Rolling Roof Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rolling Roof Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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%
15839
34%
46918
26%
15787
73%
15787
46%
22696

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
50%
720
29%
2437
22%
716
62%
716
33%
1192
January16th to endNight
45%
768
34%
2424
21%
768
63%
768
32%
1269
February1st to 15thNight
55%
700
36%
2101
28%
696
67%
696
38%
1085
February16th to endNight
54%
632
27%
1895
24%
632
62%
632
31%
1086
March1st to 15thNight
58%
720
28%
2157
23%
720
68%
720
41%
1071
March16th to endNight
62%
768
31%
1989
22%
768
69%
768
43%
1101
April1st to 15thNight
59%
719
31%
1799
18%
719
65%
719
44%
1001
April16th to endNight
65%
720
32%
1800
15%
720
70%
720
52%
932
May1st to 15thNight
65%
656
28%
1736
17%
656
68%
656
45%
933
May16th to endNight
68%
561
31%
1685
20%
561
73%
561
49%
790
June1st to 15thNight
74%
395
29%
1475
28%
395
81%
395
43%
637
June16th to endNight
79%
360
37%
1440
38%
360
86%
360
57%
475
July1st to 15thNight
80%
340
33%
1360
36%
340
84%
340
53%
482
July16th to endNight
76%
615
34%
1637
25%
575
84%
575
57%
763
August1st to 15thNight
83%
717
36%
1790
23%
713
85%
713
66%
849
August16th to endNight
85%
764
42%
1910
25%
764
88%
764
70%
872
September1st to 15thNight
82%
720
39%
1803
29%
720
84%
720
63%
888
September16th to endNight
84%
692
42%
1914
37%
692
89%
692
70%
803
October1st to 15thNight
75%
660
36%
1870
36%
660
79%
660
53%
899
October16th to endNight
70%
704
41%
2112
36%
704
79%
704
51%
974
November1st to 15thNight
66%
700
36%
2267
34%
700
74%
700
50%
978
November16th to endNight
57%
720
38%
2340
29%
720
71%
720
43%
1067
December1st to 15thNight
53%
720
35%
2340
28%
720
66%
720
34%
1186
December16th to endNight
45%
768
32%
2637
23%
768
61%
768
29%
1363

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
4312212336%67%
47982
Night
4212212336%68%
47121
TransparencyDay
18%37%17%27%24%
47673
Night
18%37%17%26%26%
46930
SeeingDay
5%13%21%33%20%6%
5998
Night
5%15%8%26%34%10%
15846

