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
20%
14894
14%
46634
5%
14849
30%
14849
14%
32895

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
11%
750
14%
2684
1%
746
27%
746
9%
1844
January16th to endNight
13%
769
17%
2505
2%
769
30%
769
12%
1690
February1st to 15thNight
12%
704
12%
2286
2%
701
24%
701
11%
1579
February16th to endNight
14%
631
13%
2027
3%
631
26%
631
10%
1465
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
30%
542
15%
1766
9%
542
38%
542
20%
1129
September16th to endNight
32%
657
22%
1829
10%
657
42%
657
27%
1155
October1st to 15thNight
24%
660
19%
1980
7%
660
35%
660
19%
1320
October16th to endNight
17%
704
15%
2128
5%
704
28%
704
14%
1505
November1st to 15thNight
22%
725
15%
2424
7%
725
31%
725
14%
1667
November16th to endNight
18%
750
15%
2520
5%
750
29%
750
11%
1770
December1st to 15thNight
10%
750
15%
2520
2%
750
25%
750
8%
1823
December16th to endNight
9%
800
12%
2838
2%
800
21%
800
6%
2109

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%
47998
Night
19%8%36%5%3445%6%32%
46801
TransparencyDay
52%411%20%9%
47683
Night
52%412%20%9%
46634
SeeingDay
22%23%26%19%7%1
7132
Night
21%27%25%18%6%
14894

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%15%36%5%23445%33%
1253
16th to endDay
16%10%47%43435%6%32%
1718
February1st to 15thDay
14%11%47%6%445%5%6%30%
1575
16th to endDay
12%16%5%8%7%33445%27%
1443
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
18%6%26%5%3445%6%36%
2080
16th to endDay
16%5%25%323337%45%
1801
October1st to 15thDay
18%8%25%424347%37%
1650
16th to endDay
22%6%38%5%24446%31%
1741
November1st to 15thDay
23%9%25%5%33336%32%
1433
16th to endDay
19%10%47%5%34345%30%
1440
December1st to 15thDay
26%10%35%324337%28%
1440
16th to endDay
20%14%6%5%5%2335%6%26%
1383
January1st to 15thNight
16%9%35%5%3445%7%33%
2684
16th to endNight
16%9%36%6%25%347%35%
2505
February1st to 15thNight
16%10%35%5%35%5%5%7%31%
2285
16th to endNight
14%13%6%7%6%24446%28%
2027
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
17%6%24425%45%8%37%
1766
16th to endNight
15%6%24323346%47%
1829
October1st to 15thNight
20%7%25%42335%6%37%
1980
16th to endNight
23%7%35%5%24446%32%
2128
November1st to 15thNight
22%7%35%424445%33%
2424
16th to endNight
22%7%36%42435%6%32%
2520
December1st to 15thNight
24%10%36%423345%30%
2520
16th to endNight
24%11%5%6%424345%27%
2838

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
52%314%19%8%1
1254
16th to endDay
52%29%21%14%
1718
February1st to 15thDay
51%413%20%8%1
1578
16th to endDay
55%412%19%8%1
1443
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
46%413%22%12%1
2080
16th to endDay
38%39%30%15%1
1801
October1st to 15thDay
44%310%29%10%
1650
16th to endDay
53%311%20%11%
1741
November1st to 15thDay
53%311%18%12%
1433
16th to endDay
55%311%19%9%
1440
December1st to 15thDay
57%310%22%5%
1440
16th to endDay
60%210%15%10%
1383
January1st to 15thNight
51%413%19%8%1
2684
16th to endNight
49%311%24%10%
2505
February1st to 15thNight
52%314%18%11%
2286
16th to endNight
57%211%18%8%1
2027
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
43%413%27%10%
1766
16th to endNight
38%313%29%13%
1829
October1st to 15thNight
46%311%26%12%
1980
16th to endNight
52%310%22%10%
2128
November1st to 15thNight
51%314%20%8%1
2424
16th to endNight
52%5%12%19%8%
2520
December1st to 15thNight
57%39%22%7%
2520
16th to endNight
61%39%17%8%
2838

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
21%26%41%10%
60
16th to endDay
20%28%33%14%3
255
February1st to 15thDay
16%34%25%17%5%
236
16th to endDay
18%29%31%17%4
216
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
19%14%28%27%8%1
294
16th to endDay
15%17%28%27%9%1
251
October1st to 15thDay
20%22%22%20%11%2
225
16th to endDay
26%24%28%12%7%
240
November1st to 15thDay
24%24%22%18%7%2
235
16th to endDay
24%31%25%12%4
240
December1st to 15thDay
30%30%25%11%1
240
16th to endDay
32%30%23%12%
103
January1st to 15thNight
20%38%24%14%2
750
16th to endNight
19%33%29%13%3
769
February1st to 15thNight
20%34%29%14%1
704
16th to endNight
23%31%25%13%4
631
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%17%28%26%9%
542
16th to endNight
16%18%28%23%10%1
657
October1st to 15thNight
22%19%28%18%8%1
660
16th to endNight
27%25%25%17%4
704
November1st to 15thNight
21%28%24%16%7%1
725
16th to endNight
21%33%20%16%6%
750
December1st to 15thNight
26%34%23%12%3
750
16th to endNight
28%34%22%11%2
800
Page generated at 2017-09-11 20:35:14. Version ac04

Copyright 2017 A. Danko


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