Tranquillitatis Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tranquillitatis 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
30%
14673
13%
46928
8%
14641
36%
14641
17%
33342

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
16%
720
7%
2506
3%
716
20%
716
7%
2032
January16th to endNight
21%
768
11%
2634
5%
768
28%
768
12%
1966
February1st to 15thNight
19%
704
10%
2287
3%
701
26%
701
11%
1733
February16th to endNight
22%
631
13%
1958
5%
631
32%
631
13%
1453
March1st to 15thNight
18%
720
12%
2091
7%
720
25%
720
15%
1570
March16th to endNight
25%
768
16%
2040
8%
768
32%
768
22%
1392
April1st to 15thNight
23%
718
15%
1796
5%
718
28%
718
19%
1324
April16th to endNight
28%
639
17%
1719
8%
639
34%
639
22%
1203
May1st to 15thNight
36%
360
16%
1440
18%
360
44%
360
17%
942
May16th to endNight
36%
375
13%
1497
11%
374
47%
374
19%
955
June1st to 15thNight
37%
360
9%
1440
8%
360
46%
360
17%
945
June16th to endNight
44%
360
8%
1440
11%
360
49%
360
18%
907
July1st to 15thNight
54%
340
15%
1360
20%
340
60%
340
27%
748
July16th to endNight
56%
376
14%
1418
17%
354
61%
354
27%
800
August1st to 15thNight
48%
450
14%
1521
12%
448
52%
448
25%
931
August16th to endNight
48%
699
19%
1845
10%
699
53%
699
36%
1148
September1st to 15thNight
46%
720
15%
1800
7%
720
49%
720
30%
1238
September16th to endNight
49%
693
23%
1891
15%
693
53%
693
32%
1207
October1st to 15thNight
32%
660
17%
1980
11%
660
41%
660
19%
1380
October16th to endNight
25%
704
11%
2194
6%
704
32%
704
13%
1682
November1st to 15thNight
26%
700
16%
2343
12%
700
34%
700
16%
1657
November16th to endNight
20%
720
9%
2520
7%
720
25%
720
10%
1953
December1st to 15thNight
18%
720
7%
2520
3%
720
23%
720
8%
2019
December16th to endNight
15%
768
9%
2688
3%
768
22%
768
8%
2157

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
18%8%36%5%3445%6%32%
48010
Night
18%10%46%5%34446%32%
47097
Cloud CoverDay
23%7%35%5%24445%33%
48019
Night
22%8%36%5%23345%34%
47103
TransparencyDay
50%5%12%20%9%1
47697
Night
52%5%11%19%9%
46928
SeeingDay
22%11%28%21%12%3
5483
Night
23%10%28%26%10%
14673

By Month

Percentage Cloud Cover NE (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
21%15%7%7%5%3343420%
1432
16th to endDay
15%15%5%8%8%345%45%23%
1587
February1st to 15thDay
13%13%5%13%6%45%435%24%
1575
16th to endDay
17%12%48%7%4345%426%
1514
March1st to 15thDay
17%11%47%6%45%44428%
1859
16th to endDay
15%7%35%5%3335%5%40%
2183
April1st to 15thDay
23%9%45%423335%34%
2152
16th to endDay
21%8%25%5%2444437%
2251
May1st to 15thDay
20%7%35%5%24346%34%
2511
16th to endDay
17%6%26%6%3445%6%35%
2618
June1st to 15thDay
21%7%35%435%5%47%30%
2520
16th to endDay
17%6%25%5%36%5%6%6%32%
2520
July1st to 15thDay
13%425%435%5%7%9%37%
2520
16th to endDay
11%5%35%5%45%5%6%9%37%
2654
August1st to 15thDay
11%6%26%6%35%5%6%7%37%
2427
16th to endDay
12%5%244345%6%9%40%
2344
September1st to 15thDay
16%6%3442445%7%40%
2160
16th to endDay
14%5%35%323346%46%
1927
October1st to 15thDay
23%7%25%5%24446%34%
1650
16th to endDay
28%8%36%6%43345%25%
1678
November1st to 15thDay
15%8%46%6%35%45%6%33%
1512
16th to endDay
25%12%47%5%3444423%
1440
December1st to 15thDay
21%16%6%9%6%35%445%15%
1440
16th to endDay
23%16%5%9%5%3333419%
1536
January1st to 15thNight
19%16%5%9%8%35%445%17%
2506
16th to endNight
13%17%6%7%6%34335%26%
2634
February1st to 15thNight
12%13%6%11%7%35%445%24%
2285
16th to endNight
17%11%5%7%7%34445%27%
1958
March1st to 15thNight
19%11%5%7%6%34335%29%
2078
16th to endNight
14%8%45%5%23335%42%
2040
April1st to 15thNight
23%8%34434435%34%
1796
16th to endNight
18%8%27%433345%37%
1719
May1st to 15thNight
21%8%34424246%36%
1440
16th to endNight
16%6%36%5%2445%7%36%
1495
June1st to 15thNight
18%6%35%5%35%45%8%33%
1440
16th to endNight
16%425%435%5%7%7%37%
1440
July1st to 15thNight
10%32443445%8%47%
1440
16th to endNight
10%4145%335%6%8%45%
1514
August1st to 15thNight
10%5%26%5%245%6%9%41%
1531
16th to endNight
9%41443445%7%50%
1845
September1st to 15thNight
15%6%25%5%43446%42%
1800
16th to endNight
17%42431323450%
1891
October1st to 15thNight
20%7%35%433446%36%
1980
16th to endNight
24%10%36%6%43445%26%
2194
November1st to 15thNight
20%8%36%5%3445%5%31%
2343
16th to endNight
23%12%47%6%33445%23%
2520
December1st to 15thNight
23%15%5%8%5%3444419%
2520
16th to endNight
24%15%6%8%5%3433419%
2688

