Yamada Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yamada Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
76%
15519
31%
47073
29%
15487
78%
15487
49%
23577

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%
716
21%
2497
25%
716
70%
716
33%
1374
January16th to endNight
63%
768
25%
2496
28%
768
64%
768
31%
1479
February1st to 15thNight
66%
700
25%
2150
27%
700
68%
700
34%
1269
February16th to endNight
61%
632
23%
1895
25%
632
64%
632
32%
1154
March1st to 15thNight
67%
720
19%
2142
20%
720
69%
720
39%
1198
March16th to endNight
68%
768
24%
2001
19%
768
72%
768
46%
1150
April1st to 15thNight
64%
719
26%
1799
15%
719
67%
719
44%
1074
April16th to endNight
68%
720
27%
1800
15%
720
71%
720
53%
982
May1st to 15thNight
76%
614
31%
1694
22%
614
77%
614
61%
809
May16th to endNight
72%
451
32%
1575
30%
451
76%
451
53%
672
June1st to 15thNight
82%
360
34%
1440
39%
360
87%
360
58%
521
June16th to endNight
93%
360
40%
1440
50%
360
95%
360
84%
407
July1st to 15thNight
95%
340
37%
1360
47%
340
96%
340
76%
415
July16th to endNight
92%
460
40%
1493
42%
431
93%
431
64%
580
August1st to 15thNight
92%
695
38%
1769
26%
692
92%
692
81%
778
August16th to endNight
94%
764
45%
1910
29%
764
94%
764
82%
857
September1st to 15thNight
93%
720
43%
1800
33%
720
94%
720
80%
819
September16th to endNight
89%
716
47%
1962
43%
716
92%
716
79%
822
October1st to 15thNight
82%
684
33%
1980
35%
684
83%
684
56%
946
October16th to endNight
83%
704
39%
2128
43%
704
84%
704
58%
972
November1st to 15thNight
80%
700
31%
2275
35%
700
82%
700
49%
1073
November16th to endNight
75%
720
27%
2340
30%
720
76%
720
40%
1226
December1st to 15thNight
68%
720
23%
2439
24%
720
71%
720
31%
1372
December16th to endNight
57%
768
22%
2688
23%
768
61%
768
26%
1628

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%312212235%66%
48136
Night
8%212212235%66%
47254
TransparencyDay
21%48%18%26%20%
47814
Night
21%39%20%25%18%
47075
SeeingDay
8%5%22%36%21%4
5927
Night
9%18%36%38%5%
15530

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
13%41232435%6%52%
1441
16th to endDay
17%424324436%45%
1728
February1st to 15thDay
14%7%23213348%47%
1711
16th to endDay
18%6%3442335%5%43%
1579
March1st to 15thDay
13%5%1342445%7%46%
1816
16th to endDay
13%5%23324447%49%
2223
April1st to 15thDay
12%414323345%53%
2149
16th to endDay
9%313413337%59%
2160
May1st to 15thDay
4212212335%71%
2256
16th to endDay
5%212222347%65%
2536
June1st to 15thDay
211212236%73%
2520
16th to endDay
11111288%
2520
July1st to 15thDay
1111213382%
2520
16th to endDay
11111123479%
2570
August1st to 15thDay
11111288%
2181
16th to endDay
11122284%
2292
September1st to 15thDay
1111112383%
2160
16th to endDay
11111113482%
1998
October1st to 15thDay
421321233469%
1774
16th to endDay
5%11212245%69%
1744
November1st to 15thDay
8%21341335%5%59%
1584
16th to endDay
8%313323347%58%
1620
December1st to 15thDay
13%6%24323345%50%
1518
16th to endDay
16%8%24423446%44%
1536
January1st to 15thNight
13%413222236%55%
2497
16th to endNight
15%5%23313247%50%
2496
February1st to 15thNight
14%41322335%8%49%
2140
16th to endNight
20%422213346%49%
1895
March1st to 15thNight
10%323313347%53%
2142
16th to endNight
11%312212347%58%
2001
April1st to 15thNight
11%312323236%58%
1799
16th to endNight
6%32232223467%
1800
May1st to 15thNight
411212236%72%
1694
16th to endNight
5%11212225%73%
1574
June1st to 15thNight
311211225%77%
1440
16th to endNight
11291%
1440
July1st to 15thNight
111112484%
1440
16th to endNight
11121223378%
1596
August1st to 15thNight
12112187%
1778
16th to endNight
111111286%
1910
September1st to 15thNight
1111122285%
1800
16th to endNight
111123383%
1962
October1st to 15thNight
5%2221333470%
1980
16th to endNight
5%1111133473%
2128
November1st to 15thNight
7%212212335%68%
2275
16th to endNight
7%31332335%5%59%
2340
December1st to 15thNight
13%313323347%52%
2439
16th to endNight
18%5%23223326%47%
2688

