5%35%45%7%39%
1752
September1st to 15thNight
16%6%24325%45%7%38%
1819
16th to endNight
15%6%23323446%46%
1995
October1st to 15thNight
19%6%25%42345%6%38%
2160
16th to endNight
23%7%345%24446%34%
2322
November1st to 15thNight
22%7%35%5%34345%34%
2632
16th to endNight
21%7%36%43435%6%32%
2730
December1st to 15thNight
24%9%36%423446%29%
2730
16th to endNight
23%11%5%6%5%24345%28%
3075

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
53%314%19%8%1
1359
16th to endDay
52%29%20%14%
1861
February1st to 15thDay
53%412%19%9%1
1713
16th to endDay
55%411%18%8%1
1501
March1st to 15thDay
55%210%18%10%1
1964
16th to endDay
53%29%20%11%2
2112
April1st to 15thDay
55%38%17%13%2
2156
16th to endDay
53%39%19%12%1
2340
May1st to 15thDay
59%47%19%9%
2410
16th to endDay
56%5%12%20%4
2622
June1st to 15thDay
59%412%16%6%
2658
16th to endDay
54%5%14%18%6%
2700
July1st to 15thDay
44%5%16%22%10%
2541
16th to endDay
51%6%14%20%5%
2442
August1st to 15thDay
47%5%16%22%7%
2327
16th to endDay
42%7%15%26%9%
2450
September1st to 15thDay
45%412%23%12%
2139
16th to endDay
38%410%28%16%1
1964
October1st to 15thDay
43%310%31%10%
1800
16th to endDay
51%311%22%11%
1899
November1st to 15thDay
54%311%18%11%
1555
16th to endDay
55%311%20%8%
1560
December1st to 15thDay
58%310%21%6%
1560
16th to endDay
58%310%15%12%
1498
January1st to 15thNight
52%413%19%8%1
2909
16th to endNight
49%311%23%10%
2714
February1st to 15thNight
52%313%18%11%
2481
16th to endNight
57%211%18%8%1
2116
March1st to 15thNight
53%211%19%11%1
1995
16th to endNight
51%210%19%13%1
2112
April1st to 15thNight
55%38%16%11%3
1790
16th to endNight
53%312%16%13%
1620
May1st to 15thNight
56%411%18%7%
1542
16th to endNight
55%6%13%17%6%
1496
June1st to 15thNight
61%5%10%17%41
1312
16th to endNight
57%5%11%18%6%
1260
July1st to 15thNight
47%5%15%22%8%
1190
16th to endNight
54%9%12%16%6%
1450
August1st to 15thNight
50%7%14%20%6%
1608
16th to endNight
42%6%18%24%8%
1752
September1st to 15thNight
42%412%28%10%
1819
16th to endNight
38%413%28%13%1
1995
October1st to 15thNight
45%311%27%11%
2160
16th to endNight
51%310%23%10%
2322
November1st to 15thNight
51%414%19%9%1
2632
16th to endNight
51%5%12%19%9%
2730
December1st to 15thNight
56%410%21%7%
2730
16th to endNight
59%39%17%9%1
3075

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
20%30%37%11%1
90
16th to endDay
22%28%32%14%2
303
February1st to 15thDay
20%32%25%16%4
281
16th to endDay
19%27%33%16%3
236
March1st to 15thDay
21%30%32%11%4
270
16th to endDay
23%28%27%13%5%
288
April1st to 15thDay
25%29%27%13%4
270
16th to endDay
21%27%25%16%7%1
270
May1st to 15thDay
28%24%22%16%6%1
366
16th to endDay
22%24%27%19%4
519
June1st to 15thDay
29%22%23%18%6%
495
16th to endDay
26%19%23%19%8%2
495
July1st to 15thDay
23%16%23%23%12%1
475
16th to endDay
18%15%25%27%11%
444
August1st to 15thDay
21%11%26%25%12%1
313
16th to endDay
15%16%21%28%15%2
332
September1st to 15thDay
18%13%28%28%9%1
315
16th to endDay
16%14%27%27%11%2
309
October1st to 15thDay
19%21%25%20%11%2
270
16th to endDay
25%23%28%14%7%
288
November1st to 15thDay
23%22%24%18%8%1
280
16th to endDay
23%30%29%11%4
285
December1st to 15thDay
33%28%25%11%1
285
16th to endDay
28%31%24%13%
138
January1st to 15thNight
20%37%25%14%2
825
16th to endNight
20%32%29%14%3
834
February1st to 15thNight
21%33%28%14%1
764
16th to endNight
23%31%26%13%4
659
March1st to 15thNight
21%31%27%16%2
720
16th to endNight
20%32%26%14%5%
768
April1st to 15thNight
22%28%25%19%4
566
16th to endNight
21%25%26%20%5%
540
May1st to 15thNight
23%26%23%17%7%
540
16th to endNight
18%26%28%19%6%
561
June1st to 15thNight
22%22%25%24%5%
412
16th to endNight
23%20%17%27%10%
360
July1st to 15thNight
16%17%22%32%9%
340
16th to endNight
17%22%19%30%9%
533
August1st to 15thNight
19%13%22%25%17%
539
16th to endNight
13%14%27%29%12%1
573
September1st to 15thNight
18%16%27%27%9%
559
16th to endNight
16%18%27%23%11%1
717
October1st to 15thNight
21%18%29%20%8%1
720
16th to endNight
26%25%24%18%5%
768
November1st to 15thNight
22%27%24%17%7%1
798
16th to endNight
21%33%21%16%5%
825
December1st to 15thNight
27%33%23%12%3
825
16th to endNight
28%33%23%11%2
880
Page generated at 2018-02-23 12:21:36. Version ac04

Copyright 2018 A. Danko


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