The Glenelg Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Glenelg Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
28%
15045
11%
46716
7%
15007
32%
15007
14%
35152

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
7%
852
3%
2573
1%
850
10%
850
4%
2296
January16th to endNight
12%
768
4%
2496
1%
768
14%
768
5%
2206
February1st to 15thNight
12%
701
4%
2287
1%
701
17%
701
6%
1960
February16th to endNight
14%
631
8%
1986
2%
631
20%
631
9%
1616
March1st to 15thNight
17%
720
12%
2007
5%
720
23%
720
12%
1575
March16th to endNight
30%
768
18%
2112
9%
768
37%
768
20%
1512
April1st to 15thNight
24%
687
14%
1819
5%
687
29%
687
17%
1374
April16th to endNight
33%
540
16%
1620
9%
540
38%
540
20%
1121
May1st to 15thNight
36%
531
14%
1611
10%
531
42%
531
23%
1087
May16th to endNight
42%
374
16%
1497
12%
374
53%
374
23%
898
June1st to 15thNight
38%
360
12%
1350
10%
360
46%
360
21%
842
June16th to endNight
47%
360
15%
1260
15%
360
53%
360
26%
759
July1st to 15thNight
56%
340
18%
1190
21%
340
61%
340
34%
646
July16th to endNight
53%
532
14%
1561
12%
499
55%
499
28%
964
August1st to 15thNight
56%
539
15%
1609
10%
536
59%
536
29%
989
August16th to endNight
51%
587
21%
1733
13%
587
56%
587
30%
1092
September1st to 15thNight
47%
720
17%
1858
9%
720
50%
720
31%
1224
September16th to endNight
46%
673
18%
1858
12%
673
49%
673
28%
1232
October1st to 15thNight
33%
660
14%
1974
10%
660
38%
660
19%
1423
October16th to endNight
18%
704
8%
2131
4%
704
22%
704
10%
1736
November1st to 15thNight
23%
700
14%
2366
11%
700
29%
700
13%
1777
November16th to endNight
17%
720
8%
2520
7%
720
21%
720
9%
2046
December1st to 15thNight
9%
720
2%
2520
1%
720
11%
720
3%
2264
December16th to endNight
6%
858
3%
2778
0%
858
8%
858
3%
2513

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
17%11%47%6%34446%28%
48095
Night
16%12%5%8%6%34445%28%
46887
Cloud CoverDay
16%11%48%6%34446%27%
48105
Night
16%11%5%8%6%34445%28%
46891
TransparencyDay
56%5%10%16%9%
47784
Night
57%5%10%16%8%1
46716
SeeingDay
20%12%28%23%11%4
5719
Night
21%13%30%24%9%1
15052

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
17%16%11%16%10%3333310%
1360
16th to endDay
11%19%8%16%11%45%34410%
1728
February1st to 15thDay
13%18%10%17%10%5%43329%
1575
16th to endDay
15%19%7%11%9%45%44412%
1485
March1st to 15thDay
15%12%6%10%9%4333424%
1942
16th to endDay
15%10%49%7%3444430%
2112
April1st to 15thDay
21%13%5%6%433445%27%
2140
16th to endDay
19%11%34323346%36%
2340
May1st to 15thDay
19%8%25%5%2335%7%35%
2340
16th to endDay
14%7%25%435%45%7%39%
2618
June1st to 15thDay
17%7%3443445%8%35%
2607
16th to endDay
16%6%25%5%2446%8%36%
2700
July1st to 15thDay
13%5%35%425%6%6%9%37%
2700
16th to endDay
12%6%35%5%36%5%7%10%33%
2498
August1st to 15thDay
13%6%26%6%35%5%5%9%34%
2340
16th to endDay
13%6%25%6%46%5%6%8%33%
2456
September1st to 15thDay
19%7%35%5%235%46%36%
2100
16th to endDay
18%7%25%424348%37%
1848
October1st to 15thDay
24%10%45%433346%29%
1656
16th to endDay
32%15%26%44433415%
1740
November1st to 15thDay
18%17%5%5%5%25%446%24%
1490
16th to endDay
20%22%7%7%5%24445%13%
1440
December1st to 15thDay
18%22%12%13%7%245%346%
1440
16th to endDay
19%23%12%13%7%232337%
1440
January1st to 15thNight
19%17%9%14%9%3433410%
2573
16th to endNight
13%16%9%14%12%46%4339%
2496
February1st to 15thNight
12%17%9%14%10%46%33313%
2285
16th to endNight
14%13%9%12%8%35%445%18%
1986
March1st to 15thNight
16%13%6%9%8%34445%25%
1995
16th to endNight
14%11%5%7%5%3434437%
2112
April1st to 15thNight
20%13%45%424346%31%
1819
16th to endNight
14%11%35%435%5%45%37%
1620
May1st to 15thNight
16%8%345%3445%7%36%
1611
16th to endNight
11%6%24435%5%5%7%43%
1495
June1st to 15thNight
15%6%26%425%45%8%38%
1350
16th to endNight
14%42432346%8%43%
1260
July1st to 15thNight
9%4243235%5%8%50%
1260
16th to endNight
10%42443447%8%44%
1667
August1st to 15thNight
11%4235%35%45%8%45%
1620
16th to endNight
11%5%26%5%33337%47%
1733
September1st to 15thNight
15%425%5%34347%44%
1858
16th to endNight
15%6%35%5%24346%43%
1858
October1st to 15thNight
21%7%25%5%34347%32%
1974
16th to endNight
27%12%36%6%25%435%20%
2131
November1st to 15thNight
17%14%37%5%35%445%27%
2366
16th to endNight
22%17%6%8%5%34345%18%
2520
December1st to 15thNight
19%23%9%12%7%2433310%
2520
16th to endNight
20%20%12%13%7%332438%
2778

