Observaterry
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observaterry clear sky chart from 2005-11-06 to 2024-03-18.

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
65%
23924
33%
79841
26%
23838
74%
23838
47%
37524

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 10thNight
64%
750
38%
3991
31%
736
74%
736
35%
1558
January11th to 20thNight
61%
753
43%
3897
30%
740
72%
740
44%
1288
January21st to endNight
57%
828
25%
4261
28%
814
73%
814
30%
2020
February1st to 10thNight
60%
760
38%
2464
27%
760
76%
760
58%
1059
February11th to 20thNight
55%
740
34%
2218
23%
740
67%
740
51%
1096
February21st to endNight
45%
628
36%
1837
21%
628
61%
628
53%
889
March1st to 10thNight
51%
760
40%
2090
21%
760
67%
760
55%
1041
March11th to 20thNight
57%
752
37%
2068
22%
752
69%
752
57%
1013
March21st to endNight
50%
792
39%
2178
17%
792
68%
792
57%
1059
April1st to 10thNight
52%
540
40%
1800
25%
540
73%
540
59%
728
April11th to 20thNight
49%
533
38%
1777
24%
533
69%
533
54%
768
April21st to endNight
52%
540
41%
1800
27%
540
74%
540
57%
728
May1st to 10thNight
57%
540
36%
1800
29%
540
71%
540
59%
736
May11th to 20thNight
66%
531
30%
1720
28%
531
73%
531
51%
794
May21st to endNight
65%
583
35%
1746
27%
582
75%
582
59%
785
June1st to 10thNight
72%
540
30%
1620
26%
540
76%
540
52%
765
June11th to 20thNight
75%
540
32%
1620
28%
540
78%
540
61%
715
June21st to endNight
75%
540
21%
1620
21%
540
76%
540
42%
886
July1st to 10thNight
75%
525
20%
1575
19%
525
75%
525
33%
926
July11th to 20thNight
77%
522
19%
1566
18%
522
78%
522
29%
975
July21st to endNight
72%
591
16%
1674
16%
558
72%
558
28%
1052
August1st to 10thNight
81%
537
18%
1654
18%
534
81%
534
33%
966
August11th to 20thNight
75%
534
22%
1778
23%
534
76%
534
31%
1039
August21st to endNight
81%
594
23%
1980
27%
594
82%
594
32%
1142
September1st to 10thNight
75%
540
25%
1800
29%
540
76%
540
34%
1019
September11th to 20thNight
81%
540
37%
1800
39%
540
83%
540
43%
903
September21st to endNight
76%
688
34%
2046
26%
688
81%
688
52%
1008
October1st to 10thNight
72%
720
32%
2160
25%
720
76%
720
50%
1086
October11th to 20thNight
73%
720
42%
2160
30%
720
80%
720
63%
945
October21st to endNight
74%
792
43%
2376
30%
792
82%
792
63%
1029
November1st to 10thNight
77%
740
44%
2220
33%
740
85%
740
69%
917
November11th to 20thNight
74%
760
43%
2280
32%
760
82%
760
64%
990
November21st to endNight
62%
862
41%
2382
27%
862
71%
862
55%
1194
December1st to 10thNight
64%
950
37%
2588
25%
950
72%
950
54%
1320
December11th to 20thNight
57%
834
33%
2988
24%
834
68%
834
41%
1451
December21st to endNight
60%
825
25%
4307
31%
817
71%
817
38%
1634

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
331332445%8%63%
78864
Night
331332445%7%63%
80970
TransparencyDay
18%5%8%16%27%26%
78591
Night
19%48%16%28%25%
80764
SeeingDay
5%8%19%29%26%13%
13465
Night
4321%43%26%3
23967

