AGS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AGS 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
60%
15290
33%
46855
23%
15244
71%
15244
45%
23142

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
58%
720
34%
2327
27%
716
70%
716
46%
1090
January16th to endNight
53%
768
36%
2496
27%
768
68%
768
41%
1216
February1st to 15thNight
53%
701
34%
2276
25%
697
68%
697
50%
1008
February16th to endNight
43%
632
43%
1825
21%
632
66%
632
50%
861
March1st to 15thNight
49%
720
40%
1980
21%
720
65%
720
50%
973
March16th to endNight
53%
768
38%
2112
20%
768
68%
768
55%
1004
April1st to 15thNight
42%
566
36%
1825
15%
566
66%
566
44%
811
April16th to endNight
41%
540
39%
1800
19%
540
68%
540
47%
745
May1st to 15thNight
53%
539
31%
1736
22%
539
67%
539
48%
798
May16th to endNight
58%
563
33%
1684
20%
561
70%
561
52%
786
June1st to 15thNight
66%
540
30%
1620
24%
540
71%
540
55%
744
June16th to endNight
75%
540
24%
1620
22%
540
76%
540
48%
798
July1st to 15thNight
72%
510
16%
1530
15%
510
73%
510
29%
937
July16th to endNight
73%
564
11%
1593
11%
531
74%
531
27%
1007
August1st to 15thNight
76%
539
17%
1645
17%
536
76%
536
29%
1009
August16th to endNight
73%
573
21%
1910
22%
573
74%
573
28%
1155
September1st to 15thNight
71%
525
23%
1750
23%
525
72%
525
29%
1045
September16th to endNight
73%
638
33%
1830
24%
638
78%
638
49%
958
October1st to 15thNight
67%
660
37%
1980
24%
660
77%
660
56%
924
October16th to endNight
71%
704
41%
2112
28%
704
81%
704
60%
935
November1st to 15thNight
69%
700
43%
2100
30%
700
79%
700
63%
889
November16th to endNight
61%
720
41%
2196
29%
720
73%
720
50%
1024
December1st to 15thNight
57%
792
36%
2412
24%
792
70%
792
46%
1162
December16th to endNight
49%
768
34%
2496
26%
768
62%
768
38%
1263

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
442442445%6%56%
47729
Night
231332345%7%62%
47060
TransparencyDay
26%46%16%27%16%
47424
Night
20%48%20%29%16%
46866
SeeingDay
9%16%21%27%18%6%
5114
Night
49%19%35%27%4
15294

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
231321345%8%62%
1611
16th to endDay
3423323235%64%
1728
February1st to 15thDay
15%33312235%66%
1578
16th to endDay
141322335%6%65%
1646
March1st to 15thDay
241432445%7%59%
1980
16th to endDay
221332435%6%64%
2112
April1st to 15thDay
2212324347%64%
2121
16th to endDay
2313313235%67%
2160
May1st to 15thDay
23145%3435%5%60%
2211
16th to endDay
331332333465%
2429
June1st to 15thDay
3212314447%63%
2340
16th to endDay
23145%4445%6%58%
2340
July1st to 15thDay
7%6%36%7%47%6%6%8%34%
2340
16th to endDay
8%5%47%8%5%7%8%8%9%25%
2467
August1st to 15thDay
9%6%37%8%46%7%7%7%30%
2304
16th to endDay
6%6%36%8%5%5%6%6%7%37%
2292
September1st to 15thDay
10%5%37%6%35%5%5%6%39%
2097
16th to endDay
4414423446%59%
1797
October1st to 15thDay
421332332467%
1650
16th to endDay
321231233471%
1760
November1st to 15thDay
2212225%6%72%
1759
16th to endDay
231331324469%
1758
December1st to 15thDay
3323312346%64%
1521
16th to endDay
16%2442436%5%58%
1728
January1st to 15thNight
231331325%6%64%
2327
16th to endNight
2313423446%62%
2496
February1st to 15thNight
1313213347%67%
2274
16th to endNight
212223448%67%
1825
March1st to 15thNight
1312313336%68%
1980
16th to endNight
222113436%71%
2112
April1st to 15thNight
121231345%6%67%
1825
16th to endNight
1211213325%73%
1800
May1st to 15thNight
3213223346%66%
1736
16th to endNight
3212212336%70%
1684
June1st to 15thNight
221121335%7%68%
1620
16th to endNight
12123345%7%8%59%
1620
July1st to 15thNight
5%325%6%47%5%9%12%38%
1620
16th to endNight
5%3246%39%6%9%13%35%
1701
August1st to 15thNight
3326%5%45%6%9%11%41%
1654
16th to endNight
5%4247%35%6%8%11%39%
1910
September1st to 15thNight
6%425%6%45%6%6%10%40%
1750
16th to endNight
4313423235%65%
1830
October1st to 15thNight
3211212345%70%
1980
16th to endNight
12121223475%
2112
November1st to 15thNight
111112346%74%
2100
16th to endNight
3412222235%70%
2196
December1st to 15thNight
3312312447%65%
2412
16th to endNight
142442346%8%56%
2496