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
33%7%12%20%20%7%
1441
16th to endDay
42%411%15%14%11%
1728
February1st to 15thDay
36%6%11%22%18%4
1711
16th to endDay
43%5%10%26%13%1
1579
March1st to 15thDay
35%6%14%19%18%5%
1816
16th to endDay
33%6%14%24%17%3
2223
April1st to 15thDay
31%6%11%28%18%5%
2149
16th to endDay
24%6%11%25%25%6%
2160
May1st to 15thDay
15%49%26%34%10%
2256
16th to endDay
17%5%8%30%29%7%
2539
June1st to 15thDay
13%38%19%32%22%
2520
16th to endDay
6%128%36%44%
2520
July1st to 15thDay
8%137%23%55%
2371
16th to endDay
10%1410%22%50%
2410
August1st to 15thDay
5%28%32%49%
2165
16th to endDay
6%138%39%41%
2292
September1st to 15thDay
8%2410%33%40%
2160
16th to endDay
8%1420%41%24%
1998
October1st to 15thDay
17%36%21%29%21%
1774
16th to endDay
16%49%23%28%18%
1744
November1st to 15thDay
25%412%20%27%8%
1584
16th to endDay
26%5%13%21%25%7%
1620
December1st to 15thDay
36%6%10%19%21%4
1518
16th to endDay
41%6%14%19%14%4
1536
January1st to 15thNight
31%411%24%20%5%
2497
16th to endNight
36%411%17%18%11%
2496
February1st to 15thNight
32%5%11%25%18%5%
2151
16th to endNight
35%5%14%27%15%2
1895
March1st to 15thNight
28%5%19%20%21%5%
2142
16th to endNight
25%417%28%19%4
2001
April1st to 15thNight
28%413%30%17%5%
1799
16th to endNight
21%315%25%27%6%
1800
May1st to 15thNight
14%38%26%35%11%
1695
16th to endNight
15%38%28%33%9%
1575
June1st to 15thNight
12%37%24%28%24%
1440
16th to endNight
328%35%49%
1440
July1st to 15thNight
6%39%24%55%
1360
16th to endNight
11%227%25%50%
1493
August1st to 15thNight
7%29%29%50%
1769
16th to endNight
7%28%39%42%
1910
September1st to 15thNight
7%1311%30%45%
1800
16th to endNight
7%1318%43%26%
1962
October1st to 15thNight
17%36%22%30%19%
1980
16th to endNight
14%37%25%30%18%
2128
November1st to 15thNight
19%313%23%28%10%
2275
16th to endNight
26%412%22%25%9%
2340
December1st to 15thNight
32%6%13%21%20%5%
2439
16th to endNight
39%5%13%20%15%5%
2688

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
37%120%26%10%4
69
16th to endDay
19%421%32%17%4
256
February1st to 15thDay
20%5%23%25%18%5%
259
16th to endDay
21%5%31%27%13%
238
March1st to 15thDay
14%8%25%28%19%4
270
16th to endDay
14%11%26%32%13%1
288
April1st to 15thDay
16%14%30%26%9%1
269
16th to endDay
10%15%33%29%9%1
270
May1st to 15thDay
412%33%32%14%2
288
16th to endDay
7%8%28%30%20%4
330
June1st to 15thDay
27%27%38%18%5%
315
16th to endDay
317%40%29%8%
315
July1st to 15thDay
14%41%33%9%
305
16th to endDay
111%44%33%7%
327
August1st to 15thDay
2120%48%20%6%
315
16th to endDay
111%46%31%8%
332
September1st to 15thDay
2215%49%24%5%
315
16th to endDay
1423%39%26%4
315
October1st to 15thDay
3428%40%20%1
278
16th to endDay
7%321%39%24%2
256
November1st to 15thDay
10%211%20%41%15%
90
16th to endDay
6%225%45%18%1
90
December1st to 15thDay
21%24%41%12%
73
16th to endDay
25%117%28%20%7%
64
January1st to 15thNight
16%8%39%28%7%
720
16th to endNight
19%19%38%27%3
768
February1st to 15thNight
15%19%39%29%3
704
16th to endNight
22%19%39%23%3
632
March1st to 15thNight
10%112%42%26%6%
720
16th to endNight
13%212%38%32%1
768
April1st to 15thNight
12%215%41%26%1
719
16th to endNight
7%315%39%31%2
720
May1st to 15thNight
413%43%35%1
615
16th to endNight
5%216%33%38%2
453
June1st to 15thNight
410%42%40%1
360
16th to endNight
441%50%3
360
July1st to 15thNight
27%65%5%
340
16th to endNight
1118%67%11%
460
August1st to 15thNight
1226%62%6%
695
16th to endNight
1119%68%8%
764
September1st to 15thNight
1227%59%8%
720
16th to endNight
16%35%48%7%
716
October1st to 15thNight
47%41%37%7%
684
16th to endNight
7%6%36%39%10%
704
November1st to 15thNight
8%7%36%37%9%
700
16th to endNight
9%19%41%30%8%
720
December1st to 15thNight
15%18%45%23%6%
720
16th to endNight
20%114%39%19%4
768
Page generated at 2017-10-07 11:07:43. Version ac04

Copyright 2017 A. Danko


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