Yamada Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yamada Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
71%
23776
31%
74698
28%
23731
75%
23731
47%
37619

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
55%
756
17%
2646
18%
756
58%
756
26%
1592
January11th to 20thNight
63%
744
26%
2497
27%
744
66%
744
33%
1408
January21st to endNight
59%
792
26%
2574
26%
792
63%
792
33%
1485
February1st to 10thNight
60%
720
27%
2218
26%
720
65%
720
36%
1272
February11th to 20thNight
61%
700
29%
2099
28%
700
67%
700
40%
1163
February21st to endNight
55%
592
23%
1776
21%
592
61%
592
32%
1074
March1st to 10thNight
56%
720
20%
2160
18%
720
61%
720
33%
1290
March11th to 20thNight
60%
720
21%
2044
18%
720
64%
720
36%
1211
March21st to endNight
59%
792
22%
2012
16%
792
63%
792
41%
1225
April1st to 10thNight
61%
720
28%
1800
16%
720
67%
720
47%
1047
April11th to 20thNight
61%
711
32%
1779
15%
711
67%
711
49%
1000
April21st to endNight
67%
720
30%
1800
13%
720
73%
720
55%
963
May1st to 10thNight
69%
653
31%
1733
18%
653
72%
653
57%
886
May11th to 20thNight
74%
531
36%
1595
28%
531
78%
531
60%
711
May21st to endNight
69%
420
32%
1584
29%
420
77%
420
51%
645
June1st to 10thNight
79%
360
36%
1440
40%
360
84%
360
55%
538
June11th to 20thNight
81%
360
40%
1440
44%
360
90%
360
73%
449
June21st to endNight
85%
360
41%
1440
47%
360
92%
360
80%
414
July1st to 10thNight
93%
350
41%
1400
50%
350
95%
350
83%
402
July11th to 20thNight
93%
348
41%
1392
51%
348
93%
348
69%
450
July21st to endNight
88%
521
40%
1608
37%
492
90%
492
63%
655
August1st to 10thNight
87%
682
38%
1747
26%
679
89%
679
79%
776
August11th to 20thNight
92%
712
41%
1780
25%
712
93%
712
84%
784
August21st to endNight
92%
792
45%
1980
29%
792
93%
792
82%
886
September1st to 10thNight
92%
720
46%
1800
34%
720
93%
720
85%
791
September11th to 20thNight
85%
720
47%
1862
38%
720
89%
720
78%
826
September21st to endNight
86%
720
45%
1980
41%
720
90%
720
79%
827
October1st to 10thNight
80%
720
36%
2052
35%
720
85%
720
62%
944
October11th to 20thNight
79%
720
39%
2160
39%
720
84%
720
62%
950
October21st to endNight
78%
792
44%
2402
43%
792
85%
792
67%
1011
November1st to 10thNight
74%
740
32%
2405
35%
740
76%
740
47%
1159
November11th to 20thNight
72%
760
32%
2470
31%
760
78%
760
50%
1150
November21st to endNight
67%
760
29%
2470
29%
760
72%
760
41%
1286
December1st to 10thNight
60%
760
24%
2533
23%
760
65%
760
33%
1411
December11th to 20thNight
57%
759
21%
3221
23%
758
63%
758
21%
2050
December21st to endNight
53%
829
13%
4799
22%
817
58%
817
15%
2888

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
7%313323346%66%
74825
Night
8%313323346%65%
75006
TransparencyDay
21%5%9%18%26%22%
74536
Night
22%410%20%25%19%
74816
SeeingDay
8%6%23%35%23%5%
14147
Night
9%213%38%33%5%
23794

