Xanadu Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Xanadu Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
75%
15736
36%
47417
31%
15698
80%
15698
53%
22660

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
69%
718
32%
2327
32%
716
74%
716
51%
1080
January16th to endNight
65%
768
34%
2496
32%
768
74%
768
41%
1281
February1st to 15thNight
70%
699
37%
2211
34%
699
79%
699
52%
1029
February16th to endNight
65%
632
39%
1828
34%
632
72%
632
49%
929
March1st to 15thNight
65%
720
40%
1980
30%
720
73%
720
55%
987
March16th to endNight
75%
768
39%
2112
28%
768
82%
768
61%
999
April1st to 15thNight
68%
679
35%
1938
25%
679
76%
679
56%
932
April16th to endNight
73%
540
45%
1797
40%
540
83%
540
70%
663
May1st to 15thNight
75%
539
41%
1619
31%
539
82%
539
72%
638
May16th to endNight
78%
561
42%
1684
35%
561
82%
561
75%
664
June1st to 15thNight
84%
540
35%
1620
30%
540
85%
540
70%
671
June16th to endNight
85%
540
32%
1620
27%
540
86%
540
61%
714
July1st to 15thNight
83%
510
21%
1530
18%
510
83%
510
41%
834
July16th to endNight
80%
564
18%
1593
16%
531
79%
531
30%
989
August1st to 15thNight
87%
539
25%
1611
23%
536
87%
536
41%
881
August16th to endNight
85%
587
31%
1871
32%
587
85%
587
39%
1012
September1st to 15thNight
78%
720
29%
1980
24%
720
79%
720
42%
1147
September16th to endNight
82%
716
45%
1980
34%
716
87%
716
67%
901
October1st to 15thNight
82%
720
40%
2097
33%
720
86%
720
66%
924
October16th to endNight
86%
768
45%
2304
41%
768
89%
768
67%
988
November1st to 15thNight
78%
700
43%
2100
36%
700
84%
700
65%
899
November16th to endNight
71%
720
38%
2283
35%
720
77%
720
51%
1066
December1st to 15thNight
70%
720
37%
2340
38%
720
75%
720
48%
1109
December16th to endNight
65%
768
34%
2496
34%
768
71%
768
39%
1323

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
3212323446%64%
48329
Night
3212313346%67%
47613
TransparencyDay
19%45%11%25%33%
48024
Night
18%35%13%26%32%
47419
SeeingDay
6%9%24%33%19%5%
5550
Night
4212%37%35%7%
15746

