Astronomical Adventures
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astronomical Adventures 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
57%
15518
33%
46832
22%
15477
69%
15477
50%
22189

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
52%
720
32%
2327
24%
716
66%
716
46%
1091
January16th to endNight
51%
768
36%
2496
25%
768
67%
768
45%
1206
February1st to 15thNight
51%
700
33%
2241
23%
700
66%
700
51%
1011
February16th to endNight
39%
632
38%
1871
21%
632
59%
632
47%
876
March1st to 15thNight
48%
720
36%
1980
21%
720
63%
720
53%
963
March16th to endNight
47%
768
35%
2112
17%
768
63%
768
54%
1005
April1st to 15thNight
39%
672
30%
1931
11%
672
55%
672
44%
939
April16th to endNight
42%
540
40%
1707
20%
540
63%
540
55%
703
May1st to 15thNight
48%
540
34%
1619
19%
539
61%
539
56%
727
May16th to endNight
48%
561
34%
1684
19%
561
61%
561
58%
725
June1st to 15thNight
51%
540
32%
1620
20%
540
61%
540
65%
680
June16th to endNight
73%
540
33%
1620
27%
540
78%
540
68%
675
July1st to 15thNight
72%
510
19%
1530
13%
510
76%
510
39%
850
July16th to endNight
71%
564
17%
1593
13%
531
73%
531
29%
992
August1st to 15thNight
77%
539
24%
1611
20%
536
78%
536
39%
879
August16th to endNight
79%
576
31%
1809
27%
576
82%
576
43%
939
September1st to 15thNight
75%
700
29%
1925
22%
700
79%
700
47%
1052
September16th to endNight
74%
656
41%
1815
27%
656
83%
656
70%
791
October1st to 15thNight
57%
660
38%
1917
23%
660
71%
660
60%
864
October16th to endNight
66%
704
41%
2112
29%
704
76%
704
61%
932
November1st to 15thNight
62%
700
36%
2136
25%
700
75%
700
57%
940
November16th to endNight
56%
720
38%
2340
29%
720
69%
720
55%
987
December1st to 15thNight
55%
720
33%
2340
23%
720
68%
720
47%
1075
December16th to endNight
46%
768
31%
2496
22%
768
59%
768
36%
1287

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
221332445%7%62%
47793
Night
1212223347%67%
47028
TransparencyDay
20%5%9%17%28%17%
47488
Night
16%5%9%19%29%19%
46834
SeeingDay
5%13%25%30%19%5%
5347
Night
38%26%33%23%4
15524