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
16%7%245%35%5%5%7%42%
1519
11th to 20thDay
12%5%2343436%7%51%
1588
21st to endDay
16%5%35%5%35%5%5%8%42%
1782
February1st to 10thDay
14%6%2332435%7%52%
1741
11th to 20thDay
13%6%25%333447%49%
1750
21st to endDay
17%7%246%2435%5%43%
1480
March1st to 10thDay
16%7%26%43445%8%40%
1800
11th to 20thDay
13%6%245%3445%8%44%
1913
21st to endDay
13%6%2432445%8%49%
2344
April1st to 10thDay
10%42442445%7%55%
2160
11th to 20thDay
11%424323346%57%
2129
21st to endDay
8%313424348%61%
2160
May1st to 10thDay
4323323346%68%
2226
11th to 20thDay
4213323445%70%
2301
21st to endDay
6%212322346%67%
2687
June1st to 10thDay
311232335%7%70%
2520
11th to 20thDay
11111122487%
2520
21st to endDay
11221122386%
2520
July1st to 10thDay
1111222386%
2520
11th to 20thDay
111121223383%
2520
21st to endDay
2112212345%77%
2611
August1st to 10thDay
11121222385%
2181
11th to 20thDay
11111122387%
2122
21st to endDay
11111123287%
2376
September1st to 10thDay
211111122386%
2160
11th to 20thDay
111121213384%
2097
21st to endDay
211222223481%
1980
October1st to 10thDay
4313322345%71%
1904
11th to 20thDay
3112222445%75%
1800
21st to endDay
5%212212245%73%
1954
November1st to 10thDay
8%31343435%6%59%
1674
11th to 20thDay
7%31332345%8%62%
1710
21st to endDay
8%423334446%59%
1710
December1st to 10thDay
11%5%2333445%6%54%
1644
11th to 20thDay
20%8%26%6%4445%6%36%
1928
21st to endDay
13%8%36%7%46%5%6%8%35%
2794
January1st to 10thNight
17%6%2442345%7%46%
2646
11th to 20thNight
10%6%2443345%8%52%
2497
21st to endNight
16%5%2331335%8%51%
2574
February1st to 10thNight
15%5%13322347%54%
2218
11th to 20thNight
12%413324347%57%
2098
21st to endNight
18%5%33313346%50%
1776
March1st to 10thNight
15%5%2442346%8%47%
2160
11th to 20thNight
13%5%2332445%7%50%
2044
21st to endNight
14%423323346%56%
2012
April1st to 10thNight
11%323323246%62%
1800
11th to 20thNight
8%313433336%64%
1779
21st to endNight
6%322322336%68%
1800
May1st to 10thNight
6%212322347%68%
1733
11th to 20thNight
5%211113336%74%
1594
21st to endNight
5%21221333474%
1584
June1st to 10thNight
4112212236%76%
1440
11th to 20thNight
1112122486%
1440
21st to endNight
1111112289%
1440
July1st to 10thNight
1112125%88%
1440
11th to 20thNight
121212223482%
1440
21st to endNight
111232334477%
1703
August1st to 10thNight
121211112285%
1756
11th to 20thNight
1211122387%
1780
21st to endNight
1121112387%
1980
September1st to 10thNight
1111212289%
1800
11th to 20thNight
121111122385%
1862
21st to endNight
211111124483%
1980
October1st to 10thNight
421221334474%
2052
11th to 20thNight
4211212345%74%
2160
21st to endNight
41221122480%
2402
November1st to 10thNight
8%312222335%67%
2405
11th to 20thNight
6%31332335%7%66%
2470
21st to endNight
9%42332345%6%59%
2470
December1st to 10thNight
12%5%24433447%53%
2533
11th to 20thNight
21%5%3443445%7%40%
3276
21st to endNight
12%7%36%7%45%5%6%8%38%
4862

