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 2017-05-01.

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%
15381
34%
45587
26%
15329
73%
15329
46%
22070

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
64%
605
29%
1601
18%
605
67%
605
43%
864
May16th to endNight
66%
513
29%
1541
18%
513
72%
513
49%
724
June1st to 15thNight
74%
362
31%
1352
29%
362
81%
362
43%
577
June16th to endNight
77%
330
34%
1320
34%
330
85%
330
56%
437
July1st to 15thNight
79%
310
35%
1240
38%
310
83%
310
52%
442
July16th to endNight
75%
569
33%
1507
24%
529
83%
529
57%
696
August1st to 15thNight
84%
657
38%
1640
25%
653
85%
653
67%
767
August16th to endNight
85%
700
40%
1750
23%
700
88%
700
70%
795
September1st to 15thNight
82%
660
42%
1653
31%
660
84%
660
64%
803
September16th to endNight
84%
656
41%
1815
35%
656
89%
656
70%
761
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%
46146
Night
4212212336%68%
45790
TransparencyDay
18%37%17%27%24%
45837
Night
18%37%17%26%26%
45599
SeeingDay
5%14%22%34%18%4
5422
Night
5%16%8%26%33%10%
15388

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
4412222248%64%
2028
16th to endDay
2312212338%68%
2221
June1st to 15thDay
4413312349%60%
2274
16th to endDay
11112235%78%
2310
July1st to 15thDay
1212213247%70%
2310
16th to endDay
2112212336%72%
2234
August1st to 15thDay
2211112225%77%
1980
16th to endDay
212235%79%
2100
September1st to 15thDay
11112225%80%
1977
16th to endDay
111211225%79%
1815
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
4312212346%66%
1601
16th to endNight
1212213226%73%
1540
June1st to 15thNight
1112113448%69%
1352
16th to endNight
11111135%81%
1320
July1st to 15thNight
121212235%76%
1320
16th to endNight
2111212247%72%
1621
August1st to 15thNight
211111237%77%
1650
16th to endNight
1112226%80%
1750
September1st to 15thNight
21111112478%
1653
16th to endNight
11111225%81%
1815
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%20%24%20%
2028
16th to endDay
15%5%10%30%30%8%
2224
June1st to 15thDay
22%310%16%30%15%
2274
16th to endDay
10%16%11%37%31%
2310
July1st to 15thDay
14%35%13%28%35%
2161
16th to endDay
14%37%20%30%23%
2085
August1st to 15thDay
11%1315%37%30%
1966
16th to endDay
8%15%12%41%31%
2100
September1st to 15thDay
9%25%13%28%40%
1977
16th to endDay
10%1414%34%34%
1815
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%26%17%
1602
16th to endNight
14%410%28%31%10%
1541
June1st to 15thNight
14%6%12%18%32%15%
1352
16th to endNight
8%18%14%36%30%
1320
July1st to 15thNight
11%28%13%25%38%
1240
16th to endNight
14%37%25%26%24%
1507
August1st to 15thNight
9%26%14%35%31%
1640
16th to endNight
8%16%13%38%31%
1750
September1st to 15thNight
11%25%13%27%39%
1653
16th to endNight
7%17%13%32%38%
1815
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%20%27%27%13%2
229
16th to endDay
320%26%33%12%3
266
June1st to 15thDay
6%14%23%36%17%2
255
16th to endDay
12%8%38%29%10%
255
July1st to 15thDay
18%8%45%30%5%
245
16th to endDay
211%7%29%36%12%
271
August1st to 15thDay
27%7%47%29%6%
255
16th to endDay
5%8%41%35%8%
268
September1st to 15thDay
16%14%45%24%6%
255
16th to endDay
9%15%44%22%7%
255
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
5%19%6%28%34%5%
606
16th to endNight
119%9%26%38%4
515
June1st to 15thNight
18%325%42%9%
362
16th to endNight
118%16%55%7%
330
July1st to 15thNight
212%7%54%22%
310
16th to endNight
217%5%49%24%
569
August1st to 15thNight
110%11%55%19%
657
16th to endNight
19%10%49%29%
700
September1st to 15thNight
29%213%49%22%
660
16th to endNight
19%120%50%16%
656
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 2017-05-02 05:43:34. Version ac04

Copyright 2017 A. Danko


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