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
141322235%6%64%
1611
16th to endDay
2313223347%64%
1728
February1st to 15thDay
1423313347%63%
1622
16th to endDay
13121245%8%67%
1602
March1st to 15thDay
121221445%8%65%
1980
16th to endDay
1213313345%67%
2112
April1st to 15thDay
212324447%65%
2015
16th to endDay
1213312346%69%
2250
May1st to 15thDay
1212213446%69%
2331
16th to endDay
2212314445%66%
2429
June1st to 15thDay
1112225%79%
2340
16th to endDay
1122434474%
2340
July1st to 15thDay
4326%6%47%7%8%7%42%
2340
16th to endDay
6%436%6%5%9%8%9%10%28%
2467
August1st to 15thDay
5%5%35%6%47%7%7%7%37%
2340
16th to endDay
42245%46%7%7%8%45%
2389
September1st to 15thDay
33145%45%6%5%7%49%
1922
16th to endDay
112212335%73%
1815
October1st to 15thDay
2212213335%72%
1711
16th to endDay
221121223474%
1760
November1st to 15thDay
11213345%74%
1721
16th to endDay
2212212235%74%
1620
December1st to 15thDay
131232345%9%61%
1620
16th to endDay
131433445%8%58%
1728
January1st to 15thNight
131231335%7%65%
2327
16th to endNight
2212314346%66%
2496
February1st to 15thNight
1212222337%70%
2230
16th to endNight
11222235%8%68%
1871
March1st to 15thNight
21121345%7%68%
1980
16th to endNight
111213346%70%
2112
April1st to 15thNight
121221445%6%67%
1931
16th to endNight
111212235%77%
1707
May1st to 15thNight
111313335%73%
1619
16th to endNight
12121323476%
1684
June1st to 15thNight
12111223478%
1620
16th to endNight
1121323478%
1620
July1st to 15thNight
22134446%8%10%51%
1620
16th to endNight
43245%37%7%7%10%41%
1701
August1st to 15thNight
323335%5%6%9%54%
1620
16th to endNight
2213325%5%7%10%55%
1809
September1st to 15thNight
121342446%8%59%
1925
16th to endNight
1111123480%
1815
October1st to 15thNight
11121234475%
1917
16th to endNight
2212211225%75%
2112
November1st to 15thNight
112212446%71%
2136
16th to endNight
2112112235%75%
2340
December1st to 15thNight
21221345%8%65%
2340
16th to endNight
241332346%7%60%
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
20%5%10%24%32%6%
1612
16th to endDay
19%5%11%21%33%8%
1728
February1st to 15thDay
20%411%25%24%14%
1622
16th to endDay
15%6%9%25%32%10%
1602
March1st to 15thDay
16%48%19%38%12%
1980
16th to endDay
18%37%24%33%12%
2112
April1st to 15thDay
16%48%19%36%14%
2015
16th to endDay
15%36%17%37%19%
2250
May1st to 15thDay
14%38%18%35%20%
2331
16th to endDay
18%47%12%36%20%
2432
June1st to 15thDay
9%148%29%45%
2340
16th to endDay
12%25%7%23%48%
2340
July1st to 15thDay
34%8%10%13%12%20%
2201
16th to endDay
42%12%16%14%11%1
2312
August1st to 15thDay
39%8%12%12%15%11%
2325
16th to endDay
31%8%13%15%21%8%
2389
September1st to 15thDay
30%7%11%15%17%16%
1922
16th to endDay
13%27%14%36%24%
1815
October1st to 15thDay
16%45%16%33%23%
1711
16th to endDay
14%26%14%42%18%
1760
November1st to 15thDay
11%29%27%34%14%
1721
16th to endDay
14%36%20%36%18%
1620
December1st to 15thDay
20%6%12%26%25%7%
1620
16th to endDay
23%7%12%27%24%5%
1728
January1st to 15thNight
18%5%9%25%34%7%
2327
16th to endNight
19%5%9%20%34%10%
2496
February1st to 15thNight
15%410%24%26%18%
2241
16th to endNight
14%410%24%30%15%
1871
March1st to 15thNight
14%48%20%37%14%
1980
16th to endNight
13%48%23%34%14%
2112
April1st to 15thNight
15%48%18%34%17%
1931
16th to endNight
10%26%19%39%21%
1707
May1st to 15thNight
12%47%20%30%23%
1620
16th to endNight
11%27%14%39%23%
1685
June1st to 15thNight
10%137%27%49%
1620
16th to endNight
10%246%20%56%
1620
July1st to 15thNight
25%8%14%14%16%21%
1530
16th to endNight
32%11%18%20%12%4
1593
August1st to 15thNight
22%10%14%18%20%14%
1611
16th to endNight
21%8%16%20%22%11%
1809
September1st to 15thNight
21%6%13%19%21%17%
1925
16th to endNight
8%36%15%36%30%
1815
October1st to 15thNight
12%37%21%27%27%
1917
16th to endNight
13%27%14%36%25%
2112
November1st to 15thNight
13%39%22%33%17%
2136
16th to endNight
12%37%19%33%23%
2340
December1st to 15thNight
15%5%13%24%29%11%
2340
16th to endNight
22%8%13%24%26%5%
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
7%22%33%23%12%1
90
16th to endDay
8%20%26%27%13%4
96
February1st to 15thDay
418%24%32%13%5%
137
16th to endDay
9%33%25%24%5%1
238
March1st to 15thDay
322%31%25%11%4
270
16th to endDay
5%22%35%23%9%3
288
April1st to 15thDay
6%24%37%17%10%4
269
16th to endDay
7%27%35%20%7%1
270
May1st to 15thDay
6%20%36%24%9%2
288
16th to endDay
420%29%26%16%2
330
June1st to 15thDay
313%37%27%11%7%
315
16th to endDay
25%23%36%26%5%
315
July1st to 15thDay
5%417%42%23%5%
305
16th to endDay
9%10%38%29%11%
327
August1st to 15thDay
5%13%34%35%10%
315
16th to endDay
5%112%35%36%9%
332
September1st to 15thDay
6%321%35%27%4
294
16th to endDay
410%22%31%26%3
255
October1st to 15thDay
215%25%35%14%5%
151
16th to endDay
7%5%27%28%30%2
96
November1st to 15thDay
6%8%20%33%20%11%
90
16th to endDay
5%18%28%31%15%
90
December1st to 15thDay
5%16%26%24%25%1
90
16th to endDay
11%18%16%39%11%2
96
January1st to 15thNight
310%29%30%19%6%
720
16th to endNight
410%30%32%17%5%
768
February1st to 15thNight
39%32%32%18%3
704
16th to endNight
219%37%25%12%2
632
March1st to 15thNight
213%32%30%15%4
720
16th to endNight
312%33%34%13%2
768
April1st to 15thNight
321%32%29%11%1
672
16th to endNight
217%35%29%11%2
540
May1st to 15thNight
18%38%37%12%1
540
16th to endNight
210%35%30%17%2
563
June1st to 15thNight
17%36%39%13%1
540
16th to endNight
1221%53%19%1
540
July1st to 15thNight
414%43%33%3
510
16th to endNight
5%9%36%41%6%
564
August1st to 15thNight
5%8%33%43%9%
539
16th to endNight
210%33%43%9%
576
September1st to 15thNight
213%30%47%6%
700
16th to endNight
15%16%32%35%9%
656
October1st to 15thNight
26%32%32%21%6%
660
16th to endNight
35%20%35%28%6%
704
November1st to 15thNight
27%26%34%24%5%
700
16th to endNight
210%28%28%21%8%
720
December1st to 15thNight
311%27%31%22%4
720
16th to endNight
5%14%30%29%15%4
768
Page generated at 2017-09-11 16:35:14. Version ac04

Copyright 2017 A. Danko


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