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Twelve Mile Post
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twelve Mile Post clear sky chart from 2005-11-05 to 2017-10-16.

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
51%
15779
22%
47241
16%
15738
58%
15738
28%
29491

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
35%
719
25%
2327
14%
716
50%
716
27%
1362
January16th to endNight
34%
768
25%
2496
14%
768
48%
768
28%
1468
February1st to 15thNight
37%
703
25%
2193
13%
701
52%
701
30%
1269
February16th to endNight
31%
631
26%
1893
13%
631
45%
631
28%
1156
March1st to 15thNight
41%
720
26%
1995
15%
720
49%
720
31%
1240
March16th to endNight
40%
768
19%
2112
11%
768
46%
768
27%
1390
April1st to 15thNight
44%
718
24%
1959
14%
718
51%
718
34%
1169
April16th to endNight
51%
564
24%
1644
15%
564
58%
564
31%
1023
May1st to 15thNight
52%
540
16%
1620
10%
540
56%
540
25%
1064
May16th to endNight
63%
561
16%
1684
13%
561
64%
561
26%
1094
June1st to 15thNight
68%
540
12%
1620
10%
540
69%
540
25%
1070
June16th to endNight
73%
540
15%
1620
13%
540
74%
540
29%
1059
July1st to 15thNight
70%
510
10%
1530
8%
510
70%
510
24%
1050
July16th to endNight
74%
564
13%
1595
11%
531
75%
531
26%
1052
August1st to 15thNight
66%
539
13%
1609
12%
536
66%
536
24%
1114
August16th to endNight
67%
621
17%
1821
16%
621
67%
621
23%
1259
September1st to 15thNight
62%
720
18%
1980
16%
720
63%
720
26%
1352
September16th to endNight
59%
717
21%
1980
18%
717
61%
717
27%
1327
October1st to 15thNight
54%
720
29%
2073
26%
720
60%
720
33%
1265
October16th to endNight
55%
708
34%
2123
27%
708
67%
708
39%
1164
November1st to 15thNight
56%
700
29%
2191
24%
700
65%
700
36%
1212
November16th to endNight
47%
720
28%
2340
21%
720
58%
720
31%
1328
December1st to 15thNight
45%
720
24%
2340
17%
720
55%
720
27%
1400
December16th to endNight
38%
768
23%
2496
16%
768
48%
768
23%
1604

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
13%4244345%5%8%43%
48176
Night
13%42442445%7%46%
47438
TransparencyDay
38%6%12%20%17%4
47877
Night
37%6%11%20%19%5%
47241
SeeingDay
16%417%23%22%15%
5634
Night
16%419%31%23%4
15783