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
7%313322335%62%
1498
16th to endDay
11%422312235%59%
1797
February1st to 15thDay
8%313212336%61%
1751
16th to endDay
10%414423336%54%
1579
March1st to 15thDay
44133235%46%61%
1800
16th to endDay
431332435%9%57%
2235
April1st to 15thDay
6%413312347%60%
2149
16th to endDay
5%212211237%69%
2160
May1st to 15thDay
4412212348%64%
2211
16th to endDay
2312212338%68%
2429
June1st to 15thDay
4423312348%60%
2481
16th to endDay
11112235%79%
2520
July1st to 15thDay
1212213236%71%
2520
16th to endDay
2112212336%72%
2411
August1st to 15thDay
221112225%76%
2160
16th to endDay
1212235%79%
2292
September1st to 15thDay
111112225%78%
2157
16th to endDay
111211225%78%
1904
October1st to 15thDay
5%23212345%69%
1757
16th to endDay
331321224470%
1760
November1st to 15thDay
3113223335%69%
1590
16th to endDay
4213323236%64%
1620
December1st to 15thDay
6%42331345%9%56%
1620
16th to endDay
10%313323347%55%
1581
January1st to 15thNight
7%412323346%59%
2437
16th to endNight
10%413212226%60%
2424
February1st to 15thNight
6%32321235%5%61%
2101
16th to endNight
13%313323345%54%
1895
March1st to 15thNight
4323213446%62%
2157
16th to endNight
4313323346%61%
1989
April1st to 15thNight
6%413213245%65%
1799
16th to endNight
3211212247%70%
1800
May1st to 15thNight
3312212346%66%
1736
16th to endNight
1212213226%73%
1684
June1st to 15thNight
1112213448%68%
1475
16th to endNight
1111113482%
1440
July1st to 15thNight
121212235%76%
1440
16th to endNight
2111212247%71%
1751
August1st to 15thNight
211111237%76%
1800
16th to endNight
1112236%79%
1910
September1st to 15thNight
21111222476%
1803
16th to endNight
11111235%81%
1914
October1st to 15thNight
311221334470%
1870
16th to endNight
3311212235%72%
2112
November1st to 15thNight
321211223473%
2267
16th to endNight
3213212336%67%
2340
December1st to 15thNight
7%323323346%60%
2340
16th to endNight
11%412222336%59%
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
24%37%12%25%25%
1498
16th to endDay
28%36%17%18%26%
1797
February1st to 15thDay
24%35%14%27%23%
1751
16th to endDay
31%38%18%27%10%
1579
March1st to 15thDay
23%39%19%23%20%
1800
16th to endDay
23%413%23%19%15%
2235
April1st to 15thDay
23%410%25%24%11%
2149
16th to endDay
16%310%22%29%16%
2160
May1st to 15thDay
20%49%21%25%18%
2211
16th to endDay
15%5%11%28%29%9%
2432
June1st to 15thDay
22%310%17%30%16%
2481
16th to endDay
10%16%11%35%35%
2520
July1st to 15thDay
14%35%12%28%36%
2371
16th to endDay
14%37%21%30%22%
2262
August1st to 15thDay
11%1314%37%31%
2146
16th to endDay
8%15%11%41%31%
2292
September1st to 15thDay
10%25%13%29%38%
2157
16th to endDay
11%1414%34%33%
1904
October1st to 15thDay
17%36%20%24%26%
1757
16th to endDay
17%3414%23%35%
1760
November1st to 15thDay
18%25%14%25%33%
1590
16th to endDay
20%36%14%21%32%
1620
December1st to 15thDay
25%5%7%16%23%22%
1620
16th to endDay
28%47%18%21%19%
1581
January1st to 15thNight
24%27%12%25%25%
2437
16th to endNight
27%27%13%16%32%
2424
February1st to 15thNight
23%35%16%24%26%
2112
16th to endNight
32%37%15%25%15%
1895
March1st to 15thNight
20%310%18%26%19%
2157
16th to endNight
22%5%10%22%23%16%
1989
April1st to 15thNight
22%38%27%24%12%
1799
16th to endNight
15%49%24%27%19%
1800
May1st to 15thNight
19%6%9%20%27%16%
1737
16th to endNight
14%410%27%30%12%
1685
June1st to 15thNight
15%6%12%18%31%15%
1475
16th to endNight
8%18%13%33%35%
1440
July1st to 15thNight
11%27%13%25%40%
1360
16th to endNight
14%37%25%25%23%
1637
August1st to 15thNight
10%26%14%33%32%
1790
16th to endNight
8%16%13%39%31%
1910
September1st to 15thNight
13%26%12%27%37%
1803
16th to endNight
7%17%14%32%36%
1914
October1st to 15thNight
16%35%18%27%28%
1870
16th to endNight
16%3414%22%38%
2112
November1st to 15thNight
15%26%14%25%35%
2267
16th to endNight
18%26%17%21%33%
2340
December1st to 15thNight
25%37%15%21%26%
2340
16th to endNight
27%47%16%23%21%
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
14%15%41%23%3
126
16th to endDay
14%25%27%24%7%1
267
February1st to 15thDay
10%18%31%28%8%3
266
16th to endDay
14%19%27%27%9%
238
March1st to 15thDay
5%22%30%24%13%3
270
16th to endDay
417%30%32%10%3
288
April1st to 15thDay
7%20%31%26%9%5%
269
16th to endDay
123%34%29%6%4
270
May1st to 15thDay
7%18%28%26%15%3
288
16th to endDay
316%25%34%14%4
330
June1st to 15thDay
6%12%21%34%19%5%
315
16th to endDay
110%7%35%33%12%
315
July1st to 15thDay
16%6%40%33%11%
305
16th to endDay
29%6%29%37%14%
327
August1st to 15thDay
35%6%45%31%7%
315
16th to endDay
47%39%36%11%
332
September1st to 15thDay
25%16%44%24%6%
315
16th to endDay
19%15%43%23%6%
288
October1st to 15thDay
212%27%38%16%3
255
16th to endDay
312%23%35%22%2
272
November1st to 15thDay
46%15%34%18%20%
96
16th to endDay
411%28%32%20%3
90
December1st to 15thDay
5%10%20%33%28%2
90
16th to endDay
7%18%32%28%12%1
71
January1st to 15thNight
8%19%15%32%18%6%
720
16th to endNight
12%20%15%30%17%3
768
February1st to 15thNight
6%18%14%33%20%5%
704
16th to endNight
13%17%8%34%22%3
632
March1st to 15thNight
5%19%11%33%25%5%
720
16th to endNight
5%18%8%31%31%4
768
April1st to 15thNight
6%18%10%31%28%4
719
16th to endNight
419%8%29%32%6%
720
May1st to 15thNight
417%6%29%34%6%
657
16th to endNight
117%9%28%37%5%
563
June1st to 15thNight
116%325%43%9%
395
16th to endNight
116%16%55%9%
360
July1st to 15thNight
211%6%56%22%
340
16th to endNight
216%5%51%23%
615
August1st to 15thNight
19%11%56%19%
717
16th to endNight
18%9%49%29%
764
September1st to 15thNight
28%216%48%21%
720
16th to endNight
18%120%50%17%
692
October1st to 15thNight
410%5%30%40%9%
660
16th to endNight
6%9%9%27%35%12%
704
November1st to 15thNight
315%10%34%25%10%
700
16th to endNight
5%18%14%27%26%8%
720
December1st to 15thNight
8%19%12%32%22%5%
720
16th to endNight
13%21%14%29%17%3
768
Page generated at 2017-09-25 06:02:19. Version ac04

Copyright 2017 A. Danko


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