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 10thDay
2313425%5%6%7%63%
2858
11th to 20thDay
221232345%7%70%
2860
21st to endDay
6%4234345%7%7%57%
3146
February1st to 10thDay
2213324347%70%
1714
11th to 20thDay
4313333446%67%
1849
21st to endDay
231222235%7%71%
1614
March1st to 10thDay
331332445%7%64%
2090
11th to 20thDay
3324323436%68%
2058
21st to endDay
121232445%7%69%
2178
April1st to 10thDay
1211213346%75%
2159
11th to 20thDay
221231323475%
2131
21st to endDay
1112213346%77%
2160
May1st to 10thDay
2112223336%75%
2160
11th to 20thDay
22123245%5%7%68%
2169
21st to endDay
2112223335%77%
2530
June1st to 10thDay
12123235%6%10%64%
2340
11th to 20thDay
221122335%6%74%
2340
21st to endDay
6%314435%5%7%9%55%
2340
July1st to 10thDay
5%315%5%46%7%8%10%46%
2340
11th to 20thDay
32245%47%7%10%13%43%
2340
21st to endDay
5%325%6%5%8%8%9%11%39%
2545
August1st to 10thDay
42146%47%9%9%12%42%
2275
11th to 20thDay
43245%35%6%10%12%45%
2123
21st to endDay
4313436%7%8%12%49%
2376
September1st to 10thDay
6%4244346%6%10%51%
2160
11th to 20thDay
6%31443445%6%59%
2160
21st to endDay
321222335%7%70%
1908
October1st to 10thDay
4213423446%67%
1800
11th to 20thDay
4212312345%74%
1800
21st to endDay
2212312235%78%
1980
November1st to 10thDay
2212212346%75%
1859
11th to 20thDay
232231235%6%73%
1900
21st to endDay
5%323323446%64%
1770
December1st to 10thDay
4413312439%65%
1587
11th to 20thDay
45%35%5%34346%59%
2099
21st to endDay
231233445%8%65%
3146
January1st to 10thNight
3415%434346%62%
4097
11th to 20thNight
3212222347%72%
4110
21st to endNight
5%5%25%4235%7%7%55%
4521
February1st to 10thNight
131222345%7%70%
2464
11th to 20thNight
4423323435%67%
2218
21st to endNight
3312423347%68%
1837
March1st to 10thNight
33242235%5%7%66%
2090
11th to 20thNight
4213323346%69%
2068
21st to endNight
3213323346%71%
2178
April1st to 10thNight
211232335%7%72%
1800
11th to 20thNight
3212323345%71%
1777
21st to endNight
2112223446%73%
1800
May1st to 10thNight
3212322345%75%
1800
11th to 20thNight
421232345%7%66%
1720
21st to endNight
2212223245%74%
1746
June1st to 10thNight
32133245%6%7%64%
1620
11th to 20thNight
22231345%6%71%
1620
21st to endNight
34245%35%5%8%9%54%
1620
July1st to 10thNight
5%3246%47%7%8%11%43%
1620
11th to 20thNight
25%26%7%5%7%8%9%13%37%
1620
21st to endNight
6%336%6%5%6%7%8%13%36%
1773
August1st to 10thNight
3325%5%47%9%11%14%38%
1663
11th to 20thNight
6%225%6%46%8%10%11%40%
1778
21st to endNight
5%3245%36%7%9%12%43%
1980
September1st to 10thNight
6%325%5%46%5%7%9%48%
1800
11th to 20thNight
6%3234245%6%7%59%
1800
21st to endNight
4314423346%67%
2046
October1st to 10thNight
431332446%7%63%
2160
11th to 20thNight
421221222477%
2160
21st to endNight
221222233477%
2376
November1st to 10thNight
2111213346%77%
2220
11th to 20thNight
2312222246%75%
2280
21st to endNight
5%312323347%66%
2382
December1st to 10thNight
5%31332335%8%65%
2588
11th to 20thNight
33245%2446%8%59%
3117
21st to endNight
3313323447%66%
4521

