Arriola Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arriola Observatory 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
61%
15716
28%
46912
22%
15677
67%
15677
39%
25829

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
62%
716
30%
2327
29%
716
67%
716
41%
1196
January16th to endNight
56%
768
32%
2496
29%
768
64%
768
37%
1344
February1st to 15thNight
56%
701
26%
2288
22%
699
64%
699
37%
1220
February16th to endNight
49%
632
31%
1903
21%
632
59%
632
36%
1068
March1st to 15thNight
55%
720
31%
1980
20%
720
63%
720
41%
1133
March16th to endNight
54%
768
26%
2112
18%
768
60%
768
36%
1263
April1st to 15thNight
46%
568
25%
1827
16%
568
58%
568
30%
1040
April16th to endNight
46%
540
30%
1797
20%
540
61%
540
34%
928
May1st to 15thNight
55%
539
27%
1619
20%
539
62%
539
38%
891
May16th to endNight
56%
562
25%
1648
19%
561
61%
561
37%
909
June1st to 15thNight
68%
540
32%
1440
24%
540
73%
540
57%
714
June16th to endNight
78%
540
32%
1455
26%
540
82%
540
61%
719
July1st to 15thNight
72%
510
16%
1530
13%
510
73%
510
29%
930
July16th to endNight
74%
564
17%
1593
16%
531
75%
531
27%
1031
August1st to 15thNight
77%
539
20%
1611
18%
536
77%
536
33%
974
August16th to endNight
77%
573
26%
1872
28%
573
79%
573
36%
1027
September1st to 15thNight
72%
525
25%
1750
26%
525
75%
525
31%
1014
September16th to endNight
73%
656
38%
1837
28%
656
78%
656
53%
919
October1st to 15thNight
65%
660
32%
1980
23%
660
72%
660
47%
1007
October16th to endNight
67%
704
38%
2112
27%
704
75%
704
50%
1032
November1st to 15thNight
68%
700
35%
2100
28%
700
74%
700
46%
1061
November16th to endNight
60%
882
34%
2478
24%
882
67%
882
48%
1277
December1st to 15thNight
56%
900
24%
2520
17%
900
61%
900
38%
1473
December16th to endNight
49%
909
23%
2637
18%
909
53%
909
29%
1659

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
5%5%2442445%6%54%
47700
Night
5%5%24423446%57%
47107
TransparencyDay
28%49%20%24%12%
47395
Night
27%48%21%24%13%
46913
SeeingDay
9%11%26%33%15%3
5480
Night
8%5%18%35%26%5%
15725

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
8%6%2331334459%
1611
16th to endDay
7%10%24313236%54%
1728
February1st to 15thDay
49%25%5%24237%51%
1575
16th to endDay
7%9%25%5%23435%48%
1566
March1st to 15thDay
5%7%2332445%6%53%
1980
16th to endDay
5%5%25%42445%6%52%
2112
April1st to 15thDay
5%7%26%5%34445%51%
2120
16th to endDay
44144345%47%54%
2160
May1st to 15thDay
45%24435%5%6%7%51%
2331
16th to endDay
431432336%7%58%
2462
June1st to 15thDay
3213222346%66%
2520
16th to endDay
12213346%72%
2500
July1st to 15thDay
22245%45%6%8%9%47%
2340
16th to endDay
5%5%245%46%7%9%10%37%
2467
August1st to 15thDay
5%425%6%36%6%8%7%41%
2340
16th to endDay
2315%6%35%6%8%9%46%
2330
September1st to 15thDay
6%3245%35%5%6%6%49%
2095
16th to endDay
331332334466%
1792
October1st to 15thDay
7%212423347%59%
1650
16th to endDay
4213322335%68%
1760
November1st to 15thDay
5%314312246%64%
1759
16th to endDay
45%1121224467%
1466
December1st to 15thDay
8%9%24323345%51%
1440
16th to endDay
8%10%36%413346%46%
1596
January1st to 15thNight
6%7%23312235%62%
2327
16th to endNight
8%7%2331233359%
2496
February1st to 15thNight
38%34313335%58%
2277
16th to endNight
7%7%24324336%54%
1903
March1st to 15thNight
5%6%23413446%56%
1980
16th to endNight
6%6%244245%5%5%52%
2112
April1st to 15thNight
8%5%244345%47%49%
1827
16th to endNight
5%4235%2343460%
1797
May1st to 15thNight
4424423347%56%
1619
16th to endNight
6%414413446%58%
1647
June1st to 15thNight
22231225%6%70%
1440
16th to endNight
11222335%7%68%
1455
July1st to 15thNight
2225%6%5%7%7%7%8%45%
1620
16th to endNight
3326%7%47%8%8%11%36%
1701
August1st to 15thNight
3225%5%35%6%7%8%49%
1620
16th to endNight
3313445%5%8%11%47%
1872
September1st to 15thNight
3235%6%36%6%7%7%48%
1750
16th to endNight
421232222470%
1837
October1st to 15thNight
5%313323346%63%
1980
16th to endNight
331321233469%
2112
November1st to 15thNight
5%5%13213345%63%
2100
16th to endNight
5%41321224466%
2478
December1st to 15thNight
8%7%24323236%55%
2520
16th to endNight
9%11%35%423345%47%
2637