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
6%113213346%65%
1611
16th to endDay
7%413313336%60%
1728
February1st to 15thDay
5%223312235%67%
1649
16th to endDay
7%313323345%61%
1645
March1st to 15thDay
5%212213336%66%
1980
16th to endDay
31121233474%
2112
April1st to 15thDay
2111312346%70%
2009
16th to endDay
11111122481%
2160
May1st to 15thDay
1121223478%
2331
16th to endDay
1111222481%
2429
June1st to 15thDay
111111235%78%
2340
16th to endDay
11121335%7%70%
2340
July1st to 15thDay
32147%36%6%7%11%44%
2340
16th to endDay
6%5%26%7%48%8%8%10%30%
2467
August1st to 15thDay
4425%5%47%6%7%8%42%
2340
16th to endDay
3215%5%46%7%6%8%48%
2326
September1st to 15thDay
4325%5%45%6%6%7%48%
1980
16th to endDay
311222243471%
1980
October1st to 15thDay
21111224474%
1863
16th to endDay
111212235%77%
1918
November1st to 15thDay
11112346%75%
1759
16th to endDay
421221333470%
1674
December1st to 15thDay
8%213213345%63%
1620
16th to endDay
6%312313346%60%
1728
January1st to 15thNight
5%31221334466%
2327
16th to endNight
7%323224445%59%
2496
February1st to 15thNight
4212213335%67%
2200
16th to endNight
6%312324346%62%
1828
March1st to 15thNight
5%212212335%68%
1980
16th to endNight
322212335%72%
2112
April1st to 15thNight
2212313335%69%
1938
16th to endNight
1111112384%
1797
May1st to 15thNight
11225%5%78%
1619
16th to endNight
1111112384%
1684
June1st to 15thNight
11111122480%
1620
16th to endNight
11232336%72%
1620
July1st to 15thNight
1214336%6%7%12%49%
1620
16th to endNight
3215%6%37%7%10%15%35%
1701
August1st to 15thNight
1113425%6%7%10%54%
1620
16th to endNight
22135%35%5%8%10%51%
1871
September1st to 15thNight
33145%25%5%5%8%53%
1980
16th to endNight
21121223475%
1980
October1st to 15thNight
11121323476%
2097
16th to endNight
2121222379%
2304
November1st to 15thNight
112211235%75%
2100
16th to endNight
5%22313335%68%
2283
December1st to 15thNight
7%22212337%64%
2340
16th to endNight
8%314323335%59%
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%35%13%29%28%
1612
16th to endDay
24%3214%27%27%
1728
February1st to 15thDay
21%2412%26%33%
1649
16th to endDay
23%4212%29%26%
1645
March1st to 15thDay
18%226%33%35%
1980
16th to endDay
14%228%33%38%
2112
April1st to 15thDay
14%235%37%36%
2009
16th to endDay
9%127%26%52%
2160
May1st to 15thDay
10%227%22%54%
2331
16th to endDay
9%216%26%53%
2432
June1st to 15thDay
10%12320%61%
2340
16th to endDay
14%336%18%53%
2340
July1st to 15thDay
31%8%13%14%14%17%
2201
16th to endDay
42%11%17%19%7%2
2312
August1st to 15thDay
35%8%10%15%16%11%
2325
16th to endDay
29%7%11%18%18%14%
2326
September1st to 15thDay
30%6%9%17%16%19%
1980
16th to endDay
15%248%34%33%
1980
October1st to 15thDay
12%3312%27%40%
1863
16th to endDay
10%239%29%45%
1918
November1st to 15thDay
10%139%36%37%
1759
16th to endDay
18%239%27%38%
1674
December1st to 15thDay
22%25%15%33%21%
1620
16th to endDay
23%37%18%31%15%
1728
January1st to 15thNight
20%26%11%29%30%
2327
16th to endNight
25%3414%29%22%
2496
February1st to 15thNight
19%1414%25%33%
2211
16th to endNight
22%2412%33%24%
1828
March1st to 15thNight
18%239%28%38%
1980
16th to endNight
14%2311%33%35%
2112
April1st to 15thNight
17%237%37%31%
1938
16th to endNight
8%118%28%52%
1797
May1st to 15thNight
7%238%30%48%
1620
16th to endNight
7%126%26%55%
1685
June1st to 15thNight
9%22420%60%
1620
16th to endNight
14%245%18%55%
1620
July1st to 15thNight
23%8%16%18%15%16%
1530
16th to endNight
31%12%22%24%7%2
1593
August1st to 15thNight
22%9%13%21%21%12%
1611
16th to endNight
25%7%13%20%18%14%
1871
September1st to 15thNight
26%7%9%21%19%15%
1980
16th to endNight
12%1413%36%31%
1980
October1st to 15thNight
11%3414%26%40%
2097
16th to endNight
11%2211%25%46%
2304
November1st to 15thNight
12%1213%34%35%
2100
16th to endNight
19%249%24%38%
2283
December1st to 15thNight
20%3316%31%24%
2340
16th to endNight
27%45%16%28%18%
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
18%427%40%8%
90
16th to endDay
9%5%28%32%20%4
96
February1st to 15thDay
9%10%24%35%16%2
164
16th to endDay
13%19%34%22%9%1
238
March1st to 15thDay
7%18%32%23%14%4
270
16th to endDay
324%32%22%12%3
288
April1st to 15thDay
419%37%24%10%3
269
16th to endDay
5%25%33%24%9%1
270
May1st to 15thDay
219%37%26%10%3
288
16th to endDay
211%36%36%11%1
330
June1st to 15thDay
36%34%37%14%4
315
16th to endDay
3122%41%23%7%
315
July1st to 15thDay
410%47%26%10%
305
16th to endDay
10%17%35%30%15%
327
August1st to 15thDay
8%15%36%35%12%
315
16th to endDay
5%15%40%36%10%
332
September1st to 15thDay
10%14%41%24%7%
315
16th to endDay
6%8%26%32%19%6%
315
October1st to 15thDay
26%23%38%23%5%
198
16th to endDay
3112%40%31%9%
144
November1st to 15thDay
414%22%37%16%4
90
16th to endDay
8%8%34%31%16%
90
December1st to 15thDay
6%321%34%32%2
90
16th to endDay
17%6%36%31%8%
96
January1st to 15thNight
7%216%49%21%3
720
16th to endNight
9%315%42%25%3
768
February1st to 15thNight
5%315%42%29%3
704
16th to endNight
8%318%46%19%2
632
March1st to 15thNight
5%5%19%36%28%4
720
16th to endNight
3413%41%31%6%
768
April1st to 15thNight
4416%48%23%2
679
16th to endNight
1419%41%28%3
540
May1st to 15thNight
1417%41%30%5%
540
16th to endNight
1214%43%33%3
563
June1st to 15thNight
219%43%39%4
540
16th to endNight
25%32%52%7%
540
July1st to 15thNight
2418%61%12%
510
16th to endNight
31116%57%19%
564
August1st to 15thNight
2114%61%20%
539
16th to endNight
3117%57%19%
587
September1st to 15thNight
5%6%25%45%16%
720
16th to endNight
39%33%42%10%
716
October1st to 15thNight
210%41%37%6%
720
16th to endNight
216%39%39%10%
768
November1st to 15thNight
3212%40%34%6%
700
16th to endNight
7%116%40%29%5%
720
December1st to 15thNight
9%212%43%28%3
720
16th to endNight
11%214%45%21%4
768
Page generated at 2017-11-01 14:23:36. Version ac04

Copyright 2017 A. Danko


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