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 10thDay
16%46%15%41%17%
2859
11th to 20thDay
12%47%20%43%14%
2860
21st to endDay
23%5%7%24%28%13%
3146
February1st to 10thDay
16%26%17%30%30%
1714
11th to 20thDay
19%35%15%32%27%
1859
21st to endDay
14%349%32%38%
1614
March1st to 10thDay
20%3410%33%29%
2090
11th to 20thDay
19%35%12%26%36%
2058
21st to endDay
15%35%11%31%34%
2178
April1st to 10thDay
12%3411%31%39%
2159
11th to 20thDay
14%239%28%45%
2134
21st to endDay
10%2411%31%41%
2160
May1st to 10thDay
13%2310%24%48%
2160
11th to 20thDay
17%5%6%12%25%35%
2172
21st to endDay
11%25%10%22%49%
2530
June1st to 10thDay
14%46%14%23%38%
2340
11th to 20thDay
10%349%21%52%
2340
21st to endDay
23%6%9%14%17%30%
2340
July1st to 10thDay
28%8%12%17%17%18%
2276
11th to 20thDay
26%10%17%23%17%8%
2271
21st to endDay
31%12%19%22%12%4
2404
August1st to 10thDay
26%11%18%22%16%6%
2260
11th to 20thDay
27%9%16%21%17%9%
2123
21st to endDay
23%10%15%21%22%8%
2376
September1st to 10thDay
28%6%11%18%23%15%
2160
11th to 20thDay
23%6%7%19%24%21%
2160
21st to endDay
15%5%6%17%33%25%
1908
October1st to 10thDay
18%49%15%25%29%
1800
11th to 20thDay
15%2410%29%40%
1800
21st to endDay
11%2318%36%30%
1980
November1st to 10thDay
12%25%18%35%29%
1859
11th to 20thDay
13%35%19%31%29%
1900
21st to endDay
21%45%15%34%21%
1770
December1st to 10thDay
18%35%23%35%15%
1587
11th to 20thDay
28%36%20%31%13%
2098
21st to endDay
14%38%19%36%19%
3146
January1st to 10thNight
20%45%16%40%14%
4097
11th to 20thNight
14%47%17%45%14%
4110
21st to endNight
25%5%7%21%30%12%
4521
February1st to 10thNight
14%46%18%28%30%
2464
11th to 20thNight
21%35%14%29%29%
2218
21st to endNight
18%35%10%29%36%
1837
March1st to 10thNight
18%35%14%29%31%
2090
11th to 20thNight
17%25%14%29%32%
2068
21st to endNight
16%35%12%34%31%
2178
April1st to 10thNight
12%36%11%34%34%
1800
11th to 20thNight
16%3411%27%40%
1777
21st to endNight
12%35%12%30%38%
1800
May1st to 10thNight
14%2311%23%47%
1800
11th to 20thNight
18%48%11%23%35%
1721
21st to endNight
14%45%10%18%50%
1746
June1st to 10thNight
17%5%6%15%22%34%
1620
11th to 20thNight
14%36%9%18%51%
1620
21st to endNight
26%6%12%13%16%28%
1620
July1st to 10thNight
31%8%13%16%18%14%
1575
11th to 20thNight
32%12%16%18%14%7%
1566
21st to endNight
34%11%22%20%10%4
1674
August1st to 10thNight
27%12%20%25%11%5%
1654
11th to 20thNight
31%9%18%19%15%8%
1778
21st to endNight
28%11%16%23%17%6%
1980
September1st to 10thNight
30%7%13%18%17%15%
1800
11th to 20thNight
22%6%11%20%20%22%
1800
21st to endNight
19%47%16%30%23%
2046
October1st to 10thNight
20%5%9%14%23%29%
2160
11th to 20thNight
14%1411%25%44%
2160
21st to endNight
13%2416%32%34%
2376
November1st to 10thNight
10%2417%35%32%
2220
11th to 20thNight
13%2416%32%33%
2280
21st to endNight
19%35%16%34%23%
2382
December1st to 10thNight
19%36%20%32%20%
2588
11th to 20thNight
22%49%20%33%12%
3117
21st to endNight
18%45%17%38%18%
4521