By Month

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
15%413423446%49%
1611
16th to endDay
14%313314445%53%
1728
February1st to 15thDay
12%424323446%50%
1666
16th to endDay
11%423423447%49%
1580
March1st to 15thDay
15%423314447%48%
1965
16th to endDay
17%42342346%6%44%
2111
April1st to 15thDay
11%31342445%8%50%
1987
16th to endDay
14%425%42445%6%45%
2325
May1st to 15thDay
13%4145%35%5%5%7%41%
2331
16th to endDay
12%4245%35%5%6%10%39%
2431
June1st to 15thDay
9%426%6%36%7%7%11%33%
2340
16th to endDay
7%3146%46%7%8%11%38%
2340
July1st to 15thDay
9%426%7%47%6%7%11%30%
2340
16th to endDay
8%3245%48%8%8%10%34%
2465
August1st to 15thDay
14%6%15%6%46%6%7%9%29%
2340
16th to endDay
13%5%16%6%36%6%8%10%31%
2367
September1st to 15thDay
13%425%5%45%6%5%7%39%
1980
16th to endDay
18%424425%45%8%40%
1980
October1st to 15thDay
17%413322135%56%
1886
16th to endDay
11%41331223460%
1770
November1st to 15thDay
11%213213335%60%
1665
16th to endDay
16%312323246%51%
1620
December1st to 15thDay
14%41442445%6%47%
1620
16th to endDay
19%5%13422347%44%
1728
January1st to 15thNight
15%412323345%52%
2327
16th to endNight
14%422324446%49%
2496
February1st to 15thNight
13%313324346%54%
2184
16th to endNight
11%425%424446%49%
1893
March1st to 15thNight
13%5%24314446%50%
1995
16th to endNight
16%424434346%46%
2112
April1st to 15thNight
11%41342245%7%52%
1959
16th to endNight
14%424324346%50%
1644
May1st to 15thNight
15%335%5%345%5%6%42%
1619
16th to endNight
10%415%5%35%5%6%9%42%
1682
June1st to 15thNight
10%415%5%45%6%7%13%35%
1620
16th to endNight
7%324435%6%7%10%43%
1620
July1st to 15thNight
9%425%5%47%7%9%10%34%
1620
16th to endNight
5%425%6%45%7%9%13%34%
1703
August1st to 15thNight
14%5%15%5%35%5%7%9%35%
1620
16th to endNight
11%5%25%5%46%7%7%9%34%
1821
September1st to 15thNight
12%5%25%6%3445%8%39%
1980
16th to endNight
19%415%42445%6%41%
1980
October1st to 15thNight
18%413312235%52%
2073
16th to endNight
12%21331333460%
2123
November1st to 15thNight
12%31331333458%
2191
16th to endNight
16%313123445%52%
2340
December1st to 15thNight
14%414334446%48%
2340
16th to endNight
21%5%24323346%42%
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
37%5%9%20%22%4
1612
16th to endDay
34%37%24%21%8%
1728
February1st to 15thDay
35%48%22%23%6%
1668
16th to endDay
35%5%10%23%18%6%
1580
March1st to 15thDay
37%48%22%21%6%
1965
16th to endDay
39%6%12%20%17%3
2112
April1st to 15thDay
32%5%12%23%20%5%
1987
16th to endDay
39%6%9%19%18%7%
2325
May1st to 15thDay
40%7%14%20%15%2
2331
16th to endDay
38%8%16%22%13%1
2435
June1st to 15thDay
42%9%18%21%7%1
2340
16th to endDay
36%10%17%19%13%2
2340
July1st to 15thDay
43%11%16%15%9%3
2201
16th to endDay
37%11%19%19%9%1
2310
August1st to 15thDay
47%10%14%18%8%1
2327
16th to endDay
44%9%15%19%8%1
2367
September1st to 15thDay
41%8%12%18%14%4
1980
16th to endDay
41%6%11%17%19%3
1980
October1st to 15thDay
33%39%22%25%6%
1886
16th to endDay
28%36%21%28%11%
1770
November1st to 15thDay
28%39%19%29%10%
1665
16th to endDay
34%36%23%24%7%
1620
December1st to 15thDay
37%5%9%21%19%6%
1620
16th to endDay
42%39%19%18%6%
1728
January1st to 15thNight
35%410%17%25%6%
2327
16th to endNight
37%37%21%23%6%
2496
February1st to 15thNight
32%48%22%25%5%
2193
16th to endNight
36%5%9%22%23%3
1893
March1st to 15thNight
35%48%21%21%7%
1995
16th to endNight
40%5%10%21%17%4
2112
April1st to 15thNight
32%49%25%22%5%
1959
16th to endNight
35%6%9%19%21%7%
1644
May1st to 15thNight
42%6%12%20%16%1
1620
16th to endNight
37%9%12%25%11%2
1684
June1st to 15thNight
39%9%20%21%7%1
1620
16th to endNight
34%11%17%18%13%3
1620
July1st to 15thNight
40%11%19%17%9%2
1530
16th to endNight
36%12%21%19%8%2
1595
August1st to 15thNight
42%9%20%14%11%1
1609
16th to endNight
42%10%17%19%9%1
1821
September1st to 15thNight
42%7%14%18%14%3
1980
16th to endNight
42%5%11%16%18%4
1980
October1st to 15thNight
35%38%22%23%5%
2073
16th to endNight
28%36%21%29%10%
2123
November1st to 15thNight
30%37%18%28%12%
2191
16th to endNight
33%45%21%27%7%
2340
December1st to 15thNight
37%411%18%20%7%
2340
16th to endNight
43%410%16%18%5%
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
23%13%37%16%8%
90
16th to endDay
15%21%44%12%5%
96
February1st to 15thDay
18%17%42%20%1
90
16th to endDay
18%14%41%18%6%
81
March1st to 15thDay
19%8%29%33%8%
255
16th to endDay
21%7%22%32%13%1
288
April1st to 15thDay
15%10%19%28%21%4
270
16th to endDay
19%120%26%18%13%
270
May1st to 15thDay
17%6%23%23%19%9%
288
16th to endDay
14%312%26%23%20%
331
June1st to 15thDay
13%112%20%27%24%
315
16th to endDay
9%115%21%24%26%
315
July1st to 15thDay
6%19%21%29%30%
305
16th to endDay
7%15%17%32%35%
326
August1st to 15thDay
21%7%21%22%27%
313
16th to endDay
15%7%18%27%31%
332
September1st to 15thDay
15%10%16%30%24%
315
16th to endDay
21%11%21%30%14%
314
October1st to 15thDay
23%212%26%26%7%
315
16th to endDay
17%311%38%22%6%
276
November1st to 15thDay
21%6%20%26%19%5%
173
16th to endDay
16%6%24%32%18%1
90
December1st to 15thDay
21%10%40%17%11%
90
16th to endDay
27%15%37%15%4
96
January1st to 15thNight
19%9%30%31%8%
720
16th to endNight
18%8%35%34%3
768
February1st to 15thNight
16%9%32%38%3
704
16th to endNight
13%10%37%33%4
631
March1st to 15thNight
16%9%28%36%8%
720
16th to endNight
20%6%27%34%11%
768
April1st to 15thNight
16%8%27%31%15%
718
16th to endNight
17%320%33%23%1
564
May1st to 15thNight
16%219%38%22%1
540
16th to endNight
15%110%29%37%7%
563
June1st to 15thNight
11%8%27%42%10%
540
16th to endNight
10%7%25%41%14%
540
July1st to 15thNight
11%5%19%52%10%
510
16th to endNight
6%423%49%16%
564
August1st to 15thNight
17%423%42%11%
539
16th to endNight
13%421%48%11%
621
September1st to 15thNight
15%17%24%42%10%
720
16th to endNight
20%19%28%34%6%
717
October1st to 15thNight
20%217%23%29%5%
720
16th to endNight
14%320%36%20%3
708
November1st to 15thNight
14%421%36%20%3
700
16th to endNight
18%7%22%33%17%1
720
December1st to 15thNight
17%5%24%40%10%1
720
16th to endNight
25%5%25%34%9%
768
Page generated at 2017-10-17 16:35:25. Version ac04

Copyright 2017 A. Danko


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