Percentage Cloud Cover SE (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
21%13%6%9%5%2344424%
1432
16th to endDay
14%14%48%8%44445%26%
1587
February1st to 15thDay
14%13%411%7%35%33427%
1575
16th to endDay
19%11%5%8%6%3343429%
1514
March1st to 15thDay
34%8%35%5%3432325%
1869
16th to endDay
32%6%2442323333%
2182
April1st to 15thDay
25%8%34322235%37%
2152
16th to endDay
23%6%25%42333439%
2251
May1st to 15thDay
32%5%25%42323432%
2511
16th to endDay
30%5%235%2333434%
2618
June1st to 15thDay
27%5%25%434346%32%
2520
16th to endDay
23%5%244345%5%6%34%
2520
July1st to 15thDay
13%425%435%6%6%8%38%
2520
16th to endDay
11%5%25%6%35%6%7%9%37%
2654
August1st to 15thDay
29%3145%335%46%32%
2427
16th to endDay
29%313322446%37%
2344
September1st to 15thDay
15%5%2442445%7%43%
2160
16th to endDay
14%5%14323347%47%
1927
October1st to 15thDay
20%6%35%434446%37%
1650
16th to endDay
27%8%36%6%23335%29%
1678
November1st to 15thDay
20%8%345%24445%34%
1512
16th to endDay
28%10%46%5%2333425%
1440
December1st to 15thDay
22%14%5%8%6%35%435%20%
1440
16th to endDay
24%14%5%8%5%2433423%
1536
January1st to 15thNight
18%15%6%10%6%3434422%
2506
16th to endNight
12%16%5%8%6%3433431%
2634
February1st to 15thNight
16%12%410%6%34335%28%
2278
16th to endNight
20%10%37%7%3434430%
1958
March1st to 15thNight
36%7%35%5%2322326%
2091
16th to endNight
32%5%2441223236%
2040
April1st to 15thNight
26%7%34423335%36%
1796
16th to endNight
20%6%36%424345%39%
1719
May1st to 15thNight
26%6%3341323439%
1440
16th to endNight
21%425%42335%5%42%
1495
June1st to 15thNight
20%5%26%443447%35%
1440
16th to endNight
20%425%425%46%6%37%
1440
July1st to 15thNight
11%325%33445%9%46%
1440
16th to endNight
10%3244345%6%8%46%
1514
August1st to 15thNight
24%324322447%39%
1531
16th to endNight
24%212323345%45%
1845
September1st to 15thNight
14%6%25%5%33345%45%
1800
16th to endNight
17%42331323452%
1891
October1st to 15thNight
19%7%24423445%39%
1980
16th to endNight
24%9%35%5%43335%30%
2194
November1st to 15thNight
27%7%35%42323434%
2343
16th to endNight
31%9%36%42333427%
2520
December1st to 15thNight
24%12%47%5%3343424%
2520
16th to endNight
26%14%47%5%2333424%
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
65%49%13%5%
1433
16th to endDay
61%411%13%7%
1587
February1st to 15thDay
63%311%16%4
1577
16th to endDay
59%411%14%8%1
1514
March1st to 15thDay
59%412%15%7%
1869
16th to endDay
45%39%19%14%5%
2183
April1st to 15thDay
52%38%19%13%2
2152
16th to endDay
49%37%19%15%3
2251
May1st to 15thDay
51%47%20%13%2
2511
16th to endDay
49%5%11%20%11%1
2622
June1st to 15thDay
52%5%11%20%8%
2520
16th to endDay
47%7%13%20%10%1
2520
July1st to 15thDay
37%8%15%26%12%
2371
16th to endDay
40%8%17%23%9%
2487
August1st to 15thDay
42%7%17%22%9%
2413
16th to endDay
37%6%17%28%9%
2344
September1st to 15thDay
41%6%13%27%10%
2160
16th to endDay
38%5%13%32%9%
1927
October1st to 15thDay
50%5%13%20%9%
1650
16th to endDay
61%412%14%6%
1678
November1st to 15thDay
49%6%14%20%7%
1512
16th to endDay
62%5%12%12%5%1
1440