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
29%315%33%16%1
1612
16th to endDay
33%311%26%21%3
1728
February1st to 15thDay
34%314%25%18%4
1575
16th to endDay
38%37%21%26%2
1566
March1st to 15thDay
30%37%29%25%4
1980
16th to endDay
31%38%22%28%5%
2112
April1st to 15thDay
34%36%19%24%11%
2120
16th to endDay
27%37%22%27%10%
2160
May1st to 15thDay
30%48%18%29%9%
2331
16th to endDay
23%48%16%32%15%
2465
June1st to 15thDay
19%2410%28%34%
2520
16th to endDay
12%3410%25%44%
2500
July1st to 15thDay
26%8%13%13%16%21%
2201
16th to endDay
33%9%17%18%12%8%
2312
August1st to 15thDay
34%9%10%15%15%14%
2325
16th to endDay
28%6%11%20%20%11%
2330
September1st to 15thDay
31%6%10%14%20%16%
2095
16th to endDay
20%45%15%32%21%
1792
October1st to 15thDay
24%26%23%32%10%
1650
16th to endDay
20%36%20%39%9%
1760
November1st to 15thDay
21%28%24%34%8%
1759
16th to endDay
22%27%32%27%7%
1466
December1st to 15thDay
35%313%29%16%1
1440
16th to endDay
40%5%17%23%12%1
1596
January1st to 15thNight
26%211%32%23%3
2327
16th to endNight
30%28%30%24%4
2496
February1st to 15thNight
28%413%27%19%7%
2288
16th to endNight
31%28%21%31%4
1903
March1st to 15thNight
28%35%29%26%6%
1980
16th to endNight
31%47%20%28%7%
2112
April1st to 15thNight
32%36%19%23%13%
1827
16th to endNight
27%3420%29%14%
1797
May1st to 15thNight
28%47%18%31%10%
1620
16th to endNight
27%48%16%25%16%
1648
June1st to 15thNight
16%2311%26%38%
1440
16th to endNight
14%349%21%45%
1455
July1st to 15thNight
32%10%12%11%12%21%
1530
16th to endNight
37%9%16%14%11%10%
1593
August1st to 15thNight
30%10%13%13%15%17%
1611
16th to endNight
27%6%12%18%20%13%
1872
September1st to 15thNight
32%6%8%14%16%20%
1750
16th to endNight
19%25%15%31%25%
1837
October1st to 15thNight
21%46%19%28%18%
1980
16th to endNight
18%3419%39%14%
2112
November1st to 15thNight
23%26%22%32%12%
2100
16th to endNight
22%27%25%30%11%
2478
December1st to 15thNight
31%312%28%20%3
2520
16th to endNight
39%313%26%15%1
2637

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
37%325%24%7%1
90
16th to endDay
15%8%23%31%17%3
96
February1st to 15thDay
13%10%20%34%22%
90
16th to endDay
13%22%32%20%10%
129
March1st to 15thDay
12%21%30%26%8%
270
16th to endDay
9%30%36%16%6%
288
April1st to 15thDay
13%24%33%19%6%2
269
16th to endDay
17%28%33%16%3
270
May1st to 15thDay
12%17%39%21%7%1
288
16th to endDay
8%17%29%27%14%2
363
June1st to 15thDay
6%9%23%36%21%3
495
16th to endDay
1423%41%21%7%
475
July1st to 15thDay
5%316%48%22%2
305
16th to endDay
7%116%44%23%6%
327
August1st to 15thDay
9%216%48%19%3
315
16th to endDay
5%326%38%23%3
332
September1st to 15thDay
7%429%43%12%2
294
16th to endDay
7%9%25%34%15%6%
232
October1st to 15thDay
312%25%30%20%8%
90
16th to endDay
8%10%39%23%14%3
96
November1st to 15thDay
8%8%20%34%26%1
90
16th to endDay
17%17%34%23%6%
90
December1st to 15thDay
12%12%33%34%7%
90
16th to endDay
22%11%17%31%15%1
96
January1st to 15thNight
10%317%38%23%5%
720
16th to endNight
13%420%34%20%5%
768
February1st to 15thNight
8%425%38%20%2
704
16th to endNight
11%7%27%36%14%2
632
March1st to 15thNight
9%6%23%34%22%3
720
16th to endNight
9%10%20%37%20%1
768
April1st to 15thNight
13%13%22%35%13%2
568
16th to endNight
10%13%25%31%17%1
540
May1st to 15thNight
7%6%23%40%17%3
540
16th to endNight
10%6%22%32%23%3
563
June1st to 15thNight
46%18%36%31%2
540
16th to endNight
1215%37%37%5%
540
July1st to 15thNight
5%10%34%42%6%
510
16th to endNight
5%16%30%46%9%
564
August1st to 15thNight
46%32%45%10%
539
16th to endNight
419%30%44%10%
573
September1st to 15thNight
4114%37%35%6%
525
16th to endNight
6%312%32%34%10%
656
October1st to 15thNight
7%5%19%40%22%4
660
16th to endNight
5%417%34%30%7%
704
November1st to 15thNight
7%5%14%40%27%6%
700
16th to endNight
9%8%19%32%23%7%
882
December1st to 15thNight
13%420%39%18%3
900
16th to endNight
15%8%17%36%19%2
909
Page generated at 2017-09-11 17:35:27. Version ac04

Copyright 2017 A. Danko


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