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
16%16%11%16%10%4432311%
1360
16th to endDay
10%18%9%16%11%45%44410%
1728
February1st to 15thDay
13%18%9%16%12%443339%
1575
16th to endDay
15%18%7%12%9%4444313%
1485
March1st to 15thDay
15%12%6%10%9%4433423%
1953
16th to endDay
14%11%5%9%7%24445%29%
2111
April1st to 15thDay
20%12%5%6%5%33445%28%
2140
16th to endDay
18%12%34323446%36%
2340
May1st to 15thDay
19%8%345%3445%7%34%
2340
16th to endDay
14%7%35%435%447%39%
2618
June1st to 15thDay
17%8%3442445%8%35%
2607
16th to endDay
16%6%25%435%46%9%36%
2700
July1st to 15thDay
13%5%36%435%6%5%9%37%
2700
16th to endDay
11%6%35%6%36%5%7%9%33%
2498
August1st to 15thDay
12%7%26%7%35%5%5%8%34%
2340
16th to endDay
13%5%36%6%5%6%6%5%8%33%
2456
September1st to 15thDay
18%7%36%5%33447%35%
2100
16th to endDay
18%6%35%423447%37%
1848
October1st to 15thDay
24%9%37%433445%29%
1656
16th to endDay
31%14%37%5%35%445%15%
1740
November1st to 15thDay
17%18%46%5%44346%24%
1490
16th to endDay
20%21%7%8%6%24445%13%
1440
December1st to 15thDay
17%21%12%13%7%243347%
1440
16th to endDay
18%23%12%15%6%232238%
1440
January1st to 15thNight
19%16%9%13%10%4443410%
2573
16th to endNight
12%16%8%14%12%5%6%34410%
2496
February1st to 15thNight
12%17%10%13%10%45%43413%
2278
16th to endNight
13%13%8%12%8%34445%17%
1986
March1st to 15thNight
16%12%5%10%8%34445%25%
2007
16th to endNight
14%10%47%42434437%
2112
April1st to 15thNight
20%12%46%424346%30%
1819
16th to endNight
13%11%35%435%5%35%36%
1620
May1st to 15thNight
15%8%35%5%3445%6%36%
1610
16th to endNight
10%6%25%335%6%5%6%43%
1495
June1st to 15thNight
15%5%35%43445%8%39%
1350
16th to endNight
14%42443345%9%43%
1260
July1st to 15thNight
8%424323448%51%
1260
16th to endNight
9%4245%445%6%7%45%
1667
August1st to 15thNight
10%424435%5%5%8%45%
1620
16th to endNight
10%5%25%6%34336%48%
1733
September1st to 15thNight
14%425%43435%6%45%
1858
16th to endNight
15%5%445%24346%43%
1858
October1st to 15thNight
21%8%26%5%34447%31%
1974
16th to endNight
26%12%37%7%3435%5%20%
2131
November1st to 15thNight
17%13%47%6%35%5%45%27%
2366
16th to endNight
20%17%7%8%5%34345%18%
2520
December1st to 15thNight
19%22%8%13%7%3433310%
2520
16th to endNight
20%18%12%15%7%243438%
2778