December1st to 15thDay
68%6%11%11%2
1440
16th to endDay
68%410%11%5%
1536
January1st to 15thNight
69%49%11%4
2506
16th to endNight
60%49%17%7%
2634
February1st to 15thNight
61%412%16%5%
2287
16th to endNight
57%410%17%9%
1958
March1st to 15thNight
59%39%19%7%
2091
16th to endNight
45%410%20%15%4
2040
April1st to 15thNight
52%47%18%15%1
1796
16th to endNight
48%38%17%17%3
1719
May1st to 15thNight
49%47%19%15%3
1440
16th to endNight
45%5%12%20%13%2
1497
June1st to 15thNight
47%6%13%22%8%1
1440
16th to endNight
43%7%13%20%15%
1440
July1st to 15thNight
33%6%13%30%15%1
1360
16th to endNight
33%7%16%27%15%
1418
August1st to 15thNight
36%8%17%23%12%
1521
16th to endNight
32%6%15%34%10%
1845
September1st to 15thNight
42%5%12%27%11%1
1800
16th to endNight
38%311%35%9%
1891
October1st to 15thNight
48%5%11%22%11%
1980
16th to endNight
59%5%12%15%6%
2194
November1st to 15thNight
52%5%12%18%9%
2343
16th to endNight
62%5%11%15%4
2520
December1st to 15thNight
66%5%12%12%3
2520
16th to endNight
68%310%12%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
28%28%23%15%5%
60
16th to endDay
30%15%36%15%2
73
February1st to 15thDay
35%16%37%10%
90
16th to endDay
34%20%24%14%5%
173
March1st to 15thDay
25%15%33%20%5%
270
16th to endDay
22%15%31%16%10%2
288
April1st to 15thDay
29%21%24%17%7%
270
16th to endDay
22%15%30%18%10%2
270
May1st to 15thDay
31%10%28%17%8%3
288
16th to endDay
21%12%32%22%9%1
331
June1st to 15thDay
28%7%31%21%8%2
315
16th to endDay
19%10%31%24%13%1
315
July1st to 15thDay
13%6%29%29%14%5%
305
16th to endDay
10%5%30%29%18%5%
326
August1st to 15thDay
9%6%26%33%17%6%
313
16th to endDay
15%424%25%19%10%
332
September1st to 15thDay
17%8%22%18%21%11%
315
16th to endDay
15%8%22%22%20%10%
287
October1st to 15thDay
22%10%27%23%14%1
255
16th to endDay
33%14%23%19%7%
257
November1st to 15thDay
20%10%29%24%13%
166
16th to endDay
35%13%31%18%1
60
December1st to 15thDay
28%16%35%16%3
60
16th to endDay
37%18%37%6%
64
January1st to 15thNight
28%14%30%21%4
720
16th to endNight
22%12%33%25%5%
768
February1st to 15thNight
20%14%37%22%5%
704
16th to endNight
22%17%30%23%5%
631
March1st to 15thNight
25%13%32%25%2
720
16th to endNight
20%16%27%26%9%
768
April1st to 15thNight
27%14%29%22%4
718
16th to endNight
22%14%28%25%8%
639
May1st to 15thNight
27%5%24%32%8%1
360
16th to endNight
21%6%32%26%13%
375
June1st to 15thNight
20%6%30%32%10%
360
16th to endNight
18%425%37%13%
360
July1st to 15thNight
11%127%41%18%
340
16th to endNight
10%322%44%16%1
376
August1st to 15thNight
12%419%40%22%1
450
16th to endNight
10%5%22%36%22%2
699
September1st to 15thNight
17%5%25%28%20%2
720
16th to endNight
18%6%22%26%22%2
693
October1st to 15thNight
26%9%25%25%11%1
660
16th to endNight
31%11%25%24%6%
704
November1st to 15thNight
25%11%29%22%10%
700
16th to endNight
32%14%24%19%8%
720
December1st to 15thNight
30%14%30%20%3
720
16th to endNight
32%13%30%17%41
768
Page generated at 2017-09-25 09:02:24. Version ac04

Copyright 2017 A. Danko


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