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
41%7%15%20%14%3
1519
11th to 20thDay
32%8%15%19%15%12%
1588
21st to endDay
43%5%14%16%17%5%
1782
February1st to 10thDay
32%6%10%25%20%6%
1741
11th to 20thDay
34%6%11%22%19%8%
1760
21st to endDay
42%7%11%24%15%1
1480
March1st to 10thDay
40%7%12%19%18%4
1800
11th to 20thDay
36%6%13%21%19%5%
1913
21st to endDay
32%8%16%25%14%4
2344
April1st to 10thDay
27%6%14%28%20%5%
2160
11th to 20thDay
28%6%11%25%21%9%
2132
21st to endDay
22%6%10%29%27%5%
2160
May1st to 10thDay
16%6%10%25%35%8%
2226
11th to 20thDay
16%48%27%32%12%
2304
21st to endDay
17%6%8%34%29%7%
2687
June1st to 10thDay
14%49%21%34%17%
2520
11th to 20thDay
5%26%15%40%32%
2520
21st to endDay
7%239%33%47%
2520
July1st to 10thDay
6%227%25%58%
2451
11th to 20thDay
8%249%28%50%
2445
21st to endDay
9%35%12%26%45%
2466
August1st to 10thDay
7%247%29%50%
2165
11th to 20thDay
6%2210%34%46%
2122
21st to endDay
5%137%37%47%
2376
September1st to 10thDay
7%147%32%50%
2160
11th to 20thDay
7%3418%39%30%
2097
21st to endDay
10%2417%39%30%
1980
October1st to 10thDay
16%46%17%29%28%
1904
11th to 20thDay
12%5%6%21%28%28%
1800
21st to endDay
14%39%19%31%23%
1954
November1st to 10thDay
24%6%9%21%25%15%
1674
11th to 20thDay
21%5%15%25%26%10%
1710
21st to endDay
26%5%11%19%25%13%
1710
December1st to 10thDay
30%6%14%20%20%9%
1644
11th to 20thDay
48%7%12%14%12%7%
1928
21st to endDay
43%10%17%18%9%3
2794
January1st to 10thNight
38%6%13%22%18%3
2646
11th to 20thNight
31%7%13%23%16%10%
2497
21st to endNight
34%414%21%20%6%
2574
February1st to 10thNight
32%410%26%20%8%
2218
11th to 20thNight
26%6%11%26%23%7%
2099
21st to endNight
35%6%13%27%16%3
1776
March1st to 10thNight
33%6%15%21%20%4
2160
11th to 20thNight
32%5%15%22%21%5%
2044
21st to endNight
30%5%15%29%16%4
2012
April1st to 10thNight
26%5%13%29%20%8%
1800
11th to 20thNight
23%411%30%23%8%
1779
21st to endNight
19%414%30%31%3
1800
May1st to 10thNight
17%5%9%24%35%10%
1733
11th to 20thNight
14%38%28%35%12%
1595
21st to endNight
15%49%29%32%11%
1584
June1st to 10thNight
13%38%24%32%19%
1440
11th to 20thNight
6%3417%37%34%
1440
21st to endNight
4128%34%50%
1440
July1st to 10thNight
4126%27%60%
1400
11th to 20thNight
8%2410%24%53%
1392
21st to endNight
11%349%27%46%
1608
August1st to 10thNight
9%1210%26%52%
1747
11th to 20thNight
5%229%34%48%
1780
21st to endNight
7%117%36%48%
1980
September1st to 10thNight
5%228%26%58%
1800
11th to 20thNight
7%3313%43%31%
1862
21st to endNight
8%1416%39%32%
1980
October1st to 10thNight
14%36%17%31%29%
2052
11th to 20thNight
13%48%20%28%28%
2160
21st to endNight
11%35%25%31%25%
2402
November1st to 10thNight
20%5%11%23%25%17%
2405
11th to 20thNight
18%5%13%24%26%14%
2470
21st to endNight
27%410%20%28%11%
2470
December1st to 10thNight
31%6%12%21%18%12%
2533
11th to 20thNight
42%7%13%17%15%6%
3276
21st to endNight
40%11%16%21%10%3
4862