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 10thDay
7%7%20%45%19%2
270
11th to 20thDay
7%420%43%21%4
270
21st to endDay
5%7%25%35%22%5%
297
February1st to 10thDay
411%20%39%20%6%
270
11th to 20thDay
9%9%27%42%14%1
270
21st to endDay
10%19%29%32%7%3
269
March1st to 10thDay
7%19%32%31%9%2
460
11th to 20thDay
8%19%26%29%14%4
449
21st to endDay
5%23%35%24%11%2
462
April1st to 10thDay
5%14%37%27%13%4
420
11th to 20thDay
6%22%31%29%10%2
412
21st to endDay
418%32%28%14%3
420
May1st to 10thDay
214%35%27%18%3
423
11th to 20thDay
39%27%34%20%7%
448
21st to endDay
39%35%30%20%4
485
June1st to 10thDay
3223%32%30%9%
450
11th to 20thDay
26%21%32%28%12%
450
21st to endDay
6%213%29%33%16%
450
July1st to 10thDay
426%22%39%27%
446
11th to 20thDay
2319%38%37%
444
21st to endDay
31315%40%38%
487
August1st to 10thDay
21319%40%34%
447
11th to 20thDay
417%19%43%26%
437
21st to endDay
41319%41%32%
495
September1st to 10thDay
7%18%22%38%25%
450
11th to 20thDay
49%32%35%19%
450
21st to endDay
36%12%29%30%20%
350
October1st to 10thDay
5%315%26%36%16%
270
11th to 20thDay
6%315%31%30%14%
270
21st to endDay
6%7%13%24%37%13%
297
November1st to 10thDay
7%5%21%34%25%7%
270
11th to 20thDay
26%13%35%36%9%
270
21st to endDay
8%10%19%38%20%5%
270
December1st to 10thDay
9%5%18%39%28%2
270
11th to 20thDay
46%25%43%20%1
270
21st to endDay
7%9%21%44%16%2
297
January1st to 10thNight
5%322%49%19%3
760
11th to 20thNight
6%327%45%19%2
760
21st to endNight
5%5%28%44%17%1
836
February1st to 10thNight
35%29%43%20%1
760
11th to 20thNight
6%5%30%49%10%1
744
21st to endNight
48%40%41%7%
628
March1st to 10thNight
45%37%43%11%1
760
11th to 20thNight
45%29%43%17%1
752
21st to endNight
36%37%43%11%
792
April1st to 10thNight
25%37%47%8%
540
11th to 20thNight
47%37%43%9%
533
21st to endNight
27%35%44%11%
540
May1st to 10thNight
35%33%49%11%
540
11th to 20thNight
4321%52%19%1
531
21st to endNight
2226%56%13%1
584
June1st to 10thNight
3118%52%25%1
540
11th to 20thNight
2118%55%24%
540
21st to endNight
2211%48%34%2
540
July1st to 10thNight
5%16%33%49%5%
525
11th to 20thNight
3326%60%8%
522
21st to endNight
6%15%19%60%10%
591
August1st to 10thNight
31320%59%13%
537
11th to 20thNight
5%15%25%55%8%
534
21st to endNight
41324%60%7%
594
September1st to 10thNight
7%15%35%48%4
540
11th to 20thNight
5%15%42%44%2
540
21st to endNight
4113%42%38%2
688
October1st to 10thNight
6%216%46%28%3
720
11th to 20thNight
5%217%48%26%3
720
21st to endNight
3316%41%32%5%
792
November1st to 10thNight
2216%47%31%3
740
11th to 20thNight
3218%46%27%4
760
21st to endNight
7%423%41%23%3
862
December1st to 10thNight
7%321%47%21%1
950
11th to 20thNight
5%327%44%19%1
836
21st to endNight
5%327%49%14%2
836
Page generated at 2024-03-15 12:01:44. Version ac07

Copyright © 2024 Attilla Danko.


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