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
79%46%6%2
1361
16th to endDay
77%47%5%3
1728
February1st to 15thDay
80%25%8%1
1577
16th to endDay
74%46%8%5%
1485
March1st to 15thDay
64%410%12%7%
1953
16th to endDay
55%6%10%14%11%1
2112
April1st to 15thDay
57%5%7%18%10%
2140
16th to endDay
48%410%19%14%1
2340
May1st to 15thDay
49%5%10%22%12%
2340
16th to endDay
44%6%13%21%13%1
2622
June1st to 15thDay
46%6%12%22%12%
2607
16th to endDay
44%7%14%22%11%
2700
July1st to 15thDay
42%6%12%22%14%1
2541
16th to endDay
45%8%12%21%10%1
2341
August1st to 15thDay
46%7%14%18%12%1
2327
16th to endDay
46%8%14%20%8%1
2456
September1st to 15thDay
48%5%12%22%9%1
2100
16th to endDay
46%5%13%26%8%
1848
October1st to 15thDay
57%49%15%11%
1656
16th to endDay
71%5%9%9%3
1740
November1st to 15thDay
60%6%12%13%7%
1490
16th to endDay
72%5%9%9%2
1440
December1st to 15thDay
82%5%5%5%
1440
16th to endDay
82%35%6%
1440
January1st to 15thNight
78%48%5%2
2573
16th to endNight
78%48%42
2496
February1st to 15thNight
74%49%9%2
2287
16th to endNight
67%5%10%9%6%
1986
March1st to 15thNight
60%5%9%16%6%
2007
16th to endNight
50%48%18%15%2
2112
April1st to 15thNight
55%5%7%18%13%
1819
16th to endNight
48%5%9%16%17%2
1620
May1st to 15thNight
46%410%22%13%2
1611
16th to endNight
38%7%12%26%12%2
1497
June1st to 15thNight
42%5%12%23%14%1
1350
16th to endNight
37%6%13%27%14%
1260
July1st to 15thNight
29%6%12%28%21%1
1190
16th to endNight
37%6%13%24%16%1
1561
August1st to 15thNight
35%7%17%24%14%1
1609
16th to endNight
37%6%12%28%14%1
1733
September1st to 15thNight
39%5%13%28%12%1
1858
16th to endNight
42%5%13%26%12%
1858
October1st to 15thNight
51%5%11%18%11%
1974
16th to endNight
64%6%12%11%4
2131
November1st to 15thNight
58%5%12%15%6%1
2366
16th to endNight
67%5%12%10%21
2520
December1st to 15thNight
79%6%8%41
2520
16th to endNight
81%47%5%
2778

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
18%33%35%12%
71
16th to endDay
27%14%39%17%1
96
February1st to 15thDay
25%32%36%5%
90
16th to endDay
24%27%39%7%1
81
March1st to 15thDay
23%20%33%17%5%
243
16th to endDay
23%11%34%21%6%1
288
April1st to 15thDay
24%15%32%16%9%1
270
16th to endDay
25%15%25%18%10%4
270
May1st to 15thDay
23%10%28%24%9%3
288
16th to endDay
19%10%31%21%13%3
331
June1st to 15thDay
20%11%24%30%11%1
402
16th to endDay
16%9%35%26%10%2
495
July1st to 15thDay
16%8%27%28%13%5%
475
16th to endDay
10%8%24%32%16%7%
327
August1st to 15thDay
14%5%21%28%18%10%
313
16th to endDay
17%5%21%24%21%9%
332
September1st to 15thDay
15%7%19%25%20%11%
315
16th to endDay
18%6%23%23%21%6%
266
October1st to 15thDay
22%10%28%25%10%2
255
16th to endDay
37%19%20%18%3
252
November1st to 15thDay
24%12%32%24%5%2
75
16th to endDay
33%16%33%11%5%
60
December1st to 15thDay
31%33%26%8%
60
16th to endDay
35%28%34%1
64
January1st to 15thNight
25%23%34%13%3
855
16th to endNight
18%16%39%20%4
768
February1st to 15thNight
20%20%37%17%2
704
16th to endNight
20%18%35%20%4
631
March1st to 15thNight
19%20%36%18%3
720
16th to endNight
19%13%30%25%8%1
768
April1st to 15thNight
25%15%31%23%4
687
16th to endNight
22%12%27%25%8%2
540
May1st to 15thNight
20%8%29%29%11%1
531
16th to endNight
13%5%33%32%14%
375
June1st to 15thNight
15%6%31%34%11%
360
16th to endNight
14%232%35%14%
360
July1st to 15thNight
9%225%44%17%
340
16th to endNight
12%323%40%19%1
532
August1st to 15thNight
11%222%37%24%1
539
16th to endNight
12%324%30%26%2
587
September1st to 15thNight
16%6%25%29%16%6%
720
16th to endNight
17%6%22%33%16%4
673
October1st to 15thNight
24%9%28%24%11%1
660
16th to endNight
31%15%30%19%3
704
November1st to 15thNight
24%15%31%19%7%
700
16th to endNight
28%19%29%18%3
720
December1st to 15thNight
27%22%33%13%2
720
16th to endNight
28%21%34%13%2
858
Page generated at 2017-09-20 04:49:48. Version ac04

Copyright 2017 A. Danko


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