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
18%46%21%35%13%
1612
16th to endDay
23%35%17%36%14%
1728
February1st to 15thDay
20%25%23%27%20%
1578
16th to endDay
18%3320%38%15%
1646
March1st to 15thDay
22%4314%38%16%
1980
16th to endDay
19%2417%39%17%
2112
April1st to 15thDay
20%3217%38%18%
2121
16th to endDay
20%2216%36%21%
2160
May1st to 15thDay
25%4314%30%22%
2211
16th to endDay
23%35%11%32%24%
2432
June1st to 15thDay
20%4311%25%35%
2340
16th to endDay
25%45%12%24%27%
2340
July1st to 15thDay
44%6%13%14%10%10%
2201
16th to endDay
48%10%20%14%5%
2312
August1st to 15thDay
47%9%14%12%11%3
2289
16th to endDay
42%8%12%16%14%5%
2292
September1st to 15thDay
42%5%10%15%16%7%
2097
16th to endDay
25%4419%26%20%
1797
October1st to 15thDay
20%35%16%31%22%
1650
16th to endDay
16%3315%36%23%
1760
November1st to 15thDay
13%3421%36%20%
1759
16th to endDay
18%2315%35%24%
1758
December1st to 15thDay
20%37%27%29%12%
1521
16th to endDay
25%410%23%28%8%
1728
January1st to 15thNight
20%26%22%37%10%
2327
16th to endNight
22%36%18%36%12%
2496
February1st to 15thNight
15%37%26%26%19%
2285
16th to endNight
15%2426%36%13%
1825
March1st to 15thNight
16%3419%40%15%
1980
16th to endNight
14%2420%41%15%
2112
April1st to 15thNight
16%2326%34%16%
1825
16th to endNight
14%2319%37%21%
1800
May1st to 15thNight
18%25%16%37%18%
1737
16th to endNight
16%36%16%34%22%
1685
June1st to 15thNight
15%3314%25%36%
1620
16th to endNight
19%5%9%15%20%30%
1620
July1st to 15thNight
34%8%17%16%12%10%
1530
16th to endNight
33%12%30%18%4
1593
August1st to 15thNight
31%11%21%18%13%3
1645
16th to endNight
34%9%17%19%13%5%
1910
September1st to 15thNight
34%7%18%16%14%8%
1750
16th to endNight
21%4420%29%20%
1830
October1st to 15thNight
15%37%21%30%21%
1980
16th to endNight
13%2420%34%23%
2112
November1st to 15thNight
11%2427%34%20%
2100
16th to endNight
18%1418%34%22%
2196
December1st to 15thNight
18%36%26%29%13%
2412
16th to endNight
22%5%10%26%27%6%
2496

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
10%21%30%21%14%3
90
16th to endDay
6%21%32%15%14%9%
96
February1st to 15thDay
6%8%27%30%20%6%
90
16th to endDay
441%21%17%12%2
147
March1st to 15thDay
8%25%31%22%11%1
270
16th to endDay
8%30%29%20%9%1
288
April1st to 15thDay
8%30%30%17%8%4
269
16th to endDay
13%34%29%12%8%1
270
May1st to 15thDay
10%26%31%22%6%2
288
16th to endDay
6%22%34%24%8%2
330
June1st to 15thDay
5%10%32%28%20%3
315
16th to endDay
6%6%16%35%26%8%
315
July1st to 15thDay
11%38%41%26%6%
305
16th to endDay
13%3426%28%22%
327
August1st to 15thDay
12%46%30%31%13%
315
16th to endDay
11%35%35%28%14%
332
September1st to 15thDay
17%414%34%24%4
294
16th to endDay
10%9%19%39%16%4
221
October1st to 15thDay
6%11%24%24%21%12%
90
16th to endDay
9%419%36%22%7%
96
November1st to 15thDay
10%15%22%28%18%4
90
16th to endDay
332%31%23%10%
90
December1st to 15thDay
216%35%25%17%2
90
16th to endDay
14%22%20%31%8%2
96
January1st to 15thNight
411%20%38%19%5%
720
16th to endNight
313%23%35%19%3
768
February1st to 15thNight
311%27%36%17%3
704
16th to endNight
218%33%33%11%
632
March1st to 15thNight
316%27%33%17%1
720
16th to endNight
214%26%39%16%1
768
April1st to 15thNight
121%30%33%11%
566
16th to endNight
219%33%29%15%
540
May1st to 15thNight
48%27%42%15%1
540
16th to endNight
5%6%25%40%21%1
563
June1st to 15thNight
2320%48%22%1
540
16th to endNight
2212%41%40%2
540
July1st to 15thNight
6%2431%48%7%
510
16th to endNight
6%1320%54%13%
564
August1st to 15thNight
42117%59%15%
539
16th to endNight
5%2323%53%11%
573
September1st to 15thNight
8%2330%48%6%
525
16th to endNight
5%310%32%42%6%
638
October1st to 15thNight
45%18%42%24%4
660
16th to endNight
25%16%37%30%6%
704
November1st to 15thNight
25%20%38%28%4
700
16th to endNight
5%11%17%32%26%7%
720
December1st to 15thNight
5%13%18%37%21%3
792
16th to endNight
214%26%38%14%2
768
Page generated at 2017-09-11 17:35:22. Version ac04

Copyright 2017 A. Danko


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