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
29%6%26%23%13%3
180
11th to 20thDay
16%8%23%31%17%5%
276
21st to endDay
15%6%24%33%19%3
374
February1st to 10thDay
16%6%26%29%16%7%
394
11th to 20thDay
16%9%32%27%14%1
415
21st to endDay
18%9%31%30%12%1
346
March1st to 10thDay
19%8%30%31%11%1
420
11th to 20thDay
15%10%31%26%15%2
420
21st to endDay
16%12%32%29%10%1
462
April1st to 10thDay
13%13%30%28%15%2
420
11th to 20thDay
15%13%27%31%12%1
412
21st to endDay
6%13%27%33%16%5%
420
May1st to 10thDay
5%14%36%26%15%3
423
11th to 20thDay
7%7%29%35%17%5%
448
21st to endDay
9%9%22%33%22%6%
485
June1st to 10thDay
27%25%33%26%7%
450
11th to 20thDay
26%23%38%24%7%
450
21st to endDay
1419%39%29%8%
450
July1st to 10thDay
115%42%34%8%
446
11th to 20thDay
17%40%37%14%
444
21st to endDay
210%38%38%11%
487
August1st to 10thDay
3217%45%22%11%
447
11th to 20thDay
1112%43%30%11%
437
21st to endDay
111%43%35%9%
495
September1st to 10thDay
3214%44%30%7%
450
11th to 20thDay
25%21%41%26%4
450
21st to endDay
25%18%39%33%4
450
October1st to 10thDay
2424%37%31%1
450
11th to 20thDay
3419%43%26%4
450
21st to endDay
6%5%19%38%28%5%
469
November1st to 10thDay
8%7%23%30%28%4
270
11th to 20thDay
6%422%37%26%5%
270
21st to endDay
12%423%34%23%4
270
December1st to 10thDay
16%326%33%18%3
239
11th to 20thDay
17%6%26%26%19%6%
180
21st to endDay
24%324%29%16%4
198
January1st to 10thNight
20%216%33%24%5%
760
11th to 20thNight
13%315%42%23%4
744
21st to endNight
20%115%37%24%3
792
February1st to 10thNight
16%216%39%24%4
720
11th to 20thNight
14%317%37%25%4
704
21st to endNight
20%317%42%17%2
592
March1st to 10thNight
16%417%41%18%3
720
11th to 20thNight
15%316%33%29%4
720
21st to endNight
16%417%39%24%1
792
April1st to 10thNight
11%319%44%22%1
720
11th to 20thNight
10%5%19%37%28%1
711
21st to endNight
7%318%41%28%3
720
May1st to 10thNight
5%219%44%29%1
653
11th to 20thNight
6%117%42%33%1
531
21st to endNight
5%418%37%33%2
422
June1st to 10thNight
5%112%43%36%3
360
11th to 20thNight
115%45%36%3
360
21st to endNight
1110%40%44%3
360
July1st to 10thNight
439%53%4
350
11th to 20thNight
1237%52%7%
348
21st to endNight
1427%58%9%
521
August1st to 10thNight
36%35%50%6%
682
11th to 20thNight
1334%56%6%
712
21st to endNight
2427%60%8%
792
September1st to 10thNight
215%32%56%6%
720
11th to 20thNight
1110%40%41%7%
720
21st to endNight
219%40%44%5%
720
October1st to 10thNight
4111%47%33%5%
720
11th to 20thNight
4212%41%36%6%
720
21st to endNight
5%114%35%35%11%
792
November1st to 10thNight
9%112%36%33%9%
740
11th to 20thNight
7%215%40%30%6%
760
21st to endNight
10%216%41%25%6%
760
December1st to 10thNight
15%216%40%21%6%
760
11th to 20thNight
19%117%39%19%4
760
21st to endNight
19%317%39%18%4
836
Page generated at 2024-01-13 16:28:33. Version ac07

Copyright 2024 Attilla Danko


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